TECHNICAL QUESTIONS
E.C.E.
TECHNICAL QUESTIONS &ANSWERS
ELECRTONIC DEVICES & CIRCUITS
1. What is the magnetic force on the election, if it is placed in a union
magnetic field with zero initial velocity?
A: Zero.
2. What are the basic constituents in CRO?
A: CRT, power supplies, time base circuit, deflection amplifier.
3. what are the basic constituents in CRT?
A. electron gun, deflection system, fluorescent screen, glass envelop.
4. which type of fluorescent material is used to provide a green spot on the screen>
A. Zinc ortho silicate.
5. what is the purpose of focusing?
A.focusing is required to produce a dominant spot on the screen.
6. define valence electrons?
A. the electrons in the outermost orbit of an atom are known as valence electrons.
7. give the example for conductors, semi conductors and insulators?
A. conductors: copper, aluminium
Semi conductors: silicon, germanium
Insulators: wood, glass
8. what is meant by forbidden energy gap?
A. the separation between conduction band and valence band in the energy level diagram is known as forbidden energy gap.
9. what is meant by intrinsic semiconductor?
A. if the semi conductor is in pure form then it is known as an intrinsic semiconductor.
10. define doping?
A. the process of adding the impurities to a pure semi conductor is called doping.
11. which type of impurities are added in the p-type semiconductor.
A. trivalent impurities.
12. define drift current?
A. because of the applied voltage, the electrons will collide with the atoms of semiconductor and moves in a random direction. This drift causes current to flow in the semiconductors. The current produced due to the drifting of free electrons is called drift current.
13. state law of mass action?
A. law of mass action states that the product of concentration of electrons (n) and holes (p) is always constant at a fixed temperature.
np=ni2 where ni is intrinsic concentration
14. define diffusion current?
A. the current due to the transport of charges in a semiconductor due to the non uniform concentration of charged particles is called diffusion current.
15. what is meant by mean life time of the charge carrier?
A. the amount of time between the creation and disappearance of a free electron or hole is called mean life time of the charge carrier.
16. what is meant by hall effect?
A. if a semiconductor carrying current ‘I’ is placed in a transverse magnetic field with flux density ‘B’ then an electric field ‘E’ is induced in the direction perpendicular to both I and B. this phenomenon is called hall effect.
17. for an ideal diode, what is the reverse resistance?
A. infinity.
18. mention the diode current equation?
A. I = I0(eV/ηVT-1)
19. what is the cut in voltage of a silicon diode?
A. 0.6 V
20. what are the breakdown mechanisms involved in PN diode and Zener diode?
A. PN diode -->avalanche breakdown
Zener diode --> zener breakdown
21. out of zener and PN diode which one is having doped?
A. zener.
22. what is breakdown voltage of a zener diode?
A. 6V
23. mention the applications of PN diode?
A. rectifier, switch, clamping circuit, clipping circuit.
24.mention the application of zener diode under reverse bias?
A. voltage regulator.
25. what is a rectifier?
A. rectifier is a device which converts Ac voltage to pulsating Dc voltage using one or more P-N function diodes.
26. what is the efficiency of half wave rectifier?
A. 40.6%.
27.define ripple factor?
A .the ratio of rms value of Ac component to the Dc component in the output is known as ripple factor.
28. what is the ripple factor of half wave rectifier?
A. 1.21
29. which rectifier has peak inverse value is 2Vm?
A. full wave centre tapped rectifier.
30. what is the out frequency in full wave bridge rectifier ( if fin is the input frequency)?
A. 2 fin
31. which type of transformers are used in rectifiers?
A. step down transformer.
32.what is the significance of arrow mark in a transistor?
A. arrow mark represents conventional current direction.
33. out of emitter, base and collector, which region is heavily doped?
A. emitter.
34. why collector is made more wider than that of emitter and base?
A. in order to dissipate the heat produced in it.
35. why transistor is called bi polar junction transistor?
A. because its current conduction depends on both majority charge carries and minority charge carriers.
36. what is the relationship between IE,IB and IC?
A. IE=IB+IC.
37.give an example for current controlled device?
A.BJT
38. define amplification factor?
A. it is defined as the ratio of output current to input current of a transistor.
39. why common emitter confismation is preferred compared to CB and CC?
A. because of its high voltage gain.
40. what is meant by early effect?
A. an increase in the collector base voltage increases the space charge width at the output junction (base-collector). This causes effective base width decrease, this phenomenon is known as the early effect.
41. what is the relationship between α, β and γ?
A. γ=1+β, β=α/1-α, γ=1/1-α.
42. which transistor confismation has low output resistance.
A. common collector.
43. what is the application of common collector configuration?
A. for impedance matching.
44. which transistor confismation has current gain less than unity.
A. common base α=IC/IE (IE is slightly greater than IC.
Important points regarding transistor naming:
Ex: BC 547
First letter (B) indicates nature of semiconductor material.
A=germanium, B=silicon, C=gallium arsenide, R=compound material
Second letter (C) indicates the device and circuit function.
A=diode, B=variable capacitance diode, C= A.F low powered transistor
D=A.F power transistor, G=tunnel diode, H=magnetic sensitive diode
L=H.F power transistor, K= Hall effect device , M=Hall effect modulator
P=radiation sensitive diode, Q=radiation generating diode, R=thyristor (SCR or triac), S=low power switching transistor, T=thyrister, power
Note : if the transistor contains 2 letters and 3 numbers it is for consumer equipment (ex: BC547), if it contains 3 letters and 2 numbers it is for industrial purpose( ex: BFX63).
45. what is the VBE sat value of a silicon transistor?
A. VBE sat(si)=0.7V
46. out of BJT and FET which one is the unipolar device?
A. FET, because its operation depends upon the flow of majority carriers only.
47. which MOSFET can be operated in both depletion and enhancement mode?
A. depletion MOSFET.
48. why MOSFET is called insulated safe FET?
A. the metal region of gate with insulating oxide layer of SiO2 forms a parallel plate capacitor. So the MOSFET is called the insulated gate FET.
49. give an example for voltage controlled device?
A. FET.
50. number of P-N junctions in a UJT?
A. one.
51. what is the other name of UJT?
A. double-based diode.
52. what is the range of η (intrinsic stand off ratio) in UJT?
A. η is between 0.51 and 0.82.
53. give the examples for negative resistance devices?
A. UJI, tunnel diode.
54. Mention the applications of UJT?
A. (i) UJT relaxation oscillator
(ii) over voltage detector.
55. What are the majority charge carrier in PNP transistor.
A. holes.
56. Define break over voltage in SCR?
A. it is the minimum forward voltage at which SCR starts conducting heavily with gate being open.
57. If the transistor is to be operated in saturation region. What are the biasing states
of input and output?
A. Input and output must be in forward bias state.
58. Define transistor biasing?
A. The proper flow of zero signal collector current and fue maintenance of proper collector emitter voltage during fue passage of signal is known as transistor biasing.
59. what is the resulting effect, if the operating point was chosen close to saturation
region?
A. positive peak clipping.
60.In which region the transistor operating point was fixed to avoid the distortion?
A. active region.
61. what is meant by stabilization?
A. for faithful amplification operating point must remain fixed making operating point independent of temperature changes and transistor replacement is known as stabilization.
62. define stability factor?
A. it is defined as the rate of chance of collector current IC with respect to the collector base leakage current ICO, keeping both IB and β constant S=∂IC/∂IO
63. what is the stability factor in fixed bias?
A. S=1+β
64. what is the drawback in fixed bias?
A. it has hish stability factor, means less stable. (thermal stability)
65. what is the stability factor in voltage divider bias?
A. S~ 1
66. what is meant by thermal runaway?
A. as temperature Is increased, which increases two collector current causes increase in power dissipation. This phenomenon is referred to as thermal runaway.
67. what is the condition for thermal stability?
A. VCE≤VCC/2
68.what is the purpose of an amplifier?
A. it is used to set large signal output from a small signal input.
69. why hi, hr, hf and ho are hybrid parameters?
A. all these are mixture of different units and haence referred to as hybrid parameters.
70.what is the formula for hfe in CE confismation?
A. hfe=∆IC/∆IB at VCE constant
71. In the analysis of single stage transistor amplifier using hybrid model , what are
the formulae for AI, AV, Ri and Y0 .
Ans. AI= (-hf /1+h0RL ) , AV=(AIRL/Ri ) , Ri =hi-(hrhf /((i/RL )+h0 ))
Y0=h0-(hfhr /RS+hi)
72. In simplified hybrid model of CC current , what is the formulae for AI and AV
A. AI = 1+hfe ,Av=1.
73. In simplified hybrid model of CB circuit , what are the formulae for Ri and Av .
A. Ri =hie /1+hfe , Av=hfeRL /hie
74. What is meant by negative feedback?
A. When input signal and part of output signal are out of phase then the feedback is called negative feedback.
75. Which type of amplifier is used in current series feedback amplifier?
A. Transconductance, Similarly current amplifier in current shunt, Voltage amplifier in voltage series.
Transresistance amplifier in voltage shunt.
Table: The input and output resistances of all the feedback amplifier compared to without feedback.
Ri R0
Current series increases increases
Current shunt decreases increases
Voltage series increases decreases
Voltage shunt decreases increases
76. In voltage amplifier, what is the gain formula with negative feedback.
A. Avf = Av/1+Avβ
Av- gain without feedback
β- feedback factor
77. What is the formula for input resistance with feedback in voltage series feedback
amplifier?
A. Rif = Ri (1+βAvf)
78. What is the formula for output resistance with feedback in current shunt feedback
amplifier?
A. Rof =R0(1+βAI).
79. What is Bark hausen Criterion.
A. |Aβ| =1 i.e., the magnitude of loop gain must be unity.
Phase angle =0⁰ or 360⁰
80. What are damped oscillations?
A. If the amplitude of the signal decreases with respect to the time of the signal , then the oscillations are called damped oscillations.
81. What is the Phase Shift produced by one RC combination in RC Phase shift
oscillator.
A. 60⁰.
82. What is the Phase Shift produced by a transistor?
A.180 ⁰.
83. Which type of feedback is used in oscillators?
A. Positive feedback.
84. What is the formula for frequency of oscillations produced in RC Phase shift
oscillator?
A. f=1/ (2πRC 6+4K))
Where K= R c /R
85. What is the formula of oscillations produced in Wien bridge oscillator.
A. f=1/(2π( R1R2C1C2)) or f=1/2πRC
Since R1=R2=R , C1=C2=C
86. what is the formula for frequency of oscillations produced in Hartley Oscillator?
A: f= 1/2π√C(L1+L2)
87. what is the formula for frequency of oscillations produced in Colpitts oscillator.
A: f=1/2π√L.C1C2/C1+C2
88. Which type of materials are used to manufacture thermistors.
A: Ceramic or polymer.
89. What are the other names of Varator diod?
A: Varicap or Taning diod or variable reactance diode.
90. what is the other name of tunnel diode?
A: Esaki diode.
91. Give the examples of photo conductive devices?
A: PN photo diode, PIN photo diode, photo transistor.
92. which semiconductor devices act like a diode and two transistors?
A: UJT.
93. what is the phenomenon involved in LED to emit the light?
A: Electroluminescence.
94. which materials are used to manufacture LEDs?
A: gallium phosphide(GaP),gallium arsenide phosphide(GaAsP).
95. what are the two liquid crystal materials used in display technology?
A: Nematic and Cholestric.
96. What are the types of LCDs?
A: i). Dynamic scattering type.
ii). Field effect type.
97. What is the forbidden energy gap for silicon?
A: |i|2ev.
98. Which amplifiers are involved in cascade amplifier?
A: CE&CB amplifiers.
99. What is the feedback factor for voltage shunt feedback amplifier?
A: β=If/Vo.
100. What is the typical value of resonant frequency of a crystal oscillator?
A: 3.275 MHZ.
101. Non-linear distortion is maximum in class A mode of power amplifiers.
102. Two -stage RC coupled amplifier is configured as two capacitively coupled
CE stages cascaded.
103. The advantage of impedance type inter stage coupling is no dc voltage drop
across collector load.
104. The major draw back of Darlington transistor pair dependence of H –
parameters on quiescent conditions.
105. The increased conversion efficiency in class B over class A operation is mainly
due to elimination of dc current in the load.
106. The ratio of slopes of the gain curve of an amplifier below lower cutoff
frequency & above cutoff frequency is unity.
107. The. slope of the gain curve of an amplifier below cut off frequency is
-20 db/decade
PULSE & DIGITAL CIRCUITS
1. What is linear wave shaping?
Ans: The process of altering the non-sinusoidal signal by transmitting it through a linear network is called as linear wave shaping
2. The low pass filter acts as an integrator for _______________
Ans: large time constant RC >> T
3. What is time constant?
Ans: The time required for the output waveform to obtain 63.2% of its final steady value is called as time constant.
4. Define rise time?
Ans: The time required for the output waveform to rise from 10% to 90% of its final steady value is called as rise time
5. Give the relation between rise time tr and time constant RC
Ans: tr = 2.2RC
6. Give the relation between rise time tr and 3-dB frequency f2.
Ans: tr = 0.35/f2
7. What is the average value of the output of the RC high pass circuit for any
periodic waveform?
Ans: ZERO
8. What is a clipper?
Ans: Clipper is an electronic circuit, which is used to transmit of a part of signal which lies above or below some reference voltage.
9. What is a comparator circuit?
Ans: The comparator circuit is one which may be used to mark the instant when an arbitrary waveform attains some particular reference level.
10.. The circuit which removes the below reference value is called as ___________ Ans: negative clipper
11. What are the other names for Clippers?
Ans: Voltage limiters, slicers
12. In a clipper circuit, the input voltage should be greater than the reference value
for clipping operation.
13. What is a clamper?
Ans: The clamper circuit shifts the dc value from one level to another level.
14. Give the other names for clampers?
Ans: dc restorer , dc inserter
15. What is a negative clamper?
Ans: The negative clamper is used to fix the positive peak of the input waveform at reference value and entire waveform appears below the reference value.
16. State the clamping circuit theorem.
Ans: ‘It states that under steady state condition, the ratio of area under the output voltage in forward direction to the area under the o/p voltage in reverse direction is equal to the ratio Rf/Rr where Rf = diode forward resistance & Rr = diode reverse resistance.’
17. The forward current of the diode is negligible until the voltage applied to the
Diode reaches _________ (Ans: Cut-in voltage)
18. The reverse leakage current of the diode is constant and very small until the
diode voltage reaches _________ (Ans: break down voltage)
19. When the diode is forward biased it acts as __________ switch (Ans: closed)
20. What is diode forward recovery time?
Ans: The time required by the diode current to reverse and obtain a steady state value when a sudden forward bias is applied to the diode is called as Forward recovery time.
21. The reverse recovery time of the diode is the sum of __________ &
___________ Ans: storage time & transition time
22. The transistor can be operated in ______, _______ & ______ regions
Ans: Cut-off, Active & Saturation
23. What are the regions in which transistor works as a switch?
Ans: Cut-off & Saturation regions
24. The turn-on time of the transistor is the sum of _______ & __________
Ans: delay time & rise time
25. The turn-off time of the transistor is the sum of _______ & _________
Ans: storage time & fall time
26. What is a multi vibrator?
Ans: A multivibrator is basically a regenerative circuit comprising of two cross coupled active elements like bi-polar junction transistors.
27. The bi-stable multivibrator has 2 stable states.
The monostable multivibrator has one stable state & one quasi-stable state.
The astable multivibrator has no stable states.
28. Write the another name(s) of the bi-stable multivibrator?
Ans: flip-flop ckt, Binary ckt, Eccles Jordan ckt
29.What is the other name for mono-stable multivibrator?
Ans: one shot multivibrator
30. The astable multivibrator is also called as Square wave generator
31. What is bi-stable multivibrator?
Ans: The bi-stable multivibrator has two stable states. The circuit remains in its stable state until an external triggering pulse is applied. If we apply an external triggering pulse to bi-stable circuit, the circuit switches to another stable state and remains in this state until another trigger pulse is applied. Hence the binary circuit requires 2- external triggering pulses to come back to its original stable state.
32. What is monostable multivibrator?
Ans: The monostable multivibrator has one quasi-stable state & one stable state.
The circuit remains in its stable state until an external triggering pulse is applied.
If we apply an external triggering pulse to monostable circuit, the circuit switches to its quasi-stable state after some time interval it will automatically come back to its original stable state.
33. What is an astable multivibrator?
Ans: The astable multivibrator has two quasi-stable states. The circuit will continuously switches between these quasi-stable states. Hence the astable circuit doesn’t require any external triggering pulse. It is also called as square wave generator.
34. Give any one application of the Binary circuit.
Ans: shift registers, counters
35.Give any one application of the monostable multivibrator
Ans: adjustable pulse generator
36. Which type of triggering employs two trigger sources
(Ans: Unsymmetrical)
37. Which circuit is called as a sine to square wave converter
(Ans: Schmitt trigger).
38. What are the applications of time base generators?
Ans: used in CROs, Radars, Televisions
39. What is sweep time?
Ans: The time required for the time base voltage to reach form Valley voltage to Peak voltage is called as sweep time
40. The time required for the time base voltage to reach form Peak voltage to Valley
voltage is called as _________ (Ans: fly back time/ restoration time/ return time)
41. What are the various types of errors occur in generation of time base signal.
Ans: slope /sweep speed error, displacement error, transmission error
42. Give the relation b/w slope error, displacement error & transmission error.
Ans: es = 8ed = 2et
43.The UJT has _____________ no.of p-n junctions ( Ans: 1)
44. The Miller sweep circuit generates a -ve going ramp signal
45. Bootstrap sweep circuit employs emitter follower ckt. with positive feed back
46. Miller sweep circuit employs high voltage gain amplifier with - ve feed back.
47. Give some examples of relaxation circuits
Ans: UJT relaxation circuit, Astable & monostable multivibrators
48. Write the condition required to achieve pulse synchronization.
Ans: T0 > TP
49. Write the condition for frequency division with a division factor 3 .
Ans: T0 > 3TP
50. What is phase jitter?
Ans: The factors which effect the phase delay is termed as phase jitter
51. What is a sampling gate?
Ans: The sampling gate is a transmission circuit in which the output is exact reproduction input waveform during a selected time interval and it is ZERO otherwise.
52. What is gating signal?
Ans: The time interval for transmission of input signal through a sapling gate is selected by gating signal or control signal
53. What are the other names for sampling gates?
Ans: transmission gates/ time selection circuits /linear gates
54. What is uni-directional sampling gate?
Ans: The uni-directional sampling gate transmits only positive going input signals./ uni-directional signals
55. The unidirectional gate which has more than one input acts as a
_____________ logic gate (Ans: OR gate)
56. Which type of sampling gate allows both the polarities of the input signal ?
Ans: Bi-directional sampling gate
57. Write the disadvantage of two diode sampling gate?
Ans: it introduces some attenuation
58.The gain of the 6-diode sampling gate is _________ (Ans: 1)
59. Write any two applications of sampling gates.
Ans: Sampling scope, multiplexers, S/H circuits, D/A converters
60. What is a logic gate?
Ans: The circuit which process digital information and takes logical decisions are called as logic gates
61. What are the basic building blocks of the digital systems.
Ans: logic gates
62. What is negative logic?
Ans: If v(1) < V(0) then it is called as negative logic. 63. The basic logic gates are ________(Ans: AND, OR & NOT gates) 64. The universal logic gates are _________(Ans: NAND & NOR gates) 65. Write any two applications of logic gates Ans: All digital systems are designed using logic gates. Ex: flip-flops, registers, memory devices, counters, adders, multiplexers…. LINEAR IC APPLICATIONS 1. The block diagram of the OP-AMP consists of the following BLOCKS 1.Cascaded diff-amp stage: STAGE-1 : Dual input balanced output diff_amp STAGE-2: Dual input unbalanced output diff-amp. 2. Level translator 3. output stage 2. What is the need for Constant current bias in Op-Amp? Ans: To provide high emitter resistance, high CMRR and to provide stable operating point 3. What is a Current mirror circuit? Ans: The circuit in which the output current is mirror image of an input current is called as current mirror circuit. 4. What is the use of level translator? Ans: The level translator in Op-Amp is used toshift the dc level to zero 5. Give an example for linear IC Ans: Ans: 741 OP-AMP, 555 timer, 566 VCO 6. Give any application in open loop configuration of an op-amp? Ans: Comparators 7. Write the applications of Comparators Ans: Zero crossing detector, Window detector 8. The Gain of the inverting amplifier with resistance R1 & Rf is ___________ Ans: -Rf / R1 9. The Gain of the non-inverting amplifier with resistance R1 & Rf is Ans: 1+ [Rf / R1] 10. As frequency increases, the practical op-amp gain decreases 11. What is dominant pole frequency compensation technique? Ans: In dominant pole compensation technique, the uncompensated transfer function of the op-amp is altered by adding a pole. 12. Which type of frequency compensation technique leads to more bandwidth than dominant pole compensation. Ans: pole-zero 13. Write the ideal OP-AMP characteristics. Ans: Voltage gain= CMRR= Input resistance= Output resistance=0. Offset voltages and currents=0. Band width = 14. Write the characteristics of Voltage follower circuit. Ans: Unity gain, high Input resistance, low output resistance. 15. ____________ circuit can be used as a buffer. ( Voltage follower) 16. Write the characteristics of Instrumentation amplifier? Ans: Very high CMRR, high Input resistance, low output resistance. 17. What is a peak detector? Ans: The peak detector is used to compute the peak voltage of the input. 18. In voltage follower circuit, the feedback factor is _________________ (Ans: 1) 19. The gain of the basic/true integrator at Zero frequency is infinity. 20. The Analog multiplier circuit can be obtained with the help of ____________ Ans:Log-Antilog method 21. What is a butterworth filter? Ans: The Butterworth filter has flat pass band and flat stop band. 22. What is an electric filter? Ans: An electric filter is a frequency selective circuit that passes the signals of specified band of frequencies and blocks (or) attenuates the signals of frequencies outside this band. 23. Give any two advantages of Active filters. Ans: 1.gain and frequency adjustment flexibility 2. .No loading problem 3.Eliminates need for inductors 24. For II order filter, the gain of the filter changes in stop band at a rate of _____________ (Ans:40 db/dec) 25. The gain of the II order LPF in the pass band is 1.586 26. The frequency at which the gain of the filter is 1/√2 times of its max. value is called as _________ (Ans: cutoff frequency) 27. _______________ filter has a pass band b/w two cut-off frequencies fH and fL such that fH > fL . (Ans: band pass filter)
28. What is a notch filter?
Ans: The notch filter is a Narrow band reject filter used to reject unwanted signal
29. Give the relation between centre frequency fc , Q and BW.
Ans: Q= fc/ BW, where fc =( fL fH )and BW= fH- fL
30. Which circuit is called as voltage to frequency converter. (Ans:VCO)
31. Write the applications of VCO.
Ans: FM Modulation, PLL, FSK, Tone generator
32. The max. output current of 555 timer is _______________ mA.. (Ans:200mA)
33. The 555 timer internal circuit consists of ____________flip-flop. (Ans:R-S)
34. Write the applications of 555 timer in Monostable mode.
Ans: Missing pulse detector, Frequency divider, Linear ramp generator, PWM
35. Write the applications of 555 timer in Astable mode.
Ans: PPM, FSK generator
36. Define Lock-in-range.
Ans: The range of frequencies over which the PLL can maintain lock is called as lock-in-range (or) tracking range
37. Define Capture range
Ans: The range of frequencies over which the initially unlocked PLL will lock on to input signal frequency is called as capture range
38. Define pull-in-time.
Ans: The time required to PLL circuit to establish lock is called as pull-in-time
39. List out the applications of PLL
Ans: frequency multiplier, FM detector, frequency translator
40. Which type of DAC uses only two values of resistors
Ans:R-2R ladder type DAC
41. What is the the disadvantages of Binary weighted resistor DAC?
Ans: it requires wide range of resistor values
42. Which is the fastest ADC?
Ans:Parallel comparator type ADC or Flash type ADC
43. The n-bit Flash type ADC require ____________ no of comparators. (Ans:2n-1)
44. The conversion time of successive approximation ADC is __________
Ans:(n+1)Tc
45. The conversion time is large for ____________type of ADC
Ans: Dual slope
46. Which type of ADC is used in digital voltmeters.
Ans: Dual slope
47. Which type of ADC doesn’t require DAC.
Ans:Dual slope
48. What is Resolution of a DAC/ADC ?
Ans: The smallest change in the output voltage as fraction of full scale range is called as Resolution.
49. What is settling time of a DAC?
Ans: The time required for the converter output to settle with in 1/2 LSB of final values is called as settling time
50. If the full-scale range of 8-bit DAC is 0-10V then,the resolution = 39mV
51. What is analog multiplexing?
Ans: Multiplexing is the process in which a no.of analog signals, one at a time are connected to a common load.
52. The analog multiplexer uses _____________________gates as switches.
Ans: C-MOS transmission gates
53. What is a S/H circuit?
54. Write the applications of S/H circuit?
55. Write the applications of Analog multiplier?
Ans: frequency doubling, phase detection, squaring a signal,
Division of two signals, calculation of real power
56. The one quadrant multiplier accepts two unipolar signals.
The two quadrant multiplier accepts one unipolar & one bipolar signals.
The four quadrant multiplier accepts two bi-polar signals.
57. Write the applications of 1496 balanced modulator?
Ans: AM Modulator, Product detector, AM detection, Mixer.
VLSI
1. What is Oxidation?
A: Forming SIO2 layer on the surface of the silicon is known as Oxidation.
2. What is meant by Latch-up condition? What are the remedies for the Latch-up problem?
A: In CMOS Latch-up is a condition in which the parasitic components
give rise to the establishment of low resistance conducting paths b/w vdd
and vss with disastrous results.
->latch up may be induced by glitches on the supply rails or by incident
radiation.
Remedies for the Latch-up
i) An increase in substrate doping levels with a consequent drop in the value or Rs
ii) Reducing Rp by control of fabrication parameters and by ensuring a low contact resistance to Vss.
iii) The introduction of guard rings.
3. What is the benefit of the BICMOS process.
A: ->Latch-up problem is eliminated in this process.
->Latch-up avoided here due
A reduction of substrate resistance Rs.
A reduction of n-well resistance Rw.
As Rs and Rw reduced it require larger lateral current required to
invite Latch up and
a higher value of holding current is also required.
The parasitic pnp transistor which is a part of the n-well latch up circuit has reduced beta owing to the presence of the buried n+ layer. It reduces carrier life time in the n-base region and there by reduces beta.
4. Define D cg?
A: D cg is defined as the gate – to – channel capture of a MOS transistor having w=l=feature size.
5. Define (Delta Unit)
A: The time required to change 1D cg capacitance through one feature size square of n channel resistance.
Time constant C= [1 Rs(channel)x1D cg] seconds
6. What is Frenhel defect.
A: It is one of the crystal point defect. Point defect is a missing atom in the lattice. The presence of a host atom b/w regular lattice sites and adjacent to a vacancy is known as Frenhel defect. Affects the oxidation process.
7. Diffusion is based on which equation.
A: Diffusion is the process of introduction of controlled amount of dopants atoms in to the emiconductor. It is governed by Fill’s first law, Which relates the net flow of the particles to the concentration gradient in the depth of the substrate.
8. What are the advantages of BICMOS conductors.
A: Transistor (Bipolar) present low impedance. When turned on into saturation and load CL will be changed or discharged rapidly at O/P.
BICMOS inverter has high noice margin.At i/p MOS transistors are used to possess high i/p impedance.It has low o/p impedance.
It has high driving capability but it occupies a relatively small area.
9. Define electron mobility?
A: The speed with electrons move under the influence of the electric field is known as electron mobility.
10. Define synthesis in VHDL.
A: The process of translating an abstract form of desired circuit into a design implementation interms of logic gates is known as synthesis.
11. what are the advantages of cell-based design methodology.
A: Designers save time as they need not design the standard cells to be induced in the design at they just import them from the ASIC or design library directly into the design. As the standard cells are predesigned ,pretested and precharecterised and kept in the standard library the risk of the design is raduced.Each standard cell can be optimized individually and the changes can be reflected through out the chip at a time.During the design of a cell library each and every transistor in every standard cell can be chosen to maximize the speed or minimize the area.
12. What is the advantage of changing transistor size in standard cell.
A: It optimizes speed and performance.
13. What is data path in digital processing circuit?
A: A data path is interconnection of basic combinational functions such as arithmetic operations(addition,multiplication,comparision and shift) or logic (AND,OR,and XOR).
14. How do you minimize the propagation delay in manchester-carry chain adder.
A: It uses a cascade of pass transistors to implement the carry chain.
15. Define flattering in VHDL synthesis.
A: The process of converting the un optimized Boolean description to a PLA format is known as flattering.
16. Define factoring in VHDL synthesis.
A: It is the process of adding intermediate terms to ad structure to a Boolean description.
17. What are the uses of flattering and factoring in synthesis?
A: The ideal case is one which the critical path was flattered for speed and the rest of the design was factored for small area and low fanon.
18. Define fault coverage.
A: Fault coverage is defined as a ratio number of detected faults to the total number of faults.
19. Which test is used to test interconnects?
A: Boundary scan testing is used to test interconnects on printed circuit(PCBs) that are implemented at the integrated circuit levels.
20. What are the advantages of BIST.
A: lower cost of test
Better fault coverage, since special test structures can be incorporated on to the chips. Shorter the times if the BIST can be designed to the test more structures in parallel.Easier customer approach.Capability to perform tests out side the production electrical testing environment.
21. Define cross talk?
A: Cross talk is a phenomenon in which a signal transmitted on one circuit, or one channel of a transmission system, creates an undesired effect in another circuit or channel.
22. What is Body effect?
A: The threshold voltage Vt is not a constant w.r.t the voltage difference b/w the substrate and the source of the MOS transistor. This effect is called substrate- bias effect or body effect.
23. What is channel length modulation?
A: The current b/w drain and source terminals is constant and independent of the applied voltage over the terminals. The effective length of the conductive channel is actually modulated by the applied Vds, increasing Vds causes the depletion region at the drain junction to grow, reduces the length of the effective channel.
24. Define threshold voltage in CMOS?
A: The threshold voltage of Vt of MOS transistor defined as the amount Vgs required to form channel b/w source and drain of the transistor.Vgs
Destination IP = present content of IP + 8-bit (or) 16-bit Dispalcement given in instruction
Ex: JMP Lable
JMP SHORT Lable
Note: (i) If the displacement is 8-bit, the destination lies within -128 bytes to +127 bytes.
This type of JUMP is called as SHORT JUMP.
(ii) If the displacement is 16-bit, the destination lies within -32 K bytes to +32 K bytes.
This type of JUMP is called as LONG JUMP.
Intrasegment Indirect -->
In this mode, the destination address is found as content of Register or Memory location.
destination IP = 16-bit Content of memory location
Ex: JMP WORD PTR[BX]
CALL WORD PTR[BX]
destination IP [BX]
(b) Inter segment mode :
In this mode, the destination address lies in different Code segment.
It provides branching from one code segment o another code segment.
Here both CS and IP registers will be modified.
Inter segment Direct :
In this mode, the CS and IP values destination are specified directly in the instruction.
Ex: JMP 4000:6000
CALL 4000:6000
destination CS = 4000H, destination IP = 6000H
Inter segment Direct:
In this mode, the CS and IP values of destination are found as content of memory locations.
Ex: JMP DWORD PTR[BX]
CALL DWORD PTR[BX]
destination IP <-- [BX] destination CS <-- [BX+2] 25. What are the two modes of operations of 8086? Explain? OPERATING MODES OF 8086/8088: The 8086 can be operated in two modes. (1) Min. mode (2).Max. mode The pin MN/MX is used to select the min. (or) max. mode of operation The pins(24-31) issues two different set of signals – for minimum & maximum mode operations MINIMUM MODE: The minimum mode operation is selected by connecting the pin MN/MX to + 5 V supply The 8086 is operated in minimum mode in simple systems with a single CPU In minimum mode operation all the control signals are generated by CPU It is least expensive way to operate and the operation is similar to 8085A. MINIMUM MODE: The maximum mode operation is selected by connecting the pin MN/MX to GND The 8086 is operated in maximum mode in multi-processor system with more than one processor. In maximum mode, the control signals are generated by external Bus-controller 8288. The maximum mode operation is used only when the system contains arithmetic co-processor such as 8087 numeric co-processor. 26. What is the use of READY pin of 8086? A slow peripheral (or) memory device can be connected to microprocessor through READY line. It is used to insert wait states in bus cycles as needed to interface with slow memory &I/O. It is used by the MPU to sense whether the peripheral (or) memory is ready to transfer data or not. If READY =1, peripheral is ready to transfer data If READY=0, the processor WAITS until it goes to HIGH. 27. Which pins of 8086 are used for DMA? Explain. (or) Explain DMA operation. The HOLD & HLDA (pins 31 & 30) signals are used in DMA operation. Whenever the peripheral device is ready to transfer a block of data directly to memory, it sends a DMA request signal to DMA controller. Now the DMA controller initiates DMA operation by sending HOLD signal to the processor. The HOLD signal indicates the processor that other bus master is requesting for the use of system bus. When HOLD =1, the p stops the normal program execution & places AB, DB & control buses at high-impedance state and sends HLDA signal to the DMA controller The HLDA signal indicates that the processor has accepted the HOLD request and the gain control of the system bus is transferred to the DMA controller. During HLDA =1 , the DMA controller is the master of the system bus & Data are directly transferred from peripheral to memory directly. At the end of DMA operation, the HLDA becomes Low. 28. Write the features of 80286? Features of 80286: It is a 16-bit microprocessor, packaged in 68- pin PGA It has 16-bit data bus & 24-bit address bus It can address 224 locations = 16 M bytes of memory It uses segmented memory Clock frequency : 12.5 MHz, 8 MHz, 10 MHz. It doesn’t have multiplexed address/data lines It supports - Multi tasking/ multi user environment - Memory management Unit (MMU) - Virtual memory of 1 GB - Protected mode of operation 29. Write the features of 80386? It is a 32-bit micro processor packaged in 132-pin PGA It has 32-bit data bus & 32-bit address bus It can address 232 locations = 4 G bytes of Physical memory Clock Frequency is : 16 M Hz – 33 M Hz Two versions : 80386DX : 32-bit Address bus, 32-bit Data bus ( 132-pins) 80386SX : 24-bit Address bus, 16-bit Data bus ( 100-pins) It supports - Multi tasking/ multi user environment - Memory management Unit (MMU) - Virtual memory of 64 T bytes - Protected mode of operation - Paging Mechanism 30. Write the features of 80486? INTEL 80486 MICRO-PROCEESOR: It is a 32-bit micro processor packaged in 168-pin PGA It has 32-bit data bus & 32-bit address bus It can address 232 locations = 4 G bytes of Physical memory Clock Frequency is : 25 M Hz – 120 M Hz Two versions : 80486DX : on-chip numeric co-processor 80486SX : no numeric co-processor It supports - Multi tasking/ multi user environment - Memory management Unit (MMU) - Virtual memory of 64 T bytes - Protected mode of operation - Paging Mechanism Advantages : - It has on-chip arithmetic co-processor which is 3 –times faster than the combination of 80386 and co-processor 80387 - It has internal Cache memory of 8 K bytes - It has 5 – stage pipe lining - It has internal Parity checker/ generator. 31. Write the features of 80586 / PENTIUM microprocessor? PENTIUM MICROPROCEESOR: It is a 32-bit micro processor packaged in 237-pin PGA It has 32-bit data bus & 64-bit address bus It can address 232 locations = 4 G bytes of Physical memory. Clock Frequency is : 60 M Hz – 233 M Hz It supports - Multi tasking/ multi user environment - Memory management Unit (MMU) - Virtual memory of 64 T bytes - Protected mode of operation - Paging Mechanism with 4 MB memory pages Advantages : - Wider data bus width ( 64-bit) - Improved Cache structure : 8 KB data cache & 8 KB instruction - Faster numeric co-processor : 5 times faster than that of 80486. - Super scalar architecture : - Branch prediction logic : which allows programs that branch to execute more efficiently 32. Explain about 80386/ 80486 Memory management? 80386/ 80486 MEMORY MANAGEMENT: There are two reasons why memory must be managed in a multi-tasking operating system - The physical memory is not large enough to hold the operating system and all application programs that are being executed by the different users. - To make sure that the executing tasks do not access the protected area of memory. The memory management unit (MMU) performs the task of converting Linear address into Physical address, that access a physical memory location located anywhere within the memory system.The paging mechanism allows any Linear address, as it is generated by a program to be placed into any physical Memory page. 33. What is the use of Descriptors & Selectors? A descriptor is a series of 8-bytes , that describes and locate a memory segment. A selector is used to index/ select a descriptor from a table of descriptors. 34. What is Memory paging? The paging mechanism allows any linear address as it is generated by a program, to be placed into any physical memory page, as generated by the paging mechanism. A linear memory page is a page that is addressed with a SELECTOR and OFFSET ADDRESS in either the real or protected mode. A physical memory page is a page that exists at some actual physical memory location. 35. What is Superscalar architecture? Super Scalar architecture: If a processor contains more the one execution unit, then it is called as superscalar architecture.The Pentium microprocessor is organized with three execution units. One executes floating point instructions and other two(U-pipe and V-pipe) execute integer instructions. This means that it is possible to execute three instructions simultaneously. For example consider the following instructions : FADD ST,ST(2) , MOV EAX, 200H, MOV EBX, 300H The above instructions can be executed simultaneously because none of these instructions depend on each other. 36. What is branch prediction logic? Branch Prediction Logic: The Pentium microprocessor uses branch prediction logic to reduce the time required for a branch caused by internal delays. These delays are minimized because when a branch instruction (short or near only) is encountered, the microprocessor begins prefetch instruction at the branch address. The instructions are loaded into the instruction cache, so when the branch occurs, the instructions are present and allow the branch to execute in some clocking period. If for any reason the branch prediction logic errors, the branch requires an extra 3- clock periods to execute. In most cases the branch prediction is correct and no delay ensues. 37. What is the use of 8255 ? Ans: The 8255 is a Programmable Peripheral Interface device used to transfer data between Microprocessor & external devices. 38. Write the features of 8255 PPI? The 8255 PPI consists of THREE 8-bit I/O parallel ports : PORT-A , PORT-B, PORT-C Again PORT-C is divided into two 4-bit ports ( PORT-C upper, PORT-C lower) These 3 – ports are arranged in TWO groups to implement handshaking I/O. Group-A of 8255 PPI consists of PORT-A & PORT-C UPPER Group-B of 8255 PPI consists of PORT-A & PORT-C LOWER. The 8255 PPI can be operated in TWO modes : I/O mode & BSR mode The PORT-C of 8255 PPI can be operated in BSR mode. The Control Word Register (CWR) defines the mode of operation of 8255 PPI. 39. What is a stepper motor? Ans: Stepper motor is a device that converts electrical pulses into mechanical movements 40. What are the different types of parallel data transfer schemes? Ans: Programmed I/O , Interrupt driven I/O , Hardware controlled I/O (DMA) 41. Which method of parallel data transfer method is the fastest method . Ans: DMA 42. How many channels does the 8257 DMA controller has? Ans: 4- channels: ( CH-0, CH-1, CH-2, CH-3 ) 43. Which channel of 8257 has highest priority in fixed priority mode? Ans: CH-0 44. Which Channels of 8257 are used in memory to memory data transfer? Ans: CH-0 & CH-1 45. What is the use of 8259 ? The 8259 is a Programmable Interrupt Controller (PIC) that can manage 8-interrupts The PIC provides the priority for the interrupts ( Fixed priority, Rotating priority) The cascading mode of 8259 PIC allows upto 64- interrupts. It supplies the TYPE of the interrupt to the Processor so that the processor can calculate the Vector address It can mask the interrupt at any stage. 46. What is Interrupt vector address? What is the vector address for TYPE-3 interrupt? Ans: The interrupt vector is a memory block which contains the address of Interrupt Service Routine ( ISR). The size of the interrupt vector is 4-bytes.( for 8086 system) The Vector address for TYPE-n is = n * 4 The Vector address for TYPE-n is = 3 * 4 = 0000:000C H 47. For which type of interrupt, the vector address is 000C8 H ? Ans: TYPE-32H 48. Give any example for simplex transmission Ans: The simplex mode allows the transmission in only one direction. Ex: Radio signal transmission 49. Give any example for Half-duplex transmission Ans: The half-duplex mode allows the transmission in both directions but only one direction at a time. Ex: walky-talky 50. What is the use of USART ? Ans: The 8251 USART is used in serial data communication for serial to parallel & parallel to serial conversion. 51. Expand USART : Ans: Universal Synchronous/Asynchronous Receiver/Transmitter. 52. What is GPIB: Ans: General Purpose Interface Bus 53. The RS-232 standard was developed to interface _______________ Ans: MODEM & Data Terminal Equipment (USART) 54. What is the need for voltage transmitters in serial data Communication? Ans: Because of incompatibility of RS-232 logic levels with TTL logic levels, the voltage transmitters (drivers/receivers) are required to interface TTL with RS-232 signals. 55. Give the differences between synchronous & asynchronous data transmissions? Ans: Synchronous data transmission Asynchronous data transmission Same CLK is applied to both TX & RX Sync. pulses are required A group of characters can be transmitted Used for High-speed transmission Different CLK pulses are applied Start & Stop pulses are required Only one character can be sent at a time Used for Low-speed transmission 56. List-out the MODEM control signals DTR : Data Terminal Ready , DSR : Data Set Ready RTS : Request To Send, CTS : Clear To Send 57. Give the differences between Microprocessors & Microcontrollers MICROPROCESSOR MICRO CONTROLLER Microprocessor is a digital computer CPU that fetches instructions from memory and executes them Micro controller is a true on-chip computer, used to control the operation of a machine using fixed program Microprocessors are used for general purpose applications Microcontrollers are used to some specific applications. Microprocessor consists of ALU, Register array and Timing & Control unit. It consists of all the features of microprocessor as well as internal RAM, ROM, parallel I/O ports, serial port, Times/counters, CLK generator…etc To make a computer, the microprocessor requires additional devices such as Memory, I/O ports, CLK generator…etc Micro controller can function as a computer with addition of no external devices. Microprocessor is concerned with rapid movement of data/code between external memory & CPU Micro controller is concerned with rapid movement of data/code within the Chip. It supports many instructions for the movement of data between external memory & CPU It supports one or two instructions for moving data between external memory & CPU. Microprocessor supports one or two types of bit-handling instructions Micro controller supports many types of bit-handling instructions 58. Give the features of 8051 micro controller. -It is an 8-bit micro controller ( consists of 8-bit ALU) - Internal CLK generator ( frequency = 11.006 MHz.) - 8051 Registers: 32-General Purpose Registers: ( A,B, first 32 bytes of internal RAM) 16-bit data pointer (DPTR = DPH : DPL ) Program Status Word ( PSW) Program Counter (PC) Stack Pointer ( SP) - Two 16- bit Timers/Counters ( T0 = TH0 : TL0 & T1 = TH1 : TL1 ) - Five- interrupt sources ( 2- external: INT0 & INT1 , 3-internal : TF0 , TF1, & serial port interrupt ) - Serial port : SBUF - Four 8-bit I/O ports : PORT-0, PORT-1, PORT-2, PORT-3 - 128 bytes of INTERNAL RAM - 4 K bytes of INTERNAL ROM 59. What is the use of DPTR ? Ans: The 16-bit DPTR is a special function register, used to access External Memory (external RAM & external ROM) & internal ROM. 60. Explain about the internal RAM of 8051? Ans: The 8051 has 128-bytes of internal RAM, which is divided into 3- parts - 32 working registers ( 00 H to 1F H) - 16 bytes of bit addressable area ( 20 H to 2F H) - 80 bytes general purpose area ( 30 H to 7F H) The first 32-bytes of internal RAM can be used as 32-working registers. This area is divided into 4-banks ( BANK-0 , BANK-1, BANK-2, BANK-3 ). Each bank consists of 8-registers (R0 ,R1, R2 ,R3, R4 ,R5, R6 ,R7 ) These banks are selected by PS1 & PS0 bits of PSW. 61. Give the bit representation of Flag register / PSW of 8051? OV - F0 PF RS1 RS0 AF CF 62. What is a special function register (SFR) ? Give some examples Ans: The SFRs are used to perform some specific function. Ex: DPTR (DPH:DPL), IE, IP, P0, P1, P2, P3, SP, PSW…. 63. Write the instructions to access external RAM? Ans: MOVX A, @DPTR MOVX @DPTR, A 64. Write the instructions to access external ROM? Ans: MOVC A, @DPTR MOVC A, @A+DPTR 65. What is the difference between timer & counter action? Timer It counts the no. of internal machine cycles Counter It counts the no. of external pulses applied to pins T0 & T1 66. Which interrupt of 8051 has highest priority ? Ans: INT0 has highest priority & Serial port interrupt has lowest priority. 67. Explain the timing & control signals of 8051. EA : (External Access) : This signal is used to access external memory When EA is active, PORT-0 emits (AD0 – AD7) & PORT-2 emits (A8 – A15) PSEN : (Program Strobe Enable) : This signal is used to read the code from external ROM. ALE : (Address Latch Enable) : This signal is used to indicate the valid address Information on multiplexed address/data bus. RESET : This pin is used to reset the micro controller. After RESET, the PC is initialized to zero & program execution starts from 0000H in internal ROM XTAL1 & XTAL2 :These two pins are provided for connecting the crystal oscillator. 68. Give the alternate function of I/O ports of 8051. PORT-0 (AD0 – AD7) PORT-1 No alternate function PORT-2 (A8 – A15) PORT-3 Each pin of PORT-3 has some alternate function. pin function description P3.0 RXD Serial data input P3.1 TXD Serial data output P3.2 INT0 External Interrupt-0 P3.3 INT1 External Interrupt-1 P3.4 T0 External input to Counter-0 P3.5 T1 External input to Counter-1 P3.6 WR External RAM write control signal P3.7 RD External RAM read control signal 69. What is a machine cycle / bus cycle? Ans: The required for the CPU to perform a basic bus operation. Ex: basic bus operation read, write, fetch… For 8086 microprocessor, one machine cycle = 4- clock periods For 8051 micro controller, one machine cycle = 12- clock periods 70. What is an instruction cycle? Ans: The time required for the CPU to execute an instruction completely is called as instruction cycle. An instruction cycle consists of one (or) more no. of bus cycles. SIGNALS & SYSTEMS 1. How do you define a Signal? A: Signal is formally defined as a function of one more variables that conveys information on the nature of a physical phenomenon. 2. What are the characteristics of a Signal? A: Amplitude, Phase, Frequency. 3. Give examples of 2-Dimenional and 3-Dimensional signals. A: Still image is an example of the 2-Dimensional signal and speech is an example of 3-Dimensional signal. 4. What is an Analog signal? Can it be stored in a computer? A: A signal which varies continuously with time is an Analog signal and it can’t be stored in a computer. 5. Based on which parameters an Analog signal differs from Digital signal? A: Amplitude and time are the parameters which differs Analog signal from Digital signal. 6. What do you mean by Random signal can u give an example? A: Random signal is a signal that takes random values at any given time. A noise is the best example. 7. How many energy signals and power signals can be differentiated? A: In energy signal the energy should be finite and the power is equal to zero and In power signal the power should be finite and the energy is equal to finite. 8. What is the one more name of Dirac delta function? A: Unit impulse function. 9. What are the transformations of independent variable(Time)? A: Time shifting , Time reversal and Time scaling. 10. What is Fourier series representation? A: Representation of a function over a certain interval by a linear combination of mutually orthogonal functions is called Fourier series representation of a function. 11. What do you know about Gibbs Phenomenon. A: The Fourier series fails to converge at the points of discontinuity shows large amounts of ripples known as the Gibbs phenomenon. UNIT-2 1. What is the purpose of Fourier series representation? A: To know the different frequency components of a given periodic signals. 2. Who found the Fourier series representation? A: Fourier 3. Mention different symmetries of a periodic signal. A: Hidden Symmetry , Rotionary symmetry. 4. What do you mean by Spectrum? A: Graphically representation of frequency versus amplitude of any signal. 5. Is it possible to obtain the negative frequency of any signal? A: If the signal is expressed in terms of exponential functions then we can observe the negative Frequency as an index of the exponential function. 6. What do you mean by the Line spectrum? A: If the spectrum is defined at discrete levels of frequency then the spectrum is known as Line spectrum. 7. What is the Fourier series representation of a periodic gating function with period T. A: Sampling function which oscillates with a period 2π. 8. What is the weak Dirichlet Condition. A: Over any period signal must be absolutely intergrable. 9. Which type of waveform will you observe from the Fourier series representation for a impulse train? A: Impulse train. UNIT-3 1. Is the Fourier applicable for a periodic signal? A: Not applicable 2. What is the relation b/w Fourier series and Fourier transformation. A: Fourier transform as a limiting case of the Fourier series by the period of a periodic function become infinite. 3. What is the spectral nature of a Periodic Signal . A: The spectral density function or the Fourier transform of a periodic signal consists of impulse located at the harmonic frequencies of the signal. 4. What is the one more name of the Modulation theorem. A: Frequency Translation theorem. 5. Can you state the frequency – translation theorem? A: Multiplication of a time domain signal by a factor translates the whole frequency spectrum by an amount Wo. 6. Give the application of Fourier transform? A: Fourier transform is used for analyzing and designing frequency relative filters. 7. What is Hilbert transform? A: Hilbert transform is a transform which provides a phase shift of 90 degrees to a given signal. 8. Is it possible to maintain same spectral density of a given signal with Hilbert transform? A: Yes, because Hilbert transform provides only phase shift. 9. Mention any two applications of Hilbert transform. A: a) It is used in SSB modulation. b) Used for mathematical representation of a gating of a band pass signal. 10. What is the Fourier transform of a Gating function. A: Sampling function. UNIT-4 1. What do you mean by System? A: System is an entity which manipulates on the given input signal to accomplish a function there by yielding new signals. 2. What is meant by a Memory less system. A: A system is said to be a memory less if the out of at any instant depends on the present i/p. 3. Which system is said to be a Linear system. A: A system which satisfies superposition principle at any instant is said to be a linear System. 4. What is an LTI System. A: A system which obeys linear and time invariance properties is known as LTI system. 5. How you can find behavior of an LTI system. A: Simply by passing impulse as an input and observing the output. 6. How can you distinguish b/w noisy signal and distorted signal? A: Noisy signal is an unwanted electrical signal. If the information of any signal is changed by noisy signal known as distorted signal. 7. What do you know about distorted less transmission system. A: Transmission of a signal through a system is said to be distortion less, if the output signal is an exact replica of the input signal. [ A constant change in magnitude and a constant time delay in the output is not considered as distortion.] 8. What are the distortions we can observe during signal transmission. A: Amplitude distortion , phase distortion. UNIT-5 1. What is meant by Sampling? A: Sampling is a process which converts a continuous signal into discrete signal. 2. What are the different types of Sampling? A: i) Ideal sampling or instantaneous sampling or impulse sampling ii) Natural sampling iv) Flat top sampling (rectangular pulse sampling) 3. How can you distinguish natural sampling and flat top Sampling. A : In case of natural sampling the tops of the samples follows the shapes of the original signal and in the case of flat top sampling the samples have flat tops 4. What is Aperture effect? A: In flat- top sampled signal, distortion get introduced by making the top as flat. This effect is called as Aperture effect. 5. What is Aliasing effect? A: The overlapping of upper side band with lower side band of the next spectrum then that effect is known as Aliasing effect. 6. How a flat top sampled signal be obtained from the ideal sampled signal? A: Flat top sampling is obtained by convolving ideal sampled signal with a rectangular pulse. 7. Which filter is used as Anti –Aliasing filter. A : Low pass filter. 8. When does Aliasing effect occur? A: Aliasing effect occurs when sampling rate is less than twice that of modeling signal. 9. What is the draw back with over sampling? A: More band width requirement due to Guard band. 10. What is the draw back of under sampling? A: Aliasing effect which leads to loss of information during reconstruction. Convolution and correlation of signals 1. What is the purpose of convolution? A: Convolution is useful for describing the input/output relationship in a linear time invariant system. 2. What is the convolved response of a rectangular pulse with itself? A: Triangular pulse. 3. What are the laws of convolution relationship? A: i) Cumulative law ii) Associative law iii) Distributive law. 4. What is the time Convolution theorem? A : Time convolution theorem states that convolution in time domain is equivalent to multiplication of their spectra in frequency domain. 5. What do you mean by Correlation? A: Correlation means estimating relation b/w two signals. 6. Give the applications of correlation? A: RADAR, SONAR, In Digital communications. 7. At what condition the correlation and convolution are equivalent. A: If the two given functions are even functions then the correlation and convolution are equivalent. 8. For which of the λ maximum value of autocorrelation function R(λ) occurs? A: λ=0 (at the origin). 9. Is the auto correlation R(λ) of a periodic waveform periodic with the same period. A: Periodic. 10. Which of the relation existing b/w auto correlation of a pulse type signal and its energy density spectrum. A: Auto correlation function of a pulse type signal and its energy density spectrum from a Fourier transform pair. 11. How can you detect periodic signals in the presence of noise? A: Correlation techniques provide a powerful tool in the solution of detecting periodic signals in the presence of noise. Laplace Transforms 1. What is the advantage of Laplace transform over Fourier transform? A: With the Fourier transform imaginary theory components can not be represented. But, it is possible with Laplace. 2. From the Laplace domain how can we say that any LTI system is Stable. A: An LTI system is a stable IFF the ROC of its system H(s) includes the jw-axis. Z-TRANSFORM 1. How the s-plane transformed in to z-plane? A: The left-half s-plane maps into the interior of the unit circle in the z-plane and the right-half s-plane maps outside the unit circle in the z-plane. 2. In z-domain when a discrete – time LTI system is caused? A: IFF the ROC of a discrete time LTI system is the exterior of a circle, including infinity then the system said to be casual. 3. How can you check the stability of a discrete time LTI system? A: An LTI system is said to be stable iff the ROC of its system function H(Z) includes the unit circle|z|=1. CONTROL SYSTEMS 1. What are the different classification of control systems? i) Open loop control systems. ii) Closed loop control systems. iii) Linear and nonlinear control systems. iv) Time variant and time invariant control systems. v) Analog and digital control systems. 2. What are the advantages and disadvantages of closed loop control systems? Advantages i) More accurate ii) It compensates for disturbances iii) Its time response can be adjusted by appropriate design Disadvantages i) More complex and expensive ii) Reduces the gain of the systems iii) If the closed loop system is not properly designed, the feedback may lead to an unacceptable response. 3. What are the fundamental components of mechanical systems? Mass, spring and dashpot are the fundamental components of a mechanical system. 4. What is the force – voltage analogy of mass M? Inductance L 5. What is the force – voltage analogy of dashpot constant B? Resistance R 6. What is the force – voltage analogy of spring constant K? Reciprocal of capacitance 1/c 7. What is force – current analogy of velocity? Voltage V 8. What is force – current analogy of displacement? Flux ø. 9. What is force – current analogy of stiffness constant K? Reciprocal of inductance 1/L 10. What is torque – voltage analogy of J? Inductance L 11. What is torque – current analogy of viscous friction coefficient B? Conductance ( 1/R ) 12. Write Mason’s Gain formula? Mason’s gain for is given by T=1/Δ∑kPkΔk Where Pk = Path gain of kth forward path Δ = Determinant of the graph = 1- (sum of individuals loop gains) + (sum of gain of all combinations of two non touching loops) - (sum of gain product of all combinations of three non touching loops) +… Δk = Δ of that part of graph not touching the kth forward path 13. What is a synchro? Synchro is an electromagnetic transducer that produces an output voltage depending upon angular displacement. 14. What are the standard test signals employed for time domain studies? The standard test signals employed for time domain studies are 1. Impulse signal 2. Step signal 3. Ramp signal 4. Parabolic signal 15. What are the time domain specifications? Time domain specifications are: 1. Delay time 2. Rise time 3. Peak time 4. Maximum overshoot 5. Settling time 6. Steady steady error 16. Define settling time Settling time is defined as the time taken by the response to reach and stay within a specified tolerance band of its final value. 17. Define peak overshoot Percentage of peak overshoot ={ C(tp) – C () } / C () X 100% 18. The transfer function G(s) of a PID controller is_____________________ G(s) = Kc (1 + 1 / Tis + Tds 19. What is steady state error? It is the difference between reference and output of the system as t -> .
20. What are the difficulties faced while applying Routh –Hurwitz criterion?
(a) All elements in a row may become zeros.
(b) First column element may become zero.
21. How is a system classified based on damping factor?
(a) Underdamped system when 0 < < 1 (b) Critically damped system when = 1 (c) Over damped system when > 1
22. In____type of controller. Ess is constant and improves only the__________response whereas__________controller increases____________and__________of systems and improves the_________response.
P, transient, P+I, order, type, steady state
23. What is BIBO stability criterion?
A system is said to be BIBO stable if for every bounded input the output is bounded. This criterion is know as BIBO stability criterion.
24. How are the locations of roots of characteristic equation related to stability?
For stability, all the roots of characteristic equation must lie on the left half of s-plane.
25. What are breakaway points?
The breakaway points on the root locus are the location of repeated roots of characteristic equation.
26. If the root loci do not cross the imaginary axis then the system is_______________.
Stable for all values of k.
27. State the rule for finding the value of k at any point s0 on the root locus diagram
The value of k at any point s0 on the root locus diagram is given by
K = { product of phasor lengths from the point s0 to open loop poles / product of phasor lengths from the point s0 to open loop zeros }
28. State the rule for finding out the root loci on the real axis.
A point on the real axis lies on the locus if the number of open loop poles plus zero on the real axis to the right of the point is odd.
29. State the root locus rule for angle of departure from a complex open loop pole.
The angle of departure from an open loop pole is given by
Øp = +1800 (2q + 1 ) + Ø; q = 0,1,2,…
Where Ø is the net angle contribution at this pole by all other open loop poles and zeros.
30. What is the effect of feedback on poles?
It modifies the location of poles
31. Is there any effect of feedback on zero?
It does not alter the location of zero for unity feedback system.
32. What is the nature of response if the poles are complex?
The response is oscillatory
33. What is root locus?
It is loci of closed loop poles as open loop gain (usually) varies from 0 to
34. How many loci are there in a root loci plot?
It is equal number of poles
35. For a system having non – repeated roots on the j axis, comment about the stability of the system.
System will be under sustained oscillations.
36. What are the effects of adding open loop pole to root locus and the system.
System becomes sluggish.
37. State the necessary and sufficient conditions of Routh – Hurwitz criterion, for stability.
For a system to be stable, it is necessary and sufficient that each tern of its first column of Routh array is to be positive if an > 0.
38. What is compensator?
The subsystem added to the original system to alter the dynamic and / or static characteristics of the original system is called compensator.
39. What are the classifications of compensators?
Lag compensator, lead compensator, lag-lead compensator and velocity compensator.
40. What is the characteristic of a lag compensator?
Lag compensator introduces lag phase shift in the system.
41. What is the characteristic of a lead compensator?
Lead compensator introduces lead phase shift in the system.
42. What is the phase shift characteristics of a lag – lead compensator?
It introduces either lag phase shift or lead phase shift depending upon the frequency of the signal
43. What is the effect of adding a pole to the system?
Addition of pole degrades the relative stability and drives the system towards in stability.
44. What is the effect of addition of zero to the system?
Addition of zero improves the relative stability and drives the system towards stable state.
45. What are the advantages and disadvantages of frequency response analysis?
Advantages
1. The design and parameter adjustment of the open loop system for the given closed loop requirement is carried out easily.
2. The effect of noise can be easily visualized in frequency response anlaysis.
Disadvantages
1. The frequency response test cannot be recommended for the system with large time constants.
2. It cannot be performed on non-interruptable systems.
46. What is polar plot?
A plot between magnitude versus phase angle in polar coordinate or A plot between imaginary part versus real part of the sinusoidal transfer function G (jw) for various values of w is known as polar plot.
47. What is the effect on the polar plot if a non – zero pole is added to the transfer function?
Addition of a non – zero pole to the transfer function results in further rotation of the end points of polar plot through an angle of 900.
48. What is the effect on the polar plot if a pole at origin is added to the transfer function?
When a pole at origin is added to the transfer function, it rotates the entire polar plot by a further angle of 900.
49. What are Bode plots?
The logarithmic plot which consists of two graphs, one between 20log\G(jw) vs w and the other G(jw) vs w are called Bode plots.
50. What are asymptotes? Define corner frequency.
In Bode plot the low – frequency and high frequency approximations can be represented by straight lines called asymptotes. These two asymptotes meet at a frequency know as corner frequency.
51. When the transfer function is said to be minimum phase?
A transfer function is called minimum phase when all the poles and zero are in left half as s–plane.
52. What is meant by principle of argument?
The principle of argument can be stated as follows
If Q(s) is a single valued function that has a finite number of poles and zero in the s-plane and C is a contour is s-plane that does not go through any of the poles and zero of Q(s); then the corresponding locus Cq mapped in the Q(s) – plane will encircle the origin as many times as the difference between the number of zeros and poles of Q(s) that are encircled by the s – plane contour C.
53. State Nyquist stability criterion.
If the contour of the open loop transfer function G(s)H(s) corresponding to the Nyquist contour in s – plane encircles the point ( - 1 + j0) in the counter clockwise direction as many times as the number of right side s – plane poles of 1 + G(s)_H(s), then the closed loop system is stable.
54. Define gain margin.
It is the factor by which the gain of the system can be increased to drive the system to the verge of instability.
55. Define phase margin.
It is the additional phase lag at the gain cross over frequency required to bring the system to the verge of instability.
56. Define gaincross over frequency.
It is the frequency at which 20 log |G(jw)H(jw) | = 0 or |G(jwH(jw))| = 1
57. Define phase crossover frequency.
The frequency at which the phase angle is 1800 is called the phase cross – over frequency
58. What are the advantages and disadvantages of the lead compensation technique?
It reshape the frequency response curve to provide sufficient phase lead angle. It amplifies noise.
59. State the properties of lead network.
It reshape the frequency response curve to provide sufficient phase lead angle. It is a high pass filter so amplifies noise.
60. What is state variable?
The variables involved in determining the state of dynamic system are called the state variables. Generally x1(t),x2(t),…,xn(t) are called the state variables.
61. What is state space?
The space whose coordinate axes are nothing but the ‘n’ state variables with time as the implicit variable is called the state space.
62. What are the properties of state transition matrix.
(a) Ø ( 0 ) = eAx0 = I (Identity matrix)
(b) Ø-1 (t) = Ø (-t)
(c) Ø(t1 + t2) = Ø(t2). Ø(t1)
(d) [Ø(t)]n = Ø (nt)
(e) Ø(t2 – t1). Ø (t1 – t0) = Ø (t2 – t0)
63. What is controllability?
A general nth order multi – input liner time invariant system X = AX + BU is completely controllable if and only if the rank of the composite matrix Qc = [B : AB : … : An-1 B] is n
64. What is observability?
A general nth order multi – input – multi – output time invariant system X = AX + BU, Y = CX is completely observable if the rank of composite matrix Qc = [CT : AT CT : … : (AT)n-1CT]T is n.
ANALOG COMMUNICATION
1. Define frequency translation ?
A. The process in which the spectrum of the original signal is shifted to a new spectral range .
2. Define mixing or heterodyning ?
A.The operation of multiplying a signal with an auxiliary sinusoidal signal is called mixing or heterodyning
3. What is modulation ?
A.Superimposing a low frequency (long wave ) voice information component on a high frequency (short wave ) carrier signal
The process by which some characteristic of a carrier is varied is accordance with a modulating wave .
4. What is the need for suppressed carrier systems ?
A.Of the total power of modulated carrier , only one 1/3rd amount is available in the side bands ie; 2/3rd of the total power is available in the carrier which carries no information.so , by suppressing the carrier before transmission 2/3rd amount of power can be saved
5. How much amount of power is saved in amplitude modulation suppressed carrier systems?
A.66.67% or 2/3rd of the total power
6. How much amount of power is saved in single side band suppressed carrier systems ?
A.83.3%
7. What is multiplexing ?
A.The process of combining several message signals for their simultaneous
transmission over the same channel
8. What is the bandwidth occupied by an AM-SC signal ?
2fm (twice that of the highest modulating signal frequency )
9. What are the advantages of SSB-SC over AMFC ?
A.Less bandwidth , less transmitted power .
10. What is the need for modulation ?
A.The antenna height can be reduced or can be adjusted according to the range of modulating signal , multiplexing is possible .
11. Wich characteristic parameter of carrier is varied in frequency modulation?
A.Frequency
12. What is the transmitted bandwidth in frequency modulation
A.2n fm ( n= number of significant side bands )
13. What happens to the transmitted power with the increased depth of modulation is FM.
A. Remains constant
14. What happens to the transmitted power with the increased depth of modulation in AM
A.Transmitted power also increases
15. What is the disadvantage of direct method of FM generation?
A.Low stability
16. How to convert a phase modulated signal is to frequency modulated signal?
A.Initially the modulating signal is integrated and then to be phase modulated
17. How to convert a frequency modulated signal in to phase modulated signal?
A.The modulating signal is differentiated and then frequency modulated .
18. What is the hard limites?
A circuite which is used to maintain the amplitude of the FM wave constant
19. In FM , before and after modulation , why is the power remains constant?
A.Because the amplitude remains constant ( if the amplitude changes the transmitted power also changes
20. What is the necessity of deempharis and preemphasis in FM ?
A.The noise power density at the demodulation o/p rises parabolically with frequency but for message signals , the power density decreases with frequency , the noise is strongest in the freq range where the signal is weakest to overcome
21. What is the relation between [SNR]0 & [SNR]i in SSB ?
A. [SNR]0 =[SNR]input
22. What is the relation between [SNR]0 &[SNR]i in DSB-SC ?
[SNR]0 =2[SNR]input
23. Which circuit is used to improve the threshold in frequency modulation by improving. [SNR]0 at the higher edge of the message signal ?
A.Pre emphasis ckt
24. What is meant by deemphasis in FM ?
A.The process which restores the amplitude distribution of message band by bringing back the original level of high frequency components
25. For what value of modulation index , the modulation is said to be critical ?
A.Modulation index = 1
26. What is quadrature null effect ?
A.The out put signal is zero where the local carrier is in phase quadrature with the transmitted carrier
27. What are the disadvantages of fitter method of SSB generation ?
A.I ) Requires sharp cutoff frequencies for fitters
2) the transmitting frequency should be properly related to frequency of modulating signal
28. What is the lock range of PLL?
A.The range of frequencies over which PLL can maintain lock with the incoming signal frequency
29. What is capture range of PLL ?
A.The range of frequencies overWhich PLL can acquire lock
30. What is the difference between narrow band FM and wide band FM ?
A.If modulation index ≤1 NBFM (Point To Point Communication )
Modulation index >>1 WBFM (used for broadcasting )
31. What is the basic application of vertigial side band modulation ?
A.TV broadcasting
32. Which modulation is used for sound (audio) broadcasting in TV ?
Frequency modulation
33. Which modulation is used for picture (video ) broad casting in TV ?
A.Amplitude modulation
34. What is the maximum allowable deviation of FM transmitter ?
A.75 KHz
35. what is the maximum allowable modulating signal frequency in AM >
A.5 KHz (Hence Bandwidth = 2 fm =10KHz )
36. what is a high power level modulator ?
A.a modulator in which , the carrier is first amplified and then modulation is done .
37. what is amstrong method ?
method of generating FM by using phase modulation technique to increase frequency stability
38. why is a super heterodyne receiver so called ?
the carrier frequency is mixed with a local oscillator frequency which is generally high then carrier .
39. what is sensitivity of receiver ?
the ability of the receiver to detect the weakest possible signal
40. what is selectivity of a receiver ?
the ability of the receiver to reject the adjacent frequencies and select the required frequency
41. what is image signal (frequency)?
A signal whose frequency fi is above the local oscillator frequency fl by the same amount as the desired signal frequency fc is below the local oscillator frequency
42. what is automatic gain control bias ?
A.a bias to keep the receiver output substantially constant with time for any variation
43. how should be the value of intermediate frequency to have higher image frequency rejection ?
A.too high
44. what are the advantages of using RF amplifier in receivers ?
A. higher selectivity
higher sensitivity
higher SNR
45. what is the necessity of mixer or super heterodyne receiver?
A.to bringdown the carrier frequency to a lower value in order to achive proper Q value of the tuned circuit.
46.What is pulse modulation?
A.the modulation is which any characteristic parameter of the carrier puls is modified in accordance with modulating signal.
PAM-amplitude of the pulse,
PWM,PDM-width of the pulse.
PPM-position of the pulse.
47.what is double spotting?
A .picking up of the same short wave station at two nearly points on the receiver dial.
48.what is superheterodyne tracking?
A . the process of tuning the local oscillator to a predetermined frequency for each station throughout the AM band.
49. how to choose intermediate frequency ?
A .if too high –poor selectivity and poor adjacent channel rejection
Increases tracking difficulties
Higher image freq rejection
if too low-sharp selectivity freq uency stability of local oscillator must be carefully.
50.what are standard broadcasting frequencies?
A . AM-tuning band 540-1650khz
If frequency 438-465khz
FM- tuning band88-108mhz
If frequency 10.7mhz.
51.what is the basic junction of intermediate frequency amplifier in superheterodyne
receivers?
A. Rejecting adjacent unwanted frequencies
52.comparision of AM & FM receivers?
A .generally much higher operating frequencies in FM
Need for limiting & deemphasis in FM
Different methods of demodulation & AGC
53.what are the dis advantages of tuned radio frequency(TRF)?
A .receives over superheterodyne receivers.
TRF-suffer from variation is band width
In sufficient adjacent frequency rejector
Unstability.
54.where is the basic application of SSB?
A. point to point communication radio telephone
Police wireless communication
Telegraph
VHF &UHF communication systems.
Digital Communications
1. List two advantages of digital communication over analog communication.
a) More noise immune
Usage of regenerative repeaters in DC
2. What are the disadvantages of Digital communication?
a) Incuased transmission bandwidth.
Incuased system complexity.
3. What is sampling?
a) Process by which a signal continues in time is converted into discrete in time.
4. What is Quantization?
a) Process of converting a continuous amplitude signal into discrete amplitude signal.
5. What is the process by which noise can be eliminated (almost) from the digital
Communication system?
a) Quantization
6. What is the process by which the dynamic range of the quantization can be improved?
(i.e suited for small and large amplitude signals)
a) Companding (compression at transmittee & expansion at receive)
7. What is DPCM?(Differential pulse code modulation)
a) The process in which the difference between two consecutive samples of signal is quantizes and transmitted to conserve bandwidth.
8. What is the modulation in which the difference between two sample of a signal is quantized into a single bit?
a) Delta modulation.
9. What is slope overload distortion?
a) In Delta modulation, the distortion which arises due to the higher slope of the modulating signal than the estimated signal,such that the estimated signal cannot follow the changes in the modulating signal.
10. what is granular noise?
a) In delta modulator, the deviation or noise from the original modulating signal to the approximated signal,as the approximated signal is represented by step like waveform.
11. List some differences between PCM &DM.
DM PCM
No of bits : single bit more than one depending or quantized levels
Type of transmission: logic 1 or logic 0 code words are transmitted
Band width : very low more
Sampling freq :can be high less than DM
12.what is the other name of Amplitude shift keying?
a) ON-OFF keying.
13.what is the bandwidth of an Ask signal?
a) ≥2fb →fb frequency of the digital data.
14. What is the band width of the fsk signal?
a) ≥4fb
15. What is the bit synchronizer?
a) In digital communication, a circuit which recognizes precisely the nomest which corresponds to the end of time interval allocated to one bit and the beginning of the next.
16.How many frequencies with which a QFSK signal is transmitted?
a) Four.
17. What is the need for DPSK over BPSK?
a) To eliminate the ambiguting about whether the demodulated data is or is not inverted. Avoids the need for synchronous carrier required at the demodulator.
18. what are the advantages of differential PSK over Binary PSK?
a)the error rate in DPSK is greater than in PSK(errors occur in pairs)
Noise is one bit interval many cause errors to two bit determination.
19. What is the effect on bandwidth with the increase in M is Many systems?
a) Bandwidth decreases
20.What is the effect of increased M is Many systems on probability of error in BPSK?
a)Probability of error increases
21. What is the effect of increased M is Many systems on probability of error in BFSK?
a) Probability of error decreases
22. Why to prefer BPSK over BFSK?
a)Probability of error is less Bandwidth occupied is less
The transmitted power contributes for the information.
23. What is the necessity of an integrator circuit before demodulation at the receiver?
a) Improves signal to noise ratio as the integrator enhances the signal relative to the noise.
24. Whre does a noise voltage causes an error in transmission?
a) If the noise voltage amplitude is greater than the signal voltage and is of opposite polarity.
25. What is an optimum filter?
a) A filter is said to be optimum, if probability of error occurrence is minimum.
26. What is a matched filter?
a) An optimum filter with the inclusion of white Gaussian noise.
27. What is the unit of information?
a) Bits
29. What is the average information associated with an extremely unlikely message or likely message?
a) Zero
29. How many bit errors that can be connected using Hamming code?
a)Single bit errors
30. What is the minimum Hamming distance of Hamming code?
a) dmin=3
31. Define code rate.
a) It is defined as the ratio of number of uncoded messages bits to the number of coded message bits.
32. Define constraint length of a convolution encoder.
a) No of shifts over which a single message bit can influence the encoder output.
i.e. shifts required for a message bit to enter the shift register and finally come out.
33. What are the three graphical representations of convolutional encode?
a) State diagram Code tree Trellis
34. Which channel codes are used if the message bits arrive serially rather than in blocks?
a) Convolutional codes [if blocks −−−−−−−block codes]
35. How many number of bit errors than can be corrected using rate ½ evolutional encoder?
a)≤
36. Which algorithm is used to decode convolutional code?
a) Viterbi algorithm
37. List two properties of mutual information?
a) Mutual information is symmetric
Mutual information is nonnegative
38. State Shannon’s channel coding theorem?
a) If information rate is less than channel capacity, then there exists a coding technique such that the output of the source may be transmitted over the channel with a probability of error in the receiver message which may be made arbitraeily same [R ≤ C]
39. Define entropy?
a) Average information content per symbol.
40. Define information rate.
a) Minimum average data rate needed to covey the information the source to the destination.
41. What is the function of the source encoder?
a) It converts the symbol sequence into a binary sequence of 0’s & 1’ by assigning codewords to the symbols.
SATELLITE COMMUNICATIONS
1. How many GEO satellites are required to cover the whole surface of the earth?
A.3.
2. What is meant by uplink signal?
A. The signal transmitted by the ES to the satellite is called uplink signal.
3. What is meant by downlink signal?
A. The signal transmitted by the satellite to the ES is called downlink signal.
4. How to locate satellite with respect to earth?
A. By estimating the orbital parameters or orbital elements.
5. How to launch satellite into the orbit?
A. There are 2 methods to launch the satellite into the orbit.
1. Expandable launch Vehicle.
2. Space Satellite.
6. what is the disadvantage of Geo-stationary satellites?
A. These don’t cover the high –latitude regions.
7. How to cover the high-latitude regions of the earth?
A. Using inclined object.
8. For elliptical orbit, what is the value of e?
A. e<1. 9. For circular orbit , what is the value of e? A. e=0. 10. What is meant by molniya object? A. It is a more elliptical orbit stretched more than 3000 km in northern direction. 11. What is progade orbit? A. If the satellite moves in the direction of earth rotation then it is called progade orbit. 12. What is Retrogade orbit? A. If the satellite moves in the opposite direction of earth rotation then it is called Retrogade orbit. 13. Define Ascending node? A. The point where the satellite crosses the equatorial plane while moving in its orbit from south to north is called Ascending node. 14. Define Descending node? A. The point where the satellite crosses the equatorial plane while moving in its orbit from north to south is called Descending node. 15. What are the advantages of Geo-stationary satellites? A. There is no need of tracking. 16. What is Apogee? A. The far away point in the elliptical orbit is called Apogee. 17. What is Perigee? A. The nearest point in the elliptical orbit is called Perigee. 18. What is equatorial orbit? A. The orbit which is directly above the equator is called equatorial orbit. 19. What is inclined orbit? A. The orbit which makes some inclination with respect to equator is called inclined orbit. 20. What is polar orbit? A. The orbit which is directly above the poles is called polar orbit. 21. What is the use of store and forward concept? A. To provide the communication between LEO satellite to MCS in non real time. 23. What is the advantage of ISL’s? A. To provide real-time communication between the LEO satellite and MCS. 24. Define Geo-stationary satellite? A. A satellite which moves in circular equatorial orbit having a radius of 42,242 km with speed as same as that of the earth is called Geo-stationary satellite. 25.What is the altitude of GEO satellite? A. 36,000 km. CMC 1.Define a Cell ? A. The Smallest Geographical Area Covered By Wireless Communication Is Said To Be a Cell. 2. What Is the Shape Of a Cell ? A. The Shape Of a Cell Is Hexagon. 3.What Is the Normal Operating Range Of Frequency For Cell Phones ? A.The Operating Frequency For Cell Phones Are 824-849 MHZ. 4.What Are He Types Of Handoff ? A. (a) Hard Handoff (b) Soft Handoff. 5.Where Are Diversity Techniques Applied ? A. Diversity Techniques Are Used For Receiving Cellular Mobile Communication Signals. 6. What Are Two Types Of Interference ? A. (a) Adjacent Channel Interference. (b) Co-Channel Interference. 7. What Is Adjacent Channel Interference? A. Interference Takes Place Due To Channels Of Different Frequencies. 8. Define Co-Channel Interference? A. Same Frequencies Are Used In Different Cells Is Said To Co-Channel Interference. 9. Mention One Technology That Depend On Radio Transmission? A. Bluetooth Technology. 10. What Is Roaming In Wireless Networks? A. In Wireless Environment The Station Has To Move As The Subscriber Moves From One Access Point To Another Access Point. 11. What Is Known As Macro Cell? A. The Macro Cells Are Used For Covering Metropolitan Areas And They Cover Areas Up To Several Kilometers. 12. Give One Technical Issues Involved In Planning A Cellular Network? A. Radio Coverage. 13. What Is the Use Of Cell Overlaid? A. To Increase The Capacity Of A Particular Cellular Network. 14. What Is the Use Of Smart Antennas? A. Smart Antennas Are Used For Capacity Expansion. 15. What Is Known As Channel Borrowing? A. The Channels Are Distributed Non-Uniformly Among The Cells. 16. What Is FCA ? A. FCA Is Fixed Channel Allocation Where The Number Of Radio Channels Are Reallocated. 17. What Is SMS? A. SMS->Short Message Service.
18. Mention Two Services Aspects In Is-95?
A. (a) Enhanced Mobile Station Identities.
(b) Slotted Paging Scheme.
19. What Is the Call Restriction Service ?
A. Subscriber PIN Access.
20. Define TDM?
A. In TDM, The Time Slices Are Used For Providing Many Channels.
21. what is FHSS?
A It Is Frequency Hopping Spread Spectrum.
22. what are the types of spread spectrum?
A. (a)FHSS (b) DSSS
23. What Is Frequency Reuse?
A. The Same Carrier Frequencies Are Reused In Cellular Communication For Effective Spectrum Utilization.
24. Mention Second Generation Cellular Standard?
A. global system mobile (GSM)
25. what are ths sub systems available in GSM?
i. Base Station Subsystem
ii. Public Networks Subsystem
iii. Network switching subsystem
26. what are the advantages of broadband cellular service?
A. (a) Convenience (B) Reduced Cost
27. what is information bearing signal ?
A. When a Signal Carries messages, it is said to be an information bearing signal.
28. Define Datarate ?
A. The Speed at Which The Message Is Transmitted.
29. Give The Equation For Nyquist Criterion ?
A. c = 2 B LOG 2 M
30. What Is A Channel Capacity?
A. The Maximum Possible Datarate At Which Data Can Be Transmitted Is Called As Channel Capacity.
31.What Is a MSC?
A. It Is Mobile Switching Center And It Enables Connectivity Between BTS and PSTN.
32. What is the frequency range of microwave transmission?
The frequency of microwave transmission are 2GHZ to 40 GHZ.
33.What are the types of Qos supported by handover protocols?
A. (i) Hard handover Qos (ii) Soft handover QOS
34. What Are The Types Of Fading?
A. (i) Fast Fading (ii) Slowfading (iii) Flat Fading (iiii) Selective Fading
35. What is the demerits of adhoc networks?
A. Power Management Is More Complex.
36. What Is The Advantage Of Cell Splitting Concept?
A. The Total Number Of Users At A Time Will Be Increased So That Traffic Congestion In An Area Can Be Avoided.
37. what is the conventional type used in early days for cellsize ?
A. Macrocell.
38. How Many voice and control channels were possible in Amps?
A. Voice Channels – 312
Control channels −21
39. What Is Frequency Spectrum Allocation In AMPS For Mobile Receive ?
A. Mobile Receive Spectrum 869 – 894 MHZ
40. WHAT IS HCA?
A. It Is Hybrid Channel Allocation Scheme Where A Combination Of Fixed Channel Allocation And Dynamic Channel Allocated Is Applied.
41. What Is A Direct Wavepath ?
A. The Path Is Very Clear With Respect To The Terrain Contour.
42. At What Frequency Ignition Noise Is Observed?
A. 800MHZ
43. What Is LOS(Line- Of -Sight) Wavepath ?
A.It is the wave path that is very clear from all buildings.
44.what is the SAT tone frequencies in HZ?
A.5970/6000/6030 HZ
45.What Is The Formula For Offered Load ?
A. A=Qi T/60 erlangs
46.where is the cross talks are heard?
A. i. Land Line Phones And
ii. Mobile Units.
47.what are the standard conditions at the mobile unit?
A. (i) Antenna Height =10 Feets(3m)
(ii) Antenna Gain =0db/Dipole Antenna
48. A Ring Combiner Can Combine ,How Many Channels ?
A.it can combine two 16 channels
49. how many number of channels the cellular mobile system operate ?
A. 666 channels.
50. what are different types of sector system ?
A. (i) 1200 sector system
(ii) 600 sector system
DIGITAL IMAGE PROCESSING
1. What Is The Use Of Different Transform Techniques ?
A. To Resolve The Frequency Components Of A Signal (Or) An Image.
2. How The Brightness Of An Image Is Analyzed?
A. F(0,0) i.e, dc Component Gives The Average Brightness
3. What Is The Use Of Homomorphic Filters ?
A.To Separate The Reflection And Illumination Components
4. What The Reflection Component Represents?
A. It Gives Abrupt Variations Of An Image.
5. What The Illumination Components Represents?
A. It Gives Slow Variations Of An Image.
6. Define Gradient Operator ?
A. f=[GX GY]=[∂f/∂x ∂f/∂y]
7. Define Laplacion Operator?
A. 2f=∂2f/∂x2+∂2f/∂y2
8. What Is The Use Of Gradient Operator?
A. Edge Detection
9 . What Is The Use Of Laplacion Operator?
A. Image Enhancement
10. What Is The Use Of Box Filter?
A. To Remove Random Noise.
11. what is the use of thresholding?
A. To Separate The Object Details From The Background.
12. What Is The Use Of LPF in Image Processing?
A. To Remove The Sharp Transitions In An Image.
13. What Is The Use Of Hpf In image processing?
A. To Do The Image Sharpening.
14. When The Wiener Filter Becomes Inverse Filter?
A. If Noise Is Zero
15. What Is The Other Name Of Salt And Pepper Noise?
A. Bipolar Impulse Noise.
16. How To Remove The Salt And Pepper Noise?
A. With The Use Of Mean Filter.
17. What Is The Property Of Gradient Operator?
A. The Sum Of Co Efficient Of The Gradient Operator Is Zero.
18. What Is The Use Of Wavelet Transform?
A. Multi-Resolution Analysis.
19. What Is The Difference Between Inverse Filter And Wiener Filter?
A. Inverse Filter Not Able To Remove Noise,Where As Wiener Filter Able To Remove Noise.
20. Define Compression Ratio?
A. CR=n1/n2=original image/compressed image
21. What Are The Redundancies Present In An Image?
A. The Three Basic Redundancies Are:
1.Coding Redundancy
2.Inrerpixel Redundancy
3.Psychovisual Redundancy
22. How To Remove Coding Redundancy?
A. With The Use Of Minimum Number Of Bits Per A Pixel.
23. How To Remove The Interpixel Redundancy?
A. By Removing The Redundant Pixels In An Image.
24. How To Remove The Psychovisual Redundancy?
A. By Eliminating The Relatively Less Important Information In An Image.
25. What Is Meant By Fidelity Criteria?
A. The Difference Between Original Image And Compressed Image Is Called Fidelity Criteria.
RADAR SYSTEMS
1. What is full form of RADAR?
A. Radio Detection And Ranging.
2. What is the simple form of Radar equation?
A. Rmax = [Pt Gt λ2 /(4π)3Pmin ] 1/4
3. What is the drawback of RADAR?
A. Radar can’t resolve the colour of an object.
4. What is the use of Doppler effect?
A. Doppler effect is used to distinguish the moving targets from stationary objects.
5. What is the destination of the Radar?
A. Display unit.
6. What type of system is used for landing of aircrafts in a bad weather?
A. Air Traffic Control.
7. In a Radar System , if PRF is 1000Hz ,what is maximum unambiguous range?
A. 150 Km.
8. What is the minimum detectable signal?
A. The weakest signal the receiver can detect is called minimum detectable signal.
9. What is the function of envelope detector?
A. It passes the modulation envelope and rejects the carrier frequency.
10. What is meant by integration?
A. The process of summing all the radar eches from a target is called Integration.
11. The amount of power reflected by the target depends on what parameters?
A. Size,Shape,Material.
12. What is second Time Around Echo?
A. The echoes that arrive at a time later than the pulse repetition period are called Second Time Around Echo.
13. What is the loss that may occur due to the transmission line?
A. Plumbing Loss.
14. What is the function of Doppler amplifier?
A. Doppler amplifier eliminates the echoes from stationary objects.
15. What is the other name of simple CW Radar Reciever?
A. Homodyne receiver.
16. What is the drawback of Flicker effect?
A. It reduces the receiver sensitivity.
17. What is the disadvantage of CW Radar?
A. CW Radar can’t measure the range of the target due to its narrow transmitted
waveform.
18. What are the two types of frequency counters?
A. 1. Average frequency counter ---> To measure range.
2. Switched Frequency counter ---> To measure velocity.
19. What is the disadvantage of frequency counter?
A. It is unable to measure the fraction of a cycle.
20. What is the function of limiter in the reciever ?
A. It removes the amplitude fluctuations of the beat frequency signal.
21. If the beat frequency is modulated at a rate ‘fm ‘ over a range ‘∆f’ ,then what is the beat frequency?
A. Beat frequency fr =(4R/C)*fm*∆f
22. What is the function of Altimeter?
A. Altimeter is used to measure the height above the surface of the earth.
23. In multiple frequency CW Radar , what is the maximum unambiguous range?
A. Runamb = e/2∆f where ∆f ---> frequency
24. What is the error caused by the delays in the circuitary and transmission lines?
A. Residual Path error.
25. What is the advantage of non-coherent MTI Radar?
A. Simplicity is the advantage of non-coherent MTI Radar.
26. What are blind speeds?
A. The relative target velocities which results in zero MTI response are called blind speeds.
27. What is Range Gating?
A. The loss of range information and the collapsing loss may be eliminated by first quantizing the range into small intervals. The process is called “Range Gating”.
28. Define MTI Improvement factor?
A. The symbol to clutter ratio at the output of the MTI System divided by signal to clutter ratio at the input is known as MTI improvement factor,denoted by “I”.
I = (s/c)o/p/(s/c)i/p
29. Define Sub Clutter Visibility (SCV)?
A. The ratio by which the target echo power may be weaker than the co-incident clutter echo power and still be detected with specified detection and false alarm probabilities.
30. What are the limitations of MTI performance?
A. 1. Instabilities of transmitter and receiver.
2. Physical motion of clutter.
3. The finite time on target.
4. Limiting in the receiver.
31. What is a tracking system?
A. A tracking system measures the co-ordinates of a target and provides necessary data to find the path of the target and to predict the future path of the target.
32. What are the various methods for generating the error signal?
A. 1. Sequential lobbing.
2. Conical scan.
3. Simultaneous lobbing (or) monopulse.
33. What is a continuous tracking radar?
A. Continuous tracking radar supplies continuous tracking data on a particular target.
34. In conical scan what is the angle between the beam axis and rotation axis?
A. Squint angle.
35. What is monopulse tracking radar?
A. Tracking the target using single pulse is known as monopulse tracking radar.
36. What is acquisition (or) search radar?
A. The radar which is used for finding the target (or) locate the target is known as acquisition (or) search radar.
37. What is the expression for phase difference ∆φ, for phase comparision in monopulse?
A. ∆φ=(2π/λ)d sinθ.
38. What is blip?
A. The presence of the target on the radar display is called blip.
39. What is the necessity of receiver protector in between the duplexer and the receiver?
A. To provide additional protection.
40. What is linear array?
A. A linear array consists of elements arranged in a straight line in one dimention.
41. What is broadside array?
A. A broadside array is one in which the direction of maximum radiation is perpendicular.
42. What is conformal array?
A. An array whose elements are distributed on a non-planar surfaces called a conformal array.
43. Which is a measure of coherence between two waveforms?
A. Cross-correlation.
44. What are the two basic functions performed by the radar?
A. 1. Detection of the presence of reflecting objects.
2. Extraction of information from the received waveform to obtain such target data as position, velocity.
45. What is a matched filter?
A. A network whose frequency response function maximized the output peak signal to mean noise ratio is called as matched filter.
46. What is the frequency response function of two pass rc filter?
A. Eout/Ein.
47. What is NWN matched filter?
A. When the noise is non-white, the filter which maximizes the output signal to noise ratio is called NWN matched filter.
48. What are the example of active ECM?
A. The noise jammers and repeater jammers are the examples.
49. To obtain high directivity and large gain which antennas are used?
A. Antenna array.
50. Which is used as radar antenna?
A. Parabolic reflector.
51. What is the gain of n-elements array?
A. N2.
52. What is parallel fed?
A. Variable phase shifters may be used at element of linear array to steer the beam by the simple form element array which is called parallel fed.
TELEVISION ENGINEERING
1. How many number of lines scanned by the electron gun in monochrone TV?
ANS : - 625 lines
2. Which type of system used in colour TV ?
ANS : - PAL-B colour TV system
3. What is PIXAL or element in TV ?
ANS : - an assemblage of a large number of tiny areas is known as pixal or element .
4. What are black & white pictures ?
ANS : - in monochrome picture , each element is either bright , some shade of grey or dark is called black & white pictures .
5. Which camera tube is used in TV cameras ?
ANS : - vidicon camera tube
6. What are primary colours?
ANS : - red , blue & green
7. What type of modulation is used for sound signal ?
ANS : - frequency modulation is used for sound signal .
8. What type of modulation is used for video signal ?
ANS : - amplitude modulation is used for video signals
9. What are two types of colour difference signals ?
ANS : - (B-Y) & (R-Y) signals
10. What type of coating on screen of TV for between B/W ?
ANS : - phosphor coating
11. TV has how many number of electron gun in B/W ?
ANS : - one electron gun
12. The frame repetation rate in TV system is ?
ANS : - The frame repetation rate is 25 per second
13. What is aspect ratio ?
ANS : - width /height ratio=4/3
14. What is contrast ?
ANS : - the difference in light intensity between black & white parts of the picture
15. What is luminance ?
ANS : - the amount light intensity as perceived by the eye regardless of the colour
16. What is hue ?
ANS : - the pre dominant spectrol colour of the received light
17. What type of focussing is used in TV ?
ANS : - electro static focusing is used in TV
18. What is the high voltage applied to EMT ?
ANS : - 18 kilovolts
19. What is the deflection angle for short picture tube length ?
ANS : - 1100
20. The emission build _up time in TV is?
ANS : - 3 to 5 seconds
21. One line duration is ?
ANS : - 64 micro seconds
22. The number of lines used in american TV system ?
ANS : -525 lines
23. How many number of fields , each frame is divided ?
ANS : -2 fields (odd & even )
24. By additive colour mixing red +blue is ?
ANS : -red+blue=magenta
25. Complementary colours used in TV are ?
ANS : - yellow , magenta & cyan
26. What is the channel bandwidth for monochrome transmission ?
ANS : - 7 MH2
27. The number of colour burst cycles used in colour TV ?
ANS : - 8 to 10 cycles
28. What is positive modulation ?
ANS : - when increase in brightness of the picture results in an increase of the amplitude of modulated envelope it is called positive modulation
29. What frequency band is used for direct to home satellite television ?
ANS : - Ku-band
30. What is the frequencies range for low powred ku-band satellite transmission ?
ANS : - 11.7 to 12.5 GH2 range
Saturday, January 1, 2011
Technical questions for eECE
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