GATE 2004 Electronics and Communication Engg Question Papers

6. The impurity commonly used for realizing the base region of a silicon n-p-n
transistor is
(a) Gallium (b) Indium (c) Boron (d) Phosphorus

7. If for a silicon n-p-n transistor, the base-to-emitter voltage (VBE) is 0.7V and the collector-to-base voltage (VCB) is 0.2V, then the transistor is operating in the
(a) normal active mode (b) saturation mode
(c) inverse active mode (d) cutoff mode

8. Consider the following statements S1 and S2.
S1: The β of a bipolar transistor reduces if the base width is increased.
S2: The β of a bipolar transistor increases if the doping concentration in the base
in increased
Which one of the following is correct?
(a) S1 is FALSE and S2 is TRUE (b) both S1 and S2 are TRUE
(c) both S1 and S2 are FALSE (d) S1 is TRUE and S2 is FALSE

9. An ideal op-amp is an ideal
(a) voltage controlled current source (b) voltage controlled voltage source
(c) current controlled current source (d) current controlled voltage source

10. Voltage series feedback (also called series shunt feedback) results in
(a) increase in both input and output impedances
(b) decrease in both input and output impedances
(c) increase in input impedance and decrease in output impedance
(d) decrease in input impedance and increase in output impedance

13. A master slave flip-flop has the characteristic that
(a) change in the input immediately reflected in the output
(b) change in the output occurs when the state of the master is affected
(c) change in the output occurs when the state of the slave is affected
(d) both the master and the slave states are affected at the same time

14. The range of signed decimal numbers that can be represented by 6-bite 1’s
complement number is
(a) -31 to +31 (b) -63 to +64 (c) -64 to +63 (d) -32 to +31

15. A digital system is required to amplify a binary-encoded audio signal. The user
should be able to control the gain of the amplifier from a minimum to a maximum
in 100 increments. The minimum number of bits required to encode, in straight
binary is
(a) 8 (b) 6 (c) 5 (d) 7

16. Choose the correct one from among the alternatives A,B,C,D after matching an
item from Group 1 with the most appropriate item in Group 2.

Group 1 Group 2
P. Shift register 1. Frequency division
Q. Counter 2. Addressing in memory chips
R. Decoder 3. Serial to parallel data conversion
(a) P – 3 Q – 2 R - 1 (b) P – 3 Q – 1 R - 2
(c) P – 2 Q – 1 R – 3 (d) P – 1 Q – 2 R - 2

22. The Fourier transform of a conjugate symmetric function is always
(a) imaginary (b) conjugate anti-symmetric
(c) real (d) conjugate symmetric

25. In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves by the factor
(a)8/6 (b) 12 (c) 16 (d) 8

26. An AM signal is detected using an envelope detector. The carrier frequency and
modulating signal frequency are 1 MHz and 2 KHz respectively. An appropriate
value for the time constant of the envelope detector is
(a) 500 µsec (b) 20 µsec (c) 0.2 µsec (d) 1 µsec

27. An AM signal and a narrow-band FM signal with identical carriers, modulating
signals and modulation indices of 0.1 are added together. The resultant signal
can be closely approximated by
(a) broadband FM (b) SSB with carrier
(c) DSB-SC (d) SSB without carrier

28. In the output of a DM speech encoder, the consecutive pulses are of opposite
polarity during time interval t1≤t≤t2. This indicates that during this interval
(a) the input to the modulator is essentially constant
(b) the modulator is going through slope overload
(c) the accumulator is in saturation
(d) the speech signal is being sampled at the Nyquist rate

29. The phase velocity of an electromagnetic wave propagating in a hallow metallic
rectangular waveguide in the TE10 mode is
(a) equal to its group velocity
(b) less than the velocity of light in free space
(c) equal to the velocity of light in free space
(d) greater than the velocity of light in free space

30. Consider a lossless antenna with a directive gain of +6db. If 1mW of power is fed
to it the total power radiated by the antenna will be
(a) 4mW (b) 1mW (c) 7mW (d)1/4 mW

37. Consider the following statements S1and S2
S1: At the resonant frequency the impedance of a series R-L-C circuit is zero.
S2: In a parallel G-L-C circuit, increasing the conductance G results in increase in
its Q factor.
Which one of the following is correct?
(a) S1 is FALSE and S2 is TRUE (b) both S1 and S2 are TRUE
(c) S1 is TRUE and S2 is FALSE (d) both S1 and S2 are FALSE

41. Consider the following statements S1 and S2.
S1: The threshold voltage (VT) of a MOS capacitor decreases with increase in gate
oxide thickness
S2: The threshold voltage (VT) of a MOS capacitor decreases with increase in
substrate doping concentration.
Which one of the following is correct?
(a) S1 is FALSE and S2 is TRUE (b) both S1 and S2 are TRUE
(c) S1 is TRUE and S2 is FALSE (d) both S1 and S2 are FALSE

42. The drain of an n-channel MOSFET is shorted to the gate so that VGS = VDS. The
threshold voltage (VT) of MOSFET is 1V. If the drain current (ID) is 1 mA for VGS =
2V, then for VGS = 3V, ID is
(a) 2 mA (b) 3 mA (c) 9 mA (d) 4 mA

43. The longest wavelength that can be absorbed by silicon, which has the bandgap
of 1.12eV, is 1.1µm. If the longest wavelength that can be absorbed by another
material is 0.87 µm, then the bandgap of this material is
(a) 1.416 eV (b) 0.886 eV (c) 0.854 eV (d) 0.706 eV

50. In a full-wave rectifier using two ideal diodes, Vdc and Vm are the dc and peak
values of the voltage respectively across a resistive load. If PIV is the peak
inverse voltage of the diode, then the appropriate relationships for this rectifier
are

(a)Vdc=Vm/p PIV=2Vm (b)Vdc=2Vm/p PIV=2Vm
(c)Vdc=2Vm/p PIV=Vm (d)Vdc=Vm/p PIV=Vm

51. The minimum number of 2 to 1 multiplexers required to realize a 4 to 1
mutliplexer is
(a) 1 (b) 2 (c) 3 (d) 4

53. 11001, 1001 and 111001 correspond to the 2’s complement representation of
which one of the following sets of number?
(a) 25, 9 and 57 respectively (b) -6, -6 and –6 respectively
(c) -7, -7 and –7 respectively (d) -25, -9 and –57 respectively

54. The 8255 Programmable Peripheral Interface is used as described below.
I. An A/D converter is interfaced to a microprocessor through an 8255. the
conversion is initiated by a signal from the 8255 on Port C. A signal on Port C
causes data to be strobed into Port A.
II. Two computers exchange data using a pair of 8255s. Port A works as a bidirectional data port supported by appropriate handshaking signals.
The appropriate modes of operation of the 8255 for I and II would be
(a) Mode 0 for I and Mode 1 for II (b) Mode 1 for I and Mode 0 for II
(c) Mode 2 for I and Mode 0 for II (d) Mode 2 for I and Mode 1 for II

55. The number of memory cycles required to execute the following 8085 instructions
I. LDA 3000H
II. LXI D, FOF 1H
Would be
(a) 2 for I and 2 for II (b) 4 for I and 3 for II
(c) 3 for I and 3 for II (d) 3 for I and 4 for II

57. Consider the sequence of 8085 instructions given below.
LXI H, 9258 MOV A, M, CMA, MOV M, A
Which one of the following is performed by this sequence?
(a) contents of location 9258 are moved to the accumulator
(b) contents of location 9258 are compared with the contents of the accumulator
(c) contents of location 8529 are complemented and stored in location 8529
(d) contents of location 5892 are complemented and stored in location 5892

58. A Boolean function f of two variables x and y is defined as follows:
f(0,0) = f(0,1) = f(1,1)=1; f(1,0) = 0
Assuming complements of x and y are not available, a minimum cost solution for
realizing f using only 2-input NOR gates and 2-input OR gates (each having unit
cost) would have a total cost of
(a) 1 unit (b) 4 unit (c) 3 unit (d) 2 unit

60. A 1 kHz sinusoidal signal is ideally sampled at 1500 samples/sec and the sampled
signal is passed through an ideal low-pass filter with cut-off frequency 800 Hz.
The output signal has the frequency
(a) zero Hz (b) 0.75 kHz (c) 0.5 kHz (d) 0.25 kHz

75. A 1mW video signal having a bandwidth of 100 MHz is transmitted to a receiver
through a cable that has 40 dB loss. If the effective one-sided noise spectral
density at the receiver is 10-20 Watt/Hz, then the signal to noise ratio at the
receiver is
(a) 50 db (b) 30 db (c) 40 db (d) 60 db

77. Two sinusoidal signals of same amplitude and frequencies 10 kHz and 10.1 kHz
are added together. The combined signal is given to an ideal frequency detector.
The output of the detector is
(a) 0.1 kHz sinusoid (b) 20.1 kHz sinusoid
(c) a linear function of time (d) a constant

78. Consider a binary digital communication system with equally likely 0’s and 1’s.
When binary 0 is transmitted the voltage at the detector input can lie between
the level s-0.25V and +0.25V with equal probability: when binary 1 is
transmitted, the voltage at the detector can have any value between 0 and 1 V
with equal probability. If the detector has a threshold of 2.0V (i.e., if the received signal is greater than 0.2 V, the bit is taken as 1), the average bit error
probability is
(a) 0.15 (b) 0.2 (c) 0.05 (d) 0.5

81. Three analog signals, having bandwidths 1200 Hz, 600 Hz and 600 Hz, are
sampled at their respective Nyquist rates, encoded with 12 bit words, and time
division multiplexed. The bit rate for the multiplexed signal is
(a) 115.2 kbps (b) 28.8 kbps (c) 57.6 kbps (d) 38.4 kbps

89. A plane electromagnetic wave propagating in free space in incident normally on a
large slab of loss-less, non-magnetic, dielectric material with ε >ε0. Maxima and
minima are observed when the electric field is measured in front of the slab. The
maximum electric field is found to be 5 times the minimum field. The intrinsic
impedance of the medium should be
(a) 120 πΩ (b) 60 πΩ (c) 600 πΩ (d) 24 πΩ

90. A lossless transmission line is terminated in a load which reflects a part of the incident power. The measured VSWR is 2. the percentage of the power that is
reflected back is
(a) 57.73 (b) 33.33 (c) 0.11 (d) 11.11

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