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Electronics & Communication papers 02 Questions And Answers No. Question
1  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

Options  A) zero Hz  B) 0.75 kHz
C) 0.5 kHz  D) 0.25 kHz

2  The minimum number of 2-to -1 multiplexers required to realize a 4-to 1 multiplexer is

Options  A) 1  B) 2
C) 3  D) 4

3  Choose the correct one front 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: Addressingin memory chips
R: Decoder  3: Serial to parallel data conversion

Options  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

4  A random variable X with uniform density in the interval 0 to 1 is quantized as follows:
If  0  £  X £ 0.3,  x q = 0
If  0.3 £ X £ 1,  x q  = 0.7
where x q  is the quantized value of X.
The root-mean square value of the quantization noise is
Options  A) 0.573  B) 0.198
C) 2.205   D) 0.266

5  In a full-wave rectifier using two ideal diodes, V dc and V m 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

Options  A)
V dc  = V m
p
, PIV = 2V m

B) V dc  = 2 V m
p
, PIV = 2V m
C) V dc  = 2 V m
p
, PIV = V m  D) V dc  = V m
p
, PIV = V m

6  The Fourier transform of a conjugate symmetric function is always

Options  A) imaginary   B) conjugate anti-symmetric

C) real  D) conjugate symmetric

7  It is desired to multiply the numbers 0AH by 0BH and store the result in the accumulator. The numbers are available in registers B and C respectively. A Part of
the 8085 program for this purpose is given below:
MVI A, 00H
Loop;- - - - - - - - -
--------------------
-------------------
HLT END
The sequence of instruction to the complete the program would be
Options  A) JNZ LOOP, ADD B, DCR C  B) ADD S, JNZ LOOP, DCR C
C) DCR C, JNZ LOOP, ADD B  D) ADD B, DCR C, JNZ LOOP

8  A solution of the following differential equation is given by

d 2 y
dx 2
- dy
dx
+ 6y = 0

Options  A)
y = e 2x + e -3x
B)
y = e 2x + e 3x

C)
y = e -2x + e 3x
D)
y = e -2x + e -3x

9  Consider the following statements S1 and S2.
S1: The threshold voltage (V T ) of a MOS capacitor decreases with increase in gate oxide thickness
S2: The threshold voltage (V T ) of a MOS capacitor decreases with increase in substrate doping concentration
Which one of the following is correct?

Options  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

10  Consider an abrupt p-junction. Let V bi be the built-in potential of this junction and V R be the applied reverse bias. If the junction capacitance (C j ) is 1 pF for
V bi + V R = 1V, then for V bi + V R - 4V, C j will be

Options  A) 4 pF  B) 2 pF
C) 0.25 pF  D) 0.5 pF

11  The impurity commonly used for realizing the base region of a silicon n-p-n transistor is

Options  A) Gallium   B) Indium

C) Boron   D) Phosphorus

12  Despite the presence of negative feedback, control system still have problems of instability because the
Options  A) components used have nonlinearities.  B) dynamic equations of the subsystems are not known exactly.
C) mathematical analysis involves approximations.  D) system has large negative phase angle at high frequencies.

13  The drain of an n-channel MOSFET is shorted to the gate so that V GS  = V DS . The threshold voltage (V T ) of MOSFET is 1 V. If the drain current (I D ) is 1 mA for V GS = 2V, then for V GS = 3V, I D is
Options  A) 2 mA  B) 3 mA
C) 9 mA  D) 4 mA

14  Let x(n) = ( 1
2
) n  u(n), y(n)=x 2 (n) and Y(e j w ) be the Fourier transform of y(n). Then Y(e j0 ) is
Options  A) 1
4
B) 2
C) 4  D) 4
3

15  Noise with uniform power spectral density of N 0 W/Hz is passed through a filter H ( w ) = 2 exp(-j w t d ) followed by an ideal low pass filter of bandwidth BHz. The output noise power in Watts is

Options  A) 2N 0 B   B) 4N 0 B

C) e N 0 B   D) 16 N 0 B

16  Consider the following statements S1 and 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?

Options  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

17  A signal x(n) = sin( w 0 n + f  ) is the input to a linear time-invariant system having a frequency response H(e (j w  ) . If the output of the system Ax(n – n 0 ), then the most general form of ÐH(ejw) will be
Options  A) - n 0 w 0 +  b   for any arbitrary real b .  B) - n 0 w 0 + 2 p k for any arbitrary integer k.
C) n 0 w 0 + 2 p k for any arbitrary integer k.  D) -n 0 w 0 f  .

18  Consider a lossless antenna with a directive gain of +6dB. If 1 mW of power is fed to it the total power radiated by the antenna will be
Options  A) 4 mW  B) 1 mW
C)
7 mW                                                        D) 1/4 mW

19  A MOS capacitor made using p type substrate is in the accumulation mode. The dominant charge in the channel is due to the presence of

Options  A)  holes   B)  electrons

C)  positively charged ions   D)  negatively charged ions

20  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.

Group1  Group 2
1 : FM
2 : DM
3 : PSK
4 : PCM  P : Slope overload
Q : m -law
R : Envelope detector
S : Capture effect
T : Hilbert transform
U : Matched filter

Options  A) 1-T,  2-P,   3-U,   4-S  B) 1-S,   2-U,   3-P,   4-T
C) 1-S,   2-P,   3-U,   4-Q  D) 1-U,   2-R,   3-S,   4-Q