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Electronics & Communication papers 03 Questions And Answers Questions And Answers No. Question
1  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

2  A causal LTI system is described by the difference equation

2y[n] = ay[n-2] - 2x[n] + b x[n-1]

The system is stable only if

Options  A) | a  | = 2, | b | < 2
B) | a | > 2, | b | >2

C) | a |  < 2, any value of b
D) |  b  | < 2, any value of a

3  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

4  The first and the last critical frequency of an RC-driving point impedance function must respectively be
Options  A) a zero and a pole  B) a zero and a zero
C) a pole and a pole  D) a pole and a zero

5  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

6  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

7  Choose the function f(t); - ¥ < t < ¥ , for which a Fourier series cannot be defined.
Options  A) 3 sin (25 t)  B) 4 cos (20 t + 3) + 2 sin (710 t)
C) exp(-|t| )sin(25t)  D) 1

8  In what range should Re(s) remain so that the Laplace transform of the function e (a+2)t+5 exits?
Options  A) Re (s) > a + 2  B) Re (s) > a + 7
C) Re (s) < 2  D) Re (s) > a + 5

9  The state variable equations of a system are:
1.  x 1 = - 3x 1 - x 2 + u
2.  x 1 = 2x 1
y  = x 1 + u
The system is

Options  A) controllable but not observable  B) observable but not controllable
C) neither controllable nor observable  D) controllable and observable

10  For the polynomial P(s) = s 5   + s 4 + 2s 3 + 2s 2 + 3s + 15, the number of roots which lie in the right half of the s-plane is

Options  A) 4  B) 2
C) 3  D) 1

11  The phase velocity of an electromagnetic wave propagating in a hollow metallic rectangular waveguide in the TE 10 mode is
Options  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

12  A device with input x(t) and output y(t) is characterized by:   y(t) = x 2 (t).
An FM signal with frequency deviation of 90 kHz and modulating signal bandwidth of 5 kHz is applied to this device. The bandwidth of the output signal is

Options  A) 370 kHz    B) 190 kHz
C) 380kHz   D) 95kHz

13  For a signal x(t) the fourier transform is X(f). Then the inverse Fourier transform of X(3f + 2) is given by
Options  A) 1
2
x ( t
2
) e (j3 p  t)  B) 1
3
x ( t
3
) e -j4 p t/3
C) 3x(3t)e -j4 p  t  D) x(3t+2)

14  The Fourier transform of a conjugate symmetric function is always

Options  A) imaginary   B) conjugate anti-symmetric

C) real  D) conjugate symmetric

15  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

16  An ideal op-amp is an ideal

Options  A) voltage controlled current source   B) voltage controlled voltage source

C) current controlled current source   D) current controlled voltage source

17  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 fusing only 2-input NOR gates and 2-input OR gates (each having unit cost) would have a total cost of
Options  A) 1 unit  B) 4 unit
C) 3 unit  D) 2 unit

18  The impulse response h[n] of a linear time-invariant system is given by
h[n] = u[n + 3] + u[n - 2] - 2u[n-7]
where u[n] is the unit step sequence. The above system is

Options  A) stable but not causal  B) stable and causal
C) causal but unstable  D) unstable and not causal

19  The cascade amplifier is a multistage configuration of
Options  A) CC-CB  B) CE-CB
C) CB-CC  D) CE-CC