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Electronics and Communication Engineering - Exam Questions Papers

Exercise : Exam Questions Papers - Exam Paper 2
26.
The logic realized by the circuit shown in figure below is
F = A - C
F = A + C
F = B ⊙ C
F = B ⊕ C
Answer: Option
Explanation:

F = A BC + ABC + A B C + ABC

= B(AC + AC) + B(AC + AC)

B(A ⊕ C) + B(A ⊕ C)

(A ⊕ C) (B ⊕ B)

A ⊕ C.

27.
An image uses 512 x 512 picture elements. Each of the picture elements can take any of the 8 distinguishable intensity levels. The maximum entropy in the above image will be
2097152 bits
648 bits
786432 bits
144 bits
Answer: Option
Explanation:

Each picture element can be represented by 3 bits. Thus total entropy = 512 x 512 x 3 = 786432.

28.
A tachometer has a sensitivity of 4 V/1000 rpm. Express the gain constant of the tachometer in the units volts/(rad/sec).
0.0489
0.0381
2
none of these
Answer: Option
Explanation:

4 V/100 rpm = V/rad/sec

= 0.0381 V/rad/sec.

29.
Consider the signal x(n) = 1 + sinn + 3 cosn + cos . Then Fourier series coefficients are __________ .
1, - j, + j, j, - j
1, + j, - j, - j , + j
1, 3 - j, 3 + j, j, - j
1, 3 + j, 3 - j, - j, + j
Answer: Option
Explanation:

The signal x(n) = 1 + sinn 3 cos n + cos n + cos

is periodic with period N, and we can expand x[n] directly in terms of complex exponentials to obtain

Collecting terms, we find that

Thus for Fourier series coefficients for this example are

a0 = 1,

a1 = + = -j,

a-1 = - = +j,

a2 = j,

a-2 = -j.

30.
A certain system has transfer function a is a parameter. Consider the standard negative unity feedback configuration as shown below.

Which of the following statements is true?
The closed loop system in never stable for any value of a a
For some positive values of a, the closed loop system is stable, but not for all positive values
For all positive values of a, the closed loop system is stable
The closed loop system is stable for all values of a, both positive and negative
Answer: Option
Explanation:

Closed loop system transfer function

Use Routh criteria

Thus for all positive value of 'a' this will be stable.

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