Electronics and Communication Engineering - Analog Electronics

6. 

An RC coupled amplifier has an open loop gain of 200 and a lower cutoff frequency of 50 Hz. If negative feedback with β = 0.1 is used, the lower cut off frequency will be

A. about 50 Hz
B. about 5 Hz
C. about 2.38 Hz
D. about 70.5 Hz

Answer: Option C

Explanation:

New lower cutoff frequency = .


7. 

In figure v1 = 8 V and v2 = 4 V. Which diode will conduct?

A. D2 only
B. D1 only
C. Both D1 and D2
D. Neither D1 nor D2

Answer: Option B

Explanation:

D1 will conduct and the output voltage will be about 7 V. Therefore D2 will be reverse biased and will not conduct.


8. 

The load impedance ZL of a CE amplifier has R and L in series. The phase difference between output and input will be

A. 180°
B. 0
C. more than 90° but less than 180°
D. more than 180° but less than 270°

Answer: Option D

Explanation:

It is 180° for purely resistive load and between 180° and 270° for R-L load.


9. 

Gain of the amplifier is 'A'. Then the I/P impedance and O/P impedance of the closed loop amplifier shown below would be

A.
B.
C.
D.

Answer: Option B

Explanation:

By using Miller theorem circuit can be redrawn as

.


10. 

If an amplifier with gain of - 1000 and feedback factor β = - 0.1 had a gain change of 20% due to temperature, the change in gain of the feedback amplifier would be

A. 10%
B. 5%
C. 0.2%
D. 0.01%

Answer: Option C

Explanation:

As we know, Gain with feedback

A = - 1000, β = -0.1 .