Monday, December 8, 2014

Previous GATE Questions on Negative Feedback Amplfiers (1987 - Till Date)



1989

3.       The feedback amplifier shown in figure has
a.       Current – Series feedback with large input impedance and large output impedance
b.      Voltage – Series feedback with large input impedance and low output impedance
c.       Voltage – Shunt feedback with low input impedance and low output impedance
d.      Current – Shunt feedback with low input impedance and low output impedance
Answer:     C
   Solution :       https://www.youtube.com/watch?v=K4UNqioWiXE       





1993

4.       Negative feedback in amplifiers
a.       improves the signal to noise ratio at the input
b.      improves the signal to noise ratio at the output
c.       does not affect the signal to noise ratio at the output
d.      reduces distortion
Answer:  D





1995

2.       To obtain very high input and output impedance in a feedback amplifier, the topology mostly used is
a.       Voltage Series
b.      Current Series
c.       Voltage Shunt
d.      Current Shunt
Answer:   B
             Solution :  https://www.youtube.com/watch?v=xfuv73dQbBA


8.       An amplifier has an open loop gain of 100, and its lower and upper cutoff frequency of 100 Hz and 100 kHz respectively. A feedback network with a feedback factor of 0.99 is connected to the amplifier. The new lower and upper cutoff frequencies are at __________ and ________
Answer:  1 Hz and 10 MHz
             Solution :   https://www.youtube.com/watch?v=R7lcv_H47gE





1996

3.       In the circuit shown, ‘N’ is a finite gain amplifier with a gain of K, large input impedance and very low output impedance. The input impedance of the feedback amplifier with the feedback impedance Z connected as shown will be ______________
 
Answer:     D
             Solution : https://www.youtube.com/watch?v=4ISLXf0p9WM 






1997

1.       In the BJT amplifier shown in figure, the transistor is based in the forward active region. Putting a capacitor across RE will
a.       Decrease the voltage gain and decrease the input impedance
b.      Increase the voltage gain and decrease the input impedance
c.       decrease the voltage gain and increase the input impedance
d.      Increase the voltage gain and increase the input impedance
Answer:  B



5.       Negative feedback in
1.       Voltage Series configuration                                  a. Increases input impedance
2.       Current Shunt configuration                                   b. Decreases input impedance
                                                                                   c. Increases closed loop gain
                                                                                   d. leads to oscillation
Answer:   1-a, 2-b
Solution:  






1998

2.       The circuit of the figure is an example of feedback of the following type
                     a.       Current Series
                     b.      Current Shunt
                     c.       Voltage Series
                     d.      Voltage Shunt
Answer:  D

 
7.       In a Shunt – Shunt negative feedback amplifier, as compared to the basic amplifier
         a.       Both, input and output impedances decreases
         b.      Input impedance decreases and output impedance increases
         c.       Input impedance increases and output impedance decreases
         d.      Both, input and output impedances increases
Answer:   A






1999

2.       Negative feedback in an amplifier
a.       Reduces gain
b.      Increases frequency and phase distortions
c.       Reduces bandwidth
d.      Increases noise
Answer:   C


 5.       An amplifier has an Open loop gain of 100, an input impedance of 1 k and an output impedance of 100 . A feedback network with a feedback factor of 0.99 is connected to the amplifier in a voltage series feedback mode. The new input and output impedances, respectively are
a.       10 and 1
b.      10 Ω and 10 kΩ
c.       100 kΩ and 1 Ω
d.      100 kΩ and 1 kΩ
Answer:   C






2000

33.   For a feedback amplifier, the open loop transfer function has three poles at 100 k rad/sec, 1 M rad/sec and 10 M rad/sec. The low frequency open loop gain is 1000 and the feedback factor (β) is 1. Use Bode plots to determine the phase margin of the amplifier. Is the amplifier stable?
Answer:  Amplifier is Unstable.





2002

1.       In a negative feedback amplifier using voltage-series (Voltage sampling and series mixing) feedback,
a.       Ri decreases and Ro decreases
b.      Ri decreases and Ro increases
c.       Ri increases and Ro decreases
d.      Ri increases and Ro increases
Answer:  C






 
2003

6.       An amplifier without feedback has a voltage gain of 50, input resistance of 1 KΩ and output resistance of 2.5 KΩ. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2 is
a.       1/11 K
b.      1/5 K
c.       5 K
d.      11 K
Answer:  A







2004

2.       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
Answer:   C






2005

1.       The effect of current shunt feedback in an amplifier is to
a.       Increase the input resistance and decrease the output resistance.
b.      Increase both input and output resistances
c.       Decrease both input and output resistances
d.      Decreases the input resistance and increase the output resistance
Answer:    D







2006

1.       The input impedance(Zi) and output impedance (Zo) of an ideal Transconductance (voltage controlled current source) amplifier are
a.       Zi = 0, Zo = 0  
b.      Zi = 0, Zo =   
c.       Zi = , Zo = 0  
d.      Zi = , Zo =   
Answer:   D






2007

1.       In a Transconductance amplifier, it is desirable to have
a.       A large input resistance and a large output resistance 
b.      A large input resistance and a small output resistance
c.       A small input resistance and a large output resistance
d.      A small input resistance and a small output resistance
Answer:  A






2010

1.       The amplifier circuit shown below uses a silicon transistor. The capacitors CC and CE can be assumed to be short at signal frequency and effect of output resistance ro can be ignored. If CE is disconnected from the circuit, which one of the following statements is TRUE.

a.       The input resistance Ri increases and magnitude of voltage gain AV decreases 
b.      The input resistance Ri decreases and magnitude of voltage gain AV increases
c.       The input resistance Ri decreases and magnitude of voltage gain AV decreases
d.      The input resistance Ri increases and magnitude of voltage gain AV increases
Answer:   A



2013

2.       In a voltage – voltage feedback as shown below, which one of the following statements is TRUE, if the gain K is increased?
a.       The input impedance increases and output impedance decreases 
b.      The input impedance increases and output impedance increases
c.       The input impedance decreases and output impedance decreases
d.      The input impedance decreases and output impedance increases
Answer:   A




2014
 
2.       A good current buffer has
a.       Low input impedance and low output impedance
b.      Low input impedance and high output impedance
c.       high input impedance and low output impedance
d.      high input impedance and high output impedance
Answer:  B
               Solution :    https://www.youtube.com/watch?v=vdYmByP9zYY



3.       In the ac equivalent circuit shown in the figure, if iin is the input current and RF is very large, then the type of feedback is 

a.       Voltage – Voltage feedback
b.      Voltage – Current feedback
c.       Current – Voltage feedback
d.      Current – Current feedback
Answer:  B
               Solution :    https://www.youtube.com/watch?v=otvYW4oudRg



2.       The feedback topology in the amplifier circuit (the base bias circuit is not shown for simplicity) in the figure is 

a.       Voltage – Shunt feedback
b.      Current – Series feedback
c.       Current – Shunt feedback
d.      Voltage – Series feedback
Answer:   B
               Solution :   https://www.youtube.com/watch?v=MNduRhMC6zk


2.       The desirable characteristics of a Transconductance amplifier are
a.       High input resistance and High output resistance
b.      High input resistance and Low output resistance
c.       Low input resistance and High output resistance
d.      Low input resistance and Low output resistance
Answer:   A
               Solution :   https://www.youtube.com/watch?v=1RsZ43lyRhs



1.       If the emitter resistance in a common emitter voltage amplifier is not bypassed, it will
a.       Reduce both the voltage gain and the input impedance
b.      Reduce the voltage gain and increase the input impedance
c.       Increase the voltage gain and reduce the input impedance
d.      Increase both the voltage gain and the input impedance

Answer:  B
               Solution :    https://www.youtube.com/watch?v=4YjclPDw5lM


2015

1.       Negative feedback in a closed loop control system DOES NOT
a.       Reduce the overall gain
b.      Reduce  bandwidth
c.       Improve disturbance rejection
d.      Reduce sensitivity to parameter variation 
   Answer:  B
Solution:        https://www.youtube.com/watch?v=TFCXqD_Tu4s            







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