1. The voltage gain without negative feedback is 40dB. What is the new voltage gain if 3%
negative feedback is introduced? (25)
2. A negative feedback amplifier with 60dB voltage gain has lower and upper cut-off
frequencies 100 kHz and 200 kHz respectively. For the amplifier bandwidth of 2 MHz,
specify the feedback needed and new cut off frequencies. (0.01)
3. Design a feedback amplifier having overall gain of 40 dB and sensitivity figure of 4% w.r.t.
its internal amplifier gain 𝐴𝑣 .( 𝐴𝑣 =2500, 𝛽 = 0.0096)
4. The open circuit voltage gain 60dB of an amplifier changes by 5%. How much change in
voltage gain will result with 2% negative feedback?
𝐴
5
5
Solution: % change in 𝐴𝑖𝑓 = % change in 1+𝐴𝑣 𝛽 = 1+100𝑥0.02 = 21 = 0.238%
𝑣
5. An amplifier without feedback has a voltage gain of 60dB. The lower and upper cut-off
frequencies of this amplifier are 100Hz and 100 kHz respectively. Inclusion of negative
feedback reduces the gain to 20dB. Determine the bandwidth and the new gain. Given 𝐴𝑣 =
60dB = 1000, 𝑓𝐿 = 100Hz, 𝑓𝐻 = 100 kHz, 𝐴𝑣𝑓 = 10. (BW = 10MHz, 10)
6. An amplifier without feedback has a gain of 100 and with negative feedback its gain falls
to 10. Design the feedback network. (𝛽 = 0.09)
7. An amplifier has a voltage gain of 100 and its voltage gain is increased to 200 by increasing
the bias conditions. Calculate the negative feedback factor that must be applied to bring
the voltage gain to the original value 100. (𝛽 = 0.005)
8. A negative feedback voltage amplifier requires 1V input to produce an output voltage while
it requires only 0.1V input voltage to produce the same output voltage without feedback.
−9
Calculate the feedback factor.(  = 𝐴 )
𝑣
9. The overall gain of a negative feedback amplifier is 60dB and the attenuation provided by
network is 80dB. Calculate the voltage gain of the amplifier without feedback. (, 𝐴𝑣 =
1000).
10. An amplifier has bandwidth of 2000 kHz at a voltage gain of 100. (a) What will be the new
bandwidth and gain if 5% negative feedback is introduced? (b) What should be the amount
of feedback if the bandwidth is to be restricted to 10MHz? (12MHz,  = 0.04).
11. A feedback amplifier with 5% negative feedback is designed to have overall gain of 20dB.
Calculate the open loop gain of the amplifier. If the above amplifier is arranged for current
feedback voltage error and its input and output resistances are 100k and 100
respectively. Calculate the new input and output resistances after feedback is introduced.
𝐴
𝐴𝑣
Solution: 𝐴𝑣𝑓 = 100 = 1+𝐴𝑣 𝛽 = 1+0.05𝐴
, 1000 + 50𝐴𝑣 = 𝐴𝑣 ; 49𝐴𝑣 = - 1000,
𝑣
𝑣
𝐴𝑣 = −28.83, 𝑅𝑖𝑓 = 144.2k, 𝑅𝑜𝑓 = = 69.35
12. A music program of frequency range from 25Hz to 15kHz is to be amplified 30 times by
an amplifier whose input and output voltage are out of phase. The amplifier while
delivering output produces 5% harmonic distortion also.
(a) What type of feedback will reduce the harmonic distortion?
(b) What is % distortion if 2% of the output voltage is feedback?
(c) What is the output voltage?
(d) What is the bandwidth with and without feedback?
(e) What is the gain of the amplifier with and without feedback?
Solution: (a) voltage series feedback
(b) = D2f = 2%
(c) 𝑣𝑜 = 30𝑣𝑖
(d) BW without feedback = (10-0.025) kHz =  15 kHz
BW with feedback  15 kHz (1+1.5) = 37.5 kHz.
(e) Gain of amplifier without feedback = 75
75
Gain of amplifier with feedback = 2.5 = 30
13. A single stage amplifier with a gain 𝐴𝑣𝑚 = 100, 𝑓𝐿 = 20Hz, 𝑓𝐻 = 50 kHz and has negative
feedback  = 0.1. Calculate the lower and upper cut-off frequencies with feedback. Also
obtain the gain at of the amplifier without feedback at 𝑓𝐻 .(𝑓𝐻𝑓 = 5.05MHz, Gain = 10)
14. A single stage amplifier has lower and upper cut-off frequencies 1 kHz and 50 kHz
respectively having midband gain = 500. What should be the feedback factor to achieve
higher cut-off of 300 kHz? What is the corresponding value of the lower cut-off frequency?
( = 0.01, 166.7Hz)
15. Each stage of a three-stage amplifier without feedback has identical pole frequencies and
its open loop transfer function is expressed as
𝐴3
𝑜
𝐴3 (𝑠) = (1+𝑠/𝜔
𝐻)
3
Determine its maximum value of feedback factor 𝛽𝑚𝑎𝑥 for which the amplifier remains stable.
Also determine the corresponding frequency.
Solution:
𝐴3
𝑜
1 + 𝐴𝛽 = 1 + (1+𝑠/𝜔
8
𝛽𝑚𝑎𝑥 = 𝐴3
𝑜
𝛽𝐴3
𝐻
𝑜
𝛽 = 1 + (1+𝑗𝜔/𝜔
)3
𝐻)
3