(a) The open-loop low-frequency voltage gain of an amplifier is A v = 5 × 10 4 and the open-loop 3 dB frequency is f H = 10 Hz . If the closed-loop low-frequency gain is A v f = 25 , what is the closed-loop bandwidth? (b) The minimum closed-loop bandwidth of a feedback amplifier is to be 20 kHz . The open-loop low-frequency voltage gain is A v = 10 5 and the open-loop 3 dB frequency is f H = 8 Hz . What is the maximum closed-loop voltage gain?
(a) The open-loop low-frequency voltage gain of an amplifier is A v = 5 × 10 4 and the open-loop 3 dB frequency is f H = 10 Hz . If the closed-loop low-frequency gain is A v f = 25 , what is the closed-loop bandwidth? (b) The minimum closed-loop bandwidth of a feedback amplifier is to be 20 kHz . The open-loop low-frequency voltage gain is A v = 10 5 and the open-loop 3 dB frequency is f H = 8 Hz . What is the maximum closed-loop voltage gain?
Solution Summary: The author explains that the formula for close loop bandwidth is given by lA_vf=
(a) The open-loop low-frequency voltage gain of an amplifier is
A
v
=
5
×
10
4
and the open-loop 3 dB frequency is
f
H
=
10
Hz
. If the closed-loop low-frequency gain is
A
v
f
=
25
,
what is the closed-loop bandwidth? (b) The minimum closed-loop bandwidth of a feedback amplifier is to be
20
kHz
. The open-loop low-frequency voltage gain is
A
v
=
10
5
and the open-loop
3
dB
frequency is
f
H
=
8
Hz
.
What is the maximum closed-loop voltage gain?
Discuss the difference between the current series negative feedback amplifier and voltage shunt feedback amplifier in terms of output impedance, input impedance, voltage gain, bandwidth, distortion and noise.
(a) Calculate the sensitivity of the closed-loop input resistance of the series-shunt feedback amplifier with respect to changes in open-loop gain A:SRinA = A/ Rin ∂Rin/ ∂A (b) Use this formula to estimate the percentage change in closed-loop input resistance if the openloop gain A changes by 10 percent for an amplifier with A = 94 dB and β = 0.01. (c) Calculate the sensitivity of the closed-loop output resistance of the series-shunt feedback amplifier with respect to changes in open-loop gain A:SRout A = A /Rout ∂Rout /∂A (d) Use this formula to estimate the percentage changeinclosed-loopoutputresistanceiftheopenloop gain A changes by 10 percent for an amplifier with A =100 dB and β =0.01.
An amplifier has an open-loop gain of 92 dB, Rid = 75 kΩ, and Ro = 1400Ω. The amplifier is used in a feedback amplifier configuration with a resistive feedback network. (a) What is the largest value of current gain that can be achieved with this feedback amplifier? (b) What is the largest valuetransconductance that can be achieved with this feedback amplifier?
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