Question 8.2: The open-loop gain of an amplifier changes by 10 per cent du...

Basic Electrical and Electronics Engineering-II

The open-loop gain of an amplifier changes by 10 per cent due to the effect of temperature, ageing, etc. A change in gain of not more then 2 per cent is allowed. If the amplifier gain with feedback is 100, find the minimum value of feedback ratio.

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Related Answered Questions

Question: 8.1

Calculate the closed-loop gain of a negative feedback amplifier with A = 10,000 and β = 0.01. Show that the closed-loop gain does not change much even when the gain of the basic amplifier is changed by ± 50 per cent. ...

Verified Answer:

A_{f}=\frac{A}{1+A \beta }

...

Question: 8.14

The open-loop gain of an amplifier changes by 20 per cent due to ageing, temperature effect, etc. A negative feedback of 20 dB is used to have a reasonably stable closed-loop gain. Calculate the percentage change in the gain of the negative feedback amplifier for an open-loop gain change of 20 per ...

Verified Answer:

The amount of feedback expressed in decibels is 20...

Question: 8.13

An amplifier has an open-loop gain of 10,000. The open-loop gain changes by 20 per cent due to ageing. Calculate the percentage change in the closed-loop gain for a feedback ratio of 0.1. ...

Verified Answer:

Taking,

\frac{dA}{A}=20

per cent A ...

Question: 8.12

The input and output voltages of an amplifier are 2 mV and 2V, respectively. The input and output impedances of the amplifier without feedback is 5 KΩ and 100 Ω, respectively. The closed-loop gain of the amplifier with negative feedback is 100. Calculate the input and output impedances with ...

Verified Answer:

Z_{in}

= 5 KΩ

Z_{0}

=...

Question: 8.11

The open-loop gain of a transistor amplifier is 1,000. The input and output impedances are 5 kΩ and 100 Ω, respectively. Calculate the voltage gain and input and output impedances when one percent negative feedback is incorporated. ...

Verified Answer:

Given, A = 1,000

Z_{in}

= 5 KΩ , [l...

Question: 8.10

The open-loop gain of an amplifier is 10,000. The input and output impedances without feedback are 100 KW and 100 W, respectively. The feedback fraction is 0.01. Calculate (a) the gain with feedback; (b) input impedance with feedback; and (c) output impedance with feedback. ...

Verified Answer:

Given, A = 10,000 β = 0.01

Z_{in} = 100[/la...

Question: 8.9

A negative feedback amplifier has an open-loop gain of 50,000. The open-loop upper cut-off frequency (i.e. BW) is 100 KHz. Calculate the closed-loop upper cut-off frequency (i.e. BW)if negative feedback of 2 per cent is introduced. Also, calculate the total harmonic distortion with feedback if ...

Verified Answer:

Given,

BW_{(OL)}

= 100 KHz A = 50,00...

Question: 8.8

The input impedance of an amplifier without feedback is 1 KΩ. The open-loop voltage gain of the amplifier is 20,000. Calculate the value of input impedance when negative feedback is used. ...

Verified Answer:

β=

\frac{R_{1}} {R_{1}+R_{2}} =\frac{500}{50...

Question: 8.7

A negative voltage feedback amplifier has been shown in Fig. 8.15. Calculate the overall voltage gain if the gain of the amplifier without feedback is 10,000. ...

Verified Answer:

V_{f} = βV_{o}

=\left...

Question: 8.6

An amplifier has an open-loop voltage amplification of A = 1000. A fraction of the output voltage is fed back in opposition to the input. If the feedback fraction is 0.01, calculate the percentage change in gain of the feedback amplifier if the amplifier gain, A gets reduced by 6 dB due to ageing. ...

Verified Answer:

Gain of the feedback amplifier,

A_{f}[/late...