Explanation Given Information: The open-loop gain of an op-amp based inverting amplifier is A v , the feedback resistance network consisting of R 1 and R 2 . The input resistance of the op-amp is R i and the output resistance is R o . Calculation: In an op-amp inverting amplifier shown in Figure 1, a feedback section with two resistors and with a transfer function β v is connected to an amplifier having open-loop gain A v ,to form a closed-loop configuration with voltage gain A v f . The term “loop gain” for a closed-loop amplifier is the product of the open-loop voltage gain of the amplifier and the feedback factor, given by, T = A v β v The closed-loop gain of the amplifier is given by, A v f = A v 1 + A v β v …… (1) Here, the open loop gain of the amplifier can be expressed in terms of the ratio of output and input voltages as, A v = V o V ε Here, V ε is the error voltage which is the difference between the input voltage and the feedback voltage as shown in the Figure 2. It is given by the expression, V ε = V i − V f b Therefore the output voltage is given by, V o = A v ( V i − V f b ) …… (2) The voltage which is sampled and fedback from the output is the voltage across the parallel combination of the input resistance of the amplifier R i and the resistor R 1 . If the input resistance is very large compared to the resistance R 1 , it is ignored since a parallel combination gives a value near to R 1 . In general, including the effect of input resistance R i , the feedback voltage is given by, V f b = R 1 | | R i R 1 | | R i + R 2 V o = 1 1 + R 2 R 1 | | R i </

Microelectronics: Circuit Analysis and Design

4th Edition

ISBN: 9780073380643

Author: Donald A. Neamen

Publisher: McGraw-Hill Companies, The

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Chapter 12, Problem 12.17EP

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To derive: The expression loop gain of the given feedback amplifier

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Chapter 12, Problem 12.16EP

Chapter 12, Problem 12.13TYU

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Chapter 12 Solutions

Microelectronics: Circuit Analysis and Design

Ch. 12 - (a) The open-loop gain of an amplifier is A=5104...Ch. 12 - (a) Consider a general feedback system with...Ch. 12 - (a) A feedback amplifier has an open-loop...Ch. 12 - (a) Consider the circuit shown in Figure...Ch. 12 - (a) The closed-loop gain of a feedback amplifier...Ch. 12 - The gain factors in a feedback system are A=5105...Ch. 12 - Prob. 12.3TYU Ch. 12 - An ideal series-shunt feedback amplifier is shown...Ch. 12 - Consider the ideal shunt-series feedback amplifier...Ch. 12 - An ideal series-series feedback amplifier is shown...

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To derive: The expression loop gain of the given feedback amplifier

Solution Summary: The author explains the expression loop gain of an op-amp inverting amplifier, which is the product of the open-loop voltage gain and the feedback factor.

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To derive: The expression loop gain of the given feedback amplifier

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Chapter 12 Solutions