(a) Explanation Given: Two poles are at: f P 1 = 1 MHz f P 2 = 10 MHz | A o | = 100 dB New low-frequency gain is 20 and the phase margin is 45 degrees when a dominant pole is added. Calculation: The value of the closed loop frequency gain is given by, 20 log A O = 100 A O = 10 5 The value of the low frequency closed loop gain is given by, A f ( f ) = A O 1 + β A O Substitute 20 for A f ( f ) and 10 5 for A O in the above equation. 20 = 10 5 1 + β ( 10 5 ) β = 0.04999 The expression for the loop gain of an amplifier is given by, T ( f ) = β ( 10 5 ) ( 1 + j ( f f P D ) ) ( 1 + j ( f 10 6 ) ) ( 1 + j ( f 10 7 ) ) ....................(1) The expression to determine the phase margin is given by, Phase margin = 180 ° + ϕ Substitute 45 ° for Phase margin in the above equation. 45 ° = 180 ° + ϕ ϕ = − 135 ° The expression for the phase from the closed loop transfer function is given by, ϕ = − tan − 1 ( f f P D ) − tan − 1 ( f 10 6 ) − tan − 1 ( f 10 7 ) Substitute − 135 ° for ϕ in the above equation (b) To determine The value of the phase margin of the amplifier.

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 12.86P

(a)

To determine

The value of the dominant pole frequency closed loop gain expression.

(b)

To determine

The value of the phase margin of the amplifier.

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Chapter 12, Problem 12.85P

Chapter 12, Problem 12.87P

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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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