Lecture 8. Feedback as superposition

Lecture 8. Feedback as superposition - 1 Abstract —A new...

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Unformatted text preview: 1 Abstract —A new approach is proposed to the description of feedback in electronic circuits. The proposed approach is based on applying superposition, involves no approximations, and is applicable to multi-transistor (multi-amplifier) circuits with multiple feedback loops. To apply superposition to dependent sources, their values are kept equal to those in original circuit, where, no source is suppressed. Compared to conventional methods the new approach is very simple and comprehensible. It is enough to understand that one can apply superposition to dependent sources, and then it readily becomes apparent how to find the partial open-loop gains and to translate them into the closed-loop gain. Equations and functional diagrams for the closed-loop gain of generic single-, double-, and triple-transistor (amplifier) circuits are developed. These equations and functional diagrams can easily be extended to circuits with a greater number of transistors or amplifiers. To illustrate the new approach, a number of example circuits is solved. Index Terms —Analog electronic courses, feedback, single-, double-, triple-transistor circuits, amplifier, multiple-feedback loops, superposition. I. INTRODUCTION EEDBACK is one of the most important and difficult topics in analog electronic circuits. The difficulty in both the description and assimilation of this topic can be related to the two following issues. First, conventional approaches to the description of feedback involve various procedures [1]-[15], following which one can find the feedback parameters. Intuitive understanding and recalling such procedures is not an easy task. Second, in many cases, conventional approaches involve different approximations, and it is not always clear how accurate these approximations are. In this paper we suggest a new approach to the description of feedback, which is intuitively simple and comprehensible. It involves no approximations and is applicable to multi- transistor (multi-amplifier) circuits with multiple feedback loops. The proposed approach is based on the most basic and powerful principle standing behind linear circuits: the superposition principle. Applying this principal to feedback circuits allows one to easily find all the partial open-lop gains and translate them into the closed loop gain. Functional models of feedback can also be very easily developed and understood. There is no need to use any other rules or procedures, except applying the superposition principle. E. Paperno is with the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel (e-mail: paperno@ee.bgu.ac.il). Feedback in electronic circuits is actually based on the interaction between at least one independent and at least one dependent sources. However, superposition is usually applied only to independent sources. The reason for this is that suppressing all the independent sources automatically suppresses all the dependent...
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This note was uploaded on 01/14/2012 for the course EE 361-1-3711 taught by Professor Prof.eugenepaperno during the Fall '11 term at Ben-Gurion University.

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Lecture 8. Feedback as superposition - 1 Abstract —A new...

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