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 multitransistor (multiamplifier) 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 openloop gains and to translate them into the
closedloop gain. Equations and functional diagrams for the
closedloop gain of generic single, double, and tripletransistor
(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, tripletransistor circuits, amplifier, multiplefeedback
loops, superposition.
I.
I
NTRODUCTION
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 (multiamplifier) 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 openlop 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,
BenGurion University of the Negev, P.O. Box 653, BeerSheva 84105, Israel
(email: [email protected]).
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
ones
and
zeroes
their
contributions. This situation can easily be avoided if after
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 Fall '11
 Prof.EugenePaperno
 RO, Negative feedback amplifier, AOL, partial openlop gains

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