文档介绍：Chapter 7
Voltage-Feedback Op pensation
Literature Number SLOA079
Excerpted from
Op Amps for Everyone
Literature Number: SLOD006A
Chapter 7
Voltage-Feedback Op pensation
Ron Mancini
Introduction
Voltage-feedback amplifiers (VFA) have been with us for about 60 years, and they have
been problems for circuit designers since the first day. You see, the feedback that makes
them versatile and accurate also has a tendency to make them unstable. The operational
amplifier (op amp) circuit configuration uses a high-gain amplifier whose parameters are
determined by external ponents. The amplifier gain is so high that without
these external ponents, the slightest input signal would saturate the amplifi-
er output. The op amp is mon usage, so this configuration is examined in detail,
but the results are applicable to many other voltage-feedback circuits. Current-feedback
amplifiers (CFA) are similar to VFAs, but the differences are important enough to warrant
CFAs being handled separately.
Stability as used in electronic circuit terminology is often defined as achieving a nonoscil-
latory state. This is a poor, urate definition of the word. Stability is a relative term,
and this situation makes people uneasy because relative judgments are exhaustive. It is
easy to draw the line between a circuit that oscillates and one that does not oscillate, so
we can understand why some people believe that oscillation is a natural boundary be-
tween stability and instability.
Feedback circuits exhibit poor phase response, overshoot, and ringing long before os-
cillation occurs, and these effects are considered undesirable by circuit designers. This
chapter is not concerned with oscillators; thus, relative stability is defined in terms of per-
formance. By definition, when designers decide what tradeoffs are acceptable, they de-
termine what the relative stability of the circuit is. A relative stability measurement is the
damping r