Environmental Engineering Reference
In-Depth Information
It is apparent that by using the virtual short circuit principle, transfer
functions of the ideal feedback amplifiers can straightforwardly be evaluated
without the need of feedback theory. Of course, finite gain and finite
resistances of the differential amplifier can be used to better model a real
feedback amplifier, but the use of more accurate models can lead to a loss in
simplicity of the circuit analysis. Sometimes, the analysis of a network
containing even only one such a “real” differential amplifier is so difficult
that is more efficient to apply the Rosenstark method.
The ideal feedback amplifiers presented in this paragraph have the
purpose of giving more insight into the feedback amplifiers performance.
Their use allows both to improve the intuitive perception of the four basic
feedback circuit topology as well as their inherent performance and to
quickly achieve approximate input-output transfer functions.
6.6
FREQUENCY COMPENSATION OF THE FUNDAMENTAL
CONFIGURATIONS
As discussed in the two previous chapters, an amplifier operated in
feedback configuration requires compensation. To be more precise, we have
to guarantee an adequate phase margin within the specific portion of the
circuit that, closed in feedback, provides the system loop gain. This key
point means that, to provide stability, we have to consider soley the circuit
path utilised to evaluate the return ratio and subject it to the compensation
techniques described in Chapter 5.
In the following, we shall present simple guidelines for the compensation
of the fundamental configurations which are amenable to pencil-and-paper
evaluation. To this end, we will reduce multi-pole systems into two-pole
ones. Of course, this constitutes a rough simplification that, nevertheless,
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