Environmental Engineering Reference
In-Depth Information
In the following three paragraphs we will study the engineering methods
and related tradeoffs underlying the key issue of the frequency compensation
for a two-pole open loop transfer function. Of course, the discussion is easily
extended to multi-pole functions with two dominant poles. The last two
paragraphs deal with the frequency compensation of three-stage amplifiers.
5.1 DOMINANT-POLE COMPENSATION
Let us consider the two-pole amplifier in Fig. 5.1 whose open-loop
transfer function is
where
The two poles are determined by the parasitic capacitances associated with
node A and B. Assuming these poles are widely separated with
the
tangent of the phase margin becomes
