Environmental Engineering Reference
In-Depth Information
4.4
THREE-POLE FEEDBACK AMPLIFIERS WITH REAL
POLES
Some amplifier architectures have three separate poles [P99], one of
which must be dominant to allow stability. Consider then the third-order
loop-gain transfer function given below
The phase margin of the loop gain is equal to (approximating
with
Since
and
relationship (4.47) can be rewritten as
Thus, assuming the non-dominant poles to be definitely set, the required
gain-bandwidth for a given phase margin can be achieved from (4.50). In
particular, we get
