Environmental Engineering Reference
In-Depth Information
Of all the possible solutions that reduce (5.67) to a single-pole function,
the one chosen also has the property of providing an inherent pole-zero
cancellation for the (open-loop) transfer function of the amplifier containing
only the second and third stage. Indeed, by denoting their second pole and
(negative) zero as
and
respectively, these are given by
whose expressions perfectly match if equations (5.68)-(5.70) are used.
However, note that the
inner
amplifier, which is closed in the feedback loop
by capacitor is now comprised between the input of the second stage
and the common node of and Therefore, according to our design
methodology, we firstly have to check the stability of this feedback loop.
The open-loop transfer function of the inner amplifier is
where is given by (5.50). From (5.73) and using (5.68) and (5.70) we
derive the expressions of the unity-gain frequency and those of the second
pole and zeros of the inner amplifier
