Environmental Engineering Reference
In-Depth Information
Unfortunately, unlike the passive compensation strategy discussed above,
the buffer utilised attenuates the achievable output swing of the amplifier.
The adoption of an ideal voltage buffer (i.e., with infinitely large input
impedance, zero output impedance, and unitary gain) gives the same
dominant pole as in (5.18) and the same second pole as in (5.19) without
depending on capacitance But by eliminating capacitive feedforward, the
troublesome RHP zero incurred by the internal interstage capacitance, is
not decreased by the compensation element In other words, the effective
feedback capacitance is while the feedforward capacitance is
The foregoing discussion presumes an ideal voltage buffer. Practical
buffers have small, but not zero, output impedance and large, but not
infinite, input impedance (see Fig. 5.5).
The resistive component of the buffer output impedance, establishes a
left-half plane zero with capacitance Asfor the case with the nulling
resistor, this zero can be exploited to increase the amplifier gain-bandwidth
[PP95].
Following this
last
compensation
strategy and with
some
approximations, the poles and zeros become [PP95]
