Environmental Engineering Reference
In-Depth Information
where is defined in (9.19).
The dominant pole of the open-loop amplifier is again given by (9.25)
after substituting
and
for
and
Thus, the gain-bandwidth product
results
For VOA, too, the second pole of the loop-gain can be assumed at the
output and is given by
Hence, to achieve phase margin
under the worst condition of unity-gain
loop, the compensation capacitance
is needed.
Since a trade-off exists between frequency performance and power
dissipation (and sometimes between gain and power dissipation), we assume,
without loss of generality, the same power consumption for both the CFOA
and VOA by setting (of VOA in Fig. 9.18) equal to (of CFOA in
Fig. 913). Consequently, the transconductance of the VOA input stage
results equal to the input resistance at the inverting terminal of the CFOA
Moreover, the VOA resistance is in the range (it is equal
to if a cascode current mirror is used in the VOA instead of a Wilson
current mirror).
Comparing the open-loop gain of the CFOA with that of the VOA, we get
