Environmental Engineering Reference
In-Depth Information
considerations hold for the second pole of (5.80). The only difference is that
and
are now in parallel.
The specified phase margin for the two cases respectively is given by
Since is set by the required unity-gain bandwidth, and assuming
and to be already set, (5.81) and (5.82) give the needed value of
Although it has been demonstrated here that ideal buffers provide a
conceptually simple vehicle for the cancellation of the zeros, we will not
stress these approaches any further because of the second-order effects of
real
buffers. In fact, the two approaches, as described above, prove to be
inefficient especially in a low-voltage low-power context. Actually, the use
of real voltage buffers unacceptably limits the output swing, while real
current buffers -matching the requirement of very low input resistance- are
expensive in terms of area and power consumption. Fortunately, we will
show in 5.5.3 and 5.5.4 that both approaches can be simply modified so as to
become suitable for practical applications.
For the sake of completeness, we shall first deal with the nulling resistor
technique, which unfortunately is rather difficult to accomplish in a RNMC.
