This paper presents an enhanced fully differential
folded-cascode op-amp topology that achieves improved dc gain
and common-mode rejection without sacrificing slew rate. The
large-signal operation of the new topology is completely symmetric,
providing equal positive and negative slew-rate behavior
by making use of active current mirrors to bias the outputs
rather than bias current sources as normally found in fully differential
folded-cascode op amps. An additional advantage of
the enhanced topology is that its common-mode output impedance
is a factor of g,r, (typically 1-2 orders of magnitude) lower
than the differential-mode output impedance, significantly improving
the common-mode rejection ratio. The predicted performance
is verified by simulations and preliminary experimental
results.
