An enhanced fully differential folded-cascode op amp

An enhanced fully differential folded-cascode operational-amplifier topology that achieves improved DC gain and common-mode rejection without sacrificing slew rate is presented. The large-signal operation of the new topology is completely symmetric, providing equal positive and negative slew-rate behavior by making use of current mirrors rather than current sources as normally found in full differential folded-cascode op-amps. An additional advantage of the enhanced topology is that its common-mode output impedance is a factor of g_mr_o (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