Fully differential operational amplifier having frequency dependent

Abstract

A fully differential operational amplifier includes first and second frequency dependent impedance dividers, preferably frequency dependent current dividers, each of which has an input, a noninverting output and an inverting output. A respective input is coupled to a differential input signal. The noninverting output of the first frequency dependent impedance divider is electrically coupled to the inverting output of the second frequency dependent impedance divider, and the noninverting output of the second impedance divider is electrically coupled to the inverting output of the first divider. A current feedback buffer electrically couples the noninverting output of a respective frequency dependent impedance divider to its associated input. The cross coupling and current feedback buffers provide positive feedback action which merges the inverting and noninverting differential signals as a function of frequency. The frequency dependent impedance dividers preferably deliver substantially all of the current at the input thereof to the associated inverted output at relatively low frequencies (DC) and split the current at the input between the associated inverting and noninverting outputs at relatively high frequencies. Each frequency dependent current divider may be implemented by a pair of cascode transistors one of which is loaded by a cascoded current mirror. High DC gain coupled with high and symmetric slew rate and high common mode rejection is thereby provided.