A slew rate enhancement technique for operational amplifiers based on a tunable active Gm-based capacitance multiplication circuit

Abstract

A slew rate enhancement technique for operational amplifiers using a tunable active Gm-based current-mode capacitance multiplication circuit instead of the standard Miller compensation capacitor is developed. Low power and low area solutions for driving large capacitive loads are enabled by this technique. In a prototype amplifier, a 0.5 pF MOSFET is multiplied to an effective value of 285 pF, setting the dominant pole at 3 Hz. The slew rate, however, is controlled by the physical MOSFET capacitor. A slew rate as high as 1.5 V/ms is obtained for a standard two stage folded cascode opamp with a 2.5 mA differential pair tail current. An open loop gain of 101 dB and a phase margin of 56° are observed.