A 1.5 V class AB CMOS buffer amplifier for driving low-resistance loads

A 1.5 V class AB CMOS op amp that can drive heavy resistive loads with low distortion is presented. Its output stage comprises an elementary shunt stage driven by a transconductor block. Only seven transistors are needed to implement the complete output stage, including the class AB current control. The gain of the output stage remains relatively constant for varying load conditions, which makes it possible to use a simple two-stage architecture for the overall amplifier. At 1.5 V, the circuit dissipates 135 /spl mu/W of quiescent power, has a gain-bandwidth of 0.85 MHz and can drive a 1.0 V/sub pp//1 kHz sine wave in a 560 /spl Omega/ load with a THD of 0.2%.