A Class AB CMOS Operational Amplifier for Application as Rail-to-Rail High Current Drive Buffer

A class AB CMOS operational amplifier specially designed to be used as unity gain buffer is presented. The novelty of the presented topology consists in using a classical rail-to-rail OTA with duplicated output port to drive the gates of the op-amp complementary output transistors and relying on a separate feedback loop to limit the quiescent current. The simplicity of classical two stage op-amps is maintained with advantages in terms of die size, transient response and process independence. The circuit, fabricated using the BCD3S process of STMicroelectronics, occupies a die size of 0.06 mm2 and operates from a single 2.2V power supply with resistive loads as low as 300 Ω.