CMOS output stages for low-voltage power supplies

Compact and power-efficient CMOS output stages are presented and compared by designing two low-voltage operational amplifiers with similar gain and gain-bandwidth performance. The amplifiers were realized in a standard 1.2-μm CMOS process with threshold voltages around 0.8 V and using a 1.5-V power supply. They achieve an open-loop gain and a gain-bandwidth product close to 65 dB and 1 MHz, respectively. By connecting them in unity-gain configuration and delivering a 1-V peak-to-peak output voltage into a 500 Ω and 50 pF load, total harmonic distortions of -77 and -67 dB can be achieved, while using quiescent currents as low as 50 μA in the output branches