A 1-V Quasi Rail-to-Rail Operational Amplifier with a Single Input Differential Pair

A quasi rail-to-rail (VDD -Vdsa, -Vss) operational amplifier with a single differential pair is presented. A new common-mode adapter circuit based on a differential pair structure is proposed. With the common-mode adapter circuit, the common-mode input range is extended; the differential-mode signal is not affected. A two-stage operational amplifier with the proposed common-mode adapter is designed with TSMC 0.18 mum CMOS technology. With a 1 V supply voltage and a 15 pF capacitance load, the simulation shows the DC gain is about 82 dB, unity-gain frequency is about 6 MHz, and the phase margin is about 60deg.