A 1.75 V rail-to-rail CMOS op amp

In this paper, a low voltage CMOS op amp, that can operate from a single 1.75 V supply voltage is presented. The op amp-has the capability of handling input signals exceeding both the positive and the negative supply rails. This is achieved by connecting n- and p-type differential pairs in parallel. The transconductance (g_m) of the op amp is kept constant within 15% in the entire input common mode range. Composite transistors are employed as tail current sources of the differential pairs to improve the common mode and the power supply rejection ratios. The output stage is also implemented by composite transistors achieving high gain from a single stage while keeping the output signal swing high. The op amp was fabricated in the standard MOSIS p-well 2 μm CMOS process. The op amp can operate with supply voltages down to 1.75 V. 80 dB DC gain and 10 MHz unity gain frequency with 8 pF load capacitance are realizable. Input signals can exceed both supply rails and the output signals can swing within 200 mV from each rail