A 0.5V Constant-gm rail-to-rail OPAMP using a bulk-driven signal compressor

This paper introduces a rail-to-rail operational amplifier with a single PMOS differential input pair, suitable for operation in ultra-low voltage environments. In order to achieve rail-to-rail input operation, this proposal employs a novel bulk-driven signal compressor which compresses the common mode voltage of input signal to the input range of PMOS input pairs. With a 0.5 V supply voltage and 1.5 muA static current, the simulation results shows the open-loop DC gain is higher than 55 dB and a closed-loop unity-gain frequency is about 70 KHz. Over the entire common-mode range, the variation of g_m is only plusmn0.45%.