A Low Power Low Voltage Rail to Rail Constant gm Differential Amplifier with 150 dB CMRR and Enhanced Frequency Performance

This paper proposes a low voltage (±0.55V supply voltage) low power (44.65µW) high common mode rejection ratio (CMRR) differential amplifier (d.a.) with rail to rail input common mode range (ICMR), constant transconductance (gm) and enhanced frequency performance. Its high performance is obtained using a simple negative averaging method so that it cancels out the common mode input signals at the same input terminals while preserving high frequency operation. The principle of operation, small signal analysis and the formula of its most important parameters are explained and derived. Simulation results with HSPICE using TSMC 0.18µm CMOS are presented showing rail to rail operation, CMRR of 150dB, voltage gain of 31.6dB, gain bandwidth of 95.8 MHz and input referred noise of 100.64nv/√Hz. Compared to conventional amplifier ones those are  94.4dB , 3.4dB, 1.62 times and 1.72 times better, respectively. The CMRR corner case simulation results are also provided showing from 52.1dB to 74.6dB improvement over conventional one.