An ultra low noise, low offset chopper Operational Amplifier in 180 nm technology

This article describes the design of a low-complexity chopper stabilized operational amplifier (op-amp) dedicated to process the output signal of Magnetic Tunnel Junctions (MTJs). The extremely low level of DC output signal produced by MTJs requires a large voltage amplification with low noise and minimal offset. The amplifier is implemented in 180 nm standard CMOS technology from X-FAB foundry. It consumes 438 µA for a 1.8 V voltage supply. It presents a 86.6 dB open loop DC gain with a 47° phase margin. The post layout simulations report a residual input DC offset mean value of −327 nV with a 11.39 µV standard deviation and an input referred noise RMS voltage (IRN) of 1.5 µVRMS.