An ECG chopper amplifier achieving 0.92 NEF and 0.85 PEF with AC-coupled inverter-stacking for noise efficiency enhancement

This paper presents an ultra-low power chopper-stabilized amplifier intended for portable or implantable ECG applications. A new technique to fundamentally improve the noise efficiency of such amplifiers is introduced that is based on Gm-boosting by AC-coupling up-modulated signals onto stacked inverters. Designed and simulated in a 65 nm CMOS process, the amplifier consumes 17.7 nW from a 1 V supply. An efficient current-reuse and better utilization of the supply voltage using the proposed technique by stacking three inverters leads to a best-reported Noise Efficiency Factor (NEF) of 0.92 and Power Efficiency Factor (PEF) of 0.85.