A 43.3-μW Biopotential Amplifier With Tolerance to Common-Mode Interference of 18 Vpp and T-CMRR of 105 dB in 180-nm CMOS

In this article, we present an electrocardiogram (ECG) amplifier that has a large total CMRR (TCMRR) regardless of contact impedance mismatch and a large tolerance to common-mode interference (CMI). To achieve these features, an adaptive TCMRR enhancing loop is implemented in parallel with a charge-pump-based common-mode suppressing loop (CMSL). It adjusts the CMI current through each contact impedance so that common-mode (CM) to differential-mode (DM) conversion is minimized. We also propose a fast settling technique for the adaptive loop so that contact impedance variation can be tracked fast enough to allow robust ECG acquisition. A prototype chip fabricated in 180-nm CMOS achieves TCMRR larger than 105 dB even when there is contact impedance mismatch of up to 30%. It also achieves tolerance to CMI of 18 VPP at 60 Hz and input-referred noise of 1.90 {\mu }\rm V_{rms} while consuming 43.3 \mu \text{W} .