A two-electrode 2.88nJ/conversion biopotential acquisition system for portable healthcare device

A 2.88 nJ/Conversion low energy biopotential acquisition system is designed for portable healthcare device. Two dry copper contact electrodes with 1.2-cm diameter are used to easily interface between skin and healthcare device. Chopping technique is adopted at readout front end to obtain thermal noise floor of 1.3 uVrms over 0.5~200 Hz and CMRR over 100 dB to mitigate common-mode body potential induced from AC power line. A 4-stage gain control and band selection blocks are integrated to digitally calibrate for different types of biomedical signal and an 8-bit synchronous successive approximation register (SAR) A/D is used to digitize sensed biopotentials. A test chip is implemented in 0.18 um, 1.8 V supply CMOS technology and successively verified by readout ECG signal with two electrodes contact at chest of body with separating 6 cm.