A low power CMOS front-end for photoplethysmongraphic signal acquisition with robust DC Photocurrent Rejection

A micro-power CMOS front-end for photoplethysmographic signal (PPG) acquisition is presented. The circuit is composed of a transimpedance amplifier (TIA), post amplifier and low-pass filter. The TIA is configured with a sample-and-hold (S/H), an error amplifier and a current-sink transistor in feedback to reject DC photocurrent generated from photodiode, which varies from person to person. To reduce power consumption, the LED is pulsed and thus the input to the TIA is a modulated current pulse. The low-pass filter is implemented by using the current-steering technique (CST). The proposed circuit is designed to generate PPG waveform with a fixed DC output to prevent signal saturation by rejecting the input pulsating DC photocurrent from modulated signal. Experimental results show that the circuit works properly from a 2.5-V power supply with a bandpass frequency from 0.1 Hz to 6.5 Hz and has a rejection range from 0.1 muA to 53.6 muA.