A fully integrated high-sensitivity wide dynamic range PPG sensor with an integrated photodiode and an automatic dimming control LED driver

This paper presents the design and implementation for a photoplethysmographic (PPG) sensor with an integrated photodiode and an automatic dimming control LED driver. The PPG front end is designed with a programmable low-pass cutoff frequency from 5 Hz up to 35 Hz, a high-pass cutoff frequency of 0.1 Hz, a total input referred noise current of 79 pA, and a maximum transimpedance gain of 144 dBΩ. The sensor fabricated in 0.35-μm CMOS technology and consumes 1.4 mA from 2.7 V-4 V single power supply. The integrated LED driver uses a duty cycle control at a pulse repetition frequency of 200 Hz and 1% duty cycle. The LED driver can supply four LEDs each with 10 mA. An automatic dimming control is implemented to reduce the LEDs current at strong PPG signal strength, to reduce the LEDs power consumption.