14.85 μW Analog Front-End for Photoplethysmography Acquisition with 142-dB Gain and 64.2-pArms Noise

A low-power, high-gain, and low-noise analog front-end (AFE) for wearable photoplethysmography (PPG) acquisition systems is designed and fabricated in a 0.35 mu m CMOS process. A high transimpedance gain of 142 dB Omega and a low input-referred noise of only 64.2 pA(rms) was achieved. A Sub-Hz filter was integrated using a pseudo resistor, resulting in a small silicon area. To mitigate the saturation problem caused by background light (BGL), a BGL cancellation loop and a new simple automatic gain control block are used to enhance the dynamic range and improve the linearity of the AFE. The measurement results show that a DC photocurrent component up-to-10 mu A can be rejected and the PPG output swing can reach 1.42 V-pp at THD < 1%. The chip consumes a total power of 14.85 mu W using a single 3.3-V power supply. In this work, the small area and efficiently integrated blocks were used to implement the PPG AFE and the silicon area is minimized to 0.8 mm x 0.8 mm.