14.85 µW analog front-end for photoplethysmography acquisition with 142-dbΩ gain and 64.2-pA_rms 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 µm CMOS process. A high transimpedance gain of 142 dBΩ 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 µA 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 µW 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 × 0.8 mm.