A Low-noise CTIA-based Non-contact PPG Sensor Analog Front End with Chopping and RDAC Compensation Techniques

This paper proposes a low-noise AFE based on a capacitive transimpedance amplifier (CTIA) for wearable PPG sensors. By separating noise from the PPG signal, the proposed AFE applies chopping technique to the CTIA for reducing flicker noise and input-referred offset. Resistive DAC (RDAC) is adopted to substitute the conventional current DAC to suppress the noise in the dual compensation loop by replacing the high transistor noise with the lower resistor thermal noise. In $0.18-\mu \mathrm{m}$ CMOS, the proposed AFE under 1.2 V consumes $68 \mu \mathrm{~W}$ power with an equivalent input-referred noise of $\mathbf{1 5. 3 2}$ pArms. Compared with the related works, the proposed AFE reduces noise by 45.3% ~ 83.3% with comparable power consumption and silicon area.