A photoplethysmogram (PPG) is an important optically-obtained bio-signal that enables convenient daily monitoring of heart rate and oxygen saturation (SpO2). Most state-of-the-art PPG sensing systems require an off-chip photodiode, and the photodiode's output parasitic capacitanc
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A photoplethysmogram (PPG) is an important optically-obtained bio-signal that enables convenient daily monitoring of heart rate and oxygen saturation (SpO2). Most state-of-the-art PPG sensing systems require an off-chip photodiode, and the photodiode's output parasitic capacitance limits the power-noise trade offs. The objective of this project is to implement a monolithic low-power PPG sensor for heart-rate detection. A novel sensing system has been developed, which has arrays of photogate imagers as front-ends and a compact successive approximation register analog-to-digital converter serving as the readout circuit. The readout power consumption is 0.64 µW at a sampling rate of 40 Hz. The minimum required LED power consumption is predicted to be 3 µW according to the post-layout simulation. The die area is 6.05 mm2 including the pads. Compared with the prior art, the readout power consumption is reduced by four times and the die area is reduced by 3 times. The chip was submitted for fabrication in June in TSMC180nm.
