A system containing an ambient light and a proximity sensor with intrinsic ambient light rejection

Low-Power Photoplethysmogram Acquisition Integrated Circuit with Robust Light Interference Compensation

“…The photoplethysmogram (PPG) is widely used for monitoring cardiovascular parameters such as heartbeat rate, blood vessel stiffness, and pulse transit time blood pressure [ 1 , 2 , 3 , 4 ]. In particular, wearable pulse rate sensors based on the PPG have become increasingly popular because of their convenience compared to electrocardiogram sensors.…”

“…A DC offset that depends on the static ambient light intensity and skin color is present in a detected signal. The DC offset is typically a hundred times larger than the pulsatile amplitude [ 3 ]. Signal saturation from the large DC offset can be prevented by using a wide dynamic range design, but this results in inefficient power consumption.…”

“…In previous works, this ambient light was cancelled by a feedback technique with a digital-to-analog converter (DAC) and correction circuit blocks [ 3 ] or by an additional analog-to-digital converter (ADC) and a digital signal processor [ 10 ]. Other studies also reported a few methods of reducing interference, such as rejecting the DC offset by a low-frequency feedback loop [ 11 ], extending the dynamic range using a logarithmic amplification [ 12 ], using digital feedback [ 13 ], and using an adaptive digital filter [ 14 , 15 ].…”