A Two-Tap NIR Lock-in Pixel CMOS Image Sensor with Background Light Cancelling Capability for Non-Contact Heart Rate Detection

A time-resolved CMOS image sensor (CIS) using two-tap near infrared (NIR) lock-in pixels with background light (BGL) cancelling capability for non-contact heart rate (HR) detection is presented. Aimed to the application, the sensor performances of $1.1\text{e}_{\text{rms}}^{-}$ temporal random noise and 90.1% maximum charge modulation ratio are achieved by using low noise readout circuit and in-pixel lateral electric field charge modulator (LEFM) techniques. The non-contact HR detection with accuracies of more than 98% is implemented by the developed sensor under both non-visible-light and fluctuant ambient-light brightness conditions. This remarkable performance indicates the superiority of the proposed technique for automotive security applications in particular.