Abstract
A 7.1- μm-pitch lock-in pixel (LIP) CMOS image sensor (CIS) that is capable of simultaneously phasing with two different near-infrared-band (NIR-band) light pulses is developed for remote physiological measurement, particularly a heart rate variability (HRV) signal monitor. The proposed dual NIR-band lock-in operation is realized by a four-tap-wise charge modulation with adjacent two-tap LIPs by means of a column-interdigital pixel driving scheme combining with in-LIP lateral electric field modulators (LEFMs). For attaining the weak HRV signal, the implemented CIS achieves a subelectron temporal noise of 0.67 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> at 64 times correlated multiple sampling (CMS) and a high charge modulation contrast (MC) up to 96% at maximum. These remarkable properties primarily result from the in-LIP dark current and LEFM controlling optimizations proposed in device domain. The experimental results show that the developed CIS exhibits not only a 98.5% accuracy in HRV signal capture with -39.1-dB signal-to-background ratio (SBR) against a fluctuant brightness ambient light but also a moderate artificial motion robustness benefited from the proposed dual NIR-band lock-in technique.
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