Abstract
This brief proposes employing each of the classical 4 transistor (4T) pinned photodiode (PPD) CMOS image sensor (CIS) pixels, for both imaging and temperature measurement, intended for compensating the CISs’ dark current, and dark signal non-uniformity (DSNU). The proposed temperature sensors rely on the thermal behavior of MOSFETs working in subthreshold region, when biased with ratiometric currents sequentially. Without incurring any additional hardware or penalty to the CIS, they are measured to have thermal curvature errors less than ±0.3 °C and $3~\sigma $ process variations within ±1.3 °C, from 108 sensors on 4 chips, over a temperature range from −20 °C to 80 °C. Each of them consumes 576 nJ/conversion at a conversion rate of 62 samples/s, when quantized by 1st-order 14 bit delta–sigma ADCs and fabricated using $0.18~\mu \text{m}$ CIS technology. Experimental results show that they facilitate digital compensation for average dark current and DSNU by 78% and 20%, respectively.
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