All-MOS self-referenced temperature sensor

Abstract

This Letter presents an all-MOS self-referenced temperature sensor, intended for thermal compensation of dark current in CMOS image sensors (CIS). Its thermal sensing front-end is based on a self-biased nMOS pair working in the subthreshold region. Biased with ratiometric currents, the differential voltage output of the nMOS pair is proportional to the absolute temperature. The thermal sensing voltage is quantised by a self-referenced first-order incremental delta-sigma ADC, which obtains its reference voltage from the thermal sensing front-end. This reference voltage has been virtually attenuated, through switch capacitor charge sampling, to improve the resolution of the temperature sensor. Measured between -20 and 80°C, the proposed temperature sensor achieves an inaccuracy within ±0.55°C.