Pixel-level temperature sensor design for image sensors

Abstract

With the development of science and technology, image sensors are more and more widely used, such as digital cameras and surveillance cameras. However, due to the physical characteristics of the photodetector, which performance is sensitive to the variation of the operating temperature. Therefore, a digital temperature sensor integrated on the chip is required to measure the operating temperature and assist in correction and compensation. Traditional scheme integrates one temperature sensor on the whole image sensor chip, which can’t reflect the temperature distribution for each pixel. It’s desirable to implement temperature measurement in pixel level for accurate correction, but existing temperature sensor occupying area of hundred μm2, which can’t be input to the pixel of image sensor. In additional, the power consumption of each temperature sensor is μW-level, which will dissipate considerable power for million temperature sensors. In this paper, a pixel-level integrated temperature sensor is proposed. The circuit is composed of only a capacitor and a conventional diode. The readout circuit is similar to that of the active pixel of image sensor, thus the ADC (Analog-to-Digital Converter) and other readout circuits and be multiplexed. The temperature sensor integrated in pixel is designed, which area is only 0.21 μm2. The simulation results show the increased power consumption for 50Hz working pixels don’t exceed 4%. It’s confirmed that the proposed pixel-level integrated temperature sensor can measure the temperature of each pixel and assisting in the accurate correction of image sensor in pixel level.