A pixel concept that simultaneously enables high dynamic range, high sensitivity and operation in intense backgrounds

摘要

There is an increasing demand for clear and accurate images in both extreme brightness and darkness, therefore imposing a challenge to pixel design. We present in this paper a detailed review of a pixel consisting of a photodetector and a tailored readout integrated circuit that features a good detection sensitivity of 63.4 mV/μA besides enabling a very High Dynamic Range (HDR) of 133 dB. The circuit is known as the Bouncing Pixel as it is designed to basically avoid saturation and maintain the signal linearity over a wide range by bouncing the signal repeatedly whenever it reaches either a high or a low threshold, and by counting the number of bounces the signal is subjected to. Pseudo voltage signals hundred times higher than the voltage supply on a chip can be achieved. Common pixel-circuit topologies for image sensors that feature HDR operation suffer from decreased sensitivity, especially for highlights. We present a detailed comparison between the traditional and ubiquitous Active Pixel Sensor (APS) and the Bouncing Pixel, showing that the latter distinctively features much higher Dynamic Range and sensitivity, even when under intense background illumination, where the APS lacks image contrast. We have done simulations of both circuit topologies, including noise analysis, based on the TMSC CMOS 180 nm technology.