CMOS Tunable-Color Image Sensor With Dual-ADC Shot-Noise-Aware Dynamic Range Extension

Abstract

A wide dynamic range CMOS tunable-color image sensor is presented. The sensor integrates an 8 × 8 array of tunable-color photogates which exploit the wavelength-dependent optical absorption properties of the polysilicon gate structure. An analysis is presented for the wide dynamic range asynchronous self-reset with residue readout architecture where photon shot noise is taken into consideration. An implementation of this architecture is presented where the (coarse) asynchronous self-reset operation and (line) residue analog-to-digital conversions are performed with separate in-pixel and off-pixel circuits, respectively, for a noise-optimized design. A prototype was fabricated in a standard 0.35 μm CMOS process and is validated in color light sensing which achieves SNRs of 24.3 dB and 28.5 dB in green and red light measurements, respectively, under a moderate input light intensity of 300 μW/cm2. The readout circuit achieves a measured dynamic range of 82 dB with a peak SNR of 46.2 dB under broadband illumination. The prototype has been integrated with a microfluidic device and experimentally validated in fluorescence contact imaging.