A wide dynamic range CMOS digital pixel sensor

Abstract

A CMOS image sensor with pixel level analog to digital conversion is presented. Each 13.8/spl mu/m /spl times/ 13.8/spl mu/m pixel area contains a photodiode and a dynamic comparator using the maximum voltage swing available (0V-1.8V). The comparator does not need any bias current and is insensitive to fabrication process variations. Also a digital to analog converter (DAC) is used to deliver a voltage reference in order to compare it with the pixel voltage for the analog to digital conversion. This DAC provides the possibility to convert the pixel voltage linearly or to compress it logarithmically. The circuit allows image captures at multiple exposure times, and the resulting values are delivered in floating digital format, offering the possibility to expand the intrascene dynamic range to more than 84 dB. The circuit was implemented in a CMOS 0.18/spl mu/m process and has been submitted for fabrication.