New method of on-sensor A/D conversion
We describe a CMOS image sensor with column parallel Analog to Digital Conversion circuits. In this method, we use small 1 bit comparator which detects each bit during integration 8 bit value is determined when the integration is finished. Consequently, both the A/D conversion and the integration of the pixel value can be done in parallel. We have designed a prototype by using column parallel architecture. The prototype outputs analog value and 8 bit digital value of pixel data. It has 32/spl times/16 pixels and digital memory for each pixel. We describe the processing scheme of our ADC and the circuit and layout design of the prototype. We show results of some experiments.