A Nyquist-rate pixel-level ADC for CMOS image sensors

Abstract
A Nyquist rate Multi-Channel Bit Serial (MCBS) ADC using successive comparisons is presented. The ADC is suited to pixel level implementation in a CMOS image sensor. It comprises a 1-bit comparator/latch pair per 4 pixels and a DAC/controller shared by all pixels. A CMOS 320 x 240 'sensor using the MCBS ADC is de- scribed. It achieves 8.9 x 8.9 pm pixel size at 25% fill fac- tor in 0.35 pm CMOS technology. Measured INL/DNL for the ADC are 2.3/1.2 LSB at 8-bit. Gain/offset FPN due to ADC are 0.24%/0.2%.

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