The dynamic range of an image sensor is often not wide enough to capture scenes with both high lights and dark shadows. A 640/spl times/512 image sensor with Nyquist rate pixel level ADC implemented in a 0.35 /spl mu/m CMOS technology shows how a pixel level ADC enables flexible efficient implementation of multiple sampling. Since pixel values are available to the ADCs at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected without the long readout time of APS. Typically, hundreds of nanoseconds of settling time per row are required for APS readout. In contrast, using pixel level ADC, digital data is read out at fast SRAM speeds. This demonstrates another fundamental advantage of pixel level ADC-the ability to programmably widen dynamic range with no loss in SNR.
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Yang et al. (2003) studied this question.