A 640×512 CMOS image sensor with ultra wide dynamic range floating-point pixel-level ADC

摘要

The dynamic range of an image sensor is often not wide enough to capture scenes with both high lights and dark shadows. In Reference 1, dynamic range is enhanced by increasing well capacity one or more times during exposure time. Another approach, which achieves consistently higher SNR is multiple sampling [2] A 640×512 image sensor with Nyquist rate pixel level ADC implemented in a 0.35μm 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 ofsettling 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.