A back-illuminated global-shutter CMOS image sensor with pixel-parallel 14b subthreshold ADC

Rolling-shutter CMOS image sensors (CISs) are widely used [1,2]. However, the distortion of moving subjects remains an unresolved problem, regardless of the speed at which these sensors are operated. It has been reported that by adopting in-pixel analog memory (MEM) in pixels, a global shutter (GS) can be achieved by saving all pixels simultaneously as stored charges [3,4]. However, as signals from a storage unit are read in a column-wise sequence, a light-shielding structure is required for the MEM to suppress the influence of parasitic light during the reading period. Pixel-parallel ADCs have been reported as methods of implementing GS on a circuit [5,6]. However, these techniques have not been successful in operations on megapixels because they do not address issues such as the timing constraint for reading and writing a digital signal to and from an ADC in a pixel owing to increase in the number of pixels and the increase in the total power consumption of massively parallel comparators (CMs).