6 A High-Speed Back-Illuminated Stacked CMOS Image Sensor with Column-Parallel kT/C-Cancelling S&H and Delta-Sigma ADC

In recent years, there has been growing demand for high-resolution and large-format CMOS image sensors in Digital Still Camera, Security, and Factory Automation uses. In addition, new uses such as airborne mapping 1 are now being reported. Focusing on the camera market, there is currently demand for simultaneously realizing high image quality, high frame rate, and low power consumption, all within a larger-than-APS-C format. For most cases, the single-slope ADC (SS ADC) 2 architecture is used in commercialized CMOS image sensors. In order to accelerate frame rate, the counting-clock frequency can be increased up to 2.376GHz as demonstrated in 3, but maintaining clock waveform quality without increasing power is a major challenge for low-power operation. Adaptive gain operation using a dual gain amplifier is reported in 4, but SS ADCs based on adaptive gain operation still have frame rate issues from increasing bit resolution, e.g., to 14b.