Noise Reduction Effect of Folding-integration ADC in an 8K Image Sensor driven at Various Frame Rates

Abstract

This paper describes the noise reduction effect of a folding-integration (FI) ADC applied to an 8K image sensor. To maximize the sampling number in correlated multiple sampling (CMS), we implement duplicated pixel source followers, which are operated alternately to reduce the time needed for them to settle. This architecture facilitates sampling numbers of 6, 14, and 30 at 120, 60, and 30 fps, respectively. To investigate the relationship between noise reduction effect and sampling number, the input referred noise of the readout circuit from the pixel-to-column ADC is estimated via theoretical calculations and compared with measurements. As a result, the random noise levels of 3.2, 2.0, and 1.5 e- were measured at sampling numbers of 6, 14, and 30, respectively, corresponding well with the calculated results. Furthermore, theoretical calculations revealed that the thermal noise component is dominant at higher frame rates while 1/f noise from the source follower becomes dominant at lower frame rates.