Low-Frequency Noise Impact on CMOS Image Sensors

CMOS image sensors are nowadays extensively used in imaging applications even for high-end applications. This is really possible thanks to a reduction of noise obtained, among others, by Correlated Double Sampling (CDS) readout. Random Telegraph Signal (RTS) noise has thus become an issue for low light level applications especially in the context of downscaling transistor size. This paper describes the analysis of in-pixel source follower transistor RTS noise filtering by CDS circuit. The measurement of a non Gaussian distribution with a positive skew of image sensor output noise is analysed. Impact of dimensions (W and L) of the in-pixel source follower is demonstrated. Circuit to circuit pixel output noise dispersion on 12 circuits coming from 3 different wafers is also analysed and weak dispersion is seen. Keywords—Low-frequency noise, CMOS image sensor, RTS noise, Correlated double sampling, noise dispersion