A correlated multiple sampling passive switched capacitor circuit for low light CMOS image sensors

After a brief review of the principle of correlated multiple sampling (CMS) and its implementation techniques in CIS readout chains, a simple CMS passive circuit that (i) requires no additional active circuitry, (ii) has no impact on the output dynamic range and (iii) does not need multiple analog-to-digital conversions (faster) is presented. The proposed circuit uses n switched capacitors to perform a CMS on 2ⁿ samples. It is validated using transient noise simulations on a CIS readout chain based on a 4T pixel, designed with a 180nm CIS process. For a line readout time of 35 μs and a column amplifier bandwidth of 256 kHz, the proposed circuit reduces the input-referred noise as expected by an ideal CMS.