Analog CDS vs Digital CDS

Correlated Double Sampling (CDS) is a technique to obtain two samples, reset and signal voltages, which is widely used in CMOS image sensor system to reduce the FPN noise.

There are two types of CDS: analog and digital CDS.
Analog CDS means that the subtraction between reset and pixel voltages is achieved in analog domain.

Digital CDS means that both reset and pixel voltages are converted to digital bits and then subtract them in digital domain.