Abstract: An image sensor includes a pixel array, and a correlated double sample circuit coupled to one of the pixels in the pixel array. The correlated double sample circuit includes first and second inputs, and first and second sample capacitors respectively coupled to the first and second inputs. The first input is for receiving an analog signal from a pixel, and the second input is for receiving a time varying reference signal. The analog signal varies during a pixel readout period, and has a first level during a first reset period and a second-level during a second read period. A comparator circuit compares the time varying reference signal and the analog signal. The analog signal and the time varying reference signal are constantly read onto one of the first and second sample capacitors during both the first reset period and the second read period.