Patent ID: 10498989

Abstract:
A digital double-sampling (DDS) circuit includes a comparator with input nodes respectively connected to a ramp voltage and an image output node of a pixel circuit via a capacitor; a reset switch connected between the input nodes for resetting the capacitor; an analog-to-digital converter (ADC) coupled to receive a comparison output of the comparator, the ADC including a counter that counts while the ramp voltage is ramping, thereby generating a reset-ADC value in a reset phase and generating a signal-ADC value in a signal phase; a subtractor that subtracts the reset-ADC value from the signal-ADC value, thereby resulting in a difference value representing a sampled output; and a clamp circuit that generates a clamp voltage at the image output node. In the reset phase, the clamp circuit is disabled after the capacitor finishes resetting but before the ramp voltage begins ramping.