Fast multi-sampling in image sensors

An image sensor comprising:

• a plurality of pixels arranged in a pixel array of rows and columns;
• a ramp generator configured to generate a plurality of first short ramps having a first level in a reset conversion phase and a plurality of second short ramps having a second level greater than the first level and a full-scale ramp having a third level greater than the second level in a signal conversion phase;
• a plurality of readout circuits each comprising a comparator configured to:
• compare a first analog signal with each one of the first plurality of short ramps to obtain a plurality of first comparison results;
• and
• compare a second analog signal with each one of the plurality of second short ramps and the full-scale ramp in the signal conversion phase to obtain a plurality of second comparison results and a third comparison result;
• and
• a controller configured to determine an output signal value of the second analog signal according to the plurality of second comparison results and the third comparison result.

A method of operating an image sensor, the method comprising:

• comparing a first analog signal with a plurality of first ramps having a first level, by a comparator, to obtain a plurality of first comparison results, the first analog signal indicative of a first charge of a pixel in a pixel array in a reset conversion phase;
• comparing a second analog signal with a plurality of second ramps having a second level greater than the first level and a full-scale ramp having a third level greater than the second level, by the comparator, to obtain a plurality of second comparison results and a third comparison result, respectively, the second analog signal indicative of a second charge of the pixel in the pixel array in a signal conversion phase;
• and
• determining an output signal value of the second analog signal according to the plurality of second comparison results and the third comparison result.