Image sensor and method of operating same

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

• generating a pixel signal in a sensor array;
• generating a ramp signal in response to a ramp enable signal, wherein the ramp signal has a decreasing slope during a ramp signal enable period extending between a first time at which a counter enable signal is activated and a third time at which the ramp signal ends falling;
• comparing the pixel signal with the ramp signal to trigger an output signal;
• and
• using at least one of a plurality of counters to perform counting during a counter enable period extending between the first time and a second time at which the comparator triggers the output signal,
• wherein the counter enable period is divided into a first section and a second section following the first section,
• the plurality of counters includes a mask counter and remaining counters among the plurality of counters except the mask counter, and
• not all of the plurality of counters perform the counting during at least one of the first section and the second section.

An image system comprising:

• an image sensor which converts incident light into a corresponding digital signal, and a memory device which stores the digital signal,
• wherein the image sensor comprises:
• a sensor array which generates a pixel signal;
• a ramp signal generator which generates a ramp signal in response to a ramp enable signal, wherein the ramp signal has a decreasing slope during a ramp signal enable period extending between a first time at which a counter enable signal is activated and a third time at which the ramp signal ends falling;
• a comparator which compares the pixel signal with the ramp signal to trigger an output signal when the ramp signal equals the pixel signal;
• and
• a counter unit including a plurality of counters, wherein at least one of the plurality of counters performs counting during a counter enable period extending between the first time and a second time at which the comparator triggers the output signal,
• wherein the counter enable period is divided into a plurality of sections, the plurality of counters includes a mask counter and remaining counters among the plurality of counters except the mask counter, and
• the mask counter performs a mask counting only during one of the plurality of first sections, and the remaining counters perform counting during other ones of the plurality of sections.