High-speed and low-power analog-to-digital converter and cmos image sensor using the same

A complementary metal oxide semiconductor (CMOS) image sensor (CIS) comprising:

• a pixel array suitable for outputting a pixel signal corresponding to incident light;
• a row decoder suitable for selecting and controlling a pixel in the pixel array at each row line;
• a ramp signal generator suitable for generating rising and falling half ramp signals;
• a ramp signal selector suitable for selecting the rising or downward ramp signal from the ramp signal generator according to a ramping direction detection result from a ramping direction detector;
• a comparator suitable for outputting an initial comparison result signal by initially comparing a half ramp signal and the pixel signal, and outputting a comparison result signal by comparing the rising or falling half ramp signal selected through the ramp signal selector to the pixel signal;
• the ramping direction detector suitable for detecting a ramping direction according to the initial comparison result signal from the comparator;
• a data converter suitable for deciding an initial bit according to the initial comparison result signal from the comparator, and performing data conversion according to the comparison result signal from the comparator;
• a controller suitable for controlling the operations of the row decoder, the ramp signal generator, the comparator, the data converter and a column readout circuit;
• and
• the column readout circuit suitable for outputting data of a memory unit according to control of the controller.

An analog-to-digital converter (ADC) comprising:

• a ramp signal selector suitable for selecting one of rising and falling half ramp signals according to a ramping direction;
• a comparator suitable for first comparing a reference half ramp signal and a pixel signal, and secondly comparing the selected half ramp signal to the pixel signal;
• a ramping direction detector suitable for detecting the ramping direction according to the first comparison;
• and
• a data converter suitable for performing data conversion according to the second comparison.