Analog-to-digital conversion circuit and image sensor including the same

An analog-to-digital converter circuit, comprising:

• a comparator configured to receive an input signal and a reference voltage;
• and
• a digital-to-analog converter (DAC) circuit having an output node electrically coupled to an input of the comparator and configured to output the reference voltage to the comparator, wherein the DAC circuit includes three charge paths electrically coupled to the output node;
• each charge path includes a charge conversion capacitor, a gain capacitor and a plurality of charge-injection cells, where each charge-injection cell in the plurality of charge-injection cells is electrically coupled to the output node, the gain capacitor is electrically coupled in series between the output node and the plurality of charge-injection cells and the charge conversion capacitor is electrically coupled in parallel with the plurality of charge-injection cells;
• each charge-injection cell is configured to transfer a fixed amount of charge from a charge source to an associated charge path and includes at least one switch configured to isolate the charge source from the output node.

An image sensor comprising:

• an array of pixel units arranged in rows and columns, each pixel unit configured to perform a photoelectric conversion and output an analog signal;
• a series of analog-to-digital converter (ADC) circuits, wherein, for each column in the array of pixel units, pixel units in a given column are electrically coupled to one of the ADC circuit in the series of ADC circuits;
• and
• a controller interfaced with each of the ADC circuits in the series of ADC circuits,
• wherein each ADC circuit includes
• a comparator configured to receive an analog signal from a pixel unit and a reference voltage;
• and
• a digital-to-analog converter (DAC) circuit having an output node electrically coupled to an input of the comparator and configured to output the reference voltage to the comparator, wherein the DAC circuit includes two or more charge paths electrically coupled to the output node;
• each charge path is formed by one or more charge-injection cells electrically coupled via a gain capacitor to the output node, and a charge conversion capacitor electrically coupled in parallel with the one or more charge-injection cells;
• each charge-injection cell is configured to transfer a fixed amount of charge from a charge source to an associated charge path and includes at least one switch configured to isolate the charge source from the output node.