Analog-to-digital conversion and method of analog-to-digital conversion

An analog-to-digital conversion apparatus comprising:

• a plurality of analog-to-digital converters;
• a ramp signal generator configured to generate N ramp signals, where N is an integer≥2, the N ramp signals having different slopes;
• and
• a clock signal generator configured to generate at least one clock signal,
• wherein an analog-to-digital converter of the plurality of analog-to-digital converters comprises:
• an analog signal input for receiving an analog signal;
• N ramp signal inputs for receiving the N ramp signals;
• a clock input for receiving the at least one clock signal;
• a comparison stage connected to the ramp signal inputs and to the analog signal input, the comparison stage comprising a minimum of two comparators and being configured to compare the ramp signals with the analog signal during a conversion period and to provide comparison outputs;
• a counter stage;
• and
• a control stage which is configured to control the counter stage.

A method of analog-to-digital conversion for an imaging device comprising:

• receiving an analog signal from a pixel array of the imaging device;
• receiving N ramp signals, where N≥2, the N ramp signals having different slopes;
• receiving at least one clock signal;
• comparing the ramp signals with the analog signal during a conversion period to provide comparison outputs by a comparator stage comprising a minimum of two comparators;
• and
• controlling a counter stage to generate a digital signal by selecting one of the comparison outputs to control the counter stage based on the comparison outputs and a selection input indicative of when at least one handover point has been reached during the conversion period, wherein the handover point is indicative of a point at which a comparison output of a different one of the ramp signals with the analog signal can be used to control the counter stage.