An analog-to-digital converter comprises a signal input (6) for receiving an analog input signal and a set of comparators (4). Each comparator (4) has a first input (21 ) connected to the signal input (6) and a second input (22) connected to a reference voltage (16). Each comparator generates an output based on the comparison of the signals at the first input (21 ) and second input (22). The reference voltage is the same for all comparators. The set of comparators (4) has a non-identical response to the reference voltage (16) and the input signal and is due to an internally arising offset. An adder (25) determines a sum of the outputs of the set of comparators and conversion logic (27) generates an output digital signal dependent on the determined sum. Multiple sets of comparators can be provided, each set having a different respective reference voltage.