A sigma-delta modulator may have a plurality of capacitor pairs, a plurality of switches to couple any pair of capacitors from the plurality of capacitor pairs selectively to an input signal or a reference signal, and a control unit operable to control sampling through the switches to perform a charge transfer in two phases wherein any pair of capacitors can be selected to be assigned to the input signal or the reference signal, and wherein after a plurality of charge transfers a gain error cancellation is performed by rotating the capacitor pairs cyclically such that after a rotation cycle, each capacitor pair has been assigned a first predetermined number of times to the input signal, and has also been assigned a second predetermined number of times to the reference signal.