Abstract: This invention relates to a method of calibrating a time-interleaved analogue-to-digital sampler (10) and to a method of performing analogue-to-digital conversion with a sampler (10) so calibrated. The invention provides a method of calibrating a sampler (10) comprising N time-interleaved ADCs (12a-d), the method comprising the steps of: (a) injecting in turn N calibration signals (13) into the sampler such that each calibration signal (13) occupies one of N related frequencies; (b) determining the input signal for each one of the N calibration frequencies (13); (c) measuring in the frequency domain the output at each of the N related frequencies for each one of the N calibration frequencies; and (d) determining the relationship that relates the input signal to the output at each of the N related frequencies for each one of the N calibration frequencies.