A frequency selective circuit configured to convert an analog input signal to a digital output signal comprises an analog-to-digital converter (44) to generate the digital output signal of the circuit based on an analog input signal to the analog-to-digital converter (44); a digital-to-analog converter (46, 47) to generate an analog feedback signal based on the digital output signal from the analog-to-digital converter (44), and an analog filter arranged to generate the analog input signal to the analog-to-digital converter based on the analog feedback signal and an analog input signal to the circuit. The analog filter comprises at least two integrators (41, 42) in series, each having a feedback path comprising the analog-to-digital converter (44) in cascade with a digital-to-analog converter (46, 47), so that the overall noise transfer function of the circuit has at least two zeros in addition to zeros in the noise transfer function of the analog-to-digital converter.