a switched - capacitor filter circuit having at least one simulated inductor and having a resonance frequency which is one - sixth of the sampling frequency as pulse - controlled switches co - operatively operable for connecting a first capacitor to a pair of input terminals during a first clock phase and simultaneously connecting a second capacitor to the output of an inverting integration circuit , followed by discharge of the first capacitor to a capacitor in the integration circuit during a second clock pulse phase , followed by a third clock pulse phase during which the first capacitor is charged from the output of the integration circuit and the second capacitor is simultaneously connected to the pair of input terminals and during a fourth clock pulse phase the second capacitor discharges to the capacitor in the integration circuit .