Band-rejection filter of the switched capacitor type.

摘要

Band-rejection filter of the switched capacitor type in which at least one unwanted frequency component present in an information signal must be suppressed. To that end this filter comprises an adder circuit 4 to which the information signal is applied via a switching device 3 and a feedback signal via a switching device 5. Both switching devices are controlled by a first control signal consisting of a sequence of control signal periods of a duration T<Sub>s</Sub> which are each divided into a tracking phase and into an interrupt phase. During the tracking phase the signal can pass uninterruptedly through the switching device, while during the interrupt phase signals are not allowed to pass. The output of adder circuit 4 is coupled inter alia via a switching device 8 to the input of a bandpass filter 9 whose passband at least coincides with the unwanted frequency component. The switching device 8 is controlled by a second control signal which is also formed by a sequence of control signal periods of a duration T, and which are each divided into a tracking and an interrupt phase.

In order to realize an adequate suppression of the unwanted frequency component the instants at which the tracking phases in the first control signal and the tracking phases in the second control signal end are mutually phase-shifted over a fixed distance.