Abstract: A synchronous filter for use as a narrow band, band-pass filter comprises a matching circuit receiving a signal to be filtered and supplying that signal to an output connected to filtering paths with switched capacitances connected in parallel. This filter also includes switches for switching the filtering paths, a summing circuit with inputs respectively connected to outputs of the filtering paths and a switch control circuit. Each filtering path has two identical filtering channels, each with a capacitance, connected to the switches. The switching control signals are symmetrical for the two channels of each path and staggered by T/2N. The sampling periods or cycles of the two channels of one path are equal to T/2.

Abstract: The present invention relates to an assembly for filtering by switching, comprising at least one filter with switched paths and means for applying to each of the filters signals for controlling switching of the paths, said assembly further comprising means for memorizing the output signal of the filter and a mixer circuit whose input receives at a given instant the signal to be filtered; a second input receives at this instant the memorized value which the output signal had, an instant earlier, separated from the instant in question by a whole number of periods of the useful component of the input signal. The invention is applicable to harmonic analysis, telecommunications, filtering of composite signals.

Abstract: In a switching follower filter of the narrow-band-pass type having n switched paths for filtering a signal having a useful component of variable frequency associated with a high background noise, the fundamental frequency of the input signal is captured and then followed by collecting a pre-filtered switching synchronization signal so that part of the input signal remains in the pre-filtered signal.