Circuit arrangement for establishing the presence or absence of at least one frequency of known value in an input signal consisting of a plurality of frequencies

摘要

Circuit arrangement for establishing the presence or absence of at least one frequency of known value in an input signal consisting of a plurality of frequencies, having means (22, 24, 25) for generating two reference signals (14, 15) which have the same frequency and are phase-shifted by 90 DEG with respect to each other, means (12, 13) for mixing the reference signals (14, 15) with an intermediate signal derived from the input signal (1), means (16, 17) for band-limiting the mixing products resulting therefrom, means (18, 19) for amplitude-evaluation of the band-limited mixing products, which amplitude-evaluation means deliver an output signal (20, 21) indicating the presence or absence of the frequency or frequencies of known value, means (22, 23, 24) for producing two further reference signals (4, 5) which have the same frequency and are phase-shifted by 90 DEG with respect to each other, means (2, 3) for mixing the further reference signals (4, 5) with the input signal (1), means (6, 7) for band-limiting the further mixing products produced therefrom and means (8, 9, 10), producing the intermediate signal, for squaring and subsequently adding the band-limited further mixing products. <IMAGE>