EVALUATION CIRCUIT FOR AC VOLTAGE PULSES

PROBLEM TO BE SOLVED: To provide a method for detecting AC voltage pulses of defined frequencies. SOLUTION: A detection circuit and a detection method for AC voltage phases of defined frequencies are disclosed. The detection circuit comprises: an analog/digital converter unit (A-D) for converting an input signal (1) into a sample value sequence (x(k)); at least one mix stage (4, 5, 12 and 21) for multiplying the sample value sequence (x(k)) by a mix frequency signal; at least one filter stage (13, 14, 22) for defining an allowable intermediate frequency band; and an evaluation unit which determines the presence/absence of AC voltage pulses using converted sample values. By this method, an input signal is transformed into a low-frequency signal by being multiplied by a mix frequency. The down-mixed signal can then be filtered and evaluated. The circuit is particularly suited for identifying charging unit signals of the telephone network. COPYRIGHT: (C)2007,JPO&INPIT