Digital multi-frequency receiver

Details Digital multi-frequency receiver Digital multi-frequency receiver

H - Electricity

04

M

379/22, 344/84,

H04M 3/00 (2006.01) H04Q 1/457 (2006.01)

Patent

CA 1137565

ABSTRACT OF THE DISCLOSURE A digital multi-frequency receiver for the use in an electronic telephone exchange system for detecting MF signals (700, 900, 1100, 1300, 1500 and 1700 Hz) in the CCITT No. 5 system has been found. The digital multi- frequency receiver comprises of a recursive digital filter for detecting each of said MF signals on a time divisional basis, an absolute value circuit for providing the abso- lute value of the output of the recursive digital filter, a comparator for comparing the output of the absolute value circuit with a variable threshold to provide the detected MF signal information, and a circuit for provi- ding said variable threshold by selecting the maximum value from among, (1) the predetermined fixed value, (2) the product of a value a which is less than but close to one and the maximum value of the variable threshold in a preceding frame of the input signal, and (3) the maximum value of the output of the absolute value circuit in a present frame of the input signal.

351577

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