ANORDNING FOR DETEKTERING AV EN FREKVENS F?711 I EN SIGNAL SOM FORELIGGER I EN PCM-KODAD FORM

摘要

The invention relates to a device for digitally detecting a frequency in a PCM signal. In accordance with the invention, an up/down counter is provided which receives a up-count pulses when there is a change of sign in the signal to be checked and which receives r down-count pulses when there is no change of sign in this signal. The numbers a and r are determined as a function of the ratio between the sampling frequency of the PCM signal and the frequency to be detected, so that it is possible to deduce the presence of this frequency from a balance between the number of up-count pulses and the number of down-count pulses. Application: detecting the neutralization tone for an echo suppressor in a PCM telephone line.