APPARECCHIATURA PER RIVELARE LA PRESENZA DI SEGNALI MULTIFREQUENZIALI IN UN SEGNALE RICEVUTO

In a multifrequency receiver, a threshold level (VTH) supplied to a group of threshold comparators (105-1 through 105-N) is controllably adjustable by a variable threshold generation circuit (104) in response to received multifrequency signals. As the envelope of the received multifrequency signal experiences a positive amplitude transition, the threshold level is increased at a fast rate (fast attack). Also, as the envelope of the received multifrequency signal exhibits a negative amplitude transition, the threshold level is decreased at a much slower rate (slow release).