UNITA' DI CONTROLLO DELLA SEGNALAZIONE DI TIPO MULTIFREQUENZA, DI PARTICOLARE APPLICAZIONE NELLE CENTRALI TELEFONICHDE TRANSITO DI TIPO NUMERICO

A circuit arrangement is provided for minimizing frequency variations in a digital telephone exchange timing unit when a drop in the phase of the reference pulses occurs owing, for instance, to a change of the PCM line from which the reference pulses are obtained. Means PM are provided which are arranged to compute the average phase error between the output of a local oscillator OL phase and the frequency f2 of the reference pulses. Means SM are also provided for computing the deviation between the average phase error and the average phase error obtained after the above mentioned drop in the phase has occurred, and for correcting the average phase error obtained after a drop in the phase by an amount such as to make a digital signal available on the output, the value of the output signal being equal to the output value before the drop in phase. A unit UF is provided for compensating fast, slow variations of the oscilator OL.