Abstract: The invention relates to a reference rectifier in a multifrequency signal receiver for obtaining a correct detection of the two signalling frequencies in an incoming voice frequency signal independently of disturbing signals of varying frequency and duration. The rectifier has a first signal path including a peak rectifier for creating a first signal level in dependence on the incoming signal level which is compared with the signal component having a frequency equal to one tone in the incoming voice frequency signal. The rectifier also has a second signal path including a mean value creating circuit which, in dependence on the incoming signal gives a second signal whose level is smaller than said first signal level.

Abstract: A reference signal circuit in a multi-frequency signal receiver for detecting the two signalling frequencies in an incoming voice frequency signal. The circuit has two paths for receiving the incoming signal. One path includes a rectifier and attenuation device to give a first signal level dependent on the incoming signal level. The other path includes a first comparator to compare the instantaneous level of the incoming signal with such first signal level, a timing circuit and a second comparator in order to obtain a second signal level whose amplitude is dependent on the duration of the incoming signal. The outputs of the two signal paths are interconnected via a gating circuit to feed a reference voltage to analog signal comparators included in the multi-frequency signal receiver.