Abstract: A keyboard type telephone station connected to a telephone subscriber's line comprises a dial pulse train generator and a dialling multifrequency signal generator. The telephone station includes a control unit connected to at least one current threshold detector for the power level of supervisory or so-called tone signals. The supervisory signals are transmitted from the linking exchange on the telephone subscriber's line and indicate the beginnings of various call dialling phases in setting up a telephone communication. In response to the detection of the supervisory signal, the control unit blocks transmission of the pulse generator and releases transmission of the multifrequency generator, so that only the multifrequency generator transmits only the dialling multifrequency signal associated with the first key of the dialling phase.

Abstract: The invention relates to a synthesizer of multifrequency code signals for a keyboard type telephone station, more particularly to a generator producing dialing signals or more generally recorder signals embodied by frequencies associated 2 by 2 in a 2-amongst-N code to represent decimal-notation digits and, if necessary, other signal-service signals. A dialing code of such a kind can be e.g. the SOCOTEL multifrequency code recommended by the CCITT.

Abstract: Synthesizer of multifrequency signals for telephone sets, each multifrequency signal being formed by two concomitant sinusoidal signals of different basic frequencies, said frequencies forming pairs respectively corresponding to the decimal digits and being sub-multiples of a common clock frequency. The sinusoidal signals are pulse trains whose repetition rate varies steppedly in function of time in the following manner. The period of a sine function is divided into p parts and the amplitude of the function taken from the tangent to the negative peaks of the sine curve for p equidistributed values of the argument 2.pi.i/p, i varying from l to p, are approximated by p amplitude values. The periods of the signals having the basic frequences are divided into p time intervals and during these time intervals, a pulse train generator is operated in such a way that its pulse repetition rate be proportional to said amplitude values.