Abstract: An electronic telephone set which includes first and second connection points for a telephone line and a transmission circuit having a send output stage including a first transistor whose first main electrode is coupled to the first connection point by means of a first resistor. The telephone set includes a supply circuit for peripheral circuits. The supply circuit has a first output terminal coupled to the first main electrode of the first transistor and has a second transistor whose first main electrode is coupled to the second connection point and whose second main electrode is coupled to the second output terminal of the supply circuit. This circuit includes an operational amplifier whose output is coupled to the gate electrode of the second transistor. the set also includes a first voltage source connected between the first main electrode of the second transistor and a first input of the operational amplifier.

Abstract: A telephone set comprising an active line voltage stabilizer circuit having two output terminals 10-1 and 10-2 between which it produces a stabilized direct voltage which is independent of the line current. A series arrangement of a capacitor (14) and a resistor (16) is connected between such output terminals, the junction thereof constituting a DC supply terminal for the telephone set. Such arrangement does not alter the a.c. impedance of the stabilizer circuit between the wires, and has a considerably lower d.c. output resistance than supply terminals previously employed.

Abstract: Transmission circuit for a telephone set for DTMF-tone selection. The required second-order tone filter is formed by arranging the speech filter (12) during the dialling procedure in series with a fixed first-order tone filter (10) by means of a switch (11). The resultant attenuation of the group II of high frequencies of the dialling tones is compensated for by increasing the amplitude of the dialling tones of the high-frequency group II and by an additional increase in the sub-group II(2) of the two highest frequencies of this group.

Abstract: When electronic circuits are used for applying a conventional ringing voltage which has been superimposed on the conventional supply voltage, they require a high supply voltage. According to the invention an a.c. voltage is used in which that portion of each period in which the polarity is positive differs from the portion in which the polarity is negative. This a.c. voltage has a DC-component by means of which the condition of the subscriber's loop can be detected. The peak-peak value of the ringing voltage may be twice the maximum permissible voltage swing of a wire of the subscriber's line, which is an optimum.