Abstract: A ringer circuit includes a rectifier unit receiving a calling alternating voltage and having first and second output terminals. An acoustic transducer has first and second terminals. A controllable first switch is connected between the first output terminal of the rectifier unit and the first terminal of the acoustic transducer. A controllable second switch is connected between the first and second terminals of the acoustic transducer. A capacitor is connected between the second terminal of the acoustic transducer and the second terminal of the rectifier unit. A switch control is supplied from the capacitor for opening and closing the first and second switches in alternation and in phase opposition to one another as a function of the calling alternating voltage.

Abstract: A circuit configuration includes a final control element being adjustable as a function of a control current, wherein the function is subject to certain fluctuations and variations. A constant current source supplies an output current being equally subject to the certain fluctuations and variations. A multiplier is connected between the constant current source and the final control element, for varying the current output by the constant current source by a factor being dependent on a control signal, and for delivering the current output by the constant current source to the final control element as the control current.

Abstract: A method for gain control of telephone sets having an electronic speech circuit and an apparatus for carrying out the method include a modulation current source. Two line terminals connect the modulation current source to a telephone line. A microphone amplifier has an input connected to a microphone terminal and an output controlling the modulation current source for generating a line signal. Signals are derived from the modulation current source and converted into mutually associated measurement signals and threshold value signals. The mutually associated measurement and threshold value signals are compared with one another. The gain of the microphone amplifier is regulated as a function of the result of the comparison.

Abstract: An electronic speech circuit configuration includes first and second line terminals to be connected to a telephone line. An AC circuit portion includes a modulator circuit for generating a line transmission current. A DC circuit portion supplies energy and generates a DC current/voltage characteristic curve. The DC circuit portion includes a reference potential source and a decoupling capacitor. A current sensing resistor is provided. A high-speed control amplifier has a control circuit and controls current through the current sensing resistor. A buffer capacitor is provided. Output terminals are connected to the buffer capacitor for the connection of external components. The DC circuit portion also includes a current toggle circuit connected upstream of the buffer capacitor. The current for feeding the buffer capacitor flows through the current sensing resistor connected to the first line terminal.