Licentia Patent-verwaltungs Gmbh

Dietrich Hoppner

Bernhard Rall

Gerhard Kohlbacher

Erich Bachle

Rudolf Schehrer

Kurt Eberhardt

To control the earphone and microphone amplifiers as well as the balancing network of a subscriber's telephone terminal which is fed, through a subscriber line in communication systems, to the effect that the attenuations in subscriber lines of unequal lengths do not affect the transmission characteristics between the exchange and the subscriber, a circuit arrangement is provided for producing the necessary control function, which is simple, integratable and has minimum tolerances. Above a predetermined threshold value, a voltage proportional to the line current variations controls the emitter-to-base junction of two grounded-base transistors at the collectors of which the control current is available. The control currents produce their effect on the negative feedback of the microphone and the earphone amplifiers. An increasing line current causes the cotrol current to decrease, thereby effecting a stronger feedback and a reduced amplification. Further, the voltage proportional to the line current variations and available at the emitter resistor of another transistor, controls the balancing impedance through a current mirror, to attenuate the sidetone independently of the length of the subscriber line.

Circuit arrangement for producing control means from line current

A monolithically integrated semiconductor circuit, provided for coupling arrangements having symmetrical cross points, comprising two through switching NPN transistors, and a composite circuit for switching through the switching transistors. The composite circuit includes a double collector PNP transistor, with one collector connected to the base of a first NPN transistor and the other collector connected to the base of a second NPN transistor. The emitter of the double collector transistor is connected to the collector of both NPN transistors and also, via a first resistor to a voltage source. The base of the double collector transistor is connected, via a component causing a constant drop in voltage, to the voltage source, and also via a second resistor, to a trigger stage. The emitters of the NPN transistor are connected, respectively, to the bases of the two through switching transistors.

Monolithically integrated semiconductor circuit

A circuit arrangement for stabilizing a direct current comprises a parallel controller for controlling a transistor connected in series with the load.

Circuit arrangement for stabilizing a direct current

Electronic switch for use as a crosspoint in switching networks of space-division telephone exchanges where it is connected to function as an open circuit stable negative resistance provding ON-attenuation compensated signal transmission, the switch being constituted by a circuit arrangement which lends itself to monolithic integration and which, when switched off, prevents undersirable attenuation of crosspoints connected to the same row or column of the switching system.

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Wippingen, Germany

Dietrich Hoppner