Bell Telephone Laboratories

Donald Gifford Hill

Theras Gordon Lewis

Patrick A Vachon

A network control circuit which allows time division switching systems of different sizes to operate with the same port circuit is disclosed. The time division switching systems utilize a port circuit with a ring counter which controls connection of the circuit to a system bus for establishing telecommunications paths. Each port circuit is provided with a ring counter which has one stage per time slot for the largest size switching system. A network control circuit generates commands which control circuitry associated with the ring counter to write bits into stages of the ring counter causing connection during appropriate time slots. When the port circuit is used with the largest sized switching system, one bit is written into the counter causing one connection per system cycle. In order to use the port circuit with switching systems that have fewer time slots, the network control generates commands to write two or more bits into the ring counter causing the ring counter to appear as if it had fewer stages.

Network control circuit for a time division switching system

A time division switching system is disclosed having a plurality of telephone line circuits and common control circuits for switching calls over a time division communication bus. Ringing loop current detectors are shared by groups of the line circuits for detecting call answer signals during active ringing on a call and for controlling the line circuits to interrupt, or trip, the ringing upon a called party answer. Each group of the line circuits is permanently connected to a ringing current supply via an individual one of the loop current detectors. Each line circuit includes ringing control circuitry operated and released by the common control circuits for connecting ringing current to a called line during an active ringing interval and for disconnecting it during a silent interval of the ringing cycle. The circuitry is responsive to a detection of a called station answer signal by the shared loop current detector for immediately tripping ringing. Apparatus is also provided in the circuitry for sensing answer signals during the silent intervals and for generating switchhook status signals during both the silent and active ringing intervals.

Ringing control circuitry with shared ringing loop current detector

An electronic switch is disclosed comprising a transistor bridge having input and output signaling nodes and bias control nodes. A pair of matched current sources are selectively activated and deactivated in a series arrangement with symmetrical turn-on turn-off circuitry in response to a receipt of instruction signals. The instruction signals control the gating of a constant current to the turn-on/off circuitry for enabling the matched current sources to selectively apply and withdraw matched currents from bias control nodes. Switched turn-off circuitry is employed for reverse biasing the transistor bridge in response to a deactivation of the matched current sources. A pair of voltage reference and antisaturation circuits cooperate with bridge discharge circuits to effect the reverse biasing of the bridge and to discharge rapidly the effective electrical capacitance of that bridge shortly after the receipt of a bridge turn off instruction.

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Boulder, CO, United States of America

Donald Gifford Hill