Conference trunk circuit for an exchange
AssigneeTokyo Shibaura Electric Co., Ltd.
InventorKiyoshi Urui
Life of this patent
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Abstract
There are disclosed first and second groups of internal office trunks used for an exchange. Each internal office trunk comprises first and second terminals for connecting two subscribers' telephones through a switching matrix circuit according to a demand signal from a central controller. The internal office trunks of the second group respectively further comprise a third terminal. The third terminal is connected to a switching circuit controlled by the central controller. The switching circuit controls a mutual connection of the internal office trunk circuits. As a result of being connected to the third terminal mutually by the switching circuit, the second group of the internal office trunks operates as a conference trunk.
Claims3
A trunk circuit for an exchange comprising:
- a plurality of subscribers' telephones,
- a plurality of internal office trunks for electrically connecting two subscribers' telephones with each other, each of the internal office trunks having first, second and third terminals,
- a switching matrix circuit for electrically connecting the subscribers' telephones to the internal office trunks, the switching matrix circuit having a first plurality of terminals and a second plurality of terminals,
- a switching circuit for electrically mutually connecting a desired number of the third terminals of the plurality of internal office trunks, the switching circuit having a plurality of terminals,
- a central controller for controlling internal connections of the switching matrix circuit, in the plurality of internal office trunks and in the switching circuit,
- means connecting the subscribers' telephones to the first plurality of terminals of the switching matrix circuit,
- means connecting the second plurality of terminals of the switching matrix circuit to the first and second terminals of the plurality of internal office trunks,
- means connecting the third terminals of the plurality of internal office trunks to the plurality of terminals of the switching circuit,
- means connecting the central controller to the switching matrix circuit, and
- means connecting the central controller to the switching circuit,
- each internal office trunk comprising:
- a first transistor,
- a second transistor,
- a third transistor,
- a first diode,
- a second diode,
- a first resistor,
- a second resistor,
- a third resistor,
- means connecting the first terminal of the internal office trunk to the collector of the first transistor,
- means connecting the second terminal of the internal office trunk to the collector of the second transistor,
- means connecting the first resistor between ground and the emitter of the first transistor,
- means connecting the second resistor between ground and the emitter of the second transistor,
- means connecting the collector of the first transistor to the anode of the first diode,
- means connecting the collector of the second transistor to the anode of the second diode,
- means connecting the cathode of the first diode and the cathode of the second diode to the third terminal of the internal office trunk,
- means connecting the third resistor between the third terminal of the internal office trunk and the collector of the third transistor,
- means connecting the emitter of the third transistor to ground,
- means connecting the base of the first transistor to the central controller,
- means connecting the base of the second transistor to the central controller, and
- means connecting the base of the third transistor to the central controller.
Dependencies are inferred from the claim text.