US 3,939,306 AGranted

Videotelephone system with centralized synchronization control

AssigneeSocieta Italiana Telecomunicazioni Siemens S.p.A.

InventorVirgilio Mosca

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Abstract

A central office of a videotelephone system has a cross-bar switch to establish connections between incoming and outgoing video lines terminating at the transmitters and receivers of the videotelephone sets of the several outlying stations. A central sync-pulse generator works into the incoming video lines to control the sweep circuits of the video receivers of stations to which connections have been established, each video receiver being linked with the associated video transmitter through a delay circuit which actuates the line-scan generators of the transmitter and of the receiver with a relative offset compensating for the transit time of the sync pulses between the central office and the station. The sync pulses are supplied to each incoming video line through an amplifier stage preceded by a shunt circuit including a transistor to which quenching pulses for grounding the line are periodically applied by the sync-pulse generator.

Claims8

Dependent claims

A videotelephone system comprising:

a central office;
a multiplicity of outlying stations served by said central office, each of said stations including a telephone apparatus with signaling means, a video transmitter provided with first sweep-control means and a video receiver provided with second sweep-control means;
circuitry connecting said stations with said central office, said circuitry including a first link extending from each video transmitter to said central office and a second link extending from said central office to each video receiver;
signal-responsive equipment at said central office for establishing a connection between two stations, said equipment including switch means with inputs tied to said first links and with outputs tied to said second links;
a source of synchronizing pulses at said central office connected in parallel to said first links;
pulse-extraction means at each of said stations connected to said second link thereof for activating said first and second sweep-control means by said synchronizing pulses;
first amplifier means inserted in said first links at said central office;
and
second amplifier means inserted in said second links at said stations, said source being connected to said first links through said first amplifier means;
said first amplifier means comprising an input stage, an output stage and a network including a capacitance and a normally open electronic shunt switch connected to said first link between said stages, said electronic switch being connected to said source for periodic closure by a train of quenching pulses at the cadence of said synchronizing pulses to discharge said capacitance, said synchronizing pulses being fed by said source to said output stage.

7 more elements

Dependencies are inferred from the claim text.