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US 4,024,349 AGranted
Quasi-resonant transfer conferencing circuit
AssigneeBell Telephone Laboratories, Incorporated
InventorJohn Francis O'Neill
Life of this patent
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AssigneeBell Telephone Laboratories, Incorporated
InventorJohn Francis O'Neill
Estimating the term…
A conference port for permitting simultaneous voice communication among a plurality of local stations and an external or central office line is shown. The stations may be part of a time division PBX or may be arranged as a time-sampled key telephone system having access to the same line. The conference port includes a first operational amplifier for summing the station port voltages on a capacitor during an interval that is a predetermined fraction of the resonant transfer interval. This first, or quasi-resonant, interval is sufficient to reduce the initial voltage on each of the station port sampling capacitors to a predetermined fraction of their initial level. At the conclusion of this interval the voltage on the summing capacitor in the conference port is multiplied by an appropriate factor in a second operational amplifier and is applied back simultaneously to all of the conference ports together with the signal incoming over the external or central office line. The voltage impulse, so applied, causes the signal contributed by each station port to appear at each other station port attenuated by a suitable factor, illustratively 6dB, while the incoming signal appears full strength at each station port. Accordingly, good return loss is provided at each station port and contrast between signals from stations and the incoming line is reduced via the controllable station-to-station loss.
A conference port for a telephone switching system including a plurality of station ports each having a resonant transfer sampling circuit, said conference port comprising:
A telephone switching system comprising:
A time division switching system comprising a plurality of station ports each having a resonant transfer sampling circuit capable of exhibiting an instantaneous voltage corresponding to a local speech signal, a communications bus, a conference port circuit having an external line connected thereto capable of exhibiting an instantaneous voltage corresponding to an incoming speech signal, and means for simultaneously controlling all of the time division sampling switches in said plurality of said station ports and a first time division switch in said conference port during an interval less than a resonant transfer interval to reduce the voltage sample on each of said station port resonant transfer sampling circuits by a predetermined factor and for operating a second time division sampling switch in said conference port circuit to reapply simultaneously to all of said station port circuits a predetermined fraction of the voltage corresponding to the charge passed through said first conference port switch together with a sample of said incoming signal on said external line.
A conference port for a telephone switching system including an external line and a plurality of station ports, each of said ports having a resonant transfer sampling circuit and being connected to a common bus, the conference port comprising:
Dependencies are inferred from the claim text.