Pulse or digital communications – Transceivers – Transmission interface between two stations or terminals
Patent
1994-03-29
1997-01-07
Chin, Stephen
Pulse or digital communications
Transceivers
Transmission interface between two stations or terminals
375257, 326 86, 326 91, H04B 138, H04L 516
Patent
active
055925103
ABSTRACT:
In a driver circuit for a twisted pair cable, a compensator for preventing appreciable common mode current flow into or out of the twisted pair cable in response to the device receiving a wide range of common mode voltage bias levels. A wide range of external bias voltages may be received as a result of variations in the ground node voltages of two coupled devices. The compensator circuit utilizes a feed back loop and monitors the bias voltage received on the twisted pair cable. As the magnitude of the common mode current increases due to external bias voltage variation from a reference bias voltage, the current flow of p-channel transistors, coupled in an arrangement of the present invention, is increased (or decreased, as necessary) so that reduced common mode current flows onto the twisted pair cable. The present invention reduces appreciable common mode current flow through the twisted pair cable from the driver that are due to variations in the external bias voltage between communication devices. The present invention provides high common mode output impedance for the driver circuit by altering the effective common mode common mode early voltage characteristics of the driver circuit while utilizing shorter channel length transistors for high speed communication capacity. The present invention also offers reduced current supply capacity of the common mode bias voltage source. The present invention operates ideally within driver circuits compatible with the IEEE P1394 communication standard.
REFERENCES:
patent: 4507793 (1985-03-01), Adams
patent: 4760282 (1988-07-01), Kuo et al.
patent: 5408497 (1995-04-01), Baumann et al.
Oprescu Florin A.
Van Brunt Roger W.
Apple Computer Inc.
Chin Stephen
Vo Don
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