Line terminal circuit for controlling the common mode voltage level on a transmission line

A system for transmitting digital data via a transmission line, said system comprising:

• a first line terminating circuit located at a transmitting side, said first line terminating circuit comprising:
• an output buffer section having an input terminal for receiving digital data from a digital signal generating section and output terminals for outputting the digital signals to said transmission line;
• a controllable current source section connected to inject or withdraw a current into or from a node between said output buffer section and said transmission line in accordance with a current control signal;
• and
• a common mode voltage control section for detecting a common mode voltage component on the transmission path connected to the output buffer section and for generating said current control signal in response to said detected common mode voltage component and outputting said current control signal to said current source section;
• wherein resistances are connected in series with conductors of said transmission line;
• and
• wherein said common mode voltage control section is adapted to output said current control signal such that said current is injected into or withdrawn from said node to generate a voltage drop across said resistances counteracting an excessive common mode voltage at said node, and to maintain said common mode voltage component within the limits of a predetermined voltage interval;
• and
• a second line terminating circuit located at a receiving side, said transmission line being connected between said first line terminating circuit and said second line terminating circuit.

A system for transmitting digital data via a transmission line, said system comprising:

• a first line terminating circuit located at a receiving side, said first line terminating circuit comprising:
• an input buffer section having input terminals for receiving digital signals from said transmission line and an output terminal for outputting the received digital data to a digital signal processing section;
• a controllable current source section connected to inject or withdraw a current into or from a node between said input buffer section and said transmission line in accordance with a current control signal;
• and
• a common mode voltage control section for detecting a common mode voltage component on the transmission path connected to the input buffer section and for generating said current control signal in response to said detected common mode voltage component and outputting said current control signal to said current source section;
• wherein resistances are connected in series with conductors of said transmission line;
• and
• wherein said common mode voltage control section is adapted to output said current control signal such that said current is injected into or withdrawn from said node to generate a voltage drop across said resistances counteracting an excessive common mode voltage at said node, and to maintain said common mode voltage component within the limits of a predetermined voltage interval;
• and
• a second line terminating circuit located at a transmitting side, said transmission line connected between said first line terminating circuit and said second line terminating circuit.

A system for transmitting digital data via a transmission line, said system comprising

• a first line terminating circuit comprising:
• an output buffer section having an input terminal for receiving digital data from a digital signal generating section and output terminals for outputting the digital signals to said transmission line;
• a controllable current source section connected to inject or withdraw a current into or from a node between said output buffer section and said transmission line in accordance with a current control signal;
• and
• a common mode voltage control section for detecting a common mode voltage component on the transmission path connected to the output buffer section and for generating said current control signal in response to said detected common mode voltage component and outputting said current control signal to said current source section;
• wherein resistances are connected in series with conductors of said transmission line;
• and
• wherein said common mode voltage control section is adapted to output said current control signal such that said current is injected into or withdrawn from said node to generate a voltage drop across said resistances counteracting an excessive common mode voltage at said node, and to maintain said common mode voltage component within the limits of a predetermined voltage interval;
• and
• a second line terminating circuit comprising:
• an input buffer section having input terminals for receiving digital signals from said transmission line and an output terminal for outputting the received digital data to a digital signal processing section;
• a controllable current source section connected to inject or withdraw a current into or from a node between said input buffer section and said transmission line in accordance with a current control signal;
• and
• a common mode voltage control section for detecting a common mode voltage component on the transmission path connected to the input buffer section and for generating said current control signal in response to said detected common mode voltage component and outputting said current control signal to said current source section;
• wherein resistances are connected in series with conductors of said transmission line;
• and
• wherein said common mode voltage control section is adapted to output said current control signal such that said current is injected into or withdrawn from said node to generate a voltage drop across said resistances counteracting an excessive common mode voltage at said node, and to maintain said common mode voltage component within the limits of a predetermined voltage interval.