Patent ID: 7221196

Claim:
A line driver circuit including a first output terminal and a second output terminal, the line driver circuit comprising: a first pull-up variable resistor and a first switch connected in series between a first power supply and the first output terminal; a second pull-up variable resistor and a second switch connected in series between the first power supply and the second output terminal; a first pull-down variable resistor and a third switch connected in series between a second power supply and the first output terminal; a second pull-down variable resistor and a fourth switch connected in series between the second power supply and the second output terminal; a floating variable resistor connected between the first output terminal and the second output terminal; and coder logic to receive data bits and adjust an output voltage across the first output terminal and the second output terminal by varying a resistance of one or more of the floating variable resistor, the first pull-up variable resistor, the second pull-up variable resistor, the first pull-down variable resistor, and the second pull-down variable resistor responsive to the received data bits, wherein the coder logic is further operable to vary a resistance of one or more of the floating variable resistor, the first pull-up variable resistor, the second pull-up variable resistor, the first pull-down variable resistor, and the second pull-down variable resistor to maintain an effective output impedance for the line driver circuit that equals an impedance of a transmission line connected to the first output terminal and the second output terminal, and wherein the coder logic is further operable to set the resistance of the first pull-up variable resistor and the second pull-up variable resistor to a value that is different from the resistance of the first pull-down variable resistor and the second pull-down variable resistor to generate a controlled common-mode voltage associated with the adjustable output voltage.