Patent ID: 7532048

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 directly connected between a first power supply and the first output terminal; a second pull-up variable resistor directly connected between the first power supply and the second output terminal; a first pull-down variable resistor directly connected between a second power supply and the first output terminal; a second pull-down variable resistor directly connected 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 resistances 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 provide amplitude modulation of the output voltage across the first output terminal and the second output terminal responsive to the received data bits and at a fixed regulated voltage of a power supply, wherein an effective parallel resistance value of the first pull-up variable resistor, the second pull-up variable resistor, the first pull-down variable resistor, the second pull-down variable resistor, and the floating variable resistor coupled together is fixed 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.