Patent ID: 7528629
Filing Date: 2009-05-05
Classification: H04L

Abstract:
1. A line driver circuit including a first output terminal and a second output terminal, the line driver circuit to transmit data through the first output terminal and the 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, the first power supply being at a fixed regulated voltage; 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 a 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 modulate an amplitude of the output voltage across the first output terminal and the second output terminal at the fixed regulated voltage of the first power supply and responsive to the received data bits, 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.