Patent attributes
A line driver includes current sources and resistors that form a bridge circuit in which a bridge resistor is connected between an internal node and ground, and a series resistor connected between the internal node and the driver's output node. The internal node is connected to receive a unit current from a first stage transistor, and the output node is connected to receive an amplified current from a second stage transistor that is N times the unit current. The bridge resistor is formed with a resistance value set such that the voltages at the internal node and the output node are equal, i.e., such that no current flows through the series resistor. The resistance value of the series resistor is thus adjustable to optimize output impedance in a manner independent of the driver's gain. An echo cancellation circuit is utilized to eliminate noise from two associated line drivers.
