Driver circuit and a method for matching the output impedance of a driver circuit with a load impedance

A method for providing a line driver circuit of an integrated circuit (IC) with a desired output impedance, the line driver circuit including current switching circuitry coupled to at least one current source, the method comprising:

• selecting a value of a first resistor;
• placing the first resistor in parallel with a first current source of the driver circuit, the first current source configured to operate in a triode region such that it has a first impedance value when the first current source is active;
• selecting a value of a second resistor;
• placing the second resistor in parallel with a second current source of the driver circuit, the second current source configured to operate in a triode region such that it has a second impedance value when the second current source is active;
• selecting a value for a source termination resistor;
• and
• placing a source termination resistor across output terminals of the driver circuit, and wherein the combination of the first and second impedance values, the first and second resistance value and the source termination resistance value produces a desired output impedance for the driver circuit, wherein the value of the source termination resistor (RST) is sufficiently large that its effect is mathematically negligible in the expression ((Rb1∥Rds1])+(Rb2∥Rds2))∥RST, wherein Rb1 is the first resistance value, Rb2 the second resistance value, Rds1 is a resistance of the first current source, and Rds2 is a resistance of the second current source.