Patent ID: 7071739

Claim:
A differential driver circuit comprising: an output driver circuit, including: differential amplifier circuitry; a first variable resistance circuit that is coupled to the differential amplifier circuitry; and a second variable resistance circuit that is coupled to the differential amplifier circuitry; and a feedback circuit that is coupled to the first and second variable resistance circuits, wherein a source resistance of the output driver circuit appears to a load as substantially similar to a termination resistance of the load, wherein the feedback circuit includes a third variable resistance circuit, the third variable resistance circuit includes a replica of the first variable resistance circuit, the third variable resistance circuit is coupled to the first variable resistance circuit, the feedback circuit further includes a fourth variable resistance circuit, the fourth variable resistance circuit includes a replica of the second variable resistance circuit, the fourth variable resistance circuit is coupled to the second variable resistance circuit, and wherein the feedback circuit further includes: a transistor that is coupled between the third variable resistance circuit and the fourth variable resistance circuit; a first operational amplifier circuit that is coupled between the transistor and the third variable resistance circuit; and a second operational amplifier circuit that is coupled between the transistor and the fourth variable resistance circuit.