An embodiment of an impedance adjustment apparatus is disclosed. For this embodiment of an impedance adjustment apparatus, a differential driver circuit has an input port, a first output port, a second output port, a first bias node, and a second bias node. A first impedance-voltage device is coupled to provide a first bias voltage to the first bias node. A second impedance-voltage device is coupled to provide a second bias voltage to the second bias node. A first analog voltage source is coupled to provide a first analog voltage to the first impedance-voltage device, and a second analog voltage source is coupled to provide a second analog voltage to the second impedance-voltage device.