Adjustable differential input and output drivers

A method of using first and second integrated circuits of a single given type in communications environments with AC-coupled and DC-coupled communications links, wherein each integrated circuit of the given type has a differential driver that is used to communicate over a differential communications path and has common-mode-voltage bias circuitry for making common-mode-voltage adjustments at the differential driver, the method comprising:

• in a first environment having a AC-coupled differential communications path with DC-blocking capacitors:
• using a first integrated circuit of the given type to communicate with a third integrated circuit over the AC-coupled differential communications path;
• and
• using the common-mode-voltage bias circuitry in the first integrated circuit to make common-mode-voltage adjustments at the differential driver in the first integrated circuit that optimize the performance of that differential driver without regard to what common-mode voltage is desired for the third integrated circuit;
• in a second environment having a DC-coupled differential communications path with no DC-blocking capacitors:
• using a second integrated circuit of the same given type to communicate over the DC-coupled differential communications path with a fourth integrated circuit;
• and
• using the common-mode-voltage bias circuitry in the second integrated circuit to make common-mode-voltage adjustments at the differential driver in the second integrated circuit while taking into account which common-mode-voltage changes result at the fourth integrated circuit due to the common-mode-voltage adjustments made by the common-mode-voltage bias circuitry of the second integrated circuit.