A self-terminating low-voltage swing CMOS output driver

A CMOS output pad driver circuit is described that automatically series-terminates a driven line in the line's characteristic impedance. The circuit has advantages in speed, power, and size over conventional designs. The key idea is the use of emitter-coupled logic (ECL) compatible low-voltage swings for signaling, combined with the use of the driver transistor as both a switch and as a termination resistor. An on-chip measurement circuit dynamically adjusts the impedance of the driver to match the impedance of an external reference impedance standard, allowing the circuit to compensate for both chip and board level fabrication variations.>