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Abstract

A method of controlling impedance of a driver capable of launching signals at a driving end of a transmission line and capable of terminating signals at the receiver end of the transmission line controls the impedance of the driver across process, voltage, and temperature (PVT) variations by selectively enabling and disabling at least one of a plurality of output elements according to an impedance control code. The impedance control code compensates for variations in output impedance due to PVT variations. The method includes selectively enabling and disabling the plurality of output elements so that a direct current impedance of a parallel combination of the plurality of output elements is within a predetermined percentage of the impedance of the transmission line, and sizing the plurality of output elements to account for a predetermined range of PVT conditions, and selectively enabling and disabling the plurality of output elements to allow an impedance of the driver to be approximately equal to the impedance of the transmission line when an output voltage from the driver is approximately half the first supply voltage. The sizing of a plurality of transistors within the plurality of output elements is such that the direct current impedance of a parallel combination of the plurality of output elements is approximately equal to the impedance of the transmission line when the output voltage is half the supply voltage.

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First Claim