US Patent 7705632 Variable off-chip drive

A driver circuit includes a set of selectable drivers each having an individual drive capability, the drivers being selectable such that i) when a subset of the drivers is selected, a signal will be driven by the drivers at a first drive level, and ii) when the subset of the drivers and at least one additional driver is selected, signal will be driven by the drivers at a level that is greater than the first level by a level of drive provided by the least one additional driver.