Multiple finger off chip driver (OCD) with single level translator

摘要

A multiple finger off chip driver (OCD) has a single level translator for each of a plurality of PFET fingers and NFET fingers which allow the impedance of the OCD to be varied to match the impedance of a driven load. A plurality of PFET and NFET finger selection devices are used to select various combinations of output FETS and ballast resistor finger combinations to drive an output signal at a desired impedance level. The ballast resistors are scaled in ohmic value to the size of the output finger it is connected to. In this configuration, a constant ratio of FET impedance to ballast resistance is maintained in each drive stage (finger). By selecting various combinations of fingers various driver impedances can be selected.