METHOD FOR VARIABLY ADJUSTING OUTPUT IMPEDANCE OF OUTPUT DRIVER CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide an output driver circuit that has a higher output impedance rage with a fewer control lines while preventing occurrence of a spike with the output impedance on the signal pad. SOLUTION: A binary weighted thermometer code is employed to adjust the output impedance of a variable impedance output driver circuit. The driver circuit includes an impedance network comprising a plurality of resistive devices each programmably electrically connectable in parallel between a first voltage source and the signal pad. The resistive devices are partitioned into a plurality of sets. A first set of the resistive devices may be programmed in a binary incremental manner to electrically connect one or more of the resistive devices in the first set between the first voltage source and the signal pad. Only if all of the resistive devices in the first set are activated may a second set of the resistive devices be started. Additional sets of the resistive devices may be likewise programmed.