Abstract: An automatic system for adjusting the output impedance of fast CMOS drivers, wherein the output impedance of a plurality of slaved drivers is adjusted by a circuit for measuring and correcting mismatch between the output impedance of one of the drivers, taken as reference and dedicated for this purpose, and the impedance at the input of a reference transmission line, equal in geometry to the lines connected to the other drivers. The voltage measured at the far end of the reference line is sent to a differential amplifier where it is compared with the supply voltage of the final driving stage. According to the comparison result at specific time intervals, a signal is supplied to the regulator which supplies power to the penultimate driving stage, thereby controlling the resistance of the driver to match the line impedance.