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Abstract

An automatic system for adjusting the output impedance of fast CMOS drivers, wherein the output impedance of a plurality of slaved drives 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 to the lines connected to the other drivers. The measuring of the output impedance of the reference drive is indirectly effected by inserting at the reference drive input a clock signal and by periodically measuring the output on the reference transmission line in correspondence with the positive half-period center. The measured voltage is sent to a comparator whereby it is compared with a reference level equal to half the maximum level present in the line under matching conditions and, according to the comparison result, a signal is supplied capable of charging or discharging a capacitor, across whose terminals a voltage controlling the driver output impedance is available.

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First Claim