In this thesis a system for on-die automatic impedance matching in current mode off-chip signaling is described. In order to perform the automatic matching operation an algorithm that integrates the sign of the impedance matching error and the sign of the coupling branch current is implemented. The advantage of this algorithm is that it works without interfering with the driver operation. The transistor level circuit implementation of the system is described and computer simulations at behavioral level and post layout extractions are presented. Also experimental results are shown for programmable resistor circuits and the full impedance matching system.