Automatic LC network tuner based on negative resistances

A novel technique to tune an inductor–capacitor (LC) network based on a receiving signal frequency is proposed. The method consists of using a negative resistor to artificially increase the quality factor of the LC circuit to reduce the decision range of the voltage detector. This approach allows the use of low complexity algorithms that converge in a few steps. The technique was validated through a demonstrator for radiofrequency identification tags in production line testing, with satisfactory results. The designed negative resistor maintained a constant resistance for a large range of input signals.