Impinj, Inc.
Self-tuning of RFID tags using nonuniform impedance steps

Abstract:

An RFID tag tuning circuit may be capable of adjusting the impedance matching between an RFID integrated circuit (IC) and an antenna on an RFID tag to increase the amount of power that the IC can extract from an incident RF wave. The tuning circuit switches a variable impedance coupling the antenna and the IC between several different impedance settings, where each impedance setting differs from an adjacent impedance setting by a respective impedance step size and at least one impedance step size has a different value than another impedance step size. The tuning circuit may switch the variable impedance by incrementing through a counter, decrementing through the counter, or performing some search algorithm. The tuning circuit may also initialize the variable impedance based on a default impedance setting or a random impedance setting derived from a random counter.