591383 Disclosed is an identification tag, configured to respond to interrogation cycles that include intervals in which an activation signal is present, and intervals in which the activation signal is absent. The tag has an inductive antenna (501) including two terminals connected to tag circuitry (500). The inductive antenna (501) forms a resonant antenna circuit tuned to resonate at the frequency of the activation signal. The tag circuitry (500) includes a non-volatile memory (511c) and is configurable, alongside the resonant antenna circuitry, as an oscillator. The tag circuitry (500) is configured to be powered by electric current induced in the resonant antenna circuit by the activation signal. The tag circuitry (500) also has at least one switchable load impedance (520) connected across the antenna resonant circuit and is configurable to amplitude modulate the activation signal appearing at the resonant antenna circuit terminals using the switchable load impedance (520). The tag circuitry (500) is configurable to frequency shift key modulate the oscillator signal appearing at the resonant antenna circuit terminals using the switchable load impedance (520) during intervals in which the activation signal is not present. The activation signal is amplitude modulated with a sequence indicative of full-duplex identification data and transmits a frequency shift keyed signal indicative of half-duplex identification data during the interrogation of the tag.
COMBINATION FULL-DUPLEX AND HALF-DUPLEX ELECTRONIC IDENTIFICATION TAG