Patent ID: 8581705

Claim:
A combined full-duplex and half-duplex 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 comprising: an inductive antenna including two terminals connected to tag circuitry, where the tag circuitry is configured to combine with the inductive antenna to form a resonant antenna circuit tuned to resonate at the frequency of the activation signal; and a charge capacitor connected to the tag circuitry; wherein the tag circuitry includes a non-volatile memory containing full-duplex identification data and half-duplex identification data; wherein the tag circuitry includes an RF threshold detector configured to determine the magnitude of the potential difference induced across the terminals of the inductive antenna by the activation signal; wherein the tag circuitry is configured to be powered by electric current induced in the inductive antenna by the activation signal; wherein the tag circuitry includes at least one switchable load impedance connected across the antenna resonant circuit; wherein the tag circuitry and the resonant antenna circuitry are configurable as an oscillator; wherein the tag circuitry is configured so that the tag circuitry amplitude modulates the activation signal using a switchable load impedance with a sequence indicative of the full-duplex identification data when the RF threshold detector detects that the amplitude of the potential difference induced across the terminals of the inductive antenna is below a full-duplex mode threshold; wherein the tag circuitry is configured so that the tag circuitry amplitude modulates the activation signal with a sequence indicative of the full-duplex identification data using the switchable load impedance and frequency shift key modulates an oscillator signal appearing at the resonant antenna circuit terminals with a sequence indicative of the half-duplex identification data using a switchable load impedance during alternating repetitions of the interrogation cycle when the RF threshold detector detects that the amplitude of the potential difference induced across the terminals of the inductive antenna is at least above the full-duplex mode threshold and is below a multiplex mode threshold; and wherein the tag circuitry is configured so that the tag circuitry amplitude modulates the activation signal with a sequence indicative of the full-duplex identification data using the switchable load impedance and frequency shift key modulates an oscillator signal appearing at the resonant antenna circuit terminals with a sequence indicative of the half-duplex identification data using a switchable load impedance during each repetition of the interrogation cycle when the RF threshold detector detects that the amplitude of the potential difference induced across the terminals of the inductive antenna is at least above the multiplex mode threshold.