Transponders, Interrogators, systems and methods for elimination of interrogator synchronization requirement

  • US 5,541,604 A
  • Filed: 09/03/1993
  • Issued: 07/30/1996
  • Est. Priority Date: 09/03/1993
  • Status: Expired due to Term
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First Claim
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1. A Radio Frequency Identification (RFID) system, said system comprising:

  • a) an interrogator, said interrogator havingi) a carrier wave generator for generating a powering burst of a powering frequency,ii) a demodulator for demodulating response data from an RF response from a transponder, said RF response being a wireless, modulated carrier signal,iii) a tuned circuit in electrical communication with said demodulator, said tuned circuit having a selected bandwidth about a communication frequency, said selected bandwidth not substantially overlapping said powering frequency and encompassing the bandwidth of the modulated carrier of said RF response,iv) a controller in electrical communication with said tuned circuit and said demodulator, said controller operable to enable said carrier wave generator to send said powering burst during a first time period and to enable said demodulator in electrical communication with said tuned circuit to receive said RF response during a second time period; and

    b) a transponder, said transponder havingi) a tuned circuit operable to oscillate with a carrier having a frequency equal to the resonance frequency of said tuned circuit,ii) a tuning circuit in electrical communication with said tuned circuit for modifying the frequency characteristics of said tuned circuit such that the tuned circuit is operable to be tuned during said powering burst to said powering frequency and to be tuned during said RF response to said communication frequency, said powering signal causing the tuning circuit to oscillate with a carrier having said powering frequency, andiii) a modulator in electrical communication with said tuned circuit for modulating the carrier therein with RF response data to form said RF response.

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