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

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments Deutschland Gesellschaft Mit Beschrã¤Nkter Haftung (Texas Instruments, Inc.)
• Inventors: Meier, Herbert
• Primary Examiner(s): ELDRED, JOHN W
• Application Number:
  US08/117,258
• Time in Patent Office: 1,061 Days
• Field of Search: 342/42, 342/44, 342/50, 342/51
• US Class Current: 342/42
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

A Radio Frequency Identification (RFID) system having an interrogator (12) and a transponder (14). The interrogator has a first tuned circuit (28) of a powering frequency for sending a powering burst to a transponder (14), a filter/demodulator (64) for receiving an wireless, modulated RF response from a transponder (14). The interrogator (12) further has a second tuned circuit (29) in electrical communication with a modulator (48), the second tuned circuit (29) having a selected bandwidth about a communication frequency, the selected bandwidth not substantially overlapping the powering frequency and encompassing the bandwidth of the modulated carrier of the RF response. The interrogator also has a controller (16) in electrical communication with the filter/demodulator (64) and the tuned circuits (28,29) and capable of enabling the first tuned circuit (28) to send the powering burst during a first time period and of enabling the modulator (48) in electrical communication with the second tuned circuit (29) to receive the RF response during a second time period. The transponder has a tuned circuit (34), a tuning circuit (54,56) in electrical communication with the tuned circuit (34) for modifying the frequency characteristics of the tuned circuit (34) such that it is can be tuned during the powering burst to the powering frequency and to be tuned during the RF response to the communication frequency. The transponder (14) also includes a demodulator (66) in electrical communication with the tuned circuit (34) for receiving the RF interrogation therefrom and for demodulating data from the RF interrogation.

Claims

1. A Radio Frequency Identification (RFID) system, said system comprising:

a) an interrogator, said interrogator having

i) 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 having

i) 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, and

iii) a modulator in electrical communication with said tuned circuit for modulating the carrier therein with RF response data to form said RF response.

2. The system of claim 1 wherein said interrogator tuned circuit comprises another tuning circuit whereby said another tuning circuit is operable to modify the frequency characteristics of said tuned circuit such that said tuned circuit is tuned during said powering burst to said powering frequency and tuned during said RF interrogation to said communication frequency.

3. The system of claim 1 wherein said modulator is a PPM modulator.

4. The system of claim 1 wherein said modulator is a FSK modulator operable to output a carrier of FSK frequencies f₂ and f₃ representing first and second data values.

5. The system of claim 4 wherein said communication frequency is between said FSK frequencies.

6. The system of claim 1 and further comprising an interrogator modulator for modulating WRITE data upon said RF interrogation.

7. The system of claim 6 wherein said interrogator modulator is a PPM modulator.

8. The system of claim 6 wherein said interrogator modulator is an FSK modulator.

9. The system of claim 6 wherein said interrogator further comprises a transmit antenna in electrical communication with said interrogator modulator and operable to transmit said RF interrogation in a wireless fashion, and a receive antenna in electrical communication with said demodulator and operable to receive said RF response from said transponder in a wireless fashion.

10. The system of claim 9 wherein said transmit antenna and said receive antenna are a single, unified antenna.

11. A Radio Frequency Identification (RFID) system, said system comprising an interrogator and a transponder wherein said interrogator and transponder are in wireless communication with each other through RF interrogations by said interrogator to said transponder and through RF responses from said transponder to said interrogator, wherein:

a) said interrogator comprises

i) an RF oscillator,

ii) a programmable divider in electrical communication with said RF oscillator and operable to selectively divide the oscillations thereof such that a first division factor causes a communication frequency signal to be output from said divider and a second division factor causes a factor causes a powering frequency signal to be output from said divider,

iii) a first tuned circuit in electrical communication with said programmable divider, said first tuned circuit having a resonant frequency of said powering frequency, said first tuned circuit operable to send a powering burst,

iv) a second tuned circuit in electrical communication with said programmable divider, said second tuned circuit having a selected bandwidth encompassing an RF response about said communication frequency, said selected bandwidth not substantially overlapping said powering frequency,

v) a transmit antenna in electrical communication with said first tuned circuit and operable to transmit said powering burst as a wireless signal to said transponder and to transmit said RF interrogation thereto,

vi) a receive antenna in electrical communication with said second tuned circuit, said receive antenna operable to receive said RF response,

vii) a demodulator for receiving said RF response from said second tuned circuit and providing RF response data therefrom, and

viii) a controller in electrical communication with said programmable divider, said demodulator, and said tuned circuits, said controller operable to enable said first tuned circuit to send said powering burst during a first time period and to enable said demodulator in electrical communication with said second tuned circuit to demodulate RF response data from said RF response during a second time period, said controller further operable to receive said RF response data from said demodulator; and

b) a transponder, said transponder having

i) 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 tuning circuit to oscillate with a carrier having said powering frequency,

iii) a demodulator in electrical communication with said tuned circuit for receiving said RF interrogation therefrom and for demodulating interrogation data from said RF interrogation,

iv) a modulator in electrical communication with said tuned circuit for modulating said RF response data upon said carrier, and

v) a controller in electrical communication with said modulator, said demodulator, and said tuning circuit, said controller operable to control said tuning circuit to modify the frequency characteristics of said tuned circuit, to receive said interrogation data from said demodulator, and to provide said RF response data to said modulator.

12. A method for communicating between an interrogator and transponder, the method comprising the steps of:

a) tuning a transponder tuned circuit to a powering frequency;

b) sending a powering burst of said powering frequency to said transponder by an interrogator tuned circuit, said powering burst causing said tuning circuit to oscillate with a carrier having said powering frequency;

c) rectifying said powering burst in said transponder to supply power to the operating circuitry thereof;

d) upon termination of said powering burst, tuning said transponder to have a communicating frequency whereby the oscillation of said carrier will be at said communicating frequency, further selecting the bandwidth of said tuned circuit to be a selected width and not substantially encompassing said powering frequency;

e) entering a Read mode during which said modulator modulates data upon said carrier to form an RF response, said RF response having a bandwidth such that a substantial portion thereof lies within the bandwidth of said tuned circuit;

f) transmitting said RF response by said tuned circuit in electrical communication with said modulator; and

g) receiving by a receiver circuit said RF response.

13. The method of claim 12 and further comprising the step of sending an "end-of-burst" signal after completion of said powering burst and prior to entering said Read mode.

14. The method of claim 12 and further comprising the step entering a Write mode prior to entering the Read mode during which the interrogator sends WRITE data to said transponder upon termination of said powering burst.

15. The method of claim 14 and further comprising the step of sending a short "end-of-burst" signal after completion of said powering burst and prior to entering said Write mode.

16. The method of claim 15 and further comprising the step of sending a long "end-of-burst" after completion of said Write mode and prior to entering said Read mode.

17. The method of claim 12 and further comprising the step of sending an "end-of-burst" signal after completion of said powering burst.

18. A transponder for a Radio Frequency Identification (RFID) system using an interrogator which sends RF interrogations to said interrogator and receives RF responses therefrom, said transponder comprising:

a) a tuned circuit operable to oscillate with a carrier having a frequency equal to the resonance frequency of said tuned circuit;

b) 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 a powering burst to a powering frequency and to be tuned during said RF response to a modulation frequency; and

c) a modulator in electrical communication with said tuned circuit for modulating the carrier therein with said RF response data to form said RF response, said modulated RF response not substantially overlapping said powering frequency.

19. An interrogator for sending RF interrogations and receiving RF responses from a transponder, said interrogator comprising:

a) a carrier wave generator for generating a powering burst of a powering frequency;

b) a demodulator for demodulating response data from an RF response from a transponder, said RF response being a wireless, modulated carrier signal;

c) a tuned circuit in electrical communication with said demodulator, said second 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; and

d) a controller in electrical communication with said receiver circuit, 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.