Switched capacitance method for the detection of, and subsequent communication with a wireless transponder device using a single antenna

• US 8,203,429 B2
• Filed: 03/31/2009
• Issued: 06/19/2012
• Est. Priority Date: 04/01/2008
• Status: Active Grant

• Current Assignee: Assa Abloy AB
• Original Assignee: Assa Abloy AB
• Inventors: Borcherding, Eric J.
• Primary Examiner(s): Lau, Hoi
• Application Number:
  US12/416,104
• Publication Number:
  US 20090251291A1
• Time in Patent Office: 1,176 Days
• Field of Search: 340/10.1, 340/572.4, 340/572.7, 340/572.5, 340/10.3, 235/439
• US Class Current: 340/10.1
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10128 the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device

Abstract

A transponder detector is provided with capabilities for detecting the presence and type of a transponder in its read range while operating at low power and also using a common antenna for detecting and executing data transactions with transponders.

Claims

1. A reader for an RFID system comprising:

a reader antenna;

a driver circuit adapted to provide current to the reader antenna; and

a tuning circuit situated between the driver circuit and the reader antenna, the tuning circuit adapted to condition current provided from the driver circuit to the reader antenna, the tuning circuit comprising control circuitry configured to switch the reader between a detection mode and a transaction mode, wherein the reader antenna is used to transmit detection signals in the detection mode and transaction signals in the transaction mode, wherein the tuning circuit comprises a second set of capacitors connected in parallel across the reader antenna, the second set of capacitors adapted to switch a carrier frequency of detection signals generated by the reader antenna between at least two different carrier frequencies.

2. The reader of claim 1, wherein the tuning circuit is coupled to the reader antenna via a 4-wire interface.

3. The reader of claim 1, wherein the tuning circuit is coupled to the reader antenna via a 2-wire interface.

4. The reader of claim 1, wherein the tuning circuit causes an operable range of the reader antenna to be greater in the detection mode than in the transaction mode.

5. The reader of claim 1, wherein a first of the at least two different carrier frequencies is about 125 kHz and wherein a second of the at least two different carrier frequencies is about 13.56 MHz.

6. The reader of claim 1, wherein the tuning circuit is further adapted to tune the reader antenna to operate at either of the at least two different carrier frequencies in the transaction mode.

7. The reader of claim 6, wherein the tuning circuit sets the carrier frequency of the reader antenna according to the carrier frequency at which a transponder was detected in the detection mode.

8. The reader of claim 1, wherein the tuning circuit further comprises a first set of the parallel capacitors connected between control circuitry that is used to initiate pings during the detection mode and the reader antenna, wherein the first set of capacitors is connected in parallel with the second set of capacitors.

9. The reader of claim 8, wherein the first set of parallel capacitors includes at least a first parallel capacitance that is operated by an inverter adapted to control the operation of the at least a first parallel capacitance by causing the at least a first parallel capacitance to be shifted or disconnected from ground thereby causing a voltage pulse to be transmitted to the reader antenna and a detection pulse or ping to be transmitted via the reader antenna into the space about the reader antenna.

10. The reader of claim 9, wherein after the detection mode has been initiated, the inverter reconnects the at least a first parallel capacitance to ground thereby putting the reader back into the transaction mode.

11. The reader of claim 10, wherein the control circuitry further comprises a Field Effect Transistor.

12. The reader of claim 11, wherein the Field Effect Transistor comprises at least one of an N-type MOSFET and a P-type MOSFET, and wherein the Field Effect Transistor further comprises an internal resistance.

13. The reader of claim 11, wherein the inverter comprises at least one AND gate and a plurality of NOT gates which are used to condition the output voltage of the control circuitry to the rest of the tuning circuit.

14. The reader of claim 13, wherein the plurality of NOT gates include six NOT gates, a first set of the NOT gates being connected in series and a second set of the NOT gates also being connected in series, wherein the first and second sets of NOT gates are connected in parallel with each other.

15. A method of operating an RFID reader, the RFID reader comprising an antenna, driver circuitry, and a tuning circuit situated between the antenna and driver circuitry, comprising:

transmitting a detection signal from the antenna, the detection signal being generated by the tuning circuit;

switching the reader from a detection mode to a transaction mode; and

transmitting a transaction signal from the antenna, wherein the detection signal is used to detect the existence of an RFID transponder within communication range of the antenna and wherein the transaction signal is used to share transaction data with the RFID transponder, wherein the tuning circuit comprises a first and second set of capacitors connected in parallel across the reader antenna, the second set of capacitors adapted to switch a carrier frequency of detection signals and transaction signals generated by the reader antenna between at least two different carrier frequencies, the first set of the parallel capacitors connected between control circuitry that is used to initiate pings during the detection mode and the antenna.

16. The method of claim 15, wherein the first set of parallel capacitors includes at least a first parallel capacitance that is operated by an inverter adapted to control the operation of the at least a first parallel capacitance.

17. The method of claim 16, further comprising:

causing the at least a first parallel capacitance to be shifted or disconnected from ground thereby resulting in a voltage pulse being transmitted to the antenna;

receiving the voltage pulse at the antenna;

comparing the voltage pulse with the detection signal transmitted from the antenna to determine a delta value between the voltage pulse and the detection signal;

determining the delta value meets or exceeds a predetermined threshold; and

causing the reader to switch from the detection mode to the transaction mode only when it is determined that the delta value meets or exceed the predetermined threshold.

18. The method of claim 16, wherein the inverter comprises at least one AND gate and a plurality of NOT gates which are used to condition the output voltage of the control circuitry to the rest of the tuning circuit.

19. The method of claim 18, wherein the plurality of NOT gates include six NOT gates, a first set of the NOT gates being connected in series and a second set of the NOT gates also being connected in series, wherein the first and second sets of NOT gates are connected in parallel with each other.

20. An RFID reader, comprising:

an antenna; and

a tuning circuit operable to cause the antenna to transmit detection signals at two or more different carrier frequencies and transaction signals at two or more different carrier frequencies, wherein the detection signals are transmitted by the antenna when the reader is in a detection mode, wherein the transaction signals are transmitted by the antenna when the reader is in a transaction mode, and wherein the tuning circuit limits operation of the reader in the transaction mode to instances where a transponder operating at one of the two or more different carrier frequencies is detected within an operating range of the antenna, wherein the tuning circuit comprises a first and second set of capacitors connected in parallel across the reader antenna, the second set of capacitors adapted to switch a carrier frequency of detection signals and transaction signals generated by the reader antenna between at least two different carrier frequencies, the first set of the parallel capacitors connected between control circuitry that is used to initiate pings during the detection mode and the antenna.

21. The reader of claim 20, wherein a first of the two or more different carrier frequencies is about 125 kHz and wherein a second of the two or more different carrier frequencies is about 13.56 MHz.

22. The reader of claim 20, wherein the first set of parallel capacitors includes at least a first parallel capacitance that is operated by an inverter adapted to control the operation of the at least a first parallel capacitance, wherein the inverter comprises at least one AND gate and a plurality of NOT gates which are used to condition the output voltage of the control circuitry to the rest of the tuning circuit.