Data transmission method and a RFID reader provided with a coil and a control circuit for field quenching outside of a communication area

• US 7,808,389 B2
• Filed: 03/13/2006
• Issued: 10/05/2010
• Est. Priority Date: 03/14/2005
• Status: Expired due to Fees

• Current Assignee: Giesecke + Devrient Mobile Security GmBH (Giesecke & Devrient GmbH)
• Original Assignee: Giesecke & Devrient GmbH
• Inventors: Finkenzeller, Klaus
• Primary Examiner(s): TRIEU, VAN THANH
• Application Number:
  US11/886,426
• Publication Number:
  US 20080136595A1
• Time in Patent Office: 1,667 Days
• Field of Search: 340/572.1, 340/572.4, 340/572.7, 340/572.8, 340/539.1, 340/539.11, 340/539.21, 340/5.86, 340/10.1, 340/10.2, 235/380, 235/381, 343/787, 343/788
• US Class Current: 340/572.4
• 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 7/10316 using at least one antenna particularly designed for interrogating the wireless record carriers antennas in general H01Q1/22
• CPC Class Codes: G06K 7/10336 the antenna being of the near field type, inductive coil
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop

Abstract

The present invention relates to a method, a reading device and a system for transmitting data and/or energy between a reading device and a transponder unit. Via a first antenna coil of the reading device generating a first magnetic field data and/or energy are transmitted to the transponder unit. By means of a second antenna coil a second magnetic field with opposite sign is generated. Within a near field or communication range (12) of the reading device the second magnetic field is weaker than the first magnetic field. In a tap-proof range (13), i.e. outside the near field, the two magnetic fields have the same absolute value and cancel each other out due to the opposite signs.

Claims

1. Method for transmitting data and/or energy between a reading device and a transponder unit, comprising the steps of:

generating a magnetic field by means of a first antenna coil of a reading device, said first antenna coil being supplied with a first current;

generating a second magnetic field by means of a second antenna coil supplied with a second current such that when a transponder unit is brought within a communication range of said reading device, current imbalances caused by impedances are induced between said first and second antenna coils; and

deriving the second current from the first current by using a current mirror to prevent said current imbalances caused by impedances induced in said coils when said transponder unit is brought within said communication range of said reading device,

said second magnetic field being generated by the second antenna coil so that in a near field of the reading device its absolute value is smaller than that of the first magnetic field and outside the near field has approximately the same absolute value with opposite sign to cause said magnetic fields to cancel outside said near field and thereby prevent tapping of a communication between said reading device and said transponder from outside of said communication range.

2. Method according to claim 1, including locating the center axis of the first antenna coil within the second antenna coil.

3. Method according to claim 1, including supplying the two antenna coils with currents, through which the magnetic fields resulting therefrom point in opposite directions.

4. Method according to claim 1, including supplying the two antenna coils with opposite-phase currents.

5. Method according to claim 1, including supplying the two antenna coils with currents whose amplitudes are proportional to each other.

6. Method according to claim 1, wherein the current controlling step comprises the step of correlating the currents in the two antenna coils to each other with respect to value and phase.

7. Method according to claim 1, further comprising the step of detecting a magnetic field strength outside the near field, and wherein the current controlling step comprises the step of controlling said currents to adapt the magnetic field of at least one of the first and the second antenna coil in such a way that the detected magnetic field strength reaches a minimum value.

8. Method according to claim 1, wherein in the first antenna coil and the second antenna coil high-frequency magnetic fields having the same frequency are generated.

9. Method according to claim 1, wherein by means of the first magnetic field a useful signal containing data is at least one of sent to the transponder unit and received from the transponder unit.

10. Method according to claim 1, including adapting the field strengths of the two magnetic fields by changing the respective coil diameters, in order to define the near field of the reading device.

11. Reading device for transmitting data and/or energy between a reading device and at least one transponder unit, the reading device comprising one first antenna coil adapted to generate a first magnetic field, the first antenna coil being supplied with a first current, a second antenna coil adapted to generate a second magnetic field, the second antenna coil being supplied with a second current such that when a transponder unit is brought within a communication range of said reading device, current imbalances caused by impedances are induced between said first and second antenna said coils, and a control circuit for the first and the second magnetic field, wherein the control circuit is adapted to control currents in at least one of said first and second antenna coils by deriving the second current from the first current by means of a current mirror to prevent said current imbalances caused by impedances induced in said coils when said transponder unit is brought within said communication range of said reading device, so as to adjust the first and second magnetic fields in such a way that outside a near field of the reading device the second magnetic field has approximately the same absolute value and an opposite sign as the first magnetic field, and in the near field is weaker than the first magnetic field and thereby prevent tapping of a communication between said reading device and said transponder from outside of said communication range.

12. Reading device according to claim 11, wherein the reading device is adapted to supply the antenna coils with currents, through which the resulting magnetic fields point in opposite directions.

13. Reading device according to claim 11, wherein the control circuit is adapted to control the currents for the antenna coils in order to adjust the magnetic fields.

14. Reading device according to claim 11, wherein the second antenna coil forms a serial resonant circuit with a serially connected capacitor, the resonance frequency of the serial resonant circuit corresponding to the transmission frequency of the reading device.

15. Reading device according to claim 11, including a resistor and/or an impedance, arranged between ground and the second antenna, and which resistor and impedance are controllable;

a field strength detector arranged to detect a field strength outside the near field and to output a field strength signal;

said field strength signal serving as input value for controlling said resistor and impendence.

16. Reading device according to claim 11, including a device for evaluating a magnetic field strength outside the near field, wherein the control circuit is adapted to adjust the magnetic fields depending on the detected magnetic field strength in such a way that the magnetic field strength reaches a minimum value.

17. Reading device according to claim 16, wherein the device for evaluating the magnetic field strength outside the near field comprises a third antenna coil and a circuit for determining a magnetic field strength measured by the third antenna coil.

18. Reading device according to claim 11, wherein the second antenna coil has a diameter which is larger in comparison to that of the first antenna coil.

19. Reading device according to claim 11, wherein the first and the second antenna coil are arranged in one common plane.

20. Reading device according to claim 11, wherein the two antenna coils are arranged coaxially.

21. Reading device according to claim 11, wherein the reading device is adapted to at least one of sending to and receiving from the at least one transponder unit via the first antenna coil a useful signal containing data.

22. System for transmitting data and/or energy between a transponder unit and a reading device according to claim 11.

23. Method according to claim 11, further comprising the steps of:

using said current mirror to compare said first current at a connection between a first attenuation resistor and said first antenna coil with said second current at a connection between said second attenuation resistor and said second antenna coils; and

causing said second current to oscillate on a transmission frequency of the reading device.

24. Reading device according to claim 11, wherein said current mirror comprises:

current comparing means for comparing currents;

a first attenuation resistor connected to said first antenna coil and to a first input of said current comparing means; and

a second attenuation resistor connected to a first end of the second antenna coils and to a second input of said current comparing means; and

further comprising oscillating means connected to an output of said current comparing means for forming, with said second antenna coil, an oscillating circuit on a transmission frequency of the reading device.