Reading device for a transponder

• US 6,070,803 A
• Filed: 02/24/1998
• Issued: 06/06/2000
• Est. Priority Date: 05/17/1993
• Status: Expired due to Term

• Current Assignee: Eyes Open, Inc. (Arthur J Gallagher & Company), Eyes Open Corporation
• Original Assignee: Anatoli Stobbe
• Inventors: Stobbe, Anatoli
• Primary Examiner(s): Lee, Michael G
• Application Number:
  US09/027,652
• Time in Patent Office: 833 Days
• Field of Search: 235/492, 235/451, 235/439, 235/472.02, 235/462.46, 235/383, 235/384, 235/385, 343/895, 343/742, 343/867, 340/572
• US Class Current: 235/492
• CPC Class Codes: G01S 13/753 using frequency selective elements, e.g. resonator
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G06K 19/0726 the arrangement including a circuit for tuning the resonance frequency of an antenna on the record carrier
• CPC Class Codes: G06K 19/07771 the record carrier comprising means for minimising adverse effects on the data communication capability of the record carrier, e.g. minimising Eddy currents induced in a proximate metal or otherwise electromagnetically interfering object
• 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: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank

Abstract

A reading device and one or more associated transponders are used for non-contact identification of persons or objects. When a transponder is moved into the vicinity of the reading device, the reading device receives and evaluates data sent from the transponder. To provide the maximum distance between the reading device (or the antenna thereof) and the transponder, an automatic tuning device is employed to adjust a resonant circuit of the reading unit to match or approximately match a resonance frequency (fo) of the transponder by tuning the reading unit to a preset frequency which matches the frequency (fo) of the transponder. The tuning unit compensates for external influences caused by the environment in which the reading unit is installed, thereby preventing the resonant circuit of the reading unit from deviating from the optimum resonance frequency of the transponder.

Claims

1. A reading device for interacting with at least one transponder having a transponder resonant circuit exhibiting a transponder resonance frequency (fo), said reading device comprising:

a reading device resonant circuit which is designed as a reading device antenna and a reading device resonant circuit capacitor, said reading device resonant circuit being tuned to said resonance frequency (fo); and

an automatic tuning unit connected to said reading device resonant circuit for automatically tuning said reading device resonant circuit to said resonance frequency (fo) of said reading device by adjusting said reading device resonant circuit to compensate said reading device resonant circuit for external influences on said reading device resonant circuit;

at least one adjustment element for altering the operating characteristics of said reading device resonant circuit; and

wherein said automatic tuning unit includes means for selectively connecting and disconnecting said at least one adjustment element to said reading device resonant circuit based on a state of said reading device resonant circuit;

wherein said automatic tuning unit defines a value such that said operating characteristics of said reading device resonant circuit are changed by incrementing or decrementing said value to tune said reading device resonant circuit to said resonance frequency (fo);

wherein said at least one adjustment element includes at least one inductor or at least one capacitor.

2. A reading device as claimed in claim 1, wherein a capacitance of the reading device resonant circuit is selected to be smaller than a capacitance corresponding to the resonance frequency (fo).

3. A reading device as claimed in claim 1, wherein an inductance of the reading device resonant circuit is selected to be smaller than an inductance corresponding to the resonance frequency (fo).

4. A reading device as claimed in claim 1, further comprising:

wherein said means for selectively connecting or disconnecting includes at least one switch for controlling whether said at least one adjustment element is connected to said reading device resonant circuit, according to instructions from said automatic tuning unit.

5. A reading device as claimed in claim 4, wherein said at least one switch includes a plurality of switches each having either an on or off state, wherein said on or off state of said plurality of switches defines a binary number as said value, further wherein said operating characteristics of said reading device resonant circuit are changed by incrementing or decrementing said binary number.

6. A reading device as claimed in claim 5, wherein said at least one adjustment element comprises at least one inductor element.

7. A reading device as claimed in claim 4, wherein a capacitance of the reading device resonant capacitor is selected to be smaller than a capacitance corresponding to the resonance frequency (fo).

8. A reading device as claimed in claim 4, wherein an inductance of the reading device resonant circuit is selected to be smaller than an inductance corresponding to the resonance frequency (fo).

9. A reading device as claimed in claim 4, wherein said at least one adjustment element comprises at least one capacitor element.

10. A reading device as claimed in claim 1, wherein the reading device includes an evaluating unit with an evaluating unit microprocessor for automatic tuning of the reading device resonant circuit and for evaluating data read from said at least one transponder.

11. A reading device as claimed in claim 10, wherein the automatic tuning unit comprises a separate tuning unit tuning microprocessor.

12. A reading device as claimed in claim 11, wherein the evaluating unit and tuning unit microprocessors are programmed with an algorithm that automatically tunes said reading device resonant circuit to its resonance frequency (fo).

13. A reading device as claimed in claim 12, wherein the algorithm for the automatic tuning of the reading device resonant circuit incrementally tunes said resonant circuit to the preset frequency by finding the maximum of a resonant circuit voltage or a resonant circuit current according to a method of successive approximation.

14. A reading device as claimed in claim 11, wherein the separate microprocessor of the tuning unit continuously conducts an automatic tuning of the reading device resonant circuit to the resonance frequency (fo).

15. A reading device as claimed in claim 1, wherein the automatic tuning takes place only within a limited, selectable tuning range.

16. A reading device as claimed in claim 1, wherein the automatic tuning is done after the operating voltage of the reader has been switched on.

17. A reading device as claimed in claim 1, wherein the automatic tuning is started in response to a switching signal sent by the at least one transponder.

18. A reading device as claimed in claim 1, wherein the automatic tuning is conducted periodically at selectable time intervals.

19. A reading device as claimed in claim 1, wherein the automatic tuning is started in response to the receipt of signals at said reading device having poor quality.

20. A reading device as claimed in claim 1, wherein the reading device resonant circuit is configured as a parallel resonant circuit.

21. A reading device as claimed in claim 1, wherein the antenna resonant circuit is designed as a series resonant circuit.

22. The reading device of claim 1, wherein said reading device includes an oscillator which generates a signal having the resonance frequency (fo) which remains substantially constant.