Compensation for holes in the read range of an RFID reader technical field

• US 20070129039A1
• Filed: 12/05/2005
• Published: 06/07/2007
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: Assa Abloy AB
• Original Assignee: Assa Abloy AB
• Inventors: Sherrets, David
• Granted Patent: US 7,844,238 B2
• Time in Patent Office: Days
• US Class Current: 455/230
• 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

Abstract

A reader and a corresponding method are provided for processing transponder data signals received from a transponder in an RFID system. The reader includes an exciter which generates excitation signals, a receiver which conditions the transponder data signals, an antenna coupled to the exciter and receiver which transmits the excitation signals and receives the transponder data signals, and a controller coupled to the receiver. The controller receives the conditioned transponder data signals and demodulates the conditioned signals to extract the transponder data. The controller is configured to detect the amplitude of the conditioned signals and to control operation of the receiver as a function of the amplitude of the conditioned signals.

Claims

1. A reader for an RFID system comprising:

an antenna configured to receive a transponder data signal;

a receiver coupled to said antenna for generating a conditioned output signal from said transponder data signal; and

a controller coupled to said receiver for detecting amplitude of said conditioned output signal and controlling operation of said receiver as a function of said amplitude.

2. The reader of claim 1, wherein said controller further includes a capability for demodulating said conditioned output signal.

3. The reader of claim 1, wherein said transponder data signal is a low voltage signal and said antenna is further configured to receive a high voltage excitation signal, said low voltage transponder data signal superposed on said high voltage excitation signal to define an antenna signal.

4. The reader of claim 3, wherein said receiver comprises a high voltage reduction circuit coupled to said antenna for generating a voltage reduced signal from said antenna signal and an amplifier coupled to said high voltage reduction circuit for generating said conditioned output signal from said voltage reduced signal.

5. The reader of claim 4, wherein said antenna signal has a voltage value exceeding an upper voltage tolerance level of said amplifier and said high voltage reduction circuit conveys peak portions of said antenna signal to said amplifier for reducing said voltage value below said upper voltage tolerance level of said amplifier.

6. The reader of claim 5, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting voltage reduction performed by said high voltage reduction circuit.

7. The reader of claim 5, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting a gain of said amplifier.

8. The reader of claim 5, wherein said controller includes an input circuit coupled to said amplifier, wherein said input circuit detects said amplitude of said conditioned output signal.

9. A reader for an RFID system comprising:

an antenna configured to receive a transponder data signal;

a receiver coupled to said antenna including a shift and clamp circuit for performing a shifting operation and a clamping operation on said transponder data signal; and

a controller coupled to said receiver for demodulating a receiver output signal to extract transponder data from said receiver output signal and further for detecting amplitude of said receiver output signal and controlling operation of said receiver in response to said amplitude.

10. The reader of claim 9, wherein said receiver further comprises an amplifier coupled to said shift and clamp circuit for receiving a shifted and clamped signal generated by said shift and clamp circuit from said transponder data signal, wherein said receiver output signal is a conditioned output signal generated by said amplifier from said shifted and clamped signal.

11. The reader of claim 10, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting a level of said shifting operation performed by said shift and clamp circuit.

12. The reader of claim 10, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces said amplitude of said conditioned output signal by adjusting a gain of said amplifier.

13. The reader of claim 9, wherein said receiver further comprises a switched capacitor filter enabling switching between at least two modulation types selected from the group consisting of frequency shift keying (FSK) modulation, phase shift keying (PSK) modulation and amplitude shift keying (ASK) modulation.

14. A method for reading a transponder data signal comprising:

receiving a transponder data signal containing transponder data on a reader antenna;

amplifying said transponder data signal to generate a conditioned amplifier output signal containing said transponder data;

attempting to extract said transponder data from said amplified output signal;

detecting an amplitude of said conditioned amplifier output signal;

comparing said amplitude to a predetermined threshold;

adjusting a level of gain performed during amplification of said transponder data signal when said amplitude is greater than said predetermined threshold such that said transponder data is not extractable from said conditioned amplifier output signal; and

demodulating said conditioned amplifier output signal to extract said transponder data from said conditioned amplifier output signal, thereby reading said transponder data signal.

15. The method of claim 14, wherein adjusting said level of gain comprises reducing gain performed by an amplifier.

16. The method of claim 14 wherein said transponder data signal is a low voltage signal, said method further comprising receiving a high voltage excitation signal on said antenna, said low voltage transponder data signal superposed on said high voltage excitation signal to define an antenna signal, said method further comprising reducing voltage of said antenna signal before amplifying said transponder data signal.

17. A method for reading a transponder data signal comprising:

receiving an antenna signal on a reader antenna, wherein said antenna signal includes a low voltage transponder data signal containing transponder data;

reducing voltage of said antenna signal to generate a voltage reduced signal containing said transponder data;

amplifying said voltage reduced signal to generate a conditioned amplifier output signal containing said transponder data;

attempting to extract said transponder data from said amplified output signal;

detecting an amplitude of said conditioned amplifier output signal;

comparing said amplitude to a predetermined threshold;

adjusting a level of voltage reduction of said antenna signal when said amplitude is greater than said predetermined threshold such that transponder data is not extractable from said conditioned amplifier output signal; and

demodulating said conditioned amplifier output signal to extract transponder data from said conditioned amplifier output signal, thereby reading said transponder data signal.

18. The method of claim 17, wherein adjusting said level of voltage reduction comprises adjusting a level of a shifting operation performed on said antenna signal by a shift and clamp circuit.

19. A reader for an RFID system comprising:

an antenna to receive a transponder data signal;

a receiver coupled to said antenna, said receiver including a voltage reduction circuit for receiving an antenna signal including said transponder data signal from said antenna and generating a voltage reduced signal, said receiver further including an amplifier coupled to said voltage reduction circuit for receiving said voltage reduced signal and generating a conditioned amplifier output signal; and

a controller coupled to said amplifier for demodulating said conditioned amplifier output signal, thereby reading said transponder data signal, wherein said controller detects said amplitude of said conditioned amplifier output signal and controls operation of said receiver as a function of said amplitude.

20. The reader of claim 19, wherein said voltage reduction circuit is a shift and clamp circuit for isolating a portion of said antenna signal.

21. The reader of claim 20, wherein said controller controls amplitude of a shift current applied to said shift and clamp circuit.

22. The reader of claim 19 further comprising an automatic gain control circuit coupled to said amplifier for adjusting a gain of said amplifier as a function of said amplitude.

23. The reader of claim 19 further comprising an automatic gain control circuit coupled to said voltage reduction circuit for adjusting amplitude of said voltage reduced signal as a function of said amplitude of said conditioned amplifier output signal.

24. The reader of claim 19, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces a gain of said amplifier.

25. The reader of claim 19, wherein when said controller detects said amplitude of said conditioned output signal greater than a predetermined threshold such that transponder data is not extractable from said conditioned output signal, said controller selectively reduces an amplitude of voltage reduced signal by adjusting an amount of voltage reduction performed by said voltage reduction circuit.