Detection signal generator circuit for an RFID reader

• US 20070229273A1
• Filed: 03/31/2006
• Published: 10/04/2007
• Est. Priority Date: 03/31/2006
• Status: Active Grant

• Current Assignee: Assa Abloy AB
• Original Assignee: Assa Abloy AB
• Inventors: Lowe, Peter, Hoemann, James
• Granted Patent: US 7,782,209 B2
• Time in Patent Office: Days
• US Class Current: 340/572.400
• 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 7/0086 the connector comprising a circuit for steering the operations of the card connector
• CPC Class Codes: G06K 7/10009 sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
• 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

An RFID transponder detector is provided having a coupled oscillator system. Coupled first and second LC pairs of the system produce a detection signal each time a combination of pulses is applied to the LC pairs. Application of the pulses is repeated periodically to produce a sequence fo detection signals having two different first and second detection frequencies. Transmitting the sequence of detection signals results in corresponding first and second response signals having the first and second detection frequencies at the LC pairs. Values of a preselected detection parameter for the detection signals are compared to the values of the detection parameter for the response signals to determine if a transponder having a transponder resonant frequency corresponding to the first or second detection frequency is present in a proximal space of the transponder detector.

Claims

1. An RFID transponder detector comprising:

a first LC pair including a first inductance coil and a first tuning capacitor;

a second LC pair including a second inductance coil and a second tuning capacitor, wherein said first LC pair is coupled to said second LC pairs;

an antenna coupled to said first and second LC pair;

a controller coupled to said first and second LC pairs for applying first pulses and second pulses to said first and second LC pairs, thereby resonating said first and second LC pairs to produce a sequence of first and second detection signals, wherein said first detection signal has a first detection frequency and said second detection signal has a second detection frequency different from said first detection frequency, further wherein transmitting said sequence of detection signals from said antenna results in corresponding first and second response signals having said first and second detection frequencies, respectively, on said antenna; and

a detection and response signal measurement circuit coupled to said antenna and said controller for receiving said first and second detection signals and said corresponding first and second response signals and measuring values of a preselected detection parameter for each of said detection signals and each of said response signals, wherein said controller or detection and response signal measurement circuit is configured to compare said values for said detection signals to said values for said response signals and determine if a transponder having a transponder resonant frequency corresponding to said first or second detection frequency is present in a proximal space of said transponder detector based on comparison of said values.

2. The RFID transponder detector of claim 1 further comprising a coupling capacitor, wherein said first LC pair is coupled to said second LC pair across said coupling capacitor.

3. The RFID transponder detector of claim 1 further comprising a first driver coupled between said first LC pair and said controller, wherein said controller applies said pulses to said first LC pair through said first driver.

4. The RFID transponder detector of claim 1 further comprising a second driver coupled between said second LC pair and said controller, wherein said controller applies said pulses to said second LC pair through said second driver.

5. The RFID transponder detector of claim 1 further comprising a mode switch in communication with said controller, said controller configured to direct transitioning of said mode switch between a first position and a second position, said first position determining a symmetric mode of oscillation of said first and second LC pairs and said second position determining an anti-symmetric mode of oscillation of said first and second LC pairs.

6. The RFID transponder detector of claim 5, wherein said mode switch is a mode logic gate.

7. The RFID transponder detector of claim 5 further comprising an enable switch in communication with said controller, said controller configured to direct transitioning of said enable switch between two positions, said two positions determining whether one of said detection signals or an excitation signal is applied on said antenna.

8. The RFID transponder detector of claim 7, wherein said enable switch is an enable logic gate.

9. The RFID transponder detector of claim 1, wherein said first and/or second inductance coil functions as said antenna.

10. The RFID transponder detector of claim 1 further comprising a third LC pair including a third inductance coil and a third tuning capacitor, wherein said third LC pair is coupled to said controller for applying third pulses to said third LC pair, thereby producing said sequence of detection signals transmitted by said antenna, wherein said sequence of detection signals includes detection signals having at least three different frequencies, thereby defining a third detection frequency in addition to said first and second detection frequencies, said detection and response signal measurement circuit coupled to said third LC pair for determining if a transponder having a transponder resonant frequency corresponding to said third detection frequency is present in said proximal space of said transponder detector.

11. A transponder detection method comprising:

applying first pulses to a first location and a second location on a coupled oscillator system having a first LC pair and a second LC pair;

resonating said first and second LC pairs in response to said first pulses to generate a first detection signal having a first detection frequency correlated to said first pulses;

applying second pulses to said first and second locations on said coupled oscillator system;

resonating said first and second LC pairs in response to said second pulses to generate a second detection signal having a second detection frequency different than said first detection frequency and correlated to said second pulses;

transmitting a sequence of said first and second detection signals into a space proximal to said first and second LC pairs;

producing first and second response signals corresponding to said first and second detection signals, respectively;

measuring values of a preselected detection parameter for said first detection signal, said second detection signal, said first response signal, and said second response signal to obtain a sequence of values of said detection parameter for said detection and response signals;

comparing said value for said first detection signal to said value for said first response signal;

comparing said value for said second detection signal to said value for said second response signal;

determining if a transponder having a first transponder resonant frequency corresponding to said first detection frequency is present in a proximal space of said transponder detector based on comparison of said values for said first detection and response signals; and

determining if a transponder having a second transponder resonant frequency corresponding to said second detection frequency is present in a proximal space of said transponder detector based on comparison of said values for said second detection and response signals.

12. The method of claim 11 further comprising separating said sequence of values into a subsequence of values for said first detection signals and a subsequence of values for said second detection signals before comparing said values for said first detection signals to said values for said first response signals.

13. The method of claim 11 further comprising separating said sequence of values into a subsequence of values for said first detection signals and a subsequence of values for said second detection signals before comparing said values for said second detection signals to said values for said second response signals.

14. The method of claim 11, wherein said detection parameter is signal voltage or signal decay rate.

15. The method of claim 11, wherein said first detection signal results from a symmetric mode of oscillation of said first and second LC pairs and said second detection signal results from an anti-symmetric mode of oscillation of said first and second LC pairs.

16. The method of claim 11, wherein said sequence of values is an alternating sequence.

17. The method of claim 11 further comprising,

applying third pulses to said first and second locations and to a third location on said coupled oscillator system having a third LC pair,

resonating said first, second and third LC pairs in response to said third pulses to generate a third detection signal having a third detection frequency correlated to said third pulses;

transmitting a sequence of said first, second and third detection signals into a space proximal to said first and second LC pairs;

producing a third response signal corresponding to said third detection signal,

measuring values of said detection parameter for said third detection and response signals,

comparing said value for said third detection signal to said value for said third response signal, and

determining if a transponder having a third transponder resonant frequency corresponding to said third detection frequency is present in a proximal space of said transponder detector based on comparison of said values for said third detection and response signals.

18. A reader for an RFID system comprising:

a detection circuit including,

a first LC pair including a first inductance coil and a first tuning capacitor,

a second LC pair including a second inductance coil and a second tuning capacitor, wherein said first LC pair is coupled to said second LC pair,

an antenna coupled to said first and second LC pair;

a detection circuit controller coupled to said first and second LC pairs for applying first pulses and second pulses to said first and second LC pairs, thereby resonating said first and second LC pairs to produce a sequence of first and second detection signals, wherein said first detection signal has a first detection frequency and said second detection signal has a second detection frequency different from said first detection frequency, further wherein transmitting said sequence of detection signals from said antenna results in corresponding first and second response signals having said first and second detection frequencies, respectively, on said antenna,

an enable switch in communication with said detection circuit controller, said detection circuit controller configured to direct transitioning of said enable switch between two positions, said two positions determining whether one of said detection signals or an excitation signal is applied on said antenna,

a mode switch in communication with said detection circuit controller, said detection circuit controller configured to direct transitioning of said mode switch between a first position and a second position, said first position determining a symmetric mode of oscillation of said first and second LC pairs and said second position determining an anti-symmetric mode of oscillation of said first and second LC pairs, and

a detection and response signal measurement circuit coupled to said antenna and said detection circuit controller for receiving said first and second detection signals and said corresponding first and second response signals and measuring values of a preselected detection parameter for each of said detection signals and each of said response signals, wherein said detection circuit controller or detection and response signal measurement circuit is configured to compare said values for said detection signals to said values for said response signals and determine if a transponder having a transponder resonant frequency corresponding to said first or second detection frequency is present in a proximal space of said transponder detector based on comparison of said values;

an exciter/reader circuit coupled to said antenna; and

a main controller coupled to said exciter/reader circuit and said detection circuit and configured to activate said exciter/reader circuit in response to a transponder recognized signal from said detection circuit controller.

19. The reader of claim 18, wherein said reader antenna is integral with said first and/or second inductance coils.

20. The reader of claim 18, wherein said main controller is integral with said detection circuit controller.