Electronic identification system with improved sensitivity
First Claim
1. A reader for use with a tag, the reader comprising:
- a coil;
at least one capacitor;
a means for coupling the capacitor(s) to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s), the combination of the coil, the capacitors and the coupling means being called the resonating circuit, the resonating circuit having a resonant frequency;
a means for driving the coil through the capacitor(s) with a driving signal;
a means for generating the driving signal;
a resonating means for automatically maintaining the resonating circuit in a tuned condition, a tuned condition being the condition where the difference between the resonant frequency and the driving frequency is a predetermined value in the range from a negative predetermined value to a positive predetermined value.
1 Assignment
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Accused Products
Abstract
The coil in the reader that is used to establish an alternating magnetic field is transformer-coupled through capacitors to a push-pull driving circuit consisting of four field-effect transistors connected in a bridge arrangement. The coil, capacitors, and coupling circuitry are maintained in a tuned condition by continually adjusting either the driving frequency, the coil inductance, or the capacitor capacitance during communications. A tag utilizes a coil to couple with the reader'"'"'s alternating magnetic field and a capacitor to resonate the coil, thereby extracting power from the field more efficiently. Transformer coupling of the coil and capacitor is utilized for improved impedance matching. The coil, capacitor, and coupling circuitry can be maintained in a tuned condition by continually adjusting either the coil inductance, or the capacitor capacitance during communications. Certain configurations of the system may require that tuning maintenance be discontinued during the transmission of data.
54 Citations
28 Claims
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1. A reader for use with a tag, the reader comprising:
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a coil;
at least one capacitor;
a means for coupling the capacitor(s) to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s), the combination of the coil, the capacitors and the coupling means being called the resonating circuit, the resonating circuit having a resonant frequency;
a means for driving the coil through the capacitor(s) with a driving signal;
a means for generating the driving signal;
a resonating means for automatically maintaining the resonating circuit in a tuned condition, a tuned condition being the condition where the difference between the resonant frequency and the driving frequency is a predetermined value in the range from a negative predetermined value to a positive predetermined value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
a means for controlling a parameter that affects the state of resonance of the resonating circuit in accordance with a control signal;
a means for generating the control signal by which the resonating circuit is brought into a tuned condition.
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3. The reader of claim 2 wherein the controlling means is a voltage-controlled oscillator and the controlled parameter is the frequency of the driving signal.
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4. The reader of claim 2 wherein the controlling means is a saturable inductor in the field of the coil and the controlled parameter is the inductance of the coil.
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5. The reader of claim 2 wherein the controlling means is a voltage-controlled capacitor and the controlled parameter is the capacitance of the capacitor.
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6. The reader of claim 2 wherein the controlling means is a plurality of switches and the controlled parameter is the total capacitance of the capacitors connected through switches to a first common terminal, one terminal of each switch being connected to the first common terminal, the other terminal of each switch being connected to a first terminal of a capacitor, the second terminals of all capacitors being connected to a second common terminal, the parameter being controlled by controlling the closure of the switches.
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7. The reader of claim 2 wherein the control signal is a function of the phase difference between the driving signal and the coupling-means signal.
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8. The reader of claim 2 wherein the generating means comprises:
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a means for converting a coupling-means signal into a coupling-means square wave having a constant amplitude and the same zero crossings as the coupling-means signal;
a means for generating a driving-signal square wave having the same zero crossings as the driving signal;
a means for obtaining an error signal from the coupling-means square wave and the driving-signal square wave;
a means for continually integrating the error signal to obtain the control signal.
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9. The reader of claim 8 wherein the error signal is obtained by multiplying the coupling-means square wave by the driving-signal square wave.
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10. The reader of claim 8 wherein the error signal is obtained by multiplying the coupling-means square wave by the driving-signal square wave to obtain a product signal and biasing the product signal by a predetermined value in the range from a predetermined negative value to a predetermined positive value.
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11. The reader of claim 2 wherein the control signal is a function of the difference between the frequency of the driving signal and the resonant frequency of the resonating circuit.
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12. The reader of claim 2 wherein the control signal is a function of the amplitude of a coupling-means signal as a function of the frequency of the driving signal.
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13. The reader of claim 12 wherein the means for generating the control signal comprises:
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a means for generating a modulating signal having a zero average value, the modulating signal constituting one of two additive components of the control signal;
a means for obtaining the amplitude of a coupling-means signal;
a means for obtaining an error signal from the modulating signal and the coupling-means signal amplitude;
a means for continually integrating the error signal to obtain the integration signal, the integration signal constituting the other additive component of the control signal.
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14. The reader of claim 13 wherein the error signal is obtained by multiplying the modulating signal and the coupling-means signal amplitude.
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15. The reader of claim 12 wherein the error signal is obtained by multiplying the modulating signal and the coupling-means signal amplitude to obtain a product signal and biasing the product signal by a predetermined value in the range from a predetermined negative value to a predetermined positive value.
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16. A tag for use with a reader, the reader establishing an alternating magnetic field in the proximity of the tag, the tag comprising:
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a coil;
a capacitor;
a means for coupling the capacitor to the coil and coupling the coil to at least one other means, the signal provided to the other means as a result of the coupling being called coupling-means signal, the combination of the coil, the capacitor and the coupling means being called the resonating circuit, the resonating circuit having a resonant frequency;
a resonating means for automatically maintaining the resonating circuit in a tuned condition, a tuned condition being the condition where the difference between the resonant frequency and the frequency of the alternating magnetic field is a predetermined value in the range from a negative predetermined value to a positive predetermined value. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
a means for controlling a parameter that affects the state of resonance of the resonating circuit with a control signal;
a means for generating the control signal by which the resonating circuit is brought into a tuned condition after a period of time.
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18. The tag of claim 17 wherein the controlling means is a saturable inductor in the field of the coil and the controlled parameter is the inductance of the coil.
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19. The tag of claim 17 wherein the controlling means is a voltage-controlled capacitor and the controlled parameter is the capacitance of the capacitor.
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20. The tag of claim 17 wherein the controlling means is a plurality of switches and the controlled parameter is the total capacitance of the capacitors connected through switches to a first common terminal, one terminal of each switch being connected to the first common terminal, the other terminal of each switch being connected to a first terminal of a capacitor, the second terminals of all capacitors being connected to a second common terminal, the parameter being controlled by controlling the closure of the switches.
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21. The tag of claim 17 wherein the generating means generates a control signal based on the difference between the frequency of the alternating magnetic field and the resonant frequency of the resonating circuit.
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22. The tag of claim 17 wherein the control signal is based on the amplitude of a coupling-means signal as a function of the frequency of the alternating magnetic field, the alternating magnetic field being frequency modulated by the reader.
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23. The tag of claim 22 wherein the means for generating the control signal comprises:
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a means for obtaining the amplitude of a coupling-means signal as a function of time;
a means for obtaining an error signal, the error signal being the amplitude of the coupling-means signal multiplied by a weighting function of time;
a means for continually integrating the error signal to obtain the control signal.
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24. The tag of claim 22 wherein the means for generating the control signal comprises:
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a means for generating a replica of the signal used by the reader in frequency-modulating the alternating magnetic field;
a means for obtaining the amplitude of a coupling-means signal as a function of time;
a means for obtaining an error signal from the replica and the coupling-means signal amplitude;
a means for continually integrating the error signal to obtain the control signal.
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25. The tag of claim 24 wherein the error signal is obtained by multiplying the replica by the coupling-means signal amplitude.
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26. The tag of claim 24 wherein the error signal is obtained by multiplying the replica by the coupling-means signal amplitude and biasing the product by a predetermined value in the range from a predetermined negative value to a predetermined positive value.
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27. An identification system consisting of a reader and at least one tag, the reader comprising:
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a coil;
at least one capacitor;
a means for coupling the capacitor(s) to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s);
a means for driving the coil through the capacitor(s) with a driving signal;
a means for generating a driving signal which incorporates a bit-timing clock signal;
a means for extracting data communicated by the tag from a coupling-means signal;
the tag comprising;
a coil;
a capacitor;
a means for coupling the capacitor to the coil;
a means for driving the coil through the coupling means with a driving signal;
a means for generating a bit-timing clock signal that is synchronized to the bit-timing clock signal embedded in the alternating magnetic field by the reader;
a means for generating the driving signal which carries a sequence of bits to be communicated to the reader, the start of each bit being controlled by the bit-timing clock signal that is generated by the tag and synchronized to the bit-timing clock signal embedded in the alternating magnetic field.
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28. An identification system consisting of a reader and at least one tag, the reader comprising:
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a coil;
at least one capacitor;
a means for coupling the capacitor(s) to the coil;
a means for driving the coil through the capacitor(s) with a driving signal;
a means for generating the driving signal;
a means for transmitting a sequence of bits to the tag by modulating the driving signal, the start of each bit being determined by a bit-timing clock signal;
a means for embedding the bit-timing clock signal in the alternating magnetic field;
the tag comprising;
a coil;
a capacitor;
a means for coupling the capacitor to the coil and coupling the coil to at least one other means, the signal(s) provided to the other means as a result of the coupling being called coupling-means signal(s);
a means for generating a bit-timing clock signal that is synchronized to the bit-timing clock signal embedded in the alternating magnetic field by the reader;
a means for identifying the bit being transmitted during each bit period, the identifying means being based on at least one weighted integration over a bit period of a demodulated coupling-means signal.
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Specification