Resonant Circuits

• US 20110025410A1
• Filed: 12/07/2006
• Published: 02/03/2011
• Est. Priority Date: 12/16/2005
• Status: Active Grant

• Current Assignee: SureFlap Ltd.
• Original Assignee: Cambridge Resonant Technologies Ltd. (Merck & Co., Inc.)
• Inventors: Hill, Nicholas Patrick Roland
• Granted Patent: US 8,471,642 B2
• Time in Patent Office: Days
• US Class Current: 327/553
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: H03J 1/0008 using a central processing unit, e.g. a microprocessor digital tuning in general H03J5/0245

Abstract

Embodiments of the invention relate to resonant circuits; particularly but not exclusively the embodiments relate to resonant circuits in RPID (radio frequency identification) responsive to a wide frequency range. A controllable electric resonator comprising an inductor coupled to a first capacitor to form a resonant circuit, the resonator further comprising a controllable element, a second capacitor controllable coupled across said first capacitor by said controllable element, and a control device to control said controllable element such that a total effective capacitance of said first and second capacitor varies over a duty cycle of an oscillatory signal on said resonator.

Claims

1. A controllable electric resonator comprising an inductor coupled to a first capacitor to form a resonant circuit, the resonator further comprising a controllable element, a second capacitor controllable coupled across said first capacitor by said controllable element, and a control device to control said controllable element such that a total effective capacitance of said first and second capacitor varies over a duty cycle of an oscillatory signal on said resonator.

2. A controllable electronic resonator as claimed in claim 1 wherein said controllable element comprises a transistor, and wherein said control device comprises a bias circuit for said transistor.

3. A controllable electronic resonator as claimed in claim 2 wherein said transistor comprises a MOS transistor.

4. A controllable electronic resonator as claimed in claim 2 further comprising a power supply circuit to derive a power supply for said bias circuit from said oscillatory signal.

5. A controllable electronic resonator as claimed in claim 2 wherein said bias circuit is configured to automatically adjust a bias on said transistor to increase an amplitude of said oscillatory signal.

6. A controllable electronic resonator as claimed in claim 1 further comprising a third capacitor connected across said controllable element.

7. A controllable electronic resonator as claimed in any preceding claim wherein said inductor has a Q of greater than 50.

8. A controllable electronic resonator as claimed in claim 1 further comprising a drive system to drive said oscillatory signal on said resonator.

9. A controllable electronic resonator as claimed in claim 8 wherein said drive system includes means for converting a current drawn by said resonator into a pulse having a duration depending on said current.

41. A controllable electronic resonator as claimed in claim 1 incorporated into an RFID tag or tag reader.

10. (canceled)

11. (canceled)

12. A controllable electric resonator comprising a resonant circuit and a system for controlling the amplitude of oscillations on the resonant circuit, when the resonant circuit is driven by an oscillatory signal, the apparatus comprising:

means for applying a reactive element to said resonant circuit with a variable coupling; and

means for varying said coupling over a cycle of said oscillatory signal to control said amplitude of oscillations.

13. A method of controlling a resonant frequency of a controllable electric resonator to substantially match said resonant frequency to a frequency of an external waveform, the controllable electric resonator comprising an inductance coupled to a capacitance, the capacitance having a switched component of capacitance, the method comprising controlling a duty cycle of said switched component of capacitance in response to a signal level of a waveform of an oscillation of said resonant circuit.

14. A method as claimed in claim 13 wherein said switched component of capacitance includes a field effect transistor (FET) switch coupled to a switched capacitance and wherein said duty cycle controlling comprises providing a voltage between a gate and a source of said FET dependent upon an instantaneous level of said waveform of said oscillation of said resonant circuit.

15. A method as claimed in claim 13 wherein a relative phase of said waveform of said oscillation of said resonant circuit and of said external waveform changes responsive to a signal level of said external waveform.

16. A method as claimed in claim 13 wherein said external waveform comprises a waveform of an rf electromagnetic field.

17. A method as claimed in claim 16 further comprising and extracting energy from said resonant circuit.

18. A method as claimed in claim 17 wherein a relative phase of said waveform of said oscillation of said resonant circuit and of said external waveform changes responsive to as signal level of said external waveform, and wherein said relative phase adjusts to limit said extracted energy as said energy in said rf electromagnetic field increases.

19. A method as claimed in claim 13 wherein said external waveform comprises a waveform derived from a crystal oscillator.

43. A method as claimed in claim 19, further comprising outputting an rf signal derived from said oscillation of said resonant circuit to provide an rf signal source.

20. (canceled)

21. (canceled)

22. (canceled)

23. A controllable electronic resonator having a controllable resonant circuit and incorporated in an RFID tag, the resonant circuit comprising an inductance coupled to a capacitance, the capacitance having a switched component of capacitance, wherein said controllable resonant circuit is configured to automatically control a duty cycle of said switched component of capacitance to select one of a plurality of frequencies of operation of said tag in response to an interrogating rf field.

28. A circuit as claimed in claim 23 in a reader wherein the stimulus period is a sub-harmonic of a desired energising field frequency.

29. A circuit as claimed in claim 23 in a reader wherein a crystal oscillator sets the operating frequency of the energising field.

24. A controllable electric LC (inductor-capacitor) resonant circuit comprising an inductor, a primary capacitive path, and at least one other secondary capacitive path that is coupled into the resonance with a variable duty cycle;

and wherein the circuit response frequency, which is dependent on the duty cycle, matches to a stimulus frequency.

25. A circuit as claimed in claim 24 wherein said variable duty cycle is controlled by a FET.

26. A circuit as claimed in claim 25 wherein the FET gate voltage is kept constant and the FET source voltage varies with the amplitude of the resonance, turning the FET on and off.

27. A circuit as claimed in claim 25 wherein the FET gate voltage is controlled with an external voltage source.

46. A circuit as claimed in claim 24 in a transponder.

30-40. -40. (canceled)

42. A controllable electric resonator comprising a resonant circuit and a system for controlling the amplitude of oscillations on the resonant circuit, when the resonant circuit is driven by an oscillatory signal, the apparatus comprising:

means for applying a reactive element to said resonant circuit with a variable coupling; and

means for varying said coupling over a cycle of said oscillatory signal to control said amplitude of oscillations.

44. A controllable electronic resonator including a circuit for controlling a resonant frequency of the resonator to substantially match said resonant frequency to a frequency of an external waveform, the resonator comprising an inductance coupled to a capacitance, the capacitance having a switched component of capacitance, the circuit comprising means for controlling a duty cycle of said switched component of capacitance in response to a signal level of a waveform of an oscillation of said resonator.

45. A comprising a circuit as claimed in claim 44, configured to extract energy from an rf electromagnetic field.