Resonant circuits
First Claim
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 and a second capacitor, said controllable element arranged to control a total effective capacitance of said first and second capacitors, said resonant circuit comprising said total effective capacitance, the resonator further comprising a control device to provide a voltage to control said controllable element, said voltage substantially constant over a cycle of oscillation of a signal on said resonator, whereinthe controllable element comprises a transistor having a gate terminal configured to receive said voltage, a source terminal configured to receive a first resonance waveform of said resonant circuit and a drain terminal configured to receive a second resonance waveform of said resonant circuit,the transistor is configured to switch when a difference between said voltage and said received first resonance waveform on said source terminal reaches a threshold voltage of the transistor, the transistor thereby configured to turn on and off during said cycle of oscillation to vary said total effective capacitance of said first and second capacitors over said cycle of oscillation.
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Accused Products
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.
27 Citations
29 Claims
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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 and a second capacitor, said controllable element arranged to control a total effective capacitance of said first and second capacitors, said resonant circuit comprising said total effective capacitance, the resonator further comprising a control device to provide a voltage to control said controllable element, said voltage substantially constant over a cycle of oscillation of a signal on said resonator, wherein
the controllable element comprises a transistor having a gate terminal configured to receive said voltage, a source terminal configured to receive a first resonance waveform of said resonant circuit and a drain terminal configured to receive a second resonance waveform of said resonant circuit, the transistor is configured to switch when a difference between said voltage and said received first resonance waveform on said source terminal reaches a threshold voltage of the transistor, the transistor thereby configured to turn on and off during said cycle of oscillation to vary said total effective capacitance of said first and second capacitors over said cycle of oscillation.
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19. 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:
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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, wherein the means for varying said coupling comprises a transistor having a gate terminal configured to receive a substantially constant voltage, a source terminal configured to receive a first resonance waveform of said resonant circuit and a drain terminal configured to receive a second resonance waveform of said resonant circuit, and the means for varying said coupling is for switching the transistor when a difference between said substantially constant voltage and said received first resonance waveform on said source terminal reaches a threshold voltage of the transistor, to thereby turn the transistor on and off during said cycle to vary said variable coupling over said cycle.
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20. A method of controlling a resonant frequency of a resonant circuit 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 first component of capacitance and a second component of capacitance coupled to a field effect transistor (FET) switch, the method comprising:
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turning on and off said FET switch during a period of oscillation of a signal on said resonant circuit to vary a total effective capacitance of said first and second components of capacitance, said turning on and off having a duty cycle that is a fraction of a period of oscillation of said resonant circuit; and controlling said duty cycle in response to a signal level of a waveform of an oscillation of said resonant circuit; wherein the FET switch comprises a source arranged to receive a first resonance waveform of said resonant circuit, a drain arranged to receive a second resonance waveform of said resonant circuit and a gate arranged to receive a voltage that is substantially constant over said period of oscillation of said resonant circuit, and wherein said duty cycle controlling comprises providing a voltage between said gate and said source of said FET dependent upon an instantaneous level of said waveform of said oscillation of said resonant circuit such that the FET switches state when said voltage between said gate and said source reaches a threshold voltage of the FET. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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27. An apparatus comprising:
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a resonant circuit and a system for automatically adjusting a resonant frequency of the resonant circuit when the resonant circuit is driven by an oscillatory signal; means for applying a reactive element to said resonant circuit with a variable coupling; and means for varying said coupling within a cycle of said oscillatory signal so as to change the resonant frequency of the resonant circuit.
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- 28. 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.
Specification