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Frequency control circuit for tuning a resonant circuit of an untethered device

  • US 8,040,329 B2
  • Filed: 12/20/2006
  • Issued: 10/18/2011
  • Est. Priority Date: 12/20/2006
  • Status: Expired due to Fees
First Claim
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1. An untethered device configured to inductively couple to a source device, the source device configured to generate a varying magnetic field having a fixed frequency, the untethered device comprising:

  • a tunable resonant circuit having a resonance frequency and configured to generate a supply voltage for the untethered device in response to the varying magnetic field, the tunable resonant circuit includingan inductive coil comprising a center tap; and

    a capacitive circuit coupled to the inductive coil, the capacitive circuit comprising an anti-series arrangement of varactor diodes that set a capacitance when placed in reverse bias; and

    a frequency control circuit coupled to the tunable resonant circuit, the frequency control circuit comprising a control voltage source coupled to the center tap of the inductive coil, the control voltage source producing a control signal to place the varactor diodes in reverse bias and to change the capacitance of the capacitive circuit, thereby effecting a change in the resonance frequency of the tunable resonant circuit.

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