Method and apparatus for generating a discretely variable capacitance for synthesizing high-frequency signals for wireless communications

  • US 6,233,441 B1
  • Filed: 05/29/1998
  • Issued: 05/15/2001
  • Est. Priority Date: 05/29/1998
  • Status: Expired due to Term
First Claim
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1. A frequency synthesizer having at least one variable frequency output, the output frequency varying as a capacitance within the synthesizer varies, comprising:

  • a discretely variable capacitance circuit integrated within the frequency synthesizer including a plurality of capacitor circuits, each capacitor circuit comprising;

    a capacitor coupled between a first node and a second node; and

    a switch coupled between the second node and a third node to selectively couple the capacitor between the first node and the third node depending upon a control signal applied to a control node for the switch;

    a multiple-bit digital control signal coupled to the control nodes of the plurality of switches to include or exclude the capacitors within the plurality of capacitor circuits within an overall capacitance for the discretely variable capacitance circuit; and

    a continuously variable capacitance circuit integrated within the frequency synthesizer and having a plurality of analog signals as inputs, the analog signals controlling a plurality of capacitor circuits within the continuously variable capacitance circuit;

    wherein at least two of the capacitor circuits within the discretely variable capacitance circuit have different capacitances with respect to each other.

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