Method and apparatus for providing analog and digitally controlled capacitances for synthesizing high-frequency signals for wireless communications

  • US 6,147,567 A
  • Filed: 05/29/1998
  • Issued: 11/14/2000
  • 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 differential amplifier having a positive side voltage node and negative side voltage node;

    a positive side discretely variable capacitance circuit including a plurality of capacitor circuits;

    a negative side discretely variable capacitance circuit including a plurality of capacitor circuits paired with the capacitor circuits in the positive side discretely variable capacitance circuit;

    wherein the paired capacitor circuits comprise;

    a positive side capacitor circuit coupled to the positive side voltage node;

    a positive side switch circuit coupled to the positive side voltage node;

    a negative side capacitor circuit coupled to the negative side voltage node;

    a negative side switch circuit coupled to the negative side voltage node; and

    an additional switch circuit coupled between the positive side and negative side circuits to reduce an overall switch resistance when the negative side switch circuit and the positive side switch are in a conductive state; and

    wherein the positive and negative side switch circuits selectively include the positive and negative side capacitor circuits within the overall capacitance for the discretely variable capacitance circuit depending upon at least one control signal applied to the positive and negative side switch circuits.

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