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Voltage controlled oscillator and PLL circuit using the same

  • US 6,768,387 B1
  • Filed: 08/08/2000
  • Issued: 07/27/2004
  • Est. Priority Date: 03/08/2000
  • Status: Expired due to Fees
First Claim
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1. A voltage controlled oscillator circuit, comprising:

  • a first node connected to a first power source having a first voltage;

    a second node connected to a second power source having a second voltage;

    a first MOS transistor;

    an oscillator arranged between the first node and a third node; and

    a first capacitive element arranged between the first node and the third node;

    a second capacitive element; and

    a node connected to the second capacitive element;

    wherein an oscillation frequency of the oscillator is controlled by connecting a source of the first MOS transistor to the second node, connecting a drain of the first MOS transistor to the third node, applying an analog control signal to a gate of the first MOS transistor, and changing a frequency of a high level and a low level of a digital control signal; and

    connection to and disconnection from the second capacitive element are selected according to the digital control signal.

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