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Phase noise reduction in voltage controlled oscillators

  • US 10,574,183 B2
  • Filed: 08/01/2018
  • Issued: 02/25/2020
  • Est. Priority Date: 01/10/2014
  • Status: Active Grant
First Claim
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1. A voltage controlled oscillator (VCO) comprising:

  • an LC tank circuit for generating an oscillator output signal at an oscillator frequency (fo);

    an oscillator core including first and second cross-coupled semiconductor devices connected to the tank circuit to provide regenerative feedback to the tank circuit to help maintain the oscillator output stable;

    a supply node connected to the tank circuit for connecting the VCO to a voltage source;

    a tail node connected to the oscillator core for connecting the VCO to a current source;

    a noise by-pass circuit having a first end connected to the supply node and a second end connected to the tail node and forming a low-impedance by-pass circuit connecting the supply node and the tail node, in parallel with the LC tank circuit and the oscillator core, at a frequency approximately twice the oscillator frequency to at least partially immunize the oscillator core from external noise and to reduce noise contribution from the cross-coupled semiconductor devices, and including a variable capacitor and a variable inductance transmission line; and

    a frequency control including a voltage control applied to the variable capacitor and a digital control applied to the variable inductance transmission line, the voltage control and the digital control being used in tandem to adjust the frequency at which the noise by-pass circuit resonates to adjust a performance of the VCO.

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