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Agilent Technologies

Crystal Colpitts Series VCO


This is a Colpitts oscillator for fundamental mode parallel resonant crystals in the 1 to 20 MHz range. Capacitive loading is primarily due to C1, which may be used to trim the operating frequency. This is not our favorite crystal oscillator structure, but was included because of its popularity. Care must be exercised to insure operation on the maximum phase slope.

  • Freq - The desired oscillation frequency.
  • Cload - The estimated load capacitance as seen by the crystal. Common values are 32 pF for lower frequencies and 20 pF for higher frequencies.
  • Manual XTL Input - Enables the crystal parameter input prompts. If this box is not selected, OSCILLATOR chooses default crystal values based on the other input prompts. These default values are typical for off-the-shelf crystals, but you should consult the manufacturer for more precise data.
  • Rs - The crystal equivalent series resistance.
  • Lm - The crystal's motional inductance (nH).
  • Cm - The crystal's motional capacitance (pF).
  • Co - The crystal's parallel, static capacitance (pF).
  • Vdev - The device operating voltage.
  • Vsup - The available supply voltage.
  • Idev - The device operating current.
  • Q1 - The device nonlinear or SPICE model.

See Also: Oscillator Types