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oscillation frequency estimate using harmonic balance

fishbed

 Hi,

 I am working on a crystal oscillator.  I want to estimate frequency pulling over temperature caused by circuit (excluding crystal).  I am looking at something around 0.01ppm/C level or less.  It takes too much time to use shooting mehod.  So I use harmonic balance to figure out oscillation frequency.  It gives good resulton 2ppm frequency pulling (matches my hand calculation).  But I do not know if 0.01ppm frequency pulling can be simulated by harmonic balance.  What parameters do I need to tighten?

 

The oscillator XIN and XOUT have small sinusoidal swing.  Not much harmonics at all.

Thank you in advance!


 

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  • Dear fishbed,

    > Am I correct?

    Basically yes. 

    I would recommend applying a sinusoidal current source whose current magnitude is set to provide the same magnitude but opposite sign as the series arm of the quartz crystal unit series arm - not a voltage source. The reason for this is that the current through the series arm of the quart crystal unit model will be essentially sinusoidal. The voltage across the series arm may not be free from harmonic distortion as some current in the sustaining amplifier and C0 may cause the voltage waveform to have distortion. However, the current through the series arm - which you are modeling with a current source will be essentially distortion free. I hope this makes sense to you.

    Shawn

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  • Dear fishbed,

    > Am I correct?

    Basically yes. 

    I would recommend applying a sinusoidal current source whose current magnitude is set to provide the same magnitude but opposite sign as the series arm of the quartz crystal unit series arm - not a voltage source. The reason for this is that the current through the series arm of the quart crystal unit model will be essentially sinusoidal. The voltage across the series arm may not be free from harmonic distortion as some current in the sustaining amplifier and C0 may cause the voltage waveform to have distortion. However, the current through the series arm - which you are modeling with a current source will be essentially distortion free. I hope this makes sense to you.

    Shawn

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