Connect with us

spice3 simulation of VCO

Discussion in 'CAD' started by ICguy, Jul 12, 2005.

Scroll to continue with content
  1. ICguy

    ICguy Guest

    Why can not I see the result of AC analysis of the VCO in spice3? I can
    observe that there is an oscilation in transient anaylisis.

    Thank you
  2. Basically, because your VCO model is not modeled, as such, in the AC
    domain. AC analysis doesn't do that sort of 'stuff'!

  3. Jim Thompson

    Jim Thompson Guest

    Sure it does, Charlie. Just do a loop gain (.AC) analysis.

    Best performed using my LoopGain technique, as described on my website

    ...Jim Thompson
  4. ICguy

    ICguy Guest

    Thank you both for your reply. I will try the loop gain analysis...
  5. Jim Thompson

    Jim Thompson Guest

    Make sure you use enough steps per octave/decade/whatever in your .AC
    analysis. Otherwise you'll completely sail right over the resonances
    of the crystal.

    ...Jim Thompson
  6. ICguy

    ICguy Guest

    I tried the .AC analysis on VCO, the output is still zero. However, if
    some noise is added to the VCO, then I can observe an nonzero output of
    the VCO in AC analysis. Does this mean that the VCO is not oscilating
    at all? if so, why I can observe an oscilltion in .TRAN analysis?

    Thank you
  7. Jim Thompson

    Jim Thompson Guest

    Do you know how to do a .AC analysis? Maybe post your schematic to


    ...Jim Thompson
  8. ICguy

    ICguy Guest

    Isn't . AC analysis like the following?

    ..AC dec No. fstar fstop

    I couldn't find <alt.binaries.schematics.electronic>.
  9. Jim Thompson

    Jim Thompson Guest

    Go to my website and E-mail me a schematic, PDF preferred but an
    LTspice listing will also work, and I'll take a look.

    ...Jim Thompson
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day