spice3 simulation of VCO

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

Reply to
ICguy
Loading thread data ...

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

Charlie

Reply to
Charlie Edmondson

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

Best performed using my LoopGain technique, as described on my website ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

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

Reply to
ICguy

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

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

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

Reply to
ICguy

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

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

Isn't . AC analysis like the following?

..AC dec No. fstar fstop

I couldn't find .

Reply to
ICguy

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

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.