[sdiy] Hopf bifurcation VCOs....... my test results!

[Ian Fritz]

At 04:48 PM 11/11/05, karl dalen wrote:
>This is a really a cool cirquit!
>You deserves DIY nobel price for publishing it Ian!
>Why havent you done it earlier? :)

LOL!  AD did it years ago!


>Heres my tests reults:
>LM13700, batch 9642, LF353 intg, TL072 feedback.
>
>I changed the cirguit gain a bit, 10K ,390 ohm OTA inputstage,
>and 5,1 v zeners (i didnt have any other at the moment)
>220k to + input at + feedback stage, otherwise all the same.

Should work about the same. Different levels maybe.


>I also use one expo tied to both Iabc inputs, no reason to use separate expos.

Same here.  Iabc's connected through 22k to a common bias source.


>Sinus has no dent!!!!!!!!!!!!!

Nothing to make a dent. All smooth functions.


>I wanted to get rid of the trimmers so i just did the 10K, 390ohm
>input, still perfect symetry!!!! And that "with or without" diode
>biasing, it simply dosent matter!!

Well, sounds like you were lucky to have good OTAs.  It always seems a bit 
of a crap shoot.


>Mine "decreases" slightely in amplitude?!(LF353 as opamps).
>Have to investigate that futher!

Well this gets into some fine second order effects.


>With your schemo and my gain scaling i get instant start up at any frequency!

Hmmm... That seems odd, since my results and Harry's simulation both show 
hundreds of cycles to build up.  The smaller feedback R should help some, 
but I'm surprised at this result.


>It sweeps all right manually.

Ah, good.


>I made it to over saturate badly into crude and unbalanced
>square waves, still performs as nice as prevoiusly, this is a
>very stable cirquit!

Yes, stable it is. :-)

   Ian