[sdiy] OTA question

[Oren Leavitt]

Ian Fritz wrote:
> Hello --
> 
> I'm working on a Tri core VCO based on a CA3080 OTA.  It's similar to 
> the EN thru-zero VCO, which is up at Bernie's site.  Currently, its 
> output is swinging 0 to 6 V.
> 
> When I drive the OTA bias current from a pot across the PS and a 22k 
> series resistor it works fine.  But when I drive it with a linear V-I 
> converter the waveform at low frequencies is distorted.  The distortion 
> makes the waveform dome shaped, ie, it is always curved downward.  It 
> appears that there must be some kind of leakage which increases with 
> increasing output signal.  But where exactly is it and why would it only 
> show with the active drive?
> 
> I've tried a couple of versions of the linear V-I converter, both of 
> which are common and include a PNP transistor driving the control input 
> pin from its collector.
> 
> Any thoughts?
> 
>   Ian
> 


Interesting problem Ian - That wave shape you describe sounds like 
something you'd get when you feed a little of the triangle wave back to 
a control voltage input. i.e. self modulation. Something reaching the CV 
or linear FM inputs?

My 2 millivolts.
- Oren