[sdiy] Gilbert Cells and VCAs with Predistortion

[Ryan Williams]

hi,

James Patchell wrote:
> I did a Gilbert Cell VCA with the LM13700 several years ago...however I 
> found that it was a lot less expensive to actually take advantage of the 
> fact that there are two OTA's in the LM13700...(by the way...this was 
> not my idea...this showed up in EDN several years ago)...I don't 
> remember where the link is for the original article (it is still on the 
> web).

I have the article.  for anyone else who might be reading it is at:
http://www.edn.com/archives/1995/011995/02di1.htm

> But I used it in my No-Tempco VCO because it is about 2 to 3 times more 
> linear than the Gilbert front end (Gilbert.... 0.4% to 0.5% 
> lineartity....dual LM13700...   0.1% lineartity).

I'm also familiar with your no-tempco VCO. that is another type of 
circuit I've been thinking about.  A few months ago I tried to do a 
circuit with both halfs of the 13700 and one in the feedback loop of an 
opamp but It had stability problems and I didn't know enough at that 
time to try and fix the problem.

the .1% you measured on the 13700 looks pretty good. I think I remember 
someone else saying they didn't have such good results? I think it's 
time for me to actually start measuring performance. I won't know 
anything until I can do that.

-ryan