[sdiy] Home made OTA ! ( Was: Hu are not Be Sma).

[karl dalen]

Well i think the CA3083 works quite well, obviously bigger
then the DIP8 of CA3080. The CA3083 are available in SMD
and are dirt cheap, outperforms the LM3046!

Q1 and Q2 used for the gillbert mirrors Q3 used for
sinking current (CV input)Q4 Q5 for current mirrors, 
NPN tought but anyway, or use Q4 and Q5 for temp
compensation! 

My one swedish krona!

REG
KD

--- Ian Fritz <ijfritz at earthlink.net> skrev:

> At 12:47 PM 6/2/05, laxt57 at aol.com wrote:
> 
> >   Well what I am planning is this. A OTA made with SMD that
> >  will fit the footprint of a ca3080. By input I guess I was not
> >  asking about the design of the OTA itself, all that is freely
> >  available on the web. I guess my question is with the available
> >  smd devices 847s,3904 etc do you think this sdiy do able?
> 
> Well, that's the question.  I haven't found any good SMD well-matched, 
> high-gain transistors.  I've been stocking up on the popular Japanese 
> matched pairs, some of which are quite good, but all discontinued.  In my 
> most recent discrete OTA I tried a pair of hand-matched ZTX795A's glued 
> together, but they didn't work very well.  They had too much LF noise, 
> presumably due to temperature fluctuations.
> 
> Maybe some of the non-monolithic SDMs could be made to work, I dunno.
> 
> Another question is whether it is even a good idea to try to reproduce the 
> 3080.  The Iabc mirror has always been a pain, requiring a mirror in the 
> expo converter.  Why not work with the simpler discrete designs that don't 
> have this "feature".
> 
>    Ian
> 
>