[sdiy] Matched transistors and EFM circuits?

[René Schmitz]

Hi Ian and List,

Ian Fritz wrote:
> At 08:00 AM 6/10/2007, Paul Schreiber wrote:
> 
>>> Further, although I'm
>>> aware that matching transistors in an expo converter is important for
>>> temperature stability,
>>
>>
>> Errr....nope.
> 
> 
> Err ... yep.
> 
> The transistors in an expo converter need to be matched so as to cancel 
> the Is prefactor.
> 
> Late night?


Well, it all comes down to the argument we had before. Let me recap real 
quick:

Does Is1/Is2 give a constant or not. If yes, then Is1/Is2 does not 
really have to be unity. I.e. a mismatch could be tolerable without 
affecting the stability. In that case a mismatch could be due to 
geometry. (still good thermal coupling assumed)

Your argument was always that there could be defects with could prevent 
Is1/Is2 to be a constant. However I still haven't seen a proof for that.

I personally take it that there have been VCOs in the past, even in 
quite prominent gear like Minimoog, Oberheim SEM etc., which were using 
humble 3046s, as a hint that this whole matching issue isn't as 
important as some people would like to believe. It worked for them back 
then so why even spending the time to worry about it. :-)

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159