[sdiy] moog high pass flter - Transistor Matching

[Scott Bernardi]

OK, I see your point, but I still just try to match within half a millivolt or
so. My 3 1/2 digit DVM works for that.
Probably the best argument for matching as a diff pair is that they will both be
at the same temperature, even with stray air currents, because you're measuring
them at the same time.

Ian Fritz wrote:

> Um, well you take one and measure the other n-1 against it.  Then pick the
> good pairs by comparing the numbers, just as if you had measured them singly.
>
> The advantage would be that you are using a differential measurement and
> therefore get better resolution.  You could in principle use a 3 1/2 digit
> DVM to determine offsets in the microvolt range.  It would be quite
> difficult to do this well with the .56 V background you have in a single
> measurement.
>
>    Ian
>
> At 08:49 PM 12/9/2002, Scott Bernardi wrote:
> >Although what you describe would work to compare two Vbe's, I'm not sure
> >how useful it would be to know just the mismatch between two
> >transistors.  If you had n transistors to work from, you'd have to
> >potentially make 2^(n-1) comparisons. Probably not bad if you were only
> >looking for one matched pair.
> >If you record the values of the Vbe's, then you make one measurement for
> >each transistor, and you compare values to see which pairs can go
> >together.