[sdiy] moog transistor matching circuit question

[Mattias Rickardsson]

I have a spare set of matched transistors for the TTSH supplied by Thonk,
if somebody needs them. Contact me privately if interested.

Speaking of transistor matchers, are there any DIY PCBs for them? I'd love
to not have to build a temporary one on a prototype board next time. :-)

/mr
Den 9 jan. 2016 5:30 em skrev "matt holland" <matt at mattholland.org>:

> Hi All,
>
> I'm in the process of helping a buddy build a TTSH and as a result am
> being thrust into the world of transistor matching. I could just get on
> with it and breadboard one of the handful of circuits out there but instead
> I've been staring at the Moog circuit linked to here [1] and trying to
> understand the theory behind it. The non DUT transistor is a current
> soruce, with the op amp giving the ability to set the current without
> having to bother biasing it with a precise Vbe. The two resistors on the
> non-inverting input bias the inverting input to -5V, which enforce a 98uA
> (~100uA) emitter current through the 51k resistor through the magic of
> negative feedback.
>
> It doesn't seem like the current value is even important at all so long as
> it stays the same from one DUT bjt to the next (i.e. temp is same from one
> measurement to the next for the tester as well as the DUT). Then we measure
> the Vbe across the DUT which is sort of a proxy for measuring Is (Vb =
> Vt*ln(Ic/Is) since it Is that models all the physical parameters that vary
> from one bjt to the next and is the temp dependent parameter that gets
> cancelled out in the expo converter to the extent that they're identical.
>
> The bit that I'm still having trouble with is the 10k resistor. It's there
> in the NPN tester but not in the PNP tester. I've seen this described as a
> "flaw" in the PNP tester but I'm not sure what it's doing int the NPN
> tester. I threw together a spice sim that steps the value of it from 0 to
> 10k with absolutely no meaningful change in the measured Vbe.
>
> Apologies if this has been covered before and appreciate any help.
>
> mh
>
> [1]
> http://www.musicfromouterspace.com/analogsynth_new/TRANSISTORMATCHER/images/moogmatchersmall.gif
>
>
>
>
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