MAT04 for ASM-1's

[Scott Bernardi]

You shouldn't need series resistors in monolithic (i.e., same chip)  matched
transistors. In fact, you can use a trick from analog circuit design and connect
the four transistors connected in a "cross coupled quad". This minimizes the effect
of temperature or manufacturing gradients between the transistors.  Given the
transistors A,B,C,D laid out as below (I looked at the MAT-04 die from the
datasheet, this is how they are situated), you connect A and D in parallel, and C
and B. Note that all of PMI's precision Opamps like the OP-07, OP-27, etc. use this
technique.

A  B
C  D


Scott Gravenhorst wrote:

> patchell <patchell at silcom.com> wrote:
> >
> >
> >Mantid wrote:
> >
> >> Hello fellow synth nuts,
> >> I am building some ASM-1's and am thinking of using MAT04's for the matched
> >> tranny pairs. I just happen to have a few of these in my possesion. If I
> >> was to use one MAT04 for two VCO's would I have to worry about the VCO's
> >> interacting with one another?
> >
> >    This is a question I am trying to answer myself.  However, there are other
> >ways of looking at this problem.  The MAT02 costs about twice as much as the
> >MAT04.  So, even if you toss the extra transistors in a MAT04, you are still
> >ahead.  Another posibility that I have been thinking of trying, is connect the
> >extra transistors in parrallel with the other two.  This should cut the bulk
> >resistance in half, but don't really know if this is worth the trouble.
>
> Won't there be a current sharing problem with this?  I seem to
> remember seeing an application with parallel transistors to
> increase the current handling capacity, but there were also small
> ohm resistors to help share the current more equally.  Or is
> this not going to be an issue because they are all carved out
> of the same rock?
>
> >>
> >> Also, is the Moog ladder filter tranny matching method appropriate for
> >> ASM-1 VCO tranny matching.
> >> It seems that the Moog method is for trannys as diodes and the ASM -1 needs
> >> trannys matched for beta.
> >> thanks- BIll
> >
> >--
> > -Jim
> >------------------------------------------------
> >* Visit:http://www.silcom.com/~patchell/
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> >
>
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--
Scott Bernardi
sbernardi at home.net