[sdiy] THAT300

[Richie Burnett]

"Substrate biasing is not required for normal operation, though the substrate should be ac-grounded to optimize speed and minimize crosstalk."

This sounds like the substrate is electrically insulated from the workings (probably by an oxide layer.) So it doesn't matter what dc voltage is on there.

However they are aware that there is still significant capacitance between the substrate and various nodes in the workings (probably because the oxide insulating layer is very thin.) Therefore they advise grounding it at least for ac signals to reduce high-frequency crosstalk. Personally I'd just tie it directly to a good *clean* analogue ground.

-Richie,

Sent from my Xperia SP on O2

---- rsdio at audiobanshee.com wrote ----

>Did anyone answer this, Crystal?
>
>The substrate is typically connected to the source for 3-pin FETs, but this is BJT technology so we should disregard FET conventions.
>
>The data sheet description holds a clue: "Substrate biasing is not required for normal operation, though the substrate should be ac-grounded to optimize speed and minimize crosstalk."
>
>My interpretation of that is you should connect a capacitor to the substrate pins and ground the other end of the capacitor. No idea what value it should be.
>
>I'm surprised that there aren't example circuits in the data sheet, but perhaps there are application notes on the THAT Corp web site. The closest I could find is a mic preamplifier based on the THAT120A array, but it has a different pinout. They show pin 14 grounded, but its data sheet only mentions "grounded" not "ac-grounded," so I think they learned something before discontinuing the THAT120A.
>
>Have you made any progress since January? Keep us posted…
>
>Brian
>
>
>On Jan 2, 2015, at 3:44 PM, crystal <crystals at sonic.net> wrote:
>> Thanx Tim Ressel for the tip of using a THAT300 for a matched pair. Haven't tested my circuit out for tracking accuracy quite just yet but i bet it's a significant improvement. my question: what to do with the substrate pin?   -V, or perhaps ground?
>> 
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