[sdiy] THAT300

Steve Lenham steve at bendentech.co.uk
Thu May 7 11:01:31 CEST 2015


Richie is right.

One of THAT Corp's USPs is their in-house, dielectrically-isolated fab 
process. Each transistor sits in a well of insulating oxide so, apart 
from a bit more capacitance, looks largely like a discrete transistor.

 From the same paragraph in the 300-series datasheet:

"Fabricated in a dielectrically isolated, complementary bipolar process, 
each transistor is electrically insulated from the others by a layer of 
insulating oxide (not the reverse-biased PN junctions
used in conventional arrays). As a result, they exhibit inter-device 
crosstalk and DC isolation similar to that of discrete transistors...
Substrate biasing is not required for normal operation, though the 
substrate should be ac-grounded to optimize speed and minimize crosstalk."

So yes, ground it.

Cheers,

Steve L.
Benden Sound Technology


On 06/05/2015 23:51, Richie Burnett wrote:
> "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.



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