[volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 14:15:53 +0000
"Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:

> >I have been pondering how to build a high resolution DAC over the weekend.
> 
> I've been looking at the same thing occationally, but every time I
> do the math I reach the conclusion that once you get past 18-20
> bits things get *really* icky.

Yes, I came to the same conclusion. Well 20bit at 5V span already
means an LSB of ~4uV, which is already close to the limit what
average opamps can do on noise performance. 24bit are 300nV
which means that anything using this voltage needs to do
some internal avaraging/integration...
 
> I don't see any realistic way to directly go beyond 24 bits which
> isn't based on time division rather than unobtainium calibrated
> artifacts (resistors/capacitors).  (Read HP's article about the
> kelvin-varley-divider they built from calibration-quality resistors...)
> 
> On the other hand, it's perfectly possible to get cheap-ish 32 bit
> ADCs, which do a pretty good job of not making you laugh.
>
> That points to a hybrid scheme.

You mean the AD7177-2? That seems to be quite hard to get by.
And those who have it, want around 50USD for it.

My goal was to stay below 30-40USD for the whole DAC if possible.
But yes.. it might not be possible.
 
> I have not tried this yet myself, but once I get down through my
> pile of more important projects, but I'll be happy to lend any
> assistance I can to the project.

Thanks for the offer! That would be really cool.
The whole project is already getting too big for me.
And new problems are popping up left and right...

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson