[volt-nuts] Building a high resolution DAC

Attila Kinali attila at kinali.ch
Mon Aug 17 10:16:25 EDT 2015


On Mon, 17 Aug 2015 10:47:15 -0300
Daniel Mendes <dmendesf at gmail.com> wrote:


> If tasked with such mission i would pick a 7.5 digits meter, connect the

7 digits is just about 23/24bits. An on-board 24bit ADC can do that
as well (with carefull design, of course)
 
> DAC to it, connect both to a computer, excite every code of the DAC and 
> log the output from the meter. 

If possible, i don't want to use an external device for calibration.
Because an internal calibrator would allow to recalibrate the system
from time to time, without the need to run to a calibration lab.
The absolute calibration is not important (the DAC is part of a control
loop), but that DNL is low and stable in the range of hours to days.
Small drift is not a problem either (again, control loop) as long
as the DNL stays within limits.

> Then i would plot and figure a way to compress the table (linearize the output). 

Compression is easy: there are 4 PWM DACs, which are inherently linear.
Ie it's enough to express the slope of each of those PWM DACs by a number.

> Probably some temp 
> compensation would play here too... so it must be done with the dac in 
> different temperatures.

That's the next thing. But I will not worry about tempco until 
the fundamental problem is solved :-)

				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


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