Re: [volt-nuts] Building a high resolution DAC

[Charles Steinmetz]

You cited one article by Steve Woodward -- have you read the other two?:





Jim Williams published a 3-part article in EDN that may be useful 
(there is some overlap with LT AN-86):







Best regards,

Charles

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Re: [volt-nuts] Building a high resolution DAC

[Brooke Clarke]

Hi:

I haven't been following this thread but see it's about making a DAC with a lot 
of bits.
While researching a Quantec GPS receiver I discovered a patent that for a 4 bit DAC to be used to drive a precision 
oscillator.

http://www.prc68.com/I/Q5200.shtml#Patent
It depends on using the carry out from an NCO that has a 48 bit input word.

PS HP/Agilent has some instruments with very high quality programmable DC sources such as the 4352 VCO tester.  These 
have very low noise but I forget how many bits.


Mail_Attachment --
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
Andreas Jahn wrote:

Hello,

its not only the plastic (epoxy) package.
Its also the epoxy PCB which creates package stress to the die.
And I do not believe that any "slots" make it significantly better.
Thats why I use the AD586LQ; and soldering only one pin to the PCB.
(the others with thin VERO-wire).

With best regards

Andreas

Am 17.08.2015 um 18:46 schrieb Daniel Mendes:


Look at LT6655 datasheet, page 14, about long term drift of MS8 versus LS8 package. If others refferences are as bad 
regarding moisture then i think this may be a problem at this level of accuracy.


Daniel

Em 17/08/2015 13:29, Andreas Jahn escreveu:

Hello,

I would rather use a reference with lower tempco than the LT1021. (typical 
7ppm/K)
E.g. (selected) AD586LQ or MAX6350.
Or at least LT1236AILS8 with around 3ppm/K.
The self heating alone gives around 3 deg C temperature difference.

With best regards

Andreas

Am 17.08.2015 um 18:19 schrieb Attila Kinali:

On Mon, 17 Aug 2015 15:38:37 +
"Poul-Henning Kamp"  wrote:



You mean the AD7177-2? That seems to be quite hard to get by.

I was thinking of the TI part intended for seismic applications.

Hmm. The ADS1262 does indeed seem quite easily available.

My goal was to stay below 30-40USD for the whole DAC if possible.
But yes.. it might not be possible.

I don't think it is.  The necessary voltage reference will set you
back almost that much...

I thought about using the LT1021. I don't need the long term
stability of the LTZ1000 and the LT1021 is available for less than 10USD.

But from the discussion here, think i have to go back and see whether
i really need such an high resolution or whether 20bit wouldnt be already
enough. Then i could get away with a 20bit DAC like the DAC1220.

Thanks

Attila Kinali



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Re: [volt-nuts] Building a high resolution DAC

[John Phillips]

I would think the noise numbers would kill most of the bits past 24. DAC
noise is bad enough but do you have a 32 bit reference. To be real the
reference voltage into the DAC need stable to 1 part in 4,.294,967,296 or
just 0.004 ppm
How can you use bits 25 to 32?

Just something to consider in your design.
If you are using this as an attenuator then what is the noise level in the
input signal.



On Mon, Aug 17, 2015 at 9:04 AM, Attila Kinali  wrote:

> On Mon, 17 Aug 2015 17:04:25 +0200
> Andreas Jahn  wrote:
>
> > see my comments on the cirquit [1] here:
> > https://www.febo.com/pipermail/volt-nuts/2010-October/000537.html
> >
> > So it will get very hard to go below 1ppm linearity. (without a
> > exact/calibrated feedback loop).
> > Since the formula in the article is wrong you will need some overlapping
> > bits anyway.
>
> Yes, when i tried to understand the circuit, more and more question
> marks popped up, until I decided to use a different approach that
> does not involve black magic and misleading descriptions.
>
> I am kind of surprised that the charge injection of the MAX4053
> does not kill a lot of the performance. At least i don't see any
> way how it would cancel somewhere.
>
>
> 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
> ___
> volt-nuts mailing list -- volt-nuts@febo.com
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-- 

*John Phillips*
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Re: [volt-nuts] Building a high resolution DAC

[John Phillips]

At this level even barometric pressure changes con be a problem.

On Mon, Aug 17, 2015 at 10:58 AM, Andreas Jahn 
wrote:

> Hello,
>
> its not only the plastic (epoxy) package.
> Its also the epoxy PCB which creates package stress to the die.
> And I do not believe that any "slots" make it significantly better.
> Thats why I use the AD586LQ; and soldering only one pin to the PCB.
> (the others with thin VERO-wire).
>
> With best regards
>
> Andreas
>
>
> Am 17.08.2015 um 18:46 schrieb Daniel Mendes:
>
>>
>> Look at LT6655 datasheet, page 14, about long term drift of MS8 versus
>> LS8 package. If others refferences are as bad regarding moisture then i
>> think this may be a problem at this level of accuracy.
>>
>> Daniel
>>
>> Em 17/08/2015 13:29, Andreas Jahn escreveu:
>>
>>> Hello,
>>>
>>> I would rather use a reference with lower tempco than the LT1021.
>>> (typical 7ppm/K)
>>> E.g. (selected) AD586LQ or MAX6350.
>>> Or at least LT1236AILS8 with around 3ppm/K.
>>> The self heating alone gives around 3 deg C temperature difference.
>>>
>>> With best regards
>>>
>>> Andreas
>>>
>>> Am 17.08.2015 um 18:19 schrieb Attila Kinali:
>>>
 On Mon, 17 Aug 2015 15:38:37 +
 "Poul-Henning Kamp"  wrote:


 You mean the AD7177-2? That seems to be quite hard to get by.
>>
> I was thinking of the TI part intended for seismic applications.
>
 Hmm. The ADS1262 does indeed seem quite easily available.

> My goal was to stay below 30-40USD for the whole DAC if possible.
>> But yes.. it might not be possible.
>>
> I don't think it is.  The necessary voltage reference will set you
> back almost that much...
>
 I thought about using the LT1021. I don't need the long term
 stability of the LTZ1000 and the LT1021 is available for less than
 10USD.

 But from the discussion here, think i have to go back and see whether
 i really need such an high resolution or whether 20bit wouldnt be
 already
 enough. Then i could get away with a 20bit DAC like the DAC1220.

 Thanks

 Attila Kinali


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>>>
>>
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>>
>
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-- 

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Re: [volt-nuts] Building a high resolution DAC

[Andreas Jahn]

Hello,

its not only the plastic (epoxy) package.
Its also the epoxy PCB which creates package stress to the die.
And I do not believe that any "slots" make it significantly better.
Thats why I use the AD586LQ; and soldering only one pin to the PCB.
(the others with thin VERO-wire).

With best regards

Andreas

Am 17.08.2015 um 18:46 schrieb Daniel Mendes:


Look at LT6655 datasheet, page 14, about long term drift of MS8 versus 
LS8 package. If others refferences are as bad regarding moisture then 
i think this may be a problem at this level of accuracy.


Daniel

Em 17/08/2015 13:29, Andreas Jahn escreveu:

Hello,

I would rather use a reference with lower tempco than the LT1021. 
(typical 7ppm/K)

E.g. (selected) AD586LQ or MAX6350.
Or at least LT1236AILS8 with around 3ppm/K.
The self heating alone gives around 3 deg C temperature difference.

With best regards

Andreas

Am 17.08.2015 um 18:19 schrieb Attila Kinali:

On Mon, 17 Aug 2015 15:38:37 +
"Poul-Henning Kamp"  wrote:



You mean the AD7177-2? That seems to be quite hard to get by.

I was thinking of the TI part intended for seismic applications.

Hmm. The ADS1262 does indeed seem quite easily available.

My goal was to stay below 30-40USD for the whole DAC if possible.
But yes.. it might not be possible.

I don't think it is.  The necessary voltage reference will set you
back almost that much...

I thought about using the LT1021. I don't need the long term
stability of the LTZ1000 and the LT1021 is available for less than 
10USD.


But from the discussion here, think i have to go back and see whether
i really need such an high resolution or whether 20bit wouldnt be 
already

enough. Then i could get away with a 20bit DAC like the DAC1220.

Thanks

Attila Kinali



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Re: [volt-nuts] Building a high resolution DAC

[Dan Kemppainen]

Hi,

20 bits is ~1ppm resolution. 1ppm is pushing stability for most 
references, is it not? I would think that at 24bit or more the reference 
is more of an issue than the DAC itself. As I recall, sub PPM/C 
references already eat up your budget and then some! One would guess 
that as soon the fundamental question of how to build one is answered, 
the details would quickly stack up against you.


If the control loop is very slow (I'm making the assumption this would 
be used as oscillator steering EFC signal...), long term drift in the 
minutes to hours range would be important, and PPM/C becomes more 
critical than noise, as the higher frequency stuff could be filtered out.


A few PPM reference, some PPM resistors, circuit traces and 
temperature/humidity affecting the circuit board could add up VERY 
quickly.


Also, once I clear up a few projects here, I would be interested 
participating in such a project!



Dan




On 8/17/2015 10:29 AM, volt-nuts-requ...@febo.com wrote:

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

Attila Kinali

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Re: [volt-nuts] Building a high resolution DAC

[David C. Partridge]

Jim Williams' Linear Technology Application Note 86 is required reading
here.



Regards,
David Partridge 

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Re: [volt-nuts] Building a high resolution DAC

[Daniel Mendes]

Look at LT6655 datasheet, page 14, about long term drift of MS8 versus 
LS8 package. If others refferences are as bad regarding moisture then i 
think this may be a problem at this level of accuracy.


Daniel

Em 17/08/2015 13:29, Andreas Jahn escreveu:

Hello,

I would rather use a reference with lower tempco than the LT1021. 
(typical 7ppm/K)

E.g. (selected) AD586LQ or MAX6350.
Or at least LT1236AILS8 with around 3ppm/K.
The self heating alone gives around 3 deg C temperature difference.

With best regards

Andreas

Am 17.08.2015 um 18:19 schrieb Attila Kinali:

On Mon, 17 Aug 2015 15:38:37 +
"Poul-Henning Kamp"  wrote:



You mean the AD7177-2? That seems to be quite hard to get by.

I was thinking of the TI part intended for seismic applications.

Hmm. The ADS1262 does indeed seem quite easily available.

My goal was to stay below 30-40USD for the whole DAC if possible.
But yes.. it might not be possible.

I don't think it is.  The necessary voltage reference will set you
back almost that much...

I thought about using the LT1021. I don't need the long term
stability of the LTZ1000 and the LT1021 is available for less than 
10USD.


But from the discussion here, think i have to go back and see whether
i really need such an high resolution or whether 20bit wouldnt be 
already

enough. Then i could get away with a 20bit DAC like the DAC1220.

Thanks

Attila Kinali



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Re: [volt-nuts] Building a high resolution DAC

[Andreas Jahn]

Hello,

I would rather use a reference with lower tempco than the LT1021. 
(typical 7ppm/K)

E.g. (selected) AD586LQ or MAX6350.
Or at least LT1236AILS8 with around 3ppm/K.
The self heating alone gives around 3 deg C temperature difference.

With best regards

Andreas

Am 17.08.2015 um 18:19 schrieb Attila Kinali:

On Mon, 17 Aug 2015 15:38:37 +
"Poul-Henning Kamp"  wrote:



You mean the AD7177-2? That seems to be quite hard to get by.

I was thinking of the TI part intended for seismic applications.

Hmm. The ADS1262 does indeed seem quite easily available.
  

My goal was to stay below 30-40USD for the whole DAC if possible.
But yes.. it might not be possible.

I don't think it is.  The necessary voltage reference will set you
back almost that much...

I thought about using the LT1021. I don't need the long term
stability of the LTZ1000 and the LT1021 is available for less than 10USD.

But from the discussion here, think i have to go back and see whether
i really need such an high resolution or whether 20bit wouldnt be already
enough. Then i could get away with a 20bit DAC like the DAC1220.

Thanks

Attila Kinali



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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 15:38:37 +
"Poul-Henning Kamp"  wrote:


> >You mean the AD7177-2? That seems to be quite hard to get by.
> 
> I was thinking of the TI part intended for seismic applications.

Hmm. The ADS1262 does indeed seem quite easily available.
 
> >My goal was to stay below 30-40USD for the whole DAC if possible.
> >But yes.. it might not be possible.
> 
> I don't think it is.  The necessary voltage reference will set you
> back almost that much...

I thought about using the LT1021. I don't need the long term
stability of the LTZ1000 and the LT1021 is available for less than 10USD.

But from the discussion here, think i have to go back and see whether
i really need such an high resolution or whether 20bit wouldnt be already
enough. Then i could get away with a 20bit DAC like the DAC1220.

Thanks

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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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 17:04:25 +0200
Andreas Jahn  wrote:

> see my comments on the cirquit [1] here:
> https://www.febo.com/pipermail/volt-nuts/2010-October/000537.html
> 
> So it will get very hard to go below 1ppm linearity. (without a 
> exact/calibrated feedback loop).
> Since the formula in the article is wrong you will need some overlapping 
> bits anyway.

Yes, when i tried to understand the circuit, more and more question
marks popped up, until I decided to use a different approach that
does not involve black magic and misleading descriptions.

I am kind of surprised that the charge injection of the MAX4053
does not kill a lot of the performance. At least i don't see any
way how it would cancel somewhere.


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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Re: [volt-nuts] Building a high resolution DAC

[Poul-Henning Kamp]

In message <20150817162946.93e5cee64c9c8a820c6a0...@kinali.ch>, Attila Kinali w
rites:

>You mean the AD7177-2? That seems to be quite hard to get by.

I was thinking of the TI part intended for seismic applications.

>My goal was to stay below 30-40USD for the whole DAC if possible.
>But yes.. it might not be possible.

I don't think it is.  The necessary voltage reference will set you
back almost that much...


-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [volt-nuts] Building a high resolution DAC

[Andreas Jahn]

Hello,

see my comments on the cirquit [1] here:
https://www.febo.com/pipermail/volt-nuts/2010-October/000537.html

So it will get very hard to go below 1ppm linearity. (without a 
exact/calibrated feedback loop).
Since the formula in the article is wrong you will need some overlapping 
bits anyway.


With best regards

Andreas


Am 17.08.2015 um 15:16 schrieb Attila Kinali:

Hi,

I have been pondering how to build a high resolution DAC over the weekend.
Something like [1] but has the disadvantage of needing a pair of resistors
that have a 1:2^16 ratio. The 1M/15.4R is kind of unwieldy.
Fidling around a bit, I came to the conclusion that using an R-100R ladder
with 4 10bit PWM DACs would be a good solution. 100R and 10k resistors
are readily available in 0.1% 25ppm/°C (and actually quite cheap).
While the first stage gives 10bits, each additional stage gives
approximately another 7bits, resulting in a total of 29bits resolution.
The 3 remaining bits per stage can be used to linearize the whole
circuit.

Now this is where the problem starts. How do I measure the circuitry
to build a linearization table? The linearity error is dominated by
the first stage error which is in the order of 0.1% and thus 10bits.
It would be necessary to measure this to somewhere close to 29bits, but
the best DACs that are readily available are 24bit. Yes, there is the
possibility to build some ADC that could do 28bit, but I am not exactly
keen on building something aking an HP3458 (mostly to avoid the
embarrasment of failing at doing so).

So, the question is how would one calibrate something like this?
Or am I missing something fundamental here?


Thanks in advance

Attila Kinali

[1] "DC-accurate 32-bit DAC achieves 32-bit resolution",
by Stephen Woodward, 2008



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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 14:15:53 +
"Poul-Henning Kamp"  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
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Re: [volt-nuts] Building a high resolution DAC

[Poul-Henning Kamp]

In message <20150817151605.6b4150803df29771b9b95...@kinali.ch>, Attila Kinali w
rites:

>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.

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.

Something like 3 twelve-bit DACs cascaded with plenty of overlap,
sampled by a 32 bit ADC, and connected to a sample&hold.

Once the desired value is obtained, switch to sample mode.

As long as you only need slow incremental response from there, you can
leave the Sample&Hold sampling all the time.

Once you get to the end of the lowest DACs range, you need to switch
to Hold until you have your DAC(-lings) into a row again.

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.



-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 10:47:15 -0300
Daniel Mendes  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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Re: [volt-nuts] Building a high resolution DAC

[Daniel Mendes]

Em 17/08/2015 10:16, Attila Kinali escreveu:


So, the question is how would one calibrate something like this?
Or am I missing something fundamental here?



If tasked with such mission i would pick a 7.5 digits meter, connect the 
DAC to it, connect both to a computer, excite every code of the DAC and 
log the output from the meter. Then i would plot and figure a way to 
compress the table (linearize the output). Probably some temp 
compensation would play here too... so it must be done with the dac in 
different temperatures.


Daniel
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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 15:16:05 +0200
Attila Kinali  wrote:

> I have been pondering how to build a high resolution DAC over the weekend.
> Something like [1] but has the disadvantage of needing a pair of resistors
> that have a 1:2^16 ratio. The 1M/15.4R is kind of unwieldy.
> Fidling around a bit, I came to the conclusion that using an R-100R ladder
> with 4 10bit PWM DACs would be a good solution. 100R and 10k resistors
> are readily available in 0.1% 25ppm/°C (and actually quite cheap).
> While the first stage gives 10bits, each additional stage gives
> approximately another 7bits, resulting in a total of 29bits resolution.
> The 3 remaining bits per stage can be used to linearize the whole
> circuit.

Maybe a small clarification here:

The goal is to build a DAC with 26bit resolution and small DNL.
INL is not the critical value, but the output should be kind of stable.
But given how reality looks like, i would already be happy with 24bit and
would accept something >20bits as well. (For 20bit there are decent
chips at cheap prices available)

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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Re: [volt-nuts] Building a high resolution DAC

[Azelio Boriani]

Best to ask volt-nuts?

On Mon, Aug 17, 2015 at 3:16 PM, Attila Kinali  wrote:
> Hi,
>
> I have been pondering how to build a high resolution DAC over the weekend.
> Something like [1] but has the disadvantage of needing a pair of resistors
> that have a 1:2^16 ratio. The 1M/15.4R is kind of unwieldy.
> Fidling around a bit, I came to the conclusion that using an R-100R ladder
> with 4 10bit PWM DACs would be a good solution. 100R and 10k resistors
> are readily available in 0.1% 25ppm/°C (and actually quite cheap).
> While the first stage gives 10bits, each additional stage gives
> approximately another 7bits, resulting in a total of 29bits resolution.
> The 3 remaining bits per stage can be used to linearize the whole
> circuit.
>
> Now this is where the problem starts. How do I measure the circuitry
> to build a linearization table? The linearity error is dominated by
> the first stage error which is in the order of 0.1% and thus 10bits.
> It would be necessary to measure this to somewhere close to 29bits, but
> the best DACs that are readily available are 24bit. Yes, there is the
> possibility to build some ADC that could do 28bit, but I am not exactly
> keen on building something aking an HP3458 (mostly to avoid the
> embarrasment of failing at doing so).
>
> So, the question is how would one calibrate something like this?
> Or am I missing something fundamental here?
>
>
> Thanks in advance
>
> Attila Kinali
>
> [1] "DC-accurate 32-bit DAC achieves 32-bit resolution",
> by Stephen Woodward, 2008
>
> --
> 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
> ___
> volt-nuts mailing list -- volt-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
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Re: [volt-nuts] Building a high resolution DAC

[Attila Kinali]

On Mon, 17 Aug 2015 15:28:10 +0200
Azelio Boriani  wrote:

> Best to ask volt-nuts?

I thought this was volt-nuts? ;-)

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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[volt-nuts] Building a high resolution DAC

[Attila Kinali]

Hi,

I have been pondering how to build a high resolution DAC over the weekend.
Something like [1] but has the disadvantage of needing a pair of resistors
that have a 1:2^16 ratio. The 1M/15.4R is kind of unwieldy.
Fidling around a bit, I came to the conclusion that using an R-100R ladder
with 4 10bit PWM DACs would be a good solution. 100R and 10k resistors
are readily available in 0.1% 25ppm/°C (and actually quite cheap).
While the first stage gives 10bits, each additional stage gives
approximately another 7bits, resulting in a total of 29bits resolution.
The 3 remaining bits per stage can be used to linearize the whole
circuit.

Now this is where the problem starts. How do I measure the circuitry
to build a linearization table? The linearity error is dominated by
the first stage error which is in the order of 0.1% and thus 10bits.
It would be necessary to measure this to somewhere close to 29bits, but
the best DACs that are readily available are 24bit. Yes, there is the
possibility to build some ADC that could do 28bit, but I am not exactly
keen on building something aking an HP3458 (mostly to avoid the
embarrasment of failing at doing so).

So, the question is how would one calibrate something like this?
Or am I missing something fundamental here?


Thanks in advance

Attila Kinali

[1] "DC-accurate 32-bit DAC achieves 32-bit resolution",
by Stephen Woodward, 2008

-- 
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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