Re: [volt-nuts] Building a high resolution DAC
You cited one article by Steve Woodward -- have you read the other two?: http://www.edn.com/design/analog/4323340/Fast-settling-synchronous-PWMDAC-filter-has-almost-no-ripple http://www.edn.com/design/analog/4329365/Combine-two-8-bit-outputs-tomake-one-16-bit-DAC Jim Williams published a 3-part article in EDN that may be useful (there is some overlap with LT AN-86): m.eet.com/media/1146038/21715-74453.pdf m.eet.com/media/1146993/21816-426013.pdf m.eet.com/media/1142215/82758.pdf Best regards, Charles ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
Best to ask volt-nuts? On Mon, Aug 17, 2015 at 3:16 PM, Attila Kinali att...@kinali.ch 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 and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
On Mon, 17 Aug 2015 10:47:15 -0300 Daniel Mendes dmend...@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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
On Mon, 17 Aug 2015 15:16:05 +0200 Attila Kinali att...@kinali.ch 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
On Mon, 17 Aug 2015 15:28:10 +0200 Azelio Boriani azelio.bori...@gmail.com 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
Jim Williams' Linear Technology Application Note 86 is required reading here. http://www.linear.com/docs/4177 Regards, David Partridge ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
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 p...@phk.freebsd.dk 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
On Mon, 17 Aug 2015 17:04:25 +0200 Andreas Jahn andreas_-_j...@t-online.de 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 To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
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 p...@phk.freebsd.dk 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Building a high resolution DAC
At this level even barometric pressure changes con be a problem. On Mon, Aug 17, 2015 at 10:58 AM, Andreas Jahn andreas_-_j...@t-online.de 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 p...@phk.freebsd.dk 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 ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. -- *John Phillips* ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
