Resolution and INL problem in DAC AD5791 - Page 1
Forum section: electronics / projects

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 09:17:31 am
content: Dear all,I m facing a problem with the use of the ad5791 evaluation board.In fact, with this card I'm supposed to get an output voltage resolution of 1 LSB ( 20 µV). Instead of this, when I increment the the 20 bit word with 1 LSB, nothing happens at the output voltage. It is updated only with 3 increments ( 3LSB = 60 µV).On the other hand, the INL error is indicated in the AD5791 datasheet to be less than 1 LSB. Here again, in our experiment and using the evaluation board its value is greater than 3lsb (60 µV).Please Find attached the screen shot of the INL and the resolution steps we measured.Could you please give me some helps , It will be appreciated.Thank you in advance

author: trevwhite
author_rank: Frequent Contributor
timestamp: July 12, 2016, 09:24:42 am
content: Hi, can you describe your set up a bit more please. What equipment are you using for measurement, etc.

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 09:31:53 am
content: Hi,I used the AD5791 EVALUATION BOARD and I interface it with an FPGA card from National Instruments.For the data acquisition, I used the 3458A Agilent multimetre with Labview.Here is the configuration of " AD5791 EVALUATION BOARD ":Vrefp = 10V and Vrefn= -10V (I applied 5V to connector Vref).Vcc = 5VDGND = 0VVss= -15VVdd = +15VBest regards,

author: TiN
author_rank: Super Contributor
timestamp: July 12, 2016, 10:09:37 am
content: Issue with sending correct data/configuration in programming? Perhaps you can post example code you use to poke AD5791, if you running own code?

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 11:14:33 am
content: No, I can send/read data from the DAC correctly. But, I want to know if there is anyone who used the same DAC and if he got the same resolution described in the Data Sheet (20µV).

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 12:11:07 pm
content: I'm using this board together with AD SDP-B controller board and AD supplied program, and I have no problems to get 1ppm steps and ~1ppm INL .CheersAlex

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 12:26:24 pm
content: What's the configuration of the Control Register ?? What reference and supply levels were you using?Regards,joseph

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 12:32:11 pm
content: Quote from: joseph on July 12, 2016, 12:26:24 pm1) I don't know. I just run the AD program supplied with the kit. It is sufficient for my needs at the moment and I didn't dig any deeper so far.2) The reference is on-board LTZ1000 based, gives me +10 or +/-10V reference voltage. (with few corrections due to some schematics and layout errors on AD part), supplies are +5 and +/-15V .CheersAlex

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 12:42:32 pm
content: And what is the output voltage resolution in µV ?Do you have exactly a resolution of 20 µV (1 LSB) ?regards,joseph

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 12:45:45 pm
content: Quote from: joseph on July 12, 2016, 12:42:32 pmYes, for +/-10V reference. For +10V reference it is obviously 10uV.CheersAlexP.S. In my case it is actually about 21.5uV / 10.75uV (as the reference is about +/-10.75V, 1.5 time the output of the LTZ1000, that allows me to go over 10V and made my scaling amp stable enough with relatively cheap resistors).

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 01:24:19 pm
content: Here is what I've just measured near bipolar zero with 1LSB steps (using HP3458A). The top graph is 1LSB steps near zero, the bottom screenshot is for the full measured span from about -7.3mV to +6mV (650 steps)CheersAlex

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 02:48:17 pm
content: thanks for your clarification Alex Nikitin!!But, for the on-board LTZ1000 reference, it gives you both 10v (or 5 V) and +/-15V ??or there is another reference for the +-15V ?regards,joseph

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 03:00:16 pm
content: Quote from: joseph on July 12, 2016, 02:48:17 pmThe on-board reference would give you whatever you configure it to, within reason, by the scaling resistors in the buffer amplifier. I've configured it to produce +/- 1.5x LTZ1000 output voltage. On-board jumpers allow you to connect internal or external references in various configurations. The +5V and +/-15V supplies are external (right now from a lab bench supply).CheersAlex

author: joseph
author_rank: Newbie
timestamp: July 12, 2016, 03:20:18 pm
content: You apply1) +-10V to both connectors "VREFP" and "VREFN" from the reference LTZ10002) +5V to the connector VCC from an external supply3) +-15V to both connector VDD and VSS from an external supply alsoam I right ?because, for my case, I applyed only 5V (low noise supply) to the connector VREF which gererates +-10 to VREFP and VREFN connectors and I didn't get the resolution of 20µV :/regards,joseph

author: Alex Nikitin
author_rank: Super Contributor
timestamp: July 12, 2016, 05:41:15 pm
content: Quote from: joseph on July 12, 2016, 03:20:18 pmWhat you did is correct for the standard reference configuration, +/-10V is amplified from 5V input and you should get 20uV/LSB. Just check that you have the reference jumpers in correct positions. In your case it should be:LK8 = ALK9 = C (or B for +10V reference only)CheersAlex

author: joseph
author_rank: Newbie
timestamp: July 13, 2016, 07:52:44 am
content: Yes, I already configured the reference jumpers in these position:LK8 = ALK9 = CBut I want to know if I got that resolution of 60µV instead of 20µV because of the power supplies noise. That's why I asked you which power supply you used for every connector.regards,joseph

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 13, 2016, 10:11:17 am
content: Quote from: joseph on July 12, 2016, 09:17:31 amWhat exactly does this have to do with Test Instruments? This should have been posted in a more appropriate forum like 'Projects, Designs, and Technical Stuff'.@Mods: please move

author: joseph
author_rank: Newbie
timestamp: July 13, 2016, 10:22:06 am
content: @WuerstchenhundI'm only testing that board !!

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: July 13, 2016, 11:37:19 am
content: Quote from: joseph on July 13, 2016, 10:22:06 amThat's fine but this forum isn't for stuff that is tested, it's for instruments that are used to test stuff with. You know, voltmeters, scopes, signal generators, and such.The name of the forum is "Test Equipment" for a reason. And if for some reason this wasn't clear, a quick reading through the topics should have quickly shown you that your post if off-topic.For topics like this 'Projects, Designs, and Technical Stuff' is much more appropriate. Again, a quick look at what is posted in the various topics should have told you where your topic should go.Really, it's not rocket science.

author: Simon
author_rank: Unknown
timestamp: July 14, 2016, 05:45:26 am
content: then just report it and we will move as appropriateno need to go around bullying people.

author: branadic
author_rank: Super Contributor
timestamp: November 14, 2017, 08:23:29 pm
content: Interesting to note the articleHigh Precision Voltage Sourcefrom Oct. 2017. We can see AD5791 evalboard with some LTZ1000 board on top.-branadic-