DIY High Precision Voltage Reference/Standard?  - Page 1
Forum section: electronics / projects

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 06:23:22 pm
content: Thinking of making a voltage reference/standard (to 0.1mV precision; nothing crazy) to use for calibration of multimeters and other devices. I know that I'll need to use some sort of calibrator to actually calibrate my DIY reference (will ask a work colleague who has the equipment), power the device 24/7 (for temperature stability), a metal enclosure (to reduce interference), and power the device from a low-noise source (ex. batteries and/or low-noise linear regulator). I don't want to simply pay for a $100+ calibrated voltage standard, because what's the fun in that?It looks like the two common ways to go about this are:- Feeding a voltage reference with a linear regulator + a lot of bulk & high frequency capacitors, and simply measuring the output of the voltage reference- Similar as above, but use an op-amp (either digitally or controlled via potentiometer) to provide additional fine-tuning of the output voltage from the voltage referenceI'm thinking of powering the device from batteries, using low-PPM + high precision resistors, many ceramic caps of various values (ex. ranging from pF to uF), and using something like a MAX6070 or ADR01 voltage reference (or others, with a 5PPM/°C + 0.08% initial accurate).Ideas/feedback on the route I should take? Maybe I should go about using a specific subtype of voltage reference or OP-AMP (chopper?)?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 11, 2025, 06:31:53 pm
content: This should move to Metrology, you will get a lot of experience over there.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 06:41:14 pm
content: Quote from: PCB.Wiz on March 11, 2025, 06:31:53 pmHow can I move it? I don't see the option.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 11, 2025, 06:55:20 pm
content: A single voltage would only be a spot check for most meters. Which voltage is needed depends on the meter - some may want 10 V while others may want 1.9 V.The way how to scale the reference voltage also depends on the needed voltage. There are ready made 10 V ref. chips, while 1.9 V would be an odd value and hard to find. Depending on the use one may not need an exact round value, but only needs to know the actual voltage. So one may not need a way to trim the voltage.One may want more than just 1 voltage, to check at least 2 ranges.There is no need to overdo it with filtering and super low noise voltage regulators - most ref. chips are OK starting with a standrard voltage regulator.For just 0.1mV range accuracy there is no need to use chopper amplifiers, though with some care they are still an option.To allow for burn in, one would likely include the option to power from an external wall wart too, not just a battery.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 07:26:45 pm
content: Quote from: Kleinstein on March 11, 2025, 06:55:20 pmMany of my multimeters use trimpots to adjust the voltage readout, and aren't calibrated digitally. For the ones that are calibrated digitally, I could simply determine the voltage offset of the meter (using this DIY voltage reference) to get a fairly-accurate reading of the measured-voltage.Do you think either theMCP6V97TorMCP6V86UTwould be good choices of op-amp (as I already own quite a few of them, from a past project)? They do only support an input voltage of about 5.5v, but their input offset voltage is quite low at +- 25uV, low temperature drift, PSSR 110, and less than 1uV drift with age. To me, it seems like they'd be perfect to reach the 100uV goal.I'd absolutely love my DIY voltage reference/standard to be capable of producing 2.5v, 5v, 10v, and 30v, but with my knowledge level, it seems like it'd be incredibly difficult/unrealistic to design a circuit which can create the 30v/10v ranges, with my current level of knowledge. The 2.5v & 5v seem significantly more feasible.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 07:29:50 pm
content: I guess maybe to start, would either theMCP6V97TorMCP6V86UTop-amps, paired with a MAX6070 or ADR01 voltage reference, be accurate/stable enough so that I could create a voltage reference with a 0.1mV precision?

author: David Hess
author_rank: Super Contributor
timestamp: March 11, 2025, 07:34:22 pm
content: I asked a very similar question here:https://www.eevblog.com/forum/metrology/what-source-to-use-with-old-multimeter-calibration-if-i-have-nothing-else/I ended up buying aninexpensive 5 volt 0.01% referencebecause I did not have the facilities to calibrate something better.Quote from: LooseJunkHater on March 11, 2025, 06:23:22 pmEven medium precision operational amplifiers are lower drift and lower noise than any available reference, so there is no disadvantage to using them, but see below.QuoteLowest noise will require a buried zener reference like the LT1021 or the various buried zener super references.All of the precision operational amplifier types, chopper stabilized, bipolar, and JFET, are competitive, except for drift on JFET parts which cannot be nulled out like on bipolars. Chopper stabilized parts may have the advantage of not requiring offset adjustment.For instance I am building a set of buffered Harmon dividers using 49.9 kilohm 0.1% resistors to generate other calibration voltages from my calibrated 5 volt reference, which will require operational amplifiers for buffering or gain for higher voltages. I made a spread sheet adding up the various errors from input bias current, common mode rejection ratio, open loop gain, and input offset, and the bipolar LT1012 and the best chopper stabilized parts were all about the same performance for dividers made from 49.9 kilohm resistors. I ended up going with the chopper stabilized OPA189 because it was 1/3rd the cost and I would not have to include offset nulling. Other chopper stabilized operational amplifiers like the OPA182, ADA4522-1, and LTC2057 were practically as good. Choosing a different resistance for the Harmon dividers would have changed the operational amplifier selection.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 08:10:00 pm
content: Quote from: David Hess on March 11, 2025, 07:34:22 pmI was actually just looking into the LT1021 and REF102 and l noticed that some package variants have a "TRIM" option + wide input voltage range, which should make it easier to reach that 0.1mV precision goal. That is something I'm going to explore more, as it seems like it'll greatly simplify the circuit + decrease BOM.

author: bdunham7
author_rank: Super Contributor
timestamp: March 11, 2025, 08:41:47 pm
content: Quote from: LooseJunkHater on March 11, 2025, 06:23:22 pmFor a 10V reference that's 10ppm. That's the 8-month spec of the VREF-10 from voltagestandard.com. To get to that level any components you buy will have to be aged and characterized for tempco and drift in addition to calibration.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 11, 2025, 10:59:58 pm
content: Quote from: bdunham7 on March 11, 2025, 08:41:47 pmPart of the reason I want to aim for 0.1mV is because in my head, I actually want to calibrate my devices to within 1mV, and I'd imagine the calibration to "last longer" if done to 0.1mV.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 12, 2025, 12:01:17 am
content: Quote from: LooseJunkHater on March 11, 2025, 07:26:45 pmYou can get more precision by trading some time.If you work on 2:1 ratios, you then have equal resistors, and you can swap those with a DPDT switch and measure twice. Any 1mV ballpark offset will reverse in the two readings.It's how chopper stabilized opamps work, but they do it internally

author: dgminala
author_rank: Contributor
timestamp: March 12, 2025, 08:31:24 pm
content: Quote from: LooseJunkHater on March 11, 2025, 10:59:58 pmYou haven't told us what kind of meters that you have; 3.5 digits, 4.5 digits, etc., and how tight the specs are for them. That info would bring more specific recommendations for your voltage reference.I would suggest that you investigate one of the AD584 or LM399 prebuilt modules that are available on eBay and AliExpress for a few dollars, such as the eBay items # 286060018506 and 256808227216.Some of these modules are built and measured with the outputs labeled on the boards. I bought a couple each of those modules and found that the measured voltages were actualy VERY close to the values posted on the modules, within 10-20uV. The LM399 module will stay much more stable over time and temperature than the AD584, but either should be suitable for your needs (assuming that your meters are of the common 3.5 digit models).To get a voltage output higher than 10 volts, you might investigate the Texas Instruments Application Note AN-272 Op Amp Booster Designs. That will give you some food for thought to go to higher voltage outputs.Cheers,DaveM

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 12, 2025, 08:45:41 pm
content: Quote from: dgminala on March 12, 2025, 08:31:24 pmPrimarily various Aneng multimeters, a 40,000 count Holdpeak HP-770D, (hacked) Siglent SDS1104X, and various low-quality voltage/current panel meters. I know that the HoldPeak + Siglent was relatively well-calibrated digitally from factory, but cannot verify the same to be true for the Aneng and others.Quote from: dgminala on March 12, 2025, 08:31:24 pmI've considered that but I'm suspicious of those prebuilt modules using counterfeit or poor-quality voltage references, leading to significant drift over time and due to temperature variations. The entire modules are significantly cheaper than the voltage references on LCSC and other marketplaces.I'm aware that much ofmylow-cost equipment will have significant drift over time + temperature, but if I can at least produce and utilize a stable voltage reference, I can compare results over time.Quote from: dgminala on March 12, 2025, 08:31:24 pmHow long have you owned the LM399 + AD584 modules from Aliexpress/EBay? Did you find that they drifted noticeably due to thermal changes or time? That's my biggest concern, since I won't have easy-access to verify their results again in the future.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2025, 09:04:08 pm
content: The LM399 should be pretty stable for the 7 V output. The other voltages are via dividers / gain and can be effected from poor parts. From the pictures I have seen the PCBs and the resistors with these reference don't look that good. Last time I looked the LM399 modules got rare or expensive.The AD584 gives 4 somewhat stable voltages depending on a jumper. No other external parts should be involved and within the limitations of the chip the voltages should be OK. Ideally the voltages are measured with a good meter. The problem is that there are at least a few of the modules around that have fake values there. With a good meter one could check the ratio and this way has a good chance to detect fakes.The references used in the cheap modules are often recycled parts. So there is even a chance to get aged parts, but also possibly ESD damaged ones.

author: dgminala
author_rank: Contributor
timestamp: March 13, 2025, 07:38:31 pm
content: Quote from: LooseJunkHater on March 12, 2025, 08:45:41 pm

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: March 13, 2025, 09:04:38 pm
content: Quote from: dgminala on March 13, 2025, 07:38:31 pmHmm, I guess I'll look into the LM399 paired with an OP-amp, and avoid the LM584 + AD584. The LM399 refs aren't as cheap as the MAX6070 or ADR01 but the built-in heater is very nice. I'll also look more into the Github page that you linked. Thanks!Just in-case anyone comes across this thread in the future, I did come across the REF50** (20, 25, 30, 40, 45, 50) series which also offers the "TRIM" functionality, just like the LT1021 + ADR0*(1, 2, 3, 6).