DC Voltage References Battle - Overview of market

[TiN]

Hi all,

Friend of mine asked me recently to check his DC voltage reference, cheap AD584KH-based module, and provide calibration if needed. I went on EEVBlog to check, if anyone already tested or reviewed reference he had, found bunch of threads, but not a single source with all data in one place. This brought me an idea, what if we summary all available boards from different people, and make overall spreadsheet with their specs/cost/performance level?

Yes, it sounds like "we have 14 standards, let's make one common standard. Now we have 15 standards", so feel free to blame me on it.
We have bunch of threads about LTZ1000, LM399-based designs, but I think they are time-consuming and overkill for someone who just want pick a ref to calibrate their gear, within given budget.

Summary

Photo	Module name	Type	Based solution	Output voltage	Accuracy	Tempco	Cost	Notes
	AD584KH Taobao	Zener IC, non-ovenized	Analog Devices AD584KH	2.5, 5.0, 7.5, 10.0 VDC	+/-500ppm?	+/-30ppm	15$	External power, low cost
	HP 3458A A9 board (STD)	Super-zener, ovenized	Linear LTZ1000A	7.2 direct VDC	2%	+/-8ppm	$100-700	Available from Keysight
	HP 3458A A9 board (002)	Super-zener, ovenized	Linear LTZ1000A	7.2 direct VDC	2%	+/-4ppm	$984	Available from Keysight
N/A	HP 3458A A9 board (HFL)	Super-zener, ovenized	Linear LTZ1000A	7.2 direct VDC	2%	+/-2ppm	$2195	Orderable from Keysight

Reviews

AD584KH quad-voltage reference - TiN's review - in works

[Vgkid]

I look forward to more additions, subscribed.

[BravoV]

Thanks, subbed. 

Side note, wonder why the MAX6350 is not oftenly discussed here in this forum. From the spec sheet, with TC of 1 ppm/C , initial accuracy 0.02% and 30ppm/1000hr longterm stability, not too shabby right ?

[Mr.B]

Bookmark.

Thanks for your effort TiN.

[crispy_tofu]

This is going to be helpful, also subbed 

[ez24]

This is going to be helpful, also subbed 

Crispy - are you going to offer Dave some stinky tofu when he delivers the meter?  I miss it.

To OP - do you mean components or completed circuit boards that people sell?  No mention of price range if this matters.

[TSL]

These little standards are handy...

http://www.voltagestandard.com/

I have one of their DMM check units that I'm very happy with.

[ez24]

These little standards are handy...

http://www.voltagestandard.com/

I have one of their DMM check units that I'm very happy with.

me too

[eas]

I have collected too many of these.

I have the plexi cased AD584KH reference from the same maker as the bare board you reviewed, TiN. I also have yet another bare PCB AD584LH reference, an AD588BQ board, an uncalibrated/untrimmed Geller, and a DMMCheck+

What I don't have is a traceably calibrated meter or a calibrated reference beyond the DMMCheck+ which only gives 5 digits.

[BravoV]

Complementing this thread, there is an excel file converted into PDF by Dave that contains all known voltage reference chips (heated and unheated) that is compiled by JBeale -> Voltage Reference Chips (2013)

[crispy_tofu]

This is going to be helpful, also subbed 

Crispy - are you going to offer Dave some stinky tofu when he delivers the meter?  I miss it.

Lol, I wish... the meter was delivered (thanks Dave!) but I was away at the time and my parents said no anyway 

[HighVoltage]

Great idea.
I have a few to contribute.

[ez24]

Great idea.
I have a few to contribute.

?  A few of what?

- tofu
- meters
- chips (IC or potato ?)
- something else

Right now I would like some stinky tofu

[tszaboo]

And then, there is this.

[ralphd]

Thanks, subbed. 

Side note, wonder why the MAX6350 is not oftenly discussed here in this forum. From the spec sheet, with TC of 1 ppm/C , initial accuracy 0.02% and 30ppm/1000hr longterm stability, not too shabby right ?

Or the 6126 with 20ppm/1000hr?
After some searching around on Aliexpress I found I can get them for $3.  So less than double the cost of a REF5050.  No tout like the ref5050 though, but I'm still thinking of ordering a couple.

[nctnico]

You can also buy PLC calibrators on Ebay. These have an adjustable voltage and current. The more expensive ones claim an accuracy of 0.01% (100ppm).

[Andreas]

Thanks, subbed. 

Side note, wonder why the MAX6350 is not oftenly discussed here in this forum. From the spec sheet, with TC of 1 ppm/C , initial accuracy 0.02% and 30ppm/1000hr longterm stability, not too shabby right ?

Or the 6126 with 20ppm/1000hr?
After some searching around on Aliexpress I found I can get them for $3.  So less than double the cost of a REF5050.  No tout like the ref5050 though, but I'm still thinking of ordering a couple.

Hello,

according to my own measurements the (typical) datasheet values have nothing to do with the real world.
The ageing numbers are only valid (if at all) for the first 1000 hours after production or first soldering.
(some datasheets specify the second 1000 hours to keep the number comparable to the usual 20-30 ppm/kHr).

A really good (buried zener) reference will settle after around 6-12 month to a ageing rate below 10ppm/year.
e.g. around 2 ppm/year at room temperature.

The MAX6350 has a low T.C. but my 2 samples have a constant ageing rate of 10ppm/year. (over 3 years).
Whereas other buried zeners (AD586LQ) go down to the 2 ppm/year after initial drift.
https://www.eevblog.com/forum/projects/newbie-precision-reference-calibrated-with-the-3478a-dinosaur/msg538036/#msg538036

The MAX6126 (and REF5050) is a bandgap reference. So even when specced with 20ppm/kHr it will be
outperformed by a buried zener reference.

The housing of the reference plays a large role in stability.
Metal can or ceramic hermetically packages give much more stability than a DIP8 housing.
A dip 8 housing gives up to factor 3 more stability against a SO-8. (found in a MAXIM datasheet).
The long term stability of the MSOP package is specced factor 5 worse than SO-8 for the MAX6126.
So size matters.

So my personal ranking for references is

hermetically sealed:
1. LTZ1000/LTZ1000A
2. LM399
3. AD587UQ/AD586LQ
(3.5 LT1027CCH/BCH: unobtanium)
4. LT1236AILS8

plastic:
5. AD586MNZ
6. LT1027CCN8 (low ageing but large humidity drift)
7. MAX6350CPA/MAX6250ACPA (low humidity but large ageing drift)

And after that all the other references.

with best regards

Andreas

[Alex Nikitin]

So my personal ranking for references is

Hi Andreas,

Do you have any experience/opinion on the ADR01/02BRZ and ADR3450ARJZ?

Cheers

Alex

[pelule]

So my personal ranking for references is

Hi Andreas,

Do you have any experience/opinion on the AD588BQ/AD588AQ?

http://www.analog.com/media/en/technical-documentation/data-sheets/AD588.pdf

BR
PeLuLe

[PA4TIM]

I build standards using a LM399, one with a LT1027B and 3 versions with 4x431 parallel. Those performed well. Also used a LT1021 -10. I builded those standards only because I wanted to build some to learn more about Vrefs. I have no real need for it because I have more standards like a Guildline standard cell cabinet with full history, a Fluke 731, 750, 760, 720, 332, 510, an ESI decavider and a Philips PM2480 standard. Besides those some Tektronix scope calibration stuff, time standards and passive standards (LCR)
I miss a temperature standard (but I repaired several from my customers so I can check my gear against those  )

How do you know the Vrefs are still correct. My LM399 drifted over 100 uV the first six months, powered 24/7 connected permanent to a 7,5 digit meter the first months.  Short time drift was influenced most by relative humidity in my lab.

[Andreas]

Do you have any experience/opinion on the ADR01/02BRZ and ADR3450ARJZ?

Hello,

the only test in this range (XFET) was (only 1 new sample) ADR4550 (violett = ADC18)
against two (aged) LT1027 in plastic DIP (ADC4 + ADC8)
and one (aged) AD586LQ (ADC13) in CERDIP
All measuring a LTZ1000A with a precision 2:1 divider (LTC1043).

I think it gets clear why I did not try a 2nd sample.
nearly 100 ppm drift over 300 days and not calming down to a sub 10ppm level.

Do you have any experience/opinion on the AD588BQ/AD588AQ?

no experience.
Opinion: should behave similar to AD586LQ/AD587UQ

With best regards

Andreas

[eas]

Do you have any experience/opinion on the AD588BQ/AD588AQ?

no experience.
Opinion: should behave similar to AD586LQ/AD587UQ
Andreas

I have a cheap Chinese board with an AD588BQ as well as some cheap bare chips that are either NOS, or pulls from sockets in old equipment. I have a week or two of data on the board, but haven't done anything with it. Not super useful either, given that I didn't have a temperature record for the period.  I have an AD +-15V PSU module that I plan to use to do a long term test the bare ICs.

One intriguing thing about the AD588 is that it has a couple of uncommitted low-dift, low-offset buffer amplifiers that can be used for kelvin sense of the output, making a precision current source (10mA, max), or...

[pelule]

I have a cheap Chinese board with an AD588BQ as well as some cheap bare chips that are either NOS, or pulls from sockets in old equipment. I have a week or two of data on the board, but haven't done anything with it. Not super useful either, given that I didn't have a temperature record for the period.  I have an AD +-15V PSU module that I plan to use to do a long term test the bare ICs.

I assume it is one of these offers from China, I have looked to also:
http://www.ebay.de/itm/252001708799?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.de/itm/251943908859?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
I have daubt, this are really BQ version, as just the chip cost > 22 USD in higher volumes. Just assume this are "refreshed" JQ or AQ types.

[pelule]

Code: [Select]

http://www.ebay.de/itm/252001708799?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.de/itm/251943908859?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
I have daubt, this are really BQ version, as just the chip cost > 22 USD in higher volumes. Just assume this are "refreshed" JQ or AQ types.
EDIT: forgot to tell, it is offered for US $14,92 including shipment.
I despite my daubts I have ordered, I have the original BQ and this offer is cheaper, than routing/ordering your own PCB. I don't care regarding the mounted chips. If this are real BQs great.
I plan to mount that board into a temp. controlled chamber 35°C (+/- 0.01°K) and to do long term drift measures. Plan to post that results than.

[Gyro]

I have an AD588BQ that I've only played with fairly briefly so far. Having the on-chip opamps for Kelvin sensing etc is very useful. The only downside is that it all adds to the device dissipation (needing +/- 15V supply) and is compounded by any loading. The increased temperature rise exaggerates it's TC, although of course the temperature will stabilize at some point if the load is constant.

Blessed are those lucky enough to have bought one of Joe Geller's AD587LQ based SVR-T while he was still producing them.

EDIT: Just had an idea - I wonder if one of the opamps could used to implement a simple on-die oven