Author Topic: Building your own voltage reference - the JVR  (Read 133148 times)

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Offline bingo600

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Re: Building your own voltage reference - the JVR
« Reply #125 on: April 26, 2016, 05:34:43 pm »
Anyone have some suggestions for economical and stable resistors in the 5ppm to 15ppm range?
For through hole, TE Connectivity Neohm- YR1 series offer 15ppm tc, and are cheap.

Ask Edwin for a quote - https://www.eevblog.com/forum/profile/?u=96921

/Bingo
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #126 on: April 26, 2016, 07:24:46 pm »
Anyone have some suggestions for economical and stable resistors in the 5ppm to 15ppm range?
For through hole, TE Connectivity Neohm- YR1 series offer 15ppm tc, and are cheap.

Ask Edwin for a quote - https://www.eevblog.com/forum/profile/?u=96921

/Bingo

That is the best suggestion  :-+ . With his resistors and using a JFET in a metal case with high Vgs (like the 2N4391 in my current prototype) it should be possible to make a reference with less than 1ppm/C tempco in 5-6 degrees range and a very good long term stability (my sample has drifted less than 5ppm for last 3 months - at least that is the limit I can measure it against HP3458A Opt002 and Fluke 731B) .

Cheers

Alex
 

Offline amspire

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Re: Building your own voltage reference - the JVR
« Reply #127 on: April 26, 2016, 11:53:14 pm »
Alex, have you done any thermal hysteresis tests? I am really interested in that one. It seems to be the test that affects the IC's signifigantly. Say

room temp ->70degC -> 0 deg C (whatever your refrigerator freezer does) -> room temp.

If the JRV does not have hysteresis, it becomes very interesting.
 

Offline amspire

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Re: Building your own voltage reference - the JVR
« Reply #128 on: April 27, 2016, 12:18:28 am »
Anyone have some suggestions for economical and stable resistors in the 5ppm to 15ppm range?
For through hole, TE Connectivity Neohm- YR1 series offer 15ppm tc, and are cheap.
Mouser stock these - around about 25c a resistor. Not bad. The specs do not mention 1000hr drift, so that needs testing.

http://www.mouser.com/ds/2/418/NG_DS_1773265_A-722435.pdf

Not sure about the higher voltage zero-TC FETS, but the 1.2V MPF102 I tested (it was the one I had) would get 5ppm/C with a 15ppm/C resistor. I guess you could find the zero TC point of the resistor and FET combined and get a lower TC over a limited range. Get a combined tempco of 1ppm, and then put it in an oven with 0.1 degC stability and it should be a nice reference.
« Last Edit: April 27, 2016, 02:09:55 am by amspire »
 

Online Kleinstein

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Re: Building your own voltage reference - the JVR
« Reply #129 on: April 27, 2016, 01:35:56 pm »
The TC of the resistor might not be such a big problem, as one could find the point for combined zero TC. The trouble is that you need a different resistor value for each FET. So individual matching / adjustment is needed. So when a pot / digi-pot is used for adjustment two resistors are needed. Otherwise you may need odd individual values - e.g. specially made for the FET or combinations of 2 or more.

The more important point than TC  is stability of the resistor and possibly the FET also. If stable, even a high TC might be acceptable - though I would not go for a PT1000.
 

Offline Squantor

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Re: Building your own voltage reference - the JVR
« Reply #130 on: May 17, 2016, 09:51:38 am »
Hello All, I am a member of the tekscopes group and I read this interesting bit of information on finding the zero tempco point of a JFET with a curve tracer:

The 577 D1 also allows you to find the ideal bias point (zero temperature
coefficient) of a FET. You can do this with a 7CT1N and a storage 7000 scope
as well. Just display a set of curves and apply heat and/or cold to the case
of the FET. The curves above the ideal bias point will drift up (and get
stored as a smear). The curves below the ideal bias point will move down
(and also get stored as a smear). The ideal bias point curve will not move
so there will be no smear. It pops right out at you.

Original post here: https://groups.yahoo.com/neo/groups/TekScopes/conversations/messages/129217
It has a few nice curvetracer tricks.
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #131 on: August 02, 2016, 09:22:38 am »
Just a quick update, I've re-measured the JVR after 4 month with the same HP3458A opt 002 (ACAL DCV done in all cases just before measurements) and the result is about -4...-5ppm over that time at the same temperature (24C). As it is in the ballpark of the meter stability, I've checked also the JVR against my Fluke 731B at the same temperature and it shows about -3ppm drift and the Fluke's drift over the same period of time, measured on the HP3458A is about -1ppm at the same 24C. So it all sort of adds up nicely (whatever the real drift is in all three  ::) ). I might now do a hysteresis test to, say, +60C unpowered (we have an oven that runs at that temperature) and back to 24C.

Cheers

Alex
« Last Edit: August 02, 2016, 11:22:33 am by Alex Nikitin »
 

Offline CJay

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Re: Building your own voltage reference - the JVR
« Reply #132 on: August 02, 2016, 11:36:52 am »
Well, my 100 of J211 arrived from DigiKey and I've measured the cut-off voltage on the lot at 5V Vgd. Actually, a very consistent batch for JFETs, it looks like the processing did improve since 1980s. All hundred measured between 2.75V and 3.35V at ~3uA current (10M of Keithley 2015 on 100V range between the source and gate). My "experimental" U440 measures 4.6V in the same setup (and the zero tempco point is at ~3.74V, so the "theory" about 0.63 or 0.64V is not working  ;) ). One obvious bad point about plastic casing - there is some photo-sensitivity, so the device should not be exposed to light when used as a reference. Not much of a problem though. I am nearly finalised a complete reference circuit, which would take 12-24V supply and provide 10V output with up to 10mA current available and would contain only two FETs, an opamp and few resistors. Not temperature regulated - that would be the next step.

Cheers

Alex

Light sensitive?

now there's interesting, I wonder if it would be possible to build a 'photonic oven' to compensate for temperature drift by exposing it to varying intensity light....

Or I may just be nuts...
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #133 on: August 02, 2016, 11:55:03 am »
First results on the hysteresis (from 24C up to 60C for an hour, then back to 25C - in that hour the temperature in the lab gone up 1 degree) - about +1.5ppm and even that is likely to be  mostly a temperature change effect. That result is for the complete unit, including the 7 to 10V amplifier and buffers. The shift at ~54C was about -2mV or -200ppm, indicating the tempco of about -7ppm/C box. Near 25C the tempco is about 1ppm/C .

Cheers

Alex

P.S. - the voltage measurements graph is added - 1ppm per vertical division scale. While the JVR was in the oven, the Fluke 731B was connected and slowly drifted down with the lab temperature increase.
« Last Edit: August 02, 2016, 12:49:37 pm by Alex Nikitin »
 
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Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #134 on: August 02, 2016, 05:46:17 pm »
Here is the graph of the hysteresis after 60 min in a fridge (temperature of the unit went down to about 12C) . There was quite a bit of condensation on the unit what I've got it back to the lab. I left for home while the voltage was still rising so the complete data will be available only tomorrow. Here is what I have so far (the "shelf" at 9.999974 is again the Fluke connected in place of the JVR while it was in the fridge):



It looks like the voltage should be back within 2ppm at least.

Cheers

Alex
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #135 on: August 03, 2016, 09:20:26 am »
Here is the complete graph. It looks like between 12C and 60C I can not reliably detect the hysteresis - if it is there, it is below 2ppm.

Cheers

Alex
 

Offline Marco

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Re: Building your own voltage reference - the JVR
« Reply #136 on: August 03, 2016, 10:51:57 am »
Anyone have some suggestions for economical and stable resistors in the 5ppm to 15ppm range?

Susumu RG for less than 15 ppm and Stackpole RNCS for 15 ppm? Both passivated with an inorganic layer instead of the usual resin.
 

Offline montemcguire

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Re: Building your own voltage reference - the JVR
« Reply #137 on: August 03, 2016, 06:27:54 pm »
Agreed - the Susumu resistors are really nice, far better than typical NiCr resistors. They're also trimmed by laser through the glass layer, after it has been deposited, so there's a lot less mechanical strain left on the part to cause drift. The only issue is that they're tiny SMD chips, but they can be attached to larger thermal masses easily.

Edit: The RG series are nice, but the new URG series are even higher precision, along with a higher price.
« Last Edit: August 03, 2016, 06:30:24 pm by montemcguire »
 

Offline montemcguire

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Re: Building your own voltage reference - the JVR
« Reply #138 on: August 07, 2016, 05:00:13 pm »
The drawback to foil is when you're using the resistors with low frequency AC signals. The low TC of a foil resistor is done by bonding the foil to an engineered ceramic that has a complementary expansion coefficient. For DC, the current induced foil heating and the substrate will stabilize thermally, and the resulting TC is low. For very high frequencies, there's also no problem, since the waveform changes so quickly that the foil heating is constant over all parts of the waveform.

However, with low frequencies, the foil and the substrate will not heat uniformly over the entire waveform, and the foil can expand and contract differently at different parts of the waveform, causing the resistance to modulate with the signal voltage. What's worse is that the thermal time constants can cause the substrate to expand and contract out of phase with the foil, actually worsening the thermal effects of the signal current foil heating. This creates third harmonic distortion, and at just the wrong frequency, the effect is worse than simply using a 'normal' higher TC resistor that doesn't try to cancel its TC with an engineered ceramic substrate.

So, for audio or other LF AC uses where distortion is important, foil resistors can perform worse than traditional NiCr films like the Susumus, and can generate more distortion than the amplifiers around them. As far as I know, the Susumus have a low TC by tweaking the alloy and the processing, and not by using a trick substrate ceramic, so they'll have better LF distortion performance than a foil.
 
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Offline guenthert

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Re: Building your own voltage reference - the JVR
« Reply #139 on: August 15, 2016, 06:44:50 am »
I've seen this schematic some days ago in the LF355 datasheet, it made me think about you! Your idea is not new.

Thank you, I always thought that it was used before but couldn't find a confirmation!

 :-+

Cheers

Alex

P.S. - would be interesting to find if that circuit was used somewhere in practice!

P.P.S. - The 2N4118 has a very low drain current (around 100uA for near-zero tempco) - it should make it good for low power but fairly noisy as a reference. A higher current device would make it a very low noise option - much quieter than ~1ppm p-p LF noise of the LM399.

Not a practical application, but the idea (as far as I understand it) is also discussed here: http://www.analog.com/media/en/training-seminars/tutorials/MT-087.pdf
(p. 9). Which is not to say that it wouldn't be worthwhile to explore this further.
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #140 on: August 15, 2016, 04:14:36 pm »
That marketing document is OK, but it contains some inaccuracies that are most likely due the fact that ADI wants to sell you on the idea of an XFET reference.  Reader beware, and check your facts.  For example in figure 10, they show that an XFET reference is somehow "better" than a buried Zener reference for long term stability.  Sorry ADI, but this is just NOT TRUE.  I think that their XFET reference might be OK if you need low power, but I think they should be more honest.  This is not the first time ADI has made false assertions about it's voltage references.

It is an old paper (and not really relevant to the topic, as these XFET references use a "band-gap" type 2-FET structure). A single JFET reference would not have that good tempco over a wide temperature range, but can be adjusted for a near-zero tempco at a particular temperature and appears (providing a metal can device is used) very stable in time.

Cheers

Alex
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #141 on: November 14, 2016, 11:37:00 pm »
Another measurements before I take the JVR to the newly calibrated HP3458A. Taken with two Keithley 2015 and Keithley 617 as a thermometer (measuring the output of LM35D, 200mV = 20C, 10mV/degree, right scale). So far both JVR and Fluke 731B drifted less than 5ppm over the last year (even with all my attempts to measure a hysteresis). Interesting that the JVR has a low tempco between 22 and 26C

Cheers

Alex

« Last Edit: November 14, 2016, 11:40:40 pm by Alex Nikitin »
 

Offline TiN

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Re: Building your own voltage reference - the JVR
« Reply #142 on: November 15, 2016, 02:39:30 am »
It is tempco of 2015, -0.9ppm/K? It's very high out of spec for 731B alone. :)
EDIT: I was thinking about 732B, sorry.
« Last Edit: November 15, 2016, 02:42:29 am by TiN »
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Offline David Hess

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Re: Building your own voltage reference - the JVR
« Reply #143 on: November 15, 2016, 08:36:02 am »
That marketing document is OK, but it contains some inaccuracies that are most likely due the fact that ADI wants to sell you on the idea of an XFET reference.  Reader beware, and check your facts.  For example in figure 10, they show that an XFET reference is somehow "better" than a buried Zener reference for long term stability.  Sorry ADI, but this is just NOT TRUE.  I think that their XFET reference might be OK if you need low power, but I think they should be more honest.  This is not the first time ADI has made false assertions about it's voltage references.

Analog Devices has neatly solved this problem by buying Linear Technology.
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #144 on: November 15, 2016, 11:45:43 am »
Well, the result from the JVR measured by HP3458A at 25C lab temperature (after 1.5 hours in my backpack and 3 hours warm-up in the lab) is essentially the same as three and half months ago (see my posts from the 2nd/3rd of August) - 10.000055V with about 0.5 ppm variations. The unit was almost continously powered up all this time (except when it was transported from my home lab to my work lab and back).

Cheers

Alex
« Last Edit: November 15, 2016, 11:48:18 am by Alex Nikitin »
 

Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #145 on: June 08, 2017, 11:37:32 am »
As the HP3458A just came back from a repair and calibration at Keysight UK, I've brought the 10V JVR unit back to the lab and measured it after a good warm-up. Here is the result for 1 hour, at NPLC100 , combined with the similar one hour measurements at the same 25C temperature in August and December last year. I need to build few more of these and get some statistics ;) .

Cheers

Alex
« Last Edit: June 08, 2017, 11:50:59 am by Alex Nikitin »
 
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Offline TiN

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Re: Building your own voltage reference - the JVR
« Reply #146 on: June 08, 2017, 01:11:35 pm »
I wish I'd have backpack big enough for the 3458A :D
Quote
by HP3458A at 25C lab temperature (after 1.5 hours in my backpack and 3 hours warm-up in the lab)
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Online Alex NikitinTopic starter

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Re: Building your own voltage reference - the JVR
« Reply #147 on: June 08, 2017, 01:15:23 pm »
I wish I'd have backpack big enough for the 3458A :D
Quote
by HP3458A at 25C lab temperature (after 1.5 hours in my backpack and 3 hours warm-up in the lab)

I wish I'd have my own HP3458A. I would find a backpack large enough to put it in, no problem   ::) .

Cheers

Alex
 

Offline guenthert

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Re: Building your own voltage reference - the JVR
« Reply #148 on: June 20, 2017, 10:13:59 am »
I need to build few more of these and get some statistics ;) .
That looks very promising.  Build many more and sell them and thereby distribute the work of collecting statistics!
 

Offline Ash

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Re: Building your own voltage reference - the JVR
« Reply #149 on: June 20, 2017, 10:36:16 am »
Just wanted to mention that I'm planning on building a few of these as well. I have some of the parts, still waiting on others. I'm also in the middle of setting up my meters and fixing some scanners so I can automate measuring of everything.  :-DMM

Looking forward to it having some fun!  :popcorn:

Ash.
 


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