Author Topic: Ultra Precision Reference LTZ1000  (Read 959918 times)

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Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #2925 on: April 20, 2020, 02:25:06 am »
I've swapped reference in experimental 3458A to explore the low-noise theories. It went with few trap pitfalls, but meter is running now and logging first data.
Click on image to see livestream recording (2.5 hours).

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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2926 on: April 20, 2020, 05:01:13 am »
Hello Illya,

I am missing some kind of air shield for the LTZ1000s to get "real low noise"

with best regards

Andreas
 

Offline maginnovision

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Re: Ultra Precision Reference LTZ1000
« Reply #2927 on: April 20, 2020, 03:13:27 pm »
https://snapshot.raintank.io/dashboard/snapshot/1bEqz2W4r5htRG56dgdJ7j2xl5qnrNEd

I set it up so that I take the first 100 readings and calculate a mean with that to calculate ppm values. That single mean value is logged once per reading. In this case one problem is plainly visible. While those 100 readings were taken the temperature was rising but as logging started the temperature started to drop. I'll have to try a running mean next. It does look better with both readings and temps but I still would like a second temp scale for the ambient temp. This is ok until I can see if that's possible.
 
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Offline nnills

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Re: Ultra Precision Reference LTZ1000
« Reply #2928 on: April 21, 2020, 08:32:43 am »
I must say it is a beautiful board you made there @TiN ! One question I have is why you spend your money on a ceramic Rogers material. Is it to reduce mechanical stress due to thermal expansion?
 

Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2929 on: April 26, 2020, 10:56:13 pm »
Ok I don't want to start major debate but I know many of you here have built multiples of different designs here.  I have my LTZ1000's, I now have 4 sets of precision ww resistors for the important ones (this was what took a while).  There are two PCB designs that can be ordered I found on github online.  Dr. Franks design and cellularmitosis little board.  Are there any other options I have?  I was thinking of trying a few so two isn't a lot of variations.  I'll have to order multiple PCB's anyhow from any FAB but that's not my concern because I'm sure any extras someone will want.  Does anyone have any others I can try?

BTW I watched the livestream video of you installing the 4 LTZ board TiN... pretty wild stuff.  I'm not going to try that.  Nice fix BTW.  I'll need a couple more 3458's before I try something like that I think :P

Thanks,

Bill
« Last Edit: April 26, 2020, 11:00:28 pm by notfaded1 »
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Offline SvanGool

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Re: Ultra Precision Reference LTZ1000
« Reply #2930 on: April 26, 2020, 11:54:08 pm »
Another one: TIN's singe LTZ1000 board https://oshpark.com/shared_projects/HfKcqjV3
Description here: https://xdevs.com/article/kx-ref
« Last Edit: April 26, 2020, 11:58:13 pm by SvanGool »
# Don't hurry, the past will wait. #
 
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #2931 on: April 29, 2020, 11:16:39 am »
@branadic

I was very interested to see your LNA  + AD2 vs. proper-DSA spectrum comparison.

Did you figure out what the shortcomings of the LNA + AD2 route were? It would be great to figure out a light way of getting good spectra instead of having to use a boat-anchor...

TIA, Alan
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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2932 on: April 29, 2020, 11:29:05 am »
Well, the biggest shortcoming is, that you need an LNA, right? There are LNAs for several ranges such as 0.1Hz - 10Hz or 10Hz - 100kHz. What it would need is an LNA for the complete range 100mHz to 100kHz instead. There are several solutions out there such as DC-1MHz or commercial gear like Stanford Research SR560, but they are expensive. Couldn't find a proper DIY solution for the 100mHz - 100kHz range yet.

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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #2933 on: April 29, 2020, 01:34:33 pm »
I was wondering whether you had any thoughts about the apparent lack of 1/f noise using that set-up - somehow down to the AD2 or the FFT settings?

Alan
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Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2934 on: April 29, 2020, 04:12:19 pm »
The LNA from Pipelie uses an AZ OP (or 2) and thus has essentially no 1/f noise, at least with a short. With a actual voltage there would be noise from the coupling cap if an electrolytic cap is used. I am not sure if the noise show for the battery is more from the battery or possibly from the coupling cap.

The downside of the usual AZ OPs is the limited bandwidth, especially if the first stage is used with a high gain. So 0.1 Hz to 100 kHz could become tricky. However 0.1 Hz to some 10 KHz may be realistic for such a setup without an intentional filter for the upper limit.

Similar one may be able to extend the lower limit a little below 0.1 Hz with a larger capacitor - however things are limited there. It is not just the cross over frequency, but also current noise (which gets visible as 1/f noise with a very larger resistance instead of a larger cap) and also dielectric absorption, so that electrolytic caps need really long settling before using it for slow processes.

For measuring down to really low frequencies the way to go would be using 2 reference and measuring the difference with a DC coupled amplifier, at least for the initial stage, possibly all the way with a DC compensation.
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2935 on: April 29, 2020, 05:13:51 pm »
Just for inspiration one could have a look at the schematic of SR560:

https://doc.xdevs.com/docs/Standford Research Systems/SR560/Stanford_Research_SR560.pdf

and build something similar to it, maybe with reduced functionality and more modern parts available such as MMBF5103 for the JFET, that was tested to have very low 1/f noise:

http://www.angelfire.com/az3/dimitri/images/AX_Dec2018_pp56-58.pdf

-branadic-
Metrology Meeting 2020 is canceled. Looking forward for MM2021
 
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Offline alanambrose

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Re: Ultra Precision Reference LTZ1000
« Reply #2936 on: May 02, 2020, 06:08:29 pm »
Interesting, following the links I see the NPD5564 pair in the original SR560 is now replaced with a LSK389B pair which is available from Linear (and some other channels) for about $6. Maybe this is drifting off the original subject though...
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Offline MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2937 on: May 03, 2020, 01:00:17 pm »
What it would need is an LNA for the complete range 100mHz to 100kHz instead. There are several solutions out there such as DC-1MHz or commercial gear like Stanford Research SR560, but they are expensive. Couldn't find a proper DIY solution for the 100mHz - 100kHz range yet.
I know it gets a bit off topic...

For 0.1Hz to 100kHz Andreas 0.1 to 10Hz LNA could be suitable with some modifications.
With e.g. another LT1037 in second stage and tweaking the lowpass filters to get the cutoff frequency to 100kHz it should do the job and is affordable - I did similar modification a while back for other application.

AN159 10Hz to 100kHz/1MHz (Layout files) might be an option.
Downside is its limitation with low cutoff at 10Hz (1/f corner ~100Hz), so one needs at least second LNA for 0.1 to 10Hz and combine them - not so easy and not so cheap.

If I got it right the SR560 has quite high noise figure at low impedances, it seems better suited for higher source impedances (maybe > 1k \$\Omega\$)
« Last Edit: May 03, 2020, 01:29:25 pm by MiDi »
 
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Offline Andreas

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Re: Ultra Precision Reference LTZ1000
« Reply #2938 on: May 03, 2020, 04:26:23 pm »
Hello,

I initially had a 2nd LT1037 on the output stage.
The result was massive oscillations.
(The reason for the LT1012 in the second stage).
So obviously you will have to do some additional
shielding between stages with 2 * LT1037.

with best regards

Andreas
 
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Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2939 on: May 08, 2020, 04:46:22 pm »
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill
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Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2940 on: May 09, 2020, 11:52:38 am »
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill

Where did you get them?
 
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Offline BU508A

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Re: Ultra Precision Reference LTZ1000
« Reply #2941 on: May 09, 2020, 12:02:32 pm »
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill

Where did you get them?

I assume, here:

https://www.ebay.com/itm/333584715972
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 
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Offline picburner

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Re: Ultra Precision Reference LTZ1000
« Reply #2942 on: May 09, 2020, 02:06:59 pm »
You are all really terrible.... I could not resist and I also took a couple :-DD
 
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Offline notfaded1

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Re: Ultra Precision Reference LTZ1000
« Reply #2943 on: May 11, 2020, 04:23:03 pm »
Yep that's where I bought them from @BU508A!  Didn't take long for you guys to buy them all up!   :-DD

I knew this was coming... complete units using new LTZ (I ordered one of these too to try):
https://www.ebay.com/itm/1-Customized-Ultra-Precision-Voltage-Reference-Board-LTZ1000ACH-LTZ1000CH/333594628743

I'm going to add some of my seasoned aged LTZ's to the other bare boards and see if I can improve on the aging time a little.  I've got some PWW to try instead as well.

Bill
« Last Edit: May 11, 2020, 04:42:31 pm by notfaded1 »
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Offline picburner

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Re: Ultra Precision Reference LTZ1000
« Reply #2944 on: May 11, 2020, 05:23:06 pm »
If it can be useful to someone, in the attachment, there is the schematic that the seller has used.
 
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Offline chuckb

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Re: Ultra Precision Reference LTZ1000
« Reply #2945 on: May 14, 2020, 10:53:10 pm »
Noopy provided links to his microscopic views of the LTZ1000 chip here -
https://www.richis-lab.de/REF03.htm

In one of the images you could see light coming from the circular Zener junction. That’s very cool. So, I had to explore that.

I made a little pcb with a tall socket for the LTZ1000. It also had selectable bias currents and operating temperature.

My friend Jim has a great collection of top-of-the-line microscopes. He coupled his new Nikon Z6 to the Nikon Metaphot Metallurgical microscope for the following images.
Thanks Jim!

As you would expect, as the current increased the light increased.
Changing the chip temperature from 50 deg C to 95 deg C at 4ma bias made no noticeable change in the light.

For one image Jim minimized all ambient light so we could capture the full 360 circle of light from the breakdown. Half of the light is hidden behind the trace on the top layer.

Offline CalMachine

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Re: Ultra Precision Reference LTZ1000
« Reply #2946 on: May 14, 2020, 11:03:51 pm »
For one image Jim minimized all ambient light so we could capture the full 360 circle of light from the breakdown. Half of the light is hidden behind the trace on the top layer.


:wtf:


 :scared:
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Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2947 on: May 14, 2020, 11:11:01 pm »
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

 

Online Magnificent Bastard

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Re: Ultra Precision Reference LTZ1000
« Reply #2948 on: May 15, 2020, 05:02:11 am »
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

Also, what might prove interesting is to hit the junction with a LASER-- and watch what happens with the 1/f noise and voltage output.  I've been wanting to do this for a long time, but it seems @chuckb beat me to it, and is pretty much ready to do this test!
 
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Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2949 on: May 15, 2020, 09:21:27 am »
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

I can also imagine the light may show some fluctuations. Changes are these may correlate with noise in the voltage.

I don't think this is a kind of junction break-down. The more likely mechanism is that the zener diode in the avalanche regime produces hot electrons and some of these can get to the surface oxide / interface. Relaxation of the electrons there can happen with light at some suitable states (similar to color centers). 

Normally the idea behind the buried zener is to avoid this effect by keeping the hot electron from reaching the surface. The second point is that they do less harm in the burried zener: this part can still work but is not so visible.
 
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