Author Topic: Ultra Precision Reference LTZ1000  (Read 854075 times)

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Offline dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2700 on: August 29, 2019, 09:31:34 pm »
Zlymex showed a table of voltage reference specs, where the 732B had 0.06 ppm noise as compared to the 732A with 0.1 ppm noise.
https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849
When you start from the 732A Allan deviations and calculate 40 nV * 0.6 then you roughly get the numbers of the paper.

In Zlymex's table the 732B is listed as "LTFLU-1" while in the paper they say "five 732B instruments fitted with Motorola reference/amplifiers". Does this mean the noise difference is not attributable to the references M or L? Somehow i don't get it.

Regards, Dieter
 

Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2701 on: August 29, 2019, 09:46:59 pm »
If a lot of the reference noise is white noise...   would it not be reduced by using a filter of some kind on the reference?
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2702 on: August 30, 2019, 06:34:29 am »
Zlymex showed a table of voltage reference specs, where the 732B had 0.06 ppm noise as compared to the 732A with 0.1 ppm noise.
https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849
When you start from the 732A Allan deviations and calculate 40 nV * 0.6 then you roughly get the numbers of the paper.

In Zlymex's table the 732B is listed as "LTFLU-1" while in the paper they say "five 732B instruments fitted with Motorola reference/amplifiers". Does this mean the noise difference is not attributable to the references M or L? Somehow i don't get it.

Regards, Dieter

AFAIK there are older 732B with Motorola Ref. and newer 732B with LTFLU. Its also possible there was a missprinp and the Motorola units were actually 732A units.
The SZA263 is long obsolete - likely the reason Fluke got the LTFLU as a replacement.
Noise is not the primary concern, it is more about the long term drift.

Noise filtering  is tricky, as at the very low level capacitor leakage, DA and temperature effects can cause more trouble than good at the very low frequencies. In many uses a DMM or similar would be used that does low pass filtering anyway. In many cases one would case about noise at some .01-.1 Hz  Though even if only white noise, filtering would be tricky, with huge caps (100s of µF of polypropylene (better PTFE) caps).
 
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Offline truser

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Re: Ultra Precision Reference LTZ1000
« Reply #2703 on: September 09, 2019, 11:59:37 am »
Bright thoughts to all!

Have the technology stopped improving over the past 20+ years or did something more accurate than the great-grandfather LTZ1000 (which have already been discontinued (for unknown reasons) from production) or so?

And...

Maybe someone will advise modern amplifiers (instead of LT1013) for a reference voltage source?
« Last Edit: September 09, 2019, 02:16:18 pm by truser »
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2704 on: September 09, 2019, 12:18:05 pm »
So far there is no newer replacement for the LTZ1000.

The LT1013 is still be best bet for the reference circuit. The LT1013 is well good enough and not too expensive  - no need for experiments there.
 

Online razvan784

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Re: Ultra Precision Reference LTZ1000
« Reply #2705 on: September 10, 2019, 10:04:00 am »
Where are you getting these rumors that the LTZ1000 is discontinued? :palm:
It clearly states "In Production" on the Analog Devices (which bought Linear Technology) website: https://www.analog.com/en/products/ltz1000.html
It may be old, but there is no real need for a replacement -- it's a very good design, with no obvious flaws, and it's a Zener after all, you can't really improve much on basic physical phenomena.
There are currently only two ultra-stable, ultra-low-noise references in integrated circuit form: the LTZ1000 and the LTFLU1, the latter being a custom design for Fluke (now also Keithley, they are under the same parent corporation) and not available for general sale. And as I said, there is really no need for more, there is not much one can improve about them.
You can do the math on how much the LT1013 offset voltage, bias current, open-loop gain and noise affect the reference voltage and you will probably find it's also adequate for the job.
 
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Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2706 on: September 10, 2019, 01:38:10 pm »
Is there any comparison on the performance of the LTZ1000 made in say 80ties/90ties and the latest silicon (especially after the merge LT+ADI)?
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #2707 on: September 10, 2019, 02:49:40 pm »
Is there any comparison on the performance of the LTZ1000 made in say 80ties/90ties and the latest silicon (especially after the merge LT+ADI)?

Well, more or less, but still ongoing: https://www.eevblog.com/forum/metrology/vintage-ltz1000-from-1986-nib-!/

-branadic-
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Offline splin

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Re: Ultra Precision Reference LTZ1000
« Reply #2708 on: September 10, 2019, 05:16:17 pm »
“O Metrologists," imo said, "the task I have designated you to perform is this. I want you to tell me" ......... "The Answer."

      The Answer?     The Answer to what?

"LTZ1000s!" urged imo. "The ultimate question of 80s/90s LTZ1000s compared to post merger ADI/LT LTZ1000s and everything!"


      <long pause>


      Tricky


"But can you do it?"


      <long pause>


      Yes.......... We can do it.

"There is an answer?" said imo with breathless excitement.

      Yes.   LTZ1000s and Everything. There is an answer. But, We'll have to think about it.

“How long?”.

      Seven and a half million minutes

"Seven and a half million minutes...!” imo cried. "That's nearly 14.27 years!

      Yes, We said we’d have to think about it, and take rather a lot of measurements didn’t we?
 

Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2709 on: September 10, 2019, 05:50:51 pm »
Hopefully there have been advances in manufacturing and materials over 30-40 years?
 

Offline Kjelt

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Re: Ultra Precision Reference LTZ1000
« Reply #2710 on: September 10, 2019, 05:56:22 pm »
Hopefully there have been advances in manufacturing and materials over 30-40 years?
Yes!................. but not on precision ultra low noise zenerdiodes  :o
 

Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2711 on: September 10, 2019, 08:35:44 pm »

Perhaps it is time to switch to AC?  :)
 

Offline dr.diesel

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Re: Ultra Precision Reference LTZ1000
« Reply #2712 on: September 10, 2019, 11:55:09 pm »
Hopefully there have been advances in manufacturing and materials over 30-40 years?
Yes!................. but not on precision ultra low noise zenerdiodes  :o

Perhaps no need/market for it?  Or maybe companies that require that performance have rolled their own, Intel maybe as an example?

Offline mrflibble

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Re: Ultra Precision Reference LTZ1000
« Reply #2713 on: September 11, 2019, 05:22:29 am »
      Yes.   LTZ1000s and Everything. There is an answer. But, We'll have to think about it.

“How long?”.

      Seven and a half million minutes

"Seven and a half million minutes...!” imo cried. "That's nearly 14.27 years!

      Yes, We said we’d have to think about it, and take rather a lot of measurements didn’t we?

I'm surprised ArthurDent hasn't made an appearance yet.  ;D
 

Offline dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2714 on: September 11, 2019, 06:20:30 am »
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.
« Last Edit: September 11, 2019, 06:25:00 am by dietert1 »
 

Offline exe

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Re: Ultra Precision Reference LTZ1000
« Reply #2715 on: September 11, 2019, 06:31:59 am »
What about this circuit? (values on the schematic are arbitrary).


I saw it in AoE. The idea is upper capacitor has zero DC voltage accross it, so leakage doesn't matter. As a result, you can use  even electrolytic cap (so it is claimed).
 

Offline dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2716 on: September 11, 2019, 07:00:02 am »
No, you want the capacitor to serve as a reference during the filter time constant. Sorry, but i guess the dirt effects will be much worse with electrolytic caps. Probably you won't even reach a time constant of 35 minutes due to self discharge.
Now i remember we have some gold supercaps that i could try as well. But then the problem will be charge balancing to reach 10 V. As Kleinstein wrote, it's not something simple.

Regards, Dieter
 

Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2717 on: September 11, 2019, 12:33:07 pm »
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.


Interesting experiment.

You could also compensate the 70pA DMM current with some kind of current source, to balance things out.   The enormous time constant would likely "eat" any noise produced by the current source.
 

Offline 3roomlab

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Re: Ultra Precision Reference LTZ1000
« Reply #2718 on: September 11, 2019, 03:00:59 pm »
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.

in some older posting by mr blackdog, he did a guarded capacitor, ie capacitor sitting on a guard voltage which sits on another capacitor to gnd. the guard rail provides all the leakage the gnded capacitor needs, while the AC goes thru 2 capacitors to ground, the precision rail is suppose to see zero leakage to the guard rail because the potential is nearly the same.
it is complex, but it looks like you can make as big a filter as you want as long as you can wait for the charge up.
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 

Offline dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2719 on: September 11, 2019, 03:17:02 pm »
Probably this is the circuit exe showed above with two capacitors, the lower one meant to be the helper (guard). Still there is one critical capacitor that needs to have reference quality up to a certain time scale. It is the one which holds the main voltage and the other one is more or less decoration, like the electrical drive in a hybrid SUV. Maybe i am wrong, but somebody needs to show the numbers.

Regards, Dieter
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2720 on: September 11, 2019, 03:40:17 pm »
Leakage is just one problem with a low pass filter. Another is dielectric absorption, that may requires hours to weeks (with electrolytic caps) for settling.  Capacitors also react to temperature changes and possibly also air pressure changes, which can add low frequency noise. Instead of using two $44 capacitors, I would prefer a second reference chip.

It also depends a lot in how the reference is used. Most DMMs act as a low pass filter. Filtering would in this case not help very much (it still can with some DMMs).

The 2 capacitor circuit helps against leakage, but only to a limited extend against dielectric absorption and one needs 2 caps of twice the size.
 

Offline imo

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Re: Ultra Precision Reference LTZ1000
« Reply #2721 on: September 11, 2019, 04:21:07 pm »
Fyi - I've seen somewhere Mickle(T) did a measurement of the current coming out of the DMM's inputs (tens pA till nA as a short pulses pos/neg during AZ etc., about 10 DMMs, as I can remember). Thus the direct measurement of the voltage at the capacitor might be somehow influenced by that current..
PS: re above 2 caps filter - do the electrolytic (and tantalum) capacitors need a "minimum polarization voltage" in order to work properly??
« Last Edit: September 11, 2019, 04:36:13 pm by imo »
 

Offline dietert1

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Re: Ultra Precision Reference LTZ1000
« Reply #2722 on: September 11, 2019, 05:02:04 pm »
Yes, somebody should write a clear statement that building analog storage devices with time constants of minutes or hours in 2019 is complete retro. Let the DVM run, take averages and use those numbers. For example i plotted the Allan deviation of my AD4522 preamplifier and found that it has a broad minimum of 3 nV at about 30 to 60 seconds. Nobody would do this exercise in the analog domain.

Regards, Dieter
 
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Offline SilverSolder

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Re: Ultra Precision Reference LTZ1000
« Reply #2723 on: September 12, 2019, 01:02:43 pm »
Of course analog filters with long time constants are retro - but they are still cool!
 

Offline TiN

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Re: Ultra Precision Reference LTZ1000
« Reply #2724 on: September 17, 2019, 02:42:33 am »
Wonder what that might be...



6-layers of ceramic substrate...
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