Author Topic: Ultra Precision Reference LTZ1000  (Read 962990 times)

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Offline Noopy

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Re: Ultra Precision Reference LTZ1000
« Reply #2975 on: June 01, 2020, 08:43:00 pm »
However I doubt that one would see light from the buried junction. This would be rather deep inside the silicon so only very little of that light can escape.

I´m not sure about this.
A view days ago I tried to use a big KD501 transistor as a photovoltaic cell.
(https://richis-lab.de/Bipolar02.htm)
Across the base-emitter-junction I got the same current as across the base-collector-junction. It seems there wasn´t significant light reduction.


The normal avalanche process  should also not produce light as the energy from the hot electron is used to generate new pairs. The normal recombination in silicon is without any light and if any it would be in the IR range (~ 1 µm). It would be only if a hot electron recombines or excites some defect in some way.

I agree with you that hot electrons generate new pairs but some of them will recombinate. Otherwise you will get a real breakdown with 0V and destruction of the junction. (I´m not absolutely sure about the last sentence but that would be my interpretation.)
The hot electrons can have a higher energy than you will see while normal current flow in the semiconductor. With "normal" current flow and "normal" recombination you don´t see any light. I agree with that. But in my view there is recombination of hot electrons.


I tried to take a "maximum tilted" picture but you can´t really say where the light is generated:




Hi all!

We talked about the avalanche breakdown light in the LTZ1000 and whether it is generated in the pn-junction. If so the light dots would stand for irregularities in the zener-junction.
Kleinstein suggested that the light dots occur in the upper layer at impurities outside the zener-junction.

Coincidentally I got a BUX22. What is the similarity between the LTZ1000 and the monster BUX22?
The BUX22 has some minor but visible defects in the base-emitter-junction:



And the glowing occurs first next to the defects not on top of the defects. In my view that means that the avalanche breakdown glowing occurs first at points where there are irregularities in the pn-junction (higher electrical field force).
q.e.d.


Whole story here:

https://richis-lab.de/Bipolar07.htm

 :popcorn:
« Last Edit: June 01, 2020, 08:45:32 pm by Noopy »
 
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Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2976 on: June 03, 2020, 07:30:16 am »
1. I don't think that this project would belong into this thread, please delete and continue with your other one, you already opened.
2. Concerning the LTZ1000, why do you want to reinvent the wheel, again?
Maybe you should define precisely your requirements concerning stability figures and noise immunity, before discussing cosmetic aspects like the form factor, and (again) over-engineering the components used. Better than A9 and compact designs are already available.

Frank
« Last Edit: June 03, 2020, 07:31:49 am by Dr. Frank »
 
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Online Cerebus

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Re: Ultra Precision Reference LTZ1000
« Reply #2977 on: June 03, 2020, 09:06:00 am »
Point 1 is well made, but how is re-using the A9 "reinventing the wheel", quite the opposite surely, and there's nothing cosmetic about form factors.

A form factor is a basic utilitarian part of a specification - there's a world of difference between a portable instrument and one intended for rack mounting. Form factor is probably point one on any outline specification for any product, so much so that the form factor implicitly or explicitly defines whole categories of products. Nobody wants a toilet that doesn't fit the implicit form factor, or a 50 cm mobile phone, or a 2.5 m long 'luxury' car.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2978 on: June 03, 2020, 07:07:35 pm »
1. I don't think that this project would belong into this thread, please delete and continue with your other one, you already opened.
2. Concerning the LTZ1000, why do you want to reinvent the wheel, again?
Maybe you should define precisely your requirements concerning stability figures and noise immunity, before discussing cosmetic aspects like the form factor, and (again) over-engineering the components used. Better than A9 and compact designs are already available.

Frank
Not the A9 from a 3458A, but an LTZ1000 reference in a A9 form factor, electrically compatible (better resistors, lower running temperature, better layout). What do you mean by reinventing the wheel? One can never have enough LTZ1000 projects or references. I haven't built one yet, why shouldn't I? I don't want to use an existing one, I don't like the form factor and the layout of the existing ones, simple as that, they are awesome piece of engineering don't get me wrong, I'm don't doubt the performance one bit, but don't fit my philosophy and needs. All the requirements are around the form factor, if compromises need to be made, they will be made to fit the form factor. Completely agree on the requirements, this is high level, not well thought yet. Considering VHD200 as overkill for an LTZ1000 project in my opinion is questionable, I certainly don't agree with it. We don't have to continue discussing, as this indeed does not fit the LTZ1000 thread, you are very welcome to jump on the other thread :)

Point 1 is well made, but how is re-using the A9 "reinventing the wheel", quite the opposite surely, and there's nothing cosmetic about form factors.

A form factor is a basic utilitarian part of a specification - there's a world of difference between a portable instrument and one intended for rack mounting. Form factor is probably point one on any outline specification for any product, so much so that the form factor implicitly or explicitly defines whole categories of products. Nobody wants a toilet that doesn't fit the implicit form factor, or a 50 cm mobile phone, or a 2.5 m long 'luxury' car.
I wholeheartedly agree with this, thanks a lot
« Last Edit: June 03, 2020, 07:50:16 pm by niner_007 »
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2979 on: June 18, 2020, 08:14:51 am »
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O
 

Online BU508A

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Re: Ultra Precision Reference LTZ1000
« Reply #2980 on: June 18, 2020, 08:34:28 am »
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Any RF sources nearby? Neonlights on the ceiling? If you have a spectrum analyzer, please check of any unwanted RF.
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2981 on: June 18, 2020, 08:40:05 am »
It is hard to tell how good the LTZ1000 reference is. With a DMM reading the DC voltage one sees a combination of the external and DMM internal reference. With the DMM7510 this is the LTFLU and LTZ1000 combined. Depending on the DMM setting one may also have some extra contributions from the DMM (the DMM7510 has relatively high noise at 100 PLC - seems to be some odd Keithley specific thing).

So some 1.8 µV peak to peak is about the value one would expect. Naturally the noise reading show quite some variations. A reliable noise reading takes quite some times, so more like the median over some 10 intervals with some 100-1000 readings.
 
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Online Echo88

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Re: Ultra Precision Reference LTZ1000
« Reply #2982 on: June 18, 2020, 09:00:39 am »
The DMM7510 isnt capable of displaying the actual LTZ-noise, for that youll need a 0.1-10Hz-LNA.
Id suggest to use batteries instead of a powersupply for such measurements.
Also the graph-function is limited by the 4LSB-noise, maybe it gives out more resolution via GPIB which can be used to produce a better/smoother diagram?
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2983 on: June 18, 2020, 09:38:33 am »
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Frankly speaking, your whole set-up, including the cables, is not looking good at all.

I also do not know, what's inside the aluminum sheet, or what your LTZ reference you're actually using.
Anyhow, you're always comparing the LTZ versus your DMM, so the noise is always a combination of both.
Your instrument should perform noise-wise nearly as good as a 3458A, the whole setup seems to have too few resolution, at least the rms noise for an LTZ is on the order of  200nVrms or 0.03ppm only.. maybe you also use Standard Deviation for measuring the noise.That 1.7µV pp is not optimal, but on the order of what to expect.

If you want to have stable measurements, you're really dealing with sub-ppm stability - what a properly built LTZ can deliver, you have first to set up everything in a stable way, not that Flying Dutchman approach..  these loosely hanging, un-shielded cables with inappropriate connection jacks are simply acting like antennas, and by themselves create a lot of other disturbances.

If your actual LTZ circuit (?) is built from the original LT schematic, then it's not inert at all against E.M.C., so the hint for SMPSUs from others, is the crucial point here.

Maybe you understand now, that 'better' components, layout, and so on are not the key points.. maybe you just do the basics first.

I will append a picture how the stability diagram will look like.


Frank
« Last Edit: June 18, 2020, 11:01:34 am by Dr. Frank »
 
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Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2984 on: June 18, 2020, 10:24:09 am »
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Any RF sources nearby? Neonlights on the ceiling? If you have a spectrum analyzer, please check of any unwanted RF.
Yes! The thing on the wall just next to it is a low energy Bluetooth device measuring temperature  |O
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2985 on: June 18, 2020, 10:26:23 am »
It is hard to tell how good the LTZ1000 reference is. With a DMM reading the DC voltage one sees a combination of the external and DMM internal reference. With the DMM7510 this is the LTFLU and LTZ1000 combined. Depending on the DMM setting one may also have some extra contributions from the DMM (the DMM7510 has relatively high noise at 100 PLC - seems to be some odd Keithley specific thing).

So some 1.8 µV peak to peak is about the value one would expect. Naturally the noise reading show quite some variations. A reliable noise reading takes quite some times, so more like the median over some 10 intervals with some 100-1000 readings.
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.
« Last Edit: June 18, 2020, 10:32:23 am by niner_007 »
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2986 on: June 18, 2020, 12:10:04 pm »
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.

That's a too elaborated approach, which will create new problems.
 
Parallel measurement with several DMMs is unnecessary, complicated, and will give big interference noise from one DMM to the other.
We had this failure recently, during our MM 2020 already, so do not repeat the same mistake.

Keep everything simple, i.e. one good DMM, make a clean setup, do the basic shielding, and then you're done.

Frank
https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382
« Last Edit: June 18, 2020, 12:12:06 pm by Dr. Frank »
 
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Offline ramon

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Re: Ultra Precision Reference LTZ1000
« Reply #2987 on: June 18, 2020, 04:28:44 pm »
Am I the only one that doesn't see any problem?

   niner_007  ->  ΔY = 1.73uVpp  (unkown interval)
   Dr. Frank  ->  ΔY = 1.33uVpp  (** 1 hour interval)

   (** assuming 7V absolute value, and +/- 0.95ppm Δ)

So results doesn't seem too bad considering power cables, and board and DMM placement.
 
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Offline exe

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Re: Ultra Precision Reference LTZ1000
« Reply #2988 on: June 18, 2020, 04:39:38 pm »
Looks like a very good result to me too, but I'm not a voltnut.
 

Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2989 on: June 18, 2020, 04:51:03 pm »
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.

That's a too elaborated approach, which will create new problems.
 
Parallel measurement with several DMMs is unnecessary, complicated, and will give big interference noise from one DMM to the other.
We had this failure recently, during our MM 2020 already, so do not repeat the same mistake.

Keep everything simple, i.e. one good DMM, make a clean setup, do the basic shielding, and then you're done.

Frank
https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382
Not paralleled, I was thinking of switched across 3 or more DMMs with a scanner
 

Offline MegaVolt

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Re: Ultra Precision Reference LTZ1000
« Reply #2990 on: June 18, 2020, 07:06:40 pm »
For comparison: I get 850 nV RMS for 1000 samples with NPLC = 5 for direct measurement of Fluke 732a vs DMM7510.
And just 300 nV RMS noise when measuring one Fluke 732a against another a range of 0.1 in the same conditions. And this is completely not caring about shielding using the most ordinary wires from a multimeter.

From this we can conclude that the direct measurement of a good reference voltage source directly against the DMM7510 does not make any sense. Because we only measure the noise of the multimeter :(
 
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Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2991 on: June 18, 2020, 09:03:20 pm »
Am I the only one that doesn't see any problem?

   niner_007  ->  ΔY = 1.73uVpp  (unkown interval)
   Dr. Frank  ->  ΔY = 1.33uVpp  (** 1 hour interval)

   (** assuming 7V absolute value, and +/- 0.95ppm Δ)

So results doesn't seem too bad considering power cables, and board and DMM placement.

Hi folks,
That discussion is quite interesting now.  :-+

The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.
The measurement from niner_007 shows 2µVpp or 700nvrms, if you look more carefully at the cursor position, which is definitely too high, and indicates additional noise.

Typical LTZs compared against a 3458A, or also against a 7510 (which has an LTFLU reference inside!?) only show 150..300nVrms.
A 732A should measure even lower.
Please have a look into the 'DMM noise' measurement campaign, we did a few years ago. You will get a good estimate of the noise figures of the different DMMs.
Maybe the 7510 is more noisy for other reasons, (I don't like the limitation to NPLC 5), I do not remember that precisely any more:
https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/


These values depend on the settings, the equipment and the environment, and then also on the quality of the LTZ / DUT and the reference inside the DMM.
So to get comparable results:

1. Averaging time of the DMM: use NPLC 100, or 1.6 .. 2 sec averaging/sampling time for one data point
2. Always use statistics: Take 16 datapoints of NPLC100, note average and StD.
The StD is also equivalent to the rms noise value, on this time scale.
With more and longer averaging data, especially the StD, will be biased by timely or temperature drift effects, or from other noise sources like Popcorn noise.
3. You may distinguish the different noise or (in-) stability effects described above by using Allan Deviation statistics
4. Digitization error/noise: For sub-ppm measurements, at least 0.1ppm resolution @ 10V is required, but the 7510 seems to have 0.5µV only
5. Use a DMM with an equivalently noisy internal reference, like another LTZ1000, or an LTFLU. The real noise figure of the DUT is then about 1/SQRT(2) of the StD
6. Avoid or mitigate external disturbance, like E.M.C. and temperature change, which will both falsify / contribute to the StD value.
7. For precise determination of the absolute value of the DUT, use low e.m.f. cables, and reverse the leads at the DUT to cancel these.

On our MM2020 meeting, we discussed this data evaluation deeply.
Many measurements on the different LTZ1000 circuits (~22EA) showed 500nVrms, or more StD. That was a clear indicator that something was wrong, and these measurements should have been discarded at once.
In the end we identified the root cause(s), so that we could reduce our disagreement of uncertainty between our reference groups from 2ppm to about 0.5ppm.

Scanning the DUT with different DMMs seems like a good idea, but the scanner itself will introduce a lot of e.m.f. errors / noise, or you invest $$$ in a nV scanner.
Notice again, that we're discussing sub-ppm absolute values also.
The other way round, i.e. scanning several LTZs with one DMM, also depends on the quality of the scanner.

Frank
« Last Edit: June 18, 2020, 11:17:01 pm by Dr. Frank »
 
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Online MiDi

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Re: Ultra Precision Reference LTZ1000
« Reply #2992 on: June 19, 2020, 04:51:33 am »
The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.

Usually the rough conversion from peak to peak noise to rms is by dividing by 6.
That would give ~200nVrms for LTZ1000.
Could you please explain the difference?

https://youtu.be/-KcODSYXiZA
 

Offline Dr. Frank

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Re: Ultra Precision Reference LTZ1000
« Reply #2993 on: June 19, 2020, 07:09:32 am »
The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.

Usually the rough conversion from peak to peak noise to rms is by dividing by 6.
That would give ~200nVrms for LTZ1000.
Could you please explain the difference?

https://youtu.be/-KcODSYXiZA

The conversion depends on the actual noise waveform, that's  missing in this video also.
If you have sinusoidal noise, instead of that Gaussian noise, then the rms value would be: Upp/(2*SQRT(2)).
For simplicity, I take this as an upper estimate, if a peak-peak value is given.
Btw.: Zener noise is mostly not Gaussian, that's why you can't filter it well.

I prefer the  direct StD measurement over p-p, because that quantity is better defined, or better established in error/stability calculus. DMMs mostly calculate this value.

Also, the formula for the StD is nearly the same as the rms calculation for a random waveform, so giving an estimate for the rms noise for a short observation time.
This will only be the case, if the mean value, i.e. the DC component is zero. That's the reason, why longer observation times will give wrong StD values concerning noise, as drifts will give a non-zero average.

Coming from frequency stability calculation, the Allan Deviation calculus is the best and most accepted method to measure and separate the different noise types  / stability figures.
peak-peak values are also not used there. In the DMM noise project, we had successfully established the Allan Deviation also for voltage noise characterization.

PS: This problem with different types of noise vs. conversion factors of rms <=> pp is briefly mentioned here:
https://www.analog.com/media/en/training-seminars/tutorials/MT-048.pdf

Frank
« Last Edit: June 19, 2020, 07:35:32 am by Dr. Frank »
 
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Online Kleinstein

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Re: Ultra Precision Reference LTZ1000
« Reply #2994 on: June 19, 2020, 07:24:34 am »
Measuring the RMS value usually gives less scattering values compared to the peak to peak numbers. For good peak to peak numbers it would take several test intervals (e.g. 100-1000 points each) and than take some mean.

There can still be some justification of the peak to peak value if one has a large contribution of popcorn (random telegraph) noise. In this case the simple approximate factor 6 does no longer apply.
For the actual use the worst case and thus the peak to peak value may be more relevant.
With more noise source (here at least the external reference and the meter internal reference) the noise gets more normal, so that one can better use RMS and the simple statistics.
 

Online BU508A

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Re: Ultra Precision Reference LTZ1000
« Reply #2995 on: June 19, 2020, 09:56:18 am »

Typical LTZs compared against a 3458A, or also against a 7510 (which has an LTFLU reference inside!?) only show 150..300nVrms.


Yes, the DMM7510 has a LTFLU inside.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2922618/#msg2922618
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Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2996 on: June 19, 2020, 10:37:21 pm »
Results seems to be about the same for me on the DMM7510, 100 sample averaging filter, and 15NPLC
 

Offline dr.diesel

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Re: Ultra Precision Reference LTZ1000
« Reply #2997 on: June 19, 2020, 11:07:57 pm »
15NPLC

In regards to the lowest noise region of the 7510, from the user manual:

 
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Offline niner_007

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Re: Ultra Precision Reference LTZ1000
« Reply #2998 on: June 20, 2020, 03:39:55 am »
Yeah, I mean to try that, I remember the discussion about the weird DMM7510 noise in the DMM noise thread, I have better meters, this one was the closest :)
« Last Edit: June 20, 2020, 08:40:23 am by niner_007 »
 

Offline Grandchuck

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Re: Ultra Precision Reference LTZ1000
« Reply #2999 on: June 20, 2020, 05:22:36 pm »
On our MM2020 meeting, we discussed this data evaluation deeply.
Many measurements on the different LTZ1000 circuits (~22EA) showed 500nVrms, or more StD. That was a clear indicator that something was wrong, and these measurements should have been discarded at once.
In the end we identified the root cause(s), so that we could reduce our disagreement of uncertainty between our reference groups from 2ppm to about 0.5ppm.

Frank
[/quote]

What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.
 


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