[volt-nuts] Some questions to zeners (1N823-1N829)
Andreas_-_Jahn at t-online.de
Mon Jan 28 17:47:56 EST 2013
Hello Warren and Volt Nuts:
for the first: from the experiences of Warren my project seems to be
Im working now since 2008 on my "project".
Eliminating step by step the drawbacks of stability.
And learning a lot of real and not ideal parts.
I changed from SMD references with large hysteresis and bad stability to
plastic DIP devices being about a factor 3 better than SMD.
Finally finding out that some buried zener devices have relative low
But air humidity was a large issue preventing stability below 10ppm over a
So finally I try to use devices in hermetically tight cases which
eliminates humidity if carefully decoupled from PCB stress.
So what is feasible with selected parts and a 3rd order temperature
compensation is shown in the attached picture. (ADC13_TC)
A AD586LJ device as reference within ADC#13 is measuring a heated LM399
reference via a 2:1 capacitive divider.
X-Axis is temperature normalized to 25 degrees celsius -10/+15 degrees
measured directly at the AD586 reference.
Y-Axis on the left is LM399 measurement value in mV (divided by 2).
The red line is the measurement value of the ADC. The blue line the
resulting correction with a 3rd order polynominal.
Y-Axis on the right side is together with the green line the resulting
deviation in uV after calculating out the tempco of the reference.
Deviation is about +/-2 uV referenced to 3.4V which gives below +/-1ppm
resulting tempco after correction.
Unfortunately the slope of the uncompensated TC is relative large (about
1.1ppm). Together with my temperature resolution of about
0.1K/step this will give a relative large temperature step noise of up to
0.6uV/step in the 5V-Range of the ADC.
But anyway ADC #13 was the first ADC which I can use for ageing
After a run in phase of nearly 1 year the ageing of ADC #13 stabilized.
Currently I compare ADC13 nearly every day with 3 heated references (1 LM399
= LM_2 and 2 LTZ1000A = LTZ_1/2).
The last half year the ageing is about 0.5 to 1.5 ppm for 6 months compared
to the heated references.
See picture ADC13_longterm:
X-Axis is day
Y-Axis left is drift in ppm with red = LM399#2, green = LTZ1000A #1, blue =
Y-axis right is temperature in degree celsius of the temperature sensor near
By the way: up to now I could not measure any effect which is related to
Ok my temperature step noise is still too high. And probably I am using the
wrong connectors in my tests:
cheap D-Sub connectors where a metal shield is equalizing the temperature of
2 relative close neighboured contacts.
With best regards
----- Original Message -----
From: "WarrenS" <warrensjmail-one at yahoo.com>
To: <volt-nuts at febo.com>
Sent: Sunday, January 27, 2013 11:23 PM
Subject: [volt-nuts] Some questions to zeners (1N823-1N829)
> 1st my two cents worth concerning comments of others that are being more
> practical than nutty.
> "it is not easy to achieve these specs",
> Too True,
> If you do not already know this, then I'd suggest you back off and do some
> major readjustment of your requirements.
> Assuming you already know it is not easy and why, then
> IMHO, what you want to make is doable with the right compromises, some of
> which being
> A little extra power.
> a lot of extra time
> a lot of test selecting
> some extra circuits or S/W
> "your expectations are not realistic "
> True, if you think it can be done from a data sheet and a few of off the
> shelf parts in a production device.
> Not true, if you want to go totally nuts and have the time to do it.
> "The thermoelectric effects causing error would swamp the performance"
> Could be true for some. If you do not already know enough to keep these
> effects well under <<0.1PPM then should find another starter project.
> "To keep everything below the 1 ppm/deg C range you would have to put the
> entire circuit in controlled temperature"
> Too true, But for these requirements, fortunately you do not have to keep
> *Everything* under 1 ppm/deg C
> ALL you have to do is to keep the sum total of Everything under 1ppm. Big
> And that is very easy to do, by a fact of ten plus if desired.
> "long term drift and noise will be intrinsic to the devices, and
> unpredictable except in a statistical sense."
> Half true,
> Using the *right device*, and a lot of time, noise can be low enough to be
> mostly insignificant
> and long term drift will follow a predicable slope.
> It ain't easy and it's going to take a lot of time. If you think
> otherwise, you need a new project..
> "provide near zero tempco at one temperature only"
> Answer too limited to be useful
> zero TCing a circuit, can provide no voltage difference at any two
> temperatures, (to the limit of the repeatability)
> Depending how flat you need it between these two temperatures, is the only
> Best to plan on having a second order TC method as well.
> A total max total deviation of 1ppm and a 0.1 PPM /deg is not too hard to
> "One of the best voltage standard Datron 4910AV (4x LTZ1000) have only 1
> ppm/year drift"
> OK, so that shows there is at least one way to do it, so it is not
> Now just need to find the best way for you to do it.
> "Don't bother with TC zeners"
> Not a bad idea, but Unfortunately Not a lot of other choices considering
> your requirements.
> The other choice you have (that you should consider if time is a big
> is to get some three terminal Fluke voltage references.
> If necessary by removing them from old test equipment such as Fluke 731
> Those have already been selected and aged, and you'd just then need to
> work on the long term drift compensation selection method.
> "There are lots of nice IC references available"
> True, and if you can live with data sheet specs, they are much better
> But hard if not impossible to find anything that will compare to 1/F pop
> corn noise, and long term stability
> "I doubt that any TCZ will match an LM399"
> True when considering a wider temperature range, and it sure makes things
> so a good suggestion if TC was your main problem.
> But TC need not be a problem, and most any good zener will outperform most
> any selected LM399 in low freq noise and stability.
> "so would have to be ovenized to get *best* performance".
> True of Any circuit when "best" TC is concerned, so not very relevant,
> The question is can it be made good enough without an oven?
> And the answer is defiantly yes with the right tempco circuit.
> And if you want it even better, can make a very low power mini-oven.
> Back to your email ******************
>> Do you have typical values over a 64-90 ?F range. Will it be above 1ppm/K
>> or below?
> I do not have any data over that Temp range in front of me.
> Over My room changes (about 1/2 that temp range), can keep the Total
> voltage error down to around 1PPM, (not just /deg)
> If it is an important consideration, I may try and see what happens over a
> wider range.
> For a backup plan, considering having an addition second order TC
> compensating method such as S/W.
> Overall compensating to 1ppm / C is no problem,
> which is Total change +- 7PPM over a +- 7 deg C range
> Ten times better is possible over narrow temp ranges like that.
> It is the hysteresis and stability that is going to be a limiting factor,
> and last I looked,
> The zeners I tested had no measurable Hysteresis over a much wider temp
> range than that.
>>>From your plot it would be 0.33ppm per 3 degrees in narrow range i.e. 0.1
>>>ppm per degree.
> Correct, but not a relevant measurement.
> ANY straight line TC as seen there can be zeroed out.
> That was just a pre-test plot to see if the part was low enough noise to
> do a more accurate Zero TC.
>> By the way: is it degrees Fahrenheit or degrees Celsius (= 3 Kelvin)?
> My world is mostly in F, and since I was not even plotting temp at the
> same time, pretty irrelevant for that data set.
>> If I understand you right then you would not use this device because it
>> behave other than the others?
> Your understaning is not correct, not even close. My comment applies to a
> preselection process of 1N82x parts.
> In the case you stated, your preselection process (assuming you have
> enough to pick from) would be to select all the parts that are less than
> say 1PPM, with maybe a 20% yield.
> If the yield is too low then make a second pass for parts that are say 2
> +-1 PPM,
> and in that case, then yes the "best" part would not go into that batch,
> because it will likely need a different compensation than the others.
>> On the other side it seems to be the device with the largest ageing rate
>> of the 5 pieces.
> likely too little data to be important, Just as likely random luck as
> anything important.
> Until after you do some pre-aging, (whatever that may mean for that part)
> I would not even bother looking at that data this early on in the
> selection process.
>> So I still hope that anyone has experiences with hysteresis of the
> Turn on after power down, and hysteresis, repeatable, etc altogether is
> under 1PPM.
> As part of my pre-test TC procedure, I hit them with cold spray to 0 C and
> heat them with a heat gun to ~50C, a few times,
> If they are not repeatable they are not used in further testing.
> I have a question about two of your requirements
> AJ> tempco below 1ppm/K
> AJ> hysteresis in the 10-40 degree range well below 1ppm
> This suggest to me that what you are really planning on making is
> something with an overall compensted TC that is well below a 1 ppm/K,
> otherwise your hysteresis requirement does not make a lot of sense to me.
> So if what you are really after is more like < 1 PPM total error over time
> and temp, all this extra trouble now makes a lot more sense.
> Now the disclaimer, I have no idea if any of the now available 1N825 or
> better parts work like I've described.
> It is VERY much a manufacture sensitive thing.
> Short term noise being the biggest rejecting thing I've seen in the past.
> 0.5 PPM (3uv steps) are not untypical for some batches.
> If someone that has enough of these parts from a single batch and
> manufacture to make it worth while testing them, and will make them
> available to others, then I'll test and report the results and compare
> them to what I have.
> There may be another less direct way to get where you want to go (You did
> not say where that was)
> Divide the task into two or more sections.
> As an example, One being the low power short term stable DVM device that
> works over a limited temperature.
> There would be no problem getting 0.1 PPM accuracy/repeatable for that
> and a second higher power device that is mostly off, and powered up Just
> long enough to calibrate the low power xfer DVM above.
> And if you can then include some sort of cal exchange program for the
> higher powered but less used device, this would make a very hard project
> into a relative easy project.
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