Author Topic: LM399 based 10 V reference  (Read 209957 times)

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Offline babysitter

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Re: LM399 based 10 V reference
« Reply #275 on: December 12, 2014, 08:27:04 PM »
Offering my travelling LTZ for this kind of project !
I'm not a feature, I'm a bug! ARC DG3HDA
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #276 on: December 13, 2014, 07:28:11 AM »

Hello Andreas,

although the AD586 is quite mediocre concerning TC and ageing, your setup with TC compensation and comparison (frequent calibration?) against your LTZ1000As gives good stability / uncertainty for your ADC#13, I think.
.....

What do you think about that?

Frank


I am also interested how is switching done between different channels?

Hello Frank, Babysitter,

together we have 5+1 references that would give a nice calibration party in Franks lab.
Wouldnt it?

How about end of next week? Thursday/Friday?

By the way: for ADC13 I am doing onlydaily measurement of offset and subtract it usually from the measurement results.
Tempco correction coefficients have been calibrated only once after having built the device.
The only thing that I have done is recalibrating once the reference voltage at 25 deg after the initial drift phase.

@TiN:

I am using a simple battery supplied relay multiplexer with 7 ground referenced inputs and two independent outputs.
Every output can be either connected to ground or to one of the 7 inputs.
So its possible to measure input voltage or input voltage differences between 2 references.

The relays are bistable signal relays (TQ2 with bifurcated contacts) so there is no heating during normal operation.
Control is done by a isolated RS232 connection+a microprocessor.
The 9V block lasts for about one week of operation without recharging.

with best regards

Andreas


 

Offline wiss

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Re: LM399 based 10 V reference
« Reply #277 on: December 13, 2014, 10:10:22 PM »

What is needed, is a traveling LTZ standard, and a group of volt-nuts willing to do the comparison.

What do you think about that?

Frank

Where in BRD are you guys located? I have some vague memory of Frank in Frankfurt am Main?

I just built a few LM399-based ref-boards where the 10V seems to be with in 10 ppm, but the Zener-voltage should be as stable as the LM399 can be (using high-Z voltmeter).

Next Saturday I will go by car from Puttgarden to Zwickau..
 

Online Dr. Frank

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Re: LM399 based 10 V reference
« Reply #278 on: December 14, 2014, 01:38:58 AM »
Hello everybody!

That happening then would be called Traveling Standards & Poor Engineers, I think. ;D ;D

Well, I'm available next Friday evening and also on Saturday, so everybody is welcome.
Maybe we find a common target date, here.

Or send me a PM, when you'd like to show up.

Frank
 

Offline TiN

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Re: LM399 based 10 V reference
« Reply #279 on: December 14, 2014, 01:56:03 AM »
Thanks for details. I was thinking about making DAQ system to logging as well.
So far decided to stop with KI2002 + 2001-TCSCAN card (which i happen to snag long ago).

As for VREF party, I wish to participate as well. I think it's worth to create separate thread and make it bigger? :)
I am about to order PCB revision with fixes for my LTZ reference, and dual LM399 version with both direct and 10V/20V outputs.
I think i will have all hardware ready to go at new year. I could ship 2-3 boards each somewhere, and you guys have party and measure it, and return refs back after.
As commitment , I will send free bare boards as well.

On my side, here in Taipei, I can only measure stuff with calibrated K2001 (cal Feb/14 by local Tek official service) and K2400 (same time cal) and 2002 (cal in 2007).
Going to calibrate my gear again in few month, as already have set of VPG HZ resistors for Keithley calibration specs, but I would like to "import" proper voltage standard into my home first. I think 3 LTZ boards in hermetic box shipped over would serve this job well.
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Online Andreas

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Re: LM399 based 10 V reference
« Reply #280 on: January 05, 2015, 07:24:39 AM »
Day 365 of 2 LM399 ageing (see above)

With best regards

Andreas
 

Offline branadic

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Re: LM399 based 10 V reference
« Reply #281 on: January 05, 2015, 08:02:30 AM »
Well done, well recorded  :-+
Prema 5000 | Prema 5017 SC | Keithley 181 | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, HDO6054, Keysight 53230A and other goodies at work
 

Offline DLWarr

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Re: LM399 based 10 V reference
« Reply #282 on: January 06, 2015, 12:56:13 AM »
I am just starting to read this "LM399 based 10V Reference" Subject,,,, am on pg 7,, But am wondering what spice model anyone might be using for the zener.. Although I use Proteus,,, I don't see anything in LTSpice on the LM399.... You all have done such a good job describing the device's in's and outs... Never seen so much activity for a 4 terminal device... Any response on this will be most appreciated..
 

Offline rob77

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Re: LM399 based 10 V reference
« Reply #283 on: January 06, 2015, 01:03:51 AM »
I am just starting to read this "LM399 based 10V Reference" Subject,,,, am on pg 7,, But am wondering what spice model anyone might be using for the zener.. Although I use Proteus,,, I don't see anything in LTSpice on the LM399.... You all have done such a good job describing the device's in's and outs... Never seen so much activity for a 4 terminal device... Any response on this will be most appreciated..

it's just a resistive heating element a diode and a zener inside - you can simulate it using regular resistor, diode and zener... the reason why people using LM399 is the extraordinary stability of that buried zener (and you can't simulate that anyway...)
 

Offline MK

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Re: LM399 based 10 V reference
« Reply #284 on: January 06, 2015, 05:48:24 AM »
The simplified schematic for the circuit is provided in the National documentation, but for modelling the general behavior of the supporting circuitry then a simple existing zener in your package of choice is most likely close enough. Remember that the "Zener" in the 399 is an active circuit and that the noise does not go down for increasing current, so approx 1mA is enough drive, that is useful if you want it battery powered to reduce ground loop issues.
 

Offline DLWarr

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Re: LM399 based 10 V reference
« Reply #285 on: January 07, 2015, 02:16:21 AM »
Wonderful then,,,,, Any thoughts on using a the "Portable Calibrator" circuit WITH   " Walt Jung's, Analog Devices, Build An Ultra-Low-Noise Voltage Reference... Electronic Design 6/24/93"....  Of course substituting both op-amps with the LTC2057...  Like everyone in the world, I'm looking for low drift,, low noise...   all in a 3 terminal package...aaahhhhhhhh. Any thoughts will be appreciated, thanks...
 

Offline rf-design

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Re: LM399 based 10 V reference
« Reply #286 on: January 07, 2015, 03:36:54 AM »
I did not understand how the flicker or 1/f noise of the reference is measured. I could understand that a chopper amp could reduce the impact of the needed voltage amplification. But the amp could only amplify a voltage difference of two potentials or one potential to a ground reference point. But the reference is the DUT itself have an offset of 7V against the chopper amplifier. So there should be second reference which significant lower or well characterized flicker noise to counter the DUT reference voltage. The difference should also be smaller than the requested gain of the measurement.

So what kind of offset source is used?
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #287 on: January 07, 2015, 10:15:34 AM »
Wonderful then,,,,, Any thoughts on using a the "Portable Calibrator" circuit WITH   " Walt Jung's, Analog Devices, Build An Ultra-Low-Noise Voltage Reference... Electronic Design 6/24/93"....  Of course substituting both op-amps with the LTC2057...  Like everyone in the world, I'm looking for low drift,, low noise...   all in a 3 terminal package...aaahhhhhhhh. Any thoughts will be appreciated, thanks...

The EDN cirquit has a edge frequency of 1.6 Hz. (time constant 0.1 s).
So the filtering is only for wideband noise (> 10 Hz).

Since your integrator filters that noise already a extra filter in this frequency range is rather useless.
For precision measurements your integration times are usually minimum 2 seconds.

I did not understand how the flicker or 1/f noise of the reference is measured. I could understand that a chopper amp could reduce the impact of the needed voltage amplification. But the amp could only amplify a voltage difference of two potentials or one potential to a ground reference point. But the reference is the DUT itself have an offset of 7V against the chopper amplifier. So there should be second reference which significant lower or well characterized flicker noise to counter the DUT reference voltage. The difference should also be smaller than the requested gain of the measurement.

So what kind of offset source is used?

I use a large (3200 uF) electrolytic capacitor selected for low leakage current.
Noise floor is <0.2 uV together with a 1K input impedance and a LT1037 OP-Amp
in the first amplifier stage.
See also AN124 of Linear Technology.

With best regards

Andreas
« Last Edit: January 07, 2015, 03:33:05 PM by Andreas »
 

Offline babysitter

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Re: LM399 based 10 V reference
« Reply #288 on: January 07, 2015, 05:13:43 PM »
Congratulations for 1 year of logging, Andreas!
I'm not a feature, I'm a bug! ARC DG3HDA
 

Offline rf-design

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Re: LM399 based 10 V reference
« Reply #289 on: January 07, 2015, 07:30:11 PM »
Quote
I did not understand how the flicker or 1/f noise of the reference is measured. I could understand that a chopper amp could reduce the impact of the needed voltage amplification. But the amp could only amplify a voltage difference of two potentials or one potential to a ground reference point. But the reference is the DUT itself have an offset of 7V against the chopper amplifier. So there should be second reference which significant lower or well characterized flicker noise to counter the DUT reference voltage. The difference should also be smaller than the requested gain of the measurement.

So what kind of offset source is used?

I use a large (3200 uF) electrolytic capacitor selected for low leakage current.
Noise floor is <0.2 uV together with a 1K input impedance and a LT1037 OP-Amp
in the first amplifier stage.
See also AN124 of Linear Technology.

With best regards

Andreas

Andreas, thanks for the AN. So the measurement is limted to 0.1Hz. I thought to oberserve the total drift spectrum. So only the integration time of the voltage logging sets the sample rate and all further effects could be observed.

I have further doubts that the dielectric absorption set the lower limit above the reference. The 24h settling could mean that the interface traps very similar to the source of high 1/f noise in MOS gates set again a limit on the 1/f noise measurement floor which is otherwise rejected by the hybrid amplifier (LT1012, Q1+Q2, LT1097). The reported floor was achieved with a $400 wet slug tantal.

To me an alternative is to measure the low 1/f noise amplified voltage difference between pairs of the same type of reference. With 10 references you have 45 pairs of drift measurements which are not limited by 0.1Hz. From the pairs you can calculate the indidividual noise spectra.

BR
Reiner
 

Offline wiss

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Re: LM399 based 10 V reference
« Reply #290 on: January 07, 2015, 07:52:57 PM »
My home-lab spent some time over Christmas measuring delta-voltages, every 16 minutes 4 measurements are taken between 3 references:

http://www.eevblog.com/forum/projects/yet-another-%28lm399%29-volt-reference/15/
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #291 on: January 08, 2015, 07:29:00 AM »

I have further doubts that the dielectric absorption set the lower limit above the reference.

From the pairs you can calculate the indidividual noise spectra.


Dielectric absorption (DA) is only a problem for measuring leakage current.
On AC-Signals a 0.1% error of the noise voltage due to DA should be no problem.

Leakage current itself contributes to the noise floor.
Of course it might be a good idea to let the input capacitor always under power to minimize leakage.

I doubt that one can calculate individual noise from pairs.
I'd rather average >9 references to get a lower noise voltage (sqrt(number)) and measure the D.U.T. against the average.

with best regards

Andreas
 

Offline rf-design

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Re: LM399 based 10 V reference
« Reply #292 on: January 09, 2015, 12:33:53 AM »
I doubt that one can calculate individual noise from pairs.

Indeed you can :) Click :

www.intersil.com/data/an/an177.pdf

The calculation is not difficult!

The measurement is a pairwise sample DUT noise density over frequency. Because the assumption is that the samples are statistical independend the noise power at sa specific frequency is simply the addition of the noise power of the DUT pair.

If you have n=4 samples you can make n*(n-1)/2=6 pairwise measurements. I will call the reference sample spectral noise power at a specific frequency simply a,b,c,d.

What you measure with the pairs is the sum of the noise powers

a+b
a+c
a+d
b+c
b+d
c+d

You get the noise power of the first sample reference by the following expression:

a=(1/3)*(((a+b)+(a+c)+(a+d))-(1/2)*((b+c)+(b+d)+(c+d)))

a=(1/3)*((3*a+b+c+d)-(1/2)*(2*b+2*c+2*d))

a=(1/3)*((3*a+b+c+d)-(b+c+d))

a=(1/3)*(3*a)

a=a

For the general case n the expression is:

a=1/(n-1)*(sumwith(a)-1/(n-2)*sumnot(a))



The application note from LT does not give a calculation example. It is only stated that you have to use a much better reference as a DUT partner.
 

Online Andreas

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Re: LM399 based 10 V reference
« Reply #293 on: January 09, 2015, 06:36:57 AM »
What you measure with the pairs is the sum of the noise powers

Hello,

what do you want to measure?
wideband noise > 10 Hz or
1/f noise 0.1 .. 10 Hz or
drift (below 0.1 Hz).

For wideband noise you are right: the power (effective value) adds.
The voltage adds only geometrically. (square root of the squared sum).

For 1/f noise you usually can only measure the peak-peak voltage value.
And if you really have done such measurements you now that
from measurement to measurement you have a lot of variation which
makes it practically not possible to measure differences.

Except when one of the 2 references has much lower noise.
-> my suggestion to average at least 9 references as
    "low noise reference" to have less than 10% error for the DUT.

With best regards

Andreas
 

Offline rf-design

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Re: LM399 based 10 V reference
« Reply #294 on: January 09, 2015, 09:54:53 PM »
What you measure with the pairs is the sum of the noise powers

Hello,

what do you want to measure?
wideband noise > 10 Hz or
1/f noise 0.1 .. 10 Hz or
drift (below 0.1 Hz).

For wideband noise you are right: the power (effective value) adds.
The voltage adds only geometrically. (square root of the squared sum).

For 1/f noise you usually can only measure the peak-peak voltage value.
And if you really have done such measurements you now that
from measurement to measurement you have a lot of variation which
makes it practically not possible to measure differences.

Except when one of the 2 references has much lower noise.
-> my suggestion to average at least 9 references as
    "low noise reference" to have less than 10% error for the DUT.

With best regards

Andreas

Andreas,

my thought about the reference noise problem was to avoid in general a requirement to have better reference to characterize or measure other references. I know that similar principles are also used for phase-noise measurements at levels where the best economical sources are less than 10dB away. As the amplifiers could be build with 1/f noise and drift much less than the expected reference noise and drift a differential measurement seems to be an easy solution.

Because for 10 references you have 45 pairs you could not measure all pairs at the same time the result will be dependend on the statistical nature of the drift and noise process. So it is assumed that the noise spectrum, which is hole picture of short drift and 1/f noise, is stationary. So otherwise the calculation of the last post is not valid.

The measurement sample could be every 100ms over 2^14=16384 samples. So a pair measurement need less than 30min. I know that it is difficult to interpret a noise spectrum extending down to 306uHz. Otherwise if the noise spectrum follow a 1/f rule the noise power integrated over a frequency range with a fixed factor of the upper limit to the lower limit will give an equal noise power. So there is no further gain in noise reduction to measure longer. If the spectrum follow (1/f)^k with k<1 than gain is small. Finally the 1/f or short time stabilty set for most systems a lower limit. And I know that it is difficult to differentiate that from an againg which typical goes only in one direction.

BR
Reiner
 

Offline blackdog

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Re: LM399 based 10 V reference
« Reply #295 on: January 14, 2015, 06:27:56 AM »
Hi,

Can i also play?  ;)

This is a portable reference i am designing, is uses a LM399.
I've done my best to keep the noise low and the current to the heater as low as possible.
Therefore, I use three 9V batteries, it gives me a lower heater current and longer live of the batteries.
Only 2 euros each, for alkaline here in the Netherlands.

The corner of the filter is about 1 a 1,5 Hz, this is low enough to filter out most of the noise.
If you are calibrating a digital multimeter, choose the longest integration time, 1 to 2 seconds.
There are also elements for the protection of the circuit on the output circuit.

I now own a calibrated Agilent 3458a, later i wil show a short term plot of the portable reference.

Shoot at it!

Kind regarts,
Blackdog
 

Offline MK

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Re: LM399 based 10 V reference
« Reply #296 on: January 14, 2015, 07:31:44 AM »
Hi Blackdog, with a rai to rail output of a cmos amp and with a FET for Q1, it should self-start without the 180K R1 resistor and the output should  be slightly more stable too.

regards.
 

Offline wiss

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Re: LM399 based 10 V reference
« Reply #297 on: January 14, 2015, 08:01:34 AM »
You should definitely remove R1 (me without an hard empirical proof).
 

Offline blackdog

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Re: LM399 based 10 V reference
« Reply #298 on: January 14, 2015, 08:16:03 AM »
Hi,

I know that R1 should be removed, but i need to do some test.
Today, i received the last components, and from other references i had build using the same schematic setup
R1 was not necessary, we will see wats come out of it...
Thanks for the remarks.

A little test print, with the LM399, LM368 10V reference and a 2K Rhopoint 8E16 who is putting the current in de reference
drift within 2PPM with long cable's to a Tektronix DMM4050 Multimeter, not bad :-)

Kind regarts,
Blackdog
« Last Edit: January 14, 2015, 08:33:04 PM by blackdog »
 

Offline Mickle T.

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Re: LM399 based 10 V reference
« Reply #299 on: January 18, 2015, 08:21:04 PM »
LM399H with the external oven :D
- Noise (0.1-10 Hz) ~ 2.6 uV p-p;
- TempCo ~ 0.25 ppm/C;
- T(oven) = 52 C;
- Long-term stability is unknown.
 


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