Author Topic: A Low Cost OSHW Voltage Calibration Reference Project  (Read 4233 times)

0 Members and 1 Guest are viewing this topic.

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #75 on: April 17, 2018, 04:56:11 am »
hello,

lm399h (datedcode: 1736) heater in "reverse" mode is a diode with the following measured characteristics:-

ambient: 27 degC

If         Vf
-------- ---------
0.5ma 0.563V
1.0ma 0.590V
1.5ma 0.607V
2.0ma 0.620V
2.5ma 0.630V
3.0ma 0.640V

i think this diode can be used for off-chip temperature regulation by using it as a die temperature sensor
and probably using the lm399 at a lower (and a tighter stabilized) temperature resulting in better noise
performance and drift characteristics.

the diode bias voltage could be derived from the main zener voltage (inverted: gain -1)

best regards.

-zia
« Last Edit: April 17, 2018, 05:04:00 am by zhtoor »
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 1864
  • Country: de
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #76 on: April 17, 2018, 05:27:27 am »
Hello,

the absolute maximum ratings allow only 0.1V in forward direction for the substrate diode.

Note 2: The substrate is electrically connected to the negative terminal of the temperature stabilizer. The voltage that can be applied to either terminal of the reference is 40V more positive or 0.1V more negative than the substrate.

So perhaps another dead LM399.

with best regards

Andreas
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #77 on: April 17, 2018, 05:39:54 am »
please see attached.

d1 = heater used as a diode by biasing VH -ve wrt Gnd
d2 = substrate diode - both ends grounded
d3 = main ref zener

best regards.

-zia
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 1864
  • Country: de
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #78 on: April 17, 2018, 06:28:30 am »
I understand the datasheet in this way:
no pin of the reference is allowed to be more negative than Pin 4 (substrate) by more than 0.1V.


 

Online cellularmitosis

  • Supporter
  • ****
  • Posts: 870
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #79 on: April 17, 2018, 06:40:46 am »
Very interesting idea zhtoor!  I am curious to see if the 399 survived.

I was looking at the Spreadbury paper again recently and was reminded that these refs don’t seem to drift much while turned off (and I seem to remember reading in another thread that Dobkin said this is also true of the 399).  Perhaps the poor man’s route is to have an additional 399 which is only turned on one day per year?
LTZs: KX FX MX CX PX Frank A9 QX
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #80 on: April 17, 2018, 06:50:42 am »
Very interesting idea zhtoor!  I am curious to see if the 399 survived.

I was looking at the Spreadbury paper again recently and was reminded that these refs don’t seem to drift much while turned off (and I seem to remember reading in another thread that Dobkin said this is also true of the 399).  Perhaps the poor man’s route is to have an additional 399 which is only turned on one day per year?

the test (sacrificial) lm399h is currently "surviving" the following configuration.

1. heater -ve and zener -ve shorted and connected to ground.
2. heater +ve being supplied with -10V via a 10K resistor resulting in -0.588V "sensing" the die temperature.
3. the zener +ve being supplied with +10V via a 10K resistor resulting in 7.00294V vref.

best regards.

-zia
 

Offline Andreas

  • Super Contributor
  • ***
  • Posts: 1864
  • Country: de
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #81 on: April 17, 2018, 07:00:48 am »
Very interesting idea zhtoor!  I am curious to see if the 399 survived.
The question is:
is there enough "before" data (zener voltage, noise, ageing rate ...) to judge any abnormal behaviour.
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #82 on: April 17, 2018, 07:03:56 am »
Very interesting idea zhtoor!  I am curious to see if the 399 survived.
The question is:
is there enough "before" data (zener voltage, noise, ageing rate ...) to judge any abnormal behaviour.

that is for the experts (mainly you in the LM399 domain) to evaluate, i am just a newbie trying to have fun.

best regards.

-zia
 

Online cellularmitosis

  • Supporter
  • ****
  • Posts: 870
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #83 on: April 17, 2018, 07:10:09 am »
Very interesting idea zhtoor!  I am curious to see if the 399 survived.
The question is:
is there enough "before" data (zener voltage, noise, ageing rate ...) to judge any abnormal behaviour.

I would be happy to offer up a few silicon sacrifices to find out if a low-temperature 399 is possible

I just need to find a way to retire early so that I can devote more time to volt nutting  :wtf:
LTZs: KX FX MX CX PX Frank A9 QX
 

Online rhb

  • Frequent Contributor
  • **
  • Posts: 911
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #84 on: April 17, 2018, 09:26:19 am »
I'd like to repeat my plea for data in ASCII format, especially data from from start up of a new device.  To date I've received very little data.  I'm going to digitize the plots from the HPJ paper on the 3458A, but that is just because finding the data 30 years later is unlikely.

I feel pretty good about the results I got for the thermal noise spectrum,  They seem reasonably plausible.  So I'm on to the 1/f noise model.  But without documented aging data, I can go no further.
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #85 on: April 18, 2018, 03:21:51 am »
hello,

update:

lm399h heater as a die temp. sensor mode:

Zener supplied through 10K with a +20V power supply: Vz = 7.00390V, Iz = 1.3ma
Heater in diode sensor mode supplied through 10K with -7V power supply (to simulate inverted ref supply): Vf = 0.555V, If = 640uA, Tamb=29 degC

seems that the approach is do-able.

best regards.

-zia
 
The following users thanked this post: cellularmitosis

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #86 on: April 18, 2018, 05:11:29 am »
hello,

revised proposal:-

please see attached. all comments in:-

http://www.eevblog.com/forum/metrology/a-low-cost-oshw-voltage-calibration-reference-project/msg1470436/#msg1470436

and

http://www.eevblog.com/forum/metrology/a-low-cost-oshw-voltage-calibration-reference-project/msg1472062/#msg1472062

apply with the caveat:-

refer to the attached schematic. D1/D3 represent the LM399, where D3 is the heater in the die-temperature-sensor mode.
the node VT generates the estimate of the die temperature (a diode drop) which can be used to implement an external heater
(maybe a TO220 transistor's tab-hole enlarged to ca. 4.75mm to install the LM399 metal body cap.) set at a lower temperature
than 88 degC and having a tighter temp. control.

in case of heater-less implementation, an accurate graph of VZ vs VT can also be used.
(or maybe use it to make some kind of a "corrected" output)

(gu)estimated BOM: $20 to $25

best regards.

-zia
« Last Edit: April 18, 2018, 05:56:32 am by zhtoor »
 
The following users thanked this post: cellularmitosis

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #87 on: April 19, 2018, 04:51:31 am »
hello,

proposal update:

added a *very* low noise voltage follower option for comments.
(might be difficult to measure it though)

V3/V4 are regular cell phone batteries like :-

https://www.amazon.com/BL-4U-Battery-Nokia-C5-03-Classic/dp/B0054MAWDO/ref=sr_1_7?ie=UTF8&qid=1524077227&sr=8-7&keywords=bl-4u

the output labelled VLN is the low-noise vref follower and may take a *long* time to settle.
(some current protection for output transistors Q1/Q2 maybe required)

the external oven may contain the critical elements like LM399, V3/V4 and maybe some resistors (hysteresis?).

best regards.

-zia
« Last Edit: April 19, 2018, 05:56:51 am by zhtoor »
 

Online rhb

  • Frequent Contributor
  • **
  • Posts: 911
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #88 on: April 19, 2018, 08:00:52 am »
It seems to me that the heater should be attached to an aluminum enclosure say 6 mm thick with 50 mm of insulation.   Placing the heater on the LM399 makes a large thermal gradient.  Self heating makes  gradients unavoidable, but they can be minimized.

I'd been working on this off and on all day.  I'll just include it as is.

Some random comments.

The resistors are as much of a problem as the zener.  The critical parts of the reference should be in an enclosure made from 5-6 mm aluminum.  Two U shaped pieces with external heaters attached to two faces and embedded in insulation should be inexpensive and provide a uniform temperature.  Place some thermistors in suitable spots to check for gradients, at least for the prototype.

One might let the user input the expected maximum ambient temperature and set the chamber temperature based on that.  But that would conflict with fitting an aging curve calculated from the first 500-1000 hours of operation.  Aside from temperature, that seems to me to be the largest error source.  There is the question of whether it is better to burn in at elevated temperature or at operating temperature.  I'm skeptical of having a stable aging curve with high temperature burn in, but it might not matter.

Interestingly, a 40 x 40 mm Peltier device is under $3 each on Amazon for 10.  For a shallow enclosure, two might allow setting the operating temperature independently of the ambient temperature.  It's a big power drain, but it might be tolerable for a lab reference if the operating temperature were average ambient.  Quite a bit more complicated to design.

Such an enclosure is easily made using a 20 ton hydraulic press and a very simple die set.  Anneal  before and after forming and then mill the mating surfaces, drill and tap.  Seal the enclosure with butyl sealant to eliminate humidity effects.

In reading back through the thread I realized I'd never properly answered the question about how you get 6.5 digits from a 5.5 digit meter.   You deliberately add random Gaussian noise which exceeds the resolution of the 5th digit.  You take two long measurements and crosscorrelate them.  The noise does not correlate so the cross correlation only sees the DC value.  It's apparently called "dithering" in metrology.  The limitation is the length of time it takes to make a measurement.  TANSTASFL.

The early part of the aging curve has the most curvature.  It might be that lowering the operating temperature would extend the duration of the large curvature region.

My original premise was that if you built a device of the best, low cost, parts and then measured the behavior during a 500-1000 hour burn in, that you could describe future performance sufficiently well to pick up an order of magnitude improvement.  Such a burn in would include temperature excursions to quantify resistor TC, tolerances and aging. in addition to the reference and buffer amp behavior.

Fluke believes that the observed hysteresis effects are due to stress on the die and have patented temperature annealing the die on cold startup on the 7001.  I'm not convinced that is sufficiently innovative to warrant a patent, but patents are really just a license to sue others.
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #89 on: April 19, 2018, 03:47:58 pm »
The early part of the aging curve has the most curvature.  It might be that lowering the operating temperature would extend the duration of the large curvature region.

hello,

i think that the initial curvature during the burn-in may have a lot to do with the die attach materials and a lot of stresses being relieved on the die and its attachment.

now do we really need to model that part of drift component?

i would think to maybe boil a bunch of lm399's or give them some kind of an un-powered cyclic thermal pre-treatment which takes care of
this factor before going in with electrical burn-in / characterisation. (anybody here with die packaging/attach experience? MisterDiodes maybe?)

sort of reducing the physics / chemistry / metallurgy.

best regards.

-zia
 

Online cellularmitosis

  • Supporter
  • ****
  • Posts: 870
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #90 on: April 19, 2018, 05:01:57 pm »
i would think to maybe boil a bunch of lm399's or give them some kind of an un-powered cyclic thermal pre-treatment which takes care of
this factor before going in with electrical burn-in / characterisation. (anybody here with die packaging/attach experience? MisterDiodes maybe?)

This approach seems to have worked in 1960 for regular zener diodes.
LTZs: KX FX MX CX PX Frank A9 QX
 
The following users thanked this post: zhtoor

Offline montemcguire

  • Regular Contributor
  • *
  • Posts: 54
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #91 on: April 19, 2018, 05:19:40 pm »
That basic process could be called 'annealing', and as you state, it can be done by thermally cycling the assembled circuitry, powered or unpowered. Aside from stresses inside of the actual semiconductor devices, there are also sources of mechanical stress caused by soldering during assembly. The thermal coefficient of expansion of copper foil is generally different than that of the PCB substrate and any of the devices soldered to the PCB, so if a PCB is being reflow assembled, the solder joints will harden first, and then all of the components will cool with usually different thermal expansion coefficients, introducing mechanical stresses to the assembly. By temperature cycling the assemblies close to the plastic temperature of the PCB substrate, a portion of these stresses can be relieved, probably minimizing long term drift caused by mechanical stress on the components.

Another approach would be to use conducive epoxy to assemble a circuit, so that the problem of the solder solidus temperature being so far above the working temperature is avoided. Epoxy can bond near the thermal set point temperature, so there's no reason why the assembly process needs to 'build in' mechanical stresses to all of the components.
 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #92 on: April 19, 2018, 05:54:11 pm »
i would think to maybe boil a bunch of lm399's or give them some kind of an un-powered cyclic thermal pre-treatment which takes care of
this factor before going in with electrical burn-in / characterisation. (anybody here with die packaging/attach experience? MisterDiodes maybe?)

This approach seems to have worked in 1960 for regular zener diodes.

so maybe 20 cycles of alternating between an ice-bath and boiling water could be good enough for an LM399?
(besides establishing the calibration points for die-temp sensor in LM399 heater in reverse mode)

best regards.

-zia
« Last Edit: April 19, 2018, 07:41:32 pm by zhtoor »
 

Offline z01z

  • Regular Contributor
  • *
  • Posts: 106
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #93 on: April 19, 2018, 07:12:16 pm »
The paper and the link mentioned here might be of interest.
 
The following users thanked this post: zhtoor

Online rhb

  • Frequent Contributor
  • **
  • Posts: 911
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #94 on: April 19, 2018, 10:58:40 pm »
The kitchen oven and freezer would be more convenient than water. There is also the question of reducing the excursions with time as shown in a Fluke paper about the 7001 in the reference teardown thread.  If you have hysteresis, you need to do that.  Consider demagnetization.

Once the curve flattens out, it becomes difficult to determine the deviation from a straight line.  The computation becomes very sensitive to numerical precision.

A physical model for the drift and the hysteresis would be very useful.  Variations due to stress imply piezoelectric effects so far as I can see.  Is there literature on that in solder joints for example?

A man was walking down the street when he saw another man run out, stomp his foot and then go back to leaning against a building.  As he approached, the man did this several times.  When he reached the man, curiousity got the better of him. 

"What are you doing?" 

"Keeping away tigers." 

"But there are no tigers around  here." 

"Works very well, doesn't it?"


 

Offline zhtoor

  • Frequent Contributor
  • **
  • Posts: 365
  • Country: pk
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #95 on: Yesterday at 04:48:09 am »
The kitchen oven and freezer would be more convenient than water. There is also the question of reducing the excursions with time as shown in a Fluke paper about the 7001 in the reference teardown thread.  If you have hysteresis, you need to do that.  Consider demagnetization.

Once the curve flattens out, it becomes difficult to determine the deviation from a straight line.  The computation becomes very sensitive to numerical precision.

A physical model for the drift and the hysteresis would be very useful.  Variations due to stress imply piezoelectric effects so far as I can see.  Is there literature on that in solder joints for example?

A man was walking down the street when he saw another man run out, stomp his foot and then go back to leaning against a building.  As he approached, the man did this several times.  When he reached the man, curiousity got the better of him. 

"What are you doing?" 

"Keeping away tigers." 

"But there are no tigers around  here." 

"Works very well, doesn't it?"

 :-DD

there shall be enough tigers to shoot !, as they say, in the fullness of time....

@rhb

you might find this interesting:-
http://scholarsmine.mst.edu/cgi/viewcontent.cgi?article=4491&context=masters_theses

best regards.

-zia
 

Online rhb

  • Frequent Contributor
  • **
  • Posts: 911
  • Country: us
Re: A Low Cost OSHW Voltage Calibration Reference Project
« Reply #96 on: Yesterday at 06:02:19 am »
One might consider building a temperature chamber with a pair of Peltier devices so one could raise or lower the temperature as desired.  That would make acquiring data on hysteresis  fairly simple.  Run a group of LM399s with the heaters off and measure differential voltages among the set for a variety of thermal cycles.  Put CPU heatsinks and fans on the Peltier devices to improve heat transfer.

That was an interesting paper, thanks.  There ought to be more data available.  If you get any of the references from the thesis I'd like to have them.

Reg
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf