Group-buy for 10V LTZ1000A reference? [Completed, no more boards].

[Andreas]

perhaps they are only soldered on the wrong edge 

with best regards

Andreas

[TiN]

I got that one messed up in order, Caps are 1210 on 1206 pads. 

[TiN]

Almost done on matching resistors. 

[TiN]

Sets ready for tempco trim of 7V stage.

Ref 3 is are my "old" prototypes, unlabelled one is USA CalClub version.

[Dr. Frank]

And what about this 7001 reference?
Is it defect, or could you determined its  oven setpoint?
Frank

[Philipp23]

Hello

I hope it is OK to write down this here. Is any one of the lucky owners of the 10V LTZ1000A reference willing to trade it against other precision metrology equipment? For example a National Instruments PXI-4071 7½-Digit FlexDMM or a very nice digital Multimeter that was way ahead of its time the Prema 8017 Multifunction Meter?

Kind Regards

Philipp

[Echo88]

@Kleinstein: Could you elaborate on the possibility to omit the Negative Voltage Supply for the bipolar output buffer stage which is used in the FX-reference?
Im at the moment testing this output-design and thinking about doing the same, but cant think of a solution which wouldnt add drift and noise when shifting the ground.
Im using an LT1054-based charge-pump for now, to generate the needed negative voltage, like its done in the 732B.

[Kleinstein]

The circuit to provide separate negative side drive and sene pins only needs a relatively low voltage. Depending on the OPs use some 0.5 or 1 V could be already enough, if one limits is to compensating normal small lead resistance.  One can create such a small negative supply with just something like 2 forward diodes to get a small voltage drop. So the external supply negative side would be the negative supply, the reference circuit ground would be behind some 2 diodes, some 1.2 V higher.  This would need the external supply to be higher by the drop of the diodes. So 12 V external supply could be too little or at least quite close to the edge. A 14 V supply could be sufficient.

Here it helps that modern AZ OPs often are Rail to Rail. So just -1.2 V or even -0.6 V could be enough to compensate a few 10 mV of drop on the wires.

[Echo88]

Indeed it works, thanks.
Im wondering about the noise contribution of the diodes and would have expected that the output-noise increases, but it stays the same no matter if i use a dedicated -6V Supply or the diodes (Noise/Noise2.asc).
Simulations are attached. Maybe i made an error? Didnt simulate noise in a long time.

[Kleinstein]

Creating the negative supply from the string of diodes makes not big difference over a real regulated -6 V. The OPs PSRR  should be quite good and the voltage over the diodes is usually quite low noise (most regulators are higher noise), just a little temperature dependent.

The noise simulation is not really correct, as Vout is relative to the ground symbol. So the negative side sense part is not correctly included. To get it better, move the GND point to the negative output.

The OPs seem to not include noise (at least not in the models used on my PC).  The noise model of the reference may also be not that accurate.

[Echo88]

Weird, if i connect the gnd-symbol to the negative supply (Q3 Collector) as you suggested, then ill actually get less measured noise than when ground-symbol is connected to the lower side of R3 across Vout.  This happens in both posted versions, with diodes and Voltage Source as negative supply.
Did you simulate your ground-symbol-suggestion? I use the normal Solver-Method and cant recall that i changed any other tolerance/etc. that might influence the simulation.
I should use other OP-Amp-Models if it doesnt include the OP-Amp-Noise and i was suspicious wether LTSpice would simulate diode-noise correctly.
I think the diode-solution might produce less noise than the cap-switcher which produces EMI, but ill have to read more about noise-simulation to get a better fitting simulation of the diode-based-solution.

[Kleinstein]

I have not done the simulation with the moved GND.  Getting a lower noise with the correct GND point is not such a surprise, as the OPs are modeled without noise.  Though the difference should be rather small as it's mainly the diodes and a few resistors.

One can kind of add some of the OP voltage noise to the simulation with a high resistor in series to one input. Some, likely more modern models do include noise for the OPs too.

AFIAK the noise of forward biased diodes is modeled reasonably good. So the diode part is definitely low noise, just a more drift for the negative supply voltage.

The charge pump chips tend to produce quite some ripple / spikes, depending on the layout - not really something to see in a simulation. Chances are a switcher with inductor is lower EMI.

[TiN]

Guess it's a big (sorta) day today.

First preliminary FX was shipped few hours ago.







Not too impressed with Pomona 3770 posts. While job getting done, they are still kinda flimsy to use. Certainly do not ooze quality as "proper" 25$ 5-way posts. 

I'm still undecided if should use LEMO multi-way connector to provide input +/-12V power for module, isolated power for EEPROM/PCB temperature sensor and I2C data, or just stick with simpler dual BNC connectors for +/-12V only. LEMO option is nice but it's expensive and over the planned budget already. If somebody have better idea, feel free to tell.

[Zucca]

Thanks for the update, personally I would love the LEMO. I wanted a Ferrari, you are getting pretty close to perfection.

"Abbiamo fatto trenta, facciamo trentuno!"

It is a phrase that is historically attributed to Pope Leo X who in 1517 had to name some new cardinals. With great work, he came to draw up the final list, reaching as many as 30 names, already a substantial number. In the end, however, he realized that he had not added a prelate of great merit and fame, not being able to exclude any cardinal, he added the name to the list, pronouncing the famous words: "We did 30, we do 31!"

[Andreas]

If somebody have better idea, feel free to tell.

For power supplies I usually use DIN (Diode) connectors.
e.g.
https://de.rs-online.com/web/p/din-steckverbinder/1564224/
https://de.rs-online.com/web/p/din-steckverbinder/0776088/
https://de.rs-online.com/web/p/din-steckverbinder/0776167/

But you could also use D-Sub connectors.

with best regards

Andreas

[guenthert]

Congrats!

Pity that they're not for sale, but I hope that, once I'm reunited with my gear, I can get on the US CalClub list and meet one of those units then ...

[TiN]

Playing with matplotlib and python. Here I can present tempco plot, captured from eight xDevs.com FX LTZ1000A references (before trim, as is):



Purpose of the test is to establish baseline for TC before readjustment, to make sure we have no problems with temperature stability. My final goal is to have each ref 10V output deliver better than 0.03 ppm/K.

In test - each reference scanned twice, one value for raw LTZ1000A output (7.x-ish volt) and second value is 10V output (before trim adjustment). Except one output, channel 12 is connected to my xDevs/Fluke 792X FX ref +9.9999779(22) VDC, outside of chamber to verify stability of scanner setup. Worst ref = channel 14, 10V output -0.059 ppm/K. 
Scanner = Two Keithley 7168 nanovolt JFET cards. Detector : Two Keysight 3458. 

Temperature swept by Keithley 2510 in DIY airchamber box, with 40W watercooled TEC and Xeon copper fansink inside as heat radiator.
Temperature in the box measured by Fluke 1529 thermometer and Honeywell RTD PT100 probe.

Used RAW data file, DSV format.
Python 2.7 app to plot graph. Depends on scipy, numpy and matplotlib.
 

[TiN]

Alright, after 95 weeks, time for long awaited update has come.
Few units are completed and delivered while ago as test drive, and feel happy so far:

MM - 1 unit [DONE]
USA cal club - 1 unit [DONE]

Now I need these people to send me their shipping information in PM, so I can proceed.

montemcguire - 1 unit [PENDING]
dr.diesel - 1 unit [TBD]
chriswebb - 1 unit [TBD]
PeLuLe - 2 unit [PENDING]
bck - 1 unit [TBD]
CM - 1 unit [TBD]
zucca - 1 unit [PENDING]

I understand it was a loooong wait, so If somebody changed mind and don't want a ref anymore, that is OK, just let me know so I update the list accordingly.

[niner_007]

If anyone changed their mind or you got extras, I’m interested, please let me know

[syau]

If anyone changed their mind or you got extras, I’m also interested, please let me know

[wolfy007]

Same here, if theres an extra, Ill take it.

[Zucca]

This is like good italian wine, the more you wait the better it gets.

PM sent.

[nexus]

Any chance that the design will become open source? I would love to build one myself and send it in for calibration!
Only components I see as being difficult to source are:

-fluke custom film resistor network, P/N 2464707
-matched precision resistors as covered in your article: https://xdevs.com/article/tcr_test/#vpg2018

If you don't plan on releasing the design for end-user assembly, I'd still be interested in buying a complete module.

Thanks!

[dr.diesel]

Merry X-Mas to me!

Many thanks to @TiN for his efforts and support of information here on the forum.  I've not yet powered this up and don't intend to until I figure out how I want to 24-7 power the unit, I don't want to just hang it off one of my linear supplies when needed.

 

[notfaded1]

Really nice presentation of this... even a carrying case aye!  The labels are super neat too.

Bill