ADR1399 reference - Page 1
Forum section: electronics / general

author: branadic
author_rank: Super Contributor
timestamp: April 11, 2022, 09:33:19 am
content: I think it's worth having a separate thread for the ADR1399 to not mess up the threads about LM399.About 2000 h ago I've started monitoring one of two ADR1399 with a Prema 5017. After playing with the integration time in the first days I kept the setup as is afterwards and recorded the output voltage. Unfortunately, the Prema has quite some t.c. and noise contributing to the measurement, so it's not the meter of choice to observe this kind of references, but all I had available at that time. Will change that setup soon and add the ambient conditions as well.-branadic-

author: jonpaul
author_rank: Super Contributor
timestamp: April 11, 2022, 11:40:40 pm
content: Brandiac, have connexions at ADI, hoping to get the 1399s and setting up tests here, have latest Keysight 34465A in CAL.Any tips on your set-up? How does 34465a compare to your meter?Bon SoiréeJon

author: macaba
author_rank: Regular Contributor
timestamp: April 12, 2022, 09:05:36 am
content: Attached is output voltage deviation vs. heater voltage. 0.37ppm/V.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 12, 2022, 09:35:25 am
content: Quote from: jonpaul on April 11, 2022, 11:40:40 pmDirectly measuring a reference with a DMM will give the combined drift and noise of the DMM and the DUT. The Prema 5017 by now likely has a well aged LM399 reference and could thus be low dirft. For the KS34465 it depends on how much that meter was used before. It may help if one has a calibration history.The noise in both case would be to a large part the meters internal noise form the LM399.

author: Andreas
author_rank: Super Contributor
timestamp: April 12, 2022, 05:47:04 pm
content: Quote from: macaba on April 12, 2022, 09:05:36 amHello,How is this measured? with or without thermal isolation of the ADR1399? (on both sides of the PCB)Additional question:Does the output voltage change also (like on LM399) when changeing the orientation. (laying on left / right side or legs above plastic cap ?)See also for a LM399 based instrument here:https://www.eevblog.com/forum/metrology/project-pimp-a-keithley-2000/msg1106829/#msg1106829with best regardsAndreas

author: bastl_r
author_rank: Regular Contributor
timestamp: April 20, 2022, 06:57:54 am
content: hello guysI found on ebay very cheap resistors with only 2ppm for 1,5€ each.With 2 sets of these and a Trimmer you can create a voltage divider for the ADR1399 to 10V.2pcs 31k623 in series and 1pcs 26k1 plus a 200Ohm trimmer.Here are the links to the resistors:https://www.ebay.de/itm/144374605346https://www.ebay.de/itm/144475379838regards

author: branadic
author_rank: Super Contributor
timestamp: April 20, 2022, 07:48:20 am
content: Why bothering with expensive single resistors, if you can use a resistor network for less the price, that can be configured in a ratio required?https://xdevs.com/guide/rnet_ratio/They offer good t.c. matching and the network can be trimmed for the final output voltage by paralleling resistors to a single element within the network, that way the t.c. of the parallel resistor is dampened by the network.Final t.c. trimming can be accomplished by adding copper in either the upper or lower branch of the network, depending on the sign of the remaining t.c. (see attachement).-branadic-

author: bastl_r
author_rank: Regular Contributor
timestamp: April 20, 2022, 06:13:01 pm
content: HiThank you for the tip.But i don't understand how i can adjust a calculatet ratio of 1.41520412358094.Can you explain what is to dofor this ratio?One of my ADR has 7,06624V and the other 7,07143V...Regards

author: branadic
author_rank: Super Contributor
timestamp: April 20, 2022, 07:37:55 pm
content: Simply start with a 2:5 ratio = 0.4 and trim the "5" part of it close to 2:4.817 = 0.4152 with parallel resistors.-branadic-

author: dietert1
author_rank: Super Contributor
timestamp: April 21, 2022, 10:42:21 am
content: The proposed design with 26100 and 26300 Ohms isn't wrong, except one should not use a trimmer. A trimmer isn't stable enough after some years. Also it is easy to lose calibration without notice.Better calculate the value needed and get a good ( < 15 ppm/K) resistor of that value. The tolerance of the 26100 resistor will be about 2.6 Ohms. Better choose a series trim resistor on the high side, then one can do ppm calibration by some parallel resistor to that trim resistor, without touching the foil resistors anymore.Regards, Dieter

author: branadic
author_rank: Super Contributor
timestamp: April 23, 2022, 06:58:35 pm
content: New datasheet availablehttps://www.analog.com/en/products/adr1399.htmlshowing ADR1399 in LCC package. Good thing about that package is: "...The LCC version adds four pins, two of which are not internally connected (NIC) and the other two split the active reference into force and sense action on the top and bottom of the shunt..." but that comes at the cost of "...The heater power for the LCC version is about 3× to 4× greater than the TO-46 version...".-branadic-

author: alm
author_rank: Super Contributor
timestamp: April 23, 2022, 07:32:26 pm
content: A higher heating power means stronger thermal gradients, which I'd expect to cause higher temperature coefficients.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 23, 2022, 08:09:55 pm
content: The actual heat needed for the LCC package version will depend a lot on the layout / PCB. With some isolation and thin traces it can be quite viable to create quite some thermal impedance on the PCB level. With a suitable PCB and cap the heater power may be comparable.The higher hyteresis would be a weak point for the LCC version - though this may also depend on the PCB / holder.

author: miro123
author_rank: Frequent Contributor
timestamp: April 23, 2022, 09:31:41 pm
content: I'm looking forward on LCC version. Leaving kovar and adding sense pins are welcomed changes. I wonder what can be made by hobbyist in insulated "dead bug" configuration.Professional world will most like appreciate LCC voltage reference @5/4.096/2.5V

author: branadic
author_rank: Super Contributor
timestamp: May 22, 2022, 09:02:25 am
content: Meanwhile, 3000 h have passed and measurement is still ongoing. As announced ambient sensors were added, hopefully giving a better clue what's going on. Maybe I should switch from Prema 5017SC to Prema 6048 to get better resolution and stability plots. But that's a task for the near future.-branadic-

author: branadic
author_rank: Super Contributor
timestamp: June 03, 2022, 03:26:07 pm
content: I was asked to perform a 1/f noise (0.1 - 10 Hz) measurement on the ADR1399, so I did exactly that, result attached. A nice match for post 2000.By the way, this reference was used to verify, whether the Prema 5017 is really limited by its ADC in terms of noise as Andreas assumed or by the low frequency noise of the LM399 used as a reference in there and Andreas was totally right. There is absolutely no improvement when replacing the reference. A short article about it can be foundhere.-branadic-

author: WillTurner
author_rank: Regular Contributor
timestamp: June 09, 2022, 02:27:51 am
content: The ADR1399 datasheet revision 0 (not the new datasheet listing the LCC package, which I am yet to read) has the following statement listed under "Thermal Resistance" on page 4 of 11 which may be missing in the new revision :-"To reduce heater power, avoid bringing power planes close to the device except on the bottom of the PCB, and use a mesh ground instead of a solid plane.In addition, mounting the device at the full height of its leads, approximately 1cm above the PCB surface reduces the heater power."Does that put an end to the long/short leads debate?The LCC package is an attractive option. I guess mechanical relief slots, and edge of board location[3, 4] come into play, or dead-bug style[1, 2], which looks promising :-).ReferencesQuote from: Andreas on June 16, 2016, 09:36:35 pmQuote from: Andreas on April 20, 2019, 01:32:22 pmQuote That App Note that discusses mechanical relief which was quoted long in the past ...Quote from: branadic on May 11, 2018, 09:17:49 amEdits 1. : Add some references, dead-bug bit.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 09, 2022, 06:39:28 am
content: For the LM399 there was never much debate over long or short leads. Long leads are preferred, just need a bit extra effort for soldering (e.g. a temporary spacer) and the extra hight.The longer leads also give some extra isolation from mechanical stress.The long / short leads discussion is with the LTZ reference with higher current (and thus more effect of the lead resistance) and a usually lower temperature setting and thus less heat flow through the leads.The question is more how much thermal/stress relief is needed / sensible on the PCB. A point to keep in mind here is that it is not only about the stress to the reference, but also stress cause by the heated reference effecting other parts (e.g. resistors) on the PCB. The heated reference is not so much a sensitive part, but in the thermal sense also a source of disturbance. While the reference itself stabilizes fast, it can take quite some time before the parts around the heated reference get a stable temperature (and even worse a stable humidity level).

author: KT88
author_rank: Frequent Contributor
timestamp: June 09, 2022, 07:45:39 am
content: QuoteThis statement is about power consumption. The ADR1399 in LCC package has a junction to ambient thermal resistance of 125°C/W with a JEDEC board (I didn't find that layout though).The layout recommendations are meant to further increase the thermal resitance to save power. The LTZ1000A has 400°C/W in comparison.Other than the TO-46 package the LCC package doesn't use Kovar thus having a lower influence of the Seebeck effect. This means that thermal gradients would have a lower impact on errors than with a TO-46 case.If highest performance is the goal I would still aim for lowest thermal gradients on the board and sacrifice a bit more power...

author: branadic
author_rank: Super Contributor
timestamp: June 09, 2022, 09:09:52 am
content: QuoteThere was a discussion about short vs. long leads before, you must have missed that. Why was there a discussion? Well, you find short leaded LM399 in HPAK meters sitting in sockets, so Keysight must have missed your arguments for long leads. There are other examples were short leads were used, but there are also also examples for long leads, same goes for mounting the reference upside down or straight into the air.I also made a few thermal imaging videos about short vs. long leads, slots vs. no slot that you can find here:https://www.youtube.com/user/TheHendi78/videosEveryone can draw his conclusion based on that results.QuoteI wouldn't sign that either, the reference is quite sensitive to tilting, as the heater resistor is located only at one edge of the reference, so it's to be expected.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: June 22, 2022, 06:11:02 pm
content: Quote from: branadic on June 03, 2022, 03:26:07 pmI had a quick look at the 5017 circuit. One point is that this meter, like the HP3457 has a prime range of some 3 V. The 30 V range already goes through the input divider and correspondingly has 10 M input resistance. So the range to test would be the 3 V range. The 30 V range may be limited by the divider / amplifer. The ADC part is a bit confusing and may also have quiite some noise.

author: MK
author_rank: Regular Contributor
timestamp: June 22, 2022, 08:15:45 pm
content: Quote from: branadic on June 09, 2022, 09:09:52 amLong leads means the heat loss is less, but it is easier to get the kovar/copper thermocouples at different temps, short leads I suspect may make it easier to keep the thermocouples under control, but give you other thermal problems.

author: Andreas
author_rank: Super Contributor
timestamp: June 23, 2022, 08:28:23 am
content: Hello,i do not agree if I look at the pictures branadic did with some LM399 with short/long legs and slotted/unslotted PCB.https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg278247/#msg278247The Pins on the PCB are much more uniform on the unslotted PCB with long leads.With best regardsAndreas

author: MK
author_rank: Regular Contributor
timestamp: June 23, 2022, 09:29:39 pm
content: Hi Andreas,I do not think the camera has the resolution to prove it for either of us, 40uV per degree.We need the pads to have less than 20 millidegree difference, the photos cannot provide that.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 24, 2022, 04:28:39 am
content: Quote from: MK on June 23, 2022, 09:29:39 pmThe requirements for the reference are not that strict: the LM399 reference is not that accurate to need better than 1 µV stability. The popcorn type jumps are usually in the 4 µV range and 1 ppm drift corresponds to 7 µV. Another point is that a stable temperature difference only adds to the reference and is thus not a problem. Only the change in the temperature difference is that causes problems.The camera is still no sufficient to directly resolve the temperature differences. However the camera can still help and show the temperature gradients a bit away from the pins. Due to thermal coupling the differences at the pins is expected to be quite a bit smaller than the differences some 5 mm away. The larger differences around the reference is that can be resolved and compare different configurations.One has to balance between temperature gradients and voltage drop with long thin copper traces.

author: Andreas
author_rank: Super Contributor
timestamp: June 24, 2022, 06:29:46 am
content: Hello,for me the resolution is sufficient to see that on the bottom side of the PCB the temperature difference is ~4 deg C from center (KOVAR) to edge (Copper) for the long leads and > 10 deg C for the short leads on the unslotted side of the PCB.with best regardsAndreas

author: MK
author_rank: Regular Contributor
timestamp: June 24, 2022, 07:35:36 am
content: Hi Andreas,My thinking is that it is necessary to keep the pads at the same temperature, a gradient in the copper is not as important.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: June 24, 2022, 02:48:03 pm
content: THANKS for a seperate ADR1399 thread :-)see the picture mine just showed up

author: iMo
author_rank: Super Contributor
timestamp: June 24, 2022, 04:00:40 pm
content: Quote from: Andreas on June 24, 2022, 06:29:46 amFun with 1399

author: iMo
author_rank: Super Contributor
timestamp: July 03, 2022, 09:03:42 am
content: @1399 owners: could you somehow compare the 1399 vs. 399 popcorning?

author: branadic
author_rank: Super Contributor
timestamp: July 03, 2022, 09:47:33 am
content: I couldn't observe any popcorn on my ADR1399 sample by now.-branadic-

author: iMo
author_rank: Super Contributor
timestamp: July 03, 2022, 08:09:24 pm
content: LCC version in LTSpice..

author: Andreas
author_rank: Super Contributor
timestamp: July 19, 2022, 04:45:12 am
content: Hello,my first LS8-samples from DigiKey showed up yesterday.From datecode the LS8 version seems to be much older than the TO-46 devices here in this thread.Unfortunately I still do not have a "ageing board" for those.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 19, 2022, 01:44:29 pm
content: Dead bug style?

author: Andreas
author_rank: Super Contributor
timestamp: July 19, 2022, 05:18:14 pm
content: Hello,dead bug is not planned as I want to see the influence of the PCB (humidity) on the output voltage.With best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: July 19, 2022, 07:00:35 pm
content: Hi Andreas,I would appreciate if you would split that group into halve, one group mounted to a rigid PCB, the other one with the reference on a flexboard that is attached to the rigid PCB. This way you could proof if a semirigid solution is better, since it is a standard industrial solution, reproducable and without magic.If you need the flex board made by someone else for this investigation, I could provide you with some.-branadic-

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 02, 2022, 07:49:15 pm
content: Just got an LCC8 package today. Hope is to dead bug it and mount it inside an old Eppley (or Weston) standard cell enclosure as a cool looking . Not sure what circuit or output voltage I'll use yet but probably a traditional opamp with the output feeding back around to the zener, though I'm not sure the 1399 needs that. Maybe just a buffer?

author: iMo
author_rank: Super Contributor
timestamp: September 02, 2022, 08:02:01 pm
content: For example in my replay #31 above there is the simplest version with the buffer transistor only.The ADI's eval kit 1399 has got the transistor too..PS: the R4 there in my sim is not part of the schematics..https://wiki.analog.com/resources/eval/adr1399e-ebzPPS:Below a Sim of ADI's Eval schematics - the TC at 1mA out.The max +REFS current is 2.19mA in this sim.The max +REFF current is 5.47mA in this sim.Interestingly the ADI Eval schematics has got the RC filter at the +REFF pin (my sim above has it at +REFS pin), not sure ADI's schematics RC wiring is the correct version (ADI's typo?)..

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 02, 2022, 11:18:20 pm
content: Would have been nice if they had revealed their board layout and done a buffered application. Hey, more to experiment with!

author: iMo
author_rank: Super Contributor
timestamp: September 03, 2022, 06:08:56 am
content: The I_load char with the by transistor buffered 1399.-1ppm at aprox 0.4mA..

author: Kleinstein
author_rank: Super Contributor
timestamp: September 03, 2022, 07:20:17 am
content: Driving the reference with just 1 external transistor is an interesting option.The Eval board has the 1µF + 5 ohms RC element at the ref force side, not at the sense side. This does make a difference for the stabilty against oscillation.The capacitor at the force side should be closer to the case with the 4 pin TO46 version and likely the better placement.It is somewhat the question if one really needs the extra external transistor. The main advantage of the external transistor is unloading the reference chip from possibly variable currents. For most cases the load to the reference is essentially constant and this essentially no gain from the extra transistor. The extra transistor as emitter follower may make sense when there is a variable load to the reference. So the extra transistor does not replace the bootstrapping ciruit to provide a very stable ref. drive current, but is more like an optional extra buffer for the 7 V reference, that may follow the reference.The separate pins allow for a lower ref. impedance and thus less need for the bootstrapping part. To a large part this already applies to the simple circuit without the transistor. The extra transistor allows for a larger resistor at the force output (so the 1.3 K are rather low) and thus a little less effect of supply variation. So it helps to some degree (e.g. a factor of 5), but would still need a stable supply.It is a bit unclear how the AC stabiltity of the reference is effected - the DC load current from the sense input is essentially constant, but it is a bit unclear how this part behaves AC wise.The simpler case is to just connect the force and sense pins externally to the chip and use the extra pins just for compensation of the exffect of the bond wires. So the circuit is than essentially the same as for the 4 pin version.

author: iMo
author_rank: Super Contributor
timestamp: September 03, 2022, 07:55:12 am
content: No idea how the ADR1399 model in LTSpice has been designed, but I've tried a simple test with pulsing 1mA load and the peak-peak transients with RC on the force side are 4x higher than when RC is on sense side (with the transistor buffer).. So the ADI's eval kit schematics with RC on the force pin (with the transistor buffer) is not correct, imho..

author: Kleinstein
author_rank: Super Contributor
timestamp: September 03, 2022, 08:21:04 am
content: With 2.2 mA the transistor as emitter follower has an output impedance of some 12 Ohms. So the somewhat worse reaction to fast peaks is not such a surprise. The extra transitor changes the circuit and can change the suitable compensation quite a bit. 1 µF at the base looks a bit high - chances are a smaller cap there and than some RC (could be different from 1 µF and 5 ohms) at the ouput would be OK.The spice model could be helping, but it really depends on how good the model actually is. A first test on the model would be how well it reporduces the output impedance in the LM399 like mode without the extra transistor. Even than it is not clear how much of the internal compensation is from which pin.

author: branadic
author_rank: Super Contributor
timestamp: September 03, 2022, 11:05:45 am
content: Quote from: Conrad Hoffman on September 02, 2022, 07:49:15 pmYou could consider building a circuit similar to the LM399-PWM-DAC, which works pretty decent and this reference was used for the EU CalClub test run within Germany.-branadic-

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 03, 2022, 07:12:48 pm
content: After playing with the LTSpice model for a bit, I'm sure I don't understand how the F & S lines work and where/why current flows where it does. On a board where everything is close together, it seems safest to just hard wire them together.

author: KT88
author_rank: Frequent Contributor
timestamp: September 03, 2022, 08:07:15 pm
content: QuoteThat's not what is happening...The emitter follower is the external part of a closed loop amplifier - it is just only a uni-polar output stage. No need to sink current...Running the sim in LTSpice gives an output impedance of only 1mOhm.Some significant advantages come with using an emitter follower:-The current through the shunt reference remains basically constant - the classic circuit shares the bias current with the load.-The bias resistor won't need to provide the load current - it can be larger.-A wide range of load currents are challenging for a shunt circuit - in paticular if larger load currents than the max bias current are required.-The power dissipation within the reference IC remains constant with changing load currents.CheersAndreas

author: MiDi
author_rank: Frequent Contributor
timestamp: September 03, 2022, 10:00:23 pm
content: Quote from: branadic on September 03, 2022, 11:05:45 amDocumentation for PWM-DAC is in threadLM399 based 10 V reference:Schematics & GerberFirmware

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 04, 2022, 03:13:20 am
content: Had some time for a crude measurement using manganin wire to isolate the package thermally. 0.011" diameter and about 0.2 ohms per inch. Just wired the heater and ran it on 15 VDC. Current stabilized at about 10 mA in free air, so I think this might be a useful trick. Probably better with some sort of insulation. I used to do the same thing with cooled CCD chips to lower the heat loss through all the wires. I got an IR reading off the edge of the chip of about 150F (65C) which is probably too low. Don't know the emissivity- usually I put a dab of flat black paint on things. Pretty sure the heater is working correctly. If you blow on the chip the current doubles. Still thinking about how to handle the reference wiring.

author: iMo
author_rank: Super Contributor
timestamp: September 04, 2022, 06:30:28 am
content: Quote from: MiDi on September 03, 2022, 10:00:23 pmIs that the latest schematics and firmware? I think there were some changes after the evaluation here by Andreas and Kleinstein..

author: iMo
author_rank: Super Contributor
timestamp: September 04, 2022, 07:51:38 am
content: The manganin leads shift the voltage a little bit (the refsense is rather fake here), but otherwise it should work.In the ADI's schematics (with the transistor) the higher the bias resistor R1 the worse regulation under variable load.@Conrad: here are the 3 classic examples - the worse load char is with the ADI's transistor, those with an opamp are the best (the graphs below are "ppm vs. load current" from 1uA to 5mA/10mA/20mA).

author: branadic
author_rank: Super Contributor
timestamp: September 04, 2022, 06:49:15 pm
content: Quote from: imo on September 04, 2022, 06:30:28 amI have a newer, slightly modified board version that also covers the ADR1399, so with the additional required filter.-branadic-

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 05, 2022, 02:43:33 am
content: Continuing with the measurements, I painted the top of the package black so I could get a good temperature reading. Seems to sit about 150-155F. With a small plastic cup to shield it, the heater current drops to 9.4 mA. I wonder if the die has some thermal insulation between it and the package.@branadic is that board available to purchase, or Gerbers?

author: branadic
author_rank: Super Contributor
timestamp: September 05, 2022, 05:59:08 am
content: Attached is the latest version of that board.-branadic-

author: miro123
author_rank: Frequent Contributor
timestamp: September 05, 2022, 08:14:05 am
content: R11 can be ten.. twenty times higher. 10K is good starting point.On such way you are avoiding the the cross couple with the noisy +15V line. For more info look at HP34401 schematics

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 05, 2022, 07:41:47 pm
content: I have tried to design the PCB for LCC version, but I'm not sure which way to go. The schematic is based on Analog design, I have only tried to add the NTC and have as much variability as possible (1 or 2 separate power supplies, with or without protection diode, added measurement/power supply point). But where I'm not sure is PCB design. I have prepared "neck" design, which is based on Analog PCB and later I have completely redrawn it to spider design, but I'm not sure which way to go.Additionally if you have the idea to make it even more universal you are welcome. At the end I want to have 2 PCB on 100x100mm plate with power supply in between and maybe also the amplifier to have 10V output.

author: branadic
author_rank: Super Contributor
timestamp: September 05, 2022, 08:30:39 pm
content: My recommendation for LCC package still is to put it on a flex board or use a flex-rigid board with the LCC package located on the flex part.-branadic-

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 05, 2022, 08:35:02 pm
content: No expert by any means but the neck design looks more straightforward. Not sure the spider buys much. I'm convinced that lowering the conduction out of the LCC package is important. Hollow an area under it- have to run traces outside only if you do that. I don't see any reason for the NIC pads to be there at all. I really want a 10V output on my board and it will almost certainly use thru-hole resistors in some pad-able/trimmable arrangement. On a small board I don't know if the sense connections buy anything if the traces have decent width. Caveat- I haven't sat down with PCB software and tried to do this yet!

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 05, 2022, 09:25:04 pm
content: @branadic I have checked the flex board pricing and for the first experiments it does not make too much sense. At least I have found prizes > $100. I will rather use 0.6mm pcb (prize is the same as for standard one $2 + shipping). But maybe it make sense to create on thin PCB only the "adapter" with pin header and create separate power and amplifier PCB from standard 1.6mm FR4. The idea with header have also advantage, that later the reference can be used in different design without need to desolder it.@Conrad Good point, I will remove the NIC padsThe enclosure around LCC package should be 3D printed or foam to hold the reference package in "stable" temperature generated by the inner oven.

author: cellularmitosis
author_rank: Unknown
timestamp: September 06, 2022, 05:44:17 am
content: Quote from: DavidKo on September 05, 2022, 07:41:47 pmHi David,Are you familiar with the "bootstrapped zener" circuit?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2022, 06:32:38 am
content: IN principle the kelvin connections with seprate sense and drive make some sense. However with the ADR1399 there is quite some current (2.2 mA) through the sense pins and this makes the separate sense pins essentially useless to compensate for trace and bond wire resistance, as most of the current still flows through the sense side. The separate force and sense pins still make sense to provider a lower output resistance, so to replace an extra buffer. However this is a relatively rare use case.Another point may be a few more options for the compensation, though the externa 1 µF + 5 ohms does not look so bad. For the shown impedance curves it looks like 1 µF is more on the low side and if a MLCC is used one needs to take into account the reduction in capacitance with bias. So I would more like plan for 2 x 1 µF or 2.2 µF or even more if this is a X7R or similar capacitor.To get a 10 V reference, the classical bootstrapped supply to the zener should be the best solution. There is than no real need to serparate the drive and sense side and one could join them right at the chip.One could still seprate the current and voltage path after connecting sense and drive.Even if mainly used as a 10 V reference it would make sense to also have the option to measure the raw 7 V. This would allow to see if drift is from the reference itself or the resistors to set the gain.

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 06, 2022, 09:21:56 am
content: @shodan@micron Kelvin point should be the two "crosses" close to the output. But I have messed that outduring my rework of the PCB (the crosses were right to the reference without cut out). The output should be directly connected the REFS not from current crosses. It will be easy modification.@cellularmitosis Such an approach can be used since the the heat power and reference power are separated. I think that the bootstrapped circuit is used in LM399 portable calibrator mentioned in datasheet. The bootstrapped circuit can be part of the free space behind the reference.I'm aware of quite high current to the sense part, that is why I have implemented transistor between power and REFS as close as possible to decrease the current as in Analog proto board. The board itself is intended to be experimental to try everything what came to your mind. This is also the reason for jumpers. For example I want to try to drive the reference sense with 2.2 mA from external current source (bootstrapped circuit will be good for it). Right now I have 3rd iteration and still I'm finding things to improve and every additional idea counts. Firstly I had planned to be able to use also TO version for ADR/LM 399 reference, but I had left that idea since there are better designs already available.Final design should be on 100x100mm board with 2 references, stabilized power supply and amplifier to 10V (ideal will be 2, but with option to use 1 amplifier and paralleling the references to experiment with noise). Thank you for your remarks, I want to remove big flaws before I publish the design.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 06, 2022, 12:09:39 pm
content: I've used the bootstrap circuit with good success when using 1N829 type diodes. It's what I had in mind for this, as I really want something just a few PPM under 10 VDC. Classic opamps might be OP-07, but what makes sense in 2022?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2022, 12:31:47 pm
content: For the amplifer on could consider an auto zero type like LTC2057, MCP6V51 or OPA189. There are a few slightly more modern alternatives to the OP07, like OPA207, OPA202 or ADA4077. The drift and noise from an OP07 or similar would still be less than the reference. So there is no absolute need for an auto zero OP-amp, but it would not really hurt either. Most of the modern ones come in SMD only.

author: iMo
author_rank: Super Contributor
timestamp: September 06, 2022, 01:33:57 pm
content: Quote from: DavidKo on September 05, 2022, 09:25:04 pmYou may create "microslots around the pads" (no idea what is the thinnest slot they can mill), say 0.3mm thick slots - that gives some flexibility too..

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 06, 2022, 04:29:37 pm
content: Quote from: Kleinstein on September 06, 2022, 12:31:47 pmI used an auto-zero in the Mini-Metrology reference and it worked OK. It didn't have much drive current, which messed me up the first time I tried to use it with low value feedback resistors. It was also easy to damage, which is OK if in a socket, but not so much for SMT parts. I'm surprised the OP-07 is still competitive! I'll look at the other choices.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 06, 2022, 04:39:37 pm
content: To get a little more drive power, one can add an NPN transistor as emitter follower in the loop. The gain setting divider already provides in minimum load.The OP07 is not really that competative - it is just one that is available in DIP and can be relatively cheap (some versions). Especially the power consumption is a bit on the high side compared to modern alternatives.

author: Extrasolar
author_rank: Contributor
timestamp: September 06, 2022, 06:15:47 pm
content: My Take to the 8LCC package, I opted for symmetric copper polygons or traces.

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 07, 2022, 07:55:52 am
content: @Extrasolar: My solution was symmetrical till I have added the transistor between REFF and REFS.@Kleinstein: I want to have DIP and SOIC option on one PCB, idea is to have "integrated" SOIC adapter.@imo: I can try that if there will be space on PCB. Additional transistor and NTC added additional connections.

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 10, 2022, 06:14:15 pm
content: I have simulated the bootstrap circuit. I have added TDP1603 in second iteration (LT5400-1 is used since it is in LTspice database). 200k start-up resistor is used since it is in original LM399 datasheet. I had played with "tuning" resistor placement and the 4R7 at the top was the winner. When I had placed the resistor in the bottom, the resistor was quite big in comparison with 1k - 1k resistor had tuned the resistor placed there.

author: iMo
author_rank: Super Contributor
timestamp: September 10, 2022, 07:19:04 pm
content: The problem with your LT5400 design is you are using 2 packages.The beauty of the LT5400 is its "ratio tempco" lower than 1ppm/C (ADI told me). That is achieved by placing all 4 resistors on the same chip. When you combine two packages you break that principle.I think there is no way to achieve <1ppm/C other than with a single LT5400 package.I did with single package w/ 10k resistors and my several measurements resulted in 0.5-0.6ppm/C (LM399), but you would get 10.57V or so. Any other discrete resistor added to the 5400 will kill that results, sure.PS: LT5400's resistor tempco is typ 8ppm/C and max 25ppm/C. Only the "ratio tempco" between the resistors (like tempco of R1/R2, or (R1+R2)/R4, etc.) on its chip is <1ppm/C.

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 10, 2022, 07:30:51 pm
content: Quote from: imo on September 10, 2022, 07:19:04 pmProbably it was not clearfrom my statement. LTspice does not have TDP1603, which I want to use (8 resistors in one package). Thus I have used 2x LT5400-1. I can have 8 standalone resistors in schematic instead, but this was simpler.

author: iMo
author_rank: Super Contributor
timestamp: September 10, 2022, 07:49:31 pm
content: Ok, when you want to simulate tempco you may simply add to the resistor value the tempco, like "10k tc=10e-6" for +10ppm/C and thus simulate N resistors with the same/similar tempco when in the same package.".step TEMP 20 50 1" will then step your simulation from 20 to 50C step 1C.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 10, 2022, 08:12:53 pm
content: The TC specs are usually for a relatively large range, considerably larger than relevant to a precision measurement. Much of the TC extremes usually happen at the temperature extremes. This especially applies to the better grade resistors, where it is not just the linear TV but also contributions from higher order terms. For the reduced temperature interval alone one can expect resistors to behave quite a bit better than the limits for the larger range.I have done some tests with NOMCA and ORN resistor arrays. In the tests involving different combinations the relative TCR was usually below 1 ppm/K, at least near room temperature. This is despite having much more tolerance in the specs.I would anyway less worry about the TC. The critical point is more the hard to predict long term dirft.From the excess noise the NOMCA type did not perform that great (barely meeting the specs), so I would not really recommend them. The noise of the LM1399 should still be a bit higher, though not much.In some circuits one can still combine the resistors from 2 chips, if they are mixed equally between the chips. Even if not perfect some interleaving can help quite a bit.A gain of 1.5 (e.g. use 3 equal resistors) combined with a -5% drop would be a real option, with the resistors for the 5% being about 20 times less important.

author: iMo
author_rank: Super Contributor
timestamp: September 10, 2022, 08:41:30 pm
content: I burned X megawatts of electricity while simulating all possible variants of the divider, but at the end of the day I always finished with a single LT5400 and 10.57V as the simplest and cheapest solution with lowest achievable tempco..Of course the long term stability of the divider is even more important (as you can measure the temperature pretty well)..

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 10, 2022, 10:47:13 pm
content: @imo: Mouser pricing TDP16031001BUF 6.62EUR (500ppm@2000h) vs. LT5400BCMS8E-4#PBF 10.03EUR (not in stock, <2ppm@2000h, cheapest version with worse matching that is not important in our case). For the testing purposes the Vishay is at least 3 times cheaper.

author: iMo
author_rank: Super Contributor
timestamp: September 11, 2022, 06:54:32 am
content: For you the most important params are the long term stability of ratio matching and ratio matching tempco. It looks like the Vishay array is much more worse than the ADI in those parameters. As the price both are comparable. There is a difference in the technology afaik, the Vishay is NiCr, the ADI is BiCMOS.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 11, 2022, 07:31:58 am
content: There is a difference in the technology: the LT5400 is NiCr on silicon. AFAIK the TDP1603 is NiCr on ceramics and in a larger size case. The case effects on how much mechanical stress from the PCB transfers to the actual resistor.The specs for those higher end resistor arrays are tricky, as some just represent the test-limits and not the actual performance. Things like the long term drift are very hard to test - at least not fast, so they can include them in the data-sheet when the part comes out.The TC specs are also hard to compare, as they are for different temperature ranges. The actual relevant range is likely much smaller again.For a single unit build one may not care that much about the spec limits, more about the typical performace. One would do some tests anyway and find out if one gets a poor sample.The big plus for the TDP1603 is that it has 8 resistors and not just 4. This allow to get a nomianl 7 to 10 ratio and thus no extra -5% step. With more resistors one also gets additional statistic averaging which can help quite a bit with the TCR matching.Despite the not that great spec limits ( < 5 ppm/K rel. TC for -55 to +125 C), I would consider the TDP1603 a reasonable choice. I would expect the TC matching more in the < 1 ppm/K range for the near room temperature range and thus good enough for the ADR1399.

author: branadic
author_rank: Super Contributor
timestamp: September 11, 2022, 07:33:34 am
content: QuoteDon't be fooled by the datasheet specifications, measure yourself. They behave way better than what the datasheet suggests. We already learned that for the noise figure and same is true for the matching. It only reflects that measurement limits of Vishay.If they were as bad as per datasheet, references such as W/F7000 wouldn't work as good as they do.-branadic-

author: iMo
author_rank: Super Contributor
timestamp: September 11, 2022, 08:23:30 am
content: FYI - I've found this PhD paper on the ADI's SiCr resistors in their 0.35um CMOS process, with an interesting measurement setup (most of you do at home, afaik)..Here is the paper..PS: it could easily be ADI will use them in the upcoming ADR1001 - that will solve all our problems, hopefully

author: cellularmitosis
author_rank: Unknown
timestamp: September 11, 2022, 08:38:36 am
content: Quote from: DavidKo on September 10, 2022, 06:14:15 pmJust a note: I don't believe the LT1001 inputs nor output extend to the negative rail (0V), so the startup resistor probably isn't needed. However, not a bad idea to include the footprint on the PCB anyway, in case you want to try other op amps.

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 20, 2022, 07:05:40 pm
content: I have updated the schematic and added the power supply. I have prepared it as symmetrical, but with half wave rectifier to be able to run from single output transformer.

author: Andreas
author_rank: Super Contributor
timestamp: September 21, 2022, 07:17:56 pm
content: Hmm,do you really think 10uF with one way rectification are sufficient for up to 200mA current on heat up?with best regardsAndreas

author: DavidKo
author_rank: Frequent Contributor
timestamp: September 22, 2022, 07:47:21 am
content: It is only placeholder. I have not calculated/simulated the correct value. The values can be different. Now I'm trying to fit 2 references + PS + amplifier to one PCB and be able to split it to 2 separate refences (without amplifier) if needed - I do not want to de-solder the refence from PCB.I'm still not sure if it make sense to use such a simple split power supply or to create one power supply with full rectifier and power both heating and reference from it. Reference part have this possibility, but the power part on PCB was intended for mainly for burn in. I have thought to use LM317+LM336 for reduced temperature coefficient as one supply for both parts.

author: Andreas
author_rank: Super Contributor
timestamp: October 01, 2022, 09:57:04 am
content: Hello,first ADR1399 populated on my ageing board.So after some initial checks/measurements the automated ageing measurement can start soon.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: October 03, 2022, 08:15:21 am
content: Hello,first 1/f noise measurement with the LS8-package here:its ~2.1uVpp in average with up to ~1uV popcorn noise on sample #01.So much more than the 1.4 uVpp from the datasheet.So following questions arise:- simply a bad sample?- is the 1.4 uVpp in the data sheet only for the metal can package. (branadic showed a measurement at beginning of this thread)https://www.eevblog.com/forum/metrology/adr1399-reference/msg4213732/#msg4213732- has the heater voltage a influence (data sheet condition 30V heater voltage against my 15V)?someone else with 1/f noise measurement for different packages/heater voltages?with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: October 03, 2022, 05:37:02 pm
content: Hello shodan,guessing that your 2 devices are both with the LS8-package.I now have measured my #01 LS8-Sample with 15V and 30 V heater supply from a linear power supply.(Zener supplied with 2K4 from 15V regulated battery voltage).Result with this setup is in both cases 2.0 uVpp average 1/f noise. -> not heater supply voltage correlated.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: October 03, 2022, 07:25:28 pm
content: I don't see the RC damping element for the ADR1399 on Andrea's PCB (it could still be on the back side). This may in theory add some noise from added rinding.The 0.1-10 Hz noise usually means a 10 second window for the observation - a longer window will add some noise from lower frequencies, from an amplifier. Over 10 s windows the noise looks a little smaller.Some of the rather low frequency part could be from mechanical stress / acoustic coupling. Without a cover there could also be thermal effects, even though there are no covar leads and thus hopefully less thermal EMF.

author: Andreas
author_rank: Super Contributor
timestamp: October 04, 2022, 05:14:33 pm
content: Hello,after populating the other ADR1399 in LS8-package I checked the Zener voltage with heater against the voltage with Heater off.on the x-Axis the zener voltage (in mV) with heater active.On the y-Axis the temperature drift (Heater active - Heater inactive) / Temperature difference.As temperature difference I assumed 60 K (95 degC - 35 deg C assumed temperature for self heating of the 3 mA zener current).Result is ppm/K between heater on and heater off.For me it looks like the the lower zener voltage has a lower unheated tempco.Maybe there is some zero T.C. near a zener voltage of ~ 7010 mV.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: October 04, 2022, 05:57:38 pm
content: It is normal to have a correlation between the zener TC and voltage. Normally a higher voltage means a more positive TC.The temperature range from some 90 C heated to some 30 C unheated is quite large and the 2nd order TC part can be relevant. So the parts with the least change from cold to hot would not have the lowest TC around 90 C.To get an idea on the TC at different temperatures one may have to look on the zener voltage chamge just after turning the heater off. I would not be surprized to see something like like voltage first going up and than down again.

author: Andreas
author_rank: Super Contributor
timestamp: October 08, 2022, 03:41:57 pm
content: Hello,overview over ADR1399#01-#04 with noise and (unheated/heated) T.C.All measured 1/f noise (0.1-10Hz) is above 1.9 uVpp/100 sec as average over 19 measurements.I found more or less popcorn noise on every sample with #4 being the worst with 1.6 uV.I want to operate the devices for at least 1-2 weeks before doing next measurements after initial ageing.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: October 09, 2022, 07:05:47 am
content: The cut-out around the references are nice for the thermals, but it would be better to have them in slightly different way. One could have them more in the 90 deg. angle scheme, so that if the center part expands from heat the center part could rotate a little in one direction to relief the stress.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 10, 2022, 09:46:36 am
content: The center island with the reference is still quite large. I think one could reduce it a bit by removing parts from the edges and corners. Less area mean less heat loss.The outside part with the OP-amps is quite dense packed and may get a bit warm. Some of the OP amps should get away with just a +15 V and GND for the supply to save on the power consumption and reduce the heat.

author: Andreas
author_rank: Super Contributor
timestamp: October 11, 2022, 04:28:27 am
content: Hmm,what is 0 deg and 90 deg (with regard to the pin position in room)the largest difference should be when the heater area is below the temperature sensor versus above the themperature sensor.https://www.richis-lab.de/images/REF01/21x06.jpgSo best guess: Pin 4 on top side versus Pin 8 on top side (with the LS8-package) would give maximum difference.Additional thermal isolation around the PCB should reduce the effect.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: October 11, 2022, 04:13:16 pm
content: The orientation effect can have two components: a chance in the thermals and a change in mechanical stress. Both would likely depend a lot on the PCB design and case. So interesting to note an order of magnitude, but a different design may behave quite different.With the TO46 metal case part of the effect can be local from the plastic cover that comes with it. Even there the air flow can be different.

author: opa627bm
author_rank: Regular Contributor
timestamp: October 13, 2022, 08:49:41 am
content: Stupid question here, any obvious improvement if I replace my LM399 in my Power Design 2010 to this ADR1399?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: October 13, 2022, 09:38:57 am
content: Quote from: opa627bm on October 13, 2022, 08:49:41 amIt is possible to reduce the output noise. This will work if the output noise is dominated by the noise of the reference source.

author: xerbo
author_rank: Contributor
timestamp: October 13, 2022, 06:49:25 pm
content: Mouser have recently got some evaluation boards in stock:https://www.mouser.co.uk/ProductDetail/?qs=4ASt3YYao0UVSWYehgmbvQ%3D%3D, users guide:https://wiki.analog.com/resources/eval/adr1399e-ebz.Bought one to test, for the price (£54 including VAT) it seems like a pretty good deal for a fully tested and assembled board.

author: Andreas
author_rank: Super Contributor
timestamp: October 17, 2022, 08:10:25 pm
content: Hello,some days ago I started with initial drift measurements on ADR1399#1 - #4.Initially I had placed the board above my LM399 ageing box.To see better the self heating of the ADR reference board I put it on a cooler place (a unused analog power supply).This gave up to 3 ppm jumps for 2-3 deg C lower board temperature.To exclude a rather large T.C. or a influence of the on board multiplexers (MAX4052A) I made T.C. measurements.So except for ADR1399#4 the box tempco near room temperature is below 0.1 ppm/K.All 4 samples had a negative T.C. near 25 deg C. (whereas on my LM399 I have more or less only a open hysteresis depending on rising/falling temperature).On ADR#1 I checked direct measurement of ADR output versus multiplexer output which gave no significant difference.So I have to look for different influence on "position dependant drift".with best regardsAndreas

author: dietert1
author_rank: Super Contributor
timestamp: October 27, 2022, 03:12:16 pm
content: Quote from: xerbo on October 13, 2022, 06:49:25 pmOne of those arrived here yesterday. It works, yet i don't know whether those AD people understand what they are doing. Not only the switchmode converter and the missing low thermal EMF output.In their wiki they explain they wanted to make something "portable calibrator style". But where is the calibration value? I got "7.05 V" that's it. Probably they can do a precision measurement, but they didn't do so?Guess their 573 € LTZ1000 kit is similar and the chinese offering an LTZ1000 board on ebay for a fraction of the price understands better what a reference is good for.Sorry for the rant.Regards, Dieter

author: xerbo
author_rank: Contributor
timestamp: October 28, 2022, 05:36:45 pm
content: The utilised switchmode converter is isolated and has a built in low noise linear regulator so should be fine. As for the terminals I think they are going for the "give it as much thermal mass as possible to minimise thermal gradients" approach, weather or not that is effective I don't know (probably not very).But as a portable calibrator it is totally and utterly useless, the fact you already need a already calibrated voltmeter is probably a killer for most people.

author: iMo
author_rank: Super Contributor
timestamp: October 28, 2022, 05:53:41 pm
content: You have to burn-in it for 1k5 hours at least.. ADI will not do it for us, imho. But a good opportunity for the voltnuts here to offer the "calibration" of the module after the burn-in period. The switching regulator - best to look at the input/output voltage with an o'scope or similar.. And it is an evaluation kit, so we have to evaluate

author: Kleinstein
author_rank: Super Contributor
timestamp: October 28, 2022, 06:12:06 pm
content: Many of the commercial, isolated DCDC converters produce quite quite some common moder interference. So there is some capacitive coupled current between the 2 ideally isolated side. This may not effect the reference circuit itself, but it may effect some DMMs or amplifiers used for the test.The problem with the common mode interference is, that it is hard to filter.

author: dietert1
author_rank: Super Contributor
timestamp: October 29, 2022, 06:55:59 am
content: Quote from: imo on October 28, 2022, 05:53:41 pmStarted evaluation by hooking it up to an unused 6.5 digit meter and it shows 7.04264 or 7.04265 from the start. Most people would do this with a pocket calibrator. I mean, the referenceisa reference at the 6 digit level, yet of unknown voltage except 7.0xx V. When i ordered references from Mr. Geller 13 years ago, they came with calibration info. This know-how has been around for many many years.When there is some spare time, i will probably add a linear supply and a 10 V output stage/buffer with a NOMC array divider in order to make it 10 V and integrate it into my scanner setup.Regards, DieterPS: First step already finished. On a LM723 based linear supply with 15.002 V (switchmode supply inactive) the reference yields 7.04277 V into the same meter. An up shift of 17 ppm.After undo and running it on USB-C again it comes back to previous value, so it isn't damaged. Supply is 14.4 V now and a bit noisy.

author: iMo
author_rank: Super Contributor
timestamp: October 29, 2022, 08:02:51 am
content: Many companies go Agile these times.. The calibration of the module will be done by ADI in the next Sprint, after the Sprint Review, Retrospective Meeting, Backlog Refinement Session, new Sprint Planning, provided the Product Owner agreed that with the Scrum Team and the Scrum Master and the Calibration will be put into the Product Backlog as the new Story in the 1399 Epic, with enough Story Points to be Burned-down during the Calibration Sprint.

author: dietert1
author_rank: Super Contributor
timestamp: October 29, 2022, 03:24:40 pm
content: My previous supply test detected another design problem of the evaluation board: The ADR1399 won't be low noise and stable to 1 uV without a well made bootstrap gain stage. Calculate: 120 uV shift for a 0.6 V supply change results in a +/- 5 mV requirement for the supply. Also i am wondering about the resistor they used to feed current into the ADR1399.Already replaced the two zero ohm resistors next to the reference by pieces of copper wire.Regards, Dieter

author: miro123
author_rank: Frequent Contributor
timestamp: October 29, 2022, 09:57:39 pm
content: Quote from: dietert1 on October 29, 2022, 03:24:40 pmHow do you calculate this numbers? Here are mine.R4=1.33k R=0.04Ohms for TO46 R=0.011Ohm for LCCTo46 sensitivity is =0.04/1330 =1/ 33250 - 33,25m shift make 1uVLCC = 0.011/1330 = 120909 - 121mV makes 1uV

author: dietert1
author_rank: Super Contributor
timestamp: October 30, 2022, 07:28:00 am
content: My numbers are an observation. When i connected a 15.002 V linear power supply to the test points, reference output shifted up about 120 uV (17 ppm of 7 V). To check whether i damaged the reference, i reverted the change and it returned to the previous output voltage. Then i measured the supply from the switchmode converter to be 14.4 V. So a 0.6 V supply change caused 120 uV output voltage change.There could be other side effects, like heat or RF emitted by the switchmode converter.Did you notice that everywhere in the datasheet they recommend to feed 3 mA into the reference, but the 1K33 in their evaluation kit feeds about 8 V/1K33 = 6 mA.Meanwhile i made the bootstrap/gain stage and i need some idea how to feed 10 V into the nice thermal protection without damaging things.Regards, Dieter

author: MiDi
author_rank: Frequent Contributor
timestamp: October 30, 2022, 07:47:06 am
content: Made the rejection ratio calculations for bootstrapped LM399 & ADR1399 some time ago, Excel attached:

author: opa627bm
author_rank: Regular Contributor
timestamp: October 31, 2022, 09:59:40 pm
content: Apology if I didnt read through the entire thread.Anyone is having the EVM drifting due to the 1Mohm isolation resistor between the AGND and PDNG?For the ADR1001 it is using the same design and I have 2 EVMs that is showing the same (kind like EMI ) issue, and I ended up bridging this resistor.

author: dietert1
author_rank: Super Contributor
timestamp: October 31, 2022, 11:57:46 pm
content: By "bridging the resistor" you mean a short? This shouldn't be necessary. You can keep isolation by using a small capacitor to bridge the resistor, like the 4.7 nF found in many switchers. Then you keep the reference voltage isolated.My impression was the switchmode converter isn't stable enough, so i am using an alternative linear supply. My ADR1399 EVM also got the bootstrap/gain stage. Not the one calculated by midi, but the "real thing". It has a chopper amplifier and a NOMC divider and outputs 10 V to some ppm. Put the whole circuit into a metal case. Running in my scanner setup, hourly averages exhibit noise of about 2 uVpp plus strong initial drift of -2 uV/day. As this is a new build, both noise and drift should calm down soon.Regards, Dieter

author: opa627bm
author_rank: Regular Contributor
timestamp: November 01, 2022, 06:59:36 am
content: Quote from: dietert1 on October 31, 2022, 11:57:46 pmYes, I can try the capacitor too. The ADI engineer told me the PSRR from the part should be good enough for it ...

author: Andreas
author_rank: Super Contributor
timestamp: November 04, 2022, 08:00:28 pm
content: Hello,some further measurements regarding PSRR of the heater voltage.compare also the measurement of macaba:https://www.eevblog.com/forum/metrology/adr1399-reference/msg4114465/#msg4114465In my case I use a positive heater voltage from 9-30V (supplied by a external analog power supply).Below 15V the PSRR gets quickly worse from ~0.5ppm/V up to 1.2 ppm/V.2 samples of LM399 (in TO-46) seem to be slightly better especially at low heater voltages.unfortunately I still have not found the "position dependant drift"https://www.eevblog.com/forum/metrology/adr1399-reference/msg4468918/#msg4468918maybe there are several different reasons:Partly a explanation may be that on the LM399 ageing box the temperature distribution at the output connector is more equal.Measured 2-3 degrees difference near left and right pin of the connector due to the heaters of the ADR1399 on one side of the pcb.But also direct soldering of the measurement lines near the "far" multiplexer did not solve the differences between hot and cold place.I additionally found out that the temperature of the multiplexers varies by up to 3 deg C depending on the level of the Adress/chip select lines.So obviously the level shifters in the MAX4052A need considerably high power when not being at the Gnd/VDD level. So I might need external level shifters to keep heating away from the multiplexers.with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: November 04, 2022, 08:09:56 pm
content: The quite variable power level for the max4052 is interesting. This could indeed be a problem for a precision measurement. There can be 2 parts: the level shifters and inputs that get a relatively weak signal. 74HCT... also show surprisingly high supply current with 3 V at an input, though a perfectly OK input level.

author: Andreas
author_rank: Super Contributor
timestamp: November 05, 2022, 07:29:39 pm
content: Hello,yes current consumption is unexpected high.With 15V supply voltage and 5V from processor on the adress and CS lines I get up to 85 mW power consumption for one MAX4052A (with the same date code).So I am waiting for the level shifter boards. (BSS138 based).with best regardsAndreas

author: dietert1
author_rank: Super Contributor
timestamp: December 03, 2022, 04:52:24 pm
content: The ADR1399 evaluation board i mentioned above was put into a hermetic enclosure. It got an OPA189 buffer that is a 7 to 10 V gain stage with a NOMC divider and a Sallen-Key low pass filter with two Wima MKP4 10 uF/250V. After observing a TC of about +0.2 ppm/K i made the enclosure a simple thermostat with an analog PI controller. Image shows heater resistor, transistor and NTC. Controller and power supplies are still external.After the most recent temperature controller mod about 32 hours ago (arrow) reference noise is down to about 0.8 uVpp in comparison to the average of our two LTFLU references. ADR1399 datasheet allows about 2 uV per 10 V. Drift estimate after one month of operation would be 180 nV/day = 6 ppm/year (probably overestimated).There are still events decreasing voltage, so it needs more "education".Regards, Dieter

author: branadic
author_rank: Super Contributor
timestamp: December 03, 2022, 05:21:25 pm
content: Why don't you add a bit of copper in the 7V --> 10V gain stage to compensate for the remaining t.c. overall?-branadic-

author: dietert1
author_rank: Super Contributor
timestamp: December 03, 2022, 05:55:38 pm
content: I didn't have the time and right now i don't know whether- the NOMC divider suffered a minor TC while fine tuning for 10 V or- whether it is the ADR1399 or- whether it is the Pomonas' fault (thermal EMF).It's an experimental setup. Next time i'd probably use soldered connections for the reference voltage output or move the hot reference further away from the Pomonas.The temperature controller and the precision parts of the power supply should go into the box. One of the tests to do yet is running the ADR1399 with its heater off. The thermostat is good for +/- 20 mK.My conclusion is that the ADR1399 with its increased zener current and its current price isvery interesting. Once the TO-46 version arrives at the distributors one should try an array.Regards, Dieter

author: Andreas
author_rank: Super Contributor
timestamp: December 22, 2022, 07:44:26 pm
content: Hello,I want to give some update to the "position dependant drift".The main factor is obviously thermal drift (ppm/K) of the references.If I do not use the environment temperature but the PCB temperature the value increases up to 0.3 ppm/K.(see overview).I tried to compensate the readings with the PCB temperature.But the improvement is much lower than I would expect it.There is a remaining "low frequency noise / instability" of the values of about 2 ppm.This is more than that what I usually get with my measurement system.So the questions for me are:- Is this related to my setup or do others also have larger instabilities with ADR1399 than with LTZ1000 or LM399?- Is it only the LS8 package or is it also characteristic for the TO package?At least it seems that the initial ageing drift is rather low.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 23, 2022, 10:50:08 am
content: Hello,I also did some tilting tests in 6 orientations of the PCB.0 = top = component side of PCB on top5 = bot = solder side of PCB on top1 = north = Pin8 ADR1399 on top2 = east = Pin6 ADR1399 on top3 = south = Pin4 ADR1399 on top4 = west = Pin2 ADR1399 on topI had guessed that between north and south (PIN 4 and 8 ) there would be the largest differences.https://www.eevblog.com/forum/metrology/adr1399-reference/msg4457818/#msg4457818But there it seems that I was not completely correct.Pin 4 on Top = south = 3 gives mostly (not always) the highest output voltage.Pin 6 on Top = east = 2 is likely to give the lowest output voltage.The tilting drift amplitude with some thermal isolation is comparable to that what I also usually have on LM399 devices.(see overview in previous post)with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: January 08, 2023, 07:08:25 pm
content: Some of you already know that I've revised the PWM-DAC board, now called xx99-PWM-DAC, that allows to populate the ADR1399 and its snubber network too. One of the boards was assembled and tested. I populated the same components such as 20 MHz crystal that I've used on the LM399-PWM-DAC and used the same firmware (8.16), but measurements weren't satisfying and I observed huge spikes.I finally ended up sacrifying my LM399-PWM-DAC board which was used for theEU-CalClub test runand frankensteined the ADR1399 to it. I also changed the 2W NTC connection to a 4W one and took, after some adjustment of the gain, first measurements. For some yet unknown reason no such spikes are visible here, but with the filtering as it is by now the noise at the output is larger than it should be, but still an improvement with respect to the former populated LM399.-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: January 08, 2023, 09:32:56 pm
content: Hello branadic,is it the TO-46 package?how much thermal isolation has been used?with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: January 08, 2023, 09:38:35 pm
content: Yes, TO-46 package as I don't have trust in that ceramic SMD packages without proper low strain assembly solution such as FlexPCB.There is a bit of foam block around it, similar to what was used for LM399-PWM-DAC.-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: January 08, 2023, 10:09:03 pm
content: Quote from: branadic on January 08, 2023, 09:38:35 pmHmm,I measured 55 mA Heater current @15V and room temperature for 4 populated ADR1399 in LS8 package on my PCB with some thermal isolation:one cotton pad around the edge of the PCB + some thin (2 mm) foam foil.So only 14 mA per LS8-package (+3mA Zener current)I fear with a FlexPCB the environment temperature limit to no thermal stability is reached soon.with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: January 10, 2023, 08:36:28 am
content: I don't see why the FlexPCB should be worse in performance. What I have in mind is a small breakout board LS8 to through hole connections on one side only, so that the FlexPCB is floating underneath the LS8 footprint to prevent mechanical stress to the package. Does that sound reasonable to you?-branadic-

author: iMo
author_rank: Super Contributor
timestamp: January 10, 2023, 06:35:03 pm
content: I mentioned this issue in the adr1001 thread too - a need for a flex board as well..@Andreas - what is the env temp limit to no thermal stability? Is that defined somehow in the DS?

author: Andreas
author_rank: Super Contributor
timestamp: January 10, 2023, 07:30:59 pm
content: Hello,no its not specified explicitly.But you should stay away from the 90 deg C setpoint with the chip temperature.And that with the 3 mA zener current.Quote from: branadic on January 10, 2023, 08:36:28 amIt is worth a try. (in comparison to the TO-46 package).By the way did you test already the T.C. of the devices in TO-46 package?My LS8-values are higher (>=0.08 ppm/K) than the values that I have from the LM399 measurements (<= 0.07 ppm/K) near room temperature.with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: January 11, 2023, 05:26:38 pm
content: QuoteNo I didn't and probably won't for the individual samples, but for the overall circuit including the gain stage. In the end I'm not that much interested in what every component contributes, but in compensating the final circuit for low (almost no) t.c.-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: February 05, 2023, 03:34:47 pm
content: Hello,to come back to the "position dependant drift"https://www.eevblog.com/forum/metrology/adr1399-reference/msg4597733/#msg4597733after having added the level shifters between processor and multiplexers I added 2 LM399 to the PCB which I had in the drawer to exclude some drift by the multiplexers.Unfortunately both LM399 (from LT) had a large initial drift.Additionally #2 of the both LM399 had initially popcorn noise which I recognized on a first T.C. testAfter some checks with constant temperature I recognized that the temperature compensation with respect to the PCB temperature (0.3 ppm/K on #4) showed some "over compensation".So I finally measured the T.C. of ADR#01 - #04 again which was surprising to me.The PCB temperature range with the same environment sweep has been reduced (and shifted to higher temperature) by the adittional "heaters" on the PCB.The ADR in LS8 package do not correlate well to the PCB temperature.But they obviously correlate good to the "environment" temperature (which is sensor glued to a heatspreader aluminium plate below the ADR1399 test PCB).Attached a "overlay" between a old and new measurement of PCB related TC and environment related TC of ADR1399#03 which obviously driftet nearly zero since last T.C. measurement which was end of november.So now I can explain the position dependant drift:I relied on the PCB temperature sensor near the multiplexers to compensate for environment temperature.Initially I had 2 degrees self heating of the multiplexers due to missing level shifters creating PCB temperature rising which does not correlate to the behaviour of the ADR1399 which react more to the environment temperature.Also placing the ADR1399 PCB above another heat source gave a large temperature gradient between the both PCB temperature sensors of +7/-2 deg C difference.Additional point:We had some rather cold days where I had down to 17 deg C in my lab.Normally the T.C. of my measurement devices (24 Bit ADCs) is temperature compensated so this should be no issue.But with my other daily measurements I recognized that the standard deviation of my ADCs has nearly doubled from 0.25 ppm to nearly up to 0.5 ppm.And partly some devices developed some kind of popcorn noise.In the beginning I only evaluated one ADC (ADC#13). Now I am evaluating all 3 stable ADCs (#13, #15, #16).comparison ADR1399 vs. LM399- the 2 lm399 show a much larger initial ageing drift as the 4 ADR1399LS8 samples.- The T.C. of both LM399 (TO-46) samples is lower than the 4 ADR1399LS8 samples.lessons learned:- the PCB temperature is not usable for temperature compensation of ADR1399LS8.instead I should use a Metal housing and measure the temperature below the PCB.- Never rely on one single measurement device for ageing measurements.- Build a ageing PCB with some kind of injection channel for a proven stable reference (Like my LTZ#4 and/or LTZ#9) as sanity check.with best regardsAndreas

author: r6502
author_rank: Regular Contributor
timestamp: February 13, 2023, 07:23:54 pm
content: Hello All,I will get some ADR1399 in LCC version and I lokked at the data sheet if there are informations given, where to place the damping network, sould it be placed cloce to the pins, like you do with caps for decoupling, or can it be a litttle more far away? Should they be close by pins 1/7 or better close by pins 2/6 or where both connections are joined when usig kelvin connection. Or connect pins 1/2 and 6/7 direct at the chip and place the damping network there?Guido

author: Andreas
author_rank: Super Contributor
timestamp: February 13, 2023, 08:58:45 pm
content: Hello,if you look at the user guide (evaluation board) schematics:https://wiki.analog.com/_detail/resources/eval/adr1399e_schem.jpg?id=resources%3Aeval%3Aadr1399e-ebzits more on pin 2 + 6.But on the other side they have used the bridges instead of the transistor.So I have simply connected both pins at the chip and put the network directly under the chip on the soldering side (together with the cap for the heater).with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: February 13, 2023, 09:09:35 pm
content: The damping part is mainly relevant for frequencies of some 50 kHz to some 1 MHz. So the exact position should not really mater. More distance from the chip (e.g. away from the heat) and also more to the sense or force should not matter that much. A position more to the force side makes sense, especially if there is an additional transistor driver in between as in the evaluation board.From the shown imedance curve it looks like the capacitance is more in the low side. Especially with MLCC capacitors I would plan with space for 2x1 µF to at least compensate of the biasing effect and not get much below 1 µF.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 14, 2023, 09:53:56 am
content: Hello all,Did anyone compare the LS8 package vs TO?Particularly, I am interested in the long term drift, but suppose nobody has this info at this stage?

author: Andreas
author_rank: Super Contributor
timestamp: February 14, 2023, 04:19:42 pm
content: Hello,I still have no TO-46 samples.The only thing that I can say:I have difficulties with the LS8 package to monitor any useful ageing data.The tempco is rather high on my samples.And the LS8 package is rather picky about the location of the temperature sensor.I hope that I will have a better setup for ageing monitoring at end of this week.with best regardsAndreas

author: alex-sh
author_rank: Regular Contributor
timestamp: February 14, 2023, 07:19:55 pm
content: Quote from: Andreas on February 14, 2023, 04:19:42 pmAndreasDo you think this is just your samples or this is a general rule of thumb for LS8?

author: Andreas
author_rank: Super Contributor
timestamp: February 14, 2023, 08:02:08 pm
content: Hello,We have still not enough measurements (4 on my side) to make any statistics.with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: February 15, 2023, 05:18:54 pm
content: I have measured my ADR1399-PWM-DAC 10 V voltage reference over temperature (18 ... 28 °C) against an internal temperature sensor with the result of -0.223 µV/V/K.-branadic-

author: JodelJonny
author_rank: Contributor
timestamp: March 01, 2023, 12:23:54 pm
content: Hello thereI am new here. After sucessfully repairing a HP3456A I solwly but surely waddle alogng the path towards voltnuttery. And after years of silent observing I now have decided to try to build a 10V reference based on the ADR1399. The LTZ1000/ADR1000 is just unreasonably expensive and overkill for now.I designed a simple PCB based on the circuit from the datasheet.I think that should work out. Do you argee? Are there any errors or things I should improve before ordering the parts?The resistor divider to amplify the aprox. 7V to close to 10V is planned to be build from Vishay TNPU e3 0805 smd resistors with 0,1% and 5ppm. There are a multiple footprints to be able to tune the output close to 10V and they are all encloed with copper planes on both sides of the pcb to keep the temperature differences between them small.I plan to supply it with stable 15V DC from a simple linear transformer power supply. Or would it be better to include a 7815 on the pcb?The reverse polarity protection is handled by a DMP3099L-7 P-channle mosfet. I think it can do that job without any additional components, or did I overlook something?Thanks for the feedback! :-)

author: iMo
author_rank: Super Contributor
timestamp: March 01, 2023, 01:28:16 pm
content: I would not place the 7815 on the board (it changes its temperature based on the mains voltage and adds a heat source).The 7815 should be there but after the protection mosfet.I would use the 1399_zener_bootstrapping from the opamps output. That would require to add a transistor in order to de-load the opamp's output.

author: dietert1
author_rank: Super Contributor
timestamp: March 01, 2023, 06:04:58 pm
content: Maybe produce a reference modul that fits into the HP 3456A? The ADR1399 can be used as an upgrade for the existing LM399. The 10 V to 7 V divider and the buffer transistor that are external to the HP reference module can be optional parts, maybe hidden on the bottom of the board.Regards, Dieter

author: JodelJonny
author_rank: Contributor
timestamp: March 01, 2023, 07:12:47 pm
content: @imo Good point about the bootstrapping. Didnt really understand that before but now I think I do. I added Q2 and reduced the value of R1 to 1k to maintain 3mA zener current.What transistor should I use? I dont have much expereince with all this. I guess the specs are not that important.@dieter1 The 3456A ist right now the only thing in my posession of wich I can at least assume that it is reasonably stable and likley even still kinda accurate.Long story short. I wont touch it until I am sure to be able to monitior the cosequences of my actions. But this might be an interesting projet for the future.

author: dietert1
author_rank: Super Contributor
timestamp: March 01, 2023, 07:36:29 pm
content: I did not propose to touch the HP 3456A, but to contribute something useful. It's a plug-in module with connectors, easy to exchange. I would never unsolder a LM399 from a HP reference module, but make a replacement module.Sooner or later compatible reference modules with ADR1399K will be requested. They also fit the HP3457A. We have in total 7 of those meters.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: March 01, 2023, 08:03:21 pm
content: Quote from: JodelJonny on March 01, 2023, 07:12:47 pmAny modern transistor will do. It also depends whether you want an output current limitation for safety reasons, that would require 2 transistors, and also sometimes people shift the opamp's output voltage to a lower value by a zener diode, like below. But is depends what you want..PS: the R7 sets the current limit roughly..

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2023, 08:08:11 pm
content: There is usually no need for the extra diode D1 in series with the zener.In many cases one would also need additional capacitive feedback directly from the OP-amp for stability.For the OP-amp there is no need for the relative expensive LT1012. A relatively cheap OPA202 may be a better choice.

author: JodelJonny
author_rank: Contributor
timestamp: March 01, 2023, 10:01:21 pm
content: Thanks for the great advice!So in the circuit shown by imo the opamp is sinking current or pulling Q1 down towards the Out_level against R4, correct?May I ask why one would like to shift the opamp's output voltage lower? And what is the idea behind D1?I copied the LT1012 from the ADR's datasheet but I'll happily save the money if OPA202 is good enough.Overcurrent protection would be nice to have. Little accidents do happen.What I want is a simple and cost effective voltage standart to give me a stable reference to compare my 3456A to and use is as a transfer standart so I could bring home a known voltage if I come across an oficially calibarted precision multimerter. That combined with learning about analog desing, pcb layout, metrology and so on. This part is already working.@dietert1 Sure but right now I have no way of evaluating the perormance of such a desing. Thats one of the reasons I am building a Voltage refernece

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2023, 10:34:31 pm
content: For a 10 V reference there is no real need to use the zener diode to shift the level. One sometimes does this to get an output voltage closer to the supplies (e.g. 14 V out from 15 V supply).The diode D1 may be wanted, so that the base current to the transisor is only from the resistor and not from the OP-amp. Usually the op-amp outputs are current limited and thus no real problem without D1, but the diode would not hurt either.The OPA202 is nearly rail to rail out, and one may still need some startup mechanism, if the zener current is taken from the 10 V. The zener diode part would provide the start-up.Ideally one would want to have both an output for the 10 V level and the raw 7 V from the reference, so that the gain drift does not matter and can be checked separately. It could be enough to just have a series resistor (e.g. 1 K range) as a crude protection for the raw reference.

author: Andreas
author_rank: Super Contributor
timestamp: March 02, 2023, 07:47:59 am
content: Quote from: JodelJonny on March 01, 2023, 10:01:21 pmHello,I think: for a single device the price of the OP-Amp should not play any role.I think you should take more care about star grounding. (A power plane easyly can carry some 10 uV from heater current).Thermal management is also to consider. (Thermally isolating and packaging into a metal housing to avoid large temperature gradients).Depending on how stable your lab temperatures are you should take also care to select the right reference and divider resistors.A LM399 might give better results than a ADR1399.At least some temperature sensor would be needed if you want to transfer the "volt".I would at least put some 100 nF capacitors directly at the Heater pins and the zener output to avoid EMI drifts. (for the ADR the 5R 100nF should be placed very close to the zener).And the buffer amp output also should be also shorted with a 100 nF (of course with a isolation cirquit against capacitive loads).see example here:https://www.eevblog.com/forum/metrology/emi-measurements-of-a-volt-nut/msg2684100/#msg2684100I would build at least 3 devices to observe ageing drifts or drifts related to temperature shocks during transport of one device.Otherwise you will never know wether the volt that you measured on calibration is the same that you imported into your lab.I had a 4 ppm drift on a LM399 before and after calibration. I finally recognized that the LM399 output is dependant on orientation.So I now mark the housing of the LM399 reference where the "Top side" has to be.with best regardsAndreas

author: JodelJonny
author_rank: Contributor
timestamp: March 03, 2023, 11:43:38 am
content: Thanks again!I tried to understand and implement your suggestions. To be honest, the amount of information in all those threads is quite overwhelming at times, especially since I have no formal education in electronics.I plan to mount the pcb in a metal housing with temperature sensing but I am not sure were I want to measure the temperature.@Andreas I have now added two 100nF caps (C6 &C7) directly at the pins of the ADR1339. One of which is now in parallel with the 5.1Ohm 1uF (R3 & C3) RC circuit from the datasheet which I also moved on the backside and very close to the pins. Is that correct or are those circuits redundant?I am not sure about what you meant with the 100nF to short the buffer amp output and the isolation circuit against capacitive loads. I added C5 in the schematic.I switched to a ground plane on the back side and added some slots to break temperature gradients and thermally isolate the ADR a bit.I hope it is now better and would appreciate further feedback :-)

author: Kleinstein
author_rank: Super Contributor
timestamp: March 03, 2023, 12:34:10 pm
content: The temperature sensor should be more at the resistors to set the gain - not directly at the ADR1399, where the temperature is regulated in parts..For the temperature sensor I would more prefer an anlog one, like PT1000 , 10 K NTC or maybe just a diode.The ground plane is not a valid replacement for a star ground. I would prefer less ground around the LM1399 to reduce the heat loss even more.The configuration for the gain setting resistors looks a bit odd. The required gain is a bit less then 3/2. So the fist approximation could be 3 identical high grade resistors (e.g. 10 K) and than some additoinal fine trim pallel to the one on the high side. To get fine trim without very high values the fine trim would ideally be 1 resistor (~ 65 K ?) in series with some 3-4 in parallel (e.g. 5 K + .... ).

author: iMo
author_rank: Super Contributor
timestamp: March 03, 2023, 02:11:20 pm
content: Here is an interesting setup with 8 resistors (an array), I've tried to sim it and a resistor in series with the low side 10k one, around 450ohm, could be used for the fine trimming (do simulate the stuff with your values first).https://www.eevblog.com/forum/metrology/statistical-arrays/msg4703825/#msg4703825Also, as I wrote above, the 15V voltage regulator should be placed "after" the mosfet, otherwise you get -2mV/C at the 15V supply.The 22k and 15ohm in the buffer were examples only in my schematics, you have to adjust that values based on your requirements.To the 100nF feedback capacitor at the opamp - do we really need it? Where the instability comes from? From the output load capacitance? Could we somehow calculate the value really required? The output buffer is an emitter follower with no gain, imho.. Moreover I did some simulation in past and I saw decreasing PSRR of the opmap with increasing the value of that capacitor. But perhaps that is just an issue with the opamp model used..

author: Kleinstein
author_rank: Super Contributor
timestamp: March 03, 2023, 02:26:33 pm
content: Some capacitance for C5 is likely needed due to the capacitive loading. How much depends. With the output capacitance one shoud aim for C5 * R5 > 2*C6*R12 . So less than 100 nF should be OK, more like the 1 nF range.The MOSFET used as a kind of ideal diode may give less than -2mV/K, but still not ideal. I would not mind a LDO on the PCB that much, at least as an option to populate.

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 03, 2023, 03:12:01 pm
content: Next week I receive several units of the ADR1399I started doing simulations in LTSPICEto volt reference 10 voltsIn your opinion, there is something to change in the circuitI have a lot of vishay precision resistors 0.01%of10K5K2.5K1K100 ohmEtc. etcSo I will use themI have dozens of units

author: iMo
author_rank: Super Contributor
timestamp: March 03, 2023, 03:36:30 pm
content: Here is an example re PSRR - the injected 200mVpp 50Hz hum into 15V Vcc translates into 3.7uVpp with the 1nF, and into 310uVpp with the 100nF feedback capacitor..

author: Andreas
author_rank: Super Contributor
timestamp: March 03, 2023, 06:45:16 pm
content: Quote from: JodelJonny on March 03, 2023, 11:43:38 amHello,C7 can only be used with a LM399C3+R3 is needed by the ADR1399 for stability. C7 will lead to oscillations here.Quote from: Kleinstein on March 03, 2023, 02:26:33 pmits more like C5 * (R5||R4) > (C6 + CLoad) * (R12 + semiconductor resistances)100nF is plenty but you do not need to optimize for speed.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: March 03, 2023, 06:47:02 pm
content: Quote from: imo on March 03, 2023, 03:36:30 pm200 mV is insane.if you have more than 5 mVpp you should work on your star grounding concept.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: March 03, 2023, 07:21:18 pm
content: Quote from: Andreas on March 03, 2023, 06:47:02 pmThat is just an example to visualize/demonstrate the issue. The larger the feedback capacitor the lower attenuation of a potential noise coming from the Vcc (provided the simulation works ok).. What is important is to see the ratio 1nF/100nF == 3.7uVpp/310uVpp.. Thus with your 100nF FB capacitor the Vcc noise attenuation (related to the 10V output) is 100x lower than with the 1nF FB capacitor..

author: dietert1
author_rank: Super Contributor
timestamp: March 03, 2023, 07:34:08 pm
content: Yes, the simulation shows that for all practical purposes there is no problem. Use a power supply with less ripple and try various capacitors to find a small capacitance that gives good stability. I'm not shure the simulation can resolve this. One possible method to improve stability is a small capacitor from the opamp output to the output transistor base, once more like 1 nF or below.One can also replace R4 10K by a JFET constant current source. With the zener between opamp and transistor one can run the opamp from the 10 V output voltage in order to eliminate supply drift/ripple going into the opamp. Then the only entry point left is the collector of the output transistor.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: March 03, 2023, 07:53:20 pm
content: @dietert1: Something like this..

author: dietert1
author_rank: Super Contributor
timestamp: March 03, 2023, 10:18:17 pm
content: Yes, appears to work. As far as i understand ripple with 100nF is down from 310 to 9 uV. With a 1 nF capacitor you should be down from 3.7 uV to about 120 nV. At 200 mV supply ripple.Regards, Dieter

author: Kleinstein
author_rank: Super Contributor
timestamp: March 04, 2023, 08:06:36 am
content: The use if the LT5400 for the gain is an interesting solution. Combining a separate resistor with the LT5400 array is not ideal, though may still be acceptable for only some 2% of the final voltage.The suggested LT1113 in the plan is however not a good choice, as it has too much 1/f noise. I would more look at LT1013, OP07, OPA202, OPA207 or ADA4077 or maybe an auto zero type like LTC2057 or MCP6V51.It would make sense to plan for at least some filtering and an output stage that is capacitive load tolerant like discussed before.

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 08:10:41 am
content: Quote from: Kleinstein on March 04, 2023, 08:06:36 ami am going to use the ltc2057 i order them the 925 ohm resistor is a 1k 20 turn trim pot

author: iMo
author_rank: Super Contributor
timestamp: March 04, 2023, 08:13:18 am
content: Do not use trimpots (10t/20t), those are source of instabilities. When you have to use a trimpot then with as small as possible value compared to the rest of the divider (1k is rather large value, imho).The LT5400 ratio TC is <1ppm/C, thus the 925 ohm resistor contributes heavily to the overall TC. The trimmers are +/-50ppm/C typically.Do a simulation over TEMP, for example:.op.step TEMP 20 40 1with "R3=925 tc=30e-6"as an example..

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 08:17:51 am
content: Quote from: imo on March 04, 2023, 08:13:18 amMy method is always to put TRIM POT resistorsAt firstCheck what the exact resistance value is after everything stabilizesAnd after that replace the resistors with the exact value

author: iMo
author_rank: Super Contributor
timestamp: March 04, 2023, 08:30:58 am
content: Quote from: dietert1 on March 03, 2023, 10:18:17 pmOutput ripple so low that is not measurable in the LTSpice with 1nF and 200mV Vcc hum..The situation changes of course with squared pulses (ie a switcher), with 200mVpp 2us/10us pulses the output ripple is around 600uVpp with both 1nF and 100nF and the OP07.

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 08:32:56 am
content: I have a problem with an error in the simulation in LTSPICEOnce I try to use the LTC2057

author: iMo
author_rank: Super Contributor
timestamp: March 04, 2023, 08:42:23 am
content: Attach your .asc file..

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 08:46:17 am
content: Quote from: imo on March 04, 2023, 08:42:23 am

author: iMo
author_rank: Super Contributor
timestamp: March 04, 2023, 09:01:27 am
content: For example with 30ppm/C trimmer..PS:and the Vrefout change in ppm: with combination of a 25ohm 30ppm/C trimmer and a 900ohm -4ppm/C resistor (as an example).

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 09:26:41 am
content: Quote from: imo on March 04, 2023, 09:01:27 amthanks i fix the error problem i update the ltspice and the error no more

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 09:30:04 am
content: Quote from: imo on March 04, 2023, 09:01:27 amHow do you make the graph of temperature in relation to voltage in LTSPICE

author: iMo
author_rank: Super Contributor
timestamp: March 04, 2023, 09:45:21 am
content: See the commands in my above simulation...op.step TEMP 20 50 1and after the simulation stops do select a voltages or currents (click on the node or wire in the schematics), etc..

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 09:57:28 am
content: Quote from: imo on March 04, 2023, 09:45:21 amAttach your .asc file.. thanks

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 10:16:11 am
content: I managed to create the graphBut it's strange that for this I have to delete the entire part of the LT3083

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 04, 2023, 11:07:04 am
content: I managed to arrange the simulation to include everythingAnd I also did a TRIM POT simulationFrom a temperature of 20 degrees to 80 degreesStrange the stability at 55 degrees

author: mawyatt
author_rank: Super Contributor
timestamp: March 04, 2023, 03:14:38 pm
content: Maybe a dumb question but will throw it out anyway.Do we knowIFthe models utilized in these simulations reflect the actual devices being simulated?Are second/third order effects such as PSRR, chip heater effects, thermal gradients and so on included is such device IC models? Not to mention effects related to actual PCB implementation and the environment. Also, noted the discrete resistor TC seem to include the linear temp coefficients and not the quadratic effects, and what about the LT resistor array TC effects?Best,

author: iMo
author_rank: Super Contributor
timestamp: March 05, 2023, 09:43:19 am
content: Quote from: DavidAzulay5000 on March 04, 2023, 11:07:04 amThat is because there is a TC of the 1399 zener combined with the TC of the trimmer - see below an example, trimmer's TC from -50ppm/C to +50ppm/C. Also your LT3083's TC may contribute as well.Vrefout in ppm.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 05, 2023, 10:09:25 am
content: I doubt the models for the parts are that accurate to worry about the 2nd order TC. The main point would be checking the coarse part (e.g. how much is the TC of the trim resistor attenuated) and for the simulation one needs some x-axis (e.g. time or temperature) to get the graphs and more conventional interface.Beside the 100K/10K LT5400 array, one could also use an array with 8 equal resistors (e.g. TDP or NOMC ) for a 1.5 to 3.5 R ratio. This starts at the nominal 3:7 ratio and would need trim options for up and down. The ADR1399 is nominal 7.05 V and thus in between the 2 approximation. The shown trim resistor in the LT5400 version only works up to some 7.2 V. A rare but still in spec higher voltage unit would need a different position trim resistors to reach 10 V.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 05, 2023, 03:44:58 pm
content: Has anybody come up with a PCB for the 1399 ceramic SMT version that's generally considered to be good?

author: Andreas
author_rank: Super Contributor
timestamp: March 05, 2023, 09:20:41 pm
content: Hello,I think I have now solved my "position dependant drift". see also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg4683005/#msg4683005I have put the PCB into a die cast housing (Hammond 1590U)https://www.reichelt.de/alugehaeuse-1590-u-120-x-120-x-58-6-mm-aluminium-1590u-p221457.html?&nbc=1The temperature sensor from CPU is now cabled + taped on the bottom of the housing.The PCB with the 4*ADR1399LS8 + 2*LM399 sits with some cloth (thermal isolation) within the metal housing.Of course the effective T.C. with respect to the "case" sensor also is different from "environment" and "MUX" temperature sensor.So I had to determine a new set of T.C. coefficients.Now the measurements are stable (as I am used from my ADCs) and the T.C. of the references can be compensated.The temperature drift of the ADR1399 is still much higher than the LM399 samples.The LM399 shows more stable uncompensated values (except for some popcorn noise on day 4 since Hammond packaging).The T.C. compensated values are additionally averaged between 3 ADCs to reduce further measurement uncertainities.The overview shows the new effective linear T.C. values which are minimum a factor 3 higher for the ADR1399LS8 samples than for the LM399s.with best regardsAndreas

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 06, 2023, 08:12:00 am
content: LM399 + OP AMP LT1001 COMBOPERFECT 10V Reference 10.000.00v

author: gamalot
author_rank: Super Contributor
timestamp: March 09, 2023, 03:32:02 pm
content: The simplest ADR1399 comes, only two 1uF capacitors and a 1K ohm resistor, measured with 34465A, it seems not bad!

author: Kleinstein
author_rank: Super Contributor
timestamp: March 09, 2023, 04:02:27 pm
content: The 34465 compares the ADR1399 to it's internal LM399.

author: gamalot
author_rank: Super Contributor
timestamp: March 09, 2023, 05:55:31 pm
content: Quote from: Kleinstein on March 09, 2023, 04:02:27 pmI also did a test with my 6581T (1000 samples, 20 NPLC, 14uV Span, 2uV Std dev), these results were almost identical to the 34465A.

author: iMo
author_rank: Super Contributor
timestamp: March 10, 2023, 08:06:12 am
content: Evaluating an ADR1399 (or an LM399 and better refs) with a 6.5digit voltmeter is difficult. You have to know your meter well at the 10V range - you have to know its TC to compensate for its internal temperature and/or ambient, you have to log an 8-10 hours long measurement (at 100NPLC) and evaluate several thousands of samples at minimum (analyze the graphs, compensate for internal/ambient temperature, remove the outliers, provide filtering/averaging/smoothing). And you get a single number (I do it this way). That all with an assumption (not valid one, btw.) the long therm drift of your meter is zero.The LM399 inside those 6.5meters does a random walk typically within 5-10uV at 10V range (therefore the minimal resolution with those meters is 10uV at 10V) and there are sporadic random jumps 4-5uV large (the popcorn) on top of that walk as well. And your DUT does the same too, basically..

author: dietert1
author_rank: Super Contributor
timestamp: March 10, 2023, 09:39:44 am
content: As long as the ADR1399KHZ isn't available, that minimum setup with the SMD part as "dead bug" is a good solution. It reduces stress on the package and the heating power. With that minimum setup one can make two or more of them. Once you observe more than one, it gets a little more conclusive.And the differences can be measured to 100 nV with a good 6.5 meter. Except one needs to avoid systematic errors affecting all of them in a similar way.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: March 10, 2023, 11:22:49 am
content: Btw. - the DCV Ratio (34401a) always returns 7 significant digits after the decimal point over the serial, could be somehow useful when having a 10V ref and the DUT is an LM399 (7V). I have not used it this way yet. Do not forget to wire the LO and the LO together

author: Andreas
author_rank: Super Contributor
timestamp: March 10, 2023, 07:08:34 pm
content: Hmm,I have here 7.5 life digits with 34401A ratio measurement.(Measuring the Ratio of a ADR1000A between 10V and 6.6V output)Ratio is in mV/V VOut/VRef.The pitfall is only 1 measurement all 12 seconds with 100 NPLC.21:57:08; 1499.99030; 121:57:20; 1499.99020; 221:57:32; 1499.99040; 321:57:44; 1499.99030; 421:57:56; 1499.99010; 521:58:08; 1499.99030; 621:58:20; 1499.99060; 721:58:32; 1499.99060; 821:58:44; 1499.99040; 921:58:56; 1499.99020; 1021:59:08; 1499.99040; 1121:59:20; 1499.99020; 1221:59:32; 1499.99040; 1321:59:44; 1499.99020; 1421:59:56; 1499.99030; 1522:00:08; 1499.99030; 1622:00:20; 1499.99040; 1722:00:32; 1499.99040; 1822:00:44; 1499.99050; 1922:00:56; 1499.99030; 2022:01:08; 1499.99020; 2122:01:20; 1499.99040; 2222:01:33; 1499.99050; 2322:01:45; 1499.99030; 2422:01:57; 1499.99040; 2522:02:09; 1499.99060; 2622:02:21; 1499.99000; 2722:02:33; 1499.99030; 2822:02:45; 1499.99020; 29The Ratio measurement is rather stable (shown by Allan Deviation mV/V of 1 minute averages)with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: March 10, 2023, 07:27:50 pm
content: Yep, as I wrote above there is always 7 sig digits after the decimal point. There is 9.12345670e-01 or 1.12345670e0 I get.It works such it makes 100NPLC with V1 and then 100NPLC with V2 and calculates the ratio. Thus the internal LM399 is still involved, afaik..

author: Kleinstein
author_rank: Super Contributor
timestamp: March 10, 2023, 08:44:34 pm
content: With many modern DMMs the ratio measurement is just measuring the the 2 external voltages relative to the internal reference and than calculating the ratio.This may not be that bad with a reasonable fast and low noise ADC. Many of the old Keithley 19x meters used a 3 reading cycle with a reading of the reference voltage on there normal AZ mode. So using the ratio mode with a reading of the external reference instead would at least not slow down things much or add extra noise.Requiring 12 seconds for a 100 PLC ratio measurement on the 34401 looks a bit slow, as 4 conversions (high and low side for the input and reference) should be enough and thus 4 x 2 seconds.I don't expect the ratio mode to be high priority for the 34401.Only very few older meter (e.g. Solartron 7071/7081) do an a true direct ratio by using one of the voltages for the ADC reference.The often much more practical solution is to looks at the difference of 2 external references, if they are comparable in voltage (e.g. less than 20 % difference).

author: JodelJonny
author_rank: Contributor
timestamp: March 11, 2023, 10:00:59 pm
content: Thanks for the feedback. I tried to implement your suggestions.-The temp sensor is moved to the resistor network. I'd like to stick to the digital one because it makes it easier to display and save the measurements with minimal external stuff needed. If it interferes with the reference it could only be powered on for brief periods between measurements.-I switched to the NOMC resistor network with pads for external trim resistors.-I tried my best at star grounding. Just for the heater it felt wrong to wire it all the way to the star point and back. I don't see any problems wiring it directly to the input.-I will try the 7815 on the board. If it causes thermal problems it is easy to short it out and use an external regulator. I want the reverse polarity protection on the pcb in any case because between the power supply and the pcb is the most likely place to mix up the polarity.Is there a better regulator than the 7815 for this application?If no one spots any big problems anymore I'm going to order the parts and the pcb and give it a try. This is just supposed to be the first step to get a feel for things.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 11, 2023, 10:15:39 pm
content: I'd probably use an LM317. I think it's a better regulator and it gives you the option of trying different voltages. Reg on board worries me, but give it a try.

author: Andreas
author_rank: Super Contributor
timestamp: March 12, 2023, 06:13:34 am
content: Quote from: JodelJonny on March 11, 2023, 10:00:59 pmYou obviously have not understood the principle: remove high courrents (heater, zener supply) from critical wiring (zener voltage sensing).Doubling the lines (seen on the zener ground) has no effect (the voltage drop from the 3 mA Zener supply will be seen on the output connector).There is nothing wrong with a 7815/LM317 if the cirquit is mains powered.With battery supply I usually prefer a LT1763.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: March 12, 2023, 07:47:51 am
content: I would also fill the circle on the bottom pcb side beneath the 399 with copper.Also - what is the pitch of the 399 pins (between the adjacent pins)?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2023, 08:39:34 am
content: The optional trim resistors R4 and R5 would have no effect as they are shorted. The trim part with 4 resistors are 4 different ends still looks a bit odd. I would more prefer 2 positions to get a trim up or down. Suitable are the resistors that are in series with another and thus have a lower weight to start with and than 2 or 3 optional resistors there.The star ground idea is still way off.The heater, regulator ground and supply to the OP-amp can be treated separate and no real need to use a star ground for these.One should use the star ground part mainly for the critical parts: the neg output terminal, the zener neg side, the low end of the resistor array and one link to the normal ground.All 3 points have or can have some current flow. The use of a start ground thus does not fully compensate for voltage drop on the ground lines. This would need exrta current compensation from a negative supply, which may be a bit overkill. Just using relatively short and not too thin traces should be good enough. The main point is to keep the heater current isolated from the critical part.

author: JodelJonny
author_rank: Contributor
timestamp: March 12, 2023, 09:52:26 am
content: The doubled up ground trace was left after thinking about using the SMD package with separate sense pins. I forgot to delete it. It does nothing in this case but as long as the enclosed are is near zero it shouldn't hurt either.The pitch between the 399 Pins is 1,796 mm.I'll think again about the ground configuration but I honestly don't see the problem right now.R4 and R5 are in series with the circuit so they have jumper links to short them out between the pins of the resistor network that could be easily cut if I'd like to use those resistors instead. I should have made that more obvious in the circuit diagram.

author: dietert1
author_rank: Super Contributor
timestamp: March 12, 2023, 10:10:52 am
content: C9 could be a 1nF film capacitor.Also i would try to avoid vias in the reference ground connection and at the negative opamp input. I'm not shure how much thermal EMF vias can contribute and whether it is possible to "untwist" the design.The thermal ring can be ground and under the sensor signal lines there can be ground, too. Same applies to the pad under the resistor array.Regards, Dieter

author: iMo
author_rank: Super Contributor
timestamp: March 12, 2023, 10:20:02 am
content: An example of a star grounding for a typical LM399 circuit (an example only).. @Kleinstein - plz do advice us directly in the schematics..

author: Andreas
author_rank: Super Contributor
timestamp: March 12, 2023, 10:34:05 am
content: Quote from: JodelJonny on March 12, 2023, 09:52:26 amJust one example:Your connection between output pin and LM1399 has about 25 mOhms (assuming 1 mm width and 35um Copper with around 50 mm length).It carries the reference current of 3 mA.This gives a increase of 75 uV of the zener voltage (or 10-11 ppm increase).If all would be constant that would not be a problem.Now the T.C. of the copper trace with nearly 0.4%/K increases the zener voltage T.C. by 40 ppb/K.Quote from: imo on March 12, 2023, 10:20:02 amThe connection between output and LM399 has to be as short as possible in this case (ok for LM399 its a factor 3 less critical).with best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: March 12, 2023, 10:56:49 am
content: The ground is indeed not that bad as it looks at first sight. Going to both sides makes it a bit hard to follow though.The neg output terminal is used as the star ground point. This is a coice for a very low output impedance, but external wires woud add anyway.The link from the neg output to the resistors should be thicker - that resistance adds to the divider and may add a tiny bit to the TC. If really needed one could still add parallel copper to correct.The link from the neg side of the reference could be made a bit shorter and maybe use 2 or 3 vias. I am not that afaid of thermal EMF of the vias, more the resistance of small vias.The 2 parallel lines are confusing, but could be used for some TC tweek if really needed, as the restances adds a little to the ref. voltage. So they are not that bad.There is no need to also have the neg supply of the OP-amp from the star ground, but as the supply current is pretty stable it is also not that bad. Ideally the ground here would not go through the star ground for the critical levels.One should avoid isolated copper islands and better connect those areas made for thermal reasons to ground or a simlar potential.Cutting a trace directly at the SO16 chip can be a bit tricky. I would prefer trim by just adding resistance in parallel and not opening a link. There are 2 suitable position for a trim up and down.

author: JodelJonny
author_rank: Contributor
timestamp: March 12, 2023, 11:21:12 am
content: Thanks. Good to know, that my thoughts were not totally off after all.I'll work on improving the "readability" of schematic and layout.One of the thoughts was to be able to support up to 10 mA output current without major problems. That's way more than needed, I know. Therefore using the output terminal as the star point was chosen.

author: Andreas
author_rank: Super Contributor
timestamp: March 12, 2023, 01:25:30 pm
content: Quote from: JodelJonny on March 12, 2023, 11:21:12 amwith 10 mA I would think about 4 Wire output.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: March 12, 2023, 03:14:23 pm
content: Quote from: Andreas on March 12, 2023, 01:25:30 pmAlso doublecheck the output buffer's capabilities - whether the buffer is able to provide those 10mA without a significant drop at the +10V output star.. (ie. the 10k base resistor and the 20ohm shunt sizing)..@Andreas: 4w is needed, sure.. 10mA is ahugecurrent. I had 16uV drop with the same buffer (but 25ohm shunt) with aprox 12mA load directly at the pcb's posts, with a ~15cm (EDIT: actually longer as I have there a ferrite bead with 2 or 3 turns) long 0.8mm dia (!) copper wiring from the pcb posts to the posts on the box I get ~160uV with 10mA. Not counting additional leads..

author: DavidKo
author_rank: Frequent Contributor
timestamp: March 13, 2023, 06:35:57 am
content: I'm not sure how much it is critical. For the start-up there is 200k resistor from the supply in "portable calibrator" onpage 6.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 13, 2023, 08:04:27 am
content: With the OPA202 the startup could indeed be an issue, as it has rail to rail outputs. Chances are it would still work even with just 1 diode vor the shift at the output, as the diode forward voltage for a small diode tends to be higher than transistor BE voltage. To be on the safe side, maybe have 2 diodes in series, so that the output would never go below some 0.6 V.

author: DavidAzulay5000
author_rank: Regular Contributor
timestamp: March 13, 2023, 10:26:44 am
content: perfect 10LM399AHLT3042 OUTPUT 15VLT1001aluminum PCB

author: branadic
author_rank: Super Contributor
timestamp: March 13, 2023, 04:55:14 pm
content: @ AndreasDid you observe jumps on all your LCC packaged ADR1399? Is it already confirmed popcorn noise or could it also be what is known for some LTZ1000ACH and its glass bead filled die attach?Can someone else report similar jumps on his devices?-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: March 13, 2023, 10:04:30 pm
content: Hello Branadic,as stated here:https://www.eevblog.com/forum/metrology/adr1399-reference/msg4453792/#msg4453792I have found popcorn noise up to 1.6 uV on every device during 1/f noise measurements.Unfortunately this is so low that I cannot confirm this by absolute voltage measurements with my equipment.The largest popcorn noise (> 1ppm at certain temperatures/times) on the same PCB is one LM399 from LT (LT#02).This is well above my standard deviation of ~0.25 ppm for 7V measurements.So now after proper packaging the only remaining issue is the rather large T.C. of the ADR1399LS8(compared with a typical LM399 near room temperature).with best regardsAndreas

author: JodelJonny
author_rank: Contributor
timestamp: April 05, 2023, 08:03:46 am
content: Hello,the parts for my reference arrived and I successfully build it without major problems. Just that I stupidly ordered the SMD package ADR1399 :/I made it fit with some copper wire. Not Ideal but the best I could do for now.I'll likely build a second one in the future.It has run for a few days now and seems stable at 10.02271V with very slight variation of the last digit.I am neither equipped nor able to actually characterise its performance right now. That is the next project to figure out.No worries, the ADR got some insulation after I took the picture.Thanks for your help. I am happy with the result and this gives me a good starting point to dive deeper in the topic.

author: iMo
author_rank: Super Contributor
timestamp: April 05, 2023, 08:57:27 am
content: Is the D2 the zener? Btw., I've been always putting a diode in series with the zener (see my schematics around). Even often commented here the diode is redundant, you will see it in action when your output posts get shorted..

author: JodelJonny
author_rank: Contributor
timestamp: April 05, 2023, 09:28:58 am
content: D2 is a standard diode. There is no Zener.

author: dietert1
author_rank: Super Contributor
timestamp: April 05, 2023, 09:38:25 am
content: Looks great, already better than the AD evaluation board, that does not have a 10V gain stage.The metal enclosure is connected to Gnd? One can use a small 50 or 100 Ohm resistor to do that. Or give it a "Guard" terminal.Regards, Dieter

author: Andreas
author_rank: Super Contributor
timestamp: April 12, 2023, 07:35:12 am
content: Hello,update of ADR1399LS8 ageing 1kHr after putting into Hammond enclosure:see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg4737989/#msg4737989The ADR1399LS8#01 - #04 are now stable (except for temperature drift which is large compared to the 2 LM399 which are running in parallel).The LM399LT#01 - 02# in comparison are much more temperature stable.But LM399LT#02 shows a rather large popcorn noise > 1 ppmThe ADR1399 seem to drift upwards by around 0.5 ppm/khr after 4.3 kHrs in total now.The LM399 after 2.5 kHrs in total show nearly no ageing drift (except for popcorn).with best regardsAndreas

author: aronake
author_rank: Frequent Contributor
timestamp: April 19, 2023, 04:23:12 am
content: Would anyone have kicad (or other circuti design program) or Gerber files to share for a ADR1399KEZ based circuit? Best if it have 10V boost stage, but if not, that would still be helpfull.

author: JodelJonny
author_rank: Contributor
timestamp: April 19, 2023, 07:16:27 am
content: I could post the KiCad, Gerber and BOM file for the circuit I build if that fits your need. But they are pretty messy since that was my first design in KiCad.I would need at least a few days to clean up the most important errors.

author: aronake
author_rank: Frequent Contributor
timestamp: April 19, 2023, 08:58:34 am
content: Quote from: JodelJonny on April 19, 2023, 07:16:27 amThat would be awesome! And I am sure many other here would appreciated that too!

author: gamalot
author_rank: Super Contributor
timestamp: April 19, 2023, 08:29:24 pm
content: Got an interesting one, maybe it could be a good candidate for a 10V reference based on the ADR1399.https://www.vishay.com/docs/60002/osop.pdf

author: Andreas
author_rank: Super Contributor
timestamp: May 22, 2023, 09:16:52 pm
content: Hello,update of ADR1399LS8 ageing 2kHr after putting into Hammond enclosure and with temperature compensation:see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg4809413/#msg4809413The ADR have now 5.3 kHrs in total operating time.The ADR1399LS8#01 - #03 are drifting slightly upwards ~0.5 ppm / kHr in average over the last 2 kHrs.The ADR1399LS8#04 has nearly no ageing drift.The LM399 after 3.5 kHrs in total show still nearly no ageing drift (except for popcorn noise).The measurement gap around day 70 is due to T.C. measurements of all devices.The repeated T.C. measurement (in ppm/K) shows nearly no change against previous measurement.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: May 25, 2023, 07:42:01 pm
content: Hello,in the mean time I have built a 2nd PCB in a Hammond housing for ageing of the ADR1399 references.And while waiting for the metal can packages which are delayed from month to monthI could not resist to do some T.C. testing with the 4 "fresh" LS8 devices on the pcb.The PCB has been operated in total 8 hours within 4 weeks before this tests.Since there was a relatively large initial ageing drift I had to wait some temperature cyclesuntil the T.C. could be measured with a reasonable ageing drift.So total measuring time was 100 hrs.here the results of the 4 devices on PCB #2Again the T.C. of the LS8-packages is relatively high compared to typical LM399 devices.with best regardsAndreas

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 26, 2023, 01:12:07 pm
content: I guess I need to ask, having bought one of the SMT versions a while back, is this reference really a good choice if you have room for a regular 399 or other device? I'm not seeing it as a "serious" reference to use as a lab standard or in a high precision instrument.

author: Andreas
author_rank: Super Contributor
timestamp: May 26, 2023, 06:00:21 pm
content: Hello,as always it depends on your needs:- low noise (better than LM399)- low T.C. (my LM399 samples are better)- low ageing drift (I am still evaluating but the ADR1399 seem to be better than the ADR1000A)For me with 18-33 deg C in my "lab" the T.C. is a enemy.with best regardsAndreas

author: dietert1
author_rank: Super Contributor
timestamp: May 26, 2023, 09:38:38 pm
content: After buying the SMD ADR1399 evaluation i ended up building a 10 V gain stage - also as bootstrap for the reference. This includes a low pass filter and outer oven to keep everything at 38 °C. It performs very well.I have seen 0.2 ppm RMS over one month.Our LTFLU references are better, as they are 4x zener arrays. I am wondering what happened to the 4x ADR1399 array designs shown before in this thread.Regards, DIeterEdit: After fixing a workstation i looked at the logs once more and the difference voltage between the references ADR1399 and LTFLU1 was 0.059 ppm RMS of hourly averages between 2023-04-02 and 2023-05-08.

author: Andreas
author_rank: Super Contributor
timestamp: July 02, 2023, 09:01:50 pm
content: Hello,update of ADR1399LS8 ageing 3kHr after putting into Hammond enclosure and with temperature compensation:see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg4875467/#msg4875467The ADR have now 6.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.The ADR1399LS8#01 - #03 are drifting slightly upwards ~2 ppm / 3 kHr in average over the last 3 kHrs.The ADR1399LS8#04 has nearly no ageing drift.with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: July 02, 2023, 09:36:54 pm
content: Unfortunately, ADR1399KHZ delivery date is shifting each month by another month. Ordered in Feb 2023 this is the history of updated delivery dates so far:MAR 28, 2023MAI 02, 2023MAI 09, 2023MAI 16, 2023JUN 20, 2023JUL 14, 2023JUN 26, 2023JUL 03, 2023JUL 07, 2023JUL 14, 2023JUL 21, 2023AUG 01, 2023Seems like ADI has some serious problems in getting them fabricated.Luckily, some forum member was kind enough to send me a few samples and they will arrive within the next days, so I can proceed with my experiments soon.-branadic-

author: DavidKo
author_rank: Frequent Contributor
timestamp: July 03, 2023, 06:15:29 am
content: During my order at 26th July 2022, the delivery date was unknown. At 28th November, they have sent update that ADR1399KHZ will be available 15th August 2023 (and ADR1399KEZ on stock). Ordered through Mouser.

author: Andreas
author_rank: Super Contributor
timestamp: July 03, 2023, 06:55:10 am
content: you are not alonemy order from Jan 22 is still waiting on delivery ...with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: July 23, 2023, 06:02:36 pm
content: Attached are multiple noise measurement of my ADR1399-PWM-DAC. Please replace µV by nV and you end up with about 2 µVpp.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: July 23, 2023, 06:22:27 pm
content: The noise looks good, with quite some of the peaks that are realatively short, possibly on a time scale where a little more filtering can help.The real question is how good the long term drift will be for the TO46 version.Let's hope it is driften less than the expected date for availabilty.

author: deepfryed
author_rank: Unknown
timestamp: July 24, 2023, 11:17:28 am
content: I have one ADR1399H-EBZ on order from Mouser, they say ETA end of September. Let's see.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: July 25, 2023, 02:56:46 pm
content: It is in stock on Digikey in TO46 can right nowhttps://www.digikey.com/en/products/detail/analog-devices-inc/ADR1399KHZ/15848880

author: gamalot
author_rank: Super Contributor
timestamp: July 30, 2023, 06:30:50 am
content: Four ADR1399KHZ from Digi-Key have just been delivered. My money is running out and I can't afford more.I don't know what printing technology in 2023 can make the silk screen on top look so blurry and dirty!

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2023, 07:43:32 am
content: Does not look like ADI's quality.. A fake?

author: gamalot
author_rank: Super Contributor
timestamp: July 30, 2023, 07:56:17 am
content: Quote from: iMo on July 30, 2023, 07:43:32 amNo, that just proves that they must be genuine, perhaps using eco-friendly printing techniques.

author: branadic
author_rank: Super Contributor
timestamp: July 30, 2023, 08:17:16 am
content: Looks really weird, as it is ADR1399 with LT logo instead of ADI logo, beside the poor printing quality.-branadic-

author: gamalot
author_rank: Super Contributor
timestamp: July 30, 2023, 08:58:31 am
content: Even the thermal shield itself is not the same as before, what happened?

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2023, 09:19:55 am
content: ..ask your supplier..

author: NNNI
author_rank: Regular Contributor
timestamp: July 30, 2023, 09:22:39 am
content: @branadicHave you already posted about the ADR1399 PWM DAC somewhere? I would love to learn more about it. I've recently been playing around simulating something similar using a passive 3 pole RC filter (3 stages of 10K/100nF C0G) which does indeed reduce ripple, but assuming I want 1uV settability, I would need a 23-bit resolution PWM signal. While that is possible, it pushes the PWM frequency very low, and I'm not sure how to make a practical implementation. Perhaps reduce settable resolution to 10uV?@gamalot: Someone I know also just got an ADR1399, the printing was similarly crusty but the package looked to be in better shape.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 30, 2023, 09:38:28 am
content: From the picture the "printing" look like laser writen, with small dot matirx depressions. Getting the LT logo is indeed odd.

author: Andreas
author_rank: Super Contributor
timestamp: July 30, 2023, 09:47:01 am
content: Quote from: NNNI on July 30, 2023, 09:22:39 amHello,it is all in the LM399 thread.We are using Sigma Delta modulation for the PWM.So it is possible to do several kHz @8 Bit PWM with 24 bit resolution.https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg2189460/#msg2189460https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1955149/#msg1955149https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg2200098/#msg2200098https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg2082544/#msg2082544with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 30, 2023, 10:43:30 am
content: @Andreas - perhaps you may open a new thread, like "x399 based PWM voltage standard" or something like that, and start with an update on the effort you, branadic and others did (like the latest schematics, firmware, etc). Otherwise it remains hidden in the rather long 399 thread..

author: Kleinstein
author_rank: Super Contributor
timestamp: July 30, 2023, 03:26:28 pm
content: The PWM DAC part is not directly related to the reference, only indirectly through the voltage and noise level / stability expected.AFAIR the LM399 10 V ref. part is not a classic PWM DAC, but in the 7 to 10 V amplfier feedback. This adds some limitations but also gets up from 7 V to 10 V without critical resistors setting the gain.A more universal voltage source would more use 2x7 V to start with 14 V and than use a more conventional PWM DAC to get the 14 to 10 V (or another voltage) step.Filtering would likely use film capacitors of some 1-10 µF, maybe even PP types to get fast settling / low DA.

author: dietert1
author_rank: Super Contributor
timestamp: July 30, 2023, 04:42:13 pm
content: That's what i started building long time ago. There is an array of 10 LM399 to generate 14.1 V and to control the mains power supply that is built as a bootstrap amplifier to 19 V. There is an aluminum enclosure.The 19 V will be used to implement the main PWM switch with a dual n-channel FET. I got the control board already with a 16 MHz MSP430 with isolated RS232, the PWM filter and the ripple compensation switch. So little missing. Just need to finish the main PWM switch and it will be a voltage calibrator.The LM399 array has been powered for one or two years now and was already used for many different precision measurements.Regards, Dieter

author: gamalot
author_rank: Super Contributor
timestamp: July 31, 2023, 07:36:02 am
content: Quote from: Kleinstein on July 30, 2023, 09:38:28 amYes you can even feel the rough surface with your fingertip. At least on voltage reference components, I would prefer LT's logo to be there instead of ADI's.

author: JodelJonny
author_rank: Contributor
timestamp: July 31, 2023, 09:37:11 am
content: I just recieved my ADR1399 from DigiKey as well and it looks the same.Unfortunately they were out of stock of the NOMC 8x10k Resistor arrays. If I can find one of those and a little bit of time I am going to build a second ADR1399 10V Ref.Number 1 has been running for approx. 2800h.I am very sorry that I havent uploaded any PCB/Gerber files yet. As this was my first real KiCAD project they are a mess and need signifacant work to be really usable.

author: KT88
author_rank: Frequent Contributor
timestamp: July 31, 2023, 10:32:09 am
content: There is a PCN related to the top marking:https://www.analog.com/media/en/PCN/ADI_PCN_22_0025_Rev_-_Form.pdf

author: Grandchuck
author_rank: Super Contributor
timestamp: July 31, 2023, 10:44:27 am
content: How about counterfeiting? Laser marking might discourage it.

author: gamalot
author_rank: Super Contributor
timestamp: July 31, 2023, 11:44:14 am
content: Quote from: KT88 on July 31, 2023, 10:32:09 amIt seems that there is no mention of the change of the logo.

author: NNNI
author_rank: Regular Contributor
timestamp: July 31, 2023, 04:28:42 pm
content: In case someone is interested, a slightly more high resolution picture of the laser marking. The carbonization, I assume, is because of the laser process itself, but is it a useful side effect or intentional? One can only guess.

author: Echo88
author_rank: Frequent Contributor
timestamp: July 31, 2023, 05:44:48 pm
content: 20€ on Mouser and the marking looks like piss in snow.

author: iMo
author_rank: Super Contributor
timestamp: July 31, 2023, 07:47:38 pm
content: ADI hired a special tattoo saloon in Parañaque City..PS: it could be it is a novel anti-counterfeiting technology..Or, simply they reuse their existing laser engraver - all other epoxy and metal chip's markings are laser engraved.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 31, 2023, 08:39:50 pm
content: The relatively exotic plastics for the case could be tricky with conventional printing. With a relatively low volume product the laser labeling makes absolute sense, as there should be little fixed costs.

author: iMo
author_rank: Super Contributor
timestamp: July 31, 2023, 08:47:22 pm
content: But why LT logo? Perhaps some legal stuff? Like patents, trade marks, IP, etc.? The Design remained mostly the same, afaik.

author: DavidKo
author_rank: Frequent Contributor
timestamp: August 04, 2023, 11:13:47 am
content: Mouser is shipping mine today. They still have 783 for dispatch today ;-)

author: maat
author_rank: Regular Contributor
timestamp: August 08, 2023, 09:51:49 am
content: *knock* *knock* Oh, look what arrived today.On the left and and right are samples I got earlier from ADI. These have a higher quality look than the production units (and also carry the ADI logo). It seems ADI tries to undercut the Ebay scammers selling refurbished diodes in terms of look and feelOff they go into the test setup. Lets see how they perform for the next 1 kh.

author: analityk
author_rank: Regular Contributor
timestamp: August 12, 2023, 10:56:21 pm
content: I've bought ADR1399KHZ and it arrived in weird ceramics package with standard that legs.It is a bit curious because in datasheet was specified only ceramics smd package and metal can hermetically sealed to-42, but mine one is hybrid? I do not know, maybe someone here have any experience.This ceramics shields act as heat insulation and inside is metal can?

author: iMo
author_rank: Super Contributor
timestamp: August 12, 2023, 11:01:43 pm
content: Yep, that is the plastic heat insulating cap, inside is the metal package.

author: Andreas
author_rank: Super Contributor
timestamp: August 13, 2023, 09:57:56 am
content: Hello after removing the cap it should look like this:and you get a thermal anemometer instead of a reference.see patend of Joe Geller.https://www.freepatentsonline.com/7380471.htmlhttps://www.nutsvolts.com/?/magazine/article/micro_gust_thermal_anemometer_mgtawith best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: August 13, 2023, 10:10:38 am
content: Quote from: Andreas on August 13, 2023, 09:57:56 amFrankly, I doubt he could get the patent for that - as it is a known general principle, nothing new..You may apply for such a patent with any similar heated device, like my old OCXO - the crystal frequency and heater current behave the same way..PS: ..but perhaps no Einsteins sitting in the Patent Office anymore..PPS: on the other hand we were laughing years back on a patent where the guy claimed uploading the binary into the mcu's flash via a bootloader, fortunately he indicated a single TI's mcu partnumber only..

author: gamalot
author_rank: Super Contributor
timestamp: August 13, 2023, 03:02:29 pm
content: Quote from: Andreas on August 13, 2023, 09:57:56 amLooks like they didn't change the structure of the thermal shield.

author: BU508A
author_rank: Super Contributor
timestamp: August 14, 2023, 06:15:05 am
content: Quote from: iMo on July 30, 2023, 07:43:32 amOn Feb. 2022 I've ordered 18 ADR1399KHZ directly from Analog Devices.They arrived on 1st of August 2023.https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg4991827/#msg4991827I have no idea, why they are using the LT logo and why the printing or engraving quality is so poor. I was surprised by myself when I saw it at first.

author: iMo
author_rank: Super Contributor
timestamp: August 14, 2023, 10:02:14 am
content: Details from my uscope..It looks like laser engraving, but the intensity of the individual pulses differs.Perhaps a code with a secret messagePS: The intensity of the pulses could be constant, but the reflectivity of the surface might differ from place to place, therefore the mess.

author: Andreas
author_rank: Super Contributor
timestamp: August 14, 2023, 08:55:52 pm
content: Hello,update of ADR1399LS8 ageing 4kHr after putting into Hammond enclosure and with temperature compensation:see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg4939813/#msg4939813The ADR have now 7.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.The ADR1399LS8#01 - #03 are drifting slightly upwards ~2.5 ppm / 4 kHr in average over the last 4 kHrs.The ADR1399LS8#04 has nearly no (<1 ppm) ageing drift.with best regardsAndreas

author: JodelJonny
author_rank: Contributor
timestamp: August 20, 2023, 04:58:35 pm
content: Hello,this Saturday I used the offer of the PTB at the Maker Faire Hannover to get inofficial calibrations. I got some quick and dirty measurements of my 10V ADR1399 ref with a calibrated 3458A. The measurements start quickly after I got the reference, that had already been powered on for a few hours with a battery, out of my backpack.I just took pictures with my phone and used the timestamps to get a graph out of it. This is why there is inconsistent timing between measurements.This was after approx. 3000h burn in time.I guess that the reference got relatively hot in the backpack and is cooling of during the measurement so that a negative tempco causes the rise in voltage.Thanks to the PTB team! I was nice to meet NNNI there as well.

author: Andreas
author_rank: Super Contributor
timestamp: August 22, 2023, 09:07:18 pm
content: Hello,my 2nd PCB is now populated additionally with 4 metal can devices. ADR1399KHZ.Ageing drift for the first 2 weeks (333 hrs) starting after 1-2 hrs total operation time.Unfortunately I have high changes in temperature in my lab between morning and evening.So two measurements per day are not optimal.Next I will check tempco of the 4 samples.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: August 25, 2023, 02:12:28 pm
content: Hello,Tempco measurement on the 4 Metal can devices (KHZ) of 2nd PCB after 333 hrs run in phase.I had hoped that the T.C. is lower than that of the LS8 packages.But in comparison this is not the case. T.C. is very individual.See also the (non pre-aged so with large drift) measurement of the LS8 packages..https://www.eevblog.com/forum/metrology/adr1399-reference/msg4879958/#msg4879958With best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: August 25, 2023, 02:34:55 pm
content: Interestingly the "red" noise decreases with the sample N..

author: Andreas
author_rank: Super Contributor
timestamp: August 25, 2023, 02:47:51 pm
content: Not shure what you see.But it could be that it is due to large changeing ramp speed (actual temperature differing from setpoint due to environment) during test.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: August 25, 2023, 03:22:55 pm
content: Ok, your ppm scale on the right side differs..

author: miro123
author_rank: Frequent Contributor
timestamp: September 17, 2023, 10:07:30 pm
content: Hallo,I want to build few boards with ADR1399 and nomc/ot lt5400 resistor networks - are there any kicad/ altium reference design from other eebvlog members.i need the design files since i want to do some modifications. I have non-standard requirements- ADR1399 & LM399 TO-46- High stability 7V, 5V and 2v5,- Something in 10....12V is nice to have.- Small size is nice to have feature.BRMiro

author: dietert1
author_rank: Super Contributor
timestamp: September 18, 2023, 07:09:34 am
content: Quote from: Andreas on August 25, 2023, 02:47:51 pmOne should be aware that a TC of 3 uV/°C is always in the range of thermal EMF. Those references run hot.Maybe the residual TCs exhibit a pattern. If the numbering of references reflects their geometrical position on the test board, the apparent TC of the references follows a linear dependency - with one exception: ADR1399#2. Maybe it had some extra solder blob..Regards, Dieter

author: Andreas
author_rank: Super Contributor
timestamp: September 19, 2023, 08:15:16 pm
content: Hello,news from the 2nd ADR1399 PCB:See alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5024692/#msg5024692now I am measuring only 1 time per day (in the morning) so the temperature differences between measurements are smaller.the 4 metal can devices have now 1kHrs. The values are now temperature compensated after having determined the T.C.the 4 LS8 (SMD) devices have 100 hrs for initial measurements including T.C. measurement (not shown on the diagram) and after that 1 kHr temperature compensated ageing drift.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: September 24, 2023, 08:05:27 pm
content: Hello,update of ADR1399LS8 on PCB#1 ageing 5kHr after putting into Hammond enclosure and with temperature compensation:see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5011936/#msg5011936The ADR have now 8.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.The ADR1399LS8#01 - #03 are drifting slightly upwards ~2-3.5 ppm / 5 kHr in average over the last 5 kHrs.(now drifting in different directions).The ADR1399LS8#04 has nearly no (~1.2 ppm) ageing drift.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: November 01, 2023, 10:10:54 am
content: Hello,update from the 2nd ADR1399 PCB now at 2 kHrs for the metal can devices (KHZ) and 2.1 kHrs for the LS8 devices (first 100 hours not shown):See alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5068999/#msg5068999The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: November 01, 2023, 10:44:42 am
content: That is some interesting result Andreas. While the ADR1399KHZ seems to drift upwards (similar to what I observe for the Valhalla 2720GS/HSR-ADR and my ADR1399-PWM-DAC) all LS8 devices seem to follow the picture we can see in the datasheet.This seems to indicate, that Figure 27 was achieved using LS8 devices, not TO-46.-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: November 01, 2023, 11:32:01 am
content: Hello branadic,I have 2 PCBs with 4 LS8 devices each.On PCB#1 all ageing drift is rising (datecode #2043)here the drift is rising.https://www.eevblog.com/forum/metrology/adr1399-reference/msg5077309/#msg5077309https://www.eevblog.com/forum/metrology/adr1399-reference/msg4308397/#msg4308397On PCB#2 (see post above) I bought the devices much laterThere I have falling drift for the LS8 devices. (unfortunately I did not write up the date code).The metal can devices have date code #2316I fear the direction of the drift is more related to the date code.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: November 05, 2023, 02:35:37 pm
content: Hello,update of ADR1399LS8 on PCB#1 ageing 6kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5077309/#msg5077309The ADR1399LS8 have now 9.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.These LS8-devices are drifting upwards.The voltage shift at the 2 LM399 (only for comparison) occurred after repair on the output connector. (while operating the cirquit).Most probably I have damaged the Multiplexer for the "upper half" of the PCB during soldering.(will have to check that when I have some time).with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: November 17, 2023, 03:11:45 pm
content: Is there any recommendation what type of the 1uF (ser 5R1) output capacitor should be used?Foil or MLCC?

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2023, 03:46:45 pm
content: The capacitor should not be hat critical. Even leakage is not a problem. When using MLCC I would plan for 2 x 1 µF to conpensate for the drop in capacitance under voltage and the 1 µF value is already on the low side to start with.

author: Andreas
author_rank: Super Contributor
timestamp: November 17, 2023, 07:08:35 pm
content: Hello,I have no issues with 1uF/50V X7R in 0805with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: November 17, 2023, 07:18:42 pm
content: @Andreas: inspired by your low noise 399 in your 34401A I put the HP399 off my DMM and been just doing some measurements..Thinking to replace it with something better, currently running the DMM with a pops free LM399H, but thinking about one of my 1399 (<2uVpp).. Not sure I've been doing the right thing with my DMM, anyhow..

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2023, 08:09:20 pm
content: If one has a rather rare LM399 without the typical popcorn noise, this would be a relatively low noise ref. Not sure that the ADR1399 is better than this. Some the LM399 still have rather rare jumps from the popcorn noise (I have one that is at about 1 jump per hour) - this can be great for some short time tests, but bad for other (no averaging for many tests, just shifting the noise to even lower frequencies).The HP34401 also has a relatively noisy ADC. Though not directly comparable, the ADC noise can be limiting on the shorter time scale. To a large part there is not much one can do about it, as it's the somethwat limited resolution / quantization noise. Significant lower noise would need more like a redesign of the ADC.With a well aged reference there is also low dirft - a new ADR1399 would need quite some time to get the drift rate of a LM399 with some 10000 hous of use.

author: iMo
author_rank: Super Contributor
timestamp: November 17, 2023, 08:34:46 pm
content: I know, but - see below (the same setup), I will run the pops free LM399H#2 (1500h BI) over night.. Both 1399 (0h BI) I have are half of the LM399H#2 noise..

author: Kleinstein
author_rank: Super Contributor
timestamp: November 17, 2023, 09:08:07 pm
content: Looking at the standard deviation of a 7 V ref reading is bit unusual. It still reflects the ref. noise, but only for a limited times scale of some 4 - 400 seconds. So more normal way would be to look at the alan deviation.Anyway the difference is not that large. It is mainly having the jumps in the external LM399 ref and less or smaller jumps for the ADR. One would always see a combination of both references: The good lm399 in the 34401 and than either a more normal LM399 or the slightly lower noise ADR1399. The fact that there is quite some difference shows that the reference in the meter is way better than normal. With a more normal ref. in the meter one would not see much difference (70% noise even with a noise free external ref., though the way the test is done may be more sensitive to peak then RMS noise).Even for the relatively long time scale use in the test, the ADC noise is still a good part of the noise.

author: iMo
author_rank: Super Contributor
timestamp: November 17, 2023, 09:17:46 pm
content: That is 10V external Vref. Both HP399 and LM399 are the 34401A's refs (inside the meter). The peaks in the STD show where a reference shifted its voltage abruptly (or it is EMI). Those pictures are not about any stability over time..I have the data thus tomorrow, after the Starship's orbital flight, I will show you ADEV/MADEV as wellBut sure, I do understand the replacement of the old HP399 with the fresh ADR1399 is tricky..PS: CONT in the ADR1001 thread..

author: diodak
author_rank: Regular Contributor
timestamp: November 18, 2023, 02:49:42 pm
content: Quote from: Kleinstein on November 17, 2023, 03:46:45 pmWhat about the capacitor itself in parallel (instead of the RC circuit) according to the datasheet:"Another single element passive that works directly with the ADR1399 is a 10 μF tantalum capacitor, even though the series resistance canmeasure less than 5 Ω on an impedance analyzer."Has anyone checked this?

author: dietert1
author_rank: Super Contributor
timestamp: November 21, 2023, 05:44:21 pm
content: I did not try that as i think the better solution is a low leakage cap with a known resistor instead of unknown capacitor ESR. Trying to save a 1 cent part on a 15 $ reference?Here i have a three month log of the ADR1399 SMD evaluation kit i got one year ago. It got an outer oven at 38.2 °C. These are 4 second measurements with residual TC corrected. The log shows a drift of about 1.4 ppm and the internal temperature of the P6048 in red. One can assume the drift of about 1.3 ppm is caused by the Vishay NOMC divider used for the 10 V gain stage. Maybe a confirmation of results Andreas showed above.Regards, Dieter

author: ivo
author_rank: Regular Contributor
timestamp: November 23, 2023, 12:40:01 pm
content: Quote from: iMo on November 17, 2023, 03:11:45 pmIt's a 1uF good MLCC + 5.1R resistor, AFAIK essentially to emulate a tantalum cap, same with older regulators wanting tants/ECs to settle on their output pin and you can generally pull the same trick with themIn the LM399 datasheets they advise you can do a similar thing with the heater: you can add 10~500R above it to limit the current draw on initial heatup, but to do so you must add a 2.2uF *tantulum* cap across it.Quote from: dietert1 on November 21, 2023, 05:44:21 pmMy guess is because people don't want to have to deal with production scale soldering polypropylene (can't stand up to high soak temps) if they don't have to, and prefer to save cost on a tant. And yes two 1 cent parts vs a 10-50c part is a big difference!

author: Andreas
author_rank: Super Contributor
timestamp: December 17, 2023, 12:39:03 pm
content: Hello,update from ADR1399 PCB#2 now at 3 kHrs for the metal can devices (KHZ) and 3.1 kHrs for the LS8 devices (first 100 hours not shown):See alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5145858/#msg5145858The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)Now the LS8 devices, which started with negative slope for ageing, trend to a slow upwards ageing slope like the TO-46 metal can devices.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 17, 2023, 12:57:08 pm
content: Hello,update of ADR1399LS8 on PCB#1 ageing 7kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5152335/#msg5152335The ADR1399LS8 have now 10.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.These LS8-devices are drifting upwards.The voltage shift at the 2 LM399 (only for comparison) occurred after repair on the output connector. (while operating the cirquit).The investigation of the PCB did not give a obvious damage.So I decided to replace the multiplexer for the LM399. This was obviously the reason for the defect as the readings reverted to the old level.For the future I will drop the defective readings.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: January 28, 2024, 03:22:44 pm
content: Hello,update of ADR1399LS8 on PCB#1 ageing 8kHr after putting into Hammond die cast enclosure and with temperature compensation (sensor on bottom of the hammond case)see alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5226999/#msg5226999The ADR1399LS8 have now 11.3 kHrs in total operating time. Tempco is calculated out for the ageing curves.These LS8-devices are drifting upwards.I had again a 5-6 ppm voltage shift on the 2 LM399 (only for comparison) on the 2nd Multiplexer (MAX4052A).This time I had no obvious reason for the shift. So it was very unreasonable that the Multiplexer should have died again.I reflected what I did last time:- Switching power off and on (on another desk) to do some measurements.- Measurements did not show any obvious error.- Exchange the MAX4052A. (with power off).- reassembling and putting all back to the measurement desk.So I decided to do power cycling only and actually this "cured" the 5-6 ppm voltage shift.Obviously there is some "latchup effect" which affects the upper channels.But what can the reason for this latchup effect be?I had introduced some level shifters to reduce the self heating of the multiplexers when having 5V logic levels.But the level shifters are relatively high ohmic (BSS138 with 330K pull-up resistors on the 15V side) to reduce self heating.Simulation with a similar FET (BSS123) showed around 20 us rise time with 20 pF for wiring and input capacitances of the multiplexers.Should this be the reason for the latchup-effects?with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: January 28, 2024, 04:06:41 pm
content: Hello,update from ADR1399 PCB#2 now at 4 kHrs for the metal can devices (KHZ) and 4.1 kHrs for the LS8 devices (first 100 hours not shown):See alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5226966/#msg5226966The values are all temperature compensated (temperature sensor at the bottom of the hammond die cast housing)The LS8 devices continue to trend to a slow upwards ageing slope like the TO-46 metal can devices.If I look closer there are also 0.5-1 ppm jumps on the measurements.One jump in down direction is on the same day as the power cycling together with PCB#1 (same transformer).so I started to investigate (see zoomed diagram).And actually: every time when I did a power cycling (half a minute followed by >15 minutes warm up time) the measurements started at lower levels.After one measurement cycle mostly the higher level was again active.So also here I have a less pronounced "latchup effect" of 0.5-1 ppm.So the question arises: Are there any multiplexers like MAX4052A which can be used as replacement (hoping that there will be no latch up effect)- low leakage current- operating from 12-15V (single supply)- in SO-16 package with same pinout as 4052 devices- at best with integrated low power level shifters from 5V to 15 Vwith best regardsAndreaswith best regardsAndreas

author: Kleinstein
author_rank: Super Contributor
timestamp: January 28, 2024, 05:10:35 pm
content: A possible choice for the MUX chips could be the relatively new TMUX4052. The specs are rather loose because it is a cheap part (so not much testing done), but the typical performance is still expected to be relative good. They accept a low control level (e.g. 2 V) at least. The DG4052 should be similar with tighter specs.

author: Andreas
author_rank: Super Contributor
timestamp: January 28, 2024, 05:55:27 pm
content: Quote from: Kleinstein on January 28, 2024, 05:10:35 pmHello,Electrically it would fit (I think). But I did not find a SO16 package. Or did I overlook something?(I do not want to resolder the references, only the multiplexers).The DG4052 might be a replacement.with best regardsAndreas

author: Mickle T.
author_rank: Frequent Contributor
timestamp: February 15, 2024, 01:34:29 pm
content: A simple, general-purpose, dual-voltage (10V and 1V) reference based on the ADR1399 in a TO-46 package. Temperature coefficient <0.2 ppm/°C (10 V), noise amplitude 0.25 ppm p-p (0.1-10 Hz). Resistors are selected with TCR 0.2...2 ppm/°C.https://youtu.be/guZnwp_DdUM

author: ivo
author_rank: Regular Contributor
timestamp: February 15, 2024, 02:28:57 pm
content: I swear most people's definitions of "simple" differwildlyfrom mine on this board 😅

author: dietert1
author_rank: Super Contributor
timestamp: February 15, 2024, 10:42:51 pm
content: Yes, it seems to be more like a calibrator for voltage, current and resistance. Very nice.Regards, Dieter

author: Andreas
author_rank: Super Contributor
timestamp: March 25, 2024, 08:01:19 pm
content: Hello,update from ADR1399 PCB#2 now at 5.4 kHrs for the metal can devices (KHZ) and 5.5 kHrs for the LS8 devices (first 100 hours not shown):See alsohttps://www.eevblog.com/forum/metrology/adr1399-reference/msg5303665/#msg5303665I have exchanged the MAX4052A multiplexers against standard HEF4052 (NXP) CMOS devices.As result ther is a relative large jump on all references.But also the "ageing" slope has changed significantly on all channels (mostly near zero).So I fear that up to now I have measured the "ageing" of the MAX4052A instead of the references.That also would explain the difficulties with my "position dependant drift".I think that the MAX4052A are not usable for higher supply voltages than ~10-12V since I never recognized something unusual with 5V.Should have used a relay multiplexer instead?In the mean time I also have some DG4052 to give them a try.with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: April 02, 2024, 03:42:25 pm
content: Quote from: Mickle T. on February 15, 2024, 01:34:29 pmThis is a beautifully executed project. How long did this simple project take? How much did it cost you when all is said and done? Anyway, thanks for sharing.PS - It costs my lab over $2700 per 3458A to backup our numbers. Voltage tests here are a bit subjective because even a Keysight ISO17025 calibration has an uncertainty of 1.1ppm.

author: ivo
author_rank: Regular Contributor
timestamp: April 03, 2024, 04:14:20 pm
content: I wonder if anyone with capable equipment, would be interested in testing if there's any appreciable difference in noise, and tempco ppm sweeps, over different reference currents? Say 3mA/6mA/10mA?

author: CalibrationGuy
author_rank: Unknown
timestamp: April 03, 2024, 04:57:35 pm
content: Quote from: ivo on April 03, 2024, 04:14:20 pmIf such a request were made, you would have to clearly define what tests you would want including tolerance, number of samples, test conditions, etc. People who have labs are usually busy people. *cough* *cough*TomG.

author: iMo
author_rank: Super Contributor
timestamp: April 03, 2024, 06:18:04 pm
content: Quote from: ivo on April 03, 2024, 04:14:20 pmThe "zener current" inside the 1399 is set to a specific "constant value" by ADI, the same as with 399 (the chip is almost the same). You cannot change that current from outside.

author: CalibrationGuy
author_rank: Unknown
timestamp: April 03, 2024, 07:11:22 pm
content: I thought they were referring to changing the heater current maybe?TomG.

author: iMo
author_rank: Super Contributor
timestamp: April 03, 2024, 07:25:06 pm
content: In 399 and 1399 the heater current is internally set such the temperature of the chip is kept "constant" at 95degC, afaik.Thus you cannot mess with zener nor heater current with 399 and 1399.For such experiments with zener/heater currents you want LTZ1000/ADR1000/ADR1001 for example..Quote from: CalibrationGuy on April 03, 2024, 07:11:22 pm

author: CalibrationGuy
author_rank: Unknown
timestamp: April 03, 2024, 08:02:32 pm
content: Quote from: iMo on April 03, 2024, 07:25:06 pmI was just perusing the LTZ threads, thanks for pointing that out.TomG.

author: Andreas
author_rank: Super Contributor
timestamp: April 04, 2024, 07:49:36 am
content: Hello,on the other side the idea is not uninteresting.Depending on location of heater, zener and temperature sensor on the chipthe temperature distribution could be affected when the cirquit around the zener gets more current(and the heater less to keep the temperature).with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: April 04, 2024, 10:25:54 am
content: Quote from: Andreas on April 04, 2024, 07:49:36 amWith a higher "excess" current you start to influence the heater's equilibrium, sure.1mA more "zener excess current" will create 7mW of heat somewhere on the chip, with Rthja 220C/W (DS value for the TO-46 version) it increases the chip temperature by 1.54C, that will force the oven to decrease the heater current to go back to 95C. The excess current through the "zener" will increase the drop at the zener's bond wire(s) as well.So you may try to increase the "zener current" till the oven gets off the regulation (my guess would be aprox 10-20mA) and then the "excess zener current" starts to dominate..Another version is to switch off the heater, and heat up the zener with the "excess zener current" only. You would need aprox 25mA of current for say 70C (23C Tamb), imho.The question is how the "zener voltage" with the excess current dependence is in reality.I would not do it, however..

author: dietert1
author_rank: Super Contributor
timestamp: April 04, 2024, 03:40:24 pm
content: In their evaluation board they use about 3 mA. If you use a 0.1 % resistor to generate that current, you expect at most 3 uA variation. Times the 0.04 Ohm dynamic impedance spec gives 120 nV. Good enough!In the datasheet they explicitly show that the same dynamic impedance applies for a 3 to 13 mA change (delta I = 10 mA gives 0.4 mV).Regards, Dieter

author: Andreas
author_rank: Super Contributor
timestamp: April 07, 2024, 03:14:06 pm
content: Hello,before changeing the mulltiplexer to DG4052 on PCB#2 I wanted to see wether the multiplexers have any influence on tempco of the references.So I started with T.C. measurements.Unfortunately I recognized that I did not repeat the T.C. measurements of the LS8- parts after I had populated the metal can parts.Due to the additional heaters on the PCB the measured temperature range on the bottom of the die cast housing has changed even with same environmental temperature profile.On the LS8 parts the temperature range was 12-45 deg C without population of the metal can parts.Now it is 18-46 deg C with the metal can parts populated.And it looks like the effective T.C. relative to the temperature sensor has increased.So most probably my temperature correction for the LS8 parts was wrong after population of the metal can parts.Further I recognized that there is still some latch up effect (2 times) after having changed from MAX4052A multiplexers to HEF4052.I looked at the power supply values at the beginning of the latchup.And surprise: on entry of the latchup the 15V supply of the LDO (LM2940) increased by 50-60 mV. Whereas the raw value 17V was about constant.At the same time the voltage appeared more noisy. (Oscillations ?)I double checked the data sheet and found that I was missing the 22uF capacitor at the output of the LM2940.There are only 12 pcs 100nF capacitors on the 15 V supply (one for each ADR1399 heater) 2 for the Multiplexers and 2 directly at Output of LM2940 / input of LM2950A.I tried to measure the oscillations with the scope. But obviously this changed something at the cirquit so no oscillations visible.I removed the Jumper for the heaters since the "latchup" occured more at higher temperatures = lower heater power.So in this condition (lower 15V load and 8 capacitors removed) I saw the oscillations 2Vpp with 45 kHz.A 100uF capacitor which I had on hand fixed the oscillations.So now I can repeat the T.C. measurements hopefully without any further "latchup" effect.But I fear the ageing measurements up to now where useless:Wrong T.C. and one never knows how the unstable 15V supply influenced the measurements.I am feeling like a bloody beginner.On the other side: the oscillations are only visible under rare conditions otherwise I would have seen them on cirquit start up.with best regardsAndreas

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 07, 2024, 03:50:26 pm
content: Guys, just for clarification - theADR1399 can not work properly below about 2.5mA reference current, with 3mA is not just a datasheet figure but the correct minimal current. For that reason if you replace LM399 with ADR1399 you must take care of the current, in many old units LM399 is run at just above 1mA reference current and without modifications to the circuit the ADR1399 as a replacement will work poorly.CheersAlexP.S. - did you really think you can get lower noise for free, without an increase in current?P.P.S. - I've scanned through the circuits uploaded in this thread, it looks like I am overreacting.

author: Andreas
author_rank: Super Contributor
timestamp: April 07, 2024, 05:03:21 pm
content: Hello,if it calms down your nerves: I am using 2K4 to 15V in my ageing box.with best regardsAndreas

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 07, 2024, 05:08:14 pm
content: Quote from: Andreas on April 07, 2024, 05:03:21 pmIt certainly does! I would be heartbroken if all your work on this reference could be wasted!CheersAlex

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 10, 2024, 11:44:24 pm
content: Now I can explain a bit, my earlier strong reaction. A few days ago I bought HP3245A unit which was modified by replacing the original LM399 with ADR1399 (on top of other service work, a new mains filter, new Dallas chips etc). Unfortunately, the minimum current issue was missed and the unit (recently calibrated using HP3458A) was not very stable. I've added a 2K7 50ppm/C resistor in parallel to R401 and had to recalibrate manually, as the reference output (and hence the unit output) increased by 2.35mV or over 300ppm! Here is the stability test results overnight in my lab with the ambient temperature variation during nighttime about 4 degrees C, before the mod and after the mod and calibration. The voltage was measured by one of my Keithley 2015 units (NPLC10 +10 averages, a rough equivalent of NPLC100), so essentially against a very well aged LM399.CheersAlex

author: iMo
author_rank: Super Contributor
timestamp: April 12, 2024, 07:53:51 am
content: I reported that 1399 instability in my "noise indicator" thread - the 1399 really needs at least those 3mA and the RC "snubber" (!!!). So for standard 7->10v you need 1k cathode resistor or even smaller..

author: IanJ
author_rank: Unknown
timestamp: April 12, 2024, 02:19:46 pm
content: My 3245A with a newly fitted ADR1399 (24hrs ago).Recently re-capped.3245A Vref circuit op-amps changed out for Chopper (yes I know....but I am experimenting!).Red trace is workshop temperature (regulated).PS. My workshop is quite noisy, LED lights, PC running, Server cabinet.......all within fairly close proximity.No snubber fitted to ADR1399:10NPLC, 5sec interval, 78mins total.Max-Min across graph =2.224uVSnubber fitted to ADR1399:10NPLC, 5sec interval, 83mins total.Max-Min across graph =2.127uVIan.

author: iMo
author_rank: Super Contributor
timestamp: April 12, 2024, 03:22:04 pm
content: Also do not solder the snubber directly on the 1399 pins (ie from bottom side of the pcb). I did it in my 34401A and the noise (stddev) rose by 20%. After removing it it went back. Caused by the thermal flows as the capacitor and resistor worked as a heatsink. I did it with the stock 399 there as the preparation for 1399 replacement, but stopped the experiment as that would require an adjustment of the meter (adjustment of everything)..

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 12, 2024, 06:25:54 pm
content: Ian, the reference noise in not a problem in HP3245A. Here are some interesting measurements I've just made using a fully passive 0.1-10Hz filter and Keithley 2015M at 100mV range, 1 NPLC, changing voltage output from HP between 1.2 and 1,3V.CheersAlex

author: IanJ
author_rank: Unknown
timestamp: April 12, 2024, 06:33:18 pm
content: Quote from: Alex Nikitin on April 12, 2024, 06:25:54 pmI have seen this before when I was playing with WinGPIB. I guess the PWM isn't properly controlled when changing output voltage. Am guessing in Lo Res mode the 3245 doesn't do it?Ian.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 12, 2024, 06:46:50 pm
content: It is not PWM control, it is a range change, 1.25V is the maximum output for the lower range. Moreover the level of noise changed with the range but doesn’t change with the voltage, it is the same voltage p-p for 3V and for 10V.CheersAlexP.S. - Low Res behaves in the same way just the ranges are different, for example if you go from 1.250V to 1.251V in Low Res, the noise doubles from about 12-13uV p-p to 25uV p-p.

author: branadic
author_rank: Super Contributor
timestamp: April 14, 2024, 08:58:16 am
content: An update of my ADR1399-PWM-DAC.Recap: I'm observing the bootstrapped reference, that uses PWM in the 7 V --> 10 V gain stage, with a S7081 and a Prema 6048 at the same time.I repeated t.c. measurement, result attached.Long-term drift observation unfortunately were corrupted by a data crash, resulting in a total loss of dataSince then 1000 h of new drift data were recorded, which appear rather stable.-branadic-

author: Andreas
author_rank: Super Contributor
timestamp: April 28, 2024, 03:39:40 pm
content: Hello,update on my ADR1399 ageing reference board after having added 100uF to the output of the LDO voltage regulator on day 246.(HEF4052 multiplexer has been used since day 190 / previously it was a MAX4052A)Now I have a much lower standard devation especially on the metal can packages (from 0.25-0.3 ppm to 0.1 - 0.15 ppm)But also the LS8-packages went down from 0.15-0.3 ppm to 0.1 - 0.17 ppmAnd again the output voltage shifted. So I fear that I will have to repeat the ageing drift measurements with a new set of references.With best regardsAndreas

author: EC8010
author_rank: Frequent Contributor
timestamp: April 28, 2024, 04:51:37 pm
content: My ADR1399 (TO46 variant) evaluation board arrived a few days ago. I replaced the 1k33 resistor with a temperature compensated LM334 set to 3mA. The periodicity is due to the central heating coming on in the (cold) lab, probably a change of 5C or so. Deviations are smoother and smaller than with resistor. Negative polarity is because I inexplicably plugged to the board the wrong way round and didn't notice.Power was 12V 7Ah lead-acid battery, meter was HPAK34470A.Next step will use op-amp bootstrapped Zener circuit instead.

author: Andreas
author_rank: Super Contributor
timestamp: April 28, 2024, 05:57:24 pm
content: Hmm,so you have around 1 ppm/K temperature drift.I think that your DMM contributes most of the T.C.Did you try to thermally isolate the ADR1399?Did you do the TC-Compensation of the LM334 from datasheet or did you adjust the 2 resistors to minimum T.C.(according to my experiences with LM334 for a LM399 project the resistor values from datasheet are not perfectly).with best regardsAndreas

author: EC8010
author_rank: Frequent Contributor
timestamp: April 28, 2024, 10:39:54 pm
content: Thanks for your thoughts. That's what I'm thinking; it's too close to the limits of my present measurement ability. I keep wondering about an 8 digit DMM. Or better, an array of at least four temperature controlled voltage references that can be compared using existing kit.The 1399 is in the cardboard box with foam the evaluation board came in, but not properly sealed; I have done much better thermal control on other experiments. This is early days. I'm also wondering about that plastic hat the device is in. For instance, is the plastic triboelectric where it wobbles and scrapes on the leads? Is the plastic hat there simply because it's cheap and easy to add by the manufacturer, but not genuinely optimised? Would foam be better? The wobblyness and rattling concerns me, too. At this level, microphony is often an issue.The LM334 is pretty much as per data sheet. I have tried tweaking the ratio of the resistors but it didn't help, suggesting that its remaining tempco was actually down to the (metal film) resistors themselves. I could perhaps do better using low-tempco wirewound resistors and trimming, but I think that's a bit of a dead end. I only put the compensated LM334 in because I had one ready-made and set for 3mA. I think the bootstrapped op-amp solution for the Zener should be better.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: April 30, 2024, 11:43:12 am
content: It might be simpler (and better) to use the LM317 + 330 Ohm resistor (and another 2K7 to ground as an additional load for the LM317) as a current source, the current variations should be below 10uA in a reasonable temperature range (10C-50C) which would give a voltage change only around 1ppm (over the range) even for LM399, with less than 0.1ppm for the ADR1399.CheersAlex

author: EC8010
author_rank: Frequent Contributor
timestamp: April 30, 2024, 04:12:52 pm
content: That's a thought. And I have an LM317-based variable CCS that could easily be connected.If I see the same result as with the LM334, fingers will be pointed at the 34470A.

author: Mickle T.
author_rank: Frequent Contributor
timestamp: June 23, 2024, 07:45:05 pm
content: I slightly complicated the circuit diagram from the previous page, adding a few more components to the ADR1399 and the ability to reproduce AC and DC voltage with ranges of 1 and 10 V, six decades of resistance from 10 Ohm to 1 MOhm and current with five ranges from 10 μA to 100 mA. DAC - as usual AD5791A, but selected for INL<1.5 ppm.The most difficult and time-consuming thing, as it turned out, was making the case. Although SCHROFF CompacPRO is convenient for installation and assembly, I did not like it at all due to its large and non-standard dimensions, and rather large weight (the entire assembled device weighs about 5 kg!). The extruded aluminum case is quite simple to machine, but unfortunately it does not accommodate domestic sealed PWW resistors and I have to install BMF or small-sized non-sealed PWW

author: bobAk
author_rank: Contributor
timestamp: June 25, 2024, 01:33:48 pm
content: Hello. Has anyone tried to connect adr1399 in series? Like lm399. It’s more interesting how it behaves, since changes in the control loop of the shunt part in comparison with lm399 led to the need to install ~1 µF 5 ohms. In theory, there should be no problems, due to low impedance. Requires ~14 volts with low noise.

author: misterpulcri
author_rank: Newbie
timestamp: July 10, 2024, 04:29:17 pm
content: Hello,Apologies, my question is pretty basic but I see a lot of expertise here and no other suitable ADR1366 forum. Happy to be redirected somewhere more appropriate if I am in the wrong place.I have attempted to build a basic voltage reference using a ADR1399K with +12v supply, 1K3 shunt for 3mA at 12V, 5R1 and 1uF as per the datasheet. Have built this three times now on breadboard and stripboard. Each iteration produces 6.920V instead of the expected 7.05V. At each power on my DVM reads 6.925 and within a few seconds this decreases and stabilises at 6.920V. I have verified that I have just over 3mA flowing through the shunt. Have checked with 2 other hand held DVMs and get the result as my bench DVM. Have checked DVMs against a fairly accurate voltage sourceAm I missing something or is my ADR1399 faulty?ThanksSean

author: Kleinstein
author_rank: Super Contributor
timestamp: July 10, 2024, 04:35:03 pm
content: There is quite some variations between different units of LM399 and ADR1399. The ref. voltage can vary quite a bit. The specs are 6.75 to 7.3 V, though the extreme values are rare. 7.05 V is just a typical value. So the 6.92 V are perfectly reasonable.

author: misterpulcri
author_rank: Newbie
timestamp: July 10, 2024, 05:31:53 pm
content: Ah, OK thanks. I can at least stop pulling my hair out.

author: Andreas
author_rank: Super Contributor
timestamp: July 10, 2024, 06:45:31 pm
content: Quote from: misterpulcri on July 10, 2024, 04:29:17 pmHmm,Are you Kelvin sensing the voltage at the zener or are you measuring the sum of the zener voltage and the voltage drop of the heater current on the ground connection?But even without that it needs some time until steady state is reached.with best regardsAndreas

author: bastl_r
author_rank: Regular Contributor
timestamp: July 11, 2024, 12:45:26 am
content: HiWhat did you use to measure the reference voltage? It is advisable to measure it with a measuring device with an input voltage divider in the G-Ohm range. I once had an aha-experience on my Solartron 7066 when I wanted to check the reference voltage before the buffer. The standard 10MOhm of the 34401a was not enough and the voltage dropped a few 10µV...Whether this also applies to the ADR1399 I cannot say at the moment.Greetings bastl_rTranslated with DeepL.com (free version)

author: misterpulcri
author_rank: Newbie
timestamp: July 11, 2024, 09:32:56 am
content: Hi all and thanks for your replies. I should explain my objective and reason for constructing an ADR1399 based voltage reference.My "best" DMM is an ancient Fluke 8050A and I wanted to check the calibration of this device. I need to be able to measure down to 100s of uV which this meter will not do, but I wanted to ensure I was ballpark in the mV range.I construct Eurorack synthesiser modules which use the 1V/octave system for voltage to pitch i.e. note C0 = 0v, C1 - 1.0v etc. Each octave is divided into 12 semitones and each semitone is a 0.0833V increment.Mouser sent a product announcement for the SMT version of the ADR1399 so I investigated and purchased the through hole version naively thinking that if I built the circuit in the datasheet adjusting my shunt value to ensure 3mA for the Zener, 7.05 volts would be present at the reference output and I could gain a degree of confidence in my meter calibration at least down to the mV range.Before cominng here I did experiment with different shunt values to swing from <3mA up to 5mA and also varied my supply voltage etc and always seeing 6.920V.I now know that my voltage reference build is fine and is accurate and stable at 6.920 instead of 7.050VThanks again for taking the time to look at my naive newbie experiments, I will most likely purchase a new DMM that gets me into the uV range.ThanksSean

author: Kleinstein
author_rank: Super Contributor
timestamp: July 11, 2024, 10:47:44 am
content: When the layout is right, the ADR1399 has a rather low output impedance (< 0.1 ohm) and should be OK even with a meter with 10 M input impedance.The ADR1399 is however the totally wrong way to hope for an absolute value of the voltage. There is quite some tolerance in the voltage, but that value is quite stable.There are other reference chips for a good accurate initial value (e.g. Ref102C or max6126A) : better accuracy, but not as stable.

author: dazz1
author_rank: Frequent Contributor
timestamp: July 12, 2024, 10:14:30 am
content: Quote from: JodelJonny on April 19, 2023, 07:16:27 amHiI like your design. Simple single purpose, no unnecessary complexity.If you haven't already, could you clean and post your files please?Are there any changes or improvements you would make?

author: Andreas
author_rank: Super Contributor
timestamp: November 06, 2024, 10:21:08 pm
content: Hello,PCB #3 with a new set of ADR1399 after first 500 Hrs (+~15 hours for first bug fixing of the new software of the multiplexer)Multiplexer is now with bistable relays.not shown: additional thermal isolation + die cast housing for the whole pcb.LS8-package has date code 2043TO-46 metal can date code 2316It seems that LS8 package needs longer time and more drift to settle than the TO-46 package which seems to stabilize after ~1 week.Measurements are still without T.C. compensation since I want to wait with T.C. measurement until the units are sufficient stable.with best regardsAndreas

author: ivo
author_rank: Regular Contributor
timestamp: November 07, 2024, 01:05:41 am
content: Quote from: Andreas on November 06, 2024, 10:21:08 pmCan you share what circuit scheme you intend to use to remove... 0.2ppm tempco?Have you looked if the LCC or TO46 package have any difference in 1/f noise?

author: Andreas
author_rank: Super Contributor
timestamp: November 07, 2024, 07:57:55 am
content: Hello,T.C. will be only calculated out (mathematically) for the ageing drift.Up to now I have only noise figures from LS8 packages on PCB#1https://www.eevblog.com/forum/metrology/adr1399-reference/msg4445218/#msg4445218https://www.eevblog.com/forum/metrology/adr1399-reference/msg4453792/#msg4453792so obviously a good idea to make some measurements on PCB#2 + PCB#3with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: November 23, 2024, 01:08:47 am
content: Andreas, I've been inspired by your efforts. I am working on aging boards. Here's a picture of my ADR1399 farm ready for planting!TomG.

author: CalibrationGuy
author_rank: Unknown
timestamp: November 24, 2024, 07:13:22 pm
content: The boards will go in this oven for a few months. Anyone have any suggestions as to optimum aging temperature? I was thinking 40/45 degrees C. Thoughts?TomG.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 24, 2024, 07:19:08 pm
content: Aging should be at a higher temperature. Under normal operation the temperature is regulated to some 90 C. So that or a little higher would be the logical temperature for aging. This could be done by using the chip internal heaters.

author: CalibrationGuy
author_rank: Unknown
timestamp: November 24, 2024, 07:26:08 pm
content: I see that I miscommunicated my intentions. I understand the operating temp is higher than the temperature I selected for the oven. What I meant to say was I will keep the parts at a temperature significantly higher than ambient so I can more accurately assess drift without ambient lab temperature being one of the variables.TomG.PS - Thanks for taking the time to reply.

author: laichh
author_rank: Regular Contributor
timestamp: November 25, 2024, 02:30:32 am
content: Quote from: CalibrationGuy on November 24, 2024, 07:26:08 pmHi TomG,Take a look at the Design Note 229 by LT (now ADI)https://www.analog.com/media/en/technical-documentation/design-notes/dn229f.pdf.

author: CalibrationGuy
author_rank: Unknown
timestamp: November 25, 2024, 04:59:26 am
content: Quote from: laichh on November 25, 2024, 02:30:32 amYes, I've read this paper, thanks. I'm going to say this once more. I am aging the parts normally, not at elevated temperatures in order to accelerate aging. The parts are going in the oven because I want a very stable thermal environment to measure initial drift accurately. I am also placing boards with different parts and configurations with the 7 to 10 volt gain stage in the oven to see if their performance is the same in a constant temperature environment.TomG.

author: Andreas
author_rank: Super Contributor
timestamp: November 25, 2024, 06:42:36 am
content: Hello,to cancel out environment temperatures it is usually sufficient to keep temperature around 10 deg C above the max environment temperature. (including self heating of your PCB).Better would be to keep the environment exact to 25 deg C (according to the datasheet conditions).The question is: how temperature stable (hysteresis) is the oven between heating phases, and how much thermal mass do you need around your references to keep the environment temperature really stable?And how temperature stable is your measurement instrument. Near room temperature the T.C. is between -0.1 and -0.3 ppm/K on the 4 metal can samples of PCB #2.My strategy is different: make the first 1000 hours run in at room temperature (and log the temperature at the bottom of the die cast housing). At the moment I am determing the T.C. of PCB#3 to compensate (mathematically) for it.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: November 25, 2024, 07:38:56 pm
content: Hello,PCB#3 now passed 1 kHr. (Still not temperature compensated).See also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg5703775/#msg5703775Unfortunately the temperature was changeing a lot the last days.At the moment I am doing T.C. measurements so that I will be able to give a better picture how the ageing drift really is.with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: November 25, 2024, 09:04:20 pm
content: Andreas, how are you measuring the voltage for those data points? I am planning on using our recently calibrated 732c as a reference to normalize the data. The 732c will be on channel one while the DUTs will be on the other channels. I can then calculate the drift of the DAQ and remove its drift from the final results.TomG.

author: Andreas
author_rank: Super Contributor
timestamp: November 25, 2024, 09:53:47 pm
content: Hello,The plan with the 732c looks good.In case of the ADR1399 boards I am using the average of my 3 most aged 24 bit ADCs. (ADC13, ADC15, ADC16)Each ADC has a LTC2400 with a (selected) AD586LQ reference and a NTC as temperature sensor.INL and 3rd order T.C. are calculated out.Example for ADC see here:https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg1224922/#msg1224922And of course each ADC has a precision capacitive 2:1 voltage divider (LT1043) which extends the range up to 10V.On ADR1399 board #3 the bypass input is used to monitor stability of the measurement by a pre-aged ADR1000 reference.Stability of the ADCs in 10V range is better than my 34401A and better than my (temperature compensated) K2000.https://www.eevblog.com/forum/metrology/stability-of-5v-references-compared-to-ad586lq/msg5257890/#msg5257890https://www.eevblog.com/forum/metrology/project-pimp-a-keithley-2000/msg1106839/#msg1106839with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: November 25, 2024, 10:14:23 pm
content: I read the posts from those links, very interesting reading. You've obviously put a ton of effort into this. I am curious about several things, but one thing interests me the most. You are using the AD586LQ reference chip. How did you select the best ones? What was your primary reference for the 10V absolute value and for measuring drift? What did you use for the comparison?Best Regards,TomG.

author: Andreas
author_rank: Super Contributor
timestamp: November 26, 2024, 07:36:50 pm
content: Hello,the AD586 selection criteria is explained in one of the links of previous message.My primary reference is a 7V LTZ1000 (#4) which is compared against different calibrators or fresh calibrated DMMs to get traceable values.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: November 26, 2024, 10:14:10 pm
content: Hello,I had switched off PCB#1 and PCB#2 for 3 weeks.on PCB#2 the metal can packages restored the old voltage after 8 hours of warmup phase.The LS8 packages on PCB#2 showed 0.5 - 1 ppm shift after warm up.A short power outage of some minutes on day 460 restored the old values.On PCB#1 the LS8 packages showed similar behaviour of 0.5 - 2 ppm shift after 3 weeks power outage.But one of the LS8 packages also showed a permanent 1 ppm shift after the short power outage. (day 625)So obviously the LS8 package has more hysteresis after long power off periods than the metal can package.with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: November 27, 2024, 04:29:37 am
content: Andreas, I wonder what would happen to those references in the ceramic package if you turned them on for a day, then turn them off for a day and then turned them on again for a day for a few months. Do you think the hysteresis drift would lessen?When I get around to building those boards, you can let me know if there's anything you want me to test (thermal cycling, power cycling, etc.)TomG.

author: Andreas
author_rank: Super Contributor
timestamp: November 27, 2024, 08:23:04 pm
content: Hello,I think that the hystersis on the LS8 package is happening by the humidity reaction of the EPOXY of the PCB.Here we have time constants of several (2-7) days. So a short interruption of one day or over the weekend will not have such a large impact.I have no preferences for your tests. The datasheet should give you enough ideas. (no one has tested dynamic resistance up to now imho).Your first goal should be to get stable values (over time).After a few hundred hours the references should be stable enough to begin T.C. measurements.With best regardsAndreas

author: JodelJonny
author_rank: Contributor
timestamp: November 28, 2024, 07:24:04 pm
content: Hello,sorry I never managed to post my KiCAD and gerber files. Here they are.Feel free to use them as you like. If you improve the design, it would be great if it was made available to everybody as well.The layout works, I get 10 V and no smoke, apart from that it is very possible that there are errors (wrong footprint for example).Thanks for all your help and adviceSince my last post I have build a second one. It has run a few khours but still needs a trim resistor to get close to 10 V.Best regads JodelJonny

author: Kleinstein
author_rank: Super Contributor
timestamp: November 28, 2024, 08:09:15 pm
content: With quite some difference between the hot and cold state there can also be hysteresis from thermal stress. The humidity could add to the stress, though from the tendency the other direction. Solder can creep / deform, especially when hot, but also at room temperature.For the humidity relaxation the time constant also depends on the temperaure. Expect a much shorter time scale when hot. So maybe 2 days hot and 2 weeks cold.

author: Andreas
author_rank: Super Contributor
timestamp: December 07, 2024, 04:33:53 pm
content: Hello,I finally managed to do the T.C. measurements for PCB#3.On the first run after ~40 hrs for the 4 LS8 devices I had no luck.I recognized too late that I had forgotten to activate the temperature compensation of my measurement ADC.(It was switched off for the ratiometric T.C. measurements of the resistance trimmers).So I had to repeat the measurement with activated T.C. compensation.I also had bad luck with the TO52 devices. One of the relays had a bad contact and the voltage variation showed several 10 uV during measurement for certain temperatures. I tried to do some cleaning (current) but had no luck. After exchangeing the relay the galvanic isolation (photocouplers) of the RS232 communication failed. So I had to do another run...Finally the results:T.C. on PCB#3 is between -0.008 ppm/K and -0.213 ppm/K near room temperature.The best is a TO52 device and the worst a LS8 device.The table shows all measured ADR1399 results and the 2 results of LM399 on PCB#1with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 15, 2024, 01:42:16 pm
content: Hello,after T.C. measurements I can now supply temperature corrected measurements.compare to the diagrams from here (which were uncompensated and so more noisy).https://www.eevblog.com/forum/metrology/adr1399-reference/msg5726673/#msg5726673with best regardsAndreas

author: ITArchitect
author_rank: Contributor
timestamp: December 16, 2024, 02:18:36 pm
content: Your graph shows ADR1000 for that square plot.

author: Andreas
author_rank: Super Contributor
timestamp: December 18, 2024, 08:44:49 pm
content: Hello,the ADR1000 (now stable) is only for sanity check of the measurement.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 18, 2024, 09:06:56 pm
content: Quote from: ivo on November 07, 2024, 01:05:41 amIvo asked for noise behaviour between LS8 or TO46 package.So I did noise measurements. Here PCB#3 (with relay multiplexer).First the noise floor together with a 2 LiIon (9V) battery on the input of the LNA.124 nVpp is low enough.then the 4 LS8 devices and the 4 TO46 devices.Generally you can say that the noise is very individual (independant of package).Most devices are over the data sheet spec of 1.44 uVpp.Even if you take into account that I am doing 100 sec measurements which give a slightly higher noise (statistically more extreme values)than the 10 second measurement duration which is minimum duration for the 0.1-10 Hz range.I also use the longer duration and 19 measurements to catch popcorn noise and calculate some average noise values + stray.Most devices have some visible popcorn noise above 0.5uV (up to 2 uV measured).Some typical graphs are shown.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: December 18, 2024, 09:17:10 pm
content: Hello,and also for PCB#2 (with MAX4051A multiplexer).again the same picture: very individual noise.Mostly above datasheet typical value.So if you need really a low noise device you should select the voltage references for noise.Since the PCB´s are measured from a (linear) mains supply. The mains frequency is rather large. (could not be further reduced).Effectively I have -165 dbV which corresponds to 6 nV eff or 20 nVpp. So the influence is low enough for the measurement.and finally a overview.only 3 devices meet ~the datasheet spec. (green)2 further devices are near that but have already some popcorn noise (yellow)the other devices either have large popcorn noise or some "high frequency looking" noise. (LS8_08 and TO46_02)with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: December 18, 2024, 10:10:30 pm
content: The T046-4 looks nice, but.. try to run it longer, like 1 day for example, whether it jumps or not.. I have such sample (EDIT: it was an LM399) with lowest noise but it jumps 1-2 times per day (jumps to a different level and stays there).

author: Andreas
author_rank: Super Contributor
timestamp: December 19, 2024, 06:38:28 am
content: Interesting,how high are the jumps and how much samples did you test?with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: December 19, 2024, 07:18:31 am
content: My brain fart.. It was LM399.. The jumps were around 5uV..https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg5684641/#msg5684641My best 1399 is currently in burn-in, no such infrequent jumps so far..

author: CalibrationGuy
author_rank: Unknown
timestamp: December 20, 2024, 01:19:20 pm
content: Andreas, how many data points are you taking per day for those eight voltage references on your board? (4 LCC + 4 TO46) I assume you take more samples for noise measurements. How many samples/sec, or min, etc. do you take for the noise measurements?TomG.

author: Andreas
author_rank: Super Contributor
timestamp: December 20, 2024, 01:57:46 pm
content: Hello,one single measurement has 100 sec and 5 MSamples in total ( so 50 kSps / sec)I am doing 19 measurements (the whole usable buffer of the oscilloscope) in one series.So I can also do averaging on the FFT outputs. (not inputs).The 19 measurements are then evaluated for average 1/f noise and AC rms values.Usually I am doing more than 1 series on one sample to screen for popcorn noise.So actually one sample needs more time than the 1900 secs for one series.with best regardsAndreas

author: CalibrationGuy
author_rank: Unknown
timestamp: December 20, 2024, 02:45:38 pm
content: That's a lot of data. How about the drift data. How often do you sample the 8 references on your aging boards?TomG.

author: Andreas
author_rank: Super Contributor
timestamp: December 20, 2024, 03:47:54 pm
content: Hello,at the moment I am starting one (automated) measurement per day.Each of the 8 references is averaged over 1 minute measurement time.The first 1000 hours I measured twice per day.During T.C. + noise measurements there is a gap in the ageing drift.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: January 05, 2025, 06:23:15 pm
content: Hello,PCB#3 (with relay multiplexer) now passed 2 kHrs of operation time.The gap in the measurements is due to T.C. measurements and noise measurements where I had to do a different setup.Some of the references show a shift after the temperature cyclings.And all of the LS8 devices changed direction of ageing.The PCB#3-Devices are shown with drift over linear time (days) and in a 2nd diagram as SQRT(kHrs) as x-axis.Y-Axis is temperature compensated according to the linear T.C. from T.C. measurements.see also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg5748407/#msg5748407with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: January 20, 2025, 06:35:58 pm
content: Attached is an update of my ADR1399-PWM-DAC reference. The reference was initially measured by Solatron 7081 and Prema 6048 white. At some point the Prema 6048 left and made its way to its owner. Then at some point the 7081 stopped working (at about hour 4700), so I had to take it from the setup and repair it. Fortunately, recapping fixed the problem.Luckily, another Prema 6048 white showed up at MM2024, stayed with me until I finally became the new owner and this meter was used to measure from hour 4900 on.Overall, this reference is constantly drifting upwards with no obvious sign of stabilizing.So continuous observation is still needed.-branadic-

author: Kleinstein
author_rank: Super Contributor
timestamp: January 20, 2025, 07:01:29 pm
content: The drift is still pretty small. The Solatron meter seemed to have been a bit temperature sensitve. Most of the "noise" there seems to be a thermal effect at the meter. With the downward temperature trend for quite some time it is a bit hard to tell if we really see the reference drifting or maybe more a temperature effect at the meter.

author: Andreas
author_rank: Super Contributor
timestamp: March 01, 2025, 03:49:35 pm
content: Hello,PCB#3 (with relay multiplexer) recently passed 3 kHrs of operation time.The gap in the measurements is due to T.C. measurements and noise measurements where I had to do a different setup.Y-Axis is temperature compensated according to the linear T.C. from T.C. measurements.2 of the TO-46 devices showed a jump during the last days. Generally they now seem to stabilize.This can also be seen when drawing the standard deviation (SDev) over the last 42 measurements (1000 hours).It is trending towards the 0.1 ppm of the ADR1000 reference.The direction change of the LS8 devices remains. Here the standard deviation is more or less constant.see also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg5771905/#msg5771905with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: March 30, 2025, 08:03:46 pm
content: Hello,PCB#3 (with relay multiplexer) now passed 4 kHrs of operation time.Most of the devices are stabilizing. (except one of each group (TO-46 and LS8))Again standard deviation is shown for all devices.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: May 12, 2025, 02:23:46 pm
content: Hello,PCB#3 (with relay multiplexer) now passed 5 kHrs of operation time.Most LS8 devices still have a drift of ~2 ppm / yearresulting in ~0.2 ppm/kHr std dev.Most of the TO-46 devices are further stabilizingstd dev here is between 0.1-0.2 ppm/khr (where 0.1 ppm/kHr is my measurement limit shown by ADR1000 comparison)with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: June 23, 2025, 05:50:39 am
content: Hello,PCB#3 (with relay multiplexer) now passed 6 kHrs of operation time.On day 220 I opened the die cast housing of the PCB to inspect the wiring of the RS232 interface.with removing and installing again the thermal isolation cloth.This had mayor influence on the LS8 devices. So also the standard deviation is rising.The TO-46 devices are not affected by day 220. Although one device has begun to drift again on day 200.with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 31, 2025, 07:50:56 am
content: I wonder how this would work in practice (provided we have quite good 1u and 3u3 foil caps handy)..PS: with 50G (an example) of parallel parasitic resistance at the foil capacitors the voltage drop from 399 to the non-inverting input of the OPA145 will be 130uV.. not good..

author: iMo
author_rank: Super Contributor
timestamp: August 03, 2025, 06:50:44 am
content: FYI - to gain clarity on the parallel resistance of one of my foil WIMA capacitor (3.3uF/50V small red box most probably MKS2B043301H00) I've made a measurement of the input resistance of my 34401A and then with the WIMA capacitor (soaked for 5h at 10V). The capacitor looks like it has aprox 80Gohm at 9.9V..Quote from: iMo on July 31, 2025, 07:50:56 am

author: Kleinstein
author_rank: Super Contributor
timestamp: August 03, 2025, 08:30:07 am
content: Measuring the isolation resistance of the capacitors is tricky. It is not so easy to tell leakage from resistance and dielectric absorbtion appart.Another point is that the DMM input has input bias and also a finite input resistance.Normally one would use somewhat smaller resistors in the filters and thus larger capacitors and less issues with PCB leakage and amplifier input bias. Filtering a reference is anyway tricky. There is a balance in the effort for a good filter and using a better or 2nd reference.

author: Andreas
author_rank: Super Contributor
timestamp: August 03, 2025, 05:41:25 pm
content: Hello,PCB#3 (with relay multiplexer) now passed 7 kHrs of operation time.see also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg5955995/#msg5955995I had to correct the temperature correction values. They were effective 1/3 too low due to a bug in the spread sheet.But the differences in diagram are nearly unvisible.The LS8 devices are again stable (since event on day 220).The TO-46 devices remain stable (except #8 which is somewhat noisy).with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: September 13, 2025, 08:19:47 pm
content: Hello,PCB#3 (with relay multiplexer) now passed 8 kHrs of operation time.see also previous postIn parallel to the power off state of the ADR1001 eval board I also had a 1 week power off state.Both the LS8 devices and the TO-46 devices returned to previous state within 14 hours after power off.The LS8 devices are drifting somewhat more than the metal can TO devices.with best regardsAndreas

author: Andreas
author_rank: Super Contributor
timestamp: September 14, 2025, 06:35:46 pm
content: Hello,I also did a 1 week switch off for PCB#2 (with CMOS multiplexers) now 18.3 kHrs total operation.see also:https://www.eevblog.com/forum/metrology/adr1399-reference/msg5727909/#msg5727909Again the metal can devices showed no influence.2 of the LS8 devices needed 48 hours to restore to the last value. (see zoomed diagrams).with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: September 15, 2025, 05:24:21 am
content: Your LS8ths are soldered directly onto the pcb, aren’t they?

author: Andreas
author_rank: Super Contributor
timestamp: September 15, 2025, 06:41:41 am
content: Hello,yes as you can see on the photos here (PCB#1 + PCB#2 CMOS MUX)https://www.eevblog.com/forum/metrology/adr1399-reference/msg4442575/#msg4442575or here (PCB#3 with relay multiplexer)https://www.eevblog.com/forum/metrology/adr1399-reference/msg5703775/#msg5703775note that the LS8 package is mounted on cut outs and PCB thickness is 1.0 mm.with best regardsAndreas