Calibration by | Accuracy / Standard | Region/Country | Contact for participants |
xDevs.com | <2ppm / 3458A-mod + 2*K2002 | Asia/Taiwan | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=26015) |
plesa | <4ppm / 3458A-002 | Europe/Sweden | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=9699) |
Alex Nikitin | <4ppm / 3458A-002 | Europe/UK | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=112202) |
To make this whole little project more interesting for me, I wanted to try two new ideas, which were not attempted before in previous builds.
*A.* Try 1K?/13K? hermetic resistor network (custom Vishay VHD200 (https://xdevs.com/doc/VPG/vhd200_144.pdf), oil-filled +/-3ppm/K two-resistor network) with 0.05% matching. This might give some interesting data, if tightly coupled oven setting thermal point resistors help to improve tempco of the reference.
I think you get answers from article ;). If it's more comforting, all 6 LTZ chips I bought directly from Linear site are not jumpy. :phew:
I have been monitoring one of my Fluke 731B for a few days continuously with a DMM7510 on 15 NPLC with averaging of 10. In the morning the measured voltage is 9.999961 and late evening the voltage is 9.999978. This cycle is consistent from day to day. At first I thought it was temperature but after some colder weather followed by warmer weather, I think the cycle is humidity.
lukier
I think you get answers from article ;). If it's more comforting, all 6 LTZ chips I bought directly from Linear site are not jumpy. :phew:
BTW, in a conversation with Edwin Pettis he told me, that the Engineers from LT told him that for the last few years they recommend the all LTZ's to be drive by 15K/1K, but this was already cover in the LTZ thread .Is this new info? I thought you only wanted to run them that hot for the "A" version in high ambient environment. Can you link to where this recommendation was discussed? I skimmed through the LTZ1000 thread but couldn't find it...
I'd expect difference at 0 would be just down in measurement errors and uncertainty.
Because the Zener in the LM399 is operated at such a low current [no matter how much current you pump into the device], you will see this "popcorn noise" more often with that part.
Hi,I have 4 TiN boards, but all populated. All are currently measured with recently calibrated 3458A/002.
I have two left, but I need them for few items in near future. Somebody here is waiting for fab using my gerbers, I believe.
Btw, I done log with K2001 for you, but have no time recently to make pretty graph. Live graph and RAW data is here (https://xdevs.com/strannik_ltz_2001). Plenty of data there to run STDEV, noise pk-pk analyze and such. K2001 column is k10v.
plesa
How's your datalogging setup going on? If you wish, I can give you space on my serv and script, so your Pi can upload CSVs periodically and I can have live plot page for you :)
Anyway just ordered 20 pcb of your project, if someone needs some I have few spares.Just to be sure, I have the right "project" in mind. Does you have ordered this?
It looks like a classic case of popcorn noise and not pink noise.
It looks like a classic case of popcorn noise and not pink noise.
Agreed that it looks like popcorn noise, but I think the explanation is wandering between zener and avalanche modes. Intrinsic to these low TC zeners is the balancing of the opposite tempcos of zener and avalanche effects. I think that's already been suggested hereabouts as a cause but I'm not sure. Popcorn noise is classically associated with relatively 'dirty' semiconductor processes which is why it's generally much less of a problem than it was, say, thirty years ago. We're dealing with a buried zener here, and the burying is done precisely to keep the junction away from the surface where impurities may lurk of the sort that cause popcorn noise.
maybe a a "two value" referenceThat's assuming both levels not change over time.
I don't see much sense in cooling and that way possibly destroying the chipI don't see either, but desired to close this topic once and for all. Maybe we could see something in doing this (not necessarily at 77K temperature). Having 24/7 cooled to -30°C unit with TEC or phase-change loop (modified window AC) isn't that difficult, if there is point in it. I've ordered copper block at CNC shop to enclose module in hermetic box to place in dewar. This way there will be less rapid shock from contact with cooling liquid.
The buried zener in this case is temperature compensated by the roughly -2mV/C Vbe of a series transistor so I am suggesting that the popcorn noise is actually coming from the transistor and not the buried zener reference.
The buried zener in this case is temperature compensated by the roughly -2mV/C Vbe of a series transistor so I am suggesting that the popcorn noise is actually coming from the transistor and not the buried zener reference.
Yes, the LTZ is using VBE compensation (and a lot of heat) rather than relying on zener versus avalanche tempco, but the zener versus avalanche thing is still going on because that's determined by the diodes 'set point*' voltage. I'm just influenced by the fact that there's some identifiable physics that we know goes on around this point. Anyway, the only way to be sure is to try the zener current versus transistor current experiment that's been suggested.
*Awkward terminology here because you'd normally say "zener voltage" or "avalanche voltage" but both are in play.
I did a search but found nothing about popcorn noise in zener diodes which may just mean that it is such a minor problem that it takes an LTZ1000 before it becomes apparent since zeners are so noisy anyway.
I did a search but found nothing about popcorn noise in zener diodes which may just mean that it is such a minor problem that it takes an LTZ1000 before it becomes apparent since zeners are so noisy anyway.
according to Warren they formerly selected 1N82x Zeners according to low frequency (= popcorn?) noise.
https://www.febo.com/pipermail/volt-nuts/2013-January/002362.html (https://www.febo.com/pipermail/volt-nuts/2013-January/002362.html)
see also attachement with a chart recorder.
http://www.febo.com/pipermail/volt-nuts/attachments/20130126/1fdc1ce7/attachment-0001.jpg (http://www.febo.com/pipermail/volt-nuts/attachments/20130126/1fdc1ce7/attachment-0001.jpg)
On another source I have read that ageing of zeners is correlated with low freqency (popcorn?) noise.
(which makes sense if you equal "popcorn noise" with "impure silicon").
I updated previous post with shipment costs.
A PM message with my PayPal address will be sent to everybody that sent me the complete address and get the shipment quotation.
Who is in overbooking please wait a couple of days, I'm still waiting a response from 4 members.
I have not received PM message :-//
What do we want to do?
but you must be brave to do this extreme repairsNo bravery needed, just have 2-3K$ cash handy and you will do fine. If A3 ADC bad - 1400$ for replacement. Repeat until it's stable :). It's no different than any other electronics repair, other than requirement of stable and verified calibration sources for DCV and OHM. For the first one you already on the correct way with LTZ module (you can calibrate 3458A to other calibrated 3458A using 7V LTZ output ;). I even had luck to transfer DCV internationally using A9 LTZ module (https://xdevs.com/article/volt_xfer/#exec), and got only 6ppm of error in the end.
I can offer you similar service like TiN in Europe.
1. Measure it with calibrated 3458A/002 in reasonable temperature range.
plesa, Alex Nikitin
If you OK, I can add this section into article on my site, with links to your profile, to keep this program afloat? :)
plesa, Alex Nikitin
If you OK, I can add this section into article on my site, with links to your profile, to keep this program afloat? :)
Calibration by | Accuracy / Standard | Region/Country Contact for participants | |
xDevs.com | <2ppm / 3458A-mod + 2*K2002 | Asia/Taiwan | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=26015) |
plesa | <4ppm / 3458A-002 | Europe/Sweden | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=9699) |
Alex Nikitin | <4ppm / 3458A-002 | Europe/UK | EEVBlog forum PM (https://www.eevblog.com/forum/profile/?u=112202) |
I can offer you similar service like TiN in Europe.
1. Measure it with calibrated 3458A/002 in reasonable temperature range.
I can do a similar service in the UK, if somebody needs it, as the HP3458A Opt 002 just came back from calibration at Keysight. I don't have a temperature chamber yet (though it may change soon), however I can monitor the lab temperature (or the reference enclosure temperature).
Cheers
Alex
What kind of KS calibration and report for your 3458As did /will you get?
The single page report, which only confirms that the instrument is in 1 years specification limits, or the elaborate, much more expensive, multi page calibration report, with all measurement results (as found) including test limits?
Hi Frank,
Here is a page from the certificate. I hope it answers your question.
Cheers
Alex
Alex, definitely.. your 10VDC uncertainty will be around 3ppm, probably better, as the 10Vdc reading of your instrument is given to < 1ppm resolution, and the "Golden 3458A", which defined the limits, may have been less uncertain than 1ppm.
mimmus78 please consider to do more boards when you are ready. I would like to buy one... may I?
Anyway let me know if someone else is interested.
Solder coax wire to +18.5V and power GND to provide separate current path for LTZ’s heater, so it would not upset reference output
I don't understand why use VR801 as integrator reference? Any reason why not route LM399 ref signal there?
Mimmus can you put some 0R jumpers or somenthing to separate the heater power supply path from the rest? See TiN article here (https://xdevs.com/fix/hp3245a/#twk_vref):QuoteSolder coax wire to +18.5V and power GND to provide separate current path for LTZ’s heater, so it would not upset reference output
So this is what I elaborated. This is based mainly on last revision of battery powered reference from "andreas".
Using chopper OPs for the LTZ1000 circuit can get tricky. They produce quite some RF spikes can have higher noise in kHz range, where the transistor in the LTZ is not helping anymore. There is no real need to replace the LT1013 or similar OP. The LT1013 is not that expensive. But at least dual OPs use the same pinout.
For the extra butter, the AZ OP is suitable, as here the error from the OP fully enters.+1
One might think about having some RC filtering here - to reduce higher frequency noise from the reference and keep spikes from the AZ OP away from the reference.
With a relatively high current, there was a good reason to have a transistor / JFET to drive the reference current. If one really wants to save on this, one could still use a bridge or diode like shown, but I would really have the space for the transistor on the board.The main intention of the FET-Buffer was LT1013-related together with reduced power supply voltage.
are you shure that C10 is on the "right" side of the resistors?
I don't really understand the protection circuit shown at the output - to me this makes little sense. If needed at all I would more expect kind of a beefy 8 V zener diode or equivalent circuit.
One point where an extra protection might make some sense would be the unbuffered output. This is known to be sensitive to a short or overload (e.g. large uncharged capacitor), as this would cause the heater to activate all the way. A protection could check for a drop of the output by more than an few millivolts and in this case turn down the heater. It could take as little as a tl431 and a few resistors and a diode.
this R is used for temperature compensation in LTZ1000A and is not necessary in not A version.It's the other way around per data sheet- don't use resistor for "A" version.
Did you already ordered resistors? They have extra long leadtime or you are going to use some thin film like PTF56/UXB series?
Good choice can be Rhopoint ( they will fit to TiN boards )
https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html (https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html)
I would like to build one reference, but I probably will not be able to find the resistors here and I don't like the idea getting these from eBay.
Do you guys plan to group buy the low TC resistors from VPG or some distributor?
collect this will take forever
Andreas: I think I lost from the LTZ1000 thread why the LT2057 was discarded at the end by you, may you just repeat the reason?
Sometimes (often?) the hysteresis is larger when having a low TC within a resistor type.
For the hysteresis, there are several possible effects to cause is. Some of them, like uneven thermal expansion might be influenced by temperature gradients and thus by the speed of temperature changes. But generally I would not expect a big influence of the heating rate.
Well, I'm finally giving into serious volt-nuttery. It seems like once I manage to obtain resistors I'll probably be building a couple of these. I'll post updates, and I will probably be interested in the unofficial calibration service. At the moment, this is all better than the best meter I have, an HP 3457A :)
Is it reasonable to consider the LTZ1000A and precision resistors water washable? My inclination is toward using entirely water soluble flux, initially washing with warm water and detergent, then multiple rinses of distilled water + isopropanol.
plesa
I used 12K/1K as temperature set poit for the LTZ1000 ... what is temperature delta vs ambient temperature inside this IKEA thermos?
Wondering if it will be too much high temperature during summertime (here gets as hot as 30 degree during summer time).
but nobody still built it in public.
3. LTC2057 was causing more than 1ppm jumps depending on what power source I was using or if I used shielded leads or not. Replaced opams with ADA4522 and now it's 1 to 2uV delta swapping power supplies or using different leads. The most of the offset was caused by the opamp driving the zener.
That's a remarkable meter you used to measure the reference - apparently with maximum and minimum voltages displayed at 7 1/2 digits, uV resolution, but manages to calculate the peak to peak to a further 7 digits, 6.8025031uV p-p. 100 femto volt resolution on a 10V range is quite incredible.
Too incredible obviously. The difference between the displayed max and min values is 7uV. There may be another digit undisplayed so 6.8uV p-p may be plausible even if the .8uV digit is mostly noise. But why would the developers choose to display a further 6 digits of completely bogus resolution? How could the value have been derived?
untruncated calculation precision is not uncommon! :popcorn:
First board up and running!
7uVpp for a source that should have 1.2uVpp.
Also not all of the LTZ1000 are equal: the TC without temperature stabilization (but still at the high temperature) can be quite different.
Having half the TC for the chip could be as good as half the drift for the divider.
The problem is that the current noise of AZ OPs is not normal, mainly low frequency noise, but there is also a significant higher frequency background. Performance of AZ OPs depends in a more complicated way on the input impedance, than just giving a current noise number. So depending on the sensitivity of the circuit, there can be extra trouble.
Don't know what too think ... but it seems too much noise for a reference.
This is LTZ1000 module:
This an LM399 module:
This is a 3V coin battery:
If I swap the zener output on the 3458a (LTZ1000 positive connected to LO and ground connected to positive) I get a difference of many ppm, don't think this is supposed to happen.
Things get even worse if I connect swapped out to K2001. With Keithley multimeter even mV digit is flapping. I think there is some capacitive load problem ...
Anyone has any idea what is going on?
OK, with resistor I have following value:
Correct connection: 7.13366
Correct connection with 120 series resistor: 7.13366
Swapped connection: 7.13350
Swapped connection with 120R series resistor: 7.13357
Swapped connection with 270R series resistor: 7.13360
Swapped connection with 1K series resistor: 7.13364
So I guess I need to add a buffer ...
I build a total of 3 of this references, all had the same problem.
With LT2057 and ADA4522 this EMI and capacitive load was even worse.
I remember millivolt difference with LT2057 and this leads swapping.
And for EMI I can make drift it up to 5 ppm by turning on of off a power supply or a led light.
Now the question is, this is happening only to me?
If you have such a high noise field that the resistors might be picking some of that up, you should definitely work on reducing the radiated noise field as it could be strong enough to be interfering with the IC's operation as well. Getting rid of noise at the source is always preferred to trying to dampen it out in the circuits you are using. Many sources, such as lamps, power supplies, TVs, laptops, ect., can generate plenty of noise that will be picked up easily several feet away or more and you make a very good antenna yourself. The only source of noise a wire wound resistor creates is normal Johnson noise, anything else is radiated and picked up.
Getting rid of noise at the source is always preferred to trying to dampen it out in the circuits you are using.
EDIT: Uploading video now ^-^. You guys make me work! :box:
Here we go. :)
One possible measure to improve EMI and load capacity tolerance might be an RC (e.g. 10-100 n and 100-220 Ohms) element to GND at the output. A ferrite bead could be a good idea too.
The LTZ circuit from the DS is made for an instrument internal reference, not really to drive an external output and thus handle capacitive loading, possible ESD and RF noise.
The OP27 and similar OPs have quite a high current noise and also bias drift and are thus not the best choice for a high source impedance (about the typical 70 K resistor).
It only takes a few 100 pF at the output to upset the LT1013. The typical LTZ1000 circuit can be even more sensitive than the simple times 1 impedance follower. A DMM can have a significant input impedance, so is a certain length of wire. Even if not oscillating extra ringing from externally injected noise can cause trouble.
The 100 Ohms and 100 nF not only function as a filter, they also represent a significant load to the OPs output and this way reduce the gain a little. This helps to improve stability at high frequency. Some amplifiers use this to stabilize the output with difficult loading.
I remember an instrument (Lockin amplifier) which had just an OP to drive an output, that could not even tolerate an 2 m coax cable on that output. :palm:
Unless you have the 3458A running all the time (and even then) the 3458A is not good enough to verify a LTZ1000. I have seen that many times. That does not contradict 3458A spec, but even if you switch a 3458A of and on shortly thereafter, you see some hysteresis (at least if you have not reduced the LTZ internal temp.) There is no way arround a precise voltage reference...
...
Channel 3: VM1=7.134162383, VM2=7.134162418, AVG = 7.134162400, 0.014 ppm
...
Channel 3: VM1=7.134161875, VM2=7.134161560, AVG = 7.134161717, -0.081 ppm
...
Channel 3: VM1=7.134161595, VM2=7.134161507, AVG = 7.134161551, -0.105 ppm
...
Channel 3: VM1=7.134162050, VM2=7.134162085, AVG = 7.134162068, -0.032 ppm
...
Too bad they can't put silkscreen over bare copper.Most of fabs can do that, but you need to ask specifically. Reason why they don't put silkscreen over bare copper by default - is if you made mistake and put silk over pad, you will not be able to solder that pad.
no hot air station for me.
I haven't soldered one of the Maxim ICs (the one on the front side) because I don't think I will be able to successfully solder it because of the surroundings.I usually solder that one first, and only after put surrounding taller parts. Common rule for PCBA is to put small parts first, then taller ones, and connectors last.
If anyone would like high resolution pictures of the board, please let me know and I'll bring the big camera for thatSure, show us your gigapixels.
I wouldn't mind seeing some more pictures! I'm going to be making 2 boards myself here in the next few weeks.
Also, something little I noticed.. Your DMM is in auto range. You want that bad boy on manual range
Here are the pictures I promised. Hopefully you enjoy them ;D
Those are small pics :P.
There are is alarming item though - R3 must be 12.5-15Kohm , not 10Kohm, unless you plan to run your LTZ in freezer all the time.You mean R5, right? (R3 is 120 Ohm) In that case, I'll order both P/N Y107312K5000T and Y107315K0000T just to be sure. And maybe even Y107313K0000T (as seen in Linear's reference schematic). Taking into account that here the temperature is usually around 18 C on Winter and 25 C on Summer, would you make any recommendation?
10Kohm is way too low for temperature setpoint for reference used in ambient.
Also it's better to clean flux residues to prevent gotcha's.
Your Z202 resistors look also very interesting as well, not usual marking font/typeface found on VPG resistors.
Perhaps I've used wrong word regarding 1013. The board design use single-amp package only, so 1013 is not a direct option here.
The LT1013 is a precision single supply OP with about the right balance of input bias / current noise and voltage noise.
Single supply is convenient as the common mode voltage is about 0.5 V in the positive ref circuit.
Voltage drift and low frequency noise is not that important, as the transistor in the LTZ1000 already provides a gain of about 200. The source impedance seen by the OP is a little below 70 K (of whatever resistors are used to set the transistor current).
There are a few rather similar alternative, like OPAx234 or maybe even OPAx171.
But likely got LTZ's temperature sense transistor killed by ESD. |O
At least you didn't do it live with witnesses like someone I know hooked up battery terminals backwards while a friend was watching remotely. :palm:
But likely got LTZ's temperature sense transistor killed by ESD. |O
Shure you didnt kill the resistors?
(bending the wires without strain relief directly at the case).
With best regards
Andreas
At least you didn't do it live with witnesses like someone I know hooked up battery terminals backwards while a friend was watching remotely. :palm:Mostly is bad luck.
+1 re forceps - that is what I used in forming the leads of the 'good' resistors of the LTZ KZ reference - pictures in reply no 257 of this thread - I also used them as a heat sink when soldering the resistors and the LTZ to reduce heat stress - but with the LTZ I think you may replace the heat stress with a mechanical one. You also end up with the LTZ 4mm or so above the PCB. Swings and roundabouts.
@MisterDiodes
Would you recommend a simple bend or one that includes a strain relief bend in the leads?
I have looked at some of the tools available but I cannot decide if it is worth the added expense. Personally, the simple plastic lead forming tools would be adequate for me. As long as I get repeatable bends I can make the right component in my CAD software.
SvanGool was kind enough to send me a PCB so I am joining the club.12.5k at the very low end (based on experience), if your ambient is pretty much always on the cooler side. You'll have to see how your board works in your enclosure, insulation, etc. We use recommended 13k as lowest value, but on a warmer production line situation we'll go with 14k~15k, as used by HP in 3458a meters.
I plan to build it using resistors sourced off of ebay. This does limit the values I can acquire a little bit. I will be using 12.5K for R5 and am wondering if people recommend keeping R4 at 1K or would 900 ohms be better to run the LTZ1000A a little hotter?
There is nothing left to shorten on the chip, also you mean 400K R9? Afair, it's not on the module. However it can be added :).
Let's hear from the owner, what he want to do.
TiN: Are you running 12k over 1k for heater resistor? That might be a little cool for your setup - being all sealed up in boxes, etc. watch your heat flow away from LTZ - it can't be zero - your heater could be running out of operating headroom for that LTZ. I wasn't sure if you've got a thermocouple on the LTZ itself.
There is something wrong there - that TC is much higher than what we've seen with PWW, both Edwin's and GR's - and Films. It's usually closer to Datasheet TC value with recommend 13k / 1k to start...and then work to a lower value as your setup permits.
Do you have the new heater ratio resistors properly mounted on the PCB this time (not mangled like pictures before, sorry), and thermally close together? I guess I didn't see the LTZ board itself, or I'm blind.
Have you done several thermal cycles? Is this a brand-new LTZ or one you've used before?Yes, it had about of week of cycles prior to the ramp on post above. It was aged for a month at VK5RC site in Australia, then he shipped it to me for tests and it was compared vs my other 5 LTZs for another ~300 hours, before any temperature cycles even start.
Why the '2057 instead of recommended LT1013? Not that it causes that high TC, just curious.Long story short - it's by historical reasons. By that I mean my first volt-nuttery entrance 3 years ago (http://vhttps://www.eevblog.com/forum/projects/project-kx-diy-calibrator-reference-sourcemeter/msg414092/#msg414092), when I've designed KX PCBA, which takes two single-opamp SO8 packages for the LTZ circuit. Back then I had less understanding about opamps, their performance measures, etc. So PCB physically incapable taking LT1013 without doing bodgewires. And it was not expected that anyone order my gerbers or make modules, but here we are. I'd design things bit different today, having negative supply rail, larger footprint to support multiple options for precision resistors, not just tiny Z202's, use LT1013, provision larger capacitor footprints for films...
LT specifically recommends against the '2057 for it's high current noise across the LTZ - it can be a source of instability long-term. We -never- use AZ amps for these LTZ current drivers.I'm not going to argue on this, valid points. Just so far on hobby level I doubt difference between 2057 or 1013 or other opamps can be distingueshed with equipment we have available, be it 3458A or null-meters and 732B, looking at the output. I have 4 my modules with LTC2057, one with LT1097 and unmodified HP3458A's A9 STD REF module, which I compare from time to time over last few years. I was not able to tell the difference from data in short-term noise on any of them without actually looking at the board.
You might want to run the test circuit as the standard, recommended setup. snip...Yep, but that would mean making new design, new boards, ordering another boatload of expensive parts and spending another year on testing everything. With likely the very similar unmeasurable difference outcome, as down to ppm level there are so many things that can go wrong. At this point in my life, I'd rather spend efforts on few other projects. Perhaps new wave of LTZ-nuts would be willing to try this road, so we can see more different and interesting designs here.
You might run a few more cycles and see if there's any indication of settling down?Having reference return to original voltage after ramp down suggest not settle/unstability issue? If it's unstable, we would see different end voltage. Power cycle for 30 minutes (moving VK5RC's REF from TEC box to near LTZ bank and K7168 scanner, reference voltage restored to -0.4 ppm (https://xdevs.com/nvs_ltz4/) of original assigned value, including 50% error from different 3458A. :)
There is nothing left to shorten on the chip, also you mean 400K R9?
Why the '2057 instead of recommended LT1013? Not that it causes that high TC, just curious. LT specifically recommends against the '2057 for it's high current noise across the LTZ - it can be a source of instability long-term. We -never- use AZ amps for these LTZ current drivers.
@ MisterDiodes
And what is your recommandation and experience on LT1013, which one would you use:
- hermetic LT1013AMJG which is e.g. still available at RS Components made by Texas Instruments (http://de.rs-online.com/web/p/operationsverstarker/7320847/ (http://de.rs-online.com/web/p/operationsverstarker/7320847/))
- one of the original available Linear Technology LT1013AC/LT1013C/LT1013D/LT1013I
- DIP (CERDIP) or SO8?
- if DIP (CERDIP) with or without precision sockets?
Since you mentioned fast hi-res ADC, you got me here though. Chopper amp definitely have source to generate extra noise, but LT still recommend using 2057 as input buffer if near DC signal need to be digitized accurately for new generation of their 32-bit SAR ADC, such as LTC2508-32. What would be better solution for DC accurate preamp for such ADC frontend/reference buffer, to digitize low signal levels in 0.1-1kHz band (e.g. as servo system for DAC).
Also 2057 datasheet covers charge injection a little, having DC average current included in bias specification.
Here's that link I posted before on a chopper noise measurement technique - with some modifications this strategy can be used to explore '2057 noise and compare to other AZ amps. Have to use shielded can. '2057 will not have lowest or loudest input noise compared to amps described here, but it's up there:
https://e2e.ti.com/cfs-file/__key/telligent-evolution-components-attachments/00-14-01-00-00-70-21-03/Chopper-Noise.pdf
It should not be important which version of the LT1013 is used. So even the SO8 version should be OK -
I would be happy TiN if you want to try anything with that unit e.g. R9 etc. Let me know the parts costs and I will happily reimburse you.Hello,
The LTZ is mounted a little high (I used forceps as a heat sink when soldering) so it is about 3-4mm above the board. I have a quote request in place for some of Edwin's 13k pww resistors to replace the 12k.
@ MisterDiodes: Always a pleasure to read about your experiences, especially since i have the 2508-32-Evalboard sitting in a corner!
Maybe you can have a look at the proposed voltage-reference-filter-design mentioned here and share your opinion: http://electronicdesign.com/energy/filter-trims-ultra-precision-voltage-reference (http://electronicdesign.com/energy/filter-trims-ultra-precision-voltage-reference) ?
Also: do you know any good ref-filter-design for a LTZ1000 regardless of the stabilizing-time?
Edit: Since the LTZ1000/Ref-Amps are the best voltage references out there apart from the superior JJA and companies like Fluke/Keithley surely like to improve their stuff: Do you know of any successful projects which improve stability/noise of those references or does it just not make sense and the only good way is to handselect and parallel those references like it is done in the Datron 4910?
LP filter with cutoff down in the 10's of mHz - watch what happens when you turn it on. You'll be waiting a while... <Grin> You'll still have noise over longer time spans now, and you'll be kicking yourself for blowing that much on those $65 caps, etc.$65? Cheapskate! How about $707 (http://www.mouser.com/ProductDetail/Vishay-Tansitor/XTV138T030R4L/?qs=sGAEpiMZZMuAysUaQfn78eS%2f4HX9MwCT)? :)
that's why the most practical approach is to average across multiple systems (Vref and ADC or whole DMM's) to help deal with 1/f noise.Hm, you got me an interesting idea for that old DMM noise test experiment. Sample 4 DMMs (2x3458 + 2x2002's) in sync together and average their common result minus the offset, to get total noise figure. That could show if noise of such rig lower than single DMM.
13k is correct abd suitable for usual conditions up to 40C ambient.
Which is right? Does it matter? I'm using a LTZ1000CH not A version).It depends on your environment temperature where the LTZ will work.
Hello,
in the US: Texascomponents
with best regards
Andreas
on the webpage they have a different E-Mail see:
http://www.texascomponents.com/store/home.asp (http://www.texascomponents.com/store/home.asp)
I like the PWW, because they have lowest hysteresis