Best solution to generate DC 1 milli volt 1 micro volt with precision ? - Page 1
Forum section: electronics / general

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 19, 2024, 04:39:03 pm
content: HelloIf solutions exist to generate DC from 1 Volt to 10V as precision component exist .Does there is a solution to generate low voltage with precision ? at a level comparable to a Ref54 for example so in the ppm ..?high ratio resistive divider don't seems to be the best solution to generate milli ou micro volt.RegardsOS

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 19, 2024, 05:34:42 pm
content: What's wrong with a precision divider? When you drop a lot of voltage the lower resistor can be low, so the output impedance is low. Look at KVDs and the old General Radio 1346 Microvolter for inspiration.

author: Gyro
author_rank: Super Contributor
timestamp: December 19, 2024, 05:38:24 pm
content: Quote from: Overspeed on December 19, 2024, 04:39:03 pmWhy not? It is the best way to achieve a low source resistance, and any active component noise and offsets are attenuated. You could use a low level current source into a low value resistor, but it would have similar properties.Edit: ^ What he said.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 19, 2024, 06:30:18 pm
content: Quote from: Conrad Hoffman on December 19, 2024, 05:34:42 pmHelloI don't know what wrong as I have asked a question on the MI 1340 and its seem that not the bestI link a GR 546 manual with schematic and BOM , doesn't look as rocket science which is a good pointRegardsOS

author: BILLPOD
author_rank: Frequent Contributor
timestamp: December 19, 2024, 06:43:46 pm
content: Good Morning Overspeed, I've got the LB06 calibrator and It is GREAT for this type of application. It costs a couple hundred bucks, but I have found lots of uses for it, and I'm sure you will too. It would work BEAUTIFULLY for what you want to do. Here is a link forone on Amazon:https://www.amazon.com/Multifunction-Process-Calibrator-Frequency-4-20mA/dp/B0CZHSXXHV?gQT=1&th=1

author: Victorman222
author_rank: Regular Contributor
timestamp: December 19, 2024, 07:00:09 pm
content: I would second the resistive divider suggestion. Check out this article about Keithley low thermal divider, it is made exactly for the purpose of getting microvolts with low noise.https://xdevs.com/fix/kei262/If you are after great linearity and stability an inductive voltage divider based decade calibrator might work (for millivolts definitely). But such solutions complexity is infinitely higher than resistor divider.

author: Gyro
author_rank: Super Contributor
timestamp: December 19, 2024, 07:28:54 pm
content: @Overspeed:That'sthe switch with PCB wafer and sprung Copper 'rivet' contacts. I knew I'd seen it somewhere when you asked a few weeks back (the Marco Reps nV scanner video). An ideal candidate for DIY low thermal emf switching.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2024, 12:04:36 am
content: Quote from: Overspeed on December 19, 2024, 04:39:03 pmResistive attenuator sections can be calibrated individually, and then stacked to get high levels of precision attenuation.If a zero output impedance is required, then the low level output from the attenuator can be buffered with a precision operational amplifier.

author: tszaboo
author_rank: Super Contributor
timestamp: December 20, 2024, 12:17:23 am
content: If you want a novel way of generating microvolts, you could intentionally heat a thermocouple. If you get an oven like used in the LTZ1000 for both ends, which gets to 1/1000K accuracy, then a thermocouple would be super accurate, and you can buffer it with an already heated (thus accurate) opamp.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 20, 2024, 08:13:44 am
content: Quote from: BILLPOD on December 19, 2024, 06:43:46 pmHelloThanks , I have a Fluke 724 and a Time Electronic 1006 but I search a solution to generate fixed value in uV range with lab precision ( able to be validated ) , problem look to be ( perhaps ) than most voltage reference have a limited current output level .RegardsOS

author: Gyro
author_rank: Super Contributor
timestamp: December 20, 2024, 11:09:58 am
content: Most 10V IC references (thinking REF102 / AD857 style) are capable of 1-10mA - obviously the higher the current, the greater the need for Kelvin sensing lead compensation.If you take a 10V reference at 1mA max, a 10k (OK, 9.999k)/1R divider will give you a nice low source impedance 1mV. Decreasing the 1R to 1mR (or increasing the 10k to 10M) will give you 1uV.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2024, 12:41:14 pm
content: If needed one can support the reference with an extra current source to provide most of the known current to the divider. The actual reference would than only deliver the smaller rest of the current. The difficulty can be the thermal EMF at the lower resistor. Not all resistors a equal in this respect and the specs may not tell you much. For a build it is also about getting a small thermal gradient at the resistor, so not just a good resistor.Chances are one would want some way to switch the voltage off for offset measurements.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 20, 2024, 01:27:22 pm
content: Quote from: Kleinstein on December 20, 2024, 12:41:14 pmHelloDoes this circuit design is a solution ? that boost the current of a reference , this circuit is similar for some references .Other concern is to draw too much current as I suppose that a Ref IC shall be used at a reasonable level of current even if the MAX current could be 10 mARegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2024, 01:35:47 pm
content: The more normal way to provide most of the current would be to amplify the voltage and than use a resistor to provide the approximate calculated current, or a little less. If one wants to include switching the divider drive side off for an offset / zero reading, one would likely more go to an amplifier to drive the current anyway. If really needed one could still use 2 mechnical switch poles (for the rough current and the fine correction).At 1 mV for the output it is anyway not so much about the stability / accuracy of the reference or amplifier, but more the divider and terminal thermal EMF.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2024, 04:08:33 pm
content: Quote from: Kleinstein on December 20, 2024, 01:35:47 pmI have done it that way before when the reference had to travel across a board. I used the reference to generate a precision current which travels across the board to a single resistor at the load. In this way, a 4-wire Kelvin connection is not required to deliver a precision reference voltage.This sort of circuit also works to transfer audio across a noisy ground without ground loop isolation like a transformer or instrumentation amplifier.

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2024, 04:13:59 pm
content: I think the question is about low voltage references. intrinsically low voltage references.The zener effect is poor until a number of volts. Usually low voltage references are only used for sensing temperature (BE junction) etc. They are not stable.A true low voltage reference would be a discovery. I assume this has something to do with current effects and the impedance of the source material.While interesting, the power loss from using a low voltage reference combined with a high stability divider, makes the low voltage reference not very appealing to develop.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2024, 04:45:53 pm
content: The Josephson junctions are low voltage to start with. For just a single junction there are a few reports getting away with 77 K. This not getting the same very high accuracy as the 4 K version, but still pretty good.The more standard way is a divider, likely a resistive divider and than a Zener or maybe even band gap reference as a start. Here it does not make a difference if one starts at 10 V, 7 V, 5 V or 1.2 V: the divider does not get much easier with a lower voltage to start with.The power loss is not that bad. One can get away with some 0.1 to 1 mA for the divider, so usually less than the power at the reference.For me the question is, if it is worth adding a way to turn off the drive side to also have 0 V from the same output. So not just a DC reference, but the extra switching to allow correction of the thermal EMF from the cables and connectors (not just at the ref. side but also the meter side).

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 20, 2024, 05:04:23 pm
content: Quote from: Gyro on December 20, 2024, 11:09:58 amHelloOK sound realistic , perhaps the 1 Ohm tolerance can be a problem as low value high precision tolerance are very hard to locate even from Vishay but a trial is possible without too much $$RegardsOS

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2024, 05:12:23 pm
content: the JJ effect I ignored because while low voltage, it needs a microwave signal to work. hardly neat low power electronics , even at room temperatureThought some kind of microwave oscillator coupled with a room temperature JJ plate? is a chip waiting to happen one day. Not much more complicated then AD voltage refernece chipsI don't think it super stable without a atomic clock though? What would happen if you use a crappy oscillator to power a joseph junnction?

author: Gyro
author_rank: Super Contributor
timestamp: December 20, 2024, 05:21:50 pm
content: Quote from: Overspeed on December 20, 2024, 05:04:23 pm... but easy to trim with parallel resistors (assuming that you can't trim the reference at the divider input). Kleinstein is right, thermal EMFs are going to be your biggest enemy (whatever method you use. You would want to put the 10k resistor lsome distance from the 1R and run tightly twisted leads to the 1R to minimize thermal difference. Much less of a problem with the 10M resistor (almost vanishingly so) but the thermal emfs are a far bigger influence at 1uV. Of course it depends on required accuracy - at 1uV, you're only likely to be able to reliably resolve 100nV, so 10%.

author: TimFox
author_rank: Super Contributor
timestamp: December 20, 2024, 05:32:44 pm
content: The classic Keithley 260 nanovolt voltage source is a precision voltage supply followed by decade-switched resistor divider networks.The final divider (to get sub-microvolt DC voltage output) is made from copper to minimize thermal emf problems.Although the resistance tempco for copper is crummy, the ratio stability is adequate for the application.The voltage outputs are low-emf Leeds & Northrup binding posts, hidden behind a front-panel door to shield them from drafts.An upside-down pdf file:https://xdevs.com/doc/Keithley/260/KEI_260_Instruction_Manual.pdf

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 20, 2024, 07:37:25 pm
content: Quote from: TimFox on December 20, 2024, 05:32:44 pmHelloInteresting instrument some internal pictures inhttps://www.eevblog.com/forum/metrology/keithley-260-teardown/all copper builtRegardsOS

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2024, 08:30:15 am
content: Quote from: coppercone2 on December 20, 2024, 04:13:59 pmA bandgap reference can be configured to deliver 0.2 volts instead of 1.2 volts.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 08:54:51 am
content: Quote from: David Hess on December 21, 2024, 08:30:15 amI thought this is the configuration they use for a temperature sensor, because it has a high but linear tempco?

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2024, 09:01:14 am
content: Quote from: coppercone2 on December 21, 2024, 08:54:51 amNo, the normal bandgap configuration also produces an signal which is proportional to absolute temperature, but this signal is not normally brought out. Some bandgap references do make this signal available.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 21, 2024, 09:54:08 am
content: Quote from: tszaboo on December 20, 2024, 12:17:23 amHelloYes that also a solution I link data on thermocouple gold platinum a very stable thermocouple and robust regarding welding pollution / oxidation , built a small oven as a TCXO can generate accurate voltage in the uV ,for buffer any idea as ? regarding the Op Amp ? an OPA387 ? or ? the problem with thermocouple voltage is the very low current levelRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2024, 05:58:48 pm
content: The low voltage dividers can be low resistance, like 1 ohm or 0.1 ohm. No extra buffer needed at the low voltage side. The buffer would be at some 5V or whatever the ref. voltage. This buffer would not be that critical and could be a classic OP07 or similar (e.g. OPA202 or AZ amplifiers). If needed for a higher current one may still want an extra transistor (e.g. as emitter follower) to reduce the power at the OP-amp.The thermal EMF gets relevant because of the low voltage. The current in the divider can actually still be relatively high (e.g. 100 µA or 1 mA range).Chances one would aim for both low thermal gradients and a low thermpower resistor, like copper or maybe manganin wire.One could generate a smal voltage from a thermcouple and a heater to generate a difined temperature gradient. So the reference would be heater power * thermal resistance * thermopower of the thermocouple. The absolute temperature may be less relevant, though still a thing to regulate, as the thermopower can be temperature dependent (e.g. copper VS constantan has a thermopower about proportional the the absolute temperature). I would still consider this way a challange in the thermal design to get really stable accurate (e.g. avoid unstable thermal contacts - so ideally most of the system monolytic of securely joined (e.g. soldered, welded).Some of the very early experiments to support / demonstrate ohms law actually used a thermovoltage as a reasonable stable (and low impedance) voltage source. Batteries at that time had quite high internal resistance.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2024, 06:36:39 pm
content: Quote from: Overspeed on December 21, 2024, 09:54:08 amThis is one of the cases where the low impedance and precision requirements allow the use of a chopper stabilized operational amplifier, unless the lowest broadband noise is required.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 06:46:13 pm
content: I had no idea band gap references could go down to 0.2 volts. Is that how something like this works?https://www.digikey.com/en/products/detail/analog-devices-inc/LT6650CS5-TRMPBF/961454I thought unless its setup as the temperature one (not very stable), the voltage is pretty high, like 2V

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2024, 08:26:31 pm
content: The basic bandgap ref. is some 1.24 V. 2 of these and minimal gain would get you 2.5 V.The 0.4 V circuit somes not look so much like a normal bandgap reference.Anyway there is essentially nothing gained from going from a 1:5000 divider to a 1:500 divider. Both have essentially the same drift and difficulties.The low voltage reference has already more problems with noise from the amplifier before the divider. So things even get a little more difficult when one reduces the ref. voltage to start with (e.g. 5 V to 0.5 V).

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 08:57:31 pm
content: Quote from: Kleinstein on December 21, 2024, 08:26:31 pmI know but its fascinating, much like trying to combine resistors and inductors. The lower parts count solution does mean SOMETHING. Even if its parts on a chip. It is elegant in some way, but also probobly a insane money pit.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2024, 09:52:22 pm
content: Quote from: coppercone2 on December 21, 2024, 06:46:13 pmI do not know about the LT6650, but Widlar described his use of it in the LM10 which is a combined operational amplifier and 0.2 volt bandgap reference. At least Widlar described it as a bandgap reference. I did not study it enough to understand what he did.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 09:59:48 pm
content: oh wow and its stable to 0.002%

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2024, 10:23:26 pm
content: Here are articles from both Pease and Widlar which discuss the LM10 0.2 volt bandgap reference.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2024, 11:00:36 pm
content: Very interesting chirstmas reading, I almost want to try to build that multi diode reference to see what I end up with. I wonder how it works out with LEDs lolHow much is a single plate from a josephson junction...20000 junctions for 10V.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 22, 2024, 03:55:15 pm
content: Quote from: Kleinstein on December 21, 2024, 05:58:48 pmHellothanksFor the Josephson junctions I pass as that far too complicatedFor the low value resistor , I will try I have 1 and 10 ohm with acceptable tempcoFor the thermocouple that can be a solution in a controlled temp oven as a OCXO I link a circuit for temperature control use on some DIY instrument base on OP07 , regarding OP07 as that obsolete TI propose the OPA177 as replacementQuestion :does the new OPA can used with single supply or that mandatory to supply +/- voltage ? as the spec says that a replacementFor the thermocouple itself I can use a PTFE block with copper screws and copper plates to keep copper copper contacts in an oven , for quick trial i have Eurotherm temp controller available and static relay , easy to set 65 deg c in the ovenGold/platinum have a very high stability and quite ''bomb proof '' regarding pollution / aging of the weldRegardsos

author: coppercone2
author_rank: Super Contributor
timestamp: December 22, 2024, 04:13:27 pm
content: use styrofoam

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 22, 2024, 05:45:38 pm
content: helloAs easy / cheap / high performance thermal insulation , difficult to be better than polyurethane foam with a Lambda of 0,022 W/mK to 0,028 W/mK.Can be cut from sheet or cast for spray canCan hold 80 deg C in service without problemsregardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: December 22, 2024, 06:11:04 pm
content: To get a stable temperature difference for a thermocouple it would be a system with a constant power heater and than a setup with a stable thermal resistance. So no crews, no clamping, just glued and soldered connections. A temperature regulator would be around the whole system. Likely not too extreme demands there. For the thermocouple I would prefer one side copper as this avoids the extra transitions. For the other side I would look for a metal that is solderable and not magnetic.The OP07 is an old standard part - the jellybean precision amplifier. Ti still makes them and will probably do so for a long time, even if they have better replacements. There are plenty of old designs that need it. Ti has changes the potting material on quite some parts. This makes some version opsolete, though there is an essentially identical replacement with a slightly different ordering code. This can cause some obsolete versions at the distributors.The OPA177 is a bit different, more like intendend as an upgrade, especially more linear, but also more expensive. In many cases I would prefer the OPA202, as it's cheaper, lower bias, lower power, a bit faster and rail to rail out. Single supply operation often comes with some downsides. Single supply precision would be mainly LT1013 or most AZ op-amps.

author: iMo
author_rank: Super Contributor
timestamp: December 22, 2024, 08:14:29 pm
content: This is what I've found in the John Markus book..Would be interesting to try with a modern low drift, low TC opamp..

author: Kleinstein
author_rank: Super Contributor
timestamp: December 22, 2024, 08:44:40 pm
content: Quote from: iMo on December 22, 2024, 08:14:29 pmWith most BJT based amplifiers the voltage one gets via the offset trim is no low TC, but more like proportional to absolute temperature. I faintly remember the idea if using an 741 as a temperature sensor this way.With FET based amplifiers the offset may not come with extra drift, but the offset drift is usually relatively poor to start with.Modern low drift OP-amps are usually factory trimmed for low offset and no more adjustment pins.The normal reference at some 2.5 V to 7 V followed by a divider is the much more promissing path for a low voltage reference.

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2024, 01:28:03 am
content: The OP-05 is an OP-07 without trimming.For parts like the OP-05/OP-07, input offset voltage drift is proportional to adjusted input offset voltage, so adjusting with the null terminals for minimum offset also adjusts for minimum input offset voltage drift.

author: coppercone2
author_rank: Super Contributor
timestamp: December 23, 2024, 01:53:28 am
content: I imagined the other end of the circuit using an array of thermocouples and switches to make a thermal to voltage DACand does parallel thermocouples... reduce nonlinearity?I feel like this circuit is a breath of fresh airAmusing to think about, if there is tens of thousands of them, to make some kind of HV micro bias supply.

author: iMo
author_rank: Super Contributor
timestamp: December 23, 2024, 09:00:33 am
content: Quote from: David Hess on December 23, 2024, 01:28:03 amIn your picture the "Rp" is the value of trimming potentiometer (in my 1976 DS the graph calls "Trimmed offset voltage drift as a function of trimming potentiometer (Rp) size and Vos").Both 05 and 07 allow trimming. From the graph when using 20k trimming potentiometer you may trim out 1mV with almost zero TC_Vos, imho..

author: Kleinstein
author_rank: Super Contributor
timestamp: December 23, 2024, 10:46:23 am
content: AFAIR the OP05 was an OP07 that needs an external capacitor for compensation when used at low gain. It is long obsolete by now anyway.Getting a low TC even with adjusted offset is unusual, but it is still not that low a TC. It's quite some improvement on the 3000 ppm/K for a proportionan to T source, but still more in the 100 ppm/K range of lower grade resistors and also more noisy.For low resistors in the 1 ohm range I had quite good results from 0.2 mm Manganin wire, that I got from Ebay:TC seems to be < 10 ppm/K and for the thermal EMF I could no even tell the sign (e.g. < 0.2 µV/K range) so that the state of the copper wire to compare to may matter.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 23, 2024, 11:41:11 am
content: Quote from: Kleinstein on December 22, 2024, 06:11:04 pmHelloThanks , i agree regarding the temperature control another solution i a use a ice bath ( zero deg c ref ) as the Au / Pt generate uV at 0 deg C another solution is over heat the thermocouple will say 70 deg C , stop heating , measure the temp with a precision thermometer as an ASL 25 with Pt 100 probe at read the voltage when the temp decrease at 65 / 60 / 55 deg C.For cheaper solution ( preliminary test also ) as Au/Pt which are $$$$ , Cu/Ni can used to but I need to check what voltage is generated at 0 deg cThe OPA 202 is a nice solution as performances are great for the cost ( 2 Euro on Mouser ) I already use LT1013 on the circuitRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: December 23, 2024, 11:55:38 am
content: The Au/Pt thercouple seems to be a poos solution, with a rather strong dependence on the absolute temperature. The tendency is to aim for a more constant thermopower, like type K with around 40 µV/K over quite some range. I would still avoid anything magnetic and type K wires are difficult to solder.For the temperature difference the question really is if one needs 2 stable temperature sensors or can rely on a stable heater power and a stable system to produce a fixed temperature difference.

author: Overspeed
author_rank: Frequent Contributor
timestamp: December 23, 2024, 12:22:35 pm
content: Quote from: Kleinstein on December 23, 2024, 11:55:38 amHelloI agree but thermocouples in pure metals are easier to duplicate , alloys have tolerances and that difficult to copy and paste from a batch to anotherI have a Gallium point so 29.766 deg C .My Gallium metal sample is not ''certified'' but looks okvoltage is proportional to the temp difference so as I try to generate low voltage I need small temp difference or low EFM metal coupleregardsOS

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2024, 05:57:31 pm
content: Quote from: Kleinstein on December 23, 2024, 10:46:23 amNo, the OP-05 has internal compensation. The OP-06 is the one with external compensation.QuoteI think Analog Devices had an application note about using an operational amplifier configured as a follower shunting its own supply for 2-wire temperature sensing, but I lost track of it. The advantage of this besides simplicity is that the low impedance output drive from the operational amplifier resists noise.QuoteI have a box full of specialty wire for resistors and temperature compensation, but would never recommend it as a solution because it is so difficult to acquire now.

author: laichh
author_rank: Regular Contributor
timestamp: December 24, 2024, 02:42:15 am
content: Tunkia (China) has a Nanovolt meter calibrator TH1200.https://www.tunkia.cn/TH1200-Nanovoltmeters-Calibration-Device-pd543173798.html

author: laichh
author_rank: Regular Contributor
timestamp: December 24, 2024, 03:20:59 am
content: My solution: a metal enclosure with banana plug (to Fluke 57x0A calibrator, w/ sense), binding post (input, output, guard) & LEMO connector (both CH1 & CH2 to 34420A & 2182A).Inside the enclosure are a divider formed by:Upper: 40 k + (40 k // 40 k // 3.9 M) + 40 k = 99.898 kohmLower: 100 ohmDivider ratio: 1000 : 1All resistor are VHP101 series 0.1% tolerance Bulk-Metal Foil resistor except the non-critical 3.9 Mohm as metal-film.To determine the actual divider ratio, 1st I source a 100 V dc to the divider using a Fluke 57x0A w/ ext sense, then measure the output at binding post using a 3458A. The ratio uncertainty is the combination of the source & the meter.