LFLNA-80 - Page 1
Forum section: electronics / general

author: iMo
author_rank: Super Contributor
timestamp: July 14, 2023, 05:49:24 pm
content: FYI

author: Andreas
author_rank: Super Contributor
timestamp: July 14, 2023, 08:21:22 pm
content: Hmm,how do they get a lower edge frequency of 0.1 Hz with 1000 uF * 1000 Ohms?And this is not a single high pass. (so the frequencies will add geometrically).with best regardsAndreas

author: iMo
author_rank: Super Contributor
timestamp: July 15, 2023, 07:51:12 am
content: The 5 parallel opamps are the ADA4528-2 (A32), the sixth is the servo, it seems.The low pass opamps are the OPA342 (B42).PS: below my current understanding of the wiring..The R7 should be 10ohm.

author: iMo
author_rank: Super Contributor
timestamp: July 15, 2023, 09:59:58 am
content: It should work from 0.1Hz with 2200uF input cap.Not sure how exactly are the three 10Meg resistors in the servo wired, though..

author: Andreas
author_rank: Super Contributor
timestamp: July 16, 2023, 08:50:29 am
content: Shure with R6 = 1K? I think it should be much higer ohmic.AC-Wise it is parallel to R1.with best regardsAndreasEdit: or we should perhaps remove R1 when R6 is populated?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2023, 09:27:50 am
content: The video of the internal shows an 1 K resistor and 1000 µF electrolytic capacitor. It however does not show R1. So I don't think that R1 is there in the real circuit and ideally there should be an extra voltage divider at the output of the DC servo OP-amp to reduce the voltage range and noise of the OP-amp. The divider would also provide extra resistance to add to the 1 K. However I don't see such a divider.R1 and R6 would make sense also acting as a divider. However this would be with different values, like 2 K and 22 K (or even higher resistors to have the first cross over intentionally lower) and than maybe an small capacitor or resistor at the integrator to compensate for a reduced gain.The DC servo acts like an additional AC coupling and it adds the amplifier noise in the transition region. A divider at the amplifier output can reduce the noise of the DC servo at the cost of a reduce compensation range. It can also reduce the need for the very long time constant at the integrator.

author: KT88
author_rank: Frequent Contributor
timestamp: July 16, 2023, 10:58:52 am
content: R6 being 1k basically defies the niose reduction due to paralleling five amps. The noise output of the servo is only divded by two...A higher value for R6 as Andreas implies makes more sense.The only benefit from the low resistance of R6 is is the quite fast settling time.Another oddity is the high resistance (780 Ohms) in front of the non-inverting inputs.

author: iMo
author_rank: Super Contributor
timestamp: July 16, 2023, 12:27:06 pm
content: This is with only R1=1k as seen on the pcb and with C1=1000uF (my previous wirings above are wrong around the input).With 2200uF the AC is peaking around 0.1Hz.Still the 3x 10Meg (R4, R5, R6) resistors in the servo are not fully clear, what I can see there the R5=10Meg is in parallel with C2.PS: there is the R109 on the pcb not populated, it is wired from the servo opamp's output to ground (not a divider with the R1 then). Also the pcb is from 2021, thus my understanding is it is an early prototype.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2023, 12:56:13 pm
content: At least the filter reponse with only the 1 K from the DC servo looks reasonable sharp and with the expecte 40 db per decade slope. Still the drop at 0.1 Hz is still more than 3 dB, more like -4 dB.With many filters the noise BW limit is different from the -3dB limit. So the shifted cross over of the filter may actuall be OK to the 0.1 to 10 Hz noise.The definition of an effective noise cut off is however tricky with non white noise. The noise BW is usually defined for white noise, which is usually OK for the upper limit. There it is normal that the noise BW is larger than the -3dB BW.

author: Rico Sonderegger
author_rank: Newbie
timestamp: July 17, 2023, 11:20:14 am
content: Hello all,I am Rico from Euler Precision.As we have seen, there is a lively discussion about the function of the "DC-Servo" circuit.Here now the solution of the mystery:The circuit consists of the components C101, R103 and the DC Servo loop U203, R105, C103, R106 and R107. These represent an integrator which is limited in bandwidth (C103 // R105 and C103*(R106+R107) and gain (R105 / (R106+R107).As some have already noticed, the theoretical cutoff frequency is above 100mHz. However, since the large capacitors also have a larger tolerance, we were able to measure that this cutoff frequency is 105mHz (-3dB) for our product over all stages.The input filter consists of the components C101 and R103 (-20dB/dec) and the integrator (-20dB/dec) and is therefore a 2nd order filter.R109 is not equipped. This resistor is intended for service purposes.We hope to have brought a little more light into the darkness with our explanation.Many greetings Rico

author: Kleinstein
author_rank: Super Contributor
timestamp: July 17, 2023, 12:27:19 pm
content: R109 and R108 should obviously not be populated at the same time with 0 ohms. It may however make sense to populate them as a divider (e.g. 1:5) to reduce the noise of the DC servo. This would than need a change (e.g. 5 x lower) to R106+R107 too. Using an Electrolytic capacitor in the DC servo could be tricky: if used with no or possibly even negative voltage can lead to drift (up) in the capacitance.

author: iMo
author_rank: Super Contributor
timestamp: July 17, 2023, 01:05:43 pm
content: While staring again at the pcb picture I see the R109 is wired to the output of the opamp against gnd, thus not creating a divider. But perhaps the picture is too blurry..Elyt caps - I was taught in past the elyt capacitors need some "minimal polarization" to work properly, not sure it is still valid, however..

author: Rico Sonderegger
author_rank: Newbie
timestamp: July 17, 2023, 01:35:42 pm
content: Hello all,An other explanation of the LFLNA-80.All these 1mF capacitors are non-polarized electrolytic capacitors!You can see this in the schematic because there is no "+" or "." attached to the schematic symbol.That's why we can use them without "bias" in the circuit.The disadvantage is that they cost more than normal types.In addition, we have spent a lot of time evaluating the best capacitors. Many types were measured over weeks and statistics were created.Using R108 and R109 as voltage divider may not be such a good idea, because the integrator then needs a bigger gain as it is part of the 100mHz filter.R109 is not populated.

author: iMo
author_rank: Super Contributor
timestamp: July 17, 2023, 01:55:54 pm
content: With Kleinstein's mods:PS: the max noise at ~100mHz has dropped from 90 to 67uV/rHz..Rsource = 1ohm.

author: KT88
author_rank: Frequent Contributor
timestamp: July 17, 2023, 01:56:05 pm
content: Without deviding the output of the servo it's (broadband-) noise would be coupled directly into the input. It would be shunted by the source impedance though......and I still don't see a need for the 392Ohms resistors other than converting the input current noise into voltage noise...

author: Rico Sonderegger
author_rank: Newbie
timestamp: July 17, 2023, 02:27:09 pm
content: These 392R resistors are required to protect the inputs of the op-amps when the user applies a high input voltage,as a large current can flow through the 1mF capacitor, which could damage the input protection diodes of the op-amps.All of these "non-essential" components are necessary when the product goes into production.There are so many different users or EMC interference, the product simply must be robust.Our measurements have shown that removing the resistors reduces the inherent noise by max. 0.3nV (see PDF)The calculated voltage noise from current noise is -> In (Current Noise Density) x sqrt(10Hz - 0.1Hz) x 392R / sqrt(Ampl. count) =0.7pA x 3.146 x 392R / 2.236 = 386pV= 0.386nV (without broadband RMS noise current)

author: iMo
author_rank: Super Contributor
timestamp: July 17, 2023, 02:59:17 pm
content: The simulation below fits your measurements (002_REV_0_Noise_compare.pdf) pretty well..Sim:392ohm 133.08uV rms from 0.1Hz-10Hz10ohm 127.56uV rms from 0.1Hz-10HzAprox 0.55nV rms diff (referenced to input)..PS: Kleinstein's mod above (with C1=C2=1150uF in order to have the same AC char):Sim:392ohm 129.87uV rms from 0.1Hz-10Hz10ohm 124.23uV rms from 0.1Hz-10HzPPS: KL's mod with all 392 ohm resistors shortedSim:0ohm 91.8uV rms from 0.1Hz-10HzAll with 50ohm input source.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 17, 2023, 04:07:27 pm
content: The 392 ohm resistors at the individual OP-amps are kind of OK. They only compete with the individual OP-amps and see the OP.amps current noise. The main point is the thermal noise of some 2.5 nV/Sqrt(Hz), which is still quite a bit less than the OP-amps noise.The not so good one is the 390 ohm from the input to the protection diodes. This would compete with the OP-amps in parallel and see the combined current noise of the 5 amplifiers.The resistor should cause about as much noise as the amplifiers.Some resistance or current limit is still needed for 2 reasons:1) protection of the amplifier when connecting a DC voltage or shorting with a charged capacitor.2) protection of a sensitive DUT (e.g. some LTZ1000 based ref. circuits) that can not safely handle to much load. Here even the 390 ohm may be too much and a switchable high resistor may be nice for a soft start.If ultimate low noise is wanted one may get current limiting with less noise / lower resistance from some pairs of JFETs or depl. MOSFETs or MOSFETs with PV gate drive and a fast turn off.

author: checksum
author_rank: Newbie
timestamp: July 28, 2023, 03:43:25 pm
content: I spent the last week working with an LFLNA-80 that was ordered a few days after seeing Marco Reps YouTube review. It's proving to be simple, reliable and repeatable as a measurement tool for trouble shooting low noise supplies.Shortly before I bought an Alpha LNA-10 but found the AC coupled noise floor was that bit too high (~5uV p-p) for the work I had in mind. Despite this, the LNA-10 has more than proved it worth for its ability to reject common mode noise whilst making measurements. Its the first differential probe I have owned, so getting clean measurements with the LNA-10 where CM noise between DUT and scope / analyser would previously have ruined them still feels very novel.The LFLNA-80 feeding the LNA-10 probe in differential mode gives almost no drift at all and resolution to measure down to ~100nV. The main benefit for me is that this spares the complication of isolating (with batteries etc) the DUTs I am working with from their mains powered environments. It works a treat, both the scope and DUT are mains connected and the measurements are rock solid down to the 100nv noise floor.The build feel and operation of the LFLNA-80 are really good too. IMHO a good product, very pleased to have taken the plunge.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: October 11, 2023, 09:34:30 pm
content: Does anyone figured out schematic and values for output filter?

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: January 21, 2024, 12:56:44 pm
content: So I am trying to replicate this for few month now but, it looks like this DC Servo circuitry is a bit tricky to make it working.In my case the op amp is always railing out when input is connected to 9V battery. The reason for that is unequal voltage in op amp input. The inverting input has around 0 V but non inversing has some strangely shaped of 50mV offset. Have no idea where it is coming from. All electrolytes in schematic are bipolar Nichicon same series as in original device. Does anyone have a guess?

author: sorin
author_rank: Frequent Contributor
timestamp: April 15, 2025, 03:09:31 pm
content: Quote from: ZhuraYuk on January 21, 2024, 12:56:44 pmHow did you resolve this problem?What exact electrolytes bipolar capacitor did you use?From your other posts, I see that you archived 17nV RMS, 120nV p-p noise.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: April 15, 2025, 03:23:04 pm
content: Quote from: sorin on April 15, 2025, 03:09:31 pmThe offset was created by current leakage in to op amp via board silkscreen and poorly washed PCB.So I did few things:1. Removed silkscreen from input circuit2. Washed board very carefully, there was some flux leftovers under the caps and SMD components. The input stage and integration circuit should have an electrometer like designs.3. The caps I used were Nichikon EP seriesBelow is photo of final PCB version where DC servo is launched stable each time.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 16, 2025, 08:19:52 pm
content: Currently have a LFLNA-80 on loan and did some measurements (see attachments).Performance and handling are excellent — very solid and well-engineered piece of test equipment.Full schematic attached with help from this thread and following sources:https://eulerprecision.com/product/low-frequency-low-noise-amplifier-lflna-80/https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/6277/LFLNA-80.PDFhttps://www.eevblog.com/forum/metrology/lflna-80/?action=dlattach;attach=1829887

author: miro123
author_rank: Frequent Contributor
timestamp: April 18, 2025, 01:34:48 pm
content: I wonder why single stage 80db amplifier is used instead of spreading it into two stages. e.g. x1000 x10. The second stage can be dedicated opaamp or LPF filter itself. The GBW requirements of active filter are already mild due to the filtering of R305 and C303.I prefer to go with two x100 gain stages. You lose some gain accuracy at the cost of better stability and robustness.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: April 23, 2025, 06:03:18 pm
content: Quote from: MiDi on April 16, 2025, 08:19:52 pmThere are mistakes on schematic definitely, in schematic R210 is 1k but on PCB I clearly see that R210 is 810 - 81Ohms. You need to double check it.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 28, 2025, 02:50:45 pm
content: Quote from: ZhuraYuk on April 23, 2025, 06:03:18 pmNice catch, PCB has 81R for each output summing resistor (R202, R206, R210, R214, R218), 1k was copied from p.19User Manual

author: Kleinstein
author_rank: Super Contributor
timestamp: April 28, 2025, 03:19:10 pm
content: The values for the averaging resistors is non critical. The offset between the channels should be relatively small (more an issue with resistor tolerances and a bit larger input signal). The noise is not critical as it is already after most of the gain. The slightly more critical ones are at the input protection: there it is a balance between protection and resistor noise.

author: 1audio
author_rank: Frequent Contributor
timestamp: May 01, 2025, 03:29:24 pm
content: In a similar application (audio analyzers) input protection vs noise is a major issue. The usual solution is an incandescent light bulb in series instead of the current limiting resistor. Low resistance when dark and resistance increases when current is demanded. In this case adding some circuitry to detect high voltages and short the output of the coupling cap to ground while the cap charges would be useful.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 01, 2025, 04:10:47 pm
content: It could be convenient to have 2 settings for the protection resistor. A relatively low one (could be a light bulb) for low noise and much igher resistor to connecto to a new source. This would not just protect the amplifier, but also the DUT from too much of a current spike. LTZ1000 references without extra protection tend to not like the current spike from charging a larger capacitor. A drop at the output tends to cause a spike in the heater power and thus can take some time to recover.If really needed one can use a pair of depletion FETs for a relatively low resistance current limit. E.g. an SK2145 (cheap, small dual JFET) would give some 120 ohms and 5 mA current limit (the values depend on the threshold).

author: iMo
author_rank: Super Contributor
timestamp: May 01, 2025, 04:26:55 pm
content: ..like this..

author: Yizhou
author_rank: Newbie
timestamp: June 08, 2025, 05:06:07 am
content: Leakage current compensation is essentially achieved through a closed-loop integrator. A single-stage gain of 80 dB is designed to ensure sufficient feedback depth, which guarantees a sufficiently flat passband response in the low-frequency range. Otherwise, the resistance and capacitance of the integrator would need to be further increased. Judging from the product frequency response curve provided by the author, the current accuracy can meet the requirements of noise testing.

author: Rico Sonderegger
author_rank: Newbie
timestamp: July 10, 2025, 12:32:36 pm
content: Hello,This is not an error in the electrical diagram.Vishay writes some code to the resistor. 810 as an example. But that is not 81 ohms.The resistance value is definitely 1kOhm.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: July 10, 2025, 03:59:24 pm
content: Quote from: ZhuraYuk on April 15, 2025, 03:23:04 pmDid you release your full schematic + PCB files anywhere? I've been looking into making my own 1/f noise measurement device for a while, but a low-cost premade PCB is just so much easier.

author: aronake
author_rank: Frequent Contributor
timestamp: July 25, 2025, 07:31:43 am
content: Quote from: LooseJunkHater on July 10, 2025, 03:59:24 pmI am interested in this too.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: July 30, 2025, 01:18:08 pm
content: Quote from: LooseJunkHater on July 10, 2025, 03:59:24 pmHere is google drive folder with schematic and gerber fileshttps://drive.google.com/drive/u/2/folders/1QSpUXKXbVdz7Gt5mVSjBKUxbcK__LReI

author: aronake
author_rank: Frequent Contributor
timestamp: August 08, 2025, 11:53:31 am
content: Quote from: ZhuraYuk on July 30, 2025, 01:18:08 pmAwesome build! Thanks for sharing! I built one now and it worked on first attempt.Maybe adding decoupling capacitors for the OP amps would have been a good idea? I hacked in some on the power rails on the back side of the PCB. Not sure if it will make any difference, and there is still a bit of PCB trace from the capacitors to the OP amps. Also, as there is quite some unused board area, it may have been an idea to make power rail traces thicker, particularly as the power rails go almost all the way around the board. I see a voltage drop of 6 mV from the last input power filter capacitor to the last OP amp. For normal stuff this would likely not matter, but as we are chasing the last pico volt RMS it may matter. And i am not complaining, its an awesome build you made and much appreciate you have been sharing. Just some ideas for potentially making it even better.And obviously, anyone with any kid of commercial ambitions or who need a more verified instrument and not only see this as some experiments for learning purposes should buy Euler Precision's LFLNA-80!

author: aronake
author_rank: Frequent Contributor
timestamp: August 15, 2025, 08:12:27 am
content: Quote from: ZhuraYuk on July 30, 2025, 01:18:08 pmFirst stage seems to have a gain of 10.000. Then for the second stage there is switch 2. It seem to me that this change amplification in stage 2, or? If so, between what values? Its an OP amp resistor configuration I have not seen before.

author: ZhuraYuk
author_rank: Regular Contributor
timestamp: August 15, 2025, 09:37:59 am
content: Quote from: aronake on August 15, 2025, 08:12:27 amSecond stage is making additional amplification of 1000 or 1, depending on switch position.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 15, 2025, 03:03:45 pm
content: Quote from: ZhuraYuk on July 30, 2025, 01:18:08 pmHonestly, thank you so much for publishing your files, I really appreciate it. I'm just wondering if you also plan to publish the Kicad (or similar) design files? The reason I ask is because I was thinking of making some minor modifications to the PCB.Thanks again

author: Okertime
author_rank: Contributor
timestamp: August 15, 2025, 03:57:09 pm
content: The LFLNA-80 is a relatively new design, developed and distributed by Eulerprecision, a two-man company in Switzerland.The two men make a living from their earnings in Switzerland, where life is more than 50 times more expensive than in China.What would you think if you were one of these two men and someone took your design, signed it with his own name, and distributed it as DIY project around the world?There are many other DIY LNA designs for the same application. Use one of them and you'll feel good about yourself.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 15, 2025, 05:49:23 pm
content: Quote from: Okertime on August 15, 2025, 03:57:09 pmNot everyone can afford the $600 USD price tag, especially when it'll be used for non-commercial (ex. educational) uses.

author: iMo
author_rank: Super Contributor
timestamp: August 15, 2025, 07:05:55 pm
content: QuoteDoing business in electronics is risky (as in any other business). The manufacturer may set any price he considers appropriate, the market will usually respond to the price set. When there is a trade secret, invention, know-how or IP (etc.) the manufacturer may file a patent, register for copyright or trademark/brand, etc..If a product is interesting and there is a demand the others start to copy it. In many businesses "the time-to-market" is the only decisive factor about your financial success with certain product or service you offer.That is how it works.. The guys know that well, sure..

author: aronake
author_rank: Frequent Contributor
timestamp: August 16, 2025, 10:25:18 am
content: Quote from: Okertime on August 15, 2025, 03:57:09 pmThis may be a point. But another more positive perspective is that if people build and tweak variations of the LFLNA-80 and post comments here, that would be a tremendous help for the very small Eulerprecision team in developing next improved version. This is how quite some commercial products are refined these days. There has already been some good suggestions on how design possibly could be improved. Up to the Eulerprecision team though, if they don't want this to happen let people know here.Pretty much anyone with some commercial intention would much rather buy a complete product which is verified and tested than a DIY build. DIY would also be way more expensive if work time should be paid for. With the existence of DIY build the original gets more publicity which likely lead to more sales. And probably none, or almost none of the DIY builders would buy the commercial product instead of building any of the other open designs. I hope and think DIY releases would give reference to the commercial version and endorse purchase of that for commercial use.Building and selling copies would be absolutely wrong of course.

author: mawyatt
author_rank: Super Contributor
timestamp: August 17, 2025, 04:25:41 pm
content: Somehow we missed this and just got pointed here from iMo over at:https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/We had just created a similar concept as shown see starting at post #402, then #403.Studying the LFLNA-80 schematic, wonder why the use of the large 1000uF feedback capacitor? We were able to achieve a reasonable 2nd order High Pass Response with a 1600uF input capacitance and 10uF (PP Film) feedback capacitance. Maybe this was to compensate for the input leakage with a similar feedback cap?Anyway, hope this might help the original developers or others.Best

author: iMo
author_rank: Super Contributor
timestamp: August 17, 2025, 08:41:08 pm
content: That is an interesting topic for regulation theory experts here. The original has got 10000 gain without any capacitive feedback in the first stage, you have there gain 1000 with 10uF in the feedback. That somehow allows servo be an "pure" integrator with 10uF in its feedback.Would be great to see some math/theory behind that..

author: mawyatt
author_rank: Super Contributor
timestamp: August 17, 2025, 10:22:44 pm
content: An integrator in the feedback "looks" like a differentiator in the forward path, or commonly known as a High Pass or AC Coupling. This is why the effect can be utilized along with the large input capacitor, which is also a differentiator, to create a somewhat like Butterworth High Pass effect as we've shown.So it benefits reducing the offset induced by the input capacitor leakage as well as aiding in adding another Quality high pass (think "Q") effect rather than a simple cascade 1st order RC type which is obviously a low "Q" effect.Note how this can also compensate for the additional simple RC AC coupling in post 1st amplifier stages and make the overall response better represented as shown in the overall response plot. This is the reason for the slight peaking in around 0.1Hz as shown when compared to an ideal Butterworth 2nd order high pass response, it helps compensate for the post 1st order effects on the next AC coupling high pass.Edit: We've added the simulation below which includes an Ideal3rd Order ButterworthHigh pass and Low Pass response (Green) to compare with the total LNA response (Blue). You can see that we attempted to approximate an overall 3rd Order Butterworth for the HP and LP responses over most of the frequency range and also took advantage of the R2 C3 and R6 C6 networks to improve the out-of-band higher frequency range to help "squash" any additional higher frequency noise sources not intended to be part of the wanted measurement range.We can provide more of the detailed math if you like, but hopefully the above describes our concept here as shown in terms of the functions of the feedback integration effects.Best

author: mawyatt
author_rank: Super Contributor
timestamp: August 18, 2025, 03:38:20 pm
content: Geez how did we miss the video in the OP 1st postIn the video there is mention of the noise spikes caused by the chopping action and how this could be augmented by the added 390Ω resistors.Our question is has anyone "seen" or "thought" about the effects of the multiple paralleled op-amp having the chopping action creatingintermodulation productsbetween the chopping action in each individual paralleled op-amp?The IMD result could beat down to aroundzero frequencysince the difference frequency between the individual op-amp chopping clocks may be small and they are not synchronized as we understand from the video and earlier schematics shown.Also does anyone know if the dual ADI ADA4528 op-amp versions (and quad types versions from the TI OPA4388 similar type op-amp) utilize the same chopping clock for each amp within the package, would suspect they use the same but don't know?Anyway, the reason for asking is we are considering the effects and unintended consequences of paralleling multiple chopper type op-amps to lower the input referred noise voltage.Best

author: iMo
author_rank: Super Contributor
timestamp: August 18, 2025, 06:32:22 pm
content: When not explicitly stated in the DS as an "advantage" I would assume the clocks are not synchronized in 2 or 4 opams packages. Noopy may look at the dies to confirm. I have some older LTC1x5x which have dedicated pins for clock sync.PS: here is a thread on that afaik -https://www.eevblog.com/forum/metrology/low-frequency-noise-of-zero-drift-amplifiers/

author: mawyatt
author_rank: Super Contributor
timestamp: August 20, 2025, 01:50:06 pm
content: Would think that these would be the same chopper clock or synchronized clocks just for the mentioned potential IMD issue, but don't find any details of such. Having 2 or 4 separatelike frequencyclocks generated on the same die seems risky.If anyone has or finds any confirmed details, please enlighten us!!!Best

author: Kofen
author_rank: Regular Contributor
timestamp: August 20, 2025, 02:52:21 pm
content: For low frequency use, e.g 0.1 - 10 Hz use, you would be really hard pressed to get any IMD products from the chopper clock difference, which is around 200k for the ada4528. So I would not worry about it.

author: mawyatt
author_rank: Super Contributor
timestamp: August 21, 2025, 04:13:01 pm
content: The classic 2 Tone IMD shows the results around the 2 tones but often doesn't tell the overall story where the 2 tones also mix down to around DC. This was our concern, not at or around the chopper clock frequency, but the clocks mixing and appearing around DC. Since these clocks are generated on-chip they will have high levels of Phase-Noise, Edge Jitter and poor overall Frequency Stability. Add to this thepossibilityof having 4 clocks on-chip close in frequency with on-chip limited isolation and you begin to see our concern.BTW long ago we experienced this effect where the harmonics of two separate higher frequency clocks within the system were mixing down to around DC and corrupting the low frequency sensitive signals of interest.Anyway, we'll wager the chopper multi op-chip op-amps types all use the same on-chip clock source or same clock frequency. Maybe one of the analog op-amp designers on here can comment wrt to such.Best

author: mawyatt
author_rank: Super Contributor
timestamp: August 21, 2025, 04:26:40 pm
content: Should mention that we made some electrolytic capacitor measurements noted over here:https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg6018343/#msg6018343These Rubycon ZLH 1500uF 16V capacitors were just laying around and we made some leakage measurements after apply a DC bias. The trend is showing the leakage is significantly reduced byDC bias aging, and after ~15hrs bias at 16V the leaking is below11na8.5na, and still very slowly trending downward. Edit: now below 4.5na after about 40hrs.Of course the low frequencycapacitive noise contributionsremains to be seen but leakage effects are encouraging!!Best

author: iMo
author_rank: Super Contributor
timestamp: August 22, 2025, 04:20:40 am
content: This is why you need a mechanism to not discharge the capacitor when manipulating with DUT. As I mentioned in one of my previous posts - we had a switch in our shielding box which maintained the DC at the capacitor during DUT replacement (and also reduced the time to settle after the replacement). Do not ask me how it was wired, it is long time back I mounted it in..Quote from: mawyatt on August 21, 2025, 04:26:40 pm

author: 2N3055
author_rank: Super Contributor
timestamp: August 22, 2025, 06:23:27 am
content: SAMWHA RD series 1000µF/50V is steady at 5nA/10V. But there is large tempco to the current.

author: mawyatt
author_rank: Super Contributor
timestamp: August 22, 2025, 01:17:40 pm
content: Not only the relatively high TC but we're seeing the SD is holding ~1.1na while the Mean leakage is dropping (~40hrs below 4.5na with the Rubycon ZLH 1500uF 16V), which indicates the dielectrichealingprocess is introducing some self-generated charge noise. Of course measurements includes any voltage fluctuations from the DC Bias source and a battery would obviously be a better source for the dielectric charge "noise" measurement.This is not surprising as the dielectrichealingin itself is a random process filling in dielectric oxide micro fissures and cracks, while thickening the overall oxide layer.Anyway, surprising how low leakage these GP electrolytics can achieve with some "bias aging". Vaguely recall way back in 70s when we needed some larger value low leakage capacitors for the MSP project, all the electrolytics we tested had significant leakage and why we used the more expensive wet-slug tantalums.@2N3055. What SD leakage current are you seeing with your 1000uF/50V SAMWHA RD capacitor and measurement setup?Best

author: 2N3055
author_rank: Super Contributor
timestamp: August 22, 2025, 06:03:44 pm
content: Quote from: mawyatt on August 22, 2025, 01:17:40 pmI was playing with it, tried direct current measurement and by using 10MΩ in volt mode as a shunt.In current mode you are at the very low end of range and instrument noise is large.Now it is back in volt mode and stabilizing. I will write down stdev once it settles.

author: mawyatt
author_rank: Super Contributor
timestamp: August 22, 2025, 06:30:03 pm
content: Quote from: 2N3055 on August 22, 2025, 06:03:44 pmThis is why we are using the KS34465A, it has very low charge injection and pa resolution. Now that we've reset the measurement it's showing ~4na bias and ~850pa SD using GPP4323 as 16V DC Bias source.Best

author: 2N3055
author_rank: Super Contributor
timestamp: August 22, 2025, 08:04:24 pm
content: Quote from: mawyatt on August 22, 2025, 06:30:03 pmKS34465A has low current modes 1µA and 10µA full scale. That is useful in this case.I have only 200µA full scale meters at hand.On SDM4000A with a bit of statistics and nulling out the 200µA range I was able to measure 5 nA DC repeatably with some care.But Stdev (you asked for) is >1nV (10NPLC) so not good for this.

author: mawyatt
author_rank: Super Contributor
timestamp: August 22, 2025, 08:18:31 pm
content: The lower current range is why we got the 34465A awhile back, and the DMM6500 has the lower ohms range and why we have that also. BTW we used 100NPLC for a little more averaging.Honestly we did not expect an electrolytic of this size to have such low leakage!!The new SDM4000A looks like a nice DMM!!Best

author: 2N3055
author_rank: Super Contributor
timestamp: August 23, 2025, 10:11:52 am
content: After 12 hours it stabilized...It is sensitive to temperature, so me entering the room is clearly visible...When looking into part where it is relatively flat, I see 5µV Std., conservatively... sometimes 3µV StdThat converts to 0,3-0,5 pA RMS noise.It is close to the point of measuring voltage source noise.That is through the 10MΩ input resistance of DMM.

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 12:44:08 pm
content: Just had a nasty storm come thru (Tampa Bay seems to be the US lightning capital) and had to unplug the TE bench. Decided to use the DMM6500 which only has a 10ua lower range (KS34465A is 1ua) when reconnecting, readings are similar. Leakage is ~3na with ~650pa SD, so downward trend continues.Maybe time to start another thread on this topic?Best

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: August 23, 2025, 12:46:56 pm
content: Quote from: mawyatt on August 23, 2025, 12:44:08 pmIf this happens, share a link here? I've been actively following-along this thread because it has been super interesting to me and I've been wanting to DIY my own LFLNA-80.

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2025, 03:09:50 pm
content: Quote from: LooseJunkHater on August 23, 2025, 12:46:56 pmhttps://www.eevblog.com/forum/projects/electrolytic-leakage-measurements-and-discussion/Best