HI-RES DVM from 24 bit ADC EVAL board? - Page 1
Forum section: electronics / general

author: Lesolee
author_rank: Regular Contributor
timestamp: May 03, 2020, 05:21:38 pm
content: I am trying to get a high resolution measuring scheme (at not much money). 1 ppm resolution would be fine so 24 bit ADCs should be suitable. But a surface mount chip on its own is not much use. So I thought EVAL modules.ADS1231REF:https://www.ti.com/tool/ADS1231REFINL ±8 ppm typical±19.5 mV FS232 nV ptp = 6 ppm ptp noise typicalhttps://www.mouser.co.uk/ProductDetail/Texas-Instruments/ADS1231REF?qs=sGAEpiMZZMsLmE2CU4Kkz1oezTaVoxJV£50It looks like the software can do recording, averaging, rms, ptp, so quite functional. Dates from 2011.It will be earthed, but a USB isolator is available from Farnell for £26.https://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-for-pc-laptop/dp/1795095ADS124S08EVM:https://www.ti.com/tool/ADS124S08EVMINL 1 ppm typ (10 max) without the PGA, 3 ppm typical at full gain19 nV rms = 0.12µV ptp at full gain. Noise free resolution better with lower gain.22 bits noise free resolution (based on ptp noise) 0.25 ppm?2.5 S/s to 4000 S/shttps://uk.farnell.com/texas-instruments/ads124s08evm/eval-board-multi-ch-delta-sigma/dp/3125729£103(Software Needs Win 7 or 10 so will not work on my old XP machine)Has export restrictions on the software. Dates from 2017.MAX11210EVKIT:https://www.maximintegrated.com/en/products/analog/data-converters/analog-to-digital-converters/MAX11210EVKIT.htmlXP and Win 7 capable software.Isolated power supply from USB.INL ±10 ppm worst case50 sps to 400 spsDates from 2014https://www.mouser.co.uk/ProductDetail/Maxim-Integrated/MAX11210EVKIT%2b?qs=%2Fha2pyFadugeyEjHEmCLG%252Bi8iAnnuRZwFXhdMU03d6rIdafBZmk9JA%3D%3D£87LTC2380-24 DEV Kit is calledDC2289A-A:https://www.mouser.co.uk/ProductDetail/Analog-Devices-Linear-Technology/DC2289A-A?qs=sGAEpiMZZMve4%2FbfQkoj%252BKQYPPN%252BDH%252BZa1oE8cSXjQY%3D£165Then need a DC590 (£44) or a DC2026 (362)2MS/s SAR ADC.There is just too much to read. Even on one part there is an overwhelming amount of detail. I just went with the ADS124S08EVM.I am just going to relate what happens, blow by blow, in case it is of any interest.The software needed logins and export restriction questions to download. It didn’t work immediately, I had to fiddle about with the USB drivers, but it seems they were expecting that this could happen and wrote about how to fix non-automatic installations.The USB cable supplied had an insertion force just short of 5000 metric fluck tonnes. I was scared it would rip the SM connector off the board. It eventually went in and connected, but not with a satisfactory click.This is what it looks like on my desk. (I can’t use it on my bench because the bench computer is an old XP machine, on which the software won’t run.And here is my connection to it.I have spent money, so I want to see it do something RIGHT NOW.10 mV, 1 Hz sine wave with 4V offset. 4000 S/sTurn on the SINC3 filterTurn on the Global Chop which reverses the input and averages the two readings.So it is doing something.I need a better signal source, or at least a better coupling method.The software is working in a sort of batch mode. It won't work live (auto trigger). The analysis is not fully coupled to the main software so it doesn't know what the sample rate is, or at least it doesn't bother giving the time base on the time domain plot (boring).The stats are numbers not voltages, even though it knows what the voltage is. I think they just got bored with the software and never finished it.

author: Andreas
author_rank: Super Contributor
timestamp: May 03, 2020, 08:38:42 pm
content: Hello,for me it is not clear what you intend to do.Is it only evaluating what is possible with one of those evaluation boards?Or do you have some target spec for a application?I did something similar on a LTC2400 basis.Target was to get for a 0..5V range somewhere near a 6.5 digit DMM.One experience was that I needed a isolation from RS232/USB connection to reduce noise.In my case I did this by photocouplers and battery supply for the LTC2400.with best regardsAndreas

author: Lesolee
author_rank: Regular Contributor
timestamp: May 03, 2020, 09:30:27 pm
content: Quote from: Andreas on May 03, 2020, 08:38:42 pmThe idea is indeed to put a front end on it to make a 6+ digit DVM. I haven't started on the design yet. That's a job for tomorrow.I was thinking 10 V full range, maybe 15V full scale (50% over-range).And a 1 V full range as well, just for added interest. Just a standard 10,000M input impedance bootstrapped amplifier.It will need to be isolated, and that USB isolator from Farnell would seem to do the job for little effort.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 04, 2020, 06:32:29 am
content: How well the USB isolator work is still not clear. USB usually includes power, while RS232 / UART isolation can be done without an extra isolated supply / DC/DC converter.One difficulty with the integrated ADCs is that the full scale range is usually some +-2.5 V or +-5 V max. The reference also needs to be some 2-5 V. So this excludes the usual LM399 reference that starts at 7 V - so it is about one of the 2.5 V or 5 V references that are usually not all that stable. Still OK, but some extra error source.A 10 V / 1 V input would need both amplification and attenuation. This makes the design a little more tricky. The best accuracy is usually with a gain of 1 for the amplifier.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 04, 2020, 07:11:21 am
content: Quote from: Kleinstein on May 04, 2020, 06:32:29 amRS232 is so old it is not found on most computers. You then need USB to RS232 converters (which are often nasty). I suppose you can still get plug in cards, but that is all a bit retro.The idea is that you buy a complete package, with software, and it hopefully worksadequatelyas is.Making the ADC is a lot of work (ie like your DIY DVM project). I hope to have avoided the digital stuff! The rest of it will just have to be as good as it can get.

author: branadic
author_rank: Super Contributor
timestamp: May 04, 2020, 09:57:02 am
content: Just in case you haven't seen it yet, here is my implementation of Andreas's LTC2400 design:https://www.eevblog.com/forum/projects/oshw-24bit-adc-measurement-system-for-voltage-references/-branadic-

author: Lesolee
author_rank: Regular Contributor
timestamp: May 04, 2020, 10:54:15 pm
content: I like to poke signals into differential amps (or differential ADCs) because I typically am unsure just exactly what the signal is supposed to be! So for this board the reference is external, but still set to 2.5V. I programmed one input to be tied to 2.5V and injected signal directly into the other input. At 0V you get -4 million counts, and at +5V you get +4 million counts.2^23 is 8 million so it looks like you have to put in a signal on both sides or you don’t get full scale readings (or you have to use a 1.25 V reference). At least now I won’t be wrong on my gain scaling by a factor of 2.The TI Delta-Sigma ADC evaluation software is really “interesting”. When it is idle it is chewing up 30% of my 3.5GHz AMD 4 logical core processor. When you ask it to acquire say 1024 points at 100 S/s it says it is ready almost immediately -- when clearly it isn’t. You have to look at the eval board to see that the acquisition LED is flashing, otherwise it looks like the software has just locked up.You have to download the old ADCPRO software to do FFTs. I only managed to get -81 dBc from the DDS generator, so clearly that needs some filtering.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2020, 05:24:47 am
content: With some ADCs one really has to drive both inputs to get the full range. The INL specs are usually also for fully differential driving both sides with opposite sign. When just driving one side, chances are one would get additional INL, especially some even power parts, that essentially vanish by using the differential signal drive.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 08:00:48 am
content: Quote from: Kleinstein on May 05, 2020, 05:24:47 amThis is looking very unpleasant. Looking back over my old designs, the high accuracy scopes started off differential and went single ended. The high speed scopes started off single ended, and went differential. And the DVMs were all single ended everywhere (at the outputs of each stage).There is no such thing as a single-ended to differential splitter (which doesn’t have a non-inverting buffer stage, and shed loads of gain defining resistors).This is more difficult than I (naively) thought.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 09:37:02 am
content: Actually, not as bad as I feared …If U2 is used then it may be better to fiddle around with the 6:1 divider, driving R7 from R3 to eliminate RL1C and R6.I am also a bit unhappy about changing the impedance seen at the ADC inputs. I put R5 half way between IK and 0R whilst I think about it!

author: macaba
author_rank: Regular Contributor
timestamp: May 05, 2020, 09:39:12 am
content: I think you are encountering my regular frustration with specifying ADCs:- Differential input usually requires the voltage at the input pin to be within 0V to V+ (i.e. no negative voltages).- 'Bipolar' can still refer to a differential input that requires 0V to V+ on input pin.- Single-ended input can be either unipolar (0V to V+ on input pin) or bipolar (V- to V+ on input pin) depending on ADC support.- Analog Devices have a parametric filter called 'True Bipolar' which gets you single-ended devices that can genuinely support V- to V+ on input pin (usually -Vref to +Vref) through the use of onboard scaling amplifiers.Have a look at the ADAQ4003 for an ADC that internally contains the single-ended to differential ADC driver with precision resistors which significantly reduces the design burden. Thus allowing the ADC to be powered from a single supply, but supports a single-ended bipolar input as per the datasheet:

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2020, 09:49:12 am
content: An amplification by one 1.6 is usually not worth the trouble. The ADC should have enough resolution to get away without it. The way it is build the negative side driver / amplifier adds the errors. It depends on the ADC, but some of the SD ADCs like a relatively low impedance drive to get good INL.If the input voltage is not directly connected to the supply of the ADC, one does not need to have the negative side input at ground or a fixed potential. For example one could use the negative side ADC input also as the negative side input. It needs a few more thought and is a bit unusual, but it can reduce the critical amplifiers in the path. The generation of the negative side signal would main contribute to the common mode signal to the ADC and thus cause little error.A fully differential amplifier can be handy, but there are very few, if any with zero drift.

author: Echo88
author_rank: Frequent Contributor
timestamp: May 05, 2020, 10:27:50 am
content: Maybe the PGA280 is of interest for this thread?https://www.ti.com/lit/ds/symlink/pga280.pdf?ts=1588673898811Id suggest the LTC2440/LTC2442 as an ADC. Low speed, high accuracy and deals with offset correction itself.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 02:05:54 pm
content: The earlier comments have now been read, but this update was done before I saw them.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 02:09:43 pm
content: Quote from: Kleinstein on May 05, 2020, 09:49:12 amAs shown in my first post, the EVAL board already has 4.12K resistors on the way to the ADC.It would be "interesting" if these had to come out to make it perform correctly.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2020, 03:00:07 pm
content: There is usually no need to trim the divider / amplifier. An off ideal value for the gain can be adjusted numerically.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 03:12:54 pm
content: Quote from: Kleinstein on May 05, 2020, 03:00:07 pmTo be honest, the pots are for 'comfort' rather than actual use. I don't have, or expect to have, any accurate reference to adjust it to!With respect to your idea of ditching the x1.6 gain, it is unclear what numerical adjustment I will have with this scheme. Obviously I can post-process the data in Excel (which would be boring). There is also some sort of scripting thing going on with the interface, but I haven't got around to worrying about that yet. Still very early days.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 05:15:53 pm
content: I had another go at the 5 Hz sinewave response, with a better filter on the DDS generator. Specifically:104.8dB SFDR is getting there, but the SNR/SINAD/ENOB are all rubbish. The ENOB was less than 5 bits, which is ridiculous.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2020, 06:23:47 pm
content: The cheap DDS generator can have relatively high noise / distortion. The DAC is using some kind of R2R and is not very accurate, more like 6-8 bit. So the ENOB / SNR is not expected to be much better - maybe a little with oversampling.I would also consider a common mode filter. Besides normal noise there can also be RF range EMI effecting the ADC.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 06:47:49 pm
content: Quote from: Kleinstein on May 05, 2020, 06:23:47 pmI would think that the 3 pole filter would kill off the bit-resolution noise.Sadly I don't have any sort of chokes to hand. R's and C's in some combination will have to do for now.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 05, 2020, 07:10:30 pm
content: The filter helps against the effect from bit resolution, but it does not help much against things like DAC nonlinearity causing the more lower harmonics.

author: splin
author_rank: Frequent Contributor
timestamp: May 05, 2020, 10:23:01 pm
content: Quote from: Kleinstein on May 05, 2020, 07:10:30 pmThe distortion is likely < 1% and the filter gives another 13dB and 22dB attenuation of the second and third harmonics o that does not explain the 5dB SNR figure which the TI software reports. In any case the FFT shows the 2nd harmonic at approx -100dBc.Is the software treating the DC offset as part of the noise perhaps? I would expect it to remove the DC when calculating SNR and SINAD but presumably the high pass filter response would need to be documentated in the user manual somewhere. What does the digitized signal look like in the time domain? 5dB SNR should be pretty obvious if it is real.

author: splin
author_rank: Frequent Contributor
timestamp: May 05, 2020, 10:43:02 pm
content: This is how Datron arranged the amplification and scaling in their 1061, 1065, 1071 and 1081 meters to give gains of x31.6, x3.16, /3.16,/31.6 and /316 for the 200mV to 1000V ranges:Your circuit introduces not insignificant errors (10s of ppm) due to relay contact resistance (50mohms+) affecting the gain/attenuation. They can be calibrated out but will change over time. Personally I would apply the gain/attenuation, then perhaps buffer before the SE to differential conversion. Adding missing DMM models numbers.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 10:48:21 pm
content: Quote from: Kleinstein on May 05, 2020, 07:10:30 pmBut no harmonics are showing. The SFDR is >100 dB.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 11:03:45 pm
content: Quote from: splin on May 05, 2020, 10:23:01 pmThe time domain signal looks fine. The software is BS. I took out the window function and tuned the DDS to the best frequency I could. I managed to back to 102dB SFDR, just. The crappy internal oscillator is drifting too quickly (even when warm) and even with 4.968,318 Hz applied, I would have needed another digit of resolution to get the ideal spot consistently.So the ADCpro software has twiddly spin controls to punch out the DC and the sidelobes on the fundamental. There does not appear to be such a feature on the main Delta-Sigma eval software. But that software does hardly anything -- they clearly never finished it. It crashes frequently. You change to SINC3 and the time domain picture (for a small number of points) is unchanged, but the FFT changes frequency by a factor of 3.The SINAD up at 67 dB for a -20dBFS signal is over 12 bits, which is poor, but then again I am driving it single-ended from an earthed generator into a board earthed via the USB, so not too bad either.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 05, 2020, 11:18:31 pm
content: Quote from: splin on May 05, 2020, 10:43:02 pmYou might have hoped that I would know that, but it was 1983 when I signed off that drawing.To be fair I never had to change those parts; it was all carried over from the 1071, done at least several years earlier by my bosses John Pickering and David Jessop.Quote from: splin on May 05, 2020, 10:43:02 pmBack to the drawing board.That's an excellent catch. Thanks.

author: splin
author_rank: Frequent Contributor
timestamp: May 06, 2020, 01:22:50 am
content: Quote from: Lesolee on May 05, 2020, 11:18:31 pmHa ha - that's funny -haven't we all been there?How many times have you searched for something and found a forum post that precisely and uncannily addresses your exact query and is clearly written by somebody who really knows their stuff - you must bookmark this important contribution! Then you (eventually) realise that it was you that wrote it and didn't really know what you were talking about at the time! Perhaps it only happens to me?Actually I have 3 1081s - it would be great to hear any hints/tips/fascinating insights/war stories etc. that you may have in their design and development. The 1271 and 1281 meters even more so given that the selfcal aspects of its design are barely described in the service manuals, unlike the HP 3458A's HP Journal descriptions.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2020, 02:38:22 am
content: Nice project. I tried something similar.https://www.eevblog.com/forum/testgear/playing-with-delta-sigma-converter-poor-mans-meter/50/It looks like they used LabView. They used it on that 32-bit board as well. You can now download LabView free of charge. If they supplied you with the source, there's a chance you could modify it to better suit your needs.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2020, 07:48:36 am
content: A point that may be missed easily in input stage design is protecting the ADC from a voltage higher than 5 V. To would with some 10-15 V the amplifier would have to be powered with some +-18 V or so. Even if the input is using a driven negative side one would still need something like +-10 V, so more than the ADCs supply.Because amplification x 1 is the easiest and most stable (gain wise) case it would make sense to have the x 1 case as one range. This may mean the other ranges would be more like +-25 V and 0.25 V. If the ADC includes internal gain, this may be an interesting option. The SD converter internal gain is usually from sampling the input more often and this gain factor is usually very stable and quite accurate, better than the usual resistors to set the gain.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 06, 2020, 08:13:32 am
content: Quote from: splin on May 06, 2020, 01:22:50 amI left before the 1271/1281 came out.> Actually I have 3 1081sWhen you see "LOG" in the checked box in the service manual for a particular board you know that is one of "mine". That's for the DC converter, AC, and ohms. Basically all the front end amps were changed to chopper stabilised dual-JFET amps, all under the direction of David Jessop. Basically incorporating all his ideas of how to improve the design.The bias current compensation originally used a crappy carbon composition resistor. I had to make a case to bin it and replace it with a proper resistor (which obviously cost more).I couldn’t believe they had the precision zeners just on the board along with everything else. So those metal blocks to give them more thermal mass were my idea. Having said that, I didn’t make any before and after measurements!That dielectric compensation in the ADC was there from the 1071, and probably earlier than that. So when Bob Pease’s article on “soakage” came out, with him saying it was a new discovery, I couldn’t help but chuckle. We had been doing it for years; we just kept it to ourselves. But it turns out others had been doing it years before that as well (and published their results.) Just finding that stuff in journals is non-trivial.>given that the selfcal aspects of its design are barely described in the service manualsYes the manuals were very descriptive in those days. I can't see anyone bothering nowadays. Too expensive.On the production line the testers would repair boards by getting a circuit diagram, and circling an area, and getting the technicians to just change all the parts in that circled area. That was apparently quicker than trying to locate the fault down to the exact part.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 06, 2020, 10:33:35 am
content: Quote from: Kleinstein on May 06, 2020, 07:48:36 amAddressed.Quote from: splin on May 05, 2020, 10:43:02 pmFixed, EOE[EDIT: corrected the diagram text label. The input divider is not a 3/7 divider it is a 3/7 ratio.]

author: Kleinstein
author_rank: Super Contributor
timestamp: May 06, 2020, 11:25:06 am
content: Driving both the negative and positive side (and still take the neg. input from ground) adds an extra Gain of 2.So the circuit as shown would be give ranges of 7.5 V and 1.25 V.The ADC has internal PGA gain . So it a gain of some 1.4 really needed of there is a gain of 2 available. The 2.5 V range (directly to the ADC) would be probably more accurate in essentially all aspects than an 1.5 V range with a little gain.With the internal gain present, there is essentially no need for any external gain, only attenuation.So the natural ranges could be something like 15 V with an external divider (one is free to choose a ratio), optional 7.5 V with the divider and internal gain of 2.2.5 V with just the buffer and than 1.25 , 0.6 , 0.3 , 0.15 V with internal gain of 2,4,8,16.The odd point would be that the negative input would be the - Input of the ADC, driven from a not so critical OP.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 06, 2020, 11:37:24 am
content: Quote from: Kleinstein on May 06, 2020, 11:25:06 amAccording to my test in post #6 I have to drive both sides to their rails (±2.5V) to get full scale on the converter. So I think +15V scaled by 1/7 gives 2.14 V (both sides) which is about 85% of Full scale. I needed a bit in hand to allow for clamping.It should be 1/7 on the top range and 10/7 on the bottom range, giving a 10:1 ratio change. Not sure how you got 6:1. Using the old design?I won't be confident that it is actually correct-ish until I build it of course.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 07, 2020, 10:44:16 am
content: I had another go at the Concept, and managed to eliminate one of the NOMCA arrays (which is nice). The downside is the 1V range is now low by 2%, so that will have to be calibrated out.[EDIT: removed 1N4148 clamp diodes are they are not low leakage devices.]

author: Lesolee
author_rank: Regular Contributor
timestamp: May 09, 2020, 09:49:49 pm
content: The active clamps were a bit thin on detail, so I have studied them in depth and documented what I found.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 10, 2020, 07:29:20 am
content: For the OP selection it is no only the slew rate but also the BW that matters: With Fet input OP the maximum slew rate is reached with a relatively large voltage at the input possibly exceeding 1 V. For lower voltage at the input the relevant parameter is the GBW, as this gives the rate of change at a low differential input voltage ( dU/dt = U_in * GBW).The part on overloading the OP is a little confusing: the fast slew rate phase is not overloading the OP. There is saturation before the OP engages. So the recovery time does still matter.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 10, 2020, 08:51:34 am
content: Quote from: Kleinstein on May 10, 2020, 07:29:20 amInteresting. Could you explain in more detail please, especially the formula. Slew rate for a sine wave should involve 2 x PI x f x Vmax for example.Whilst I am pondering your statements above, I did a quick sim (in SIMetrix) of the test circuit and waveform from the paper using a macro-model for the MCP6021.The red line is the clamp reference level, which is eventually reached. The green line is the clamped point, overshooting by the full diode drop because the opamp doesn't 'wake up' until then.It was a big ask, but the macro-model is not behaving correctly in this situation. I imagine that some people would be very trusting of such a sim

author: Kleinstein
author_rank: Super Contributor
timestamp: May 10, 2020, 03:52:41 pm
content: Quote from: Lesolee on May 10, 2020, 08:51:34 amforgot the factor 2 *Pi. So the formula should bedU/dt = U_in * 2*pi* GBW , valid for OP with single pole compensation (usually at least a good approximation).With single pole compensation the rate of voltage change is proportional to the differential input voltage. This gives the usualy 90 deg. phase shift. The gain at a frequency f is GBW/f and this would a sine input one gets am amplitude of U_in* GBW /f and thus a rate of change of 2x PI x f x U_in* GBW /f.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 10, 2020, 05:22:42 pm
content: Quote from: Kleinstein on May 10, 2020, 03:52:41 pmWe need to be a bit careful with symbolic names here.For the slew rate formula we have a sine wavev = Vmax * sin(wt)dv/dt = Vmax * cos(wt) * wdv/dt (max) = Vmax * w = 2 * PI * f * VmaxSo Vmax is thepeakof the sine, not the ptp or the RMS. Not what you would normally call theamplitude.We do agree that there issomedependence on the GBW. Just exactly what eludes me currently.If we apply a small step input (say 100µV) to the open loop amplifier it will (eventually) hit the rail. This will not be slew rate limited. But if the step is increased to 1mV then it is going to go 10x faster. And 10 mV is 10x faster again. And 100 mV 10x faster again, and so on, until we reach the slew rate limit. That’s step inputs. For a ramp it is different again. Getting from the frequency domain to the time domain is non-trivial.Typically slew rate and bandwidth go hand in hand for an opamp (in order to get the “full power bandwidth” spec). The question then becomes how much GBW do we need so that the slew rate is the limiting factor in this situation. That is simultaneously interesting -- and difficult.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 14, 2020, 10:47:50 am
content: Quote from: Kleinstein on May 10, 2020, 03:52:41 pmI have updated the (master copy) of the clamp report, but I have some more measurements to do before releasing the update. In the meantime, to show that I have not forgotten it, here is a partial experimental result.

author: Lesolee
author_rank: Regular Contributor
timestamp: May 20, 2020, 02:32:23 pm
content: I have finally completed the active clamp report update.There is a plot of the MMBF4417 used as a clamp included which may be of wider interest, so I have given it as a separate image below:In the updated report, the new measurements of slew rate gain on page 11 should be of technical interest in the sense of WTF?

author: Lesolee
author_rank: Regular Contributor
timestamp: May 31, 2020, 06:17:12 pm
content: The image below is just a teaser. Some people might be interested in how I went about getting HD2 and HD3 readings of -120 dBc on a 100 Hz waveform.I give a full account in the pdf document.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 07:45:28 am
content: Continuing to the next phase of the project I bought a full speed USB 2.0 isolator from Digikey -Seeed Studio 114991949. (£15.82, to which you have to add 20% VAT). Incidentally, the box it came in is actually a 52Pi device (http://www.52pi.com)I tried it on a flash memory device. Fine. I tried it on my XP machine with a Picoscope 3206 USB oscilloscope. Fine. I tried it on the EVAL board. Not fine - Code 10 driver error.Goggled that and started checking registry settings, reloading drivers, … An entire day of frustration. Finally I went on to the Texas E2E forum and got a (much appreciated) very rapid response from Bob Benjamin.My isolator, and also most isolators, areFULL SPEED USB 2.0. Ideal right? Nope! It’s a GOTCHA. The EVAL board isHIGH SPEEDUSB 2.0, which is all part of this historic naming convention.Full Speed USB 2.0 = 12 MbpsHigh Speed USB 2.0 = 480 MbpsThank you “Standards” writers for creating such a mess. Thank you Windows softies for writing a useful error code that tells me that the device is not capable of running at the correct speed (despite the fact that they handshake at full speed, so the error will be known.)I found a couple of Full Speed USB isolators, the cheapest being£100. Without isolation, use as a DVM is not realistically possible. The whole DVM from (this) EVAL board project is dead.I did see one eval board (of the ones I checked) that had built in USB isolation. Maybe another look is in order in a few months time, once I complete the current work.I am going to continue with the harmonic distortion measurement improvements though.Incidentally I also mentioned to Bob that the Analysis Engine was mis-reporting the ENOB of my 100 Hz -10 dBFS signal with 100 dB SFDR (since it gives an ENOB of around 3). Bob says that is because it thinks the fundamental is noise because it is expecting a DC signal. They are displaying “effective resolution” based on the “noise” as a fraction of full scale.I understand the problem, namely that getting a 24 bit pure sine wave may not be possible, but calling their calculation ENOB is not the solution!Maybe they should call it "Peak Music Power ENOB"

author: ramon
author_rank: Regular Contributor
timestamp: June 14, 2020, 09:02:52 am
content: Hardware schematic shows that there are usb full speed signals connected to the MCU and USB mux (and a usb_mux_sel wire connected to mcu too) so there is still a chance to ask them for a firmware version that use low speed 'Full Speed USB'.

author: TexasRanger
author_rank: Contributor
timestamp: June 14, 2020, 12:07:55 pm
content: Why not use something like LTC6363-0.5, for the single ended to differential conversion?This might not get as good as the ground lift circuit with expensive components, but seems much simpler to me.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2020, 03:23:09 pm
content: The LTC6363 is a really nice chip, but not so suitable for DC it is a little noisy at low frequency and has some drift.The input is low impedance - so if would need an additional buffer / amplifier in front. Any resistance at the input would effect the gain. So it would need really low impedance (e.g. << 1 Ohm) like from a fast buffer.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 03:29:44 pm
content: Quote from: TexasRanger on June 14, 2020, 12:07:55 pmIt is an interesting part. It is not cheap, at £5 each.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2020, 03:57:21 pm
content: Quote from: Lesolee on June 14, 2020, 03:29:44 pmThis would still be a good price for the AC performance.

author: bnz
author_rank: Regular Contributor
timestamp: June 14, 2020, 04:43:15 pm
content: Quote from: Lesolee on May 31, 2020, 06:17:12 pmA less instructive but easy and flexible way to get a good 100Hz-ish sine and analyse it would be to use an good audio analyser.This is a -6dBV 101Hz sine (+ a -130dBV 233Hz sine as marker) generated and analyzed with a RTX6001, the outcome of this project:https://www.diyaudio.com/forums/equipment-and-tools/277808-diy-audio-analyzer-ak5397-ak5394a-ak4490.htmland the audiotester software.There is still room for optimization, by playing with the amplification of the out and input, as well as with the digital volume of the sine.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 04:44:59 pm
content: Quote from: Kleinstein on June 14, 2020, 03:57:21 pmTo be quite honest, I am not sure what the application is. Specifically where it should go. I have an OPA320 driving the other side of the differential input of the eval board, using a NOMCA array for the resistors. I get 8.6 lsb rms with the input shorted. Driving that stage from the twin-T harmonic filter pushes the noise up a factor of 16x, so the differential part is irrelevant.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 04:57:52 pm
content: Quote from: ramon on June 14, 2020, 09:02:52 amA quick test: 100,000 points at 1kS/s. It takes about 100 seconds for the acquire phase, then it transfers in around 50 seconds (2 min 32 total). Assuming 24 bits, as 4 bytes, gives 8000 B/s. Assuming 12 bits per byte to allow for framing, say 100,000 b/s.That is 100 kb/s compared to the full speed spec of 10 Mb/s. It is already dog slow for no apparent reason.They did suggest using a laptop (which I don’t have, in Win 10 at least). I could also isolate the DDS with a mains transformer, but the point is the USB isolator should have had low capacitance. A mains transformer, not so much.[EDIT: changed text in brown, as a result of Kleinstein's comments below.]

author: TexasRanger
author_rank: Contributor
timestamp: June 14, 2020, 05:16:33 pm
content: Another very cheap way to analyze ac linearity of ADCs is to analyze intermodulation Distortion.There you can use standard signal generators and you're only limited by their noise floor.The actual THD of the DS360 is also much better at low frequencys than the data sheet, you get around -128dB THD at 220Hz there at medium output voltages.If you want to get serious about this topic, you can take a look at the apx555:

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: June 14, 2020, 07:02:24 pm
content: Quote from: Lesolee on June 14, 2020, 07:45:28 amA couple of years ago I got a free MAX11410EVKIT that Maxim was giving away. It does have isolation between the ADC and the microprocessor. I didn't look in detail at dynamic performance, but here is the noise spectrum with shorted inputs at maximum PGA gain. The software that comes with it is a bit limited. But they provide source code for the microprocessor, so one could setup something else.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2020, 07:04:20 pm
content: The 12 MBps should be sufficient for the relatively slow ADC: with 32 Bits per sample and 1 kSPS is would be only 32 kBps, so something like 3% of the speed available in the full speed mode. So for most cases the USB interface would not be the limiting factor.How good the isolation of an isolated USB depends on the implementation. The faster couplers may not be that good and aa ready made DC/DC coverter may be lower capacitance than a mains transformer, but there can be additional common mode interference, that is really hard to block.For the input amplifier there was an older thread, that may be interesting.https://www.eevblog.com/forum/projects/need-advice-for-adc-buffer/msg1627207/#msg1627207It still needs some attenuation.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 08:00:56 pm
content: Quote from: maxwell3e10 on June 14, 2020, 07:02:24 pmIt is almost a clone of the chip I am using. As an eval board it is only £45, the cheapest I have seen. Somehow it was not on my list.(I did have a MAX11210EVKIT on the list at £87)The MAX11410EVKIT doesn't have anything to say about the USB, type 2.0? full speed? or anything. Trying to compare chips is hard work!

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 08:03:07 pm
content: Quote from: Kleinstein on June 14, 2020, 07:04:20 pmI checked your calculation. I checked mine (post #50) I can't see an error in either. The conclusions are different.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 14, 2020, 08:34:35 pm
content: The actual transmission may very well not use the full available bandwidth. So the slow transfer could be due to a long overhead of the µC just slow to handle the data. The conclusion that using full speed (12 Mbps) instead of high speed (480 Mbps) would take 10 times longer is not clear. It looks like not even 12 Mbps are used.The other calculation may assume 2 channels and the 8000 byte per second. I also did not add the 8 -> 12 Bit overhead. This explains the step from 32 kbps to 100 kbps. still both are much below the full speed rating.It could be considerably more if the data are send in ASCII format instead of binary.

author: Lesolee
author_rank: Regular Contributor
timestamp: June 14, 2020, 09:31:12 pm
content: Quote from: Kleinstein on June 14, 2020, 08:34:35 pmI have revised my post above. I blame the excessive ambient temperature (27°C).They must be sending the data in Morse code, with 64 bit words per bit, or something equally stupid!Or maybe it is some .NET bloatware thing.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 08, 2020, 12:38:32 pm
content: This is pretty specialist stuff. TheHarmonics Laballows you to create harmonic distortion on a synthetic waveform and see the effect on the ENOB. It also allows you to measure the ENOB of your data acquisition system. It is another small step in the overall plan of action.link to direct download page:http://lesliegreen.byethost3.com[EDIT: Had to update to v1.01 as the ADCPro header was corrupted by a spurious edit which changed an "and" into an "And". July 8th 2020][EDIT: Update to v1.02 to fix load and save headers for ADCPro on residuals, and load header detection from TI software. Also fixed linearity graph scaling. July 17th 2020][EDIT: Update to v1.03 to allow predistorted waveforms to be loaded into ARB generators. July 21st 2020]

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 09, 2020, 01:32:10 pm
content: Code:Сигнатура проблемы:Имя события проблемы:CLR20r3Сигнатура проблемы 01:HarmonicsLab.exeСигнатура проблемы 02:1.0.1.0Сигнатура проблемы 03:5f0647e6Сигнатура проблемы 04:mscorlibСигнатура проблемы 05:4.7.2053.0Сигнатура проблемы 06:58fa6bd6Сигнатура проблемы 07:1073Сигнатура проблемы 08:96Сигнатура проблемы 09:System.InvalidOperationExceptionВерсия ОС:6.1.7601.2.1.0.256.1Код языка:1049Дополнительные сведения 1:0a9eДополнительные сведения 2:0a9e372d3b4ad19135b953a78882e789Дополнительные сведения 3:0a9eДополнительные сведения 4:0a9e372d3b4ad19135b953a78882e789Ознакомьтесь с заявлением о конфиденциальности в Интернете:http://go.microsoft.com/fwlink/?linkid=104288&clcid=0x0419Если заявление о конфиденциальности в Интернете недоступно, ознакомьтесь с его локальным вариантом:C:\Windows\system32\ru-RU\erofflps.txt

author: Lesolee
author_rank: Regular Contributor
timestamp: July 09, 2020, 02:54:33 pm
content: Quote from: MegaVolt on July 09, 2020, 01:32:10 pmSorry about that. I have no idea what that error report is saying (even if it was in English). It should be a bog-standard VB.net application. Are you running 64bit Windows 10, or something else?Code:Problem Signature:Problem Event Name: CLR20r3Signature Problem 01: HarmonicsLab.exeProblem Signature 02: 1.0.1.0Problem Signature 03: 5f0647e6Problem Signature 04: mscorlibProblem Signature 05: 4.7.2053.0Problem Signature 06: 58fa6bd6Problem Signature 07: 1073Signature problems 08: 96Problem Signature 09: System.InvalidOperationExceptionOS Version: 6.1.7601.2.1.0.256.1Language Code: 1049Additional Information 1: 0a9eAdditional information 2: 0a9e372d3b4ad19135b953a78882e789Additional Information 3: 0a9eAdditional Information 4: 0a9e372d3b4ad19135b953a78882e789View our online privacy statement:http://go.microsoft.com/fwlink/?linkid=104288&clcid=0x0419If an online privacy statement is not available, check out its local option:C: \ Windows \ system32 \ ru-RU \ erofflps.txtSeems like Windows 7. Is it 64 bit?Did you do something like try to open or save a file?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 09, 2020, 03:08:41 pm
content: Quote from: Lesolee on July 09, 2020, 02:54:33 pmYes, I have Win7 x64. I just started the application and immediately got an error. I did not even see the application form.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 09, 2020, 03:15:17 pm
content: Quote from: MegaVolt on July 09, 2020, 03:08:41 pmI just tried it again (with the 1.01 build) on Win7, via a remote desktop, and it works fine. I don't think I have the skills to understand the problem, let alone fix itI would have thought that if the .NET version was not high enough it would complain rather than crash.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 09, 2020, 03:21:40 pm
content: Could the Russian language and the comma instead of the period as a separator of the fractional part be a problem?

author: Lesolee
author_rank: Regular Contributor
timestamp: July 09, 2020, 03:28:17 pm
content: Quote from: MegaVolt on July 09, 2020, 03:21:40 pmIf we were talking about reading files then yes. But the program is written so it does not (intentionally) use any registry entries or ini files or anything. Of course my experience of Russian operating systems is not extensive. (Ok, it’s zero!)

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 09, 2020, 04:03:13 pm
content: Quote from: Lesolee on July 09, 2020, 03:28:17 pmOne possible mistake is to convert the text to a fractional number. For example, a window for entering a number stores numbers in the form of text. And this number was introduced at the development stage. When the program starts, it is possible that this text is transferred from the input window to a number. And since the separator character is invalid, an error occurs.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 09, 2020, 06:29:17 pm
content: Quote from: MegaVolt on July 09, 2020, 04:03:13 pmIt's a good thought. I tried an experiment on the basis that maybe the edit box swaps commas for decimal points behind the scenes, depending on locale.Code:DP2 = CDbl("0,2345")The convert-to double function normally has the string from the edit box, after I clean it up.The code doesn'timmediatelycrash, it just accepts the number as 2345.0 which is wrong but not so bad.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 09, 2020, 08:31:19 pm
content: Quote from: Lesolee on July 09, 2020, 02:54:33 pmI have googled the CLR20r3 code and it is not a good sign. One easy suggestion I found is to right mouse click on the exe, and use the context menu to "run as administrator". Failing that there is loads of pain of validating the .NET install.Maybe we could get reports back from other users with a Win 7 system to see if it is more of an application issue than a specific machine issue?

author: MegaVolt
author_rank: Frequent Contributor
timestamp: July 10, 2020, 12:04:47 am
content: Quote from: Lesolee on July 09, 2020, 08:31:19 pmI understood the problem. What version of NET is needed for the application?

author: Lesolee
author_rank: Regular Contributor
timestamp: July 13, 2020, 05:13:30 pm
content: Quote from: MegaVolt on July 10, 2020, 12:04:47 amSorry for the delay. I somehow missed or failed to receive a notification.I checked the project settings and the target is .NET 4.5.2, I have no idea why.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 13, 2020, 05:24:28 pm
content: I effectively posed this question earlier: “Given a sine source connected to an FFT analyser, where the FFT analyser is showing one or more harmonic tones, how do you know which end of the cable the harmonic distortion is being produced at?”The answer to this question is a new tool/device/method which I have called a “Harmonic Discriminator”http://lesliegreen.byethost3.com/articles/discriminator.pdf[EDIT: Added a direct link so it is not necessary to login to this site to access the document]

author: Kleinstein
author_rank: Super Contributor
timestamp: July 13, 2020, 05:45:39 pm
content: The idea of analyzing the source of the harmonics is interesting. It absolutely makes sense to check the source of the harmonics, as there can be 3 sources: the generator, the DUT and the analyzer. I have not read the test in detail, but I think it is not fully taking into account that the harmonics may show some phase shifts. So its no just a scalar value but complex values to include the phase. If the DUT and analyzer are wide band with low low phase shift, the scalar approximation may be OK, but this is not always the case. The can be harmonics not just from a quasi static nonlinear transfer function, but also harmonics cause my the rate of change.For the source and analyzer pair, the filter idea should work OK, especially to measure the distortion from the analyzer. With an unknown DUT it would probably be better to subtract the known harmonics from the source and analyzer, including the phase. So one would need an extra measurements of the DUT at the harmonic frequencies too. If the DUT has gain or attenuation one would have to know the separation in source and analyzer.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 13, 2020, 06:49:50 pm
content: Quote from: Kleinstein on July 13, 2020, 05:45:39 pmSee, for example, page 15.Also the bottom of page 14 suggests using the Harmonics Lab to look at the phase of the residual.There is no way to subtract the harmonics from the source/analyser when looking at a DUT (which I do not even consider in this report). You need to know that harmonics in the source and analyser are not cancelling first!

author: bnz
author_rank: Regular Contributor
timestamp: July 13, 2020, 08:31:51 pm
content: Here real life measurements that come close to your 140dBc setting in the intro of your discriminator.pdf ... again from the "audio-world"http://www.diyaudio.com/forums/equipment-and-tools/335005-osva-source-versatile-analyzer-post5962088.htmlhttp://www.diyaudio.com/forums/equipment-and-tools/277808-diy-audio-analyzer-ak5397-ak5394a-ak4490-228.html#post5446579The source is not that expensive:http://www.diyaudio.com/forums/equipment-and-tools/287892-eosc10kv3-lt-an67-10khz-oscillator-updated-version.htmlThe above measured 1kHz version differs only in few parts.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 13, 2020, 09:36:20 pm
content: Quote from: bnz on July 13, 2020, 08:31:51 pmThe “audio world” is the ideal place for up to 20 kHz low harmonic distortion (and low hum) stuff.I don’t have a login for that site, but from the visible pictures the -130 dBc results are very good. The problem is, what do they mean?-130 dBc can be obtained by using a 115 dB generator and a nearly 115 dBc ADC that just fortuitously happens to cancel. I have never seen anyone explain how they KNOW that one or the other is causing the problem (hence the discriminator).Using a “good notch filter” is not without its problems since we know that capacitors can give distortion well before this level, and a notch filter (eg twin-T) is not a simple thing. I have also seen use of a notch filter and 40dB linear amplifier in order to see the residuals (Cyril Bateman). That is two more possible error sources.[EDIT: updated to include the need for a 40 dB linear amplifier.]

author: bnz
author_rank: Regular Contributor
timestamp: July 14, 2020, 06:55:32 am
content: The other graph you need the login for this one:[iIn the two links the generator is measured with two essential different analyzers. The results seem to suggest that the limits come from the analyzers not the generator, as it is unlikely that cancelation would accidently happen with both. But yes, to be sure the discriminator is a fine thing.

author: bnz
author_rank: Regular Contributor
timestamp: July 15, 2020, 08:09:15 am
content: I do not see why for analysing harmonic distortion frequently a notch filter is used. A high pass would yield the same information as we are not interested in the signal below the fundamental. And a high pass filter is simpler than a notch.Speaking of high pass filters, wouldn't it be good also to add to the Harmonic Discriminator a high pass filter? As the Harmonic Discriminator only introduces a slight attenuation a hight pass filter, attenuating the fundamental the same amount, would not need to be steep.This could perhaps be advantageous in the case that the harmonics are due to the source and just slightly above the resolution of the analyser.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 15, 2020, 08:25:17 am
content: [ Specified attachment is not available ]Quote from: bnz on July 15, 2020, 08:09:15 amGood question. The fact is that you need a multipole high pass, which is actually much harder than a notch filter. Here I have "cheated" and used the filter wizard. It says I need a 7 pole Chebyshev filter, which is not "easy".

author: Kleinstein
author_rank: Super Contributor
timestamp: July 15, 2020, 01:35:24 pm
content: Notch filters can be tuned quite well and than offer very good suppression (e.g. 40 - 60 dB) of the fundaments. It helps to suppress the effect of harmonics from the analyzers. So it was a really good ideal in old days when using a scope was the normal way and ADCs were more like 8 Bits.One could still consider using a notch to check the harmonics of the source. With the fundamental suppressed there should be much lower harmonics from the analyzer. It can still be tricky as gain after the notch is also not perfect.This is the more conventional way to check a high end oscillator for harmonics.For the harmonic discriminator a high pass filter could be tricky, as the the fundamental would be attenuated and thus more attenuator for the other channel needed.For the harmonic discriminator one could think about an all pass, that is a filter only effecting the phase, but these filters are usually more complicated and normally include an amplifier, that can easily add distortion.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 15, 2020, 03:31:50 pm
content: Quote from: Kleinstein on July 15, 2020, 01:35:24 pmOf course I already published the way to get >70dB out of a twin-T using 5% capacitors in the first few pages of "100Hz Harmonic Distortion testing". Post #41 in this thread.https://www.eevblog.com/forum/metrology/hi-res-dvm-from-24-bit-adc-eval-board/msg3085249/#msg3085249or for those without a loginhttp://lesliegreen.byethost3.com/articles/Harmonic_testing.pdf

author: Lesolee
author_rank: Regular Contributor
timestamp: July 16, 2020, 10:40:33 pm
content: I completed the testing of the Active Harmonic filter I have been working on for the last month or so. Spoiler alert: whilst I have managed to achieve >60dB harmonic suppression at 100 Hz, and an overall harmonic level of around -120dBc, the phase noise introduced in the process is excessive.The design is therefore not suitable for its ideal intended purpose of providing a DDS-controlled stable sine source for ENOB testing.Direct link for lurkers and casual readers:http://lesliegreen.byethost3.com/articles/filter.pdf

author: Kleinstein
author_rank: Super Contributor
timestamp: July 17, 2020, 07:28:43 am
content: The filter should not produce phase modulation or amplitude modulation. It may make it more visible or convert existing amplitude variations to a fm modulation. DDS generation of low quality has quite some close in crap, not so much harmonic distortion.Why use 100 Hz ? There could be mains hum at this frequency.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 17, 2020, 08:00:41 am
content: Quote from: Kleinstein on July 17, 2020, 07:28:43 amOutput using active filterDirect output (single ended) from DDSThere is certainly a case for saying that some of the phase noise is from the DDS, and it is just being exposed. Neither response has a useful ENOB.Quote from: Kleinstein on July 17, 2020, 07:28:43 amMains hum is typically odd harmonics. I don't see any to the level of -125 dBc.The ADC can only go to 4 kS/s and 100 Hz seemed more like a metrology grade frequency. It does want to be a bit off the grid, so 95 Hz would have been a better choice.[EDIT: Updated as the images got corrupted or mis-linked by the server at some time in the last few days!]

author: Lesolee
author_rank: Regular Contributor
timestamp: July 24, 2020, 09:23:10 am
content: As a further step, I have digitally corrected the harmonic distortion on my FY6800 DDS AWG as a proof of concept.It also means that accurate harmonic calibration is now possible at audio frequencies.BEFORE:AFTER

author: bnz
author_rank: Regular Contributor
timestamp: July 24, 2020, 02:46:21 pm
content: You generate the distortions by a polynomial of degree five of the signal, if I see it correctly.I see that you can get any harmonic distribution up to the fifth harmonic this way. But you have no influence on the phase this way.If you aim to simulate cancellations, would there not also control of the phase distribution be of importance?P.S. for easy application in audio in/output in .wav or some other common audio format would be helpful.

author: Lesolee
author_rank: Regular Contributor
timestamp: July 24, 2020, 10:35:04 pm
content: Quote from: bnz on July 24, 2020, 02:46:21 pmYes, quite right, it is a 5th order polynomial. So the interesting thing is that odd phase angles do not appear to be present on this setup. And I don't think a polynomial can create them. It may be that the quasi-static correction is adequate. I am working on a setup where the DP factors can be adjusted on the fly.I have assumed that some/most AWGs would have an import facility in txt or csv format. I have no other kit of that type, so I couldn't test it either way.

author: Lesolee
author_rank: Regular Contributor
timestamp: August 21, 2020, 12:29:38 pm
content: I have been doing quite a bit more work on this topic, and have managed to push the ENOB up from a miserable 9.6 bits to 16.6 bits (both at around 100Hz)Direct link for lurkers:http://lesliegreen.byethost3.com/articles/pure_sine.pdf