DIY Evaluation ADS8354, 16-bits/ dual channels/ 700 ksps - Page 1
Forum section: electronics / projects

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 12:13:21 am
content: My new hobby grade SA, dual channels this time. Nucleo-H743zi2 runs two SPI to get data over two data lines.Edit: "real-time" performance.

author: moffy
author_rank: Super Contributor
timestamp: December 01, 2024, 01:55:01 am
content: That is very impressive performance, congrats.I assume you sample to memory then do the DFT and display and then back to sampling, what is your sample size? and what are you using for your buffer amps?

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 02:26:01 am
content: Quote from: moffy on December 01, 2024, 01:55:01 amFFT size 32768.Regarding buffer amps, I spend some time to make selection. Can't get reliable results using ths4521 /ths4531 - throw in garbage can. Could be my adapter soic-dip8 boards is the reason, but FDA is very unstable and prone to oscillate.MCP6D11 is good only up to 2.5Vp-p, than failed on THD . So, I use simple inverting config with second degree feedback network.Results THD-3:opa2626 = -103tlv3542 = -92tsh82 = -103tlv2365 = -96ada4891 = -84lme49721= -64mcp662 = -92lmh6612 = -103 !(Vp-p < 2.5)Edit:I forget to mention, that first video made with FFT results averaging = 5.Here is "fast" no averaging version:

author: moffy
author_rank: Super Contributor
timestamp: December 01, 2024, 05:16:45 am
content: Quote from: MasterT on December 01, 2024, 02:26:01 amThat info about the THDs of the buffer amps is very usefull.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 11:03:29 am
content: Quote from: moffy on December 01, 2024, 05:16:45 amHa. THD data posted over is raw data in Secific circuits: G = -2 with aggressive SAR at the output.In my experiments, many glorious & expensive OP-amps show quite different results when driving SAR.Edit:The problem is that load is not a simple resistive, so charts in DS and Spice/ Tina simulation tools are NOT related and no use here

author: mawyatt
author_rank: Super Contributor
timestamp: December 01, 2024, 03:52:48 pm
content: Way back we ran into issues with driving various higher speed ADCs inputs which was found to be related to ADC input charge injection. Many op-amps didn't like this and would cause significant output "glitches" due to the charge injection. ADC sources started issuing recommended driver circuits for their higher speed ADCs because of this, which usually involved a driver with very low intrinsic source impedance and some small series resistance to reduce the charge injection ADC induced glitch.Recall some op-amps were much better at driving ADCs than others, but can't recall which. Also recall a simple test was to "ping" the op-amp with a significant short duration current pulse and monitor the response with a fast analog scope and capture the event with a scope camera (DSOs weren't around back then!!).Some of the THD that's being reviewed might be attributed to the core driving capability of the DUT op-amp and it's ability to directly handle the ADC input artifacts. If one could place an isolation buffer on the ADC input, this would allow direct op-amp comparisons without the ADC effects.@ MasterT, are you using the recommended ADC driver circuit with the THS4521? If so, it's interesting that the recommended driver circuit with THS4521 is causing problems driving the ADC while others don't, might be worthwhile to contact TI wrt such.Best

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 05:05:31 pm
content: Quote from: mawyatt on December 01, 2024, 03:52:48 pmI solder ths4521 to soic-8 /dip-8 adapter first, so there could be de-coupling issues. Design and order complete PCB from PCBway just to discover stability problems later -on was not an option.TI datasheet depicts ths4521. but EVM build with ths4561. I doubt TI's board could outperform my design, if not on THD than on noise level, look video and compare to DS (can't find video from TI for EVM)Even high-drive-power video IC like tsh82 requires R in series with feedback capacitor, same time TI circuits has none. One resistor lower noise by 10 dB, settling time likely involved

author: mawyatt
author_rank: Super Contributor
timestamp: December 01, 2024, 06:14:23 pm
content: Quote from: MasterT on December 01, 2024, 05:05:31 pmThat might be your problem since high speed/performance op-amps often require tight physically & electrically (low Z) close decoupled Vcc and Vee for proper use.QuoteTI indicates newer versions are recommended for the 4521.QuoteThe added R creates a break/limit in the feedback impedance due to the capacitance which has to do with feedback compensation for stability. This is tailored for each device/configuration/use and can't be unilaterally applied across other devices and/or configurations. This is a complex subject and best to study up on Feedback Control Theory and Applications.Best

author: KE5FX
author_rank: Super Contributor
timestamp: December 01, 2024, 06:46:32 pm
content: Quote from: MasterT on December 01, 2024, 05:05:31 pmYou need to move past that. Either use PCBs, or dead-bug.Seriously. You're ready. Time for the next level.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 07:02:58 pm
content: Quote from: KE5FX on December 01, 2024, 06:46:32 pmPeople say bad dancer always has a problem with the balls. Same apply to loosy designed IC, FDA amp in particular, that intrinsicaly unstable.Dual (helps a lot with lowering THD-2) video driver have no issue with adapters or complex loads.

author: moffy
author_rank: Super Contributor
timestamp: December 01, 2024, 09:41:25 pm
content: Thanks for sharing your driver circuit, I'll tuck that away. If the TSH82 is capable as shown of such excellent performance, it is a great find especially considering its low price, also having a 4.5V to 12V supply helps.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 10:02:20 pm
content: You are wellcome. My tests limited by noise, so I can't see below -103 dBc THD-3. In overall , TSH82 is even better than OPA2626 on thd-2, but loosing ground on Noise specification. For application where averaging or another noise reduction technics possible, its not an obstacle.I also looked through AD EVAL modules for theirs Pulsar product lines , 16 - 18-bitters, and seems ad4841 is the most in use, but costs is just insane. AD designed with +7.5V & -2.5V for driver to have a headroom and minimize THD. Sure TSH82 in similar condition likely beats up ad4841, I only tests on +5V power lines.

author: MasterT
author_rank: Frequent Contributor
timestamp: December 01, 2024, 10:57:55 pm
content: Quote from: mawyatt on December 01, 2024, 06:14:23 pmAnother way to put zero information in manny words.Tell you a funny story.In the mid 90-th, around 1995-96 significantly distorted series ofdifferential equations get into MIT's electronics engineering text book.(Operation was conducted by KGB, with local partners support in US, of course.)Interesting things, equations that violate basic physics laws passed allnecessary re-viewing and check-ups. Nobody notices, professours, doctors,etc.Moreover, fake theory was tought to students over a decade, tillin 2007 defector discloses details in interogation room.Des-information was referenced in the huge amount of another scientific books, magasines.A lot of internal documents, reseachers works in TI, AD and NS relyon scientificaly worded BS about phase and stability in the operational amplifiers.Now you know who was a Master-Mind.NB: Be sceptical with a person that speaks like a philosopher on subject of electronics theory.there is a chance that he get degree about that time.

author: moffy
author_rank: Super Contributor
timestamp: December 02, 2024, 12:42:12 am
content: How are you generating such a high purity 100kHz test signal? that is a non trivial task in its own right, unless you are using 200kHz and 300kHz notch filters.

author: mawyatt
author_rank: Super Contributor
timestamp: December 02, 2024, 02:33:16 am
content: Quote from: MasterT on December 01, 2024, 10:57:55 pmDoubt that's true, care to prove me wrong and quote the source of the mis-information at MIT, in scientific books, magazines and works at TI, AD and NS.Yes we're calling your bluff, post your proof!!Best

author: MasterT
author_rank: Frequent Contributor
timestamp: December 02, 2024, 04:27:25 am
content: Quote from: mawyatt on December 02, 2024, 02:33:16 amYou need to forward request to FBI, agents name Johnson. If case is restricted, inquiry release year.

author: coppercone2
author_rank: Super Contributor
timestamp: December 02, 2024, 04:33:19 am
content: Ok, I thought they were just copy pasting stuff that seemed somewhat relevant to some stuff they found through trial and error. Kind of like "which equation is the best fit for a chaotic data set". Sometimes it makes sense when you can closely define it for physics reasons... however its really delicate. They invented so much statistical magic to clear things up.I can believe that there is bad data because I noticed its really easy to fuck up a large data gathering operation with bad procedures or assumptions, and that this data might lead to some bullshit trend being found.I think its often dubious they came to the conclusions they have with the 'back ground math' they sometimes talk about.Because someone with no idea about the process gives some random good sounding number for the # of electrical tests needed, resolution required, etc. Then someone is told to implement this, but its not possible to actually implement like that, but its done anyway, because it is the job. Then they start cranking data by any means necessary.Data gathering roles in corporate, they often have the side effect of being related to hard quotas. And this is a place where management thinks that the process is simple enough to automate and give to total drones. And the assumption that every case takes a similar amount of time to analyze is very often completely false, some tests end up having alot of complications that are swept up under the rug. AKA the outlier count is way higher then expected. Then it gets 'simplified' on the spot so the quota is capable of being met. This is the domain of non technical managers. No one wants to hear that some sample is taking a extremely longer amount to analyze, because the operation is typically deemed to be a 'easy job' that should 'run smooth'.In essence, it might have a similar result to KGB sabotage.This often makes me dubious of 'advanced conclusions' that are achieved through 'data science', which are used for certain equations. It kind of like those people that think they can get 32 bits from a 10 bit MCU ADC by doing enough data processing. Sometimes I think it should be called 'bored with matlab'And the review process is done by people that don't know the mechanisms of the underlying process well, but they are taught to trust statistical math. I heard that before from a analyst, the "I don't need to know how it works..." Sure they catch some things, but the conclusions that they sometimes reach are totally asinine. And the people in charge of them think that they can some how figure out if the data their getting is bad. No, they can't, they don't know why, or what it is, or how it was obtained on any thing more then a superficial level. They are not telepathic. GIGOSo to me its totally expected that there are garbage equations that got put together from bad data from dodgy labs.And naturally you know there are statistical tests to determine if you are trying to read tea leaves. However, it tends to get 'normalized' aka 'new normal' for those coefficients to be within some small range because of whatever special circumstance they cite. It can take a REALLY long time to discover these kinds of issues.And then sometimes the cases that are used to 'prove' things later are exceedingly simplified. And external people making assumptions that there is good and bad companies for trust, but failing to take into account that there are good and bad labs inside the same organization.

author: Bud
author_rank: Super Contributor
timestamp: December 02, 2024, 05:37:50 am
content: Quote from: MasterT on December 02, 2024, 04:27:25 amWhat a piece of bullshit. Put up or shut up.

author: mawyatt
author_rank: Super Contributor
timestamp: December 02, 2024, 01:26:09 pm
content: Quote from: MasterT on December 02, 2024, 04:27:25 amSorry you can't hide behind the FBI, they don't have control of any of this.Where's all the MIT Text Books, magazine articles, and the TI, ADI and NS uses you claim show misguided use of phase and stability in op amp use??Where's all the MIT students that were taught this mis-information, or TI, ADI and NS Application Engineers and Designers that used this? Did the FBI lock all them up??This is total BULLSHIT and we're calling you out on it.Please don't run off and hide in the corner, keep it coming, this is the best laugh we've had in a long timeBest

author: MasterT
author_rank: Frequent Contributor
timestamp: December 02, 2024, 02:49:38 pm
content: Quote from: Bud on December 02, 2024, 05:37:50 amGet lost, stupid pig

author: MasterT
author_rank: Frequent Contributor
timestamp: December 02, 2024, 02:51:45 pm
content: Quote from: mawyatt on December 02, 2024, 01:26:09 pmYou are stupid or what?Undervover agent name provided, along with organization. Imbicile, your bla-la put in your f. ass

author: mawyatt
author_rank: Super Contributor
timestamp: December 02, 2024, 03:19:59 pm
content: Quote from: MasterT on December 02, 2024, 02:51:45 pmJohnson who?? Maybe the agent is Smith, or Jones, or Doe, or maybe 007 on loan from the MI6Where's all these misguided MIT students and TI, ADI and NS misguided engineers!!So Dr James Roberge @ MIT was teaching mis-information from his Operational Amplifiers Theory and Practice text under the influence of the Russian KGBhttps://web.mit.edu/6.101/www/reference/Op_Amps_J_Roberge.pdfCome on Bozo, as already said,Put Up or Shut Updon't hide behind the skirts of the FBIBest

author: MasterT
author_rank: Frequent Contributor
timestamp: December 02, 2024, 03:45:50 pm
content: Quote from: mawyatt on December 02, 2024, 03:19:59 pmNobody hiding, what I say: you are bunch of idiots pretending to be a human beans. Your dumpb stupid AI that I'm talking with even more stupid.Go and fuck yourself, fucking Moron, from gorrila servise.

author: mawyatt
author_rank: Super Contributor
timestamp: December 02, 2024, 04:18:04 pm
content: Quote from: MasterT on December 02, 2024, 03:45:50 pmIt's folks like you that ruin a perfectly good discussion about Op Amp Stability then get all defensive because they don't understand the subject, feedback stability in this case, then try and cover up with total BS like your Russian KGB ramblings about MIT, TI, ADI, NS and such.From your comments, suspect that the TI Op Amp is fine and it's your lack of knowledge and understanding wrt to op amp stability that make you think its a crap Op Amp.If you want to see a "fucking Moron", stand in front of a mirror my friend

author: MasterT
author_rank: Frequent Contributor
timestamp: December 02, 2024, 11:40:13 pm
content: Quote from: mawyatt on December 02, 2024, 04:18:04 pmImbecile, have problem like dislexia? I already say that:1. I'm an author of stability theory.2. I'm the best mathematician in the world3. The best electronics enginneer that was ever born4. TI - crappy company, stealing design on black market, their dumb stupid engineers never understand how it's works. O'k to full around chinesian monkey , or australian aboriginal idiots. You just cann't imagine how intelectual property theft cases known to me, as an inventor.5. Western doesn't capable to produce ultrasonic weaponry for the same reason, lack of brain tissue to solve differential equation 280-degree.

author: gnif
author_rank: Unknown
timestamp: December 03, 2024, 12:35:07 am
content: @MasterThas been banned for multiple forum infractions.