Chips with built-in RFI protection - Page 1
Forum section: electronics / general

author: mawyatt
author_rank: Super Contributor
timestamp: August 23, 2021, 03:10:56 pm
content: Noticed that some precision op-amps are stating they have some level of RFI built-in suppression. How widespread is this with newer chip designs?Best,

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 07:01:47 am
content: Seems that no one knows or caresI have noticed that TI is making a big deal of it and datasheets of their newer opamps for industrial market (and some audio too, like OPA1656) show plots of "EMIRR".NE5534 had some distributed capacitance over input stage collector load resistors 45 years ago; not sure what other purpose that could serve given the high RC corner.

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 07:28:19 am
content: You noticed right, I also see this being marketed lately a lot, even for bog standard parts like TL071 where TI has new "improved" series TL07XH that claim " High ESD (1.5 kV, HBM), integrated EMI and RF filters"...I was actually thinking of ordering some to see what it actually means, because datasheet doesn't specify a single number to that regard, except ESD resilience.No mention what EMI and RF filters do, what are the characteristics or how it was measured and how can be verified..Is it RF filters in signal path? Is improved PSRR on power inputs? What ?But it has a typo where unity-gain bandwidth became "Utility-gain bandwidth" in some tables ...In layman terms, if that means that bass guitar amplifier will be more resilient to those pulses you get when you put your GSM phone nearby, just by changing out old TL071 to new TL071H that would be great.But it won't. That is all about circuit and layout of the components, grounding and shielding.So I really don't know what they mean by it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 25, 2021, 08:34:59 am
content: I don't have anything quantitative to contribute, I've just noticed it in a few parts.It does indeed appear effective against input rectification, particularly at the high frequencies where the attenuation is strong.Most do not plot attenuation/immunity unfortunately; perhaps the same structures are used for all parts (why not copy-paste them, right?) and we can assume typical response?Quote from: 2N3055 on August 25, 2021, 07:28:19 amIt will! Immunity certainly depends on all those things, but it is the product of all factors together, and dropping one of them by a solid 20dB or greater is an unambiguous win. Not bad for not having to rev the PCB.You do need it in all low-level signal paths, and you do need to avoid unfiltered signals into discrete semiconductor junctions, which might not be so easily managed in guitar pedals/amps specifically. But at least you aren't being held back by the overabundance of RF-susceptible ICs, and on-board filtering and grounding can be relaxed to a certain extent.Tim

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 08:42:05 am
content: They define it as a sort of immunity to amplitude demodulation of out-of-band RF.https://www.ti.com/lit/pdf/sboa128That being said, given how laconic the TL07xH spec is, I'm not sure if it really was tested for "EMIRR" or "EMIRR IN+" by their own nomenclature... Also, no specification is given on the old part for comparison purposes. Good question to ask their tech supportI wanted to tear one down but they aren't very widely available yet.editIs it just me or is the new part really a flicker noise monster with twice the amplitude and corner at several kHz? Are they even serious?QuoteFuck. Now that's starting to look like they have rebranded one of their CMOS opamps. Note the lack of J in front of FET. This cannot be real

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 09:12:27 am
content: Quote from: T3sl4co1l on August 25, 2021, 08:34:59 amTim, thanks!!As I said, I plan to order a handful and try. If if does work that way, that is actually great news. Even few dB less for what is basically free upgrade is welcome.But as you rightly noted, it is hard to suppress outside world influence on things that are directly connecting to the outside world, and guitars are quite good antennas for all kinds of crap....Best,Sinisa

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 09:14:03 am
content: Quote from: magic on August 25, 2021, 08:42:05 amHeh, good catch.. this DOES call for a closer look..

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 09:20:59 am
content: Those assholes really did itThey think we are moronsLook at these two consecutive revisions of the datasheet.CTRL+F "JFET" in SLOS080O: nothing found.

author: JPortici
author_rank: Super Contributor
timestamp: August 25, 2021, 12:14:50 pm
content: Wow!BTW: Current revision of the datasheet is "S"There was this rumor i have no idea where i've heard it, might have been back in school so at least 10 years ago.. that TI had actually manufactured a metric crapton of wafers for the TL07x, LM13700 many years ago, they were not in production anymore and someday stock would have ended.Yes it sounds a rumor from a guy whose uncle was working for TI but maybe.. maybe..

author: DiTBho
author_rank: Super Contributor
timestamp: August 25, 2021, 12:27:34 pm
content: JFET -> _FET, this must be clearly a typo, ain't it? ain't it?(or should I start worrying?)

author: DiTBho
author_rank: Super Contributor
timestamp: August 25, 2021, 12:35:53 pm
content: Anyway, "FET" is the super-class of devices:junction field-effect transistor -> JFET is member of FET classmetal–oxide–semiconductor field-effect transistor -> MOSFET is member of FET classmetal–nitride–oxide–semiconductor transistor -> MNOS is is member of FET classinsulated-gate bipolar transistor -> IGBT is member of FET classso, "FET" means nothing in this case, which one? -> it must be a typo, cannot be anything else

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 01:29:14 pm
content: In Texas Instruments datasheets there is exactly one thing that "FET input" can possibly mean. Take it from the horse's mouth:They know how to ride the audiophool hype train when they have an actual JFET product to sell:Quote from: JPortici on August 25, 2021, 12:14:50 pmWell, the old TL072 is still for sale for now.

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 02:46:08 pm
content: Quote from: magic on August 25, 2021, 01:29:14 pmProblem is that new "improved" one has almost order of magnitude more noise in audio range and going down to DC it shoots towards sky..It has some better specs, it is faster, lower input bias current, etc.It is different enough that it deserves different name : TLM072It might not be drop in replacement at all, depending of your circuit..I'll stick to NJM072 ...

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 06:22:14 pm
content: Sadly JRC has nuked most of their jellybean products a year or two ago. I doubt that 072 made it through.I suppose TI undercut them on price offering parts that more accurately follow the original 1970's specsI found TI's jellybeans, including OP07, to have more flicker noise than competition. And I'm talking legitimate second source bipolar chips, no "next-generation" rubbish.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 25, 2021, 06:47:34 pm
content: The TL072H looks really a bit different than the normal one: nearly more like an TLE2071.There are some improvements in some aspects, but not so much for audio. By todays standard the TL072 is no longer a good choice for audio - more like a low cost OP that has input common mode range close to the positive supply.EMI filtering is now quite common with AZ OPs. The ADA4522 has some specs on it. It is not just the expensive one from Analog, but also cheap ones from Microchip. Chances are that without sich filtering the copper stabilized OPs may be quite sensitve to RF and with increasingly more phones and WLAN this can become an issue.

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 07:08:42 pm
content: It's not even remotely comparable to any classic JFET part and it smells a lot like CMOS.Output saturation curve - straight line, starting from 0V at 0mA. Not only is it R2R, but a bipolar part would typically have some minimum saturation voltage and less output impedance when saturated.Input offset vs common mode: discontinuous at mid-supply, like in R2R inputs but at a different threshold.PSRR vs frequency: that one is weird too, equal on both sides.

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 09:54:38 pm
content: Quote from: magic on August 25, 2021, 06:22:14 pmNJR shows them as active product ..https://www.njr.com/electronic_device/products/NJM072C.htmlThey have few thousands of them on Mouser..

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 10:12:29 pm
content: Quote from: Kleinstein on August 25, 2021, 06:47:34 pmThere are still many devices in music world that use them. They are still good enough for guitar amps, even for a first preamp stage... Some pro bass amps (like MarkBass) use them in many models.Even if you wanted to do better, only first stage would need to be a quieter amp... For tone shaping circuits they are all you need.

author: magic
author_rank: Super Contributor
timestamp: August 25, 2021, 10:18:37 pm
content: Quote from: 2N3055 on August 25, 2021, 09:54:38 pmInteresting, I will have to look at their lineup.Note that it's a C suffix part. There is something weird going on with certain parts appearing with C suffix in parallel with old ones or after old ones have been discontinued (I can't find the old NJM072 anymore). I first noticed it with NJM5532, where the new variant in SO8 probably involved a die shrink or they would have offered a SO8 long ago. The C variants are only sold in SMD packages while the old ones in all the packages they have always been.https://www.njr.com/electronic_device/products/NJM5532.htmlhttps://www.njr.com/electronic_device/products/NJM5532C.htmlhttps://www.njr.com/electronic_device/products/NJM4558.htmlhttps://www.njr.com/electronic_device/products/NJM4558C.html

author: 2N3055
author_rank: Super Contributor
timestamp: August 25, 2021, 10:40:30 pm
content: Quote from: magic on August 25, 2021, 10:18:37 pmThey are not hiding NJM072C is modern redesign, but specs are very similar to standard TL072 and it is JFET for sure. That one I'm sure would be drop in replacement for classic TL072. In fact they usually have lower noise and are very good.

author: magic
author_rank: Super Contributor
timestamp: August 26, 2021, 05:30:08 am
content: Presumably there is nothing wrong with their new parts. But it's weirdOne consequence is that you can no longer get a DIP 072 from them.BTW, TI's could be called TLC072 in accordance with their old naming scheme.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 26, 2021, 05:56:18 am
content: There is an TLC072 already (looks more like an improved version of the TLC272).The naming of the TL072 H is really confusing. It looks more like a lower cost version of the OPA2991 / TLV9352.They really should have given it a different name.A rail to rail design with the cross over between the stages in the middle of the range is odd. That can cause quite some nasty surprised.

author: magic
author_rank: Super Contributor
timestamp: August 26, 2021, 06:09:31 am
content: Yep, I too went to their parametric search and these parts are about the only ones rated for 40V supply that they have.I'm not really convinced that it's RRI because the discontinuity is less severe than in OPA2991 and there is some sign of trouble starting at 2V above the negative rail. But then I don't know what the mid-supply discontinuity is. Some X-Files stuffIt could simply be that they replaced the P-ch input stage with N-ch which is the reason for all the input-related differences (noise, offset) if the process was optimized for P-ch. And they sell it as 072 because it addresses the "I want something cheap with input range to Vcc" problem.Still,

author: magic
author_rank: Super Contributor
timestamp: August 26, 2021, 07:30:43 am
content: JRC also plays the RF immunity gamehttps://www.njr.com/electronic_device/products/NJM8087.html

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 26, 2021, 11:56:05 am
content: Quote from: magic on August 25, 2021, 07:08:42 pmSuspect the Vos vs. Vcm is an artifact of the measurement. Wouldn't make any sense for that to happen if it's an RRI structure, how would it know what GND is? It's certainly NOT an RRI type, as it doesn't include GND, but does include VCC as any other classic JFET input stage.The output range is suspicious, and at the very least must be common-emitter, but could in fact be BiCMOS. It's also PTC, i.e. the apparent Rds(on) increases with temperature.Slew rate appears to be the boosted kind, with a high-slew bypass at high |Vin| and smooth settling otherwise. Rates are somewhat asymmetrical, again suggesting a monopolar input stage.Ed: oh also, the input bias current, is very clearly not a junction. JFET gate leakage increases exponentially with temperature, from <pA at RT to ~nA at max. The -H shows pretty flat ~pA, ticking up only a little at high temp. That, plus the input noise being literally worse than a fucking TL431, is pretty damning.Tim

author: magic
author_rank: Super Contributor
timestamp: August 26, 2021, 12:55:04 pm
content: Well, the most damning evidence I found so far is the product's own web page.QuoteQuote from: T3sl4co1l on August 26, 2021, 11:56:05 amI agree it makes no sense, although it could know mid-supply if it wanted to (not ground) by a resistive divider. But it's inconceivable what technical or even marketing reasons could motivate that.There is no such artifact in datasheets of similar chips listed by Kleinstein, that's the strangest thingI am not sure why I should disbelieve the manufacturer if it's them telling me that their product sucks.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 26, 2021, 02:42:06 pm
content: Quote from: Kleinstein on August 26, 2021, 05:56:18 amThat is my biggest beef with this whole thing. They should have given it a different name. Even the curves on the datasheet are split between "H" and "non-H".

author: Kleinstein
author_rank: Super Contributor
timestamp: August 26, 2021, 04:36:28 pm
content: There are a few chips with odd part numbering: take the LM2904 and LM2902 and guess which is dual and quad of the same internals.To add to the confusion they have a TL082H too - chances are it's the same internals.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 26, 2021, 08:08:03 pm
content: Quote from: Kleinstein on August 26, 2021, 04:36:28 pmThese weird numbers are inherited from National Semiconductor, so blame on them I guess. Years ago I had the same confusion with Burr Brown's super opamps OPA541, OPA548 and OPA549 - guess which one is the most powerful?Quote from: Kleinstein on August 26, 2021, 04:36:28 pmIndeed it is the same case.