Why Your 4.7µF Capacitor Becomes a 0.33µF Capacitor - Page 1
Forum section: electronics / projects

author: ketil b
author_rank: Regular Contributor
timestamp: October 27, 2013, 09:25:12 am
content: Hi allJust found this via reddit and thought it might interest sume of youhttp://www.maximintegrated.com/app-notes/index.mvp/id/5527

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 27, 2013, 09:57:04 am
content: Something even seasoned engineers often not realise.A very quick and dirty solution could be to always use 50V rated ceramics in your lets say <10V circuits. A 50V ceramic at 5 or 3.3V is very close to its rated capacitance. Saves u a lot of datasheetreading and u dont have to specify every ceramic in detail in the BOM.Ofcourse goodluck finding your 0402 variants

author: Kjelt
author_rank: Super Contributor
timestamp: October 27, 2013, 10:09:09 am
content: Yes this is quite a problem if you are not aware of this, that is why I suggested it as a subject for a fundamental friday:Quote from: Kjelt on September 07, 2013, 01:52:38 pm

author: tszaboo
author_rank: Super Contributor
timestamp: October 27, 2013, 11:23:24 am
content: Once I was measuring 96% loss:http://nandblog.com/avoid-y5v-capacitors/

author: mzzj
author_rank: Super Contributor
timestamp: October 27, 2013, 12:25:22 pm
content: Quote from: NANDBlog on October 27, 2013, 11:23:24 amPlenty of people already know to avoid Y5V capacitors but don't really realize how bad X5R and X7R can also be, ie. -90% of the rated capacity for small high-capacity X5R or X7R caps.

author: nukie
author_rank: Frequent Contributor
timestamp: October 27, 2013, 01:08:14 pm
content: Newbie trap. Theres more to study about capacitors.

author: jmaja
author_rank: Frequent Contributor
timestamp: October 27, 2013, 01:20:45 pm
content: Quote from: DutchGert on October 27, 2013, 09:57:04 amIt's not really about voltage rating. In some cases the lower voltage rating one can have higher capasitance at 5 V than a higher one. Voltage spec is about capacitance durability not about staying close enough to it's rated capacitance.Best choise is to look at the specs (not typically in the datasheet) and choose big enough size. 22+ uF at 5 V you really need to pick 1210. Requiring 50 V makes you choose a bigger package, but then you can select the lower voltage version of that package as well.I always look the DC biases for critical caps from these:http://www.tdk.co.jp/ccv/step1.asphttp://www.kemet.com:8080/webspice/http://ds.murata.co.jp/software/simsurfing/en-us/index.html(this one is the easiest for comparisons)One X5R 0805 22 uF 6.3 V is ~6 uF at 5V and the 25 V version is 10 uFOne X5R 1210 22 uF 6.3 V is ~17 uF at 5 V and 25 V version 20 uFSo 1210 6.3V is a much better choise than 0805 25V for 5V DC bias.

author: SeanB
author_rank: Super Contributor
timestamp: October 27, 2013, 01:23:34 pm
content: And if you are dealing with high voltages then dielectric absorption can really be nasty.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 27, 2013, 02:15:47 pm
content: Quote from: jmaja on October 27, 2013, 01:20:45 pmI know its not about voltage rating. But a lot of times u don't want to specify all of your C's in detail and let procurement decide what is going to be on your board. Also, you want to use as much of the same to keep your BOM small and your production process fast.Thats why I said its a quick and dirty way of working aroudn this problem. If you simply pick a high rated version of lets say 50V for lyour 5/3.3V circuits you may not have the best compromise between rating, size and real capacitance but it saves u a lot of time designing and gives procurement a lot more freedom. The fact that u use a higher. Voltage rating automatically ensures the bigger physical size thats it about.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: October 27, 2013, 02:56:13 pm
content: Quote from: DutchGert on October 27, 2013, 09:57:04 amThe data in the linked article contradicts this. The only factors involved seem to be the physical size of the capacitor, the manufacturer and the dielectric used. The curves for caps with the same capacitance and physical size yet different maximum operating voltage overlaps perfectly.So using a 50V cap on a low voltage rail accomplishes nothing.

author: Rufus
author_rank: Super Contributor
timestamp: October 27, 2013, 03:19:57 pm
content: Quote from: ElectroIrradiator on October 27, 2013, 02:56:13 pm1210 does not specify physical size. The 3rd dimension is required and it can vary over about a 5:1 range.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 27, 2013, 03:21:18 pm
content: Quote from: ElectroIrradiator on October 27, 2013, 02:56:13 pmThere are no 50V ones in the graph.What I mean is that if u take a 50V one u automatically end up with a physical bigger cap that probably hasaboutthe same real capacitance at 3.3 or 5V as what u want it to have.Ofcourse u can find better ones if u look at the data but often u just want to be able to say to procurement "just place any A-brand 10uF 50V 1210 u can buy and it will be fine".

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: October 27, 2013, 03:33:36 pm
content: Quote from: Rufus on October 27, 2013, 03:19:57 pmFootprint then.Still trying to find enough datasheets with the relevant info on them to check for this.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2013, 03:53:22 pm
content: Here is another one: a freshly soldered ceramic cap decays at a rate of 1% the first hour, 1% the next day, 1% the next month and a 1% the next 2 years (it's a 1:25 ratio... 24 hours a day , 24 days a month , 24 months : 2 years).Heating the dielectric above 148 degree centrigrade resets the decay process !So: you can't make frequency stable oscillators with these suckers ! Worse. If you got the frequency spot on , don't reheat the cap : it'll reset !

author: jmaja
author_rank: Frequent Contributor
timestamp: October 27, 2013, 04:24:59 pm
content: Quote from: DutchGert on October 27, 2013, 09:57:04 amIs there some standard for that or does it just happen to be so? You can find many 35 V caps, which give poor performance at 5V DC (e.g. 0805 10 uF 35V is only about 4 uF at 5 V), but 50V caps seem to be clearly better (=bigger footprint).If you compare all the X5R/X7R 1210 10 uF caps Murata has available, the worst one is one 16V rated giving 8.5 uF at 5 V. All the rest (a few 10 V ones included) give more than 9.5 uF. The one giving "only" 8.5 uF is a thin one. It is only 1.0 mm thick while all the others are 2.2 or 2.7 mm. Still at 10 V all the others give more than 8 uF and the thin one 6 uF. The 50V ones are 9.8 uF at 5V and 9.1uF at 10V.50V ones are clearly more expensive, if that matters.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: October 27, 2013, 04:26:55 pm
content: Oh this is gold.There is no rule that a higher VW cap of the same footprint and capacity is inherently better, as I just found a counter example: 10 uF 1206 size muRata GRM31CR71 series, available from 6.3 to 25VW. All of these are the same thickness, 1.6mm. The 10V edition is noticeable better between about 2.5(!) and 10V, compared to the 25V type.For other types, like the 0.1uF 0603 size GRM188R71 family, 0.8mm thick, it doesn't matter one iota what VW you use between 0 and 6.3V. There is a worst case difference in capacity at 10V of about 5-7% between the 10V and the 50V specimen. The major differences are near the rated maximum voltages for each type, where you really need the elevated ratings. For instance the 50VW is down about 50% at 50V, while the 25VW is down 45% at 25V.So tl;dr: You better double check in each and every case, if this parameter is important to you.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 27, 2013, 05:15:09 pm
content: Quote from: jmaja on October 27, 2013, 04:24:59 pmNo, there is no standard, its just that in my experience a 50V usually is a step bigger in size so 'automattically' gives u better (satisfying) performance when using it at 3.3 or 5V.Thats all, i wont argue that outting considerable time into each ceramic u use will give u better results. Ofcourse it does.But it also increases your development costs (but could be lowering your BOM cost) and makes your BOM and procurement considerably more complex.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 27, 2013, 05:26:22 pm
content: Quote from: ElectroIrradiator on October 27, 2013, 04:26:55 pmNobody said that. I think we can agree that physical size matters in this case. I am mentioning 50V in 5V and 3.3V circuits for a reason, not because the voltage rating is higher but because it fairly safe to say that it ensures the physical size needed to function properly at 5 or 3.3 volt because it will be close to the value u want it to be at that given voltage.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2013, 06:24:07 pm
content: Hang on guys. There is more.... Every cap maker has his own dielectric . And certain series behave differently than others. Never assume that a cap from tdk behaves the same as a murata...Ceramic caps drift under temperature, current, voltage, frequency , dc bias , size and dielectric material. Even the electrode material has an impact.NPoO dont drift under temperature but they are susceptible to dc bias.BaTio dielectric based also exhibit microphony efect. Send a pulsing signal throught them and they will 'sing' audibly ! Vibrate the board and you will get ripple voltage !That is why those barium titanate dielectricc aps like x7r are a nono in filters or amplifiers that will be mounted in vinration rich environment !

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: October 27, 2013, 06:29:47 pm
content: Quote from: free_electron on October 27, 2013, 06:24:07 pmAll of which means there are no rules of thumb, and that caps cannot be expected to substitute between brands. You always need to check the parameters, which are important to your application.

author: free_electron
author_rank: Super Contributor
timestamp: October 27, 2013, 07:07:25 pm
content: Quote from: ElectroIrradiator on October 27, 2013, 06:29:47 pmbingo !that is why cpaacitor mkers have software avaialble that will give you the plots for each and every cap they make. that osftware is free.i have already posted the link to such software on the forum here.Part of what i do professionally is tweak switching regulators . tuning the input and output caps is a tedious work. frequently we connect network analysers and sweep the impedance plots over frequency with bias applied to the caps. i call the cap makers and tell em : here is what i need : they run a couple of scenarios , send me samples , i build the board and verify it works fine with our switchers. once a good outcome is found you do not touch it. that is the bill of material going into production. there will be NO substitutes !

author: tszaboo
author_rank: Super Contributor
timestamp: October 27, 2013, 08:20:18 pm
content: Quote from: free_electron on October 27, 2013, 06:24:07 pmWell you can make "acceptable" filters with NP0 or COG capacitors. X5R and X7R is suitable for power supply, bypassing and such applications. I really expect a superior technology to be available in mass quantities in the near future, as there is the demand for it. In fact we already have it in the 18-20 bit SAR ADCs and zero drift PGAs. But it is time to give something for the discrete guys.

author: Kjelt
author_rank: Super Contributor
timestamp: October 27, 2013, 09:38:14 pm
content: I really wonder the following:So where and when did we accept in this industry that capacitors are allowed to be graded as X uF and Y Volts when they only will reach that X uF's at 1/Y the Voltage, and only have 1/Xth the uF's at Y volts? I sense a deliberate form of false information.If this is allowed what keeps electrolytic capacitor manufacturers from doing the same thing? This can become a sliding scale.

author: SeanB
author_rank: Super Contributor
timestamp: October 28, 2013, 05:00:23 am
content: Electrolytics already have a +50 -85% rating so how could it be worse? At least they are not so voltage sensitive.

author: DutchGert
author_rank: Frequent Contributor
timestamp: October 28, 2013, 08:26:42 am
content: Quote from: free_electron on October 27, 2013, 06:24:07 pmNobody argues with that free_electron. Just sharing a rule of thumb I myself find very useful.

author: Carrington
author_rank: Super Contributor
timestamp: October 28, 2013, 02:41:20 pm
content: Quote from: free_electron on October 27, 2013, 07:07:25 pmPlease. Where are these links?Thanks.

author: Unknown
author_rank: Unknown
timestamp: October 28, 2013, 02:48:53 pm
content: A Google search quickly found this:https://www.eevblog.com/forum/beginners/esr-meter/msg109145/#msg109145

author: free_electron
author_rank: Super Contributor
timestamp: October 28, 2013, 02:56:42 pm
content: Quote from: NANDBlog on October 27, 2013, 08:20:18 pmOf course. That's what i said. NPO dont use BaTi as a dielectric so there is no reset behavior due to soldering. C0g is the jedec name for NPO. C0g is in the same line as x7r and y5v naming convention. Letter number letterNP0 means negative positive zero. No temperature drift.

author: Carrington
author_rank: Super Contributor
timestamp: October 28, 2013, 03:35:51 pm
content: Quote from: alm on October 28, 2013, 02:48:53 pmalm thank you very much.It is the same software that I had. Excepting Murata's SimSurf. Instead I had used Murata Chip Capacitor Characteristics Data Library.UltraCap also is interesting, although it is not the same type of software.Woow this forum is great.

author: Poe
author_rank: Frequent Contributor
timestamp: October 28, 2013, 05:16:52 pm
content: Quote from: free_electron on October 27, 2013, 03:53:22 pmBecause of the trend to replace expensive seasoned engineers with cheap green engineering students, our company accepted the return of >100k PCBAs due to "poor solder joints". Fresh out of college myself, I discovered the actual cause was due to this 'aging' effect a month later while reading this tech paper:http://www.johansondielectrics.com/technical-notes/product-training/basics-of-ceramic-chip-capacitors.htmlReally wish companies still understood the value of mentor programs. A single engineer with a dozen years experience would have immediately known their timing circuit should not have relied on a cheap capacitor... and that they could not hold calibration because their techs just got done reflowing the cap.

author: c4757p
author_rank: Super Contributor
timestamp: October 28, 2013, 06:02:49 pm
content: *I* know not to use a ceramic cap for timing and I have no industry experience! It's too bad that the companies don't have mentor programs, but it is equally sad that the students don't have the motivation to pursue extracurricular experience before they graduate.

author: Kjelt
author_rank: Super Contributor
timestamp: October 28, 2013, 06:39:59 pm
content: Quote from: c4757p on October 28, 2013, 06:02:49 pmSad that you blame the students while the real blame actually IMO lies with the colleges and universities that skimp on the education and society that pressures students to graduate asap. What is really shocking is the difference in educational institutions, a MscEE from a midlevel university should be equal to an MscEE from MIT, that this is obviously not the case is proof of the problem that a level of education can not really be measured in a degree.Then there is the big difference between dry theory and the cold and harsh real world of electronics, the world is moving fast and there is a lot to learn even for seniors.The given problem of scrapping >100k PCB's by a certain company because they fired the (too expensive) seniors and let a (cheap) junior design and create the pcb's without rigorous testing or second opinion is just what they deserve, you get what you pay for and I just can't helpmy ass off. I just hope that the responsible manager is still there and now has to inform his management about the loss.

author: westfw
author_rank: Super Contributor
timestamp: October 29, 2013, 02:28:17 am
content: QuoteOk, I'm curious. Did anyone with a BSEE or MSEE actually have a college class (or lab) that talked about the different characteristics of real-world capacitor types? I don't recall any such thing; I'm not even sure whether they covered polarized vs non-polarized caps. (too busy using calculus to figure out the capacitance of a plate capacitor with a non-uniform dielectric. That was SO useful!)

author: IanB
author_rank: Super Contributor
timestamp: October 29, 2013, 02:42:06 am
content: Quote from: westfw on October 29, 2013, 02:28:17 amI doubt it. This would be called "on the job learning".It's a similar story in my field (chemical engineering). As a student you learn precious little about the practical operating characteristics and limitations of real equipment. (Some engineering schools are trying to correct the balance here, but it's far from being a universal philosophy.)The thing is, it is easier to learn the practical stuff hands on at work and the underlying theory in college than the opposite. If you got taught the practical things in college and had to learn the theory on the job, you would be left up the creek without a paddle.

author: c4757p
author_rank: Super Contributor
timestamp: October 29, 2013, 03:01:54 am
content: Quote from: Kjelt on October 28, 2013, 06:39:59 pmThis is why I saidextracurricular. So far, with the exception of Semiconductor Physics, I have yet to take a class which I did not already know in depth before the class started, because I'm studying something that interests me and I put in the effort to teach it to myself before I even study it in school.When I was studying CS, a good two thirds of the students were like that. There were many somewhat proficient programmers in my freshman Intro to CS class, and they improved as the curriculum became more advanced, always ahead of the curve. In EE, I am the only one I have met who does that.And if you want to "blame" society, that's fine, then society is the reason they have no motivation. But the point stands that they do not, and that I think this is sad. Not sad in a sarcastic way, just frowny-face sad.In my electronics lab, I work with a kid who can't look at a pinout diagram and figure out what goes where, and he's quite content to sit back and just let me do it. Part of me doesn't want to be his lab lackey, but the other part understands that if I try to force him to do more than punch buttons on the scope, we'll be there all damn day. At least he seems to be genuinely interested in some parts of the field, so I talk about them as much as I can and try to teach him practical knowledge about the circuits, and hopefully I can instill some desire to learn even more. Seems to be working, a bit, I thinkApologies for the thread derailment, I'll shut up now.Back to capacitors?

author: george graves
author_rank: Super Contributor
timestamp: October 29, 2013, 03:22:13 am
content: Quote from: Kjelt on October 27, 2013, 10:09:09 amGood idea. Hope Dave does it.

author: Kjelt
author_rank: Super Contributor
timestamp: October 29, 2013, 09:44:21 am
content: Quote from: westfw on October 29, 2013, 02:28:17 amCome on you must have had the difference in ESR, frequency response between elco's, tantals and ceramics? Maybe the differences between MKT, MKP and the likes?We didn't have much SMT unfortunately, was not a main topic back then.Maybe it also depends on the graduation topic. In our schoolsystem we have a couple of years general classes, lots of math and theory in them, then you choose the direction you like to graduate and get more in depth knowledge of that topic and surroundings. Unfortunately I choose Technical Computer Science so I had a lot of digital electronics theory but too little of the analog stuffQuote from: c4757p on October 29, 2013, 03:01:54 amHold on I didn't say that. I wonder how a student without motivation can still graduate, explain that to me? Because if that is the case then there is something wrong with the educational system don't you think? There could be tons of reasons for this. From my own experience I remember some classes where the first lecture was given by a professor that came from the industry, he held a very good lecture that made everyone enthousiastic and energetic to follow and pass the course. The rest of the classes were given by an assistant that just read page and page of the textbook and all the energy was gone.Another class was given by an academic professor that the entire hour just wrote formula's on the board and showed how a great mind he was. No energy there.So what I am trying to say is that if there is more then 10% unmotivated students, how can you blame the students? Why are they unmotivated and why is the university/college not stopping them after a semester if they have no motivation?QuoteI agree, very sad.QuoteI understand that this is the easiest way out for you and I do not want to judge, but do you see that in this way you are part of the system? I don't know the person so maybe if you enthousiastic try to transfer knowledge he panics, on the other hand maybe you give him that sparc of energy that he needed to go read more about his job en study and go for example to this forum and show him there is more then just turning knobs and magical things happenQuoteGreat , that is what I mean, I'll take my hat of for you sir.Quoteyep same here, let's get back on topic.

author: c4757p
author_rank: Super Contributor
timestamp: October 29, 2013, 11:43:41 am
content: Not to continue this more, but since you asked me a few questions, I'll slip in answers... I really did intend to comment on the topic.Of course any student who graduates has at least the motivation to do exactly as he is told. That's not useful motivation, he might as well do that for the manager at the local McDonalds. I meantinternalmotivation to learn about things that interest him.Again, I never said I "blame" them for being unmotivated. If there are more than 10% unmotivated students, there stillare unmotivated students, which is all I said. And I don't think the university is to blame - the students areadultsfor Christ's sake. We ought to be able to expect that once a child reaches adulthood, he'll have a somewhat healthy mindset about learning and work ethic. A motivated character has to be shaped all throughout childhood, and if the blame is to rest anywhere, it is with the society that allows children to be pushed through grade school the way they are, as little test-taking machines: supposed to be 250% "motivated", but only to do exactly as they're told, screw any personal curiosity and passion (and for the "gifted" ones, milk as much extreme effort out as you can at a young age so they're burned out by 18).Now, to contribute to the thread, because this is interesting to me as well:While anyone who really depends on capacitors regularly will eventually develop an intuition for just how much capacitance is left at a given bias, I really, really wish manufacturers would start including this data in the datasheet!! It's not like it's hard to measure, I've done it myself on an LCR bridge with a significantly larger bias-blocking cap and bias fed in through a 1meg resistor... But even though that Maxim document says to always read the datasheet, lots of datasheets don't even specify voltage coefficient!

author: jmaja
author_rank: Frequent Contributor
timestamp: October 29, 2013, 12:29:14 pm
content: Quote from: c4757p on October 29, 2013, 11:43:41 amThat is so true! I first run into this problem last spring (no, I haven't studied EE, just Physics including one course in electronics, but quite a few courses on quantum physics including what happens in e.g. a PN junctions at that level):https://www.eevblog.com/forum/projects/ceramic-capacitor-dimension-for-a-buck-converter/msg224126/#msg224126I had read several cap datasheets very carefully and yet this was a total surprise for me. And it wasn't at all easy to find the manufacturer provided more detailed data. There were no links to them from their websites etc. I didn't get any feedback when I asked about it from online questionary. Once I understood to put the keyword "spice" in search engines I started to find out the online calculators and program downloads.Still I don't know where is this data for e.g. Samsung capacitors, which I would otherwise have used in some cases.Another thing about ceramic caps: Is there a way to know beforehand will there be audible noise or not? Can you choose a ceramic one (still with high capacitance and low ESR), which wouldn't make noise. One of my buck converters makes a bit annoying noise, but only at very low load. There was a warning about this in the converter datasheet, thus it didn't come as a surprise.

author: c4757p
author_rank: Super Contributor
timestamp: October 29, 2013, 12:32:36 pm
content: Quote from: jmaja on October 29, 2013, 12:29:14 pmI'd just get a bunch of samples and test them! Drive them at the highest ripple current you can do without damaging them through a range of expected operating frequencies and see if they do anything.Are you sure it's not the inductor?

author: jmaja
author_rank: Frequent Contributor
timestamp: October 29, 2013, 12:46:11 pm
content: Quote from: c4757p on October 29, 2013, 12:32:36 pmNo. They are side by side, so it's hard to tell. But seems most likely, since the datasheet says: "The LTC3630’s burst frequency depends on the load current, and in some applications at light load the LTC3630 can excite the ceramic capacitor at audio frequencies, generating audible noise. If the noise is unacceptable, use a high performance tantalum or electrolytic capacitor at the output."

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2013, 01:41:59 pm
content: I've heard about this before.Here's an article I read awhile ago about using a ceramic capacitor as a varactor. It's probably not much use as a practical VCO, unless it's used to make something like a siren which isn't critical.http://www.edn.com/design/analog/4334383/Multilayer-capacitor-doubles-as-varactor

author: westfw
author_rank: Super Contributor
timestamp: October 29, 2013, 05:44:53 pm
content: QuoteNope; never. I mean lossy dielectrics were part of the theoretical physics in the EM class(es), but I don't recall it ever being related to practical circuit design. (OTOH, that was a long time ago, so my memory could be faulty.)It COULD have been a good topic for the lab classes, but those were rather useless (IMO) collections of "build this circuit using the components provided and learn to use various pieces of lab equipment by measuring the behavior and writing it up." And the usual measurements were of semiconductor characteristics.Has anyone seen an online class covering real-world component selection?I took a look through MITs open courseware and didn't see anything that jumped out, for example.(I think you can blame a lot of the current neglect on the prevalence of digital circuits. People don't actually need a 10uF 6V cap, they need "a cap that is small enough to sprinkle around the power pins of my microprocessor, and will adequately bypass noise on the power rails." As the requirements get tighter, the microprocessor datasheet gets more specific about "use THIS capacitor and put it HERE", and the actual operating point values are a bit irrelevant. If you DO have an analog segment of your design, you're still following an app note that warns you when cap parameters are particularly important, or tells you what type of cap to use.)

author: c4757p
author_rank: Super Contributor
timestamp: October 29, 2013, 05:48:58 pm
content: Quote from: westfw on October 29, 2013, 05:44:53 pmSo in other words, they're training a generation of useless engineers who are only capable of crapping out the most popular designs, and must defer to arealengineer who wrote them a nice, shiny app note when they have to do something out of their comfort zone.Sounds about right.

author: Neilm
author_rank: Super Contributor
timestamp: October 29, 2013, 06:56:17 pm
content: When I went to uni, the course was mostly about digital systems. Analogue was covered, but it only really went for op-amp circuits. Mostly assuming the signal was going into an ADC. Lots of control theory, maths, Fourier and Z transforms, IC design but I don't recall anything about component constructions. I don't even think there was anything on different caps or resistor types.Result being I learned the hard way that caps have voltage co-efficients, vary with temperature and the like.