Do bypass caps invert the signal? 1010101 to 0101010 - Page 1
Forum section: electronics / beginners

author: Beamin
author_rank: Super Contributor
timestamp: August 10, 2018, 10:31:01 pm
content: I watched the video on bypass caps and since they re put in series on high speed lines on processors wouldn't it invert the signal? The cpu/mcu puts out a pulse it charges up the cap then the cap discharges on the next pulse sending it along: wouldn't this exactly invert the signal? Not the caps the smooth out power but when you see them around/under a high speed chip. Or do electron not work like this? Data lines are kind of like RF due to the speed.On a related note is there a limit how fast processors can go? I notice on pcbs they go to great lengths to make the traces the same length and other things but when do these start turning into antennas that are giving off GHz signals, so much that it just won't work outside a silicon die?

author: Zero999
author_rank: Super Contributor
timestamp: August 10, 2018, 10:51:23 pm
content: How the heck can a bypass capacitor invert the signal?Post a link to the video. No one knows what you're talking about without having seen the video first!The only thing I can think of is there's an RC time constant and the signal is being shifted by 180o, but that's not how one would use a bypass capacitor, which should be high pass.

author: enjoy.cowboy
author_rank: Contributor
timestamp: August 10, 2018, 11:14:29 pm
content: Thats not how this works at all. The bypass cap will filter out some frequencies to ground, it doesnt tap off into another data line. All the bypass cap does is cut some of the judder and flutter in the data line/clock line so the noise doesnt add up,when going to another tranny. Also the DC phase shift wouldnt cause the digital signal to be inverted. If that would be the case, all we would need to build a computer would be enough caps to build nand gatesThe signal measured at the cap cannot be considered logical, as well

author: iainwhite
author_rank: Unknown
timestamp: August 11, 2018, 12:29:57 am
content: @ Hero999I would guess it was one of these videos:EEVblog # 859 - Bypass Capacitor TutorialEEVblog #1085 - Bypass Capacitors Visualised!EEVblog #1081 - Are Bypass Capacitors REALLY needed?

author: hamster_nz
author_rank: Super Contributor
timestamp: August 11, 2018, 08:05:13 am
content: I think you have confused bypass capacitors (between a signal and ground) and coupling capacitors (between the source and sink for a signal).Coupling capacitors block any DC, but pass the high frequency digital data from the source to the sink. They acts is a high pass filter.A bypass capacitor allows any high frequency signal (usually noise) to go to ground. You wouldn't usually use them on a digital signal, only on the power.rails.

author: Beamin
author_rank: Super Contributor
timestamp: August 11, 2018, 04:03:26 pm
content: Quote from: enjoy.cowboy on August 10, 2018, 11:14:29 pmThat's what I was thinking of: phase shift; like in an RF signal where you can use it to change wave length of things without making it longer or shorter physically. Cap charges and no electricity flows, the other end becomes negative and electricity flows. Kind of like a rectifier doubles the frequency. No crossing of data lines don't know why you would do that.I also realized that was a hero999 post before looking at the name: Just so you know those type of responses' scare away beginners because they are afraid to ask questions because someone make think they are dumb. Fortunately that doesn't work on me because I have no shame... or rather I don't value the opinion of hostile people, choosing to ignore them, and their insecurities that they try to project onto others. Remember at some point EVERY ONE here had no idea of what an electron even was. What's an electron you ask? OMG that's a stupid question google it, the nerve, asking questions on the internet, god people are stupid... Then you say: "fuck this hobby I don't want to end up like those people." More parts for you right? There was an Arduino forum like that when it first became popular and most people didn't understand it. I watch the forum die, because every time a question was asked there would just be a hostile and/or way overly technical answer or, of course; "google it". Ironic because I'm sure that forum is not on google and that's where all the new members went and found better forums.

author: ataradov
author_rank: Super Contributor
timestamp: August 11, 2018, 04:08:16 pm
content: Quote from: Beamin on August 11, 2018, 04:03:26 pmHero999never said anything bad about you or your knowledge, he just commented on a way you asked a question.If you say you watched a video, then post a link to the video. There are a lot of videos out there, some are good, and some a bat shit crazy. Who knows what exactly did you watch.You don't have to be an expert on the subject, but learn how to ask question properly.

author: Beamin
author_rank: Super Contributor
timestamp: August 11, 2018, 04:27:14 pm
content: Quote from: ataradov on August 11, 2018, 04:08:16 pmI wasn't attacking him: I said I ignore those people. I replied with a friendly tip. If it makes you feel better I thought you were responding at first... Just kidding... And when I talk about videos on the electronics enthusiastvideoforum I am talking about the eevblog episodes, my other posts always include links. There is a chronic problem of people on technical forums responding this way, with this forum being an exception, hence it's popularity and beginner section. Honestly your avatar thing even says "I have informed you thusly" which can be seen as arrogant not as joking like I see it.But that's all before this turns into a back and fourth.

author: enjoy.cowboy
author_rank: Contributor
timestamp: August 11, 2018, 04:56:07 pm
content: Quote from: Beamin on August 11, 2018, 04:03:26 pmThe phase shift is between the voltage and the current. Yes, you could say that when theres postiive voltage on one end of the cap, theres a negative one on the other end, but that doesnt make it a NOT gate. When dealing with digitals, its either sink or source, and the cap is an analog component. So, no, the capacitor doesnt invert the signal, under DC it adds a phase shift but thats a different thing altogether to a logical (what a NOT gate does e.g. 01010 -> 10101). Bypass caps filter out low freq noise that the switching may carry to the next transistor

author: mikerj
author_rank: Super Contributor
timestamp: August 11, 2018, 05:37:17 pm
content: Quote from: Beamin on August 11, 2018, 04:03:26 pmIt a cunning ploy to encourage people to make an effort at helping themselves before seeking help, and when they do seek help they are encouraged to ask questions in an intelligent way. You mentioned a video you watched, but don't provide a link to it, and then say you are talking about bypass caps when you meant coupling caps. This kind of thing makes it enormously difficult to understand exactly what you are asking since it makes no sense.Even at this point I'm pretty sure no-one knows the thought process that made you think coupling caps can invert a signal. A single coupling cap is part of a single pole RC high pass filter, so the maximum phase shift would be close to 90 degrees, but in the frequency range that the coupling cap was chosen to pass, phase shift will be small.

author: amyk
author_rank: Super Contributor
timestamp: August 11, 2018, 05:40:23 pm
content: Quote from: ataradov on August 11, 2018, 04:08:16 pmThis, absolutely this. We're not psychic, we have no idea what you're thinking if you don't explicitly state it. You said you watchedavideo, so specify which one. The onus is on the asker to make him/herself not look like an idiot.

author: Beamin
author_rank: Super Contributor
timestamp: August 11, 2018, 07:57:40 pm
content: Quote from: mikerj on August 11, 2018, 05:37:17 pmI often don't know my terms so thanks for clarifying (A big reason why I sometime struggle with "googling" as bypass caps were not yielding results totally different thing.So the coupling cap gets charged by the logic chip sending out one pulse of data. Since it goes into a cap in series that pulse is absorbed into the cap. That pulse doesn't get sent out until the logic chip puts a new potential on the cap which would have to be negative to get the charge out. How does it do that? If I think of a light switch turning on/off connected to a cap it's not going to work until I somehow get the cap to discharge by reversing polarity or something this is what I don't understand.

author: Nerull
author_rank: Frequent Contributor
timestamp: August 11, 2018, 08:20:20 pm
content: Quote from: Beamin on August 11, 2018, 04:27:14 pmI hope you understand that "I need help with something but I refuse to tell you what" is just as annoying as overly critical pendant posts.

author: hamster_nz
author_rank: Super Contributor
timestamp: August 11, 2018, 08:24:34 pm
content: I will explain a bit better later, but at high frequency an idea cap acts as a wire, and at a low frequency it is if it isn't there.It is only in between these two regions where things get trick and you have to analyse things in detail bacause it is acting like a filter.

author: Nerull
author_rank: Frequent Contributor
timestamp: August 11, 2018, 08:27:47 pm
content: Quote from: Beamin on August 11, 2018, 07:57:40 pmIf the cap is properly sized, that's not what happens. Capacitors resist changes in voltage across them, so pulling one side of the capacitor up will result in the voltage at the other terminal going up as well, unless it is held low. The current flowing into one side of the capacitor will be equal to the current flowing out the other side. As long as the signal changes rapidly enough that it never fully charges the capacitor the signal passes through, with a phase shift.

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2018, 09:05:20 pm
content: Quote from: Beamin on August 11, 2018, 04:03:26 pmIf you ignore people who are tying to help, that's your loss.If you bothered to read the rest of the reply, you'll find I made some effort in trying to guess and provide, as gooder answer as possible.If you can't be bothered to spend five minutes looking for the video your question pertains to, then you're obviously not serious about this. This sort of laziness only insults those who are trying to help.

author: Jester
author_rank: Frequent Contributor
timestamp: August 11, 2018, 09:19:23 pm
content: If the goal is to invert a signal, an inverter costs about $0.1

author: rstofer
author_rank: Super Contributor
timestamp: August 11, 2018, 09:19:31 pm
content: Hero999 is one of the better responders. Look at his post count; he's been doing this for a very long time!Here's the problem: A lot of us are real, live, engineers. Been to school and everything. We don't get up in the morning without documentation and something to doodle with/on. I can't even talk without making a sketch!If the OP can't post a link, why bother to form a reply? I didn't... In fact, that should have been the only reply. "Where's the video, where's the schematic and where are the links to any applicable datasheets?"

author: hamster_nz
author_rank: Super Contributor
timestamp: August 11, 2018, 10:16:15 pm
content: Gosh, with replies like that, next time the OP might want to post in the beginners section.... oh, hang on.....

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2018, 10:44:39 pm
content: Quote from: hamster_nz on August 11, 2018, 10:16:15 pmWhat's your point?

author: StillTrying
author_rank: Super Contributor
timestamp: August 11, 2018, 10:58:40 pm
content: A capacitor acts exactly the same as a small fast rechargeable battery, there's no inversion or delays anywhere.

author: tggzzz
author_rank: Super Contributor
timestamp: August 11, 2018, 11:38:09 pm
content: Quote from: rstofer on August 11, 2018, 09:19:31 pmJust so.I must admit being surprised that someone with so many posts couldn't be bothered to ask a "good" well thought out question. Now we all make similar mistakes occasionally, but it behooves us to quickly acknowledge our mistake and apologise.Beginners, and I don't count the OP in that category, are often unaware of what constitutes a "good question". They night benefit from understandinghttps://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/

author: Brumby
author_rank: Unknown
timestamp: August 12, 2018, 12:52:45 am
content: Asking a question in the beginner's section that just seems bizarre shouldnotevoke fire and brimstone responses. Somebody is obviously confused, got the wrong end of the stick and needs guidance.However, making mention of a video withoutanyqualification limits the content that was viewed to anything on the planet earth. This includes not only internet, but anything on someone's PC, a VHS tape or even a super-8 film if you want to take the definition to its broadest extent.This is something of which ANY question raiser should be aware. We aren't mind readers - and the only response to suggest it may have been some of Dave's videos correctly noted this as aguess. Guessing at the start can take a discussion in any one of a thousand wrong directions.The more information provided in the question, the better the question can be understood and the better the chance a useful answer can be offered sooner.The comment about asking "good" questions is a very fair one - and it is more about the structure of the question.

author: Simon
author_rank: Unknown
timestamp: August 12, 2018, 09:12:49 am
content: Quote from: Beamin on August 11, 2018, 04:03:26 pmYour first post covers several areas and is vague. We have many people rocking up asking such short open ended questions that a book could be the answer and it gets annoying. Bypass caps and speed of processers along with EMC are 3 entirely different threads if you want proper answers.Bypass capacitors go in parallel not series so you may not have watched that video clearly or it was rubbish. As stated we don't know where you are coming from as we have not seen the video.

author: tooki
author_rank: Super Contributor
timestamp: August 12, 2018, 01:54:01 pm
content: Quote from: hamster_nz on August 11, 2018, 08:24:34 pmWhat a great explanation of how caps work!!