Good practice for MLCC power by pass capacitor - Page 1
Forum section: electronics / projects

author: Wilson__
author_rank: Frequent Contributor
timestamp: July 27, 2024, 05:27:52 pm
content: What isgood practice for multi-layer ceramic capacitor used for power by pass capacitorto reduce noise on the power supply line.Sensor use 0.1uF. Power regulator uses 2.2uF and 4.7uFLiterature says capacitance is lowered when voltage (as a percent of rated voltage) is applied and advises to use higher rated voltage (so working voltage is a smaller percent of maximum rated voltage).What percent is good? Many thanks

author: Wilson__
author_rank: Frequent Contributor
timestamp: July 27, 2024, 05:36:56 pm
content: A random web search showed this curve for X7R material. There are half dozen or so materials. Any pointer on which material is good? for 3.3 and 5 volts

author: Siwastaja
author_rank: Super Contributor
timestamp: July 27, 2024, 06:09:11 pm
content: That percentage derating advice is bullshit, might be slightly better than assuming based on observing how frogs behave today, but not by much. This is because voltage rating is what guarantees survival of the part. Anecdotal evidence says that manufacturers sometimes even sell the exact same part under different voltage ratings.Assuming true capacitance from package size is already much better (i.e.: if something looks too good to be true, it isn't; 1µF in 0402 drops much more in capacitance at any DC bias than 1µF in 0805 at the same DC bias; you can ignore the voltage rating completely in this analysis), but nothing beats actual data from manufacturer. DC bias curves are not that exotic anymore, probably even half of the manufacturers have those nowadays, but you might need to look further than datasheet linked at Digikey/Mouser. Possibly manufacturer's website, some web based tool, etc.And there are no curves for "materials", just curves for each product. And one X7R might be just -40% at the rated DC voltage and other -85%.Note that when a manufacturer gives "example circuit" or "typical application" which says 4.7uF MLCC, it doesn't mean 4.7uF true capacitance, but that they actually have characterized it with a 4.7uF nominal part, which already has less than this capacitance at their DC bias. If they don't show a part number, the sane thing to do is to ignore worst offenders. So maybe for example a 3.3V regulator showing 4.7uF example circuit works fine with capacitor for which the effective capacitance drops by 50% at this 3.3V bias, but do not choose one which drops by 80%.It would be optimal to actually model/calculate true capacitance needed and then choose according to data (DC bias, aging, temperature, tolerance), but in reality IC manufacturers rarely give helpful data on true capacitance needed so things are a bit hand-wavy and even cargo cult sometimes.

author: nctnico
author_rank: Super Contributor
timestamp: July 27, 2024, 08:40:36 pm
content: Yep. Check manufacturer specs. There are differences in how much an MLCC's capacitance drops for the same part size. The higher rated voltage parts are the ones to start looking at if you really need as much capacitance as possible in a tight space. But you'll need to make sure the assembler doesn't substitute for a different part.

author: Smokey
author_rank: Super Contributor
timestamp: July 27, 2024, 09:19:03 pm
content: Nothin magic about 0.1ufhttps://www.signalintegrityjournal.com/articles/1589-the-myth-of-three-capacitor-values

author: mawyatt
author_rank: Super Contributor
timestamp: July 27, 2024, 10:31:33 pm
content: Here's some information related to capacitor behavior wrt to applied DC Bias voltage.https://www.eevblog.com/forum/projects/ceramic-capacitor-behavior/The very reason we developed the DC Bias Adapter below was to investigate the effects of DC Bias on capacitors (including SMD types), since our LCR Meters didn't have this capability (TH2830) or with limited built-in bias range (IM3536).https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/Best,

author: floobydust
author_rank: Super Contributor
timestamp: July 28, 2024, 12:00:56 am
content: The fact that MLCC age within the first hour, value drops almost right off the bat, is another trap, in addition to their voltage coefficient of capacitance.The capacitor industry needs to update the standards and tests, specs etc. instead of being quiet about it.Continental lobbying the industry but not sure what if anything happened.https://www.eevblog.com/forum/projects/mlcc-x5r-capacitor-degradation/msg4841828/?topicseen#msg4841828

author: ejeffrey
author_rank: Super Contributor
timestamp: July 28, 2024, 02:26:29 am
content: In addition to the package footprint size (0402 vs 0805) MLCC are available in a variety of thicknesses. Thicker capacitors will retain more capacitance at higher voltage. For a given material class It's basically total volume of the dielectric material that determines the energy stirage capability.Be super careful of this when looking for alternatives. The same manufacturer may make parts with the same nominal capacitance, package footprint, voltage rating, and dielectric type, but different thickness and different voltage derating. If a given part is out of stock and someone suggest an "equivalent replacement" that is thinner it may not actually be suitable at all.

author: Martinn
author_rank: Frequent Contributor
timestamp: July 28, 2024, 09:19:59 am
content: Quote from: Wilson__ on July 27, 2024, 05:36:56 pmX7R is not a material, it is a temperature characteristics classification.Murata has very detailed specs on their capacitors, see for example GRM022D80G104ME15Lhttps://www.murata.com/en-us/products/productdetail?partno=GRM022D80G104ME15%23

author: iMo
author_rank: Super Contributor
timestamp: July 28, 2024, 09:32:40 am
content: Btw., I've got some 1206 10u-22u MLCC capacitors from various scrapped boards. Is there a way to estimate or measure somehow their max operating voltage (none marking on them, of course)?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 28, 2024, 09:52:07 am
content: C(V) reduction is always below breakdown, and a part isn't very useful beyond some point of reduction anyway (say -30%, -50%, whatever), so you can simply measure the bias effect and write down thepracticalvoltage rating instead.Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2024, 11:02:01 am
content: Quote from: Smokey on July 27, 2024, 09:19:03 pmYeah, it's more like a minimum value; more is fine; as long as package size is not increased, high frequency impedance keeps equally good, but lower frequency impedance gets better.Only at the point where you have had to increase package size, you have gone overboard. For example, 0402 is handy for bypassing say 0.5mm pitch microcontroller power pins; you can get them relatively close, and still route out some signals too. Then you really don't have to use 0.1µF "just because". You can get 1µF in 0402 too. Or anything in-between. On the other hand, if you think "oh, more is better" and go to 10µF, then surely you pick a package like 1210 and now you need to route the caps far away from the power pins. You have significantly added parasitic inductance - including higher ESL of the larger package itself + added PCB track length, so have made high frequency impedance worse, and being so far from what IC manufacturer thought you would normally do, this might matter.But in case datasheet asks for 1µF for one pin, and 0.1µF for another, in the same supply rail, just use 1µF for both! Or, if datasheet shows paralleled 1µF and 0.1µF for a single power pin, just use 1µF alone. Or if you want to leverage the (albeit small) positive effect on ESL of paralleling parts, use two 1µF parts in parallel; but if one of them must be routed significantly further away, then it does not help.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2024, 11:09:42 am
content: Quote from: iMo on July 28, 2024, 09:32:40 amBigger problem than knowing the operating voltage is that desoldered 1206 MLCCs are too likely to crack after resoldering into the new project. MLCCs at 1206 and above are quite finicky, even just wrong soldering process can produce hidden cracks that make the parts fail short circuits weeks, possibly years after, even without board flexing ever happening. I have been hit with capacitor cracking a few timeseven whenI don't reuse parts, so I would never take that risk; capacitors are not that expensive, and knowing the part number instead of just a measured value is useful.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 28, 2024, 11:13:49 am
content: Quote from: Martinn on July 28, 2024, 09:19:59 amYeah, this is an interesting thing. Every beginner can google that these acronyms like X7R, Y5V are temperature specifications, where each symbol has a definite meaning, just for specifying operating temperature ranges in concise form.Then they come into forums like this and learn that "X7R is much more than temperature rating, it's amaterial" and that "X7Rmaterialonly loses up to 50% of capacitance at full DC bias, while Y5Vmaterialloses up to 80%".And finally, when they find out* above advice is 100% made up bullshit, and the initial explanation of this being just temperature rating short-hand is correct, they have grown into quite capable engineers.*) for example, seeing a datasheet of actual X7R product losing 85% of capacitance at rated DC bias

author: mawyatt
author_rank: Super Contributor
timestamp: July 28, 2024, 12:53:41 pm
content: Quote from: Martinn on July 28, 2024, 09:19:59 amMurata, TDK, AVX/Kyocera are some of the better ceramic capacitor sources.Here's a SPICE model for the mentioned 0402 0.1uF valid @ 0 DC Bias and 25C, as one can see far from a simple C or CRL with ESR and ESL included.This alone should give caution in casual swapping capacitors because they are"just for decoupling/bypassing", one needs to understand a little more about the actual use, especially when high di/dt is involved!!Experienced folks intuitively know how/when the complexity of this type capacitor is justified, chip designers know exactly what this meansBest,Code:*----------------------------------------------------------------------* SPICE Model generated by Murata Manufacturing Co., Ltd.* Copyright(C) Murata Manufacturing Co., Ltd.* Description :0402M(01005)/X6T/0.1uF/4V* Murata P/N :GRM022D80G104ME15* Property : C = 0.1* Data Generated on Nov 6, 2018*----------------------------------------------------------------------* Applicable Conditions:* Frequency Range = 100Hz-6GHz* Temperature = 25 degC* DC Bias Voltage = 0V* Small Signal Operation*----------------------------------------------------------------------.SUBCKT GRM022D80G104ME15_DC0V_25degC port1 port2C1 port1 11 9.06e-8L2 11 12 1.20e-10R3 12 13 2.60e-2C4 13 14 5.31e-6R4 13 14 750C5 14 15 6.61e-6R5 14 15 94.4C6 15 16 7.83e-6R6 15 16 8.61C7 16 17 1.31e-5R7 16 17 7.50e-1C8 17 18 6.87e-6R8 17 18 2.96e-1C9 18 19 3.48e-6R9 18 19 4.50e-2C10 19 20 4.74e-3R10 19 20 6.84e-4L11 20 21 5.05e-12R11 20 21 1.65e-1L12 21 22 2.96e-11R12 21 22 1.23e-1L13 22 port2 4.56e-11R13 22 port2 2.48e-2R100 port1 11 5.00e+8.ENDS GRM022D80G104ME15_DC0V_25degC

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2024, 04:00:21 am
content: Quote from: Siwastaja on July 28, 2024, 11:13:49 amNot 100% (unless you want to be labeled as such yourself): the fact remains [unsourced, so, as I understand it--], all(?) type 2 formulations are based on BaTiO3 or close relatives, and the main differentiators are grain size, doping, and sintering aids. I've heard it suggested that the temp curves are too restrictive -- there is real development that could be made, but as long as engineers are shopping for, and sourcing is buying, X7R and such categories, there's not much they can do outside of making that particular flavor of BaTiO3.So they do the next best thing they can do: maximize rated value, while tucking the C(V) curve away in a database. The system is a bit overconstrained and real innovation requires massive effort (promoting new standards, spreading awareness, advertising the new parts themselves) -- not to mention coordinated effort (you can't introduce a single-source jellybean, the whole industry needs access to the formulation). An open standard might prove valuable, but the gain is minor so no one has any reason to share whatever secret sauce they may have on the books.But it may be simpler than that. Perhaps there just isn't any innovation, at least as yet, so no reason to promote such a process. It could even be externalities, like use of other toxic elements -- note that barium is RoHS restricted by default, and we have capacitors by exemption specifically; I can't imagine introducing a similar material is very easy. (But, there are plumbate and etc. piezo devices, so maybe it's not that horrible.)Recall there used to be a type 3 dielectric; I forget what the issues with these even were (even worse C(V) or tempco? expensive? unreliable e.g. extreme aging?), but in any case they didn't survive in the market, so here we are still with type 2.Tim

author: selcuk
author_rank: Frequent Contributor
timestamp: July 29, 2024, 08:33:15 am
content: This depends on the design and ICs used. You need to follow manufacturer's application notes and consider the noise frequencies on your board. You need to inspect the characteristics of each capacitor as suggested before since they are very different there is no 100% equivalent.For example let's assume you want to decouple a MCU which has BLE connectivity. The manufacturer recommends a 1uF capacitor on VCC net. But you may think that it is a good idea to add a parallel capacitor to attenuate 2.4GHz noise. You need to read many datasheets and graphs to have good candidates.This one is 10pF/50V in a 0603 package. You can see from the frequency graph that it has the lowest impedance at very close to 2.4GHz.https://product.samsungsem.com/mlcc/CL10C100JB8NNN.doThen you think that 0603 package is too big to place on your layout. You want 0402 but, should you place a very similar part only with different footprint? Unfortunately no. Yo need to search again. Then you can find a 15pF/50V in a 0402 package. Different value but similar impedance at 2.4GHz.https://www.yageo.com/en/Chart/Index/CC0402JRNPO9BN150If you use different capacitors in parallel, you may run a SPICE simulation to see the total attenuation. They can have high impedance points at some resonance frequencies.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2024, 11:21:00 am
content: Quote from: selcuk on July 29, 2024, 08:33:15 amI'm afraid you are repeating a mistake that have been discussed in this very thread.The impedance notch is not some intrinsic property of the capacitor.It is merely how the capacitor is measured in the test jig.In particular, a few mm of trace and via inductance (or even the pads themselves, depending on where exactly the test jig is open/short/thru calibrated to) will shift that resonance down byone or two octaveseasily. The notch frequency is not meaningful.Tim

author: selcuk
author_rank: Frequent Contributor
timestamp: July 29, 2024, 01:04:42 pm
content: Quote from: T3sl4co1l on July 29, 2024, 11:21:00 amI agree that via and traces add inductance more than a small MLCC capacitor's ESL. I think you are referring the article in the Signal Integrity Journal about usefulness of frequency graphs. The manufacturers did some measurements and shared the graphs with us to save our time while picking the parts. I don't agree that we should ignore the frequency graphs and assume more generic knowledge as a rule of thumb or a starting point.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 29, 2024, 02:17:32 pm
content: Quote from: selcuk on July 29, 2024, 01:04:42 pmThe problem isn't anyone ignoring any graphs, but you not understanding how to interpret and apply them.Just for fun: try to plot multiple capacitors on same plotusing same absolute y (impedance) axis. The enlightenment is when you see the curves on the right to SRF match, i.e., larger value capacitor being just as good for high frequency bypassing than a smaller value capacitor (as long as they are in same package size); pretty much larger capacitor being equal or bettereverywhereat that graph.All that remains to support the argument of paralleling multiple different values are those tiny notches right at SRF of each cap, but these are very narrow and once you understand they shift up and down in frequency due to normal part variation, you will understand that if you made a marginal EMC test pass by adding a random part, that result probably isn't valid in production.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 29, 2024, 02:19:25 pm
content: You seem to be making a chunking error -- or not reading and understanding my post correctly. Or I didn't write it well. Communication is always two ways, after all. I think it's unlikely I was unclear, but perhaps I shall review it, and add more specificity.Quote from: selcuk on July 29, 2024, 01:04:42 pmI'm not referring to anything, actually; these are things I know independently. They may be found (to varying degrees of correctness) in various publications, perhaps SIJ among them, though, at a glance, the above link doesn't really illustrate the frequency shift specifically that I mentioned.Or, these things can be derived from first principles, applying EM theory and a bit of network theory; or by experiment, setting up test jigs with exactly these varying conditions and measuring them. (For what it's worth, I arrived at my state of knowledge through a mix of all of the above. Not so much direct experiment, in this frequency range exactly, but inferring from other cases which I have encountered directly, and also knowing, by theory, and others' experiments, that there does not exist a cutoff, or fundamental shift; everything is still just as applicable at smaller dimensional scales and proportionally higher frequencies, my inference is justified.)For one, if I meant "disregardthe impedance plot", I would've said so. I very specifically said:Quote from: T3sl4co1l on July 29, 2024, 11:21:00 amI didn't say todisregardthe notch in general: its depth, or width, nor the asymptotes flanking it. You seem to have misconstrued this.I suspect you've made a category/chunking error: I said "ignore specific aspect of thing", but you've parsed it as -- you've stuffed it into a bin labeled "ignore thing". What I said, is more nuanced than what you appear to have internalized.Moreover, I said it in the context of:QuoteI demonstrate a network of knowledge: the impedance curve has the specific shape that it does, because it fairly reasonably resembles a lumped-equivalent circuit, C + ESR + ESL; by mentioning inductance, and knowing AC steady-state circuit analysis, we know inductors in series add; and knowing the general scale of things (1mm trace length ~= 0.5nH ballpark*). From this, we can readily conclude that, yes, frequency will shift down, going as sqrt(L_total), and -- if the added inductance is lossless -- the valley resistance (ESR) remains constant. (Whereas if Q remains constant, ESR goes up as sqrt(L) as well. Or maybe Q goes down, who knows.)*I could've detailed the reasons justifying this figure, for example; but thought it unnecessary, leaving it simply as a point of reference, something understood "by those skilled in the art". (For those curious, it's mu_0, times a geometric factor determined by the cross-section of the trace (as a transmission line) geometry. The factor is usually less than 1, so rather than 1.257nH/mm, it's more like 0.5 for average microstrip.)Or perhaps I'm taking you too literally -- perhaps you wrote "ignore" in the context of "ignore ". I have little choice, in technical matters, but to take words literally, at face value -- and assume you wrote what you meant.The alternative anyway seems worse: if you think even ignoring a minor and readily mutated aspect of a curve should be avoided, that implies you takealtogether too much confidencein the curves, or, perhaps even that they depend on circumstances at all -- in which case, my earlier point remains correct, you've just declined to accept it. Even more chillingly, this would suggest you assume, at least less "generic knowledge" (if not necessarily none), particularly as a rule of thumb or starting point (but, what is a "rule of thumb" anyway, but a piece of "generic knowledge"?) -- which sounds like you must be hardly capable if at all in electronics, a field that assumes vast swaths of generic background knowledge to work at much depth within! So, this seems anywhere from "worse" to "contradictory", and I wouldn't tend to assume this interpretation.Tim

author: mawyatt
author_rank: Super Contributor
timestamp: July 29, 2024, 04:38:32 pm
content: Capacitive reactance has a slope of -6dB/Oct, Inductive +6/Oct. When viewing a graph of Impedance vs Frequency as shown in the Samsung 10pF 0603 case above, one can see that the negative slope increases as the frequency closely approaches the "notch". This is caused by a more complex impedance involving capacitance and some inductance acting together, and at the "notch" cancel showing the impedance leftover as ESR.Capacitance can be estimated as the Impedance Z at Frequency when Z slope is within the -6dB/Oct range. The Samsung 10pF example, from the graph Z ~ 100 ohms @ 160MHz, implying a Capacitance of 9.95pF. The notch indicates an effective inductance of ~0.5nH with an ESR of ~0.31ohms, all reasonable values in our experience for a 0603 C0G type capacitor.Best,

author: iMo
author_rank: Super Contributor
timestamp: July 29, 2024, 05:51:16 pm
content: FYI - This is how Intel perceived the power voltage filtering model with parasitics with their Xeon cpus in 2005..From Intel's "VRM and EVRD 10.0 Design Guidelines", 2005.

author: TimFox
author_rank: Super Contributor
timestamp: July 29, 2024, 07:11:40 pm
content: The actual material properties of a given dielectric are a function of the E field (voltage gradient) applied to the dielectric layer. That, in turn, depends on the terminal voltage and the physical construction (especially layer thickness) of the actual capacitor.As stated above, the X7R designation is mainly the temperature co-efficient of capacitance, and will not specify the voltage dependence. For that behavior, you must consult the data sheet of the manufacturer, which will vary between reputable manufacturers and part numbers.The voltage rating is only a guarantee of the safe voltage that will not damage the part, and is not necessarily a recommended operating condition.

author: selcuk
author_rank: Frequent Contributor
timestamp: July 29, 2024, 10:01:28 pm
content: Quote from: T3sl4co1l on July 29, 2024, 02:19:25 pmYes. You are right about not saying to ignore the graph all together. I assumed that and wrote the reply based on that. My bad.Quote from: Siwastaja on July 29, 2024, 02:17:32 pmI can understand that the frequencies can shift from part to part and from test setup to test setup.I plotted some capacitors as you suggested. I didn't use the previous parts since another manufacturer has a web interface allowing me to plot multiple capacitors easily.Let's assume a chip manufacturer recommends to use 4.7uF + 100nF at a VCC rail. Then I want to decouple 2.4GHz noise from the VCC rail as well. So I expect to add a capacitor having very low impedance at this frequency. You may say that lowest impedance frequency is not exact. But that is the only clue for me at the beginning. So I pick the below parts. I cannot find 4.7uF in a 0402 footprint. So it is different and it may have a higher ESL than others as expected.0805_885012207053_4.7uF0402_885012205086_100nF0402_885392005127_12pFI've attached impedance graph from manufacturer measurements. I simulated the capacitors of 4.7uF + 100nF together and then simulated 4.7uF + 100nF + 12pF together with ngspice.This is the spice circuit. It may not the best one for impedance graphs.Code:*.include "models/WCAP-CSRF.lib".include "models/WCAP-CSGP_50V.lib".include "models/WCAP-CSGP_16V.lib"vac1 1 0 dc 0 ac 1R11 1 2 50X11 2 0 0805_885012207053_4.7uFX12 2 0 0402_885012205086_100nFX13 2 0 0402_885392005127_12pF.controlac dec 1000 1k 3Gplot vdb(2) xlog.endc.endSo it seems that adding the 12pF capacitor is an improvement on filtering the noise at 2.4GHz.

author: nctnico
author_rank: Super Contributor
timestamp: July 29, 2024, 10:56:17 pm
content: These simulations are not very useful without modelling the board layout as well. The board layout plays a huge role in what the actual impedance versus frequency is going to be.

author: tggzzz
author_rank: Super Contributor
timestamp: July 29, 2024, 11:09:44 pm
content: Quote from: Wilson__ on July 27, 2024, 05:27:52 pmFor SMD capacitors, use 0306 rather than 0603.Yes, that is a gross simplification of power distribution design, but it is worth remembering.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 30, 2024, 04:06:13 am
content: Again, even pad length itself may be a factor in the capacitor impedance; let alone the gap between neighboring capacitors. There is no such thing as an ideal (all points perfectly joined) net at those frequencies. An EM model of the PCB must be extracted, using fancy software like Ansys (though it looks like there are several other options nowadays, even a Solidworks plugin?) to generate a model between all component ports (pad pairs) of given layout.Bypass for 2.4GHz RF applications -- discrete amplifiers -- involves alternating stages of 1/4 wave traces and stubs (hence the typical motif, a thin trace joining to a wide sector shape), chains of bypass caps with lots of GND stitching vias, and ferrite beads to absorb rather than reflect residual energy. Impedances are modest (10s Ω), so the mismatch of a few stubs and bypass caps achieves adequate filtering.Bypassing an IC at such frequencies is absurd -- at least, in anywhere near the same way we do for lower frequencies. For small radios (supply is high impedance, i.e. some ohms or more), only one or a few supply pins are taken out, and we might employ the above solution; some 2.45GHz leaks into the board, or 900MHz or whatever we're doing, and we need to isolate and absorb whatever is left before joining it to the main board supply. DC current is low, too, so a small chip ferrite (or few) suffices.What we do for lower frequencies, high currents, low impedances, is make mass connections. Like VCORE/GND on a BGA SoC, multiple pads are wired in parallel, and more or less each one (or pairwise or other small groupings) must be locally bypassed, and still the fact that the package sits 0.5mm or whatever above the say 1mm thick PCB, means we can't get less than some, whatever, 10s pH, between the closest possible bypasses (underneath chip, flanked by vias) and the device itself. If the threshold impedance is say 0.1Ω or less, then we have a cutoff frequency in the low 100s MHz, above which the impedance must rise and there's nothing we can do about it on the board level.Which is perfectly fine, chip makers know this. That's why you see tiny, wide-format, and even LGA style, bypass caps on the interposer for these devices; that's why the interposer itself is made out of so many layers, and such fine-pitch wiring (it also needs to wire-bond or solder-bump directly onto a chip with hundreds or thousands of pads on it..!). That's why the die itself may have piggyback caps, or in any case is made with multiple alternating metal layers distributing power around, to crank up the capacitance; even individual groups of transistors may be arranged so their capacitance acts as bypass for each other (skewed clocks between adjacent domains, designing logic blocks so that only a fraction of transistors switch on any given edge, etc.).Probably anything more powerful than Bluetooth has a similar scheme, i.e. onboard bypass, or decoupling in any case, to keep the impedance requirement at 2.45GHz high, so that extremely wide / numerous-pinned connections aren't required at the board level. A typical RF amp anyway has a constant-current characteristic, either supplied through a choke (decoupling!), or balanced (push-pull cancelling out the fundamental), or both, and all you have to do at the board level is mop up the residuals, and not make a resonance with the onboard decoupling (i.e. keep it modestly low impedance, and resistive/flat).Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: July 30, 2024, 07:10:07 am
content: Quote from: selcuk on July 29, 2024, 10:01:28 pmSo you proved my point, and demonstrated that you indeed went for the notch! This is a mistake for two reasons:* Improvement outside of the notch remains very small.* At notch, improvement seems significant, but as you understand, is prone to shifting in frequency.You handpicked, in simulation, a part which has notch exactly at your frequency of interest. In real world though, you usually want wide-band power bypassing, and even if you needed narrow-band low impendace, then you cannot control the capacitor and layout properties so that the notch would stay exactly there.Therefore, the advice of ignoringthe notch(not the graph!) is decent.Try paralleling two of those 100nF parts instead.