When I first replied to your thread here, I pulled uc ic datasheet and I pulled NOT gate ic datasheet. I looked at their recommended circuits, guess what I found? uC ic datasheet showed decoupling capacitors. The simple NOT gate ic DID NOT show decoupling capacitors. So. The uC ic manufacturer clearly telling you that you REALLY want those decoupling capacitors to be there. The NOT gate ic, well, it is up to you.I mean where I need to put them exactly I don't see capacitors everywhere in the circuits, did I need them just in the supplies of the ICs or in other places too...something like that.
Actually, you CAN put too much and hurt circuit performance, particularly from the standpoint of noise, by doing so.You can not put to much decoupling on a circuit, but you can put to little.
If you put to little, the faults can be very hard to find.
So, what process do you use to decide NOT to use a decoupling capacitor? That is, your next sentence seems to contradict your first sentence, and I was wondering how you distinguish between the two and determine when one should not add decoupling.Actually, you CAN put too much and hurt circuit performance, particularly from the standpoint of noise, by doing so.
The problem is that there is no such thing as a pure capacitor, so any real capacitor comes with parasitic resistance and inductance and those parasitic values tend to be a function of capacitance (due to the nature of how capacitors are physically constructed). So if you use too large of a capacitor, you can easily end up with a device that looks more like an inductor at the very frequencies where need it to be capacitive.
The best solution is to consider each circuit case-by-case. But for most circuits (beyond the low-speed circuits where even brutish rules-of-thumb are often adequate) a reasonable cookie-cutter approach is to use decade-tiering where you put several capacitors in parallel that step down in value by either 10x or 100x and by minimizing the lead distance of the smallest valued capacitors as much as possible (i.e., putting more emphasis on doing it for the smaller values relative to the large values).
Huh?So, what process do you use to decide NOT to use a decoupling capacitor? That is, your next sentence seems to contradict your first sentence, and I was wondering how you distinguish between the two and determine when one should not add decoupling.
All the advice given so far is good. Now, for the real world, for small circuits with only a few ICs I often omit them completely. But there is no wisdom in taking bad advice.Hi
Can you tell me in which cases, in general, I need to use a bypass or decoupling capacitors and how to calculate their values in the case of a DC signal.
Bad advice.Build your circuit without them and see if you have a problem. No problem, then no need for a solution.
Thanks.I fixed the link. The Murata excerpt is nice, but I could not trace the title to its complete document. However, here is a link to a more complete piece from Murata: http://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx?la=en-us
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