> Now, when I said that 100nF “works well enough” above, what I really mean is your circuit usually doesn’t completely break if you use a 100nF decoupling capacitor. But given that the cost to use a larger, better capacitor is effectively nil in most cases
This is simply not true.
That Samsung cap he quoted is about 1 or 2 cents in volume from Digikey or Mouser. That cheap Chinese quote means that they are probably substituting inferior parts.
By contrast, the 0.1uF(100nF) in the same size is at least an order of magnitude cheaper. This matters a lot as you can wind up with a lot of bypass caps on your board (a significant percentage of 100 isn't uncommon). In addition, you can get 10V rating instead of 6V which means that you don't have to worry about USB transients destroying your cap and you get much better bias derating.
However, this article has a kind of fundamental misunderstanding:
"Bypass" caps (mostly) aren't about charge storage.
The point of a "bypass" cap is to provide a return path for high frequency signals--the "bypass".
All electrical signals require a circuit--that's a full loop. That loop goes positive power supply->chip A power->chip A out->chip B in->chip B gnd->negative power supply.
In the case of slow signals, it is fine for that loop to be that big. The problem is that as the signal speed increases, the resistance/capacitance/inductance of that loop the whole way back to the power supply gets bigger and bigger and starts slowing everything down.
You use your bypass capacitor so that the loop looks like chip A bypass (positive)->chip A power->chip A out->chip B in->chip B gnd->chip A bypass (negative). That loop is a LOT smaller than going the whole way back to the power supply. Which means that you want your capacitor to look a whole lot like a short circuit at the frequencies of interest, which 0.1uF(100nF) does.
In fact, given how much faster signals are nowadays, you probably want to use 10nF bypass caps, but that's an argument for another day.
As for RF bypassing, you almost always have to go to small value 0402 and 0201 in values like 100pF or lower, anyway. So, this discussion is mostly moot for RF.
Yes, if I have to use a ceramic 1uF capacitor for some other reason already, I won't sweat the idea of it serving as a bypass capacitor. But I'm certainly not going to upvalue all my nice, cheap 100nF bypasses.
> That Samsung cap he quoted is about 1 or 2 cents in volume from Digikey or Mouser. That cheap Chinese quote means that they are probably substituting inferior parts.
No, they aren't. LCSC is a very reputable distributor that has lower margins by having much cheaper labor and having absolutely insane economies of scale.
This is simply not true.
That Samsung cap he quoted is about 1 or 2 cents in volume from Digikey or Mouser. That cheap Chinese quote means that they are probably substituting inferior parts.
By contrast, the 0.1uF(100nF) in the same size is at least an order of magnitude cheaper. This matters a lot as you can wind up with a lot of bypass caps on your board (a significant percentage of 100 isn't uncommon). In addition, you can get 10V rating instead of 6V which means that you don't have to worry about USB transients destroying your cap and you get much better bias derating.
However, this article has a kind of fundamental misunderstanding:
"Bypass" caps (mostly) aren't about charge storage.
The point of a "bypass" cap is to provide a return path for high frequency signals--the "bypass".
All electrical signals require a circuit--that's a full loop. That loop goes positive power supply->chip A power->chip A out->chip B in->chip B gnd->negative power supply.
In the case of slow signals, it is fine for that loop to be that big. The problem is that as the signal speed increases, the resistance/capacitance/inductance of that loop the whole way back to the power supply gets bigger and bigger and starts slowing everything down.
You use your bypass capacitor so that the loop looks like chip A bypass (positive)->chip A power->chip A out->chip B in->chip B gnd->chip A bypass (negative). That loop is a LOT smaller than going the whole way back to the power supply. Which means that you want your capacitor to look a whole lot like a short circuit at the frequencies of interest, which 0.1uF(100nF) does.
In fact, given how much faster signals are nowadays, you probably want to use 10nF bypass caps, but that's an argument for another day.
As for RF bypassing, you almost always have to go to small value 0402 and 0201 in values like 100pF or lower, anyway. So, this discussion is mostly moot for RF.
Yes, if I have to use a ceramic 1uF capacitor for some other reason already, I won't sweat the idea of it serving as a bypass capacitor. But I'm certainly not going to upvalue all my nice, cheap 100nF bypasses.