G
Guest
- Jan 1, 1970
- 0
When referring to capacitors with the term "bypass capacitor"
or "decoupling capacitor" , is that the same thing ?
or "decoupling capacitor" , is that the same thing ?
When referring to capacitors with the term "bypass capacitor"
or "decoupling capacitor" , is that the same thing ?
I forgot, there is also coupling capacitor, so coupling/decoupling/by pass
are different terms for the same thing ?
For example, the capacitor that we use at the output of an electret microphone
is a by-pass capacitor because it allows the hi frequecny to pass while
blocking the dc component ?
undesired signal feed-through, as from a supply rail to ground. And a
"bypass cap" means, most generally, "a capacitor shunted across
something".
But the words don't matter; the actual function does.
John
That is a coupling capacitor. It couples the AC signal to the next stage.nws said:How would you call the capacitor that we use at the output of an electret
microphone, decoupling or coupling ?
John said:I never understood this reasoning. This argues that a chip cap will be
a poor supply bypass for, say, a common opamp. If a 0.33 uF 0805 cap
has 1 nH inductance, its SRF is about 9 MHz. But it's still a 0.33 uF
cap, and has a 0.5-ohm impedance from about 900 KHz to 90 MHz, and is
<5 ohms over four decades of frequency. What's wrong with that?
John
Keith said:Not agreed. It depends on how you view the situation. If one views the
function of the the capacitor as a shunt for high-frequency noise,
perhaps "bypass" is a better word. However, I've always used
"decoupling" because I view the capacitor as being used to "decouple"
(I.e. reduce inductance of) the source (power supply) from the load.
It really is six of one half-dozen of the other type of thing.
Keith R. Williams said:Though it is all in how you look at it, I disagree. All those little
caps are storing charge such that the transient currents can be
supplied locally (without the inductance from the power distribution).
Thus I prefer "decoupling" over "bypass".
John said:I see it a different way. If the cap is intended to improve the
quality (stability) of the voltage for a single device, it is a bypass
cap, but if it is intended to keep some signal generated by one
circuit from showing up in a second circuit, it is a decoupling cap.
Bypass caps serve a single customer, while decoupling caps isolate two
customers. It is just the difference between the words "across" and
"between".
Roy McCammon said:Well, I know what you mean if you say either term, but I
notice that Howard Johnson uses the term "bypass".