How does coupling capacitor works ?

Hello everybody,

could somebody explain how does coupling capacitor work ?
I tried to study common emitor amplifier, but I am still not able to understand how does this capacitor maintain that input AC signal is superimposed on operating DC voltage ??
Looks like magic to me...

Thanks in advance

the relation I(t) = C*v'(t) applies to a capacitor. V' is the derivative of the voltage across it. If there is no change in the voltage over time we notice from the relation that the current trough the capacitor is zero and thus it has no affect on the circuitry around. However if the voltage is fluctuating due to for example an AC signal source you will notice that current will be flowing trough it. In a CE amplifier assuming it's coupling the signal into the base of the transistor it means that the capacitor is either injecting current into the node at the base or drawing current away according to that last relation. Which means that the voltage in that node will fluctuate either up or down.

It is actually more complex then this since the circuitry around plays in. But this might give you an idea of how it works

Never thought about it this way, it makes sense ...

Thank you very much *thumbs up*