# Imput impedance

#### omar-rodriguez

Joined Jun 24, 2015
67
Hello,I have a very basic question ¿What's the imput impedance on this circuit?

I'm not sure if it is Zin=Vsignal/i or Zin=Va/i ?

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#### WBahn

Joined Mar 31, 2012
30,076
Why do you think it might be Va/i?

#### omar-rodriguez

Joined Jun 24, 2015
67
because I believed that with imput, they are talking about all the input branch

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#### WBahn

Joined Mar 31, 2012
30,076
First, the word is "input", not "imput".

What is are the input terminals for this circuit?

#### omar-rodriguez

Joined Jun 24, 2015
67
I'm sorry I don't speak English I'm just trying... now I understand your point it is Zin=Vsignal/i, because Vsignal is the input

#### WBahn

Joined Mar 31, 2012
30,076
I'm sorry I don't speak English I'm just trying...
Don't worry -- you're English is far better then my (fill-in-your-native-tongue-here).

now I understand your point it is Zin=Vsignal/i, because Vsignal is the input
Correct. Vsignal is the input voltage and i is the input current. The ratio between them is therefore the input impedance.

Though there are really two input impedances -- large signal and small signal; but I don't know if you have gotten to that yet.