Hello,I have a very basic question ¿What's the imput impedance on this circuit?

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

 

Why do you think it might be Va/i?

 

because I believed that with imput, they are talking about all the input branch

 

First, the word is "input", not "imput".

What is are the input terminals for this circuit?

 

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

 

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.