CE Amplifier Input Impedance question

Thread Starter


Joined Nov 25, 2011
I'm trying would the input impedance would be for the circuit shown below..

I understand the input signal will see the Beta*Re resistance, but if I assume the constant current source is a resistor, would it just be:

Rb || Beta*Re?

I've seen it defined as Re + (1 + Beta)*RE

where RE is an emitter resistor, as there is no RE in this diagram I'm not really sure how to derive the input impedance.

Any advice would be appreciated!



Joined Feb 17, 2009
The input resistance

Rin = RB|| ( Beta + 1) * re

re = 26mV/Ic ---> dynamic emitter resistance ( looking into the emitter to base).
And this intrinsic resistance (re) acts as if is is in series with the emitter.

gm = 1/re