These figures are from book by Sedra/smith.
I have a doubt regarding input impedence or resistance (Rin) shown in figure.
In book it is written that "The input resistance (Rin) represents the loading effect of the amplifier input on the signal source. It is found from Rin=Vi/Ii"(in figure).
it started with common emitter configuration (small signal π model shown in 1st figure ) and then author introduces another model( CE amplifier with an emitter resistance Re ) with slight modification shown in figure2 and one of the main motive to add emitter resistance is increase input resistance(Re)
I am not sure ,how increasing input resistance lead to a better amplifier (specially bjt circuits shown in figures )?
Specially after adding emitter resistance , voltage drop across Rπ (π model of CE with emitter resistance) decreases which causes lower amplification that's why I asked this question
There are lot of questions of input impedence on web but i hope someone answer it for that particular amplifier circuit rather than general one.