I have this curcuit. I want to discover the output impedance. Using h-parameter model I get the second circuit. I know that Zout= V(open circuit)/I(short circuit) and ie = C ib, where C is an appropriate proportionality factor.
Vol = V1 Re/(Rb+Re) = (Rb ib + Re ie) Re/(Rb+Re)
Isc = ie = C ib
Then, if I consider Rb << Re I get:
Zout = Re + Rb/C
The problem is that the answer is just Rb/C. What are my mistakes?