# Rin, Rout and Gain of Power Amplifier

I'm trying to find the input resistance, output resistance and gain of this circuit.

simulate this circuit – Schematic created using CircuitLab

My textbook only has the simpler case when $R_1 = 0$ and $R_2 = 0$, wich are

$R_{in} \approx \beta \left [ R_L+ (r_{eN}||r_{eP}) \right ]$

$R_{out} = r_{eN}||r_{eP}$ (I'm not sure if this one is exact)

$\frac{v_o}{v_i} = \frac{R_L}{ R_L + r_{eN}||r_{eP} }$

• I am not sure of the models you are supposed to use for the transistors, but I guess that it is sufficient that you sum R1 to Ren, and R2 to Rep, at least for input and output resistance. Just write down the full schematic and solve it. – Vladimir Cravero Jul 30 '17 at 22:01
• Seems almost obvious how to go from where you are already at to where you need to be, which makes me wonder what question you really have. I think one simplification you might include is to realize that in this class-AB (probably) stage you can assume only one of the BJTs will be active at a time and ignore the other one's little-re. – jonk Jul 30 '17 at 22:28