An ideal common emitter amplifier simply multiples the input function by a constant value while also inverting the signal. The voltage amplification factor, $$A_v$$, is largely a function of the AC load resistance at the collector and the internal emitter resistance, $$r’_e$$. This internal resistance is, in turn, inversely proportional to the DC emitter current. Therefore, if the underlying bias is stable with changes in beta, the voltage gain will also be stable. The circuit will appear as an impedance to the signal source, $$Z_{in}$$. This impedance is approximately equal to the base biasing resistor(s) in parallel with the impedance seen looking into the base $$(Z_{in(base)})$$ which is approximately equal to $$\beta$$ $$r’_e$$. Consequently, the amplifier’s input impedance may experience some variation with beta. In contrast, the circuit’s output impedance as seen by the load is approximately equal to the DC collector biasing resistor.