output resistance and gain of amplifier

https://ibb.co/TPFZbQn In calculation of gain why r_o (output resistance of transistor) doesn't count in output resistance? Why only Rc is written in gain calculation?

by Aig
August 12, 2021

Your reference takes forever to open, for me.

I assume that you use a BJT in common emitter, like in Wikipedia, figure 2.

Any resistor (or complex impedance) between $V_{out}$ and the ground would tend to bypass the transistor and $V_E$. An exceptionally low resistor, imagine a wire, will bypass it entirely. A larger one will have less bypassing effect and we reach a maximum effect with an infinite resistor, or an open circuit between $V_{out}$ and the ground. So is the formulation $A_v$ as the maximum possible one.

by vanderghast
August 12, 2021

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