Online consultation The output resistance is a parameter used to reflect the characteristics of the amplifier circuit itself. The output resistance is the output resistance and has nothing to do with the load resistance. When the amplifier circuit is regarded as a two-port network, ro has nothing to do with external conditions, and in fact there is no such resistor (rce is generally a resistance of tens of kΩ or above, and in the three-pole theoretical circuit model it is It is connected in parallel at the output end, so it is ignored. For specific derivation, just use a full differential). In order to reflect in theoretical calculations the dissipation caused by non-ideal conditions in the output circuit of the amplifier, this concept is introduced based on the I-V characteristics of the output. In layman's terms, it is "carrying capacity".
In the circuit topology, for a multi-stage amplifier circuit, the input resistance of each stage is the external load resistance of the previous stage, and the load resistance and the output resistance have nothing to do with each other.
The load resistance is related to the output resistance. For analytical modeling calculations, the load resistance RL' of the amplifier circuit = the parallel connection of the external load resistance RL and the output resistance ro. Because dissipation is related to electric current, it is stipulated in this way, just like a truck, when pulling goods, it must pull the body of the truck along with it.
