半导体管小信号模型可行的原因 (Reasonability of Small Signal Model for BJT/FET)

最近在看MIT 6.002x，弄明白了学习模电和电分时关于小信号模型和叠加性的可行性和证明方法问题，下面是我的笔记，贴出来给大家参考。

I am learning MIT 6.002x these days, in which I make myself understood the reasonability of small signal model for BJT/FET element in Analogue Electronics, and the proof method of superposition theorem in Circuit Analysis. The following is my note. Hope it will be useful for other classmates.

The small signal model is right because the large signal model works for the overall signal with both the small signal and operating point.
The large signal model has network equations, which is based on the KCL/KVL from the topology of the circuit. The operating point signal is a special conditions of the large signal model. Two identical equations give the third identical equation, then the same topology of the circuit.