(1)微变等效电路就不画了，可以参考模电书。 (2)输入电阻RIN = (RG3 + RG1//RG2) = 1M + 180k//20k ~ 1M欧姆；输出电阻RO = RD//RL = 3K//27K = 2.7k欧姆。放大倍数AU = VO/VI = gm * RO = 1.2m * 2.7k = 3.24
