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运放的两条黄金定律(golden rules)，在《the art of electronics》这本书中，有两条golden rule：

1、The output attempts to do whatever is necessary to make the voltage difference between the inputs zero.
1、无论输出端试图做什么，都是为了使输入端电压差值为0。

2、The inputs draw no current.
2、输入端没有电流流入。

    One important note of explanation: Golden rule  I doesn't mean that the opamp acturally changes the voltage at its inputs.It can't do that.(How could it,and be consistent with golden rule Ⅱ?) What it does is "look" at its input terminals and swing its output terminal around so that the external feedback network brings the input differential to zero (if possible) 
    并不是说运放可以改变其输入电压，它根本做不到这一点，它所做的仅是“盯”住输入电压，而调整输出电压，通过外部反馈网络，使输入端电压差为0。明白了吗？总之一句话：如果运放存在一个外部反馈网络，则输出端所做的就是使输入端电压差为0。