Biasing

1. Introduction

Biasing in electronics means establishing predetermined voltages or currents at various points of an electronic circuit for the purpose of establishing proper operating conditions in electronic components.

这个时候你可能会想到叠加定理，是的，没错，只是我以前忘了做查询。这东西就是做叠加定理时会用到的手段。只不过这里要把概念扩大一下。

Many electronic devices such as transistors and vacuum tubes, whose function is processing time-varying (AC) signals also require a steady (DC) current or voltage to operate correctly — a bias.

这里讲的是。。。有些元件，比如三极管，既需要一个稳定的直流电给它把电路导通，又需要一点点交流电让它完成工作(比如把小信号放大：小交流电流控制大直流电流，最终输出大交流电流)

The AC signal applied to them is superposed(叠加) on this DC bias current or voltage. The operating point of a device, also known as bias point, quiescent(静态) point, or Q-point, is the steady-state (DC) voltage or current at a specified terminal of an active device (a transistor or vacuum tube) with no input signal applied. A bias circuit is a portion of the device's circuit which supplies this steady current or voltage.

然后它又说了，给只分析直流时的电路状态取一个名字，叫做静态工作点。这时的电路可以由原电路变化而来，具体做法我等会儿再讲。

2. How to bias a Bipolar Junction Transistor (三极管)

1. 电流从 $V_{cc}$ 开始，到地为止

2. 遇到电容断路，后面的就不要了

实在不行问你老师，你可是交过钱的

3. What we will get from this operation?

如果最后成功了，你会得到这个：

$V_{CC} = I_B R_B + V_{BE}$

$V_{CC} = I_C R_L + V_{CE}$

总之你给我记住：

放大电路既要有直流、又要有交流

直流导通三极管，为交流以及整个电流提供一条固定的路经，然后电子才可以在里面跑，然后 magic thing 才可以发生

提示：

$I_B$ 指基极上的整个电流

$I_C$ 指集极上的整个电流

$I_E$ 指射极上的整个电流

$R_e$ 指射极上的所有电阻之合，以此类推

$V_{CE}$ 指的是三极管上从C(collector)到E(emitter)的电压差；我中文老师是用的$U_{CE}$，不明所以