Common Emitter Amplifier – Characteristics, Biasing, Solved Examples

这种配置称为公共发射极配置，因为这里的发射极被用作输入基本信号和输出负载的共同负终端。换句话说，发射极终端成为输入阶段和输出阶段的参考终端（基础和集电极终端共有）。

常见的发射极放大器是PNP和NPN晶体管下面的图3.13中最常用的晶体管配置。

basically, here the transistor base terminal is used as the input, the collector is configured as the output, and the emitter is wired common to both (for example, if the transistor is NPN the emitter may be joined to the ground line reference), hence it gets its name as the common emitter. For an FET, the analogous circuit is termed as the common-source amplifier.

常见的发射极特征

Just like常见的基本配置在这里，两个特征的范围再次成为充分解释共同发射器设置的性质至关重要的：一个用于输入或基本发射机电路，另一个用于输出或收集器发射机电路。

These two sets are shown in Fig. 3.14 below:

根据标准的常规规则，指示发射器，收集器和底座的当前流动方向。

Although, the configuration has changed, the relationship for the current flow which was established in our previous common base configuration still applies here without any modifications.

This may be represented as:我e= IC+ Ib和我C=Ie。

For our present common-emitter configuration, the indicated output characteristics are a graphical representation of the output current (IC）与输出电压（VCE）对于选定的输入电流值集（ib）。

输入特性可以看作是输入电流的绘图（ib）反对输入电压（V是）对于给定的一组输出电压值（VCE）

Observe that the characteristics of Fig. 3.14 indicates the value of Ibin microamperes, instead of milliamperes for IC.

Also we find that the curves of Ibare not perfectly horizontal like the ones achieved for Ie在公共基本配置中，这意味着收集器对发射器电压具有影响基本电流值的能力。

通用发射极配置的活动区域可以理解为右上象限的部分，该部分具有最大数量的线性，含义是该特定区域，其中ib倾向于几乎是笔直且均匀散布的。

在图3.14a中，可以在V的垂直虚线的右侧见证该区域CEsatand over the curve of Ibequal to zero. The region on the left of VCEsat称为饱和区域。

在公共发射极放大器的活性区域内，收集器基数连接将是反向偏置的，而基本发射极连接将是正向偏置的。

如果您记得这些完全相同的因素，这些因素持续存在于公共基础设置的活动区域中。可以实现通用发射极配置的活动区域，以用于电压，电流或功率扩增。

与公共基本配置相比，公共发射极配置的截止区域似乎没有很好地表征。请注意，在图3.14的收集器特征中C我并不是真的与零相对应b为零。

For the common-base configuration, whenever the input current Iehappens to be near zero, the collector current becomes equal only to the reverse saturation current Ico, in order that the curve Ie= 0 and the voltage axis were one, for all practical applications.

可以通过等式的适当修改来评估收集器特性变化的原因。（3.3）和（3.6）。如下所示：

Assessing the above discussed scenario, where IB = 0 A, and by replacing a typical value like 0.996 for α, we are able to achieve a resultant collector current as expressed below:

如果我们考虑我CBOas 1 μA, the resulting collector current with Ib= 0 a将为250（1μA）= 0.25 mA，如图3.14的特征中所述。

我n all our future discussions, the collector current established by the condition Ib= 0 μA will have the notation as determined by the following Eq. (3.9).

The conditions based on the above newly establish current could be visualized in the following Fig 3.15 using its reference directions as outlined above.

为了在公共发射极模式下以最小扭曲的最小扭曲启用放大，截断是由收集器电流i建立的C= I首席执行官。

我t means the area just under Ib应避免=0μA，以确保放大器的清洁和未发生的输出。

How Common Emitter Circuits Work

如果您希望配置像逻辑开关一样工作，例如与微处理器一起使用，则配置将显示几个感兴趣的运营点：first as the cut off point, and the other one as the saturation region.

截止可能是理想情况下设定的C= 0 mA for the specified VCEvoltage.

自从我首席执行官i对于所有硅BJT来说，通常很小b= 0 μA or IC= I首席执行官

如果您记得在公共基础配置中，则通过直线等效的直线建立了一组输入特性，从而导致结果v是= 0.7 V, for all levels of Iewhich was greater than 0 mA

We can apply the same method for a common-emitter configuration as well, which will produce the approximate equivalent as depicted in the Fig. 3.16.

结果符合或我们以前的扣除额，根据该扣除率，根据该扣除率，在活动区域​​内BJT的基本发射极电压或状态为0.7V，无论基本电流如何，这将是固定的。

解决了实践示例3.2

如何偏向普通发射极放大器

biasing a common-emitter amplifier appropriately could be established in the same way as it was implemented for the公共基网络。

Suppose you had a npn transistor just as indicated in Fig. 3.19a, and wanted to enforce a correct biasing through it, in order to establish the BJT in the active region.

For this you would require to first indicate the Iedirection as proven by the arrow marks in the symbol of the transistor (see Fig. 3.19b). After this, you'd require establishing the other current directions strictly as per Kirchhoff’s current law relationship: IC+ Ib= IE.

随后，您必须以正确的极性引入供应线，以补充I的指示b和我Cas indicated in Fig. 3.19c, and finally conclude the procedure.

我n the similar manner a pnp BJT could be also biased in its common emitter mode, for this you simply have to reverse all the polarities of the Fig. 3.19

典型应用：

低频电压放大器

下面显示了公共发射极放大器电路使用的标准说明。

交流耦合电路的功能像液位变速器放大器。在这种情况下，基本 - 发射极电压下降应该约为0.7伏。

输入电容器C可以摆脱输入的任何DC元素，而电阻R1和R2用于偏置晶体管以使其能够在整个输入范围内处于活动状态。输出是输入的交流分量的倒置复制，该复制已由比率RC/RE增强，并通过所有4个电阻器决定的度量进行了移动。

由于RC通常非常庞大，因此该电路上的输出阻抗可能确实很大。为了最大程度地减少这种关注点，RC的维持尽可能小，加上放大器伴随着电压缓冲液，例如发射机跟随器。

射频电路

Common-emitter amplifiers有时也在射频电路，例如放大弱信号通过天线。在这种情况下，通常由包括调谐电路的负载电阻代替。

这可以实现将带宽限制为在所需的工作频率中构造的一些薄带。

此外，它还允许电路以更大的频率工作，因为调谐电路使其能够引起任何电极间的电极和run-a-away电容，这通常会禁止频率响应。普通发射器也可以被广泛用作低噪声放大器。