BJT&Early&effect厄利尔效应&基区宽度调制效应&miller&effect&密勒效应
early effect
基区宽度调制效应　　
这是BJT在较大工作电压时所出现的一种现象。因为BJT在放大状态工作时，集电
结上的反偏电压（直流电压+交流电源）是变化的，则集电结的势垒厚度也将随
着变化，这就会导致基区宽度发生变化；这种由集电结电压而引起基区宽度发生
变化的现象，最早是由Early提出并加以说明的，故称为Early效应（爱里效应）
，又称为基区宽度调制效应。（注意：Early效应不能译成“欧拉效应”，欧拉
是古代数学家！）
　　Early效应将直接导致BJT的输出伏安特性不饱和；这种不饱和的程度可以利
用输出伏安特性曲线（多条直线）与横轴（电压轴）的交点处的电压值（称为
Early电压）来表征。输出特性曲线的不饱和也就意味着BJT的输出交流电阻减小
，并从而将造成BJT的电压增益下降。另外，由于Early效应也表现出BJT的电流
放大系数β随着集电极电压的增大而提高。所以，在设计、制造BJT时，应该尽
量设法减小Early效应，即增大Early电压（理想BJT的输出交流电阻=∞，则
Early电压=∞）。
　　从物理本质上来说，由于Early效应是由集电结势垒厚度的变化所引起的，
所以凡是能够减小这种变化及其影响的各种措施都将有利于减弱Early效应。例
如，提高基区掺杂浓度，增大基区宽度，都可以增大Early电压，并从而提高输
出交流电阻和电压增益。但是，这些措施往往又要影响到器件的其他性能，故需
要折中处理。
　　最后补充两点：①Early效应对于BJT的不同组态，影响的大小是有所不同的
。一般，对于共发射极组态的输出特性的影响最大；但是，对于共基极组态的输
出特性的影响却很小（往往可以忽略），这是由于电流放大系数α以及集电极反
向饱和电流都与基区宽度的变化关系不大的缘故。同时，也可以说明，Early效
应对共发射极组态的输入特性的影响很小；而对共基极组态的输入特性的影响很
大。②Early效应可以引起集电结出现扩散电容。反偏的集电结总是存在势垒电
容，一般是不存在扩散电容的；但是基区宽度随着集电结电压的变化，即使得基
区中的存储电荷数量也相应的随着集电结电压而变化，这就是扩散电容。所以
Early效应的这种影响也将要影响到器件的速度性能。
密勒效应（Miller effect）是在电子学中，反相放大电路中，输入与输出之间
的分布电容或寄生电容由于放大器的放大作用，其等效到输入端的电容值会扩大
1+K倍，其中K是该级放大电路电压放大倍数。虽然一般密勒效应指的是电容的放
大，但是任何输入与其它高放大节之间的阻抗也能够通过密勒效应改变放大器的
输入阻抗。
　　米勒效应是以约翰·米尔顿·密勒命名的。1919年或1920年密勒在研究真空
管三极管时发现了这个效应，但是这个效应也适用于现代的半导体三极管。
　　——————————
　　*密勒效应可以采用平衡法（或中和法）等技术来适当地减弱密勒电容的影
响。平衡法即是在输出端与输入端之间连接一个所谓中和电容，并且让该中和电
容上的电压与密勒电容上的电压相位相反，使得通过中和电容的电流恰恰与通过
密勒电容的电流方向相反，以达到相互抵消的目的。
　　*密勒电容对器件的频率特性有直接的影响。例如，对于BJT：在共射（CE）
组态中，集电结电容势垒电容正好是密勒电容，故CE组态的工作频率较低。对于
MOSFET：在共源组态中，栅极与漏极之间的覆盖电容Cdg是密勒电容，Cdg正好跨
接在输入端(栅极)与输出端(漏极)之间，故密勒效应使得等效输入电容增大，导
致频率特性降低。
　　*密勒效应的好处：① 采用较小的电容来获得较大的电容（例如制作频率补
偿电容），这种技术在IC设计中具有重要的意义（可以减小芯片面积）；② 获
得可控电容 (例如受电压或电流控制的电容) 。
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ensearchweb高中英语 |
阅读理解。
Early people had very little effect on the environment. They lived in
 试题类型：
完形填空题
 试题难度：
 试题内容：
阅读理解。
Early people had very little effect on the environment. They lived in eaves in very small " clan" groups.They collected or killed only enough for the clan"s survival. Early clans were nomadic, which means thatthey did not stay in one place. Instead, they moved around, following the animals that were their main food source and seeking areas where seasonal plants grew wild. Moving around seasonally helped to protect the environment. The land had time to recover and animals had time to breed (繁殖) before the clanreturned for the next season.
As time went by, these small family clans joined with others to form larger groups for protection. Joining with other clans gave them more hunters and more women to help cut up the meat and share it between families. Eventually, people tamed (驯养) wild animals such as dogs and horses. People settled around riversand fertile plains to share responsibilities and duties. Then, people began to plant crops instead of moving to areas where the plants grew. This development changed the environment.
Traditional forms of work also changed. Some people were hatter at performing a particular task than other clan members, so they began to specialize in things they were good at doing. This also meant that theybegan to exchange their goods for things that others produced.
People began to communicate with distant tribes. Land was cleared for roads. Foreign plants and animalswere transported to places where they had not existed before. Specialization also gave people more free time.So art, dance and music became important ways of expressing feelings and thoughts. This was how many great civilizations started.
Compared to the past, modern civilization has experienced many changes to become the highly developed society that exists today. Populations have increased rapidly. Forests have been cleared for farms. Inventionsand technology have made work easier.
However, pollution and other serious problems have also resulted from human progress. As concerned citizens, it is up to us to learn from past mistakes and to help maintain and improve our environment.
1. Early tribes didn"t have much effect on animal population because _____.
A. they kept animals for themselves B. they ate only vegetables C. they killed only enough for food D. they loved animals
2. The main purpose for small clans to join together was _____.
A. to hunt animalsB. to seek safety C. to share caves D. to protect environment
3. Which of the following is TRUE according to this passage
A. Early people moved to new places looking for new sources of food. B. Modem civilization began when people started to live together in big groups.C. Modem advancements are always good for the environment. D. People began to exchange goods because they didn"t have enough money.
4. It can be concluded from the passage that _____.
A. human progress has brought civilization to the societyB. civilization has improved traditional forms of work C. our environment has been affected by human progress D. early people understood environmental protection
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