Looking at the DC behavior of the almlifier and following the convention that lower case letters represent changes in the respective quantities:

The gain is

which for small r_E can be approximated by

Add bypass capacitor 添加旁路电容器

Looking at the DC behavior of the almlifier and following the convention that lower case letters represent changes in the respective quantities:

The gain is

but for AC signal variations for which C_E is an effective bypass, the gain is

Remove bypass capacitor 移除旁路电容器

With the bypass capacitor in place, the voltage gain is dertemined by the collector resistor R_C and the effective resistance of the transistor r_E.

This effective resistance is 这种有效电阻是 where RBE is the forward resistance of the base-emitter diode. Remove bypass capacitor 移除旁路电容器 其中 R BE 是基极-发射极二极管的正向电阻