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电 子 技 术 - PowerPoint PPT Presentation


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电 子 技 术. 欢迎各位光临指导. 执教者:谢婷. 第四章 放大电路中的反馈. 基本概念及判别方法 负反馈放大电路组态. 练习. 定义:将放大电路的输出量 X 0 (U 0 或 I 0 ), 通过一定的方式传送到放大电路的输入回路来. 反馈. 净输入量。 它是 Xi 和 X f 的共同作用结果. 输入量 Xi. Xi ’. 输出量 Xo. . 放大电路. 反馈. 反馈量 X f. 正反馈与负反馈. 引入反馈后产生结果: 正反馈 : 使输出量的变化增大 负反馈 : 使输出量的变化减小 从引入反馈后净输入量的变化:

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电 子 技 术

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X0(U0I0),.

XiXf

Xi

Xi

Xo

Xf


:

:

:

:



:,


:

  • ,,,,,,

  • Xi=Xi+Xf

  • Xi=Xi-Xf


Ui=Ui- Uf

Ui=Ui+ Uf

-

+

-

+

Uf

Uf

-

+


Ii=Ii- If

If

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Ii

Ii

+


Ui

C


//

R2R3


;;

R2C


R1b1T1c1b2T2c2

e2R3b1


1

  • ,


2

Ii

Ii

+

+

Ui

-

If

Ui

+

Uf

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  • Xi=Xi+Xf

  • Ui=Ui+Uf

  • Ii=Ii+If


  • Uo=0Uf=0

  • Uo=0Uf0


Ui=Ui+Uf

Uo=0

Uf=0


Ii=Ii+If

Uo=0

If=0


Ui=Ui+Uf

Uo=0

Uf


Ii=Ii+If

If


4-1




48XiXo;Xi=Xi+Xf


AXoXi


A=Xo/Xi (4.1)


FXfXo


F=Xf/Xo (4.2)

AfXoXi


Af=Xo/Xi (4.3)


4.1) (4.2)Xo=AXi,Xf=Fxo=FAXiXi=Xi+Xf=1+AFXiAf


Af=A/1+AF (4.4)


AF0Af1/1+AFAf


XiXo4.2


Af--



4.4AF>>1


Af=1/F (4.5)


AF>>1(4.5)AfAf


(4.2)(4.3)(4.5)


Xo/Xi~~Xo/Xf


Xi~~Xf4.6)



Ui~~UfUi~~0Ii~~IfIi~~0


Af=Xo/Xi~~1/FAfXo~~1/FXiXoXiXXUiUo~~I/FUiIiUo~~I/FIiUiIo~~I/FUiIo~~I/FIiFXoXi


F



4-7(a)


F=Uf/Uo=R1/R1+R2 (4.7)


4-7(b)


IR2=U--Uo/R2 (4.7)


IfUoU-=0R2


If=-Uo/R2



F=If/Uo=-1/R2 (4.8)


4-7(c)


Uf=IoR1



F=Uf/Io=R1 (4.9)


4-7(d)U-=0


If=-R3/R2+R3Io


IfIoF


F=If/Io=-R3/(R2+R3) (4.10)




AUF4-7AUI~~UF


AUF=UO/UI~~UO/UF=1/F 4.11


4.7)AUF=1+R2/R1


4-7BII~~IFII~~0UIR1


AUF=U0/UI~~U0/IIR1~~U0/IFR1=1/F1/R 4.12)


(4.8),ARF=-R2/R1


R1RSUIUSAUSF


AUSF~~1/F1/RS 4. 13


4-7CUI~~UF


AUF=U0/UI~~I0RL/UF=1/FRL 4.14)


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