模电复习答案

Ri?rbe1//R1, Ro?R4,AV?

??1(R3//rbe2)??2R4?rbe1rbe2

共基-共集电路

Ri?rbe1//R41??1,

Ro?R3//R4?rbe2//R51??2

AV?

?1(R3//{[rbe2?(1??2)R5]//R4}rbe1?(1??2)R5rbe2?(1??2)R5

共源-共集电路

Ri?R1, Ro?

R2?rbe2(1??2)R4//R4AV??gm(R2//[rbe2?(1??2)R4]?,rbe2?(1??2)R41??2

共源-共射电路

Ri?R3?R2//R1, Ro?R8,AV??gm(R4//R6//R7//rbe2)?

2. 一个直接耦合的两级放大电路如图所示,已知:

??2R8rbe2

?1?25,?2?100,

rbb1'?rbb2'?300?,UBE1?0.7V,UBE2??0.3V,试求:

a) 为了使Ui?0时,Uo?5.1V,Rb的阻值应为多大?

b) 设电路的静态工作点已经由所求出的Rb确定,则电路的电压放大倍数

?/U?是多少? Au?Uoic) 若电阻Rb与T1的基极脱焊,T1和T2的集电极静态电位Uc1和Uc2分

别为多少?

答:(a)IC2?IE2?1mAIE2Re2?0.3?(IC1?IC2/?2)Rc1,,

IC1?0.8mA?IE1,

(b)

Vcc?VBE1V?IC1/?1?BE1R?5.8k? Rb0.5,brbe1?300?(1??1)26mV?1.134k?,IE126mV?2.926k? IE2rbe2?300?(1??2)AV?Ri1??(R//Ri2)??2RC2?1C1??142

Rs?Ri1rbe1rbe2?(1??2)Re2Ri1?Rb//rbe1,Ri2?rbe2?(1??2)Re2

(c) UC1?9V

3. 直接耦合放大电路如图所示,已知:已知:?1??2?30,rbb1'?rbb2'?300?,

UC2?0V

UBE1?0.7V,UBE2??0.2V,试求:

a) 计算T1和T2的静态工作点及晶体管的rbe; b) 画出简化的h参数微变等效电路;

?/U?、输入电阻Ri和输出电阻Ro。 c) 计算电路的电压放大倍数Au?Uoi

答:(a)IC1?1mA,

IB1?33uA,UCE1?5.3V,rbe1?1.1k?,IC2?0.43mA,

IB2?14uA,UCE2??7.6V,rbe2?2.1k?

(c)AV1??8.24,

AV2?0.987,AV??8.24?0.987??8.13Ri?7.58k?,

Ro?215?,

差分放大电路

1. 电路如图所示,T1和T2的低频跨导gm均为2mA/V。试求解差模放大倍

数、输入电阻和输出电阻。

答:Rid??,

Rod?2Rd?40k?,Avd??gmRd??40

2. 图示电路参数理想对称,晶体管的β均为50,rbb'=100Ω,UBEQ≈0.7V。

试计算RW滑动端在中点时T1管和T2管的发射极静态电流IEQ,以及动态参数Ad、Ac、KCMR、Rid和ROd。

答:

IE1?IE2?1mA,rbe1?rbe2?100?(1??)26mV?1.4k? IE1,

Ad?1?(Rc//RL)??252R?r?(1??)Rwbbe2??(Rc//RL)Ac???1.25?10?5 RwRb?rbe?(1??)(?2Ro)2KCMR?Ad?200000Ac,

Rid?2[Rb?rbe?(1??)Rw]?9.8k?2,

Rod?Rc?10k?

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