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Multisim Audio Signal Amplifier Design
Performance Index Requirements
提示：alt+0177：±
1. The voltage gain at 3kHz is |150|±15, the input impedance is greater than or equal to 1MΩ, the load of the amplifier is an 8Ω speaker, connected to the input end of the amplifier through a 1200:8 matching transformer, and the power supply voltage is ±15v.
设计思路：
1、由电压增益较大，采用多级放大电路级联——本例取三级
2、放大信号为音频信号，极间耦合电容取10μF，音频旁路电容取100μF
3、由输入阻抗大于或等于1MΩ，故第一级放大电路采用场效应管组成的放大电路
4、放大器输出通过1200:8匹配变压器接8Ω扬声器，则放大器输出的等效负载为1200Ω
5、+15v直流电压源
从最后一级逐级向前设计
First, the design of the third stage amplifier circuit
1. Select a common emitter triode amplifier circuit
1、输入信号和输出信号反相；
2、有较大的电流和电压增益；
3、一般用作放大电路的中间级。
4、共射极放大器的集电极跟零电位点之间是输出端,接负载电阻.
2. Determine the static working point with the help of Multisim
3. Select the resistance value from the static operating point parameters
1、由静态工作点数据 求得 Rc+Re1+Re2 = 600.66Ω
2、Re1的作用是减少温度的变化或晶体管的电流放大倍数的分散性对电路Q点的影响，在此取20Ω。
3、Re2保证集电极电压尽可能接近电压范围的中间值,从而可在输出端获得较好的电压摆幅，在此选280Ω
4、Rc选为300Ω
5、由分压原理与通用设计准则来选择Rb1、Rb2的阻值 6700Ω、3300Ω
6、确定输入阻抗 取β为150 由共发射极BJT放大器的输入阻抗确定Ri = 1363Ω
7、确定电压增益、共发射极BJT放大器增益计算公式 Av=10.84
Second, the design of the second stage amplifier circuit
The second level and the first level components take different values
Third, the design of the first stage amplifier circuit
1. The first stage adopts common source field effect amplifier circuit
Refer to the specific information for the specific selection of parameter components
重点讲解Multisim的仿真学习
Fourth, create a Multisim simulation circuit
Simulation of the third stage circuit
The voltage gain is 10.64 which meets the design