Foreword
Write negative feedback amplifier circuit design today
The basic principle of negative feedback circuit
The following figure shows the direct coupling using NPN + PNP negative feedback amplification circuit
AC path as shown in FIG
exchange view, \ (Q_1 \) emitted electric potential equal to \ (u_i \) , then \ [i_4 = \ frac {v_i } {R_4} \] is \ (R_f \) voltage across \ ((u_o-u_i) \ ) is, \ [I_F = \ FRAC \]} {{u_o-u_i R_f}
when removing the negative feedback (the \ ( R_f \) is connected to the output section of the ground), the total gain is set at this time a, the \ (V ^ \ prime_i = \ FRAC V_o} {a} {\) , then \ [i_e = \ frac {v ^ \ } // {R_4 R_f prime_i} = \ {V_o FRAC} {A} {\ CDOT} \ {R_4 FRAC + R_f R_4 {} {\ R_f CDOT}} \]
\ [i_4 are used I_E = I_F + \]
simultaneous on formula have \ [\ frac {v_i} { R_4} = \ frac {u_o-u_i} {R_f} + \ frac {v_o} {A} {\ cdot} \ frac {R_4 + R_f} {R_4 {\ cdot} R_f } \]
Solutions have \ [A_u = \ frac {v_o
} {u_i} = \ frac {1} {\ frac {1} {A} + \ frac {R_4} {R_4 + R_f}} \] when A very large Time\[A_u{\approx}\frac{R_4+R_f}{R_4}\]
100 times the voltage amplifier circuit design
Design PNP NPN + 100 directly coupled voltage doubler amplifier circuit
1. 确定直流电源电压
这里选\(12V\)电压电源。
2. 确定\(R_3\)和\(R_4+R_5\)
方法和之前讲的一样，这里静态集电极电流取\(I_{CQ1}=2mA\)。
静态集电极与发射极间电压取电源电压的一半\(U_{CEQ1}=V_{CC}/2=6V\),则\(R_3+R_4+R_5=6V/2mA=3k\Omega\)。
取\(R_4+R_5\)的压降为2V，则\(R_4+R_5=2V/2mA=1k\Omega\)，则\(R_3=2k\Omega\)。
3. 偏置电路的设计
方法在第一篇讲过，取标称电阻值得 \(R_1=13k\Omega\)和\(R_2=39k\Omega\)。
4. 确定PNP放大电路
\(Q_1\)的静态集电极电位\(U_{CQ1}=2mA\times2k\Omega=4V\)，则 \(Q_2\)的静态发射极电位\(U_{EQ2}=4V-0.7V=3.3V\)。
取\(I_{CQ2}=2mA\)，则\(R_7=3.3V/2mA=1.65k\Omega\)，取标称值电阻\(1.6k\Omega\)。
为使\(U_{CEQ2}=V_{CC}/2=6V\)，则\(R_6=\frac{12V-3.3V-6V}{2mA}=1.35k\Omega\)，取标称值电阻\(1.3k\Omega\)。
5. 确定负反馈电路
由开篇讲的理论可知，取\(R_f=10k\Omega\)时，\(R_4=\frac{10k\Omega}{100-1}=101\Omega\)，取标称值电阻值\(100\Omega\)，则\(R_5\)取\(910\Omega\)。
然后耦合电容和旁路电容都取\(22uF\)。
6. Multisim仿真验证
设置好参数进行仿真，如下图
测得此电路电压放大倍数\ (A_u = \ frac {776.246mV } {10mV} \ approx77.6 times \) , a value calculated from the deviation, to adjust the resistance R4 a voltage magnification of 100 times measured \ (R_4 \) take \ (75 \ Omega \) satisfy the requirements, as shown in FIG.
At this time, the voltage amplification factor \ (A_u = \ frac {1.017V } {10mV} \ approx100 times 40dB = \) , the output voltage waveform shown below
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