Common Emitter Amplifier Circuit Design and Simulation with Multisim for -100 Gain

To design a common emitter amplifier circuit using Multisim, follow these steps:

1. Start by selecting the BC109 transistor, which is a commonly used NPN transistor. This transistor has a low noise figure and good gain characteristics, making it suitable for amplification.

2. Determine the values of resistors R1 and R2, which are used to set the biasing point of the transistor. The values of these resistors can be calculated using the following formulas:

   • R1 = (Vcc - Vbe) / Ic
   • R2 = Vbe / Ib Here, Vcc is the supply voltage, Vbe is the base-emitter voltage of the transistor (typically around 0.7V), Ic is the desired collector current, and Ib is the base current.

3. Choose appropriate values for Vcc, Ic, and Ib based on your requirements. In this case, to achieve a gain of -100, we need to select a suitable collector current and base current. Let's assume Ic = 2mA and Ib = 20µA.

4. Calculate the values of R1 and R2 using the formulas mentioned in step 2. Let's assume Vcc = 9V.

   • R1 = (9 - 0.7) / 0.002 = 4.15kΩ
   • R2 = 0.7 / 0.00002 = 35kΩ

5. Connect the circuit components as shown in the schematic diagram below:

   Vcc -------- R1 -------- Base of BC109 transistor | R2 | GND | Emitter of BC109 transistor | GND | Collector of BC109 transistor -------- Load resistor -------- Vout

6. Configure the function generator as an input sinusoidal signal source with an appropriate amplitude and frequency.

7. Connect an oscilloscope to measure the input and output voltages. Adjust the oscilloscope scale to clearly visualize the signals.

8. Measure the voltage drops at the collector, emitter, R1, R2, and the collector-emitter voltage using the oscilloscope. Note down the values.

9. Measure the current at the collector, emitter, R1, R2, and the collector-emitter voltage using a current probe or a multimeter. Note down the values.

10. Simulate the frequency response of the circuit using the bode plotter in Multisim. Sweep the frequency range from a low value (e.g., 10Hz) to a high value (e.g., 100kHz) to observe the lower and upper cutoff frequencies.

11. Comment on the frequency response results obtained from the bode plotter. Analyze the gain and phase shift at different frequencies and observe the cutoff frequencies. To obtain the cutoff frequencies, you need to find the frequencies at which the gain of the amplifier drops by 3dB (or approximately 30% of the maximum gain). You can do this by examining the Bode plot and identifying the points where the gain curve intersects the -3dB line. The lower cutoff frequency is the frequency at which the gain starts to roll off, and the upper cutoff frequency is the frequency at which the gain starts to drop significantly.

Translation in Chinese: 使用Multisim模拟实现一个共射极放大器电路，使用BC109晶体管实现增益为-100。

1. 选择BC109晶体管，这是一种常用的NPN晶体管。该晶体管具有低噪音系数和良好的增益特性，非常适合放大器。

2. 确定电阻器R1和R2的值，这些电阻器用于设置晶体管的偏置点。可以使用以下公式计算这些电阻器的值：

   • R1 = (Vcc - Vbe) / Ic
   • R2 = Vbe / Ib 这里，Vcc是电源电压，Vbe是晶体管的基极-发射极电压（通常约为0.7V），Ic是所需的集电极电流，Ib是基极电流。

3. 根据您的要求选择Vcc、Ic和Ib的合适值。在这种情况下，为了实现增益为-100，我们需要选择适当的集电极电流和基极电流。假设Ic = 2mA，Ib = 20µA。

4. 使用步骤2中提到的公式计算R1和R2的值。假设Vcc = 9V。

   • R1 = (9 - 0.7) / 0.002 = 4.15kΩ
   • R2 = 0.7 / 0.00002 = 35kΩ

5. 按照下面的原理图连接电路组件：

   Vcc -------- R1 -------- BC109晶体管的基极 | R2 | GND | BC109晶体管的发射极 | GND | BC109晶体管的集电极 -------- 负载电阻 -------- 输出电压（Vout）

6. 将函数发生器配置为输入正弦信号源，使用适当的幅值和频率。

7. 使用示波器测量输入和输出电压。调整示波器刻度以清晰可见信号。

8. 使用示波器测量集电极、发射极、R1、R2和集电极-发射极电压的电压降。记录这些值。

9. 使用电流探头或万用表测量集电极、发射极、R1、R2和集电极-发射极电压的电流。记录这些值。

10. 使用Multisim中的波特图绘制器模拟电路的频率响应。从低值（例如10Hz）到高值（例如100kHz）扫描频率范围，以观察低截止频率和高截止频率。

11. 对从波特图绘制器获得的频率响应结果发表评论。分析不同频率下的增益和相移，并观察截止频率。 为了获得截止频率，需要找到放大器增益下降3dB（或大约最大增益的30%）的频率。可以通过检查波特图，并确定增益曲线与-3dB线交叉的点来实现。低截止频率是增益开始衰减的频率，高截止频率是增益开始显著下降的频率。