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

To design a common emitter amplifier circuit using a BC109 transistor to achieve a gain of -100, follow these steps:

Gather the required components: BC109 transistor, resistors, capacitors, and power supply.
Determine the values of the resistors and capacitors using the module theory. For example, you can select R1 = 10kΩ, R2 = 100kΩ, R3 = 1kΩ, R4 = 10kΩ, C1 = 1μF, and C2 = 10μF.
Connect the components as per the circuit diagram below:

+12V
   |
   R1
   |
  _|_ 
 |   |
  C1  R3
 |   |
Gnd  |
 |   |
Base  |
 |   |
  E   |
  |
  R2
  |
  |
  |
  |
  |
  C2
  |
Gnd

Connect the input signal source to the base terminal of the transistor.
Connect the output load to the collector terminal of the transistor.
Connect the emitter terminal to the ground.
Connect the power supply to the collector and emitter terminals of the transistor.
Simulate the circuit using Multisim by following these steps:

a. Open Multisim and create a new blank project.

b. Place the components on the workspace according to the circuit diagram.

c. Connect the components using wires.

d. Set the values of the resistors and capacitors as determined earlier.

e. Set the input signal source and the output load.

f. Connect the power supply to the circuit.

g. Run the simulation.
Once the simulation is complete, analyze the frequency response using the Bode plotter. To do this:

a. Go to the 'Analysis' menu and select 'AC Analysis'.

b. Set the frequency range that shows both the lower and upper cutoff frequencies, for example, 10Hz to 100kHz.

c. Select the input and output nodes for the Bode plotter.

d. Run the AC analysis.
The Bode plotter will display the frequency response of the circuit, showing the gain and phase shift at different frequencies. Analyze the plot and comment on the results.

How to analyze the Bode plot:

The Bode plot will show two distinct regions, one for low frequencies and another for high frequencies. You will observe:

Low-frequency region: The gain will be relatively constant and close to the desired value of -100dB. The phase shift will be close to 180 degrees (since we are aiming for an inverting amplifier).
High-frequency region: The gain will start to decrease, and the phase shift will start to change from 180 degrees. The frequency at which the gain drops by 3dB (half the power) is considered the upper cutoff frequency (also known as the high-frequency cutoff). This is where the amplifier starts to lose its ability to amplify signals. The frequency at which the phase shift reaches 45 degrees is known as the phase margin.

Expected Bode Plot Appearance:

The Bode plot will have two plots: gain (in dB) vs frequency (logarithmic scale) and phase (in degrees) vs frequency (logarithmic scale).

Gain plot: The gain plot will be relatively flat at low frequencies, then start to roll off at a rate of 20dB per decade (a steep decline) after the upper cutoff frequency.
Phase plot: The phase plot will be close to 180 degrees at low frequencies and start to decrease towards 0 degrees as the frequency increases, eventually reaching the phase margin of 45 degrees at a certain frequency.

Note: The exact shape of the Bode plot will depend on the specific component values used in your circuit.