Exp 9. BJT Fixed Bias CE Amplifier

Concept : To demonstrate the working of a BJT Fixed Bias CE Amplifier

Explanation:

A BJT (Bipolar Junction Transistor) amplifier is a type of electronic amplifier that uses bipolar junction transistors to amplify electrical signals. BJTs are three-layer semiconductor devices consisting of an N-type layer (negatively doped), a P-type layer (positively doped), and another N-type layer. There are two main types of BJTs: NPN and PNP.

 

Working Principle

In a BJT amplifier, the transistor operates in the active region, where the base-emitter junction is forward-biased, and the collector-base junction is reverse-biased. This configuration allows the transistor to amplify the input signal applied to the base, resulting in a larger output signal at the collector12.

 

Types of BJT Amplifiers

  • Common Emitter (CE) Amplifier
  • Common Base (CB) Amplifier
  • Common Collector (CC) Amplifier

 

Here we are going  to try out the Fixed Bias Common Emitter (CE) Amplifier.

 

Simulation Mode: Transient

Simulation Parameters: .tran 0.01 10m 0

 

Simulation Type

Start Time(sec)

Stop Time(sec)

Step Time(sec)

.tran

0

10m

0.01

 

Reference Netlist:

* BJT Fixed Bias CE Amplifier

 

.model mybjt NPN

 

V1 COM.1 0 dc 0 ac 1 sin(0 1m 500) 

C1 COM.2 COM.1 10u 

R1 COM.3 COM.4 22k 

R2 COM.3 COM.2 50k 

V2 COM.3 0 5 

C2 COM.4 COM.5 10u 

R3 COM.5 0 100k 

Q3 0 COM.2 COM.4 mybjt 

 

 .tran 0.01 10m 0

 

.control 

run 

plot all 

.endc 

.end

 

Reference Circuit Schematic:

Make the circuit diagram with the exact pin-to-pin connection as shown below to practice. This will help you to complete the experiment successfully.

Note: Please check the following parameters of Q1.

 

Reference Circuit Details:

Supply=COM.3, Input=COM.1 and Output=COM.5

Reference Output:

After the simulation is done, the following output graph appears at the screen showing the voltages and currents across all the nodes.

 

Conclusion

We can see that the output signal is amplified by almost 60 times. Thus the gain of the amplifier is Vout/Vin=60.

Assignment: Implement a Common Collector(CC) Amplifier using a PNP transistor. Note: Change the NPN to PNP in device parameters.

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