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Hi Learners, I hope you are doing good. This lesson is about implementation of one of the types of  Amplifiers i.e, Common Emitter BJT Amplifier. But, prior to this, we'll revise some basic concepts so that it will be easy for you to understand the roots of the Experiment. We'll talk about:
  1. What are Common Emitter Bi-Junction Transistors.
  2. Concepts of Common Emitter Bi-Junction Transistors.
  3. Implementation of Common Emitter BJT Amplifiers in Proteus ISIS.
  4. Why we use Common Emitter BJT in Amplifiers.

What are Common Emitter Bi-Junction Transistors

There are three types of Configurations of a transistor named:
  1. Common Emitter Configuration
  2. Common Base Configuration
  3. Common Collector Configuration
We chose the Common Emitter Configuration due to its suitability (You will learn the reason). We can Define Basic Common Emitter BJT Amplifier as: "A type of amplifier circuit made by a Bi-Polar junction Transistor that uses NPN BJT Transistor, inverts the voltage output wave at 180 degree and is the one from the three basic BJT amplifier Configuration." Recall that A Transistor is made by combining two diodes in required manner. Hence, It there are two types of Transistors:
  1. NPN configuration.
  2. PNP Configuration.
Here N is the symbol for Negative doping and P is the symbol for positive doping.
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Concepts of Common Emitter Bi-Junction Transistors

At this instance We'll look at some basic concepts, on the basis of which we chose these Components along with the values of Components  of amplifier. Current gain: In BJT Amplifiers, current gain is the ratio of change in collector current to the change in the current of base.

mathematically,           Current Gain= Change in collector current/Change in Base Current


At the same token, Voltage Gain: The Voltage Gain of an amplifier is the product two Quantities. One is the ratio of output resistance of the collector to the input resistor of the base, and the other is the current gain.

Voltage Gain=ß(Rc/Rb)

During the Practical work we take  AC output voltage from collector with respect to emitter and the Output of Amplifier is taken from Collector. On the other hand, the input is given to the base terminal. It is obvious to notice that the emitter is Common to Base and Collector. It consist of Voltage divider biasing, hence one of the basic part of circuit is consist of two resistors so that their mid-point is used for supply Base Bias voltage. One more importance point to remember is gain is different from one transistor to the other.
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Biasing: Biasing is a technique  to add the Battery in a circuit. It is important in Electronic devices because it establishes the correct operating point of the Transistor amplifier when it is ready to receive the signal from input and hence the plays an important role in reducing the distortion in the output. If we look at the characteristics then we come to know that Common Emitter BJT Amplifiers has high voltage gain, the current gain is medium and the circuit has a high power gain.

Implementation of Common Emitter BJT Amplifiers in Proteus ISIS

For the practical verification of the circuit It is always Advisable to Perform it at any simulation software. Hence open Your Proteus ISIS. Components Required:
  1. NPN transistor (2N171) .
  2. Vsine
  3. Capacitor
  4. Resistor
  5. DC Power source
  6. ground Terminal
  7. Oscilloscope


  • Choose 1st four Components from the Pick Library "P" one by one by writing their name in it.
  • Collect the DC power supply from "Generator mood" present on the left most tab.
  • To get the Ground terminal, left Click on the working screen and go to Place>Terminal>Ground and fix it on the screen.
  • Oscilloscope is present in the "Virtual Instrument Mood" on the same tab.
  • Once you have chosen all the  required Device  then set them one by one on the Working area according to the Picture given below and connect them with the help of wires.
Circuit of BJT amplifier, common Emitter bjt amplifier, Proteus circuit for BJT amplifier
  • At the Instance we will change the values of some devices So I have made a table for this:
  • Components Values
    Resistor R1 60ohm
    Resistor R2 500ohm
    Resistor R3 1000ohm
    Resistor R4 2000ohm
    Resistor R5 100ohm
    Oscilloscope A=20V, B=2V
    Vsine Frequency=1000Hz, Amplitude=110V
    DC source 10V
After substituting the value we get the prepared circuit for the amplifier as:
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It seems that all the things are ready. Once you play the simulation then you can change its values and You will acquire the following output.
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  • Select the Current probe from the left most bar and connect them in the circuit one with the Base wire and the other with the collector.
One can find the current gain by simply putting the values in the formulas given in the concepts portion.


Current gain=6.2*10-12/6.1


as it is a ratio, hence has no unit.

At the same token,

Voltage gain=1.01*10-9*(500/2000)


NOTE: The Gain is vary from transistor to transistor and the temperature is also an important feature. Therefore, the gain is always unpredictable.
  •  We got the required output in the Proteus ISIS as required.
let's find out why we used this for our experiment.

Why we use BJT in Amplifiers

Common Emitter BJT Amplifiers are important in the World of Electronics. One can get the idea of their influence by the following points:
  1. These Amplifiers are used in low frequency voltage amplifier.
  2. The are useful because of their high power gain with medium voltage and current gain hence they are cheap.
  3. The output impedance is high.
  4. It has inverting effect so can be used in the different appliances for different purposes.
In today's tutorial, We learnt what is Common Emitter BJT amplifiers, some basic concepts along with the simulation in the Proteus ISIS. We also saw why these Amplifiers are used in the real life. The circuit and the output may vary for other circuits but don't worry about that because it is a very sensitive circuit.