Experiment-1
Single Stage BJT Amplifier : Common Emitter
Aim : Signal Analysis of Single Stage CE Amplifier
Software Required : LT Spice
Components Required : 2N2222 NPN BJT ,47kΩ resistor ,10 kΩ resistor ,680 Ω
resistor ,2.2 kΩ resistor ,100 µF capacitor ,two 10µF capacitors ,22 V DC
supply , 1 kV AC supply.
Theory : Bipolar Junction Transistor (BJT) is a device with three terminals
known as emitter, base, and collector. The BJT can be categorized into two
types which known as NPN and PNP .For NPN, the emitter and collector of the
BJT are made from n-type material while its base is made from p-type
material. In contrast, the emitter and the collector of PNP are made from
p-type material while its base is made from n-type material. In either type,
a common emitter amplifier is configured by passing an input signal to the
base terminal while measuring an output signal at the collector terminal.
For the purpose of theoretically calculation, we would consider NPN type of
BJT. Figure 1 shows an example of NPN type of BJT that configured as a
common emitter amplifier. In this configuration, the input signal is
voltage input (V1) while the output signal is voltage output (V2).The
emitter terminal is common to both the input and output voltages and
therefore it is known as a common emitter.
Circuit Diagram :
Figure : 1
Procedure : A common emitter BJT amplifier constructed in LTSpice . The model
of BJT is NPN type 2N2222 .Figure 2 shows the DC operating point analysis .
It basically shows the voltage through the nodes and the current through
the capacitors and resistors.
DC OP POINT ANALYSIS :
Figure :2
TRANSIENT ANALYSIS:
LTSpice transient analysis function is applied to the circuit in order to
visualize graphically both the input and output voltages (V1,V2).Figure 3
shows both the input voltage (bottom) and output voltage (top).
Figure : 3
AC ANALYSIS :
Figure 4 shows the AC Analysis of the circuit when the capacitor C2 is 10 micro farad.
Figure : 4
Figure 5 shows the AC Analysis of the circuit when the capacitor C2 is 15 micro farad.
Figure : 5
Conclusion :
A common emitter Bipolar Junction Transistor (BJT) amplifier has been
constructed and simulated by LTSpice simulation tool. The simulation
results on the four basic characteristics of the BJT amplifier which are
emitter current, voltage gain, input impedance, and output impedance were
observed graphically .