Department of Electrical Engineering
Faculty Member: ___Sir Usman___________ Dated: __13-12-2020_______
Semester:____3_________ Section: ___A_____________
EE215: ELECTRONIC DEVICES AND CIRCUITS
Lab 9: Common Emitter Amplifier
Name Reg. No Viva / Analysis Modern Ethics Individual
Quiz / Lab of data Tool and and Team
Performa in Lab Usage Safety Work
nce Report
5 Marks 5 Marks 5 Marks 5 Marks 5 Marks
Haleema Ushaq 291196
Kainat Khalid 284126
EE215: Electronic Devices and Circuits Page 1
LABORATORY EXERCISE-9
Common Emitter Amplifier
Theory and Background
The common-emitter transistor amplifier configuration is widely used. It provides large
voltage gain ( typically tens to hundreds) and provides moderate input and output
impedance. The AC signal voltage gain is defined as
AV=Voutput / Vinput
Where Voutput and Vinput can both be rms, peak, or peak-peak values. The input
impedance, Zi, is that of the amplifier (as seen by the input signal). The output
impedance Zo, is that seen looking from the load into the output of amplifier.
For the voltage-divider DC bias configuration Figure 1, all DC bias voltages can be
approximately determined without knowing the exact value of transistor beta. The
transistors AC dynamic resistance re can be calculated using
re=26mV / IEQ mA (Eq.1)
Assuming that IEQ≈ICQ
AC voltage gain : The AC voltage gain of a CE amplifier under no load can be
calculated using
Av= -Rc/ (RE+re)
If RE is bypassed by a capacitor then RE=0 in the equation above therefore.
Av= -Rc/ (re) (Eq.2)
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Part 1: Calculations
For the circuit in figure 1.
V1
10Vdc
R 3
3k C 3
out
R 1
15u
33k Q 2
R 5 C 1
50 15u
V
Q 2N 2222 C 2
Output
VO FF = 0
100u
VAM PL = 20m V _ s ig n a l R 2
FR EQ = 1k R 4
Input
10k
1k
Fig. 1: Common-Emitter amplifier (with input divider)
a. Calculate the DC bias values for the circuit of figure 1. And Record them below.
VB(Calculated)=_____2.32V___________
VE(Calculated)=________1.62V________
VC(Calculated)=________5.39V________
IE(Calculated)=_________1.48mA_______
b. Calculate re using Equation 1.
re (Calculated)=_______20.3ohm_________
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c. Calculate the amplifier voltage gain for the bypassed emitter using Equation 2
Av(Calculated)=________147.7________
Part 2: Simulation
a. Construct the circuit, shown in figure 1, in PSpice, Do not add the parts in dashed
boxes initially.
b. Perform a bias point analysis and Record the values
VB(Simulated)=____2.250 V____________
VE(Simulated)=_____1.593 V___________
VC(Simulated)=_______5.252 V_________
IE(Simulated)=____-1.593 mA____________
c. Now add the parts in the dashed boxes and perform a transient analysis. Display
both input and output waveforms and sketch them.
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GRAPH:
Input Wave sin signal
Green graph shows the input signal.
Red graph shows the output amplified signal.
d. Calculate the gain from the waveforms and record the value
Av(Simulated)=____131.17____________
e. Comment on the proximity of the calculated and simulated values for part b and d
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Values calculated through theoretical by given circuit and by stimulating the
graph are very much close.
Part 3: Implementation
a. Patch the circuit in figure 1 on a breadboard ignoring the 50 Ohms resistor as it is
used to simulate the internal resistance of signal source. Do not supply any AC
voltage for the first part. Measure the resistances using handheld multimeter and
note their values. (keep in mind that the capacitors are polarized. Longer pin is
positive and shorter pin is negative)
b. Measure the values of
VB(Measured)=________________
VE(Measured)=________________
VC(Measured)=________________
c. Using measured value of VE calculate IE i.e. VE (Measured)/ RE (measured)
d. Using results of Part C and equation 2, find out the re
re( Practical):_________________
e. Apply an AC signal V_signal=20mV, rms at frequency of 1KHz. Observe the
output waveform on an oscilloscope and sketch it. Measure the resulting output
voltage.
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Voutput:______________________
f. Calculate the gain of the implemented circuit and record the value below.
Av(measured):_______________________
g. Compare all the values expecially re and Av for all the parts (calculated,
measured and simulated) and comment on their proximity!
Conclusion:
In this lab we studied the application of transistor as amplifier and one kind of discrete transistor
Common Emitter Amplifier, it is widely used because of high voltage and power gain ,even
higher power gain than CB(Common Base) and CC(Common Collector). We calculated it’s gain
both theoretically and by stimulation through pspice.
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