Experiment #8, Pt. 3
Common Base, Common Emitter, and Common
Collector Configurations for Transistor Circuits
Laboratory Report No. 09
Submitted by:
Xxxxxxxxxx, Xxxxxx
Xxxxxx, Xxxx
Submitted in partial fulfillment of the requirements for
ELET3156, Electronics Laboratory VI, Section 01.
Submitted to Professor Owen
Date Performed: 04/16/2010
Date Due: 04/23/2010
Date Submitted: 04/23/2010
Equipment List
Equipment Type
Digital Oscilloscope
Digital Multi-Meter
Signal Generator
DC Current Source
Multisim
Model Number
Agilent 54621 A
Protek D-910F
Leader LG 1311
HP E3612A
10.1
Asset Number
00006956
00008954
00006821
00008978
Model Number
2N2222A
47 kΩ
10 kΩ
1 kΩ
12 kΩ
470 Ω
10 µF
Quantity
1
1
1
1
1
1
2
Parts List
Part
NPN BJT
Resistor
Resistor
Resistor
Resistor
Resistor
Capacitor
9.0
Introduction
In this experiment, two Common Collector Amplifier circuits were built. The first circuit in
Figure 9.11 consisted of a Common Collector Amplifier with an open-circuit as its output. A
coupling capacitor was connected to the input. The open-circuit voltage gain, input resistance,
and output resistance of the amplifier was measured using a digital oscilloscope. A 470 Ohm
resistor was connected across the output of the circuit as a load. The voltage gain of the loaded
circuit was measured.
The second circuit, Figure 9.21, was built to demonstrate the effectiveness of the Common
Collector Amplifier as a buffer between a high impedance source and a low impedance load. A
buffer is any circuit that keeps the source from being affected by a load. A coupling capacitor
was connected to the input of the circuit. The input and output voltage was measured with an
oscilloscope and the voltage gain was calculated. Each value measured in the lab was simulated
in Multisim Schematic Capture to verify the accuracy of the results.
9.1
Open Circuit Voltage Gain
Figure 9.11 Common collector amplifier schematic.
A common collector amplifier was constructed in the lab according to Figure 9.11. The dual
trace digital oscilloscope connected trace 1 to the input node ( ) and trace 2 to the output node
( ). The DC power supply was connected to
and set to 15 V. The signal generator
frequency was set to 10 kHz. The signal generator output voltage ( ) was increased to a
maximum undistorted circuit output of 1.52 V.
The output voltage ( ) was measured using the oscilloscope:
Figure 9.12 Voltage at the circuit output.
The voltage gain of the circuit was calculated according the following formula:
Figure 9.13 Voltage at the circuit output.
The phase angle was measured with the oscilloscope:
Figure 9.14 Phase angle of the circuit.
The voltage gain of the circuit (
) was calculated according to the following formulas:
Figure 9.15 Calculated voltage gain.
A 200 Ω potentiometer was connected across . The resistance of the potentiometer was
adjusted until the voltage at was one half the original reading of 1.47 V. The potentiometer
was removed and the resistance (
) was measured using the DMM:
Figure 9.16 Calculated voltage gain.
The input resistance (
) of the common base amplifier was measured by connecting a 50
kΩ potentiometer in series from the function generator to the input coupling capacitor. The
potentiometer was adjusted until the output voltage ( ) was one half of the previous voltage
reading. The potentiometer was then removed from the circuit and the resistance was measured
using the DMM:
Figure 9.19 Input resistance.
The circuit was set up according to Figure 9.11. A 1 kΩ resistor was added as a load across ( ),
and the voltage at was measured:
Figure 9.1A Loaded output voltage.
A 470 Ω resistor was connected across the output node. The input voltage and the output voltage
were measured using the oscilloscope:
Figure 9.1B Input and output voltage measurements.
Simulation of Open Circuit Voltage Gain
The circuit in Figure 9.11 was constructed in Multisim schematic capture. Probes were placed
behind the input coupling capacitor and at the output node. The simulation was activated by
selecting the run button:
Figure 9.1C Location of simulation button.
The voltages across resistor
(probe 1) and
(probe 2) were recorded from the simulation:
Figure 9.1D Simulated values input and output voltage.
The simulated voltage gain (
) was calculated for the circuit:
Figure 8.1E Simulated voltage gain.
9.2
Common Emitter Amplifier
Table 9.21 Schematic of common emitter amplifier.
A common emitter amplifier was constructed in the lab according to Figure 9.21. The dual trace
digital oscilloscope connected trace 1 to the input node ( ) and trace 2 to the output node ( ).
The DC power supply was connected to
and set to 15 V. The signal generator frequency was
set to 10 kHz. The signal generator output voltage ( ) was increased to a maximum
undistorted circuit output of 1.03 V.
The output voltage was measured using the oscilloscope:
Table 9.22 Output voltage.
The voltage gain was calculated according to the following measurements:
Table 9.23 Voltage gain of common emitter amplifier.
The voltage gain was calculated according to the following formula:
Table 9.24 Calculated voltage gain.
Simulation of Common Emitter Amplifier
The circuit in Figure 9.21 was constructed in Multisim schematic capture. Probes were placed
behind the source resistor ( ) coupling capacitor and at the output node ( ). The simulation
was activated and the voltage at
and were recorded:
Table 9.25 Simulated input and output voltages.
The simulated voltage gain was calculated:
Table 9.26 Simulated voltage gain.
9.3
Conclusion
It was expected that the measured gain of the Common Collector Amplifier would be
approximately unity. The circuit in Figure 9.11 had a voltage gain of 0.86. When a resistive
load was added to the circuit the voltage gain became 0.87. Adding a load to the circuit had no
effect on the gain. The circuit in Figure 9.21 had a voltage gain of 8.43. It was expected that
this circuit would act as a buffer and try to keep the source from being affected by the load. The
source dropped only 0.5V when the 470 Ohm load was connected across the output.
Common Collector Amplifiers are extremely useful because of their very high input resistance,
high current gain, small output resistance, and unity voltage gain. The high input resistance and
low output resistance make the Common Collector Amplifier an ideal buffer between a high
impedance source and a low impedance load.