Electronics Engineering 1, Laboratory | July 18, 2019

Experiment No. 1
Frequency Response of Common Emitter Amplifier
Rod Diego T. Palaganas1, Ronnie S. Concepcion II2
1
Computer Engineering Department, University of Perpetual Help System Dalta
2
School of Graduate Studies, Mapua University
1,2
Manila, Philippines
1
palaganas_reggie@gmail.com
2
concepcionriis@gmail.com

Abstract— The common emitter circuit is popular because it’s the collector current in the whole collector resistor Rc. Thus,
well-suited for voltage amplification, especially at low the amplified load resistor appears across the collector
frequencies. It is also used in radio frequency transceiver circuits. resistor.
Also, common emitter configuration commonly used in low-noise
amplifiers.

Index Terms— Bipolar junction transistor, Oscilloscope,

IV. PROCEDURE
emitter-base junction, Sinusoidal waveform, bypassed
capacitor Measuring the DC bias voltage of the common-emitter
amplifier
I. OBJECTIVES
The objectives of this experiment are first to be able to [1] Connect the circuit shown in Figure 2. Do not turn on the
determine the input impedance and the output impedance of a power supply and do not apply any signal from the signal
CE amplifier, second is to be able to measure the voltage gain generator.
and examine the input & output waveform and phase [2] Turn on the power supply.
characteristic of a CE amplifier. [3] With no AC signal from the signal generator, measure the
DC bias voltages of the circuit as indicated in Table 1.

II. MATERIALS NEEDED AC operation of a Common -emitter amplifier

Power Supply Resistors:
Function/Signal Generator 1 - 91 kΩ [1] Make sure that the equipment’s are properly calibrated.
Multi-meter 1 – 8.2 kΩ [2] Using the oscilloscope, measure 1 kHz, 20 mV(peak)
Oscilloscope 2 – 3.3 kΩ output voltage from the signal generator and connect this
1 - 1 kΩ signal to the input of the Common-emitter amplifier. Measure
Transistors: the following ac currents and voltages using an analog or a
1 pc 2N6672 or equivalent (npn) digital multi-meter.
[3] Remove the bypassed capacitor C3 and repeat procedure 1.
Capacitors: Record your data in the third column of the table. What is the
3 - 10µF effect of removing the bypassed capacitor C3?
[4] Connect the oscilloscope probes of Channel A and
III. INTRODUCTION Channel B at the output terminals and input terminals of the
common-emitter configuration, Set the oscilloscope to dual
There are three basic stage of bipolar-junction-transistor (BJT) mode, and adjust the horizontal scale to 10ms/div. Adjust the
and one of it is common-emitter. A circuit called common- vertical scale of Channel A to 200 mV/div and the vertical
emitter because both the signal source and the load share the scale of Channel B to 500 mV/div. Adjust the vertical position
emitter lead as a common connection. When a signal is of the two and determine the phase difference between the
applied across the emitter-base junction, the forward bias input and the output voltages.
across this junction increases during the upper half cycle. This
leads to increase the flow of electrons from the emitter to a
collector through the base, hence increases the collector
current. The increasing collector current makes more voltage
drops across the collector load resistor RC. The negative half
cycle decreases the forward bias voltage across the emitter-
base junction. The decreasing collector-base voltage decreases
 Electronics Engineering 1, Laboratory | July 18, 2019

Tab.1 AC operation of a Common-emitter amplifier

Parameters Bypassed Unbypassed

𝑅𝐵 𝑅𝐸
Ii .8mA .18mA
Io .62mA .71mA
Vi 4.1w 7.7mA
Vo 8.6w 3.4w

Fig.1 Actual setup to measure the DC bias voltage of the

common-emitter amplifier

V. ANSWERS TO QUESTIONS
What are the characteristics of a common-emitter amplifier
base from the measured and computed values of its
parameters? A common-emitter amplifier has high voltage,
current, and power gains, but a relatively low input resistance.
The common emitter configuration has the emitter as the
common terminal, or ground, to an ac signal. CE amplifiers
exhibit high voltage gain and high current gain. The common-
collector and common- base configuration.
Fig.2. Waveform of the AC operation of a Common-emitter amplifier
Can you increase the voltage gain by just merely adjusting the
value of Rc? Explain your answer. In addition to voltage
amplification “Av” amplifier circuit must also have current VII. CONCLUSION
amplification “Ai” Power amplification “Rp” can also be The common-emitter is a single stage bipolar junction
expected from an amplifier circuit, but as well as have these transistor (BJT) that is used as voltage amplifier. There are
three important characteristics an amplifier must have also advantages and disadvantages of in using CE amplifier one of
other like high input impendence “Zin” low input impendence the advantages are as a low input impedance and it is an
“Zout” inverting amplifier, current gain of the common emitter
amplifier is high, and it has the highest power gain when
What is a swapping circuit? What is its purpose in an combined with medium voltage and current gain. The
amplifier? Swamping is a method used to minimize the effect disadvantages are when in the high frequencies, the common
of without reducing the voltage gain to its minimum value. emitter amplifier does not respond, voltage gain of this
This method “swamps” out the effect of Re on the voltage amplifier is unstable, and output resistance is very high in these
gain. Swamping is, in effect, a compromise between having a amplifiers.
bypass capacitor across Re and having no bypass capacitor at
all. The AC input resistance, looking in at the base of common-
emitter amplifier with Re completely bypassed. Bypassed ACKNOWLEDGMENT
emitter resistance to minimize the effect of Re on the gain in The researcher takes this opportunity to express gratitude to
order to achieve gain stability the people who have been instrumental in the successful
completion of this project. Especially, to those who laid time
and effort in conceptualizing this project. He would also like
VI. ANALYSIS OF RESULTS
to show his greatest appreciation to his adviser, Engr. Ronn
In this experiment the emitter resistor RE is required to obtain Conception II. for the support, advices and assistance
the DC quiescent point stability. However, the inclusion of RE throughout the research project. Without his encouragement
in the circuit causes a decrease in amplification at higher and guidance this project would not have materialized.
frequencies. In order to avoid such a condition, it is bypassed
by a capacitor so that it acts as a short circuit for AC and
contributes stability for DC quiescent condition. Hence REFERENCES
capacitor is connected in parallel with emitter resistance. [1]https://www.elprocus.com/common-emitter-amplifier-ce-
Emitter bypass capacitors are used to short circuit the emitter circuit-working-applications/
resistor and thus increases the gain at high frequency. The
coupling and bypass capacitors cause the fall of the signal in [2]http://www.electronics-tutorials.ws/amplifier/amp_2.html
the low frequency response of the amplifier because their
impedance becomes large at low frequencies. The stray [3]https://www.allaboutcircuits.com/textbook/semiconductors/
capacitances are effectively open circuits. chpt-4/common-emitter-amplifier/
Tab.1 CE amplifier DC bias voltages
𝑉𝐵 𝑉𝐶 𝑉𝐵𝐸 𝑉𝐸 𝑉𝐶𝐸
9.2v 8.57v .724v 2.9v 12.8mV