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Lab 8

The document describes Lab #8 which examines a common emitter amplifier circuit. Key details include: 1) The circuit uses a BJT transistor with the base as input, collector as output, and emitter common. 2) Measurement of voltages and gains showed the output signal was greater than the input signal and 180 degrees out of phase, verifying characteristics of a common emitter amplifier. 3) Removal of the load resistor and bypass capacitor changed the output, demonstrating their roles in the circuit.

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Naeem Prince
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470 views3 pages

Lab 8

The document describes Lab #8 which examines a common emitter amplifier circuit. Key details include: 1) The circuit uses a BJT transistor with the base as input, collector as output, and emitter common. 2) Measurement of voltages and gains showed the output signal was greater than the input signal and 180 degrees out of phase, verifying characteristics of a common emitter amplifier. 3) Removal of the load resistor and bypass capacitor changed the output, demonstrating their roles in the circuit.

Uploaded by

Naeem Prince
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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Lab # 8 Common Emitter Amplifier

Introduction:
A common-emitter amplifier is a bipolar-junction-transistor (BJT) amplifier typically used
as a voltage amplifier. In common emitter amplifier circuit the base terminal of the
transistor serves as the input, the collector is the output, and the emitter is common.

The common emitter amplifier is characterized by the application of the amplifier input
signal to the base lead while its output is taken from the collector, which always gives
the 180 ◦ phase shift.

EQUIPMENT AND MATERIALS


DC power supply, DMM, Bread Board
Oscilloscope, Function Generator
Transistor: Q2N3904
Resistors: 150 Ω, 2.7 kΩ, two 3.9 kΩ, 4.7 kΩ, 10 kΩ
Capacitors: 2 2.2uF and 10 uF

Fig 1 Common Emitter Amplifier

Experimental procedure:
 After connecting the circuit as shown in figure 1, the signal generator and power supply of 15-
V was connected.
 With DMM, the measurement of the transistor dc base, emitter, and collector voltages
with respect to ground was measured results were recorded in Table 1. Based on the actual
resistor values, determine the expected values of these voltages the values were compared
with the measured values in Table 1.
 The Channel 1 of oscilloscope to point I ( ) and Channel 2 to point O ( ) was connected
and sine wave output level of the generator at 0.2 V peak-to-peak with frequency of 5 kHz.
 The output signal level was greater than the input signal level ) with out of
phase, with respect to . Then, using measured value for the dc collector voltage obtained,
the dc collector current was calculated. Using the value of , the resistance and trans
conductance was recorded in Table 2.
 The ac peak-to-peak voltage at the junction of and was measured using oscilloscope.

 After that, the expected voltage gain from base to collector and the actual voltage gain by
dividing the peak-to-peak output voltage by the peak-to-peak input voltage , was
recorded in Table 3.
 After removing . the output voltage level increased.

 The 3.9 kΩ load resistor was reconnected as in the original circuit and 10µF bypass capacitor
was removed from the circuit. The output voltage decreased tremendously.

TABLE 1
Parameter Measured Value Expected Value % Error

4.76 V 4.58 V 4%

4.24 V 4.33 V 3%

7.98 V 8.0 V 0.2%


TABLE 2

Parameter Value

Ie (calculated) 1.46 mA

Ic (calculated) 2.04mA

𝑟𝜋

𝑔𝑚 0.081

TABLE 3

Measured Expected
Condition % Error
VIN VOUT Gain(AvL) Gain(AvL)

Normal Circuit

0.26 2.88 11.07 11.07 0

No Load

3 7.6 2.5 2.5 0

No bypass
capacitor 5 4.11 1.26 1.26 0

Critical Analysis:

In this lab we verified the two major characteristics of a common-emitter amplifier. One of the
characteristic was phase shift and other was voltage amplification. For observation of phase shift
it was noted that the signals were to be displayed at the same time observe the phase shift you
must display both signals simultaneously on the oscilloscope, otherwise you will not see any
phase shift.

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