# Lab 6 – The Common-Emitter Amplifier

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Date
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Lab 6 – The Common-Emitter Amplifier
Introduction
The purpose of this experiment is to demonstrate the operational characteristics of a small
signal common emitter amplifier with a 180 degree phase shift. The input is applied to
the base and the output is measured from the collector.
Parts
Two 3.9 k Ω resistor
4.7 k Ω resistor
10 k Ω resistor
2.2 μF capacitors
100 μF capacitors
2N3904 NPN Transistor
Procedure
Wire up the following circuit:
Be sure the signal generator is in ’50 Ohm’ mode.
Biasing (dc) REGIME
Calculate the base, collector, and emitter voltages with respect to ground. Now measure
these voltages. How do your numbers compare? Beta for this transistor can be
considered to be 120, and VA = 100V. Remember, in DC, the capacitors are large
enough to be considered open circuits.
VB (calculated) = ________ V
VB (measured) = ________ V
VC (calculated) = ________ V
VC (measured) = ________ V
VE (calculated) = ________ V
VE (measured) = ________ V
Explain possible differences between the measured and calculated values:
Small-signal (ac) REGIME
How are the large caps to be considered as when in ac regime?
Calculate the small signal parameters and draw the small signal circuit of the amplifier.
Calculate the amplifier characteristics RIN, ROUT, Av, and output swing. Use your notes
if needed.
Now simultaneously measure vin and vout and record your results. What is your measured
voltage gain? What about the phase shift?
AV (measured) = __________ V/V
Phase Inversion (Yes or No): ___________
Explain possible differences between measured and calculated gains:
Now start increasing your input voltage until you see your output starting to look funky.
At what output voltage does the upper half of your cycles look incorrect? How about the
bottom half? What is going on here - why is it the transistor no longer working at those
specific values?
Explain the behavior of the circuit at those amplitudes and compare your results to the
calculation of amplifier swing.
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