Name:
________________________________
Section: _________________
Date:
_______________
57:018 Laboratory Experiment 12
BJT AMPLIFIER
OBJECTIVES
 Study the behavior of a single-stage BJT amplifier
 Measure the input resistance of a single-stage BJT amplifier
REQUIRED PARTS AND EQUIPMENT
 2N2222 BJT,
capacitors, 470 Ω, 6.8K, 10K, 120K resistors
PRE-LAB
Part (a) Analyze the single-stage BJT common emitter amplifier in Figure 1. The transistor is a
PN22222 with a nominal
. Assume that
for the transistor. Complete Table 1.
Figure 1. Left: BJT common-emitter amplifier. Right: PN2222 pins
Pre-Lab
Lab
0.7 V
Do not measure
Do not measure
with
Table 1
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Show your work as Appendix A that you attach to the lab report.
Part (b) The single-stage BJT amplifier in Figure 2 is identical to the amplifier in Figure 1, except for the
addition of the emitter bypass capacitor , and the dc analysis for the two amplifiers are identical.
However, the addition of
increases the gain to > 100. Analyze the circuit and then complete Table 2.
Figure 2. BJT common-emitter amplifier with emitter bypass capacitor
Pre-Lab
Lab
with
Do not measure
Table 2
One needs a small input signal to measure the gain of this amplifier. However, recall from previous
laboratory experiments that setting the signal generator to generate signals less than ~100 mV is
problematic. One solution is to set the signal generator to some higher voltage, and use two resistors to
attenuate the signal to the desired level. This is shown in shown in Figure 3.
Pre-Lab
to have
with no load
with 4K load
Figure 3. Generating small signal voltages
Table 3
For the pre-lab, determine the Thevenin equivalent circuit for the signal generator and the attenuator
combination. Do not forget to include the
internal resistance of the signal generator. What should
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the signal generator voltage
load at this setting for
be so that
with no external load? What will
be with a 4K
? Complete Table 3.
Show your work as Appendix A that you attach to the lab report.
Lab Activities
Part (a) BJT Common-Emitter Amplifier
1. Construct the circuit shown in Figure 1. Use a multimeter and measure
and add the values
to the “Lab” column in Table 1.
2. Apply a 200 mV, 5 kHz sinusoidal signal to the amplifier and measure the output voltage and voltage
gain. Add the values to the “Lab” column in Table 1.
1. Next, you have to measure the input resistance of the amplifier. Below, explain how to accomplish
the task, using figures and equations as needed.
2. Now measure the input resistance, showing your work below.
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Part (b) BJT Common-Emitter Amplifier with Emitter Bypass Capacitor
3. Add the emitter bypass capacitor so that your circuit now resembles Figure 2.
4. Add the attenuator network shown in Figure 3 between the signal generator and the amplifier input.
5. In the pre-lab you determined the signal generator amplitude ( ) required so that the attenuated
output voltage (
is 10 mV. Set the signal generator to that value.
6. Measure the output voltage, determine the voltage gain, and complete Table 2.
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Appendix A
Part (a)
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Part (b)
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Grading
PRE-LAB
*Rate the pre-lab analysis for the BJT CE amplifier. (0–8)
Rate the pre-lab analysis for the signal attenuator. (0–4)
Rate the pre-lab analysis for the BJT CE amplifier with bypass capacitor. (0–3)
*Note: It is imperative to show pre-lab calculations in Appendix A.
LAB ACTIVITIES: BJT COMMON EMITTER AMPLIFIER
Rate the measurement of the dc value for the BJT amplifier. (0–3)
Rate the measurement for the voltage gain. (0–2)
Rate the measurement of the input resistance. (0–5)
LAB ACTIVITIES: BJT COMMON EMITTER AMPLIFIER WITH BYPASS CAPACITOR
Rate the measurement for the voltage gain. (0–2)
Rate the measurement of the input resistance. (0–5)
GENERAL
Rate the overall presentation (neatness, spelling, …). (0–5)
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