ECE 311
Fundamentals of Electronics Lab
Page 1 of 7
BJT Amplifier Analysis
ECE 311 - Fundamentals of Electronics Lab
Department of Electrical and Computer Engineering
University of Idaho
Title: BJT Amplifier Analysis
Goal: To analyze and test a BJT Common-Emitter Amplifier (with emitter resistor) and to
compare the results of the analysis with laboratory measurements.
Preliminary:
Consider the circuit depicted in Figure 1. Assume the following values: RB1=91kS, RB2=51kS,
RC=5.1kS, RE=150S, RE1=3.9kS,RL=10kS, and RS=50S. Also, let $ for Q1 be 100. Set
VCC=15V.
Do a DC analysis on the circuit and determine the following: VB, VC, VE, IB, IC, IE, IRB1, and
IRB2.
Do an AC analysis and determine vO/vS. Also, determine the peak values of vb, vc, and ve, assuming
vs has a peak voltage of 100mV.
Make a copy of your calculations as you will repeat these in the laboratory.
Laboratory Procedure:
1. Construct the circuit in Figure 1 using the values given in the preliminary. Let CC1=CC2=1:F
and CB=10:F. Measure the values of your resistors before you construct the circuit. For now, turn
the function generator off (set vS = 0).
2. Measure VB,VC, and VE. From these values, you may calculate IC, IB, and VBE, and from these
calculations, you may approximate $ for your transistor. Record the values of VB, VC, VE, VBE,
IC, IRB1, IRB2, and IB in the provided table.
3. Using your measured values in (1) and the value of $ from (2), calculate the following: VB, VC,
VE, IB, IC, IE, IRB1, and IRB2. Record your values in provided table.
4. Using the DC calculations in (3) to determine the small-signal parameters for the BJT, calculate
vO/vS. Also, calculate the peak values for vo vb, vc, and ve. Assume vS = 100mVpeak. Enter the values
into the table.
5. Set vs = 100mV peak at a frequency of 5kHz. Measure the peak values of vO, vb, vc, and ve. Use
the oscilloscope to measure these voltages. Calculate the gain of the circuit vO/vS from these
measurements. How do these values compare with the predictions?
ECE 311
Fundamentals of Electronics Lab
Page 2 of 7
BJT Amplifier Analysis
7. Sketch the total signal at vO and vC (This is the “AC” plus the “DC”) What should the look like?
How does the signal compare?
8. Vary the frequency of vS and measure vO. Take enough points that will enable you to plot vO/vS
vs. frequency. At what frequencies are the upper and lower 3dB points?
9. Increase the magnitude of vs until the output no longer looks sinusoidal (the signal is distorted).
The TA will help you define distortion. Record the value of vS.
10. Increase further the magnitude of vs until the output saturates (either the peak or valley begins
to flatten. Record the value of vS.
11. Increase further the magnitude of vS until the remaining peak or valley saturates and record the
value of vS. Sketch this signal.
From parts 9, 10, and 11 we have established the limitations of this amplifier.
VCC
RB1
RS
RC
CC2
vo
CC1
Q1
VS
RL
RE
RB2
RE1
CB
Report:
Please include a cover page, your data sheets with calculations, and a section on conclusions. Also,
please plot the results from (8) using Excel.
ECE 311
Fundamentals of Electronics Lab
Data sheet
1.
RB1 - _______________
RB2 - _______________
RE - _______________
RE1 - _______________
RC - _______________
RL - _______________
2.
DC Calculations and Measurements:
Table 1
Voltage or
Current
Measured
value
VB
VC
VE
VBE
IC
IRB1
IRB2
IB
Calculated $ _____________
Calculated
Value
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BJT Amplifier Analysis
ECE 311
Fundamentals of Electronics Lab
Data sheet
3. Calculations for VB, VC, VE, IB, IC, IE, IRB1, and IRB2.
4.
Table 2
Parameter
vo
vs
vo/vs
vb
vc
ve
Calculated
Measured
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BJT Amplifier Analysis
ECE 311
Fundamentals of Electronics Lab
Data sheet
Calculations for vO, vb, vc, ve, and vO:
7. Sketch for vO:
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BJT Amplifier Analysis
ECE 311
Fundamentals of Electronics Lab
Page 6 of 7
BJT Amplifier Analysis
Data sheet
Sketch for vC.
8.
Freq
vO
Freq
vO
Freq
vO
Freq
vO
ECE 311
Fundamentals of Electronics Lab
Data sheet
11. Sketch for vO (AC component only)
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BJT Amplifier Analysis