lab report eet 211
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EET211 Laboratory 6
Timers and Oscillators
This laboratory will give the students experience designing, building, and troubleshooting oscillators and discrete astable multivibrator.
Part 1:
Before coming to lab , design a discrete (using only transistors, resistors, and capacitors) astable multivibrator which oscillates at 1KHz. The output amplitude should oscillate between 0 and 10V. Select resistors to limit the DC saturation current through the transistors to approximately 20mA. Show your design to the instructor. Construct the circuit and show to instructor for initials.
Design circuit Instructor OK: _________
Operational circuit Instructor OK: _________
By changing just two components, how could the frequency be increased to 2KHz?
Part 2:
Before coming to lab , design an astable multivibrator with an output frequency of 5KHz and a duty cycle of 70% using two transistors. Include all calculations in your lab report. Show your design to the instructor. Construct the circuit and show to instructor for initials.
Design circuit Instructor OK: _________
Operational circuit Instructor OK: _________
Part 3:
In this part a sine wave oscillator will be built. First, the amplifier will be constructed and tested in part A, then the feedback network will be added in part B, to complete the oscillator construction.
Part A:
Construct the following BJT amplifier shown below. Calculate and measure the DC parameters VB, VC, VE, VCE, and IC. The measured DC parameters should be within +/- 10% of the calculated values. If the calculated and measured values are not with +/- 10%, find and correct the problem or explain why.
Calculate the AC voltage gain of the amplifier.
Apply a 500KHz. 100mVpp sine wave to the input and measure the output magnitude. Based on the measured output magnitude, calculate the voltage gain of the amplifier. Once the circuit is functional, demonstrate it to the instructor.
Instructor OK: ________
In order to make a sine wave oscillator, a feedback network has to be added to the amplifier built in part A. Remove the 500KHz. 100mVpp sine wave from the input and add the LC feedback network outlined in the circuit below. What type of sine wave oscillator is this? Calculate the output frequency.
Note the only input to this circuit is the 12V DC power supply. Connect the o-scope probe to Vout and apply power. Using the o-scope, measure the output frequency of the oscillator. Once the circuit is functional, demonstrate it to the instructor.
Instructor OK: _________
How does the measured output frequency compare to the calculated output frequency?
Lab Report:
Your lab report should include schematics of the original designs, schematics of the final working circuits, all calculations, measured output frequency, duty cycle, and amplitude, a description of the changes required to get the final circuits operational and within specifications, and why these changes were necessary. Include a copy of this hand-out with instructor’s signatures. The summary/conclusion should include a detailed (component level) description of how discrete astable multivibrator function.
VCC
12V
Q1
2N3904
C1
0.1µF
C2
0.1µF
C3
0.1µF
RE1
47Ω
RE2
1kΩ
RC
2.7kΩ
R2
3.3kΩ
R1
10kΩ
Vout
Vin
+
+
+
VCC
12V
Q1
2N3904
R1
10kΩ
R2
3.3kΩ
RC
2.7kΩ
RE2
1.0kΩ
RE1
47Ω
C1
0.1µF
C2
0.1µF
C3
0.1µF
C4
1000pF
C5
0.01µF
L1
100µH
Vout
+
+
+
+
+