ELECTRONIC CIRCUITS – EE301
DEPARTMENT OF ELECTRICAL ENGINEERING
LAB WORK – EE301 ELECTRONIC CIRCUITS
EXPERIMENT :
5
TITLE
ACTIVE FILTERS
:
OUTCOME
:
Upon completion of this unit, the student should be able to:
1. gain experience with design and construction of active filter circuits.
2. explore simple active low pass and high pass filter concepts and
functional circuits.
3. develop skills with the laboratory equipment.
MATERIALS REQUIRED:
i.
Resistors – 2 x 1 kΩ, and 10 kΩ.
ii.
Integrated Circuit series 741
iii.
DC Power Supply (13 -15 Vdc)
iv.
Analogue / Digital Multimeter
v.
Oscilloscope
vi.
Laboratory Trainer
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
Part 1: THEORY
ACTIVE LOW-PASS FILTER
At low frequencies, the capacitor has an extremely high capacitive
reactance. At higher frequencies, the capacitive reactance of Cf decreases. This
causes the voltage gain to decrease due to the increased amount of negative
feedback. When Xcf = Rf, the voltage gain equals 70.7% of its midband value.
ACTIVE HIGH-PASS FILTER
At high frequencies, Xc1 ≈ 0 Ω and the voltage gain Av, equals –Rf/R1. At
very low frequencies, Xc1 ≈ ∞ Ω and the voltage gain Av approaches zero.
Note: In the circuits below the pin numbers for the various op amp connections are
shown. Pins not shown are to be left unconnected.
Part 2: LABORATORY PROCEDURE
PROCEDURE A:
Part 1: ACTIVE LOW-PASS FILTER
The op-amp circuits are the only type of active circuit that we will
encounter in EE301. Active circuits require an external source of energy to operate
properly. Figure below shows a picture of the LM741 op-amp that we will use, with
the pin numbers conventionally labeled (for more detail, a copy of the LM741 data
sheet is posted at the class web site - CIDOS). Most op-amps have the same pin
configuration. Use the outputs of your bench power supply, adjusted appropriately,
for the +/- 13 Vdc sources.
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
1. Assemble the non-inverting ACTIVE LOW-PASS FILTER circuit shown in figure 1
below.
2. Remember to shut off the +/-13 V supply before assembling a new circuit.
3. Add a capacitor of 1uF parallel with the Rf on your circuit.
4. Apply a 1 Volt amplitude, 1 kHz sine wave at the input.
5. Display both input and output on the oscilloscope.
Figure 1: Active Low Pass circuit
6. Make a plot of the input / output waveforms in your lab report.
Note: In the circuits above change all resistor (1 kΩ to 2 kΩ) and (10 kΩ to 22 kΩ)
also change the op-amp supply from +/- 15 to +/- 13Vdc.
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
PROCEDURE B:
Part 2: ACTIVE HIGH-PASS FILTER
1. Assemble the non-inverting ACTIVE HIGH-PASS FILTER circuit shown in figure 2
below.
2. Remember to shut off the +/-13 V supply before assembling a new circuit.
3. Add a capacitor of 1uF before the R1 on your circuit. (series)
4. Apply a 1 Volt amplitude, 1 kHz sine wave at the input.
5. Display both input and output on the oscilloscope.
6. Adjust the frequency generator until you get a stabile output waveform.
7. Make a plot of the input / output waveforms in your lab report.
Figure 2: Active High Pass circuit
Note: In the circuits above change all resistor (1 kΩ to 2 kΩ) and (10 kΩ to 22 kΩ)
also change the op-amp supply from +/- 15 to +/- 13Vdc.
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
Part 3: RESULT (GRAPH SECTION)
Part 1: ACTIVE LOW-PASS FILTER
Be sure to note the scale Volt/div and Time/div settings.
Volt / div: ______________
Time / div: ______________
Graph 1.1: Input waveforms
Volt / div: ______________
Time / div: ______________
Graph 1.2: Output waveforms
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
Part 2: ACTIVE HIGH-PASS FILTER
Be sure to note the scale Volt/div and Time/div settings.
Volt / div: ______________
Time / div: ______________
Graph 2.1: Input waveforms
Volt / div: ______________
Time / div: ______________
Graph 2.2: Output waveforms
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session
ELECTRONIC CIRCUITS – EE301
Part 4: DISCUSSION
Write discussion base for your result of the experiment and most
importantly, what you learned from performing it. It is also encouraged to
include personal statements and suggestions about the lab activities.
Part 5: CONCLUSION
Write conclusions base for your outcome of the experiment and
most importantly, what you learned from performing it.
Polytechnic Kota Kinabalu, Sabah
Jun 2012 Session