Band-Pass Filter Design Project
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Lab 6: Filter Design Project ENG214: Circuit Analysis Laboratory
Tim Laux, Eric Brokaw, Thomas Approvato, Alin Bojkovic
The College of New JerseyDecember 11th 2014
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Table of Contents1. Application2. Requirements3. Research4. Calculations5. Solution6. Equipment7. Procedure8. Results9. References
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Application• A singular loudspeaker is
generally incapable of reproducing the entire audio spectrum with a linear frequency response and without distortion.
• Most professional and high-end systems use two or more drivers, each catering to a specific range of frequencies.
• Each loudspeaker needs to be driven by a signal with frequencies in its linear range of operation.
Figure 1. Three-way speaker system
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Requirements
Figure 3. HiVi M4N Frequency Response
Figure 2. HiVi M4N
• We picked out the HiVi M4N, a commercially available driver.
• After examining its frequency response plot, we determined that it responded linearly between 100Hz and 5kHz. This makes it a low-midrange driver.
• Therefore, we require a band-pass filter which has -3dB cutoff frequencies of 100Hz and 5kHz.
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Research• There are two ways to filter audio
signals: before or after amplification (active or passive crossovers)
• Before amplification (active): Better overall sound quality Highly tunable Less expensive Smaller/lighter Requires multiple amplifiers
• After amplification (passive): Requires only one amplifier Lower complexity Potentially expensive Bulky/heavy Power losses and non-linearities
Figure 4. Active Crossover
Figure 5. Passive Crossover
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Research• We chose the active filter route.
• The two popular active filter topologies are Sallen-Key and multiple feedback (MFB).
• We chose the Sallen-Key topology because of its simplicity and its suitability for our application.
• In order to pass a wide band of frequencies, we need to cascade two filters, one high-pass and one low-pass.
Figure 6. Sallen-Key
Figure 7. Multiple Feedback
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Research• There are three major
responses possible from an active filter.o Besselo Butterwortho Tschebyscheff
• We chose a Butterworth response because of its passband flatness and its relatively sharp transition into the stopband.
• Bessel was not steep enough, while Tschebyscheff introduces some ringing in the passband.
Figure 8. Comparison of different filter responses
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• We used “Op-Amps for Everyone” by Texas Instruments to design our filter according to our needs.
Calculations
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Solution• First, we used LTSpice
to confirm the design worked.
• Then, we swapped in the closest E12 capacitor values and the closest E24 resistor values. We resimulated with these values.
• We were able to achieve acceptable performance even with the adjusted values.
Figure 9. Schematic diagram of the filter
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Solution• Bill of materials
Op-amp1. LM324 Quad Op-amp
Carbon film resistors1. 12K2. 15K3. 22K4. 30K
Ceramic capacitors1. 0.1μF (2x)2. 1nF (3x)
Total cost (single quantity) : $0.98
Figure 10. Circuit on a breadboard
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Equipment
Figure 11. HP 64645D Oscilloscope
Figure 12. Agilent 33220A Function Generator
• HP 54645D Oscilloscope
• Agilent 33220A Function Generator
• Elenco XP-581 Quad Power Supply
• Breadboard
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Procedure1. Using sources from online about op-amps and filter design
techniques, we drew the schematic for our filter
2. We built the circuit on a breadboard
3. We tested this filter using frequencies ranging from 10Hz to 60kHz• The op amp was powered by a ±12V supply• The function generator was used to create the test
frequencies• The output was probed with the oscilloscope and the peak-
to-peak voltage was recorded at each frequency
4. We created the circuit using LTSpice
5. We compared our experimental data with our calculated data using LTSpice
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Results
10 100 1000 10000-36
-33
-30
-27
-24
-21
-18
-15
-12
-9
-6
-3
0
3
Band-pass Filter Gain vs. Frequency
LTSpice
Frequency (Hz)
Ga
in
(dB
)
Figure 13. Gain vs. Frequency Plot (Simulated and Measured)
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ResultsIdeal LTSpic
eMeasure
d
Cutoff frequency 1(-3dB)
100 Hz 103 Hz 107 Hz
Cutoff frequency 2 (-3dB)
5000 Hz
5010 Hz 5400 Hz
-3dB bandwidth 4900Hz
4907 Hz 5293 HzFigure 13. Results comparison
• The results from LTSpice were very close to the ideal figures.
• The measured results were close, and had errors less than 10%.
• Taking component variations into consideration, our results were satisfactory.
LTSpice
Measured
Error (cutoff frequency 1)
2.96 % 6.76 %
Error(cutoff frequency 2)
0.20 % 7.69 %Figure 14. Percent error
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References• Carter, B. (2001). Active Filter Design Techniques. In Op-Amps for
Everyone.
• HiVi Speaker. (2006). M4N Full Frequency. Retrieved from Swan Speaker: http://www.swanspeaker.com/product/htm/view.asp?id=83
• Maxim Integrated Products. (2003, February 4). A Beginner's Guide to Filter Topologies. Retrieved from Maxim Integrated: http://www.maximintegrated.com/en/app-notes/index.mvp/id/1762
• bibin3210. (2012, May 8). Active vs. Passive Crossovers. Retrieved from HiFi Vision: http://www.hifivision.com/active-speakers/17925-active-vs-passive-crossover.html