An Analysis of Active vs. Passive Electronic Filters

Overview

Objectives/Goals The goal of this science project was to understand the properties of active filters. I studied the basic theory behind operational amplifiers (op amps) and showed how they can be used along with capacitors and resistors to create any kind of filter in the audio frequency range. I designed many working active electronic filters and compared their performance to same-value passive electronic filters and simulated filter designs. Methods/Materials After studying op amp theory, I began by designing simple op amp circuits like integrators and voltage followers to understand the advantages of high input impedance. I also experimented with negative feedback to understand how it can change the shape of filter plots. I designed active filters and tested their properties and compared them to their passive versions. Using Microcap circuit simulation software I compared my actual bode plots with the simulated plots. I designed and built low pass, high pass, band pass and band stop filters. Finally, I tested a very high quality Klipsch passive crossover filter and compared it's bode plot to a Microcap simulation of the circuit and then designed and built an active filter version of this device ending with a 6th order active crossover. My test bench was a PC with a sound card and shareware spectrum analyzer/oscilloscope software, woofer and tweeter speakers, and an audio amplifier. Results Active filters allowed much finer control of the filter shape and Q, did not have losses and were, in some ways, easier to design than passive filters. They were easily modified and had greater linearity. Conclusions/Discussion This experiment showed how active filters can duplicate much of the functionality of passive filters at lower cost, higher performance, greater flexibility and smaller size. The high input impedance and low output impedance made higher order filter designs straightforward.

Awards (1)

• Category Award

Competition history

• CSEF 2004 Electricity & Electronics · Entry J0718

Resources

• CSEF project summary ↗

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