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PASSIVE AND ACTIVE FILTERS

Passing and Rejecting Signals Based on Their Frequency

by James Antonakos

Start ý A Filter by Any Other Name ý Whatýs the Frequency, Kenneth? ý A Closer Look ý Itýs Just a Phase ý Whatýs Load Got to Do with It? ý Activate That Filter! ý Filters to the Rescue ý Sources and PDF

Last month, I discussed some of the basic aspects of the common emitter amplifier. This included mention of a high-pass filter in the amplifier, formed by the input coupling capacitor and input resistance of the amplifier. This month, letýs take a step farther back and review the theory behind high-pass, low-pass, and other types of filters.

WHAT AND WHY?

If you are familiar with the filters used for making coffee, then you may understand the principle behind the filter. In the case of a coffee filter, the large coffee grains are blocked, and the smaller molecules of water pass through. Such is the case with an electronic filter. Some signals pass through the filter and others are blocked based on their frequency.

There are many applications that require the use of one or more types of filters. Radio, television, and other communications equipment make use of filters to capture and process specific audio and video signals. A speaker employs a filter network to control its woofer and tweeter. Other filters eliminate 60-cycle hum and other unwanted noise.

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