Filter schematic symbols

Updated February 19, 2006

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New for March 2006! Below we will review the commonly-used schematic symbols for filters. These and many other symbols are available in a Word document in our download area.

The two types of schematic symbols both attempt to tell you something about the frequency response. On the left, the symbols each have three sine waves plotted, signifying low frequency (the lowest sine wave), medium frequency and high frequency. By placing a bar through one or more of the waves, you indicate which of the three frequency bands your filter blocks. Thus a filter symbol with the botton and middle sine waves "blocked" indicates a high-pass filter. You might argue that a high pass filter also passes the medium band, but we are following the convention that is used in Eagleware's Genesys simulation tool.

The symbols on the right try to give the same indications, by showing a very simplified filter frequency response.