Operational Amplifier Active Filters

Last modified by Microchip on 2023/11/09 08:59

This section compares the gain-versus-frequency responses of the basic low-pass, high-pass, and band-pass filters. It also describes and analyzes the three basic filter response characteristics and other filter parameters.

For detailed information, see the pages linked in the "Learn More" section. The next points provide a quick overview:

  • The critical frequency of a filter is called the cut-off frequency and defines the pass band of the filter at the point where the output reaches -3 dB of the maximum.
  • Feedback or bypass circuits are used to determine the frequency of operation, usually a simple R-C network. Each network is called a “pole.”
  • The number of “poles” determines how rapidly the output decreases after hitting the critical frequency. This is called the “roll-off” rate.
  • Butterworth response provides a very flat amplitude response, referred to as a maximally flat response.
  • Chebyshev response provides a rapid roll-off and is characterized by variations or ripples in the pass band.
  • Bessel response exhibits a linear phase characteristic and is used for filtering pulse waveforms due to minimal distortion.
  • Order of a filter is the number of poles it has. (2nd order = 2 poles)
  • A high-pass filter passes frequencies above the cut-off frequency.
  • A band-stop filter is used to reject a range of frequencies.
  • A band-stop filter is also referred to as a notch filter.

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