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.
- Low-pass filter (LPF)
- Passive Low-Pass Filters
- Active Low-Pass Filter (LPF)
- Active High-Pass Filter (HPF)
- Active Band-Pass Filter (BPF)
- Microchip FilterLab® Filter Design Software
- Butterworth Filter Topology
- Chebyshev Filter Topology
- Bessel Filter Topology
- 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 -3dB 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.