Types of Electronic Filters

Filters fundamentally separate something wanted from something not wanted. These are some examples:

• direct current from a mixture of direct and alternating current
• alternating current from a mixture of direct and alternating current
• one or more desired radio signals from one or more undesired signals and noise
• upper- or lower-sidebands from double-sideband (DSB) signals
• carrier-waves or sidebands from amplitude-modulated (AM) signals
• long pulses or short pulses from mixtures of long and short pulses
• sand or gravel from mixtures of sand and gravel

Filter Names
Filters are variously named by:

• what they pass or suppress, e.g., low-pass, band-pass, high-pass, band-reject, notch, signal, noise
• technologies used to accomplish separation, e.g., analog, digital, LCR (or RLC), crystal, Fast Fourier Transform (FFT), fractal transform, wavelets
• part of the frequency spectrum where they are used, e.g., audio, radio, microwave, infrared, optical, ultraviolet, x-ray
• bandwidths, e.g., wideband, narrowband
• type categories, e.g., Tuned Filter and Wave Filters
• names of developers, e.g., Butterworth, Lamb
• names of associated mathematicians, e.g., Bessel, Chebyshev, Fourier
• names of mathematical processes, e.g., integrating, differentiating, elliptic integral (or commonly just elliptical), moving-average
• effects on waveforms, e.g., smoothing, averaging, phase-shifting
• intended applications, e.g., music, voice, SSB, CW, DSL, noise-reduction
• and many other ways, e.g., leading, lagging, comb, etc.

The result is a wide assortment of both specific and category names, combinations of which can be correctly applied to any filter. For example, all these names and more could be correctly applied to the same filter:

• Digital Filter
• FFT Filter
• Low-Pass Filter
• Smoothing Filter
• Audio Filter
• High Frequency Noise Reduction Filter
• Lagging-Phase Filter

Tuned & Wave Filters
Tuned Filters and Wave Filters are two especially important filter types that are widely used in radio transmitters, receivers, and associated components.

• Tuned Filters Tuned filters are widely used to separate signals in relatively-narrow bands of frequencies from signals in wider spectrums ...
• Wave Filters Wave filters are widely used to separate bands of frequencies ...