Crystal filter

A crystal filter is an electronic filter that uses the mechanical resonance of piezoelectric crystals, usually quartz, to shape a circuit's frequency response. Its early development was driven by carrier telephony, which required steep filters to separate voice channels spaced just a few kilohertz apart. Crystal resonators have a much higher Q factor than ordinary tuned circuits made from inductors and capacitors, allowing accurately controlled passbands and stopbands with steep transition regions.

Crystal filters are used in radio receivers and transmitters, carrier-telephone equipment, and other communication systems. Crystal filters can be built from individual matched crystals in ladder or lattice networks, or from several resonators formed on a single quartz blank as a monolithic crystal filter. Amateur radio operators also build crystal filters for superheterodyneintermediate-frequency and single-sideband equipment.