Quartz filter
A quartz filter is an electromechanical filter based on piezoelectricity , which consists of an oscillating quartz and, by means of resonance , suppresses or allows certain frequency components of a signal , for example in the form of a bandpass , to pass.
construction
The parameters of the quartz filter, such as its cut-off frequency and attenuation values, are determined by the mechanical dimensions of the quartz and the quartz cut . In contrast to passive electronic filters , quartz filters have a very high quality factor Q - typical values for Q are in the range from 10,000 to 100,000, which also justifies the comparatively high manufacturing costs for quartz filters. The primary area of application of crystal filters are wireless communication systems, where they are used in the intermediate frequency levels with commercial values such as 9 MHz or 10.7 MHz. In order to further increase the quality factor, more single crystal filter or more identical quartz oscillators can be used in series are switched as English Crystal Ladder Filters referred.
Closely related and similar in structure are the more cost-effective ceramic filters, which use a ceramic resonator instead of the quartz plate . Since the ceramic resonator has a lower quality factor, the quality levels achieved with ceramic filters are not as high as with quartz filters.
history
Quartz filters were first described in 1922 by Walter Guyton Cady , with the area of application in the newly created telephone network . Back then, quartz filters were pure single-pole filters due to the fact that manufacturing technologies were not so advanced. This means that the transfer function of the quartz filter only has a single pole and thus the design options for the filter were limited. In the 1960s and 1970s, complex transfer functions such as Butterworth filters or Chebyshev filters were simulated , and multipole filters were developed. Crystal filters are used in various wireless and better quality communication devices than filters in intermediate frequency stages.
Web links
- Classic and modern quartz filters (Horst Steder)
- Crystals and quartz filters (Horst Steder)
Individual evidence
- ^ I. Poole: Quartz crystal filter . Radio-Electronics.com ( online ).
- ↑ Horst Steder, Jack A. Hardcastle: Crystal Ladder Filters for All . In: QEX . Nov / Dec American Radio Relay League , 2009, p. 14–18 ( online (PDF; 461 kB)).
- ^ RG Kinsman: A History of Crystal Filters . IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society, 1998 ( online ). Online ( Memento of the original from September 9, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
