Crystal Filter is a filter consisting of a Crystal Resonator. Compared with LC filter resonance circuit, crystal filter is much superior in frequency selectivity, frequency stability, transition zone steepness and insertion loss. It has been widely used in communication, navigation, measurement and other electronic equipment. There are Monolithic Crystal Filter and discrete crystal filter.
MCF consists of a number of capacitor, its advantage is to adjust the working frequency and suppress the parasitic frequency. The multiple crystal filters are composed of a coupled resonator, i can form a number of attenuation peaks near the band frequency, which is beneficial to suppress interference and improve the filtering performance. MCF has advantages of small volume, high stability and low cost. It is usually used as bandpass. Quartz crystal is used as substrate. Its working principle is the same as mechanical filter, this can be made up of many blocks to reduce technological requirements.