Monolithic Crystal Filter

A monolithic crystal filter is a bandpass filter that utilizes piezoelectric quartz crystals in its realization. When forming a discrete crystal filter one crystal is formed on each quartz blank. Coupling between resonators is achieved externally via an inductor. However, a 2 pole monolithic is realized by placing two crystal resonators on the quartz blank and coupling them together acoustically through the substrate. Hence, a monolithic filter performs all functions, except impedance matching, on a single substrate of quartz. Higher order monolithic crystal filters are made possible by cascading two pole structures together. In this case each section is impedance matched with the addition of coupling capacitor. Moreover, any monolithic filter can be transformed in impedance by an external LCR network.

The Monolithic crystal filter is most effectively used when a narrow band filter is required. This is because of the high Q factor of a crystal, in the range of 10,000 to 100,000. The principle limitation on bandwidth, about 0.6% of the center frequency, is dictated by the physical proximity limitation of the resonators on the quartz blank. Filtronetics can supply discrete and monolithic crystal filters that utilize from 1 to 22 crystals. Discrete crystal filters have the advantage of very complex and custom designs along with much wider bandwidths. However, they are larger and more expensive than monolithic crystal filters. The practical frequency range for monolithic bandpass crystal filters is from 10 kHz to 150 MHz. 10.7 MHz, 21.4 MHz, 45 MHz, 55 MHz, 70 MHz and 90 MHz are some of the more common monolithic crystal filter center frequencies. 12.5 KHz, 20 KHz, 25 KHz, and 50 KHz being the more common channel spacing. However Filtronetics, Inc can supply almost any custom monolithic crystal filter you require.

Filtronetics, Inc utilizes fundamental and overtone crystals in its monolithic filters. We supply monolithic crystal filters with monotonic designs and with characteristic responses of Buterworth, Chebyshev, Gaussian, Bessel (maximally flat delay), Equal ripple delay, as well as custom responses. These filters can be amplitude matched, delay matched, or phase matched, amplitude tracked, delay tracked, or phase tracked. We have special designs for good ring-down or overshoot response as well as good IP3 or 3rd order intermodulation characteristics.

Our Monolithic crystal filters have been utilized in systems in space, military, airborne, testing, and commercial applications. We can produce from one to millions of monolithic filters for your application. We can supply both SMD monolithic crystal filters as well as through hole monolithic crystal filters.