Some recent advances in integrated crystal filters

Integrated crystal filters-monolithic, tandem monolithic, and hybrid monolithic (polylithic) quartz crystal filters-are widely used in HF, VHF, UHF, and satellite communications equipments, in both commercial and military, in telephone FDM equipment, and in a number of other applications including frequency synthesizers and airborne navigation aids. Frequencies range from 5 to 180 MHz and occasionally to 250 MHz. Maximum inductorless bandwidths are usually 0.25 to 0.35 percent of center frequency below about 30-35 MHz and less at higher frequencies where overtones must be used. In the past decade, piezoelectric resonator theory has been extended to model accurately the linear and nonlinear behavior of monolithic filter devices. While most integrated crystal filters are all-pole networks, techniques for the design of filters with real and complex frequency transmission zeros are finding increasing application. A number of examples of current production filters are presented.