Motorola Corporation

Stanley Malinowski

Aristotelis S Arvanitis

Corwin E Livenick

Craig P Smith, Deceased

Thomas W Re

By Paul Page, Administrator

A monolithic crystal filter is disclosed that provides much wider bandwidths than were obtainable by prior art crystal filters. The inventive wide-bandwidth monolithic filter includes a piezoelectric substrate, an output electrode, a plurality of input electrodes arranged in orthogonal relationship with the output electrode and common electrodes disposed opposite to the input and output electrodes. The input and output electrodes are preferably disposed on the substrate along the crystallographic axes thereof. Increased bandwidth is realized due to the increased coupling resulting from the combination of the individual couplings from each input electrode at the outputelectrode. As a result of the increased coupling provided by the inventive crystal filter, overtone mode operation is now possible at much higher frequencies which heretofore were not obtainable by prior art crystal filters due to impractically close electrode spacing requirements.

Wide-bandwidth monolithic crystal filter

Three electrode pairs are formed on a monolithic piezoelectric element which exhibits anisotropic properties with respect to its X and Z axes. The electrodes of each pair are located on opposite sides of the piezoelectric element, with all electrodes being of predetermined dimensions. The first and second electrode pairs are aligned on the X axes at a predetermined spacing therebetween. The second and third electrode pair are aligned on the Z axis, also at a predetermined spacing. In circuit operation, a signal to be processed is coupled to the first electrode pair and extracted from the third electrode pair, with the electrodes of the second pair shorted together. In this manner, the resonator displays a three pole passband characteristic having excellent spur suppression.

Multipole resonator

A dual-coupled monolithic crystal element is connected to a crystal filter to bypass signals of a predetermined frequency which are applied through the filter. The shunt connected crystal element can be used with a bandpass filter to bypass frequencies at which the crystal filter produces a spurious response so that such frequencies will not appear in the filter output. Alternatively, the monolithic element can be selected to bypass frequencies adjacent the edges of a band which is selected, to provide sharp attenuation at the edges of the band thereby providing a very steep filter characteristic. The monolithic element includes a flat quartz wafer with electrodes provided on both sides at two separate portions of the wafer to form two resonant portions coupled through the wafer. The electrodes of one portion are connected across the input or the output of the crystal filter, and both electrodes of the other resonating portions are grounded.

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Park Ridge, IL, United States of America

Stanley Malinowski