FILTER DEVICES HAVING REDUCED SPURIOUS EMISSIONS FROM LAMB WAVES

• Main Authors: Fujiwara, Joji, Komatsu, Tomoya
• Format: Patent
• Language: English
• Published: 16.05.2019
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRICITY; IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS

A filter device including a first filter having a first passband, and a second filter having a second passband, the first and second filters each being connected between a common contact and a respective signal contact, and the filter device configured to reduce spurious emissions generated in one filter due to propagation of Lamb waves in the other filter. In one example the first filter includes a SAW filter formed on a piezoelectric substrate, a SAW resonator formed on the piezoelectric substrate and connected in series between the common contact and the SAW filter, and a dielectric film formed over the piezoelectric substrate covering the SAW filter and the SAW resonator. The dielectric film has a first thickness over the SAW filter and a second, lesser, thickness over the SAW resonator, a difference between the first and second thicknesses being selected to suppress spurious emissions in the second passband generated by propagation of a Lamb wave in the SAW filter.