Ladder filter device and elastic wave resonator

摘要

A ladder filter device includes elastic wave resonators with IDT electrodes. An apodization angle θ in an IDT electrode of a series arm resonator in the ladder filter device falls within a range from about 2° to about 14° with respect to an elastic wave propagation direction. This arrangement provides a ladder filter device that has a smaller insertion loss in a low frequency side portion of a passing band.

主权项

1. A ladder filter device comprising:
a first signal terminal and a second signal terminal; a series arm that connects the first signal terminal and the second signal terminal; a plurality of series arm resonators connected in series in the series arm; a parallel arm that connects the series arm and a ground potential; and at least one parallel arm resonator arranged in the parallel arm; wherein at least one of the series arm resonators includes an elastic wave resonator including a piezoelectric substrate and an IDT electrode arranged on the piezoelectric substrate; the IDT electrode includes a first comb-shaped electrode and a second comb-shaped electrode, each of which includes a busbar and a plurality of electrode fingers connected to the busbar, the first comb-shaped electrode and the second comb-shaped electrode being inserted into each other in a staggered arrangement; in each of the first comb-shaped electrode and the second comb-shaped electrode, an apodization angle falls in a range from about 2° to about 14°, the apodization angle being an angle between an elastic wave propagation direction and an envelope line that connects tips of the plurality of electrode fingers; the at least one parallel arm resonator is defined by an elastic wave resonator including a piezoelectric substrate and an IDT electrode arranged on the piezoelectric substrate; the IDT electrode of the at least one parallel arm resonator includes a third comb-shaped electrode and a fourth comb-shaped electrode, each of which includes a busbar and a plurality of electrode fingers connected to the busbar, the third comb-shaped electrode and the fourth comb-shaped electrode being inserted into each other in a staggered arrangement; the apodization angle in the at least one of the series arm resonators is less than the apodization angle in the at least one parallel arm resonator; and the apodization angle in the at least one parallel arm resonator is about 28° or less and is greater than the apodization angle in the at least one of the series arm resonators.