LADDER FILTER AND MULTIPLEXER

To provide a ladder filter that reduces a temperature coefficient of frequency.SOLUTION: A ladder filter comprises: a support substrate 10; a piezoelectric layer 14 provided on the support substrate 10; one or a plurality of parallel resonators P, each of which comprises a plurality of first electrode fingers 18 provided on the piezoelectric layer 14 and having a first average pitch D1 and a first average duty ratio R1, where the largest first average pitch D1 is double or more of the thickness of the piezoelectric layer 14, the parallel resonators having respective one ends connected to a path between an input terminal and an output terminal and respective other ends connected to the ground; and one or a plurality of series resonators S, each of which comprises a plurality of second electrode fingers 18 provided on the piezoelectric layer 14 and having a second average pitch D2 and a second average duty ratio R2, where at least one series resonator has a second average duty ratio R2 smaller than the smallest first average duty ratio R1, the respective series resonators connected in series between the input terminal and the output terminal.SELECTED DRAWING: Figure 1 【課題】周波数温度係数を小さくするラダー型フィルタを提供する。【解決手段】ラダー型フィルタは、支持基板１０と、支持基板１０上に設けられる圧電層１４と、圧電層１４上に設けられ第１平均ピッチＤ１と第１平均デュティ比Ｒ１とを有する複数の第１電極指１８を各々備え、最も大きい第１平均ピッチＤ１は圧電層１４の厚さの２倍以上であり、一端が入力端子と出力端子との間の経路に各々接続され他端がグランドに各々接続された１または複数の並列共振器Ｐと、圧電層１４上に設けられ第２平均ピッチＤ２と第２平均デュティ比Ｒ２とを有する複数の第２電極指１８を各々備え、少なくとも１つの直列共振器における第２平均デュティＲ２比は最も小さい第１平均デュティ比Ｒ１より小さく、入力端子と出力端子との間に各々直列接続された１または複数の直列共振器Ｓとを備える。【選択図】図１