Elastic wave filter device and duplexer

Abstract

A second band-pass filter for use in a filter device which can not only increase attenuation sufficiently by increasing impedance in the pass band of a first band-pass filter in the second band-pass filter having a relatively high pass band, but also can improve insertion loss in the pass band of the first band-pass filter. In the second band-pass filter, a second IDT (10b) in a second longitudinal coupling resonator type surface acoustic wave filter section (10) has one end connected with a first balance terminal (7) and the other end connected with a second balance terminal (8), first and second longitudinal coupling resonator type surface acoustic wave filter sections (9, 10) each have a narrow pitch electrode finger portion, and the number of electrode fingers at the narrow pitch electrode finger portion of a second IDT (9b) in the first longitudinal coupling resonator type surface acoustic wave filter section (9) is set larger than the number of electrode fingers at the narrow pitch electrode finger portion of a second IDT (10b) in the second longitudinal coupling resonator type surface acoustic wave filter section (10).

Description

technical field [0001] The present invention relates to an acoustic wave (elastic wave) filter device such as a duplexer for an RF band of a portable telephone, and more specifically, to a duplexer having a balanced-unbalanced conversion function, and in the duplexer, An acoustic wave filter device used as a filter on a side with a relatively high passband, and a duplexer including the acoustic wave filter device. Background technique [0002] Conventionally, in cellular phones, in order to reduce the number of parts, efforts have been made to use parts having various functions. Various proposals have been made for a duplexer including a transmission-side band filter and a reception-side band filter as an example of a component having such a variety of functions. [0003] For example, in the following Patent Document 1, it is disclosed that Figure 11 The schematic floor plan of the duplexer is shown. The duplexer 1001 has a piezoelectric substrate 1002 . By forming on th...

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Problems solved by technology

[0010] As described in Patent Document 1, there is a problem that the surface acoustic wave is connected in series between the receiving side band filter 1005, that is, the longitudinally coupled resonator type surface acoustic wave filter, and the common terminal 1003 connected to the antenna. In the structure of the resonators 1006 and 1007, the insertion loss of the receiving side band filter 1005 increases due to the insertion of the surface acoustic wave resonators 1006 and 1007

[0015] However, in the method of reducing the number of pairs of electrode fingers of the IDTs 1005a and 1005c, the resistance value of the passband of the transmission side band filter 1004 of the reception side band filter 1005 becomes large.

Therefore, when the duplexer 1001 is configured, there is a problem that the insertion loss of the transmission-side band filter 1004 deteriorates.

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