Filter device

Patent metadata

Field	Value
Publication number	US-10158341-B2
Application number	US-201715633850-A
Country	US
Kind code	B2
Filing date	Jun 27, 2017
Priority date	Jan 23, 2015
Publication date	Dec 18, 2018
Grant date	Dec 18, 2018

Abstract

A filter device includes first, second and third filter circuits that are connected to a common terminal. The first filter circuit includes a first inductor that is closest to the common terminal along a first signal line and a first capacitance element that is connected in parallel with the first inductor, the second filter circuit includes a series arm resonator, which is a second acoustic resonator, that is closest to the common terminal along a second signal line, and the third filter circuit includes a third acoustic resonator that is closest to the common terminal along a third signal line.

First claim

What is claimed is:

1. A filter device comprising:
a common terminal;
a first filter circuit that includes a first signal line that is connected to the common terminal and is a low pass filter with a first pass band;
a second filter circuit that includes a second signal line that is connected to the common terminal and is a band pass filter with a second pass band that is located at a higher frequency than the first pass band of the first filter circuit; and
a third filter circuit that includes a third signal line that is connected to the common terminal and includes a third pass band that is located at a higher frequency than the second pass band of the second filter circuit; wherein
the first filter circuit includes a first inductor that is closest to the common terminal along the first signal line and a first capacitance element that is connected in parallel with the first inductor and defines an LC resonance circuit;
the second filter circuit includes a second acoustic resonator that is closest to the common terminal along the second signal line; and
the third filter circuit includes a third acoustic resonator that is closest to the common terminal along the third signal line.

2. The filter device according to claim 1 , wherein the first filter circuit includes a first acoustic resonator that includes an anti-resonant frequency and a resonant frequency, the resonant frequency being located inside the second pass band, and a second capacitance element that is connected between the first signal line and a ground potential.

3. The filter device according to claim 2 , wherein the second capacitance element of the first filter circuit includes an acoustic resonator;
the second filter circuit includes a parallel arm that connects the second signal line, which is a series arm, and the ground potential, and an acoustic resonator is provided in the parallel arm; and
a resonant frequency of the acoustic resonator that defines the second capacitance element of the first filter circuit and a resonant frequency of the acoustic resonator provided in the parallel arm of the second filter circuit are the same or substantially the same as a resonant frequency of the second acoustic resonator.

4. The filter device according to claim 3 , wherein the resonant frequency of the second acoustic resonator, the resonant frequency of the acoustic resonator that defines the second capacitance element of the first filter circuit, and the resonant frequency of the acoustic resonator provided in the parallel arm of the second filter circuit are within a range of about ±5% of an average value of the resonant frequencies of the acoustic resonators.

5. The filter device according to claim 1 , wherein the second filter circuit is a ladder filter that includes the second acoustic resonator and a fourth acoustic resonator that is provided in a parallel arm that connects the second signal line and a ground potential.

6. The filter device according to claim 1 , wherein the third filter circuit is an LC filter that includes a second inductor that is connected between the third signal line and the ground potential, and a third capacitance element that is connected in series with the second inductor.

7. The filter device according to claim 1 , wherein the third filter circuit is a band pass filter.

8. The filter device according to claim 7 , wherein the third filter circuit is a ladder filter.

9. The filter device according to claim 2 , wherein at least one of the first, second and third acoustic resonators is an elastic wave resonator.

10. The filter device according to claim 9 , wherein the elastic wave resonator is a surface acoustic wave resonator.

11. The filter device according to claim 1 , wherein the first capacitance element includes an acoustic resonator.

12. The filter device according to claim 2 , wherein the second capacitance element provides impedance adjustment.

13. The filter device according to claim 1 , wherein the second filter circuit includes a plurality of series arm resonators provided along the second signal line.

14. The filter device according to claim 13 , wherein the second filter circuit includes a plurality of parallel arm resonators in parallel arms connected to connection points between the plurality of series arm resonators and a ground potential.

15. The filter device according to claim 1 , further comprising a low pass filter connected between the third filter circuit and a third terminal along the third signal line.

16. The filter device according to claim 15 , wherein the third filter circuit is a high pass filter.

17. The filter device according to claim 15 , wherein the low pass filter includes an inductor provided along the third signal line, and a capacitance element connected in parallel with the inductor.

18. The filter device according to claim 1 , wherein an anti-resonant frequency of the third acoustic resonator of the third filter circuit is located in the second pass band of the second filter circuit.

Assignees

• Murata Manufacturing Co

Inventors

• Nosaka Koji

Classifications

• H03H9/6483

  Ladder SAW filters · CPC title

• H03H9/70

  Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source · CPC title

• H03H9/64 Primary

  using surface acoustic waves · CPC title

• H03H9/72 Primary

  Networks using surface acoustic waves · CPC title

• H03H7/175

  Series LC in series path (H03H7/1783 takes precedence) · CPC title