US-12627019-B2 - Filter device and radio-frequency front-end circuit equipped with the same

Abstract

A filter device includes an input terminal, an output terminal, a shield conductor, and a resonant circuit including at least one resonator, and inductors. A first inductor connects the input terminal and the shield conductor. A second inductor connects the output terminal and the shield conductor. The input terminal and the output terminal are capacitively coupled to the resonant circuit.

Inventors

• Takashi Nihei

Assignees

• MURATA MANUFACTURING CO., LTD.

Dates

Publication Date

20260512

Application Date

20231010

Priority Date

20210426

Claims (19)

1. 1 . A filter device comprising: a multilayer body including a plurality of dielectric layers; an input terminal; an output terminal; a grounding terminal; a resonant circuit including a plurality of resonators; a first inductor that conductively connects the input terminal to the grounding terminal; a second inductor that conductively connects the output terminal to the grounding terminal; a first flat electrode and a second flat electrode spaced apart from each other in a lamination direction in the multilayer body; and a first shield conductor and a second shield conductor that are connected to the grounding terminal; wherein the resonant circuit is between the first flat electrode and the second flat electrode and includes the plurality of resonators extending in a first direction perpendicular or substantially perpendicular to the lamination direction; the first shield conductor and the second shield conductor are on a first side surface and a second side surface of the multilayer body, respectively, which are perpendicular to the first direction and are connected to the first flat electrode and the second flat electrode; the plurality of resonators are arranged in the multilayer body in a second direction perpendicular or substantially perpendicular to both the lamination direction and the first direction; respective first end portions of the plurality of resonators are connected to the first shield conductor and respective second end portions of the plurality of resonators are spaced apart from the second shield conductor; and the input terminal and the output terminal are capacitively coupled to the resonant circuit.
2. 2 . The filter device according to claim 1 , wherein surfaces of the input terminal and the output terminal are covered with a metal having corrosion resistance.
3. 3 . The filter device according to claim 2 , wherein the metal is Au or Sn.
4. 4 . The filter device according to claim 2 , wherein the metal is an electrolytically plated metal.
5. 5 . The filter device according to claim 1 , further comprising capacitor electrodes that face the corresponding second end portions of the plurality of resonators and that are connected to the second shield conductor.
6. 6 . The filter device according to claim 5 , wherein each of the capacitor electrodes includes multiple conductors that at least partially protrude from one of the plurality of resonators to an adjacent resonator of the plurality of resonators in the second direction.
7. 7 . The filter device according to claim 1 , wherein a length of each of the plurality of resonators is about λ/4, where λ represents a wavelength of a transmitted radio-frequency signal.
8. 8 . The filter device according to claim 1 , wherein the plurality of resonators are a distributed-constant TEM mode resonator.
9. 9 . The filter device according to claim 1 , wherein the plurality of resonators are magnetically coupled with each other.
10. 10 . The filter device according to claim 1 , wherein the filter device is a bandpass filter.
11. 11 . A radio-frequency front-end circuit comprising the filter device according to claim 1 .
12. 12 . A communication device comprising the radio-frequency front-end circuit according to claim 11 .
13. 13 . The communication device according to claim 12 , wherein the communication device is a mobile terminal.
14. 14 . The communication device according to claim 12 , further comprising: an antenna; a mixer; a local oscillator; a digital/analog converter, and an RF circuit.
15. 15 . The radio-frequency front-end circuit according to claim 11 , further comprising: bandpass filters; an amplifier; and an attenuator.
16. 16 . The radio-frequency front-end circuit according to claim 15 , wherein each of the bandpass filters includes: an input terminal; an output terminal; a grounding terminal; a resonant circuit including at least one resonator; a first inductor to connect the input terminal and the grounding terminal; and a second inductor to connect the output terminal and the grounding terminal; wherein the input terminal and the output terminal are capacitively coupled to the resonant circuit.
17. 17 . The radio-frequency front-end circuit according to claim 11 , further comprising: a transmission circuit to transmit a radio-frequency signal or a reception circuit to receive a radio-frequency signal.
18. 18 . The filter device according to claim 1 , wherein each of the plurality of resonators extends in the first direction and includes a plurality of conductors laminated in the lamination direction.
19. 19 . The filter device according to claim 18 , further comprising, in each of the plurality of resonators, a connection conductor on a side where the second end portion is located to electrically connect the plurality of conductors.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to Japanese Patent Application No. 2021-074257 filed on Apr. 26, 2021 and is a Continuation Application of PCT Application No. PCT/JP2022/004299 filed on Feb. 3, 2022. The entire contents of each application are hereby incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present disclosure relates to a filter device and a radio-frequency front-end circuit including the filter device, and, more particularly, to techniques to protect an input terminal and an output terminal of the filter device. 2. Description of the Related Art Japanese Unexamined Patent Application Publication No. 2007-235465 discloses a bandpass filter including a laminated dielectric resonator obtained by laminating a plurality of inner electrode layers in a dielectric. In the bandpass filter disclosed in Japanese Unexamined Patent Application Publication No. 2007-235465, an inductor portion of the inner electrode layers is formed by a long pattern having a shape in which the width of the long pattern partly gradually narrows. Since this configuration achieves the decrease in a resonant frequency without the decrease in a Q value, a resonator can be miniaturized. SUMMARY OF THE INVENTION In the filter device disclosed in Japanese Unexamined Patent Application Publication No. 2007-235465, a radio-frequency signal input to an input terminal passes through a filter portion (resonant circuit) formed by the resonator and is output from an output terminal. At that time, the case may arise where the input terminal and the output terminal are capacitively coupled to the filter portion. The above input terminal and the above output terminal function as connection terminals for the connection to an external device and are electrically connected to an external device by, for example, soldering. An input terminal and an output terminal are typically formed with Cu or Ag, but the surfaces of an input terminal and an output terminal may be covered with a metal with high corrosion resistance such as Au or Sn for preventing, for example, a soldering erosion. A metal with high corrosion resistance such as Au or Sn is generally formed by electrolytic plating after a filter device has been formed. However, in the case where the input terminal and the output terminal are capacitively coupled to the filter portion as described above, the input terminal and the output terminal are not connected to a grounding terminal and are in an electrically floating state (insulated state). A current therefore does not flow through the input terminal and the output terminal. As a result, the input terminal and the output terminal may be insufficiently covered with a metal with high corrosion resistance. Preferred embodiments of the present invention cover, in a filter device in which an input terminal and an output terminal are capacitively coupled to a resonant circuit, the input terminal and the output terminal with a metal with high corrosion resistance. A filter device according to a preferred embodiment of the present disclosure includes an input terminal, an output terminal, a grounding terminal, a resonant circuit including at least one resonator, a first inductor, and a second inductor. The first inductor is structured to connect the input terminal and the grounding terminal. The second inductor is structured to connect the output terminal and the grounding terminal. The input terminal and the output terminal are capacitively coupled to the resonant circuit. In a filter device according to a preferred embodiment of the present disclosure, an input terminal and an output terminal that are capacitively coupled to a resonant circuit are connected to a grounding terminal via corresponding inductors. Since the input terminal and the output terminal are not in an electrically insulated state, the input terminal and the output terminal can be covered with a metal with high corrosion resistance. The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a communication device including a radio-frequency front-end circuit to which a filter device according to a preferred embodiment of the present invention is applied. FIG. 2 is an external perspective view of a filter device according to a preferred embodiment of the present invention. FIG. 3 is a transparent perspective view of a filter device according to a preferred embodiment of the present invention which illustrates the internal configuration of the filter device. FIG. 4 is a cross-sectional view of a filter device according to a preferred embodiment of the present invention. FIG. 5 is a plan view of a filter device according to a preferred embodiment of