Filter device and high-frequency front-end circuit incorporating same

Abstract

This filter device (100) comprises: an input terminal (T1); an output terminal (T2); a shield conductor (121); a resonant circuit (200) including at least one resonator; and inductors (L10, L20). The inductor (L10) connects the input terminal (T1) and the shield conductor (121). The inductor (L20) connects the output terminal (T2) and the shield conductor (121). The input terminal (T1) and the output terminal (T2) are connected to the resonance circuit (200) by capacitive coupling.

Description

[Technical field]

[0001] The present disclosure relates to a filter device and a high-frequency front-end circuit equipped with the same, and more particularly to a technique for protecting input / output terminals of the filter device. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2007-235465 (Patent Document 1) discloses a bandpass filter using a laminated dielectric resonator in which multiple internal electrode layers are laminated in a dielectric. In the bandpass filter disclosed in Japanese Patent Laid-Open Publication No. 2007-235465 (Patent Document 1), the inductor part of the internal electrode layer is configured as a longitudinal pattern, and the longitudinal pattern has a shape in which the width of a part of the longitudinal pattern gradually narrows. With this configuration, the resonant frequency can be lowered without lowering the Q value, and therefore the resonator can be made smaller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-235465 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a filter device such as that disclosed in JP 2007-235465 A (Patent Document 1), a high-frequency signal input to an input terminal passes through a filter section (resonant circuit) composed of a resonator and is output from an output terminal. At this time, the input terminal and the filter section, and the output terminal and the filter section may be coupled by capacitive coupling.

[0005] The input and output terminals described above function as connection terminals for connecting to external devices, and are electrically connected to the external devices by solder, etc. The input and output terminals are typically made of copper (Cu) or silver (Ag), but in order to prevent erosion by solder, etc., the surfaces may be covered with highly corrosion-resistant metals such as gold (Au) or tin (Sn).

[0006] A highly corrosion-resistant metal such as gold (Au) or tin (Sn) is generally formed by electrolytic plating after the filter device is formed. However, as described above, when the input terminal and the filter section, and the output terminal and the filter section are capacitively coupled, the input terminal and the output terminal are not connected to the ground terminal and are in an electrically floating (insulated) state, so no current flows through the input terminal and the output terminal. As a result, the input terminal and the output terminal may not be sufficiently covered with the highly corrosion-resistant metal.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide 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 being covered with a highly corrosion-resistant metal. [Means for solving the problem]

[0008] The filter device according to the present disclosure includes an input terminal, an output terminal, a ground terminal, a resonant circuit including at least one resonator, and a first inductor and a second inductor. The first inductor connects the input terminal and the ground terminal. The second inductor connects the output terminal and the ground terminal. The input terminal and the output terminal are capacitively coupled to the resonant circuit. Effect of the Invention

[0009] In the filter device according to the present disclosure, the input terminal and the output terminal capacitively coupled to the resonant circuit are connected to the ground terminal via the corresponding inductor, so that the input terminal and the output terminal are not electrically insulated, and therefore the input terminal and the output terminal can be covered with a highly corrosion-resistant metal. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram of a communication device having a high-frequency front-end circuit to which a filter device according to an embodiment of the present invention is applied. [Diagram 2] 1 is an external perspective view of a filter device according to an embodiment; [Diagram 3] FIG. 2 is a transparent perspective view showing the internal structure of the filter device according to the embodiment. [Figure 4] 1 is a cross-sectional view of a filter device according to an embodiment. [Diagram 5] FIG. 2 is a plan view of the filter device according to the embodiment. [Figure 6] 5A and 5B are diagrams for explaining filter characteristics of the filter device according to the embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0012] (Basic configuration of communication device) 1 is a block diagram of a communication device 10 having a high-frequency front-end circuit 20 to which a filter device according to the present embodiment is applied. The communication device 10 is, for example, a mobile terminal such as a smartphone, or a mobile phone base station.

[0013] 1, a communication device 10 includes an antenna 12, a high-frequency front-end circuit 20, a mixer 30, a local oscillator 32, a digital-to-analog converter (DAC) 40, and an RF circuit 50. The high-frequency front-end circuit 20 also includes band-pass filters 22 and 28, an amplifier 24, and an attenuator 26. Note that, although a case in which the high-frequency front-end circuit 20 includes a transmission circuit that transmits a high-frequency signal from the antenna 12 will be described with reference to FIG. 1, the high-frequency front-end circuit 20 may also include a reception circuit that receives a high-frequency signal via the antenna 12.

[0014] The communication device 10 up-converts a signal transmitted from the RF circuit 50 into a high-frequency signal and radiates the signal from the antenna 12 as a transmission signal. The modulated digital signal output from the RF circuit 50 is converted into an analog signal by the D / A converter 40. The mixer 30 mixes the signal converted into an analog signal by the D / A converter 40 with an oscillation signal from the local oscillator 32 and up-converts the signal into a high-frequency signal. The band-pass filter 28 removes unnecessary waves generated by the up-conversion and extracts only signals in a desired frequency band. The attenuator 26 adjusts the strength of the signal. The amplifier 24 amplifies the power of the signal that has passed through the attenuator 26 to a predetermined level. The band-pass filter 22 removes unnecessary waves generated during the amplification process and passes only signal components in a frequency band defined by the communication standard. The signal that has passed through the band-pass filter 22 is radiated from the antenna 12 as a transmission signal.

[0015] As the bandpass filters 22, 28 in the communication device 10 as described above, a filter device according to the present disclosure can be adopted.

[0016] (Configuration of filter device) Next, a detailed configuration of the filter device 100 of this embodiment will be described with reference to Figures 2 to 5. In this embodiment, a dielectric filter constituted by a plurality of resonators, which are distributed constant elements, will be described as an example of the filter device 100, but the filter device 100 may be another type of filter, such as a filter constituted by an inductor and a capacitor.

[0017] Fig. 2 is an external perspective view of filter device 100. Fig. 2 shows only the configuration that can be seen from the outer surface of filter device 100, and omits the internal configuration. Fig. 3 is a see-through perspective view showing the internal structure of filter device 100. Fig. 4 is a cross-sectional view of filter device 100. Fig. 5 is a plan view of filter device 100 as viewed from the stacking direction.

[0018] 2, the filter device 100 includes a rectangular or substantially rectangular laminate 110 in which a plurality of dielectric layers are laminated in a predetermined direction. The laminate 110 has an upper surface 111, a lower surface 112, a side surface 113, a side surface 114, a side surface 115, and a side surface 116. The side surface 113 is a side surface in the positive direction of the X-axis, and the side surface 114 is a side surface in the negative direction of the X-axis. The side surfaces 115 and 116 are side surfaces perpendicular to the Y-axis direction. FIG. 4 is a cross-sectional view of a resonator constituting the filter device 100 as viewed from the X-axis direction.

[0019] Each dielectric layer of the laminate 110 is formed of ceramics such as low temperature co-fired ceramics (LTCC) or resin. Inside the laminate 110, a plurality of flat conductors provided in each dielectric layer and a plurality of vias provided between the dielectric layers form distributed constant elements constituting resonators, as well as capacitors and inductors for coupling between the distributed constant elements. In this specification, the term "via" refers to a conductor that connects conductors provided in different dielectric layers and extends in the lamination direction of the dielectric layers. The vias are formed, for example, by conductive paste, plating, and / or metal pins.

[0020] In the following description, the stacking direction of the dielectric layers in laminate 110 is referred to as the "Z-axis direction", the direction perpendicular to the Z-axis direction and along the long side of laminate 110 is referred to as the "X-axis direction" (second direction), and the direction along the short side of laminate 110 is referred to as the "Y-axis direction" (first direction). In the following, the positive direction of the Z axis in each figure may be referred to as the upper side, and the negative direction as the lower side.

[0021] 2, the filter device 100 includes shield conductors 121 and 122 that cover the side surfaces 115 and 116 of the laminate 110, respectively. The shield conductors 121 and 122 have a substantially C-shape when viewed from the X-axis direction of the laminate 110. That is, the shield conductors 121 and 122 cover parts of the upper surface 111 and the lower surface 112 of the laminate 110. The parts of the shield conductors 121 and 122 that cover the lower surface 112 of the laminate 110 are connected to a ground electrode on a mounting board (not shown) by a connecting member such as a solder bump. That is, the shield conductors 121 and 122 also function as ground terminals.

[0022] The filter device 100 also includes an input terminal T1 and an output terminal T2 provided on a lower surface 112 of the laminate 110. The input terminal T1 is disposed on the lower surface 112 at a position close to a side surface 113 in the positive direction of the X-axis. On the other hand, the output terminal T2 is disposed on the lower surface 112 at a position close to a side surface 114 in the negative direction of the X-axis. The input terminal T1 and the output terminal T2 are electrically connected to corresponding electrodes on a mounting board by connecting members such as solder bumps. The input terminal T1 and the output terminal T2 are terminals used for inputting and outputting signals. The input / output relationship may be reversed.

[0023] Next, the internal structure of the filter device 100 will be described with reference to Fig. 3. The filter device 100 further includes plate electrodes 130 and 135, a plurality of resonators 141-145, capacitor electrodes 161-165, connecting conductors 171-175, and inductors L10 and L20 in addition to the configuration shown in Fig. 2. In the following description, the resonators 141-145, the capacitor electrodes 161-165, and the connecting conductors 171-175 may be collectively referred to as "resonators 140," "capacitor electrodes 160," and "connecting conductors 170," respectively.

[0024] The plate electrodes 130, 135 are disposed facing each other at positions spaced apart in the stacking direction (Z-axis direction) inside the laminate 110. The plate electrode 130 is provided on a dielectric layer close to the upper surface 111, and is connected to the shield conductors 121, 122 at its end in the Y-axis direction. The plate electrode 130 has a shape that almost covers the dielectric layer when viewed from above in the stacking direction.

[0025] The plate electrode 135 is provided on a dielectric layer close to the lower surface 112 of the laminate 110. When viewed from above in the lamination direction, the plate electrode 135 has a substantially H-shape with cutouts formed in portions facing the input terminal T1 and the output terminal T2. The plate electrode 135 is connected to the shield conductors 121 and 122 at its ends in the Y-axis direction.

[0026] In the laminate 110, the resonators 141 to 145 are disposed between the plate electrode 130 and the plate electrode 135. Each of the resonators 141 to 145 extends in the Y-axis direction (first direction). An end (first end) of each of the resonators 141 to 145 in the positive direction of the Y-axis is connected to the shield conductor 121. On the other hand, an end (second end) of each of the resonators 141 to 145 in the negative direction of the Y-axis is spaced apart from the shield conductor 122. The resonators 141 to 145 form a "resonant circuit 200" in the present disclosure.

[0027] In the filter device 100, the resonators 141 to 145 are arranged side by side in the X-axis direction (second direction) inside the laminate 110. More specifically, the resonators 141, 142, 143, 144, and 145 are arranged in this order from the positive direction to the negative direction of the X-axis.

[0028] Each of the resonators 141 to 145 is composed of a plurality of conductors arranged along the stacking direction. In a cross section of each resonator 140 parallel to the ZX plane (i.e., a cross section viewed from the Y-axis direction), the plurality of conductors as a whole have a substantially elliptical shape. In other words, the dimension in the X-axis direction of the conductors arranged on the uppermost and lowermost layers among the plurality of conductors is narrower than the dimension in the X-axis direction of the conductors arranged on the layer near the center.

[0029] In the resonator 140, the multiple conductors constituting each resonator are electrically connected by a connecting conductor 170 at a position close to the second end on the shield conductor 122 side. In each resonator, if the wavelength of the high-frequency signal transmitted is λ, the length of each resonator in the Y-axis direction is approximately λ / 4. The resonator 140 functions as a distributed constant type TEM mode resonator with the multiple conductors as the central conductor and the plate electrodes 130 and 135 as the outer conductors.

[0030] The input terminal T1 is connected to one end of the plate electrode PL10 by a via V10. The plate electrode PL10 has a rectangular shape and extends from the via V10 in the negative direction of the Y-axis. A via V11 is connected to the other end of the plate electrode PL10. The plate electrode PL10 is connected to the plate electrode PL11 by the via V11. The plate electrode PL11 has a rectangular shape and faces the lower surface of the resonator 141. That is, the input terminal T1 is coupled to the resonator 141 of the resonance circuit 200 by capacitive coupling.

[0031] The output terminal T2, like the input terminal T1, is connected to the plate electrodes PL20 and PL21 through vias. The plate electrode PL21 has a rectangular shape and faces the lower surface of the resonator 145. That is, the output terminal T2 is coupled to the resonator 145 of the resonance circuit 200 by capacitive coupling.

[0032] The inductor L10 is connected to the via V10 connected to the input terminal T1. The inductor L10 extends from the via V10 in the negative direction of the Y-axis, turns back just before the shield conductor 122, extends in the positive direction of the Y-axis, and is connected to the shield conductor 121. As shown in Fig. 5, when viewed in a plan view from the stacking direction (Z-axis direction) of the laminate 110, it is desirable to arrange the inductor L10 at a position that does not overlap with the resonant circuit 200.

[0033] Similarly, the output terminal T2 is connected to the shield conductor 121 by the inductor L20. It is preferable that the inductor L20 does not overlap the resonant circuit 200 when viewed from above in the lamination direction of the laminate 110.

[0034] The resonators 141 to 145 are magnetically coupled to each other, and a high-frequency signal input to the input terminal T1 is transmitted in this order through the resonators 141 to 145 and output from the output terminal T2. At this time, the filter device 100 functions as a band-pass filter depending on the degree of coupling between the resonators.

[0035] A capacitor electrode is provided on the second end side of the resonator 140, protruding between the resonator and the adjacent resonator. The capacitor electrode has a structure in which a part of a plurality of conductors constituting the resonator protrudes. The degree of capacitive coupling between the resonators can be adjusted by the length of the capacitor electrode in the Y-axis direction, the distance between the adjacent resonators, and / or the number of conductors constituting the capacitor electrode.

[0036] 3, in the filter device 100, a capacitor electrode C10 is provided to protrude from the resonator 141 toward the resonator 142, and a capacitor electrode C20 is provided to protrude from the resonator 142 toward the resonator 141. A capacitor electrode C30 is provided to protrude from the resonator 143 toward the resonator 142, and a capacitor electrode C40 is provided to protrude from the resonator 144 toward the resonator 143. Furthermore, a capacitor electrode C50 is provided to protrude from the resonator 145 toward the resonator 144.

[0037] Note that the capacitor electrodes C10 to C50 are not essential components, and as long as a desired degree of coupling between the resonators can be achieved, some or all of the capacitor electrodes may not be provided. In addition to the configuration of Fig. 3, the filter device may include a capacitor electrode provided to protrude from the resonator 142 toward the resonator 143, a capacitor electrode provided to protrude from the resonator 143 toward the resonator 144, and a capacitor electrode provided to protrude from the resonator 144 toward the resonator 145.

[0038] In the filter device 100, a capacitor electrode 160 is disposed opposite the second end of the resonator 140. A cross section of the capacitor electrode 160 parallel to the ZX plane is similar to that of the resonator 140. The capacitor electrode 160 is connected to the shield conductor 122. As a result, a capacitor is formed by the resonator 140 and the corresponding capacitor electrode 160. The magnitude of the capacitance of the capacitor formed by the resonator 140 and the corresponding capacitor electrode 160 can be adjusted by the gap (distance in the Y-axis direction) GP between the resonator and the capacitor electrode in FIG. 4.

[0039] In the above-described filter device 100, the input terminal T1 and the output terminal T2 function as connection terminals for connecting to an external device, and are electrically connected to the external device by solder, etc. The input terminal T1 and the output terminal T2 may be typically made of copper or silver, but may have a surface covered with a highly corrosion-resistant metal such as gold or tin to prevent erosion by the solder, etc.

[0040] The highly corrosion-resistant metal is generally formed by electrolytic plating after the filter device is formed, but when the input terminal T1 and the output terminal T2 are capacitively coupled to the resonant circuit as described above, the input terminal T1 and the output terminal T2 are electrically insulated unless they are connected to the ground terminal, which may result in the input terminal T1 and the output terminal T2 not being sufficiently covered with the highly corrosion-resistant metal.

[0041] In the filter device 100 of this embodiment, the input terminal T1 and the output terminal T2 are connected to a shield conductor 121 that functions as a ground terminal via inductors L10 and L20, respectively. This prevents the input terminal T1 and the output terminal T2 from being electrically insulated when electrolytic plating is performed to form a highly corrosion-resistant metal, so that a current can be passed through the input terminal T1 and the output terminal T2 through the shield conductor 121. This makes it possible to keep the input terminal T1 and the output terminal T2 covered with a highly corrosion-resistant metal.

[0042] In addition, The inductance of inductors L10 and L20 is This is set according to the frequency and the desired filter characteristics. In the filter device 100 of this embodiment, the inductance of the inductors L10 and L20 is 5 nH or more.

[0043] Fig. 6 is a graph showing the filter characteristics of the filter device 100 of the present embodiment and a comparative filter device not including inductors L10 and L20. In Fig. 6, the horizontal axis shows frequency, and the vertical axis shows insertion loss (solid lines LN10 and LN20) and return loss (dashed lines LN11 and LN21) as pass characteristics.

[0044] As shown in FIG. 6, even in the configuration of the filter device 100 including the inductors L10 and L20, by appropriately setting the inductances of the inductors L10 and L20, it is possible to achieve pass characteristics equivalent to those of the comparative example.

[0045] In this way, even if the input terminal and the output terminal are capacitively coupled to the resonant circuit, by connecting each of the input terminal and the output terminal to the ground terminal via an inductor of appropriate inductance, it is possible to suppress the effect on the pass characteristics of the filter device while keeping the input terminal and the output terminal covered with a highly corrosion-resistant metal.

[0046] The "inductor L10" and "inductor L20" in this embodiment correspond to the "first inductor" and "second inductor" in this disclosure, respectively. The "plate electrode 130" and "plate electrode 135" in this embodiment correspond to the "first plate electrode" and "second plate electrode" in this disclosure, respectively. The "shield conductor 121" and "shield conductor 122" in this embodiment correspond to the "first shield conductor" and "second shield conductor" in this disclosure, respectively. The "side surface 115" and "side surface 116" in this embodiment correspond to the "first side surface" and "second side surface" in this disclosure, respectively.

[0047] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0048] 10 communication device, 12 antenna, 20 high frequency front-end circuit, 22, 28 bandpass filter, 24 amplifier, 26 attenuator, 30 mixer, 32 local oscillator, 40 D / A converter, 50 RF circuit, 100 filter device, 110 laminate, 111 upper surface, 112 lower surface, 113-116 side surface, 121, 122 shield conductor, 130, 135, PL10, PL11, PL20, PL21 flat plate electrode, 140-145 resonator, 160-165, C10-C50 capacitor electrode, 170, 171-175 connecting conductor, 200 resonant circuit, L10, L20 inductor, T1 input terminal, T2 output terminal, V10, V11 via.

Claims

1. A laminate having a plurality of dielectric layers; An input terminal; An output terminal; A ground terminal; a resonant circuit including at least one resonator; a first inductor connecting the input terminal and the ground terminal; a second inductor connecting the output terminal and the ground terminal; A first electrode having a flat plate shape connected to the input terminal; a second electrode having a flat plate shape connected to the output terminal; the first inductor and the second inductor are disposed inside the laminate, the input terminal is capacitively coupled to the resonant circuit via the first electrode, the output terminal is capacitively coupled to the resonant circuit via the second electrode, the first electrode is disposed on a dielectric layer between a dielectric layer on which the first inductor is disposed and a dielectric layer on which the resonant circuit is disposed in the laminate; A filter device, wherein the second electrode is arranged in a dielectric layer between a dielectric layer on which the second inductor is arranged and a dielectric layer on which the resonant circuit is arranged in the laminate.

2. 2. The filter device according to claim 1, wherein surfaces of the input terminal and the output terminal are covered with a highly corrosion-resistant metal.

3. The filter device comprises: a first plate electrode and a second plate electrode disposed in the stacked body and spaced apart from each other in a stacking direction; a first shield conductor and a second shield conductor connected to the ground terminal; the resonant circuit includes a plurality of resonators disposed between the first plate electrode and the second plate electrode and extending in a first direction perpendicular to the stacking direction, the first shielding conductor and the second shielding conductor are respectively disposed on a first side surface and a second side surface of the laminate perpendicular to the first direction and connected to the first plate electrode and the second plate electrode; the plurality of resonators are arranged side by side in a second direction perpendicular to both the stacking direction and the first direction within the stack; 3. The filter device according to claim 1, wherein a first end of each of the plurality of resonators is connected to the first shield conductor and a second end is spaced apart from the second shield conductor.

4. The filter device according to claim 3 , wherein each of the plurality of resonators is formed of a plurality of conductors extending in the first direction and stacked in the stacking direction.

5. The filter device according to claim 4 , further comprising: a connection conductor arranged on the second end side of each of the plurality of resonators, the connection conductor electrically connecting the plurality of conductors to each other.

6. 6. The filter device according to claim 3, further comprising a capacitor electrode facing the second end of each of the plurality of resonators and connected to the second shield conductor.

7. A high-frequency front-end circuit comprising the filter device according to any one of claims 1 to 6.

8. A filter device as described in claim 1, wherein, when viewed in a plane from the stacking direction of the laminate, the first inductor and the second inductor are positioned so as not to overlap with the resonant circuit.

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