Filters and Multiplexers

Abstract

To provide a filter that improves the steepness of an attenuation pole, and a multiplexer having the filter.SOLUTION: A filter 100 has an input terminal Tin, an output terminal Tout, a ground terminal Tg, a first capacitor C1, a second capacitor C2, a capacitive element C3 and an inductor L1. The first capacitor C1 and the second capacitor C2 are connected in series between the input terminal Tin and the output terminal Tout. The capacitive element C3 is connected in parallel with the first capacitor C1 and the second capacitor C2 between the input terminal Tin and the output terminal Tout, and has a Q value which is smaller than the Q value of the first capacitor C1 and is smaller than the Q value of the second capacitor C2. The inductor L1 has one end connected to a node N1 which is provided between the first capacitor C1 and the second capacitor C2 and is connected to the capacitive element via the first capacitor C1 and the second capacitor C2, and the other end connected to the ground terminal Tg.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to filters and multiplexers, for example filters and multiplexers having capacitors and inductors. [Background technology]

[0002] A filter having an attenuation pole in the vicinity of the passband by connecting an acoustic wave resonator in parallel to the capacitor of a T-type CLC filter is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-129683 A Summary of the Invention [Problem to be solved by the invention]

[0004] In filters that have an attenuation pole, it is sometimes necessary to increase the steepness of the attenuation pole (i.e., to increase the quality factor). In order to improve the quality factor, it is common to increase the quality factor of the capacitors and inductors that form the attenuation pole. However, it is difficult to increase the quality factor of capacitors and inductors.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to improve the steepness of the attenuation pole. [Means for solving the problem]

[0006] The present invention is a filter comprising an input terminal, an output terminal, a ground terminal, a first capacitor and a second capacitor connected in series between the input terminal and the output terminal, a capacitive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal and having a Q value smaller than a Q value of the first capacitor and smaller than a Q value of the second capacitor, a node provided between the first capacitor and the second capacitor and connected to the capacitive element via the first capacitor and the second capacitor, and an inductor having one end connected to the node and the other end connected to the ground terminal.

[0007] In the above configuration, the Q value of the capacitive element may be 0.6 times or less the Q value of the first capacitor and 0.6 times or less the Q value of the second capacitor.

[0008] In the above configuration, the filter can be a high-pass filter having a pass band, and the first capacitor, the second capacitor, the capacitive element, and the inductor can be configured to form a first minimum of a first attenuation pole at a frequency lower than the pass band.

[0009] In the above configuration, the capacitive element may be an acoustic wave resonator, and the acoustic wave resonator may form a second minimum of a second attenuation pole between the first minimum and the pass band.

[0010] In the above configuration, the capacitive element may be a third capacitor.

[0011] The present invention is a filter comprising an input terminal, an output terminal, a ground terminal, a first capacitor and a second capacitor connected in series between the input terminal and the output terminal, a capacitive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal, a resistive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal and connected in series and / or in parallel to the capacitive element, a node provided between the first capacitor and the second capacitor and connected to the capacitive element via the first capacitor and the second capacitor, and an inductor having one end connected to the node and the other end connected to the ground terminal.

[0012] In the above configuration, a combined Q value of the capacitive element and the resistive element may be 0.6 times or less the Q value of the first capacitor and 0.6 times or less the Q value of the second capacitor.

[0013] In the above configuration, the filter can be a high-pass filter having a pass band, and the first capacitor, the second capacitor, the capacitive element, and the inductor can be configured to form a first minimum of a first attenuation pole at a frequency lower than the pass band.

[0014] In the above configuration, the capacitive element may be an acoustic wave resonator, and the acoustic wave resonator may form a second minimum of a second attenuation pole between the first minimum and the pass band.

[0015] In the above configuration, the capacitive element may be a third capacitor.

[0016] In the above configuration, the first capacitor, the second capacitor, and the third capacitor may have substantially equal Q values.

[0017] The present invention is a multiplexer including the above filter. Effect of the Invention

[0018] According to the present invention, the steepness of the attenuation pole can be improved. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a circuit diagram of a filter in accordance with a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the laminate in the first embodiment mounted on a substrate. [Diagram 3] 3(a) to 3(f) are plan views of the dielectric layer in the first embodiment. [Figure 4] 4(a) and 4(b) are diagrams showing the pass characteristic of the filter in the first embodiment. [Diagram 5] FIG. 5(a) is a diagram showing the pass characteristic of the filter in the first embodiment, and FIG. 5(b) is a diagram showing the Q value with respect to frequency. [Figure 6] 6(a) and 6(b) are diagrams showing the pass characteristic of the filter in the first embodiment. [Figure 7] FIG. 7 is a circuit diagram of a filter according to a first comparative example. [Figure 8] FIG. 8 is a diagram showing the pass characteristic of the filter in the first comparative example. [Figure 9] 9(a) and 9(b) are circuit diagrams of filters according to first and second modifications of the first embodiment, respectively. [Figure 10] 10(a) and 10(b) are diagrams showing pass characteristics of filters in first and second modifications of the first embodiment, respectively. [Figure 11] 11(a) and 11(b) are circuit diagrams of a filter according to a second embodiment and a first modified example thereof, respectively. [Figure 12] 12(a) and 12(b) are diagrams showing the pass characteristic of the filter in the second embodiment. [Figure 13] 13(a) and 13(b) are diagrams showing pass characteristics of a filter in the first modification of the second embodiment. [Figure 14] 14(a) and 14(b) are circuit diagrams of a filter according to a third embodiment and a first modified example thereof, respectively. [Figure 15] FIG. 15(a) is a plan view of an acoustic wave resonator according to a third embodiment and its first modification, and FIG. 15(b) is a cross-sectional view of another acoustic wave resonator according to the third embodiment and its first modification. [Figure 16] FIG. 16 is a diagram illustrating pass characteristics of the filters according to the third embodiment and the first modification thereof. [Figure 17] FIG. 17 is a circuit diagram of a filter according to a second modification of the third embodiment. [Figure 18] FIG. 18 is a circuit diagram of a triplexer in accordance with the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0021] Example 1 is an example of a high-pass filter. FIG. 1 is a circuit diagram of the filter according to Example 1. As shown in FIG. 1, in the filter 100 according to Example 1, capacitors C1 and C2 are connected in series between the input terminal Tin and the output terminal Tout. Between the input terminal Tin and the output terminal Tout, a capacitor C3 is connected in parallel to the capacitors C1 and C2. The node between the capacitors C1 and C2 is a node N1. One end of an inductor L1 is connected to the node N1 and the other end is connected to a ground terminal Tg, and the inductor L1 is shunt-connected to a path between the input terminal Tin and the output terminal Tout. The node to which the capacitors C1 and C3 are connected is a node N2. The node to which the capacitors C2 and C3 are connected is a node N3. The node N1 is connected to the capacitor C3 only through the capacitors C1 and C2. That is, the node N1 is not connected to the capacitor C3 without the capacitors C1 and C2. The filter 100 passes, among high-frequency signals input to an input terminal Tin, signals in a passband to an output terminal Tout and suppresses signals of other frequencies.

[0022] Fig. 2 is a cross-sectional view of the laminate in Example 1 mounted on a substrate. As shown in Fig. 2, the laminate 10 and an electronic component 26 are mounted on a substrate 20. The laminate 10 includes capacitors C1, C2 and an inductor L1, and includes a plurality of dielectric layers 11a to 11f. A terminal 14 is provided on the lower surface of the laminate 10. A terminal 28 is provided on the lower surface of the electronic component 26. A terminal 22 is provided on the substrate 20. The terminals 14 and 28 are bonded to the terminal 22 by a bonding material 24.

[0023] Fig. 3(a) to Fig. 3(f) are plan views of the dielectric layers in Example 1. Fig. 3(a) to Fig. 3(e) are plan views of the dielectric layers 11b to 11f, respectively, as viewed from above. Fig. 3(f) is a plan view of the terminal 14 seen through the dielectric layer 11f. The dielectric layer 11a is omitted from the illustration.

[0024] As shown in Figures 3(a) to 3(f), conductor patterns 12b to 12f are provided on dielectric layers 11b to 11f, respectively, and via wirings 13b to 13f are provided penetrating the dielectric layers 11b to 11f, respectively. As shown in Figure 3(a), conductor pattern 12b provided on dielectric layer 11b forms line L1a. As shown in Figure 3(b), conductor pattern 12c provided on dielectric layer 11c forms line L1b. Lines L1a and L1b are electrically connected by via wiring 13b to form inductor L1.

[0025] As shown in Fig. 3(c), a conductor pattern 12d provided on the dielectric layer 11d forms upper electrodes C1a and C2a of the capacitors C1 and C2, respectively. As shown in Fig. 3(d), a conductor pattern 12e provided on the dielectric layer 11e forms lower electrodes C1b and C2b of the capacitors C1 and C2, respectively. The dielectric layer 11d and the electrodes C1a and C1b sandwiching the dielectric layer 11d form a capacitor C1, and the dielectric layer 11d and the electrodes C2a and C2b sandwiching the dielectric layer 11d form a capacitor C2.

[0026] As shown in FIG. 3(e), the conductor pattern 12f provided on the dielectric layer 11f connects the terminal 14 through the via wiring 13f. As shown in FIG. 3(f), the terminal 14 provided on the lower surface of the dielectric layer 11f forms an input terminal Tin', an output terminal Tout', and a ground terminal Tg. The laminate 10 does not include a capacitor C3, and the input terminal Tin' and the output terminal Tout' correspond to the nodes N2 and N3 in FIG. 1. The capacitor C3 may be mounted on the laminate 10, for example. The capacitor C3 may be provided within the laminate 10.

[0027] The dielectric layers 11a to 11f are made of, for example, a ceramic material and contain, as a main component, an oxide of, for example, Si, Ca, and Mg (for example, CaMgSiO6, which is a diopside crystal). The main component of the dielectric layers 11a to 11f may be an oxide other than Si, Ca, and / or Mg. Furthermore, the dielectric layers 11a to 11f may contain at least one oxide of Ti, Zr, and Al as an insulating material. The dielectric layers 11a to 11f may be made of a resin such as glass epoxy resin, or a ceramic such as LTCC (Low Temperature Co-fired Ceramics) or HTCC (High Temperature Co-fired Ceramics). The conductor patterns 12b to 12f, the via wirings 13b to 13f, and the upper portion of the terminal 14 are non-magnetic metal layers mainly composed of, for example, Ag, Pd, Pt, Cu, Ni, Au, an Au-Pd alloy, or an Ag-Pt alloy. The upper part of the terminal 14 may include a non-conductive material such as TiO2, ZrO2, or Al2O3 in addition to the above metal materials. The lower part of the terminal 14 is a Ni film and a Sn film.

[0028] A circuit simulation was performed to determine the pass characteristic of filter 100 having an attenuation pole at 3.9 GHz. Table 1 shows the capacitances and Q values ​​of capacitors C1 to C3 and the inductance of inductor L1 used in the simulation. [Table 1]

[0029] As shown in Table 1, the capacitances of the capacitors C1 to C3 and the inductance of the inductor L1 were set to 0.4 pF, 0.4 pF, 0.5 pF and 1.5 nH, respectively. The Q values ​​of the capacitors C1 and C2 were set to 50. The Q value is the Q value at the frequency of the attenuation pole.

[0030] 4(a) and 4(b) are diagrams showing the pass characteristics of the filter in the first embodiment. In FIG. 4(a), the Q value of the capacitor C3 is 50, and in FIG. 4(b), the Q values ​​of the capacitor C3 are 10 and 50, and are enlarged views of the vicinity of the attenuation pole. As shown in FIG. 4(a), the capacitors C1 and C2 and the inductor L1 are a T-type CLC high-pass filter, and the pass band Pass is about 5.5 GHz or higher. By adding the capacitor C3, the attenuation pole Att having a local minimum at a frequency lower than the pass band Pass is formed by the capacitors C1 to C3 and the inductor L1. The frequency of the attenuation pole Att is 3.9 GHz. When the node N1 is directly connected to the capacitor C3, the attenuation pole Att is not formed. When the capacitor C3 is connected to the node N1 only through the capacitors C1 and C2, the attenuation pole Att is formed. As shown in FIG. 4(b), the filter with the Q value of the capacitor C3 of 10 has a steeper attenuation pole Att than the filter with the Q value of 50.

[0031] A circuit simulation was performed on the pass characteristic of the filter 100 having an attenuation pole Att of 1.8 GHz. Table 2 shows the capacitances and Q values ​​of the capacitors C1 to C3 and the inductance of the inductor L1 in the simulation. [Table 2]

[0032] As shown in Table 2, the capacitances of the capacitors C1 to C3 and the inductance of the inductor L1 were set to 0.8 pF, 0.8 pF, 1.0 pF and 3.5 nH, respectively. The Q values ​​of the capacitors C1 and C2 were set to 100.

[0033] Fig. 5(a) is a diagram showing the pass characteristic of the filter in Example 1, and Fig. 5(b) is a diagram showing the Q value versus frequency. As shown in Fig. 5(b), the Q value increases as the frequency decreases. A capacitor with a Q value of 50 at 3.9 GHz has a Q value of 100 at 1.8 GHz. Therefore, the Q values ​​of capacitors C1 and C2 are set to 100 as shown in Table 2.

[0034] As shown in FIG. 5(a), even if the frequency of the attenuation pole Att is set to 1.8 GHz, the filter with a Q value of 20 for the capacitor C3 has a steeper attenuation pole Att than the filter with a Q value of 100.

[0035] For a filter having an attenuation pole Att of 3.9 GHz, the pass characteristics of the filter 100 were simulated by fixing the Q value Q12 of the capacitors C1 and C2 to 50 and varying the Q value Q3 of the capacitor C3 to 50, 30, 20, 15, 10, 5, 4, and 3. The Q value Q3 of the capacitor C3 relative to the Q value Q12 of the capacitors C1 and C2 is Q3 / Q12.

[0036] 6(a) and 6(b) are diagrams showing the pass characteristic of the filter in the first embodiment. As shown in FIG. 6(a) and FIG. 6(b), when the Q value Q3 of the capacitor C3 becomes smaller, the attenuation pole Att becomes steeper. When Q3=30 (Q3 / Q12=0.6) or less, especially when Q3=20 (Q3 / Q12=0.4) or less, and further when Q3=15 (Q3 / Q12=0.3) or less, the attenuation pole Att becomes extremely steep. When Q3=5 (Q3 / Q12=0.1), the attenuation pole Att becomes the steepest. When Q3=4 (Q3 / Q12=0.08), the steepness of the attenuation pole Att becomes poor, and when Q3=3 (Q3 / Q12=0.06), the steepness of the attenuation pole Att becomes the same as when Q3=50.

[0037] [Comparative Example 1] Fig. 7 is a circuit diagram of a filter according to Comparative Example 1. As shown in Fig. 7, in a filter 110 of Comparative Example 1, a capacitor C3 is connected in series with an inductor L1 between a node N1 and a ground terminal Tg. In Comparative Example 1, an attenuation pole Att can be formed by a series resonant circuit of the capacitor C3 and the inductor L1 equivalent to that in Example 1. The other configurations are the same as those in Example 1, and therefore description thereof will be omitted.

[0038] A circuit simulation was performed to determine the pass characteristic of filter 110 having an attenuation pole at 3.9 GHz. Table 3 shows the capacitances and Q values ​​of capacitors C1 to C3 and the inductance of inductor L1 in the simulation. [Table 3]

[0039] As shown in Table 3, the capacitances of the capacitors C1 to C3 and the inductance of the inductor L1 were set to 1.35 pF, 1.35 pF, 1.12 pF, and 1.5 nH, respectively. The Q values ​​of the capacitors C1 and C2 were set to 50.

[0040] Fig. 8 is a diagram showing the pass characteristic of the filter in Comparative Example 1. As shown in Fig. 8, an attenuation pole Att is formed at 3.9 GHz. In filter 110, the frequency characteristic of the attenuation pole Att is the same in a filter with a Q value of 10 for capacitor C3 and a filter with a Q value of 50.

[0041] In the filter 110 of the comparative example 1, which is considered to be equivalent to the filter 100 of the first embodiment, the attenuation pole Att does not become steep even if the Q value of the capacitor C3 is made smaller than the Q values ​​of the capacitors C1 and C2. In this way, the phenomenon that the steepness of the attenuation pole Att improves when the Q value of the capacitor C3 is made lower than the Q values ​​of the capacitors C1 and C2 is a phenomenon unique to the filter 100 of the first embodiment. According to the common technical knowledge of a person skilled in the art, the attenuation pole becomes steep when the Q values ​​of the capacitors and inductors that form the attenuation pole are increased. It was found that the behavior of the filter 100 of the first embodiment is opposite to the common technical knowledge of a person skilled in the art.

[0042] [Modifications 1 and 2 of Example 1] 9(a) and 9(b) are circuit diagrams of filters according to Modifications 1 and 2 of Example 1, respectively. As shown in Fig. 9(a), in a filter 101 according to Modification 1 of Example 1, a capacitor C4 is connected between a node N3 and an output terminal Tout, and an inductor L2 is connected between the node N3 and a ground terminal Tg. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted.

[0043] As shown in Fig. 9(b), in the filter 102 of the second modification of the first embodiment, the capacitors C4 and C5 are connected in series between the node N3 and the output terminal Tout, and the capacitor C6 is connected in parallel to the capacitors C4 and C5 between the nodes N5 and N6. One end of the inductor L2 is connected to the node N4 between the capacitors C4 and C5. The other end of the inductor L1 and the other end of the inductor L2 are commonly connected to a node N7. One end of the inductor L3 is connected to the node N7, and the other end is connected to the ground terminal Tg. The other configuration is the same as that of the first embodiment, and therefore a description thereof will be omitted.

[0044] Circuit simulation was performed on the pass characteristics of filters 101 and 102 according to modifications 1 and 2 of Example 1. Table 4 shows the capacitances and Q values ​​of capacitors C1 to C4 and the inductances of inductors L1 and L2 in the simulated filter 101. [Table 4]

[0045] As shown in Table 4, the capacitances of the capacitors C1 to C4 and the inductances of the inductors L1 and L2 were set to 0.77 pF, 0.2354 pF, 0.25 pF, 1.241 pF, 2.055 nH, and 1.29 nH, respectively. The Q values ​​of the capacitors C1, C2, and C4 were set to 50. The Q values ​​of the capacitor C3 were set to 50 and 10 to simulate the pass characteristics.

[0046] Table 5 shows the capacitances and Q values ​​of the capacitors C1 to C6 and the inductances of the inductors L1 to L3 in the simulated filter 102. [Table 5]

[0047] As shown in Table 5, the capacitances of capacitors C1 to C6 and the inductances of inductors L1 to L3 were set to 0.22pF, 0.25pF, 0.4pF, 0.25pF, 0.22pF, 0.4pF, 3.0nH, 3.0nH, and 0.005nH, respectively. The Q values ​​of capacitors C1, C2, C4, and C5 were set to 50. The Q values ​​of capacitors C3 and C6 were set to 50 and 10 to simulate the pass characteristics.

[0048] 10(a) and 10(b) are diagrams showing the pass characteristics of filters in Modifications 1 and 2 of Example 1, respectively. As shown in Fig. 10(a), in filter 101 in Modification 1 of Example 1, the attenuation between the passband Pass and the attenuation pole Att changes more steeply than in Example 1 due to the provision of capacitor C4. If the Q value of capacitor C3 is 10, the steepness of the attenuation pole Att is improved compared to when the Q value is 50.

[0049] As shown in Fig. 10(b), in the filter 102 of the second modification of the first embodiment, a filter including capacitors C1 to C3 and an inductor L1 and a filter including capacitors C4 to C6 and an inductor L2 are provided, so that the attenuation between the passband Pass and the attenuation pole Att changes sharply. Since two attenuation poles Att are formed, the width of the attenuation pole Att becomes large. If the Q value of the capacitors C3 and C6 is 10, the steepness of the attenuation pole Att is improved compared to a Q value of 50.

[0050] As in the first and second modifications of the first embodiment, when the capacitors C1 to C3 and the inductor L1 are provided, the steepness of the attenuation pole Att increases when the Q value of the capacitor C3 is reduced, even if other elements are provided. A method for reducing the Q value of the capacitor C3 can be to use a material with a high tan δ for the dielectric of the capacitor C3, or to use a material with a high resistivity for the electrodes of the capacitor C3. In these cases, since it is difficult to form the capacitor C3 within the laminate 10, the capacitor C3 is provided as an electronic component 26 separate from the laminate 10, as shown in FIG. 2.

[0051] According to the first embodiment and its modified example, the capacitor C1 (first capacitor) and the capacitor C2 (second capacitor) are connected in series between the input terminal Tin and the output terminal Tout. The capacitor C3 is connected in parallel with the capacitors C1 and C2 between the input terminal Tin and the output terminal Tout. The node N1 is provided between the capacitors C1 and C2, and is connected to the capacitor C3 (capacitive element, third capacitor) via the capacitors C1 and C2. The inductor L1 has one end connected to the node N1 and the other end connected to the ground terminal Tg. In such a filter, the Q value of the capacitor C3 is made smaller than the Q value of the capacitor C1 and smaller than the Q value of the capacitor C2. This makes it possible to make the attenuation pole Att formed by the capacitors C1 to C3 and the inductor L1 steep.

[0052] The Q value of the capacitor C3 is preferably 0.6 times or less, more preferably 0.4 times or less, and further preferably 0.3 times or less, of the Q value of the capacitor C1 and the Q value of the capacitor C2. The Q value of the capacitor C3 is preferably 0.04 times or more, more preferably 0.08 times or more, of the Q value of the capacitor C1 and the Q value of the capacitor C2.

[0053] 3(a), the filter 100 is a high-pass filter having a passband Pass and has a minimum attenuation pole Att at a frequency lower than the passband Pass. By making the second Q value smaller than the first Q value, the steepness of the attenuation pole Att can be improved. EXAMPLES

[0054] In the second embodiment, even if the Q values ​​of the capacitors C1 to C3 are approximately equal to the manufacturing error, the Q value of the capacitor C3 can be substantially lowered by connecting a resistive element in series or parallel to the capacitor C3.

[0055] 11(a) and 11(b) are circuit diagrams of a filter according to a second embodiment and its modified example 1, respectively. As shown in FIG. 11(a), in a filter 103 according to the second embodiment, a resistor R is connected in series with a capacitor C3 between nodes N2 and N3. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0056] 11(b), in the filter 104 of the first modification of the second embodiment, a resistor R is connected in parallel to a capacitor C3 between nodes N2 and N3. The other configurations are the same as those of the first embodiment, and therefore the description will be omitted.

[0057] 2 may be formed with the capacitors C1 to C3 and the inductor L1, and the electronic component 26 may be formed with the resistor R. Alternatively, the capacitors C1 to C3, the inductor L1, and the resistor R may be formed within the laminate 10.

[0058] Circuit simulation was performed on the pass characteristics of filters 103 and 104 of Example 2 and Modification 1. The capacitances and Q values ​​of capacitors C1 to C3 and the inductance of inductor L1 are the same as those in Table 1 of Example 1. The Q value of capacitor C3 is 50, the same as the Q value of capacitors C1 and C2.

[0059] 12(a) and 12(b) are diagrams showing the pass characteristic of the filter 103 in the second embodiment. As shown in FIG. 12(a) and FIG. 12(b), the resistance value of the resistor R is changed to 0Ω, 1Ω, 2Ω, 4Ω, 6Ω, 10Ω, 15Ω, 20Ω, and 25Ω. When the resistor R is 0Ω, the pass characteristic is the same as that of the filter 100 in FIG. 4(b) when the Q value of the capacitor C3 is 50. When the resistance value of the resistor R is higher, the steepness of the attenuation pole Att is improved. When R=10Ω, the steepness of the attenuation pole Att is the highest. When the resistance value of the resistor R is higher than 10Ω, the steepness of the attenuation pole decreases, and when R=25Ω, the steepness is approximately the same as when R=0Ω.

[0060] 13(a) and 13(b) are diagrams showing the pass characteristic of the filter 104 in the first modification of the second embodiment. As shown in FIG. 13(a) and FIG. 13(b), the resistance value of the resistor R is changed to ∞, 4000Ω, 2000Ω, 1500Ω, 1000Ω, 500Ω, 400Ω, 300Ω, and 250Ω. When the resistor R is ∞, the pass characteristic is the same as that of the filter 100 in FIG. 4(b) when the Q value of the capacitor C3 is 50. When the resistance value of the resistor R is lower, the steepness of the attenuation pole Att is improved. When R=500Ω, the steepness of the attenuation pole Att is the highest. When the resistance value of the resistor R is lower than 500Ω, the steepness of the attenuation pole is lowered, and when R=250Ω, the steepness is approximately the same as when R=∞.

[0061] According to the second embodiment and its modified example, the resistor R (resistance element) is connected in parallel to the capacitors C1 and C2 and in series and / or in parallel to the capacitor C3 between the input terminal Tin and the output terminal Tout. This makes the combined Q value of the capacitor C3 and the resistor R between the nodes N2 and N3 lower than the Q value of the capacitor C3 alone. Therefore, even if the Q value of the capacitor C3 is approximately the same as the Q values ​​of the capacitors C1 and C2 within the manufacturing error range, the steepness of the attenuation pole Att can be improved.

[0062] The combined Q value of the capacitor C3 and the resistor R between the nodes N2 and N3 is preferably 0.6 times or less, more preferably 0.4 times or less, and even more preferably 0.3 times or less, of the Q value of the capacitor C1 and the Q value of the capacitor C2. The combined Q value of the capacitor C3 and the resistor R is preferably 0.04 times or more, more preferably 0.08 times or more, of the Q value of the capacitor C1 and the Q value of the capacitor C2. EXAMPLES

[0063] 14(a) and 14(b) are circuit diagrams of a filter according to a third embodiment and its first modification, respectively. As shown in FIG. 14(a), in a filter 105 according to the third embodiment, an acoustic wave resonator 30 is provided instead of a capacitor C3. The other configurations are the same as those in the first embodiment, and therefore descriptions thereof will be omitted. As shown in FIG. 14(b), in a filter 106 according to a first modification of the third embodiment, a resistor R is connected in series with the acoustic wave resonator 30 between nodes N2 and N3. The other configurations are the same as those in the third embodiment, and therefore descriptions thereof will be omitted.

[0064] FIG. 15(a) is a plan view of an acoustic wave resonator according to the third embodiment and its first modification, and FIG. 15(b) is a cross-sectional view of another acoustic wave resonator according to the third embodiment and its modification. In the example of FIG. 15(a), an acoustic wave resonator 30 is a surface acoustic wave resonator. An IDT (Interdigital Transducer) 40 and a reflector 42 are provided on the upper surface of a substrate 41. The IDT 40 has a pair of comb-shaped electrodes 40a facing each other. The comb-shaped electrode 40a has a plurality of electrode fingers 40b and a bus bar 40c connecting the plurality of electrode fingers 40b. The reflectors 42 are provided on both sides of the IDT 40. The IDT 40 excites a surface acoustic wave in the substrate 41. The substrate 41 is, for example, a piezoelectric substrate such as a lithium tantalate substrate, a lithium niobate substrate, or a quartz substrate. The substrate 41 may be, for example, a composite substrate in which a piezoelectric substrate is bonded to a support substrate such as a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, or a silicon substrate. The IDT 40 and the reflector 42 are formed of, for example, an aluminum film or a copper film. A protective film or a temperature compensation film may be provided on the substrate 41 so as to cover the IDT 40 and the reflector 42.

[0065] In the example of FIG. 15(b), the acoustic wave resonator 30 is a piezoelectric thin film resonator. A piezoelectric film 46 is provided on a substrate 41. A lower electrode 44 and an upper electrode 48 are provided so as to sandwich the piezoelectric film 46. A gap 45 is formed between the lower electrode 44 and the substrate 41. A region where the lower electrode 44 and the upper electrode 48 face each other with at least a part of the piezoelectric film 46 sandwiched therebetween is a resonance region 47. The lower electrode 44 and the upper electrode 48 in the resonance region 47 excite an acoustic wave in the piezoelectric film 46 in a thickness longitudinal vibration mode or a thickness shear vibration mode. The substrate 41 is, for example, a sapphire substrate, a spinel substrate, an alumina substrate, a glass substrate, a quartz substrate, or a silicon substrate. The lower electrode 44 and the upper electrode 48 are, for example, metal films such as a ruthenium film, a single crystal lithium tantalate film, or a single crystal lithium niobate film. The piezoelectric film 46 is, for example, an aluminum nitride film. An acoustic reflection film may be provided instead of the gap 45.

[0066] Circuit simulation was performed on the pass characteristics of filters 105 and 106 of Example 3 and Modification 1. The capacitances and Q values ​​of capacitors C1 and C2 and the inductance of inductor L1 are the same as those in Table 1 of Example 1. In filter 106 of Modification 1 of Example 3, the resistance value of resistor R was set to 6 Ω.

[0067] FIG. 16 is a diagram showing the pass characteristic of the filter according to the third embodiment and its first modification. The capacitance and Q value of the capacitors C1 and C2, and the inductance of the inductor L1 are the same as those in Table 1. The resonant frequency of the acoustic wave resonator 30 is 3.893 GHz, and the Q value at the attenuation pole Att is about 20. As shown in FIG. 16, the pass band Pass is about 4.5 GHz or higher. At the attenuation pole Att1, the acoustic wave resonator 30 is capacitive. The attenuation pole Att1 is formed by the capacitors C1 and C2, the inductor L1, and the capacitance of the acoustic wave resonator 30. Between the pass band Pass and the attenuation pole Att1, the attenuation pole Att2 is formed by the resonant frequency of the acoustic wave resonator 30. The attenuation pole Att2 can improve the steepness of the attenuation between the pass band Pass and the attenuation region. In the filter 106, the steepness of the attenuation pole Att1 can be improved compared to the filter 105. Furthermore, in filter 105, by making the Q value of acoustic wave resonator 30 at the frequency of attenuation pole Att1 smaller than the Q values ​​of capacitors C1 and C2, it is possible to make attenuation pole Att1 steep.

[0068] Fig. 17 is a circuit diagram of a filter according to Modification 2 of Example 3. As shown in Fig. 17, in filter 107 according to Modification 2 of Example 3, a resistor R is connected in parallel to elastic wave resonator 30 between nodes N2 and N3. The other configurations are the same as those in Example 3, and therefore description thereof will be omitted. In Modification 2 of Example 3 as in Modification 1 of Example 3, the steepness of attenuation pole Att1 can be improved.

[0069] According to the third embodiment and its modified example, the capacitive element is an acoustic wave resonator 30, and the acoustic wave resonator 30 forms a second minimum of an attenuation pole Att2 (second attenuation pole) between a first minimum of an attenuation pole Att1 (first attenuation pole) and a pass band Pass. In this manner, the capacitive element may be the acoustic wave resonator 30. EXAMPLES

[0070] The fourth embodiment is an example of a multiplexer using the first to third embodiments and their modified examples. FIG. 18 is a circuit diagram of a triplexer according to the fourth embodiment. As shown in FIG. 18, a triplexer 32 includes filters 34, 36, and 38. The filters 34, 36, and 38 are connected between a common terminal Ant and terminals LB, MB, and HB, respectively. An antenna 35 is connected to the common terminal Ant. The filter 34 is, for example, a low-pass filter, which passes a high-frequency signal in a low band and suppresses signals of other frequencies. The filter 36 is, for example, a band-pass filter, which passes a high-frequency signal in a middle band, which is a frequency higher than the low band, and suppresses signals of other frequencies. The filter 38 is, for example, a high-pass filter, which passes a high-frequency signal in a high band, which is a frequency higher than the middle band, and suppresses signals of other frequencies. The filter 38 can be a filter according to the first embodiment and its modified examples. Although the triplexer has been described as an example of a multiplexer, the multiplexer may be a diplexer, a duplexer, or a quadplexer.

[0071] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0072] 10 Laminate 11a to 11f Dielectric layers 12b~12f Conductive patterns 13b~13f Via wiring 14, 22 terminals 20 Substrate 24 Bonding material 26 Electronic Components 30 Elastic Wave Resonator 32 Triplexer 34, 36, 38 Filters

Claims

1. An input terminal; An output terminal; A ground terminal; a first capacitor and a second capacitor connected in series between the input terminal and the output terminal; a capacitive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal, the capacitive element having a Q value smaller than a Q value of the first capacitor and smaller than a Q value of the second capacitor; a node provided between the first capacitor and the second capacitor and connected to the capacitive element via the first capacitor and the second capacitor; an inductor having one end connected to the node and the other end connected to the ground terminal; A filter comprising:

2. 2. The filter of claim 1, wherein the Q value of the capacitive element is less than or equal to 0.6 times the Q value of the first capacitor and less than or equal to 0.6 times the Q value of the second capacitor.

3. the filter is a high-pass filter having a pass band; 3. The filter according to claim 1, wherein the first capacitor, the second capacitor, the capacitive element and the inductor form a first minimum of a first attenuation pole at a frequency lower than the passband.

4. the capacitive element is an acoustic wave resonator; 4. The filter of claim 3, wherein the acoustic wave resonator forms a second minimum of a second attenuation pole between the first minimum and the passband.

5. 4. A filter according to claim 1, wherein the capacitive element is a third capacitor.

6. An input terminal; An output terminal; A ground terminal; a first capacitor and a second capacitor connected in series between the input terminal and the output terminal; a capacitive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal; a resistive element connected in parallel with the first capacitor and the second capacitor between the input terminal and the output terminal, and connected in series and / or in parallel with the capacitive element; a node provided between the first capacitor and the second capacitor and connected to the capacitive element via the first capacitor and the second capacitor; an inductor having one end connected to the node and the other end connected to the ground terminal; A filter comprising:

7. 7. The filter according to claim 6, wherein a combined Q value of the capacitive element and the resistive element is 0.6 times or less the Q value of the first capacitor and 0.6 times or less the Q value of the second capacitor.

8. the filter is a high-pass filter having a pass band; 8. The filter according to claim 6, wherein the first capacitor, the second capacitor, the capacitive element and the inductor form a first minimum of a first attenuation pole at a frequency lower than the passband.

9. the capacitive element is an acoustic wave resonator; 9. The filter of claim 8, wherein the acoustic wave resonator forms a second minimum of a second attenuation pole between the first minimum and the passband.

10. 9. A filter according to claim 6, wherein the capacitive element is a third capacitor.

11. The filter of claim 10 , wherein the Q values ​​of the first capacitor, the second capacitor and the third capacitor are substantially equal to each other.

12. A multiplexer comprising a filter according to any one of claims 1 to 11.

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