WO2024101346A1

WO2024101346A1 - Composite filter, module, and communication device

Info

Publication number: WO2024101346A1
Application number: PCT/JP2023/040028
Authority: WO
Inventors: 安藤　智洋; 武宏奥道; 雅史堀内; 直史笠松
Original assignee: 京セラ株式会社
Priority date: 2022-11-11
Filing date: 2023-11-07
Publication date: 2024-05-16

Abstract

This composite filter comprises: an elastic wave filter; an LC filter; and an electrical element. The elastic wave filter has at least one elastic wave resonator. The LC filter is electrically interposed between the elastic wave filter and a first terminal. The electrical element is electrically interposed between the elastic wave filter and a second terminal. The electrical element is an inductor, a wiring having inductance of 0.3 nH or higher, or a capacitor. An attenuation slope of at least one of a high-frequency side and a low-frequency side of a passband of the composite filter satisfies the following expression.　Min. Loss (dB)≤a×Δf^-b

Description

Composite filter, module and communication device

The present disclosure relates to a composite filter having two or more filters, as well as a module and a communication device having the composite filter.

A filter that combines an LC filter with an elastic wave resonator is known (for example, see Patent Document 1 below). In Patent Document 1, the attenuation slope in the transition band between the passband and the stopband is made steeper by combining an LC filter with an elastic wave resonator.

International Publication No. 2016/013659

A composite filter according to an aspect of the present disclosure includes an acoustic wave filter, an LC filter, and an electrical element. The acoustic wave filter includes at least one acoustic wave resonator. The LC filter is electrically interposed between the acoustic wave filter and a first terminal. The electrical element is electrically interposed between the acoustic wave filter and a second terminal. The electrical element is an inductor, a wiring having an inductance of 0.3 nH or more, or a capacitor. At least one of the attenuation slopes on the high frequency side and the low frequency side of the pass band of the composite filter satisfies the following formula 1.
Equation 1: Min. Loss (dB) ≦ a × Δf ^{− b}
However, the parameters in the above formula 1 are as follows:
Min. Loss (dB): The minimum insertion loss of the composite filter in the pass band Δf=|f1.5−f30|/f1.5
f1.5: The frequency at which the insertion loss of the composite filter is 1.5 dB larger than the Min. Loss (dB). f30: The frequency at which the insertion loss of the composite filter is 30 dB larger than the Min. Loss (dB). a=aa×(log ₁₀ (order-1)) ^−ab
b = b a × (log ₁₀ (order-1)) ^bb
aa = 0.00079217 × exp (0.055664 × (order-1))
ab = 3.9180 x exp (-0.0041245 x (order-1))
ba = 2.8407 × exp (0.0078456 × (order-1))
bb = 0.54831 x exp (0.0032121 x (order-1))
order: the number of series arms and parallel arms that have at least one of an inductor and a capacitor and do not have an acoustic wave resonator, electrically interposed between the first terminal and the acoustic wave filter and between the acoustic wave filter and the second terminal

A module according to one aspect of the present disclosure includes the composite filter and a second filter. The second filter is connected to at least one of the first terminal and the second terminal, and has a pass band different from the pass band of the composite filter.

A communication device according to one aspect of the present disclosure includes the composite filter, an antenna, and an integrated circuit element. The antenna is connected to one of the first terminal and the second terminal. The integrated circuit element is connected to the other of the first terminal and the second terminal.

FIG. 2 is a circuit diagram showing a first configuration example of a composite filter according to the embodiment. FIG. 4 is a circuit diagram showing a second configuration example of the composite filter according to the embodiment. 5 is a schematic diagram for explaining parameters used in an inequality that defines the configuration of a composite filter. FIG. 4 is a schematic diagram for explaining the tendency of changes in the parameters. FIG. 11 is another schematic diagram for explaining the tendency of changes in the parameters. FIG. 4 is a schematic diagram showing an example of a passband of the composite filter according to the embodiment. 5A and 5B are schematic diagrams showing examples of attenuation poles of an LC filter included in the composite filter according to the embodiment. FIG. 6B is a circuit diagram showing an example of a configuration for realizing the attenuation pole of FIG. 6A. FIG. 6B is a circuit diagram showing another example of the configuration for realizing the attenuation pole of FIG. 6A. FIG. 2 is a schematic cross-sectional view showing an example of the structure of a composite filter according to an embodiment. 5A to 5C are schematic diagrams showing variations in the structure of the composite filter according to the embodiment. 5A to 5C are schematic diagrams showing other variations in the structure of the composite filter according to the embodiment. 11A to 11C are schematic diagrams showing still another variation of the structure of the composite filter according to the embodiment. 11A to 11C are schematic diagrams showing still another variation of the structure of the composite filter according to the embodiment. FIG. 4 is a plan view illustrating a schematic configuration example of an elastic wave resonator included in the composite filter. FIG. 1 is a block diagram showing a main part of a communication device according to an embodiment.

(Composite Filter Overview)
Fig. 1 is a circuit diagram showing a first example of a composite filter 1 (reference numeral is shown in Fig. 7) according to an embodiment. Fig. 2 is a circuit diagram showing a second example of a composite filter 1 according to an embodiment. The composite filter 1 according to the first example of a composite filter 1 may be referred to as a composite filter 1A, and the composite filter 1 according to the first example of a composite filter 1 may be referred to as a composite filter 1B.

The composite filter 1 is disposed between a first terminal 3A and a second terminal 3B (hereinafter, sometimes referred to as "terminal 3" (reference numeral in FIG. 7) without distinction between the two terminals) and passes components having frequencies in a predetermined pass band among the signals passing between the two terminals. In other words, the composite filter 1 attenuates components having frequencies outside the pass band. Note that either the first terminal 3A or the second terminal 3B may be the input side or the output side.

The composite filter 1 has an elastic wave filter 5, an LC filter 7, and an additional circuit 9 (reference numerals shown in FIG. 8A). The configuration of the additional circuit 9 is different between the

composite filters

1A and 1B. The additional circuit 9 in the composite filter 1A may be referred to as the additional circuit 9A, and the additional circuit in the composite filter 1B may be referred to as the additional circuit 9B. The elastic wave filter 5 has at least one elastic wave resonator 11 (hereinafter, may be simply referred to as the "resonator 11"). The LC filter 7 is interposed between the first terminal 3A and the elastic wave filter 5. The additional circuit 9 is interposed between the elastic wave filter 5 and the second terminal 3B.

The additional circuit 9 has at least one electrical element 13 (reference numeral in FIG. 2). The electrical element 13 is, for example, an inductor L, a capacitor C, or a specific wiring 15 (reference numeral in FIG. 8B). The specific wiring 15 is assumed to be a wiring having an inductance of 0.3 nH or more. The specific wiring 15 may be regarded as an inductor L. Therefore, in the description of the embodiment, the description of the inductor L of the additional circuit 9 may be applied to the specific wiring 15 of the additional circuit 9, unless a contradiction arises.

Figure 3 is a schematic diagram showing an example of the attenuation characteristics (or, from another perspective, the transmission characteristics) of the composite filter 1.

In this diagram, the horizontal axis indicates frequency f (Hz), with higher frequencies toward the right of the diagram. The vertical axis indicates insertion loss (sometimes called "Loss"). The vertical axis is in dB, with the loss decreasing toward the top of the diagram. Note that in such graphs, values with "-" may be shown on the vertical axis. In the explanation of the embodiment, explanations regarding the magnitude of Loss are given with Loss treated as a positive value, or the absolute value of Loss is mentioned.

Line L1 in the figure indicates the attenuation characteristics of composite filter 1. In the illustrated example, a bandpass filter is assumed as the composite filter 1. Therefore, loss is small in a predetermined passband PB1. Furthermore, loss is large in the stopbands EB1L or EB1H (symbols in Figure 5) on both sides (low frequency side and high frequency side) of the passband PB1. In the attenuation characteristics of the composite filter 1, the portion where loss gradually increases from the passband PB1 to the stopband EB1L or EB1H is referred to as the attenuation slope SLP.

In the composite filter 1 according to the embodiment, the attenuation slopes SLP on the high frequency side and the low frequency side satisfy the following formula 1.
Equation 1: Min. Loss (dB) ≦ a × Δf ^{− b}
Min. Loss is an index indicating the magnitude of Loss in the passband PB1. Δf is an index indicating the steepness of the attenuation slope SLP. a and b are parameters whose values vary depending on the size of the LC filter 7 and the additional circuit 9 (more specifically, the number of stages described later). These will be described in detail later.

The composite filter 1 having the above configuration has the following effects, for example:

The LC filter 7 generally makes it easy to ensure a wide pass band and/or stop band. On the other hand, the elastic wave filter 5 generally makes it easy to increase the steepness of the attenuation slope. Therefore, by combining the two, it becomes easy to make the attenuation slope steep while ensuring a wide band as the pass band or stop band.

Also, an LC filter 7 is interposed between the first terminal 3A and the elastic wave filter 5, and an additional circuit 9 is interposed between the elastic wave filter 5 and the second terminal 3B. Therefore, both the impedance of the composite filter 1 as viewed from the input side and the impedance of the composite filter 1 as viewed from the output side can be adjusted by adjusting the inductance and/or capacitance of the components of the LC filter 7 and the additional circuit 9.

When an inductor L and/or a capacitor C (LC filter 7 and additional circuit 9) are combined with both the first terminal 3A side and the second terminal 3B side of the elastic wave filter 5, for example, loss increases. However, when the composite filter 1 is configured so that formula 1 is satisfied, the size of the LC filter 7 and additional circuit 9 is limited. This makes it possible to achieve both a steeper attenuation slope and a reduced insertion loss.

The above is an overview of the composite filter 1 according to the embodiment. The following will generally be described in the following order.
1. Formula 1 (FIGS. 3, 4A and 4B)
1.1. Definition of parameters in Equation 1 1.2. Configuration specified by Equation 1 1.3. Method for determining Equation 1 1.4. Counting of orders 1.5. Other equations 2. General configuration of composite filters (Figs. 1 and 2)
3. Structure of acoustic wave filter (Figures 1 and 2)
4. LC filter configuration (Figures 1 and 2)
5. Configuration of additional circuit (Fig. 1 and Fig. 2)
6. Examples of attenuation characteristics 6.1. Passband and stopband (Figure 5)
6.2. Examples of attenuation poles (FIGS. 6A to 6C)
7. Example of a composite filter structure 7.1. Structural components (Fig. 7)
7.2. Structural variations (FIGS. 8A to 8D)
7.3. Supplementary information on structure 8. Specific example of elastic wave resonator structure (Figure 9)
9. Example of using composite filters (Figure 10)
10. Summary of the embodiment

(1. Equation 1)
(1.1. Definition of parameters in formula 1)
3, the Min. Loss in Equation 1 refers to the minimum value of the loss in the passband. Usually, the smaller the Min. Loss, the smaller the loss is over the entire passband. In other words, the Min. Loss is a kind of representative value of the loss in the passband.

Δf in Equation 1 refers to a normalized value obtained by dividing the absolute value of the frequency difference (Hz) indicated as "Δf×f1.5" in FIG. 3 by the frequency f1.5 (Hz). "Δf×f1.5" is the frequency difference (Hz) between the frequency f1.5 and the frequency f30. That is, Δf is expressed by the following equation.
Δf=|f1.5−f30|/f1.5

Frequency f1.5 is the frequency f (Hz) when the loss is 1.5 dB greater than the Min. Loss. Frequency f30 is the frequency f (Hz) when the loss is 30 dB greater than the Min. Loss. In general, the passband is often a band where the loss is 3 dB or less. Therefore, Δf indicates the steepness of the attenuation slope in a frequency band relatively close to the passband. The smaller Δf is, the steeper the slope is.

a and b in formula 1 are represented by the following formulas.
a = aa × (log ₁₀ (order-1)) ^{- ab}
b = b a × (log ₁₀ (order-1)) ^bb
aa = 0.00079217 × exp (0.055664 × (order-1))
ab = 3.9180 x exp (-0.0041245 x (order-1))
ba = 2.8407 × exp (0.0078456 × (order-1))
bb = 0.54831 x exp (0.0032121 x (order-1))
For convenience, the above formulas may be referred to as "formula a", "formula b", "formula aa", "formula ab", "formula ba" and "formula bb" in that order.

In the above, order is the number (stages) of series arms 17S and parallel arms 17P (FIGS. 1 and 2; hereinafter, these are sometimes referred to as "arms 17" (reference numerals in FIG. 2) without distinction between the two) located on both sides of the acoustic wave filter 5. The definition and method of identifying the arms 17 will be described later (Section 1.4). Here, to easily understand the order, the order will be counted using FIGS. 1 and 2 as examples.

Take FIG. 1 as an example. LC filter 7 has, in order from first terminal 3A to acoustic wave filter 5, a series arm 17S consisting of a capacitor C, a parallel arm 17P consisting of an inductor L, and a series arm 17S consisting of a capacitor C. Therefore, the number of stages in LC filter 7 is 3. Additional circuit 9A has a series arm 17S consisting of an inductor L. Therefore, the number of stages in additional circuit 9A is 1. As a whole, the number of stages related to order for composite filter 1A is 4.

Take FIG. 2 as an example. The number of stages in LC filter 7 is three, just like in FIG. 1. The number of stages in additional circuit 9B in FIG. 2 is three, just like the number of stages in LC filter 7. Therefore, the number of stages related to order for composite filter 1B as a whole is six.

The composite filter 1 has an LC filter 7 on the first terminal 3A side, and an additional circuit 9 on the second terminal 3B side. Each of the LC filter 7 and the additional circuit 9 has at least one arm 17. Therefore, in the configuration of the embodiment, the order is necessarily 2 or more. As a result, the calculation of log ₁₀ 0 does not occur.

(1.2. Configuration specified by formula 1)
4A is a schematic diagram showing the relationship between Δf and Min. Loss when the inequality sign (≦) in Equation 1 is changed to an equal sign (=).

In this diagram, the horizontal axis is a logarithmic axis showing Δf, with values increasing toward the right side of the diagram (the attenuation slope becomes gentler). The vertical axis is a logarithmic axis showing Min. Loss (dB), with loss increasing toward the top of the diagram. Line L3 in the diagram shows the relationship between Δf and Min. Loss when the order is a specific value.

As shown by line L3, in Equation 1, the smaller Δf is, the larger Min. Loss is. In other words, the steeper the attenuation slope is, the larger the Loss is. Therefore, Equation 1 shows a trade-off between the steepness of the attenuation slope and the reduction of Loss.

FIG. 4B is a schematic diagram showing the relationship between log ₁₀ (order-1) and a and b.

In this figure, the horizontal axis is a logarithmic axis showing log ₁₀ (order-1), and the value of the parameter is larger toward the right side of the figure. It may be considered that the order is larger toward the right side of the figure. The vertical axis on the left side is a logarithmic axis showing a, and the value of a is larger toward the top of the figure. The vertical axis on the right side is a logarithmic axis showing b, and the value of b is larger toward the top of the figure. It should be noted that the size of the vertical axis on the left side and the size of the vertical axis on the right side are different from each other. Line La in the figure shows the relationship between log ₁₀ (order-1) and a. Line Lb shows the relationship between log ₁₀ (order-1) and b.

As shown by line La, the larger the order, the smaller the value of a. Meanwhile, a is a positive parameter that is multiplied by Δf in Equation 1. Therefore, the larger the order, the larger the value of the right hand side of Equation 1 (from another perspective, Min. Loss shown in Figure 4A).

As shown by line Lb, the larger the order, the larger the value of b. On the other hand, b is made negative in Equation 1 and used as an exponent related to the power of Δf. Also, Δf is usually less than 1. Therefore, the larger the order, the larger the value of the right hand side of Equation 1 (from another perspective, Min.Loss shown in Figure 4A).

Although not shown in the figure, from the changes in a and b relative to the above order, the larger the order, the more the line L3 in Figure 4A shifts toward the upper right side of the figure. In other words, when the inequality sign in Equation 1 is changed to an equal sign, the larger the order, the larger the Min. Loss value corresponding to a specific value of Δf becomes.

Therefore, as described in the overview of the embodiment, when the composite filter 1 is configured so that Equation 1 is satisfied, the order of the LC filter 7 and the additional circuit 9 can be determined so that the loss is suppressed to a certain degree in relation to Δf. Furthermore, as can be understood from the method for determining Equation 1 described below, the certain degree of the above-mentioned loss is for an LC filter with a steep attenuation slope. Therefore, it is possible to achieve both a steep attenuation slope and a reduced insertion loss.

(1.3. Method for determining formula 1)
The formula 1 has been obtained based on simulation calculations performed by the applicant. Specifically, it is as follows.

Several elliptic function type (Cauer type) LC filters were designed with different numbers of stages and passband bandwidths. Specifically, the variations in the number of stages were 3, 4, 5, 6, 7, and 9. The passbands for all LC filters were set so that the frequency at which the loss was 10 dB on the attenuation slope on the low frequency side was approximately 5 GHz. The passband variations were set so that the frequency band width at which the loss was 10 dB or less was approximately 0.5 GHz, 1 GHz, 2 GHz, and 3 GHz. The LC filters were designed so that the loss in the stopband was 40 dB or more. In the LC filters, the inductance of the inductor L and the capacitance of the capacitor C were optimized to satisfy the above requirements.

For the above-mentioned various LC filters, Δf and Min. Loss were calculated by simulation calculation. Then, when these values were plotted by the number of stages, a correlation was shown as shown by line L3 in FIG. 4A. Therefore, an equation that approximates the relationship between Δf and Min. Loss by the number of stages was searched for. As a result, it was found that the above relationship can be approximated by Equation 1. When the above relationship was approximated by Equation 1 (when a and b were calculated by regression analysis), the coefficient of determination ^R2 was 0.996 or more.

Next, we searched for an equation that approximates the relationship between order and a or b. As a result, we found that the above relationship can be approximated by the above-mentioned equation for a or b, that is, an equation in which log ₁₀ (order-1) is raised to the power and multiplied by a coefficient. When the above relationship was approximated by the above equation (when aa, ab, ba, and bb were calculated by regression analysis), the coefficient of determination ^R2 was 0.992 or more.

Furthermore, the applicant found that the accuracy of the approximation formula showing the relationship between Δf and Min. Loss is improved by making aa, ab, ba, and bb functions of order as well. More specifically, as a result of intensive research, the applicant found that the relationship between order and aa, ab, ba, or bb can be approximated by the above-mentioned formula of aa, ab, ba, or bb, that is, the formula in which the Napier's number is raised to the power of the value obtained by multiplying (order-1) by a first coefficient as an exponent, and then multiplied by a second coefficient. Then, the applicant found the above-mentioned formula of aa, ab, ba, or bb by regression analysis to determine the first coefficient and the second coefficient.

The applicant has confirmed that the relationship between Δf and Min. Loss can be approximated by Equation 1 obtained as above, even under conditions (number of stages, etc.) different from those used when Equation 1 was obtained.

(1.4. How to count orders)
As described above, the formula 1 has an order as a parameter. Therefore, the following describes matters related to the counting of the order.

The arms (e.g., arm 17 and arm 21 described below) refer to, for example, multiple intersecting portions of a circuit configured in a ladder type. In the example of Figs. 1 and 2, a ladder type circuit is configured by providing a signal path from the first terminal 3A to the second terminal 3B via the acoustic wave filter 5, and one or more parallel arms (e.g.,

parallel arms

17P and 21P) that connect multiple positions on the signal path to the reference potential section 19. Of the above signal paths, each separated by one or more connection positions to one or more parallel arms is a series arm (e.g.,

series arms

17S and 21S).

As can be understood from the above description, each arm may have only one electrical element (e.g., an inductor L or a capacitor C), or may include two or more electrical elements. For example, in Figures 6B and 6C described below, a parallel resonant circuit 23P and a series resonant circuit 23S are shown, and such resonant circuits may be included in one arm. Furthermore, a more complex circuit (e.g., a dual resonant circuit) may be included in one arm.

Note that even if two parallel arms appear at first glance, if the connection positions from an electrical perspective to the signal path (series arm) are substantially the same, they may be regarded as one parallel arm. For example, even if two parallel arms appear at first glance, if there is no electrical element (e.g., inductor L or capacitor C) between the connection positions of the two to the signal path (the part that should correspond to the series arm), the two parallel arms may be regarded as one parallel arm.

In addition, electrical elements may be connected in parallel to the signal path across the connection position of the parallel arm to the signal path. Such electrical elements can also be considered as a type of series arm. However, electrical elements such as those described above often contribute to fine-tuning the characteristics. Therefore, the above electrical elements do not need to be included in the series arm when counting the order. In addition, specific parts such as those described above may be appropriately excluded from the arms when counting the order, taking into account the impact they have on the ladder-type circuit.

A filter may be constructed by electric field coupling and/or magnetic field coupling between the inductors L of the two parallel arms. The presence or absence of such coupling may be ignored when counting the order. The same applies to couplings in other parts.

The series arm 17S and parallel arm 17P related to the order refer to those that the composite filter 1 has on the first terminal 3A side and the second terminal 3B side with respect to the acoustic wave filter 5. In other words, the order is the number of stages of the arms 17 interposed between the first terminal 3A and the acoustic wave filter 5 and between the acoustic wave filter 5 and the second terminal 3B.

In the description of the embodiment, it is assumed that only the LC filter 7 is interposed between the first terminal 3A and the elastic wave filter 5. Furthermore, unless otherwise specified, the term "between the first terminal 3A and the elastic wave filter 5" and the term "LC filter 7" may be treated as synonymous terms. Similarly, it is assumed that only the additional circuit 9 is interposed between the elastic wave filter 5 and the second terminal 3B, and the two terms may be treated as synonymous terms.

From another perspective, for example, if a matching circuit for impedance matching and an LC filter are provided between the first terminal 3A and the acoustic wave filter 5, the combination of the matching circuit and the LC filter may be defined as the LC filter 7. In other words, the entire circuit having L and C and performing a filter function, and located between the first terminal 3A and the acoustic wave filter 5, may be regarded as the LC filter 7. Similarly, the entire circuit having L and C and located between the acoustic wave filter 5 and the second terminal 3B may be regarded as the additional circuit 9.

In the examples of Figures 1 and 2, the capacitor C on the right side of the LC filter 7 and the leftmost resonator 11 of the acoustic wave filter 5 are not separated by a parallel arm, and therefore can be considered to form one series arm. However, according to the definition of the arm 17 related to the order above, the series arm 17S on the right side of the LC filter 7 is composed only of the right-side capacitor C. However, even if the right-side series arm 17S is interpreted as including the leftmost resonator 11, this does not affect the value of the order. In other words, when counting the order, it is up to the user to interpret whether or not the leftmost resonator 11 is included in the series arm 17S. The same is true for the additional circuit 9.

As described above, the series arm 17S and the parallel arm 17P related to the order are included in the LC filter 7 or the additional circuit 9. Furthermore, the LC filter 7 and the additional circuit 9 each include an inductor L (including the specific wiring 15) or a capacitor C. Therefore, the series arm 17S and the parallel arm 17P are arms that have at least one inductor L and one capacitor C. The series arm 17S and the parallel arm 17P may include other electrical elements. Examples of such electrical elements include resistors and resonators. The resonators may not include elastic wave resonators.

As can be understood from the above explanation that the order in the examples of Figures 1 and 2 is 4 and 6, respectively, the order is the sum of the number (number of stages) of the series arms 17S and the number (number of stages) of the parallel arms 17P, as well as the sum of the number of stages in the LC filter 7 and the number of stages in the additional circuit 9. However, for example, the number of stages in the LC filter 7 may be determined by substituting the number of stages in the LC filter 7 into Equation 1 as the value of order, or the number of stages in the additional circuit 9 may be applied to Equation 1 as the value of order to determine the number of stages in the LC filter 7. In this case, the smaller the value of the order in Equation 1, the smaller the value of the right side becomes, so that a composite filter 1 with better characteristics is obtained. Also, for example, the larger of the number of stages in the LC filter 7 and the number of stages in the additional circuit 9 may be substituted into Equation 1 as the value of order to determine the number of stages in the circuit with the larger number of stages.

(1.5. Other Formulas)
Depending on the configuration of the composite filter 1, it may be difficult to specify f30. In such a case, Δf may be calculated based on f20. f20 is the frequency f at which the loss is 20 dB smaller than the Min. Loss. Specifically, Δf is calculated from f20 by the following formula.
Δf=α×Δf20+β
Δf20=|f1.5−f20|/f1.5
α=0.985×exp(1.0309×0.61941 ^order−1 )
β = 0.01009 × exp (-19.04 × 0.3729 ^order-1 )

The above formula was obtained based on simulation calculations. Specifically, f30, f20, and f1.5 were identified based on the results of simulation calculations under the various conditions used when formula 1 was obtained. Next, Δf was calculated using the formula Δf = |f1.5 - f30|/f1.5. Then, a formula that approximates f20 and Δf was searched for, and the above formula was obtained as a result.

(2. Overall configuration of composite filters)
The composite filter 1 shown in Fig. 1 and Fig. 2 may be configured with a focus on either the pass band or the stop band. In addition, in the composite filter 1, the pass band or the stop band may be specified by both the lower limit (low frequency end) frequency and the upper limit (high frequency end) frequency, or only one of them. From another perspective, the composite filter 1 may be regarded as, for example, any of a band pass filter, a high pass filter, a low pass filter, and a band elimination filter. The description in this paragraph may also be applied to each of the acoustic wave filter 5, the LC filter 7, and the additional circuit 9 (when a filter is configured).

In distributed products, the passband and stopband may be specified as appropriate. For example, they may be specified by a specification, or they may be specified by measuring the filter characteristics of the product. The attenuation required for the passband and stopband differs depending on the device to which the composite filter 1 is applied. As an example, a frequency band with a loss of 5 dB or less or 3 dB or less may be specified as the passband. Also, as an example, a frequency band with a loss of 30 dB or more or 40 dB or more may be specified as the stopband. f1.5 may be located within the passband or outside the passband.

The composite filter 1 may have any configuration from a structural standpoint. For example, the composite filter 1 may be configured as a chip-type electronic component and mounted on a circuit board or the like, or it may be part of an electronic component, part of a multilayer board, or part of a module consisting of a circuit board and multiple electronic components. Examples of the structure of the composite filter 1 will be given later (Section 7).

The configuration of the electrical elements (e.g., inductor L and capacitor C) of the composite filter 1 (or, from another perspective, the acoustic wave filter 5, the LC filter 7, and/or the additional circuit 9) from a structural standpoint is also arbitrary. For example, the electrical elements may be chip-type, or may be built into a multilayer board. Furthermore, the chip-type electrical elements may be mounted on the multilayer board, or may be embedded in the multilayer board. Furthermore, the characteristics of the electrical elements (e.g., inductance and capacitance) may be set appropriately according to the characteristics required of the composite filter 1.

In the composite filter 1, signals having frequencies outside the passband are, for example, discharged to the reference potential section 19. The reference potential section 19 is a section to which a reference potential is applied. A representative example of the reference potential is 0 V, but is not limited to this. The specific configuration of the reference potential section 19 is arbitrary. For example, the reference potential section 19 may be the terminal 3 (Figure 7) and a ground layer in the circuit board.

In the drawings, the reference potential sections 19 are shown in multiple positions. The reference potential sections 19 shown in multiple positions may actually be different locations from each other, or may simply be considered to be shown separately from each other for convenience of illustration. Furthermore, two or more reference potential sections 19 as different locations from each other may or may not be connected to each other within the composite filter 1.

(3. Structure of Acoustic Wave Filter)
The acoustic wave filter 5 (resonator 11) filters electrical signals using acoustic waves. Various types of acoustic waves may be used. For example, the acoustic waves used may be surface acoustic waves (SAWs), bulk acoustic waves (BAWs), boundary acoustic waves, or plate waves. Note that these acoustic waves are not necessarily clearly distinguishable. BAWs may propagate in the direction in which the piezoelectric layer (see the description of the chip substrate 41 described later) expands, or may propagate in the thickness direction of the piezoelectric layer.

The elastic wave filter 5 may have various configurations as long as it utilizes elastic waves. Typical examples of elastic wave filter configurations include a ladder filter in which multiple resonators 11 are connected in a ladder configuration, and a multimode filter (including a dual mode filter) in which multiple resonators 11 are arranged in the propagation direction of the elastic waves. These filters are bandpass filters. The elastic wave filter 5 may also be the same as such typical examples.

In the example of Figures 1 and 2, the elastic wave filter 5 has a configuration in which multiple arms 21 (series arms 21S and parallel arms 21P) are connected in a ladder shape (however, this differs from the configuration generally referred to as a ladder-type filter). More specifically, the elastic wave filter 5 has multiple (or one) series arms 21S. Each series arm 21S includes at least one resonator 11. The elastic wave filter 5 also has multiple (or one) parallel arms 21P. Each parallel arm 21P includes an inductor L rather than a resonator 11, which differs from the configuration generally referred to as a ladder-type filter.

The elastic wave filter 5 in the illustrated example functions, for example, as a band elimination filter. Although not specifically illustrated, the absolute value of the impedance of the resonator 11 becomes a minimum value at the resonant frequency and a maximum value at the anti-resonant frequency. The resonator 11 in the series arm 21S forms an attenuation pole at the anti-resonant frequency of the resonator 11, and thus attenuates signals having frequencies within a predetermined stopband. The anti-resonant frequencies (and/or resonant frequencies) of the multiple resonators 11 may be the same as each other or may be different from each other.

The parallel arm 21P, for example, reduces the likelihood that the entire group of resonators 11 (series arms 21S) will function as a capacitor with a large capacitance, and thus contributes to reducing the likelihood that a signal having a frequency within the stopband will pass through the series arms 21S. The inductor L of the parallel arm 21P may cooperate with the resonator 11 (series arm 21S) to form a high-pass filter. Unlike the example shown in the figure, the parallel arm 21P may include a capacitor C, or may include an inductor L and a capacitor C. Coupling of the electric fields and/or magnetic fields of the inductors L included in two or more parallel arms 21P may be used for filtering.

Unlike the illustrated example, the elastic wave filter 5 may not have a resonator 11 in the series arm 17S (e.g., may have an inductor L or a capacitor C) and may have a resonator 11 in the parallel arm 17P. In the elastic wave filter 5 of the illustrated example or an elastic wave filter 5 configured with a normal ladder-type filter, the resonators 11 in the multiple series arms 17S may have the same resonance frequency (and/or anti-resonance frequency) as each other or may be different from each other. Similarly, in an elastic wave filter 5 in which only the parallel arm 17P has a resonator 11 or an elastic wave filter 5 configured with a normal ladder-type filter, the resonators 11 in the multiple parallel arms 17P may have the same resonance frequency (and/or anti-resonance frequency) as each other or may be different from each other.

(4. Configuration of LC Filter)
As already mentioned, the LC filter 7 may have various configurations, for example, a known configuration, as long as it has L and C and performs a filter function. Also, as already mentioned, the LC filter 7 may be defined as the entire circuit between the first terminal 3A and the acoustic wave filter 5, and may include a matching circuit. For the same reason, the LC filter 7 may include two or more filters that can be recognized as different filters from the viewpoint of structure and/or characteristics. In relation to the above, the LC filter 7 may include a piezoelectric filter including a piezoelectric body, and/or a dielectric filter that utilizes electromagnetic waves in a dielectric. Coupling of electric fields and/or magnetic fields of two or more inductors L may be used for filtering.

The LC filter 7 may or may not be configured as a ladder type. In other words, the LC filter 7 may be configured with only one series arm 17S or only one parallel arm 17P. Typical examples of LC filters include, for example, an LC series resonant circuit or an LC parallel resonant circuit that connects the first terminal 3A and the second terminal 3B, an LC series resonant circuit or an LC parallel resonant circuit that connects the signal path between the first terminal 3A and the second terminal 3B and the reference potential unit 19, or a combination of two or more of these. The LC filter 7 may have, for example, an appropriate number of such typical examples of LC filters.

1 and 2, the LC filter 7 has one or more (multiple (two) in the illustrated example) series arms 17S including a capacitor C, and one or more (one in the illustrated example) parallel arms 17P including an inductor L. Such an LC filter 7 functions, for example, as a high-pass filter. As will be understood from the above explanation, the LC filter 7 in the illustrated example is merely one example, and for convenience of explanation, it has a relatively simple configuration. Another example close to the illustrated example, although not specifically shown, is one that has one or more series arms 17S including an inductor L and one or more parallel arms 17P including a capacitor C and functions as a low-pass filter.

As can be understood from the above explanation, the LC filter 7 may have at least one series arm 17S connecting the first terminal 3A and the acoustic wave filter 5. Alternatively, the LC filter 7 may not have a series arm 17S, but may have only one parallel arm 17P, and may simply be connected between the first terminal 3A and the acoustic wave filter 5. In this disclosure, when the term "electrically intervening" or simply "intervening" is used to refer to the LC filter 7 being electrically intervened between the first terminal 3A and the acoustic wave filter 5, the LC filter 7 may include either of the above two aspects. Similarly, the term "electrically intervening" or simply "intervening" is used for the additional circuit 9, etc.

(5. Configuration of Additional Circuit)
As already mentioned, the additional circuit 9 may have various configurations as long as it has L and C and is electrically interposed between the acoustic wave filter 5 and the second terminal 3B. For example, the additional circuit 9 may function only as a matching circuit, may function as a filter, or may function as both. The matching circuit may have a known configuration. The LC filter may also have a known configuration, and the above description of the LC filter 7 may be applied to the LC filter included in the additional circuit 9.

The additional circuit 9A in the example of FIG. 1 has only an inductor L (or from another point of view, only one series arm 17S). Such an inductor L functions, for example, as a matching circuit and/or a low-pass filter. An example of a configuration similar to this example is, for example, an additional circuit 9 consisting of only a capacitor C as the series arm 17S, or only a capacitor C or an inductor L as the parallel arm 17P, although not shown in the figure. The additional circuit 9B in the example of FIG. 2 has a similar configuration to the LC filter 7 (although the specific characteristics may be different).

As can be understood from the above explanation, the

additional circuits

9A and 9B in the illustrated example are merely examples, and for convenience of explanation, they have a relatively simple configuration. The additional circuit 9 may have a more complex configuration, for example, a more complex configuration than the LC filter 7, or may have more stages than the LC filter 7.

(6. Examples of attenuation characteristics)
(6.1. Passband and Stopband)
As described in Section 2, each of the composite filter 1, the acoustic wave filter 5, the LC filter 7, and the additional circuit 9 (if a filter) may be regarded as a band-pass filter, a high-pass filter, a low-pass filter, or a band elimination filter. Examples are shown below.

FIG. 5 shows an example of the attenuation characteristics of the composite filter 1. In this figure, the vertical and horizontal axes are the same as in FIG. 3.

In this figure, line LNB shows the characteristics of composite filter 1, and lines LNH, LNL, and LNE show the characteristics of the filters that make up composite filter 1. The characteristics of line LNH are those of a high-pass filter, with small loss in the pass band higher than a specified frequency. The characteristics of line LNL are those of a low-pass filter, with small loss in the pass band lower than a specified frequency. The characteristics of line LNE are those of a band elimination filter, with large loss in a specified stop band.

The lower limit (low-frequency end) of the passband of the high-pass filter (line LNH) is lower than the upper limit (high-frequency end) of the passband of the low-pass filter (line LNL). Therefore, a band-pass filter (line LNB) is formed in which the overlapping band of both passbands is the passband PB1. In this band-pass filter, the attenuation slope on the low-frequency side is formed by the attenuation slope of the high-pass filter. The attenuation slope on the high-frequency side is formed by the attenuation slope of the low-pass filter.

The attenuation slope on the high frequency side of the band elimination filter (line LNE) is steeper than the attenuation slope of the high pass filter. The former attenuation slope overlaps at least part of the latter attenuation slope, forming at least part of the attenuation slope on the low frequency side of the band pass filter (line LNB). This results in a band pass filter (composite filter 1) with a steep attenuation slope and a wide bandwidth of the pass band PB1.

In the illustrated example, by making the attenuation slope on the low frequency side steeper as described above, the attenuation slope on the low frequency side is steeper than the attenuation slope on the high frequency side (the attenuation slope of the low pass filter). From another perspective, in the composite filter 1, the transition band (symbol omitted) between the stop band EB1L on the low frequency side and the pass band PB1 is narrower than the transition band (symbol omitted) between the stop band EB1H on the high frequency side and the pass band PB1.

The band elimination filter (line LNE) is, for example, composed of an elastic wave filter 5 (part or all of it). The high-pass filter (line LNH) is, for example, composed of one of an LC filter 7 and an additional circuit 9. The low-pass filter (line LNL) is, for example, composed of the other of an LC filter 7 and an additional circuit 9. However, the LC filter 7 may include both a high-pass filter and a low-pass filter.

Here are some examples of filter combinations other than those shown.

In the illustrated example, instead of or in addition to the band elimination filter (line LNE) having a stop band on the low frequency side of the pass band PB1, a band elimination filter (from another perspective, elastic wave filter 5) having a stop band on the high frequency side of the pass band PB1 may be provided. Then, the attenuation slope on the low frequency side of the band elimination may be made steeper on the high frequency side of the band pass filter (composite filter 1).

In the illustrated example, a bandpass filter (LC filter 7 or additional circuit 9) may be provided instead of the lowpass filter (line LNL). The passband of this bandpass filter includes the passband PB1, and the attenuation slope on the high frequency side constitutes an attenuation slope on the high frequency side adjacent to the passband PB1, instead of the lowpass filter in the illustrated example. And, the attenuation slope on the low frequency side and/or high frequency side of the composite filter 1 (bandpass filter) may be made steeper by the attenuation slope of the band elimination filter (elastic wave filter 5) as before.

Only two types of filters may be combined: a bandpass filter (LC filter 7 or additional circuit 9) and a band elimination filter (elastic wave filter 5). The attenuation slope on the low frequency side and/or high frequency side of the composite filter 1 (bandpass filter) may be made steeper by the attenuation slope of the band elimination filter (elastic wave filter 5), as in the past.

A band elimination filter may be constructed by making the pass band of the high pass filter (LC filter 7 or additional circuit 9) higher than the pass band of the low pass filter (LC filter 7 or additional circuit 9). The attenuation slope of this band elimination filter may be made steeper by the attenuation slope of the acoustic wave filter 5 (band elimination filter).

Note that FIG. 5 is merely a schematic diagram. Actual characteristics are usually represented by curves and/or complex lines. Also, unlike the schematic diagram, the characteristics may vary in the passband and stopband of each filter. An attenuation pole (minimum value) may appear in the stopband. The line LNE showing the characteristics of the elastic wave filter 5 (band elimination filter) may be an inverted triangle with one attenuation pole as its apex, rather than an inverted trapezoid as in the illustrated example, or may be a wave shape with multiple attenuation poles. The same applies to other diagrams showing characteristics.

The specific values of the bandwidth and center frequency of the passband PB1 are arbitrary. For example, the passband PB1 may be partially or entirely within the range of 3 GHz to 10 GHz. The passband PB1 may be set in accordance with an appropriate communication standard. In this case, the passband PB1 may correspond to only one band defined by the standard, or may include two or more bands defined by the standard. For example, the fractional bandwidth of the acoustic wave filter 5 may be smaller than the fractional bandwidth of the composite filter 1.

(6.2. Examples of attenuation poles)
The LC filter 7 and/or the additional circuit 9 may have an attenuation pole in the second and/or third harmonic band of the passband PB1.

FIG. 6A is a diagram showing the characteristics of such an embodiment. In this diagram, the horizontal axis and the vertical axis on the left side are the same as those in FIG. 5. The vertical axis on the right side shows the absolute value |Z| (Ω) of the impedance of the LC filter 7 and/or the additional circuit 9, with the value increasing toward the top of the diagram.

In this figure, an attenuation pole appears at frequency fa where |Z| is a maximum value. Frequency fa is located in the double harmonic band of passband PB1. The double harmonic band may be a band ranging from twice the frequency of the low-frequency end of passband PB1 to twice the frequency of the high-frequency end of passband PB1. Instead of or in addition to the attenuation pole located in the double harmonic band, an attenuation pole may be formed in the triple harmonic band. The triple harmonic band may be defined as the above double harmonic band, with "double" replaced by "triple".

The configuration for forming the attenuation pole as described above is arbitrary. Figures 6B and 6C show typical examples. Figure 6B illustrates a parallel resonant circuit 23P that constitutes one series arm 17S (all or part of it). The resonant frequency of the parallel resonant circuit 23P is frequency fa. Figure 6C illustrates a series resonant circuit 23S that constitutes one parallel arm 17P (all or part of it). The resonant frequency of the series resonant circuit 23S is frequency fa.

(7. Example of Composite Filter Structure)
As described above, the configuration of the composite filter 1 from a structural standpoint may take various forms. Examples are shown below. In the following description, first, an example of the structure of the composite filter 1 will be described (Section 7.1). In this description, the structures of the LC filter 7 and the additional circuit 9 will be omitted, and the structural components of the composite filter 1 will be described. Next, variations in the structure of the composite filter 1 will be described, including the structures of the LC filter 7 and the additional circuit 9 (Section 7.2).

(7.1. Structural Components)
Fig. 7 is a schematic cross-sectional view showing an example of the structure of the composite filter 1. Any direction of the composite filter 1 may be regarded as the upper side, but for convenience, in the description of Fig. 7, the upper side of the figure (the upper side along the paper surface) is regarded as the upper side, and terms such as the upper surface and the lower surface may be used.

The composite filter 1 is configured, for example, as a surface-mounted chip component. Its overall shape is, for example, roughly a thin rectangular parallelepiped (with the thickness being shorter than the length of the short side in a plan view) with the thickness direction being in the vertical direction. A plurality of terminals 3 (external terminals) are provided on the underside of the composite filter 1 for mounting the composite filter 1. The plurality of terminals 3 include, for example, the first terminal 3A, the second terminal 3B, and the reference potential portion 19 (consisting of terminals) already described. The composite filter 1 is mounted on the circuit board by joining the plurality of terminals 3 to a plurality of pads on the circuit board with a plurality of conductive bumps (for example, solder).

The composite filter 1 has, for example, a circuit board 31, a chip 33 mounted on the circuit board 31, and a sealing portion 35 that seals the chip 33. The multiple resonators 11 of the acoustic wave filter 5 may be provided on the chip 33. Some or all of the other components of the acoustic wave filter 5 (inductor L constituting the parallel arm 21P in the example of FIG. 1) may be provided on the chip 33 or on the circuit board 31.

The circuit board 31 is formed, for example, in a generally thin rectangular parallelepiped shape with its thickness direction extending in the vertical direction. The basic structure and materials of the circuit board 31 (excluding the specific conductor patterns and dimensions, etc., for forming the composite filter 1) may be similar to the structures and materials of various known printed circuit boards. For example, the circuit board 31 may be a Low Temperature Co-fired Ceramics (LTCC) board, a High Temperature Co-fired Ceramic (HTCC) board, an Integrated Passive Device (IPD) board, or an organic multilayer board.

An example of an LTCC substrate is one in which a glass-based material is added to alumina, allowing firing at low temperatures (e.g., around 900°C). In an LTCC substrate, for example, Cu or Ag may be used as the conductive material. An example of an HTCC substrate is one that uses ceramics whose main component is alumina or aluminum nitride. In an HTCC substrate, for example, tungsten or molybdenum may be used as the conductive material. An example of an IPD substrate is one in which passive elements are formed on a Si substrate. An example of an organic multilayer substrate is one in which a prepreg impregnated with resin is laminated on a base material made of glass or the like.

The circuit board 31 has, for example, a substantially insulating plate-like base 37 and a conductor 39 located inside and/or on the surface of the base 37. The base 37 may have, for example, a plurality of insulating layers 37a stacked on top of each other. The conductor 39 may have, for example, a conductor layer 39a located on the main surface of the insulating layer 37a and a via conductor 39b penetrating the insulating layer 37a.

The chip 33 is configured as, for example, a surface-mounted chip component. Its overall shape is, for example, roughly a thin rectangular parallelepiped with the thickness direction being in the vertical direction. The basic structure and material of the chip 33 (excluding the specific conductor pattern and dimensions for configuring the composite filter 1) may be similar to the structure and material of chips that configure various known acoustic wave devices. For example, the chip 33 may be a bare chip, a WLP (Wafer level Package) type having a cover that covers the surface of the bare chip facing the circuit board 31, or a FO (Fan Out)-WLP type having a molded part that covers the side of the bare chip. Here, an example is taken in which the chip 33 is a bare chip. The chip 33 has, for example, a chip substrate 41 and a conductor layer 43 located on the surface (one of the main surfaces) of the chip substrate 41 facing the circuit board 31.

For example, at least a predetermined region of the surface of the chip substrate 41 on the circuit substrate 31 side is made of a piezoelectric material. The piezoelectric material is made of a single crystal having piezoelectricity. The single crystal is, for example, quartz (SiO ₂ ), lithium niobate (LiNbO ₃ ) single crystal, or lithium tantalate (LiTaO ₃ ) single crystal. The cut angle may be set appropriately according to the type of elastic wave to be used. For example, the chip substrate 41 may be entirely made of a piezoelectric material (may be a piezoelectric substrate), may be a piezoelectric substrate and a support substrate bonded together, may be a substrate in which a plurality of films are laminated on a support substrate and a piezoelectric layer is laminated thereon, or may have a cavity between the piezoelectric layer and the support substrate. The material of the conductor layer 43 may be an appropriate metal such as Al.

Although not shown in particular, the chip 33 may have an insulating layer that covers the conductor layer 43 and the surface of the chip substrate 41 facing the circuit substrate 31 while exposing the terminals of the chip 33. Such an insulating layer may simply serve to reduce corrosion of the conductor layer 43, or may have an acoustically advantageous effect. The material of such an insulating layer may be any appropriate material, such as _SiO2 . The side and bottom surfaces of the chip substrate 41 may be covered with an insulating layer or the like that is thinner than the thickness of the chip substrate 41.

The conductor layer 43 of the chip 33 has, for example, a terminal 43a of the chip 33. Furthermore, the conductor layer 39a located on the upper surface of the circuit board 31 has a pad 39c facing the terminal 43a. The terminal 43a and the pad 39c are joined by conductive bumps 45, and the chip 33 is mounted on the circuit board 31. That is, the chip 33 is fixed to and electrically connected to the circuit board 31 by the bumps 45. The material of the bumps 45 is, for example, solder. The solder includes lead-free solder.

The sealing portion 35, for example, covers the upper surface of the circuit board 31 from above the chip 33. A gap is formed between the chip 33 and the circuit board 31 by the thickness of the terminals 43a, the bumps 45, and the pads 39c. The sealing portion 35 is not filled in this gap, and the gap is made into an airtight space sealed by the sealing portion 35. The airtight space may be in a vacuum state or may be filled with an appropriate inert gas (e.g., nitrogen). The material of the sealing portion 35 may be an organic material, an inorganic material, or a combination of both. More specifically, for example, the sealing portion 35 may be made of a resin, or a resin containing particles (filler) made of an inorganic material.

The chip 33 may constitute another filter in addition to the composite filter 1 (elastic wave filter 5). For example, a resonator 11 for an elastic wave filter other than the composite filter 1 may be provided on the chip 33. More specifically, for example, the illustrated chip components may constitute a splitter (e.g., a duplexer) having a transmit filter and a receive filter. In this case, the composite filter 1 may constitute one of the transmit filter and the receive filter, and the other filter may constitute the other of the transmit filter and the receive filter.

An acoustic wave chip other than chip 33 may be mounted on circuit board 31. More specifically, for example, chip components including chip 33 and another acoustic wave chip may form a splitter (e.g., a duplexer). Then, composite filter 1 may form one of the transmit filter and the receive filter, and a filter formed by another acoustic wave chip may form the other of the transmit filter and the receive filter.

The mounting of electronic components such as chips 33 on circuit board 31 is not limited to using bumps 45. For example, electronic components may be fixed to circuit board 31 with an insulating adhesive and electrically connected to circuit board 31 with bonding wires.

(7.2. Structural Variations)
8A to 8D are schematic diagrams showing variations of the structure. These diagrams show the circuit board 31 and the chip 33 more typically than FIG. 7. Note that for the structural examples described later, only the differences from the structural examples described earlier will basically be described. Items that are not specifically mentioned may be considered to be the same as the structural examples described earlier, or may be inferred from the structural examples described earlier.

In the composite filter 1 (1E) in the example of FIG. 8A, the LC filter 7 and the additional circuit 9 are built into the circuit board 31. The incorporation may be achieved by building the LC filter 7 and the additional circuit 9 into the circuit board 31, or by embedding chips that constitute the LC filter 7 and the additional circuit 9 into the circuit board 31. When the LC filter 7 and the additional circuit 9 are built into the circuit board 31, for example, the inductor L and the capacitor C are formed by the conductor 39 of the circuit board 31. The base 37 may function as a dielectric between the electrodes of the capacitor C.

The specific configuration of the inductor L and capacitor C built into the circuit board 31 (multilayer board) is arbitrary. For example, the inductor L may be configured with a meandering or spiral conductor pattern included in the conductor layer 39a, or may be configured with a spiral conductor formed by appropriately combining the conductor layer 39a and the via conductor 39b. Also, for example, a pair of electrodes of the capacitor C may be configured with the same conductor layer 39a, or may be configured with different conductor layers 39a. Examples of the former include a pair of strip-shaped electrodes facing each other in a planar view, and a pair of comb-tooth electrodes that mesh with each other in a planar view (see the comb-tooth electrodes of the resonator 11 described later). Examples of the latter include flat plate electrodes facing each other across the insulating layer 37a in the thickness direction of the insulating layer 37a.

In the composite filter 1 (1F) in the example of FIG. 8B, the additional circuit 9 is composed of the specific wiring 15 (a wiring having an inductance of 0.3 nH or more) already described. The specific wiring 15 is not composed of only via conductors 39b, but includes a conductor layer 39a, for example, to ensure its length and increase its inductance. Of course, the specific wiring 15 may be composed of only via conductors 39b. In a relatively small device, the inductance of a via conductor that penetrates a 50 μm to 100 μm thick portion of a multilayer substrate is about 0.1 nH. Therefore, for example, the length of the specific wiring 15 may be three times or more the above length. Also, the specific wiring 15 may be a wiring having an inductance of 0.5 nH or more, unlike the description here.

In the composite filter 1 (1G) in the example of FIG. 8C, the additional circuit 9 is configured by electronic components mounted on the upper surface of the circuit board 31. The specific configuration of the electronic components may be various, for example, they may be publicly known. The electronic components may be, for example, chip inductors, chip capacitors, or chip-type filters. The mounting method of the electronic components is also arbitrary. For example, the electronic components may be surface-mounted with pads like the chip 33, may be through-hole mounted, or may be surface-mounted with leads instead of pads.

The composite filter 1 (1H) in the example of FIG. 8D is not a chip component, but is part of a module 51. More specifically, in the illustrated example, two circuit boards 31 are mounted on a module board 47. One circuit board 31 has an LC filter 7 built in and a chip 33 mounted thereon. The other circuit board 31 has an additional circuit 9 built in. The module 51 is, for example, configured as a chip-type component, and is mounted by joining the terminals 49 to a circuit board (not shown). Alternatively, the module 51 may function like a motherboard. As can be understood from the example of this figure, the first terminal 3A and the second terminal 3B may be located on different circuit boards 31.

In the illustrated example, the first terminal 3A and the second terminal 3B are simply connected to the terminal 49 by wiring, so the terminal 49 may be regarded as the first terminal 3A and the second terminal 3B shown in FIG. 1, and the module 51 may be regarded as the composite filter 1. Also, unlike the illustrated example, the first terminal 3A and the second terminal 3B may be connected to another circuit (e.g., an IC (Integrated Circuit)) included in the module 51. The other circuit may be mounted on the surface of the module substrate 47, or may be built into the module substrate 47.

The above-mentioned variations may be combined or modified as appropriate. For example, in addition to or instead of the additional circuit 9 in FIG. 8C, the LC filter 7 (part or all) may be configured with an electronic component (chip) mounted on the circuit board 31. Also, for example, instead of the additional circuit 9 in FIG. 8D, the LC filter 7 (part or all) may be built into a circuit board 31 other than the circuit board 31 on which the chip 33 is mounted. The LC filter 7 and part or all of the additional circuit 9 may be provided on the chip 33.

(7.3. Supplementary information on structure)
As illustrated in FIGS. 8A to 8C, the chip 33 having the resonator 11 may be mounted on the circuit board 31 having the additional circuit 9 (part or all of it) by the bump 45. In this case, in a plan view, the center of the bump 45 and the center of the second terminal 3B may not overlap (may be shifted). Furthermore, at least a part of the second terminal 3B may not overlap the bump 45. And/or at least a part of the bump 45 may not overlap the second terminal 3B. Furthermore, the entire bump 45 and the entire second terminal 3B may not overlap each other. Of course, unlike the above, the center of the bump 45 and the center of the second terminal 3B may overlap. The description of the bump 45 in this paragraph may be applied to the terminal 43a and the pad 39c.

(8. Specific Examples of Elastic Wave Resonator Configurations)
The resonator 11 of the acoustic wave filter 5 may have various configurations. For example, the resonator 11 may be a SAW resonator, a BAW resonator that has electrodes similar to those of a SAW resonator and uses a BAW, or a film bulk acoustic resonator (also called an FBAR (Film Bulk Acoustic Resonator)) that vibrates a piezoelectric thin film on a cavity. A SAW resonator will be described below as an example of the resonator 11.

FIG. 9 is a plan view showing a schematic configuration of a SAW resonator as the resonator 11. This figure shows a partial area of the surface of the chip 33 that faces the circuit board 31.

For convenience, FIG. 9 shows an orthogonal coordinate system consisting of the D1 axis, the D2 axis, and the D3 axis. Either direction of the resonator 11 may be considered to be upward or downward. However, in the following description, for convenience, the positive side of the D3 axis may be considered to be upward, and terms such as upper surface and lower surface may be used. Note that the D1 axis is defined to be parallel to the propagation direction of the elastic wave propagating along the surface (upper surface 41a) of the chip substrate 41 facing the circuit substrate 31. The D2 axis is defined to be parallel to the upper surface 41a and perpendicular to the D1 axis. The D3 axis is defined to be perpendicular to the upper surface 41a.

The resonator 11 is configured as a so-called one-port elastic wave resonator. For example, the resonator 11 outputs a signal input from one of the two wirings 55 shown on both sides of the figure from the other of the two wirings 55. At this time, the resonator 11 converts the electrical signal to an elastic wave and converts the elastic wave back to an electrical signal.

The resonator 11 includes, for example, a chip substrate 41 (at least a part of its upper surface 41a), an excitation electrode 57 located on the upper surface 41a, and a pair of reflectors 59 located on either side of the excitation electrode 57. The excitation electrode 57 and the reflectors 59 are formed of layered conductors provided in the region. A plurality of resonators 11 may be formed on one chip substrate 41. In other words, the chip substrate 41 may be shared by a plurality of resonators 11.

The excitation electrode 57 is composed of a so-called IDT (Interdigital Transducer) electrode, and has a pair of comb-tooth electrodes 61 (one of which is hatched for ease of visibility). Each comb-tooth electrode 61 has, for example, a bus bar 63, a number of electrode fingers 65 extending in parallel from the bus bar 63, and a number of dummy electrodes 67 protruding from the bus bar 63 between the electrode fingers 65. The pair of comb-tooth electrodes 61 are arranged so that the electrode fingers 65 interdigitate with (intersect with) each other.

The pair of reflectors 59 are located on both sides of the multiple excitation electrodes 57 in the propagation direction of the elastic wave. Each reflector 59 may be, for example, electrically floating or may be applied with a reference potential. Each reflector 59 is formed, for example, in a lattice shape. That is, the reflector 59 includes a pair of bus bars 69 facing each other and multiple strip electrodes 71 extending between the pair of bus bars 69.

When a voltage is applied to a pair of comb-tooth electrodes 61, the voltage is applied to the upper surface 41a (piezoelectric body) by the multiple electrode fingers 65, causing the piezoelectric body to vibrate. In other words, elastic waves are excited. Of the elastic waves of various wavelengths that propagate in various directions, the elastic waves that propagate in the arrangement direction of the multiple electrode fingers 65 with the pitch p of the multiple electrode fingers 65 being approximately half the wavelength (λ/2) tend to have large amplitudes because the multiple waves excited by the multiple electrode fingers 65 overlap in phase.

In addition, the elastic waves propagating through the piezoelectric body are converted into an electrical signal by the multiple electrode fingers 65. At this time, similar to when an elastic wave is excited, the strength of the electrical signal converted from the elastic wave propagating in the arrangement direction of the multiple electrode fingers 65, with the pitch p of the multiple electrode fingers 65 being approximately half the wavelength (λ/2), tends to be strong.

Due to the above-mentioned action (and other actions not described here), the resonator 11 functions as a resonator whose resonant frequency is the frequency of elastic waves whose pitch p is approximately half the wavelength (λ/2). The anti-resonant frequency is determined by the resonant frequency and the capacitance of the excitation electrode 57, etc. The pair of reflectors 59 contribute to confining the elastic waves.

Note that a BAW resonator using an electrode similar to excitation electrode 57 may, for example, generate a BAW that propagates in the D1 direction by a similar action as described above, or may generate thickness-shear vibration by a different action than described above. In the latter case, the resonant frequency is relatively highly dependent on the thickness of the piezoelectric layer and relatively less dependent on the pitch p. Also, reflector 59 is not required.

(9. Example of using composite filters)
10 is a block diagram showing a main part of a communication device 151 as an example of the use of the composite filter 1. The communication device 151 has a module 171 and a housing 173 that houses the module 171. The module 171 performs wireless communication using radio waves and includes the composite filters 1 (1C and 1D). More specifically, in the illustrated example, the

composite filters

1C and 1D are used as the two filters that make up the diplexer 154.

In the diplexer 154, the two composite filters 1, for example, share the first terminal 3A and have separate second terminals 3B. However, contrary to the description here, the shared terminal may be the second terminal 3B. Or, the first terminal 3A of one composite filter 1 and the second terminal 3B of the other composite filter 1 may be shared. Also, contrary to the description here, one of the two filters of the diplexer 154 does not have to be a composite filter 1. The composite filter 1 may be part of the filter that constitutes the diplexer 154.

In module 171, the radio signal (radio wave) received by antenna 159 is converted to an electrical signal by antenna 159 and input to diplexer 154 (more specifically, first terminal 3A shared by two composite filters 1). Of the input received signals, received signal RS1 having a frequency in the pass band of composite filter 1C is output from composite filter 1C (more specifically, second terminal 3B of composite filter 1C). Also, of the input received signals, received signal RS2 having a frequency in the pass band of composite filter 1D is output from composite filter 1D (second terminal 3B of composite filter 1D).

The received signal RS1 output from the composite filter 1C is amplified by the amplifier 155A, and unnecessary components outside a predetermined passband are removed by the bandpass filter 157A. The received signal RS1 is then frequency-downshifted and demodulated by the RF (Radio Frequency)-IC 153 to become the received information signal RIS1.

Similarly, the received signal RS2 output from the composite filter 1D is amplified by the amplifier 155B, and unnecessary components outside the specified passband are removed by the bandpass filter 157B. The received signal RS2 is then frequency-downshifted and demodulated by the RF-IC 153 to become the received information signal RIS2.

The received information signals RIS1 and RIS2 may be low-frequency signals (baseband signals) containing appropriate information. For example, these signals may be analog audio signals, digitized audio signals, or signals using a satellite positioning system. The modulation method may be, for example, phase modulation, amplitude modulation, or frequency modulation, or a combination of two or more of these. Although a direct conversion method is illustrated as the circuit method, other appropriate methods may be used, for example, a double superheterodyne method. Also, FIG. 10 shows only the essential parts in a schematic manner, and filters, isolators, etc. may be added in appropriate positions, and the positions of amplifiers, etc. may be changed.

The module 171 has, for example, components from the RF-IC 153 to the antenna 159 on the same circuit board (they may be either built-in or mounted). That is, the composite filter 1 is combined with other components to be modularized. This circuit board may be the circuit board 31, a board on which the circuit board 31 is mounted, or a module board 47. The composite filter 1 may not be modularized and may be included in the communication device 151. The components exemplified as components of the module 171 may be located outside the module or may not be housed in the housing 173. For example, the antenna 159 may be exposed to the outside of the housing 173.

(10. Summary of the embodiment)
As described above, the composite filter 1 according to the embodiment includes the acoustic wave filter 5, the LC filter 7, and the electric element 13 (included in the additional circuit 9). The acoustic wave filter 5 includes at least one acoustic wave resonator 11. The LC filter 7 is electrically interposed between the acoustic wave filter 5 and the first terminal 3A. The electric element 13 is electrically interposed between the acoustic wave filter 5 and the second terminal 3B. The electric element 13 is an inductor L, a wiring (specific wiring 15) having an inductance of 0.3 nH or more, or a capacitor C. At least one of the attenuation slopes SP on the high frequency side and the low frequency side of the pass band PB1 of the composite filter 1 satisfies the above-described formula 1.

Therefore, for example, as described in the description of the outline of the embodiment, it is possible to achieve both a steeper attenuation slope and a reduced insertion loss, and the LC filter 7 and the electrical element 13 can be used in the matching circuit, which allows the composite filter 1 to be made smaller. Since the impedance of the composite filter 1 can be adjusted by the LC filter 7 and the electrical element 13, the design freedom of the elastic wave filter 5 is improved, and it is easier to steepen the attenuation slope of the elastic wave filter 5.

The electrical element 13 may be part of a second LC filter (additional circuit 9 constituting an LC filter) electrically interposed between the acoustic wave filter 5 and the second terminal 3B.

In this case, for example, not only the LC filter 7 but also the additional circuit 9 can be used as both a filter and a matching circuit, which allows for miniaturization.

The composite filter 1 may have a chip 33 having an elastic wave resonator 11, a multilayer substrate (circuit board 31) on which the chip 33 is mounted, and a conductive joint (bump 45) joining the chip 33 to the circuit board 31. The electrical element 13 may be located in or on the circuit board 31. The bump 45 may electrically connect the resonator 11 to the electrical element 13. When the circuit board 31 is viewed in a plane, the center of the bump 45 and the center of the second terminal 3B do not have to overlap.

In this case, for example, when the second terminal 3B is an output terminal, the likelihood that the frequency components to be attenuated by the additional circuit 9 will be mixed into the second terminal 3B due to radiation from the bump 45 is reduced. Also, for example, when the second terminal 3B is an input terminal, the likelihood that the frequency components to be attenuated by the additional circuit 9 will be mixed into the acoustic wave filter 5 due to radiation from the second terminal 3B to the bump 45 is reduced. From another perspective, the need to provide a shielding layer inside the circuit board 31 in consideration of the above-mentioned radiation is reduced.

At least a portion of the passband PB1 of the composite filter 1 may be above 3 GHz.

In this case, for example, the composite filter 1 can be said to be compatible with relatively high frequencies. In high frequency bands, the passband is widened and the frequency band between the passbands is often narrow. When the passband is widened, it becomes difficult to make the attenuation slope steep. Therefore, the effect of achieving both a steeper attenuation slope and a reduced insertion loss in the embodiment is effective.

The fractional bandwidth of the elastic wave filter 5 may be smaller than the fractional bandwidth of the composite filter 1.

In this case, for example, the narrower the relative bandwidth, the easier it is to make the attenuation slope steeper, and therefore it becomes easier to make the attenuation slope of the elastic wave filter 5 steeper. As a result, it is possible to make the attenuation slope of the composite filter 1 steeper while widening the bandwidth of the composite filter 1.

One of the LC filter 7 and the second LC filter (additional circuit 9) may be a high-pass filter and the other a low-pass filter.

In this case, for example, it is easy to configure a bandpass filter with a wide passband or a band elimination filter with a wide stopband. In addition, the acoustic wave filter 5 located between the two improves isolation between them.

The LC filter 7 and the second LC filter (additional circuit 9) may have an attenuation pole in the second or third harmonic band of the passband PB1 of the composite filter 1.

In the elastic wave filter 5, which is used to make the attenuation slope steeper, it is difficult to form an attenuation pole at a frequency far from the passband PB1. On the other hand, an LC filter can easily form an attenuation pole at any frequency. And by forming an attenuation pole in the harmonic band, it is possible to reduce noise caused by harmonics.

The module 171 according to the embodiment includes a composite filter 1 (e.g., 1C) according to the embodiment, and a second filter (e.g., composite filter 1D) that is connected to at least one of the first terminal 3A and the second terminal 3B and has a passband different from the passband PB1 of the composite filter 1.

In this case, for example, as described above, the composite filter 1 can make the attenuation slope steeper, thereby reducing the likelihood of interference between the composite filter 1 and the second filter.

The communication device 151 according to the embodiment includes the composite filter 1 according to the embodiment, an antenna 153 connected to one of the first terminal 3A and the second terminal 3B, and an integrated circuit element (RF-IC 159) connected to the other of the first terminal 3A and the second terminal 3B.

In this case, for example, the insertion loss of the composite filter 1 is reduced, thereby improving the quality of communication.

In the above embodiment, when the additional circuit 9 forms an LC filter, it is an example of a second LC filter. The bump 45 is an example of a joint. The RF-IC 159 is an example of an integrated circuit element.

The technology disclosed herein is not limited to the above embodiments and may be implemented in various forms.

For example, a splitter including a composite filter is not limited to a duplexer or diplexer. For example, it may be a triplexer or quadplexer. Also, a module including at least one composite filter and having two or more filters with different passbands is not limited to a splitter. For example, both the first terminal and the second terminal may be shared between two filters. And the module may function as a filter that attenuates components outside the passbands of the two filters.

1...composite filter, 3A...first terminal, 3B...second terminal, 5...elastic wave filter, 7...LC filter, 9...additional circuit (second LC filter), 11...elastic wave resonator, 13...electrical element, 15...specific wiring, L...inductor, C...capacitor.

Claims

1. A composite filter comprising:
an acoustic wave filter having at least one acoustic wave resonator;
an LC filter electrically interposed between the acoustic wave filter and a first terminal;
an electrical element electrically interposed between the acoustic wave filter and a second terminal;
the electrical element is an inductor, a wiring having an inductance of 0.3 nH or more, or a capacitor;
At least one of the attenuation slopes on the high-frequency side and the low-frequency side of the passband of the composite filter satisfies the following formula 1:
Compound filters.
Equation 1: Min. Loss (dB) ≦ a × Δf − b
However, the parameters in the above formula 1 are as follows:
Min. Loss (dB): The minimum insertion loss of the composite filter in the pass band Δf=|f1.5−f30|/f1.5
f1.5: The frequency at which the insertion loss of the composite filter is 1.5 dB larger than the Min. Loss (dB). f30: The frequency at which the insertion loss of the composite filter is 30 dB larger than the Min. Loss (dB). a=aa×(log 10 (order-1)) −ab
b = b a × (log 10 (order-1)) bb
aa = 0.00079217 × exp (0.055664 × (order-1))
ab = 3.9180 x exp (-0.0041245 x (order-1))
ba = 2.8407 × exp (0.0078456 × (order-1))
bb = 0.54831 x exp (0.0032121 x (order-1))
order: the number of series arms and parallel arms that have at least one of an inductor and a capacitor and do not have an acoustic wave resonator, electrically interposed between the first terminal and the acoustic wave filter and between the acoustic wave filter and the second terminal
the electrical element is a part of a second LC filter electrically interposed between the acoustic wave filter and the second terminal;
2. The composite filter of claim 1.
a chip having the acoustic wave resonator;
a multilayer substrate on which the chip is mounted;
a conductive joint that joins the chip and the multilayer substrate;
It has
the electrical components are located within or on the multi-layer substrate;
the joint portion electrically connects the elastic wave resonator and the electrical element,
When the multilayer substrate is viewed in a plan view, a center of the joint portion and a center of the second terminal do not overlap with each other.
A composite filter according to claim 1 or 2.
The composite filter according to any one of claims 1 to 3, wherein at least a portion of the passband is at or above 3 GHz.
The composite filter according to any one of claims 1 to 4, wherein the fractional bandwidth of the acoustic wave filter is smaller than the fractional bandwidth of the composite filter.
The composite filter according to claim 2 or any one of claims 3 to 5 which directly or indirectly cites claim 2, in which one of the LC filter and the second LC filter is a high-pass filter and the other is a low-pass filter.
The composite filter of claim 6, wherein the LC filter and the second LC filter have attenuation poles in the second or third harmonic band of the passband.
A composite filter according to any one of claims 1 to 7;
a second filter connected to at least one of the first terminal and the second terminal and having a pass band different from the pass band of the composite filter;
A module having the following:
A composite filter according to any one of claims 1 to 7;
an antenna connected to one of the first terminal and the second terminal;
an integrated circuit element connected to the other of the first terminal and the second terminal;
A communication device having the above configuration.