JP2018098691A - Multiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiplexer having superior communication quality.SOLUTION: A multiplexer 1 comprises a first filter F1, a second filter F2 and a third filter F3 that have resonators 21 and have different pass bands to each other; a connection point 10 to which first-third filters F1-F3 are commonly connected; and a capacitive element C1 that is serially connected between a connection point 10 and a first filter F1. The capacitive element C1 has a loss being smaller than a first resonator 21A which is connected to the most capacitive element C1 side of a plurality of resonators 21 of the first filter F1 in a frequency band of the pass band of the filter positioning in a connection point 10 side than the capacitive element C1 of the second filter F2 and the third filter F3.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a multiplexer mounted on a communication device and connected to an antenna, and more particularly to a multiplexer provided with a filter having three or more different passbands.

  In recent years, carrier aggregation (Carrier Aggregation; hereinafter referred to as CA) is a technology that has attracted attention in communication standards. CA is a technique that enables broadband transmission using a plurality of carriers simultaneously.

  In communication equipment compatible with CA, a plurality of frequency bands are used simultaneously. Therefore, a communication device compatible with CA requires a duplexer (multiplexer) that can simultaneously separate a plurality of signals in a plurality of frequency bands.

  As such a multiplexer, Patent Document 1 discloses a triplexer that separates signals in three different frequency bands.

JP 2005-57342 A

  In recent years, there has been a demand for further high-speed communication and low power consumption. Along with this, a technique for suppressing insertion loss in each of a plurality of passbands is required for filters. This technique is particularly necessary when the frequency bands used simultaneously in CA are close to each other.

  The present application has been devised under such circumstances, and an object thereof is to provide a multiplexer that can realize high communication quality.

  A multiplexer according to one embodiment of the present invention includes a first filter, a second filter, a third filter, a connection point, and a capacitor. The first filter, the second filter, and the third filter are each configured to include at least one resonator, and have different passbands. At the connection point, the first filter, the second filter, and the third filter are electrically connected in common. The capacitive element is connected in series between the connection point and the first filter. There is no branch path to the reference potential between the connection point and the first filter. The capacitive element includes the at least one of the first filter in a frequency band of a pass band of a filter located on the connection point side of the capacitive element among the second filter and the third filter. Among the resonators, the loss is smaller than that of the first resonator connected to the capacitive element side most.

  According to said structure, the signal of a different frequency band can be isolate | separated suitably and high communication quality can be implement | achieved.

3 is a circuit diagram illustrating a configuration of a multiplex according to the first embodiment of the present disclosure. FIG. (A), (b) is a circuit diagram which respectively shows the structure of the filter of the multiplexer of FIG. It is a circuit diagram which shows the structure of the modification of the multiplex shown in FIG. It is a circuit diagram which shows the structure of the multiplex which concerns on 2nd Embodiment of this indication. It is a top view which shows the structure of the resonator in FIG. It is a schematic circuit diagram of a multiplexer. (A), (b) is a diagram which respectively shows the frequency characteristic of the multiplexer which concerns on an Example. (A)-(d) is the principal part enlarged view of FIG. 7, respectively, and is a diagram which shows the reflection coefficient of the other filter in the pass-band zone | band of each filter.

  Hereinafter, a multiplexer according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

  In the second and subsequent embodiments, for the same or similar configurations as those already described, the same reference numerals as those used for the configurations already described are used, and illustration and description are omitted. There are things to do. Further, in the second and subsequent embodiments, especially for the configurations corresponding to (similar to) the configurations of the already described embodiments, especially when the reference numerals different from the symbols attached to the configurations of the already described embodiments are given. Matters that are not noted are the same as the configurations of the embodiments already described.

<First Embodiment>
(Basic configuration)
FIG. 1 is a circuit diagram showing a configuration of a multiplexer 1 according to the first embodiment of the present invention. The multiplexer 1 includes an antenna terminal ANT, a connection point 10, a first terminal S1, a second terminal S2, and a third terminal S3.

  The antenna terminal ANT is connected to the connection point 10, and the first to third terminals S1 to S3 are connected in parallel from the connection point 10, respectively. A first filter F1, a second filter F2, and a third filter F3 are connected between the connection point 10 and each of the first to third terminals S1 to S3. That is, the first filter F1 to the third filter F3 are connected in parallel to the antenna terminal ANT, and are connected in common at the connection point 10 for the first time. Further, a capacitive element C1 is connected in series between the connection point 10 and the first filter F1.

  As will be described later, according to the multiplexer 1, the capacitance element C1 can increase the reflection coefficient in each pass band of the filters F2 and F3 on the other side of the first filter F1 to which the capacitance element C1 is connected in the previous stage. it can.

  Here, there is no branch path to the reference potential between the connection point 10 and the first filter F1. In this example, there is no branch path to the reference potential in any path between the connection point 10 and the filters F1 to F3. This indicates that there is no matching circuit or other filter between each of the filters F1 to F3 and the connection point 10.

  The first to third filters F <b> 1 to F <b> 3 are filters that function as a transmission filter and a reception filter, and include at least one resonator 21. FIGS. 2A and 2B are schematic circuit diagrams showing connection examples of resonators in each filter.

  The filter that functions as a transmission filter may be configured by a ladder type filter as shown in FIG. That is, the transmission filter includes one or more (3 in the present embodiment) series resonators 13A connected in series between the input side I1 and the output side O1, and between the series line and the reference potential portion. And one or more (2 in this embodiment) parallel resonators 13B. That is, as the resonator 21, a series resonator 13A and a parallel resonator 13B are provided. Note that the individual series resonators 13A and the parallel resonators 13B are not exactly the same, and are individually designed according to their arrangement positions and the required filter characteristics.

  Here, the input side I1 of the transmission filter is connected to the first terminal S1, the second terminal S2, or the third terminal S3, and the output side O1 is connected to the antenna terminal ANT side.

  The filter functioning as a reception filter includes, for example, a multimode filter 15 and an auxiliary connected in series to the input side between the input side I2 and the output side O2 as shown in FIG. And a resonator 13C. That is, in this example, the resonator 21 is the auxiliary resonator 13C. In the present embodiment, the multiplex mode includes a double mode.

  Here, the output side O2 of the reception filter is connected to the first terminal S1, the second terminal S2, or the third terminal S3, and the input side I2 is connected to the antenna terminal ANT side.

(Capacitance element)
The capacitive element C1 includes a port p1 on the side where the capacitive element C1 is connected to the first filter F1, and a port p2 on the connection point 10 side. Here, in terms of a circuit based on the capacitive element C1, a filter located on the port p1 side (first filter F1 in this example) and a filter located on the port p2 side (second filter, third filter in this example) Filter F3). The filter located on the port p2 side can also be referred to as a filter connected in parallel to the filter located on the port p1 side as viewed from the antenna terminal ANT. Hereinafter, the filter located on the port p1 side may be referred to as the filter located in the subsequent stage, and the filter located on the port p2 side may be referred to as the filter located in the preceding stage.

  Capacitance element C1 has a smaller loss in the frequency band of the pass band of the filter located in the previous stage than in resonator 21 located closest to antenna terminal ANT among the filters located in the subsequent stage. Specifically, the capacitor has a high Q value in the frequency band of the pass band of the filter located in the preceding stage.

  In the case of the transmission filter shown in FIG. 2A, the resonator 21 (first resonator 21A) located closest to the antenna terminal ANT among the plurality of resonators 21 is a series resonator located on the output side O1. In the case of the reception filter shown in FIG. 2B, the auxiliary resonator 13C. In the case of a ladder filter as shown in FIG. 2A, when the parallel resonator 13B is located at the most output side O1, the parallel resonator 13B becomes the first resonator 21A.

  The capacitance element C1 is not particularly limited as long as the above-described conditions are satisfied. A chip capacitor may be used, or the capacitance element C1 may be formed by an electrode pattern formed on the piezoelectric substrate 2 or a mounting substrate (not shown). In any case, the capacitance value of the capacitive element C1 is adjusted as appropriate in relation to other components.

  When the capacitive element C1 is a chip capacitor, the Q value can be increased. Further, it can be appropriately replaced or switched according to a desired capacitance value.

  When the capacitor element C1 is formed with an electrode pattern, the size can be reduced. Moreover, the number of parts as the whole multiplexer 1 can be reduced. When the capacitive element C1 is configured by an electrode pattern, it may be a rectangular counter electrode or a shape similar to a comb-like electrode that excites a surface acoustic wave. In that case, a desired capacity can be obtained with a small area. When the piezoelectric substrate 2 is composed of comb-like electrodes, the resonance frequency may be adjusted or may be shifted from the propagation direction of the surface acoustic wave in order to suppress unintended generation of the elastic wave. Good.

  By connecting such a capacitive element C1 in series to the position shown in FIG. 1, the filter located in the subsequent stage can have a high reflection coefficient in the frequency band of the pass band of the filter located in the preceding stage. As a result, the multiplexer 1 having a plurality of filters can realize excellent filter characteristics with little insertion loss even in the passband of the other filter.

  In addition, in a multiplexer in which a plurality of filters are connected in parallel, an example in which an LC filter is provided in front of the filter in order to separate unnecessary signals is known. However, such an LC filter has a large specific bandwidth and is effective for carving a wide signal such as carving between a low band and a high band, but for switching signals between a plurality of filters having close passbands. It cannot be applied. Specifically, it can be said that the passbands are close to each other when the interval between the passbands of the plurality of filters connected in parallel is, for example, five times or less the passband. In the actual multiplexer 1, there are cases where the pass bandwidth is not more than twice or less than one.

  Here, when the resonator 21 of the first filter F1 is a surface acoustic wave resonator (hereinafter referred to as a SAW resonator), a filter (first filter F1) located at the subsequent stage of the capacitive element C1. ) May be made lower than the passband of the filter located in front of the capacitive element C1. In other words, when a plurality of filters are connected in parallel, the capacitive element C1 may be connected to a filter other than the filter having the highest passband.

  In a filter using a SAW resonator, loss due to bulk wave radiation occurs remarkably on the high frequency side of the passband. Communication quality deteriorates when the passband of another filter overlaps the frequency band in which the loss due to the bulk wave radiation has increased. Therefore, by disposing the capacitive element C1, it is possible to increase the reflection coefficient in this frequency band, and as a result, it is possible to improve the characteristics of another filter whose pass band overlaps with this frequency band.

  Furthermore, when there is a filter whose pass band is located on the lower frequency side than the pass band of the first filter F1 among the filters positioned in front of the capacitive element C1, the capacitive element C1 is placed on the piezoelectric substrate 2. You may comprise by the comb-tooth electrode formed in this. More specifically, the comb electrode is formed along the SAW propagation direction, and the resonance frequency thereof is formed to be higher than the resonance frequency of the resonator 21 located closest to the antenna terminal ANT. In other words, the electrode finger period (described later) of the comb-shaped electrode of the capacitive element C1 is smaller than the electrode finger period of the comb-shaped electrode constituting the resonator 21 located closest to the antenna terminal ANT.

  With this configuration, the capacitive element C1 functions as a SAW resonator that resonates at a higher frequency that is not related to the passband of the filter (first filter F1) located at the subsequent stage. Since the SAW resonator has a small loss due to bulk wave radiation in a region on the lower frequency side than the resonance frequency, the capacitive element C1 causes the SAW resonator on the lower frequency side than the pass band of the filter (first filter F1) located at the subsequent stage. Loss can be reduced. As a result, the reflection coefficient can be increased with respect to the filter located on the lower frequency side than the pass band of the filter (first filter F1) located in the subsequent stage.

  More preferably, the electrode finger period may be adjusted so that the resonance frequency of the capacitive element C1 is located on the higher frequency side than the pass band of all the filters (F1 to F3).

  In the example shown in FIG. 1, the example of the multiplexer 1 in which three filters are connected in parallel is shown, but four or more may be used. Furthermore, although the case where a capacitive element is provided in only one filter among the three filters has been described, a capacitive element may be provided for each of a plurality of filters (including the case of all filters). FIG. 3 shows an example in which a capacitive element C is provided for each of a plurality of filters (two in this example). In addition to the capacitive element C1 connected between the first filter F1 and the connection point 10, a second capacitive element C2 connected between the second filter F2 and the connection point I0 is provided. The third port p3 of the second capacitive element C2 corresponds to the first port p1 of the capacitive element C1, and the fourth port p4 of the second capacitive element C2 corresponds to the second port p2 of the capacitive element C1. The magnitude of the loss required for the second capacitive element C2 is the same as that of the capacitive element C1. That is, the loss in the frequency region of the pass band of the filter (first filter F1, third filter F3) located in the previous stage of the second capacitive element C2 is the filter (second filter F2) located in the subsequent stage of the second capacitive element C2. ) Is designed to be smaller than the loss of the resonator 21 (referred to as the second resonator 21B) located closest to the antenna terminal ANT. In such a case, the reflection coefficient can be increased for more passbands, and as a result, communication quality can be improved.

<Second Embodiment>
In the above-described example, an example in which one capacitive element C1 is provided in one filter has been described, but one capacitive element may be provided for two or more filters. A circuit diagram of an example of such a multi-filter 1A is shown in FIG.

  In FIG. 4, a multiplexer 1A includes an antenna terminal ANT, a connection point 10, a first connection point 11, a second connection point 12, a first terminal S1, a second terminal S2, a third terminal S3, and a fourth terminal S4. .

  The antenna terminal ANT is connected to the connection point 10, and the first to fourth terminals S1 to S4 are connected in parallel from the connection point 10, respectively. More specifically, the first filter F1 is connected between the first connection point 11 and the first terminal S1. A third filter F3 is connected between the first connection point 11 and the third terminal S3. That is, the first filter F1 and the third filter F3 are connected in parallel to the first connection point 11.

  Similarly, the second filter is connected between the second connection point 12 and the second terminal S2, and the fourth filter F4 is connected between the second connection point 12 and the fourth terminal S4.

  The first connection point 11 and the second connection point 12 are connected in parallel to the connection point 10. That is, the first filter F1 to the fourth filter F4 are connected in parallel to the antenna terminal ANT, and are connected in common at the connection point 10 for the first time. Further, a capacitive element C1 is connected in series between the connection point 10 and the first filter F1. In this example, the capacitive element C <b> 1 is connected between the connection point 10 and the first connection point 11. Similarly, the second capacitive element C2 is connected in series between the connection point and the second filter F2, and between the connection point 10 and the second connection point 12 therein.

  In the case of such a configuration, the second filter F2 and the fourth filter F4 are the filters positioned in the preceding stage with respect to the capacitive element C1, and the first filter F1 and the third filter are the filters positioned in the subsequent stage. F3. Similarly, the first-stage filter F1 and the third filter F3 are the filters positioned in the previous stage with respect to the second capacitor element C2, and the second filter F2 and the fourth filter F4 are the filters positioned in the subsequent stage.

  The characteristics required for the capacitive elements C1 and C2 are as described in the first embodiment. For example, for the capacitive element C1, a capacitor with less loss than the first resonators 21 of both the first filter F1 and the third filter F3 is used in both the pass bands of the second filter F2 and the fourth filter F4. ing.

  In this way, the number of components can be reduced by increasing the reflection coefficient with one capacitive element for the two filters.

  Further, in this example, an inductance L that branches from the wiring between the antenna terminal ANT and the connection point 10 and is connected to the reference potential is located. The capacitive element C1 and the second capacitive element C2 are components inserted to increase the reflection coefficient, but the two capacitive elements C1 and C2 and the inductance L may match the antenna terminal ANT. it can. When one side (first and third filters F1 and F3) is viewed from the other side (second and fourth filters F2), an inductance L branches between the capacitive element C1 and the second capacitive element C2 connected in series. And grounded. Since the two capacitors are connected in series in this way, the phase rotation can be reduced, and matching can be easily achieved.

  Moreover, in the above-mentioned example, although the example which provided the structure which provided one capacitive element with respect to two filters was connected in parallel, one capacitive element may be abbreviate | omitted and two filters may be omitted. A configuration in which one capacitive element is provided and a configuration in which one capacitive element C1 is provided in one filter may be combined.

(Each component)
Hereafter, each component which comprises the above-mentioned multiplexer 1 and 1A is demonstrated using FIG. In FIG. 5, any direction may be set upward or downward, but in the following, for convenience, an orthogonal coordinate system including the D1 axis, the D2 axis, and the D3 axis is defined, and the positive side of the D3 axis Assume that words such as the upper surface are used with the upper side (the front side in FIG. 5) as the upper side.

  The resonator 17 may be a SAW resonator, a piezoelectric thin film resonator, or a quartz crystal resonator. In this example, a case where the resonator 17 is a surface acoustic wave resonator will be described. The SAW resonator is formed by forming a conductor pattern such as an IDT electrode 19 described later on the piezoelectric substrate 2.

  The piezoelectric substrate 2 is a substrate having an upper surface parallel to the D1 axis and the D2 axis (perpendicular to the D3 axis). The planar shape and dimensions may be set as appropriate. The piezoelectric substrate 2 is made of a single crystal having piezoelectricity such as a lithium niobate (LiNbO 3) single crystal or a lithium tantalate (LiTaO 3) single crystal. The cut angle may be appropriately set according to the type of SAW to be used. For example, the piezoelectric substrate 2 has a rotational Y-cut X propagation. That is, the X axis is parallel to the upper surface (D1 axis) of the piezoelectric substrate 2, and the Y axis is inclined at a predetermined angle with respect to the normal line of the upper surface of the piezoelectric substrate 2.

  It is assumed that the relationship between the orthogonal coordinate system composed of the D1 axis, the D2 axis, and the D3 axis and the orthogonal coordinate system composed of the X axis, the Y axis, and the Z axis (that is, the crystal orientation) is constant. Therefore, hereinafter, the orientation of the crystal orientation of the piezoelectric substrate 2 may be indicated by the D1 axis, the D2 axis, and / or the D3 axis.

  Here, a support substrate made of a material having a smaller linear expansion coefficient than the material constituting the piezoelectric substrate may be bonded to the back surface of the piezoelectric substrate 2, and the speed of sound is between the support substrate and the piezoelectric substrate 2. An acoustic reflection structure layer obtained by laminating a fast material and a low material may be interposed.

  FIG. 5 is a plan view showing the structure of a SAW resonator such as a series resonator 13A, a parallel resonator 13B, and an auxiliary resonator 13C (hereinafter, they may be referred to as “resonator 13” without being distinguished from each other). It is.

  The resonator 13 is configured, for example, as a 1-port SAW resonator, and includes the piezoelectric substrate 2, an IDT electrode 19 and a reflector 21 provided on the upper surface of the piezoelectric substrate 2. In addition to the above, the resonator 13 includes an additional film disposed on the upper surfaces of the IDT electrode 19 and the reflector 21, an underlayer interposed between the IDT electrode 19 and the reflector 21 and the piezoelectric substrate 2, and the piezoelectric substrate 2. There may be provided a protective layer or the like that covers the upper surface of the substrate from above the IDT electrode 19 and the reflector 21 (or additional film).

  The IDT electrode 19 is composed of a conductive pattern (conductive layer) formed on the upper surface of the piezoelectric substrate 2, and has a positive comb electrode 23A and a negative comb electrode 23B. In the following, the positive comb electrode 23A and the negative comb electrode 23B are simply referred to as “comb electrode 23”, and they may not be distinguished from each other. The positive comb-tooth electrode 23A refers to the comb-tooth electrode 23 positioned on the positive side of the D2 axis in the pair of comb-tooth electrodes 23, and the negative-side comb-tooth electrode 23B is a pair of comb-tooth electrodes 23. Of these, the comb-tooth electrode 23 positioned on the negative side of the D2 axis is indicated (these names do not indicate the positive side or the negative side of the potential).

  Each comb electrode 23 includes, for example, two bus bars 25 facing each other, a plurality of electrode fingers 27 extending in parallel from each bus bar 25 toward the other bus bar 25, and each bus bar 25 between the plurality of electrode fingers 27. And a plurality of dummy electrodes 29 extending to the other bus bar 25 side. The pair of comb-tooth electrodes 23 are arranged so that the plurality of electrode fingers 27 mesh with each other (intersect).

  Note that the SAW propagation direction is defined by the orientation of the plurality of electrode fingers 27, but in the present embodiment, for convenience, the orientation of the plurality of electrode fingers 27 will be described with reference to the SAW propagation direction. There is.

  For example, the bus bar 25 is formed in a long shape having a substantially constant width and extending linearly in the SAW propagation direction (D1-axis direction, X-axis direction). The pair of bus bars 25 oppose each other in the direction (D2 axis direction) that intersects (is orthogonal to the present embodiment) in the SAW propagation direction. The pair of bus bars 25 are, for example, parallel to each other, and the distance between the pair of bus bars 25 is constant in the SAW propagation direction.

  The plurality of electrode fingers 27 are, for example, formed in an elongated shape having a substantially constant width and extending linearly in a direction orthogonal to the SAW propagation direction (D2-axis direction). The SAW propagation direction (D1-axis direction, (X-axis direction) are arranged at substantially constant intervals. The plurality of electrode fingers 27 of the pair of comb electrodes 23 have a pitch p (for example, a distance between the centers of the electrode fingers 27) equal to, for example, a half wavelength of the wavelength λ of the SAW at a frequency to be resonated. Is provided. The wavelength λ is, for example, 1.5 μm to 6 μm.

  The lengths (D2 axis direction) of the plurality of electrode fingers 27 are, for example, equal to each other. Moreover, the width | variety (D1 axial direction) of the several electrode finger 27 is mutually equivalent, for example. These dimensions may be appropriately set according to the electrical characteristics required for the resonator 13. For example, the width of the electrode finger 27 is 0.4 p to 0.7 p with respect to the pitch p of the plurality of electrode fingers 27.

  The plurality of dummy electrodes 29 are, for example, formed in an elongated shape extending in a straight line in a direction (D2 axis direction) perpendicular to the SAW propagation direction with a substantially constant width, and are formed at the center between the plurality of electrode fingers 27. Are arranged (arranged at the same pitch as the plurality of electrode fingers 27). The tip of the dummy electrode 29 of one comb-tooth electrode 23 is opposed to the tip of the electrode finger 27 of the other comb-tooth electrode 23 via the gap G. The width (D1-axis direction) of the dummy electrode 29 is, for example, equal to the width of the electrode finger 27. The lengths (D2-axis direction) of the plurality of dummy electrodes 29 are, for example, equal to each other.

  The number of the plurality of gaps G is the same as the number of the plurality of electrode fingers 27. In addition, the widths of the plurality of gaps G (in the D1-axis direction) are equal to the widths of the plurality of electrode fingers 27 and the plurality of dummy electrodes 29, and the gaps G are equal to each other. The lengths (D2 axis direction) of the plurality of gaps G are the same in the gaps G. This length may be appropriately set according to electrical characteristics required for the resonator 13. For example, the length of the gap G is 0.1λ to 0.6λ.

  The IDT electrode 19 is made of, for example, metal. Examples of the metal include Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al—Cu alloy. The IDT electrode 19 may be composed of a plurality of metal layers. The thickness of the IDT electrode 19 may be set as appropriate.

  When a voltage is applied to the piezoelectric substrate 2 by the IDT electrode 19, SAW propagating in the D1 axis direction along the upper surface is induced near the upper surface of the piezoelectric substrate 2. The SAW is reflected by the electrode finger 27. And the standing wave which makes the pitch p of the electrode finger 27 a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as that of the standing wave, and is taken out by the electrode finger 27. In this way, the resonator 13 functions as a resonator or a filter.

  The reflector 21 is composed of a conductive pattern (conductive layer) formed on the upper surface of the piezoelectric substrate 2 and is formed in a lattice shape in plan view. That is, the reflector 21 includes a pair of bus bars (reference numerals omitted) facing each other in a direction crossing the SAW propagation direction, and a plurality of bus bars extending in a direction (D2 axis direction) perpendicular to the SAW propagation direction between these bus bars. And electrode fingers (not shown). The plurality of electrode fingers of the reflector 21 are arranged at substantially the same pitch as the plurality of electrode fingers 27 of the IDT electrode 19.

  When the configuration of the SAW resonator shown in FIG. 5 is used as a capacitive element, the reflector 21 and the dummy electrode 29 may be omitted.

  By providing the resonator 17 configured as described above, a small multiplexer can be provided.

  First, in order to confirm the effect of inserting the capacitive element C1, the multiplexer shown in the circuit diagram shown in FIG. 6 was examined.

  The pass band of the first filter F1 is located on the lower frequency side than the pass band of the second filter F2, and the interval between the pass bands of the filters is about three times the pass band width. In this case, the capacitance of the first capacitive element C1 is 3.2 pF, the Q value in the frequency band of the pass band of the second filter F2 is 100, the capacitance of the second capacitive element C2 is 1.1 pF, and the inductance of the inductor L is A multiplexer model with 3.3 nH was created. This model is referred to as Example 1.

  Similarly, as a comparative example, a multiplexer model in which the capacitance element C1 and the second capacitance element C2 were not provided and the size of the inductor L was 3.0 nH was created. Note that the size of the inductor L differs depending on whether or not the capacitive element C1 and the second capacitive element C2 are provided. This is because each configuration is optimized so as to be matched with the antenna terminal ANT.

  As a result of the simulation, in the comparative example not including the capacitive element C1 and the second capacitive element C2, the reflection coefficient Γ in the frequency band of the pass band of the second filter F2 of the first filter F1 was 0.864. On the other hand, when the capacitive element C1 and the second capacitive element C2 are provided, the reflection coefficient Γ is 0.903, which can be close to the ideal value of 1. As a result, the loss of the entire multiplexer can be reduced.

  As the next example (Example 2), a multiplexer 1A shown in FIG. 4 was manufactured and its frequency characteristics were measured. Similarly, as a comparative example, a multiplexer without the capacitive elements C1 and C2 in the example shown in FIG. 4 was manufactured, and the frequency characteristics were measured in the same manner.

  The frequency bands of the pass bands of the four filters were set to increase in the order of the second filter F2, the first filter F1, the third filter F3, and the fourth filter F4. In other words, of the four pass bands, two filters having adjacent pass bands located in the middle are connected to the first connection point 11, and two filters having the lowest pass waiting and the highest pass band are the second. It is connected to the connection point 12.

  Here, each of the capacitive element C1 and the second capacitive element C2 is a chip capacitor, and the inductor L is a conductor pattern formed on a circuit board (mounting board) (not shown). The configuration of the capacitive element C1, the second capacitive element C2, and the inductor L is as follows.

Capacitance element C1: Capacity value 12 pF, Q value at 1 GHz 60
Second capacitive element C2: Q value at capacitance value 10 pF, 1 GHz 60
Inductor L: Inductance 1.6 nH, Q value at 1 GHz 62
Capacitance element C1, second capacitance element C2, inductor L: all mounted on a mounting board (not shown), and the pass band of chip elements F1 to F4: 1.7 GHz to 2.2 GHz
FIG. 7 shows the frequency characteristics of Example 2 and the comparative example having such a configuration. FIG. 7A shows the correlation between the frequency of each filter and the magnitude of the reflection coefficient Γ for the multiplexer of the comparative example. FIG. 7B shows the correlation between the frequency of each filter and the magnitude of the reflection coefficient Γ for the multiplexor of the second embodiment.

  As is clear from this figure, the reflection coefficient on the high frequency side of the passband gradually decreases as the frequency increases, but the slope of the drop in the example is smaller than that in the comparative example. It could be confirmed. Thereby, it was confirmed that the multiplexer according to the example can increase the reflection coefficient in a plurality of counterpart passbands.

  FIG. 8 shows an enlarged view of the main part of FIG. Specifically, (a) to (d) show the reflection coefficients of other filters in the passbands of the first filter F1 to the fourth filter F4, respectively. In (a) to (d), a thinly painted area is a pass band. Furthermore, confirming the magnitude of the reflection coefficient Γ of other filters within the passband of each filter suppresses the drop near the center of the passband and the deterioration of the reflection coefficient Γ at the shoulder on the high frequency side of the passband. It was confirmed that it was made. From the above, it was confirmed that the communication quality was improved by the multiplexer according to the example.

Claims (8)

A first filter, a second filter, and a third filter, each including at least one resonator and having different passbands;
A connection point at which the first filter, the second filter, and the third filter are electrically connected in common;
A first port and a second port, wherein the first port is connected to the first filter side, and the second port is connected to the connection point side, whereby the connection point and the first filter And a capacitive element connected in series between
There is no branch path to the reference potential between the connection point and the first filter,
In the frequency band of the pass band of the filter located on the second port side of the second filter and the third filter, the capacitive element is the most of the at least one resonator of the first filter. Less loss than the first resonator connected to the capacitive element side,
Multiplexer.   2. The multiplexer according to claim 1, wherein a pass band of the first filter is on a lower frequency side than a pass band of a filter located on the second port side of the second filter and the third filter.   The multiplexer according to claim 1 or 2, wherein the at least one resonator of the first filter includes an acoustic wave resonator.   The multiplexer according to claim 1, wherein the capacitive element is a chip capacitor.   The multiplexer according to claim 3, wherein the capacitive element includes a pair of comb-like electrodes having a resonance frequency higher than that of the acoustic wave resonator. The second filter is located on the second port side;
A third port and a fourth port; the third port is connected to the second filter side; and the fourth port is connected to the connection point side, whereby the connection point and the second filter are connected. A second capacitive element connected in series between and
Of the at least one resonator of the second filter, the second capacitive element is in a frequency band of a pass band of the filter located on the fourth port side of the first filter and the third filter. Less loss than the second resonator connected to the second capacitor element side,
The multiplexer according to any one of claims 1 to 5. A fourth filter including a plurality of resonators and having a pass band different from any of the first filter, the second filter, and the third filter;
A first connection point commonly connecting the first filter and the third filter;
A second connection point for connecting the second filter and the fourth filter in common,
As for the connection point, the first connection point and the second connection point are electrically connected to each other through wiring,
The capacitive element is connected between the first connection point and the connection point;
The multiplexer according to claim 6, wherein the second capacitive element is connected between the second connection point and the connection point. An antenna terminal to which the connection point is electrically connected;
The multiplexer according to claim 1, wherein a matching circuit is connected between the connection point and the antenna terminal.