JP6798866B2 - Multiplexer - Google Patents

Description

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

In recent years, there is carrier aggregation (hereinafter referred to as CA) as a technology that has attracted attention in communication standards. CA is a technology that enables wideband transmission by using a plurality of carriers at the same time.

In a communication device compatible with CA, a plurality of frequency bands are used at the same time. Therefore, in a communication device compatible with CA, a demultiplexer (multiplexer) capable of simultaneously separating a plurality of signals in a plurality of frequency bands is required.

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

Japanese Unexamined Patent Publication No. 2005-57342

In recent years, further high-speed communication and low power consumption have been required, and along with this, a technique for suppressing insertion loss in each of a plurality of pass bands is required for a filter. This technique is particularly required when the frequency bands used simultaneously in CA are close to each other.

The present application was devised under such circumstances, and an object thereof is to provide a multiplexer capable of achieving high communication quality.

The multiplexer according to one aspect of the present invention includes a first filter, a second filter, a third filter, a connection point, and a capacitive element. The first filter, the second filter, and the third filter are configured to include at least one resonator, and have different pass bands from each other. Then, 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 this connection point and the first filter. Then, the capacitive element is the at least one of the first filter in the frequency band of the pass band of the filter located closer to the connection point than 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 capacitance element side.

According to the above configuration, signals of different frequency bands can be suitably separated, and high communication quality can be realized.

It is a circuit diagram which shows the structure of the multiplex which concerns on 1st Embodiment of this disclosure. (A) and (b) are circuit diagrams showing the configuration of the filter of the multiplexer of FIG. 1, respectively. 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 the 2nd Embodiment of this disclosure. It is a top view which shows the structure of the resonator in FIG. It is a schematic circuit diagram of a multiplexer. (A) and (b) are diagrams showing the frequency characteristics of the multiplexer according to the embodiment, respectively. Each of (a) to (d) is an enlarged view of a main part of FIG. 7, and is a diagram showing the reflection coefficients of other filters in the pass band of each filter.

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

In the second and subsequent embodiments, for configurations that are the same as or similar to those of the embodiments already described, the same codes as those assigned to the configurations of the embodiments already described are used, and illustrations and explanations are omitted. I have something to do. In addition, in the second and subsequent embodiments, particularly when a configuration corresponding to (similar to) the configuration of the embodiment already described is assigned a code different from the reference numeral assigned to the configuration of the embodiment already described. Matters not specified are the same as those of the embodiments already described.

<First Embodiment>
(Basic configuration)
FIG. 1 is a circuit diagram showing a configuration of a multiplexer 1 according to a 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. Then, the first filter F1, the second filter F2, and the 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 commonly connected for the first time at the connection point 10. Further, a capacitance 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 capacitive 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 capacitive 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 of the paths between the connection point 10 and the filters F1 to F3. This indicates that there is no matching circuit or other filter between the filters F1 to F3 and the connection point 10.

The first to third filters F1 to F3 are filters that function as a transmission filter and a reception filter, and are configured to include at least one resonator 21. 2 (a) and 2 (b) are schematic circuit diagrams showing a connection example of a resonator in each filter.

The filter that functions as a transmission filter may be configured by, for example, a ladder type filter as shown in FIG. 2A. That is, the transmission filter is provided between one or more (3 in this embodiment) series resonator 13A connected in series between the input side I1 and the output side O1 and between the series line and the reference potential portion. It has one or more parallel resonators 13B (2 in this embodiment) provided in the above. That is, as the resonator 21, a series resonator 13A and a parallel resonator 13B are provided. The individual series resonator 13A and parallel resonator 13B are not exactly the same, and are individually designed according to their arrangement positions and desired 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 that functions as a reception filter is, for example, as shown in FIG. 2B, between the input side I2 and the output side O2, the multiple mode type filter 15 and the auxiliary connected in series to the input side. It has a resonator 13C. That is, in this example, the resonator 21 is the auxiliary resonator 13C. In this embodiment, the multiple mode includes the 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.

(Capacitive element)
The capacitance element C1 includes a port p1 on the side where the capacitance element C1 is connected to the first filter F1 and a port p2 on the connection point 10 side. Here, looking at the circuit with reference to the capacitive element C1, the filter located on the port p1 side (first filter F1 in this example) and the filter located on the port p2 side (second filter, third filter in this example). There is a filter F3). The filter located on the port p2 side can also be said to be a filter connected in parallel to the filter located on the port p1 side when viewed from the antenna terminal ANT. Hereinafter, the filter located on the port p1 side may be referred to as a filter located in the subsequent stage, and the filter located on the port p2 side may be referred to as a filter located in the front stage.

The capacitance element C1 has a smaller loss than the resonator 21 located on the antenna terminal ANT side of the filters located in the rear stage in the frequency band of the pass band of the filter located in the front stage. Specifically, the capacitor has a high Q value in the frequency band of the pass band of the filter located in the previous stage.

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

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

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 capacity value.

When the capacitive element C1 is formed by an electrode pattern, miniaturization is possible. Further, the number of parts of the multiplexer 1 as a whole can be reduced. When the capacitive element C1 is composed of an electrode pattern, it may be a rectangular counter electrode or a comb-toothed electrode that excites a surface acoustic wave. In that case, the desired capacity can be obtained in a small area. When the piezoelectric substrate 2 is composed of comb-shaped electrodes, the resonance frequency may be adjusted or arranged so as to be offset from the propagation direction of the surface acoustic waves in order to suppress the generation of unintended surface acoustic waves. Good.

By connecting such a capacitive element C1 in series at the position shown in FIG. 1, the filter located in the rear stage can have a high reflectance coefficient in the frequency band of the pass band of the filter located in the front stage. As a result, in the multiplexer 1 provided with a plurality of filters, it is possible to realize excellent filter characteristics with little insertion loss even in the pass band of the filter on the other side.

In a multiplexer in which a plurality of filters are connected in parallel, there is known an example in which an LC filter is provided in front of the filter in order to separate unnecessary signals. However, such an LC filter has a large specific bandwidth and is effective for separating a wide signal such as separating a Low Band and a High Band, but is effective for switching signals between a plurality of filters having close pass bands. Cannot be applied. Specifically, when the interval between the pass bands of a plurality of filters connected in parallel is, for example, 5 times or less the pass band, it can be said that the pass bands are close to each other. Further, in the actual multiplexer 1, there are cases where the pass bandwidth is twice or less and one time or less.

Here, when the resonator 21 of the first filter F1 is a surface acoustic wave resonator (hereinafter referred to as a SAW resonator), the filter (first filter F1) located after the capacitive element C1. ) May be lower than the pass band 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 pass band.

In a filter using a SAW resonator, a loss due to bulk wave radiation occurs remarkably on the high frequency side of the pass band. Communication quality deteriorates when the pass band of another filter overlaps the frequency band where the loss due to bulk wave radiation increases. Therefore, by arranging the capacitive element C1, the reflection coefficient in this frequency band can be increased, and as a result, the characteristics of other filters whose pass bands overlap in this frequency band can be enhanced.

Further, if 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 located before the capacitance element C1, the capacitance element C1 is placed on the piezoelectric substrate 2. It may be composed of the comb tooth electrode formed in. More specifically, the comb-tooth electrode is formed along the propagation direction of the SAW, and its resonance frequency is formed to be higher than the resonance frequency of the resonator 21 located closest to the antenna terminal ANT side. In other words, the electrode finger cycle (described later) of the comb-toothed electrode of the capacitive element C1 is smaller than the electrode finger period of the comb-toothed electrode constituting the resonator 21 located closest to the antenna terminal ANT side.

With this configuration, the capacitive element C1 functions as a SAW resonator that resonates at a higher frequency side, which has nothing to do with the pass band of the filter (first filter F1) located in the subsequent stage. Since the loss due to bulk wave radiation of the SAW resonator is small in the region on the lower frequency side than the resonance frequency, the capacitance element C1 causes the SAW resonator to be on the lower frequency side than the pass band of the filter (first filter F1) located in the subsequent stage. The loss can be reduced. As a result, the reflectance coefficient can be increased with respect to the filter located on the lower frequency side than the pass band of the filter located in the subsequent stage (first filter F1).

More preferably, the electrode finger cycle 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, an example of the multiplexer 1 in which three filters are connected in parallel is shown, but the number may be four or more. Further, although the case where the capacitive element is provided in only one of the three filters has been described, the capacitive element may be provided in each of a plurality of filters (including the case of all filters). FIG. 3 shows an example in which the capacitive element C is provided for each of the 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 capacitance element C2 is the same as that of the capacitance element C1. That is, the loss in the frequency domain of the pass band of the filters (first filter F1, third filter F3) located in the front stage of the second capacitance element C2 is the filter located in the rear stage of the second capacitance element C2 (second filter F2). ), It is designed to be smaller than the loss of the resonator 21 (referred to as the second resonator 21B) located on the antenna terminal ANT side. In such a case, the reflection coefficient can be increased for more pass bands, and as a result, the communication quality can be improved.

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

In FIG. 4, the 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. More specifically, the first filter F1 is connected between the first connection point 11 and the first terminal S1. Then, 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, a second filter is connected between the second connection point 12 and the second terminal S2, and a fourth filter F4 is connected between the second connection point 12 and the fourth terminal S4.

Then, 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 commonly connected for the first time at the connection point 10. Further, a capacitance element C1 is connected in series between the connection point 10 and the first filter F1. In this example, the capacitive element C1 is connected between the connection point 10 and the first connection point 11. Similarly, a second capacitance 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 in the connection point.

In such a configuration, the filters located in the front stage with respect to the capacitive element C1 are the second filter F2 and the fourth filter F4, and the filters located in the rear stage are the first filter F1 and the third filter. It is F3. Similarly, with respect to the second capacitance element C2, the filters located in the front stage are the first filter F1 and the third filter F3, and the filters located in the rear stage are the second filter F2 and the fourth filter F4.

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 having less loss than the first resonator 21 of both the first filter F1 and the third filter F3 is used in the pass bands of both the second filter F2 and the fourth filter F4. ing.

By increasing the reflectance coefficient with one capacitive element for the two filters in this way, the number of parts can be reduced.

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

Further, in the above example, an example in which two configurations in which one capacitance element is provided for two filters is connected in parallel is shown, but one capacitance element may be omitted, or for two filters. A configuration in which one capacitance element is provided and a configuration in which one capacitance element C1 is provided in one filter may be combined.

(Each component)
Hereinafter, each component constituting the above-mentioned multiplexers 1 and 1A will be described with reference to FIG. In FIG. 5, any direction may be 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 is defined. Words such as the upper surface may be used with (the front side of the paper in FIG. 5) facing upward.

The resonator 17 may be a SAW resonator, a piezoelectric thin film resonator, or a crystal oscillator, but in this example, a case where the resonator 17 is composed of 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 (orthogonal to the D3 axis). Its planar shape and dimensions may be set as appropriate. Further, the piezoelectric substrate 2 is made of a single crystal having piezoelectricity such as a lithium niobate (LiNbO3) single crystal or a lithium tantalate (LiTaO3) single crystal. The cut angle may be appropriately set according to the type of SAW to be used and the like. For example, the piezoelectric substrate 2 is a rotary 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 of the upper surface of the piezoelectric substrate 2.

It is assumed that the relationship between the Cartesian coordinate system consisting of the D1 axis, the D2 axis and the D3 axis and the Cartesian coordinate system consisting of the X axis, the Y axis and the Z axis (that is, the crystal orientation) is constant. Therefore, in the following, 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 coefficient of linear expansion smaller than that of the material constituting the piezoelectric substrate may be attached to the back surface of the piezoelectric substrate 2, or a sound velocity may be provided between the support substrate and the piezoelectric substrate 2. An acoustic reflection structure layer in which a fast material and a low material are laminated 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, these may be referred to as “resonator 13” without distinction). Is.

The resonator 13 is configured as, for example, a 1-port SAW resonator, and has a piezoelectric substrate 2 and 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 arranged on the upper surface of the IDT electrode 19 and the reflector 21, a base layer interposed between the IDT electrode 19 and the reflector 21 and the piezoelectric substrate 2, and the piezoelectric substrate 2. It may have a protective layer or the like that covers the upper surface of the IDT electrode 19 and the reflector 21 (or an 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 side comb tooth electrode 23A and a negative side comb tooth electrode 23B. In the following, the positive side comb tooth electrode 23A and the negative side comb tooth electrode 23B are simply referred to as "comb tooth electrode 23", and these may not be distinguished. Further, the positive side comb tooth electrode 23A refers to the comb tooth electrode 23 located on the positive side of the D2 axis among the pair of comb tooth electrodes 23, and the negative side comb tooth electrode 23B refers to the pair of comb tooth electrodes 23. Of these, the comb tooth electrode 23 located on the negative side of the D2 axis is referred to (these names do not refer to the positive side and the negative side of the potential).

Each comb tooth electrode 23 is, for example, between two bus bars 25 facing each other, a plurality of electrode fingers 27 extending in parallel from each bus bar 25 toward another bus bar 25, and each bus bar 25 between the plurality of electrode fingers 27. It has a plurality of dummy electrodes 29 extending from the bus bar 25 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).

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

The bus bar 25 is formed, for example, in a long shape having a substantially constant width and extending linearly in the propagation direction of the SAW (D1 axis direction, X axis direction). The pair of bus bars 25 face each other in a direction (D2 axis direction) intersecting (orthogonal in the present embodiment) in the propagation direction of the SAW. Further, 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 propagation direction of the SAW.

The plurality of electrode fingers 27 are formed in a long shape extending linearly in a direction (D2 axis direction) orthogonal to the SAW propagation direction with a substantially constant width, for example, and the SAW propagation direction (D1 axis direction, They are arranged at substantially regular intervals in the X-axis direction). The pitch p (for example, the distance between the centers of the electrode fingers 27) of the plurality of electrode fingers 27 of the pair of comb tooth electrodes 23 is equal to, for example, half the wavelength of the SAW wavelength λ at the frequency to be resonated. It is provided in. 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. Further, the widths (D1 axial direction) of the plurality of electrode fingers 27 are, for example, equal to each other. These dimensions may be appropriately set according to the electrical characteristics required for the resonator 13. For example, the width of the electrode fingers 27 is 0.4p to 0.7p with respect to the pitch p of the plurality of electrode fingers 27.

The plurality of dummy electrodes 29 are formed in a long shape extending linearly in a direction orthogonal to the propagation direction of the SAW (D2 axis direction) with a substantially constant width, and are formed in the center between the plurality of electrode fingers 27. They are arranged (arranged at the same pitch as a plurality of electrode fingers 27). The tip of the dummy electrode 29 of one comb tooth electrode 23 faces the tip of the electrode finger 27 of the other comb tooth electrode 23 via the gap G. The width of the dummy electrode 29 (in the D1 axial direction) is, for example, the same as the width of the electrode finger 27. The lengths (D2 axis direction) of the plurality of dummy electrodes 29 are, for example, equivalent to each other.

The number of the plurality of gaps G is the same as the number of the plurality of electrode fingers 27. Further, the widths of the plurality of gaps G (in the D1 axial direction) are equivalent to the widths of the plurality of electrode fingers 27 and the widths of the plurality of dummy electrodes 29, and the gaps G are also equivalent to each other. The lengths of the plurality of gaps G (in the D2 axis direction) are the same among the gaps G. This length may be appropriately set according to the 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 this 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 appropriately set.

When a voltage is applied to the piezoelectric substrate 2 by the IDT electrode 19, SAW propagating in the D1 axial direction is induced near the upper surface of the piezoelectric substrate 2. The SAW is also reflected by the electrode finger 27. Then, a standing wave having a pitch p of the electrode finger 27 as a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as 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 formed of a conductive pattern (conductive layer) formed on the upper surface of the piezoelectric substrate 2, and is formed in a grid pattern in a plan view. That is, the reflector 21 includes a pair of bus bars (reference numerals omitted) facing each other in a direction intersecting the propagation direction of the SAW, and a plurality of bus bars extending in a direction orthogonal to the propagation direction of the SAW (D2 axis direction). It has an electrode finger (reference numeral omitted). 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 structure 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 having the above configuration, 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 was located on the lower frequency side than the pass band of the second filter F2, and the distance between the pass bands of the filters was about three times the pass bandwidth. 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 set. A model of a multiplexer with 3.3 nH was created. This model is referred to as Example 1.

Similarly, as a comparative example, a model of a multiplexer not provided with the capacitive element C1 and the second capacitive element C2 and having an inductor L with a size of 3.0 nH was created. The size of the inductor L differs depending on whether the capacitive element C1 or the second capacitive element C2 is provided or not. This is because each configuration is optimized so that it can be matched with the antenna terminal ANT.

As a result of the simulation, in the case of the comparative example not including the capacitive element C1 and the second capacitive element C2, the reflectance 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 capacitance element C1 and the second capacitance element C2 are provided, the reflection coefficient Γ is 0.903, which can be brought close to the ideal 1. As a result, the loss of the entire multiplexer can be reduced.

As the next embodiment (Example 2), the multiplexer 1A shown in FIG. 4 was manufactured and its frequency characteristics were measured. Similarly, as a comparative example, the multiplexers not provided with the capacitive elements C1 and C2 were manufactured in the example shown in FIG. 4, and the frequency characteristics were measured in the same manner.

The frequency band of the pass band of the four filters was set to be higher 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 passbands, two filters with adjacent passbands located in the middle are connected to the first connection point 11, and two filters with the lowest passband and the highest passband are the second. It is connected to the connection point 12.

Here, the capacitance element C1 and the second capacitance element C2 are chip capacitors, respectively, and the inductor L is a lead wire pattern formed on a circuit board (mounting board) (not shown). The configurations of the capacitive element C1, the second capacitive element C2, and the inductor L are as follows.

Capacitive element C1: Capacitance value 12 pF, Q value at 1 GHz 60
Second capacitive element C2: capacitive value 10 pF, Q value 60 at 1 GHz
Inductor L: Inductance 1.6 nH, Q value at 1 GHz 62
Capacitive element C1, 2nd capacitive element C2, inductor L: Both are mounted on a mounting board (not shown) and the pass band of the chip element filters F1 to F4 is 1.7 GHz to 2.2 GHz.
FIG. 7 shows the frequency characteristics of Example 2 and Comparative Example having such a configuration. FIG. 7A shows the correlation between the frequency of each filter and the magnitude of the reflectance 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 reflectance coefficient Γ for the Luciplexer of Example 2.

As is clear from this figure, as the frequency increases, the reflectance coefficient on the high frequency side of the pass band gradually decreases, but in the examples, the slope of the descent is smaller than that of the comparative example. It could be confirmed. As a result, it was confirmed that the multiplexer according to the embodiment can increase the reflectance coefficient in a plurality of pass bands on the other side.

FIG. 8 shows an enlarged view of a main part of FIG. 7. Specifically, (a) to (d) indicate the reflection coefficients of the other filters in each pass band of the first filter F1 to the fourth filter F4, respectively. In (a) to (d), the lightly filled area is the pass band. Furthermore, when the magnitude of the reflection coefficient Γ of other filters in the pass band of each filter is confirmed, the drop near the center of the pass band and the deterioration of the reflectance Γ on the shoulder on the high frequency side of the pass band are suppressed. I was able to confirm that it was done. From the above, it was confirmed that the communication quality was improved by the multiplexer according to the embodiment.

Claims (8)

A first filter, a second filter, and a third filter, each containing at least one resonator and having different pass bands,
A connection point to which the first filter, the second filter, and the third filter are electrically connected in common,
The connection point and the first filter are provided by providing a first port and a second port, connecting the first port to the side of the first filter, and connecting the second port to the side of the connection point. With a capacitive element connected in series between and
The first filter includes a first resonator connected to the side of the capacitive element most of the at least one resonator.
There is no branch path to the reference potential between the connection point and the first filter.
The capacitive element has less loss than the first resonator of the first filter in the frequency band of the pass band of the filter located on the side of the second port of the second filter and the third filter. Ku,
The second filter is located on the side of the second port.
The connection point and the second filter are provided by providing a third port and a fourth port, connecting the third port to the side of the second filter, and connecting the fourth port to the side of the connection point. Further equipped with a second capacitance element connected in series between and
The second capacitive element is among the at least one resonator of the second filter in the frequency band of the pass band of the filter located on the side of the fourth port of the first filter and the third filter. It has less loss than the second resonator connected to the side of the second capacitance element.
Multiplexer. The multiplexer according to claim 1, wherein the pass band of the first filter is on the lower frequency side of the pass band of the filter located on the side of the second port 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 elastic wave resonator. The multiplexer according to any one of claims 1 to 3, wherein the capacitive element is a chip capacitor. The multiplexer according to claim 3, wherein the capacitive element is composed of a pair of comb-shaped electrodes having a resonance frequency higher than that of the elastic wave resonator. A fourth filter containing a plurality of resonators and having a pass band different from that of the first filter, the second filter, and the third filter is further provided.
A first connection point that connects the first filter and the third filter in common,
A second connection point for connecting the second filter and the fourth filter in common is provided.
At the connection point, the first connection point and the second connection point are electrically connected to each other via wiring.
The capacitive element is connected between the first connection point and the connection point.
The multiplexer according to any one of claims 1 to 5, wherein the second capacitance element is connected between the second connection point and the connection point. Further provided with an antenna terminal to which the connection point is electrically connected,
The multiplexer according to any one of claims 1 to 6 , wherein a matching circuit is connected between the connection point and the antenna terminal. Said first filter, when the passband of the second filter and the third filter arranged in order of frequency, interval of the passband the adjacent is not more than 5 times the pass bandwidth of claims 1 to 5 The multiplexer described in either.