multiplexer

Abstract

The present application provides a multiplexer capable of reducing an IMD and suppressing degradation of sensitivity of a reception filter. A multiplexer (1) has a first transmission filter (11), a second transmission filter (13), and a first reception filter (12) each having a plurality of resonators, which are commonly connected to a common terminal (2), a passband of the first transmission filter is set to Tx1, a passband of the second transmission filter is set to Tx2, a passband of the first reception filter is set to Rx1, center frequencies of the respective passbands are set to Tx1c, Tx2c, and Rx1c, respectively, at this time, Tx1c < Rx1c < Tx2c, a resonator of the first reception filter (12) closest to the common terminal (2) is a series arm resonator (S11), an electrode finger pitch of an IDT electrode in a resonator closest to the common terminal (2) in the second transmission filter (13) is set to p(Tx2), an electrode finger pitch of an IDT electrode of the series arm resonator (S11) closest to the common terminal (2) in the first reception filter (12) is set to pS1(Rx1), in this case, a pitch ratio represented by pS1(Rx1) / p(Tx2) is greater than 1 and is 1.035 or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a multiplexer in which a plurality of transmission filters and a plurality of reception filters are connected to a common terminal. BACKGROUND

[0002] Conventionally, a multiplexer connected to an antenna is widely used in a smartphone or the like. In the multiplexer described in Patent Literature 1 below, a plurality of transmission filters having different passbands and a plurality of reception filters are connected to a common terminal. A passband of a first reception filter is positioned between passbands of a first transmission filter and a second transmission filter. A passband of a second reception filter is positioned on a higher frequency side than the passbands of the first transmission filter and the second transmission filter and the passband of the first reception filter. In Patent Literature 1, the first transmission filter and the second transmission filter and the first reception filter and the second reception filter are ladder filters each having a parallel arm resonator and a series arm resonator. Further, the parallel arm resonator and the series arm resonator include an elastic wave resonator.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: International Publication No. 2018 / 123545 SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In the above-described multiplexer, sometimes, dual uplink carrier aggregation in which signals of two frequency bands are simultaneously transmitted is performed. In this case, IMD (Intermodulation Distortion) is generated, and sometimes, sensitivity of the first reception filter or the second reception filter is deteriorated.

[0008] An object of the present application is to provide a multiplexer capable of reducing IMD and suppressing deterioration of sensitivity of a reception filter.

[0009] TECHNICAL SOLUTION FOR SOLVING THE PROBLEM

[0010] The multiplexer involved in this invention includes a common terminal and a first transmitting filter, a second transmitting filter, and a first receiving filter, each having multiple resonators connected to the common terminal. The passband of the first transmitting filter is set to Tx1, the passband of the second transmitting filter is set to Tx2, and the passband of the first receiving filter is set to Rx1. The center frequencies of each passband are set to Tx1c, Tx2c, and Rx1c, respectively, where Tx1c < Rx1c < Tx2c. The resonator of the first receiving filter closest to the common terminal is a series arm resonator. The electrode finger spacing of the IDT electrode in the resonator of the second transmitting filter closest to the common terminal is set to p(Tx2), and the electrode finger spacing of the IDT electrode of the series arm resonator of the first receiving filter closest to the common terminal is set to pS1(Rx1). In this case, the spacing ratio represented by pS1(Rx1) / p(Tx2) is greater than 1 and less than 1.035.

[0011] Invention Effects

[0012] In the multiplexer of the present invention, IMD can be reduced and the degradation of the receiving sensitivity of the receiving filter can be suppressed. Attached Figure Description

[0013] Figure 1 This is a simplified circuit diagram of a multiplexer according to the first embodiment of the present invention.

[0014] Figure 2 This is a more detailed circuit diagram of the multiplexer according to the first embodiment of the present invention.

[0015] Figure 3 This is an attenuation-frequency response diagram showing the relationship between the passbands of the first receiving filter and the second receiving filter, and the first transmitting filter and the second transmitting filter in the multiplexer of the first embodiment.

[0016] Figure 4 (a) and Figure 4 (b) is a front sectional view of the elastic wave resonator and a simplified top view showing its electrode structure.

[0017] Figure 5 This is a graph showing the relationship between the pitch ratio and the size of the IMD at 2110MHz.

[0018] Figure 6 This is a graph showing the relationship between the pitch ratio and the size of the IMD at 2140MHz.

[0019] Figure 7 This is a graph showing the relationship between the pitch ratio and the size of the IMD at 2170MHz.

[0020] Figure 8 This is a graph showing the relationship between IMD level difference and frequency in each multiplexer when the electrode finger pitch ratio is 1.019 and when the electrode finger pitch ratio is 1.028.

[0021] Figure 9 This is a graph showing the relationship between phase difference and frequency in each multiplexer when the electrode finger spacing ratio is 1.019 and when the electrode finger spacing ratio is 1.028.

[0022] Figure 10 (a) and Figure 10 (b) are graphs showing the relationship between current density and frequency in the resonators on the antenna side of the first and second transmit filters, respectively.

[0023] Figure 11 (a) and Figure 11 (b) are graphs showing the relationship between current density and frequency in the resonators on the antenna side of the first and second receiving filters, respectively. Detailed Implementation

[0024] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0025] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0026] Figure 1 This is a simplified circuit diagram of the multiplexer according to the first embodiment of the present invention. Figure 2 It is its more detailed circuit diagram.

[0027] like Figure 1 As shown, the multiplexer 1 has a common terminal 2. Common terminal 2 is the terminal connected to the antenna ANT. One end of the first transmit filter 11, the first receive filter 12, the second transmit filter 13, and the second receive filter 14 are all connected to common terminal 2. The passband of the first transmit filter 11 is set to Tx1, the passband of the first receive filter 12 is set to Rx1, the passband of the second transmit filter 13 is set to Tx2, and the passband of the second receive filter 14 is set to Rx2. Furthermore, the center frequencies of each passband are set to Tx1c, Rx1c, Tx2c, and Rx2c, respectively.

[0028] In this embodiment, the first transmitting filter 11 and the first receiving filter 12 are the transmitting filter and receiving filter of Band 3, and the second transmitting filter 13 and the second receiving filter 14 are the transmitting filter and receiving filter of Band 1.

[0029] The positional relationship of the passbands of the first transmitting filter 11, the first receiving filter 12, the second transmitting filter 13, and the second receiving filter 14 is shown in the figure. Figure 3 .exist Figure 3 In the diagram, the thin line represents the attenuation frequency characteristic of the first transmitting filter, the dashed line represents the attenuation frequency characteristic of the first receiving filter, the dashed line represents the attenuation frequency characteristic of the second transmitting filter, and the solid line represents the attenuation frequency characteristic of the second receiving filter.

[0030] Therefore, the frequencies of the aforementioned passband are as follows.

[0031] Tx1 = 1710MHz ~ 1785MHz

[0032] Rx1 = 1805MHz ~ 1880MHz

[0033] Tx2 = 1920MHz ~ 1980MHz

[0034] Rx2 = 2110MHz ~ 2170MHz

[0035] Furthermore, the center frequencies of each passband are as follows.

[0036] Tx1c = 1747.5MHz

[0037] Rx1c = 1842.5MHz

[0038] Tx2c = 1950MHz

[0039] Rx2c = 2140MHz

[0040] like Figure 2 As shown, the first transmitting filter 11, the first receiving filter 12, the second transmitting filter 13, and the second receiving filter 14 are all trapezoidal filters with series arm resonators and parallel arm resonators. Moreover, the aforementioned series arm resonators and parallel arm resonators include elastic wave resonators.

[0041] Figure 4 (a) and Figure 4(b) is a front cross-sectional view of the elastic wave resonator and a simplified top view showing its electrode structure. The elastic wave resonator 101 has a piezoelectric substrate 102. The piezoelectric substrate 102 includes a piezoelectric single crystal, piezoelectric ceramic, or a laminate of a piezoelectric film and a support substrate. IDT electrodes 103 and reflectors 104 and 105 are provided on the piezoelectric substrate 102. The IDT electrodes 103 have multiple first electrode fingers 103a and multiple second electrode fingers 103b. The multiple first electrode fingers 103a and multiple second electrode fingers 103b are interleaved with each other. Moreover, an alternating electric field is applied between the first electrode fingers 103a and the second electrode fingers 103b to excite elastic waves. Here, the distance between the centers of adjacent electrode fingers of the first electrode fingers 103a and the second electrode fingers 103b is defined as the electrode finger spacing p of the IDT electrode 103.

[0042] The electrode finger spacing p = (1 / 2)λ. λ is the wavelength of the elastic wave, which is determined by the electrode finger spacing p mentioned above.

[0043] Return to Figure 2 The first transmitting filter 11 is connected between the common terminal 2 and the transmitting terminal 11a. Series arm resonators S1 to S5 are configured in the series arm connecting the transmitting terminal 11a and the common terminal 2. Furthermore, four parallel arms are provided to connect the series arm to ground potential. Parallel arm resonators P1, P2, P3, or P4 are configured in each of the four parallel arms.

[0044] In addition, although not specifically limited, the series arm resonator S5 closest to the antenna terminal has a configuration that divides one elastic wave resonator into three elastic wave resonators in series.

[0045] The series arm resonators S2 to S4 also include the segmented type series arm resonators that divide an elastic wave resonator into two parts.

[0046] The first receiving filter 12 is connected between the common terminal 2 and the receiving terminal 12a. As shown in the figure, series arm resonators S11 to S15 are arranged in the series arm. Parallel arm resonators P11, P12, P13, or P14 are respectively arranged in the multiple parallel arms that connect the series arm to the ground potential. Here, the series arm resonators S11, S12, S13, and S14 are also configured to divide a single elastic wave resonator into multiple series arm resonators connected in series with each other.

[0047] The second transmitting filter 13 is connected between the transmitting terminal 13a and the common terminal 2. In the second transmitting filter 13, series arm resonators S21 to S23 are arranged in the series arm connecting the transmitting terminal 13a and the common terminal 2, starting from the transmitting terminal 13a side. Furthermore, a capacitor C is connected between the common terminal 2 and the series arm resonator S23. In addition, parallel arm resonators P21, P22a, P22b, and P23 are connected in the multiple parallel arms connecting the series arm to ground potential, as shown in the figure.

[0048] The second receiving filter 14 is connected between the common terminal 2 and the receiving terminal 14a, and its circuit structure is substantially the same as that of the first transmitting filter 11. However, series arm resonators S31 to S35 are arranged sequentially from the common terminal 2 side. Furthermore, parallel arm resonators P31, P32, P33, and P34 are arranged in each parallel arm from the common terminal 2 side.

[0049] In the multiplexer 1 described above, in the first transmit filter 11, the second transmit filter 13, the first receive filter 12, and the second receive filter 14, Tx1c < Rx1c < Tx2c < Rx2c. Furthermore, the resonator closest to the common terminal 2 in the first receive filter 12 is a series arm resonator S11. The electrode finger spacing of the IDT electrodes in the parallel arm resonator P23 in the second transmit filter 13, which is the resonator closest to the common terminal 2, is set to p(Tx2). The electrode finger spacing of the IDT electrodes in the series arm resonator S11 in the first receive filter 12, which is closest to the common terminal 2, is set to pS1(Rx1). In this case, the spacing ratio represented by pS1(Rx1) / p(Tx2) is set to be greater than 1 and less than 1.035. Therefore, the generation of IMD can be suppressed, and the degradation of the receiving sensitivity in the second receive filter 14 can be suppressed. (Refer to...) Figures 5-11 This needs to be explained.

[0050] The inventors of this application investigated the degradation of the receiving sensitivity in the second receiving filter 14 within the aforementioned multiplexer. As a result, it was discovered that an IMD (Instantaneous Modulation) occurs when signals from both the first transmitting filter 11 and the second transmitting filter 13 are transmitted simultaneously, and this IMD may degrade the receiving sensitivity of the second receiving filter 14. Furthermore, it was found that adjusting the spacing ratio of the electrode finger spacing can suppress the magnitude of such IMD. Figures 5-7 The figures show the size of the IMD appearing on the common terminal 2 side at 2110MHz, 2140MHz, or 2170MHz.

[0051] When evaluating the IMD, the ratio of the electrode finger spacing of the IDT electrode of the parallel arm resonator P23 closest to the common terminal 2 of the second transmit filter 13 to the electrode finger spacing of the IDT electrode of the series arm resonator S11 closest to the common terminal 2 of the first receive filter 12 was changed. The IMD was evaluated when the input power was +26 dBm in the passband of the second transmit filter 13 and the transmit signal of Band 3 (i.e., the transmit signal of the passband of the first transmit filter 11) was input at the common terminal 2 with a power of +10 dBm. The IMD generated in the passband of Band 1, which is the second receive filter, was evaluated when power was applied at the transmit frequencies of Band 1 and Band 3, with IMD = 2 × (center frequency of the passband of Band 1) - (center frequency of the transmit band of Band 3) = (receive frequency of the receive band of Band 1).

[0052] like Figure 5 As shown, at 2110MHz, within the pitch ratio range of 1.035 to 1.01, the smaller the pitch ratio, the smaller the IMD. Therefore, to improve IMD, simply set the aforementioned pitch ratio below 1.035. Furthermore, as... Figure 6 As shown, at 2140MHz, the smaller the pitch ratio, the smaller the IMD becomes. However, in this case, as... Figure 7 As shown, the IMD increases slightly at 2170MHz.

[0053] As described above, setting the spacing ratio to 1.035 or less improves the IMD (Instantaneous Displacement), which is believed to be due to the following reasons. In a multiplexer with transmit and receive filters having Band 1 and Band 3 as described above, the characteristics of the second transmit filter and the first receive filter are generally dominant in terms of IMD magnitude. However, if the IMD levels of both filters are equal and the phase difference is 180°±90°, the IMDs can be canceled out. In this embodiment, it is believed that at the low-frequency side of 2110MHz, the IMDs cancel each other out on the common terminal side, thereby reducing the IMD magnitude.

[0054] Figure 8 as well as Figure 9 This diagram illustrates the relationship between the level difference and frequency, and the relationship between the phase difference and frequency, of the IMD at the common terminal 2 of the second transmitting filter 13 and the IMD on the side of the common terminal 2 of the first receiving filter 12, when the spacing ratio is 1.028 and 1.019, respectively. When the spacing ratio is 1.028, the level difference of the IMD on the lower frequency side is as large as 20 dB, and the phase difference is also greater than 240°. That is, the aforementioned cancellation effect is reduced.

[0055] However, if the spacing ratio decreases to 1.019, the level difference of the IMD on the lower frequency side becomes less than 10dB, and the phase difference also decreases to less than 240°. That is, the elimination effect becomes greater.

[0056] according to Figure 7 It is clear that if the above spacing ratio is above 1.01, the IMD on the 2170MHz side does not increase much.

[0057] Furthermore, although a second receiving filter 14 is provided in the above embodiment, in this invention, it is sufficient that the first transmitting filter 11, the second transmitting filter 13, and the first receiving filter 12 are in the relationship of Tx1c < Rx1c < Tx2c, and the spacing ratio is greater than 1 and less than 1.035. Therefore, if the IMD problem is not in the second receiving filter 14 but in the first receiving filter 12, a second receiving filter 14 with a passband higher than that of the second transmitting filter 13 may not be required. Additionally, in this invention, the resonator closest to the common terminal 2 of the second transmitting filter 13 can be a parallel arm resonator or a series arm resonator.

[0058] Figure 10 (a) and Figure 10 (b) are graphs showing the relationship between current density and frequency in the resonators on the antenna side of the first and second transmit filters, respectively. Figure 11 (a) and Figure 11 Figure (b) shows the relationship between current density and frequency in the resonators on the antenna side of the first and second receiving filters, respectively. Additionally, the above figures show the waveforms of the IMD signal. Figure 10 (a) and Figure 11 As shown in (b), there are cases where the waveforms of the IMD signals are similar in the second transmit filter 13 and the first receive filter 12. In this case, IMD can be canceled by adjusting the phase difference of the IMD signals in the second transmit filter 13 and the first receive filter 12 to 180°. Here, the multiplexer 1 preferably has a phase shifting circuit. This allows the phase difference of the IMD signals to be adjusted. More preferably, the phase shifting circuit is connected between the second transmit filter 13 and the common terminal 2. The second transmit filter 13 is the transmit filter of Band 1. Therefore, high power is input to the second transmit filter 13. Consequently, the phase of the IMD signal can be easily adjusted, and IMD can be canceled more reliably. Figure 10 (b) and Figure 11As shown in (a), the relationship between the first transmitting filter 11 and the second receiving filter 14 is the same as the relationship between the second transmitting filter 13 and the first receiving filter 12. A phase-shifting circuit may also be connected between at least one of the first transmitting filter 11, the first receiving filter 12, the second transmitting filter 13, and the second receiving filter 14 and the common terminal 2. As a phase-shifting circuit, for example, a circuit or transmission line that uses capacitors or inductors, or a combination of them, can be used.

[0059] Explanation of reference numerals in the attached figures

[0060] 1: Multiplexer;

[0061] 2: Common terminal;

[0062] 11: First transmitting filter;

[0063] 11a: Transmitter terminal;

[0064] 12: First receiving filter;

[0065] 12a: Receiver terminal;

[0066] 13: Second transmitting filter;

[0067] 13a: Transmitter terminal;

[0068] 14: Second receiving filter;

[0069] 14a: Receiver terminal;

[0070] 101: Elastic wave resonator;

[0071] 102: Piezoelectric substrate;

[0072] 103: IDT electrode;

[0073] 103a: First electrode indicator;

[0074] 103b: Second electrode indicator;

[0075] 104, 105: Reflectors;

[0076] P1~P4: Parallel arm resonators;

[0077] P11~P14: Parallel arm resonators;

[0078] P21, P22a, P22b, P23: Parallel arm resonators;

[0079] P31~P34: Parallel arm resonators;

[0080] S1~S5: Series arm resonators;

[0081] S11~S15: Series arm resonators;

[0082] S21~S23: Series arm resonator;

[0083] S31~S35: Series arm resonators.

Claims

1. A multiplexer comprising: a common terminal; and a first transmission filter, a second transmission filter, and a first reception filter commonly connected to the common terminal and each having a plurality of resonators, wherein a passband of the first transmission filter is set to Tx1, a passband of the second transmission filter is set to Tx2, a passband of the first reception filter is set to Rx1, and center frequencies of the respective passbands are set to Tx1c, Tx2c, and Rx1c, respectively, Tx1c < Rx1c < Tx2c, a resonator closest to the common terminal of the first reception filter is a series arm resonator, an electrode finger pitch of an IDT electrode in a resonator closest to the common terminal in the second transmission filter is set to p(Tx2), and an electrode finger pitch of an IDT electrode of the series arm resonator closest to the common terminal in the first reception filter is set to pS1(Rx1), and a pitch ratio represented by pS1(Rx1) / p(Tx2) is greater than 1 and is 1.035 or less.

2. The multiplexer according to claim 1, wherein the pitch ratio represented by pS1(Rx1) / p(Tx2) is 1.01 or more.

3. The multiplexer according to claim 1 or 2, wherein in the second transmission filter, a resonator closest to the common terminal is a parallel arm resonator.

4. The multiplexer according to claim 1 or 2, wherein in the second transmission filter, a resonator closest to the common terminal is a series arm resonator.

5. The multiplexer according to claim 1 or 2, further comprising a second reception filter having a passband higher than the passband of the second transmission filter.

6. The multiplexer according to claim 1 or 2, further comprising a phase shift circuit connected between the second transmission filter and the common terminal. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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