Filter device, multiplexer, high frequency front-end circuit and communication device
By connecting an additional circuit in parallel to the filter circuit and adjusting the configuration of the IDT electrodes, the problem of insufficient attenuation on the high-frequency side of the filter passband in the prior art is solved, and higher attenuation outside the passband and steeper filter characteristics are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MURATA MFG CO LTD
- Filing Date
- 2020-11-11
- Publication Date
- 2026-07-10
AI Technical Summary
In the existing technology, phase shift circuits are difficult to sufficiently improve the attenuation of the high-frequency passband side of the filter.
An additional circuit is connected in parallel in the filter circuit. The additional circuit consists of at least three IDT electrodes, which are configured along the direction of elastic wave propagation and connected to the series arm resonator through a specific node. The average electrode finger spacing of the IDT electrodes is adjusted to improve the phase reversal effect.
The passband attenuation of the filter was significantly increased, especially near the high-frequency and low-frequency ends of the receiving filter, resulting in a steeper filter characteristic.
Smart Images
Figure CN114982130B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to filter devices, multiplexers, high-frequency front-end circuits, and communication devices having multiple series arm resonators. Background Technology
[0002] Previously, various bandpass filters with multiple series-arm resonators have been proposed. In the duplexer described in Patent Document 1 below, a bandpass filter serving as a transmitting filter is connected between the input terminal and the common terminal. This bandpass filter has multiple series-arm resonators and multiple parallel-arm resonators. Furthermore, to improve the out-of-band attenuation of the filter, a phase-shifting circuit is connected in parallel with the filter between the input terminal and the common terminal. In Patent Document 1, the phase-shifting circuit, for example, has four IDT electrodes. Two of the four IDT electrodes are connected at the node between the input terminal and the filter. The remaining two IDT electrodes are connected at the node between the common terminal and the filter.
[0003] Prior art literature
[0004] Patent documents
[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-38040 Summary of the Invention
[0006] The problem the invention aims to solve
[0007] In Patent Document 1, the two IDT electrodes of the phase shift circuit are connected to the same node between the input terminal and the filter. The remaining two IDT electrodes are also connected to the same node between the common terminal and the filter.
[0008] In a phase-shifting circuit as described in Patent Document 1, the phase in the phase-shifting circuit is reversed relative to the out-of-band phase of the filter. This results in an improvement in out-of-band attenuation.
[0009] However, in structures using the phase shift circuit described in Patent Document 1, the attenuation on the high-frequency side of the filter's passband is sometimes not sufficiently improved.
[0010] The purpose of this invention is to provide a filter device that can significantly increase the attenuation outside the passband.
[0011] Technical solutions for solving the problem
[0012] The filter device of the present invention comprises: a filter circuit having a first terminal, a second terminal, and a plurality of series arm resonators disposed in a series arm connecting the first terminal and the second terminal; and an additional circuit connected in parallel with at least a portion of the series arm resonators in the series arm, the additional circuit having at least three IDT electrodes including a first IDT electrode, a second IDT electrode, and a third IDT electrode, the at least three IDT electrodes being disposed along the direction of elastic wave propagation, the first IDT electrode being connected to a first node, the first node being one end of the series arm resonator having the lowest anti-resonance frequency among the plurality of series arm resonators, the second IDT electrode being connected to a second node, the potential of the second node being different from that of the first node, the third IDT electrode being connected to a third node, the potential of the third node being different from that of the first node and the second node, the first node and the second node being closer to the first terminal than the third node.
[0013] Invention Effects
[0014] According to the present invention, a filter device capable of significantly increasing the attenuation outside the passband can be provided. Attached Figure Description
[0015] Figure 1 This is a circuit diagram of a filter device according to the first embodiment of the present invention.
[0016] Figure 2 This is a top view showing the electrode configuration of the IDT electrode used in the first embodiment.
[0017] Figure 3 This is the circuit diagram of the filter device in Comparative Example 1.
[0018] Figure 4 This is the circuit diagram of the filter device in Comparative Example 2.
[0019] Figure 5 The graph shows the attenuation-frequency characteristics of the embodiments and Comparative Examples 1 and 2.
[0020] Figure 6 This is a circuit diagram of a filter device according to the second embodiment of the present invention.
[0021] Figure 7 This is a circuit diagram of a filter device according to the third embodiment of the present invention.
[0022] Figure 8 This is a structural diagram of a communication device and a high-frequency front-end circuit as embodiments of the present invention. Detailed Implementation
[0023] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.
[0024] 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.
[0025] Figure 1 This is a circuit diagram of a filter device according to the first embodiment of the present invention.
[0026] The filter device 1 has an input terminal as a first terminal 2a and a second terminal 2b. Although in Figure 1 Not shown, but terminal 2b is connected to one end of other bandpass filters to form a multiplexer. This filter device 1 constitutes the transmit filter of Band 26. The passband of the transmit filter of Band 26 is 814MHz to 849MHz. On the other hand, the passband of the receive filter of Band 26 is 859MHz to 894MHz. Therefore, in filter device 1, the attenuation in the 859MHz to 894MHz range is required to be sufficiently large.
[0027] A trapezoidal bandpass filter circuit 3 is connected between terminal 1 2a and terminal 2b. The filter circuit 3 has multiple series arm resonators S1 to S4 and multiple parallel arm resonators P1 to P3. The series arm resonators S1 to S4 and the parallel arm resonators P1 to P3 are each composed of a surface acoustic wave (SAW) resonator. The construction of this SAW resonator is not particularly limited; a SAW resonator using a Y-cut LiNbO3 substrate and utilizing a Love wave is employed.
[0028] The anti-resonant frequencies of the series arm resonators S1 to S4 constitute the attenuation poles on the high-frequency side of the passband. However, the resonant frequencies and anti-resonant frequencies of the series arm resonators S1 to S4 are shown in Table 1 below.
[0029] [Table 1]
[0030] Series arm resonator S1 S2 S3 S4 Resonant frequency (MHz) 838 832 839 831 Anti-resonance frequency (MHz) 875 868 858 867
[0031] As can be clearly seen from Table 1, the anti-resonance frequency of the series arm resonator S3 becomes lower than that of the other series arm resonators S1, S2, and S4.
[0032] In addition, the resonant frequencies and anti-resonant frequencies of the parallel arm resonators P1 to P3 are shown in Table 2 below.
[0033] [Table 2]
[0034] Parallel arm resonator P1 P2 P3 Resonant frequency (MHz) 794 801 796 Anti-resonance frequency (MHz) 830 836 833
[0035] In the series arm resonator S3, which has the lowest anti-resonance frequency, a capacitor C1 is connected in parallel as a bridging capacitor. The so-called anti-resonance frequency of the series arm resonator S3 shown here refers to the anti-resonance frequency after the capacitor C1 is connected in parallel as a bridging capacitor.
[0036] Furthermore, in this invention, the anti-resonance frequency of the series arm resonator, when a bridging capacitor is connected in parallel, as mentioned above, refers to the anti-resonance frequency after the bridging capacitor is connected; when a bridging capacitor is not connected in parallel, it refers to the anti-resonance frequency of the series arm resonator itself.
[0037] In the filter device 1, an additional circuit 4 is connected in parallel with the filter circuit 3 between the first terminal 2a and the second terminal 2b. Specifically, the additional circuit 4 is connected in parallel with the series arm resonators S2 to S4 of the series arm resonators S1 to S4 provided in the filter circuit 3. It is assumed that the case in which the additional circuit 4 is connected in parallel with at least a portion of the series arm resonators provided in the filter circuit 3 also includes the case of "connecting the additional circuit in parallel with the filter circuit".
[0038] The additional circuit 4 has multiple IDT electrodes 5-8. The multiple IDT electrodes 5-8 are arranged along the direction of elastic wave propagation. Figure 2 The electrode structure of IDT electrodes 5-8 is shown in a top view.
[0039] according to Figure 2 It is clear that reflectors 9 and 10 are actually arranged on both sides of the elastic wave propagation direction of the multiple IDT electrodes 5 to 8. This constitutes a longitudinally coupled resonator. However, in this invention, as long as at least three IDT electrodes 5 to 8 are arranged along the elastic wave propagation direction, reflectors 9 and 10 may not be provided. Therefore, it is not limited to a longitudinally coupled type; a transverse elastic wave device can also be used.
[0040] Among IDT electrodes 5 to 8, IDT electrode 7 corresponds to the first IDT electrode in this invention, IDT electrode 5 corresponds to the second IDT electrode in this invention, and IDT electrodes 6 and 8 correspond to the third IDT electrode.
[0041] One end of each of IDT electrodes 5-8 is connected to ground potential. The other end of each of IDT electrodes 5-8 is connected to filter circuit 3. More specifically, the other ends of IDT electrodes 5 and 7 are connected to the node on the side of the first terminal 2a of filter circuit 3. IDT electrode 7 is connected to the first node N1. IDT electrode 5 is connected to the second node N2. Here, the node on the side of the first terminal 2a in filter circuit 3 refers to the node located on the side of the first terminal 2a that includes the center and is closer to the center than the center in the part constituting series arm resonators S1-S4. Here, the second node N2 is different from the first node N1. That is, the first node N1 is located at one end of the series arm resonator S3 with the lowest anti-resonance frequency. The second node N2 is the node between series arm resonators S1 and S2.
[0042] On the other hand, one end of IDT electrodes 6 and 8 is connected to ground potential, and the other end is connected to the third node N3. The third node N3 is a node located on the side of the second terminal 2b, specifically, it is the node between the second terminal 2b and the series arm resonator S4. IDT electrodes 6 and 8 are connected to the third node N3, which is the same node, as described above.
[0043] IDT electrodes 6 and 8 are connected to the third node N3 via capacitors C2 and C3, respectively.
[0044] The aforementioned additional circuit 4 includes at least three IDT electrodes 5-8, optional reflectors 9 and 10, and optional capacitors C2 and C3. By connecting this additional circuit 4 in parallel with the filter circuit 3, the attenuation on the high-frequency side of the passband can be significantly increased in the filter device 1, and more specifically, the attenuation in the 859MHz to 894MHz frequency band can be significantly increased. This will be explained in more detail below.
[0045] Furthermore, the average finger spacing of IDT electrodes 5–8 are 2.024 μm, 1.976 μm, 2.030 μm, and 1.990 μm, respectively. The average finger spacing is calculated as the sum of the finger spacings of all electrodes in the IDT electrode divided by the number of electrodes. The average finger spacing of IDT electrode 7, connected to node 1 N1, is greater than the average finger spacing of IDT electrode 5, connected to node 2 N2.
[0046] exist Figure 5 The attenuation-frequency characteristic of the filter device 1 described above is shown in solid lines. For comparison, the attenuation-frequency characteristic of Comparative Example 1 is shown in thick dashed lines, and the attenuation-frequency characteristic of Comparative Example 2 is shown in thin dashed lines. Furthermore, the circuit diagram of the filter device 101 of Comparative Example 1 is shown in... Figure 3 Furthermore, the circuit diagram of the filter device 102 of Comparative Example 2 is shown in [the diagram]. Figure 4 .
[0047] according to Figure 3 It is clear that filter device 101 does not have additional circuit 4. On the other hand, although filter device 102 of Comparative Example 2 has additional circuit 4, IDT electrodes 5 and 7 are both connected to the second node N2. The other structures of filter devices 101 and 102 of Comparative Example 1 and Comparative Example 2 are the same as those of the embodiment.
[0048] according to Figure 5 It is clear that the minimum attenuation of the passband of the receiving filter of Band 26 is 47.9 dB in Comparative Example 1 and 49.8 dB in Comparative Example 2. In contrast, it is 57.9 dB in the embodiment. Therefore, according to the embodiment, it is possible to increase the passband of the receiving filter of Band 26, that is, the attenuation in the attenuation band on the high-frequency side of the transmitting filter of Band 26.
[0049] Furthermore, regarding the loss in the passband of the transmit filter, Band 26, from 814MHz to 849MHz, it was 2.08dB in Comparative Example 1 and 2.27dB in Comparative Example 2. In contrast, it was 2.08dB in this embodiment.
[0050] Therefore, according to the above embodiment, the attenuation of the passband of the receiving filter, which is outside the passband, can be sufficiently increased. Moreover, in the embodiment, compared with Comparative Example 1 which does not have the additional circuit 4, the loss caused by the 814MHz to 849MHz passband is not degraded.
[0051] In addition, such as Figure 5 As shown, in Comparative Example 1, the attenuation near the low-frequency end Lch = 859MHz and the high-frequency end Hch = 894MHz of the passband of the receiving filter decreases. This deterioration in the low-frequency end Lch can be attributed to the capacitor C1 connected in parallel to the series arm resonator S3. In the transmitting filter of Band 26, the frequency interval between the passband of the transmitting filter and the passband of the receiving filter is narrow. Therefore, a steeper filter characteristic is required in the high-frequency end of the passband in the transmitting filter. To improve the steepness of the high-frequency end of the passband, it is sufficient to connect a capacitor in parallel to the series arm resonator to lower the anti-resonance frequency. However, if the attenuation near the anti-resonance frequency increases, the so-called bounce, where the attenuation on the high-frequency end decreases, becomes larger. Therefore, there is a problem of deteriorating attenuation near the low-frequency end Lch of the receiving filter's passband.
[0052] To address the attenuation degradation near the low-frequency end Lch, as described above, a phase-shifting circuit, as described in Patent Document 1, could be considered. However, because the phase change near the attenuation pole caused by the anti-resonant frequency of the series arm resonator is large, it is difficult to reverse the phase using a phase-shifting circuit. Furthermore, it is difficult to reliably reverse the phase across a wide range between the low-frequency end Lch and the high-frequency end Hch of the receiver filter's passband. Therefore, in the phase-shifting circuit described in Patent Document 1, it is difficult to sufficiently reduce the attenuation throughout the entire passband of the receiver filter.
[0053] Furthermore, compared to Comparative Example 1 which lacks the aforementioned additional circuit 4, in the above embodiment, the attenuation can be sufficiently increased near both the low-frequency end Lch and the high-frequency end Hch of the passband of the receiving filter. First, the IDT electrodes 5 and 7 connected to the input terminals of the additional circuit 4 are connected to different first nodes N1 and second nodes N2, thereby improving the attenuation at the low-frequency end Lch of the passband of the receiving filter. In addition, by relatively increasing the average electrode finger spacing of the IDT electrode 7 connected to the first node N1, the center frequency of the passband formed by the path from IDT electrode 7 to IDT electrode 8 in the additional circuit 4 becomes lower. Therefore, by passing through the first node N1, the attenuation at the low-frequency end Lch of the passband of the receiving filter is further improved across a wide frequency range. On the other hand, by relatively decreasing the average electrode finger spacing of the IDT electrode 5 connected to the second node N2, the center frequency of the passband formed by the path from IDT electrode 5 to IDT electrode 6 becomes higher. Therefore, by passing through the path of node 2 N2, the attenuation at the high-frequency end Hch of the passband of the receiving filter can be improved.
[0054] Therefore, according to the embodiment, the attenuation can be sufficiently increased in either the vicinity of the low-frequency band end Lch or the vicinity of the high-frequency band end Hch. Moreover, the attenuation can be increased across the entire passband of the receiving filter.
[0055] In particular, in the above embodiment, capacitor C1 is connected in parallel with series arm resonator S3, which has the lowest anti-resonance frequency. By connecting IDT electrode 7 to the first node N1, which is one end of series arm resonator S3, the effect of improving the attenuation of the entire passband region of the receiving filter is further enhanced. This is because by connecting the additional circuit 4 directly to series arm resonator S3 without passing through other components, the phase near the anti-resonance frequency can be effectively reversed.
[0056] In addition, according to Figure 5It is clear that in Comparative Example 2, the same attenuation as in the embodiment was obtained near the high-frequency end Hch of the passband of the receiving filter. However, near the low-frequency end Lch, the attenuation in Comparative Example 2 was almost unimproved compared to Comparative Example 1 without the additional circuit 4. This is believed to be because the phase change in the bounce portion near the low-frequency end Lch, caused by the anti-resonant frequency of the series arm resonator S3, is large, making it difficult to reverse the phase in the additional circuit 4.
[0057] That is, because IDT electrodes 5 and 7 are connected to the same second node N2, the path from IDT electrode 7 to IDT electrode 8, which improves attenuation near the high-frequency end Hch, and the path from IDT electrode 5 to IDT electrode 6, which improves attenuation near the low-frequency end Lch, interfere with each other. Therefore, it is difficult to share the phase adjustment near the low-frequency end Lch and near the high-frequency end Hch.
[0058] Furthermore, when the first terminal 2a is an input terminal, it is preferable that the multiple IDT electrodes 5 and 7 connected to the input terminal side are connected to the first node N1 or the second node N2, which are different nodes. This makes it difficult for the additional circuit 4 to break down when a large power is applied. Therefore, preferably, at least one of the IDT electrodes 5 and 7 is preferably connected to a node other than the node between the first terminal 2a and the series arm resonator S1 to S4 closest to the first terminal 2a.
[0059] However, like Figure 6 As shown in the second embodiment, the IDT electrode 5 can also be connected to the node between the first terminal 2a and the series arm resonator S1 closest to the first terminal 2a. That is, at least one of the IDT electrode 7 and the IDT electrode 5 can be connected between the series arm resonator S1 closest to the first terminal 2a and the first terminal 2a.
[0060] In addition, it can also be like Figure 7 As shown in the third embodiment, the IDT electrodes 6 and 8, which are connected to the filter circuit 3 on the second terminal 2b side, are connected to different nodes, namely, the third node N3 and the fourth node N4. In this case, IDT electrode 6 is the third IDT electrode in this invention, and IDT electrode 8 is the fourth IDT electrode in this invention.
[0061] exist Figure 1In the circuit, the additional circuit 4 includes capacitors C2 and C3 to invert the phase and adjust the amplitude of the signal. These capacitors C2 and C3 are not necessarily required. Furthermore, although IDT electrodes 5 and 7 are directly connected to filter circuit 3, capacitors can also be connected between IDT electrode 5 and the second node N2, and between IDT electrode 7 and the first node N1. This allows for correction of the amplitude of the signal that inverts the phase.
[0062] Alternatively, capacitors C2 and C3 can be used instead of capacitors C3, and can be connected to the IDT electrodes 5 and 7 as described above, thus applying the capacitors of the series arm resonator.
[0063] In addition, although Figure 1 In the present invention, filter circuit 3 is a trapezoidal filter with multiple elastic wave resonators; however, the circuit structure of filter circuit 3 in filter device 1 is not limited to this. Various bandpass filters with multiple series arm resonators can be used as filter circuit 3.
[0064] Furthermore, the filter device 1 of the present invention is not limited to a transmitting filter, but may also be a receiving filter or other bandpass filter. Therefore, the first terminal 2a may also be a receiving terminal.
[0065] Furthermore, in the above embodiment, an example of a transmit filter applied to Band 26 is shown, and in this case, as a passband high-frequency band side, an improvement in the attenuation in the passband of the receive filter of Band 26 is achieved. This improvement in attenuation on the passband high-frequency band side is not limited to the passband of the receive filter of Band 26.
[0066] Furthermore, the filter device 1 of the present invention can be used as a duplexer, for example, by connecting the second terminal 2b to one end of the receiving filter. Moreover, the filter device 1 can be suitably used as one bandpass filter in a multiplexer where one end of three or more bandpass filters are connected to each other.
[0067] Furthermore, although in the above embodiments, the series arm resonators S1 to S4 and the parallel arm resonators P1 to P3 are composed of surface acoustic wave resonators, they can also be composed of bulk wave resonators.
[0068] The filter devices described in the above embodiments can be used as duplexers or similar devices in high-frequency front-end circuits. An example will be described below.
[0069] Figure 8This is a structural diagram of the communication device and the high-frequency front-end circuit. Additionally, the diagram also illustrates various components connected to the high-frequency front-end circuit 230, such as the antenna element 202 and the RF signal processing circuit (RFIC) 203. The high-frequency front-end circuit 230 and the RF signal processing circuit 203 constitute the communication device 240. Furthermore, the communication device 240 may also include a power supply, a CPU, and a display.
[0070] The high-frequency front-end circuit 230 includes a switch 225, duplexers 201A and 201B, filters 231 and 232, low-noise amplifier circuits 214 and 224, and power amplifier circuits 234a, 234b, 244a, and 244b. Additionally, Figure 8 The high-frequency front-end circuit 230 and the communication device 240 are an example of a high-frequency front-end circuit and a communication device, and are not limited to this structure.
[0071] Duplexer 201A has filters 211 and 212. Duplexer 201B has filters 221 and 222. Duplexers 201A and 201B are connected to antenna element 202 via switch 225. Alternatively, the filter devices described above can be filters 211 and 212, or filters 221, 222, 231, and 232.
[0072] Furthermore, this invention can also be applied to multiplexers having three or more filters, such as a tripper that makes the antenna terminals of three filters common, or a sextupler that makes the antenna terminals of six filters common.
[0073] Furthermore, multiplexers are not limited to structures with both a transmit filter and a receive filter; they can also be structures with only a transmit filter or only a receive filter.
[0074] Switch 225 connects antenna element 202 to a signal path corresponding to a given frequency band according to a control signal from a control unit (not shown). Switch 225 is, for example, an SPDT (Single Pole Double Throw) type switch. Furthermore, the signal path connected to antenna element 202 is not limited to one; multiple paths can also be used. That is, the high-frequency front-end circuit 230 can also handle carrier aggregation.
[0075] Low-noise amplifier circuit 214 is a receiving amplifier circuit that amplifies the high-frequency signal (here, the high-frequency received signal) that has passed through antenna element 202, switch 225, and duplexer 201A, and outputs it to RF signal processing circuit 203. Low-noise amplifier circuit 224 is a receiving amplifier circuit that amplifies the high-frequency signal (here, the high-frequency received signal) that has passed through antenna element 202, switch 225, and duplexer 201B, and outputs it to RF signal processing circuit 203.
[0076] Power amplifier circuits 234a and 234b are transmitting amplifier circuits that amplify the high-frequency signal (here, a high-frequency transmitting signal) output from RF signal processing circuit 203 and output it to antenna element 202 via duplexer 201A and switch 225. Power amplifier circuits 244a and 244b are transmitting amplifier circuits that amplify the high-frequency signal (here, a high-frequency transmitting signal) output from RF signal processing circuit 203 and output it to antenna element 202 via duplexer 201B and switch 225.
[0077] The RF signal processing circuit 203 processes the high-frequency received signal input from the antenna element 202 via the received signal path using down-conversion or the like, and outputs the received signal generated by the signal processing. Furthermore, the RF signal processing circuit 203 processes the input transmitted signal using up-conversion or the like, and outputs the high-frequency transmitted signal generated by the signal processing to the power amplifier circuits 234a, 234b, 244a, and 244b. The RF signal processing circuit 203 is, for example, an RFIC. Alternatively, the communication device may include a BB (baseband) IC. In this case, the BBIC processes the received signal processed by the RFIC. Furthermore, the BBIC processes the transmitted signal and outputs it to the RFIC. The received signal processed by the BBIC and the transmitted signal before the BBIC's signal processing are, for example, image signals and audio signals.
[0078] Alternatively, the high-frequency front-end circuit 230 can replace the duplexers 201A and 201B described above and have the duplexer involved in the modified examples of duplexers 201A and 201B.
[0079] On the other hand, filters 231 and 232 in communication device 240 are connected between RF signal processing circuit 203 and switch 225 without passing through low-noise amplifier circuits 214 and 224 and power amplifier circuits 234a, 234b, 244a, 244b. Filters 231 and 232 are also connected to antenna element 202 via switch 225, similar to duplexers 201A and 201B.
[0080] The above description illustrates the filter device, high-frequency front-end circuit, and communication device according to the embodiments of the present invention. However, the present invention also includes other embodiments implemented by combining any of the constituent elements in the above embodiments, variations of the above embodiments that can be conceived by those skilled in the art without departing from the spirit of the present invention, and various devices that incorporate the high-frequency front-end circuit and communication device of the present invention.
[0081] This invention, as an elastic wave resonator, filter, duplexer, multiplexer applicable to multi-band systems, front-end circuit, and communication device, can be widely used in communication equipment such as portable telephones.
[0082] Explanation of reference numerals in the attached figures
[0083] 1: Filter device;
[0084] 2a, 2b: Terminal 1 and Terminal 2;
[0085] 3: Filter circuit;
[0086] 4: Additional circuitry;
[0087] 5, 6, 7, 8: IDT electrodes;
[0088] 9, 10: Reflectors;
[0089] 201A, 201B: Duplexers;
[0090] 202: Antenna element;
[0091] 203: RF signal processing circuit;
[0092] 211, 212: Filters;
[0093] 214: Low-noise amplifier circuit;
[0094] 221, 222: Filters;
[0095] 224: Low-noise amplifier circuit;
[0096] 225: Switch;
[0097] 230: High-frequency front-end circuit;
[0098] 231, 232: Filters;
[0099] 234a, 234b: Power amplifier circuit;
[0100] 240: Communication device;
[0101] 244a, 244b: Power amplifier circuits;
[0102] C1, C2, C3: Capacitors;
[0103] N1, N2, N3, N4: Node 1, Node 2, Node 3, Node 4;
[0104] P1, P2, P3: Parallel arm resonators;
[0105] S1, S2, S3, S4: Series arm resonators.
Claims
1. A filter device comprising: A filter circuit having a first terminal, a second terminal, and a plurality of series-arm resonators disposed in a series arm connecting the first terminal and the second terminal; and An additional circuit is connected in parallel with at least a portion of the resonators in the series arm. The additional circuit has at least three IDT electrodes, including a first IDT electrode, a second IDT electrode, and a third IDT electrode, which are arranged along the direction of elastic wave propagation. The first IDT electrode is connected to the first node, which is one end of the series arm resonator with the lowest anti-resonance frequency among the plurality of series arm resonators. The second IDT electrode is connected to the second node, and the potential of the second node is different from that of the first node. The third IDT electrode is connected to the third node, and the potential of the third node is different from that of the first node and the second node. The first node and the second node are closer to the first terminal than the third node. The first terminal is an input terminal, the second terminal is an output terminal, and the first IDT electrode and the second IDT electrode are connected to the first terminal side.
2. The filter device according to claim 1, wherein, The average electrode finger spacing of the first IDT electrode is greater than the average electrode finger spacing of the second IDT electrode.
3. The filter device according to claim 1 or 2, wherein, At least one of the first IDT electrode and the second IDT electrode is connected to a node other than the node between the first terminal and the first terminal of the plurality of series arm resonators.
4. The filter device according to claim 1 or 2, wherein, At least one of the first IDT electrode and the second IDT electrode is connected to the node between the first terminal and the first terminal of the plurality of series arm resonators.
5. The filter device according to claim 1 or 2, wherein, It also includes: a capacitor element connected in parallel with the series arm resonator having the lowest anti-resonant frequency.
6. The filter device according to claim 1 or 2, wherein, At least three of the IDT electrodes also have a fourth IDT electrode connected to a fourth node, the fourth node having a different potential than the second node, the fourth node being located in the series arm closer to the second terminal than the first node and the second node, and the fourth node having a different potential than the third node.
7. The filter device according to claim 1 or 2, wherein, The filter circuit also has multiple parallel arm resonators.
8. A multiplexer comprising: a plurality of filter devices whose ends are connected to each other in a common manner. One of the plurality of filter devices is the filter device according to any one of claims 1 to 7.
9. A high-frequency front-end circuit, comprising: The multiplexer as claimed in claim 8; and An amplifier connected to the multiplexer of claim 8.
10. A communication device comprising: The high-frequency front-end circuit as described in claim 9; and An RF signal processing circuit is connected to the high-frequency front-end circuit described in claim 9.