Filter circuit and diplexer

Abstract

The embodiment of the present application provides a filter circuit and a duplexer, wherein the filter circuit comprises: at least two series resonance branches, the series resonance branches are connected in series between an input terminal and an output terminal, each of the series resonance branches comprises a first resonator; at least three parallel resonance branches, each of the parallel resonance branches comprises a second resonator; a first coupling structure connected between a first pair of parallel resonance branches; a second coupling structure connected between a second pair of parallel resonance branches; wherein the first pair of parallel resonance branches connected by the first coupling structure and the second pair of parallel resonance branches connected by the second coupling structure are different at least in one parallel resonance branch.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, specifically to a filter circuit and a duplexer. Background Technology

[0002] Filtering circuits, especially thin-film bulk acoustic resonator (FBAR) filtering circuits, are widely used in mobile communication systems, such as duplexers in portable mobile terminals.

[0003] Figure 1 A conventional multi-stage cascaded FBAR filter circuit is shown, comprising series resonant branches 11A to 11D and parallel resonant branches 12A to 12E, as well as a matching inductor 14A located at the input terminal and a matching inductor 14B located at the output terminal. The series resonant branches consist of a single resonator, while the parallel resonant branches consist of a resonator and an inductor connected in series with it. However, this filter circuit has a narrow bandwidth, making it difficult to meet the requirements of broadband signal communication scenarios. Figure 2 As can be seen from the insertion loss curve, the peak value of low-frequency signals outside the passband is about -23dB, and the peak value of high-frequency signals is about -33dB. The filtering circuit has insufficient suppression capability for high-frequency and low-frequency signals outside the passband, which seriously affects the filtering performance of the filtering circuit. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a filter circuit and a duplexer to solve at least one of the problems of poor suppression capability of high-frequency and low-frequency signals outside the passband and narrow bandwidth in the prior art.

[0005] According to a first aspect, embodiments of the present invention provide a filter circuit, comprising: at least two series resonant branches connected in series between an input terminal and an output terminal, each series resonant branch including a first resonator; at least three parallel resonant branches, one end of each parallel resonant branch being connected between two adjacent series resonant branches, and / or between the input terminal and the series resonant branch closest to the input terminal, and / or between the series resonant branch closest to the output terminal and the output terminal, the other end of each parallel resonant branch being grounded, each parallel resonant branch including a second resonator; and a first coupling structure connected between a first pair of parallel resonant branches, the first coupling structure including a first coupling element, one end of the first coupling element being connected to the first electrode of the second resonator of the parallel resonant branch closest to the input terminal in the first pair of parallel resonant branches, and the other end of the first coupling element being connected to the first electrode of the second resonator of the parallel resonant branch closest to the output terminal in the first pair of parallel resonant branches. The second electrode of the second resonator of the second resonant branch in the second pair of parallel resonant branches; and a second coupling structure connected between the second pair of parallel resonant branches, the second coupling structure including a second coupling element and a third coupling element, one end of the second coupling element being connected to the first electrode of the second resonator of the parallel resonant branch near the input terminal in the second pair of parallel resonant branches, the other end of the second coupling element being connected to the second electrode of the second resonator of the parallel resonant branch near the output terminal in the second pair of parallel resonant branches, and one end of the third coupling element being connected to the second electrode of the second resonator of the parallel resonant branch near the input terminal in the second pair of parallel resonant branches, the other end of the third coupling element being connected to the first electrode of the second resonator of the parallel resonant branch near the output terminal in the second pair of parallel resonant branches; wherein, at least one of the parallel resonant branches of the first pair of parallel resonant branches connected by the first coupling structure is different from the second pair of parallel resonant branches connected by the second coupling structure.

[0006] Optionally, the first coupling element is a capacitor.

[0007] Optionally, the second coupling element and the third coupling element are resonators.

[0008] Optionally, the resonator is a thin-film bulk acoustic resonator.

[0009] Optionally, at least one parallel resonant branch is connected between two adjacent series resonant branches; or at least one parallel resonant branch is connected between the input terminal and the series resonant branch closest to the input terminal; or at least one parallel resonant branch is connected between the output terminal and the series resonant branch closest to the output terminal.

[0010] Optionally, at least one of the series resonant branches further includes an inductor connected in series with the first resonator.

[0011] Optionally, at least one of the parallel resonant branches further includes an inductor connected in series with the second resonator.

[0012] Optionally, the filtering circuit further includes: a matching circuit disposed between the input terminal and the series resonant branch closest to the input terminal; and / or disposed between the output terminal and the series resonant branch closest to the output terminal.

[0013] Optionally, the first resonator and the second resonator are thin-film bulk acoustic resonators.

[0014] Optionally, the first coupling structure is connected between the first pair of parallel resonant branches near the middle; and / or the second coupling structure is connected between the second pair of parallel resonant branches near the middle.

[0015] According to a second aspect, embodiments of the present invention provide a duplexer, the duplexer comprising a receiving filter and a transmitting filter, wherein the receiving filter employs the filtering circuit described in any one of the first aspects; and / or the transmitting filter employs the filtering circuit described in any one of the first aspects.

[0016] According to embodiments of the present invention, a filter circuit and a duplexer are provided by respectively setting a first coupling structure and a second coupling structure between two parallel resonant branches. The first coupling structure includes a first coupling element, one end of which is connected to the first electrode of the second resonator of the parallel resonant branch near the input terminal in the first pair of parallel resonant branches, and the other end of which is connected to the second electrode of the second resonator of the parallel resonant branch near the output terminal in the first pair of parallel resonant branches. The second coupling structure includes a second coupling element and a third coupling element, one end of which is connected to the first electrode of the second resonator of the parallel resonant branch near the input terminal in the second pair of parallel resonant branches. The other end of the coupling element is connected to the second electrode of the second resonator in the parallel resonant branch near the output terminal in the second pair of parallel resonant branches, and one end of the third coupling element is connected to the second electrode of the second resonator in the parallel resonant branch near the input terminal in the second pair of parallel resonant branches, and the other end of the third coupling element is connected to the first electrode of the second resonator in the parallel resonant branch near the output terminal in the second pair of parallel resonant branches; wherein, at least one parallel resonant branch of the first pair of parallel resonant branches connected by the first coupling structure is different from the second pair of parallel resonant branches connected by the second coupling structure, which greatly enhances the suppression capability for high-frequency and low-frequency signals outside the passband and improves the filtering performance of the filter circuit. Attached Figure Description

[0017] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings:

[0018] Figure 1 This illustrates a filter circuit in the prior art;

[0019] Figure 2 It shows Figure 1 The insertion loss curve of the filter circuit shown;

[0020] Figure 3 A schematic diagram of a filter circuit according to an embodiment of the present invention is shown;

[0021] Figure 4 It shows Figure 3 The insertion loss curve of the filter circuit shown;

[0022] Figure 5 A schematic diagram of a filter circuit according to another embodiment of the present invention is shown;

[0023] Figure 6 It shows Figure 5The insertion loss curve of the filter circuit shown is presented. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Figure 3 A filter circuit according to an embodiment of the present invention is shown. The filter circuit may include series resonant branches 11A to 11D and parallel resonant branches 12A to 12F. The series resonant branches 11A to 11D are connected in series between the input terminal and the output terminal. Figure 3 The example illustrates 4 series resonant branches and 6 parallel resonant branches; however, those skilled in the art will understand that more or fewer series or parallel resonant branches are feasible. Each series resonant branch includes a first resonator, and each parallel resonant branch includes a second resonator. The first and second resonators can be thin-film bulk acoustic resonators, and those skilled in the art will understand that other types of resonators are also feasible.

[0026] like Figure 3 As shown, one end of the parallel resonant branch 12A closest to the input terminal is connected between the input terminal and the series resonant branch 11A closest to the input terminal; more specifically, it is connected between the matching circuit 14A on the input terminal side and the series resonant branch 11A. One end of the parallel resonant branch 12F closest to the output terminal is connected between the series resonant branch 11D closest to the output terminal and the output terminal; more specifically, it is connected between the matching circuit 14B on the output terminal side and the series resonant branch 11D. One end of the remaining parallel resonant branches 12B-12E is connected between two adjacent series resonant branches, and the other end of the parallel resonant branches 12A-12F is grounded. Figure 3 In this circuit, matching circuits 14A and 14B are inductors. Those skilled in the art should understand that the present invention is not limited thereto, and any circuit or component that can provide inductive reactance or capacitive reactance can be used as a matching circuit.

[0027] It should be noted that, in Figure 3In the example, a parallel resonant branch 12A is connected between the input terminal and the series resonant branch 11A; a parallel resonant branch 12B is connected between the series resonant branches 11A and 11B; a parallel resonant branch 12C is connected between the series resonant branches 11B and 11C; two parallel resonant branches 12D and 12E are connected between the series resonant branches 11C and 11D; and a parallel resonant branch 12F is connected between the output terminal and the series resonant branch 11D. However, those skilled in the art should understand that the present invention is not limited thereto. The nodes between two adjacent series resonant branches, the node between the input terminal and the series resonant branch closest to the input terminal, and the node between the output terminal and the series resonant branch closest to the output terminal do not necessarily all need to be connected to parallel resonant branches. Those skilled in the art can also choose to connect parallel resonant branches only at some nodes; and at least one of these nodes can be connected to two or more parallel resonant branches.

[0028] See also Figure 3 A first coupling structure 13A is provided between the first pair of parallel resonant branches 12B and 12E, wherein the parallel resonant branch 12B is close to the input terminal and the parallel resonant branch 12E is close to the output terminal. The first coupling structure includes a first coupling element, one end of which is connected to the first electrode of the second resonator of the parallel resonant branch 12B, and the other end is connected to the second electrode of the second resonator of the parallel resonant branch 12E.

[0029] Furthermore, a second coupling structure 13B is provided between the second pair of parallel resonant branches 12C and 12D, wherein parallel resonant branch 12C is close to the input terminal and parallel resonant branch 12D is close to the output terminal. The second coupling structure includes a second coupling element and a third coupling element. One end of the second coupling element is connected to the first electrode of the second resonator of the parallel resonant branch 12C, and the other end is connected to the second electrode of the second resonator of the parallel resonant branch 12D. One end of the third coupling element is connected to the second electrode of the second resonator of the parallel resonant branch 12C, and the other end is connected to the first electrode of the second resonator of the parallel resonant branch 12D. That is to say, the second coupling element and the third coupling element in the second coupling structure 13B form a cross structure.

[0030] Figure 4 It shows Figure 3 The insertion loss curve of the filter circuit shown in the figure indicates that the peak value of the low-frequency signal outside the passband is approximately -37dB, and the peak value of the high-frequency signal is approximately -46dB. This is significantly higher than the existing filter circuits where the peak value of the low-frequency signal outside the passband is approximately -23dB and the peak value of the high-frequency signal is approximately -33dB. Figure 3The filter circuit shown in the embodiment of the present invention significantly enhances the suppression capability of high-frequency and low-frequency signals outside the passband by setting a first coupling structure and a second coupling structure between two pairs of parallel resonant branches, thereby improving the performance of the filter circuit.

[0031] Although Figure 3 In the example, the first coupling structure 13A is connected between two non-adjacent parallel resonant branches 12B and 12E, and the second coupling structure 13B is connected between two adjacent parallel resonant branches 12C and 12D. Those skilled in the art should understand that the invention is not limited thereto; the first coupling structure 13A can also be connected between two adjacent parallel resonant branches, and the second coupling structure 13B can also be connected between two non-adjacent parallel resonant branches. Although in Figure 2 In the example, the parallel resonant branches 12D and 12E connected to one end of the first coupling structure 13A and the second coupling structure 13B are connected between the same two series resonant branches 11C and 11D. Those skilled in the art should understand that the invention is not limited thereto, and the first and second coupling structures can be coupled between any two parallel resonant branches. Although in Figure 2 In the example, the parallel resonant branches 12B and 12E connected by the first coupling structure 13A are different from the parallel resonant branches 12C and 12D connected by the second coupling structure 13B. Those skilled in the art should understand that the present invention is not limited thereto. The parallel resonant branches connected by the first coupling structure and the parallel resonant branches connected by the second coupling structure may also have one of the same characteristics, that is, at least one of the parallel resonant branches connected by the first coupling structure and the parallel resonant branches connected by the second coupling structure needs to be different.

[0032] As an optional embodiment of the present invention, the first coupling element in the first coupling structure 13A can be a capacitor.

[0033] As an optional embodiment of the present invention, the second coupling element and the third coupling element in the second coupling structure 13B can be resonators. Further, the resonator can be a thin-film bulk acoustic resonator.

[0034] exist Figure 3In the example, the filter circuit of this embodiment may further include a matching circuit 14A disposed between the input terminal and the series resonant branch 11A closest to the input terminal, and a matching circuit 14B disposed between the output terminal and the series resonant branch 11D closest to the output terminal. Matching circuits 14A and 14B are connected in series with the series resonant branches 11A to 11D. As another optional embodiment of this invention, matching circuits 14A and 14B may also be configured similarly to parallel resonant branches 12A to 12F, i.e., one end of matching circuit 14A is connected between the input terminal and the series resonant branch 11A closest to the input terminal, and the other end is grounded; one end of matching circuit 14B is connected between the output terminal and the series resonant branch 11D closest to the output terminal, and the other end is grounded. Those skilled in the art should understand that matching circuits may also be provided only on one side, either the input terminal side or the output terminal side. Furthermore, matching circuits 14A and 14B are not limited to... Figure 3 The inductor shown in the example can be used as a matching circuit by any circuit or component that can provide inductive or capacitive reactance.

[0035] exist Figure 3 In the series resonant branches 11B and 11C, an inductor connected in series with the first resonator is also included. Figure 1 Compared to the existing filter circuits shown, the passband bandwidth is improved. Although in Figure 3 In the example, only the series resonant branches 11B and 11C also include an inductor connected in series with the first resonator. Those skilled in the art should understand that the present invention is not limited thereto, and the filter circuit of the embodiments of the present invention may have more or fewer arbitrary series resonant branches including inductors.

[0036] exist Figure 3 In the example, parallel resonant branches 12A to 12F all include inductors connected in series with the second resonator. Those skilled in the art should understand that the present invention is not limited thereto; the parallel resonant branches in the embodiments of the present invention may not all include inductors, or more or fewer parallel resonant branches may include inductors.

[0037] Figure 5 A filter circuit according to another embodiment of the present invention is shown, and... Figure 3 The difference in the filter circuit shown is that, Figure 5 The first coupling structure 13A connects parallel resonant branches 12A and 12C, and the second coupling structure 13B connects parallel resonant branches 12A and 12C. The parallel resonant branches connected to the first coupling structure 13A and the second coupling structure 13B have one in common, that is, both the first coupling structure 13A and the second coupling structure 13B are connected to the parallel resonant branch 12C.

[0038] Figure 6 It shows Figure 5 The insertion loss curve of the filter circuit shown is from... Figure 6 As can be seen, the peak value of low-frequency signals outside the passband is approximately -40dB, and the peak value of high-frequency signals is approximately -36dB. Compared with existing filter circuits, Figure 5 The filter circuit shown, by setting a first coupling structure and a second coupling structure between two pairs of parallel resonant branches, also significantly enhances the suppression capability of high-frequency and low-frequency signals outside the passband, thus improving the performance of the filter circuit. However, compared with... Figure 3 Compared to the filter circuit shown, Figure 5 The filter circuit shown has the same ability to suppress low-frequency signals outside the passband as... Figure 3 The filter circuit shown is comparable, but its ability to suppress high-frequency signals outside the passband is not as good. Figure 3 The filter circuit shown.

[0039] Figure 5 The parallel resonant branch connected to the second coupling structure 13B of the filter circuit shown is... Figure 3 The filter circuits shown are the same, but Figure 5 The parallel resonant branch connected to the first coupling structure 13A in the filter circuit shown is... Figure 3 The filter circuits shown are different. Figure 5 The parallel resonant branch connected to the first coupling structure 13A of the filter circuit shown is closer to the input terminal side of the filter circuit. Therefore, it can be seen that the first coupling structure and the second coupling structure connected between the two pairs of parallel resonant branches near the middle can further improve the suppression capability of high-frequency and low-frequency signals outside the passband.

[0040] Furthermore, embodiments of the present invention also provide a duplexer, which includes a receiving filter and a transmitting filter, wherein the receiving filter and / or transmitting filter can employ the filtering circuit described in the embodiments of the present invention above.

[0041] For specific details regarding the receiving filter and transmitting filter in the duplexer of this invention, please refer to the corresponding references. Figures 2 to 6 The relevant descriptions and effects in the illustrated embodiments are for understanding purposes only and will not be repeated here.

[0042] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A filter circuit, characterized by, The filter comprises: at least two series resonance branches, the series resonance branches being connected in series between an input terminal and an output terminal, each of the series resonance branches comprising a first resonator; at least three parallel resonance branches, one end of each of the parallel resonance branches being connected between adjacent two of the series resonance branches, and between the input terminal and the series resonance branch closest to the input terminal, and between the series resonance branch closest to the output terminal and the output terminal, the other end of each of the parallel resonance branches being grounded, each of the parallel resonance branches comprising a second resonator; at least one of the parallel resonance branches is closer to the input terminal relative to the series resonance branch closest to the input terminal, and at least one of the parallel resonance branches is closer to the output terminal relative to the series resonance branch closest to the output terminal; a first coupling structure connected between a first pair of the parallel resonance branches, the first coupling structure comprising a first coupling element, one end of the first coupling element being connected to a first electrode of the second resonator of the parallel resonance branch closest to the input terminal in the first pair of the parallel resonance branches, the other end of the first coupling element being connected to a second electrode of the second resonator of the parallel resonance branch closest to the output terminal in the first pair of the parallel resonance branches; and a second coupling structure connected between a second pair of the parallel resonance branches, the second coupling structure comprising a second coupling element and a third coupling element, one end of the second coupling element being connected to the first electrode of the second resonator of the parallel resonance branch closest to the input terminal in the second pair of the parallel resonance branches, the other end of the second coupling element being connected to the second electrode of the second resonator of the parallel resonance branch closest to the output terminal in the second pair of the parallel resonance branches, and one end of the third coupling element being connected to the second electrode of the second resonator of the parallel resonance branch closest to the input terminal in the second pair of the parallel resonance branches, the other end of the third coupling element being connected to the first electrode of the second resonator of the parallel resonance branch closest to the output terminal in the second pair of the parallel resonance branches; wherein at least one of the parallel resonance branches in the first pair of the parallel resonance branches connected by the first coupling structure is different from at least one of the parallel resonance branches in the second pair of the parallel resonance branches connected by the second coupling structure; the first coupling structure is connected between the first pair of the parallel resonance branches close to the middle; and the second coupling structure is connected between the second pair of the parallel resonance branches close to the middle. The first coupling element is a capacitor.

2. The filter circuit of claim 1, wherein, The second coupling element and the third coupling element are resonators.

3. The filter circuit of claim 1, wherein, The resonators are film bulk acoustic resonators.

4. The filter circuit of claim 3, wherein, at least one of the parallel resonance branches is connected between adjacent two of the series resonance branches; or 5. The filter circuit of claim 1, wherein, at least one of the parallel resonance branches is connected between the input terminal and the series resonance branch closest to the input terminal; or at least one of the parallel resonance branches is connected between the output terminal and the series resonance branch closest to the output terminal. ​ 6. The filter circuit of claim 1, wherein, At least one of the series resonant branches further comprises an inductor connected in series with the first resonator.

7. The filter circuit of claim 1, wherein, At least one of the parallel resonant branches further comprises an inductor connected in series with the second resonator.

8. The filter circuit of claim 1, wherein, Further comprising: a matching circuit arranged between the input terminal and the series resonant branch closest to the input terminal; and / or arranged between the output terminal and the series resonant branch closest to the output terminal.

9. The filter circuit of claim 1, wherein, The first resonator and the second resonator are thin film bulk acoustic resonators.

10. A diplexer comprising a receive filter and a transmit filter, characterized in that, The receive filter employs the filter of claim 1 9. The filter circuit of any one of claims 1-8. and / or The transmit filter employs the claim 1 9. The filter circuit of any of claims 1-8.

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