CN114337594A - Filter circuit and duplexer - Google Patents
Filter circuit and duplexer Download PDFInfo
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- CN114337594A CN114337594A CN202111603984.9A CN202111603984A CN114337594A CN 114337594 A CN114337594 A CN 114337594A CN 202111603984 A CN202111603984 A CN 202111603984A CN 114337594 A CN114337594 A CN 114337594A
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Abstract
The embodiment of the invention provides a filter circuit and a duplexer, wherein the filter circuit comprises: 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, each of the parallel resonant branches including a second resonator; a first coupling structure connected between the first pair of parallel resonant branches; the second coupling structure is connected between the second pair of parallel resonance branches; at least one parallel resonance branch of the first pair of parallel resonance branches connected with the first coupling structure is different from at least one parallel resonance branch of the second pair of parallel resonance branches connected with the second coupling structure.
Description
Technical Field
The invention relates to the technical field of electronic circuits, in particular to a filter circuit and a duplexer.
Background
Filter circuits, particularly, Film Bulk Acoustic Resonator (FBAR) filter circuits are widely used in mobile communication systems such as duplexers of portable mobile terminals.
Fig. 1 shows a conventional multi-stage cascaded FBAR filter circuit, which includes series resonant branches 11A to 11D and parallel resonant branches 12A to 12E, and a matching inductor 14A on the input terminal side and a matching inductor 14B on the output terminal side, wherein the series resonant branches are formed by a single resonator, and the parallel resonant branches are formed by a resonator and an inductor connected in series therewith, however, the filter circuit has a narrow bandwidth, which is difficult to meet the requirements in a wideband signal communication scenario, and as can be seen from the insertion loss graph of fig. 2, the high point of a low-frequency signal outside the passband is about-23 dB, the high point of a high-frequency signal is about-33 dB, and the filter circuit has insufficient suppression capability for the high-frequency and low-frequency signals outside the passband, which seriously affects the filter performance of the filter circuit.
Disclosure of Invention
In view of this, embodiments of the present invention provide a filter circuit and a duplexer, so as to solve at least one of the problems of the prior art that the filter circuit has poor high-frequency and low-frequency signal rejection capability outside the passband and has a narrow bandwidth.
According to a first aspect, an embodiment of the present invention provides a filter circuit, including: 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 resonance branches, one end of each parallel resonance branch is connected between two adjacent series resonance branches, and/or between the input terminal and the series resonance branch closest to the input terminal, and/or between the series resonance branch closest to the output terminal and the output terminal, the other end of each parallel resonance branch is grounded, and each parallel resonance branch comprises a second resonator; a first coupling structure connected between a first pair of parallel resonance arms, the first coupling structure including a first coupling element having one end connected to a first electrode of a second resonator of a parallel resonance arm of the first pair of parallel resonance arms that is close to the input terminal and the other end connected to a second electrode of the second resonator of the parallel resonance arm of the first pair of parallel resonance arms that is close to the output terminal; and a second coupling structure connected between a second pair of parallel resonant legs, the second coupling structure including 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 resonance branch of the second pair of parallel resonance branches that is close to the input terminal, the other end of the second coupling element is connected to the second electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the output terminal, and one end of the third coupling element is connected to the second electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the input terminal, the other end of the third coupling element is connected to the first electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the output terminal; at least one parallel resonance branch of the first pair of parallel resonance branches connected with the first coupling structure is different from at least one parallel resonance branch of the second pair of parallel resonance branches connected with the second coupling structure.
Optionally, the first coupling element is a capacitor.
Optionally, the second coupling element and the third coupling element are resonators.
Optionally, the resonator is a film bulk acoustic resonator.
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.
Optionally, at least one of the series resonant legs further comprises an inductor connected in series with the first resonator.
Optionally, at least one of the parallel resonant legs further comprises an inductor connected in series with the second resonator.
Optionally, the filter circuit further includes: a matching circuit disposed between the input terminal and the series resonant branch closest to the input terminal; and/or between the output terminal and the series resonant branch closest to the output terminal.
Optionally, the first resonator and the second resonator are film bulk acoustic resonators.
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 portion.
According to a second aspect, an embodiment of the present invention provides a duplexer, where the duplexer includes a receiving filter and a transmitting filter, where the receiving filter employs the filter circuit of any one of the first aspects; and/or the transmission filter employs the filter circuit of any one of the above first aspects
According to the filter circuit and the duplexer of the embodiment of the present invention, by respectively providing the first coupling structure and the second coupling structure between the two parallel resonance arms, wherein the first coupling structure includes the first coupling element, one end of the first coupling element is connected to the first electrode of the second resonator of the parallel resonance arm close to the input terminal of the first pair of parallel resonance arms, and the other end of the first coupling element is connected to the second electrode of the second resonator of the parallel resonance arm close to the output terminal of the first pair of parallel resonance arms; 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 resonance arm of the second pair of parallel resonance arms close to the input terminal, the other end of the second coupling element is connected to the second electrode of the second resonator of the parallel resonance arm of the second pair of parallel resonance arms close to the output terminal, and one end of the third coupling element is connected to the second electrode of the second resonator of the parallel resonance arm of the second pair of parallel resonance arms close to the input terminal, the other end of the third coupling element is connected to the first electrode of the second resonator of the parallel resonance arm of the second pair of parallel resonance arms close to the output terminal; at least one parallel resonance branch of the first pair of parallel resonance branches connected with the first coupling structure is different from at least one parallel resonance branch of the second pair of parallel resonance branches connected with the second coupling structure, so that the suppression capability of high-frequency and low-frequency signals outside a pass band is greatly enhanced, and the filtering performance of the filter circuit is improved.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
FIG. 1 illustrates a prior art filter circuit;
FIG. 2 shows a graph of insertion loss for the filter circuit shown in FIG. 1;
FIG. 3 shows a schematic diagram of a filter circuit according to an embodiment of the invention;
FIG. 4 shows a graph of insertion loss for the filter circuit shown in FIG. 3;
FIG. 5 shows a schematic diagram of a filter circuit according to another embodiment of the invention;
fig. 6 shows a graph of the insertion loss of the filter circuit shown in fig. 5.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 3 shows a filter circuit according to an embodiment of the present invention, which may include series resonant branches 11A to 11D and parallel resonant branches 12A to 12F, the series resonant branches 11A to 11D being connected in series between an input terminal and an output terminal, in the example of fig. 3, 4 series resonant branches and 6 parallel resonant branches are exemplarily shown, however, it should be understood by those skilled in the art that more or fewer series resonant branches or parallel resonant branches are possible. Each series resonant branch comprises a first resonator and each parallel resonant branch comprises a second resonator, which may be film bulk acoustic resonators, as will be appreciated by those skilled in the art, other types of resonators are also possible.
As shown in fig. 3, 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, 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, between the matching circuit 14B on the output terminal side and the series resonant branch 11D; one end of each of the other parallel resonant branches 12B to 12E is connected between two adjacent series resonant branches, and the other end of each of the parallel resonant branches 12A to 12F is grounded. In fig. 3, the matching circuits 14A and 14B are inductors, and those skilled in the art will appreciate that the present invention is not limited thereto, and any circuit or component capable of providing inductive reactance or capacitive reactance can be used as the matching circuit.
It should be noted that, in the example of fig. 3, 1 parallel resonant branch 12A is connected between the input terminal and the series resonant branch 11A, 1 parallel resonant branch 12B is connected between the series resonant branches 11A and 11B, 1 parallel resonant branch 12C is connected between the series resonant branches 11B and 11C, 2 parallel resonant branches 12D and 12E are connected between the series resonant branches 11C and 11D, and 1 parallel resonant branch 12F is connected between the output terminal and the series resonant branch 11D. However, it should be understood by those skilled in the art that the present invention is not limited thereto, and nodes between two adjacent series resonant branches, a node between the input terminal and the series resonant branch closest to the input terminal, and a node between the output terminal and the series resonant branch closest to the output terminal, which are not necessarily all connected with a parallel resonant branch, may be selected by those skilled in the art to connect the parallel resonant branches at only a part of the nodes; and at least one of these nodes may connect two or more parallel resonant legs.
With continued reference to fig. 3, a first coupling structure 13A is provided between the first pair of parallel resonant legs 12B and 12E, wherein the parallel resonant leg 12B is close to the input terminal and the parallel resonant leg 12E is close to the output terminal, the first coupling structure comprising a first coupling element having one end connected to the first electrode of the second resonator of the parallel resonant leg 12B and the other end connected to the second electrode of the second resonator of the parallel resonant leg 12E.
And, a second coupling structure 13B is provided between the second pair of parallel resonance arms 12C and 12D, in which the parallel resonance arm 12C is close to the input terminal and the parallel resonance arm 12D is close to the output terminal, 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 resonance arm 12C, the other end being connected to the second electrode of the second resonator of the parallel resonance arm 12D, one end of the third coupling element being connected to the second electrode of the second resonator of the parallel resonance arm 12C, the other end being connected to the first electrode of the second resonator of the parallel resonance arm 12D, that is, the second coupling element and the third coupling element in the second coupling structure 13B form a cross structure.
Fig. 4 shows an insertion loss curve diagram of the filter circuit shown in fig. 3, and it can be seen from the diagram that a high point of a low-frequency signal outside a passband is about-37 dB, a high point of a high-frequency signal is about-46 dB, and compared with a high point of a low-frequency signal outside a passband which is about-23 dB and a high point of a high-frequency signal which is about-33 dB in a filter circuit in the prior art, the filter circuit shown in fig. 3 according to the embodiment of the present invention greatly enhances the high-frequency and low-frequency signal rejection capability outside the passband by arranging the first coupling structure and the second coupling structure between two pairs of parallel resonant branches, thereby improving the performance of the filter circuit.
Although in the example of fig. 3, the first coupling structure 13A is connected between the non-adjacent two parallel resonant branches 12B and 12E, and the second coupling structure 13B is connected between the adjacent two parallel resonant branches 12C and 12D, it should be understood by those skilled in the art that the present invention is not limited thereto, and the first coupling structure 13A may also be connected between the adjacent two parallel resonant branches, and the second coupling structure 13B may also be connected between the non-adjacent two parallel resonant branches. Although the parallel resonant branches 12D and 12E to which one ends of the first coupling structure 13A and the second coupling structure 13B are connected between the same two series resonant branches 11C and 11D in the example of fig. 2, it should be understood by those skilled in the art that the present invention is not limited thereto, and the first coupling structure and the second coupling structure may be coupled between any two parallel resonant branches. Although in the example of fig. 2, the parallel resonant branches 12B and 12E connected to the first coupling structure 13A are different from the parallel resonant branches 12C and 12D connected to the second coupling structure 13B, it should be understood by those skilled in the art that the present invention is not limited thereto, and the parallel resonant branch connected to the first coupling structure and the parallel resonant branch connected to the second coupling structure may be the same, that is, the parallel resonant branch connected to the first coupling structure and the parallel resonant branch connected to the second coupling structure are at least different.
As an alternative to the embodiment of the present invention, the first coupling element in the first coupling structure 13A may be a capacitor.
As an alternative to the embodiment of the present invention, the second coupling element and the third coupling element in the second coupling structure 13B may be resonators. Further, the resonator may be a film bulk acoustic resonator.
In the example of fig. 3, the filter circuit of the embodiment of the present invention may further include a matching circuit 14A provided between the input terminal and the series-resonant branch 11A closest to the input terminal, and a matching circuit 14B provided between the output terminal and the series-resonant branch 11D closest to the output terminal, the matching circuits 14A and 14B being connected in series with the series-resonant branches 11A to 11D. As another alternative of the embodiment of the present invention, the matching circuits 14A and 14B may also be the same as the parallel resonant branches 12A to 12F, that is, one end of the 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 the 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. It should be understood by those skilled in the art that the matching circuit may be provided only on one of the input terminal side or the output terminal side. In addition, the matching circuits 14A and 14B are not limited to the inductor illustrated in fig. 3, and any circuit or component capable of providing an inductive reactance or a capacitive reactance can be used as the matching circuit.
In fig. 3, since the series resonant branches 11B and 11C further include an inductor connected in series with the first resonator, the passband bandwidth is improved compared to the prior art filter circuit shown in fig. 1. Although in the example of fig. 3 only the series resonant legs 11B and 11C further comprise an inductor connected in series with the first resonator, it will be appreciated by a person skilled in the art that the invention is not so limited and that more or less any series resonant legs may comprise an inductor in the filter circuit of an embodiment of the invention.
In the example of fig. 3, the parallel resonant legs 12A to 12F each comprise an inductor connected in series with the second resonator. Those skilled in the art will appreciate that the present invention is not so limited and that no parallel resonant legs of embodiments of the present invention may include an inductor, or more or fewer parallel resonant legs may include an inductor.
Fig. 5 shows a filter circuit according to another embodiment of the present invention, which is different from the filter circuit shown in fig. 3 in that a first coupling structure 13A in fig. 5 connects parallel resonant branches 12A and 12C, a second coupling structure 13B connects parallel resonant branches 12A and 12C, and one of the parallel resonant branches to which the first coupling structure 13A and the second coupling structure 13B are connected is the same, that is, the first coupling structure 13A and the second coupling structure 13B are both connected to the parallel resonant branch 12C.
Fig. 6 shows a graph of the insertion loss of the filter circuit of fig. 5, and it can be seen from fig. 6 that the high point of the low frequency signal outside the passband is about-40 dB and the high point of the high frequency signal is about-36 dB. Compared with the filter circuit in the prior art, the filter circuit shown in fig. 5 has the advantages that the first coupling structure and the second coupling structure are arranged between the two pairs of parallel resonance branches, so that the high-frequency and low-frequency signal suppression capability outside the passband is greatly enhanced, and the performance of the filter circuit is improved. However, compared to the filter circuit shown in fig. 3, the filter circuit shown in fig. 5 has a suppression capability for low-frequency signals outside the passband comparable to that of the filter circuit shown in fig. 3, but has a suppression capability for high-frequency signals outside the passband inferior to that of the filter circuit shown in fig. 3.
The parallel resonant branch connected to the second coupling structure 13B of the filter circuit shown in fig. 5 is the same as the filter circuit shown in fig. 3, while the parallel resonant branch connected to the first coupling structure 13A of the filter circuit shown in fig. 5 is different from the filter circuit shown in fig. 3, and the parallel resonant branch connected to the first coupling structure 13A of the filter circuit shown in fig. 5 is closer to the input terminal side of the filter circuit, so that the first coupling structure and the second coupling structure are connected between the two pairs of parallel resonant branches close to the middle, and the suppression capability for high-frequency and low-frequency signals outside the passband can be further improved.
Further, an embodiment of the present invention also provides a duplexer, where the duplexer includes a receiving filter and a transmitting filter, and the receiving filter and/or the transmitting filter may employ the filtering circuit of the embodiment of the present invention as described above.
The details of the receiving filter and the transmitting filter in the duplexer according to the embodiment of the present invention may be understood by referring to the corresponding related descriptions and effects in the embodiments shown in fig. 2 to fig. 6, and are not described herein again.
Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.
Claims (11)
1. 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 resonance branches, one end of each parallel resonance branch is connected between two adjacent series resonance branches, and/or between the input terminal and the series resonance branch closest to the input terminal, and/or between the series resonance branch closest to the output terminal and the output terminal, the other end of each parallel resonance branch is grounded, and each parallel resonance branch comprises a second resonator;
a first coupling structure connected between a first pair of parallel resonance arms, the first coupling structure including a first coupling element having one end connected to a first electrode of a second resonator of a parallel resonance arm of the first pair of parallel resonance arms that is close to the input terminal and the other end connected to a second electrode of the second resonator of the parallel resonance arm of the first pair of parallel resonance arms that is close to the output terminal; and
a second coupling structure connected between a second pair of parallel resonant legs, the second coupling structure including 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 resonance branch of the second pair of parallel resonance branches that is close to the input terminal, the other end of the second coupling element is connected to the second electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the output terminal, and one end of the third coupling element is connected to the second electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the input terminal, the other end of the third coupling element is connected to the first electrode of the second resonator of the parallel resonance branch of the second pair of parallel resonance branches that is close to the output terminal;
at least one of the first pair of parallel resonant branches connected to the first coupling structure and the second pair of parallel resonant branches connected to the second coupling structure is different from the other.
2. The filter circuit of claim 1, wherein the first coupling element is a capacitor.
3. The filter circuit of claim 1, wherein the second coupling element and the third coupling element are resonators.
4. The filter circuit of claim 3, wherein the resonator is a film bulk acoustic resonator.
5. The filter circuit according to claim 1, wherein at least one of the parallel resonant branches 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 of the parallel resonant branches is connected between the output terminal and the series resonant branch closest to the output terminal.
6. The filter circuit of claim 1, wherein at least one of the series-resonant legs 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 legs further comprises an inductor connected in series with a second resonator.
8. The filter circuit of claim 1, further comprising:
a matching circuit disposed between the input terminal and the series resonant branch closest to the input terminal; and/or
Is 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 film bulk acoustic resonators.
10. The filter circuit according to any of claims 1-9, wherein the first coupling structure is connected between the first pair of parallel resonant legs near the middle portion; and/or
The second coupling structure is connected between the second pair of parallel resonant branches near the middle.
11. A duplexer comprising a receive filter and a transmit filter, characterized in that,
the receiving filter adopts the filter circuit of any one of claims 1-10; and/or
The transmission filter employs the filter circuit of any one of claims 1-10.
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| CN202111603984.9A CN114337594A (en) | 2021-12-24 | 2021-12-24 | Filter circuit and duplexer |
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| CN202111603984.9A CN114337594A (en) | 2021-12-24 | 2021-12-24 | Filter circuit and duplexer |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114465601A (en) * | 2022-04-13 | 2022-05-10 | 苏州汉天下电子有限公司 | Filter, duplexer and multiplexer |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114465601A (en) * | 2022-04-13 | 2022-05-10 | 苏州汉天下电子有限公司 | Filter, duplexer and multiplexer |
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