CN113556095A - Cross-coupled acoustic filter - Google Patents
Cross-coupled acoustic filter Download PDFInfo
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- CN113556095A CN113556095A CN202110835188.1A CN202110835188A CN113556095A CN 113556095 A CN113556095 A CN 113556095A CN 202110835188 A CN202110835188 A CN 202110835188A CN 113556095 A CN113556095 A CN 113556095A
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- 230000008878 coupling Effects 0.000 claims abstract description 44
- 238000010168 coupling process Methods 0.000 claims abstract description 44
- 238000005859 coupling reaction Methods 0.000 claims abstract description 44
- 239000003990 capacitor Substances 0.000 claims description 11
- 238000003780 insertion Methods 0.000 abstract description 13
- 230000037431 insertion Effects 0.000 abstract description 13
- 230000001965 increasing effect Effects 0.000 abstract description 8
- 230000005540 biological transmission Effects 0.000 abstract description 6
- 238000010586 diagram Methods 0.000 description 5
- 238000006880 cross-coupling reaction Methods 0.000 description 4
- 230000001629 suppression Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 230000005764 inhibitory process Effects 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000010295 mobile communication Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000010897 surface acoustic wave method Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02007—Details of bulk acoustic wave devices
- H03H9/02062—Details relating to the vibration mode
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/56—Monolithic crystal filters
- H03H9/564—Monolithic crystal filters implemented with thin-film techniques
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/54—Filters comprising resonators of piezo-electric or electrostrictive material
- H03H9/58—Multiple crystal filters
- H03H9/582—Multiple crystal filters implemented with thin-film techniques
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
- H03H9/703—Networks using bulk acoustic wave devices
- H03H9/706—Duplexers
Abstract
A capacitive cross-coupled acoustic filter comprising: a series main circuit formed by connecting m first acoustic resonators in series between an input terminal and an output terminal; one end of each of the n parallel branches is connected to m-1 nodes between the adjacent first acoustic resonators and/or the head end and the tail end of the series main loop, and the other end of each of the n parallel branches is grounded; n parallel branches are numbered in sequence, and each parallel branch comprises at least one second acoustic resonator; at least 2 coupling branches connected with one end of the n parallel branches, wherein the difference value between the serial number of the parallel branch connected with the first end and the serial number of the parallel branch connected with the second end is more than or equal to 2; the first end of at least one of the coupling branches is connected between the first end and the second end of another of the coupling branches, and the second end is connected outside the first end and the second end of the other of the coupling branches. According to the acoustic filter of the invention, an extra transmission zero is added, the rejection on both sides of the pass band is increased and the in-band insertion loss is optimized.
Description
Technical Field
The present invention relates to a cross-coupled acoustic filter, and more particularly, to a capacitive cross-coupled acoustic filter.
Background
In recent years, with the progress of mobile communication systems, portable information terminals and the like have rapidly spread. Related efforts have been made to reduce the size and improve the performance of the above terminals. Both analog and digital are used in mobile telephone systems. It has been proposed to employ a piezoelectric surface acoustic wave filter or a thin film bulk acoustic wave (SAW or FBAR) resonator filter for use in devices of a mobile communication system.
Fig. 1A to 1C respectively show circuit diagrams of an acoustic filter constructed by using FBARs in the related art. In the prior art shown in fig. 1A, the left/right roll-off and the near stop-band rejection of the filter are modified by cascading the electromagnetic LC filter circuit 00 and the ladder-type FBAR network composed of the FBAR resonators 131-133 and connecting the two parallel branches FBARs with the inductor/capacitor 20. However, the adopted method can only adjust the roll-off and the inhibition of one side independently, and cannot control the inhibition of both sides simultaneously.
In the prior art shown in fig. 1B, the extra capacitors 103 and 104 are used to connect the FBARs 101 and 102 in parallel to adjust their resonant frequencies so as to optimize the roll-off coefficient and in-band matching of the whole filter/duplexer, but this approach belongs to self-tuning of the FBARs themselves and intrinsic tuning, and cannot generate extra transmission zeros and transmission poles.
In the prior art shown in fig. 1C, a mode of connecting the electromagnetic LC network 11 and the FBAR 12 in series is adopted to achieve the effect of enhancing the sideband roll-off in the conventional duplexer, and this mode belongs to simple performance superposition, increases the insertion loss, increases the difficulty of matching the antenna end, and is not beneficial to practical application.
Disclosure of Invention
It is therefore an object of the present invention to provide an FBAR filter that overcomes the above technical obstacles.
The invention provides a cross-coupled acoustic filter, comprising:
a series main circuit formed by connecting m first acoustic resonators in series between an input terminal and an output terminal, wherein m is an integer of 3 or more;
one end of each of the n parallel branches is connected to m-1 nodes between adjacent first acoustic resonators and/or the head end and the tail end of the series main loop respectively, and the other end of each of the n parallel branches is grounded; n parallel branches are numbered in sequence, each parallel branch comprises at least one second acoustic resonator, and n is an integer greater than or equal to 4;
at least 2 coupling branches connected with one ends of the n parallel branches, wherein the difference value between the serial number of the parallel branch connected with the first end of each coupling branch and the serial number of the parallel branch connected with the second end of each coupling branch is more than or equal to 2;
the first end of at least one coupling branch is connected between the first end and the second end of another coupling branch, and the second end of the at least one coupling branch is connected outside the first end and the second end of the another coupling branch.
And a matching circuit is further arranged between the input terminal and/or the output terminal and the series main loop. Wherein the matching circuit comprises a capacitor and/or an inductor in series and/or in parallel.
Wherein each parallel branch further comprises a series inductance between the second FBAR resonator and ground potential.
Wherein all or a portion of the coupling branch comprises a series capacitor or a series inductor.
The invention also provides a duplexer comprising a cross-coupled acoustic filter according to any of the preceding claims.
According to the acoustic filter disclosed by the invention, a plurality of cross-coupling structures with different polarities are introduced on the FBAR ladder network, an extra transmission zero point is added, the suppression on two sides of a pass band is increased, and the in-band insertion loss is optimized.
The stated objects of the invention, as well as other objects not listed here, are met within the scope of the independent claims of the present application. Embodiments of the invention are defined in the independent claims, with specific features being defined in the dependent claims.
Drawings
The technical solution of the present invention is explained in detail below with reference to the accompanying drawings, in which:
FIGS. 1A-1C show circuit diagrams of prior art FBAR filters, respectively;
fig. 2 shows a circuit diagram of a cross-coupled acoustic filter according to the invention;
FIG. 3A shows a circuit diagram of a cross-coupled acoustic filter according to one embodiment of the present invention;
FIG. 3B shows the insertion loss of the cross-coupled acoustic filter of FIG. 3A;
FIG. 4A shows a circuit diagram of a cross-coupled acoustic filter according to another embodiment of the present invention;
fig. 4B shows the insertion loss of the cross-coupled acoustic filter of fig. 4A.
Detailed Description
The features and technical effects of the technical solution of the present invention are described in detail below with reference to the accompanying drawings and illustrative embodiments, and a cross-coupled acoustic filter is disclosed. It is noted that like reference numerals refer to like structures and that the terms "first", "second", "upper", "lower", and the like as used herein may be used to modify various device structures. These modifications do not imply a spatial, sequential, or hierarchical relationship to the structures of the modified devices unless specifically stated.
As shown in fig. 2, the cross-coupled acoustic filter according to the principles of the present invention comprises a series-parallel network of a plurality of first acoustic resonators (FBARs) and a plurality of inductors between a first (input) terminal a and a second (output) terminal B, wherein m (m is an integer equal to or greater than 3) first FBAR resonators S1, S2 … Sm are connected in series in sequence to form a series main loop, N (where N is an integer equal to or greater than 4) parallel branches are connected at one end to m-1 nodes N1, N2 … Nm-1 between adjacent first FBAR resonators and/or at the head end of the series main loop and at the other end to ground, N parallel branches are numbered in sequence, each parallel branch comprises at least one second acoustic resonator, i.e. each parallel branch comprises a second FBAR resonator P1, P2 … Pm-1 connected in series to ground, preferably, inductors L1, L2 … Lm-1 can be additionally connected in series on the respective parallel branches in addition to the m-1 second FBAR resonators P1, P2.. Pm-1 to achieve an adjustment of the zero-order point, which has no additional influence on the coupled section. At least 2 capacitive coupling structures C1, C2 … Cm-3 are coupled between m-1 nodes and preferably the difference between the number of nodes coupled at the first end (e.g., N1, N2) and the number of nodes coupled at the second end (e.g., N3, N4) of each coupling structure is greater than or equal to 2, such that the node coupled at the first end of the latter coupling structure is between the two coupling nodes of the former coupling structure. The first end of at least one coupling branch is connected between the first end and the second end of another coupling branch, and the second end of the at least one coupling branch is connected outside the first end and the second end of the another coupling branch. Preferably, the matching circuit is further included between the input terminal a and the series main loop, the matching circuit in the embodiment of fig. 2 includes a capacitor C0 (only shown in series in the figure, actually, parallel in the figure, or a plurality of LCs in series and parallel), which are connected in series or in parallel, and the matching circuit is further included between the output terminal B and the series main loop, and the matching circuit in the embodiment of fig. 2 includes an inductor L0 (only shown in parallel in the figure, actually, series in the figure, or a plurality of LCs in series and parallel), which are connected in parallel or in series, and are used to adjust the loading phase of the filter to satisfy the basic chebyshev filter function. Preferably, the coupling structures are all capacitors, and the capacitive negative coupling structure can bring about the functions of increasing the suppression on two sides of the passband and optimizing the in-band insertion loss. It is further preferred that at least one of the coupling structures is inductive and the remaining part is capacitive (i.e. the coupling structure is partly capacitive), the addition of a coupling structure of different polarity will also produce a similar effect to capacitive coupling.
Fig. 3A shows an N79 full band filter with a frequency band of 4.4-5GHZ, which is formed by cross-coupled acoustic filters, according to a preferred embodiment of the present invention. Where m is 5, the two coupling structures are capacitors C1 and C2, the four inductances added to the parallel branch are L1-1.07911 pH, L2-1.54999 pH, L3-3.19846 pH and L4-1.10204 pH, respectively, and with respect to port C0, for example, 0-50pF, L0, for example, 0-50nH, and L1-L4, for example, 0-10 nH. The L2 and the L3 are important parts for expanding the bandwidth of the whole filter, the action mechanism is that the series resonance frequency of the P2 and the P3 is reduced, and the equivalent electromechanical coupling coefficient (kteff) which is the representation value of the difference between the resonance frequencies of the FBARs is increased, so that the bandwidth is expanded. Two coupling capacitances are loaded between P1 and P3 and P2 and P4, increasing the near stop band rejection and roll-off across the filter. As also described with reference to fig. 2, the matching circuits on both sides, i.e., the matching devices C0 and L0, are adjusted in phase.
Fig. 3B shows the insertion loss of the cross-coupled acoustic filter of fig. 3A, where the horizontal axis is the frequency GHz and the vertical axis is the insertion loss dB. The curve marked by the dotted line in the figure is the circuit simulation result before no cross-coupling is added, and the solid line is the insertion loss of the added new scheme. It can be obviously seen that after the coupling capacitor is added, the zero point is added on the right side of the near stop band, the near stop band inhibition on both sides is enhanced by 5-10dB, and the right side of the pass band is collapsed to a certain degree.
Fig. 4A shows an N79 full band filter with a frequency band of 4.4-5GHZ, which is formed by cross-coupled acoustic filters, according to another preferred embodiment of the present invention. Where m is chosen to be 5, one of the two coupling structures Lc and the other Cc, the four inductances added to the parallel branches are respectively L1-0.992685 pH, L2-1.99773 pH, L3-4.09519 pH and L4-1.19841 pH, C0 is, for example, 0-50pF, L0 is, for example, 0-50nH, alternatively L1-L4 is chosen to be 0-10 nH. The L2 and the L3 are important parts for expanding the bandwidth of the whole filter, the action mechanism is that the series resonance frequency of the P2 and the P3 is reduced, and the equivalent electromechanical coupling coefficient (kteff) which is the representation value of the difference between the resonance frequencies of the FBARs is increased, so that the bandwidth is expanded. The coupling inductor Lc and the coupling capacitor Cc are respectively loaded between P1 and P3 and P2 and P4, and the near stop band rejection and roll-off on two sides of the filter are increased. The matching devices C0 and L0 on both sides adjust the respective phases.
Fig. 4B shows the insertion loss of the cross-coupled acoustic filter of fig. 4A, where the horizontal axis is the frequency GHz and the vertical axis is the insertion loss dB. The curve marked by the dotted line in the figure is the circuit simulation result before no cross-coupling is added, and the solid line is the insertion loss of the added new scheme. Compared with pure capacitive coupling, the suppression level of the lower sideband (frequency band lower than the lower edge of the passband) is obviously enhanced, and an additional transmission zero point is added. At the same time, the upper sideband (the band above the upper edge of the passband) rejection also remains at a 30dB level.
According to the acoustic filter disclosed by the invention, a plurality of cross-coupling structures with different polarities are introduced on the FBAR ladder network, an extra transmission zero point is added, the suppression on two sides of a pass band is increased, and the in-band insertion loss is optimized.
While the invention has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the disclosed device structure and its method of manufacture will include all embodiments falling within the scope of the present invention.
Claims (6)
1. A cross-coupled acoustic filter comprising:
a series main circuit formed by connecting m first acoustic resonators in series between an input terminal and an output terminal, wherein m is an integer of 3 or more;
one end of each of the n parallel branches is connected to m-1 nodes between adjacent first acoustic resonators and/or the head end and the tail end of the series main loop respectively, and the other end of each of the n parallel branches is grounded; n parallel branches are numbered in sequence, each parallel branch comprises at least one second acoustic resonator, and n is an integer greater than or equal to 4;
at least 2 coupling branches connected with one ends of the n parallel branches, wherein the difference value between the serial number of the parallel branch connected with the first end of each coupling branch and the serial number of the parallel branch connected with the second end of each coupling branch is more than or equal to 2;
the first end of at least one coupling branch is connected between the first end and the second end of another coupling branch, and the second end of the at least one coupling branch is connected outside the first end and the second end of the another coupling branch.
2. The cross-coupled acoustic filter of claim 1, wherein the input and/or output terminals further comprise a matching circuit with the main series loop.
3. A cross-coupled acoustic filter according to claim 2, wherein the matching circuit comprises a capacitor and/or an inductor in series and/or in parallel.
4. The cross-coupled acoustic filter of claim 1, wherein each parallel branch further comprises a series inductance between the second FBAR resonator and ground potential.
5. The cross-coupled acoustic filter of claim 1, wherein all or a portion of the coupling branches comprise a series capacitor or a series inductor.
6. A duplexer comprising a cross-coupled acoustic filter according to any of claims 1-5.
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| CN202110835188.1A CN113556095B (en) | 2021-07-23 | 2021-07-23 | Cross-coupled acoustic filter |
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| CN202110835188.1A CN113556095B (en) | 2021-07-23 | 2021-07-23 | Cross-coupled acoustic filter |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116865714A (en) * | 2023-09-05 | 2023-10-10 | 深圳新声半导体有限公司 | Filter for N79 frequency band |
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| CN113556095B (en) | 2024-04-19 |
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