CN117097298B - Filter circuit for improving out-of-band rejection - Google Patents
Filter circuit for improving out-of-band rejection Download PDFInfo
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- CN117097298B CN117097298B CN202311356509.5A CN202311356509A CN117097298B CN 117097298 B CN117097298 B CN 117097298B CN 202311356509 A CN202311356509 A CN 202311356509A CN 117097298 B CN117097298 B CN 117097298B
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- 238000010897 surface acoustic wave method Methods 0.000 claims abstract description 115
- 239000000178 monomer Substances 0.000 claims abstract description 114
- 230000000452 restraining effect Effects 0.000 claims abstract description 16
- 239000002131 composite material Substances 0.000 claims description 5
- 230000005764 inhibitory process Effects 0.000 claims description 2
- 230000001629 suppression Effects 0.000 description 44
- 238000010586 diagram Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 238000004891 communication Methods 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 238000003780 insertion Methods 0.000 description 2
- 230000037431 insertion Effects 0.000 description 2
- 230000006978 adaptation Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000010295 mobile communication Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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Classifications
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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
- H03H9/64—Filters using surface acoustic waves
- H03H9/6489—Compensation of undesirable effects
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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
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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
Abstract
The invention discloses a filter circuit for improving out-of-band rejection, which comprises a filter connected between an input end and an output end, and the filter circuit also comprises a left side rejection resonance structure or/and a right side rejection resonance structure; the left side restraining resonance structure comprises at least one left side surface acoustic wave resonator monomer or a left side bulk acoustic wave resonator monomer, the right side restraining resonance structure comprises at least one right side surface acoustic wave resonator monomer or a right side bulk acoustic wave resonator monomer, positive resonance peaks of any one left side surface acoustic wave resonator monomer or left side bulk acoustic wave resonator monomer are all positioned on the left side of a passband of the filter, and positive resonance peaks of any one right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer are all positioned on the right side of the passband of the filter. The filter circuit can improve the out-of-band rejection performance without affecting the performance of the filter, and can realize the out-of-band rejection of the low-frequency stop band or/and the high-frequency stop band of the filter.
Description
Technical Field
The invention relates to the technical field of filters, in particular to a filter circuit for improving out-of-band rejection.
Background
In recent years, with the rapid development of mobile communication technology, filters such as mobile phones and base stations are required in electronic products. The filter is mainly used for filtering out unwanted radio frequency signals and improving the performance of a transmitting path or a receiving path. The current communication system is developed towards multiple frequency bands, multiple systems and multiple modes, the frequency bands used are more and more dense, in order to improve the communication quality and reduce the interference between the frequency bands, higher requirements are required for the out-of-band rejection of the filter, in the prior art, the number of filter stages is generally increased to improve the out-of-band rejection, the method can improve the out-of-band rejection to a certain extent, but the improvement effect is limited, and meanwhile, due to the influence of external electromagnetic environment, particularly along with the increase of communication equipment, higher additional rejection requirements are required for the out-of-band designated frequency of the filter in order to reduce the interference between the frequency bands.
In order to solve the above-mentioned problems, an embodiment of the present invention provides a filter, a multiplexer, and a radio frequency front end module, which are described in a publication CN202310785336.2, including: a series arm resonator connected between the input terminal and the output terminal; a parallel arm resonator having one end connected to the series arm resonator and the other end connected to a ground terminal; a first resonator; the series arm resonator includes a second resonator, the first resonator being connected in parallel with the second resonator; the anti-resonant frequency of the first resonator is smaller than the resonant frequency of the parallel arm resonator to generate transmission zero at the low-frequency stop band outside the filter passband, however, the structure is not reasonable, and although the second resonator and the first resonator are connected in parallel, the purpose of trapping outside the filter passband and improving the out-of-band rejection performance is achieved, but the trap circuit formed by connecting the second resonator and the first resonator in parallel is a part of a series branch of the ladder filter, which negatively affects the overall performance of the filter, in particular, the trap circuit generates a rejection zero due to the characteristic that the circuit is open when passing through the parallel resonance, that is, generates a zero when the anti-resonant peak frequency is open, which may generate additional insertion loss inside the filter passband.
In addition, the filter with the structure can only generate transmission zero points on the low-frequency stop band, but cannot be realized on the high-frequency stop band, and meanwhile, the out-of-band zero point restraining frequency also needs to meet the requirement of a formula, so that the calculation and the design are complex.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: a filter circuit for improving out-of-band rejection is provided, which can improve out-of-band rejection of a filter circuit without affecting the performance of the filter itself, and can realize out-of-band rejection of a specified frequency of a low-frequency stop band or/and a high-frequency stop band of the filter.
In order to solve the technical problems, the technical scheme of the invention is as follows: the filter circuit comprises a filter connected between an input end and an output end, and further comprises a left side suppression resonance structure and a right side suppression resonance structure, wherein one ends of the left side suppression resonance structure and the right side suppression resonance structure are connected between the output end and the input end, and the other ends of the left side suppression resonance structure and the right side suppression resonance structure are grounded; the left side restraining resonance structure comprises at least one left side surface acoustic wave resonator monomer or left side bulk acoustic wave resonator monomer, the right side restraining resonance structure comprises at least one right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer, positive resonance peaks of any one left side surface acoustic wave resonator monomer or left side bulk acoustic wave resonator monomer are all positioned on the left side of a passband of the filter, and positive resonance peaks of any one right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer are all positioned on the right side of the passband of the filter.
As a preferable mode, the left side suppressing resonant structure includes at least two left side surface acoustic wave resonator units or left side bulk acoustic wave resonator units, and positive resonant frequencies of at least two left side surface acoustic wave resonator units or left side bulk acoustic wave resonator units are different from each other.
As a preferable mode, the right side suppressing resonant structure includes at least two right side surface acoustic wave resonator monomers or right side bulk acoustic wave resonator monomers, and positive resonant frequencies of at least two right side surface acoustic wave resonator monomers or right side bulk acoustic wave resonator monomers in each right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer are different.
As a preferred solution, the left side rejection resonant structure is connected between the input terminal and the filter or between the output terminal and the filter; the right side reject resonator structure is connected between the input end and the filter or between the output end and the filter.
As a preferred embodiment, the filter is a surface acoustic wave filter, a bulk acoustic wave filter, or an LTCC filter.
As a preferred embodiment, when the filter is a surface acoustic wave filter, the filter is a DMS filter or a ladder filter or a composite structure filter of a ladder and a DMS.
After the technical scheme is adopted, the invention has the following effects: the filter circuit further comprises a left side resonance suppressing structure and a right side resonance suppressing structure, wherein one ends of the left side resonance suppressing structure and the right side resonance suppressing structure are connected between the output end and the input end, and the other ends of the left side resonance suppressing structure and the right side resonance suppressing structure are grounded; the left side restraining resonance structure comprises at least one left side surface acoustic wave resonator monomer or left side bulk acoustic wave resonator monomer, the right side restraining resonance structure comprises at least one right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer, positive resonance peaks of any one left side surface acoustic wave resonator monomer or left side bulk acoustic wave resonator monomer are all positioned at the left side of the passband of the filter, and positive resonance peaks of any one right side surface acoustic wave resonator monomer or right side bulk acoustic wave resonator monomer are all positioned at the right side of the passband of the filter, so that, firstly, the left side restraining resonance structure and the right side restraining resonance structure are independent of the filter, and have little influence on the performance of the filter; secondly, the left side restraining resonance structure and the right side restraining resonance structure can respectively generate out-of-band restraining to the designated frequency on the low-frequency stop band and the high-frequency stop band, and a specific mathematical formula is not required to be satisfied; and meanwhile, the left side suppression resonance structure and the right side suppression resonance structure are connected in parallel, and are independent of the inductance or capacitance, so that the high Q value of the filter is ensured, and the requirement of the out-of-band suppression circuit on the chip size is greatly reduced.
Because the positive resonant frequencies of at least two left side surface acoustic wave resonators or left side bulk acoustic wave resonators are different in each left side surface acoustic wave resonator or left side bulk acoustic wave resonator, the left side surface acoustic wave resonators or the left side bulk acoustic wave resonators can be mutually overlapped in a specific frequency range of the low-frequency stop band through different integral resonant frequencies to generate good out-of-band rejection, and the adaptability is wider.
Because the positive resonant frequencies of at least two right-side surface acoustic wave resonator monomers or right-side bulk acoustic wave resonator monomers are different in each right-side surface acoustic wave resonator monomer or right-side bulk acoustic wave resonator monomer, the right-side surface acoustic wave resonator monomers or right-side bulk acoustic wave resonator monomers with different whole resonant frequencies can be mutually overlapped to generate good out-of-band rejection in a specific frequency range of a high-frequency stop band, and the adaptability is wider.
Drawings
The invention will be further described with reference to the drawings and examples.
FIG. 1 is a schematic view of a first embodiment of the present invention;
fig. 2 is an equivalent circuit diagram of a left-side surface acoustic wave resonator element according to the first embodiment of the present invention;
FIG. 3 is a schematic view showing a specific structure in the first embodiment of the present invention;
FIG. 4 is a schematic diagram of a second embodiment of the present invention;
FIG. 5 is a schematic diagram of a specific structure in a second embodiment of the present invention;
FIG. 6 is a schematic view of a third embodiment of the present invention;
FIG. 7 is a schematic view showing a specific structure in a third embodiment of the present invention;
FIG. 8 is a graph of the frequency response of a conventional ladder filter;
FIG. 9 is a graph of admittances of the main resonators of a conventional ladder filter;
FIG. 10 is a plot of frequency response for a first embodiment of the invention;
FIG. 11 is a graph of admittance of a resonator according to the first embodiment of the present invention;
FIG. 12 is a plot of frequency response for a second embodiment of the invention;
FIG. 13 is a graph of admittance of a resonator according to second embodiment of the present invention;
FIG. 14 is a plot of the frequency response of a third embodiment of the invention;
FIG. 15 is a schematic diagram of a right side reject resonator structure connected between adjacent series resonators;
fig. 16 is a schematic diagram of the connection structure of the DMS filter;
FIG. 17 is a schematic diagram of the connection structure of a ladder and DMS composite filter
In the accompanying drawings: 1. a filter; 11. a series resonator; 12. a parallel resonator; 13. a DMS filter; 14. a second stage DMS filter; 2. an input end; 3. an output end; 4. a left side resonance suppressing structure; 41. a first left side SAW resonator element; 42. a second left side SAW resonator element; 43. a third left side saw resonator element; 5. right side suppresses the resonance structure; 51. a first right-side surface acoustic wave resonator element; 52. a second right-side saw resonator element; 53. a third right-side saw resonator element; 6. target index line.
Detailed Description
The present invention will be described in further detail with reference to the following examples.
Example 1
As shown in fig. 1, 2 and 3, a filter circuit for improving out-of-band rejection includes a filter 1 connected between an input terminal 2 and an output terminal 3, and the filter circuit in the present invention is not limited to the structure of the filter 1, and the filter 1 is, for example, a surface acoustic wave filter 1 or a bulk acoustic wave filter 1 or an LTCC filter 1. When the filter 1 is a surface acoustic wave filter 1, the filter 1 is a DMS filter 1 or a ladder filter 1 or a filter 1 with a complex structure of a ladder and a DMS.
In the present embodiment, the filter 1 is exemplified by a ladder filter 1, and as shown in fig. 3, the ladder filter 1 includes a plurality of series resonators 11 connected in series with each other and a plurality of parallel resonators 12 connected in parallel with each other, wherein the number of the series resonators 11 and the parallel resonators 12 is not limited, and the present embodiment adopts a combination of five series resonators 11 and four parallel resonators 12.
The filter circuit further comprises a left side suppression resonance structure 4, one end of the left side suppression resonance structure 4 is connected between the input end 2 and the filter 1, and the other end of the left side suppression resonance structure 4 is grounded; the left side suppression resonance structure 4 comprises at least one left side surface acoustic wave resonator unit, and the positive resonance peak of any one left side surface acoustic wave resonator unit is positioned at the left side of the passband of the filter 1. The number of the left side surface acoustic wave resonator elements in the present embodiment is three and three left side surface acoustic wave resonator elements are defined as the first left side surface acoustic wave resonator element 41, the second left side surface acoustic wave resonator element 42, and the third left side surface acoustic wave resonator element 43, respectively, and the number of the left side surface acoustic wave resonator elements is not limited to three, and may be selected according to the frequency range of the out-of-band suppression zero point of the required specified frequency.
Of course, when the bulk acoustic wave filter is selected for the filter 1, the corresponding left side suppression resonant structure 4 may further include at least one left side bulk acoustic wave resonator, and similarly, positive resonance peaks of the left side bulk acoustic wave resonator are all located at the left side of the passband of the filter 1, so that out-of-band suppression of the specified frequency can be achieved.
As shown in fig. 15, the connection position of the left suppression resonance structure 4 is located on the branch of the series resonators 11 and between the adjacent series resonators 11.
As shown in fig. 16, the filter in fig. 16 is a DMS filter, which includes a first-stage DMS filter 13 and a second-stage DMS filter 14, taking as an example a two-stage cascade of DMS filters, with the left side suppression resonance structure 4 connected between the first-stage DMS filter 13 and the second-stage DMS filter 14.
As shown in fig. 17, the filter in fig. 17 is a composite structure filter of a trapezoid and a DMS, and the composite structure filter includes a trapezoid structure which also includes at least one series resonator 11 and one parallel resonator 12, and the DMS resonant structure is further connected to the series branch, and the connection position of the left suppression resonant structure 4 is located between the trapezoid structure and the DMS resonant structure.
In this embodiment, at least two positive resonant frequencies of the first left surface acoustic wave resonator element 41, the second left surface acoustic wave resonator element 42, and the third left surface acoustic wave resonator element 43 are different, as shown in fig. 11, the positive resonant frequencies of the first left surface acoustic wave resonator element 41, the second left surface acoustic wave resonator element 42, and the third left surface acoustic wave resonator element 43 in this embodiment are different and sequentially reduced, and any one positive resonant frequency of the first left surface acoustic wave resonator element 41, the second left surface acoustic wave resonator element 42, and the third left surface acoustic wave resonator element 43 is smaller than the positive resonant frequency of any one of the series resonators 11 and any one of the parallel resonators 12.
As shown in fig. 2, fig. 2 is an equivalent circuit diagram of the left side surface acoustic wave resonator element; when the working frequency of the equivalent circuit is equal to the series resonance frequency formed by Lm and Cm in the equivalent circuit, the two ports of the equivalent circuit become short circuit; when the working frequency of the equivalent circuit is equal to the parallel resonance frequency formed by Lm, cm and Ca in the equivalent circuit, an open circuit is formed between two ports of the equivalent circuit; and the positive resonance peak in the admittance curve of the left surface acoustic wave resonator unit is generated by the series resonance formed by Lm and Cm in the equivalent circuit, and the anti-resonance peak is generated by the parallel resonance formed by Lm, cm and Ca in the equivalent circuit.
Therefore, the plurality of left surface acoustic wave resonator monomers are connected in parallel on the signal path of the filter 1, and the positive resonance peak of the left surface acoustic wave resonator monomers is selected to be positioned on the low-frequency resistance band at the left side of the passband of the filter 1, so that the specified frequency of the low-frequency resistance band can have extra out-of-band rejection performance, and the frequency points needing to be added for rejection on the signal path of the filter 1 are added with a circuit which is short-circuited to-ground.
As shown in fig. 8 and 9, fig. 8 illustrates a frequency response plot of a conventional filter circuit without additional out-of-band rejection structure; fig. 9 is an admittance graph of the main resonator of the conventional ladder filter 1; FIG. 10 is a graph showing frequency response of a first embodiment of the present invention; FIG. 11 is a graph of admittance of a resonator according to the first embodiment of the present invention; as can be seen from fig. 8 and 10, the target index line 6 of fig. 8 has no out-of-band rejection zero on both the out-of-band low-frequency stop band and the high-frequency stop band; as can be seen from fig. 10, the target index line 6 of the low-frequency stop band in fig. 10 has an additional out-of-band rejection zero point, so that the frequency at the target index line 6 has a good additional rejection effect; further avoiding interference between signals; as shown in fig. 11, it can be found in fig. 11 that the positive resonant frequencies of the first left side surface acoustic wave resonator element 41, the second left side surface acoustic wave resonator element 42, and the third left side surface acoustic wave resonator element 43 are different and gradually reduced, the positive resonant peak a of the first left side surface acoustic wave resonator element 41, the positive resonant peak b of the second left side surface acoustic wave resonator element 42, and the positive resonant peak c of the third left side surface acoustic wave resonator element 43 are staggered and partially overlapped, so that an additional out-of-band rejection zero point at the target index line 6 is formed as shown in fig. 10, and the positions of the target index line 6 can be adjusted by adjusting the positive resonant frequencies of the first left side surface acoustic wave resonator element 41, the second left side surface acoustic wave resonator element 42, and the third left side surface acoustic wave resonator element 43, so that the rejection requirement of a specific frequency range on the low-frequency stop band is satisfied, and the range of the specific frequency range can be at least one, so that the range of the specific frequency range is relatively small, but the out-of-band rejection effect can be still achieved.
Example two
As shown in fig. 4, 5 and 12, the structure of the present embodiment is substantially the same as that of the first embodiment, except that the filter circuit further includes a right side suppression resonance structure 5, one end of the right side suppression resonance structure 5 is connected between the output terminal 3 and the filter 1, and the other ends of the right side suppression resonance structures 5 are all grounded; the right side suppression resonance structure 5 includes at least one right side surface acoustic wave resonator monomer, one end of the right side surface acoustic wave resonator monomer is connected between the output end 3 and the filter 1, the other end is grounded, the number of the right side surface acoustic wave resonator monomers in the embodiment is 5, and positive resonance peaks of any one right side surface acoustic wave resonator monomer are all located on the right side of the passband of the filter 1.
The number of the right parallel resonators 12 is not limited, and in this embodiment, three right parallel resonators 12 are taken as an example, and positive resonant frequencies of at least two right saw resonators are different from each other. Three right side surface acoustic wave resonator elements are defined as a first right side surface acoustic wave resonator element 51, a second right side surface acoustic wave resonator element 52 and a third right side surface acoustic wave resonator element 53, respectively.
The filter 1 of the present embodiment still takes the ladder filter 1 as an example, and the positive resonance frequency of the right surface acoustic wave resonator is larger than the positive resonance frequency of any one of the series resonators 11 and the parallel resonators 12 in the ladder filter 1. In this embodiment, the positive resonant frequencies of the three right-side surface acoustic wave resonator monomers are all different, the positive resonant frequencies of the first right-side surface acoustic wave resonator monomer 51, the second right-side surface acoustic wave resonator monomer 52 and the third right-side surface acoustic wave resonator monomer 53 are gradually increased, and the positive resonant peaks of the three right-side surface acoustic wave resonator monomers are also partially overlapped at the target index line 6 of the high-frequency stop band to form an additional out-of-band rejection zero point, so that the out-of-band rejection effect of the high-frequency stop band appointed frequency can be realized.
As shown in fig. 14, it can be found from fig. 14 that the positive resonance peak d of the first right side surface acoustic wave resonator element 51, the positive resonance peak e of the second right side surface acoustic wave resonator element 52, and the positive resonance peak f of the third right side surface acoustic wave resonator element 53 partially overlap to form an additional out-of-band rejection zero at the frequency range of the target index line 6 of the high-frequency stop band.
Of course, in this embodiment, when the bulk acoustic wave filter is selected for the filter 1, the corresponding right side suppressing resonant structure 5 may further include at least one right side bulk acoustic wave resonator monomer, and similarly, positive resonance peaks of the right side bulk acoustic wave resonator monomer are all located on the right side of the passband of the filter 1, and out-of-band suppression of the specified frequency can be achieved.
Example III
As shown in fig. 6, 7 and 13, the structure of this embodiment is a combination of the solution of the first embodiment and the solution of the second embodiment, and the filter circuit further includes a left side suppression resonance structure 4 and a right side suppression resonance structure 5, where one end of the left side suppression resonance structure 4 is connected between the input terminal 2 and the filter 1, one end of the right side suppression resonance structure 5 is connected between the output terminal 3 and the filter 1, and the other ends of the left side suppression resonance structure 4 and the right side suppression resonance structure 5 are both grounded; the left side suppression resonance structure 4 includes at least one left side surface acoustic wave resonator monomer, the right side suppression resonance structure 5 includes at least one right side surface acoustic wave resonator monomer, in this embodiment, preferably, the number of the left side surface acoustic wave resonator monomer and the right side surface acoustic wave resonator monomer is three, the positive resonance peak of any one left side surface acoustic wave resonator monomer is located on the left side of the passband of the filter 1, and the positive resonance peak of any one right side surface acoustic wave resonator monomer is located on the right side of the passband of the filter 1.
At least two of the left surface acoustic wave resonators are different in positive resonant frequency. Among the right surface acoustic wave resonators, at least two right surface acoustic wave resonators have different positive resonant frequencies. Thus, the left side suppression resonance structure 4 forms out-of-band suppression of a specified frequency section on the low-frequency stop band on the left side of the pass band of the filter 1; the right side rejection resonance structure 5 forms an out-of-band rejection in a specified frequency interval on the high frequency stop band on the right side of the pass band of the filter 1.
In this embodiment, when the filter 1 is a bulk acoustic wave filter, the corresponding left side suppression resonance structure 4 may further include at least one left side bulk acoustic wave resonator unit, where positive resonance peaks of the left side bulk acoustic wave resonator unit are all located at the left side of the passband of the filter 1; the corresponding right side suppressing resonant structure 4 may further include at least one right side bulk acoustic wave resonator monomer, where positive resonance peaks of the right side bulk acoustic wave resonator monomer are all located on the right side of the passband of the filter 1; this can achieve out-of-band rejection of the specified frequencies of the low-frequency stop band and the high-frequency stop band.
Compared with the existing out-of-band rejection structure, the embodiment of the invention has the following technical advantages:
1. the left side suppression resonance structure 4 and the right side suppression resonance structure 5 forming the additional out-of-band suppression zero point are completely independent of the filter 1, and can be used for enhancing the additional out-of-band suppression performance of various filters 1 such as a sound surface filter 1, a bulk acoustic wave filter 1, an LTCC filter 1 and the like. In addition, in the scheme of the invention, the left side suppression resonance structure 4 and the right side suppression resonance structure 5 can be formed by adopting a low-cost acoustic surface wave resonator monomer or a bulk acoustic wave resonator monomer, and the filter 1 can be made of a material with high cost but high performance, so that the area of the filter 1 is reduced, the performance of the filter 1 is improved, and the cost of the whole filter circuit is reduced.
2. The left side suppression resonance structure 4 and the right side suppression resonance structure 5 only meet the requirement that the positive resonance peak is out of band of the filter 1, the out-of-band suppression zero point can be arbitrarily selected from a low-frequency stop band and a high-frequency stop band at two sides outside the pass band of the filter 1, and only the positive resonance frequency of the left side surface acoustic wave resonator monomer or the left side bulk acoustic wave resonator monomer and the right side surface acoustic wave resonator monomer or the right side bulk acoustic wave resonator monomer is required to be adjusted, and a certain specific mathematical formula is not required to be met.
3. Because the left side surface acoustic wave resonator monomer or the left side bulk acoustic wave resonator monomer and the right side surface acoustic wave resonator monomer or the right side bulk acoustic wave resonator monomer are adopted to be connected in parallel into the signal path, and the left side surface acoustic wave resonator monomer or the left side bulk acoustic wave resonator monomer and the right side surface acoustic wave resonator monomer or the right side bulk acoustic wave resonator monomer which are connected in parallel are only used for the out-of-band inhibition purpose at the serial resonance frequency, the size can be made smaller, and the influence on the insertion loss of the pass band is small.
4. The left side restraining resonance structure 4 and the right side restraining resonance structure 5 do not depend on the effect of inductance or capacitance at all, so that the high Q value of the filter 1 is guaranteed, and the requirement of a filter circuit on the chip size is greatly reduced.
The above examples are merely illustrative of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and adaptations of the technical solution of the present invention should and are intended to fall within the scope of the present invention as defined in the claims.
Claims (3)
1. A filter circuit for improving out-of-band rejection, comprising a filter connected between an input and an output, said filter being a surface acoustic wave filter or a bulk acoustic wave filter or an LTCC filter, characterized in that: the filter circuit further comprises a left side resonance suppressing structure and a right side resonance suppressing structure, wherein one ends of the left side resonance suppressing structure and the right side resonance suppressing structure are connected between the output end and the input end, and the other ends of the left side resonance suppressing structure and the right side resonance suppressing structure are grounded; the left side restraining resonance structure comprises three left side surface acoustic wave resonator monomers or left side bulk acoustic wave resonator monomers, one ends of the three left side surface acoustic wave resonator monomers or the left side bulk acoustic wave resonator monomers are connected between an output end and an input end, and the other ends of the three left side surface acoustic wave resonator monomers or the left side bulk acoustic wave resonator monomers are grounded; defining three left-side surface acoustic wave resonator monomers as a first left-side surface acoustic wave resonator monomer, a second left-side surface acoustic wave resonator monomer and a third left-side surface acoustic wave resonator monomer respectively, and defining three left-side bulk acoustic wave resonator monomers as a first left-side bulk acoustic wave resonator monomer, a second left-side bulk acoustic wave resonator monomer and a third left-side bulk acoustic wave resonator monomer respectively; the right side restraining resonance structure comprises three right side surface acoustic wave resonator monomers or right side bulk acoustic wave resonator monomers, one ends of the three right side surface acoustic wave resonator monomers or right side bulk acoustic wave resonator monomers are connected between an output end and an input end, the other ends of the three right side surface acoustic wave resonator monomers are grounded, the three right side surface acoustic wave resonator monomers are defined as a first right side surface acoustic wave resonator monomer, a second right side surface acoustic wave resonator monomer and a third right side surface acoustic wave resonator monomer respectively, and the three right side bulk acoustic wave resonator monomers are defined as a first right side bulk acoustic wave resonator monomer, a second right side bulk acoustic wave resonator monomer and a third right side bulk acoustic wave resonator monomer respectively;
the positive resonance peak of any one left surface acoustic wave resonator monomer or left bulk acoustic wave resonator monomer is positioned at the left side of the passband of the filter, and the positive resonance peak of any one right surface acoustic wave resonator monomer or right bulk acoustic wave resonator monomer is positioned at the right side of the passband of the filter;
the positive resonance peak of the first left side surface acoustic wave resonator monomer or the first left side bulk acoustic wave resonator monomer, the positive resonance peak of the second left side surface acoustic wave resonator monomer or the second left side bulk acoustic wave resonator monomer, the positive resonance peak of the third left side surface acoustic wave resonator monomer or the third left side bulk acoustic wave resonator monomer are staggered and partially overlapped at the target index line of the low-frequency stop band to form an additional out-of-band inhibition zero point
The positive resonance peak of the first right side surface acoustic wave resonator monomer or the first right side bulk acoustic wave resonator monomer, the positive resonance peak of the second right side surface acoustic wave resonator monomer or the second right side bulk acoustic wave resonator monomer, and the positive resonance peak of the third right side surface acoustic wave resonator monomer or the third right side bulk acoustic wave resonator monomer are staggered with each other and partially overlapped at the target index line of the high-frequency stop band to form an additional out-of-band rejection zero point.
2. A filter circuit for improving out-of-band rejection as in claim 1, wherein: the left side resonance suppressing structure is connected between the input end and the filter or between the output end and the filter; the right side reject resonator structure is connected between the input end and the filter or between the output end and the filter.
3. A filter circuit for improving out-of-band rejection as in claim 2 wherein: when the filter is a surface acoustic wave filter, the filter is a DMS filter or a ladder filter or a composite structure filter of a ladder and a DMS.
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| CN202311356509.5A CN117097298B (en) | 2023-10-19 | 2023-10-19 | Filter circuit for improving out-of-band rejection |
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| CN202311356509.5A CN117097298B (en) | 2023-10-19 | 2023-10-19 | Filter circuit for improving out-of-band rejection |
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| CN117097298B true CN117097298B (en) | 2024-02-09 |
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Citations (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH09116379A (en) * | 1995-10-16 | 1997-05-02 | Murata Mfg Co Ltd | Surface acoustic wave filter |
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| JP5723667B2 (en) * | 2011-04-27 | 2015-05-27 | 太陽誘電株式会社 | Ladder filter, duplexer and module |
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| JP2002359541A (en) * | 2000-10-27 | 2002-12-13 | Toyo Commun Equip Co Ltd | Resonator-type surface acoustic wave filter |
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| CN117097298A (en) | 2023-11-21 |
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