CN113346868A - Surface acoustic wave filter - Google Patents
Surface acoustic wave filter Download PDFInfo
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- CN113346868A CN113346868A CN202110814610.5A CN202110814610A CN113346868A CN 113346868 A CN113346868 A CN 113346868A CN 202110814610 A CN202110814610 A CN 202110814610A CN 113346868 A CN113346868 A CN 113346868A
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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
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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
- H03H9/02535—Details of surface acoustic wave devices
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Abstract
The embodiment of the invention discloses a surface acoustic wave filter. The surface acoustic wave filter includes: two surface acoustic wave band elimination filters, a low-pass filter and a high-pass filter; the surface acoustic wave band elimination filter, the low-pass filter and the high-pass filter are cascaded to form the surface acoustic wave filter, and the frequency bands blocked by the two surface acoustic wave band elimination filters are different. The surface acoustic wave filter designed by the technical scheme has the advantages that the required passband is formed by the two surface acoustic wave band elimination filters in a clamping way, and then the low-frequency signal and the high-frequency signal are restrained by the low-pass filter and the high-pass filter, so that the surface acoustic wave filter meets the requirement of the ultra wide band of any frequency band, the technical problem that the relative bandwidth of the conventional SAW cannot be enlarged is solved, the performance of the surface acoustic wave filter is improved, and the cost of the surface acoustic wave filter is saved.
Description
Technical Field
The embodiment of the invention relates to the technical field of filters, in particular to a surface acoustic wave filter.
Background
In recent years, the fifth Generation Mobile Communication Technology (5th Generation Mobile Communication Technology, 5G) has been rapidly developed, and a Surface Acoustic Wave (SAW) filter is used in many products. Such as cell phones, navigators, etc., while SAW technology is coming up with new demands and challenges.
Currently, in the design of SAW, a conventional design method of a band pass filter is used. Due to the limitation of materials, the electromechanical coupling coefficient cannot be increased, the relative bandwidth cannot be increased further, the achievement of more than 9% is very difficult, and the cost rises sharply along with the expansion of the relative bandwidth.
Disclosure of Invention
The embodiment of the invention provides a surface acoustic wave filter, aiming at solving the technical problem that the relative bandwidth of the conventional SAW cannot be large.
An embodiment of the present invention provides a surface acoustic wave filter, including:
two surface acoustic wave band elimination filters, a low-pass filter and a high-pass filter;
the surface acoustic wave band elimination filter, the low-pass filter and the high-pass filter are cascaded to form the surface acoustic wave filter, wherein the frequency bands blocked by the two surface acoustic wave band elimination filters are different.
Optionally, part or all of the transition sections of the low-pass filter and part or all of the transition sections of the high-pass filter are respectively located in the frequency band blocked by each saw band reject filter.
Optionally, the two surface acoustic wave band reject filters include a low-frequency surface acoustic wave band reject filter and a high-frequency surface acoustic wave band reject filter.
Optionally, part or all of the transition section of the low-pass filter is located in the frequency band blocked by the high-frequency surface acoustic wave band-stop filter.
Optionally, part or all of the transition section of the high-pass filter is located in the frequency band blocked by the low-frequency surface acoustic wave band reject filter.
Optionally, the surface acoustic wave band reject filter, the low pass filter, and the high pass filter are cascaded to form a surface acoustic wave filter, which includes:
the high-pass filter, the low-frequency surface acoustic wave band elimination filter, the high-frequency surface acoustic wave band elimination filter and the low-pass filter are sequentially connected in series to form the surface acoustic wave filter.
Optionally, the saw band reject filter includes at least one first resonator with an interdigital transducer structure as a basic structure.
The embodiment of the invention designs the surface acoustic wave filter by cascading two surface acoustic wave band elimination filters, a low-pass filter and a high-pass filter. The surface acoustic wave filter designed by the technical scheme has the advantages that the required passband is formed by the two surface acoustic wave band elimination filters in a clamping way, and then the low-frequency signal and the high-frequency signal are restrained by the low-pass filter and the high-pass filter, so that the surface acoustic wave filter meets the requirement of the ultra wide band of any frequency band, the technical problem that the relative bandwidth of the conventional SAW cannot be enlarged is solved, the performance of the surface acoustic wave filter is improved, and the cost of the surface acoustic wave filter is saved.
Drawings
Fig. 1 is a schematic structural diagram of a surface acoustic wave filter according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a surface acoustic wave filter according to an embodiment of the present invention;
FIG. 3A is a frequency response diagram of two SAW band reject filters provided in accordance with an embodiment of the present invention;
fig. 3B is a frequency response diagram of various saw filters according to an embodiment of the present invention;
fig. 3C is a superimposed frequency response diagram of various saw filters according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a resonator of an interdigital transducer structure, according to an embodiment of the present invention;
fig. 5A is a schematic design diagram of a high-frequency surface acoustic wave band reject filter according to an embodiment of the present invention;
fig. 5B is a graph of S-parameter of a high-frequency saw band reject filter according to an embodiment of the present invention;
fig. 6A is a schematic design diagram of a low-frequency saw band reject filter according to an embodiment of the present invention;
fig. 6B is a graph of S-parameter of a low-frequency saw band reject filter according to an embodiment of the present invention;
FIG. 7A is a schematic diagram of a low pass filter according to an embodiment of the present invention;
FIG. 7B is a graph of the S-parameter of a low pass filter according to an embodiment of the present invention;
FIG. 8A is a schematic diagram of a high pass filter according to an embodiment of the present invention;
FIG. 8B is a graph of the S-parameter of a high pass filter according to an embodiment of the present invention;
fig. 9 is a graph of S-parameter of a saw filter according to an embodiment of the present invention;
fig. 10 is a schematic structural diagram of a first-order LC low-pass circuit according to an embodiment of the present invention;
FIG. 11 is a schematic structural diagram of a first-order LC high-pass circuit according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of the structure and waveforms of a high-pass filter according to an embodiment of the present invention;
fig. 13 is a schematic diagram of a structure and waveforms of a band stop filter according to an embodiment of the present invention;
fig. 14 is a schematic diagram of a structure and waveforms of a low-pass filter according to an embodiment of the present invention;
fig. 15 is a schematic structural diagram of a filter according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
The embodiments and features of the embodiments of the present invention may be combined with each other without conflict.
The term "include" and variations thereof as used herein are intended to be open-ended, i.e., "including but not limited to". The term "based on" is "based, at least in part, on". The term "one embodiment" means "at least one embodiment".
It should be noted that the concepts of "first", "second", "third", etc. mentioned in the present invention are only used for distinguishing the corresponding contents, and are not used for limiting the order or interdependence relationship.
It is noted that references to "a", "an", and "the" modifications in the present invention are intended to be illustrative rather than limiting, and that those skilled in the art will recognize that reference to "one or more" unless the context clearly dictates otherwise.
Fig. 1 is a schematic structural diagram of a surface acoustic wave filter according to an embodiment of the present invention. As shown in fig. 1, the surface acoustic wave filter includes: two surface acoustic wave band reject filters 5, a low pass filter 4 and a high pass filter 1. The surface acoustic wave band elimination filter 5, the low-pass filter 4 and the high-pass filter 1 are cascaded to form a surface acoustic wave filter, wherein the frequency bands blocked by the two surface acoustic wave band elimination filters 5 are different.
In the embodiment of the invention, the surface acoustic wave filter is formed by clamping a required passband frequency band by two surface acoustic wave band elimination filters 5; unnecessary low-frequency signals are suppressed by a high-pass filter 1; unnecessary high-frequency signals are suppressed by the low-pass filter 4.
The high-pass filter 1 may be a filter that allows signals above a cutoff frequency to pass through without attenuation, or may be a filter that allows signals above the cutoff frequency to pass through normally, while signals below the cutoff frequency are blocked and attenuated. The cut-off frequency may refer to a boundary frequency at which the energy of an output signal of a system starts to decrease or increase greatly, or may refer to a boundary frequency between a pass band and a stop band, for example, the cut-off frequency in the high-pass filter 1 may be a frequency point on the left side of the pass band; the passband can refer to a frequency range in the surface acoustic wave filter through which signals pass relatively without attenuation; the stop band may refer to a frequency range in which a signal is greatly attenuated or completely suppressed in the saw filter.
The low-pass filter 4 may be a filter allowing signals below a cut-off frequency to pass through without attenuation, or may be a filter allowing signals below the cut-off frequency to pass through normally, and blocking and attenuating signals above the cut-off frequency; for example, the cut-off frequency may be the frequency point to the right of its pass band in the low-pass filter 4.
The surface acoustic wave band-pass filter can be a filter which allows signal frequencies in a certain range to pass and filters other signal frequencies, wherein the frequency in a certain range can be a frequency between a lower limit frequency and an upper limit frequency range; the lower limit frequency can refer to the frequency point on the left side of the passband of the surface acoustic wave band-pass filter, and the upper limit frequency can refer to the frequency point on the right side of the passband of the surface acoustic wave band-pass filter. The surface acoustic wave band elimination filter 5 is just opposite to the surface acoustic wave band pass filter, and can be used for filtering signal frequency between a lower limit frequency range and an upper limit frequency range and passing other signal frequencies.
Cascade may refer to connecting a plurality of objects in series in order, for example, connecting a surface acoustic wave band reject filter 5, a low pass filter 4, and a high pass filter 1 in series in order to form a surface acoustic wave filter. The series connection order of the filters is not limited here.
The frequency band blocked by the surface acoustic wave band-stop filter 5 can refer to the stop band frequency band of the filter; the blocked frequency band may comprise part or all of the transition of the high-pass filter 1 and/or the low-pass filter 4; the transition section can be a transition band of a certain frequency range existing between a pass band and a stop band of the filter; the frequency in the transition section is not completely suppressed but attenuated to different degrees, which may also mean that the slope of the frequency curve of the transition section represents the degree of the frequency attenuation in the transition section, and the larger the slope of the frequency curve of the transition section is, the faster the frequency attenuation is, and the better the filtering performance of the filter is.
The difference of the frequency bands blocked by the two surface acoustic wave band elimination filters 5 can mean that the ranges of the blocked frequency bands are not coincident. The blocked frequency ranges are not coincident, and the required pass band can be formed by clamping two surface acoustic wave band elimination filters 5. The band range blocked by the two saw filters 5 is not limited here. The invention can be clamped into any broadband by two surface acoustic wave band elimination filters 5. In addition, the requirements for the Q values of the low-pass filter 4 and the high-pass filter 1 can be reduced by the two surface acoustic wave band reject filters 5.
The specific structures of the surface acoustic wave band reject filter 5, the low pass filter 4, and the high pass filter 1 are not limited in this embodiment.
The surface acoustic wave filter provided by the embodiment of the invention designs the surface acoustic wave filter by cascading two surface acoustic wave band elimination filters, a low-pass filter and a high-pass filter. The surface acoustic wave filter designed by the method has the advantages that the required passband is formed by clamping the two surface acoustic wave band elimination filters, and then the low-frequency signal and the high-frequency signal are restrained by the low-pass filter and the high-pass filter, so that the surface acoustic wave filter meets the requirement of the ultra wide band of any frequency band, the technical problem that the relative bandwidth of the conventional SAW cannot be enlarged is solved, the performance of the surface acoustic wave filter is improved, and the cost of the surface acoustic wave filter is saved.
Alternatively, the two surface acoustic wave band reject filters 5 include a low frequency surface acoustic wave band reject filter 2 and a high frequency surface acoustic wave band reject filter 3.
The low frequency and the high frequency are relative concepts and are different in different technical fields, for example, in an amplitude modulation radio, the sound electric signal is low frequency, and the sound electric signal is high frequency above 535 KHz; for human ear listening, the low frequency is below 200-300Hz, and the high frequency is above 800-1000 Hz. In the embodiment, the low frequency and the high frequency are also relative concepts, for example, the surface acoustic wave band reject filter with the low blocked frequency band in the two surface acoustic wave band reject filters 5 can be regarded as a low frequency surface acoustic wave band reject filter 2, and the surface acoustic wave band reject filter with the high blocked frequency band can be regarded as a high frequency surface acoustic wave band reject filter 3; for example, the low-frequency blocking saw filter 5 is a low-frequency saw filter 2, and the high-frequency blocking saw filter is a high-frequency saw filter 3.
The surface acoustic wave filter of the present invention can be regarded as an ultra-wideband surface acoustic wave filter, wherein the wideband can refer to the width of the pass band of the surface acoustic wave filter, and can also refer to the width of the frequency range in the surface acoustic wave filter, through which signals can pass.
The surface acoustic wave band pass filter can be formed by combining the high pass filter 1 and the low pass filter 4, but the design mode has high requirement on the Q value of the parameters of the high pass filter 1 and the low pass filter 4 and is not easy to realize. The low-frequency surface acoustic wave band elimination filter 2 and the high-frequency surface acoustic wave band elimination filter 3 are formed by clamping and pressing required passband frequency bands, a surface acoustic wave band-pass filter with any frequency band can be formed, the high-pass filter 1 and the low-pass filter 4 with high Q value requirements do not need to be designed at the moment, and the implementation is easy. The Q value may refer to a quality factor of the filter, which represents a parameter of the performance of the filter, and the magnitude of the Q value affects the magnitude of the slope of the transition section, for example, the higher the Q value, the larger the slope of the transition section, the faster the frequency attenuation of the transition section, and the better the filtering performance of the filter.
Optionally, the high-pass filter 1, the low-frequency surface acoustic wave band-stop filter 2, the high-frequency surface acoustic wave band-stop filter 3, and the low-pass filter 4 are sequentially connected in series to form a surface acoustic wave filter.
Fig. 2 is a schematic structural diagram of a surface acoustic wave filter according to an embodiment of the present invention. As shown in fig. 2, a high-pass filter 1, a low-frequency surface acoustic wave band reject filter 2, a high-frequency surface acoustic wave band reject filter 3, and a low-pass filter 4 are connected in series in this order to form a surface acoustic wave filter.
FIG. 3A is a frequency response diagram of two SAW band reject filters provided in accordance with an embodiment of the present invention; fig. 3B is a frequency response diagram of various saw filters according to an embodiment of the present invention; fig. 3C is a superimposed frequency response diagram of the saw filters according to the embodiment of the present invention. In the present embodiment, as shown in fig. 3A, a desired passband band can be approximated by a low frequency saw band reject filter 2 and a high frequency saw band reject filter 3, where fHIs the upper limit frequency in the low frequency SAW band reject filter 2, where fLFor the lower limit frequency, f, in the high-frequency SAW band reject filter 3HAnd fLThe frequency band clamped by the clamp can be a required pass band frequency band.
Optionally, part or all of the transition sections of the low-pass filter 4 and part or all of the transition sections of the high-pass filter 1 are respectively located in the frequency band blocked by each saw band reject filter 5.
In the embodiment, the requirements on the Q values of the low-pass filter 4 and the high-pass filter 1 are reduced by positioning part or all of the transition sections of the low-pass filter 4 and part or all of the transition sections of the high-pass filter 1 in the frequency band blocked by each surface acoustic wave band elimination filter 5.
As shown in fig. 3B, a part of the transition section of the low-pass filter 4 and a part of the transition section of the high-pass filter 1 are respectively located in the frequency band blocked by the surface acoustic wave band reject filter 5, and the parts of the transition sections of the low-pass filter 4 and the high-pass filter 1 located in the frequency bands blocked by the two surface acoustic wave band reject filters 5 are as much as possible, so as to reduce the Q value requirement. Further, the low-pass filter 4 and the high-pass filter 1 are provided for suppressing unnecessary frequencies outside the band blocked by the two surface acoustic wave band reject filters 5. In this embodiment, the size of the part of the transition segment located in the blocked frequency band is not limited herein.
In the present embodiment, the steepness of the transition sections of the two surface acoustic wave band reject filters 5 may be larger than a certain value to more accurately clamp to a desired frequency band.
Optionally, part or all of the transition section of the low-pass filter 4 is located in the frequency band blocked by the high-frequency saw band reject filter 3.
In the above, the transition section of the low-pass filter 4 is located in the frequency band blocked by the high-frequency saw band reject filter 3, which can reduce the requirement of the Q value of the low-pass filter 4.
The fact that part or all of the transition section of the low-pass filter 4 is located in the frequency band blocked by the high-frequency surface acoustic wave band-stop filter 3 also means that the size of the transition section of the low-pass filter 4 can be determined by the range of the frequency band blocked by the high-frequency surface acoustic wave band-stop filter 3, for example, if the range of the frequency band blocked by the high-frequency surface acoustic wave band-stop filter 3 is enlarged, the transition section of the low-pass filter 4 can be set to be enlarged accordingly, wherein the enlargement of the transition section of the low-pass filter 4 means that the Q value of the low-pass filter is reduced, and at this time, the requirement on the Q value of the low-pass filter 4 does not need to be high, and is relatively easy to implement.
Optionally, part or all of the transition section of the high-pass filter 1 is located in the frequency band blocked by the low-frequency saw band reject filter 2.
The transition section of the high-pass filter 1 is located in the frequency band blocked by the low-frequency surface acoustic wave band elimination filter 2, and the size of the transition section of the high-pass filter 1 can be determined according to the range of the frequency band blocked by the low-frequency surface acoustic wave band elimination filter 2, for example, the range of the frequency band blocked by the low-frequency surface acoustic wave band elimination filter 2 is enlarged, the transition section of the high-pass filter 1 can be set to be enlarged, wherein the enlargement of the transition section of the high-pass filter 1 indicates that the Q value of the high-pass filter 1 is reduced, at the moment, the requirement on the Q value of the high-pass filter 1 is not required to be high, and the implementation is relatively easy.
Fig. 3C is a frequency response diagram after outputs of four surface acoustic wave filters, i.e., the high-pass filter 1, the low-frequency surface acoustic wave band reject filter 2, the high-frequency surface acoustic wave band reject filter 3, and the low-pass filter 4, are superimposed. The Q values of the low-pass filter 4 and the high-pass filter 1 can be determined based on the out-of-band rejection requirement of the frequency band except the pass band in fig. 3c and the size of the frequency band blocked by the low-frequency surface acoustic wave band reject filter 2 and the high-frequency surface acoustic wave band reject filter 3.
The invention can form the resonator by taking the interdigital transducer structure as a basic structure, and the invention does not limit the realization mode of the resonator of the interdigital transducer structure. Fig. 4 is a schematic structural diagram of a resonator of an interdigital transducer structure according to an embodiment of the present invention. As shown in fig. 4, the resonators of the interdigital transducer structure are basic units constituting a surface acoustic wave filter, and can be used to convert an acoustic signal into an electric signal; the resonators of the interdigital transducer structure may be composed of a plurality of metal electrodes alternately connected to two bus bars, which have frequency selectivity, for example, surface acoustic wave filters of different frequencies may be obtained by designing the resonators of the interdigital transducer structure for different wavelengths.
Alternatively, the surface acoustic wave band reject filter 5 includes at least one first resonator having an interdigital transducer structure as a basic structure. The first resonator formed with the interdigital transducer structure as the basic structure is not limited herein. Such as a first resonator of a two-mode surface acoustic wave structure or a first resonator of a multimode structure.
It should be noted that "first", "second", and "third" of the first resonator, the second resonator, and the third resonator are only used to distinguish different resonators, and the respective contents are not limited.
In the present embodiment, the design of the surface acoustic wave band reject filter 5 is not limited. For example, the saw band reject filter 5 comprises at least one first resonator of an interdigital transducer structure and at least one inductor. When the surface acoustic wave band-stop filter 5 comprises a first resonator and an inductor of an interdigital transducer structure, one end of the inductor is connected with one end of the first resonator, the other end of the first resonator is connected with the ground, and the connecting end of the first resonator and the inductor and the other end of the inductor can be used as the input end and the output end of the surface acoustic wave band-stop filter 5; when the surface acoustic wave band elimination filter 5 comprises at least two first resonators of an interdigital transducer structure and an inductor, the first resonators and the inductor are connected in series in sequence after being connected according to the connection mode.
Fig. 5A is a schematic design diagram of a high-frequency surface acoustic wave band reject filter according to an embodiment of the present invention. As shown in fig. 5A, the high-frequency surface acoustic wave band reject filter 3 includes five first resonators (X49, X66, X69, X68, and X67 in the drawing) of an interdigital transducer structure and 4 inductors.
Fig. 5B is a graph of S-parameters of a high-frequency saw band reject filter according to an embodiment of the present invention. As shown in fig. 5B, the abscissa is the frequency of the high-frequency surface acoustic wave band reject filter 3, and the ordinate is the attenuation of the signal of the high-frequency surface acoustic wave band reject filter 3. The abscissa of m1 is 2.2GHz, and the abscissa of m2 is 2.28 GHz; the ordinate of m1 and m2 in the S21 curve represents the insertion loss of the pass band, the insertion loss can represent the loss of power generated by the access of the high-frequency surface acoustic wave band elimination filter 3 in the transmission of signals or power supplies, the ordinate of m1 is-0.968 dB, and the ordinate of m2 is-27.532 dB; the abscissa 2.2GHz of m1 is the lower limit frequency of the high-frequency surface acoustic wave band elimination filter 3; the ordinate of m1 and m2 in the S11 curve represents the return loss of the pass band, the return loss can represent the loss caused by attenuation due to signal reflection, such as signal transmission loss increase and signal distortion, caused by reflection when the signal encounters uneven wave impedance during transmission, the ordinate of m1 is-25.759 dB, and the ordinate of m2 is-1.624 dB.
Fig. 6A is a schematic design diagram of a low-frequency surface acoustic wave band reject filter according to an embodiment of the present invention. As shown in fig. 6A, the low frequency surface acoustic wave band reject filter 2 includes five first resonators of an interdigital transducer structure and 4 inductors. Fig. 6B is a graph of S-parameters of a low-frequency saw band reject filter according to an embodiment of the present invention. Wherein, as shown in FIG. 6B, the abscissa of m1 is 1.7GHz, the abscissa of m2 is 2.2GHz, and the abscissa of m3 is 1.5 GHz; in the S21 curve, the ordinate of m1 is-0.664 dB, the ordinate of m2 is-0.899 dB, and the ordinate of m3 is-20.037 dB; the abscissa 1.7GHz of m1 is the upper limit frequency of the low-frequency SAW band reject filter 2; in the S11 curve, the ordinate of m1 is-37.399 dB, the ordinate of m2 is-23.876 dB, and the ordinate of m3 is-1.943 dB.
Optionally, the low-pass filter 4 comprises at least one second resonator of an interdigital transducer structure.
Wherein the low-pass filter 4 comprises at least one second resonator of the interdigital transducer structure and at least one first resonance circuit, wherein the first resonance circuit can be formed by a polar capacitor and an inductor in parallel. When the low-pass filter 4 includes a first resonance circuit and a second resonator, one end of the first resonance circuit is connected to one end of the second resonator, and the other end of the second resonator is connected to ground; the connection end of the second resonator and the first resonant circuit and the other end of the first resonant circuit can be used as the input end and the output end of the low-pass filter 4; when the low-pass filter 4 includes at least two second resonators of interdigital transducer structure and at least two first resonance circuits, each of the first resonance circuits and each of the second resonators are connected in series in such a manner that one second resonator is connected in parallel, one first resonance circuit is connected in series, one second resonator is connected in parallel, and one first resonance circuit is connected in series … …, respectively, to form a low-pass filter.
Fig. 7A is a schematic diagram of a design of a low-pass filter according to an embodiment of the present invention. As shown in fig. 7A, the low-pass filter 4 includes five interdigital transducer structured second resonators and 4 first resonance circuits.
Fig. 7B is a S-parameter graph of a low-pass filter according to an embodiment of the present invention. Wherein, as shown in FIG. 7B, the abscissa of m1 is 2.2GHz, and the abscissa of m2 is 2.35 GHz; the ordinate of m1 in the S21 curve is-1.856 dB, and the ordinate of m2 is-26.898 dB; the abscissa 2.2GHz of m1 is the cut-off frequency of the low-pass filter 4; the ordinate of m1 in the S11 curve is-28.059 dB, and the ordinate of m2 is-0.933 dB.
Optionally, the high-pass filter 1 comprises at least one third resonator of the interdigital transducer structure.
In this embodiment, the high-pass filter 1 includes at least one third resonator of an interdigital transducer structure and at least one second resonant circuit, where the second resonant circuit may be a pi-type LC filter circuit, and the pi-type LC filter circuit may be composed of three polar capacitors and two inductors. When the high-pass filter 1 comprises a third resonator and a second resonant circuit of an interdigital transducer structure, one end of the second resonant circuit is connected with one end of the third resonator, one ends of two inductors in the second resonant circuit are connected with a capacitor, and the other ends of the two inductors are connected with the ground; the other end of the third resonator and the other end of the second resonant circuit can be used as the input end and the output end of the high-pass filter 1; when the high-pass filter 1 includes at least two third resonators and two second resonant circuits of the interdigital transducer structure, the third resonators and the second resonant circuits are connected in series in sequence after being connected according to the connection mode.
For example, fig. 8A is a schematic diagram of a design of a high-pass filter according to an embodiment of the present invention. As shown in fig. 8A, the high-pass filter 1 includes three third resonators of the interdigital transducer structure and two second resonance circuits. Fig. 8B is a S-parameter graph of a high-pass filter according to an embodiment of the present invention. Wherein, as shown in fig. 8B, the abscissa of m1 is 1.5GHz, the abscissa of m2 is 1.7GHz, and the abscissa of m3 is 2.25 GHz; in the S21 curve, the ordinate of m1 is-25.616 dB, the ordinate of m2 is-1.132 dB, and the ordinate of m3 is-0.436 dB; the abscissa 1.7GHz of m2 is the cut-off frequency of the high-pass filter 1; in the S11 curve, the ordinate of m1 is-2.12 dB, the ordinate of m2 is-32.873 dB, and the ordinate of m3 is-33.144 dB.
Fig. 9 is a S-parameter graph of a surface acoustic wave filter according to an embodiment of the present invention. FIG. 9 is a graph showing S-parameters of cascaded SAW filters designed as described above, where m1 has an abscissa of 1.694GHz, m2 has an abscissa of 2.198GHz, m3 has an abscissa of 1.559GHz, and m4 has an abscissa of 2.262 GHz; in the S21 curve, the ordinate of m1 is-1.2466 dB, the ordinate of m2 is-1.731 dB, the ordinate of m3 is-21.978 dB, and the ordinate of m4 is-21.093 dB. The passband of the surface acoustic wave filter is 1694MHz-2198MHz, and the left and right near-end rejection is +/-80 MHz @20 dB. The passband range of 1694MHz-2198MHz can indicate that the lower limit frequency of the surface acoustic wave filter is 1694MHz, the upper limit frequency is 2198MHz, and the passband bandwidth is 504 MHz; center frequency f0The frequency in the middle of the filter passband can be represented, generally by f0＝(fL+fH) The center frequency was calculated to be 1946MHz by/2. The channel-to-channel spacing in a certain frequency range is required and can be expressed by relative bandwidth, for example, the relative bandwidth of a narrow band is less than 1%, the relative bandwidth of a wide band is between 1% and 25%, and the relative bandwidth of an ultra-wide band is greater than 25%; the relative bandwidth can be calculated by the ratio of the passband bandwidth to the center frequency, so that the saw filter has a relative bandwidth of about 25.9%, and above about 25%.
It should be noted that, in the present invention, the design manner of the low-pass filter 4 and the high-pass filter 1 is not limited. For example, fig. 10 is a schematic structural diagram of a first-order LC low-pass circuit provided in the embodiment of the present invention, and as shown in fig. 10, the low-pass filter 4 may also use a first-order LC low-pass circuit, a second-order LC low-pass circuit … …, or an nth-order LC low-pass circuit to implement low-pass filtering. The second-order LC low-pass circuit can be formed by sequentially connecting two first-order LC low-pass circuits in series, and by analogy, the n-order LC low-pass circuit can be formed by sequentially connecting n first-order LC low-pass circuits in series; the higher the order, the better the steepness of the edge of the filter, and the better the filtering effect; the steepness may refer to a slope of a transition curve of the filter, for example, the higher the order, the higher the slope, the smaller a transition frequency range from the pass band to the stop band of the filter, and thus the better the filtering effect of the filter. Wherein n is a positive integer.
Fig. 11 is a schematic structural diagram of a first-order LC high-pass circuit according to an embodiment of the present invention, and as shown in fig. 11, the high-pass filter 1 may also implement high-pass filtering by using a first-order LC high-pass circuit, a second-order LC high-pass circuit … …, or an m-order LC high-pass circuit. Similarly, the second-order LC high-pass circuit may be formed by sequentially connecting two first-order LC high-pass circuits in series, and in this way, the m-order LC high-pass circuit may be formed by sequentially connecting m first-order LC high-pass circuits in series. Wherein m is a positive integer.
Fig. 12 is a schematic diagram illustrating a structure and waveforms of a high-pass filter according to an embodiment of the present invention, and as shown in fig. 12, the high-pass filter 1 may include three capacitors and two inductors.
Fig. 13 is a schematic diagram of a structure and waveforms of a band-stop filter according to an embodiment of the present invention, and as shown in fig. 13, the band-stop filter includes three first resonant circuits, two inductors, and two capacitors.
Fig. 14 is a schematic diagram of a structure and waveforms of a low-pass filter according to an embodiment of the present invention, and as shown in fig. 14, the low-pass filter 4 includes three inductors and two capacitors.
Fig. 15 is a schematic structural diagram of a filter according to an embodiment of the present invention, and as shown in fig. 15, the filters in fig. 12, 13, and 14 are cascaded in the order of the high-pass filter 1, the band-stop filter, and the low-pass filter 4 to form the filter.
The surface acoustic wave filter provided by the invention solves the technical problem that the relative bandwidth of the conventional SAW (surface acoustic wave band-pass filter) cannot be enlarged, improves the performance of the SAW and saves the cost of the SAW. The surface acoustic wave filter provided by the invention introduces the design concept of a band elimination filter, is used for breaking through the requirement of ultra wide band which cannot be realized by a common band-pass filter, is added with a high-pass and low-pass structure to realize far-end inhibition, can be popularized in any frequency band, and has strong popularization. The existing sputtering process is adopted, and the scheme is simple and feasible.
The invention is described below by way of example:
(1) the band elimination filter is formed by two sound surface band elimination filters and pressing a required passband frequency band, and simultaneously the requirement of near-end out-of-band rejection is met.
(2) The unnecessary high-frequency signal is suppressed by a low-pass filter to meet the high-frequency far-end suppression requirement.
(3) The unwanted low frequency signals are suppressed by a high pass filter to achieve the low frequency far end suppression requirement.
(4) 1 low-pass filter, 1 high-pass filter and 2 band-stop filters are cascaded to form a broadband filter of any frequency band.
(5) The design and processing are finished through the traditional manufacturing process.
(6) The verification result is consistent with the design.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (7)
1. A surface acoustic wave filter, comprising: two surface acoustic wave band elimination filters, a low-pass filter and a high-pass filter;
the surface acoustic wave band elimination filter, the low-pass filter and the high-pass filter are cascaded to form the surface acoustic wave filter, wherein the frequency bands blocked by the two surface acoustic wave band elimination filters are different.
2. A surface acoustic wave filter as set forth in claim 1, wherein part or all of the transition sections of said low-pass filter and part or all of the transition sections of said high-pass filter are located in the frequency band blocked by each of said surface acoustic wave band reject filters, respectively.
3. A surface acoustic wave filter according to claim 1, wherein said two surface acoustic wave band reject filters include a low frequency surface acoustic wave band reject filter and a high frequency surface acoustic wave band reject filter.
4. A surface acoustic wave filter as set forth in claim 3, wherein part or all of the transition section of said low-pass filter is located in a frequency band blocked by said high-frequency surface acoustic wave band reject filter.
5. A surface acoustic wave filter as set forth in claim 3, characterized in that part or all of the transition section of the high-pass filter is located in a frequency band blocked by the low-frequency surface acoustic wave band reject filter.
6. A surface acoustic wave filter as set forth in claim 3, wherein said surface acoustic wave band reject filter, said low pass filter, and said high pass filter are cascaded to form a surface acoustic wave filter, comprising:
the high-pass filter, the low-frequency surface acoustic wave band elimination filter, the high-frequency surface acoustic wave band elimination filter and the low-pass filter are sequentially connected in series to form the surface acoustic wave filter.
7. A surface acoustic wave filter according to any of claims 1-6, characterized in that the surface acoustic wave band reject filter comprises at least one first resonator having an interdigital transducer structure as a basic structure.
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| CN202110814610.5A CN113346868A (en) | 2021-07-19 | 2021-07-19 | Surface acoustic wave filter |
| CN202111033629.2A CN113630102A (en) | 2021-07-19 | 2021-09-03 | Acoustic wave filter |
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| CN202110814610.5A CN113346868A (en) | 2021-07-19 | 2021-07-19 | Surface acoustic wave filter |
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| CN115833789A (en) * | 2023-02-09 | 2023-03-21 | 成都湖山电子科技有限公司 | Switch filtering system |
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| CN100502239C (en) * | 2004-07-13 | 2009-06-17 | 中国科学院声学研究所 | An acoustic surface wave duplexer |
| CN103152002A (en) * | 2011-12-07 | 2013-06-12 | 天津海泰超导电子有限公司 | Conode series resonance structure inductance-capacitance filter |
| CN103929148B (en) * | 2013-01-11 | 2017-09-19 | 中兴通讯股份有限公司 | A kind of filter with low insertion loss piezoelectric sound wave bandpass filter and implementation method |
| CN111988007A (en) * | 2020-09-28 | 2020-11-24 | 偲百创(深圳)科技有限公司 | Band-pass filter and filter |
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| CN115833789A (en) * | 2023-02-09 | 2023-03-21 | 成都湖山电子科技有限公司 | Switch filtering system |
| CN115833789B (en) * | 2023-02-09 | 2023-05-02 | 成都湖山电子科技有限公司 | Switch filtering system |
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Application publication date: 20210903 |