A low-frequency, low-loss surface acoustic wave filter and electronic equipment

Abstract

The present invention relates to the technical field of surface acoustic wave filters, and discloses a low-frequency, low-loss surface acoustic wave filter and an electronic device. The low-frequency, low-loss surface acoustic wave filter adopts a three-transducer linear structure of a Rayleigh wave fluctuation mode, including an intermediate transducer made on a substrate and two-end transducers located at both ends of the intermediate transducer, the intermediate transducer adopts a variable-track weighted transducer, and the two-end transducers adopt a total reflection transducer. The Rayleigh wave fluctuation mode design is easy to implement in terms of process; the three-transducer linear design structure is more conducive to reducing the area of ​​the surface acoustic wave filter, and is more conducive to controlling the acoustic wave transmission of the transducer, thereby realizing the miniaturized design of the low-frequency, low-loss surface acoustic wave filter.

Description

Technical Field

[0001] The invention relates to the technical field of surface acoustic wave filters, and in particular to a low-frequency, low-loss surface acoustic wave filter and electronic equipment. Background Art

[0002] Surface acoustic wave filter is a device that realizes filtering function by making interdigital transducers on piezoelectric materials, using the piezoelectric effect and inverse piezoelectric effect of piezoelectric materials to complete the mutual conversion of electrical signals and acoustic signals, and performing signal processing during the propagation of acoustic signals. Its performance parameters are jointly determined by the piezoelectric substrate material, the design parameters of the interdigital transducer, and the process manufacturing accuracy.

[0003] The characteristic of low-loss surface acoustic wave filter is low insertion loss (IL = 1dB ~ 5dB). The method of achieving low loss in surface acoustic wave filter is: reasonably design the period of the interdigital transducer and the corresponding metal film thickness, so that the surface acoustic wave excited by the interdigital transducer has the optimal intensity and purity; adopt the reflection grating design at both ends of the transducer to confine the sound wave (energy) in the transducer; design the transducer and the reflection grating with equal aperture to reduce the leakage of sound wave (energy). The wavelength (period) λ of the surface acoustic wave filter = speed V / frequency f. The speed is most related to the substrate type. When the frequency of the surface acoustic wave filter to be manufactured is fixed, the wavelength is also determined. The common surface acoustic wave fluctuation modes are divided into Rayleigh waves and leaky waves. Rayleigh waves are easy to be excited and have good purity, but the available optimal excitation intensity frequency band is narrow, which is suitable for making narrow-band small-loss surface acoustic wave filters; leaky waves can only be excited with optimal intensity and purity under a specific metal film thickness, which is suitable for making miniaturized and wide-bandwidth small-loss surface acoustic wave filters, but for low-frequency filters, the wavelength is large (the wavelength corresponding to a frequency of 21.4MHz is about 200μm), and the thickness of the metal film that excites the optimal intensity and purity leaky waves is too thick (about 8μm~20μm), which has exceeded the upper limit of the metal film thickness produced by the lithography equipment. Therefore, the design of low-frequency and small-loss surface acoustic wave filters gives priority to the Rayleigh wave fluctuation mode in the surface acoustic wave.

[0004] At present, in the design of low-frequency, low-loss surface acoustic wave filters, the Rayleigh wave fluctuation mode cannot be used to achieve miniaturization due to the long wavelength. Filters designed using the leaky wave fluctuation mode are difficult to achieve in terms of technology because the thickness of the metal film required for manufacturing is too thick, which seriously hinders the application of low-frequency, low-loss surface acoustic wave filters in signal processing equipment. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a low-frequency, low-loss surface acoustic wave filter and an electronic device in view of the problems existing in the prior art.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a low-frequency, low-loss surface acoustic wave filter. The low-frequency, low-loss surface acoustic wave filter adopts a three-transducer linear structure of a Rayleigh wave fluctuation mode, an intermediate transducer made on a substrate and two-end transducers located at both ends of the intermediate transducer. The intermediate transducer adopts a variable-track weighted transducer, and the two-end transducers adopt a total reflection transducer.

[0007] The beneficial effects of the present invention are as follows: the present invention adopts the Rayleigh wave fluctuation mode design, which is easy to implement in terms of process; the middle transducer adopts the apodization weighted design, and the first-stage structure can obtain the stopband suppression performance that can only be obtained by the two-stage structure with equal finger length design, thereby reducing the width of the filter chip; at the same time, the transducers at both ends adopt the total reflection design structure, which can reduce the leakage of sound waves (energy) without the need for a reflection grating structure, thereby not only reducing the length of the filter chip, but also achieving low-loss performance. The three-transducer linear design structure is more conducive to reducing the area of ​​the surface acoustic wave filter, and is more conducive to controlling the sound wave transmission of the transducer, thereby realizing the miniaturization design of the low-frequency low-loss surface acoustic wave filter, thereby improving the performance and application range of the low-frequency low-loss surface acoustic wave filter, and the present invention can be widely used in electronic information fields such as radar, base stations, and radio stations.

[0008] Based on the above technical solution, the present invention can also be improved as follows.

[0009] Further, the function expression of the interdigital length variation curve of the intermediate transducer is: h(t)=E(t)+jG(t); E(t) is the real part of the expression, G(t) is the imaginary part of the expression; t is the signal transmission time;

[0010] The fingers of the intermediate transducer adopt a split-finger structure, and each period includes a pair of signal electrode fingers and a pair of ground electrode fingers. The length of the left finger in each pair of signal electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t); the length of the left finger in each pair of ground electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t).

[0011] Furthermore, the finger width of the intermediate transducer is λ / 8, where λ is the wavelength of the surface acoustic wave filter.

[0012] Furthermore, the target amplitude-frequency curve function of the intermediate transducer is:

[0013]

[0014] By simulating and calculating the target amplitude-frequency curve function, the minimum number of fingers and the corresponding finger length of each finger that meet the stopband suppression and rectangularity requirements are obtained; where k is the weighting coefficient, t is the delay of any finger, τ is the total delay, a is the compensation coefficient, and B is the bandwidth.

[0015] Furthermore, the two-end transducer is provided with six fingers with a width of λ / 12 in each period, λ being the wavelength of the surface acoustic wave filter, one for the signal electrode and one for the ground electrode, and the remaining four for the suspension electrodes. The reflection coefficient is maximized by adjusting the position of the suspension electrode.

[0016] Furthermore, the signal electrode and the ground electrode of each cycle of the transducer at both ends can be interchanged, and the electrode polarity setting complies with the tap principle.

[0017] In order to solve the above technical problem, an embodiment of the present invention further provides an electronic device, which includes the low-frequency, low-loss surface acoustic wave filter described in the above technical solution.

[0018] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description or learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic diagram of the structure of a low-frequency, low-loss surface acoustic wave filter provided by an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of a partial structure of an intermediate transducer provided in an embodiment of the present invention;

[0021] Figure 3 This is a schematic diagram of the structure of a low-frequency, low-loss surface acoustic wave filter when G(t) is zero according to an embodiment of the present invention;

[0022] Figure 4 Schematic diagram of the local structure of the intermediate transducer when G(t) is zero in an embodiment of the present invention;

[0023] Figure 5 A schematic diagram of the local structure of a two-terminal transducer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present disclosure through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0025] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present disclosure, it should be understood by those skilled in the art that an aspect described herein may be implemented independently of any other aspect, and two or more of these aspects may be combined in various ways. For example, any number of aspects described herein may be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein may be used to implement this device and / or practice this method.

[0026] Figure 1 It is a schematic diagram of the structure of a low-frequency, low-loss surface acoustic wave filter provided by an embodiment of the present invention, which adopts a three-transducer linear structure of the Rayleigh wave fluctuation mode. Rayleigh waves do not need to meet the conditions of metal film thickness, are relatively easy to be excited and have good purity, and are suitable for making miniaturized and wide-bandwidth low-loss surface acoustic wave filters, and are suitable for making narrow-band low-loss surface acoustic wave filters. The three-transducer non-reflection grating linear design structure is more conducive to reducing the area of ​​the surface acoustic wave filter, and is more conducive to controlling the sound wave (energy) transmission of the transducer, and realizing the miniaturized design of the low-frequency, low-loss surface acoustic wave filter.

[0027] The low-frequency, low-loss surface acoustic wave filter includes an intermediate transducer 1 made on a substrate and two-end transducers 2 located at both ends of the intermediate transducer, wherein the intermediate transducer adopts a variable-track weighted transducer, and the two-end transducers adopt a total reflection transducer. A design period 3 of the intermediate transducer includes a pair of fingers of a split-finger structure of a signal electrode and a ground electrode; a design period 4 of the two-end transducers includes six fingers, one for the signal electrode and one for the ground electrode, and the remaining four are suspended electrodes. The intermediate transducer of the low-frequency, low-loss surface acoustic wave filter provided in an embodiment of the present invention serves as an input transducer, and the two-end transducers serve as output transducers. The input transducer and the output transducer can be used interchangeably.

[0028] The middle transducer adopts a variable-trace weighted design, which has the effect of increasing the stopband suppression performance and reducing the width of the filter chip; the transducers at both ends adopt a full-reflection design structure, which can reduce the leakage of sound waves (energy) without the need for a reflection grating structure, thereby achieving low-loss performance while reducing the length of the filter chip.

[0029] The target amplitude-frequency curve is expressed by the function H(f) (H(f) can have multiple expressions), and the change curve h(t) of the length of the interdigital finger of the interdigital transducer with apodization weighting structure and its realized amplitude-frequency characteristic curve H(f) are in Fourier transform relationship. According to the function of the target amplitude-frequency characteristic curve, the function expression of the interdigital length change curve h(t) = E(t) + jG(t) is obtained by Fourier transform, thereby completing the design of the apodization weighted interdigital transducer. E(t) is the real part of the expression, G(t) is the imaginary part of the expression, and t is the signal transmission time. The signal transmission time t can be converted into position reflected on the chip, that is, the finger length at different positions is expressed as a function of the position.

[0030] like Figure 2 As shown, the fingers of the intermediate transducer adopt a split-finger structure, which can effectively reduce inter-finger reflection and suppress second harmonics. Each cycle includes a pair of signal electrode fingers 11 and a pair of ground electrode fingers 12. The length of the left finger in each pair of signal electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t); the length of the left finger in each pair of ground electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t). The finger width of the intermediate transducer is λ / 8, where λ is the wavelength of the surface acoustic wave filter.

[0031] When G(t) is zero, the low-frequency, low-loss SAW filter structure is as follows: Figure 3 As shown; the local structure of the intermediate transducer is as follows Figure 4 As shown. Figure 3 and Figure 4 It can be seen that when G(t) is zero, the length of the left finger and the length of the right finger in each pair of signal electrode fingers are both E(t). The length of the left finger and the length of the right finger in each pair of ground electrode fingers are both E(t).

[0032] In the embodiment of the present invention, the target amplitude-frequency curve function is:

[0033]

[0034] By simulating and calculating the target amplitude-frequency curve function, the minimum number of fingers and the corresponding finger length of each finger that meet the stopband suppression and rectangularity requirements are obtained; where k is the weighting coefficient, t is the delay of any finger, τ is the total delay, a is the compensation coefficient, and B is the bandwidth.

[0035] like Figure 5 As shown, the two-end transducer is provided with six fingers with a width of λ / 12 in each period, λ is the wavelength of the surface acoustic wave filter, one for the signal electrode 21 and one for the ground electrode 22, and the remaining four for the suspension electrodes 23. By adjusting the position of the suspension electrode 23, the reflection coefficient is maximized.

[0036] Optionally, in one embodiment, the signal electrode and the ground electrode of each cycle of the two-terminal transducer can be interchanged, and the electrode polarity setting complies with the tap principle.

[0037] An embodiment of the present invention further provides an electronic device, the electronic device comprising the low-frequency, low-loss surface acoustic wave filter provided by the above embodiment. The electronic device may be a radar, a base station, a radio station, and the like.

[0038] In the above embodiment, the middle transducer 1 adopts the design structure of the apodization weighted interdigital transducer, and the first-stage structure can obtain the stopband suppression performance that can only be obtained by the two-stage structure of equal finger length design, thereby reducing the width of the filter chip; the transducers 2 at both ends adopt a full reflection design structure, which does not require a reflection grating structure, can also reduce the leakage of sound waves (energy), reduce the length of the filter chip, and achieve low-loss performance at the same time, thereby achieving the area of ​​the low-frequency and low-loss surface acoustic wave filter reduced to 1 / 3 of the original area, which is conducive to the miniaturization of the filter, and improves the performance and application range of the low-frequency and low-loss surface acoustic wave filter. The present invention can be widely used in electronic information fields such as radars, base stations, and radio stations.

[0039] The low-frequency, low-loss surface acoustic wave filter provided by the embodiment of the present invention is suitable for the frequency range of 5MHz to 200MHz, when the insertion loss is less than 8dB, the metal film thickness h (unit: μm) is less than 4v / 100f (speed v unit: m / s; frequency f unit: MHz), and the chip width (unit: mm) is less than 300 / f.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A low-frequency, low-loss surface acoustic wave filter, characterized in that: The low-frequency, low-loss surface acoustic wave filter adopts a three-transducer linear structure of a Rayleigh wave fluctuation mode, including a middle transducer made on a substrate and two-end transducers located at both ends of the middle transducer, the middle transducer adopts an apodization weighted transducer, and the two-end transducers adopt a total reflection transducer; The two-end transducer is provided with six fingers with a width of λ / 12 in each period, λ being the wavelength of the surface acoustic wave filter, one for the signal electrode and one for the ground electrode, and the remaining four for the suspension electrodes. The reflection coefficient is maximized by adjusting the position of the suspension electrodes.

2. The low-frequency, low-loss surface acoustic wave filter according to claim 1, characterized in that: The function expression of the interdigital length variation curve of the intermediate transducer is: h(t)=E(t)+jG(t); E(t) is the real part of the expression, G(t) is the imaginary part of the expression; t is the signal transmission time; The fingers of the intermediate transducer adopt a split-finger structure, and each period includes a pair of signal electrode fingers and a pair of ground electrode fingers. The length of the left finger in each pair of signal electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t); the length of the left finger in each pair of ground electrode fingers is E(t)+G(t), and the length of the right finger is E(t)-G(t).

3. The low-frequency, low-loss surface acoustic wave filter according to claim 2, characterized in that: The finger width of the intermediate transducer is λ / 8, where λ is the wavelength of the surface acoustic wave filter.

4. The low-frequency, low-loss surface acoustic wave filter according to claim 1, characterized in that: The target amplitude-frequency curve function of the intermediate transducer is: Where f0 is the target center frequency and f is an arbitrary frequency; By simulating and calculating the target amplitude-frequency curve function, the minimum number of fingers and the corresponding finger length of each finger that meet the stopband suppression and rectangularity requirements are obtained; where k is the weighting coefficient, t is the delay of any finger, τ is the total delay, a is the compensation coefficient, and B is the bandwidth.

5. The low-frequency, low-loss surface acoustic wave filter according to claim 1, characterized in that: The signal electrode and the ground electrode of each cycle of the transducer at both ends can be interchanged, and the electrode polarity setting complies with the tap principle.

6. An electronic device, characterized in that: The electronic device comprises the low-frequency, low-loss surface acoustic wave filter according to any one of claims 1 to 5.

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