Surface acoustic wave band-pass filter

Abstract

The invention belongs to the technical field of filters, and particularly relates to a surface acoustic wave band-pass filter. The filter comprises a parallel acoustic resonator group and a series acoustic resonator group, wherein all resonators are connected through metal wires; the parallel acoustic resonator group is composed of at least two parallel resonators, and each parallel resonator comprises a piezoelectric substrate, a metal interdigital transducer and a temperature compensation function film layer; the metal interdigital transducer is located on the piezoelectric substrate, and the temperature compensation function film layer completely covers the upper surface of the metal interdigital transducer; wherein the metal interdigital transducer comprises a signal input interdigital and a signal output interdigital; the series acoustic resonator group is composed of at least two series resonators, and the series resonator structure adopts a first resonator structure, a second resonator structure or a third resonator structure; the problem that a traditional broadband surface acoustic wave filter is poor in temperature stability is solved, meanwhile, the pass band group delay flatness of the filter is improved, and the filter has better comprehensive filtering performance.

Description

Technical Field

[0001] The invention belongs to the technical field of filters, and in particular relates to a surface acoustic wave bandpass filter. Background Art

[0002] Surface acoustic wave filters have the advantages of small size, light weight, and good consistency. With the rapid growth of mobile communications, surface acoustic wave filters have been widely used in mobile communication equipment. As various RF front-end systems have higher requirements for signal transmission rate and bandwidth, the demand for broadband low-loss filters is increasing.

[0003] Traditional broadband surface acoustic wave filters have poor temperature stability, and the filter frequency varies greatly with temperature. Surface acoustic wave filters covered with a temperature compensation functional layer have good temperature stability, but there are serious surface acoustic waves in the functional layer on the surface of the filter, which can easily cause spikes in the group delay of the filter passband, resulting in large fluctuations in the filter group delay, causing signal delay and distortion in the receiving link, and affecting the actual use of the filter. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a surface acoustic wave bandpass filter, which includes: a parallel acoustic wave resonator group and a series acoustic wave resonator group, and all resonators are connected by metal wires;

[0005] The parallel acoustic wave resonator group is composed of at least two parallel resonators, and the parallel resonator includes a piezoelectric substrate, a metal interdigital transducer, and a temperature compensation functional film layer; the metal interdigital transducer is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; wherein the metal interdigital transducer includes a signal input interdigital transducer and a signal output interdigital transducer;

[0006] The series acoustic wave resonator group is composed of at least two series resonators, and the series resonator structure adopts the first resonator structure, the second resonator structure or the third resonator structure; the three resonator structures all include a piezoelectric substrate, a metal interdigital transducer, a temperature compensation functional film layer and a metal pattern array.

[0007] Preferably, the metal interdigital transducer in the first resonator structure is located on the piezoelectric substrate, the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; and the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer.

[0008] Preferably, the second resonator structure also includes a protective film layer, the metal interdigital transducer in the second resonator structure is located on the piezoelectric substrate, the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer, and the protective film layer completely covers the upper surface of the temperature compensation functional film layer; the metal pattern array is periodically arranged on the upper surface of the protective film layer.

[0009] Preferably, the third resonator structure also includes a protective film layer, the metal interdigital transducer in the third resonator structure is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer; the protective film layer completely covers the metal pattern array, and the protective film layer has the same protrusion shape as the metal array.

[0010] Furthermore, the period of the metal pattern array is twice the center distance between adjacent interdigital fingers in the metal interdigital transducer.

[0011] Furthermore, the metal pattern array is composed of multiple groups of metal pattern strips, each group of metal pattern strips is parallel to the fingers in the metal interdigital transducer, and the center of each group of metal pattern strips is located directly above the center of the gap between adjacent signal output fingers and signal input fingers.

[0012] Furthermore, the metal pattern strip is composed of at least three sub-patterns of the same shape, which are symmetrical from large to small along both sides toward the center.

[0013] Furthermore, the piezoelectric substrate material is lithium niobate material, and the temperature compensation functional layer film material and the protective film layer material are SiO2 or SiN.

[0014] The beneficial effects of the present invention are as follows: the surface acoustic wave bandpass filter designed by the present invention solves the group delay spikes that appear in the passband of the traditional broadband temperature-compensated surface acoustic wave filter, improves the passband flatness of the filter and reduces the group delay fluctuation, so that the filter has better comprehensive filtering performance. At the same time, it is easy to implement in terms of technology and can be promoted in any frequency band. In the receiving system, the filter can improve the waveform distortion caused by the fluctuation of the group delay in the receiving link, the inter-code interference of the baseband signal and other problems, which helps to improve the signal transmission quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the surface acoustic wave bandpass filter in the present invention;

[0016] Figure 2 A top view of a parallel resonator according to a preferred embodiment of the present invention;

[0017] Figure 3 The parallel resonator of the present invention is Figure 2 A cross-sectional side view of the dashed line 1;

[0018] Figure 4 A top view of a first resonator structure of a series resonator in a preferred embodiment of the present invention;

[0019] Figure 5 The series resonator in the present invention is Figure 4 A cross-sectional side view of dashed line 2;

[0020] Figure 6 The series resonator in the present invention is Figure 4 A cross-sectional side view of the dashed line 3;

[0021] Figure 7 The series resonator in the present invention is Figure 4 a cross-sectional side view of the dashed line 4;

[0022] Figure 8 The schematic diagram of the sub-pattern of the metal pattern strip in the present invention being an ellipse;

[0023] Fig. 9 The sub-pattern of the metal pattern strip in the present invention is a schematic diagram of a diamond shape;

[0024] Fig.10 A cross-sectional side view of a second resonator structure of a series resonator in a preferred embodiment of the present invention;

[0025] Fig.11 A cross-sectional side view of a third resonator structure of a series resonator in a preferred embodiment of the present invention;

[0026] Fig.12 It is a comparison diagram of the group delay fluctuation of the surface acoustic wave bandpass filter in the present invention and the group delay fluctuation of the conventional structure. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The present invention proposes a surface acoustic wave bandpass filter, such as Figure 1 As shown, the filter includes: a parallel acoustic wave resonator group and a series acoustic wave resonator group, and all resonators are connected by metal wires.

[0029] The parallel acoustic wave resonator group consists of at least two parallel resonators, such as Figure 2 , Figure 3 As shown, the parallel resonator includes a piezoelectric substrate 201, a metal interdigital transducer 202, and a temperature compensating functional film layer 203; the metal interdigital transducer is located on the piezoelectric substrate, and the temperature compensating functional film layer completely covers the upper surface of the metal interdigital transducer; wherein the metal interdigital transducer includes a signal input interdigital transducer 2021 and a signal output interdigital transducer 2022, and the temperature compensating functional film layer has a flattened upper surface.

[0030] The series acoustic wave resonator group is composed of at least two series resonators, and the series resonator structure adopts the first resonator structure, the second resonator structure or the third resonator structure; the three resonator structures all include a piezoelectric substrate, a metal interdigital transducer, a temperature compensation functional film layer and a metal pattern array.

[0031] First resonator structure:

[0032] like Figures 4 to 7 As shown, the metal interdigital transducer is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer.

[0033] The metal pattern array is composed of multiple groups of metal pattern strips, each group of metal pattern strips is parallel to the interdigital fingers in the metal interdigital transducer, and the center of each group of metal pattern strips is located directly above the center of the gap between adjacent signal output interdigital fingers and signal input interdigital fingers.

[0034] Preferably, the period of the metal pattern array is twice the center spacing between adjacent fingers in the metal interdigital transducer.

[0035] Preferably, the metal pattern strip is composed of at least three sub-patterns of the same shape, symmetrical from large to small along the two sides toward the center. The sub-patterns can be circular, diamond, elliptical, triangular, etc. Figure 8 , Fig. 9 As shown; wherein a single sub-graphic is not limited to a symmetrical image.

[0036] Second resonator structure:

[0037] like Fig.10 As shown, the second resonator structure also includes a protective film layer. The metal interdigital transducer in the second resonator structure is located on the piezoelectric substrate. The temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer. The protective film layer completely covers the upper surface of the temperature compensation functional film layer. The metal pattern array is periodically arranged on the upper surface of the protective film layer.

[0038] The third resonator structure:

[0039] like Fig.11 As shown, the third resonator structure also includes a protective film layer. The metal interdigital transducer in the third resonator structure is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer; the protective film layer completely covers the metal pattern array, and the protective film layer has the same protrusion shape as the metal array.

[0040] It should be noted that the metal pattern array structures of the first resonator structure, the second resonator structure and the third resonator structure are the same.

[0041] Preferably, the piezoelectric substrate material is lithium niobate material, the Euler angle range of the lithium niobate material is within (0, -120° to -30°, 0), and the temperature compensation functional layer film material is SiO2 or SiN.

[0042] Evaluation of the present invention:

[0043] The filter designed by the present invention and the existing conventional filter are simulated, and the comparison results of the group delay fluctuation of the filter structure of the present invention and the group delay fluctuation of the conventional filter structure are shown as follows: Fig.12 As shown in the figure, it can be seen that the structure of the present invention improves the delay spurs in the passband. Compared with the conventional structure, the group delay fluctuation in the range of 520MHz to 540MHz of the present invention is reduced from 60ns to 10ns.

[0044] In summary, the surface acoustic wave bandpass filter designed in the present invention can improve the problem of poor temperature stability of traditional broadband surface acoustic wave filters, while improving the flatness of the filter passband group delay, so that the filter has better comprehensive filtering performance, and helps to improve the waveform distortion caused by the fluctuation of the group delay in the receiving link, the inter-code interference of the baseband signal and other problems.

[0045] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface acoustic wave bandpass filter, characterized in that: include: A parallel acoustic wave resonator group and a series acoustic wave resonator group, all resonators are connected by metal wires; The parallel acoustic wave resonator group is composed of at least two parallel resonators, and the parallel resonators include a piezoelectric substrate, a metal interdigital transducer, and a temperature compensation functional film layer; the metal interdigital transducer is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; The metal interdigital transducer comprises a signal input interdigital and a signal output interdigital; The series acoustic wave resonator group is composed of at least two series resonators, and the series resonator structure adopts the first resonator structure, the second resonator structure or the third resonator structure; the three resonator structures all include a piezoelectric substrate, a metal interdigital transducer, a temperature compensation functional film layer and a metal pattern array.

2. A surface acoustic wave bandpass filter according to claim 1, characterized in that: The metal interdigital transducer in the first resonator structure is located on the piezoelectric substrate, the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer.

3. A surface acoustic wave bandpass filter according to claim 1, characterized in that: The second resonator structure also includes a protective film layer. The metal interdigital transducer in the second resonator structure is located on the piezoelectric substrate. The temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer. The protective film layer completely covers the upper surface of the temperature compensation functional film layer. The metal pattern array is periodically arranged on the upper surface of the protective film layer.

4. A surface acoustic wave bandpass filter according to claim 1, characterized in that: The third resonator structure also includes a protective film layer. The metal interdigital transducer in the third resonator structure is located on the piezoelectric substrate, and the temperature compensation functional film layer completely covers the upper surface of the metal interdigital transducer; the metal pattern array is periodically arranged on the upper surface of the temperature compensation functional film layer; the protective film layer completely covers the metal pattern array, and the protective film layer has the same protrusion shape as the metal array.

5. A surface acoustic wave bandpass filter according to any one of claims 1 to 4, characterized in that: The period of the metal pattern array is twice the center spacing between adjacent interdigital fingers in the metal interdigital transducer.

6. A surface acoustic wave bandpass filter according to any one of claims 1 to 4, characterized in that: The metal pattern array is composed of multiple groups of metal pattern strips, each group of metal pattern strips is parallel to the interdigital fingers in the metal interdigital transducer, and the center of each group of metal pattern strips is located directly above the center of the gap between adjacent signal output interdigital fingers and signal input interdigital fingers.

7. A surface acoustic wave bandpass filter according to claim 6, characterized in that: The metal pattern strip is composed of at least three sub-patterns of the same shape and symmetrical from large to small along both sides toward the center.

8. The surface acoustic wave bandpass filter according to claim 1, characterized in that: The piezoelectric substrate material is lithium niobate material, and the temperature compensation functional layer film material and the protection film layer material are SiO2 or SiN.

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