Miniaturized surface acoustic wave filter

Abstract

The invention belongs to the technical field of filters, and particularly relates to a miniaturized surface acoustic wave filter. The filter comprises a signal input end, a signal output end and a resonator which are connected with one another, the resonator comprises an interdigital transducer region and two short-circuit reflecting grating regions; the interdigital transducer region is located between the two short-circuit reflecting grating regions; each of the three areas is composed of an input bus bar, an output bus bar and an internal finger bar; the input bus bar in the interdigital transducer area is connected with the common lead, and the output bus bar is grounded; the internal finger strips are located between the input bus bar and the output bus bar and comprise multiple sets of electrode finger strips and multiple sets of extension finger strips, the electrode finger strips of the three areas are the same in period, each electrode finger strip is formed by sequentially connecting three area finger strips with different duty ratios, and the three area finger strips form a high-frequency stop band, an intermediate-frequency stop band and a low-frequency stop band respectively; according to the invention, good anti-interference performance can be realized while the advantages of small size and compact structure are maintained, and the band elimination requirements of different frequency bands are met.

Description

Technical Field

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

[0002] Surface acoustic wave (SAW) filters have been widely used in modern mobile communication systems due to their small size, light weight, low power consumption and high consistency. With the rapid development of wireless communication technology, especially in the fields of 5G, Internet of Things (IoT), smart terminals, etc., the performance requirements of RF front-end modules for filters are gradually increasing. With its excellent frequency selectivity and stability, surface acoustic wave filters have gradually become one of the key components for signal selection and interference suppression in mobile communication equipment. Its flexibility and adaptability in high-frequency and multi-band application scenarios have further promoted its importance in the RF field, making it an indispensable core component in wireless communication equipment.

[0003] Although surface acoustic wave filters have many advantages, the existing technology still has some obvious shortcomings when facing multi-band signal interference. The typical anti-interference method is to use a band-stop filter to suppress interference signals in different frequency bands by increasing the number of stopbands. However, the two commonly used solutions - using multiple independent band-stop filters or a multi-stopband band-stop filter chip - both have their limitations. Whether using a multi-chip design or a single-chip multi-stopband design, increasing the stopband usually requires increasing the number of resonators, resulting in an increase in the overall filter volume, which in turn limits the miniaturization of the filter. In addition, increasing the number of resonators will also increase the design complexity and manufacturing cost, which is not conducive to meeting the current mobile communication equipment requirements for miniaturization, high integration, and low cost. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a miniaturized surface acoustic wave filter, which includes: a signal input end, a signal output end and a resonator; the signal input end and the signal output end are directly connected through a common wire, and the resonator is connected to the common wire; the resonator includes an interdigital transducer area and two short-circuit reflective grid areas; the interdigital transducer area is located between the two short-circuit reflective grid areas; the three areas are all composed of input bus bars, output bus bars and internal fingers; the input bus bars in the interdigital transducer area are connected to the common wire, and the output bus bars in the three areas are all grounded. The internal fingers are located between the input bus bars and the output bus bars, and include multiple groups of electrode fingers and multiple groups of extended fingers.

[0005] Furthermore, the multiple sets of electrode fingers have the same shape and are arranged periodically, and the electrode fingers in the interdigital transducer region and the two short - circuit reflection grating regions have the same period. The electrode fingers are sequentially connected by three regions of finger strips with different duty cycles. The duty cycle of the finger strips in the first region is from 0.15 to 0.18, the duty cycle of the finger strips in the second region is from 0.28 to 0.34, and the duty cycle of the finger strips in the third region is from 0.56 to 0.8. The finger strips in the three regions respectively form a high - frequency stopband, a medium - frequency stopband and a low - frequency stopband, forming a relatively flat filter passband and multiple stopbands within the frequency spectrum range.

[0006] Furthermore, in the short - circuit reflection grating region, both ends of each set of electrode fingers are respectively connected to the input bus bar and the output bus bar through extended fingers.

[0007] Furthermore, in the interdigital transducer region, one of the adjacent two sets of electrode fingers is connected to the input bus bar through an extended finger, and the other is connected to the output bus bar through an extended finger.

[0008] Furthermore, the duty cycle of the extended finger is consistent with the duty cycle at the connection of the electrode finger it is connected to.

[0009] Furthermore, the width of the finger strips in the first region is greater than the width of the finger strips in the second region, and the width of the finger strips in the second region is greater than the width of the finger strips in the third region.

[0010] Furthermore, the electrode thicknesses of each set of electrode fingers, extended fingers and bus bars are the same, and the thickness ≥ 0.1 times the electrode finger period.

[0011] Furthermore, the electrode uses a high - density metal material with a density > 10 g / cm 3 ³.

[0012] The beneficial effects of the present invention are as follows: The surface acoustic wave band - stop filter proposed by the present invention has a simple structure, without the need for cascading multiple resonators. Only through the discrete design of the duty cycle of a single resonator, the suppression of three stopbands is realized. Compared with the impedance - element surface acoustic wave filter structure of traditional multiple resonators, the number of resonators is effectively reduced, thereby reducing the volume of the filter. Without sacrificing the filter performance, the miniaturization of the chip is achieved, with higher integration, and the cost is kept low, which can meet the requirements for the miniaturization and multi - stopbands of filters in mobile communication devices. The present invention provides an efficient anti - interference solution for the radio frequency front - end system, which helps to promote the application and development of surface acoustic wave filters in the direction of more miniaturization and multi - functionality. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic structural diagram of the surface acoustic wave band - stop filter in the present invention; Figure 2 is a schematic overall structural diagram of the resonator in the present invention; Figure 3 Variation diagram of different duty cycles of the regional finger bars with the sound speed in a preferred embodiment of the present invention; Figure 4 Response diagram of a multi-stopband band-stop filter in a preferred embodiment of the present invention. Detailed implementation manners

[0014] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0015] The present invention proposes a miniaturized surface acoustic wave filter, as Figure 1 , Figure 2 shown. The filter includes the following: a signal input terminal 101, a signal output terminal 102, and a resonator 103; the signal input terminal and the signal output terminal are directly connected through a common wire, which simplifies the external circuit connection, and the resonator is connected to the common wire; the resonator includes an interdigital transducer region 201 and two short-circuit reflection grating regions 202; the interdigital transducer region is located between the two short-circuit reflection grating regions; all three regions are composed of an input bus bar 203, an output bus bar 204, and internal finger bars; the input bus bar in the interdigital transducer region is connected to the common wire for receiving signal input and transmitting it to the internal finger bars, and the output bus bar in the interdigital transducer region is grounded for providing a reference potential.

[0016] In some preferred embodiments, the internal finger bars are located between the input bus bar and the output bus bar, and the internal finger bars are composed of multiple groups of electrode finger bars and multiple extension finger bars. The multiple groups of electrode finger bars have the same shape and are arranged periodically, and the electrode finger bars in the interdigital transducer region and the two short-circuit reflection grating regions have the same period.

[0017] In the short-circuit reflection grating region, both ends of each group of electrode finger bars are respectively connected to the input bus bar and the output bus bar through extension finger bars. In the interdigital transducer region, one group of adjacent two groups of electrode finger bars is connected to the input bus bar through an extension finger bar 208, and the other group is connected to the output bus bar through an extension finger bar 209; the duty cycle of the extension finger bar is consistent with the connection part of the electrode finger bar to which it is connected.

[0018] In some preferred embodiments, each group of electrode finger bars is sequentially connected by three regional finger bars with different duty cycles. The duty cycle of the first regional finger bar 205 is 0.15 to 0.18, and the regional width is W1; the duty cycle of the second regional finger bar 206 is 0.28 to 0.34, and the regional width is W2; the duty cycle of the third regional finger bar 207 is 0.56 to 0.8, and the regional width is W3.

[0019] The widths of the three region finger bars satisfy the following relationship: The width of the finger bar in the first region is greater than that in the second region, and the width of the finger bar in the second region is greater than that in the third region, that is, W1>W2>W3.

[0020] Preferably, the electrodes of each group of electrode finger bars, extension finger bars and bus bars are made of high-density metal materials such as gold and platinum with a density > 10 g / cm 3 , and the electrodes have the same thickness, and the thickness ≥ 0.1 times the electrode finger bar period.

[0021] The working principle of the present invention is as follows: Under the heavy-density metal and the metal electrode with a thickness not less than 0.1 times the finger bar period, the duty cycle change of the resonator can greatly adjust the propagation sound velocity of the surface acoustic wave. The duty cycles of different regions change the local propagation characteristics of the surface acoustic wave, and stop bands are formed at corresponding frequencies by modulating the sound velocity: a high-frequency stop band is formed in the first region; a medium-frequency stop band is formed in the second region; a low-frequency stop band is formed in the third region, and finally multiple stop bands are formed within the frequency spectrum range. The widths of the three regions satisfying W1>W2>W3 can achieve internal impedance matching of the finger bars and form a relatively flat filter passband.

[0022] Perform simulation verification on the present invention: The piezoelectric substrate is an ST-cut quartz crystal, and the electrode is located on the surface of the piezoelectric substrate. When the electrode material is platinum and the electrode thickness is 0.1 times the period, the sound velocity change of the surface acoustic wave corresponding to the duty cycle of 0.1 to 0.8 is as Figure 3 shown, where when the duty cycle is 0.1, the maximum sound velocity is 3840 m / s, and when the duty cycle is 0.74, the minimum sound velocity is 3060 m / s.

[0023] To avoid the influence of sound waves in adjacent stop band channels when constructing a multi-stop band filter, according to the sound velocity distribution diagram, the curve is divided into three regions with a boundary width of 100 m / s: the sound velocity range of region 1 is 3600 m / s to 3700 m / s, and the duty cycle is 0.15 to 0.18 at this time; the sound velocity range of region 2 is 3300 m / s to 3400 m / s, and the duty cycle is 0.28 to 0.34 at this time; the sound velocity range of region 3 is 3000 m / s to 3100 m / s, and the duty cycle is 0.56 to 0.8 at this time.

[0024] Using the structure of the present invention, as Figure 4 shown, if the finger bar period is 3.82 μm and the duty cycles of the finger bars in the three regions are 0.17, 0.3, and 0.56 respectively, a band-stop filter with 3 stop bands is formed, and the band-stop frequencies are 411 MHz, 439 MHz, and 477 MHz respectively.

[0025] In summary, the present invention proposes a compact miniaturized surface acoustic wave filter, which can realize a band-stop filter with a flat passband and multiple stopbands through a single resonator to meet the requirements for miniaturization and multiple stopbands of filters in mobile communication devices. The present invention can achieve multiple stopband suppression without increasing the chip volume, thereby realizing better anti-interference performance while maintaining the advantages of small size and compact structure, and meeting the band-stop requirements of different frequency bands.

[0026] The above-described embodiments further elaborate on the purpose, technical solutions, and advantages of the present invention. It should be understood that the above-described embodiments are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made to the present invention within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A miniaturized surface acoustic wave filter, characterized in that, Comprising: A signal input terminal, a signal output terminal and a resonator; the signal input terminal and the signal output terminal are directly connected through a common wire, and the resonator is connected to the common wire; the resonator includes an interdigital transducer region and two short-circuit reflection grating regions; the interdigital transducer region is located between the two short-circuit reflection grating regions; all three regions are composed of an input bus bar, an output bus bar and internal finger bars; the input bus bar in the interdigital transducer region is connected to the common wire, and the output bus bar in the interdigital transducer region is grounded.

2. The miniaturized surface acoustic wave filter according to claim 1, characterized in that, The internal finger bars are located between the input bus bar and the output bus bar, and are composed of multiple groups of electrode finger bars and multiple extension finger bars. The multiple groups of electrode finger bars have the same shape and are arranged periodically, and the electrode finger bars in the interdigital transducer region and the two short-circuit reflection grating regions have the same period.

3. The miniaturized surface acoustic wave filter according to claim 2, wherein In the short-circuit reflection grating region, both ends of each group of electrode finger bars are respectively connected to the input bus bar and the output bus bar through extension finger bars.

4. A miniaturized surface acoustic wave filter according to claim 2, wherein In the interdigital transducer region, one group of adjacent two groups of electrode finger bars is connected to the input bus bar through an extension finger bar, and the other group is connected to the output bus bar through an extension finger bar.

5. A miniaturized surface acoustic wave filter according to claim 2, characterized in that, The duty cycle of the extension finger bar is consistent with the duty cycle at the connection of the electrode finger bar to which it is connected.

6. The miniaturized surface acoustic wave filter according to claim 2, wherein The electrode finger bar is sequentially connected by three region finger bars with different duty cycles. The duty cycle of the first region finger bar is 0.15 to 0.18, the duty cycle of the second region finger bar is 0.28 to 0.34, and the duty cycle of the third region finger bar is 0.56 to 0.

8.

7. A miniaturized surface acoustic wave filter according to claim 6, wherein The width of the first region finger bar is greater than the width of the second region finger bar, and the width of the second region finger bar is greater than the width of the third region finger bar.

8. A miniaturized surface acoustic wave filter according to claim 2, characterized in that, The electrode thickness of each group of electrode finger bars, extension finger bars and bus bars is the same, and the thickness ≥ 0.1 times the period of the electrode finger bar.

9. The miniaturized surface acoustic wave filter according to claim 8, wherein, The electrode uses a high-density metal material with a density > 10 g / cm 3 .

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