A miniaturized surface acoustic wave filter

Abstract

The present invention belongs to the technical field of filters, and specifically relates to a miniaturized surface acoustic wave filter; the filter comprises: a signal input end, a signal output end and a resonator that are interconnected; the resonator comprises an interdigital transducer region and two short-circuit reflective grating regions; the interdigital transducer region is located between the two short-circuit reflective grating regions; the three regions are all composed of an input bus bar, an output bus bar and an internal finger bar; the input bus bar in the interdigital transducer region is connected to a common conductor, and the output bus bar is grounded; the internal finger bar is located between the input bus bar and the output bus bar, and comprises a plurality of groups of electrode finger bars and a plurality of groups of extended finger bars, the electrode finger bars of the three regions have the same period, and each electrode finger bar is formed by three regional fingers with different duty cycles connected in sequence, and the three regional fingers respectively form a high-frequency stop band, a medium-frequency stop band and a low-frequency stop band; the present invention can achieve good anti-interference performance while maintaining the advantages of small size and compact structure, and meet the band-stop requirements of different frequency bands.

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 are 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, particularly in areas such as 5G, the Internet of Things (IoT), and smart terminals, the performance requirements for filters in RF front-end modules are gradually increasing. With their 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 devices. Their flexibility and adaptability in high-frequency and multi-band applications have further promoted their importance in the RF field, making them an indispensable core component in wireless communication equipment.

[0003] Although surface acoustic wave filters have many advantages, existing technologies still have some obvious shortcomings when facing multi-band signal interference. The typical anti-interference method is to use band-stop filters to suppress interference signals in different frequency bands by increasing the number of stopbands. However, the two commonly used solutions currently - 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] To address the shortcomings of the existing technology, the present invention proposes a miniaturized surface acoustic wave filter, comprising: a signal input terminal, a signal output terminal, and a resonator; the signal input terminal and the signal output terminal are directly connected via a common conductor, and the resonator is connected to the common conductor; the resonator includes an interdigital transducer region and two short-circuit reflector regions; the interdigital transducer region is located between the two short-circuit reflector regions; all three regions are composed of input bus bars, output bus bars, and internal fingers; the input bus bars in the interdigital transducer region are connected to the common conductor, and the output bus bars in the three regions are all grounded. The internal fingers are located between the input and output bus bars and include multiple groups of electrode fingers and multiple groups of extended fingers.

[0005] Furthermore, multiple groups of electrode fingers have the same shape and are arranged in a periodic pattern. The electrode fingers in the interdigital transducer region and the two short-circuit reflector regions have the same periodic pattern. The electrode fingers are formed by sequentially connecting three regional fingers with different duty cycles: the first regional finger has a duty cycle of 0.15 to 0.18, the second regional finger has a duty cycle of 0.28 to 0.34, and the third regional finger has a duty cycle of 0.56 to 0.8. The three regional fingers form a high-frequency stopband, a mid-frequency stopband, and a low-frequency stopband, respectively, forming a relatively flat filter passband and multiple stopbands within the frequency spectrum.

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

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

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

[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 thickness of each group of electrode fingers, extension fingers and bus bars is the same, and the thickness is ≥ 0.1 times the electrode finger period.

[0011] Furthermore, the electrode adopts a density of >10g / cm 3 High density metal materials.

[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, does not require multiple resonators in cascade, and only realizes three-stopband suppression through the discrete design of the duty cycle of a single resonator. Compared with the traditional multi-resonator impedance element surface acoustic wave filter structure, it effectively reduces the number of resonators, thereby reducing the volume of the filter. Without sacrificing the performance of the filter, the miniaturization of the chip is achieved, with a higher degree of integration and a lower cost, which can meet the needs of mobile communication equipment for filter miniaturization and multiple stopbands. The present invention provides an efficient anti-interference solution for RF front-end systems, which helps to promote the application and development of surface acoustic wave filters in the direction of smaller size and multi-function. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the structure of the surface acoustic wave band-stop filter in the present invention;

[0014] Figure 2 Schematic diagram of the overall structure of the resonator in the present invention;

[0015] Figure 3 This is a graph showing how the duty ratios of the regional fingers vary with the speed of sound in a preferred embodiment of the present invention;

[0016] Figure 4 This is a response diagram of a multi-stopband filter according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0018] The present invention proposes a miniaturized surface acoustic wave filter, such as Figure 1 、 Figure 2 As shown, the filter includes the following contents: 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 IDT area 201 and two short-circuit reflector areas 202; the IDT area is located between the two short-circuit reflector areas; the three areas are all composed of an input bus bar 203, an output bus bar 204 and internal fingers; the input bus bar in the IDT area is connected to the common wire for receiving signal input and transmitting it to the internal fingers, and the output bus bar in the IDT area is grounded for providing a reference potential.

[0019] In some preferred embodiments, the internal fingers are located between the input bus bar and the output bus bar, and the internal fingers are composed of multiple groups of electrode fingers and multiple extended fingers. The multiple groups of electrode fingers have the same shape and are arranged periodically, and the electrode fingers in the interdigital transducer area and the two short-circuit reflector areas have the same period.

[0020] In the short-circuit reflector region, each set of electrode fingers connects to the input and output busbars via extended fingers at both ends. In the interdigital transducer region, one set of two adjacent sets of electrode fingers connects to the input busbar via extended finger 208, while the other set connects to the output busbar via extended finger 209. The duty cycle of the extended finger matches the connection point of the electrode finger to which it connects.

[0021] In some preferred embodiments, each group of electrode fingers is composed of three regional fingers with different duty cycles connected in sequence, the duty cycle of the first regional finger 205 is 0.15 to 0.18, and the regional width is W1; the duty cycle of the second regional finger 206 is 0.28 to 0.34, and the regional width is W2; the duty cycle of the third regional finger 207 is 0.56 to 0.8, and the regional width is W3.

[0022] The widths of the three area bars satisfy the following relationship:

[0023] The width of the finger strips in the first region is greater than that in the second region, and the width of the finger strips in the second region is greater than that in the third region, that is, W1>W2>W3.

[0024] Preferably, all electrodes of each group of electrode fingers, extension fingers and bus bars are made of gold, platinum or other materials with a density greater than 10 g / cm 3 The high-density metal material has the same electrode thickness, and the thickness is ≥ 0.1 times the electrode finger period.

[0025] The working principle of the present invention is as follows:

[0026] By varying the resonator's duty cycle under a heavy-density metal and metal electrodes with a thickness no less than 0.1 times the finger period, the propagation velocity of surface acoustic waves can be significantly adjusted. The duty cycle of different regions modulates the local propagation characteristics of the surface acoustic wave, forming stopbands at corresponding frequencies by modulating the sound velocity: the first region forms a high-frequency stopband; the second region forms a mid-frequency stopband; the third region forms a low-frequency stopband, ultimately forming multiple stopbands within the frequency spectrum. The widths of the three regions satisfying W1>W2>W3 achieve internal impedance matching within the fingers, forming a relatively flat filter passband.

[0027] The present invention is simulated and verified:

[0028] The piezoelectric substrate is an ST-cut quartz crystal, and the electrodes are 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 of the surface acoustic wave corresponding to the duty cycle of 0.1 to 0.8 changes as shown below: Figure 3 As shown, when the duty cycle is 0.1, the maximum sound speed is 3840m / s, and when the duty cycle is 0.74, the minimum sound speed is 3060m / s.

[0029] To avoid the influence of acoustic waves from adjacent stopband channels when constructing a multi-stopband filter, the curve is divided into three regions with a boundary width of 100 m / s according to the sound velocity distribution diagram: 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; 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; 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.

[0030] Using the structure of the present invention, Figure 4 As shown in FIG, if the finger period is 3.82 μm and the finger duty ratios of the three regions are 0.17, 0.3, and 0.56, respectively, a band-stop filter with three stop bands is formed, and the stop frequencies are 411 MHz, 439 MHz, and 477 MHz, respectively.

[0031] In summary, the present invention proposes a compact, miniaturized surface acoustic wave (SAW) filter that achieves a flat passband and multiple stopbands through a single resonator, meeting the demand for miniaturized filters and multiple stopbands in mobile communication devices. This invention achieves multi-stopband suppression without increasing chip size, thereby maintaining the advantages of a small size and compact structure while achieving good anti-interference performance and meeting the band-stop requirements of different frequency bands.

[0032] 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 plans 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 scope of protection of the present invention.

Claims

1. A miniaturized surface acoustic wave filter, characterized in that: include: A signal input terminal, a signal output terminal and a resonator; the signal input terminal and the signal output terminal are directly connected via a common wire, and the resonator is connected to the common wire; the resonator includes an IDT region and two short-circuit reflector regions; the IDT region is located between the two short-circuit reflector regions; the three regions are all composed of an input bus bar, an output bus bar and an internal finger bar; the input bus bar in the IDT region is connected to the common wire, and the output bus bar in the IDT region is grounded; the internal finger bar is located between the input bus bar and the output bus bar, and is connected to the common wire. The device is composed of multiple groups of electrode fingers and multiple extended fingers. The multiple groups of electrode fingers have the same shape and are arranged periodically. The electrode fingers in the interdigital transducer area and the two short-circuit reflector areas have the same period. The electrode fingers are connected in sequence by three regional fingers with different duty cycles. The duty cycle of the fingers in the first regional area is 0.15 to 0.18, the duty cycle of the fingers in the second regional area is 0.28 to 0.34, and the duty cycle of the fingers in the third regional area is 0.56 to 0.

8. The width of the fingers in the first regional area is greater than that of the fingers in the second regional area, and the width of the fingers in the second regional area is greater than that of the fingers in the third regional area.

2. The miniaturized surface acoustic wave filter according to claim 1, characterized in that: In the short-circuit reflector region, two ends of each group of electrode fingers are connected to the input bus bar and the output bus bar through extended fingers.

3. The miniaturized surface acoustic wave filter according to claim 1, characterized in that: In the IDT region, one of two adjacent groups of electrode fingers is connected to the input bus bar through an extended finger bar, and the other group is connected to the output bus bar through an extended finger bar.

4. The miniaturized surface acoustic wave filter according to claim 1, characterized in that: The duty cycle of the extended finger is consistent with the duty cycle of the connection of the electrode finger to which it is connected.

5. The miniaturized surface acoustic wave filter according to claim 1, characterized in that: The electrode thickness of each group of electrode fingers, extended fingers and bus bars is the same, and the thickness is ≥ 0.1 times the electrode finger period.

6. The miniaturized surface acoustic wave filter according to claim 5, characterized in that: Electrode density>10g / cm 3 High density metal materials.

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