Double-stop-band surface acoustic wave filter

Abstract

The invention relates to the technical field of surface acoustic wave filters, and discloses a double-stop-band surface acoustic wave filter, which comprises an input port, a high-frequency series resonator and a low-frequency series resonator which are connected with the input port and are connected in parallel, and an output port which is respectively connected with the high-frequency series resonator and the low-frequency series resonator. Two series resonators of two stop bands are connected in parallel, one ends of the parallel resonators working in the two stop bands are connected to the same signal path, the other ends of the parallel resonators working in the two stop bands are connected to the metal ground, and the resonators are connected in parallel, so that the overall capacitance value of each parallel resonator is the sum of the static capacitance of the single resonator; and reduction of the area of a single resonator is facilitated.

Description

Technical Field

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

[0002] In modern wireless communication systems, band-stop filters are often used to eliminate noise and interference signals and are widely used in various fields. Especially when the interference in the signal transmission process is very strong or the interference signal is concentrated in a specific frequency band, the out-of-band suppression ability of the bandpass filter often cannot meet the needs of eliminating interference, and the band-stop filter has more advantages. Therefore, the research and design of different types of band-stop filters are increasingly valued, and different applications have different requirements for the performance of band-stop filters, but the overall trend of change is to develop towards low insertion loss, high suppression, and miniaturization. In addition, as various types of communication equipment have put forward increasingly greater requirements for communication capacity, multi-frequency and broadband are becoming more and more common, so the design of multi-frequency band-stop filters or broadband band-stop filters is also increasingly valued.

[0003] Surface acoustic wave (SAW) filters have gained favor in the mobile communication market due to their superior filtering performance and extremely small size. It is common to use high-Q SAW resonators to design passband filters, but there are not many methods to use them in band-stop filter design or multi-frequency band-stop filter design. In the existing methods, designers usually combine SAW resonators with lumped element capacitors and inductors, or combine SAW resonators with microstrip transmission lines to design band-stop filters. It is common to use traditional microstrip transmission lines to design band-stop filters. In traditional multi-band-stop filter design, a design scheme of coupling multiple resonators of different frequencies on one transmission line is usually adopted.

[0004] In the design of traditional multi-stopband filters, the same-frequency resonators arranged along the transmission line need to be spaced apart by an odd multiple of a quarter wavelength, and in order to achieve multi-frequency requirements, multiple groups of resonators in multiple frequency bands need to be arranged, resulting in a larger size of the band-stop filter. In addition, the Q value of traditional resonators is low, and to achieve high in-band suppression, multiple stages of resonators need to be cascaded, which will further worsen its size problem and increase the insertion loss of the passband. Therefore, the band-stop filter based on traditional microstrip transmission lines cannot meet the needs of scenarios with strict requirements for miniaturization.

[0005] SAW resonators have great advantages in miniaturization due to the use of acoustic wave resonance. However, the design process of the multi-stopband filter by combining SAW resonators with lumped inductors and capacitors mentioned above is often complicated. Lumped components are often used for input and output matching or between stages, as well as for stopband control; and the lower Q value of lumped components often leads to a decrease in filtering performance; secondly, the uncertainty when soldering multiple discrete components on a printed circuit board will also affect the performance of the final filter. The design method of combining SAW resonators with microstrip lines also has the same problems as the previous method. In addition, the addition of microstrip lines will further weaken the volume advantage of SAW resonators. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a dual-stopband surface acoustic wave filter.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0008] A dual-stopband surface acoustic wave filter, comprising:

[0009] An input port, a high-frequency series resonator and a low-frequency series resonator connected in parallel to the input port, and an output port connected to the high-frequency series resonator and the low-frequency series resonator, respectively;

[0010] One side of the connection path between the high-frequency series resonator and the low-frequency series resonator and the input port is connected to the first high-frequency parallel resonator and the second high-frequency parallel resonator, and the other side of the connection path is connected to the first low-frequency parallel resonator and the second low-frequency parallel resonator;

[0011] One side of the connection path between the high frequency series resonator and the low frequency series resonator and the output port is connected to the third high frequency parallel resonator and the fourth high frequency parallel resonator, and the other side of the connection path is connected to the third low frequency parallel resonator and the fourth low frequency parallel resonator.

[0012] In an optional implementation, the high-frequency series resonator and the low-frequency series resonator form a dual stopband by adjusting the resonant frequencies in the high-frequency stopband and the low-frequency stopband respectively.

[0013] In an optional implementation, the high-frequency series resonator and the low-frequency series resonator form a high-frequency stop band by adjusting the anti-resonance point frequency to be lower than the resonance point of each parallel resonator.

[0014] In an optional implementation, the high-frequency series resonator and the low-frequency series resonator adjust the suppression depth by adjusting the number and diameter of the fingers of the resonator.

[0015] In an optional implementation, the high-frequency series resonator and the low-frequency series resonator form a high-frequency stopband by adjusting the anti-resonance point frequency to be lower than the resonance point of each parallel resonator and both are in the low-frequency stopband range.

[0016] In an optional implementation, a dual-stopband surface acoustic wave filter is characterized in that the anti-resonance point frequency of the high-frequency series resonator and the low-frequency series resonator is adjusted by adjusting the finger spacing of the resonator.

[0017] In an optional implementation, the input port is a coplanar waveguide.

[0018] In an optional implementation manner, a first inductor is connected in parallel between the input port and the metal ground.

[0019] In an optional implementation, the output port is a coplanar waveguide.

[0020] In an optional implementation manner, a second inductor is connected in parallel between the output port and the metal ground.

[0021] The present invention has the following beneficial effects:

[0022] The present invention connects two series resonators of two stopbands in parallel, one end of the parallel resonator working in the two stopbands is connected to the same signal path, and the other end is connected to the metal ground. The resonators are connected in parallel so that the overall capacitance value of each parallel connection is the sum of the static capacitance of a single resonator, which is beneficial to reducing the area of ​​a single resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the principle of a dual-stopband surface acoustic wave filter;

[0024] Figure 2 It is a schematic diagram of the structure of a dual-stopband surface acoustic wave filter;

[0025] Figure 3 A side view of a dual stopband surface acoustic wave filter;

[0026] Figure 4 This is a simulated S-parameter diagram of a dual-stopband surface acoustic wave filter. DETAILED DESCRIPTION

[0027] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0028] like Figure 1 As shown, a dual-stopband surface acoustic wave filter provided by an embodiment of the present invention includes:

[0029] An input port, a high-frequency series resonator and a low-frequency series resonator connected in parallel to the input port, and an output port connected to the high-frequency series resonator and the low-frequency series resonator, respectively;

[0030] One side of the connection path between the high-frequency series resonator and the low-frequency series resonator and the input port is connected to the first high-frequency parallel resonator and the second high-frequency parallel resonator, and the other side of the connection path is connected to the first low-frequency parallel resonator and the second low-frequency parallel resonator;

[0031] One side of the connection path between the high frequency series resonator and the low frequency series resonator and the output port is connected to the third high frequency parallel resonator and the fourth high frequency parallel resonator, and the other side of the connection path is connected to the third low frequency parallel resonator and the fourth low frequency parallel resonator.

[0032] like Figure 1 and Figure 2 As shown, this embodiment includes ten SAW resonators, including four first high-frequency parallel resonators UP1, second high-frequency parallel resonators UP2, third high-frequency parallel resonators UP3, fourth high-frequency parallel resonators UP4 and high-frequency series resonators US working in the high-frequency stop band, and four first low-frequency parallel resonators LP1, second low-frequency parallel resonators LP2, third low-frequency parallel resonators LP3, fourth low-frequency parallel resonators LP4 and low-frequency series resonators LS working in the low-frequency stop band; the resonators are connected to the input and output ports through metal wiring, wherein the dotted lines are marked as internal signal wiring, and the outer circle metal is the metal ground of the chip.

[0033] The dual-stopband SAW filter of this embodiment is designed with an on-chip test structure, and the input and output ends are coplanar waveguide probe test structures. Figure 2The input and output positions marked in the middle are composed of the metal grounds on both sides thereof. The metal connected to each other around the chip is the grounding metal of the entire chip. From the input port to the output port, it is connected to two parallel high-frequency series resonators and low-frequency series resonators through internal metal routing. The first high-frequency parallel resonator UP1 and the second high-frequency parallel resonator UP2 are located on the left side of the high-frequency series resonator, one end of which is connected to the metal transmission line, and the other end is connected to the upper metal ground; the third high-frequency parallel resonator UP3 and the fourth high-frequency parallel resonator UP4 are located on the right side of the high-frequency series resonator, one end of which is connected to the metal transmission line, and the other end is connected to the upper metal ground; the first low-frequency parallel resonator LP1 and the first low-frequency parallel resonator LP2 are located on the left side of the low-frequency series resonator, one end of which is connected to the metal transmission line, and the other end is connected to the lower metal ground; the third low-frequency parallel resonator LP3 and the fourth low-frequency parallel resonator LP4 are located on the right side of the low-frequency series resonator, one end of which is connected to the metal transmission line and the other end is connected to the lower metal ground.

[0034] In this embodiment, the input and output probes are connected to the input and output coplanar waveguides of the chip for excitation. The signal is short-circuited to the ground at the resonance point of the parallel resonator, and the path is blocked at the anti-resonance point of the series resonator, forming two stop bands.

[0035] The dual-stopband surface acoustic wave filter of this embodiment is an on-chip test structure, the input and output ports are coplanar waveguides, and the metal around the chip is interconnected as a metal ground. First, the series resonators of the two frequency bands are connected in parallel, and the overall capacitance value formed is the sum of the static capacitance values ​​of the two series resonators, which is conducive to reducing the number of fingers and the caliber of a single resonator, that is, reducing the resonator area.

[0036] In this embodiment, the first high-frequency parallel resonator UP1, the second high-frequency parallel resonator UP2, the first low-frequency parallel resonator LP1, the second low-frequency parallel resonator LP2 and the third high-frequency parallel resonator UP3, the fourth high-frequency parallel resonator UP4, the third low-frequency parallel resonator LP3, and the third low-frequency parallel resonator LP4 are respectively placed on both sides of the series resonator composed of the high-frequency series resonator and the low-frequency series resonator. Then, the four parallel resonators on the left and right sides are connected in parallel, and the equivalent capacitance formed as a whole is the sum of the static capacitance values ​​of the four parallel resonators, which is conducive to the reduction of the area of ​​a single resonator, and the structure distributed on both sides is relatively stacked, which is convenient for the overall matching of the filter. When the signal passes through the filter, the parallel resonator behaves as a short circuit at the resonance point, and the series resonator behaves as an open circuit at the anti-resonance point. In the high-frequency stop band, the anti-resonance point frequency of the series resonator is lower than the resonance point of the parallel resonator, so a high-frequency stop band can be formed. Adjusting the distribution of the resonance points of different resonators can adjust the stop band bandwidth within a certain range. At the same time, adjusting the number of fingers and the caliber of the resonator can adjust the depth of suppression. In the low-frequency stopband, the anti-resonance frequency of the series resonator is adjusted to be lower than the resonant frequency of the parallel resonator by adjusting the finger spacing, and both are in the low-frequency stopband range. Therefore, the resonant frequencies of the high-frequency stopband and low-frequency stopband resonators are adjusted separately to form a dual stopband. At the same time, since the two stopband frequency band resonators are connected to the same path, adjusting the number of fingers and the caliber of a single frequency band resonator will affect the suppression degree of the other stopband. Therefore, the adjustment of the dual stopband suppression degree needs to consider the slight influence of each other. The parallel inductance of the input and output ports, combined with the static capacitance of the two series resonators, can achieve a better matching effect of the passband and avoid the situation where an extremely narrow passband appears only on both sides of the stopband.

[0037] like Figure 1 and Figure 2 As shown, the on-chip test coplanar waveguide input and output ports are shown in the dotted box; two inductors are set between the input and output ports and the metal ground, including a first inductor L1 and a second inductor L2; the first inductor L1 and the second inductor L2 are connected in parallel to the input port and the output port respectively.

[0038] In this embodiment, the inductor is connected in parallel to the input and output ports, and the static capacitance of the two series resonators is adjusted to achieve a better matching effect of the passband, avoiding the situation where an extremely narrow passband appears only on both sides of the stopband. In addition to providing a zero point to form the stopband, the static capacitance of the series resonator also cooperates with the input and output inductors to play a matching role.

[0039] A novel dual-stopband surface acoustic wave filter structure proposed in this embodiment connects two series resonators of two stopbands in parallel, one end of the parallel resonator working in the two stopbands is connected to the same signal path, and the other end is connected to the metal ground. The resonators are connected in parallel so that the overall capacitance value of each parallel connection is the sum of the static capacitance of a single resonator, which is conducive to reducing the area of ​​a single resonator.

[0040] This embodiment uses a series resonator and input and output shunt inductors to achieve a good matching effect between two stop bands. When the order is increased, there is no need to use lumped elements or microstrip transmission lines for inter-stage matching, making the filter structure more compact.

[0041] In this embodiment, the resonator frequencies of the two stopbands do not affect each other, and the resonant frequencies of the two resonators can be adjusted independently. The bandwidths of different stopbands can also be adjusted independently by designing the orders of the two stopbands to be inconsistent and reasonably allocating the resonant frequencies of each stopband.

[0042] like Figure 3 The figure shows a side view of a dual-stopband surface acoustic wave filter. This embodiment adopts a high-performance surface acoustic wave (IHPSAW) structure. When viewed vertically from top to bottom, the entire filter is composed of: an aluminum layer (M2 layer) with a thickness of 2.5 μm, an aluminum layer (0 layer) with a thickness of 0.315 μm, a lithium tantalate film with a thickness of 0.6 μm, a silicon dioxide layer with a thickness of 0.5 μm, a silicon substrate with a thickness of 200 μm, and a copper layer with a thickness of 0.1 mm.

[0043] like Figure 4 As shown in the figure, it is the S21 curve obtained by the joint simulation of the circuit simulation software ADS and the electromagnetic simulation software HFSS, in which the suppression of the two stopbands is higher than 36.5dB, the minimum insertion loss of the passband is 0.66dB, the maximum insertion loss is 1.6dB, and the overall size of the filter is 1.2mm*1.2mm. From the layout, there is still room for further size reduction. Therefore, the dual stopband filter design method proposed in the present invention can achieve excellent performance of high suppression, low insertion loss and small size while using a small number of surface acoustic wave resonators.

[0044] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0045] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0046] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0047] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0048] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A dual-stopband surface acoustic wave filter, characterized in that: include: An input port, a high-frequency series resonator and a low-frequency series resonator connected in parallel to the input port, and an output port connected to the high-frequency series resonator and the low-frequency series resonator, respectively; One side of the connection path between the high-frequency series resonator and the low-frequency series resonator and the input port is connected to the first high-frequency parallel resonator and the second high-frequency parallel resonator, and the other side of the connection path is connected to the first low-frequency parallel resonator and the second low-frequency parallel resonator; One side of the connection path between the high frequency series resonator and the low frequency series resonator and the output port is connected to the third high frequency parallel resonator and the fourth high frequency parallel resonator, and the other side of the connection path is connected to the third low frequency parallel resonator and the fourth low frequency parallel resonator.

2. A dual-stopband surface acoustic wave filter according to claim 1, characterized in that: The high frequency series resonator and the low frequency series resonator form a dual stop band by adjusting the resonant frequencies in the high frequency stop band and the low frequency stop band, respectively.

3. A dual-stopband surface acoustic wave filter according to claim 2, characterized in that: The high frequency series resonator and the low frequency series resonator form a high frequency stop band by adjusting the anti-resonance point frequency to be lower than the resonance point of each parallel resonator.

4. A dual-stopband surface acoustic wave filter according to claim 3, characterized in that: The high-frequency series resonator and the low-frequency series resonator are used to adjust the suppression depth by adjusting the number of fingers and the diameter of the resonator.

5. A dual-stopband surface acoustic wave filter according to claim 2, characterized in that: The high frequency series resonator and the low frequency series resonator are adjusted so that the anti-resonance point frequency is lower than the resonance point of each parallel resonator and both are in the low frequency stop band range to form a high frequency stop band.

6. A dual-stopband surface acoustic wave filter according to claim 5, characterized in that: A dual-stopband surface acoustic wave filter, characterized in that the anti-resonance point frequency of the high-frequency series resonator and the low-frequency series resonator is adjusted by adjusting the finger spacing of the resonator.

7. The dual-stopband surface acoustic wave filter according to claim 1, characterized in that: The input port is a coplanar waveguide.

8. The dual-stopband surface acoustic wave filter according to claim 1, characterized in that: A first inductor is connected in parallel between the input port and the metal ground.

9. The dual-stopband surface acoustic wave filter according to claim 1, characterized in that: The output port is a coplanar waveguide.

10. The dual-stopband surface acoustic wave filter according to claim 1, characterized in that: A second inductor is connected in parallel between the output port and the metal ground.

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