Surface acoustic wave broadband band-pass filter

Abstract

The invention relates to the technical field of surface acoustic wave filters, and discloses a surface acoustic wave broadband band-pass filter, which comprises an input port, an output port, and a first series resonator, a second series resonator, a third series resonator and a fourth series resonator which form a series path between the input port and the output port, adjacent nodes of the input port, the first series resonator, the second series resonator, the third series resonator, the fourth series resonator and the output port are sequentially connected with a first parallel resonator, a second parallel resonator, a third parallel resonator, a fourth parallel resonator and a fifth parallel resonator which are grounded in parallel. According to the invention, the area of each single resonator connected in parallel can be reduced, the overall size of the filter is reduced, and the influence of the resonators on the passband is small due to the parallel connection relation, so that the insertion loss of the passband is low.

Description

Technical Field

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

[0002] As the electromagnetic environment becomes more and more complex, communication systems are often subject to a large amount of electromagnetic interference. For a specific communication system in a certain environment, the electromagnetic interference with higher intensity is often in the specific frequency band of the surrounding receiving or sending signals, such as the interference between the uplink and downlink in the transceiver system, and the interference between two different frequency bands with close distances, etc. At this time, it is necessary to suppress the frequency of the strong interference signal to a higher degree.

[0003] Acoustic wave devices are widely used in the microwave field by utilizing the piezoelectric effect and inverse piezoelectric effect of piezoelectric materials. Among them, surface acoustic wave (SAW) filters have occupied a large share in the mobile communication market due to their advantages of miniaturization, integration and high performance. Since the speed of sound waves is five orders of magnitude lower than the speed of light, the volume of the resonator that resonates using sound waves is much smaller than the volume of the resonator that directly resonates using electromagnetic waves. Therefore, compared with traditional microstrip filters, SAW filters have an absolute advantage in miniaturization. According to different performance requirements for filters, such as bandwidth, cost, operating frequency, temperature characteristics, etc., SAW filter design can adopt different substrate structures. Among them, the high-performance surface acoustic wave resonator (IHPSAW) mainly draws on the solid-state assembly structure in the bulk acoustic wave resonator. It suppresses the propagation of sound waves into the resonator body and the substrate through sound wave reflection, and limits the energy to the piezoelectric layer and the electrode area, thereby improving the Q value of the resonator. Compared with the ordinary SAW structure, the IHPSAW structure has higher stability of the resonator due to the presence of the substrate.

[0004] In the design of SAW filters, in order to produce a targeted strong suppression effect on specific interference frequency bands, there are roughly the following methods that can be used: one is to directly add an extra stage of band-stop filter to the system to suppress strong interference signals; the second is to improve the overall out-of-band suppression of the bandpass filter; the third is to distribute the zero points of the bandpass filter in the frequency band that needs to be suppressed and ensure its depth, which includes adjusting the zero points of the resonator or changing some resonators in the traditional stepped structure into suppression resonators.

[0005] For the first method mentioned above, that is, connecting a bandpass filter and a bandstop filter in series in the path, although the interference signal can be suppressed twice in a specific frequency band to achieve a good suppression level, the signal required by the system will also be lost twice, thus causing unnecessary loss of useful signals, and the two-stage cascade method will occupy too much area, which is not conducive to the realization of miniaturization; the second is a method for improving the out-of-band suppression of the overall filter. On the one hand, for filter design, out-of-band suppression and in-band insertion loss are a pair of contradictory indicators. While improving the suppression, the out-of-band insertion loss will also increase. On the other hand, when the passband frequency of the SAW filter is wide, its out-of-band suppression will be difficult to reach a very high level. If the suppression is improved by optimizing the parameters of the traditional ladder structure, the insertion loss characteristics in the passband will be sacrificed and the filter area will be increased; in the SAW filter, the third method is difficult to achieve because the distance between the resonance point and the anti-resonance point of the SAW resonator is basically determined by the material properties, that is, when the pole position is constant, the variable range of the zero position is small, and the zeros are closely distributed on both sides of the passband and cannot be distributed in the frequency range far away from the passband. Another method is to adjust the resonant frequency of some resonators of the traditional ladder structure to the stopband frequency that needs to be suppressed as a suppression resonator. Using this method to achieve a wider stopband bandwidth requires multiple series resonators and parallel resonators. At this time, for the passband frequency, it is equivalent to parallel and series capacitors at the corresponding positions in the circuit, which increases the number of components that the sound wave passes through during propagation, and there will also be a problem of increasing the in-band insertion loss to a certain extent. Summary of the invention

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

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

[0008] A surface acoustic wave broadband bandpass filter comprises the following steps:

[0009] An input port, an output port, and a first series resonator, a second series resonator, a third series resonator, and a fourth series resonator forming a series path between the input port and the output port;

[0010] The input port, the first series resonator, the second series resonator, the third series resonator, the fourth series resonator and the adjacent nodes of the output port are sequentially connected to the first parallel resonator, the second parallel resonator, the third parallel resonator, the fourth parallel resonator and the fifth parallel resonator connected to the ground;

[0011] The first series suppression resonator is connected in parallel to both ends of the first series resonator; the second series suppression resonator is connected in parallel to both ends of the fourth series resonator; the first parallel suppression resonator is connected in parallel to both ends of the first parallel resonator; and the second parallel suppression resonator is connected in parallel to both ends of the fifth parallel resonator.

[0012] In an optional embodiment, the anti-resonance point frequencies of the first series suppression resonator and the second series suppression resonator are lower than the resonance point frequencies of the first parallel suppression resonator and the second parallel suppression resonator to form a stop band.

[0013] In an optional embodiment, the first series suppression resonator, the second series suppression resonator, the first parallel suppression resonator and the second parallel suppression resonator adjust the suppression degree and suppression bandwidth of the stopband by adjusting the size and period of the resonator.

[0014] In an optional implementation, the first series resonator, the fourth series resonator, the first series suppression resonator, and the second series suppression resonator adjust the suppression degree and suppression bandwidth of the stopband by adjusting the finger logarithm and aperture of the resonator.

[0015] In an optional implementation, the first parallel resonator is grounded via a first gold wire jumper.

[0016] In an optional implementation manner, the second parallel resonator and the fourth parallel resonator are commonly grounded via a second gold wire jumper.

[0017] In an optional implementation manner, the third parallel resonator is grounded via a third gold wire jumper.

[0018] In an optional implementation, the fifth parallel resonator is grounded via a fourth gold wire jumper.

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

[0020] In an optional implementation, the output port is a coplanar waveguide.

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

[0022] (1) The present invention proposes a novel bandpass-bandstop structure, that is, a suppression resonator is connected in parallel on both sides of the main resonator forming the passband. This method can reduce the area of ​​each single resonator connected in parallel, reduce the overall size of the filter, and because the parallel relationship suppresses the resonator. The influence on the passband is small, so that the passband insertion loss is low;

[0023] (2) The present invention uses an external grounding inductor for matching, achieving a larger passband bandwidth under a given piezoelectric material condition;

[0024] (3) The present invention improves the out-of-band suppression by using a specific grounding relationship of the main parallel resonator and an equivalent grounding inductance of a grounding gold wire jumper;

[0025] (4) The present invention specifically improves the suppression degree of the strong interference frequency band by connecting suppression resonators in parallel on both sides of the main resonator, and achieves a high suppression effect in a specific frequency band by using a smaller number of suppression resonators, while having less adverse effects on other indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the principle of a surface acoustic wave broadband bandpass filter;

[0027] Figure 2 It is a schematic diagram of the structure of a surface acoustic wave broadband bandpass filter;

[0028] Figure 3 A side view of a surface acoustic wave broadband bandpass filter;

[0029] Figure 4 This is a simulated S-parameter diagram of a surface acoustic wave broadband bandpass filter. DETAILED DESCRIPTION

[0030] 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.

[0031] like Figure 1 As shown, an embodiment of the present invention provides a surface acoustic wave broadband bandpass filter, comprising:

[0032] An input port, an output port, and a first series resonator, a second series resonator, a third series resonator, and a fourth series resonator forming a series path between the input port and the output port;

[0033] The input port, the first series resonator, the second series resonator, the third series resonator, the fourth series resonator and the adjacent nodes of the output port are sequentially connected to the first parallel resonator, the second parallel resonator, the third parallel resonator, the fourth parallel resonator and the fifth parallel resonator connected to the ground;

[0034] The first series suppression resonator is connected in parallel to both ends of the first series resonator; the second series suppression resonator is connected in parallel to both ends of the fourth series resonator; the first parallel suppression resonator is connected in parallel to both ends of the first parallel resonator; and the second parallel suppression resonator is connected in parallel to both ends of the fifth parallel resonator.

[0035] like Figure 1 and Figure 2 As shown, this embodiment mainly includes five parts, including (1) four first series resonators S1, second series resonator S2, third series resonator S3, fourth series resonator S4 and five first parallel resonators P1, second parallel resonator P2, third parallel resonator P3, fourth parallel resonator P4, fifth parallel resonator P5 constituting passband, (2) two first series suppression resonators SS1, second series suppression resonator SS4 and two first parallel suppression resonators SP1, second parallel suppression resonator SP5 constituting stopband, (3) input and output signal gold wire jumpers, (4) grounding gold wire jumpers, (5) metal traces on the chip connecting the input and output ports and the resonators, and (6) a test substrate.

[0036] In this embodiment, the coplanar waveguides on the left and right sides of the test substrate are the input and output lines of the signal, and the input and output gold wire jumpers connect the input and output ports of the chip with the input and output signal lines of the test substrate; two inductors are set between the input and output ports and the metal ground, including an input matching inductor and an output matching inductor; the input matching inductor and the output matching inductor are respectively connected in parallel to the input port and the output port. The first series resonator S1, the second series resonator S2, the third series resonator S3, and the fourth series resonator S4 are connected in series to form a series path. One end of the first parallel resonator P1, the second parallel resonator P2, the third parallel resonator P3, the fourth parallel resonator P4, and the fifth parallel resonator P5 are connected to each node of the series path in sequence, and the other end is connected to the ground of the chip and connected to the ground of the test substrate through a grounding gold wire jumper. The first parallel resonator P1, the second parallel resonator P2, and the fourth parallel resonator P4 are located on the upper side of the series resonator path, the first parallel resonator P1 is grounded through the upper left corner jumper, and the second parallel resonator P2 and the fourth parallel resonator P4 are connected to the same end at the upper right corner for grounding; the third parallel resonator P3 and the fifth parallel resonator P5 are located on the lower side of the series resonator path, and are grounded through the lower left and lower right gold wire jumpers respectively. The first series suppression resonator SS1, the second series suppression resonator SS4, the first parallel suppression resonator SP1, and the second parallel suppression resonator SP5 are connected in parallel on both sides of the first series resonator S1, the fourth series resonator S4, the first parallel resonator P1, and the fifth parallel resonator P5, respectively.

[0037] In this embodiment, the four series resonators are equivalent to short circuits at the resonance point, and the five parallel resonators are equivalent to open circuits at the anti-resonance point. The path from the input to the output port to the ground is open, thus forming a passband. The series resonator is open at the anti-resonance point to form a near-end zero point on the right side of the passband, and the parallel resonator short-circuits the signal to the ground at the resonance point to form a near-end zero point on the left side. The second parallel resonator P2 and the fourth parallel resonator P4 are connected to the same jumper, which is equivalent to a small inductor, thereby forming an additional zero point, located on the left side of the parallel resonator zero point, to improve the left side suppression. Four more suppression resonators are introduced, namely the first series suppression resonator SS1, the second series suppression resonator SS4, the first parallel suppression resonator SP1, and the second parallel suppression resonator SP4, so that the resonance point frequency of the first series suppression resonator SS1 and the second series suppression resonator SS4 is lower than the anti-resonance point frequency of the first parallel suppression resonator SP1 and the second parallel suppression resonator SP5, forming a high suppression stopband in the required frequency band, and adjusting the size and period of the suppression resonator can adjust the suppression degree and suppression bandwidth of the stopband. Since the suppression resonator and the passband main resonator are in parallel, each parallel overall capacitance is equal to the sum of the parallel capacitances. Therefore, when the required overall capacitance value is constant, the logarithm or caliber of each resonator can be reduced to reduce a certain area.

[0038] In this embodiment, the input signal is connected to the input port of the chip through the 50-ohm coplanar waveguide feeder of the test board through the input gold wire jumper. The series resonator is short-circuited at the resonance point frequency, and the parallel resonator is open at the anti-resonance point to form a passband. The series resonator is open at the anti-resonance point frequency, and the parallel resonator is short-circuited at the resonance point to form a zero point. The anti-resonance point frequency of the series resonator in the suppression resonator is made lower than the resonance point frequency of the parallel resonator to form a stopband. The finger logarithm and caliber of the main resonator forming the passband and the suppression resonator are adjusted so that the suppression frequency band achieves the desired suppression effect and bandwidth, and the two parallel grounding inductors are combined to achieve a matching effect of the filter at the input and output ports.

[0039] like Figure 3 The figure shows the side view of the SAW broadband bandpass filter. From top to bottom, they are: 2.5μm thick aluminum layer (M2 layer); 0.18μm thick aluminum layer (0 layer); 0.6μm thick 50° YX lithium tantalate film; 0.5μm thick silicon dioxide layer; 200μm thick silicon substrate; 0.1mm thick copper layer, which is for the convenience of connecting with the copper layer of the test board; 0.035mm copper layer, which is the upper metal layer of the test substrate; 0.203mm Rogers RO4003 layer; 0.035mm copper layer, which is the metal ground of the test substrate.

[0040] like Figure 4As shown in the figure, it is the S parameter curve obtained by the joint simulation of the circuit simulation software ADS and the electromagnetic simulation software HFSS. The passband range is 1.661-1.782GHz, achieving a 7% 3dB relative bandwidth, and the minimum in-band insertion loss is 0.628dB; the specific suppression frequency band range is 1.365-1.507GHz, and the suppression degree in this frequency band reaches 45dBc. In addition, the suppression degree on the right side of the passband is as high as 45dBc, and the overall suppression degree on the left side of the passband is higher than 30dBc. From the simulation results, the filter achieves a large relative bandwidth under a limited electromechanical coupling coefficient and keeps the passband loss at a low level. Secondly, the filter can also achieve high suppression of a specific frequency band, and the suppression range is wide, while maintaining a good overall out-of-band suppression effect.

[0041] 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.

[0042] 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 including 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.

[0043] 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 The steps for the functions specified in one or more boxes.

[0044] 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.

[0045] 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 surface acoustic wave broadband bandpass filter, characterized in that: include: An input port, an output port, and a first series resonator, a second series resonator, a third series resonator, and a fourth series resonator forming a series path between the input port and the output port; The input port, the first series resonator, the second series resonator, the third series resonator, the fourth series resonator and the adjacent nodes of the output port are sequentially connected to the first parallel resonator, the second parallel resonator, the third parallel resonator, the fourth parallel resonator and the fifth parallel resonator connected to the ground; The first series suppression resonator is connected in parallel to both ends of the first series resonator; the second series suppression resonator is connected in parallel to both ends of the fourth series resonator; the first parallel suppression resonator is connected in parallel to both ends of the first parallel resonator; and the second parallel suppression resonator is connected in parallel to both ends of the fifth parallel resonator.

2. A surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The anti-resonance point frequencies of the first series suppressed resonator and the second series suppressed resonator are lower than the resonance point frequencies of the first parallel suppressed resonator and the second parallel suppressed resonator to form a stop band.

3. A surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The first series suppression resonator, the second series suppression resonator, the first parallel suppression resonator, and the second parallel suppression resonator adjust the suppression degree and suppression bandwidth of the stop band by adjusting the size and period of the resonator.

4. A surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The first series resonator, the fourth series resonator, the first series suppression resonator, and the second series suppression resonator adjust the suppression degree and suppression bandwidth of the stop band by adjusting the finger logarithm and aperture of the resonator.

5. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The first parallel resonator is grounded through a first gold wire jumper.

6. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The second parallel resonator and the fourth parallel resonator are grounded together through a second gold wire jumper.

7. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The third parallel resonator is grounded through a third gold wire jumper.

8. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The fifth parallel resonator is grounded through a fourth gold wire jumper.

9. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The input port is a coplanar waveguide.

10. The surface acoustic wave broadband bandpass filter according to claim 1, characterized in that: The output port is a coplanar waveguide.

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