Surface acoustic wave duplexer

Abstract

The application provides a surface acoustic wave duplexer, and belongs to the technical field of radio frequency. The surface acoustic wave duplexer comprises an antenna terminal, a transmitting filter, a receiving filter, a transmitting terminal and a receiving terminal formed on an element substrate; the transmitting filter comprises transmitting series arm resonators and parallel arm resonators, and the receiving filter comprises receiving series arm resonators and a longitudinal coupling resonator DMS; a low-impedance common ground network is formed by directly electrically connecting part of ground pins inside a packaging structure to suppress the out-of-band suppression at the double frequency of the transmitting filter. The application has the advantages of low insertion loss, high transmitting-receiving isolation and small size, and can be widely applied to radio frequency front-end modules such as mobile communication terminals and group communication systems.

Description

Technical Field

[0001] This application relates to the field of radio frequency technology, and in particular to a surface acoustic wave duplexer. Background Technology

[0002] With the large-scale commercialization of technologies such as 5G and the Internet of Things (IoT), radio frequency (RF) front-end devices, as the core modules for signal transmission and reception in communication terminals, directly determine the communication quality and compliance of the terminals. The duplexer, a key passive component in the RF front-end, utilizes surface acoustic wave (SAW) technology to integrate two highly selective filters on the same chip. Through an internal matching network, it enables simultaneous signal transmission and reception using a single antenna, with the two processes operating independently. Its core function is to achieve signal isolation between the transmit (TX) and receive (RX) links, preventing mutual interference between transmitted and received signals. It is currently widely used in various communication devices such as mobile phones, IoT terminals, and base stations. Under the current trend of miniaturization and high integration in RF front-ends, SAW duplexers have become the mainstream duplexer solution for mid- and low-frequency communication terminals due to their advantages such as small size, low cost, low insertion loss, and good consistency.

[0003] However, conventional surface acoustic wave duplexers typically consist of a transmitting filter and a receiving filter integrated on a piezoelectric substrate. After packaging, they achieve electrical interconnection and environmental protection. In the miniaturization of conventional devices, more complex structures are usually used to compensate for the performance loss caused by the reduction in size. For example, a dual busbar structure is used to suppress lateral energy leakage or the secondary gap length is adjusted to enhance energy confinement and reduce leakage. However, this will excite intense lateral modes and nonlinear distortion, thereby deteriorating the second and third harmonic responses. In addition, the reduction in package size will lead to an increase in parasitic parameters, forming additional parasitic passbands or resonance peaks at the second harmonic, thereby worsening the second harmonic suppression effect.

[0004] Existing technology discloses a surface acoustic wave (SAW) duplexer that adds an adjustable additional inductance component to the low-pass band-side transmit filter through a grounding pattern design in a multilayer package substrate, thereby improving the duplexer's frequency characteristics (especially out-of-band rejection). However, this solution has a complex package design, high manufacturing difficulty and cost, and it is difficult to achieve precise parasitic parameter control and continuous inductance adjustment; its anti-interference capability depends entirely on the outer package structure, and its frequency response is fixed, making it unable to adapt to multi-band requirements.

[0005] Therefore, it is necessary to design a surface acoustic wave duplexer that can effectively suppress second harmonics and has a simple structure. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a surface acoustic wave duplexer. This surface acoustic wave duplexer forms a low-impedance common ground network by directly connecting some ground pins inside the package structure, thereby suppressing out-of-band rejection at the second harmonic of the transmitting filter.

[0007] The duplexer includes a component substrate, a packaged chip, a metal ball, and an isolation structure. The component substrate is located above the packaged chip, and the two are connected by the metal ball. An isolation structure is also provided on the outside of the component substrate. The component substrate, serving as the core carrier of the entire surface acoustic wave (SAW) duplexer, includes an antenna terminal (ANT), a transmit filter, a receive filter, a transmit terminal (TX), a receive terminal (RX), and several grounding points. The antenna terminal (ANT) is the common port of the SAW duplexer, used to connect to the antenna of a communication terminal, both transmitting and receiving signals. The transmit terminal (TX) is used to input the transmit signal, and the receive terminal (RX) is used to output the receive signal. The transmit filter, located between the antenna terminal (ANT) and the transmit terminal (TX), includes a transmit series arm resonator, a parallel arm resonator, and grounding points. The antenna terminal (ANT), the transmit filter, and the transmit filter together constitute the transmit link. The receive filter, located between the antenna terminal (ANT) and the receive terminal (RX), includes a receive series arm resonator and a longitudinally coupled resonator (DMS). The antenna terminal (ANT), the receive filter, and the receive terminal (RX) together constitute the receive link. Furthermore, the transmit filter is used to filter the transmit signal, allowing only signals in the transmit frequency band to pass through, while preventing signals in the receive frequency band from entering the transmit link; the receive filter is used to filter the receive signal, allowing only signals in the receive frequency band to pass through, while preventing signals in the transmit frequency band from entering the receive link. Furthermore, the transmitting series arm resonator includes a first series resonator S1a, a second series resonator S1b, a third series resonator S2a, a fourth series resonator S2b, a fifth series resonator S3a, a sixth series resonator S3b, a seventh series resonator S4a, and an eighth series resonator S4b. These series resonators are connected in series sequentially. The other end of the first series resonator S1a is connected to the antenna terminal ANT, and the other end of the eighth series resonator S4b is connected to the transmitting terminal TX. The impedance characteristics of the transmitting series arm resonator change with frequency, exhibiting low impedance in the passband to allow the signal to pass through, while exhibiting high impedance in the stopband to block the signal from passing through. Furthermore, the parallel arm resonator includes a first parallel resonator P1, a second parallel resonator P2, and a third parallel resonator P3. One end of the first parallel resonator P1 is connected between the second series resonator S1b and the third series resonator S2a, and the other end is grounded. One end of the second parallel resonator P2 is connected between the fourth series resonator S2b and the fifth series resonator S3a, and the other end is grounded. One end of the third parallel resonator P3 is connected between the sixth series resonator S3b and the seventh series resonator S4a, and the other end is grounded through an inductor. The parallel arm resonator presents high impedance in the passband without affecting the signal, and low impedance in the stopband to bypass the signal to ground. It works in conjunction with the transmitting series arm resonator to form filtering characteristics. Furthermore, the receiving series arm resonator includes a ninth series resonator S5a, a tenth series resonator S5b, and an eleventh series resonator S6. A longitudinal coupling resonator DMS is disposed between the tenth series resonator S5b and the eleventh series resonator S6. One end of the ninth series resonator S5a is connected to the antenna terminal ANT, and the other end is connected to the tenth series resonator S5b. The other end of the tenth series resonator S5b is connected to the longitudinal coupling resonator DMS. The longitudinal coupling resonator DMS is connected to the receiving terminal RX via the eleventh series resonator S6. The longitudinal coupling resonator DMS achieves wideband, low-loss filtering characteristics to improve the sensitivity of the receiving link. The grounding of the receiving filter is independent of the grounding of the transmitting filter to avoid crosstalk generated by the transmitting and receiving links through grounding loops; Packaged chips are used to encapsulate and protect component substrates, providing mechanical support and environmental isolation (moisture-proof, dust-proof, shock-resistant), while also serving as an electrical interconnection platform between the component substrate and external circuits; packaged chips use a stacked substrate, which consists of four layers, one of which is used to set various pins, and the other three layers are used to set wire-wound inductors; Furthermore, the packaged chip is provided with antenna pins ANT Pin, TX Pin, and RX Pin corresponding to the antenna terminal ANT, transmit terminal TX, and receive terminal RX provided on the component substrate; these pins serve as connection ports for connecting the packaged chip to the outside. The packaged chip also has floating terminals and several vias. The antenna terminal ANT, transmit terminal TX, receive terminal RX, and ground on the component substrate are electrically connected to the antenna pin ANT, transmit pin TX, receive pin RX, and ground pin GND on the packaged chip through the vias. The floating terminals are not connected to the component substrate but are connected to the packaged chip through vias. The floating terminals improve resonance and filtering performance by affecting the electric field distribution and sound wave propagation inside the device, and at the same time suppress noise.

[0008] The antenna pin (ANT) is electrically connected to the antenna terminal (ANT) on the component substrate and is used to solder onto the PCB of the terminal device and connect the antenna; the transmit pin (TX) is electrically connected to the transmit terminal (TX) and is used to connect external RF devices; the receive pin (RX) is electrically connected to the receive terminal (RX) and is used to connect external RF devices; several ground pins (GND) are used to connect the internal ground points of the surface acoustic wave duplexer to the reference ground plane of the system PCB. In addition, the packaged chip is also provided with a ground pin (GND Pin) and at least one inductor. One end of the inductor is connected to the ground pin (GND Pin), and the other end is connected to the ground in the transmitting filter. The grounding of the first parallel resonator P1, the grounding of the second parallel resonator P2, and the grounding of the third parallel resonator P3 on the component substrate are all connected to the same grounding pin GND Pin. The longitudinally coupled resonator DMS includes several groundings, of which one is selected and all the remaining groundings are connected to the grounding pin GND Pin of the parallel resonator. The groundings of the parallel resonator and the groundings of the longitudinally coupled resonator DMS are connected to the same grounding pin GND Pin, which together form a low-impedance common grounding network, reducing grounding inductance and improving grounding performance. This is denoted as the second grounding GND Pin. The grounding of the longitudinally coupled resonator DMS is selected independently from the second grounding GND Pin and is denoted as the first grounding GND Pin. Furthermore, in the low-impedance common ground network, the angle θ between the straight line formed by the via connected to the floating terminal and the center point of the second ground GND pin and the straight line formed by the center point of the transmit pin TX pin on the package chip is 105°~162°. Through this via arrangement, on the one hand, the position of the stopband zero point can be adjusted so that the zero point position is in the second harmonic band, thereby improving the stopband suppression in the second harmonic band. On the other hand, it can also serve as a signal shield, thereby improving the isolation of the duplexer.

[0009] Furthermore, the inductor is connected in series in the ground path of the transmitting filter. Its function is to form a series resonance with the parasitic capacitance in the path, generate a notch at the second harmonic, bypass the second harmonic signal to ground, and improve the suppression capability. The inductor is formed by the winding pattern of the metal layer of the laminated substrate. Furthermore, the metal sphere is made of gold or a tin-silver-copper alloy, and the electrical interconnection and mechanical fixation between the two are achieved through a flip-chip bonding process.

[0010] The beneficial effects of the invention are: This invention provides a surface acoustic wave (SAW) duplexer, comprising an antenna terminal, a transmit filter, a receive filter, a transmit terminal, and a receive terminal formed on a component substrate. The transmit filter includes a transmit series arm resonator and a parallel arm resonator, and the receive filter includes a receive series arm resonator and a longitudinally coupled resonator (DMS). By directly electrically connecting some ground pins inside the package structure to form a low-impedance common ground network, out-of-band rejection at the second harmonic of the transmit filter is suppressed. This invention has advantages such as low insertion loss, high transmit / receive isolation, and small size, and can be widely used in RF front-end modules such as mobile communication terminals and trunked communication systems. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0012] Figure 1 This shows an overall schematic diagram of the surface acoustic wave duplexer provided in Embodiment 1 of this application; Figure 2 A topological schematic diagram of the surface acoustic wave duplexer provided in Embodiment 1 of this application is shown; Figure 3 The diagram shows a cross-section and a top view of the component substrate and packaged chip in the surface acoustic wave duplexer provided in Embodiment 1 of this application; Figure 4 This shows a schematic diagram of the structure of the surface acoustic wave duplexer packaged chip provided in Embodiment 1 of this application; Figure 5 This shows a schematic diagram of the inductor structure in the surface acoustic wave duplexer packaged chip provided in Embodiment 1 of this application; Figure 6 A schematic diagram of the structure of a conventional packaged chip provided in Comparative Example 1 of this application is shown; Figure 7 This paper shows a comparison of the insertion loss-frequency curves of the transmitting filter in the surface acoustic wave duplexer provided in Embodiment 1 of this application and the conventional surface acoustic wave duplexer in Comparative Example 1. Figure 8 The graph shows the insertion loss value -θ in the second harmonic band of the surface acoustic wave duplexer provided in Embodiment 1 of this application; Among them, 1. Component substrate; 2. Packaged chip; 3. Metal sphere; 4. Isolation structure. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] Example 1 This embodiment provides a surface acoustic wave duplexer, the structure of which is as follows: Figure 1 As shown, it includes a component substrate, a packaged chip, a metal sphere, and an isolation structure. The component substrate is located inside the packaged chip, and the two are connected by the metal sphere. The component substrate, serving as the core carrier of the entire surface acoustic wave (SAW) duplexer, includes an antenna terminal (ANT), a transmit filter, a receive filter, a transmit terminal (TX), a receive terminal (RX), and several grounding points. The antenna terminal (ANT) is the common port of the SAW duplexer, used to connect to the antenna of a communication terminal, both transmitting and receiving signals. The transmit terminal (TX) is used to input the transmit signal, and the receive terminal (RX) is used to output the receive signal. The transmit filter, located between the antenna terminal (ANT) and the transmit terminal (TX), includes a transmit series arm resonator, a parallel arm resonator, and grounding points. The antenna terminal (ANT), the transmit filter, and the transmit filter together constitute the transmit link. The receive filter, located between the antenna terminal (ANT) and the receive terminal (RX), includes a receive series arm resonator and a longitudinally coupled resonator (DMS). The antenna terminal (ANT), the receive filter, and the receive terminal (RX) together constitute the receive link. Transmit filters are used to filter transmitted signals, allowing only signals in the transmit frequency band to pass through while preventing signals in the receive frequency band from entering the transmit link; receive filters are used to filter received signals, allowing only signals in the receive frequency band to pass through while preventing signals in the transmit frequency band from entering the receive link. The topology of a surface acoustic wave duplexer is as follows: Figure 2 As shown, the transmitting series arm resonator includes a first series resonator S1a, a second series resonator S1b, a third series resonator S2a, a fourth series resonator S2b, a fifth series resonator S3a, a sixth series resonator S3b, a seventh series resonator S4a, and an eighth series resonator S4b. These series resonators are connected in series sequentially. The other end of the first series resonator S1a is connected to the antenna terminal ANT, and the other end of the eighth series resonator S4b is connected to the transmitting terminal TX. The impedance characteristics of the transmitting series arm resonator change with frequency, exhibiting low impedance in the passband to allow the signal to pass through, while exhibiting high impedance in the stopband to block the signal from passing through. The parallel arm resonator includes a first parallel resonator P1, a second parallel resonator P2, and a third parallel resonator P3. One end of the first parallel resonator P1 is connected between the second series resonator S1b and the third series resonator S2a, and the other end is grounded. One end of the second parallel resonator P2 is connected between the fourth series resonator S2b and the fifth series resonator S3a, and the other end is grounded. One end of the third parallel resonator P3 is connected between the sixth series resonator S3b and the seventh series resonator S4a, and the other end is grounded through an inductor. The parallel arm resonator presents high impedance in the passband without affecting the signal, and low impedance in the stopband to bypass the signal to ground. It works in conjunction with the transmitting series arm resonator to form a filtering characteristic. The receiving series arm resonator includes a ninth series resonator S5a, a tenth series resonator S5b, and an eleventh series resonator S6. A longitudinal coupling resonator DMS is positioned between the tenth series resonator S5b and the eleventh series resonator S6. One end of the ninth series resonator S5a is connected to the antenna terminal ANT, and the other end is connected to the tenth series resonator S5b. The other end of the tenth series resonator S5b is connected to the longitudinal coupling resonator DMS. The longitudinal coupling resonator DMS is connected to the receiving terminal RX via the eleventh series resonator S6. The longitudinal coupling resonator DMS achieves wideband, low-loss filtering characteristics to improve the sensitivity of the receiving link. The receiving filter's own grounding point is independent of the transmitting filter's grounding point to avoid crosstalk generated by the transmitting and receiving links through grounding loops; Packaged chips are used to encapsulate and protect component substrates, providing mechanical support and environmental isolation (moisture-proof, dust-proof, shock-resistant), while also serving as an electrical interconnection platform between the component substrate and external circuits; packaged chips use a stacked substrate, which consists of four layers, one of which is used to set various pins, and the other three layers are used to set wire-wound inductors; The structure of the packaged chip is as follows Figure 4 As shown, it is provided with antenna pins ANT Pin, TX Pin, and RX Pin corresponding to the antenna terminals ANT, TX, and RX provided on the component substrate; these pins serve as connection ports for connecting the packaged chip to the outside; the antenna terminals ANT, TX, RX, and ground on the component substrate are electrically connected to the antenna pins ANT Pin, TX Pin, RX Pin, and GND Pin provided on the packaged chip through vias; The packaged chip also has floating terminals and several vias, such as Figure 3As shown, the floating terminal is located on the top layer of the laminated substrate and is not electrically connected to the component substrate. Vias are cylindrical metal pillars that electrically connect the layers of the laminated substrate. The floating terminal is not connected to the component substrate but is connected to the packaged chip through vias; the floating terminal improves resonance and filtering performance by influencing the electric field distribution and acoustic wave propagation within the device, and simultaneously suppresses noise.

[0015] The antenna pin (ANT) is electrically connected to the antenna terminal (ANT) on the component substrate and is used to solder onto the PCB of the terminal device and connect the antenna; the transmit pin (TX) is electrically connected to the transmit terminal (TX) and is used to connect external RF devices; the receive pin (RX) is electrically connected to the receive terminal (RX) and is used to connect external RF devices; several ground pins (GND) are used to connect the internal ground points of the surface acoustic wave duplexer to the reference ground plane of the system PCB. In addition, the packaged chip is also provided with a ground pin (GND Pin) and at least one inductor. One end of the inductor is connected to the ground pin (GND Pin), and the other end is connected to the ground in the transmitting filter. The grounding of the first parallel resonator P1, the grounding of the second parallel resonator P2, and the grounding of the third parallel resonator P3 on the component substrate are all connected to the same grounding pin GND Pin. The longitudinally coupled resonator DMS includes several groundings, of which one is selected and all the remaining groundings are connected to the grounding pin GND Pin of the parallel resonator. The groundings of the parallel resonator and the groundings of the longitudinally coupled resonator DMS are connected to the same grounding pin GND Pin, which together form a low-impedance common grounding network, reducing grounding inductance and improving grounding performance. This is referred to as the second GND Pin. The grounding of the longitudinally coupled resonator DMS is selected independently from the second grounding GND Pin and is referred to as the first GND Pin. In a low-impedance common ground network, the angle θ between the straight line formed by the via connecting the floating terminal and the center point of the second ground GND pin, and the straight line formed by the center point of the transmit pin TX pin on the package chip, is 105°~162°. Figure 4 As shown, this via arrangement can, on the one hand, adjust the position of the stopband zero point so that the zero point is in the second harmonic band, thereby improving the stopband suppression in the second harmonic band; on the other hand, it can also serve as a signal shield, thereby improving the isolation of the duplexer.

[0016] The inductor is connected in series in the ground path of the transmitting filter. Its function is to form a series resonance with the parasitic capacitance in the path, generate a notch at the second harmonic, bypass the second harmonic signal to ground, and improve the suppression capability. The inductor is based on the metal layer of the laminated substrate to form inductance through the winding pattern. The metal ball is gold or tin-silver-copper alloy, and the electrical interconnection and mechanical fixation between the two are achieved by flip-chip bonding process.

[0017] Figure 5 This is a schematic cross-sectional view of one layer in a laminated substrate. Except for the metal wire-wound inductor, the other parts are ordinary metal plates.

[0018] To verify the performance of the duplexer, this embodiment tests the insertion loss-frequency relationship of the transmit filter in the duplexer provided by this invention and in a conventional duplexer. The structure of the conventional duplexer's packaged chip is as follows: Figure 6 As shown, several grounding points are set independently; the final test results are as follows. Figure 7 As shown in the curve, the out-of-band suppression effect of the transmitting filter at twice the center frequency in the surface acoustic wave duplexer of this embodiment is 15dB better than that of the transmitting filter at twice the center frequency in the conventional surface acoustic wave duplexer. This proves that the duplexer provided in this application can significantly improve performance.

[0019] To verify the effectiveness of the surface acoustic wave duplexer provided in this embodiment, the insertion loss value -θ in the second harmonic band was tested. The test results are as follows: Figure 8 As shown, by Figure 8 It can be seen that within the θ angle range provided by this invention, the loss value is less than -40dB, which has a good stopband suppression effect in the second harmonic band.

[0020] The principles and implementation methods of the present invention have been described above. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A surface acoustic wave duplexer, characterized in that, The duplexer includes a component substrate, a packaged chip, a metal ball, and an isolation structure. The component substrate is located inside the packaged chip, and the two are connected by the metal ball. The component substrate is provided with an antenna terminal ANT, a transmit filter, a receive filter, a transmit terminal TX, a receive terminal RX, and a corresponding ground. The packaged chip is provided with antenna pins ANT Pin, TX Pin, and RX Pin corresponding to the antenna terminal ANT, transmit terminal TX, and receive terminal RX provided on the component substrate. The packaged chip is also provided with several ground pins GND Pin and at least one inductor. One end of the inductor is connected to the ground pin, and the other end is connected to the ground in the transmit filter, forming a series resonance with the parasitic capacitance on the path. Several grounding pins (GND pins) within the packaged chip are directly electrically connected inside the package structure, forming a common grounding network.

2. The duplexer according to claim 1, characterized in that, The packaged chip is also provided with a floating terminal and several vias. The floating terminal is not electrically connected to the component substrate. The antenna terminal ANT, the transmitting terminal TX, the receiving terminal RX, and the ground pin GND pin on the component substrate are connected to the antenna pin ANT Pin, the transmitting pin TXPin, the receiving pin RX Pin, and the ground pin GND Pin on the packaged chip through the vias. The grounding of the transmitting filter and the receiving filter is connected to the same grounding pin GND pin on the packaged chip, forming a common grounding network. In the common grounding network, the angle θ between the straight line formed by the via connected to the floating terminal and the center point of the grounding pin GND Pin, and the straight line formed by the via connected to the floating terminal and the center point of the transmitting pin TX Pin on the packaged chip, is 105°~162°.

3. The duplexer according to claim 2, characterized in that, The antenna terminal ANT is used to connect to the antenna of the communication terminal. The transmitting terminal TX is used to input the transmitted signal, and the receiving terminal RX is used to output the received signal. The transmitting filter is disposed between the antenna terminal ANT and the transmitting terminal TX, and includes a transmitting series arm resonator, a parallel arm resonator, and ground. The antenna terminal ANT, the transmitting filter, and the transmitting filter together constitute the transmitting link. The receiving filter is disposed between the antenna terminal ANT and the receiving terminal RX, and includes a receiving series arm resonator and a longitudinally coupled resonator DMS. The antenna terminal ANT, the receiving filter, and the receiving terminal RX together constitute the receiving link. The transmitting filter is used to filter the transmitted signal, allowing only signals in the transmitting frequency band to pass through, while preventing signals in the receiving frequency band from entering the transmitting link; the receiving filter is used to filter the received signal, allowing only signals in the receiving frequency band to pass through, while preventing signals in the transmitting frequency band from entering the receiving link.

4. The duplexer according to claim 3, characterized in that, The transmitting series arm resonator includes a first series resonator S1a, a second series resonator S1b, a third series resonator S2a, a fourth series resonator S2b, a fifth series resonator S3a, a sixth series resonator S3b, a seventh series resonator S4a, and an eighth series resonator S4b connected in series in sequence. The other end of the first series resonator S1a is connected to the antenna terminal ANT, and the other end of the eighth series resonator S4b is connected to the transmitting terminal TX. The impedance characteristics of the transmitting series arm resonator change with frequency, exhibiting low impedance in the passband to allow the signal to pass through, and high impedance in the stopband to block the signal from passing through. The parallel arm resonator includes a first parallel resonator P1, a second parallel resonator P2, and a third parallel resonator P3; one end of the first parallel resonator P1 is connected between the second series resonator S1b and the third series resonator S2a, and the other end is grounded; one end of the second parallel resonator P2 is connected between the fourth series resonator S2b and the fifth series resonator S3a, and the other end is grounded; one end of the third parallel resonator P3 is connected between the sixth series resonator S3b and the seventh series resonator S4a, and the other end is grounded through an inductor; The parallel arm resonator presents high impedance in the passband, which does not affect the signal, and low impedance in the stopband, which bypasses the signal to ground; it works in conjunction with the transmitting series arm resonator to form filtering characteristics.

5. The duplexer according to claim 4, characterized in that, The receiving series arm resonator includes a ninth series resonator S5a, a tenth series resonator S5b, and an eleventh series resonator S6. The longitudinal coupling resonator DMS is disposed between the tenth series resonator S5b and the eleventh series resonator S6. One end of the ninth series resonator S5a is connected to the antenna terminal ANT, and the other end is connected to the tenth series resonator S5b. The other end of the tenth series resonator S5b is connected to the longitudinal coupling resonator DMS. The longitudinal coupling resonator DMS is connected to the receiving terminal RX through the eleventh series resonator S6.

6. The duplexer according to claim 5, characterized in that, The grounding that constitutes the low-impedance common grounding network includes the grounding of the first parallel resonator P1, the grounding of the second parallel resonator P2, the grounding of the third parallel resonator P3, and all groundings of the longitudinally coupled resonator DMS except for one of the optional groundings.

7. The duplexer according to claim 6, characterized in that, The grounding of the receiving filter and the grounding of the transmitting filter are independent of each other on the component substrate to avoid crosstalk generated by the transmitting and receiving links through the grounding loop.

8. The duplexer according to claim 7, characterized in that, The packaged chip is used to encapsulate and protect the component substrate, providing mechanical support and environmental isolation, and also serving as an electrical interconnection platform between the component substrate and external circuits. The packaged chip uses a multilayer substrate, which includes four layers, one of which is used to set various pins, and the other three layers are used to set wire-wound inductors. The antenna pin ANT Pin is electrically connected to the antenna terminal ANT on the component substrate and is used to solder the antenna onto the PCB of the terminal device. The transmit pin TX Pin is electrically connected to the transmit terminal TX and is used to connect external radio frequency devices. The receive pin RX Pin is electrically connected to the receive terminal RX and is used to connect external radio frequency devices. Several ground pins GND Pin are used to connect the grounding points inside the surface acoustic wave duplexer to the reference ground plane of the system PCB.

9. The duplexer according to claim 8, characterized in that, The inductor is formed by a wire winding pattern on a metal layer of a multilayer substrate.

10. The duplexer according to claim 9, characterized in that, The metal sphere is made of gold or a tin-silver-copper alloy, and the electrical interconnection and mechanical fixation between the two are achieved through a flip-chip bonding process.

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