Filter and communication equipment comprising same
By introducing multiple series and parallel branches into the RF filter, with the parallel branches having a lower resonant frequency than the series branches, and combining this with a suppression boosting unit to optimize the resonator parameters and coupling relationship, the problem of insufficient out-of-band suppression in SAW filters at high frequencies is solved, achieving high selectivity and low loss filtering performance.
Patent Information
- Application Number
- CN202422494707.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-15
- Publication Date
- 2025-11-18
- Estimated Expiration
- 2034-10-15
AI Technical Summary
Existing SAW filters have insufficient out-of-band suppression capability in the high-frequency range, affecting their selectivity and anti-interference capability.
An RF filter was designed by introducing multiple series and parallel branches into the filter network. The resonant frequency of the parallel branch is lower than that of the series branch. Combined with the suppression boosting unit to generate a zero on the high-frequency side, the parameters and coupling relationship of the resonator are optimized to improve the high-frequency out-of-band suppression.
It significantly improves the filter's suppression capability in the high-frequency range, achieving filtering performance with high selectivity and low insertion loss.
Smart Images
Figure CN223567597U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a filter, and more specifically, to a radio frequency filter and communication device incorporating a surface acoustic wave device. Background Technology
[0002] Surface acoustic wave (SAW) filters are electronic devices that utilize sound waves propagating from the surface of solid materials to perform signal processing. Due to their excellent performance in the high-frequency range, SAW filters are widely used in mobile communication devices.
[0003] Out-of-band rejection (OBS) is the ability of a filter to suppress unwanted frequency components outside its passband. High-frequency OBS is one of the most important performance indicators for SAW filters, as it directly affects the selectivity and anti-interference capability of SAW filters. Therefore, providing an SAW filter with high-frequency OBS is what the industry desires. Utility Model Content
[0004] This invention addresses the aforementioned technical problems by meticulously designing an RF filter, successfully developing an RF filter that can improve the high-frequency out-of-band suppression of SAW filters.
[0005] A brief overview of the present invention will be given below to provide a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the present invention. It is not intended to identify key or essential parts of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.
[0006] According to one aspect of the present invention, a radio frequency filter is provided, comprising: a first signal transmission end, a second signal transmission end, a filter network, a coupled resonator filter, and a suppression and boosting unit. The filter network is disposed between the first signal transmission end and the second signal transmission end and includes multiple series branches and at least one parallel branch. Each series branch includes at least one series surface acoustic wave resonator, and each parallel branch includes at least one parallel surface acoustic wave resonator. The coupled resonator filter is disposed between the series branch closest to the second signal transmission end and the second signal transmission end. A suppression and boosting unit is connected between the second signal transmission end and ground to generate a zero on the high-frequency side of the passband of the radio frequency filter.
[0007] Furthermore, the suppression and enhancement unit includes a surface acoustic wave resonator, the series resonant frequency of which is set on the high-frequency side of the RF filter passband.
[0008] Furthermore, the series resonant frequency of the parallel surface acoustic wave resonators in the parallel branch is the same as and lower than the series resonant frequency of the surface acoustic wave resonators in the suppression and enhancement unit.
[0009] Furthermore, the series resonant frequencies of the series surface acoustic wave resonators in each series branch are the same or similar, while the series resonant frequencies of the parallel surface acoustic wave resonators in the parallel branch are lower than the series resonant frequencies of the series surface acoustic wave resonators in each series branch.
[0010] Furthermore, there are multiple coupled resonator filters between the first signal transmission end and the second signal transmission end.
[0011] Furthermore, the coupled resonator filter is composed of LC passive devices, surface acoustic wave resonators, or photonic crystal resonators.
[0012] Furthermore, when each series branch and each parallel branch has multiple surface acoustic wave resonators, the multiple surface acoustic wave resonators are connected in series and / or in parallel.
[0013] Furthermore, each series branch and each parallel branch further includes LC lumped elements.
[0014] Furthermore, the first signal transmission terminal and the second signal transmission terminal are connected by two series branches and one parallel branch. The first series branch has a first surface acoustic wave resonator, and the second series branch has a second surface acoustic wave resonator. The first surface acoustic wave resonator, the second surface acoustic wave resonator, and the coupling resonator filter are connected in sequence. The parallel branch is connected between the node between the first series branch and the second series branch and the ground. The parallel branch includes a parallel surface acoustic wave resonator. The suppression and boosting unit is connected between the output of the second signal transmission terminal and the ground. The suppression and boosting unit includes a parallel surface acoustic wave resonator.
[0015] According to one aspect of the present invention, a communication device is provided, the communication device comprising any of the preceding radio frequency filters. Attached Figure Description
[0016] The specific details of this utility model are described below with reference to the accompanying drawings, which will help to more easily understand the above and other objects, features, and advantages of this utility model. The drawings are only for illustrating the principle of this utility model. The dimensions and relative positions of the units are not necessarily drawn to scale in the drawings.
[0017] Figure 1 A schematic diagram of a surface acoustic wave filter with a stepped topology is shown.
[0018] Figure 2 Show Figure 1 Working principle of surface acoustic wave filter with a first-order trapezoidal topology;
[0019] Figure 3 The circuit structure of the radio frequency filter in this utility model is shown;
[0020] Figure 4 The circuit structure of the radio frequency filter for the comparative example is shown;
[0021] Figure 5 The amplitude-frequency curves of the RF filter provided by this utility model and the RF filter provided by the comparative example are shown. Detailed Implementation
[0022] The exemplary disclosure of this utility model will be described below with reference to the accompanying drawings. For clarity and brevity, not all features implementing this utility model are described in the specification. However, it should be understood that many utility model-specific decisions can be made in the development of any such implementation of this utility model in order to achieve the developer's specific objectives, and these decisions may vary depending on the specific implementation of this utility model.
[0023] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structure closely related to the solution according to the present invention is shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.
[0024] It should be understood that this invention is not limited to the described embodiments by reference to the accompanying drawings. In this invention, features may be substituted or borrowed between different embodiments where feasible, and one or more features may be omitted in one embodiment.
[0025] Please see Figure 1 , Figure 1 A schematic diagram of a surface acoustic wave filter with a trapezoidal topology is shown. Figure 1 As shown, a surface acoustic wave (SAW) filter with a stepped topology consists of a series SAW resonator S1 and a parallel SAW resonator P1. The series SAW resonator S1 in the stepped topology SAW filter provides the low-pass characteristics of the filter, while the parallel SAW resonator P1 defines the high-pass characteristics. By designing the parameters of the SAW resonators, such as frequency, quality factor (Q value), and coupling strength, the passband, stopband, and roll-off characteristics of the SAW filter can be controlled.
[0026] The following is combined Figure 2 Detailed explanation Figure 1 Working principle of surface acoustic wave filter with a ladder topology.
[0027] like Figure 2 As shown, the frequency corresponding to the impedance minimum of the series surface acoustic wave resonator S1 should be basically the same as the frequency corresponding to the impedance maximum of the parallel surface acoustic wave resonator P1. When the surface acoustic wave filter is as follows... Figure 2 As shown, when operating at frequency a, the impedance of the parallel surface acoustic wave resonator P1 is at its minimum, and the signal is almost entirely short-circuited to ground. Therefore, a transmission zero of the surface acoustic wave filter appears at frequency a. When the surface acoustic wave filter... Figure 2 As shown, when operating at frequency b, the parallel surface acoustic wave (SAW) resonator P1 has extremely high impedance and can be considered an open circuit, while the series SW resonator S1 has extremely low impedance and can be considered a short circuit. In this case, the signal can pass through the filter almost without loss, and a passband appears near the b frequency. When the surface acoustic wave filter is as follows... Figure 2 As shown, when operating at frequency c, the impedance of the series surface acoustic wave (SAW) resonator S1 is at its maximum, and almost no signal can pass through. Therefore, a transmission zero appears in the filter, and the resonant characteristics of the series SW resonator S1 and the parallel SW resonator P1 form the bandpass characteristic of the SAW filter. The passband of a SAW filter is the frequency range in which a signal can pass without significant attenuation. In a stepped SAW filter, the passband is defined by the series and parallel configuration of the resonators and their coupling relationships. During design, the center frequency of the resonator is set within the passband range, while the width and shape of the passband depend on the Q value of the resonator, the coupling coefficient, and the overall cascade structure of the filter. By optimizing these parameters, ideally, a filter with high selectivity, a flat passband response, and low insertion loss can be achieved.
[0028] Please see Figure 3 , Figure 3 The circuit structure of the radio frequency filter in this invention is shown, as follows: Figure 3 As shown, the RF filter 1 includes a first signal transmission terminal 100, a second signal transmission terminal 200, a filter network 300, a coupled resonator filter 400, and a suppression boosting unit 500. A first end of the filter network 300 is connected to the first signal transmission terminal 100, a second end of the filter network 300 is connected to the first end of the coupled resonator filter 400, the second end of the coupled resonator filter 400 is connected to the second signal transmission terminal 200, and a first end of the suppression boosting unit 500 is connected to the second end of the coupled resonator filter 400, with the second end of the suppression boosting unit 500 grounded. The suppression boosting unit 500 is used to generate a zero on the high-frequency side of the RF filter's passband. For example, the suppression boosting unit 500 can be constructed from a surface acoustic wave resonator P2.
[0029] Specifically, the trapezoidal topology filter network 300 includes two series branches and one parallel branch. The first series branch includes a first series surface acoustic wave (SAW) resonator S1, the first end of which is the first end of the filter network 300. The second series branch includes a second series SAW resonator S2. The second end of the first series SAW resonator S1 is connected to the first end of the series SAW resonator S2, and the second end of the second series SAW resonator S2 is connected to the first end of the coupled resonator filter 400. The first parallel branch includes a first parallel SAW resonator P1. The first end of the first parallel SAW resonator P1 is connected to the second end of the first series SAW resonator S1, and the second end of the first parallel SAW resonator P1 is grounded.
[0030] Furthermore, when the suppression boosting unit 500 connected to the second end of the coupled resonator filter 400 is composed of a surface acoustic wave resonator P2, the series resonant frequency point of the surface acoustic wave resonator P2 is set on the high-frequency side of the passband of the radio frequency filter 1.
[0031] Furthermore, the first series surface acoustic wave resonator S1 and the second series surface acoustic wave resonator S2 are configured to have the same or similar series resonant frequency points, and the series resonant frequency point of the first parallel surface acoustic wave resonator P1 is configured to be lower than the series resonant frequency points of the first series surface acoustic wave resonator S1 and the second series surface acoustic wave resonator S2; the series resonant frequency point of the parallel surface acoustic wave resonator P1 in the parallel branch is lower than the series resonant frequency point of the surface acoustic wave resonator P2 in the suppression and enhancement unit.
[0032] Please see Figure 4 , Figure 4 The circuit structure of the comparative example RF filter is shown. For example... Figure 4 As shown, the RF filter 2 includes a first signal transmission terminal 110, a second signal transmission terminal 210, a filter network 310, and a coupled resonator filter 410. The first end of the filter network 310 is connected to the first signal transmission terminal 110, the second end of the filter network 310 is connected to the first end of the coupled resonator filter 400, and the second end of the coupled resonator filter 400 is connected to the second signal transmission terminal 210.
[0033] Specifically, the trapezoidal topology filter network 310 also includes two series branches and one parallel branch. The first series branch includes a first series surface acoustic wave (SAW) resonator S11, the first end of which is the first end of the filter network 310. The second series branch includes a second series SAW resonator S21, the second end of which is connected to the first end of the series SAW resonator S21, and the second end of which is connected to the first end of the coupled resonator filter 410. The first parallel branch includes a first parallel SAW resonator P11, the first end of which is connected to the second end of the first series SAW resonator S11, and the second end of which is grounded.
[0034] Furthermore, the first series surface acoustic wave resonator S11 and the second series surface acoustic wave resonator S21 are configured to have the same or similar resonant frequency points, and the resonant frequency point of the first parallel surface acoustic wave resonator P11 is configured to be lower than the resonant frequency points of the first series surface acoustic wave resonator S11 and the second series surface acoustic wave resonator S21.
[0035] Please see Figure 5 , Figure 5 The amplitude-frequency curves of the RF filter provided by this utility model and the RF filter provided by the comparative example are shown. Figure 5 In the diagram, blue curve 2 represents the amplitude-frequency curve of the RF filter provided in the comparative example, and red curve 1 represents the amplitude-frequency curve of the RF filter provided in this invention. Figure 5 It can be seen that the RF filter provided by this utility model improves the high-frequency out-of-band suppression compared with the RF filter provided by the comparative example. The RF filter provided by this utility model can achieve a high-frequency out-of-band suppression of up to about 10 dB compared with the RF filter provided by the comparative example.
[0036] Although Figure 3 The RF filter's filtering network provides only one parallel branch and two series branches. However, it is understood that the number of parallel and series branches in an RF filter is not limited to this; for example, the number of parallel and series branches in an RF filter can be a natural number greater than or equal to two. Furthermore, although... Figure 3The RF filter shown includes only one surface acoustic wave (SAW) resonator in each series branch and only one SAW resonator in each parallel branch. However, it is understood that multiple SAW resonators can also be present in the series and parallel branches, and these resonators can be connected in series and / or parallel. It is also understood that LC lumped elements can be further present in the series and parallel branches.
[0037] Although Figure 3 Only one coupled resonator filter S31 is shown between the first signal transmission terminal 110 and the second signal transmission terminal 210. It can be further understood that, since the coupled resonator filter achieves frequency selection through the mutual coupling between resonant elements, multiple coupled resonator filters can be connected in series between the first signal transmission terminal 110 and the second signal transmission terminal 210. Furthermore, the coupled resonator filter can be constructed from LC passive devices, surface acoustic wave resonators, photonic crystal resonators, etc.
[0038] The filter of this invention can be widely used in communication devices, such as mobile phones, personal digital assistants, electronic game devices, and wearable terminals.
[0039] The present invention has been described above with reference to specific embodiments. However, those skilled in the art should understand that these descriptions are exemplary and not intended to limit the scope of protection of the present invention. Those skilled in the art can make various modifications and variations to the present invention based on its spirit and principles, and these modifications and variations are also within the scope of the present invention.
Claims
1. A filter, characterized by, The communication device comprises the filter of any one of claims 1-9. The filter comprises: a first signal transmission end, a second signal transmission end, a filter network, a coupled resonator filter, and a suppression boosting unit, the filter network being arranged between the first signal transmission end and the second signal transmission end and comprising a plurality of series branches and at least one parallel branch; each series branch comprising at least one series surface acoustic wave resonator, and the parallel branch comprising at least one parallel surface acoustic wave resonator; the coupled resonator filter being arranged between the series branch closest to the second signal transmission end and the second signal transmission end; 2. The filter of claim 1, wherein: a suppression boosting unit being connected between the second signal transmission end and the ground to generate a zero point on the high frequency side of the passband of the radio frequency filter.
3. The filter of claim 2, wherein: The suppression boosting unit comprises a surface acoustic wave resonator, and a series resonance frequency point of the surface acoustic wave resonator is arranged on the high frequency side of the passband of the radio frequency filter.
4. The filter of claim 3, wherein: The series resonance frequency points of the parallel surface acoustic wave resonators in the parallel branch are the same and lower than the series resonance frequency point of the surface acoustic wave resonator in the suppression boosting unit.
5. The filter of claim 4, wherein: The series resonance frequency points of the series surface acoustic wave resonators in each series branch are the same, and the series resonance frequency point of the parallel surface acoustic wave resonator in the parallel branch is lower than the series resonance frequency points of the series surface acoustic wave resonators in each series branch.
6. The filter of claim 5, wherein: The filter comprises a plurality of coupled resonator filters between the first signal transmission end and the second signal transmission end.
7. The filter of any one of claims 1-6, wherein: The coupled resonator filter is composed of LC passive devices, surface acoustic wave resonators, or photonic crystal resonators.
8. The filter of claim 7, wherein: When the filter comprises a plurality of surface acoustic wave resonators in each series branch and each parallel branch, the plurality of surface acoustic wave resonators are connected in series and / or in parallel.
9. The filter of claim 6, wherein: The filter further comprises LC lumped elements in each series branch and each parallel branch.
10. A communication device, characterized by: The filter comprises two series branches and one parallel branch between the first signal transmission end and the second signal transmission end, the first series branch comprises a first surface acoustic wave resonator, the second series branch comprises a second surface acoustic wave resonator, the first surface acoustic wave resonator, the second surface acoustic wave resonator, and the coupled resonator filter are connected in sequence; the parallel branch is connected between a node between the first series branch and the second series branch and the ground, and comprises a parallel surface acoustic wave resonator; the suppression boosting unit is connected between the second signal transmission end and the ground, and comprises a parallel surface acoustic wave resonator. The communication device comprises the filter of any one of claims 1-9.