Filtering trace structure, device, flexible circuit board

Abstract

This application discloses a filtering trace structure, device, and flexible circuit board. The filtering trace structure includes at least one high-impedance trace and at least one low-impedance trace. The high-impedance and low-impedance traces are alternately arranged and connected in series. The characteristic impedance of the high-impedance trace is greater than a preset threshold, and the characteristic impedance of the low-impedance trace is less than the preset threshold. By alternately arranging and connecting at least one high-impedance and at least one low-impedance trace in series, a transmission line structure with periodic impedance changes is formed. The filtering effect is achieved by utilizing the impedance mismatch effect between the high-impedance and low-impedance segments, thereby directly integrating the filtering capability into the signal trace and effectively suppressing radio frequency interference.

Description

Technical Field

[0001] This application relates to the field of filtering, and more specifically, to a filtering trace structure, device, and flexible circuit board. Background Technology

[0002] In consumer electronics devices, the Mobile Industry Processor Interface (MIPI) signal line is often used for high-speed data transmission between the camera and the main control chip.

[0003] In related technologies, the design of MIPI traces is usually aimed at meeting transmission requirements such as impedance matching and timing integrity.

[0004] However, MIPI traces in related technologies are susceptible to radio frequency interference when transmitting signals. Summary of the Invention

[0005] This application provides a filter routing structure, device, and flexible circuit board.

[0006] According to one aspect of the embodiments of this application, a filter trace structure is provided, including: at least one high-impedance trace; at least one low-impedance trace; wherein the at least one high-impedance trace and the at least one low-impedance trace are alternately arranged and connected in series, the characteristic impedance of the high-impedance trace is greater than a preset threshold, and the characteristic impedance of the low-impedance trace is less than the preset threshold.

[0007] In an exemplary embodiment, the filter trace structure includes: N high-impedance traces and N-1 low-impedance traces, wherein the N high-impedance traces and N-1 low-impedance traces are arranged alternately and connected in series, wherein N is an integer and N is greater than or equal to 2.

[0008] In an exemplary embodiment, the filter trace structure includes: N low-impedance traces and N-1 high-impedance traces, wherein the N low-impedance traces and N-1 high-impedance traces are arranged alternately and connected in series, wherein N is an integer and N is greater than or equal to 2.

[0009] In one exemplary embodiment, the preset threshold is greater than or equal to 40Ω and less than or equal to 60Ω.

[0010] In an exemplary embodiment, the cross-sections of the at least one high-impedance trace and the at least one low-impedance trace are regular hexagonal, regular octagonal, or regular dodecagonal.

[0011] In an exemplary embodiment, the filter trace structure further includes a shape memory alloy embedded in the at least one high-impedance trace, which is used to deform and adjust the linewidth of the at least one high-impedance trace when the ambient temperature of the filter trace structure changes, so as to keep the characteristic impedance of the at least one high-impedance trace unchanged.

[0012] In one exemplary embodiment, both the at least one high-impedance trace and the at least one low-impedance trace are microstrip lines.

[0013] According to another aspect of the embodiments of this application, a filtering routing device is also provided, including the aforementioned filtering routing structure, a first impedance matching routing trace, and a second impedance matching routing trace, wherein:

[0014] The first end of the first impedance matching trace is connected to the first end of the filter trace structure;

[0015] The first end of the second impedance matching trace is connected to the second end of the filter trace structure;

[0016] Wherein, the characteristic impedance of the impedance matching trace is equal to the preset threshold.

[0017] In an exemplary embodiment, the filtering trace device further includes: a switching module, which is connected in series between the first end of the first impedance matching trace and the filtering trace structure. The first end of the switching module is connected to the first end of the first impedance matching trace, and the second end of the switching module is connected to the first ends of a plurality of filtering trace structures. The switching module is used to open the path between the first end of the first impedance matching trace and the first end of the target filtering trace structure, wherein the cutoff frequencies of the plurality of filtering trace structures are different.

[0018] According to another aspect of the embodiments of this application, a flexible circuit board is also provided, including the filtering routing device, the first connector and the second connector as described above, wherein: the first connector is connected to the second end of the first impedance matching routing; and the second connector is connected to the second end of the second impedance matching routing.

[0019] The aforementioned filtering trace structure forms a transmission line structure with periodic impedance abrupt changes by alternating and connecting at least one high-impedance trace and at least one low-impedance trace in series. Utilizing the impedance mismatch effect between the high-impedance and low-impedance segments, reflection and interference are generated in the radio frequency band, thereby selectively attenuating interference signals and achieving low-pass or band-stop characteristics similar to LC filters. This structure eliminates the need for discrete components such as capacitors and inductors, relying directly on the geometric design and material parameter control of the traces to ensure that the characteristic impedance of the high-impedance trace is higher than a preset threshold and the characteristic impedance of the low-impedance trace is lower than a preset threshold, collaboratively constructing a passive filtering function. Thus, without increasing the number of components or the layout area, the filtering capability is directly integrated into the MIPI signal trace, effectively suppressing radio frequency interference. This solves the problems of complex wiring, increased cost, and large space occupation caused by the lack of integrated filtering mechanisms in existing MIPI signal traces, which necessitate the use of external discrete components, achieving synergistic optimization of signal integrity and electromagnetic compatibility. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a structural diagram of a filter trace structure according to an embodiment of this application;

[0023] Figure 2 This is an equivalent circuit diagram of a filter routing structure according to an embodiment of this application;

[0024] Figure 3 This is a second structural diagram of a filter routing structure according to an embodiment of this application;

[0025] Figure 4 This is a second equivalent circuit diagram of a filter routing structure according to an embodiment of this application;

[0026] Figure 5 This is a third structural diagram of a filter routing structure according to an embodiment of this application;

[0027] Figure 6 This is a structural diagram of a filtering wiring device according to an embodiment of this application;

[0028] Figure 7This is a second structural diagram of a filtering wiring device according to an embodiment of this application;

[0029] Figure 8 This is the third structural diagram of a filtering wiring device according to an embodiment of this application;

[0030] Figure 9 This is the fourth structural diagram of a filtering wiring device according to an embodiment of this application;

[0031] Figure 10 This is a structural diagram of a flexible circuit board according to an embodiment of this application.

[0032] Explanation of reference numerals in the attached diagram: 10-High impedance trace, 20-Low impedance trace, 100-Filter trace structure, 31-First impedance matching trace, 32-Second impedance matching trace, 40-Switching module, 200-Flexible circuit board, 51-First connector, 52-Second connector. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data used in this way can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0038] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. Furthermore, in the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if there is transmission of electrical signals or data between the connected objects.

[0039] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0040] In one embodiment, such as Figure 1 As shown, a filter trace structure is provided, including: at least one high-impedance trace 10 and at least one low-impedance trace 20, wherein:

[0041] At least one high-impedance trace 10 and at least one low-impedance trace 20 are arranged alternately and connected in series. The characteristic impedance of the high-impedance trace 10 is greater than a preset threshold, and the characteristic impedance of the low-impedance trace 20 is less than a preset threshold.

[0042] Specifically, the MIPI signal line is designed as a stepped impedance transmission line structure. By alternately setting high-impedance and low-impedance segments, the signal trace itself forms a network with low-pass filtering characteristics. This structure utilizes the physical characteristics that the high-impedance segment is equivalent to a series inductor and the low-impedance segment is equivalent to a parallel capacitor. At least one high-impedance trace 10 and at least one low-impedance trace 20 are alternately arranged and connected in series. This means that the signal path is formed by several segments with distinct impedance characteristics connected end to end to form a continuous path. The characteristic impedance of the high-impedance trace 10 is greater than a preset threshold, and the characteristic impedance of the low-impedance trace 20 is less than the same preset threshold. Thus, without introducing discrete components, a frequency-selective transmission structure is constructed through the periodic change of the trace's own impedance. Due to the alternating series connection of high and low impedance segments, this structure naturally forms a cumulative reflection and attenuation mechanism for high-frequency components, achieving a passive suppression function for interference in specific frequency bands.

[0043] Specifically, the MIPI signal line is designed to include at least one high-impedance trace 10, forming a microstrip segment with a specific characteristic impedance in the signal transmission path. This high-impedance trace 10 is equivalent to a series inductor in high-frequency signal transmission, with an impedance value higher than a preset threshold (e.g., a standard 50Ω characteristic impedance). Thus, without introducing discrete components, the inductive suppression of interference signals is achieved through changes in the trace geometry. This structure directly acts on the MIPI signal link, causing high-frequency interference components to experience impedance increases and energy attenuation due to inductive characteristics when passing through the trace. This passively filters out interference in specific frequency bands while maintaining the complete transmission path and impedance continuity of the baseband signal.

[0044] Specifically, at least one low-impedance trace 20 is provided, making this trace equivalent to a parallel capacitor structure during high-frequency signal transmission. This introduces a capacitive load into the MIPI signal path, creating a shunt and suppression effect on interference signals in a specific frequency band. The low-impedance trace 20 directly constitutes a parallel element in the filter structure, and its characteristic impedance is lower than the system reference impedance. This allows high-frequency interference energy to be absorbed or reflected through this path, reducing its coupling strength to subsequent circuits and achieving passive attenuation of interference in the target frequency band. Furthermore, this effect relies solely on the physical existence of the low-impedance trace 20 itself, without depending on other auxiliary components or additional structures.

[0045] For example, such as Figure 2 As shown, low-pass filtering can be achieved by constructing the simplest LC topology. Figure 2 The cutoff frequency of the structure is:

[0046]

[0047] Considering the integrated design of flexible printed circuit (FPC) traces and the skin effect of high-frequency signals, LC components need to be equivalent to microstrip lines.

[0048] A length of Characteristic impedance When the transmission line is terminated with a matching load:

[0049]

[0050] The impedance of the inductor is:

[0051]

[0052] From formulas (2) and (3), we can obtain:

[0053]

[0054] Therefore, the higher the impedance of a microstrip line, the more it is equivalent to a series inductor. That is, a high-impedance trace 10 can be equivalent to a series inductor.

[0055] The admittance of the capacitor is:

[0056]

[0057] From formulas (2) and (5), we can obtain:

[0058]

[0059] Therefore, the lower the impedance of a microstrip line, the more it is equivalent to a parallel capacitor. That is, the low-impedance trace 20 can be equivalent to a parallel capacitor. Therefore, only a high-impedance trace 10 and a low-impedance trace 20 are needed to construct a first-order low-pass LC filter circuit, where the high-impedance trace 10 is equivalent to a series inductor and the low-impedance trace 20 is equivalent to a parallel capacitor.

[0060] For example, the preset threshold is greater than or equal to 40Ω and less than or equal to 60Ω. By limiting the preset threshold to greater than or equal to 40Ω and less than or equal to 60Ω, and combining it with an alternating series structure where the characteristic impedance of high-impedance trace 10 is higher than this threshold and the characteristic impedance of low-impedance trace 20 is lower than this threshold, a significant and stable impedance jump is formed between adjacent traces. This impedance difference precisely matches the filtering requirements of 2.4GHz band interference signals. Without introducing any discrete components, an effective low-pass filtering effect is generated through the impedance discontinuity of the traces themselves, thereby achieving an attenuation capability of ≥20dB for high-frequency radio frequency interference. This ensures that the MIPI high-speed signal transmission path maintains signal integrity while effectively suppressing external interference. This solves the defects of existing technologies where insufficient impedance difference leads to weak filtering effect and reliance on external devices, realizing an integrated, low-cost, and highly reliable solution that integrates filtering functions at the PCB trace level.

[0061] For example, at least one high-impedance trace 10 and at least one low-impedance trace 20 are both microstrip lines. By designing at least one high-impedance trace 10 and at least one low-impedance trace 20 as microstrip line structures, they can be directly integrated into the planar layer of a flexible printed circuit (FPC). Utilizing the unique impedance controllability of microstrip lines, the characteristic impedance of each trace segment can be precisely configured according to the line width and dielectric layer parameters, forming a low-pass filter structure with a stepped impedance distribution. This effectively suppresses high-frequency radio frequency interference without relying on external discrete components. At the same time, the closed-field distribution characteristics of microstrip lines significantly reduce signal radiation loss and are fully compatible with FPC manufacturing processes. This solves the problems of unstable impedance control, poor signal integrity, and low process adaptability caused by traditional traces due to their non-microstrip form. It achieves an integrated design of filtering function and signal trace, improving the transmission reliability and anti-interference capability of MIPI signals in high-frequency environments.

[0062] Specifically, in this application, the integrated routing method of the FPC refers to the direct reconstruction of MIPI traces, originally used only for signal transmission, into passive networks with low-pass filtering characteristics on the flexible printed circuit board (FPC) through geometric structure design (stepped impedance routing design), rather than relying on externally mounted LC components or ferrite beads. This structure uses the equivalent principle of "high impedance section = series inductor" and "low impedance section = parallel capacitor," achieving filtering functionality entirely through the linewidth, length, and dielectric parameters of the FPC traces. The filtering function is not externally added but rather an inherent characteristic of the traces themselves; it is a physical reconstruction of the signal path structure, not a simple superposition of functional modules. Applying measures to address the impact of radio frequency signals to the MIPI traces of the baseband FPC involves low-pass filtering technology, specifically setting a cutoff frequency (e.g., 1 GHz) to attenuate interference energy above that frequency. In traditional solutions, such measures are typically implemented by independent discrete filters (e.g., ferrite beads, LC networks), placed at the motherboard or module interface.

[0063] In this application, the "filtering measures" are moved from "external devices" to "internal signal path," meaning that the filtering design originally used to suppress radio frequency interference is directly embedded into the FPC traces connecting the main control chip and the camera module, becoming part of the signal link. This means that the anti-interference measures originally used in the RF frontend have been creatively transplanted to the physical layer of the baseband signal path (MIPI), achieving cross-domain technology migration and applying the RF filtering concept to baseband signal integrity design.

[0064] This filtering effect has two advantages: first, it filters out MIPI harmonics to solve the desensitization problem; second, it can filter out radio frequency signals in reverse to solve the camera's anti-interference problem. MIPI signals are high-speed differential digital signals (such as DPHY 2.5Gbps), and their spectrum contains rich high-order harmonics (such as 2.4GHz, 3.6GHz, etc.). These harmonic energies can be radiated to nearby radio frequency receiving links (such as WiFi, LTE receiving antennas) through FPC traces or PCB coupling, resulting in degraded receiving sensitivity, i.e., the "desense" problem.

[0065] The stepped impedance low-pass filter in this application has a cutoff frequency set to 1 GHz, which can effectively attenuate harmonic components in the MIPI signal that are higher than 1 GHz (such as 2.4 GHz, 3.6 GHz, etc.), thereby suppressing the radiative coupling of MIPI as an interference source to the external radio frequency receiver and alleviating desense.

[0066] The solution proposed in this application can also filter out radio frequency signals in reverse to solve camera immunity problems. "Reverse" refers to the opposite direction of interference propagation: when WiFi or cellular radio frequency signals (such as 2.4GHz) enter the FPC traces through spatial coupling or common-ground coupling, they will interfere with the analog front-end or clock signal (MCLK) of the camera module, causing noise, frame errors, color distortion, and other "camera immunity" problems. Although the low-pass filter constructed in this application is designed as a "low-pass" filter, its physical structure has an attenuation effect on interference signals above the cutoff frequency (1GHz), regardless of whether the interference comes from MIPI or external radio frequency. Therefore, when a 2.4GHz WiFi signal invades the FPC from the outside, this structure can also attenuate its energy and prevent it from reaching the receiving end of the camera module (such as MCLK, MDATA lines), thereby improving the camera's electromagnetic immunity (EMS).

[0067] In this application, the low-pass filter structure is directly integrated into the MIPI signal trace in the form of a "stepped impedance microstrip line" as the physical wiring structure of the FPC, thereby solving the radio frequency interference problem in the mobile phone system.

[0068] In this embodiment, by employing a structural design in which at least one high-impedance trace 10 and at least one low-impedance trace 20 are alternately arranged and connected in series in the MIPI signal trace, the trace itself forms a transmission line filtering network with frequency-selective characteristics. The characteristic impedance of the high-impedance trace 10 is greater than a preset threshold, while the characteristic impedance of the low-impedance trace 20 is less than this threshold. This significantly attenuates radio frequency interference in specific frequency bands during normal signal transmission, achieving passive suppression of high-frequency noise. This structure eliminates the need for additional discrete filtering components such as capacitors and inductors, directly integrating the filtering function at the PCB trace level. It fundamentally solves the problems of existing technologies where MIPI signal traces cannot integrate filtering capabilities and must rely on external devices to suppress radio frequency interference, leading to complex layouts, increased costs, and reduced reliability. This achieves a comprehensive technical effect of simplifying the wiring structure, reducing system costs, and improving anti-interference performance and signal integrity.

[0069] In one embodiment, such as Figure 3 As shown, the filter trace structure includes: N high-impedance traces 10 and N-1 low-impedance traces 20, which are arranged alternately and connected in series, where N is an integer and N is greater than or equal to 2.

[0070] Specifically, by designing N high-impedance traces 10 and N-1 low-impedance traces 20, it is possible to cascade multiple high and low impedance transmission lines to construct an equivalent high-order stepped impedance low-pass filter, thereby improving the filter's frequency selectivity, increasing the stopband attenuation rate, and improving the roll-off characteristics.

[0071] For example, such as Figure 4 As shown, the N-segment high-impedance trace 10 is equivalent to series inductors L1, L2, and L3, and the N-1-segment low-impedance trace 20 is equivalent to parallel capacitors C1 and C2.

[0072] In this embodiment, by setting N high-impedance traces 10 and N-1 low-impedance traces 20 alternately and connected in series, where N is an integer greater than or equal to 2, the high-impedance traces 10 are equivalent to series inductors and the low-impedance traces 20 are equivalent to parallel capacitors, together forming at least a second-order low-pass filter structure. Compared with a first-order structure containing only a single high-impedance and a single low-impedance segment, this significantly improves the stopband attenuation rate and frequency selectivity, thereby stably achieving a suppression effect of more than 20dB on 2.4GHz radio frequency interference signals. This effectively solves the technical problem that existing MIPI signal traces rely on discrete components due to the lack of integrated filtering functions and have insufficient anti-interference capabilities, realizing the integrated design of filtering functions and signal traces, and improving system integration and electromagnetic compatibility performance.

[0073] In one embodiment, such as Figure 5 As shown, the filter trace structure includes: N low-impedance traces 20 and N-1 high-impedance traces 10, which are arranged alternately and connected in series, where N is an integer and N is greater than or equal to 2.

[0074] Specifically, N low-impedance traces 20 and N-1 high-impedance traces 10 can be used to achieve the same effect as an equivalent filter circuit.

[0075] In this embodiment, by setting N low-impedance traces 20 and N-1 high-impedance traces 10 alternately in series, with N being an integer greater than or equal to 2, the trace structure forms a low-pass filter network of at least second order. The high-impedance traces 10 are equivalent to series inductors, and the low-impedance traces 20 are equivalent to parallel capacitors. By clearly defining the relationship between the number of traces, the filter is ensured to have a sufficient and predictable order, thereby significantly improving the attenuation capability against RF interference in the 2.4GHz band.

[0076] In one embodiment, the cross-sections of at least one high-impedance trace 10 and at least one low-impedance trace 20 are regular hexagonal, regular octagonal, or regular dodecagonal.

[0077] In this embodiment, by defining the cross-sectional structure of the high-impedance trace 10 and the low-impedance trace 20 as regular hexagons, regular octagons, or regular dodecagons, and combining them with an alternating series stepped impedance layout, the geometric consistency and electromagnetic field distribution uniformity of the traces in high-frequency signal transmission are significantly improved. This effectively avoids the edge field distortion and impedance fluctuation problems that are prone to occur under manufacturing tolerances in traditional circular or rectangular cross-sections. Thus, without relying on external filtering components, the batch repeatability and working stability of the filtering structure are enhanced. This solves the problem of MIPI signal interference suppression performance drift caused by irregular trace shape, and finally realizes an efficient, reliable, and mass-producible intrinsic filtering function for radio frequency interference in a compact wiring space.

[0078] In one embodiment, the filter trace structure further includes a shape memory alloy. The shape memory alloy is embedded in at least one high-impedance trace 10 to deform and adjust the linewidth of the at least one high-impedance trace 10 when the ambient temperature of the filter trace structure changes, so as to keep the characteristic impedance of the at least one high-impedance trace 10 unchanged.

[0079] In this embodiment, by embedding shape memory alloy into at least one high-impedance trace 10, the linewidth of the high-impedance trace 10 is dynamically adjusted by utilizing its controllable deformation characteristics when the ambient temperature changes. This compensates for the changes in material properties caused by temperature drift, ensuring that the characteristic impedance of the high-impedance trace 10 is always kept above a preset threshold. Together with the series-connected low-impedance trace 20, it maintains the impedance matching relationship and frequency response stability of the overall filter structure, effectively avoiding the problems of impedance shift and filter performance degradation caused by temperature changes in traditional MIPI traces.

[0080] In one embodiment, such as Figure 6 As shown, a filtering trace device is provided, including the filtering trace structure 100 in any of the above embodiments, a first impedance matching trace 31, and a second impedance matching trace 32, wherein:

[0081] The first end of the first impedance matching trace 31 is connected to the first end of the filter trace structure 100.

[0082] Specifically, the first impedance matching trace 31 refers to a transmission line segment connected to a section of the filter trace structure 100 (e.g., near the baseband chip or signal source). Its characteristic impedance is set to a preset threshold, such as 50Ω, which is the industry standard impedance in RF and microwave circuits. The function of this trace segment is to achieve continuous impedance matching between the input end of the filter structure and the upstream signal source, avoiding signal reflection caused by impedance abrupt changes, thereby ensuring the timing integrity and amplitude stability of the MIPI high-speed differential signal. Its length can be freely adjusted (because the impedance is determined only by the line width) to adapt to the FPC layout space without affecting the filtering performance; it serves as a buffer segment.

[0083] The first end of the second impedance matching trace 32 is connected to the second end of the filter trace structure 100.

[0084] Among them, the characteristic impedance of the impedance matching trace is equal to the preset threshold.

[0085] Specifically, the second impedance matching trace 32 refers to a section of transmission line connected to the filter trace structure 100, such as the output end (i.e., near the camera module or signal receiver). Its characteristic impedance is also set to equal the "preset threshold"—50Ω. The function of this trace is to achieve continuous impedance matching between the output end of the filter structure and the downstream load (such as the MIPI receiver of the camera sensor), preventing signal reflection due to impedance discontinuity when entering the load, which could lead to eye diagram closure and increased bit error rate. Similar to the first matching trace, its length can be flexibly designed according to FPC wiring requirements. It is only used for physical connection and impedance transition and does not participate in the construction of the filtering function, ensuring that the net performance of the filter structure is not degraded by port mismatch.

[0086] For example, such as Figure 7 As shown, the first impedance matching trace 31 and the second impedance matching trace 32 can be connected to the high impedance trace 10, respectively.

[0087] For example, such as Figure 8 As shown, the first impedance matching trace 31 and the second impedance matching trace 32 can be connected to the low impedance trace 20, respectively.

[0088] In this embodiment, by connecting impedance matching traces with characteristic impedances equal to a preset threshold to both ends of the stepped impedance filter structure, a continuous impedance transition is achieved between the filter structure and the preceding and following signal paths. This effectively suppresses signal reflections caused by impedance discontinuities, ensuring the integrity of MIPI high-speed signal transmission. While maintaining the original filtering performance, this design ensures low insertion loss and low distortion when signals enter and exit the filter structure, improving the overall signal link stability. It is also compatible with standard 50Ω RF system design specifications, facilitating direct integration into existing FPC layouts without requiring additional adjustments to the impedance matching network of the terminal connectors or motherboard interfaces.

[0089] In one embodiment, such as Figure 9As shown, the filtering trace device further includes a switching module 40. The switching module 40 is connected in series between the first end of the first impedance matching trace 31 and the filtering trace structure 100. The first end of the switching module 40 is connected to the first end of the first impedance matching trace 31, and the second end of the switching module 40 is connected to the first ends of the plurality of filtering trace structures 100. The switching module 40 is used to open the path between the first end of the first impedance matching trace 31 and the first end of the target filtering trace structure 100, wherein the plurality of filtering trace structures 100 have different cutoff frequencies.

[0090] Specifically, the switching module 40 is a controllable electrical path switching element, physically connected in series between the first impedance matching trace 31 and the common input terminal of multiple filter trace structures 100. Its function is to selectively turn on one of the filter paths while disconnecting the others. This module can be a miniaturized integrated switching device such as a PIN diode switch, MEMS switch, or CMOS analog switch. It is itself an active or passive electronic component, embedded in an FPC or integrated with an FPC package to achieve dynamic switching of signal paths.

[0091] For example, among multiple filtering structures, the switching module 40 allows only one selected "target filter trace structure 100" to connect to the input signal, while the remaining paths are in a high-blocking open state. The optimal filter is dynamically selected based on the current operating scenario (such as WiFi band switching or 5G NR band changes). For instance, when the device switches from 2.4GHz WiFi to 5.8GHz WiFi, the control system triggers the switching module 40 to select a filtering structure with a cutoff frequency of 5GHz, instead of the original 2.4GHz suppression structure.

[0092] The multiple filter trace structures 100 have different cutoff frequencies, and the stepped impedance geometric parameters (line width, line length, and order) of each filter trace structure 100 are designed differently, resulting in different cutoff frequencies for their equivalent LC networks. By adjusting the combination of high-impedance sections (equivalent inductance) and low-impedance sections (equivalent capacitance), filter structures such as: Filter structure A: cutoff frequency 1.0 GHz (suppressing 2.4 GHz WiFi), Filter structure B: cutoff frequency 1.5 GHz (suppressing 5 GHz WiFi), and Filter structure C: cutoff frequency 2.0 GHz (suppressing 5.8 GHz WiFi) can be designed. Each structure is different, forming a filter bank with adjustable frequency bands, providing targeted suppression for interference in different frequency bands.

[0093] In this embodiment, a switching module 40 is connected in series between the first end of the first impedance matching trace 31 and the filter trace structure 100, and the second end of the switching module 40 is connected to multiple filter trace structures 100 with different cutoff frequencies. This allows the system to dynamically switch on the filter trace structure 100 that matches the target interference frequency band according to the frequency band characteristics of the current radio frequency interference. Thus, without changing the physical wiring layout, adaptive frequency selection suppression of interference signals in different frequency bands can be achieved. This effectively overcomes the problem of poor adaptability and limited filtering effect of traditional single cutoff frequency filter structures in complex electromagnetic environments with multiple frequency bands, and achieves the effect of flexibly responding to various radio frequency interferences and improving signal integrity and system anti-interference capability.

[0094] In one embodiment, such as Figure 10 As shown, a flexible circuit board 200 is provided, including the aforementioned filtering wiring device, a first connector 51, and a second connector 52, wherein:

[0095] The first connector 51 is connected to the second end of the first impedance matching trace 31.

[0096] Specifically, the first connector 51 refers to a physical interface device located at one end of the flexible circuit board 200, which is used to electrically connect the signal traces on the FPC to an external circuit board (such as a motherboard).

[0097] For example, the first connector 51 corresponds to the end connecting the FPC and the motherboard. Its function is to receive MIPI signals from the motherboard (or output signals to the motherboard). Its electrical characteristics are a standard 50Ω impedance system, and it is directly connected to the second end of the first impedance matching trace 31. This connector itself does not participate in filtering, does not change the signal characteristics, and only serves as a mechanical and electrical interface to realize the signal path access between the FPC and the system motherboard.

[0098] The second connector 52 is connected to the second end of the second impedance matching trace 32.

[0099] Specifically, the second connector 52 refers to the physical interface device located at the other end of the FPC, which is used to electrically connect the signal traces on the FPC to the circuit board on the other side (such as a camera module).

[0100] For example, the second connector 52 is directly connected to the second end of the second impedance matching trace 32, and its electrical characteristics are also 50Ω system, to ensure that the FPC end signal can be input to the MIPI receiver of the camera sensor without reflection.

[0101] In this embodiment, by integrating the filter trace with a stepped impedance structure into the FPC and achieving stable connections with the signal source and load ends through the first and second connectors respectively, the filter structure can achieve lossless transmission of MIPI signals and high-frequency interference suppression without introducing additional discrete components. This ensures signal integrity while effectively reducing the impact of 2.4GHz band radio frequency interference on the image transmission link, improving the overall radio frequency sensitivity and electromagnetic compatibility. Furthermore, the termination design of the connector and impedance matching section maintains the consistency of the system characteristic impedance, avoiding signal reflection caused by impedance discontinuity, and enhancing the reliability and compatibility of the structure in actual assembly.

[0102] In the description of this specification, references to terms such as "some embodiments," "other embodiments," and "ideal embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0103] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A filter trace structure, comprising: include: At least one high-impedance trace; At least one low-impedance trace; Wherein, the at least one high-impedance trace and the at least one low-impedance trace are arranged alternately and connected in series, the characteristic impedance of the high-impedance trace is greater than a preset threshold, and the characteristic impedance of the low-impedance trace is less than the preset threshold.

2. The filtering trace structure of claim 1, wherein, include: N high-impedance traces and N-1 low-impedance traces are arranged alternately and connected in series, wherein N is an integer and N is greater than or equal to 2.

3. The filter trace structure according to claim 1, characterized in that, include: N low-impedance traces and N-1 high-impedance traces are arranged alternately and connected in series, wherein N is an integer and N is greater than or equal to 2.

4. The filter trace structure according to any one of claims 1-3, characterized in that, The preset threshold is greater than or equal to 40Ω and less than or equal to 60Ω.

5. The filter trace structure according to any one of claims 1-3, characterized in that, The cross-sections of the at least one high-impedance trace and the at least one low-impedance trace are regular hexagonal, regular octagonal, or regular dodecagonal.

6. The filter trace structure according to any one of claims 1-3, characterized in that, Also includes: A shape memory alloy is embedded in the at least one high-impedance trace to deform and adjust the linewidth of the at least one high-impedance trace when the ambient temperature of the filter trace structure changes, so as to keep the characteristic impedance of the at least one high-impedance trace unchanged.

7. The filter trace structure according to claim 2, characterized in that, Both the at least one high-impedance trace and the at least one low-impedance trace are microstrip lines.

8. A filtering wiring device, characterized in that, Includes the filter trace structure, the first impedance matching trace, and the second impedance matching trace as described in any one of claims 1-7, wherein: The first end of the first impedance matching trace is connected to the first end of the filter trace structure; The first end of the second impedance matching trace is connected to the second end of the filter trace structure; Wherein, the characteristic impedance of the impedance matching trace is equal to the preset threshold.

9. The filtering wiring device according to claim 8, characterized in that, The filtering wiring device also includes: A switching module is connected in series between the first end of the first impedance matching trace and the filter trace structure. The first end of the switching module is connected to the first end of the first impedance matching trace, and the second end of the switching module is connected to the first end of a plurality of filter trace structures. The switching module is used to conduct the path between the first end of the first impedance matching trace and the first end of the target filter trace structure, wherein the cutoff frequencies of the plurality of filter trace structures are different.

10. A flexible circuit board, characterized in that, Includes the filtering wiring device as described in claim 8 or 9, the first connector, and the second connector, wherein: The first connector is connected to the second end of the first impedance matching trace; The second connector is connected to the second end of the second impedance matching trace.

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