High speed circuit and method of manufacturing low crosstalk differential traces

Abstract

A high speed circuit and a method of manufacturing low crosstalk differential traces are disclosed. The high speed circuit includes a printed circuit board, a ground plane layer, a pair of first and second differential traces, and a cascading common mode filter. The printed circuit board has a first surface and a second surface opposite the first surface. The ground plane layer has a first surface that contacts the second surface of the printed circuit board. The pair of first and second differential traces are located on the first surface of the printed circuit board. The first differential trace and the second differential trace carry an electrical signal. The cascading common mode filter includes an external common mode filter and an internal common mode filter. The external common mode filter includes a U-shaped gap segment located on the first surface of the ground plane layer. The internal common mode filter includes an H-shaped gap segment located on the first surface of the ground plane layer. The H-shaped gap segment is located adjacent to the U-shaped gap segment.

Description

Technical Field

[0001] This invention relates to a high-speed differential trace. More specifically, this invention relates to a high-speed differential trace with a return path to reduce interference radiation in multiple frequency bands. Background Technology

[0002] High-speed differential signal traces are widely used in the design of server / storage products. Many server / storage products include a chassis for mounting various printed circuit boards (PCBs) of electronic devices. PCBs include various signal traces to provide signals to the devices on the board. For a particular signal line, the signal traces are typically arranged in differential trace pairs. These differential traces on a PCB have different modes, including differential mode, common mode, and mode transitions between differential signals during transmission. As more and more product applications involve differential signal transitions between different PCBs or between a PCB and a cable, common-mode energy will radiate through the connectors into the vias in the chassis during these transitions. Common-mode energy generates a signal on both differential traces. Therefore, common-mode energy generates noise that interferes with signal transmission on the traces and causes interference problems.

[0003] Figure 1 This illustrates an example of an existing return current circuit trace 10 on a printed circuit board 12. The printed circuit board 12 is attached to a ground plane layer 14. The current circuit trace 10 comprises two differential traces 22 and 24 on a surface 20 of the printed circuit board 12. The ground plane layer 14 contacts the opposite surface of the printed circuit board 12. Arrow 30 indicates the inserted current in differential trace 22. Arrow 32 indicates the induced current in differential trace 24. Arrow 34 indicates the return current generated in the ground plane layer 14 beneath differential trace 22. Figure 1 As shown, common-mode energy is generated by subtracting the coupling term from the insertion current indicated by arrow 30.

[0004] Figure 2 This is an electronic signal interference diagram of signals originating from the server chassis. The server chassis includes components with similar characteristics... Figure 1 The diagram shows multiple boards of differential traces. A server chassis has several circuit boards. Transitions between different circuit boards allow common-mode energy to radiate through vias in the chassis. Line 50 represents the permissible trace noise in an FCC Class A digital device, and line 60 represents the permissible system noise in an FCC Class A-AV device. This illustrates the permissible noise levels for more modern Class A-AV devices. Spike 80 represents unacceptable noise radiation at approximately 8 GHz, generated by example systems such as server chassis.

[0005] To reduce radiation caused by common-mode energy, the routing design needs to minimize common-mode energy while maintaining a constant total energy for the differential signal. Since high-speed traces can be used to transmit data at different frequencies, it is also necessary to reduce interference and noise at the different transmission frequencies of interest. Summary of the Invention

[0006] The terms "implementation," "configuration," "aspect," "example," and "option" are intended to broadly refer to all subject matter of the invention and the following claims. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the following claims. The embodiments of the invention covered herein are defined by the following claims rather than by the content of this invention. The content of this invention is a superior summary of various aspects of the invention and introduces some concepts further described in the following Description section. The content of this invention is not intended to identify key or essential features of the claimed subject matter. Nor is the content of this invention intended solely for determining the scope of the claimed subject matter. This subject matter should be understood by referring to appropriate portions of the entire specification of the invention, any or all of the drawings, and each claim.

[0007] According to certain aspects of the present invention, a high-speed circuit includes a printed circuit board, a ground plane layer, a pair of first differential traces and a second differential trace, and a cascading common-mode filter. The printed circuit board has a first surface and a second surface opposite the first surface. The ground plane layer has a first surface, and the first surface of the ground plane layer contacts the second surface of the printed circuit board. The pair of first differential traces and the second differential trace are located on the first surface of the printed circuit board. The first differential traces and the second differential trace carry an electronic signal. The cascading common-mode filter includes an external common-mode filter and an internal common-mode filter. The external common-mode filter includes a U-shaped gap segment located on the first surface of the ground plane layer. The internal common-mode filter includes an H-shaped gap segment located on the first surface of the ground plane layer. The H-shaped gap segment is located near the U-shaped gap segment.

[0008] In one implementation, the U-shaped gap segment includes a first gap segment, a second gap segment, and a third gap segment, with the first and second gap segments connected by the third gap segment. The H-shaped gap segment includes a fourth, a fifth, and a sixth gap segment. The first and fifth gap segments are connected by the sixth gap segment. The sixth gap segment divides the fourth gap segment into a first portion having a first length and a second portion having a second length. The first and second gap segments have the same shape. In one embodiment, the fourth and fifth gap segments have the same shape. In one embodiment, the length of the second gap segment depends on noise cancellation at a first radiation frequency, and the second length of the second portion of the fourth gap segment depends on noise cancellation at a second radiation frequency, wherein the second radiation frequency is a harmonic of the first radiation frequency. In one embodiment, the interval between the third and sixth gap segments is greater than the ideal length of a gap segment when eliminating noise at a target radiation frequency. In one embodiment, the lengths of the first and second gap segments are determined by the following constraints:

[0009] L1 = L X -L 4X

[0010] 2L 4X ≥L2≥L 4X

[0011] L3≤L 4X

[0012] L4 = L 2X

[0013] Where L1 is the length of the first gap segment and the length of the second gap segment, L2 is the interval between the third gap segment and the sixth gap segment, L3 is the first length of the first part of the fourth gap segment, and L... X = 1 / (4f×TD), where TD is the time delay per mil of a differential signal propagating on the first and second differential lines, and f is the target radiation frequency.

[0014] In one embodiment, the distance between the first gap segment and the first differential trace is the same as the distance between the second gap segment and the second differential trace. In one embodiment, the distance between the fourth gap segment and the first differential trace is the same as the distance between the fifth gap segment and the second differential trace. In one embodiment, the distance between the first gap segment and the first differential trace is greater than the distance between the fourth gap segment and the first differential trace. In one embodiment, the width of the H-shaped gap segment is smaller than the width of the U-shaped gap segment.

[0015] According to certain aspects of the present invention, a method of manufacturing a low-interference differential trace includes forming a first differential trace and a second differential trace on a first surface of a printed circuit board. A first gap segment is formed in a ground plane layer. The ground plane layer is connected to a second surface of the printed circuit board, and the second surface of the printed circuit board is relative to its first surface. A cascaded common-mode filter is formed on the ground plane layer by means of a plurality of steps, the steps including: (a) determining the length of a second gap segment according to a first target radiation frequency, and connecting the first gap segment and the second gap segment to form an external common-mode filter having a U-shape; (b) determining the length of a first portion of a fifth gap segment according to a second target radiation frequency, wherein the second target radiation frequency has harmonic correlation with the first target radiation frequency; and (c) connecting the fifth gap segment to a fourth gap segment through a sixth gap segment to form an internal common-mode filter having an H-shape. The width of the H-shape is smaller than the width of the U-shape.

[0016] In one embodiment, the first gap segment and the second gap segment have the same shape. In one embodiment, the fourth gap segment and the fifth gap segment have the same shape. In one embodiment, the radiation frequency of the second target is twice the radiation frequency of the first target. In one embodiment, the first gap segment is connected to the second gap segment by a third gap segment, and the lengths of the first and second gap segments are determined by the following constraints:

[0017] L1 = L X -L 4X

[0018] 2L 4X ≥L2≥L 4X

[0019] L3≤L 4X

[0020] L4 = L 2X

[0021] Where L1 is the length of the first gap segment and the length of the second gap segment, L2 is the interval between the third gap segment and the sixth gap segment, L3 is the first length of the first part of the fourth gap segment, and L... X = 1 / (4f×TD), where TD is the time delay per mil of a differential signal propagating on the first and second differential lines, and f is the target radiation frequency.

[0022] In one embodiment, the distance between the first gap segment and the first differential trace is the same as the distance between the second gap segment and the second differential trace. In one embodiment, the distance between the fourth gap segment and the first differential trace is the same as the distance between the fifth gap segment and the second differential trace. In one embodiment, the distance between the first gap segment and the first differential trace is greater than the distance between the fourth gap segment and the first differential trace.

[0023] The foregoing summary is not intended to represent every embodiment or aspect of the invention. Rather, it provides only examples of some novel aspects and features set forth herein. The foregoing features and advantages, as well as other features and advantages of the invention, will become apparent from the following detailed description of representative embodiments and modes for carrying out the invention, when taken in conjunction with the accompanying drawings and claims. Other aspects of the invention will be apparent to those skilled in the art from the detailed description of various embodiments with reference to the accompanying drawings, and a brief description thereof is provided below. Attached Figure Description

[0024] The invention, its advantages, and the accompanying drawings will be better understood from the following description of representative embodiments, taken in conjunction with the accompanying drawings. These drawings depict only representative embodiments and should not be considered as limiting the scope of the various embodiments or claims.

[0025] Figure 1 An example diagram showing prior art differential traces on a printed circuit board;

[0026] Figure 2 This is a schematic diagram of electronic signal interference at a specific frequency from signals originating from existing differential traces within the chassis.

[0027] Figure 3 This is a rear view of an electronic device comprising multiple circuit boards, which include traces having exemplary interference reduction return paths, according to certain aspects of the present invention.

[0028] Figure 4 This is a perspective view of an example differential trace with return paths to reduce common-mode energy, representing certain aspects of this disclosure;

[0029] Figure 5 This is a top view of an example differential trace having a common-mode filter according to some embodiments of the present invention;

[0030] Figure 6 These are certain aspects of the present invention, in Figure 5 The example differential trace's return current characteristic curve is shown in the first type.

[0031] Figure 7 These are certain aspects of the present invention, in Figure 5 The example differential trace has a second type of return current characteristic curve.

[0032] Symbol Explanation

[0033] 10: Return current circuit routing

[0034] 12: Printed Circuit Board

[0035] 14: Grounding Plane Layer

[0036] 20: Surface

[0037] 22: Differential routing

[0038] 24: Differential routing

[0039] 30: Arrow (inserted current)

[0040] 32: Arrow (Induced Current)

[0041] 34: Arrow (Returning Current)

[0042] 50: Cable noise (tethering noise)

[0043] 60: Line (System Noise)

[0044] 80: Spike (noise radiation)

[0045] 100: Electronic devices

[0046] 110: Chassis

[0047] 120: Components

[0048] 130: Power Supply Unit

[0049] 140: Components

[0050] 200: Cable routing configuration

[0051] 202: Printed Circuit Board

[0052] 204: First Surface

[0053] 206: Second Surface

[0054] 208: Grounding Plane Layer

[0055] 210: Wiring

[0056] 212: Wiring

[0057] 220: First Surface

[0058] 222: U-shaped current return path pattern

[0059] 224: First gap section

[0060] 226: Second gap section

[0061] 228: Third gap section

[0062] 232: Arrow (inserted current)

[0063] 234: Arrow (Induced Current)

[0064] 236: Arrow (returning current)

[0065] 238: Dashed line (cancelled return current)

[0066] 500: Series Common-Mode Filter

[0067] 502: Printed Circuit Board

[0068] 504: First Surface

[0069] 510: Differential routing

[0070] 512: Differential routing

[0071] 521: Sixth gap section

[0072] 522: External Common-Mode Filter

[0073] 524: First gap section

[0074] 526: Second gap section

[0075] 528: Third gap section

[0076] 542: Internal Common-Mode Filter

[0077] 544: Fourth gap section

[0078] 546: Fifth gap section

[0079] 548: The first part of the fourth gap section

[0080] 552: The second part of the fifth gap section

[0081] 554: The second part of the fourth gap section

[0082] 550: The first part of the fifth gap section

[0083] 700: Curve Graph

[0084] 800: Curve Graph

[0085] L1~L4: Length Detailed Implementation

[0086] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a preferred embodiment is described below in detail with reference to the accompanying drawings.

[0087] This invention provides a common-mode filter for reducing signal radiation. The common-mode filter is implemented in printed circuit board wiring and can be used to reduce signal radiation across multiple frequency bands. In applications requiring high data rate support, such as Peripheral Component Interconnect Express (PCIe) and SAS, a single common-mode filter designed for a narrow frequency band is insufficient to reduce radiation risk. Therefore, the common-mode filters provided in various embodiments of this invention utilize cascading technology to reduce radiation across multiple radiation bands.

[0088] Various embodiments are described with reference to the accompanying drawings, wherein the same reference numerals are used throughout the drawings to denote similar or equivalent elements. The drawings are not necessarily drawn to scale and are provided only to illustrate aspects and features of the invention. While those skilled in the art to which this application pertains will recognize that certain aspects and features of the invention can be practiced without one or more specific details, with other relationships or other methods, numerous specific details, relationships, and methods are set forth herein to provide a full understanding of these aspects and features. In some cases, well-known structures or operations are not shown in detail for illustrative purposes. The various embodiments disclosed herein are not necessarily limited to the order of the described actions or events, as some actions may occur in a different order and / or simultaneously with other actions or events. Furthermore, not all illustrated actions or events are necessary to realize certain aspects and features of the invention.

[0089] For the purposes of this detailed description, unless otherwise stated, and where appropriate, the singular includes multiples, and vice versa. The word “including” means “including, but not limited to”. Furthermore, approximate words such as “about,” “almost,” “substantially,” “probably,” etc., may be used herein to mean “in,” “near,” “almost,” “within 3 to 5 percent,” “within acceptable manufacturing tolerances,” or any logical combination thereof. Similarly, the terms “vertical” or “horizontal” are intended to additionally include “within 3 to 5 percent” in the vertical or horizontal direction, respectively. Additionally, directional words such as “top,” “bottom,” “left,” “right,” “above,” and “below” are intended to be associated with the equivalent directions described in the accompanying drawings, understood from the context of the referenced object or element (e.g., from its usual location), or as otherwise noted herein.

[0090] See Figure 3An example electronic device 100 is provided. The electronic device 100 is a server that includes multiple different components contained within a chassis 110. For example, one set of components 120 is mounted on one side of the chassis 110 above two power supply units 130. Another set of components 140 is mounted in a vertical slot within the chassis 110. Each of the two sets of components 120 and 140 includes a printed circuit board. These printed circuit boards include multiple differential traces that connect the on-board electronic components and conduct signals between the components. The chassis 110 may have multiple holes through which noise generated by the circuit boards of components 120 and 140 may be emitted.

[0091] Figure 2 This is a graph showing the output noise through holes in chassis 110 with known differential wiring circuitry. For example... Figure 2 As shown, in this example, the output noise appears at approximately 8 GHz. This output noise is due to common-mode energy from the differential traces on the circuit board within the chassis.

[0092] To reduce this interference, components 120 and 140 (displayed in...) Figure 3 Each circuit board in the ( ) includes multiple differential traces that are combined into a return path design in the ground plane layer, which reduces common-mode energy at the target frequency of 5 GHz. This merging of traces reduces electronic noise generated by the electronics 100. The target frequency is determined by interference testing of the chassis 110. The target frequency depends on the data rate of the traces transmitted on the board in the chassis 110.

[0093] The process of designing a return trace to reduce common-mode energy relies on the fact that differential traces can be modeled using a four-port S-parameter. For a four-port (two signal traces) S-parameter, there is an insertion term S. 31 and S 42 and the induction term S 41 and S 32 According to Lenz's Law, the inductive term and the insertion term are in opposite directions. Based on the mixed-mode s-parameter formula, the differential-mode output (S) of the differential signal... dd21 )for:

[0094]

[0095] Common-mode output of differential signal (S cc21 Then it is:

[0096]

[0097] To reduce common-mode output energy, coupling terms need to be added. For example... Figure 1 A return current for a differential signal, indicated by arrow 34, will exist in the ground plane 14 directly below trace 22. This return current flows in the opposite direction to the current indicated by arrow 30 in trace 22. Therefore, a return current path can be designed that causes destructive interference at the target frequency. In this case, a nearby trace, such as trace 24, will become a new path for the return current. This new return current path increases coupling terms. Therefore, common-mode interference will be significantly reduced. The equation for the length of the new return current path is:

[0098] L X =1 / (4f×TD) (Equation 3)

[0099] In this equation, L X This represents the length of the new path. TD represents the time delay per mil of the differential signal propagating in the trace, and f represents the target radiation frequency.

[0100] Figure 4 This is a perspective view of an example wiring configuration 200 designed according to the standard indicated in Equation 3. Figure 4 A trace configuration 200 is formed on a printed circuit board 202. The printed circuit board 202 has a first surface 204 and an opposing second surface 206. The second surface 206 contacts a ground plane layer 208. Two parallel traces 210 and 212 are formed on the first surface 204 of the printed circuit board 202. The ground plane layer 208 has a first surface 220 that contacts the second surface 206 of the printed circuit board 202. A U-shaped current return path pattern 222 is formed on the first surface 220 of the ground plane layer 208. The U-shaped current return path pattern 222 includes a first void segment 224, which in this example is located on one side of the trace 210. A void segment is a patterned channel, hollow space, or gap in the material (e.g., in the ground plane layer 208). In one example, the ground plane layer 208 may be patterned in a manner described herein, and such patterning shapes the material of the ground plane layer 208 to include hollow spaces, gaps, insulators, etc., for forming the void segment. In this example, the first gap segment 224 is approximately parallel to trace 210. The U-shaped current return path pattern 222 also includes a second gap segment 226, which in this example is located on one side of trace 212. In this example, the second gap segment 226 is approximately parallel to trace 212. A third gap segment 228 connects the first gap segment 224 and the second gap segment 226. Therefore, the first gap segment 224 and the second gap segment 226 are located in the ground plane layer 208 and outside their respective traces 210 and 212.

[0101] like Figure 4 As shown, arrow 232 represents the inserted current in trace 210. Arrow 234 represents the induced current flowing through trace 212. At the desired frequency, the U-shaped current return path pattern 222 causes destructive interference to any return current in the ground plane layer 208. Therefore, arrow 236 indicates that the return current has been offset to the parallel trace 212. In doing so, the destructive interference from the direction of the induced current 212 cancels out the current generated from the opposite direction of the inserted current 232. Dashed line 238 represents the return current that is eliminated based on the destructive interference from the first gap segment 224, the second gap segment 226, and the third gap segment 228 of the U-shaped current return path pattern 222.

[0102] exist Figure 4 In this example, it is desired that the U-shaped current return path pattern 222 avoids a target radiation frequency (e.g., a target radiation frequency of 8 GHz). The length of the gap segment 226 constitutes the new current return path as determined by Equation 3. In this example, it is assumed that the target radiation frequency is 8 GHz and the time delay (TD) per mil is 1.4285 × 10⁻⁶. -13 Then the length L of the return path at 8GHz X The value is determined to be 437.5 mil.

[0103] Figure 4 This illustrates a design focused on a single frequency. When multiple target design frequencies are required, a cascading structure is used on the ground plane, such as... Figure 5 As shown. Figure 5 This is a top view of example differential traces 510 and 512 of a cascaded common-mode filter 500 according to some embodiments of the present invention. The cascaded common-mode filter 500 is disposed on a printed circuit board 502, and the differential traces 510 and 512 are disposed on a first surface 504 of the printed circuit board 502. The cascaded common-mode filter 500 includes an internal common-mode filter 542 and an external common-mode filter 522 connected in series therewith. The external common-mode filter 522 is similar to or identical to... Figure 4 The U-shaped current return path pattern 222. The external common-mode filter 522 includes a first gap segment 524 and a second gap segment 526. The external common-mode filter 522 also includes a third gap segment 528, which connects the first gap segment 524 and the second gap segment 526 to form a U-shape. Similar to... Figure 4 ,exist Figure 5 In the middle, the first gap section 524 is located on one side of the trace 510, while the second gap section 526 is located on one side of the trace 512.

[0104] An internal common-mode filter 542 forms an H-shaped pattern. The internal common-mode filter 542 includes a fourth gap segment 544 on one side of trace 510, a fifth gap segment 546 on one side of trace 512, and a sixth gap segment 521 connecting the fourth gap segment 544 and the fifth gap segment 546. By combining the fourth gap segment 544 and the fifth gap segment 546 to form an H-shape, the sixth gap segment 521 divides the fifth gap segment 546 into a first portion 550 and a second portion 552. Similarly, the first portion 548 and the second portion 554 of the fourth gap segment 544 are formed side-by-side.

[0105] The design length associated with the cascaded common-mode filter 500 is Figure 5 The numbers L1, L2, L3, and L4 are used to indicate the length of the first gap segment 524 of the external common-mode filter 522. In some embodiments, the lengths of the first gap segment 524 and the second gap segment 526 are equal. Therefore, L1 can also indicate the length of the second gap segment 526. In some embodiments, the lengths of the first gap segment 524 and the second gap segment 526 are not equal; for example, the length of the first gap segment 524 is greater than (or less than) the length of the second gap segment 526. L2 is the interval length between the third gap segment 528 and the sixth gap segment 521. L3 is the length of the first portion 548 of the fourth gap segment 544. In some embodiments, the first portion 548 of the fourth gap segment 544 has the same length as the first portion 550 of the fifth gap segment 546. L4 is the length of the second portion 554 of the fourth gap segment 544. In some embodiments, the second portion 552 of the fifth gap segment 546 and the second portion 554 of the fourth gap segment 544 have the same length.

[0106] The series common-mode filter 500 has design constraints around different lengths L1, L2, L3, and L4 for filtering return current at multiple frequencies. The series common-mode filter 500 provides additional inductance and capacitance and acts as an LC filter for return current at multiple frequencies.

[0107] exist Figure 5 In this context, the dimensions of the internal common-mode filter 542 and the external common-mode filter 522 are limited by the following equations 4a to 4d.

[0108] L1 = L X -L 4X (Equation 4a)

[0109] 2L 4X ≥L2≥L 4X (Equation 4b)

[0110] L3≤L4X (Equation 4c)

[0111] L4 = L 2X (Equation 4d)

[0112] In equations 4a to 4d, L X It is a common-mode filter used to reduce radiation at the fundamental frequency as defined in Equation 3 (e.g., Figure 4 The path length of the U-shaped current return path pattern. 2X It is used to reduce the length of a common-mode filter at twice the fundamental frequency, and L 4X Equation 3 can be used to determine the length of a common-mode filter used to reduce radiation at four times the fundamental frequency. X L 2X 、and L 4X From equations 4a and 4d, L1 and L4 are fixed based on the selected frequencies. That is, L1 is the difference between the path length determined for the fundamental frequency and the path length determined for a frequency equal to four times the fundamental frequency. L4 uses the path length value for a frequency equal to twice the fundamental frequency. Then, L2 and L3 can be chosen to satisfy the constraints of equations 4b and 4c.

[0113] Figure 6 and Figure 7 According to some embodiments of the invention, simulation results are provided using design constraints of equations 4a to 4d to select a cascaded common-mode filter. Figure 6 Is Figure 5 The first example of a differential trace is shown in Figure 600, illustrating the return current characteristics. Figure 5 The example differential trace in the example is a microstrip structure with differential traces 510 and 512. For microstrip structures, L X =526mil (for 4GHz), L 2X = 263 mil (for 8GHz), L 4X =132.5mil (for 16GHz). In this example, L1 = 396mil, L2 = 132mil, L3 = 30mil, L4 = 263mil. Furthermore, the frequencies are reduced to 4.32GHz, 8.09GHz, and 15.97GHz. As shown in the figure. Figure 6 As shown, the drop in return current occurs approximately at lower frequencies, which leads to additional coupling and then reduces common node noise at specific frequencies. Symbol 602 indicates a drop at 4.32 GHz, symbol 604 indicates a drop at 8.09 GHz, and symbol 606 indicates a drop at 15.97 GHz.

[0114] Figure 7When manufactured using a strip wire structure, in Figure 5 The second type of return current characteristic curve for example differential traces is shown in Figure 700. For stripline structures, L... X = 464 mil (for 4GHz), L 2X =232mil (for 8GHz), L 4X = 116mil (for 16GHz). In this example, L1 = 348mil, L2 = 116mil, L3 = 116mil, L4 = 232mil. Furthermore, the frequencies are reduced to 4.11GHz, 8.0GHz, and 16.39GHz. For example... Figure 7 As shown, the drop in return current occurs approximately at the reduced frequency, which leads to additional coupling and then reduces common node noise at specific frequencies. Symbol 702 indicates a drop at 4.11 GHz, symbol 704 indicates a drop at 8.0 GHz, and symbol 706 indicates a drop at 16.39 GHz. The reduced frequency is harmonic-dependent. Embodiments of the present invention, whether in microstrip structures or stripline structures, can be used to reduce interference in high-speed traces.

[0115] Although the disclosed embodiments have been illustrated and described with respect to one or more implementations, those skilled in the art will discover or know equivalent modifications and alterations upon reading and understanding this specification and the accompanying drawings. Furthermore, while specific features of the invention may be disclosed only in one of several embodiments, such features may be combined with one or more other features of other embodiments, which may be desirable and advantageous for any given or particular application.

[0116] While various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitation. Many modifications may be made to the disclosed embodiments based on the present disclosure without departing from the spirit or scope of the invention. Therefore, the breadth and scope of the invention should not be limited by any of the embodiments described above. Rather, the scope of the invention should be defined by the appended claims and their equivalents.

[0117] Although the present invention has been disclosed in conjunction with the above preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A high-speed circuit, comprising: A printed circuit board having a first surface and a second surface relative to the first surface; A ground plane layer having a first surface, wherein the first surface of the ground plane layer contacts the second surface of the printed circuit board; A pair of first differential traces and second differential traces are located on the first surface of the printed circuit board, wherein the first differential traces and the second differential traces carry electronic signals; and Cascading common-mode filters include: An external common-mode filter includes a U-shaped gap segment located on the first surface of the ground plane layer; and An internal common-mode filter includes an H-shaped gap section located on the first surface of the ground plane layer, wherein the H-shaped gap section is located near the U-shaped gap section; The U-shaped gap section includes a first gap section, a second gap section, and a third gap section, with the first gap section and the second gap section connected via the third gap section. The H-shaped gap section includes a fourth gap section, a fifth gap section, and a sixth gap section, with the fourth gap section and the fifth gap section connected via the sixth gap section. The sixth gap section divides the fourth gap section into a first portion having a first length and a second portion having a second length. The first length of the first portion of the fourth gap segment is less than the second length of the second portion of the fourth gap segment.

2. The high-speed circuit as described in claim 1, wherein, The first gap segment has the same shape as the second gap segment, or the fourth gap segment has the same shape as the fifth gap segment.

3. The high-speed circuit as described in claim 1, wherein, The length of the second gap segment depends on the elimination of noise at the first radiation frequency, the second length of the second portion of the fourth gap segment depends on the elimination of noise at the second radiation frequency, and the second radiation frequency is a harmonic of the first radiation frequency, and wherein the interval between the third gap segment and the sixth gap segment is greater than the ideal length of the gap segment when noise at the target radiation frequency is eliminated.

4. The high-speed circuit as described in claim 1, wherein, The lengths of the first void segment and the second void segment are determined by the following constraints: Wherein, L1 is the length of the first gap segment and the length of the second gap segment, L2 is the interval between the third gap segment and the sixth gap segment, and L3 is the first length of the first portion of the fourth gap segment. TD is the time delay per mil of the differential signal propagating on the first and second differential traces, and f is the target radiation frequency; where L 2X The length L of a common-mode filter used to reduce radiation at twice the fundamental frequency. 4X L4 is the length of a common-mode filter used to reduce radiation at four times the fundamental frequency, and L4 is the length of the second part of the fourth gap segment.

5. The high-speed circuit as described in claim 1, wherein, The distance between the first gap section and the first differential trace is the same as the distance between the second gap section and the second differential trace, the distance between the fourth gap section and the first differential trace is the same as the distance between the fifth gap section and the second differential trace, and wherein the distance between the first gap section and the first differential trace is greater than the distance between the fourth gap section and the first differential trace.

6. A method for manufacturing low-interference differential traces, comprising: A first differential trace and a second differential trace are formed on the first surface of the printed circuit board; A first gap segment is formed in a ground plane layer, wherein the ground plane layer is connected to a second surface of the printed circuit board, and the second surface of the printed circuit board is relative to the first surface of the printed circuit board; and A cascaded common-mode filter is formed on the ground plane layer through the following multiple steps, wherein the multiple steps include: The length of the second gap segment is determined based on the radiation frequency of the first target. Connect the first gap segment and the second gap segment to form an external common-mode filter with a U-shape; The length of the first portion of the fifth gap segment is determined based on the radiation frequency of the second target, wherein the radiation frequency of the second target has a harmonic correlation with the radiation frequency of the first target; and The fifth gap segment is connected to the fourth gap segment via the sixth gap segment to form an H-shaped internal common-mode filter, wherein the width of the H-shape is smaller than the width of the U-shape, wherein the sixth gap segment divides the fourth gap segment into a first part having a first length and a second part having a second length, and the first length of the first part of the fourth gap segment is smaller than the second length of the second part of the fourth gap segment.

7. The method for manufacturing low-interference differential traces as described in claim 6, wherein, The first gap segment has the same shape as the second gap segment, and the fourth gap segment has the same shape as the fifth gap segment.

8. The method for manufacturing low-interference differential traces as described in claim 6, wherein, The second target radiation frequency is twice the radiation frequency of the first target, and the first gap segment is connected to the second gap segment via a third gap segment, and the lengths of the first and second gap segments are determined by the following constraints: Wherein, L1 is the length of the first gap segment and the length of the second gap segment, L2 is the interval between the third gap segment and the sixth gap segment, and L3 is the first length of the first part of the fourth gap segment. TD is the time delay per mil of the differential signal propagating on the first and second differential traces, and f is the radiation frequency of the target; where L 2X The length L of a common-mode filter used to reduce radiation at twice the fundamental frequency. 4X L4 is the length of a common-mode filter used to reduce radiation at four times the fundamental frequency, and L4 is the length of the second part of the fourth gap segment.

9. The method for manufacturing low-interference differential traces as described in claim 6, wherein, The distance between the first gap section and the first differential trace is the same as the distance between the second gap section and the second differential trace, the distance between the fourth gap section and the first differential trace is the same as the distance between the fifth gap section and the second differential trace, and wherein the distance between the first gap section and the first differential trace is greater than the distance between the fourth gap section and the first differential trace.

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