Differential transmission line and printed circuit board

Abstract

The embodiment of the invention provides a differential transmission line and a printed circuit board, the differential transmission line comprises a first differential structure, a second differential structure and a connecting structure, the width of the first differential structure is larger than that of the second differential structure, the thickness of the first differential structure is smaller than that of the second differential structure, and the thickness of the second differential structure is larger than that of the first differential structure. The first differential structure and the second differential structure are connected through a connecting structure. According to the embodiment of the invention, the problems of over-high differential impedance and poor channel impedance continuity of a narrow area of a differential transmission line in the prior art can be solved, a smaller line width is adopted in the narrow area, impedance matching is realized by adjusting the thickness of the line, impedance mutation caused by over-narrow interconnection transmission lines is reduced, and the transmission efficiency is improved. Therefore, the impedance curve is smoother, and the influence on the quality of transmitted high-speed signals is reduced.

Description

Technical Field

[0001] The present application relates to the field of high-speed communications, and in particular to a differential transmission line and a printed circuit board. Background Art

[0002] With the rapid development of the electronic communications industry, communication equipment has become more complex and more integrated, and signal rates have gradually increased, which means that there are higher requirements for the signal integrity (SI) performance of high-speed signals, and the requirements for transmission lines have also increased.

[0003] In high-speed products, chips are indispensable components, and the chip pin area needs to be connected by transmission lines. However, if the differential signal spacing is small, it means that the line-out area is very narrow. Due to the combined influence of various factors, the impedance of differential transmission lines is high: on the one hand, differential transmission lines are needed to ensure the quality of high-speed signal transmission, and on the other hand, the limitations of processes such as drilling and back drilling result in very small line widths of differential lines in narrow areas. In order to meet the standard channel setting, high-speed materials with smaller dielectric constants are used. However, the high impedance of differential transmission lines affects the impedance continuity of the channel, which can lead to a decrease in channel performance.

[0004] As signal rates continue to increase, the dielectric constant of the material needs to be further reduced, resulting in higher differential impedance in narrow areas, making the impedance of the differential transmission line an important factor affecting the continuity of the entire channel impedance. Summary of the invention

[0005] The embodiments of the present application provide a differential transmission line and a printed circuit board to at least solve the problems of excessively high differential impedance and poor continuity of channel impedance in narrow areas of the differential transmission line in the related art.

[0006] According to one embodiment of the present application, a differential transmission line is provided, which includes: a first differential structure, a second differential structure and a connecting structure, wherein the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected via the connecting structure.

[0007] Preferably, the first differential structure includes two mutually parallel first differential lines; the second differential structure includes two mutually parallel second differential lines; wherein the width of the first differential line is greater than the width of the second differential line, and the spacing between the two first differential lines is greater than the spacing between the two second differential lines.

[0008] Preferably, the width of the first differential structure is the sum of the spacing between two first differential lines and the width of the two first differential lines, the width of the second differential structure is the sum of the spacing between two second differential lines and the width of the two second differential lines, the thickness of the first differential structure is the thickness of the first differential line, and the thickness of the second differential structure is the thickness of the second differential line.

[0009] Preferably, the connection structure includes two connection components, wherein each of the connection components connects one of the first differential lines and one of the second differential lines.

[0010] Preferably, the first differential line, the second differential line and the connecting component are made of conductive materials.

[0011] Preferably, the differential transmission line further comprises: a first reference layer, a first dielectric layer, a second dielectric layer and a second reference layer arranged in sequence from top to bottom, wherein the first differential structure, the second differential structure and the connection structure are located between the first dielectric layer and the second dielectric layer.

[0012] Preferably, the thickness of the first dielectric layer between the second differential structure and the first reference layer is less than the thickness of the first dielectric layer between the first differential structure and the first reference layer; and / or, the thickness of the second dielectric layer between the second differential structure and the second reference layer is less than the thickness of the second dielectric layer between the first differential structure and the second reference layer.

[0013] Preferably, the width and thickness of the connecting component on the side close to the first differential line are the same as those of the first differential line, and the width and thickness of the connecting component on the side close to the second differential line are the same as those of the second differential line.

[0014] Preferably, the width of the connection member transitions from the width of the first differential line to the width of the second differential line, and the thickness of the connection member transitions from the thickness of the first differential line to the thickness of the second differential line.

[0015] According to another embodiment of the present application, a printed circuit board is provided, comprising one or more differential transmission lines as described in any one of the embodiments of the present application.

[0016] The embodiment of the present application provides a differential transmission line and a circuit board, wherein the differential transmission line includes: a first differential structure, a second differential structure and a connection structure, wherein the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected by the connection structure. The embodiment of the present application adopts a smaller line width in a narrow area, and achieves impedance matching by adjusting the line thickness, thereby reducing the impedance mutation caused by the interconnection transmission line being too narrow, thereby solving the problem of too high differential impedance and poor channel impedance continuity in the narrow area of ​​the differential transmission line in the related art, making the impedance curve smoother and reducing the impact on the quality of high-speed signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of a differential transmission line structure according to an embodiment of the present application;

[0018] Figure 2 is a schematic diagram of a cross-sectional structure of a differential transmission line according to an embodiment of the present application;

[0019] Figure 3 is a schematic cross-sectional structure diagram of a differential transmission line according to an embodiment of the present application;

[0020] Figure 4 is an impedance comparison diagram of a differential transmission line according to an embodiment of the present application;

[0021] Figure 5 is an insertion loss comparison diagram of a differential transmission line according to an embodiment of the present application;

[0022] Figure 6 4 is a comparison diagram of return losses of differential transmission lines according to an embodiment of the present application. DETAILED DESCRIPTION

[0023] The embodiments of the present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0024] It should be noted that the terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0025] According to an embodiment of the present application, a differential transmission line is provided.

[0026] Figure 1 is a schematic diagram of a differential transmission line structure according to an embodiment of the present application, such as Figure 1 As shown, the differential transmission line includes the following structures:

[0027] A first differential structure 10 , a second differential structure 20 and a connection structure 30 .

[0028] In this embodiment, the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected via the connection structure.

[0029] In this embodiment, the first differential structure 10 can be arranged in a region with loose wiring, and the second differential structure 20 can be arranged in a region with narrow wiring, so as to save wiring space.

[0030] In the embodiment of the present application, the use of differential transmission lines can ensure the quality of high-speed signal transmission, but due to the limitations of drilling and back drilling processes, the line width of the differential line in the narrow area of ​​the chip is very small, resulting in higher impedance. The embodiment of the present application achieves impedance matching by adjusting the thickness of the differential line, which can reduce the impedance mutation caused by the interconnection transmission line being too narrow, thereby solving the problem of too high differential impedance in the narrow area of ​​the differential transmission line and poor channel impedance continuity in the related art.

[0031] In some embodiments, the first differential structure 10 includes two first differential lines 11 and 12 parallel to each other; the second differential structure 20 includes two second differential lines 21 and 22 parallel to each other.

[0032] In this embodiment, the width of the first differential line is greater than the width of the second differential line, and the spacing between the two first differential lines is greater than the spacing between the two second differential lines.

[0033] In some embodiments, the width of the first differential structure is the sum of the spacing between two first differential lines and the width of the two first differential lines, the width of the second differential structure is the sum of the spacing between two second differential lines and the width of the two second differential lines, the thickness of the first differential structure is the thickness of the first differential line, and the thickness of the second differential structure is the thickness of the second differential line.

[0034] In some embodiments, the connection structure 30 includes two connection components 31 and 32 , wherein each of the connection components connects one of the first differential lines and one of the second differential lines.

[0035] In some embodiments, the first differential line, the second differential line and the connecting component are made of conductive materials, including but not limited to copper foil.

[0036] In some embodiments, the differential transmission line further includes: a first reference layer, a first dielectric layer, a second dielectric layer, and a second reference layer arranged in sequence from top to bottom, wherein the first differential structure, the second differential structure, and the connecting structure are located between the first dielectric layer and the second dielectric layer.

[0037] In some embodiments, the thickness of the first dielectric layer between the second differential structure and the first reference layer is less than the thickness of the first dielectric layer between the first differential structure and the first reference layer; and / or the thickness of the second dielectric layer between the second differential structure and the second reference layer is less than the thickness of the second dielectric layer between the first differential structure and the second reference layer.

[0038] In some embodiments, the width and thickness of the connecting component close to the first differential line are the same as the width and thickness of the first differential line, and the width and thickness of the connecting component close to the second differential line are the same as the width and thickness of the second differential line.

[0039] In some embodiments, a width of the connection member transitions from a width of the first differential line to a width of the second differential line, and a thickness of the connection member transitions from a thickness of the first differential line to a thickness of the second differential line.

[0040] Through the embodiments of the present application, differential transmission lines can be arranged in narrow areas to ensure the transmission quality of high-speed signals. At the same time, impedance matching is achieved by adjusting the thickness of the differential transmission lines, reducing the impedance mutation problem caused by the transmission lines being too narrow, further improving the channel performance, and reducing the impact on the quality of high-speed signals.

[0041] Figure 2 is a schematic diagram of a cross-sectional structure of a differential transmission line according to an embodiment of the present application, such as Figure 2 As shown, the differential transmission line also includes the following structures:

[0042] The first reference layer 41 , the first dielectric layer 42 , the second dielectric layer 43 and the second reference layer 44 are arranged in sequence from top to bottom.

[0043] In this embodiment, the first differential structure 10, the second differential structure 20 and the connection structure 30 are located between the first dielectric layer 42 and the second dielectric layer 43. The first differential structure 10, the connection structure 30 and the second differential structure 20 are arranged and connected along a horizontal direction.

[0044] In some embodiments, the first dielectric layer 42 and the second dielectric layer 43 may be substrates of a printed circuit board (PCB).

[0045] In some embodiments, the material of the first reference layer 41 and the second reference layer 44 can be copper foil, and its thickness is the copper thickness of the PCB stack. The material of the first differential structure 10, the second differential structure 20 and the connecting structure 30 can be copper foil or other conductive materials.

[0046] In some embodiments, the first differential structure 10 is applied in a space with ample routing, and the copper thickness t10 of the PCB stack can be used in the vertical direction. The second differential structure 20 is applied in a space with narrow routing, and a copper thickness t20 greater than the PCB stack is used in the vertical direction. The thickness of the connection structure 30 on one side of the first differential structure is t10, and the thickness on the other side of the second differential structure is t20.

[0047] In some embodiments, the thickness of the connection structure 30 may be uniformly transitioned between t10 and t20, but the present application is not limited thereto.

[0048] In this embodiment, the two second differential lines in the second differential structure 20 can respectively form a parallel plate capacitor structure with the first reference layer 41 or the second reference layer 44, and the capacitance of the second differential line satisfies the following capacitance formula:

[0049] Wherein, C is capacitance, A is the area facing the capacitor plates, h is the distance between the capacitor plates, that is, the distance between the second differential line and the first reference layer or the second reference layer, and ε0 is the dielectric constant of the medium between the plates.

[0050] It can be seen from this that Figure 2 The dielectric thickness h at the second differential structure 20 is smaller, so the capacitance is larger and the impedance is smaller.

[0051] Through the embodiments of the present application, it is possible to use differential lines in narrow spatial areas, and also to ensure that the impedance curve is smoother, thereby improving the quality of high-speed signal transmission.

[0052] Figure 3 is a schematic cross-sectional structure diagram of a differential transmission line according to an embodiment of the present application, such as Figure 3 As shown, the differential transmission line includes the following structures:

[0053] Two first differential lines 11 and 12 are parallel to each other, and two second differential lines 21 and 22 are parallel to each other.

[0054] In this embodiment, the line width of the first differential lines 11 and 12 is greater than the line width of the second differential lines 21 and 22, and the spacing between the first differential lines 11 and 12 is greater than the spacing between the second differential lines 21 and 22. Therefore, the first differential line can be used in a location with ample wiring space, and the second differential line can be used in a location with narrow wiring space, such as between two rows of through holes.

[0055] In this embodiment, the thickness of the first differential lines 11 and 12 is smaller than the thickness of the second differential lines 21 and 22 .

[0056] In this embodiment, Figure 3The connecting parts 31 and 32 are not shown. The connecting parts are used for transition connection between the first differential line and the second differential line. The width of the connecting parts transitions from the width of the first differential line to the width of the second differential line, and the thickness of the connecting parts also transitions from the thickness of the first differential line to the thickness of the second differential line.

[0057] Through the embodiments of the present application, the impedance consistency of the traditional structure differential transmission line can be improved, and the bandwidth of the differential signal can be increased.

[0058] In one embodiment, in a BGA ball grid array package with a differential signal pitch of 0.8 mm, the fan-out part adopts a line width of 3 mil and a spacing of 3 mil, and the impedance, insertion loss and return loss of the traditional structure differential transmission line and the differential transmission line in the embodiment of the present application are tested respectively.

[0059] Figure 4 is an impedance comparison diagram of a differential transmission line according to an embodiment of the present application, such as Figure 4 As shown, the solid line is the impedance of the differential transmission line in the present application, and the dotted line is the impedance of the differential transmission line in the traditional structure.

[0060] In this embodiment, the impedance of the differential transmission line in the present application is significantly smaller than the impedance of the differential transmission line in the traditional structure, thereby improving impedance continuity.

[0061] Figure 5 is a comparison diagram of insertion loss of differential transmission lines according to an embodiment of the present application, such as Figure 5 As shown, the solid line is the insertion loss of the differential transmission line in the present application, and the dotted line is the insertion loss of the differential transmission line in the traditional structure.

[0062] In this embodiment, the insertion loss of the differential transmission line in the present application is slightly smaller than the insertion loss of the differential transmission line with a traditional structure, that is, the insertion loss of the differential transmission line is improved.

[0063] Figure 6 is a comparison diagram of the return loss of the differential transmission line according to the embodiment of the present application, such as Figure 5 As shown, the solid line is the return loss of the differential transmission line in the present application, and the dotted line is the return loss of the differential transmission line in the traditional structure.

[0064] In this embodiment, the absolute value of the return loss of the differential transmission line in the present application is greater than the absolute value of the return loss of the differential transmission line with a traditional structure, that is, the return loss of the differential transmission line can also be improved.

[0065] According to another embodiment of the present application, a printed circuit board is provided, comprising one or more differential transmission lines as described in any one of the above embodiments.

[0066] The embodiments of the present application can be applied to multi-layer PCB structures with narrow lead-out areas such as ball grid array packages (BGA), especially PCB structures in high-speed backplane systems with a rate of 112 Gbps or above.

[0067] For specific examples in this embodiment, reference may be made to the examples described in the above embodiments and exemplary implementation modes, and this embodiment will not be described in detail herein.

[0068] Obviously, those skilled in the art should understand that the above modules or steps of the present application can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order from that herein, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present application is not limited to any specific combination of hardware and software.

[0069] The above is only an exemplary embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the principles of the present application shall be included in the protection scope of the present application.

Claims

1. A differential transmission line, characterized in that: The differential transmission line includes: a first differential structure, a second differential structure and a connecting structure, wherein the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected via the connecting structure.

2. The differential transmission line according to claim 1, characterized in that: The first differential structure comprises two first differential lines parallel to each other; The second differential structure comprises two second differential lines parallel to each other; The width of the first differential line is greater than the width of the second differential line, and the spacing between the two first differential lines is greater than the spacing between the two second differential lines.

3. The differential transmission line according to claim 2, characterized in that: The width of the first differential structure is the sum of the spacing between two first differential lines and the width of the two first differential lines, the width of the second differential structure is the sum of the spacing between two second differential lines and the width of the two second differential lines, the thickness of the first differential structure is the thickness of the first differential line, and the thickness of the second differential structure is the thickness of the second differential line.

4. The differential transmission line according to claim 3, characterized in that: The connection structure includes two connection components, wherein each of the connection components connects one of the first differential lines and one of the second differential lines.

5. The differential transmission line according to claim 4, characterized in that: The first differential line, the second differential line and the connecting component are made of conductive materials.

6. The differential transmission line according to claim 1, characterized in that: The differential transmission line further includes: a first reference layer, a first dielectric layer, a second dielectric layer and a second reference layer arranged in sequence from top to bottom, wherein the first differential structure, the second differential structure and the connection structure are located between the first dielectric layer and the second dielectric layer.

7. The differential transmission line according to claim 6, characterized in that: The thickness of the first dielectric layer between the second differential structure and the first reference layer is less than the thickness of the first dielectric layer between the first differential structure and the first reference layer; and / or, The thickness of the second dielectric layer between the second differential structure and the second reference layer is smaller than the thickness of the second dielectric layer between the first differential structure and the second reference layer.

8. The differential transmission line according to claim 4, characterized in that: The width and thickness of the connecting component on the side close to the first differential line are the same as those of the first differential line, and the width and thickness of the connecting component on the side close to the second differential line are the same as those of the second differential line.

9. The differential transmission line according to claim 8, characterized in that: The width of the connection member transitions from the width of the first differential line to the width of the second differential line, and the thickness of the connection member transitions from the thickness of the first differential line to the thickness of the second differential line.

10. A printed circuit board, characterized in that: Comprising one or more differential transmission lines as described in any one of claims 1 to 9.

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