Common-mode signal band elimination structure, common-mode signal band elimination circuit and digital interface circuit

Abstract

The utility model relates to the technical field of common-mode signal filtering, in particular to a common-mode signal band elimination structure, a common-mode signal band elimination circuit and a digital interface circuit, and the structure comprises two differential signal lines which are arranged at an interval, and a grounding reference plane which is parallel to the plane where the differential signal lines are located; a hollowed-out hole is formed in the position, below the differential signal line, of the grounding reference face, a snakelike wire is arranged in the hollowed-out hole, and the two ends of the snakelike wire are connected with the grounding reference face respectively. According to the ground wire structure of the snakelike routing, the backflow path length of common-mode current can be increased, so that the common-mode impedance within a certain frequency range can be increased, the band elimination characteristic of common-mode signals is achieved, and the sufficiently high common-mode impedance is designed on the premise that the differential-mode impedance is not increased. A common-mode signal band elimination structure is used for replacing an existing common-mode inductor structure, filtering design is carried out on a digital signal interface circuit with radiation emission exceeding the standard easily occurring at a specific frequency point, common-mode noise is restrained, the design requirement is met, and reliability and stability of data transmission are guaranteed.

Description

Technical Field

[0001] The utility model relates to the technical field of common mode signal filtering, in particular to a common mode signal band-stop structure, a circuit and a digital interface circuit. Background Art

[0002] In the differential transmission design of digital interface circuits, in order to ensure the reliability and stability of data transmission, it is necessary to suppress electromagnetic radiation emission to meet the standard limit. At present, the commonly used suppression solution is to set a common mode inductor in the circuit.

[0003] Common-mode inductors separate common-mode signals from differential-mode signals through the principle of electromagnetic induction. Common-mode signals refer to the common mode between two signals, which have the same frequency and phase, and are usually caused by electromagnetic interference or ground loops; differential-mode signals refer to the difference mode between two signals, which have different frequencies and phases, and are usually caused by data transmission. Common-mode inductors filter out common-mode signals and transmit differential-mode signals, thereby achieving a suppression effect.

[0004] However, in the suppression solution using common-mode inductors, the common-mode inductors are additional components that not only increase the cost of the circuit, but also have limited optional models and fixed technical parameters, which cannot meet some design requirements and have low versatility. Utility Model Content

[0005] In order to solve at least the above technical problems existing in the prior art, the utility model provides a common-mode signal band-stop structure, circuit and digital interface circuit.

[0006] On the one hand, the utility model provides a common-mode signal band-stop structure, including two differential signal lines arranged at intervals, and a ground reference plane arranged parallel to the plane where the differential signal lines are located; a hollow hole is provided on the ground reference plane below the differential signal line, a serpentine trace is provided in the hollow hole, and both ends of the serpentine trace are respectively connected to the ground reference plane.

[0007] In some embodiments, a surface ground line is further included, and the surface ground line is located on a side of the differential signal line away from the ground reference plane; the surface ground line is connected to the serpentine trace through a first via.

[0008] In some embodiments, a jumper element is further included, and the jumper element is located on the surface where the surface ground line is located; one end of the jumper element is connected to the surface ground line, and the other end is connected to the differential signal line through a second via hole.

[0009] In some embodiments, the jumper element is a capacitor.

[0010] In some embodiments, the two differential signal lines are arranged in parallel and spaced apart.

[0011] In some embodiments, in a vertical projection of the differential signal line onto the serpentine routing line, a vertical projection of the serpentine routing line of a set area coincides with the serpentine routing line.

[0012] In some embodiments, the serpentine trace has a set length for increasing the return path length of the common mode current; and / or the shape of the serpentine trace is a centrally symmetrical shape.

[0013] In some embodiments, the hollow hole is in a rectangular shape, the contour shape of the serpentine line is in a rectangular shape, and there is a set interval between the edge of the serpentine line and the inner wall of the hollow hole.

[0014] On the other hand, the utility model further provides a circuit, comprising the above common mode signal band-stop structure.

[0015] In another aspect, the utility model further provides a digital interface circuit, comprising the above-mentioned common-mode signal band-stop structure or the above-mentioned circuit.

[0016] The utility model provides a common-mode signal band-stop structure, circuit and digital interface circuit, in which a serpentine ground wire structure is set on the ground reference plane. The serpentine has a certain length, which can increase the return path length of the common-mode current, thereby increasing the common-mode impedance within a certain frequency range, and realizing the common-mode signal band-stop characteristics, that is, designing a sufficiently high common-mode impedance without increasing the differential mode impedance. The technical solution of the utility model uses a common-mode signal band-stop structure to replace the existing common-mode inductor structure, and performs a filtering design on the digital signal interface circuit that is prone to excessive radiation emission at a specific frequency point, suppressing common-mode noise, that is, meeting the design requirements, and ensuring the reliability and stability of data transmission. In addition, this structure can adapt to more usage scenarios by changing the length of the serpentine, the layout of the routing, etc., and has higher versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] By reading the detailed description below with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, wherein:

[0018] In the drawings, the same or corresponding reference numerals represent the same or corresponding parts.

[0019] Figure 1 A schematic structural diagram of a common-mode signal band-stop structure provided in an embodiment of the utility model;

[0020] Figure 2 A schematic diagram of the structure of a differential signal line in a common-mode signal band-stop structure provided by an embodiment of the utility model;

[0021] Figure 3 A schematic diagram of the structure of the ground reference plane in the common-mode signal band-stop structure provided by an embodiment of the utility model;

[0022] Figure 4 A schematic diagram of the structure of the surface ground wire in the common-mode signal band-stop structure provided by an embodiment of the utility model;

[0023] Figure 5 This is a diagram of the simulation S-parameter results of the common-mode signal band-stop structure provided in an embodiment of the utility model.

[0024] In the figure:

[0025] 1: differential signal line; 2: ground reference plane; 3: surface ground line; 4: first via; 5: jumper element; 6: second via;

[0026] 21: Hollow hole; 22: Serpentine routing. DETAILED DESCRIPTION

[0027] In order to make the purpose, features and advantages of the utility model more obvious and easy to understand, the technical solutions in the embodiments of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of them. Based on the embodiments of the utility model, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the utility model.

[0028] In the circuit, for differential mode signals, the two differential lines are referenced to each other, while for common mode signals, the two differential lines are referenced to the ground. In order to ensure the integrity of the differential mode signal and suppress the common mode signal, it is necessary to design a sufficiently high common mode impedance without increasing the differential mode impedance.

[0029] The common-mode signal band-stop structure technical solution disclosed in the embodiment of the utility model can provide sufficient common-mode impedance to achieve the purpose of suppressing common-mode signals. The common-mode signal band-stop structure includes two differential signal lines arranged at intervals, and a ground reference plane arranged parallel to the plane where the differential signal lines are located. By changing the structure of the ground reference plane, the common-mode impedance is increased. The specific solution is described below.

[0030] In conjunction with the accompanying drawings, various structures in the common-mode signal band-stop structure provided by the embodiment of the utility model, as well as the positional relationship and connection relationship between the various structures are described in detail below.

[0031] like Figures 1 to 4As shown, a hollow hole 21 is provided on the ground reference plane 2 below the differential signal line 1 , a serpentine trace 22 is provided in the hollow hole 21 , and two ends of the serpentine trace 22 are respectively connected to the ground reference plane 2 .

[0032] For example, as shown in the figure, the hollow hole 21 is in the shape of a rectangle, which includes a group of opposite sides, and connection points are respectively set on the opposite side structures. The two ends of the serpentine trace 22 are respectively connected to the connection points on the same side to realize the connection between the serpentine trace 22 and the ground reference plane 2, and keep them in the same plane.

[0033] In the embodiment of the utility model, two differential signal lines 1 are arranged in parallel and at intervals, for example, Figure 2 As shown, the overlapping parts of the two differential signal lines 1 and the serpentine trace 22 are two parallel straight line structures arranged at intervals. This structural setting method can ensure the stability of the differential mode impedance value, thereby effectively ensuring the integrity of the differential signal.

[0034] For example, the material selected for the differential signal line 1 is pure copper, whose electrical conductivity is 5.96e+07 (S / m) and relative magnetic permeability is 1. The material selected for the ground reference plane 2 and the serpentine trace 22 is an ideal electrical conductor. The material selected for the dielectric layer is FR-4 flame retardant material, whose dielectric constant is 4.3 and relative magnetic permeability is 1.

[0035] For differential signals, the two differential signal lines 1 are referenced to each other. When a differential signal with common-mode noise flows through the differential signal line 1, the quality of the differential signal itself is guaranteed because the two differential signal lines 1 are parallel and of equal length. For common-mode signals, the two differential signal lines 1 are referenced to the ground. Therefore, when the ground line is intentionally lengthened, it means that the high-frequency common-mode impedance increases, which can suppress the common-mode signal flowing through the two differential signal lines 1.

[0036] Therefore, a hollow hole 21 (perforation) is provided on the ground reference plane 2 below the differential signal line 1, and a serpentine trace 22 is provided in the perforation. The serpentine trace 22 has an effectively increased structural trace distance compared to the existing ground reference plane 2, and thus can effectively increase the return path length of the common-mode current, thereby increasing the common-mode impedance within a certain frequency range.

[0037] Continue to refer Figures 1 to 4As shown, in the embodiment of the utility model, the common-mode signal band-stop structure also includes a surface ground line 3, and the surface ground line 3 is located on the side of the differential signal line 1 away from the ground reference plane 2; the surface ground line 3 is connected to the serpentine trace 22 through the first via 4. Similarly, the surface ground line 3 is also in the form of a winding serpentine trace 22. The common-mode signal band-stop structure also includes a jumper element 5, for example, the jumper element 5 is a capacitor, and the capacitance of the capacitor is 5pF; the jumper element 5 is located on the surface where the surface ground line 3 is located; one end of the jumper element 5 is connected to the surface ground line 3, and the other end is connected to the differential signal line 1 through the second via 6. The differential signal line 1 extends to the surface through the via, and is jumpered to the surface ground line 3 (surface ground) through the jumper element 5.

[0038] In the embodiment of the utility model, a serpentine trace 22 is set on the ground reference plane 2, and a jumper element 5 is added between the differential signal line 1 and the ground line, so as to change the characteristics of the differential signal line 1, change the slot capacitance, slot inductance and slot resistance of the differential signal line 1, and then change the priority resistance, capacitance and inductance of the differential signal line 1, thereby forming an obvious attenuation pole or frequency band in some frequency points or frequency bands, and then realizing the common-mode signal band-stop characteristics.

[0039] Continue to refer Figures 1 to 4 As shown, in the embodiment of the utility model, the shape of the serpentine trace 22 is a central symmetrical shape, and the serpentine trace 22 has a set length, which is used to increase the return path length of the common mode current; when the central symmetry is met, in a limited space structure, the longer the length of the serpentine trace 22 part is, the better. For example, the shape of the hollow hole 21 is a rectangle, the outline shape of the serpentine trace 22 is a rectangle, the edge of the serpentine trace 22 and the inner wall of the hollow hole 21 have a set interval, and the serpentine trace 22 is fully distributed in the hollow hole 21.

[0040] In addition, factors that limit / define the routing path of the serpentine routing 22 also include: when the capacitance value on the differential signal line 1 tends to be fixed, by adjusting the mutual inductance between the differential signal line 1 and the serpentine routing 22, that is, the length of the relatively parallel routing between the differential signal line 1 and the serpentine routing 22, the resonant frequency of the common mode signal is adjusted by the length of the parallel routing, that is, in the vertical projection of the differential signal line 1 onto the serpentine routing 22, the vertical projection of the serpentine routing 22 of the set area coincides with the serpentine routing 22. The overlapping portion reflects the length of the relatively parallel routing between the differential signal line 1 and the serpentine routing 22. Preferably, the adjusted resonant frequency coincides with the noise frequency point that needs to be filtered out.

[0041] It can be seen that the resonant frequency of the common mode signal is adjusted by adjusting the length of the relatively parallel line between the differential signal line 1 and the serpentine line 22 , and the corresponding routing path of the serpentine line 22 is designed in different usage scenarios.

[0042] The embodiment of the utility model further provides a circuit, including the common-mode signal band-stop structure. And the embodiment of the utility model further provides a digital interface circuit, including the common-mode signal band-stop structure or the circuit.

[0043] When designing a circuit or a digital interface circuit, the structural form of the signal differential line 1 and the routing path of the serpentine routing line 22 are designed based on the implementation principle and structure of the common-mode signal band-stop structure.

[0044] Taking the filtering operation for the USB2.0 clock signal multiplication point 960MHz as an example, in order to ensure the quality of the differential signal, the above common mode signal band-stop structure is used in the circuit.

[0045] The capacitance of the filter capacitor on the USB2.0 signal line is generally not greater than 5pF. Due to the small capacitance of the capacitor, in order to make the common mode resonance frequency fall at around 960MHz, it is necessary to adjust the mutual inductance between the differential signal line 1 and the serpentine line 22. From the above description, it can be seen that the way to adjust the mutual inductance between the two is to change the structure of the signal differential line 1 and the routing path of the serpentine line 22, thereby changing the vertical overlap between the serpentine line 22 and the differential signal line 1.

[0046] First, a high overlap method is adopted. For example, the differential signal line 1 is designed with a non-straight structure, and its shape is basically the same as the shape of the serpentine trace 22. Therefore, there is a high overlap between the two. When the overlap of the vertical projection between the two is high, the resonant frequency is around 790MHz. At this time, it does not meet the design requirements. Therefore, it is necessary to reduce the mutual inductance to increase the frequency of the resonant frequency. After adjusting the structure of the differential signal line 1, that is, setting it to a parallel straight line structure, and adjusting the overlap of the vertical projection, it is gradually adjusted to the resonant frequency of 960MHz to meet the filtering requirements.

[0047] like Figure 5 The above is a simulation S parameter result diagram of the common mode signal band stop structure provided by the embodiment of the utility model. In the figure, Scom is the insertion loss of the common mode signal, and Sdif is the insertion loss of the differential mode signal. It can be seen from the schematic diagram that from 0.90GHz to 1.05GHz, the suppression of the common mode signal is above -10dB, which means that the common mode signal is effectively filtered out.

[0048] When applied to filtering of a USB2.0 clock signal at a frequency multiplication point of 960 MHz, the common-mode signal suppression of the common-mode signal band-stop structure provided by the embodiment of the utility model is approximately -16.1 dB.

[0049] The utility model provides a common-mode signal band-stop structure, circuit and digital interface circuit, in which a ground wire structure of a serpentine trace 22 is set on a ground reference plane 2, and the serpentine trace 22 has a certain length, which can increase the return path length of the common-mode current, thereby increasing the common-mode impedance within a certain frequency range, and realizing the common-mode signal band-stop characteristics, that is, designing a sufficiently high common-mode impedance without increasing the differential mode impedance. The technical solution of the utility model uses a common-mode signal band-stop structure to replace the existing common-mode inductor structure, and performs a filtering design on a digital signal interface circuit that is prone to excessive radiation emission at a specific frequency point, suppresses common-mode noise, and meets the design requirements, and ensures the reliability and stability of data transmission. In addition, this structure can adapt to more usage scenarios by changing the length of the serpentine trace, the layout of the trace, etc., and has higher versatility.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0051] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0052] The above are only specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A common mode signal band-stop structure, characterized in that: It comprises two differential signal lines (1) arranged at an interval, and a ground reference plane (2) arranged parallel to the plane where the differential signal lines (1) are located; A hollow hole (21) is provided on the ground reference plane (2) below the differential signal line (1), a serpentine trace (22) is provided in the hollow hole (21), and two ends of the serpentine trace (22) are respectively connected to the ground reference plane (2).

2. The common mode signal band-stop structure according to claim 1, characterized in that: It also includes a surface ground line (3), wherein the surface ground line (3) is located on a side of the differential signal line (1) away from the ground reference plane (2); The surface ground line (3) is connected to the serpentine line (22) through a first via hole (4).

3. The common mode signal band-stop structure according to claim 2, characterized in that: It also includes a jumper element (5), and the jumper element (5) is located on the surface where the surface ground line (3) is located; One end of the jumper element (5) is connected to the surface ground line (3), and the other end is connected to the differential signal line (1) through a second via hole (6).

4. The common mode signal band-stop structure according to claim 3, characterized in that: The jumper element (5) is a capacitor.

5. The common mode signal band-stop structure according to claim 1, characterized in that: The two differential signal lines (1) are arranged in parallel and at intervals.

6. The common mode signal band-stop structure according to claim 5, characterized in that: In a vertical projection of the differential signal line (1) in the direction of the serpentine line (22), a vertical projection of the differential signal line (1) of a set area coincides with the serpentine line (22).

7. The common mode signal band-stop structure according to claim 1, characterized in that: The serpentine line (22) has a set length, which is used to increase the return path length of the common mode current; and / or The shape of the serpentine wiring (22) is a centrally symmetrical shape.

8. The common mode signal band-stop structure according to claim 7, characterized in that: The hollow hole (21) is in the shape of a rectangle, the contour of the serpentine wiring (22) is in the shape of a rectangle, and the edge of the serpentine wiring (22) and the inner wall of the hollow hole (21) have a set interval.

9. A circuit, characterized in that: The method comprises the common-mode signal band-stop structure as claimed in any one of claims 1 to 8.

10. A digital interface circuit, characterized in that: The method comprises the common-mode signal band-stop structure according to any one of claims 1 to 8 or the circuit according to claim 9.

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