Asymmetric double-bend skew compensation for reduced differential-to-common-mode conversion

Abstract

In one embodiment, a method includes placing a first component for generating a differential signal on a printed circuit board, placing a second component for receiving a differential signal on the printed circuit board, and routing a differential conductor pair on a path between the first component and the second component, wherein the path includes at least one turn at which the differential conductor pair changes direction. The first conductor and the second conductor of the differential conductor pair each include a plurality of sets of bends near the turn to provide skew compensation while reducing differential-mode to common-mode conversion, and wherein each set of bends in the second conductor is aligned with a set of bends in the first conductor.

Description

Technical Field

[0001] The present disclosure relates generally to printed circuit boards (PCBs), and more particularly to skew compensation of signals routed on a printed circuit board in order to reduce the generation of common mode signals, thereby reducing electromagnetic interference from the PCB. Background Art

[0002] Signal lines (conductors, traces) are used to relay signals between devices on a printed circuit board, semiconductor chip package, or other electronic device. Differential signaling can be used to relay signals by transmitting two equal but opposite signal components simultaneously in a differential conductor pair. If the two conductors in a differential conductor pair have a length difference, the simultaneously transmitted signals will arrive at the destination at different times. The difference in arrival time is called skew. Traditional methods for eliminating skew include introducing bends in the shorter conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Figure 1 is a schematic diagram of a printed circuit board having electrical components connected by differential conductor pairs according to one embodiment.

[0004] Figure 2A An example of an asymmetric double-bend configuration of a differential conductor pair is shown according to one embodiment.

[0005] Figure 2B Another example of an asymmetric double-bend configuration is shown.

[0006] Figure 2C Yet another example of an asymmetric double-bend configuration is shown.

[0007] Figure 3A is a cross-sectional view showing the stack-up of stripline traces.

[0008] Figure 3B It is a top view of the straight strip trace line.

[0009] Figure 3C yes Figure 3B Equivalent circuit of a straight stripline trace.

[0010] Figure 3D is a top view of the inclined stripline trace line.

[0011] Figure 3E yes Figure 3D Equivalent circuit of a tilted stripline trace.

[0012] Figure 4 Fixed length routing of differential conductor pairs is shown.

[0013] Figure 5A Shown by Figure 2AAn example of the deflection compensation length provided by the asymmetric double-bend configuration is shown.

[0014] Figure 5B Shown by Figure 2B An example of the deflection compensation length provided by the asymmetric double-bend configuration is shown.

[0015] Figure 5C Shown by Figure 2C An example of the deflection compensation length provided by the asymmetric double-bend configuration is shown.

[0016] Fig. 6A is shown for stripline Figure 4 A graph of the insertion loss of a differential conductor pair is shown.

[0017] Figure 6B is shown for stripline Figure 4 A graph of the differential-mode to common-mode conversion of a differential conductor pair is shown.

[0018] Fig. 7A is shown for microstrip Figure 4 A graph of the insertion loss of a differential conductor pair is shown.

[0019] Figure 7B is shown for microstrip Figure 4 A graph of the differential-mode to common-mode conversion of a differential conductor pair is shown.

[0020] Figure 8 Fixed position routing for differential conductor pairs is shown.

[0021] Fig. 9A is shown for stripline Figure 8 A graph of the insertion loss of a differential conductor pair is shown.

[0022] Fig. 9B is shown for stripline Figure 8 A graph of the differential-mode to common-mode conversion of a differential conductor pair is shown.

[0023] Fig. 10A is shown for microstrip Figure 8 A graph of the insertion loss of a differential conductor pair is shown.

[0024] Fig. 10B is shown for microstrip Figure 8 A graph of the differential-mode to common-mode conversion of a differential conductor pair is shown.

[0025] Fig.11 is an overview of a process for routing differential conductor pairs with asymmetric double bends according to one embodiment.

[0026] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0027] Overview

[0028] Various aspects of the invention are set out in the independent claims, preferred features are set out in the dependent claims. Features of one aspect may be applicable to each aspect alone or in combination with the other aspects.

[0029] In one embodiment, a device generally includes a printed circuit board and a differential conductor pair, which extends along a path between a first component configured to generate a differential signal and a second component configured to receive a differential signal. The path includes at least one turn, and the differential conductor pair changes direction at the at least one turn. The first conductor of the differential conductor pair includes a first set of bends at a position near the turn to provide skew compensation. The first set of bends includes a first bend and a last bend, the first bend is tilted away from a first straight portion, the first straight portion extends along a longitudinal axis substantially parallel to the second conductor of the differential conductor pair, and the last bend is tilted toward a second straight portion, the second straight portion extends along a longitudinal axis substantially parallel to the second conductor. The second conductor includes a second set of bends to reduce differential mode to common mode conversion. The second set of bends is asymmetrical with the first set of bends and is aligned with the first set of bends so that the second set of bends is longitudinally placed between the first bend and the last bend of the first set of bends.

[0030] In one embodiment, the first set of bends, the second set of bends, or both sets of bends include four bends. In one embodiment, the second set of bends includes eight bends.

[0031] In one embodiment, the first set of bends, the second set of bends, or both sets of bends define a frusto-conical shape.

[0032] In one embodiment, the second set of bends defines a first stepped segment extending upward and a second stepped segment extending downward such that a straight segment between the first and second stepped segments is positioned parallel to and above straight segments of the second conductor disposed before and after the second set of bends.

[0033] In one embodiment, the second set of bends comprises a pair of matching bends. In one embodiment, the straight segment between the pair of matching bends extends along the longitudinal axis of the straight segments of the second conductor before and after the second set of bends.

[0034] In another embodiment, a method generally includes placing a first component for generating a differential signal on a printed circuit board, placing a second component for receiving a differential signal on the printed circuit board, and routing a differential conductor pair on a path between the first component and the second component, wherein the path includes at least one turn at which the differential conductor pair changes direction. The first conductor and the second conductor in the differential conductor pair each include a plurality of sets of bends near the turn to provide skew compensation while reducing differential-mode to common-mode conversion, and wherein each set of bends in the second conductor is aligned with a set of bends in the first conductor.

[0035] In yet another embodiment, an apparatus generally includes a printed circuit board and a differential conductor pair extending along a path between a first component configured to generate a differential signal and a second component configured to receive the differential signal. The path includes at least one turn at which the differential conductor pair changes direction. A first conductor of the differential conductor pair includes a first set of bends at a location proximate the turn to provide skew compensation, and a second conductor includes a second set of bends to reduce differential-to-common-mode conversion. The second set of bends is asymmetric to the first set of bends, and the number of bends in the second set of bends is greater than the number of bends in the first set of bends.

[0036] A further understanding of the features and advantages of the embodiments described herein may be realized by reference to the remainder of the specification and drawings.

[0037] Example Embodiments

[0038] The following description is presented to enable those skilled in the art to make and use the embodiments. The description of specific embodiments and applications is provided as examples only, and various modifications will be apparent to those skilled in the art. The general principles described herein may be applied to other applications without departing from the scope of the embodiments. Therefore, the embodiments are not limited to those shown, but conform to the widest range consistent with the principles and features described herein. For the sake of clarity, details related to technical materials known in the technical field related to the embodiments are not described in detail.

[0039] Differential pairs are often used in high-speed digital circuits to introduce differential signaling to improve data quality and reduce electromagnetic (EM) emissions from printed circuit boards (PCBs). However, the benefits of using differential pairs quickly diminish if there is any imbalance in the differential wiring. Both physical and electrical characteristics can cause imbalance, but the most common is the skew generated between the P and N traces due to bends, input / output (I / O) connections in integrated circuits, or connectors. The generated skew can be a concern for both SI (signal integrity) and EMC (electromagnetic compatibility).

[0040] A turn in the differential pair path causes one conductor in the pair to have a length that is longer than the length of the other conductor in the pair. For example, when a pair of parallel conductors turns a corner, one conductor will be on the inside of the turn and the other conductor will be on the outside of the turn. At the end of the turn, the outside conductor will have a longer length than the inside conductor relative to the starting point. This longer length results in a longer travel path for the signal component on the outside conductor relative to the signal component on the inside conductor, and therefore results in a phase difference (skew) between the signals at the end of the turn. When phase skew occurs, the signal components operate essentially in common mode, and the signal will emit significant EMI (electromagnetic interference) relative to the differential mode transmission that occurs when the signal components are in phase, and the signal quality may be reduced.

[0041] In conventional systems, bends are introduced into one of the traces (signal lines, conductors) of a differential pair to eliminate the skew between the positive (P) and negative (N) signals. However, these bends also introduce an imbalance between the P and N traces. For example, the corners of the bend introduce additional parasitic parameters into one trace and cause an imbalance between the P and N traces. The impact of conventional skew compensation techniques on EMI makes it difficult to meet EMC standards. The additional imbalance worsens the differential-to-common-mode conversion (Scd21), and the common-mode noise generated by the conversion may radiate from leakage in the cable, connector, or chassis and cause EMI problems.

[0042] Embodiments described herein involve an asymmetric double-bend configuration that not only compensates for the skew between the P and N traces in a differential conductor pair, but also reduces the imbalance between the traces, thereby significantly reducing differential mode (DM) to common mode (CM) conversion compared to traditional skew compensation techniques.

[0043] Now referring to the drawings, first Figure 1 , a simplified schematic diagram of a printed circuit board (PCB) 11 according to one embodiment is shown. A first electrical component 10 and a second electrical component 12 are connected by a differential conductor pair (differential pair) 14 including first (P) and second (N) parallel conductors (traces, signal lines) 16a, 16b. The first electrical component 10 can be any electrical component or element configured to generate a differential signal, and the second electrical component 12 can be any electrical component or element configured to receive a differential signal.

[0044] The first electronic component 10 is configured to generate a differential signal for transmission to the second electronic component 12. The differential signal includes first and second equal but opposite signal components that are transmitted simultaneously on two separate conductors 16a, 16b of the differential conductor pair 14. These components of the differential signal include two signals that are 180 degrees out of phase and are transmitted simultaneously along the differential conductor pair 14.

[0045] like Figure 1 As shown in the example of FIG. 1 , the path followed by the differential conductor pair 14 includes a plurality of turns at which the differential pair changes direction. In this example, there are four changes in direction (turns T 1 , T 2 , T 3 , T 4 ), which may be needed, for example, to accommodate other components on PCB 11. Phase skew is corrected by using skew compensation bends. The skew compensation bend is located (i.e., positioned close to) one or more turns so that after the skew compensation bend, the lengths of conductors 16a, 16b are substantially the same. Using this skew compensation technique ensures that the signal components remain substantially in phase for most of the travel time. It should be understood that Figure 1 The number of turns, arrangement and location of bends, and lengths of the differential conductor pairs 14 shown in are examples only, and different routings having any number of turns or bends or any number of bend groups may be used without departing from the scope of the embodiments. Figure 1 The asymmetric double-bend configuration shown is merely one example, and other configurations may be used, as described in detail below.

[0046] like Figure 1 As shown, the first conductor 16a of the differential conductor pair 14 includes a T near one of the turns. 1 The first set of bends 15a are provided at the positions of the first and second conductors 16b to provide skew compensation, however, these bends also introduce additional imbalance between the P and N traces. The asymmetric dual-bend skew compensation scheme described herein introduces a second set of bends 15b into the second conductor 16b aligned with the first set of bends to reduce differential-mode to common-mode conversion, thereby improving EMI performance without additional cost and without degrading SI (signal integrity) performance.

[0047] Any number of bend groups may be included to provide skew compensation while also reducing differential-to-common-mode conversion. For example, the first conductor 16a and the second conductor 16b of the differential conductor pair 14 may each include multiple groups of bends near turns to provide skew compensation while also reducing differential-to-common-mode conversion, wherein each group of bends 15b in the second conductor is aligned with a group of bends 15a in the first conductor. The differential conductor pair 14 may include multiple unit structures, each unit structure including a group of bends in each conductor (a first group of bends in the first conductor, a second group of bends in the second conductor). Figure 1 In the example shown, the first conductor 16a includes a 1 The second conductor 16b includes two sets of aligned bends 15a (one set of bends for one unit structure) at positions to provide skew compensation, and the second conductor 16b includes two sets of aligned bends 15b to reduce differential-to-common-mode conversion by compensating for the additional imbalance introduced by the skew compensation bends in the first conductor.

[0048] Figure 2A , 2B Three examples of asymmetric dual-bend configurations for a unit structure (a set of bends in each conductor of a differential conductor pair) are shown in 2C. Figure 2A-2C In the example shown, the P trace includes four 45 degree corners, and the N trace includes transitions at substantially the same locations (e.g., at x 1 and x 2 Between x 3 and x 4 Between, at the longitudinal distance y 1 have the same ( Figure 2A ) or different ( Figure 2B and 2C ) number of asymmetric bends. It should be understood that Figure 2A-2C The shapes, angles, lengths, numbers, and positions of the bends shown in the drawings are examples only and may be varied without departing from the scope of the embodiments. For example, although a 45 degree bend is shown and described herein, the embodiments may be extended to include bends of other degrees or circular bends.

[0049] Each conductor in a differential conductor pair includes a set of bends (e.g., Figure 1 15a, 15b in the figure). The first set of bends in the first conductor 20a, 24a, 27a includes a first bend 22a and a last bend 22d, the first bend 22a is inclined away from the first straight portion 21a, the first straight portion 21a extends along the longitudinal axis A and is generally parallel to the second conductor 20b, 24b, 27b of the differential conductor pair, and the last bend 22d is inclined toward the second straight portion 21e, the second straight portion 21e extends along the longitudinal axis A and is generally parallel to the second conductor. As described below, the second conductor 20b, 24b, 27b includes a second set of bends to compensate for the additional imbalance caused by the first set of bends in the first conductor 20a, 24a, 27a and reduce the conversion of differential mode to common mode. The second set of bends is asymmetrical with the first set of bends and is located longitudinally between the first bend 22a and the last bend 22d of the first conductor (for example, at x 1 and x 4 The longitudinal distance between the first bend and the last bend of the second conductor is substantially equal to or less than y 1 ). Thus, the second set of bends is aligned with the first set of bends such that the second set of bends is longitudinally positioned between the first bend and the last bend of the first set of bends in the first conductor.

[0050] Each bend 22a, 22b, 22c, 22d in the first conductors 20a, 24a, 27a is located at a position respectively defined by the line x 1 、x2 、x 3 、x 4 denoted as a horizontal distance along the longitudinal axis A. In each example, the first conductor 20a, 24a, 27a includes a first segment 21b and a third segment 21d that are inclined relative to the longitudinal axis A of the conductor (the straight portions 21a and 21e). The second segment 21c is disposed between the first segment 21b and the third segment 21d and connects them. The second segment 21c is substantially parallel to the longitudinal axis A of the first conductor. Four bends 22a, 22b, 22c, 22d connect the three segments 21b, 21c, 21d and the straight portions 21a, 21e to define a truncated cone shape extending upward from the straight portions. It should be understood that the term "upward" used herein is a relative term depending on the orientation of the trace and the PCB, and does not limit the orientation or arrangement of the trace or the PCB.

[0051] The bend in the first conductor may be referred to as a skew compensation bend (or a local skew compensation bend). The angle of the bend may vary depending on, for example, the characteristics of the differential pair, the shape of the turn, the differential signal characteristics, etc. In one example, the angle is approximately 45 degrees. Figure 2A-2C As shown in the examples of FIG. 1 , the length of each segment 21a, 21b, 21c, 21d and 21e may also vary. In addition, it should be noted that in these examples, the first conductor is labeled as the positive trace and the second conductor is labeled as the negative trace, however, these may be switched along the path, such as Figure 1 It should also be noted that although Figure 2A-2C One unit structure of a differential conductor pair is shown (defined as starting with a straight line portion 21a and ending with a straight line portion 21e in a first conductor 20a, and including bends 22a, 22b, 22c, and 22d), but the differential conductor pair may include any number of unit structures, such as Figure 1 , 4 and 8.

[0052] In order to compensate for the imbalance caused by the corners of the bends (first set of bends) 22a, 22b, 22c, 22d in the first conductors 20a, 24a, 27a, asymmetric bends (second set of bends) are provided in the second conductors 20b, 24b, 27b. Figure 2A-2C As shown, each set of bends in the second conductor is located at x 1 (the first bend 22a is inclined from the first straight portion 21a, which extends along the longitudinal axis A and is substantially parallel to the second conductor) and x 4 (The last bend 22d is inclined towards the second straight portion 21e, which extends along the longitudinal axis A and is substantially parallel to the second conductor). Figure 2A-2CIn the example shown, the transitions in the second conductor (the beginning and end of the second set of bends) are located between (e.g., substantially aligned with) the transitions in the first conductor (the beginning and end of the first set of bends). Each set of bends in the second conductor is aligned with a set of bends in the first conductor. Figure 2A-2C Different asymmetric double-bend configurations of the second conductor are shown in .

[0053] First reference Figure 2A , the second conductor 20b includes straight segments 23a, 23c and 23e connected by inclined segments 23b and 23d, which define a frustoconical shape. This configuration includes four bends in the first conductor 20a and the second conductor 20b. The shape defined by the bends in the first and second conductors is asymmetric, and therefore the bends are referred to herein as asymmetric bends.

[0054] As mentioned before, the additional imbalance caused by the corner may cause odd and even modes, and these two modes will be on the straight trace after the corner (e.g., Figure 2A Each line L1, L2 has a corresponding delta time T1, T2, and since the two modes have different propagation speeds, since L1>L2, T1>T2. More delta times cause greater imbalance, so in order to compensate for this imbalance as much as possible, Figure 2B and 2C Additional variations of asymmetric double-bend configurations are provided as shown in . In these asymmetric double-bend configurations, additional turns are introduced in the N trace (second conductors 24b, 27b) to compensate for the imbalance caused by the difference in L1 and L2.

[0055] Figure 2B The second conductor 24B includes straight sections 26a, 26c, 26e, 26g and 26i connected by inclined portions 26b, 26d, 26f and 26h. In this example, the unit structure of the second conductor 24b includes eight bends. The bends of the second conductor 24b define a first stepped section extending upward and a second stepped section extending downward, so that a straight section 26e between the stepped sections is parallel to the straight sections 26a, 26i located before and after the bends and is located above these straight sections. In this example, the bends included in the second conductor 24b are twice the bends of the first conductor 24a, wherein the bends in the second conductor are located between the first bend 22a and the last bend 22d in the first conductor (at x 1 and x 4 between).

[0056] Reference now Figure 2C, the second conductor 27b includes a pair of matching bends defining two frustoconical shapes. The eight bends define inclined segments 28b, 28d, 28f and 28h connecting straight segments 28a, 28c, 28e, 28g and 28i. The bend in the second conductor 27b is located between the first bend 22a and the last bend 22d of the first conductor 27a (at x 1 and x 4 between).

[0057] It should be understood that Figure 2A-2C The asymmetric double-bend configuration shown in is merely an example, and a different number of bends, different angles, or a different number or lengths of straight and angled segments may be used without departing from the scope of the embodiments.

[0058] The following describes a process by which additional imbalance is introduced by a bend in a first conductor and how the bend in a second conductor compensates for the imbalance, thereby reducing differential-mode to common-mode conversion.

[0059] Reference now Figures 3A-3E , shows an example to illustrate how corners (bends) can introduce additional imbalance in a differential pair. Figure 3A The stack-up of stripline traces is shown in cross-section. Figure 3B is a top view of a segment 30 of a straight line trace, and Figure 3C The corresponding equivalent circuit (inductance L and capacitance C) of the straight line trace 30 is shown. Figure 3D is a top view of the inclined ribbon trace line 32, and Figure 3E Shows Figure 3D The corresponding equivalent circuit for the trace shown.

[0060] Figure 3C The inductance (L o ) and capacitance (C o ) can be calculated as follows:

[0061]

[0062]

[0063]

[0064] Figure 3E The inductance (L o ) and capacitance (C o ) can be calculated as follows:

[0065]

[0066]

[0067] in,

[0068]

[0069] according to Figures 3A-3E From equations (2)-(5), different equivalent circuit topologies and inductance and capacitance parameter values ​​can be observed between 45 degree corners and straight traces. Considering a 45 degree corner in the P trace and a corresponding straight section in the N trace, additional imbalance is introduced.

[0070] To compensate for the additional imbalance caused by the corner, an asymmetric double bend is introduced to replace the conventional skew compensation bend located only in one trace (e.g. Figure 4 Compared with the traditional differential conductor pair shown in example (a), Figure 4 The asymmetric double bending schemes shown in Examples (b)-(d) in Figure 2A-2C ) includes bends in two traces (P and N). For one unit structure, each trace includes a bend, and less additional imbalance is caused by one trace having a corner and the other trace being a straight line. The bend in the second conductor is aligned with the bend in the first conductor and is provided to compensate for the imbalance caused by the skew compensation bend in the first conductor.

[0071] For the skew compensation function, the distance D between two traces in the curved section can be designed to be the same as Figure 4 The same as shown in Example (a) of FIG. 1 , thus ensuring that each configuration has the same skew compensation function. Moreover, since D is the same, the impedance in the curved section also remains the same. This ensures that the asymmetric dual-bend configuration can provide the same Figure 4 The single bend compensation scheme shown in (a) of FIG. 1 shows almost the same SI performance (Sdd21) while substantially improving the mode conversion performance (Scd21), as shown below with respect to Figures 6A-7B In one or more embodiments, the length of the bend may be modified to ensure manufacturability, as long as the distance D between the two traces remains the same as Figure 4 The same as the single bending scheme shown in example (a).

[0072] Simulations were performed to compare stripline ( Fig. 6A , 6B , 9A, 9B) and microstrip ( Fig. 7A , 7B , 10A, 10B) Mode conversion (Scd21) (conversion between differential mode and common mode) and insertion loss (Sdd21) (input differential insertion loss) between single-bend and asymmetric double-bend configurations in wiring. Figures 6A-7B Shows Figure 4 For the fixed length case shown, Figures 9A-10B Shows Figure 8 The fixed position scenario is shown. The fixed length scenario is evaluated to compare the benefits achieved by the asymmetric skew compensation technique described herein without adding any ambiguity due to differences in insertion loss caused by different overall lengths. The fixed position scenario is evaluated to understand the benefits of the asymmetric skew compensation technique in an actual PCB where the position of the component / pin is initially fixed based on the integrated circuit package, relative position to other components, and other constraints such as thermal constraints. Since the position of the component is fixed, routing traces are required to keep the relative distance between the ends of the P and N traces fixed.

[0073] First reference Figure 4 , route the traces so that all traces have equal length (e.g., 613 mils). Figure 4 Five examples are shown: (a) a conventional single bend configuration with a skew compensating bend in the first conductor 40a and a straight second conductor 40b; (b) a conventional single bend configuration with a skew compensating bend in the first conductor 40a and a straight second conductor 40b; Figure 2A (c) for conductors 44a, 44b Figure 2B (d) for conductors 46a, 46b Figure 2C an asymmetric double-bend configuration; and (e) a reference trace having two straight conductors 48a, 48b. Figure 5A , 5B and 5C (corresponding to Figure 2A , 2B and 2C) show the Figure 4 The configurations shown in (b)-(d) provide skew compensation length.

[0074] for Figure 4 The skew compensation length of the bend (i.e., the delta length between the P and N traces) for example (a) in Figure 1 (a 45 degree bend in the P trace has a horizontal length of 12 mils and a vertical length of 12 mils) is calculated as follows:

[0075] 12×(√2-1)×2=9.95mil

[0076] for Figure 5A The delta length between the P and N traces of the example shown in is calculated as follows:

[0077] 15×(√2-1)×2-3×(√2-1)×2=9.95mil

[0078] for Figure 5B The delta length between the P and N traces of the example shown in is calculated as follows:

[0079] 18×(√2-1)×2-6×(√2-1)×2=9.95mil

[0080] for Figure 5C The delta length between the P and N traces of the example shown in is calculated as follows:

[0081] 12×(√2-1)×2-3×(√2-1)×4=4.97mil (9.95mil for one pair of bends)

[0082] Fig. 6A and 6B They are shown respectively Figure 4 The Sdd21 and Scd21 performance of the stripline for the example shown. The asymmetric double bend of configuration (c) has the best EMI (minimum Scd21) performance among all the bend differential pairs, while the single bend ( Figure 4 (shown in (a)) has the worst EMI (maximum Scd21) performance.

[0083] Fig. 7A and 7B They are shown respectively Figure 4 Microstrip Sdd21 and Scd21 performance of the example shown. Simulation results show that the configurations have similar SI performance and the asymmetric double-bend configurations ((b)-(d)) have better EMI performance than the single-bend configuration (a).

[0084] Figure 8 Fixed start and stop positions for differential routing are shown. The traces are routed assuming the positions of the P / N terminals are fixed. Figure 8 Each of the examples (a)-(d) shown has the same start and end points and a different overall length. Figure 8 As shown, the total width of the bend can be increased from 29 mils to 32 mils or even 35 mils, which may require a little more space. Figure 8 Reference (e) is not shown (from Figure 4 ), but it will be the same type of reference line and will be included in Figures 9A-10B in simulation.

[0085] EMI and SI performance in stripline Fig. 9A and 9B The EMI and SI performance in the microstrip Fig. 10A and 10B In stripline applications, Figure 8 The asymmetric double bend shown in (c) has the best EMI performance, and all configurations have similar SI performance. In microstrip routing, Figure 8 The asymmetric double bend shown in (c) has the best EMI performance, while Figure 8 The asymmetric double bend shown in (d) has the worst SI performance due to the longest length.

[0086] In these simulations, Figure 4 and 8 The Sdd21 variation between configurations (a)-(d) is less than 0.1 dB. The Scd21 variation, which determines the EMC performance of the differential conductor pair, is high. Figure 2B The asymmetric double-bend configuration shown appears to provide the smallest Scd21 under the conditions evaluated.

[0087] Fig.11 1 is a flow chart showing an overview of a process for routing a differential conductor pair having an asymmetric double bend according to one embodiment. At step 110, a first component configured to generate a differential signal is placed on a PCB. A second component configured to receive a differential signal from the first component is also placed on the PCB (step 112). In one or more embodiments, a differential conductor pair including an asymmetric double bend is routed between the first and second components along a path including at least one turn, wherein the bend of the second conductor is aligned with the skew compensation bend of the first conductor and is longitudinally located between the skew compensation bends of the first conductor to reduce differential mode to common mode conversion (step 114). In one or more embodiments, the first conductor and the second conductor of the differential conductor pair each include multiple groups of bends near the turn to provide skew compensation while reducing differential mode to common mode conversion, and wherein each group of bends in the second conductor is aligned with a group of bends in the first conductor.

[0088] As can be seen from the above, the embodiments described herein provide many advantages over conventional skew compensation techniques. For example, asymmetric double bend skew compensation introduces bends in the P and N traces of a differential pair to compensate for skew and mitigate additional imbalance, which can help reduce mode conversion and improve EMI performance. Asymmetric double bends do not introduce additional cost and can provide slight benefits in SI performance. Simulation results for various routing scenarios show a 5-10 dB improvement in Scd21.

[0089] It should be understood that the asymmetric dual-bend configurations (size, shape, angle, length, number of bends, etc.) described herein are merely examples and that other configurations may be used in any arrangement without departing from the scope of the embodiments.

[0090] Although the method and apparatus have been described according to the illustrated embodiments, it will be readily appreciated by those skilled in the art that changes may be made to the embodiments without departing from the scope of the invention. Therefore, all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not limiting.

Claims

1. A device for a printed circuit board, comprising: Printed circuit boards; and a differential conductor pair extending along a path between a first component and a second component, the first component being configured to generate a differential signal and the second component being configured to receive the differential signal, wherein the path includes at least one turn and the differential conductor pair changes direction at the at least one turn; wherein the first conductor of the differential conductor pair comprises a first set of bends at a position close to the turn to provide skew compensation, the first set of bends comprises a first bend and a last bend, the first bend is inclined away from a first straight portion, the first straight portion extends along a longitudinal axis substantially parallel to the second conductor of the differential conductor pair, the last bend is inclined toward a second straight portion, the second straight portion extends along a longitudinal axis substantially parallel to the second conductor, the second conductor comprises a second set of bends to reduce differential mode to common mode conversion, the second set of bends is asymmetric with the first set of bends, and is aligned with the first set of bends so that the second set of bends is longitudinally placed between the first bend and the last bend of the first set of bends, wherein the first conductor is on the inner side of the turn and the second conductor is on the outer side of the turn.

2. The device according to claim 1, wherein: The first set of bends includes four bends.

3. The device according to claim 1 or 2, wherein: The second set of bends includes four bends.

4. The device according to claim 1 or 2, wherein: The first set of bends defines a frusto-conical shape and the second set of bends defines at least one frusto-conical shape.

5. The device according to claim 1 or 2, wherein: The first conductor includes a first plurality of bends and the second conductor includes a second plurality of bends, each bend in the second plurality of bends being aligned with a corresponding one of the first plurality of bends.

6. The device according to claim 1 or 2, wherein: The second set of bends includes eight bends.

7. The device according to claim 1 or 2, wherein: The second set of bends defines a first stepped segment extending upward and a second stepped segment extending downward such that a straight segment between the first stepped segment and the second stepped segment is positioned parallel to and above straight segments of the second conductor disposed before and after the second set of bends.

8. The device according to claim 1 or 2, wherein: The second set of bends includes a pair of matched bends.

9. The device of claim 8, wherein: A straight segment between the pair of matching bends extends along a longitudinal axis of the straight segments of the second conductor before and after the second set of bends.

10. A method for printing a circuit board, comprising: placing a first component for generating a differential signal on a printed circuit board; placing a second component for receiving the differential signal on a printed circuit board; as well as routing a differential conductor pair on a path between the first component and the second component, wherein the path includes at least one turn at which the differential conductor pair changes direction; The first conductor and the second conductor of the differential conductor pair each include a plurality of groups of bends near the turn to provide skew compensation while reducing differential mode to common mode conversion, each group of bends in the second conductor is aligned with a corresponding group of bends in the first conductor, the number of bends in the second conductor is greater than the number of bends in the first conductor, and the first conductor is on the inside of the turn and the second conductor is on the outside of the turn.

11. The method of claim 10, wherein: Each set of bends in the first conductor includes four bends, and each set of bends in the second conductor includes eight bends.

12. The method according to claim 10 or 11, wherein: Each set of bends in the second conductor defines a first stepped segment extending upward and a second stepped segment extending downward, such that a straight segment between the first stepped segment and the second stepped segment is positioned parallel to and above straight segments of the second conductor before and after the set of bends disposed in the second conductor.

13. The method according to claim 10 or 11, wherein: A set of bends in the second conductor includes a pair of matched bends.

14. The method according to claim 10 or 11, wherein: Each set of bends in the second conductor has the same configuration.

15. The method according to claim 10 or 11, wherein: Each set of bends defines a frusto-conical shape extending in an upward direction.

16. A device for a printed circuit board, comprising: Printed circuit boards; and a differential conductor pair extending along a path between a first component and a second component, the first component being configured to generate a differential signal and the second component being configured to receive the differential signal, wherein the path includes at least one turn and the differential conductor pair changes direction at the at least one turn; wherein the first conductor of the differential conductor pair includes a first set of bends near the turn to provide skew compensation, and the second conductor includes a second set of bends to reduce differential mode to common mode conversion, the second set of bends being asymmetric to the first set of bends and aligned with the first set of bends, wherein the number of bends in the second set of bends is greater than the number of bends in the first set of bends, wherein the first conductor is on the inside of the turn and the second conductor is on the outside of the turn.

17. The device of claim 16, wherein: The second set of bends includes twice the number of bends in the first set of bends.

18. The device according to claim 16 or 17, wherein: The first set of bends and the second set of bends define a frusto-conical shape extending in the same direction, and wherein the second set of bends is longitudinally positioned between a first bend and a last bend in the first set of bends.

19. The device according to claim 16 or 17, wherein: The second set of bends defines a first stepped section extending upward and a second stepped section extending downward such that a straight section between the first stepped section and the second stepped section is positioned parallel to and above straight sections disposed before and after the second set of bends.

20. The device according to claim 16 or 17, wherein: The second set of bends includes a pair of matched bends.

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