1, laminated design with the same level
Many times, the root of crosstalk over the standard is from laminated design. That is, our first article said in the design, it is difficult to correct it.
It is said that there is another picture of the crosstalk to the crosstalk, and there is a picture of the reference plane mentioned above. We can see that interlayer distance h is a key factor affecting crosstalk. When D = 3h, the crosstalk is about 10% without considering K. This is also the result of the so-called 3h principle. After understanding crosstalk, we need to change 3W principles to 3h principles.
It can also be noted from the above figure. If you want to reduce crosstalk, you can reduce H or increase D. However, H is too small, in order to control the impedance, the line width will also become small accordingly, increase the difficulty of processing, or increase the conductor loss. Increase D, of course, will be bound by the wiring space. Therefore, we have been advocated, the PCB design is the art of weighing, and the skills weighing are from the in-depth understanding of theory, as well as the appropriate engineering quantitative capacity.
2, laminated design and interlayer crosstalk
It is necessary to tell the more double-line lines mentioned in various rules now, that is, the DualStripline structure. The major companies have developed very detailed design rules for Dualstripline.
Taking Intel's Purley platform rules as an example, in order to reduce costs, the double-strap wire structure is often employed, pay attention to the interlayer crosstalk. The recommended lamination can be seen that between the L2 to L4 constitutes the distance between the two-stranded wire structure, the distance between L3 and L4 is 10 mil, while the L2 to L3 and L4 to L5 are 3 miL, from the laminated source to control the interlayer crosstalk.
In the specific design recommendation, a method of avoiding cross-strip-line structural interlayer crosstalk is proposed in a 30 degree angle. And use jogging to balance crosstalk. The following figure is our test board we do for these different walking methods.
Always pay attention to the friends of the high-speed, know that we will often do some test boards to verify the differences in the details of various traces. Through verification analysis, we have been shared in the articles of Workshop Paper and Mr. Expressway. There are also some conclusions, or we are also confused, or the conclusion is not enough, we will continue to study. The 30-degree angle of the double line line and the Jogging trace belong to what we think is not enough, and there are also some doubts. So this time I don't disclose the conclusion.
Interested friends, or friends who want to analyze the high-speed, you can pay attention to the high-speed Mr. WeChat public number (search: high speed Mr.), and leave specific contact information in the background (name, company, email, phone and other information) ), We can send a phased research results separately, let's take a look at there is any problem now, which direction should be studied next.
Anyway, double-stranded interlayer crosstalk is the problem that is concerned in the industry. This structure is very important, and it is necessary to plan from the beginning.
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