Consider a PC board layout that has a high frequency trace that goes 1 cm on the
ID: 2080858 • Letter: C
Question
Consider a PC board layout that has a high frequency trace that goes 1 cm on the outer layer of a board, drops through a visa to an inner layer where it travels 0.5 cm, drops through another via to the bottom layer, and then travels 0.03 cm, makes a 90 degree turn, and travels 0.02 cm before reaching its destination at another part. Using the concepts of characteristic impedance, reflection coefficients, electrical length relative to wavelength, and your understanding of transmission line theory, describe the design consideration you must think about. When can you ignore certain sections of the transmission line (s), when must your account for it. and what do you expect to happen at each transition point. No math is required, this is a conceptual problem, and you can assume either a power plane or ground plane one layer away (always).Explanation / Answer
As mentioned in question it is high frequency trace so the width of the trace has to be wider than regular width of trace because it carries high frequency data as well as it can carry high current. The reason behind keeping trace width higher is that the if it carrying a current through it, it has to able to tranport that current to its destination without fail high frequency data can require a high current and this high valued current can cause heat of trace.
Next when it drop to a via and travel for a certain distance drop through another via while if the new layer has reference plane, this can cause a impedence change. the use of vias is essential in most routings. But the designer has to be careful when using them. They add additional capatiance and inducatnce, and reflection occurs due to change in charateristic impedence. And also increases the trace length.
as we can see the signal is travelling for a some distance thst can cause a delay for signal trasmission.after reaching to bottom layer it takes full 90 degree turn that can cause a more radition. the capacitace increases in a region of corner and the charateristics impedence changes. This impedence can cause reflection. avoid 90 degree curve bend n try to make two 45 degree curve to minimize impedence change.
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