PCB Serpentine Alignment
Serpentine is a type of alignment that is often used in PCB layout. Its main purpose is to adjust the delay to meet the system timing design requirements. Two most critical parameters are the parallel coupling length (Lp) and the coupling distance (S). It is obvious that when the signal is transmitted on the serpentine alignment, the parallel segments will be coupled and form a differential mode. The smaller the S, the larger the Lp, the greater the degree of coupling.This may result in reduced transmission delays and greatly reduced signal quality due to crosstalk.
Here are a few tips for layout engineers when working with serpentine lines:
1.Increase the parallel line segment distance (S) as much as possible, at least greater than 3H, here H refers to the distance from signal trace to the reference plane. In simple terms, go around the big bend alignment as long as S is large enough, it can almost completely avoid the mutual coupling effect.
2.By reducing the coupling length Lp, when the delay time of double Lp approaches or exceeds the signal rise time, the resulting crosstalk will reach saturation.
3.The transmission delay caused by the serpentine lines of the strip-line or embedded micro-strip is less than that of the micro-strip. In theory, the strip-line will not affect the transfer rate due to differential mode crosstalk.
4.Not use serpentine alignment if signal lines required strict high-speed and timing requirements. In particular, you can not wind a line within a small area.
5.To effectively reduce the coupling between each other, you can often use any angle of the serpentine alignment.
6.In a high-speed PCB design, serpentine lines have no so-called filtering or anti-interference capability which can only reduce the signal quality, so they are only used for timing matching purposes.
7.Spiral alignment can sometimes be considered, because simulation shows that its effect is better than the normal serpentine alignment.