談玻纖編織效應如何影響訊號完整性

談玻纖編織效應如何影響訊號完整性

近年來，由於AI應用的發展，高速訊號差分走線的應用頻率愈來愈高，對於訊號完整性的要求也愈來愈大，因為走線不等長、參考層不對稱等因素造成的skew（訊號延遲）對誤碼率（Bit Error Rate）的影響也愈來愈大，本章即是探討由玻纖編織效應造成的訊號延遲所造成的影響及可能的解決方式。

由於skew造成的相位延遲

skew造成的Insertion Loss

Insertion Loss的共振點可由上述公式算出，也就是說，共振頻率與玻纖、樹脂之介電常數（Dk）以及走線經過的玻纖長度有關。

以下列舉幾個常見的解決方法：

1. 差動對以Zig-Zag形式走在玻纖上。

2. 將玻纖與走線的相對角度旋轉7至10度。

3. 選用經向與緯向有相同玻紗數的玻纖布。

4. 選用與樹脂相近Dk的玻纖布。

Zig-Zag形式走線

How Fiber Weave Effect Affects Signal Integrity

Recently, due to the development of AI applications, the application frequency of high-speed differential signals have become higher and higher, and the requirements for signal integrity have also increased. Due to skew caused by factors such as lengths mismatch of traces and asymmetry of the reference layers, it has the increasing impact on the bit error rate of the entire system. This chapter discusses the impact of signal delay caused by the fiberglass weave effect and the corresponding possible solutions.

Phase delay due to skew

Insertion Loss due to skew

The resonant frequency of Insertion Loss can be calculated from the above formula, that is to say, the resonant frequency is related to the dielectric constant of the glass fiber, resin and the length of the glass fiber that the trace passes through.

Here are some common solutions:

1. The differential pair runs on glass fiber in Zig-Zag form.

2. Rotate the relative angle between the glass fiber and the differential trances by 7 to 10 degrees.

3. Choose fiberglass cloth with the same number of glass yarns in the warp and weft directions.

4. Choose fiberglass cloth with a Dk similar to that of the resin.

Routing in Zig-Zag form