差模傳輸線跨越不連續參考平面及EMI之效應分析

Abstract

在高速數位系統的設計中，隨著信號頻率越來越高，差模傳輸線逐漸成為高速訊號採用的傳輸界面，同時成為高速印刷電路板上積體電路的主要相互連接的高速傳輸架構。與單端信號傳輸相比，雖然差模信號需要雙倍數量的傳輸線，但其抗串擾和抑制電磁干擾的能力優於單端。然而，如果不對差模傳輸線對進行恰當的平衡、佈局，或者存在共模信號，就可能產生嚴重的EMI問題。 本文旨在探討差模傳輸線在跨越不連續參考平面所產生的EMI效應分析。以及在印刷電路板完成佈局後，準備進入印刷電路板製作前，會進行接地銅箔鋪設的步驟。當此步驟所產生的接地銅箔包圍鄰近的差模傳輸線則會形成了差模屏蔽式共平面波導(CPWG)的結構。本文則探討連續接地銅箔與差模傳輸線間的間距對於抑制EMI防護上的不同效果。

In the design of high-speed digital system, when the signal frequency becomes higher and higher, the differential pair becomes the transmission interface used in high-speed signal and the main connection high-speed transmission architecture of the integrated circuit on the high-speed PCB. Compared to single-ended signal transmission, although the differential signal needs double transmission lines, its ability to resist cross-talk interference and electromagnetic interference is superior to the sigle-ended signal. However, if the differential pair is not properly balanced, or laid out, or if common mode signal exists, serious EMI problems may arise. This paper is to find out the EMI effect which is produced when the differential transmission line passes over discontinuous reference plane. Before the PCB fabrication, the PCB board will be fully covered with the Copper plane. At this step, the differential transmission line surrounded by the continuous Copper plane becomes the coplanar waveguide with ground (CPWG) architecture. The paper disscusses the different effects of the gap between the continuous Copper plane and the differnetial transmission line on the reduction of EMI protection.