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摘要
过去的低速电路中,微带线和带状线的阻抗不连续不会对信号的传输产生影
响。然而,当数据传输速率上升到 GHz 成为高速电路后,单端信号线就会受到各
种噪声源的影响。相比之下,差分线具有更多优点。比如,目前高速数字通信就
采用低压差分信号(LVDS)线对作为高速数据传输线,用以提高信号的完整性和
减小电磁干扰(EMI)。
在实际的 PCB 设计中,由于元器件的密集度和布局布线的复杂性不断增加,
走线不可避免的出现拐角。这使得两条传输线的线长不一致,从而引起了时延差。
如果线长的偏差超过了上升空间沿拓的 20%,就会使差分信号边沿失真,从而使
得部分差分信号转化为共模信号,造成共模噪声,导致信号完整性问题及其辐射
效应。于是针对共模噪声的产生,本文首先比较了四种模型,并提出了自己的分
析模型,接着利用 S 参数分析了它的共模噪声。其次本文介绍了一种补偿电容的
方法,并对其进行了仔细分析。最后提出了两种新的补偿方法,实验证明第一种
补偿方法由于改变了线间距而没能有效地减小共模噪声;第二种补偿方法因有效
地减小了差分线对的不对称性,从而抑制了差分信号向共模信号的转化。同时,
本文对差分线上过孔的物理结构及其如何影响信号的传输质量做了详细的分析,
其中包括差分过孔的孔径、焊盘以及反焊盘对信号完整性的影响,从而确定了应
该选择孔径小、焊盘半径小及反焊盘半径大的差分过孔,该结论为差分走线上差
分过孔的设计提供了有力依据。
综上,本文提出的有关差分拐角的补偿方法以及对差分过孔的研究为差分传
输线的设计提供了一定的理论基础。
关键词:信号完整性 差分传输线 S 参数 差分信号 共模噪声 差分过孔

Abstract
In the low-speed circuits, the impedance discontinuity of microstrip and stripline
don’t have an impact on the signal transmission. However, as the data transfer rate
rising to the GHz, the single-ended signal lines will influenced by various noise sources.
In contrast, differential lines have a variety of advantages. Today's high-speed digital
communications use low-voltage differential signal pairs (LVDS) as high-speed data
transmission lines,which is used to improve signal integrity and reduce EMC.
Due to the intensity of component placement and routing complexity increased, in
the actual design of PCB, unavoidably there will be a corner in the line, and those make
the length of the two transmission lines inconsistent which will cause a transmission
delay. If the length deviation exceeds the space extension by 20%, it will makes part of
the differential signal edge distortion and makes a differential signal into a common
mode signal,which will cause common mode noise and lead to signal integrity issue
and radiation effects. For the generation of common mode noise, this paper compares
four models,put forwards its own model, and use S-parameter to make an analysis of its
common-mode noise. Then this paper describes a method of compensation capacitor
and makes an analysis of it. Finally, two new compensation methods are proposed and
the experiments show that the first compensation method is not effective to reduce
common noise due to the distance between transmission lines have been changed.
However, the second compensation method is effective to reduce the asymmetry
between the differential lines, which can suppress differential to common-mode signal
conversion. At the same time, the physical structure of differential vias and how it
affects the physical structure of the signal transmission quality are detailed analysis in
this paper, including impact of the pore size, pads and anti-pad of differential vias on
signal integrity, so as to determine that we should choose the differential vias with a
small pore size, a small pad radius and an anti-pad radius, which provide a basis for the
differential vias design on differential lines.
The proposed compensation method for the corner on differential lines and the
study of differential vias design in this paper have provided a theoretical basis for the
differential transmission lines.
Keyword: Signal integrity Differential transmission line S parameters
Differential signal Common mode noise Differential via

目录
第一章 绪论 ......................................................................................................................... 1
1.1 本课题研究背景 .................................................................................................... 1
1.2 研究现状 ................................................................................................................. 1
1.3 本文研究内容和安排 ........................................................................................... 2
第二章 高速电路中的信号完整性理论 ........................................................................... 5
2.1 高速电路的基础理论 ............................................................................................ 5
2.1.1 高速电路的概述 ........................................................................................... 5
2.1.2 高速信号的定义 ........................................................................................... 6
2.1.3 高速电路中的电气模型............................................................................... 6
2.2 信号完整性的理论分析 ....................................................................................... 7
2.2.1 信号完整性概述 ........................................................................................... 7
2.2.2 信号完整性的研究方法............................................................................. 10
2.2.2.1 信号完整性的电磁场理论分析 ............................................................. 10
2.2.2.2 信号完整性的电路分析 ......................................................................... 12
2.3 传输线理论及其分析方法 .................................................................................. 13
2.3.1 传输线的分类及其基本特征 ................................................................... 14
2.3.2 传输线的研究方法 .................................................................................... 16
2.3.3 传输线的原理 ............................................................................................ 16
2.4 本章小结 .............................................................................................................. 18
第三章 高速差分传输线理论及其设计方法 ................................................................. 19
3.1 差分线与差分信号 .............................................................................................. 19
3.2 奇模与偶模 .......................................................................................................... 20
3.3 差分阻抗与共模阻抗 .......................................................................................... 21
3.3.1 差分阻抗与奇模阻抗 ................................................................................ 21
3.3.2 共模阻抗与偶模阻抗 ................................................................................. 22
3.4 差分、共模信号及奇模、偶模电压分量 ........................................................ 23
3.5 高速差分线对的 PCB 设计方法 ........................................................................ 24
3.5.1 差分线对的等长 ......................................................................................... 24
3.5.2 差分线间的等距 ........................................................................................ 24
3.5.3 差分线对与其他信号的距离 .................................................................... 25
3.5.4 差分线对中高速低压差分信号(LVDS)的应用 ................................. 26
3.5.5 其他一些设计规则 .................................................................................... 26
3.6 本章小结 .............................................................................................................. 27
第四章 差分线对拐角的分析与补偿设计 ..................................................................... 29
4.1 差分线拐角的建模与仿真 .................................................................................. 29
4.2 差分线的 S 参数理论及共模噪声问题 ............................................................ 31
4.2.1 差分线传输线的 S 参数理论 .................................................................... 31
4.2.2 差分线的混合 S 参数理论 ........................................................................ 32
4.2.3 差分线对拐角的模型分析 ........................................................................ 33
4.3 差分/共模信号的转化 ........................................................................................ 35
4.4 补偿模型的分析及实验结果............................................................................. 36
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