寬頻共模濾波器之設計

Design of Broadband Common-Mode Filters

翁翠微(Tsui-Wei Weng)

指導教授 ： 吳宗霖

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.10248

摘要

因應市場需求，現代電子產品體積越來越小，功能走向強大多元，操作方式不斷求新求快，電路亦趨密集與複雜，致使信號完整度和電磁相容問題日益嚴重。在高速數位電路傳輸介面中，由於時脈偏差與佈局考量所造成差動電路的不平衡輸出，寬頻共模雜訊隨之而生，進而造成嚴重的電磁干擾問題。故如何濾掉寬頻的共模雜訊且同時維持良好的信號完整度，遂成為當前重要的研究課題。
過去共模濾波器以鐵磁性材料做成，顯已不適用於現今高頻電路系統；後來內埋式共模濾波器的概念被提出，主要以蕈狀結構或缺陷式結構來實現。但蕈狀結構複雜，且需要多層金屬板來實現，成本耗費大；而缺陷式結構所占面積龐大，且比例頻寬小，兩者均缺乏效益。針對以上缺點，本論文致力於以成本低廉之印刷電路板實現寬頻共模濾波器之設計，並提出一套有效且有系統的設計方法。
本論文提出一種新型吉赫茲寬頻共模濾波器，係由一對差動傳輸線及C字型缺陷式接地結構所組成。藉由設計C字型缺陷式接地結構和其上方的蜿蜒傳輸線，可巧妙地在共模產生兩個傳輸零點，進而達成寬頻的共模抑制。同時，由於結構的對稱性，差模信號能保持良好的傳輸品質。
在理論分析方面，本論文提出新的結構建立一精準等效電路模型，藉此推導出共模傳輸零點公式，並根據此公式，提出一套完整的設計流程。利用此設計方法，可以設計出任意兩個指定的共模傳輸零點，這對實務應用相當有幫助。而本論文利用此流程設計出一共模濾波器，其比例頻寬能達到130%，電路尺寸僅0.04 λg2，而只需要使用兩層金屬板，與文獻中的共模濾波器相比，這種新技術能使比例頻寬大幅提升，電路尺寸也明顯縮小，效能甚為優越。
根據共模傳輸零點公式，本論文更進一步探討共模傳輸零點與此寬頻共模濾波器結構間的關係。其中，共模傳輸零點的個數與其如何隨結構的變化而移動皆有詳細的討論，並以此建立三個共模傳輸零點之設計流程。利用此設計方法所實現的共模濾波器，其比例頻寬達129%，而電路尺寸則較文獻縮小，僅為0.10λg2。

關鍵字

共模濾波器 ； 缺陷式接地結構 ； 共模雜訊 ； 信號完整度 ； 高速數位電路

並列摘要

In this thesis, a GHz broadband common-mode filter is firstly proposed by using a C-shaped PGS plus meandered signal lines. An equivalent circuit model is constructed to predict common-mode behavior of the proposed filter, and a condition for common-mode transmission zeros is derived accordingly. Moreover, a design procedure is provided and discussed. Based on design methodology, a common-mode filter with two desired transmission zeros is designed with a FBW of 130% and a compact size of 0.21 λg ×0.21 λg. Compared with the related literature, the proposed filter possesses the largest FBW with a very compact size.
Next, a theory of multiple transmission zeros of the proposed common-mode filter is given to illustrate the effect of line meandering. With an in-depth discussion on the transmission zeros condition, the relationsips between transmission zeros and circuit parameters are investigated; meanwhile, conditions for generating three transmission zeros are given. The analysis shows that the electrical length ratio and the characteristic impedance ratio of the meandered signal lines and etching slots of the PGS are critical to generate multiple transmission zeros in the frequencies of concern. Finally, from the analysis, a common-mode filter with three transmission zeros is designed with a FBW of 129 % and a compact size of 0.31 λg ×0.31 λg. Compared with other work in the related literature, it has a superior FBW performance with a compact size.
The proposed common-mode filters have the merits of wide common-mode stopbands, compact sizes, and simple structures. Most importantly, systematic design procedures and a full picture on common-mode filter design are described and illustrated in this thesis, which should be helpful for future applications.

並列關鍵字

Common-mode filters ； Patterned ground structure ； Common-mode noises ； Signal integrity ； High-speed digital circuit

參考文獻

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