基於全通濾波器之共模濾波器設計

Abstract

若高速差動傳輸系統中的共模雜訊流經轉接介面等不連續處時，將會有輻射能量以干擾的形式而產生，並衍生電磁干擾及射頻干擾等嚴重問題。實務上常使用共模遏流線圈或共模濾波器將共模雜訊濾除。共模遏流線圈雖然具有體積小以及價格低的優勢，但其在高頻卻受到導磁係數下降的限制，導致整體效能下降。另一方面，大多數之共模濾波器通因此其體積難以縮小，也因此應用範圍嚴重受到限制。在本論文中，提出多種基於全通濾波器之共模濾波器，此類濾波器可同時具有共模遏流線圈與傳統共模濾波器之優勢。首先，此類共模濾波器的差模響應可以被合成，且理論上可以達到無限好的響應，因此可以符合各種訊號完整度的要求。其次，本篇論文中共提出三種不同共模響應的共模濾波器，包含帶止共模濾波器、低通共模濾波器與無反射式共模濾波器，因此，此類共模濾波器可根據需求適用於不同的場合，擴大此類共模濾波器的應用範圍。此外，本篇論文中針對各種響應之共模濾波器都有完整的合成程序，因此可讓設計者能預先決定規格，並迅速得到完整電路，大幅減少設計時間。另一方面，由於此類共模濾波器皆使用集總元件，因此很容易實現於不同的製程之中，例如印刷電路板、低溫共燒陶磁以及薄膜製程。相較於傳統共模濾波器，此類濾波器容易針對不同應用情境進行最佳化，例如減少製作成本或者達成縮小化設計。最後，在每一章節中，各種架構之共模濾波器都經實際製作與量測，其結果顯示此類架構之共模濾波器最終響應皆與理想電路相近，因此可驗證此類架構之共模濾波器在非理想效應(包含元件寄生效應以及元件損耗)存在下，仍具有實務上的可行性。

In differential signal transmission systems, common mode (CM) noise is one of the most serious sources that cause the radio frequency interference/electromagnetic interference (RFI/EMI) problems, which may degrade the throughput of the wireless circuits or cause interferences to other electronic devices. Conventionally, common mode chokes (CMCs) and common mode filters (CMFs) are used to eliminate the CM noise. Though CMCs have the advantages of compact size and low cost, they suffer from degradation of performance due to low permeability at high frequency. On the other hand, most of the previous CMFs suffer from large size, and therefore the applications are strictly limited. In this dissertation, proposed CMFs based on all pass filters can achieve both advantages of CMCs and CMFs. First, the differential mode (DM) responses can be synthesized as pre-specified functions to meet arbitrary signal integrity (SI) specification. Second, three different CM suppression responses, such as bandstop, low pass, and reflectionless can be achieved to meet requirements in various applications. In addition, complete synthetization flows of all the proposed CMFs are stated. Therefore, it can shorten the time for the engineers to validate the performance of CMFs in real applications. On the other hand, the proposed CMFs can be easily implemented in various process, such as PCB, LTCC, and thin film process. Compared to those CMFs based on physical resonance structures, the proposed CMFs can easily meet different requirements such as cost reduction or miniaturization. At last, in each chapter, the proposed CMFs are implemented and measured, and the measured results show good agreement to ideal circuit models, even if the losses and parasitic effects are included. Therefore, the feasibility of the proposed CMFs are also validated in practice.