多層薄膜式耦合傳輸線共模濾波器設計之研究

Abstract

薄膜式共模濾波器被應用於抑制當IEEE1394、USB2.0 以及HDMI等以差動式傳輸(differential transmission)方式傳遞訊號時，因線路本身不完美對稱或外在輻射干擾等原因造成的「共模雜訊」。本研究中，提出一從元件相關尺寸與材料性質等出發，直接預測薄膜式耦合傳輸線共模濾波器(thin-film coupled transmission line common mode filter)相關電性表現的方法。本研究成功地以類解析解的方式建立一數學模型，將薄膜式耦合傳輸線共模濾波器電性表現以公式型式表示出來。本研究先利用有限元模擬軟體建立數個相異元件模型驗證公式預測之準確性，並驗證改變相關參數所造成濾波器效能的影響；除此之外，也驗證當鐵磁層具隨頻率變化與否之磁耗損性(magnetic loss)時所造成濾波器效能的影響；最後針對薄膜式耦合傳輸線共模濾波器Scc21 第一個極小值頻率點進行理論預測與模擬驗證以達到濾波器設計的初衷。從相關比較圖表顯示，本研究所提出的方法除了能夠有效地預測薄膜式耦合傳輸線共模濾波器相關之電性表現外，在參數改變的預測上也極正確，且符合物理意義；並且也能藉本研究之方法看出磁耗損性對薄膜式耦合傳輸線共模濾波器濾波效能的影響；濾波器Scc21 第一個極小值頻率點的預測也能符合趨勢。本研究所提出之薄膜式耦合傳輸線共模濾波器分析與設計方法，物理意義明確；並且由於是從元件尺寸及材料性質直接預測濾波器電性表現，將提供設計者一初期設計時的參考指標。未來將能以本研究所提出之分析方法進一步對濾波器進行優化設計；更能將此分析方法，延伸分析其他不同傳輸金屬佈局型式的薄膜式共模濾波器。

Thin-film common mode filter is applied to suppress the common mode noise which results from non-perfect-symmetric circuit or external radiation. This work derives a method which predicts the electric performance of thin-film coupled transmission line common filter from component dimensions and material property. This work sets up a mathematical model and expresses the electric performance of thin-film coupled transmission line common filter with quasi-analytical formulae. Firstly, this work derives mixed-mode scattering parameter transformation by lossy coupled transmission line model. This work constructs the distributed equivalent circuit model of thin-film coupled transmission line common filter, and derives the analytical formulae of the distributed parameters; then puts them into the transformation above and rearranges to obtain the mixed-mode scattering parameters we concern. This work utilizes FEM simulator to construct several components to verify the formulae prediction and the influence on the filter while changing related parameters; also to verify the influence on the filter while the magnetic loss (frequency-dependent or frequency-independent) of the ferrite layer is considered; finally, to verify the prediction of the first lowest peak of Scc21 of thin-film coupled transmission line common filter. According to the verification, it shows that the method this work introduces is effective and corresponds with physical sense. The method that directly predicts the electric performance from component dimensions and material property also provide a reference for filter design. In the future, one can optimize the common mode filter design by this work and can also extend this work to analyze other thin-film common mode filter with various type of transmission line layout.