以低溫共燒陶瓷製程設計之寬頻縮小化共模濾波器

Abstract

本論文提出一種表面貼著元件(Surface-Mount Device, SMD)形式的共模濾波器及其微縮化的方法與寬頻設計的技術。此共模濾波器應用多層蘑菇結構(multilayer mushroom structure)達到微縮化並設計於低溫共燒陶瓷(Low Temperature Co-fire Ceramic, LTCC)基板上。此共模濾波器，擁有六個接腳(pin)，包含四個信號線接腳與兩個接地接腳。該濾波器可安裝在印刷電路板(PCB)上採用表面貼裝技術（SMT）。由對稱設計的信號線，使共模訊號和差模訊號得到不同的效果。共模信號的返回電流(return current)將通過蘑菇結構被抑制，而差模返回電流將不通過此蘑菇結構。本文之濾波器，系利用低溫共燒陶瓷製程之可多層化特性、蛇行狀繞線(meander line routing)、及多層蘑菇結構(railway-shaped mushroom structure)達到微縮化特性；並以此製作表面貼著元件類型的共模濾波器，此濾波器的大小是0.021λg × 0.036λg與相應的實際尺寸為 1.2 mm × 2 mm。共模雜訊可被降低10dB以上，從1.5GHz至3.9GHz的89％寬頻帶抑制，且差模信號的完整度和傳輸品質保持良好的特性。除此，本文將針對利用多層蛇行鐵路狀蘑菇結構下的不同架構、物理參數與特性變化進行分析，並以此結構引入新的傳輸零點，以此增加頻寬之設計。

A design concept of broadband and miniaturized SMD-typed common-mode filters applying multi-layer mushroom structure is proposed in this thesis. Based on the low-temperature co-fired ceramic fabrication technology, miniaturized common-mode filters with six pins are realized. The filters can be mounted on PCB using surface-mount technology (SMT). By routing the signal traces symmetrically, different effects are produced to common mode and differential mode. For common mode signal, the return current go through the railway-shaped mushroom structure, while the odd-mode return current is zero at the railway-shaped mushroom structure. In this paper, the common mode filter was miniaturized by using multilayer structure, meander lines and railway-shaped mushroom structure. The SMD-typed filters are unlike the conventional common-mode choke. The filter size is 0.021λg × 0.036λg with the corresponding real size 1.2 mm× 2 mm. It is found that the common-mode noise can be reduced over 10dB from 1.5 GHz to 3.9 GHz with the 89% of fractional bandwidth. In addition, the design, analysis and investigation of the effect on differential geometry parameters of the railway-shaped mushroom structure. More importantly, the good differential signal integrity is still maintained within the wide stopband.