使用橋式 T 形電路改善導通孔共振

Abstract

在高速實體電路互連中，多層印刷電路板因其靈活且多功能的電路布局特性被廣為使用，然而，如何實作垂直連通與傳輸速度上限息息相關，其中一種熱門的實現方式是導通孔，因為該製程技術成熟且成本低廉。儘管如此，它們的簡單結構卻也是嚴重的缺點，例如當信號線做一三層垂直連通時，在其他層的部分便形成一開路殘段，因此限制信號的傳輸速率上限，所以如何改善其高頻響應是重要的研究課題。本論文旨在將此不理想的共振經過適當的電路設計移至更高的頻率，以使此具成本競爭力的垂直連通技術能用使用在更高速率的信號傳輸。本研究以橋式電路為基礎，本研究以橋式電路為基礎，整合導通孔等效電路，於第一個共振點形成全通電路；另外，考量高頻模擬的複雜寄生效應，本研究另提出基於多重共振腔的橋式電路模型。本研究的兩重點特性為面積小和與跨層信號布局整合，所以能避免使用額外的鑽孔補償或另外銲被動元件。最高至20 GHz的量測與模擬皆顯示頻域和時域上良好的改善，其中，頻域量測結果指出，單導通孔約於8 GHz發生共振，而單導通孔加上本論文提出的電路布局則可將共振往高頻移至16 GHz。此外，時域量測亦指出，對信號速率高於8 Gb/s的數位信號，其眼圖有明顯改善。

Multilayer printed circuit boards (PCBs) prevail in high-speed interconnect because of high routing functionality and flexibility as well as small size. However, the implementation of vertical transition could constrain the speed. Through-hole vias serve as the most popular way on account of the mature process and low cost. Despite the strong preference, their simplicity may also be an Achilles heel since their unused portion widely interpreted as an open stub can impose serious functional constraint on the transmission bandwidth. Accordingly, there is an urgent need for research in ameliorating the high-frequency response. This thesis aims at shifting this undesirable resonance to a higher frequency, enabling the economic technique in high-speed signaling. The research adopts the basic bridged-T network topology to address the issue. Two prominent characteristics of the PCB design are the small area and the integration with the cross-layer signal transition. This design requires neither back-drilling nor additional passive lumped elements. Measurement and simulation up to 20 GHz show significant performance improvement in frequency and time domain. Specifically, the measurement results indicate that the long-stub transition causes resonance at 8 GHz, while the proposed design resonates at 16 GHz. Plus, the measured eye diagrams demonstrate obvious enhancement of eye opening for data rate above 8 Gb/s.