蜿蜒型延遲線的快速分析方法

Abstract

在高速數位電路系統中，為使邏輯閘切換能夠同步，在做電路板上元件的連接時常須加入延遲線，而最常用的就是蜿蜒型延遲線。 本論文介紹以等效電路的方式來分析蜿蜒型延遲線傳輸特性的問題。整個結構由一個或多個單位晶格構成，而每個單位晶格又由三個結構單元所組成，本論文先以HFSS的全波分析軟體求其個別結構單元的S參數，再將之轉換成雙埠網路的Z參數，進而求取其T型等效電路的元件值。之後再以串接方式建構單位晶格及完整延遲線結構的等效電路，並利用SPICE模擬其傳輸特性。本法的主要優點在於可以快速分析相同耦合間距但不同單位晶格數和/或耦合長度的蜿蜒型延遲線結構。 在應用方面，本論文探討下列兩種蜿蜒型延遲線常見的現象：（1）由耦合電感及電容引起的輸出超前現象，（2）階梯波失真現象。分析結果顯示：（1）當總長度固定，較少晶格的結構因耦合長度較長，階梯波失真較嚴重，尤其耦合間距較小時。（2）反之，若晶格數增加，耦合長度縮短，彎角效應增加，但階梯波失真較不明顯，尤其是採用較大的耦合間距時。（3）較大耦合間距雖可改善信號傳輸效果，但須耗費較大板面。

In high-speed digital system, in order to synchronize the logic gates, use of delay line in board level interconnection is usually required. A popular delay line design is the meander delay line. In this thesis, we develop an equivalent circuit approach to analyze the stripline type of meander delay line. The all structure is composed by one or more unit cells, and each unit cell can be constructed from three types of building block.The full wave analysis program-HFSS is first used to determined the S parameters of each building block, which are then, it can be transformed into the two-port Z parameters for the extraction of T-type equivalent circuit parameters. These circuits are them cascaded to from the equivalent circuits of a single unit cell and the complete delay line structure. SPICE simulation is then performed to evaluate delay lines transmission characteristics. For a fixed coupled-line spacing, the ability to analyze structures with different numbers of unit cell and/or lengths of coupled line are the two main advantagesof the proposed method of analysis.. In the application, we discuss the two common phenomenon of the meander delay line: (1) speed-up of the signal due to inductive/capacitive coupling between coupled lines and(2) the ladder wave distortion. From the results obtained, it’s found that: (1) if the total length is fixed, using less number of unit cells which results in longer coupled line length, ladder wave becomes serious, especially for the narrower coupled line spacing. (2) On the contrary, increasing the number of unit cells, the effects of bends increase, but ladder wave distortion is redused, especially when coupled line spacing gets wider. (3)Although wider coupled line spacing can improve the signal transmission, it consumes more board areas.