使用RL終端的方法改善SATA差動傳輸線的殘段

Abstract

當一條導線分枝成兩條導線，那分枝點會造成反射，這是由於阻抗不連續。維持固定的特性阻抗將會提供最大能量轉移和最小衰減或損耗，關鍵信號的佈局要避免分枝。SATA設備的實現通常是用點對點連接到主埠端口，SATA端口選擇器的功能可以允許設備連接到兩個不同主埠中的一個，這是帶有多工器的解決方案，但那將會是相對複雜又昂貴的。 針對一個SATA應用的特例，SATA設備被連接到兩個不同資料率的SATA主埠。SATA設備的差動對分枝為兩對分枝線，從設備到主埠的主要傳播通路被稱為eSATA路徑，它是工作在3 Gbps (第二代)，而另一條被稱為iSATA路徑，它是工作在1.5 Gbps (第一代)。eSATA路徑在沒有額外晶片負載情況下帶有54.16 mils的殘段而iSATA路徑則是帶有49 mils的開路殘段，我們可以使用被動元件來改善SATA差動傳輸線的殘段效應。在有額外晶片負載的eSATA路徑上，RL終端的方法可以使用簡單的電感和電阻形成如同高通濾波器，這個解決方案在3 GHz時可以改善55%的介入損失。

When a wire branches into two wires, the branch point will cause reflection. This is due to impedance discontinuity. Maintaining constant characteristic impedance will provide maximum energy transfer with minimal attenuation or loss. Avoid branching in the layout of critical signal. The SATA device is normally implemented with point-to-point connection to host port. The port selector function of SATA allows a device to connect to one of two different hosts with the multiplexer solution. But that will be relatively complex and expensive. For a special case of SATA application, the SATA device is connected to two SATA hosts with different data rates. The differential pair of SATA device branches out into two branch lines. The main communication channel of device to host is called the eSATA path that works at data rate of 3 Gbps (Gen2) and the other is called the iSATA path that works data rate of 1.5 G bps (Gen1). The eSATA path has stub of 54.16 mils without extra chip loading and iSATA path has open-ended stub of 49 mils. We can use passive components to improve the effect of stub for SATA differential transmission line. The method of RL termination uses simple inductor and resistor as high-pass filter on the eSATA path with extra chip loading. This solution had 55% insertion loss improvement at 3 GHz.