原创 端接_10

5.4 Tee/star

B1 Star

分支表现出明显的振铃

B2 Tee型结构+长分支

B3 Tee结构+短分支

如前所述，可以通过将两个分支的阻抗增大为原来的2倍，并进行末端端接，可以得到较好的信号质量。[24]

仿真显示，末端端接不能满幅值驱动，可以考虑采用thevenin端接来改善

5.5 Advanced multi-drop

当线路上存在多个负载时，负载有可能不能同时放置在线路的末端，或者线路上存在多个双向I/O的时候，每个I/O器件都能够单独的驱动总线。这时，可以采用末端端接的方案来端接总线。某些情况下，可以采用一些独特的设计。

5.5.1 uni-direction multi-drop
(1) localbus: PLX9054 localbus 和four AudioCodes AC491(DSP) localbus。Clock: 35MHz。只考虑数据从PLX9054驱动到AC491.四片AC491在电路板上无法放在在线路的末端。

[25]you can arrange to have a couple of loads nearby, and a couple of loads lumped together at a distance, here is my preferred topology (please used fixed width font):
         LOAD A                                        LOAD C
DRIVER---+-----SERIES-R---------------------------+
         LOAD B                                        LOAD D
Select a powerful, low-impedance CMOS driver with a risetime of about 2-3 ns. Keep the total net length comprising the DRIVER, LOAD A, LOAD B, and the SERIES-R down to 4 inches or     less. The distance from the SERIES-R to loads C and D can be anything, but you will want to keep loads C and D within a couple of inches of each other. Lastly, pick the SERIES-R to match the expected transmission line impedance of the long section of the net.

A1 不端接

B1 串联端接

信号质量得到明显的改善。