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LMH1297 LMH1219 LMH1208 的75欧姆单端输入输入线长的问题。

user4123229
Prodigy 60 points

Other Parts Discussed in Thread: LMH1208, LMH1297, LMH1219, LMH1228

以LMH1208来举例：SDI_OUT1± 和SDI_OUT2± 的单端75欧姆输出，用户手册上说尽量缩短芯片端口到BNC的距离，但是我现在有一个产品，硬件上已经决定了LMH1208到BNC的距离比较长，且中间有经过接插件（金手指，以及SMTEC30G速率接插件），（参考附件）。  请问这种情况我们应该如何处理？更改板材能否达到效果？   以上情况需要支持 12G速率的  2160P50SDI

  • 0
    Prodigy 60 points
    以及LMH1297和LMH1219 单端75欧姆12GSDI输入。 共有10个BNC ，芯片也不能放在BNC所在的板子上。
  • 0
    TI__Guru**** 295050 points
    您好，我的建议是SDout输出尽可能的靠近BNC接口，因为是从插值损耗，AC 耦合，输出上升沿和下降沿三个方面考虑的，从而来满足SMPTE 标准。您现在实际有没有验证信号的完整性？ rise time，fall time，眼图都还理想吗?

    datasheet中有SMPTE 对SDI接口的几点要求：TI recommends placing the LMH1208 as close as possible to the 75-Ω BNC ports to meet SMPTE specifications.


    1. Return Loss: This specification details how closely the port resembles 75-Ω impedance across a specified frequency band. The LMH1208 features a built-in 75-Ω return-loss network on SDI_OUT1 and SDI_OUT2 to minimize parasitics and improve overall signal integrity.

    2. AC Coupling: AC-coupling capacitors are required for transporting uncompressed serial data streams with heavy low-frequency content. The use of 4.7-μF, AC-coupling capacitors is recommended to avoid lowfrequency DC wander.

    3. Rise/Fall Time: Output 75-Ω signals are required to meet certain rise and fall timing depending on the data rate. This improves the eye opening observed for the receiving device. The LMH1208 SDI_OUT1 and SDI_OUT2 cable drivers feature programmable edge rate adjustment to meet SMPTE rise and fall time requirements.
  • 0 回复 Kailyn Chen
    Prodigy 60 points

    我也是看到手册这个地方的说明

    目前还没有实物，也没法看眼图质量如何.

    之前用过LMH1208/LMH1228,但是1208和BNC很近，新产品中产品条件限制了1208和BNC的距离比较远。  所以想提前咨询一下。

    或者有没有资料 线长不同，眼图等差距对比说明呢。