司机和车辆现在更依赖于高级驾驶员援助系统（ADA）。虽然在此处使用雷达和LIDAR等系统，但是，在车辆中的ADA也依赖于高质量的视频图像。由于车辆变得更加自主，这些视频流的质量将更为重要。从设计方面，高速视频链路设计需要考虑如何维护如此恶劣环境中所需的信号完整性。
有些汽车已经采用了系统，可以自动识别道路标志或检测汽车在自己的车道之外漂移。这些是至少目前，只能使用车辆内部和周围的视频传感器实现的特征。
Even though the use and importance of video data is increasing in the automotive sector, there are still no globally recognised standards in place to define how the video data should be shared around a vehicle. It is still left up to the manufacturer to choose their preferred solution. This includes proprietary standards such as APIX, GSML and FPD-Link, which support speeds of 6 Gbit/s, 10 Gbit/s and 13 Gbit/s respectively. In addition, the use of automotive-grade Ethernet with speeds of up to 1 Gbit/s is also increasing.
随着带宽和分辨率的需求增加，普通车辆中使用的视频链路数量也将构建。标准清晰度仅短时间内，对于逆转摄像机而言完全良好，将用高清，高帧传感器代替，高分辨率在高行程速度下捕获。
Maintaining signal integrity is key
从设计方面，高速视频链路设计需要考虑如何维护如此恶劣环境中所需的信号完整性。添加到视频数据路径的每个组件都会引入损耗，这将影响所使用的同轴电缆的选择，连接器的质量以及信号如何路由到链路的物理接口（PHY）。保持信号完整性是至关重要的，但这需要通过添加适当的防止电位脉冲和故障条件的保护水平来平衡，例如电池轨道的短路。该界面还需要承受高达10kV的瞬态电压。必须仔细考虑与所使用的保护装置相关联的插入电容的影响，以便在不影响信号完整性的情况下提供保护。可以在此找到更多细节白皮书.
作为示例，推荐用于将ESD设备放置尽可能接近PHY以保护IC。此建议已发生变化，ESD保护的首选位置现在可以尽可能靠近连接器放置保护。这通常意味着ESD设备现在在DC阻塞电容器的连接器侧，如图1所示。如果使用可选的共模扼流圈（CMC），这也意味着将ESD设备从PHY侧移动到CMC的连接器侧。
ESD保护的最佳位置是什么？
从技术角度来看，ESD保护的最佳位置实际上尽可能靠近连接器。这里，ESD设备可以将ESD脉冲撞击到地，同时仍然从电路和尤其是PHY本身的物理偏差。这就是为什么汽车领域中的一些规范的原因，例如开放联盟特殊兴趣组（SIG）提出的那些规格，现在建议ESD保护更接近ESD脉冲进入PCB的点。目的是根据系统的需求而不是一个特定组件提供ESD保护。图2显示了如何改变ESD设备的位置。
Also, because the ESD protection device is now closer to the ‘outside world’ it will be exposed to different threats. This includes a potential fault on the cable that could lead to a short between a signal and a supply rail. In an automotive environment, this means the ESD device needs to be able to withstand a short of at least 12 V across its terminals without failure. If the ESD device were placed behind the CMC and DC blocking capacitors, this requirement is not valid anymore. Figure 1 includes a selection of devices that could be used in either of the two positions, highlighting the different reverse standoff voltage, (Vrwm.).
Simulations are essential to modern automotive designs
在汽车设计中，项目概念阶段模拟的重要性正成为必不可少的。Nexperia了解这一点，并支持ESD事件本身的仿真以及SI模拟。可以使用种子（系统有效的ESD设计）模型进行ESD保护装置的评估。
Simulation using the SEED methodology considers the interface along with the rest of the circuit. Models are based on an equivalent circuit to represent the PHY, CMC and blocking capacitors. Both static and dynamic behaviour of the ESD protection can be modelled. Using SEED simulations and models the design engineers can test their ESD circuitry design choices and use the results to help them choose the right ESD protection device, even at the concept phase. Nexperia has used this approach to characterise its ESD protection devices and analyse how they perform against initial and residual currents induced by a controlled electrostatic discharge. Nexperia also provides S-parameter data for all its ESD protection devices, including those used for High-Speed interfaces and especially video links. The S-parameters can be used by design engineers in the SI simulation of their individual system.
Discover more information aboutNexperia's ESD products for multimedia bus protection in the automotive industryand to learn more about how SEED models and simulation are used in the protection and SI of high-speed automotive interfaces, check out thisuseful resource.
作者：Andreas HardockAndreas Hardock在汉堡的技术大学获得了他的博士学位，专门从事信号完整性领域。自2015年以来，Andreas一直在汽车行业为BHTC和大陆工作，他参与了ESD和EMC主题。在2020年，他加入了Nexperia，主要关注汽车高速应用中的ESD。
