Drivers and vehicles are now increasingly relying on advanced driver assistance systems (ADAS). In the ADAS of vehicles, although the use of radar and lidar systems is very important, they are highly dependent on high-quality video images. With the continuous improvement of vehicle automation, the importance of the quality of these video streams has become increasingly prominent. From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments.

How to provide excellent ESD protection for automotive A/V interfaces

Drivers and vehicles are now increasingly relying on advanced driver assistance systems (ADAS). In the ADAS of vehicles, although the use of radar and lidar systems is very important, they are highly dependent on high-quality video images. With the continuous improvement of vehicle automation, the importance of the quality of these video streams has become increasingly prominent. From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments.

How to provide excellent ESD protection for automotive A/V interfaces

Some cars are already equipped with systems that can automatically recognize road signs or detect when the car deviates from the lane. So far, these functions can only be implemented using video sensors inside and around the vehicle.

Despite the increasing use and importance of video data in the automotive field, there is still a lack of globally recognized standards to define the way video data is shared around vehicles. Manufacturers will choose their own preferred solutions. These include proprietary standards such as APIX, GSML, and FPD-Link, which support 6 Gbit/s, 10 Gbit/s, and 13 Gbit/s speeds, respectively. In addition, the use of automotive Ethernet with speeds of up to 1 Gbit/s is increasing day by day.

As bandwidth and resolution requirements continue to increase, the average number of video links used in vehicles will also increase. Not long ago, the standard definition, which was also suitable for reversing cameras, will be replaced by high-definition, high-frame-rate sensors to capture high-resolution images when driving at high speeds.

Maintaining signal integrity is a top priority

From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments. Every component added to the video data path introduces loss, which will affect the choice of coaxial cable, the quality of the connector, and how the signal is routed to the physical interface (PHY) of the link. Maintaining signal integrity is a top priority, but there is still a need to add appropriate levels of protection to prevent potential ESD pulses and fault conditions (such as battery rail shorts). The interface also needs to withstand transient voltages up to 10 kV. The impact of the insertion capacitance associated with the protection device used must be carefully considered in order to provide protection without compromising signal integrity. More detailed information can be found in this white paper.

For example, the past recommendation was to place the ESD device as close as possible to the PHY to protect the IC. This recommendation has long been changed, and now the preferred location for ESD protection is to place the protection as close as possible to the connector. This usually means that the ESD device is now on the connector side of the DC blocking capacitor, as shown in Figure 1. If an optional common mode choke (CMC) is used, this also means moving the ESD device from the PHY side to the connector side of the CMC.

How to provide excellent ESD protection for automotive A/V interfaces
Figure 1. ESD placement options

So, why change the previous method? The original location is close to the PHY, and it is clear that the ESD device is designed to protect the sensitive Electronic circuits of the PHY. In order to do this, the electrostatic shock needs to pass through the DC blocking capacitor and CMC. In this position, the insertion loss associated with ESD protection can be minimized. But it is obvious that other components and parts of the circuit cannot be protected.

What is the best place for ESD protection?

From a technical point of view, the best location for ESD protection should actually be as close as possible to the connector. In this way, ESD can clamp the ESD pulse to ground while still maintaining a physical distance from the circuit, especially the PHY itself. This is why some specifications in the automotive industry, such as those proposed by the Open Technology Alliance Special Interest Group (SIG), now suggest that ESD protection should be closer to the point where the ESD pulse enters the PCB. Its purpose is to provide ESD protection based on the needs of the system, not for a specific component. Figure 2 shows the change in the position of the ESD device.

How to provide excellent ESD protection for automotive A/V interfaces
Figure 2. The physical location of the ESD protection device is closer to the connector

Moving the ESD device closer to the connector can provide protection for more circuits, but because it is close to the connector’s terminals, it also has other effects. These effects will determine the design choices made by automotive engineers when implementing high-speed interfaces (such as video connections). These choices are related to the capacitance introduced by the ESD device and how this affects the rise/fall time of the current digital signal.

In addition, since ESD protection devices are now closer to the “outside world”, they will face completely different threats. This includes potential faults on the cable, which can cause a short circuit between the signal and the power rail. In the automotive environment, this means that the ESD device needs to withstand a short circuit of at least 12V between its terminals without failing. If the ESD device is placed after the CMC and the DC blocking capacitor, this requirement does not need to be considered. Figure 1 includes a selection of devices that can be used in either position, highlighting the different reverse off-state voltages (VRWM).

Simulation is essential to modern car design

In automotive design, the importance of simulation in the concept phase of the project is becoming increasingly prominent. Nexperia (Anshi Semiconductor) knows this well and supports the simulation and SI simulation of the ESD event itself. Efficient system-level ESD design (SEED) models can be used to evaluate ESD protection devices.

The simulation using the SEED method also considers the interface and the rest of the circuit. The model is based on the equivalent circuit to represent the PHY, CMC, and blocking capacitor. The static and dynamic behavior of ESD protection can be modeled. Using SEED simulation and models, design engineers can test their ESD circuit design choices and then select the appropriate ESD protection device based on the results, even in the concept stage. Nexperia (Anshi Semiconductor) has used this method to characterize its ESD protection devices and analyze how they resist the initial and residual currents caused by controlled electrostatic discharge. Nexperia (Anshi Semiconductor) also provides scattering parameter data for all its ESD protection devices, including those used for high-speed interfaces, especially video links. Design engineers can use scattering parameters to perform SI simulations of their independent systems.

Please click here to learn more about Nexperia’s ESD products for multimedia bus protection in the automotive industry, and explore how to use SEED models and simulations for high-speed automotive interface protection and SI.

About the Author

How to provide excellent ESD protection for automotive A/V interfaces
Andreas Hardock

Dr. Andreas Hardock, Application Marketing Manager of Nexperia ESD, graduated from Julius-Maximilians-University in Würzburg in 2010 and received his PhD from TU Hamburg in 2015. He works in the field of signal processing based on VIA-based filters and couplers. Andreas Hardock has been working for BHTC and Continental in the automotive industry since 2015, responsible for ESD and EMV. Since 2020, Andreas has been responsible for the application of ESD in automobiles at Nexperia.

Drivers and vehicles are now increasingly relying on advanced driver assistance systems (ADAS). In the ADAS of vehicles, although the use of radar and lidar systems is very important, they are highly dependent on high-quality video images. With the continuous improvement of vehicle automation, the importance of the quality of these video streams has become increasingly prominent. From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments.

How to provide excellent ESD protection for automotive A/V interfaces

Drivers and vehicles are now increasingly relying on advanced driver assistance systems (ADAS). In the ADAS of vehicles, although the use of radar and lidar systems is very important, they are highly dependent on high-quality video images. With the continuous improvement of vehicle automation, the importance of the quality of these video streams has become increasingly prominent. From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments.

How to provide excellent ESD protection for automotive A/V interfaces

Some cars are already equipped with systems that can automatically recognize road signs or detect when the car deviates from the lane. So far, these functions can only be implemented using video sensors inside and around the vehicle.

Despite the increasing use and importance of video data in the automotive field, there is still a lack of globally recognized standards to define the way video data is shared around vehicles. Manufacturers will choose their own preferred solutions. These include proprietary standards such as APIX, GSML, and FPD-Link, which support 6 Gbit/s, 10 Gbit/s, and 13 Gbit/s speeds, respectively. In addition, the use of automotive Ethernet with speeds of up to 1 Gbit/s is increasing day by day.

As bandwidth and resolution requirements continue to increase, the average number of video links used in vehicles will also increase. Not long ago, the standard definition, which was also suitable for reversing cameras, will be replaced by high-definition, high-frame-rate sensors to capture high-resolution images when driving at high speeds.

Maintaining signal integrity is a top priority

From a design perspective, high-speed video link design needs to consider how to maintain the required signal integrity in harsh environments. Every component added to the video data path introduces loss, which will affect the choice of coaxial cable, the quality of the connector, and how the signal is routed to the physical interface (PHY) of the link. Maintaining signal integrity is a top priority, but there is still a need to add appropriate levels of protection to prevent potential ESD pulses and fault conditions (such as battery rail shorts). The interface also needs to withstand transient voltages up to 10 kV. The impact of the insertion capacitance associated with the protection device used must be carefully considered in order to provide protection without compromising signal integrity. More detailed information can be found in this white paper.

For example, the past recommendation was to place the ESD device as close as possible to the PHY to protect the IC. This recommendation has long been changed, and now the preferred location for ESD protection is to place the protection as close as possible to the connector. This usually means that the ESD device is now on the connector side of the DC blocking capacitor, as shown in Figure 1. If an optional common mode choke (CMC) is used, this also means moving the ESD device from the PHY side to the connector side of the CMC.

How to provide excellent ESD protection for automotive A/V interfaces
Figure 1. ESD placement options

So, why change the previous method? The original location is close to the PHY, and it is clear that the ESD device is designed to protect the sensitive Electronic circuits of the PHY. In order to do this, the electrostatic shock needs to pass through the DC blocking capacitor and CMC. In this position, the insertion loss associated with ESD protection can be minimized. But it is obvious that other components and parts of the circuit cannot be protected.

What is the best place for ESD protection?

From a technical point of view, the best location for ESD protection should actually be as close as possible to the connector. In this way, ESD can clamp the ESD pulse to ground while still maintaining a physical distance from the circuit, especially the PHY itself. This is why some specifications in the automotive industry, such as those proposed by the Open Technology Alliance Special Interest Group (SIG), now suggest that ESD protection should be closer to the point where the ESD pulse enters the PCB. Its purpose is to provide ESD protection based on the needs of the system, not for a specific component. Figure 2 shows the change in the position of the ESD device.

How to provide excellent ESD protection for automotive A/V interfaces
Figure 2. The physical location of the ESD protection device is closer to the connector

Moving the ESD device closer to the connector can provide protection for more circuits, but because it is close to the connector’s terminals, it also has other effects. These effects will determine the design choices made by automotive engineers when implementing high-speed interfaces (such as video connections). These choices are related to the capacitance introduced by the ESD device and how this affects the rise/fall time of the current digital signal.

In addition, since ESD protection devices are now closer to the “outside world”, they will face completely different threats. This includes potential faults on the cable, which can cause a short circuit between the signal and the power rail. In the automotive environment, this means that the ESD device needs to withstand a short circuit of at least 12V between its terminals without failing. If the ESD device is placed after the CMC and the DC blocking capacitor, this requirement does not need to be considered. Figure 1 includes a selection of devices that can be used in either position, highlighting the different reverse off-state voltages (VRWM).

Simulation is essential to modern car design

In automotive design, the importance of simulation in the concept phase of the project is becoming increasingly prominent. Nexperia (Anshi Semiconductor) knows this well and supports the simulation and SI simulation of the ESD event itself. Efficient system-level ESD design (SEED) models can be used to evaluate ESD protection devices.

The simulation using the SEED method also considers the interface and the rest of the circuit. The model is based on the equivalent circuit to represent the PHY, CMC, and blocking capacitor. The static and dynamic behavior of ESD protection can be modeled. Using SEED simulation and models, design engineers can test their ESD circuit design choices and then select the appropriate ESD protection device based on the results, even in the concept stage. Nexperia (Anshi Semiconductor) has used this method to characterize its ESD protection devices and analyze how they resist the initial and residual currents caused by controlled electrostatic discharge. Nexperia (Anshi Semiconductor) also provides scattering parameter data for all its ESD protection devices, including those used for high-speed interfaces, especially video links. Design engineers can use scattering parameters to perform SI simulations of their independent systems.

Please click here to learn more about Nexperia’s ESD products for multimedia bus protection in the automotive industry, and explore how to use SEED models and simulations for high-speed automotive interface protection and SI.

About the Author

How to provide excellent ESD protection for automotive A/V interfaces
Andreas Hardock

Dr. Andreas Hardock, Application Marketing Manager of Nexperia ESD, graduated from Julius-Maximilians-University in Würzburg in 2010 and received his PhD from TU Hamburg in 2015. He works in the field of signal processing based on VIA-based filters and couplers. Andreas Hardock has been working for BHTC and Continental in the automotive industry since 2015, responsible for ESD and EMV. Since 2020, Andreas has been responsible for the application of ESD in automobiles at Nexperia.

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