How to solve the EMC problem of high-speed data connection in cars

With the gradual development of China's automobile industry towards the direction of "software defined automobile", the whole vehicle development is gradually carried out around the SOA electronic and electrical architecture centered on the intermediate integration OIB and sub-domain control VIU, with rich data processing capabilities. An efficient hardware system can take over the active operation of the vehicle. With the support of huge computing power, it not only improves the stability of vehicle control, but also promotes the hardware upgrade and evolution of the whole life cycle. As the amount of information increases, EMC high-speed data connection has become a necessary choice for intelligent driving.

Figure 1. New electronic and electrical architecture

The era of electrification of automobile and the whole society has come, and various EMI related problems have emerged in the modern automobile environment. This EMI effect leads to signal weakening or damage; The transmission signal solution consists of various connections. Once there is a problem with the signal, it may lead to abnormalities of important sensors and ADAS systems, sometimes even devastating consequences.

EMC Challenges

The strict management of vehicle interference signal (EMI) is one of the most serious challenges faced by all on-board equipment. With the increase of data transmission, the demand for signal transmission rate is also increasing. The first test in this field is to set the limit and bandwidth of fast connection technology. The purpose of automobile industry and automobile enterprises is to achieve relevant electromagnetic compatibility (EMC) requirements, which are mainly divided into two categories:

First, we must ensure that the electronic products themselves will not emit too much interference signal noise (EMI);

Second, it is not affected by other software noise (EMS).

Note

At present, the key methods to reduce the harm of electronic noise by adopting the vehicle-mounted connection solution of traditional technology include: reducing bandwidth, reducing cable length, and adding expensive shielded cables. However, all of the above processing methods are not the best solution, but they will cause major obstacles to the high-speed communication of the next generation of intelligent driving.

● Reduce bandwidth

One of the simplest and effective ways to reduce electronic interference and improve signal-to-noise ratio (SNR) is to reduce bandwidth.

However, with the increase of the number of excellent cognitive sensors (such as cameras, radars and lidars) and the improvement of transmission quality, the bandwidth demand will increase rapidly.

Here, we can see that the goal of all designs is to continuously improve the connection bandwidth of the EE architecture, so we will encounter many difficulties at the technical level. With the improvement of vehicle edge computing, the additional transmission requirements of software must be improved in theoretical speed. This requires improving the level of the chip in the design process. If EMC wants to meet the requirements, it should be based on high-speed transmission and high bandwidth.

Figure 2. Increase of vehicle bandwidth

● Limit cable length

Reducing the spacing between signal transmissions also greatly reduces the impact of interference signals, because it limits the loss of signals in all channels and maintains the initial strength. However, the automotive industry has replaced the distributed E/E architecture into a domain and centralized E/E architecture to help promote sensor integration and "Software Defined Vehicle" (SDV), but these new automotive architectures must be longer (point-to-point connection).

It can be seen that in all centralized architectures, although the overall cable length is reduced, the signal transmission length is extended for a single signal because it may need to cover the entire vehicle, especially for high-speed signals that do not want to be transmitted directly.

Figure 3. Distributed (edge), partitioned and centralized E/E architecture

● Lifting frequency

The increase in frequency can support the channel to push higher bandwidth, which are some vehicular connection solutions that meet the current requirements. However, with the increase of frequency, the signal attenuation will increase, the remote transmission effect will be affected, and the connecting cable is extremely vulnerable to EMI.

● Improve shielded cable

Improve the shielded cable to reduce the impact of EMI and reduce the radiation interference of the cable itself. This plan seems very suitable.

However, a recent study pointed out that due to the aging and stress of shielded cables, they will be seriously reduced, especially in equipment involving necessary movement (such as doors, side mirrors and trunk covers). EMI has a negative impact on aging and worn shielded cables, making them invalid and riskier. The most serious is that the shielded cable itself will become an EMI radiation source due to its invalidity over time.

At present, there are deficiencies in EMC testing

At present, EMC testing methods in the industry focus on new short shielded cables, without considering the standards and pressures of connecting cables in the real world. If the EMC test is conducted in this way again, the relevant vehicles will face large-scale return or other accidents in the future.

Solution - MIPIA-PHY

In order to solve many of the above tests, the MIPIA-PHY specification was published in 2020, which is applicable to promoting the innovation of advanced driverless vehicles. It uses digital signal processing (DSP) and other response methods to complete high bandwidth, long connection, and instant link, and also has a strong ability to solve EMI problems.

The DSP used by the Valens VA7000 chipset conforms to the actual MIPIA-PHY model chipset, which contains three main elements and can handle EMI:

(1) Immediate noise elimination (JITNC)

In order to reduce the impact of EMI, a fast and adaptive noise elimination method is proposed. Solve the problem of narrowband impact. (NBI) is extremely reasonable. This kind of sharp and sudden noise cannot be handled by the general vehicular connection solution. JITNC can eliminate noise up to 36dbm.

(2) Advanced Pulse Amplitude Modulation (PAM)

Valens chipset can work with PAM16, which is a form of simultaneously pushing a large amount of data, suitable for higher data rate, while maintaining a lower carrier frequency to avoid signal attenuation and impact. Although PAM4 is indeed applied to some traditional vehicle connection solutions, it still cannot support the high bandwidth required by current ADAS and infotainment systems. Valens PAM16 not only meets the current bandwidth requirements, but also provides enough space for future requirements.

(3) Dynamic PHY level retransmission

Sometimes the noise is very loud, and the packet may fail to transmit due to the impact. When this happens, the MIPIA-PHY standard transmits data packets again at the PHY level. PHY level operation allows fast data transfer. Since the original fault EMI may not have subsided, the retransmission of real-time control will use the PAM lower than the original push. For example, if the initial transmission is sent by PAM16, the retransmission will be pushed by PAM8. This can reduce the chance of transmission failure again, which is one of the reasons why Valensa-PHY adapts to the minimum error rate in the chipset completion industry.

Valens' unique UTP function

The DSP number in the Valens chipset can reduce the impact of interference signals, and then use unshielded twisted pair (UTP) with a speed of 4Gbps and a transmission distance of 10m. This makes Valens chipset have many advantages, such as reducing system cost, improving system design and layout efficiency, and providing more choices when designing system architecture. The application of UTP is a great progress of Valens chipset.

Result

Modern cars are in a complicated signal environment. With the gradual enrichment of ADAS components, digital cockpit and every component on the vehicle, the volume of the equipment will only become larger and larger. In the past, the impact of EMI has been proved to cause serious harm to important systems, leading to several car recalls and even fatal accidents. The first thing to limit EMI in various areas is to understand the problem. If this point is not fully taken into account in the design of the complete vehicle factory, ADAS will not be able to achieve breakthrough design in the fields of V2X communication, information and entertainment in the application of automotive products.