Solve the problem of audio and video transmission and open up a perfect third living space in the future under the trend of automated driving

Cables for car audio systems make up a significant portion of the total cable weight because analog lines require expensive shielded cables from the audio source to the end. In addition, active noise cancellation and road noise cancellation systems require multiple microphones in the car, which add many input nodes to the audio network. ADI introduced an innovative car audio bus (A2B) in 2014 to meet the growing demand for car audio connectivity.

Solve the problem of audio and video transmission with innovative technology and open up a perfect third living space in the future under the trend of automated driving

Market research data shows that 70% of young millennials believe that technology/infotainment systems are a must-have option when purchasing a vehicle, and it is clear that the cockpit is where automotive technology/infotainment systems are concentrated. The future of the automotive cockpit is driven by three concepts: 1. digitization of content, including maps, contacts, media, and more; 2. personalization of drivers and users, and migration of the home environment into the vehicle; Use apps like noise cancellation to improve the audio and voice experience in the cockpit.

In addition, with the rapid development of electric vehicles and autonomous driving technologies, the corresponding demand for data transmission bandwidth such as audio and video in the car is also increasing. Now there are as many as a dozen cameras in a car, and the resolution has generally been increased from the original 720P to 2M pixels or even up to 8M pixels, and there are rich audio-visual entertainment systems, etc. This situation has given birth to a high level of satisfaction. The generation of bandwidth, simplified wiring, and high reliability transmission scheme. The key challenge posed by this trend is, can these applications be better supported by traditional automotive buses in terms of performance, cost and scalability? This article looks at current and future trends in this type of technology from the perspective of the automotive audio and video bus that is widely used by Analog Devices (ADI).

Innovative audio bus with expandable functions meets the trend of cockpit upgrades

Cables for car audio systems make up a significant portion of the total cable weight because analog lines require expensive shielded cables from the audio source to the end. In addition, active noise cancellation and road noise cancellation systems require multiple microphones in the car, which add many input nodes to the audio network. ADI introduced an innovative car audio bus (A2B) in 2014 to meet the growing demand for car audio connectivity. As a high-bandwidth bidirectional digital bus, it was originally used to solve audio distribution challenges in automotive applications. Because existing car audio networks typically use multiple point-to-point analog connections, A2B technology can address many of the challenges associated with point-to-point analog connections, including cable weight, cable cost, wiring challenges, and the reliability of multiple connections. It facilitates the transmission of fully synchronized audio and control data throughout a distributed multi-drop audio system over an unshielded twisted pair and connector infrastructure.

Solve the problem of audio and video transmission and open up a perfect third living space in the future under the trend of automated driving
Traditional Car Audio Cables vs. A2B Simplified In-Car Audio System Cables

A2B is an innovative technology introduced by ADI that supports serial topology, that is, a single master connects up to 10 slaves in a daisy-chain form. A2B is optimized for audio applications and has a speed of 50Mbps. By using unshielded twisted pair cables, connections are greatly simplified, reducing the overall weight of the harness by up to 75%. The distance between nodes can be up to 15 meters, and the maximum network length is 40 meters. The same UTP transmit power (phantom power) can be up to 300mA, ideal for digital microphones.

If the power distribution provided by the master node is insufficient, the slave node can be powered by the local power supply. The bus supports bidirectional communication, master-to-slave, slave-to-master, up to 32 channels downstream and upstream (12, 16, 24 bits). Best of all, guaranteed latency of up to 2 clock cycles provides determinism for latency-sensitive applications like ANC/RNC. The A2B bus can transmit I2C messages and support the remote configuration of peripherals such as ADC/DAC on the slave node.

In recent years, the active noise reduction function has been derived from headphone products to a wider field. As the third living space, the active noise reduction function is very important under complex environmental noise. Considering that road or engine noise takes only about 0.009 seconds to reach the passenger, the path to achieve noise suppression is critical. A2B is optimized for audio applications, with a speed of 50Mbps, ideal for digital microphones, A2B can guarantee a delay of up to 2 clock cycles, providing time determinism for delay-sensitive applications such as ANC/RNC. It is the delay of two clock cycles at 50Mbps that creates the necessary conditions for noise cancellation under the condition of sound propagation of 0.009 seconds.

Gigabit multimedia serial link supports rich automotive video applications under the trend of intelligence

According to MarketsandMarkets, the global automotive cameras and integrated radar and cameras market size is expected to grow from $6.1 billion in 2021 to $10.1 billion in 2026. With the popularity of vision-based autonomous driving technology applications, today’s surround view systems with four or more cameras are beginning to become mainstream, and higher frame rates and resolutions will put more pressure on automotive bus bandwidth, and in addition to ADAS System, high-quality cockpit audio-visual entertainment system has become the standard configuration of current mid-to-high-end cars, and the transmission of visual information is facing higher demands.

Solve the problem of audio and video transmission and open up a perfect third living space in the future under the trend of automated driving
Various sensors including cameras are widely used in modern cars

The current market mainstream is that the camera is only responsible for collecting and outputting the original video signal, and integrating the processing and computing functions into the central processing unit. Therefore, the key design challenge is how to quickly and efficiently transmit the original image data from the camera to the processing unit, and from the processing unit. Units are transmitted to each Display screen, which involves the quality, bandwidth, latency, reliability, cost and power consumption of image signal transmission between units. In this process, the video data converts parallel signals into serial signals through a serializer, and then restores them into parallel signals through a deserializer. At present, the high-speed SerDes on the car is mainly used to transmit camera and video signals. This interface, which is often called LVDS in the industry, has the characteristics of high speed (Gbps level), low latency and low power consumption. Regardless of Camera Link or Display Link, it is currently an LVDS solution.

ADI’s Gigabit Multimedia Serial Link (GMSL) SerDes technology provides the high bandwidth needed to transmit the bursting volume of multi-class data, successfully deploying complex advanced driver assistance systems (ADAS) and infotainment functions in vehicles, comprehensive Support the high bandwidth, complex interconnection and data integrity required by automotive infotainment and ADAS systems, including ultra-low power requirements for cameras, broadband requirements for sensor data aggregation, and more. The advantages of GMSL include: faster aggregation of data, the ability to maintain data integrity for safety applications, and enabling the system to display different content on multiple screens in the vehicle. In addition, GMSL can effectively replace uncompressed Ethernet transmission, with 10 times higher data rate, 50% lower cable loss, and better EMC performance than Ethernet. At present, there are more than 500 million GMSL technology nodes used in automobiles around the world.

Solve the problem of audio and video transmission and open up a perfect third living space in the future under the trend of automated driving
GMSL four-channel deserializer MAX9286 ​​can support the signal transmission of four cameras at the same time

For multi-sensor fusion, since the ADI GMSL serializer and deserializer ICs have video slicing capabilities, a single serializer can be used to combine multiple channels of video data and feed them to the display or sensor, respectively. Taking the ADI GMSL four-channel deserializer MAX9286 ​​as an example, it can automatically generate camera synchronization signals, align the image data of multiple sensors to the same pixel, and realize user programming of key parameters, effectively reducing design risks and accelerating product launch. At the same time, the integrated solution can replace four discrete deserializers and one FPGA, and only one MAX9286 ​​can receive and synchronize video signals from four cameras, greatly reducing board area and component count.

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