An important system in the process of automotive electronics: autonomous driving

In recent years, the automobile market has been a rapidly developing market in China and has made a huge contribution to the growth of our country's GDP.

As cars become more "electronic" and "systemized," they are no longer just machines, but a combination of multiple electronic systems and mechanical parts. The electronic system affects the mechanical parts, and the movement of the mechanical parts sends signals back to the electronic system for processing... In this series of cycles, there will be less and less things that we "drivers" need to do, and our hands and feet will gradually be liberated.

And this is the emerging automotive electronic system that has gradually emerged in the past two years - the ADAS system.

ADAS (Advanced Driving Assistant System), also known as automatic driving system or advanced driving system, uses various sensors installed on the car to sense the surrounding environment at any time during driving, collect data, identify, detect and track static and dynamic objects, and combine navigation map data to perform system calculations and analysis, so as to make the driver aware of possible dangers in advance, effectively increasing the comfort and safety of car driving.

According to the definition of NHTSA (National Highway Traffic Safety Administration), we divide autonomous driving into five stages, Level 0-Level 4. Level 0-Level 2 belongs to the popularization and promotion stage of ADAS, and the realization of Level 3-Level 4 requires ADAS to be combined with vehicle networking and cloud computing technology. Currently, Level 1 and Level 2 have been commercialized. In the near future, Level 3 and above will also be commercialized.

In the entire ADAS system, the main key technologies are: sensor technology (camera, radar), chips and algorithms.

Among them, CMOS photosensitive chips, the core components of cameras, are mainly controlled by Japanese and Korean companies represented by Sony and Samsung.

Radars are divided into ultrasonic radar, millimeter-wave radar, and laser radar. Ultrasonic radar has a lower technical threshold and many suppliers; laser radar is expensive and has not been commercialized; millimeter-wave radar has a cost between the two and a higher technical threshold, and is mainly in the hands of industry-leading companies such as ZF TRW, Bosch, and Continental.

Chips and algorithms are crucial in ADAS systems, and the industry is highly concentrated, with major companies including Mobileye and ADI.

The systems such as "front-view camera" and "360-degree surround-view camera" that we come into contact with in our daily lives are actually close to our ADAS cameras in terms of functions.

As for the camera, as a small gadget spread all over the car body, it needs to be powered and transmit data to the onboard host. The winding cables are particularly troublesome to design. How can we reduce this part of the design cost?

(Pictures from the Internet)

SerDes chips came into being.

SERDES is the abbreviation of SERializer/DESerializer. It is a mainstream time division multiplexing (TDM) and point-to-point (P2P) serial communication technology. That is, multiple low-speed parallel signals are converted into high-speed serial signals at the sending end, and then passed through the transmission media (optical cable or copper wire), and finally the high-speed serial signals are converted back into low-speed parallel signals at the receiving end. This point-to-point serial communication technology makes full use of the channel capacity of the transmission media, reduces the number of transmission channels and device pins required, and increases the transmission speed of the signal, thereby greatly reducing the communication cost.

SerDes can greatly save wiring harness costs, but the power cord cannot be omitted. A car with four cameras requires at least eight wires to connect, which is quite troublesome to design.

Thus, the PoC circuit came into being.

PoC (Power over Coax) is the transmission of power via coaxial cable. The DC power of the power supply is coupled to the coaxial cable used to transmit the signal. At the receiving end, a biasT circuit is used to separate the signal from the power supply, which can save a lot of power lines.

As shown in the figure above, the power line is coupled to the green coaxial line in the middle through the PoC filter, and then split into DCDC again after reaching the camera end.

Currently, the main SerDes design manufacturers include TI, MAXIM, Ambarella, etc. The signal frequency and acceptable loss of each manufacturer are different, so each manufacturer's PoC circuit has certain differences.

However, the most important thing about PoC circuits is the isolation effect on data signals, which needs to be obtained through actual measurement or simulation.

The figure above is the PoC partial isolation simulation model recommended by the reference design of MAXIM's 96705 chip. It can be seen that for 1MHz-1GHz signals, the PoC circuit in the reference design generates an impedance of about more than 500ohm.

Whether this impedance is sufficient is a matter of opinion, but the most important thing about the PoC circuit is to "reject signal inflow", so there is no doubt that this solution is not problematic in principle.

The three inductors L1-L3 shown in the figure above mainly play the role of isolation.

Murata, as a professional inductor provider in the industry, also has circuit solutions designed specifically for the above PoC circuits, which can support SerDes chips from various manufacturers, including but not limited to:

● TI FPDLINKIII (913, 933, 953)

●MAXIM GSML1, GSML2 (96705, 9275, 9295)

● Amba B6

Murata can also provide customized simulation services, which can intuitively show the impedance effect of your selected solution.

In summary, the autonomous driving system is an important system in the process of automotive electrification in recent years. It also needs to cooperate with new technologies such as vehicle networking and 5G communications. It will become a hot topic in the automotive market. Murata also hopes to meet customer needs by providing differentiated products and technical services.