SubTitleIconNo01Spread of Automotive Ethernet in Automobiles


Today, various sensors and cameras are installed as devices for supporting advanced driver-assistance systems (ADAS). Although LVDS and other interfaces are being used for transfer of camera data, automotive Ethernet is being used in growing numbers of cases for transfer of LiDAR and other sensor data. Whereas standards such as 100Base-TX and 1000Base-T are being used for office environments, standards such as 100Base-T1 and 1000Base-T1 are specified for use in automobiles.



SubTitleIconNo02Signal Transmission by Automotive Ethernet


Ethernet and other automotive interfaces use differential transmission signals that have minimal emissions and are resistant to the effects of external noise. Because external noise often enters both differential transmission signal lines in the same way, this does not affect their difference, and these lines feature strong resistance to external noise. Another advantage is that, because the signal lines in the pair are adjacent to each other, any magnetic field generated by signal currents are canceled out, and so it is difficult for noise to be emitted externally.


For external noise


For noise emissions


SubTitleIconNo03Noise Issues in Automotive Ethernet


In differential transmission lines, where noise does not tend to be generated, noise issues can still occur when a common mode current is generated by a variety of factors.

Common mode current flows due to variety of factors


 

SubTitleIconNo04Factors for Generation of Common Mode Noise


One characteristic of differential transmission lines is that, generally, common mode noise is not generated. However, if skew (time difference) or an amplitude difference occurs in the signals between both lines, the signal balance between both lines will be lost, and common mode noise will be generated.

Normal differential signal

When skew occurs

When amplitude difference occurs


Differential


Common