Noise suppression technologies/case study introduction (Automotive)

Automotive Ethernet for ADAS Noise suppression measures for 1000Base-T1 (1)

Production of some products (DLW32SH101XK2) introduced in this article has been discontinued.

1. Spread 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.

Spread of Automotive Ethernet in Automobiles_image

2. Signal 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 external noise_image

For noise emissions

For noise emissions_image

3. Noise 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

Common mode current flows due to variety of factors_image

4. Factors 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_image
When skew occurs_image
When amplitude difference occurs_image


Differential_Normal differential signal_image
Differential-When skew occurs_image
Differential-When amplitude difference occurs_image


Common-Normal differential signal_image
Common-When skew occurs_image
Common-When amplitude difference occurs_image

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