SubTitleIconNo01What is Onboard Ethernet?


Onboard Ethernet: “Communication systems used in automobiles”

Various interface standards are used in automobiles, depending on the application.


Table 1: Communication systems used in automobiles

Communication system
Speed
Applications, features
CAN/LIN
33k/125k/250k/500kbps
Onboard LAN standard adopted for general ECUs
FlexRay
2M/5M/10Mbps
Used in the powertrain, chassis, and other control systems
MOST
25M/50M/150Mbps
Adopted for use in onboard audio multimedia systems
Ethernet
100M/1Gbps
PC LAN standard, also used in diagnostics
100BASE-TX, 100Base-T1


Table 2: Onboard Ethernet standards
Standard Transmission speed
Number of pairs Notes
100Base-T1
100Mbps
1 pair
Supports full-duplex communication at 100 Mbps with 1 pair. Standardized by OPEN Alliance.
100Base-TX
100Mbps
2 pairs
Based on the existing 100Base-TX and used to improve onboard EMC performance.
RTPGE
(1000Base-T1)
1000Mbps
1 or 2 pairs
Being reviewed for standardization by IEEE. The standard reduced the amount of wiring in the existing 1000Base-T for vehicle and industrial device applications.


SubTitleIconNo02Necessity of Noise Suppression in Onboard Ethernet


  1. Differential transmission noise
  2. Ethernet problems
  3. Noise standards of onboard devices


1.Differential transmission noise

In differential transmissions including Ethernet, noise occurs due to a common mode current caused by various factors.


2.Ethernet problems

The cables used for Ethernet are different from USB and HDMI cables.




3.Noise standards of onboard devices
Onboard devices have a shorter antenna distance and stricter limit values than consumer products.


Recommended!

A common mode choke coil is an effective way to suppress noise in a differential transmission.



  • The reverse phase (differential mode) signal is canceled by the magnetic field → penetrates
  • The magnetic field superimposes the in-phase (common mode) noise → reflects

You can selectively drop just the common mode!

We recommend the DLW43MH series as the optimal common mode choke coil for 100Base-T1 noise suppression.