1. What 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
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.|
|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.|
2. Necessity of Noise Suppression in Onboard Ethernet
1.Differential transmission noise
In differential transmissions including Ethernet, noise occurs due to a common mode current caused by various factors.
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.
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.