An Introduction to Noise Suppression in Onboard Ethernet 100Base-T1 | Noise suppression examples for Automotive

Contents

1What 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.

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.

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.