EMI Suppression Filters(EMC and Noise Suppression)

EMI Suppression Filters (EMC and Noise Suppression)EMI Suppression Using Common Mode Chokes for Both 100BASE-T1/1000BASE-T1 Systems [my Murata]

05/21/2026

Both 100BASE-T1 and 1000BASE-T1 standards are increasingly being supported within a single automotive Ethernet system (100/1000BASE-T1) to simplify design and reduce engineering effort.
This article focuses on common mode chokes (CMCs) for EMI suppression in such systems and examines their compatibility for shared use across both standards. The results introduce CMC capable of supporting 100/1000BASE-T1 applications.

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Contents

1. Introduction
2. CMC Selection for 100/1000Base-T1 Design
3. Radiated Emissions Testing
4. Bulk Current Injection (BCI) Testing
5. Conclusion

1. Introduction

With the ongoing advanced driver-assistance systems (ADAS) and the evolution toward autonomous driving (AD), the importance of in-vehicle communication is steadily increasing. As a result, automotive Ethernet standards such as 100BASE-T1 and 1000BASE-T1, which enable higher speed communication, are being adopted more widely in modern vehicles.
In automotive LANs, including automotive Ethernet, proper EMI suppression is essential to prevent electromagnetic radiation from LAN cables from interfering with other devices, as well as to avoid malfunction caused by external noise entering through the LAN cables. Since most of the problematic noise is common-mode noise, common mode chokes (CMCs) are generally employed for mitigation.
Meanwhile, to reduce design costs, there is a growing trend toward building communication systems that share both 100BASE-T1 and 1000BASE-T1 standards (100/1000BASE-T1). In such designs, it becomes necessary to select CMCs that can be applied across both systems for effective EMI suppression.

Figure 1 - Common mode chokes in an automotive Ethernet Multi-rate PHY supporting 100/1000BASET1.

2. CMC Selection for 100/1000Base-T1 Design

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