Common Mode Choke Circuit for Automotive Ethernet EMI Reduction
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Solution Overview
Problem
Conventional in-vehicle networks are plagued by complexity, cost, and weight issues due to heterogeneity and electromagnetic interference (EMI) concerns, particularly when using unshielded twisted-pair cables for Ethernet communications in automotive applications.
Innovation Solution
Implementing a physical layer device (PHY) in Ethernet transceivers that converts standard Ethernet media independent interface (MII) data from a 4-bit packet stream to a 3-bit packet stream, using pulse amplitude modulation (PAM-3) over unshielded twisted-pair cables, and employing common mode choke (CMC) and differential mode choke (DMC) circuits to provide common mode noise isolation and reduce EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If unshielded twisted-pair cables are used for Ethernet communications, then cost and weight are reduced, but electromagnetic interference (EMI) increases
Solution Approach 1:
The patent introduces common mode choke circuits as intermediary components between the Ethernet transceiver and the unshielded twisted-pair cable. These chokes act as mediators that block common mode noise from propagating onto the cable while allowing differential mode data signals to pass through, thus enabling the use of lightweight unshielded cables without excessive EMI.
Solution Approach 2:
The patent converts the potentially harmful common mode noise into a controlled phenomenon by using common mode choke circuits that specifically target and attenuate common mode signals while preserving the useful differential mode data transmission. This transforms the EMI problem into a manageable filtering task.
2Object-affected harmful factors
If common mode noise isolation is implemented using choke circuits, then EMI requirements are met, but device complexity increases
Solution Approach 1:
The common mode choke circuits are designed to perform multiple functions simultaneously: they provide common mode noise filtering, enable impedance matching, and support differential mode data transmission. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
3Adaptability or versatility
If conventional heterogeneous network infrastructure is used, then different domain requirements are met, but system complexity and cost increase
Solution Approach 1:
The patent promotes the adoption of a homogeneous Ethernet-based network infrastructure that can serve multiple domains (powertrain, chassis, body, driver assistance, HMI) with a single standardized protocol and physical layer technology. By using unshielded twisted-pair Ethernet with common mode noise filtering across all domains, the system eliminates the complexity of heterogeneous networks while maintaining the ability to meet different domain requirements through Ethernet's inherent flexibility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the cost and weight of in-vehicle network infrastructure while meeting automotive EMI requirements by minimizing common mode noise conversion and maintaining reliable data transmission across domains.
Implementation Method 1
employing common mode choke (CMC) and differential mode choke (DMC) circuits to provide common mode noise isolation and reduce EMI
Data Source
AI summary
The present disclosure is directed to apparatuses for preventing significant amounts of common mode noise from a PHY transceiver, such as an Ethernet PHY transceiver, from coupling to an unshielded twisted-pair cable. The apparatuses can provide common mode noise isolation, while limiting any common mode noise to differential mode noise (CM-DM) conversion. Common mode noise is generally ignored by a PHY transceiver that receives a differential data signal because of differential signaling. However, when common mode noise is converted to differential mode noise, then data errors can result. Thus, limiting any CM-DM conversion is important.