Class AB Common Mode Suppression Circuit for EMI Reduction
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Solution Overview
Problem
Magnetic transformers used in power distribution over Ethernet networks are cumbersome, costly, and limit current, leading to electromagnetic compatibility (EMC) issues and frequent failures, while also consuming significant PCB space and creating fire hazards.
Innovation Solution
A network device incorporating a class AB common mode suppression (CMS) circuit coupled between a line voltage source and a physical layer (PHY) device, which provides active EMI suppression, terminates open-drain transmit drivers, and improves EMC performance by blocking common-mode noise while passing differential mode data signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic transformers are used for power distribution, then DC isolation and signal transfer are provided, but device complexity increases, PCB space increases, cost increases, and reliability decreases
Solution Approach 1:
The patent extracts and eliminates the magnetic transformer from the power distribution system, replacing it with a solid state transformer (STAT) that uses electronic components. This removal of the problematic magnetic transformer directly addresses the reliability and complexity issues while maintaining the essential power distribution function.
Solution Approach 2:
The patent replaces the mechanical/magnetic transformer system with an electronic solid state transformer using field effect transistors and control circuitry. This substitution eliminates magnetic core saturation, reduces PCB space, lowers cost, and improves reliability while maintaining DC isolation and signal transfer capabilities.
2Reliability
If magnetic transformers are used for power distribution, then power supply function is provided, but electromagnetic compatibility performance deteriorates due to magnetic fields
Solution Approach 1:
The patent replaces the magnetic transformer with a solid state transformer that uses electronic switching components. This eliminates magnetic field generation, thereby removing the source of electromagnetic interference and improving EMC performance while maintaining reliable power supply function.
3Power
If magnetic transformers are used for power distribution, then current limitation is achieved, but communication channel performance is limited
Solution Approach 1:
The patent replaces the magnetic transformer's passive current limitation with an active solid state transformer that uses controlled electronic switching. This enables precise control of power delivery while maintaining high-speed communication performance through electronic rather than magnetic current management.
4Reliability
If magnetic transformers are used for power distribution, then power isolation is provided, but fire hazard increases due to thermal issues
Solution Approach 1:
The patent replaces the magnetic transformer's thermal-based power isolation with a solid state approach using electronic switching and control circuitry. This eliminates the thermal issues and fire hazards associated with magnetic transformers while maintaining effective power isolation through electronic means.
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
The class AB CMS circuit enhances EMC performance, reduces EMI, and eliminates the need for magnetic transformers, thereby improving reliability, reducing costs, and increasing component density, while maintaining essential transformer functions like DC isolation and signal transfer.
Implementation Method 1
the class AB CMS circuit suppresses common mode noise, and terminates open-drain transmit drivers of the PHY device, thereby minimizing EMI
Data Source
AI summary
Embodiments disclosed herein describe a network device including a class AB common mode suppression (CMS) circuit coupled in parallel between a line voltage source and a physical layer (PHY) device that provides active EMI suppression and Phy device termination. A network connector is coupled to provide the line voltage source to the class AB CMS circuit. The class AB CMS circuit provides current to the PHY device, terminates open-drain transmit drivers of the PHY device and suppresses common mode noise thereby minimizing electromagnetic interference. In other embodiments, the class AB CMS circuit is coupled in parallel between the network connector and a physical layer (PHY) device. The class AB CMS circuit suppresses common mode noise, and terminates open-drain transmit drivers of the PHY device, thereby minimizing electromagnetic interference.