Midspan Power Adapter Reducing Radiated Emissions
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Solution Overview
Problem
Conventional midspan power adapters for VoIP phones cause increased radiated emissions due to discontinuities in Ethernet cables, leading to electromagnetic compatibility issues and higher energy radiation, which existing solutions fail to adequately address without adding significant cost or complexity.
Innovation Solution
A midspan power adapter with a common mode choke and transformer, which isolates signal pairs and provides common mode termination, reduces radiated emissions by maintaining cable symmetry and balance, and powers devices through spare pairs or phantom feed, minimizing noise currents and radiated energy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If power is provided through midspan power adapter using spare pairs, then power delivery to VoIP phone is achieved, but radiated emissions increase due to cable discontinuities
Solution Approach 1:
A common mode choke is introduced as an intermediary component between the power source and the spare wire pairs. This choke acts as a mediator that allows power to be delivered to the VoIP phone through the spare pairs while simultaneously blocking the generation of common mode currents that cause radiated emissions. The choke presents high impedance to common mode signals while maintaining low impedance for differential mode power transmission.
Solution Approach 2:
The invention changes the electrical parameters at the cable discontinuity point by introducing the common mode choke, which modifies the impedance characteristics. The choke transforms the abrupt impedance change at the spare pair connection into a controlled impedance transition, thereby reducing the imbalance between differential and common mode impedances that causes radiation.
2Power
If conventional midspan power adapter is used, then power is delivered to device, but electromagnetic compatibility compliance is difficult to achieve
Solution Approach 1:
The common mode choke serves as an intermediary filtering component that mediates between the power delivery function and electromagnetic compatibility requirements. It allows the midspan adapter to deliver power while actively suppressing the electromagnetic emissions that would otherwise cause compliance failures with standards like IEC CISPR 22 Class B.
3Object-generated harmful factors
If shielded cables or additional filtering components are added to reduce emissions, then radiated emissions decrease, but system cost increases
Solution Approach 1:
The invention extracts the emission reduction function from complex solutions like shielded cables or multiple filtering components and implements it through a single, integrated common mode choke. This extraction approach maintains the emission suppression capability while significantly reducing system complexity and cost.
Solution Approach 2:
The common mode choke performs multiple functions simultaneously: it delivers power through the spare pairs, suppresses common mode currents, reduces radiated emissions, and maintains cable balance. This multi-functionality eliminates the need for separate shielding or additional filtering components, thereby reducing overall system cost.
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 solution significantly reduces electromagnetic emissions, meeting compliance standards like IEC CISPR 22 Class B, while maintaining signal integrity and reducing costs associated with shielded cables or additional filtering components.
Implementation Method 1
A common mode choke suppresses common mode currents and noise by presenting high impedance to electromagnetic interference, reducing radiated emissions
Implementation Method 2
The transformer has device side terminals connected to signal pairs of the device connectors and system side terminals connected to signal pairs of the system connectors
Data Source
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AI summary
A midspan power adapter is provided for use in a balanced communication system, such as an Ethernet system, where differential signals are transmitted between two devices. The adapter passes data signals through, and provides power to an end device, such as an IP phone, with significantly less contribution to the electromagnetic emissions of the system than known midspan adapters. Balance and symmetry inherent in a structured cable can be maintained by a termination network connecting center taps of a transformer and the spare pairs of both the incoming and outgoing cables to a common point. The adapter can provide power through unused wires (known as spare pair power) or by combining power with data signals (known as phantom feed). A common mode choke is included in the power feed to prevent noise currents from flowing through the power supply connections to earth ground, helping to minimize radiated noise.