Split Winding Isolation Transformer for PoDL DC and Data Coupling
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Solution Overview
Problem
Existing Power over Data Lines (PoDL) systems face challenges in achieving low differential data insertion loss, high common mode noise insertion loss, and high differential mode return loss while minimizing component count and size, particularly in providing DC isolation of the Physical Layer (PHY) without adversely affecting signal integrity.
Innovation Solution
The use of a center tap isolation transformer to couple DC power and differential data over a twisted wire pair, where the primary winding is coupled across capacitors for data transmission, and the secondary windings are connected to the power supply to inject and return DC current, while a common mode choke attenuates common mode RF noise, optionally eliminating the need for additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transformer is used to provide DC isolation of the PHY, then the PHY is protected from DC power and common mode RF noise is attenuated, but the component count increases and size and cost increase
Solution Approach 1:
The patent combines the DC isolation transformer with the existing isolation transformer already present in the system. By integrating the DC isolation function into the existing transformer structure, the patent avoids adding a separate component while still providing the necessary DC isolation protection for the PHY. This merging approach resolves the contradiction by achieving the protective function without increasing component count.
2Power
If separate inductors are used to couple DC voltage to the wires, then DC power is delivered to the wire pair, but AC signal integrity is adversely affected due to additional loading
Solution Approach 1:
The patent applies different properties to different parts of the transformer windings. The primary winding is optimized for AC signal coupling with low impedance to differential mode signals, while the secondary winding is optimized for DC power delivery. This local differentiation allows the system to deliver DC power without adversely affecting AC signal integrity, as each winding is designed with the appropriate characteristics for its specific function.
3Object-affected harmful factors
If a common mode choke is added to attenuate common mode RF noise, then noise attenuation is improved, but the component count and size increase
Solution Approach 1:
The patent designs the isolation transformer to perform multiple functions simultaneously. The transformer provides DC isolation, AC signal coupling, and common mode noise attenuation all through a single component structure. By making the transformer multi-functional, the patent eliminates the need for separate common mode choke components while still achieving effective noise attenuation, thus resolving the contradiction between noise protection and component count.
4Reliability
If additional components are added to achieve DC isolation and noise attenuation, then protection and noise filtering are improved, but cost and size increase
Solution Approach 1:
The patent merges the DC isolation function with the existing isolation transformer structure. By integrating multiple functions (DC isolation, AC coupling, noise attenuation) into a single transformer component rather than using separate components for each function, the patent achieves the required protection and filtering while minimizing component count, size, and 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
This configuration reduces component count, minimizes loading on the PHY, achieves low differential data insertion loss, high common mode noise insertion loss, and high differential mode return loss, while providing effective DC isolation and noise attenuation, thus optimizing the PoDL system's efficiency and cost-effectiveness.
Implementation Method 1
A primary (PHY side) winding of an isolation transformer is coupled to the PHY for the transmission and reception of differential data
Implementation Method 2
A common mode choke (CMC) is connected in series between the wires in the wire pair and the secondary windings to attenuate common mode RF noise on the wire pair
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A PHY is coupled across split primary windings of an isolation transformer for differential data transmission and reception between PHYs and for DC isolation. Positive and negative low impedance terminals of a DC power supply are coupled to first and second secondary windings of the transformer as split center taps of the transformer. Respective ends of the wires in the wire pair are coupled to the other ends of the secondary windings. Therefore, the power supply conducts DC current through the secondary windings, while the differential data signals also flow through the secondary windings, generating corresponding differential data signals at the inputs to the PHY. The transformer also attenuates common mode noise. Therefore, the circuit makes multi-use of the isolation transformer, allowing fewer components to be used for the DC coupling, wire termination, and common mode noise cancellation.