PoDL Differential Choke Pairing for Common-Mode Noise and Impedance Matching
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Solution Overview
Problem
Existing Power over Data Lines (PoDL) systems face challenges in delivering DC power while minimizing common mode noise attenuation and differential mode insertion loss, and in reducing the requirements for common mode chokes (CMCs), particularly due to interference from DMCs with the RC termination circuitry and the need for robust CMCs to handle full current drawn by powered devices.
Innovation Solution
A PoDL system employing a multiphase power supply to couple DC power through both tightly and loosely coupled DMCs, where the tightly coupled DMC presents low impedance to AC common mode noise and the loosely coupled DMC preserves the impedance of the RC termination circuitry, allowing for reduced current requirements and cost of CMCs, and efficient common mode noise attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a DMC is added to improve AC common mode rejection, then common mode noise attenuation is improved, but the DMC distorts the common mode matching impedance and causes reflections
Solution Approach 1:
The patent divides the single DMC function into two separate DMCs with different coupling coefficients. The first DMC (tightly coupled) focuses on common mode noise attenuation, while the second DMC (loosely coupled) focuses on preserving impedance matching. This segmentation allows each component to optimize its specific function without interfering with the other.
Solution Approach 2:
The patent applies different local qualities to the two DMCs by using different coupling coefficients. The first DMC uses tight coupling (high coupling coefficient) to maximize common mode rejection, while the second DMC uses loose coupling (low coupling coefficient) to minimize impact on differential mode impedance matching. Each DMC is locally optimized for its specific purpose.
2Power
If a robust CMC is used to handle full current drawn by powered device, then current handling capability is improved, but cost and size of CMC increase
Solution Approach 1:
The patent segments the current handling function between the two DMCs and the CMC. Instead of requiring the CMC to handle the full current alone, the system uses multiple DMCs to share the power delivery function. This reduces the current burden on the CMC, allowing for a smaller, less expensive design.
Solution Approach 2:
The DMCs act as intermediaries that share the power delivery burden. By introducing these intermediate components with opposite polarity windings, the system distributes the current handling requirements across multiple components, reducing the stress on any single component including the CMC.
3Loss of energy
If CMC windings are reduced to lower DCR and parasitic capacitance, then insertion loss is improved, but current handling capability and magnetic shielding are compromised
Solution Approach 1:
The patent segments the power delivery function across multiple components (two DMCs and the CMC) rather than relying on a single CMC to handle all current. This allows the CMC windings to be optimized for low loss with fewer turns, while the overall current handling capability is maintained through the combined capacity of all components.
Solution Approach 2:
The patent combines multiple components (two DMCs with opposite polarity windings and the CMC) to achieve the total current handling capability. By merging these components in parallel, the system achieves both low insertion loss in the CMC and sufficient overall current handling through the combined capacity of all components.
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 effectively attenuates AC common mode noise while minimizing the impact on RC termination circuitry and reduces the current and cost requirements of CMCs, enhancing the overall performance and efficiency of the PoDL system in electromagnetic interference environments.
Implementation Method 1
The first DMC has windings that are tightly coupled, so that the first DMC has a large coefficient of magnetic field coupling
Implementation Method 2
the second DMC has windings that are loosely coupled, so that the second DMC has a low coefficient of magnetic field coupling
Implementation Method 3
the windings have the same polarity, so the magnetic fields generated by a differential mode signal are substantially cancelled out. Common mode currents, such as ambient noise in the wire pair, however, see a high impedance due to the combined inductances of the windings
Implementation Method 4
The DMC 20 has windings with opposite polarities (dots on opposite ends). The DMC 20 presents a high impedance to AC differential mode signals while it shunts the common mode signals to the power supply 22 due to its low impedance to common mode signals
Data Source
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AI summary
In a Power over Data Lines (PoDL) system that conducts differential data and DC power over the same wire pair, various DC coupling techniques are described that improve DC voltage coupling while attenuating AC common mode noise. Pairs of differential mode chokes (DMCs) are used to share current supplied by a single phase or multi-phase power supply. In one embodiment, one DMC is coupled to the line side of a common mode choke (CMC), and one DMC is coupled to the PHY side of the CMC. The line-side DMC has windings that are loosely magnetically coupled so that DMC does not present a very low impedance to AC common mode noise on the wires. Therefore, the performance of the wires' RC termination circuitry is not adversely affected by the line-side DMC when minimizing reflections of common mode signals.