Common Mode Filter with Segmented Floating Grounds
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Solution Overview
Problem
Conventional common mode filters struggle to effectively attenuate high-frequency common mode signals, leading to signal reflection and electromagnetic radiation, which complicates the transmission of ultra high-speed differential signals.
Innovation Solution
A common mode filter design featuring conductive lines on a dielectric layer with divided floating grounds and passive two-terminal networks connected between these grounds and the external ground potential, forming a series resonance circuit to absorb and attenuate common mode signals, while allowing differential signals to pass through.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional common mode chalk coil is used, then the structure is simple and easy to manufacture, but the attenuation of high-frequency common mode signals is insufficient
Solution Approach 1:
The patent divides the floating ground into multiple segments (first floating ground and second floating ground) separated by a gap, rather than using a single continuous ground. This segmentation creates multiple reflection points for common mode signals, enhancing attenuation effectiveness across broad frequency ranges while maintaining manufacturing feasibility through standard PCB fabrication processes.
Solution Approach 2:
The patent introduces a capacitor connected between the segmented floating grounds and external ground as an intermediary element. This capacitor forms a resonance circuit with the inductance of the conductive lines, creating a tuned filtering effect that significantly improves common mode signal attenuation at specific frequencies while allowing differential signals to pass unaffected.
2Reliability
If a common mode chalk coil is inserted to attenuate common mode signals, then common mode attenuation is improved, but signal reflection and electromagnetic radiation increase
Solution Approach 1:
By segmenting the floating ground into multiple parts with gaps between them, the patent creates multiple distributed reflection points along the transmission line. This segmentation reduces the impedance discontinuity at any single point, thereby minimizing signal reflection and electromagnetic radiation while maintaining effective common mode attenuation through the cumulative effect of multiple reflections.
Solution Approach 2:
The patent applies different ground configurations at different locations: continuous external ground connection at the ends for stable reference, but segmented floating ground in the middle section for optimal common mode rejection. This local differentiation of ground quality allows the system to achieve both low reflection and high attenuation performance.
3Speed
If the transmission speed is increased to 3G bits/second or higher, then the data transmission capability is improved, but the influence of noise and common mode signals increases
Solution Approach 1:
The capacitor connected between the segmented floating grounds and external ground acts as a frequency-selective intermediary that blocks high-frequency common mode noise while allowing the ultra high-speed differential signal to pass. This intermediary element creates a resonance circuit that specifically targets and attenuates noise frequencies without affecting the data transmission band.
Solution Approach 2:
The segmented floating ground structure creates multiple small inductance sections along the transmission line, which together provide effective common mode noise rejection at ultra high speeds. The segmentation reduces the overall inductance to differential signals while maintaining high impedance to common mode noise, enabling clean signal transmission at 3G bits/second and higher.
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 proposed filter achieves significant attenuation of common mode signals across a broad frequency range, reducing signal reflection and electromagnetic radiation, thereby ensuring successful transmission of ultra high-speed differential signals.
Implementation Method 1
a first passive two-terminal network connected between the first divided floating grounds located at least at an input side or an output side of the first divided floating grounds, and the external ground potential
Data Source
AI summary
To sufficiently attenuate a common mode signal by passing an ultra-high speed differential signal through an ultra-high speed differential transmission line. A common mode filter comprises: a pair of conductive lines formed on a first dielectric layer to transmit a differential signal; a plurality of first divided floating grounds in a state of being separated from an external ground potential, and facing the conductive lines, with the first dielectric layer interposed between them, and formed by being divided into a plurality of numbers in a length direction of the conductive lines, and forming a distribution constant type differential transmission line for the differential signal, together with the conductive lines; and a first passive two-terminal network connected between the first divided floating grounds located at least at an input side or an output side of the first divided floating grounds, and the external ground potential.