Ground-Coupled LC Noise Suppression for GHz Differential Transmission
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Solution Overview
Problem
Existing common mode noise suppression techniques are ineffective at high frequencies and occupy large areas, making them unsuitable for modern miniaturized circuits and high-speed digital systems.
Innovation Solution
A common mode noise suppression circuit utilizing an inductance-capacitance resonant structure formed by electromagnetic coupling between differential transmission conductors and a ground structure, which provides serial and parallel resonances to effectively suppress common mode noise at specific frequencies without affecting differential signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a common mode choke is used to suppress common mode noise, then common mode noise suppression is achieved in MHz scope, but it cannot be applied above high frequency section of GHz due to frequency characteristic and parasitics of ferromagnetic material
Solution Approach 1:
The patent changes the fundamental operating parameters from ferromagnetic material-based inductors to planar transmission line structures with controlled impedance. This allows the common mode filter to operate effectively at GHz frequencies by eliminating the frequency limitations and parasitic effects inherent in ferromagnetic materials, while maintaining common mode noise suppression capability through electromagnetic coupling between differential and common mode paths.
Solution Approach 2:
The patent replaces the traditional mechanical/ferromagnetic inductor structure with an electromagnetic field-based planar transmission line system. This substitution eliminates the physical limitations of ferromagnetic materials at high frequencies and enables broadband operation across MHz to GHz ranges by utilizing distributed electromagnetic coupling rather than concentrated inductive elements.
2Reliability
If a pattern ground structure is used to eliminate common mode noise, then broadband common mode suppression effect within GHz scope is achieved, but dimension is half or quarter of wavelength of transmission signal which occupies large ground area of the circuit board
Solution Approach 1:
The patent transitions from two-dimensional planar pattern ground structures to three-dimensional vertically stacked configurations. By utilizing the vertical dimension with multiple signal layers and ground layers separated by dielectric substrates, the design achieves wavelength/4 electrical length for common mode suppression while occupying minimal planar area on the circuit board, thus resolving the contradiction between broadband suppression and area occupation.
Solution Approach 2:
The patent embeds the common mode filter structure within the existing multi-layer PCB architecture by nesting signal layers between ground layers. The differential signal path is embedded within the vertical stack, with ground structures providing both mechanical support and electromagnetic shielding, thereby achieving compact integration without requiring additional external space.
3Area of stationary object
If conventional common mode suppression filters are designed for miniaturization, then area is reduced, but operation performance at high frequency deteriorates
Solution Approach 1:
The patent changes the scaling parameters from reducing physical dimensions to optimizing electrical characteristics. By adjusting the impedance values, coupling coefficients, and layer spacing in the planar transmission line structure, the design maintains high frequency performance while achieving miniaturization through efficient use of the vertical stacking factor in multi-layer PCB configurations.
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 achieves broadband common mode noise suppression within the GHz frequency range while maintaining low loss for differential signals, enabling miniaturization and cost benefits, and is suitable for high-speed digital systems.
Implementation Method 1
a differential transmission structure disposed to form an electromagnetic coupling with the reference potential structure, wherein the differential transmission structure has a pair of transmission conductors for transmitting the differential signal
Implementation Method 2
a ground structure electrically connected to the reference potential structure and the ground layer for forming an inductance-capacitance resonant structure together with the electromagnetic coupling formed by the reference potential structure and the differential transmission structure, and an inductance formed by the ground structure itself, so as to suppress a common mode signal at a specific frequency
Data Source
AI summary
A common mode noise suppression circuit applicable to differential signal transmission performs common mode noise suppression with respect to differential signals transmitted by a transmission line. An inductance-capacitance resonant structure is formed based on electromagnetic coupling combining a ground structure to suppress common mode noise of differential mode signals at broadband meanwhile keeping low loss of the differential mode signals at broadband via differential transmission lines. By this, the common mode noise suppression circuit performs broadband suppression with related to the common mode noise within a frequency scope of several GHz without affecting the differential mode signals and improves manufacturing process miniaturization to decrease cost.