Embedded Common Mode Filter in Differential Signal Lines
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Solution Overview
Problem
Integrated circuits face significant electromagnetic interference (EMI) issues due to common mode noise on ground and power lines, particularly exacerbated by multiple serializer/deserializer outputs clocked from a common source, which is challenging to shield effectively using discrete components.
Innovation Solution
A circuit board configuration with differential signal lines featuring a portion of higher common mode impedance, achieved by hollowing out impedance reference planes and adjusting signal line widths, to create an embedded common mode filter that reduces noise amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If discrete components are used to shield common mode noise, then noise filtering capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges the shielding function with the existing differential signal line structure by creating an embedded common mode filter within the circuit board layers. The filter uses the differential signal line traces themselves as part of the filtering structure, combining signal transmission and noise filtering into a single integrated solution rather than adding separate discrete shielding components.
Solution Approach 2:
The differential signal line structure serves dual purposes: transmitting differential signals and providing common mode noise filtering. The circuit board's own structural elements (traces, planes, vias) are configured to automatically provide filtering functionality without requiring external discrete components, making the system self-sufficient for both signal transmission and EMI protection.
2Object-affected harmful factors
If discrete components are used to filter common mode noise, then noise filtering capability is improved, but manufacturing cost increases
Solution Approach 1:
The filtering function is merged into the circuit board's differential signal line structure, eliminating the need for separate discrete filtering components. This integration reduces part count, assembly steps, and overall manufacturing cost while maintaining effective common mode noise filtering capability.
Solution Approach 2:
The circuit board structure itself provides the filtering functionality through its own traces and geometric configurations, eliminating the need to purchase and install external discrete filtering components, thereby reducing material costs and assembly complexity.
3Object-affected harmful factors
If embedded common mode filter is implemented, then common mode noise is reduced, but differential signal line impedance varies
Solution Approach 1:
The patent applies local quality by creating a specific section of the differential signal line with different geometric properties (the embedded filter section) that has higher common mode impedance. This localized modification is confined to specific portions of the trace, allowing the rest of the signal line to maintain its original impedance characteristics while the filter section provides noise filtering.
Solution Approach 2:
The embedded common mode filter is implemented by changing geometric parameters (trace width, spacing, distance from reference planes) in specific sections of the differential signal line to create higher common mode impedance regions. These parameter changes are carefully controlled to achieve filtering while minimizing impact on overall signal integrity.
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 effectively reduces common mode noise amplitudes by up to 9 dB across various frequencies, mitigating EMI issues with minimal added differential loss and avoiding the cost and complexity of discrete components.
Implementation Method 1
a first portion 58'' of the differential signal line 58 has a higher common mode impedance than another portion of the differential signal line, whereby the first portion 58'' of the differential signal line 58 is configured to provide a common mode noise filter
Data Source
AI summary
In order to provide filtering of clock noise from an integrated circuit at least one differential signal line connected to the integrated circuit is provided with an embedded common mode filter. The common mode filter can be provided in the form of a hollowed out portion of an impedance reference plane.