Shared PCB Memory Trace Layout for Floating-Trace EMI Control
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Solution Overview
Problem
Electronic apparatuses with printed circuit boards (PCBs) designed for variable quantities of memories face increased electromagnetic interference (EMI) issues due to reflection effects, particularly when only one memory is implemented, leading to antenna effects from floating traces.
Innovation Solution
The implementation of a PCB design with strategically placed fingers and conductive traces that share common segments between a controller and branch points, along with damping or connecting resistors, to minimize reflection effects by optimizing signal path lengths and impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a common PCB is designed for multiple memories with series termination, then cost is reduced and design is simplified, but floating traces cause reflections due to antenna effect when only one memory is implemented
Solution Approach 1:
The patent extracts and removes the floating traces from the PCB design by implementing complete signal path termination. When only one memory is used, the traces that would otherwise be floating (unused connection paths) are eliminated or terminated to prevent antenna effects and reflections, while still maintaining the PCB's capability to support multiple memories when needed.
Solution Approach 2:
The patent applies different termination strategies to different signal paths based on local requirements. Each signal path is configured with appropriate termination (series or parallel) depending on whether it connects to an active memory or remains inactive, allowing the PCB to maintain good signal integrity regardless of how many memories are actually implemented.
2Ease of manufacture
If series termination is used on signal paths without ODT, then cost is reduced, but floating traces on the PCB cause reflections due to antenna effect
Solution Approach 1:
The patent removes the source of the problem by extracting floating traces from the design. Instead of relying on series termination alone, the design eliminates the floating traces that cause antenna effects, thereby preventing reflections while maintaining cost-effectiveness.
Solution Approach 2:
The patent takes preliminary action to prevent reflections before they occur by designing the PCB to eliminate floating traces from the outset. This preventive approach ensures that when only one memory is implemented, there are no antenna effects or reflections, rather than trying to correct the problem after it arises.
3Reliability
If parallel termination is used on signal paths without ODT, then reflection effects are reduced, but device complexity increases
Solution Approach 1:
The patent segments the signal paths into distinct categories based on their usage status. By dividing the PCB design into active and inactive signal path segments, the patent can apply appropriate termination only where needed, reducing overall complexity compared to uniform parallel termination across all paths.
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 design reduces electromagnetic interference and antenna effects, achieving wider eye openings and smaller signal skews, thereby enhancing signal integrity and reducing manufacturing costs by allowing a common PCB to support various electronic apparatuses with different memory configurations.
Implementation Method 1
a memory with high data rate may induce reflection effects at signal paths between the memory and a controller thereof... I/O pins of a memory with on-die termination (ODT) or damping resistors disposed on the signal paths between the controller and the I/O pins of the memory without ODT are generally used to decrease the reflection effects
Implementation Method 2
the floating traces on the common PCB that are designed to couple the other memories may cause reflections due to antenna effect
Data Source
AI summary
An electronic apparatus is provided. A PCB has first and second signal paths therein. First and second fingers are disposed on the first and second signal paths, respectively. A controller is coupled to a first memory via the first finger and a second memory via the second finger, and accesses the first and second memories through the first and second signal paths, respectively. The first and second signal paths share a common segment between the controller and a branch point. First and second components are disposed between the first finger and the branch point and between the second finger and the branch point, respectively. The distances between the first component and the branch point and between the second component and the branch point are smaller than or equal to the distance between the first component and the first finger and between the second component and the second finger, respectively.