HDMI Control Symbol Scrambling for Clock-Pattern EMI Mitigation
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Solution Overview
Problem
Current HDMI implementations generate significant electromagnetic interference (EMI) due to the repeated transmission of control symbols with predominant clock pattern content, which can negatively impact nearby wireless services such as Wi-Fi and cellular networks.
Innovation Solution
The method involves generating pseudo-random values using a linear feedback shift register (LFSR) to scramble control symbols, distributing them across a larger set of random values, and selecting scrambled control symbols with desirable electromagnetic interference properties for transmission, thereby minimizing EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control symbols are transmitted repeatedly with predominant clock pattern content, then control signaling reliability is improved, but electromagnetic interference increases
Solution Approach 1:
The patent applies parameter changes by modifying the bit pattern of control symbols from fixed predetermined patterns to scrambled patterns with controlled transition density. The scrambling process changes the electromagnetic characteristics of transmitted symbols while maintaining their control function, thereby reducing EMI without sacrificing reliability
Solution Approach 2:
The patent introduces dynamic scrambling sequences that vary the control symbol patterns over time. Instead of using static predetermined patterns, the system dynamically selects from multiple possible patterns based on transition density requirements, creating a more flexible system that can adapt to reduce EMI while maintaining control signaling integrity
2Measurement precision
If control symbols use fixed predetermined bit patterns, then control symbol recognition is improved, but electromagnetic radiation increases
Solution Approach 1:
The patent changes the bit pattern parameters of control symbols by applying scrambling sequences that control the number of transitions. This allows the system to maintain sufficient pattern distinguishability for recognition while reducing the electromagnetic radiation caused by excessive transitions
Solution Approach 2:
The patent introduces an intermediary scrambling process between the original control symbol and its transmission. This intermediary layer transforms the fixed predetermined patterns into variable patterns with controlled transition density, mediating between the need for recognition and the need to reduce EMI
3Object-generated harmful factors
If scrambling is applied to control symbols, then electromagnetic interference is reduced, but system complexity increases
Solution Approach 1:
The patent segments the control symbol transmission into multiple possible patterns, each with different transition densities. By dividing the single fixed pattern into multiple alternatives and selecting based on transition density requirements, the system reduces EMI through a relatively simple selection process rather than complex scrambling
Data Source
AI summary
Methods and apparatus for the scrambling of control symbols. In one embodiment, the control symbols are associated with an HDMI interface, and the methods and apparatus are configured to scramble the symbols to as to mitigate the effects of electromagnetic interference (EMI) created by the transmission of otherwise unscrambled sequences of symbols which may contain significant “clock pattern” or other undesirable artifact.