HDMI Control Symbol Scrambling for Lower EMI and Spurious Emissions
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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 undesirable electromagnetic radiation and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control symbols are transmitted repeatedly with predominant clock pattern content, then control signal transmission reliability is improved, but electromagnetic interference increases
Solution Approach 1:
The patent applies parameter changes by transforming the transmission characteristics of control symbols through scrambling with pseudo-random sequences. This changes the spectral distribution and temporal patterns of the transmitted signals, converting concentrated clock patterns into dispersed random patterns that maintain reliability while reducing EMI.
Solution Approach 2:
The patent introduces pseudo-random sequences as an intermediary element between the control symbols and the transmission medium. These sequences act as a mediator that preserves the essential control information while masking the harmful clock pattern characteristics that cause electromagnetic interference.
2Object-generated harmful factors
If control symbols are scrambled with pseudo-random values, then electromagnetic interference is reduced, but signal complexity increases
Solution Approach 1:
The patent uses copying by generating pseudo-random sequences that are replicated and applied to scramble control symbols. The same scrambling sequences are copied and used at both transmitter and receiver ends, enabling simple implementation through sequence repetition rather than complex processing algorithms.
Solution Approach 2:
The patent simplifies complexity by changing the parameter representation from complex modulation schemes to simple XOR operations with pseudo-random sequences. This parameter change transforms a potentially complex signal processing task into a straightforward bitwise operation that is easy to implement in hardware.
3Measurement precision
If control symbols are transmitted with high transition content for synchronization, then symbol alignment is improved, but spurious emissions increase
Solution Approach 1:
The patent applies periodic action by inserting unscrambled control symbols at regular intervals within the scrambled transmission stream. These periodic unscrawbled segments provide consistent synchronization references with high transition content for accurate symbol alignment, while the majority scrambled portions minimize spurious emissions.
Solution Approach 2:
The patent segments the transmission stream into alternating portions of scrambled and unscrawbled control symbols. This segmentation allows different portions to serve different functions: scrambled segments reduce EMI while unscrawbled segments provide synchronization, resolving the contradiction between alignment precision and emission levels.
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.