Display Clock Modulation for EMI Reduction and Defect Prevention
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Solution Overview
Problem
Display devices using spread spectrum clock generation (SSCG) to reduce electro-magnetic interference (EMI) often suffer from horizontal line defects and waterfall defects due to periodic changes in clock signal frequencies, leading to inconsistent pixel charging rates and luminance issues.
Innovation Solution
A method and apparatus for a display device that randomly selects the output frame frequency and/or modulation frequency within a predetermined range for each frame, adjusting the output timing of image data to synchronize with a modulated clock signal, thereby preventing or mitigating horizontal line and waterfall defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If spread spectrum clock generation is used to reduce EMI, then electro-magnetic interference is reduced, but horizontal line defects and waterfall defects occur due to periodic clock frequency changes
Solution Approach 1:
The patent applies dynamics by making the clock signal frequency variable rather than fixed. The SSCG module dynamically modulates the clock signal frequency around a center frequency according to a modulation signal, creating a spread spectrum effect that reduces EMI while the randomization technique dynamically changes the modulation pattern to prevent periodic defects
Solution Approach 2:
The patent uses periodic action through the modulation signal that periodically varies the clock frequency. The modulation signal has a specific modulation frequency that creates periodic frequency deviations from the center frequency, achieving spread spectrum clock generation. Additionally, a randomization signal is applied to periodically change the modulation parameters to prevent horizontal line and waterfall defects
Solution Approach 3:
The patent implements parameter changes by modifying the clock signal frequency parameter through spread spectrum modulation. The frequency parameter is changed from a fixed value to a varying value that spreads across a frequency range, reducing EMI. The randomization technique further changes the modulation frequency and depth parameters to eliminate periodic defects
2Object-affected harmful factors
If clock signal frequency is periodically changed to disperse power across frequency domain, then EMI is reduced, but pixel charging rates vary according to horizontal lines
Solution Approach 1:
The system dynamically adjusts the clock frequency using SSCG modulation, making it variable rather than static. The randomization technique adds another layer of dynamics by continuously changing the modulation parameters, ensuring that pixel charging rates remain consistent across different horizontal lines despite the frequency variations
Solution Approach 2:
The patent changes the clock signal frequency parameter through spread spectrum modulation, dispersing power across the frequency domain to reduce EMI. The randomization technique further changes the modulation frequency and depth parameters to prevent systematic variations in pixel charging rates across horizontal lines
Data Source
AI summary
A method of operating a display device includes: receiving image data at an input frame frequency; generating a modulated clock signal by modulating an input clock signal according to a modulation frequency; randomly selecting an output frame frequency within a data frequency selection range, the input frame frequency being within the data frequency selection range; determining an output start timing of the image data based on the output frame frequency; initiating, at the output start timing, output of the image data in synchronization with the modulated clock signal; and displaying an image based on the outputted image data.