Imaging Clock Spread Spectrum Modulation for EMI Without Row Noise
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Solution Overview
Problem
Existing electronic devices face challenges in reducing electromagnetic interference (EMI) from video clock signals, particularly under voltage and temperature variations, which can lead to artifacts like row noise in video images, and require effective methods to comply with regulatory limits without compromising image quality.
Innovation Solution
A clock signal generator that determines the pixel count in a horizontal line of an image and spreads the frequency of the imaging clock signal across a range at a modulation rate based on this count, using a phase-lock loop and modulation circuit, and adjusts the frequency range to compensate for voltage and temperature variations, thereby reducing EMI without causing undesirable artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the frequency of the video clock signal is spread over a frequency band to reduce electromagnetic interference, then electromagnetic interference is reduced, but artifacts such as row noise occur in the video image
Solution Approach 1:
The patent applies dynamics by making the modulation rate variable rather than fixed. The modulation rate is dynamically adjusted based on the horizontal sync signal frequency and pixel count to ensure it remains below the threshold that causes row noise. This allows the system to maintain effective EMI reduction while preventing image artifacts under varying operating conditions.
Solution Approach 2:
The patent changes the modulation rate parameter adaptively based on operating conditions. By calculating the modulation rate as a function of horizontal sync frequency and pixel count, and adjusting it to stay below the critical threshold, the system optimizes the balance between EMI reduction effectiveness and video image quality across different operating scenarios.
2Manufacturing precision
If the video clock signal is modulated with the horizontal sync signal to spread frequency and reduce artifacts, then artifacts are reduced, but the technique becomes sensitive to voltage and temperature variations
Solution Approach 1:
The patent implements feedback by continuously monitoring the actual modulation rate and comparing it against the calculated threshold. When voltage or temperature variations cause drift in the clock signal frequency, the system detects this through the horizontal sync signal and adjusts the modulation rate accordingly to maintain it below the artifact-causing threshold, ensuring consistent performance.
Solution Approach 2:
The system dynamically adjusts the modulation rate in response to changing operating conditions. By making the modulation rate dependent on real-time measurements of horizontal sync frequency and pixel count, the system adapts to voltage and temperature variations, maintaining reliable operation across different environmental conditions.
3Object-generated harmful factors
If a fixed modulation rate is used to spread the clock signal frequency, then electromagnetic interference is reduced, but row noise occurs in the video image
Solution Approach 1:
The patent changes the modulation rate parameter from a fixed value to a variable that depends on operating conditions. By calculating the appropriate modulation rate based on horizontal sync frequency and pixel count, and adjusting it dynamically, the system maintains EMI reduction effectiveness while avoiding the row noise that occurs with fixed modulation rates.
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 approach effectively minimizes electromagnetic interference in video clock signals, ensuring compliance with regulatory limits while maintaining image integrity and reliability across varying conditions, reducing the need for electromagnetic shielding and enhancing the system's overall performance.
Implementation Method 1
The voltage-controlled oscillator is phase-locked to a reference clock signal
Implementation Method 2
spreads the frequency of the imaging clock signal across a frequency range at a modulation rate
Data Source
AI summary
A clock signal generator includes a phase-lock loop for generating an imaging clock signal having a frequency based on a reference clock signal. The imaging clock signal generator also includes a modulation circuit for determining a number of pixels in a horizontal line of an image to be generated based on the imaging clock signal. The modulation circuit generates a modulation signal based on the determined number of pixels and the clock signal generator spreads the frequency of the imaging clock signal across a frequency range based on the modulation signal. In this way, the clock signal generator reduces electromagnetic interference in the imaging clock signal. In further embodiments, the clock signal generator generates an adjustment signal for adjusting the frequency range based on the frequency of the reference clock signal and the frequency of the imaging clock signal.