Analog Video Sampling Clock Offset Detection by Frame Differencing
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Solution Overview
Problem
Existing methods for determining the sampling frequency and phase in analog-to-digital conversion for digital video devices are imprecise and unreliable, often relying on noisy clocks, test patterns, or static tables, which fail to accurately convert analog signals to digital formats, especially when dealing with wide-mode analog graphics sources or images with blanked regions.
Innovation Solution
A method and apparatus that use frame differencing to adjust and verify the sampling clock frequency by computing the difference between successive frames in a columnar region, allowing for accurate conversion without predefining image properties or excluding images with blanked areas, and employing a sequence of selectable phases to optimize the sampling clock frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If noisy clocks or static tables are used to determine sampling frequency, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The system uses the video signal itself to determine the sampling frequency by analyzing frame differences and pixel transitions, rather than relying on external clocks or pre-stored tables. The video signal provides the reference information needed for accurate frequency determination.
Solution Approach 2:
The patent replaces mechanical/clock-based frequency determination with a digital signal processing approach that analyzes video content characteristics (frame differences, pixel transitions) to derive sampling frequency information.
2Measurement precision
If test patterns are used to determine sampling frequency, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The system automatically determines sampling frequency using the actual video signal being processed, eliminating the need for manual test pattern generation and analysis. The video content itself serves as the reference for frequency determination.
3Manufacturing precision
If precise image data across the active region is required, then manufacturing precision is improved, but loss of substance increases
Solution Approach 1:
The patent extracts frequency determination information from specific regions of the video signal (frame differences, pixel transitions) rather than requiring analysis of the entire active region. This reduces the amount of image data needed while maintaining conversion precision.
Solution Approach 2:
The system focuses analysis on specific local characteristics of the video signal (such as pixel transitions and frame differences in particular regions) rather than requiring precise data across the entire active region, achieving accurate frequency determination with reduced data requirements.
Data Source
AI summary
A method and apparatus for an analog-to-digital video signal converter. The converter is controlled by a clock with controllable frequency and phase for sampling an analog signal. A circuit corrects the clock frequency using a period of a columnar frame differences as a function of columnar location. The sampling clock frequency is changed by an amount dependent on the period of the columnar differences. A second measure of the difference between successive frames is computed for a sequence of clock phases. The frequency of the clock is verified using a characteristic of the second measure. The characteristic can be the ratio of the maximum to the minimum of the second measure over selected clock phases. Other characteristics can be used such as a difference of a maximum and a minimum measure.