Optical Disc Skew Detection Using Adjacent Track Crosstalk Cancellation
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Solution Overview
Problem
Existing optical disc systems face challenges in accurately detecting skew due to warpage or tilt, leading to increased aberration and crosstalk, which complicates signal reproduction and requires complex skew sensors, making gain setting difficult and costly.
Innovation Solution
A method and device that utilize reproduction signals from adjacent tracks to cancel crosstalk by combining output signals from filters, controlling coefficients to reduce errors, and detecting skew from filter tap coefficients, eliminating the need for a skew sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a skew sensor is used to detect skew of the optical disc, then the detection accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The patent creates a virtual copy of the skew sensor functionality by using signal processing algorithms that analyze reproduction signals from adjacent tracks. Instead of using a physical skew sensor, the system computes skew information from existing optical signals through digital processing, effectively copying the detection capability through software rather than hardware
Solution Approach 2:
The patent replaces the mechanical/optical skew sensor system with a signal processing-based detection method. By using digital filters and coefficient analysis on reproduction signals, the system substitutes physical measurement mechanisms with computational methods, thereby reducing device complexity while maintaining detection capability
2Manufacturing precision
If the numerical aperture of the objective lens is increased to narrow the beam spot diameter, then the surface recording density is improved, but the aberration increases leading to signal quality deterioration
Solution Approach 1:
The patent changes the parameter being optimized from beam spot characteristics to signal processing characteristics. By using digital filters with adjustable coefficients and analyzing reproduction signals through computational methods, the system compensates for optical aberrations introduced by high numerical aperture lenses, thereby maintaining signal quality while achieving high recording density
Solution Approach 2:
The patent introduces digital signal processing as an intermediary between the optical system and the final data reproduction. The signal processing unit acts as a mediator that corrects distortions and crosstalk caused by high NA optics, allowing the system to benefit from high recording density while mitigating the negative effects of increased aberration
3Reliability
If reproduction signals from adjacent tracks are used to cancel crosstalk, then the signal quality is improved, but the processing complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing optimal filter coefficients that are used to cancel crosstalk from adjacent tracks. Instead of performing complex real-time calculations during signal reproduction, the system prepares correction parameters in advance, reducing the computational burden during actual operation while maintaining effective crosstalk cancellation
Solution Approach 2:
The patent implements feedback by using the detected skew information and crosstalk characteristics to adjust filter coefficients dynamically. The system continuously monitors reproduction signal quality and adapts the signal processing parameters accordingly, creating a closed-loop control system that improves signal quality while managing processing complexity through intelligent adaptation
Data Source
AI summary
There is provided a skew detection method including supplying reproduction signals, which are respectively reproduced approximately simultaneously from at least two tracks including a first adjacent track and a second adjacent track located on both sides of a main track, to first and second filters, causing a combining unit to combine output signals of the first and second filters with a reproduction signal which is reproduced from the main track approximately simultaneously with the first adjacent track and the second adjacent track so as to cancel crosstalk, causing a coefficient control unit to obtain an error with a target value of the output signal of the combining unit and control coefficients of the first and second filters so as to reduce the error, and detecting a skew of an optical disc from values of coefficients of predetermined taps of the first and second filters.