Optical Disc Drive LVDS Write Strategy Signal Impedance Matching
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Solution Overview
Problem
Conventional optical disc drives with high-speed recording capabilities experience increased error rates due to distortion and jitter in the write strategy signal transmission, particularly when using low voltage differential signaling (LVDS) for cost reduction, leading to suboptimal recording quality.
Innovation Solution
Incorporating a resistor between the differential lines of the LVDS driver output to reduce pattern jitter by matching impedance and suppressing reflected waves, thereby enhancing the transmission quality of the write strategy signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LVDS transmission is used to reduce cost and chip size, then manufacturing cost and device complexity are reduced, but signal transmission quality deteriorates due to high output impedance causing pattern jitter and reflected waves
Solution Approach 1:
A series resistor is introduced as an intermediary element between the LVDS driver output and the transmission line. This resistor acts as a mediator to match the impedance between the driver and the transmission line, reducing reflected waves and pattern jitter while maintaining the cost benefits of LVDS transmission.
Solution Approach 2:
The output impedance parameter of the LVDS driver is modified by adding a series resistor. This changes the overall impedance characteristic to better match the transmission line impedance, thereby reducing signal reflections and improving transmission quality without abandoning LVDS architecture.
2Use of energy by moving object
If LVDS driver with high output impedance is used, then power consumption is reduced, but pattern jitter increases leading to higher error rates in high-speed recording
Solution Approach 1:
The series resistor serves as an intermediary that decouples the high output impedance characteristic from its harmful effect. It allows the LVDS driver to maintain its low power consumption while the resistor network (driver output impedance + series resistor) collectively provides the appropriate impedance matching to reduce pattern jitter.
Solution Approach 2:
The total series resistance in the signal path is adjusted by adding the external resistor to the driver's output impedance. This parameter change optimizes the damping effect to reduce pattern jitter, improving recording precision while preserving the energy efficiency of LVDS transmission.
3Reliability
If complicated write strategy circuit is integrated in LDD chip, then chip size increases, but write strategy signal quality improves
Solution Approach 1:
The write strategy circuit is extracted from the LDD chip and placed in the DSP. This separation allows the LDD chip to maintain its compact size while the write strategy signal quality is improved through the combination of DSP-generated signal and optimized transmission path with impedance matching.
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 configuration effectively reduces pattern jitter and error rates in high-speed recording, achieving high-quality recording with reduced errors, even in low-cost configurations, by optimizing the resistance value and placement of the resistor between the differential lines.
Implementation Method 1
Incorporating a resistor between the differential lines of the LVDS driver output to reduce pattern jitter by matching impedance and suppressing reflected waves
Data Source
AI summary
There is provided an optical disc drive comprises an optical pick-up including a laser diode (LD) and a laser diode driver (LDD) for driving the laser diode, a digital signal processor (DSP) including a write strategy circuit and low voltage differential signaling (LVDS) drivers for transmitting a produced write strategy signal, a circuit board having the DSP mounted thereon and including a line for transmitting the write strategy signal, a transmission line connecting the circuit board and the LDD and transmitting a write strategy signal, and differential resistors connected between differential lines of outputs of the LVDS drivers. Especially, a resistor having a resistance value in a range of 80 to 500Ω is inserted between the differential lines of outputs of the LVDS driver inside the DSP.