Disk Drive Servo Master Timer SAM Detection Error Compensation
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Solution Overview
Problem
Existing servo control systems in disk drives face challenges in making precise timing adjustments when servo address marks (SAMs) are not detected within the allowable window, particularly in power-saving modes, leading to issues with jitter and errors.
Innovation Solution
A single servo master timer is used to control timing critical signals, adjustable to compensate for SAM detection errors by selecting between the disk lock clock (DLC)/disk synchronous write clock (DSW) and system clock, allowing for precise timing adjustments and power management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the disk lock clock (DLC)/disk synchronous write clock (DSW) is used for SAM detection, then timing precision is improved, but power consumption increases due to additional active electronics
Solution Approach 1:
The system dynamically switches between two clock sources (DLC/DSW and system clock) based on operational state. During active operation, the DLC/DSW clock is used for precise SAM detection. During power-saving modes, the system switches to the lower-power system clock, thereby adapting the timing source to current power requirements while maintaining detection capability.
Solution Approach 2:
The patent changes the clock source parameter based on power management state. By selecting different clock sources (DLC/DSW versus system clock) depending on whether the drive is in active or power-saving mode, the system optimizes the balance between detection precision and power consumption without requiring continuous high-power operation.
2Use of energy by moving object
If the read channel is shut down in power-saving modes, then power consumption is reduced, but the DSW clock becomes unavailable for SAM detection
Solution Approach 1:
The system introduces an intermediary solution by using the system clock as a substitute for the DSW clock when the read channel is powered down. This intermediary clock source allows the master timer to continue operating and maintaining timing functionality even when the primary DSW clock is unavailable due to power-saving mode.
Solution Approach 2:
The system dynamically adapts its clock source based on power management state. When the read channel is active, the DSW clock is used. When the read channel is shut down for power saving, the system automatically switches to using the system clock, thereby maintaining operational reliability across different power states without requiring the read channel to remain active.
3Reliability
If a shorter SAM detection window is used, then misdetection is reduced, but timing precision requirements increase
Solution Approach 1:
The system uses feedback from the master timer to continuously monitor and adjust timing parameters. By measuring actual SAM intervals and comparing them against expected values, the system can dynamically adjust the timing window and compensate for drift, thereby maintaining both a relatively short detection window for reduced misdetection and sufficient timing precision through active correction.
4Use of energy by moving object
If the system clock is used instead of DLC/DSW clock, then power consumption is reduced, but SAM detection precision deteriorates
Solution Approach 1:
The system dynamically selects the appropriate clock source based on operational state. During active operation when precision is critical, the DLC/DSW clock is used. During power-saving modes when precision requirements are reduced, the system clock suffices. This dynamic selection optimizes the trade-off between power consumption and precision based on current operational needs.
Solution Approach 2:
The patent changes the clock source parameter based on power management state. By selecting different clock sources (DLC/DSW versus system clock) depending on whether the drive is in active or power-saving mode, the system optimizes the balance between detection precision and power consumption without requiring continuous high-power operation.
Data Source
AI summary
A disk drive is described with a single servo master timer that is used to control timing critical signals such as servo gate, SAM windows, channel power save, PREAMP power save and so on. The master timer is adjusted to compensate for SAM detection errors (early, late or missed) and provides improved servo timing quality. In an embodiment the adjustable master timer can be selectably clocked by either the DLC/DSW clock or the system clock.