Dynamic Wave Shaper Write Driver for Magnetic Disk Drive Overshoot Control
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Solution Overview
Problem
Magnetic recording hard disk drives face challenges in generating optimal write current pulses for closely-spaced transitions and long sequences of non-transitions, leading to data degradation due to far track erasure caused by excessive overshoot amplitude.
Innovation Solution
A dynamic wave shaper write driver that adjusts overshoot current amplitude based on the frequency of transitions in the data signal, using logic circuitry to generate different overshoot current levels, ensuring adequate flux for closely-spaced transitions and minimizing far track erasure for long sequences of non-transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a larger-than-nominal overshoot amplitude is used for closely-spaced transitions, then adequate flux is generated to saturate the media, but far track erasure occurs due to excessive overshoot amplitude affecting other tracks
Solution Approach 1:
The patent applies dynamics by making the overshoot amplitude adjustable rather than fixed. The write driver dynamically changes the overshoot amplitude based on detected data patterns - using larger overshoot for closely-spaced transitions and smaller overshoot for long sequences of non-transitions. This dynamic adjustment resolves the contradiction by adapting the overshoot level to the specific writing conditions, ensuring adequate flux for saturation when needed while preventing far track erasure when not needed.
Solution Approach 2:
The patent implements parameter changes by varying the overshoot amplitude parameter according to the transition frequency in the data pattern. The system detects whether transitions are closely-spaced or separated by long non-transition sequences, and accordingly adjusts the overshoot amplitude parameter to either larger-than-nominal or smaller-than-nominal values. This parameter adaptation allows the system to optimize write performance for different data patterns while avoiding the harmful effects of excessive overshoot.
2Adaptability or versatility
If a fixed nominal overshoot amplitude is used, then the device complexity is low, but it cannot optimize write current for both closely-spaced transitions and long sequences of non-transitions
Solution Approach 1:
The patent applies feedback by incorporating logic circuitry that detects the data pattern (transition frequency) and uses this information to control the overshoot amplitude. The write driver monitors the incoming data, identifies whether transitions are closely-spaced or separated by long non-transition sequences, and automatically adjusts the overshoot amplitude accordingly. This feedback mechanism enables the system to adapt to different writing conditions without requiring manual intervention or complex external control.
Solution Approach 2:
The patent uses an intermediary logic circuit within the write driver that acts as a mediator between the data input and the overshoot amplitude control. This logic circuit detects transition patterns and generates control signals that select appropriate overshoot amplitude levels. By introducing this intermediary element, the system achieves adaptive write current optimization while keeping the overall device complexity manageable through integration within the existing write driver architecture.
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
The solution effectively generates appropriate write current pulses, preventing or minimizing far track erasure by adjusting overshoot current amplitude in response to transition patterns, thereby improving data integrity and reducing data degradation.
Implementation Method 1
The preamp IC is typically located on the arm of the actuator that moves the read/write heads to the selected data tracks on the disks. The data to be written by the write head is sent from the SOC to the preamp IC, where the write driver generates analog write current pulses that are applied to the inductive coil in the write head to write data by selectively magnetizing the magnetic media of the recording layer on the disk.
Data Source
AI summary
A disk drive dynamic wave shaper (DWS) write driver includes a write current generator that produces a baseline output current for the write current pulses and an overshoot current generator that produces an overshoot current with different values. The overshoot current is added to the baseline current, with the value of the overshoot current amplitude (OSA) being selected in response to the frequency of transitions in the write data signal. The write driver includes logic circuitry that detects the pattern of transitions. Transitions that are immediately followed by a transition will receive a larger-than-nominal OSA1, transitions that are not immediately followed by a transition and that are not preceded by a long sequence of non-transitions will receive a nominal OSA2, and transitions after longer sequences of non-transitions will receive a smaller-than-nominal OSA3.