Nonlinear MR Head Biasing Circuit Calibration
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Solution Overview
Problem
The calibration of magneto-resistive (MR) heads in hard disk drives is slow due to linearly increasing calibration currents, which can damage the MR heads if the voltage overshoots beyond the maximum allowable limit, and existing methods do not efficiently balance the calibration process for accurate bias voltage determination.
Innovation Solution
A system that uses a biasing circuit and a calibration module to nonlinearly increase the calibration current, employing a first and second head with matched resistances to safely and quickly calibrate the MR head by generating a reference voltage and adjusting the current non-sequentially to prevent overshoot, ensuring the MR head is not damaged during calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If linearly increasing calibration current is used, then the calibration process is simple to implement, but the calibration speed is slow and voltage overshoot may damage the MR head
Solution Approach 1:
The patent applies dynamics by making the calibration current increase rate variable rather than constant. The current increases slowly when approaching the target voltage to prevent overshoot and damage, then increases faster when away from the target, optimizing both safety and speed. This is implemented through monitoring the voltage across the MR head and adjusting the current ramp rate dynamically based on the proximity to the calibration target.
Solution Approach 2:
The patent implements feedback by continuously monitoring the voltage across the MR head during calibration and using this information to control the calibration current. The system measures the voltage, compares it to the target calibration voltage, and adjusts the current accordingly - reducing the ramp rate when approaching the target to prevent overshoot, thus ensuring both safety and efficiency.
2Ease of operation
If linearly increasing calibration current is used, then the calibration method is easy to control, but the calibration time is extended
Solution Approach 1:
The patent makes the calibration process adaptive by dynamically adjusting the current increase rate based on real-time voltage measurements. The system transitions from a static linear increase to a dynamic process where the ramp rate changes automatically - slower near the target for precision, faster away from it for speed, thus reducing total calibration time while maintaining ease of control through automated adjustment.
Solution Approach 2:
The patent changes the parameter of current increase rate from constant to variable during calibration. By modifying this parameter dynamically based on the calibration progress and voltage feedback, the system optimizes the balance between control simplicity and calibration time, achieving faster calibration without complex manual intervention.
3Measurement precision
If voltage is increased to improve calibration accuracy, then the bias voltage determination becomes more precise, but the risk of voltage overshoot and head damage increases
Solution Approach 1:
The patent uses feedback to continuously monitor the voltage across the MR head and compare it to the target calibration voltage. This feedback mechanism allows the system to determine when the calibration voltage is approaching the target and automatically reduce the current increase rate, ensuring precise bias voltage determination while preventing voltage overshoot that could damage the head.
Solution Approach 2:
The patent applies beforehand cushioning by reducing the current increase rate in advance when the calibration voltage approaches the target value. This proactive reduction in ramp rate creates a cushioning effect that prevents voltage overshoot before it can occur, protecting the MR head from damage while still achieving accurate bias voltage determination.
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 method allows for rapid and safe calibration of MR heads by nonlinearly increasing the calibration current, preventing voltage overshoot and ensuring accurate bias voltage determination, thus enhancing the reliability and speed of the calibration process.
Implementation Method 1
The magneto-resistive read element in the head 20 typically comprises a sensing layer made of MR material. The resistance of the MR material in the sensing layer changes in response to changing magnetic field.
Implementation Method 2
The operational amplifier communicates with the MR head and generates an output based on the second reference voltage and a second voltage across the MR head
Data Source
AI summary
A system for calibrating a magneto-resistive (MR) head includes a biasing circuit and a calibration module. The biasing circuit generates a first current to bias a first head during a calibration mode and a calibrated current to bias the MR head during an operating mode. The calibration module calibrates the first current during the calibration mode by adjusting the first current using nonlinear steps to determine the calibrated current.