Differential RTD Sensing With Chopping Amplifier for Fly Height Feedback
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Solution Overview
Problem
Current hard disk drives (HDDs) face challenges in accurately monitoring and controlling fly height due to limitations in resistance detection architectures, which often require switching between AC and DC modes and involve time-consuming averaging to reduce noise.
Innovation Solution
A dual path resistance detection and monitoring architecture that supports continuous operation in both AC and DC modes, reduces test time, and eliminates the need for extensive averaging by modulating the RTD signal to higher frequencies, demodulating, and filtering out 1/f noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If AC mode detection is used for defect scanning during manufacturing, then measurement precision is improved, but device complexity increases due to mode switching requirements
Solution Approach 1:
The patent divides the detection architecture into separate AC and DC paths, each optimized for specific functions. The AC path handles defect scanning with high precision, while the DC path enables continuous monitoring without mode switching. This segmentation allows each path to be independently optimized, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The dual path architecture provides multi-functionality by enabling both AC and DC modes to operate simultaneously or independently. The system can perform defect scanning using AC mode while maintaining continuous fly height monitoring via DC mode, eliminating the need to switch between modes and reducing overall system complexity.
2Ease of operation
If DC mode detection is used for real-time fly height monitoring, then ease of operation is improved, but measurement precision deteriorates due to low frequency noise
Solution Approach 1:
The patent applies periodic action by modulating the DC bias signal at a high frequency (e.g., 100 kHz) to create an AC-like signal that can be processed with higher precision. This modulation technique allows the system to maintain the ease of continuous DC monitoring while achieving the measurement precision typically associated with AC mode detection.
Solution Approach 2:
The patent introduces a modulator as an intermediary component that converts the DC bias signal into a high-frequency modulated signal. This intermediary enables the DC monitoring path to achieve AC-level precision by transforming the signal characteristics without requiring a complete mode switch, thus maintaining ease of operation while improving measurement precision.
3Measurement precision
If extensive averaging is applied to reduce noise in DC mode measurements, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent changes the frequency parameter of the bias signal from DC (0 Hz) to a high frequency (e.g., 100 kHz). This parameter change shifts the measurement bandwidth away from low-frequency noise sources, allowing for rapid measurements without extensive averaging. The high-frequency modulation enables precision measurement while maintaining real-time monitoring capability.
4Device complexity
If a single electrical path is used for resistance detection, then device complexity is reduced, but adaptability deteriorates due to inability to perform both defect scanning and continuous monitoring simultaneously
Solution Approach 1:
The patent segments the electrical path into distinct AC and DC paths, each optimized for specific detection functions. The AC path is dedicated to defect scanning with high sensitivity, while the DC path handles continuous fly height monitoring. This segmentation allows the system to perform both functions simultaneously without mode switching, enhancing adaptability while maintaining manageable complexity.
Solution Approach 2:
The dual path architecture provides universal functionality by enabling the system to perform multiple detection tasks concurrently. Both defect scanning and continuous fly height monitoring can operate simultaneously through their respective paths, eliminating the trade-off between complexity and adaptability that would exist in a single-path system.
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 solution enables real-time feedback on fly height with reduced noise interference, improving the accuracy and efficiency of fly height monitoring and control in HDDs.
Implementation Method 1
The resistance value or change in resistance value of the RTD may be detected using a direct current (DC) mode or an alternating current (AC) mode
Implementation Method 2
eliminates the need for extensive averaging by modulating the RTD signal to higher frequencies, demodulating, and filtering out 1/f noise
Implementation Method 3
filtering out 1/f noise
Data Source
AI summary
A data storage device comprises a first resistive temperature detector (RTD) and a second RTD coupled to a first voltage source. A tuning bridge coupled between the first and second RTDs and a second voltage source reduces offset between a first bias voltage across the first RTD and a second bias voltage across the second RTD. A low noise amplifier (LNA) receives the first and second bias voltages as a differential bias voltage. A modulator coupled between the first and second RTDs and the LNA modulates the differential bias voltage.