Digital Extrapolation for Analog Filter Bandwidth Calibration
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Solution Overview
Problem
Conventional closed-loop calibration of analog filters in disk drives is slow, taking hundreds of microseconds to converge, which impacts seek times and format efficiency, requiring redundant calibration and causing missed servo or data wedges due to the lengthy calibration process.
Innovation Solution
A digital processor extrapolates a proportionality constant for the programmable analog filter based on initial settings and temperature/voltage variance, allowing for rapid computation and application of new filter settings when shifting between data and servo zones, reducing calibration time to approximately 1 μs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If closed-loop calibration is used to accurately fix analog filter bandwidth, then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The patent replaces the conventional closed-loop analog calibration mechanism with an open-loop digital calibration approach. Instead of using analog time-constant sensing and closed-loop control, the system uses digital signal processing to measure the PLL frequency and compute filter bandwidth settings, eliminating the slow analog convergence process while maintaining calibration accuracy.
Solution Approach 2:
The patent creates a digital replica or model of the filter bandwidth characteristics based on the measured PLL frequency. By establishing a relationship between PLL frequency and optimal filter bandwidth through digital measurement and computation, the system can determine filter settings without performing slow closed-loop analog calibration, thus reducing calibration time while preserving accuracy.
2Reliability
If redundant and independent calibration of data and servo is performed, then reliability is improved, but productivity decreases
Solution Approach 1:
The patent implements a universal open-loop calibration methodology that can be applied to both data and servo channels using the same digital processing approach. Instead of performing separate closed-loop calibrations for each channel, the system uses a unified digital calibration process that determines filter bandwidth settings based on PLL frequency measurements, making the calibration process applicable to multiple channels simultaneously and improving format efficiency.
3Measurement precision
If head goes over disk-track multiple times for calibration, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent performs preliminary digital calibration measurements of the PLL frequency and computes the filter bandwidth settings in advance using open-loop digital processing. By determining the optimal filter settings through digital computation before actual data or servo reading begins, the system eliminates the need for multiple track passes that were required in conventional closed-loop calibration, thus reducing seek time while maintaining calibration accuracy.
Data Source
AI summary
Systems and methods for improving seek times in a read channel performing a read operation on a disk drive are disclosed. The method includes extrapolating, based on initial filter settings corresponding to a first user-data region or a first servo-data region and tracked settings varying over time, a proportionality constant for the programmable analog filter, in response to determining a new target frequency for the programmable analog filter corresponding to a second user-data region or a second servo-data region, computing new filter settings for the programmable analog filter based on the extrapolated proportionality constant, and transmitting, to the programmable analog filter, the computed new filter settings corresponding to the new target frequency of the second user-data region or the second servo-data region.