US5301080A
Expired / Lapsed
US
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Bias servo loop for magneto-resistive read/write head
Assignee: HGST Netherlands BV
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Filing: 1992-12-31
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Granted: 1994-04-05
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Expires: 2012-12-31
Abstract
Abstract A bias current servo loop for a magneto-resistive recording head detects distortion in the read signal from the MR head, and adjusts the operating point for the head to minimize the distortion. The distortion is detected by monitoring the second harmonic of a digitized sample of the read signal. A running average of the digitized amplitude of the second harmonic is generated by a digital bandpass filter. The root mean square of the running average of the digitized amplitude of the second harmonic is estimated. The estimated RMS value is compared against a reference value indicative of minimum distortion and the difference between the estimated RMS value and the reference value is used to adjust the bias current.
Inventors
- 👤 Hal H. Ottesen
- 👤 Gordon J. Smith
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 08:38
CPC Classifications
G; G11; G11B; G11B27/00; G11B27/36; G11B5/00; G11B5/02; G11B5/027; G11B5/035; G11B2005/0002; G11B2005/0005; G11B2005/001; G11B2005/0013; G11B2005/0016; G11B2005/0018
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
101 words
Apparatus for linearizing the magnetic field to output signal transfer characteristic of a magneto-resistive element comprising: means for biasing the element at an operating point where fluctuations in magnetic field produce a substantially linear fluctuation in resistance of the element; means for monitoring the amplitude of an even harmonic of the digitized signal sensed by the element; and means responsive to the amplitude of the even harmonic for adjusting said biasing means to move the operating point until the amplitude of the even harmonic is minimized whereby the element is biased at the optimum operating point for linearizing the transfer characteristic.
Claim 2
Dependent Claim
101 words
Apparatus for linearizing the magnetic field to output signal transfer characteristic of a magneto-resistive element comprising: means for biasing the element at an operating point where fluctuations in magnetic field produce a substantially linear fluctuation in resistance of the element; means for monitoring the amplitude of an even harmonic of the digitized signal sensed by the element; and means responsive to the amplitude of the even harmonic for adjusting said biasing means to move the operating point until the amplitude of the even harmonic is minimized whereby the element is biased at the optimum operating point for linearizing the transfer characteristic.
Claim 3
Dependent Claim
43 words
The apparatus of claim 1 wherein said monitoring means comprises: means for digitizing the signal sensed by the element; and means for filtering the digitized signal to produce an amplitude signal indicative of the amplitude of the second harmonic of the digitized signal.
Claim 4
Dependent Claim
19 words
The apparatus of claim 2 and in addition: means for determining the root mean square of the amplitude signal.
Claim 5
Dependent Claim
68 words
The apparatus of claim 3 wherein said adjusting means comprises: means for comparing the root mean square of the amplitude of the second harmonic to a reference value and generating a bias current error signal; and means responsive to the bias current error signal for driving the bias current to reduce the error signal and thereby bring the amplitude of the second harmonic equal with the reference value.
Claim 6
Dependent Claim
27 words
The apparatus of claim 4 and in addition: means for calibrating the reference value to produce the minimum amplitude of the second harmonic of the digitized signal.
Claim 7
Dependent Claim
63 words
The apparatus of claim 1 wherein said adjusting means comprises: means for comparing the amplitude of the even harmonic to a reference value and generating a bias current error signal; and means responsive to the bias current error signal for driving the bias current to reduce the error signal and thereby bring the amplitude of the even harmonic equal with the reference value.
Claim 8
Dependent Claim
27 words
The apparatus of claim 4 and in addition: means for calibrating the reference value to produce the minimum amplitude of the even harmonic of the digitized signal.
Claim 9
Dependent Claim
84 words
Bias current servo apparatus for a magneto-resistive (MR) read/write head for controlling a bias current applied to the head and thereby the operating point of the head, said apparatus comprising: means for driving the MR head with the bias current; means for digitizing the read signal from the head; means for detecting the amplitude of a harmonic of the digitized read signal; and means responsive to the harmonic amplitude for adjusting said driving means to change the bias current applied to the MR head.
Claim 10
Dependent Claim
84 words
Bias current servo apparatus for a magneto-resistive (MR) read/write head for controlling a bias current applied to the head and thereby the operating point of the head, said apparatus comprising: means for driving the MR head with the bias current; means for digitizing the read signal from the head; means for detecting the amplitude of a harmonic of the digitized read signal; and means responsive to the harmonic amplitude for adjusting said driving means to change the bias current applied to the MR head.
Claim 11
Dependent Claim
27 words
The servo apparatus of claim 8 wherein said digitizing means comprises: means for periodically sampling the analog read signal to produce digital samples of the read signal.
Claim 12
Dependent Claim
34 words
The servo apparatus of claim 9 wherein said detecting means comprises: means for digitally filtering the digital samples to produce an amplitude value indicative of the amplitude of a harmonic of the digital samples.
Claim 13
Dependent Claim
83 words
The servo apparatus of claim 10 wherein: said adjusting means responsive to the harmonic amplitude value for comparing the amplitude value to a reference value indicative of the optimum operating point for the MR head and for generating a bias current error signal indicative of the difference between the amplitude value and the reference value; and said driving means responsive to said bias current error signal for changing the bias current applied to the MR head to reduce the bias current error signal.
Claim 14
Dependent Claim
66 words
The servo apparatus of claim 9 wherein said detecting means comprises: means for digitally filtering the digital samples to produce an amplitude value indicative of the amplitude of the second harmonic of the digital samples; and means for taking the root mean square (RMS) of the second harmonic amplitude value and generating an RMS value from the amplitude of the second harmonic of the digital samples.
Claim 15
Dependent Claim
82 words
The servo apparatus of claim 12 wherein: said adjusting means responsive to the RMS value for comparing the RMS value to a reference value indicative of the optimum operating point for the MR head and for generating a bias current error signal indicative of the difference between the RMS value and the reference value; and said driving means responsive to said bias current error signal for changing the bias current applied to the MR head to reduce the bias current error signal.
Claim 16
Dependent Claim
34 words
The servo apparatus of claim 13 and in addition: means responsive to the RMS value for calibrating the reference value by incrementing and decrementing the reference value until the RMS value reaches a minimum.
Claim 17
Dependent Claim
34 words
The servo apparatus of claim 8 wherein said detecting means comprises: means for digitally filtering the digitized signal to produce an amplitude value indicative of the amplitude of a harmonic of the digitized signal.
Claim 18
Dependent Claim
83 words
The servo apparatus of claim 15 wherein: said adjusting means responsive to the harmonic amplitude value for comparing the amplitude value to a reference value indicative of the optimum operating point for the MR head and for generating a bias current error signal indicative of the difference between the amplitude value and the reference value; and said driving means responsive to said bias current error signal for changing the bias current applied to the MR head to reduce the bias current error signal.
Claim 19
Dependent Claim
36 words
The servo apparatus of claim 16 and in addition: means responsive to the harmonic amplitude value for calibrating the reference value by incrementing and decrementing the reference value until the harmonic amplitude value reaches a minimum.
Claim 20
Dependent Claim
66 words
The servo apparatus of claim 8 wherein said detecting means comprises: means for digitally filtering the digitized signal to produce an amplitude value indicative of the amplitude of the second harmonic of the digitized signal; and means for taking the root mean square (RMS) of the second harmonic amplitude value and generating an RMS value from the amplitude of the second harmonic of the digitized signal.
Claim 21
Dependent Claim
82 words
The servo apparatus of claim 18 wherein: said adjusting means responsive to the RMS value for comparing the RMS value to a reference value indicative of the optimum operating point for the MR head and for generating a bias current error signal indicative of the difference between the RMS value and the reference value; and said driving means responsive to said bias current error signal for changing the bias current applied to the MR head to reduce the bias current error signal.
Claim 22
Dependent Claim
105 words
Apparatus for linearizing the magnetic field to output signal transfer characteristic of a magneto-resistive element comprising: means for biasing the element at an operating point where fluctuations in magnetic field produce a substantially linear fluctuation in resistance of the element; means for monitoring the amplitude of more than one even harmonic of the digitized signal sensed by the element; and means responsive to the amplitude of more than one even harmonic for adjusting said biasing means to move the operating point until the amplitude of the even harmonics is minimized whereby the element is biased at the optimum operating point for linearizing the transfer characteristic.
Claim 23
Dependent Claim
105 words
Apparatus for linearizing the magnetic field to output signal transfer characteristic of a magneto-resistive element comprising: means for biasing the element at an operating point where fluctuations in magnetic field produce a substantially linear fluctuation in resistance of the element; means for monitoring the amplitude of more than one even harmonic of the digitized signal sensed by the element; and means responsive to the amplitude of more than one even harmonic for adjusting said biasing means to move the operating point until the amplitude of the even harmonics is minimized whereby the element is biased at the optimum operating point for linearizing the transfer characteristic.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1997-04-04 | 1997-10-04 | 1998-04-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-04-04 | 2001-10-04 | 2002-04-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-04-04 | 2005-10-04 | 2006-04-05 | $7700.00 | Window Closed / Lapsed |