US3794987A
Expired / Lapsed
US
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Mfm readout with assymetrical data window
Assignee: Unisys Corp
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Filing: 1972-11-01
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Granted: 1974-02-26
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Expires: 1992-11-01
Abstract
Abstract In the data retrieval system utilizing a recording medium with digital data encoded in accordance with a modified frequency modulation (MFM) encoding scheme, an encoded data detection method and apparatus utilizes an assymetrical data window, the longer time period window for the binary ''''one'''' information, to retrieve the recorded data. The length of this longer time period window and its occurrence in time is selectively adjusted until a minimum error ratio for the recovery process is obtained. The MFM encoded data, recovered from the recording medium is detected by the skewable assymetrical data windows, the detected data converted to NRZ encoded digital data to be supplied to an NRZ discrimination circuit and then to a utilization circuit.
Inventors
- 👤 I Walenta
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 20:26
CPC Classifications
H; H04; H04L; H04L25/00; H04L25/38; H04L25/40; H04L25/49; H04L25/4904; G; G11; G11B; G11B20/00; G11B20/10; G11B20/14; G11B20/1403; G11B20/1423
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
178 words
Apparatus used with data retrieval systems wherein binary data bits are stored within bit cells on a record medium at a base frequency as flux transitions, a first data bit value represented by a transition occurring at the middle of a bit cell and a second date bit value represented by a transition occurring at the beginning of a bit cell, except when the second bit value follows the first bit value, for detecting the first data bit values and the second data bit values recovered from the record medium, comprising: means for generating a data window signal at said base frequency, the window signal having first and second timed portions at diverse voltage polarities, the first timed portions at one voltage polarity being longer in time than the second timed portions at another voltage polarity; and means for selectively displacing in time the first timed portions of the window signal and varying the length of the first timed portions of the window signal with respect to the length of the second timed portions of the window signal.
Claim 2
Dependent Claim
178 words
Apparatus used with data retrieval systems wherein binary data bits are stored within bit cells on a record medium at a base frequency as flux transitions, a first data bit value represented by a transition occurring at the middle of a bit cell and a second date bit value represented by a transition occurring at the beginning of a bit cell, except when the second bit value follows the first bit value, for detecting the first data bit values and the second data bit values recovered from the record medium, comprising: means for generating a data window signal at said base frequency, the window signal having first and second timed portions at diverse voltage polarities, the first timed portions at one voltage polarity being longer in time than the second timed portions at another voltage polarity; and means for selectively displacing in time the first timed portions of the window signal and varying the length of the first timed portions of the window signal with respect to the length of the second timed portions of the window signal.
Claim 3
Dependent Claim
77 words
The apparatus of claim 1 wherein said data bit window signal generating means comprises: a first monostable multivibrator responsive to a recovered data synchronized clock signal for establishing the start of the first timed portion of the data bit window signal; and a second monostable multivibrator connected to said first monostable multivibrator and responsive to the output of said first monostable multivibrator for establishing the end of the first timed portion of the data bit window signal.
Claim 4
Dependent Claim
57 words
The apparatus of claim 2 wherein said first timed portion selectively displacing and varying the length means comprises: a first capacitor and variable resistor pair connected to said first monostable multivibrator to effectively vary its time constant; and a second capacitor and variable resistor pair connected to said second monostable multivibrator to effectively vary its time constant.
Claim 5
Dependent Claim
62 words
The apparatus of claim 1 further comprising: means responsive to the output of said data bit window signal generating means and the data recovered from the record medium for representing each first data bit value by one polarity voltage and each stored data bit value by another polarity voltage, the voltage transitions occurring at the beginning and end of the bit cells.
Claim 6
Dependent Claim
58 words
The apparatus of claim 4 wherein said recovered data representing means comprises: a first flip-flop responsive to the outpUt of said data bit window signal generating means and the data recovered from the second medium; and a second flip-flop responsive to the output of said first flip-flop and the output of said data bit window signal generating means.
Claim 7
Dependent Claim
37 words
The apparatus of claim 4 further comprising: means responsive to the output of said representing means and a recovered data clock signal for synchronizing the represented data from said representing means to the recovered data clock signal.
Claim 8
Independent Claim
175 words
A method for recovering binary coded data in a data retrieval system wherein data bits are stored within bit cells, on a record medium, at a base frequency, as flux transitions, a first data bit value represented by a transition occurring at the middle of a bit cell and a second data bit value represented by a transition occurring at the beginning of a bit cell, except when the second bit value follows the first bit value, for identifying the first and second data bit values recovered from the record medium, comprising: generating a data bit window signal at said base frequency, the window signal having first and second timed portions at diverse voltage polarities, the first timed portions at one voltage polarity being longer in time than the second timed portions at another voltage polarity; and selectively displacing in time and the first timed portions of the window signal in a positive or a negative direction until the error ratio in the data recovery process of said data retrieval system is at a minimum.
Claim 9
Independent Claim
175 words
A method for recovering binary coded data in a data retrieval system wherein data bits are stored within bit cells, on a record medium, at a base frequency, as flux transitions, a first data bit value represented by a transition occurring at the middle of a bit cell and a second data bit value represented by a transition occurring at the beginning of a bit cell, except when the second bit value follows the first bit value, for identifying the first and second data bit values recovered from the record medium, comprising: generating a data bit window signal at said base frequency, the window signal having first and second timed portions at diverse voltage polarities, the first timed portions at one voltage polarity being longer in time than the second timed portions at another voltage polarity; and selectively displacing in time and the first timed portions of the window signal in a positive or a negative direction until the error ratio in the data recovery process of said data retrieval system is at a minimum.
Claim 10
Dependent Claim
55 words
The method of claim 7 further comprising, after said displacing step, the step of: varying the length of the first timed portion of the window signal with respect to the second timed portion of the window signal until the error ratio in the data recovery process of said data retrieval system is at a minimum.
Claim 11
Dependent Claim
65 words
The method of claim 7 wherein said data bit window signal generating step comprises: signalling the start of the first timed portion of the data bit window signals in response to a recovered data synchronized clock signal; and signalling the end of the first timed portion of the dtat bit window signal in response to said signalling the start of the first timed portion step.
Claim 12
Dependent Claim
59 words
The method of claim 7 further comprising, after said displacing step, the step of: converting the indicia of the data recovered from the record medium by representing each first data bit value by one polarity voltage and each second data bit value by another polarity voltage, the voltage transitions occurring at the beginning and end of the bit cells.
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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) | 1977-02-25 | 1977-08-27 | 1978-02-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-02-25 | 1981-08-27 | 1982-02-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-02-25 | 1985-08-27 | 1986-02-26 | $7700.00 | Window Closed / Lapsed |