WO1998018128A1 - Procede et appareil pour la precompensation de bruit multiplicatif pour enregistrements magnetiques - Google Patents

Procede et appareil pour la precompensation de bruit multiplicatif pour enregistrements magnetiques Download PDF

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Publication number
WO1998018128A1
WO1998018128A1 PCT/US1997/019201 US9719201W WO9818128A1 WO 1998018128 A1 WO1998018128 A1 WO 1998018128A1 US 9719201 W US9719201 W US 9719201W WO 9818128 A1 WO9818128 A1 WO 9818128A1
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WIPO (PCT)
Prior art keywords
signal
medium
noise
data signal
function
Prior art date
Application number
PCT/US1997/019201
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English (en)
Inventor
Joseph Andrew O'sullivan
Ronald Scott Indeck
Marcel Wettstein Muller
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Washington University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Washington University filed Critical Washington University
Priority to AU49163/97A priority Critical patent/AU4916397A/en
Publication of WO1998018128A1 publication Critical patent/WO1998018128A1/fr

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
    • G11B27/36—Monitoring, i.e. supervising the progress of recording or reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/10—Digital recording or reproducing
    • G11B20/18—Error detection or correction; Testing, e.g. of drop-outs
    • G11B20/1816—Testing
    • G11B20/182—Testing using test patterns
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
    • G11B20/24—Signal processing not specific to the method of recording or reproducing; Circuits therefor for reducing noise
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/09—Digital recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/488—Disposition of heads
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G11B2005/0005—Arrangements, methods or circuits
    • G11B2005/001—Controlling recording characteristics of record carriers or transducing characteristics of transducers by means not being part of their structure
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B2005/0002—Special dispositions or recording techniques
    • G11B2005/0026—Pulse recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
    • G11B5/027—Analogue recording
    • G11B5/035—Equalising

Definitions

  • the sources of noise in a readbac signal from a magnetic recording medium have been investigated and identified.
  • One of those sources includes the irregu- larities and defects in the microstructure of the magnetic medium itself.
  • the noise generated from this source has been thought, as with the noise generated from other identified sources, to be random and subject only to statistical analysis for its determina- tion.
  • the inventors hereof have demonstrated that this noise component is instead deterministic, i.e. is permanent and repeatable, depending entirely on the transducer-medium position and on the magnetic history of the medium.
  • the observed readback signals are almost identical .
  • the magnetic contribution to the readback signal under these conditions results from spatial variations in the medium's magnetization: magnetic domains, ripple, local fluctuations of the anisotropy field and saturation magnetization. These local properties, in turn, are affected by the morphology and magnetic properties of the individual grains which make up the domain and which do not change after deposition. Hence, the noise from a nominally uniformly magnetized region measured at a fixed position on the magnetic medium is reproducible.
  • a magnetic medium may be DC saturated and its output then measured to determine its remanent state or remanent noise.
  • this remanent noise is a function of the magnetic microstructure by comparing the remanent noise after a positive DC saturation with the remanent noise after a negative DC saturation. It has been found that these waveforms are virtual "mirror images" of each other, thereby demonstrating a close correlation. Similarly, other methodologies were used to confirm that the remanent noise was determinative, repeatable, and related to the physical microstructure of the magnetic medium itself. Remanent noise arising from the permanent micro- structure exhibits identifiable features characteristic of that permanent microstructure after practically any magnetic history. See Spatial Noise Phenomena of Longi tudinal Magnetic Recording Media by Hoinville, Indeck and Muller, IEEE Transactions on Magnetics, Volume 28, No. 6, November 1992, the disclosure of which is incorporated herein by reference.
  • Each particle or grain in the medium is hundreds to thousands of angstroms in dimension. Due to their size, a small region of the magnetic surface will contain a very large number of these physical entities. While the fabrication process may include efforts to align these entities, there is always some dispersion of individual orientations. The actual deviations will be unique to a region of the medium's surface making this orientation deterministic and making its corrupting effects susceptible to elimination. As can be appreciated by those skilled in the art, noise reduction enables increases in storage capacity and data rates, and eases the burden on transducers, magnetic media, and system design and fabrication.
  • the device and method of the present invention can create uncorrupted prerecorded signals on a magnetic medium.
  • a diagnostic signal is first written on the magnetic medium, the diagnostic signal is then read from the magnetic medium, and the readback signal is then compared with the original signal. The differences therebetween are determined to be noise, the greatest component of which is deterministic medium noise.
  • a data signal desired to be recorded which may or may not be the same as the diagnostic signal, is then compensated for the repeatable noise of the medium prior to being recorded back at the same location on the magnetic medium as was the diagnostic signal.
  • any other readback or playback machine will produce a signal which has been compensated for remanent noise.
  • medium noise compensation as described above are applicable to both analog and digital magnetic recording as used in entertainment, instrumentation, and computer applications.
  • special considerations apply to digital magnetic storage, in which saturation recording, including conventional longitudinal recording as well as more experimental perpendicular recording, is used virtually exclusively.
  • the inventors among many others have demonstrated that some of the medium noise in digital saturation recording is signal dependent. This means that the effect of the magnetic medium's microstructural irregularities cannot be represented solely as additive noise, but must also comprise multiplicative noise effects. Accordingly, medium noise compensation techniques for digital recordings must be capable of diagnosing and addressing the effects of both additive and multiplicative noise.
  • Figure 1 is a magnified representative depiction of the microscopic structure of a region of magnetic medium
  • Figure 2 is a magnified depiction of several tracks of a magnetic medium having microscopic structure representatively shown thereon;
  • Figure 3 is a block diagram of the write-read- write embodiment of the invention where the heads are moving to the right ;
  • Figure 7 is a block diagram of a specific implementation of a medium noise estimator shown in Figure 6 ;
  • Figure 8 is a block diagram of a specific implementation of a precompensated signal generator shown in Figure 6 ; and Figure 9 is a block diagram of a specific implementation of the precompensated signal generator shown in Figure 8.
  • the inventors' methodology involves the steps of writing a diagnostic signal at a fixed location on the magnetic medium, reading the recorded signal, estimating the medium noise (or parameters in the medium noise) by comparing the read signal with the original signal to determine the differences therebetween, compensating a data signal desired to be recorded for the effects of the medium noise, and writing the precompensated data signal at the same location as was the diagnostic signal .
  • the magnetic medium will thus receive a recorded data signal which has been compensated for the remanent noise inherent therein.
  • compensated recordings may then be played back by any conventional playback device and produce a signal which more closely represents a recording of the original data signal on an ideal or noiseless magnetic medium.
  • transducers 32, 34, 36 Although only three transducers 32, 34, 36 are shown in Figure 3, it should be understood that a plurality of recording transducers of any number may just as easily be provided and, as taught herein, may be required in order to effect various aspects of the present invention. Because conventional transducers can be utilized, the teachings of the present invention are readily implemented using existing and available technology.
  • the functions performed by the electronics 40 shown generally in Figure 3 are based upon a mathematical model that accounts for the fact that medium noise has both signal and spatial dependence. It is signal dependent in the sense that its statistical properties at a particular place on the medium change with changes in the write signal . It is spatially dependent in the sense that the statistical properties depend on medium position.
  • medium noise characteristics strongly depend on the number and proximity of consecutive transitions in the magnetization pattern. For example, medium noise for an isolated transition, a pair of closely spaced transitions (called a dibit) , and three closely spaced transitions (called a tribit) have different statistical properties.
  • Multiplicative transition noise can be decomposed into a number of modes.
  • amplitude modulation the spatial displacement of a transition from its intended location
  • transition jitter the spatial displacement of a transition from its intended location
  • pulse broadening the spatial dependence in the presence of a signal
  • the inventors have experimentally demonstrated that, depending upon the location on the medium, the transition jitter in an isolated transition can have a non- zero mean value and can thus give rise to spatial dependence of medium noise.
  • a conventional magnetic recording system with signal dependent medium noise is illustrated in Figure 4.
  • a write head 44 and a read head 46 are modeled as linear time- invariant systems with impulse responses h(t) and g(t) , respectively.
  • the random process n d (t) represents independent signal and/or spatially dependent medium noise, and is represented by the medium noise model set forth above.
  • a medium noise generator 48 produces n d (t) as a function of the signal and the spatial location on the medium.
  • a second independent noise component, n x (t) accounts for head noise and any non- repeatable medium noise not represented by the model .
  • An independent and random process w(t) represents additive electronic noise present in the read circuit.
  • the writing of a similar waveform at two time instants and at the same physical location on the medium yields the same realization of the physical randomness in the medium noise.
  • the first pair of write and read operations for the input signal s(t) in the write-read-write architecture produces an estimate of the medium noise for a particular signal/spatial combination.
  • the final write signal s 2 (t) can then be designed to compensate for the medium noise.
  • this scheme can be thought of as using the recording channel twice, first to estimate the channel, and second to use it more efficiently.
  • the mechanics and electronics of the system are synchronized, in a manner well-known in the art, to ensure that the third transducer 36 shown in Figure 3 writes the precompensated data signal s 2 (t) at the same location at which the first transducer 32 wrote the diagnostic signal s x (t).
  • the design criterion for the final write signal s 2 (t) is established as follows: let n dl (t) and n d2 (t) be the medium noise in the first and second writes .
  • the diagnostic signal s ⁇ (t) is the actual data signal intended to be recorded
  • the design criterion is to select ⁇ (t) to minimize the expected noise power in y 2 (t) (the readback of the precompensated data signal s 2 (t)) due to the medium noise and due to the compensation signal itself, given y- ⁇ t) .
  • ⁇ A for ⁇ and Kg may be easily derived:
  • multiplicative noise There may be various sources of multiplicative noise that can be included in the multiplicative noise model.
  • Amplitude modulation, timing jitter, and pulse broadening are three effects of medium noise that fall into this category. When examined over short time durations, each of these effects may be captured through the use of one parameter. Over longer time durations, these parameters vary.
  • the amplitude variation is modeled as a variable times the write signal
  • the jitter is modeled as a variable times the derivative of the write signal
  • pulse broadening is modeled as a variable times the time index times the derivative of the write signal.
  • the write-read-write precompensation scheme for multiplicative noise is based on optimally compensating for these effects by estimating the parameters associated with each, then using these estimated parameters, along with measures of the accuracy of these estimates, in building a compensated write signal.
  • Other sources of multiplicative noise may be compensated as well with appropriate circuits.
  • Figure 6 illustrates generally the electronics 40 shown in Figure 3, which implements the multiplicative noise model of the present invention.
  • the electronics 40 includes a diagnostic signal generator 50 which processes, or passes through, the data signal s(t) desired to be recorded to produce or output the diagnostic signal s x (t), a medium noise estimator 60 for estimating repeatable noise components of the magnetic medium based on the diagnostic signal s x (t) and the readback y x (t) of the diagnostic signal, and a precompensated signal generator 70 for compensating the data signal s(t) , based on the estimate of the medium noise, to produce the compensated write signal s 2 (t) .
  • a diagnostic signal generator 50 which processes, or passes through, the data signal s(t) desired to be recorded to produce or output the diagnostic signal s x (t)
  • a medium noise estimator 60 for estimating repeatable noise components of the magnetic medium based on the diagnostic signal s x (t) and the readback y x (t) of the diagnostic
  • the diagnostic signal s x (t) is provided to an ideal channel 62 having a convolution function b(t) that is equivalent to a write and read operation.
  • the output of the ideal channel 62 is subtracted from the readback signal y x (t) by an adder 64, and this difference is provided to a jitter estimator 66 and an amplitude estimator 68.
  • the jitter estimator outputs a jitter compensation signal e 1 (t ) that estimates a factor by which the amplitude of the diagnostic signal was multiplied by the determinative medium noise.
  • the amplitude estimator outputs an amplitude compensation signal ⁇ 2 (t) that estimates a factor by which the derivative of the diagnostic signal was multiplied by the determined medium noise.
  • the medium noise estimator 60 shown in Figure 7 only estimates the transition jitter and amplitude modulation noise components of the medium noise, other or additional components can also be estimated as apparent to those skilled in the art, including the pulse broadening component, although perhaps with an increased system complexity and at a greater cost .
  • the precompensated signal generator 70 comprises a feedback circuit employing several filters.
  • the input data signal s (t) is provided to an adder 72 that subtracts several additional signals therefrom as described below.
  • the output of the adder 72 which is the precompensated write signal s 2 (t) is fed back to a jitter compensation filter 74a, an amplitude compensation filter 76a, and a signal shaping filter 78.
  • the jitter compensation filter 74a convolves the signal output of the adder 72 with a function c ⁇ t), which represents the transition jitter noise component obtained from the inverse Fourier transform of C (w) .
  • the output of the jitter compensation filter 74a is provided to a multiplier 80 for multiplication with the jitter
  • the amplitude compensation filter 76a convolves the signal output of the adder 72 with a function c 2 (t), which represents the amplitude modulation noise component obtained from the inverse Fourier transform of C (w) .
  • the output of the amplitude compensation filter 76a is provided to a multiplier 82 for multiplication with the amplitude compensation signal ⁇ 2 (t), and the output of the multiplier 82, which represents the amplitude modulation expected to be added to the input signal s(t) by the medium, is provided to the adder 72 for subtraction from the input data signal.
  • the input data signal s(t) can be appropriately modified so that the data signal s 2 (t), once recorded on the medium and corrupted by the medium noise, more closely represents the input data signal s(t) than would the input data signal itself after being corrupted by the medium noise.
  • the precompensated signal generator 70 as described thus far would be complete, and the signal shaping branch of the precompensated signal generator could be eliminated. Because the compensation signals ⁇ 1 (t) and ⁇ 2 (t) are merely estimates, however, and cannot perfectly estimate the multiplicative medium noise parameters due to the presence of additive medium noise, they will introduce at least some degree of error into the precompensation process.
  • a signal shaping branch is provided in the precompensated signal filter 70 to quantitatively weigh the amount of compensation provided to the input signal based upon the level of certainty of the compensation scheme for particular frequency ranges of the signal .
  • the signal shaping branch includes the signal shaping filter 78, which convolves the signal output of the adder 72 with a function c 3 (t) obtained from the inverse Fourier transform of C (w) and the equation for the conditional covariance matrix given above.
  • the output of the signal shaping filter 78 is provided to an adder 84, and the output of the adder 84 is provided to the adder 72 for subtraction from the input data signal s(t) .

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Digital Magnetic Recording (AREA)
  • Signal Processing For Digital Recording And Reproducing (AREA)

Abstract

La présente invention concerne un dispositif électronique (40) permettant de mettre en oeuvre le modèle de bruit multiplicatif de l'invention. Le générateur (50) de signal de diagnostic traite le signal de données de façon à produire un signal de diagnostic. L'estimateur de bruit moyen (60) prévoit des composantes de bruit répétitif sur la base d'une analyse du signal de diagnostic. En utilisant l'estimation du bruit moyen, le générateur de signal précompensé (70) produit un signal d'écriture corrigée.
PCT/US1997/019201 1996-10-23 1997-10-23 Procede et appareil pour la precompensation de bruit multiplicatif pour enregistrements magnetiques WO1998018128A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU49163/97A AU4916397A (en) 1996-10-23 1997-10-23 Method and apparatus for multiplicative noise precompensation for magnetic recordings

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US74004096A 1996-10-23 1996-10-23
US08/740,040 1996-10-23

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WO1998018128A1 true WO1998018128A1 (fr) 1998-04-30

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2339324A (en) * 1998-07-06 2000-01-19 Hewlett Packard Co A magneto resistive head read amplifier

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4027250A (en) * 1975-10-21 1977-05-31 Lang Gordon R Apparatus and method for reducing effects of amplitude and phase jitter

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4027250A (en) * 1975-10-21 1977-05-31 Lang Gordon R Apparatus and method for reducing effects of amplitude and phase jitter

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2339324A (en) * 1998-07-06 2000-01-19 Hewlett Packard Co A magneto resistive head read amplifier
US6331921B1 (en) 1998-07-06 2001-12-18 Agilent Technologies, Inc Magneto-resistive head read amplifier
GB2339324B (en) * 1998-07-06 2002-09-18 Hewlett Packard Co A magneto-resistive head read amplifier

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Publication number Publication date
AU4916397A (en) 1998-05-15

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