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Magnetics, IEEE Transactions on

Issue 1  Part 1 • Date Jan. 1998

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Displaying Results 1 - 25 of 34
  • Conference Author Index

    Publication Year: 1998 , Page(s): 03 - 04
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    Freely Available from IEEE
  • Disk drive pivot nonlinearity modeling and compensation through fuzzy logic

    Publication Year: 1998 , Page(s): 30 - 35
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The pivot nonlinearity of a disk drive actuator is a complex phenomenon. Various models and compensation schemes were designed to cope with the nonlinearity. In this paper, a fuzzy logic based actuator pivot nonlinearity model is proposed. The fuzzy model can learn the dynamics of the actuator pivot nonlinearity by training with measured data. After the fuzzy model is trained, it can be augmented into a servo controller design as a disturbance observer to cancel the effects of the pivot nonlinearity. The fuzzy model, its modeling performance and a laboratory implementation to demonstrate its effectiveness in pivot nonlinearity compensation are presented View full abstract»

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  • Signal space detectors for MTR-coded magnetic recording channels

    Publication Year: 1998 , Page(s): 141 - 146
    Cited by:  Papers (2)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    In this paper, we present signal space detectors for use with maximum transition run (MTR) codes. A three-dimensional signal space detector Is first derived for an MTR=2 coded channel. The bit error rate performance of this detector is close to MTR-coded FDTS/DF(2) throughout the user density range of interest. The detector is then modified to be used with a time-variant MTR code. Simulation as well as experimental results are presented View full abstract»

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  • 8th Annual Magnetic Recording Conference (TMRC) on Magnetic Recording Systems

    Publication Year: 1998
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    The following topics were dealt with: servo systems; magnetic heads; coding/decoding systems; decision feedback equalisers; recording noise; and channel characterization View full abstract»

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  • An overview of the PES Pareto Method for decomposing baseline noise sources in hard disk position error signals

    Publication Year: 1998 , Page(s): 17 - 23
    Cited by:  Papers (28)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    This paper gives an overview of the PES Pareto Method, a useful tool for identifying and eliminating key contributors to uncertainty in the Position Error Signal (PES) of a magnetic disk drive servo system. Once identified and ranked according to their overall effect on PES, the top-ranking sources can be worked on first, either by finding ways to reduce their magnitude or by altering system components to reduce sensitivity to the contributors. The PES Pareto Method is based on three ideas: (1) an understanding of how Bode's Integral Theorem applies to servo system noise measurements, (2) a measurement methodology that allows for the isolation of individual noise sources, and (3) a system model that allows these sources to be recombined to simulate the drive's Position Error Signal. The method requires the measurement of frequency response functions and output power spectra for each servo system element. Each input noise spectrum can then be inferred and applied to the closed loop model to determine its effect on PES uncertainty. The PES Pareto Method is illustrated by decomposing PES signals that were obtained from a hard disk drive manufactured by Hewlett-Packard Company. In this disk drive, it is discovered that the two most significant contributors to PES baseline noise are the turbulent wind flow generated by the spinning disks (“Windage”) and the noise involved in the actual readback of the Position Error Signal (“Position Sensing Noise”) View full abstract»

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  • A novel robust time-optimal algorithm for servo systems with bias disturbance

    Publication Year: 1998 , Page(s): 7 - 12
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    This paper presents a novel robust time-optimal algorithm for servo systems with bias disturbance. The proposed method specifically minimizes the settling time of the servo positioning system by applying a constant feed-forward signal at the initial time. Unlike many other time-optimal control algorithms, additional computation is not needed once the constant optimal control signal is applied. Since the control is achieved through a constant change in the system's initial condition, the overall stability of the original control system is not affected by the addition of the time-optimal controller. The proposed control scheme has been implemented on a 3.5" disk drive servo system with a rotary actuator. Significant improvement in seeking time has been demonstrated by both simulation and experiments View full abstract»

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  • Analysis of and detector comparisons using the microtrack model of magnetic recording

    Publication Year: 1998 , Page(s): 63 - 68
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    We rely on accurate and relatively simple models of the magnetic recording process so that signal processing algorithms that operate with different system parameters can be compared fairly. The microtrack model of thin-film recording, posed by researchers to mimic the random, zig-zag transition boundaries, satisfies our requirements for an accurate and simple model. This paper summarizes analysis of the microtrack model done by Caroselli and Wolf (1995, 96) and presents additional results including simulations of detectors. Parallels are drawn between the microtrack model and other models including a stationary additive noise model, a model of partial erasure, and a model of transition jitter, amplitude reduction, and pulse width jitter. The parameters used by the microtrack model can be derived from physical media; we derive parameters for these other models from those of the microtrack model View full abstract»

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  • Performance of TCPR in magnetic azimuth recording

    Publication Year: 1998 , Page(s): 124 - 128
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The 8/10 DC-free code was developed into 8/10-PR1ML in azimuth recording. We previously discussed the performance of the 8/10 MSN code for Class 1 partial response (8/10 TCPR1) (1997). In this paper, TCPR1 and TCPR4 are applied to azimuth recording channels with cross-talk noise and white Gaussian noise. A simulated performance of several different user densities, azimuth angles and track pitches was carried out and the results presented. After determining suitable azimuth recording parameters for TCPR, we found a large off-track margin can be achieved on a removable medium such as magnetic tape View full abstract»

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  • Improvements in detectors based upon colored noise

    Publication Year: 1998 , Page(s): 94 - 97
    Cited by:  Papers (15)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    Two techniques which improve the performance of partial response maximum likelihood systems (PRML) without increasing the number of states in the Viterbi algorithm (VA) are studied. Both techniques rely on the fact that the noise samples going into the VA are correlated. One technique, known as partial local feedback noise prediction, uses estimates of the past noise samples taken from the path memory of the VA to form a prediction of the current noise sample. The predicted noise is subtracted from the current equalizer output prior to updating the path metrics. In the other technique, the VA operates in a block mode simultaneously on X consecutive equaliser outputs. A branch metric appropriate for colored noise is used within each block of K samples. Simulation results for a Lorentzian channel equalized to a PR4 target show that block processing with 4 samples gives almost the same error probability as noise prediction using a 2-tap predictor. Results also show that the feedback in the noise prediction technique increases the length of error events View full abstract»

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  • Read-back nonlinearity in longitudinal keepered recording

    Publication Year: 1998 , Page(s): 51 - 56
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    Read-back from media with a high permeability saturable keeper over-layer is nonlinear. These nonlinearities are most pronounced at bias levels where the media demagnetization fields are comparable to the head bias field. We propose a simple model for read-back from keepered media. In this model, the medium demagnetizing field modulates the size of the region in which the keeper is saturated and thus modulates head efficiency. This effect distorts the flux waveform. The read voltage, as the derivative of this distorted flux waveform, shows timing asymmetry and shape asymmetry. We demonstrate that distortion of the flux waveform can be treated as a memoryless nonlinear operator over a wide range of recording densities. We demonstrate a method for estimating this memoryless operator and briefly examine strategies for linearizing the read channel View full abstract»

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  • A BiCMOS implementation of a 276 MS/s forward equalizer and 200 MS/s FDTS detector

    Publication Year: 1998 , Page(s): 160 - 165
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB)  

    An analog finite impulse response filter (FIR) and an analog fixed delay tree search (FDTS) tau=l detector suitable for disk drive applications are presented. The FIR uses a rotary architecture with interleaved operation which allows clock rates up to 276 MS/s to be used. The FIR has seven taps, all programmable to six bit weights, and is implemented in fully differential form. The detector operates with clock rates up to 200 MS/s with no code restrictions. It makes use of a reduced minimum mean square error equation set to simplify the detector. Dual feedback filters are also used to shorten the critical path. A seven tap feedback filter is used with six bits of resolution per tap. The FIR consumes 180 mW while the detector uses 270 mW. The die size including all test buffers for the FIR and detector is 5.2 mm2 View full abstract»

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  • Low complexity signal space detection for MTR coded channels

    Publication Year: 1998 , Page(s): 104 - 109
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    Two new signal space detectors designed to take advantage of maximum transition run (MTR) coded modulation are presented. These detectors are designed to perform across a wide range of densities and offer lower error rates than a 3D-110 detector at low densities while requiring only modest increases in complexity. The first scheme, 2D-121α employs an equalization constraint that reduces low density noise correlation relative to the 3D-110 target. The second uses a 3D-110 detector but includes a linear noise predictive filter to reduce the effective noise between the minimum distance sequences. Analysis and simulation results indicate that the two detectors perform equally well in terms of bit error rate View full abstract»

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  • An estimation technique for nonlinear distortion in high-density magnetic recording channels

    Publication Year: 1998 , Page(s): 40 - 44
    Cited by:  Papers (2)  |  Patents (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Nonlinear distortions, which limit detector performance at high recording densities, are known as the nonlinear transition shift and partial erasure. The nonlinear transition shift is known to be reduced substantially by the precompensation technique, while the partial erasure requires sophisticated nonlinear equalization techniques. In this paper, a new calculation intensive adaptive technique is presented that uses stochastic gradient method to minimize the mean squared error between actual playback signal samples and modeled signal samples. The effectiveness of the proposed adaptive approach to separately estimate these two nonlinear parameters uniquely is demonstrated by computer simulation View full abstract»

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  • Distance-enhancing codes for digital recording

    Publication Year: 1998 , Page(s): 69 - 74
    Cited by:  Papers (30)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    We review recent progress in the design of high-rate, distance-enhancing codes that achieve the matched-filter-bound (MFB) on the E2PR4 channel, h(D)=(1-D)(1+D)3, including a rate 8/9 block code satisfying a time-varying maximum-transition-run (TMTR) constraint. We then prove that these TMTR codes also achieve the MFB on the E3PR4 channel, h(D)=(1-D)(1+D)4. Finally, we describe a TMTR constraint that achieves the MFB on the PR2 channel, h(D)=(1+D)2, and the EPR2 channel, h(D)=(1+D)3 , both of which are of interest as channel models in optical recording, and we present a new, rate 3/4 block code that satisfies this constraint. Computer simulation results confirm that the codes provide substantial performance improvement in additive, white, Gaussian noise (AWGN) View full abstract»

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  • The performance of generalized maximum transition run trellis codes

    Publication Year: 1998 , Page(s): 85 - 90
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    There has been considerable recent activity in the design and implementation of codes for magnetic saturation recording which achieve a 2.2 dB gain on the ideal EEPR4 partial response channel. This paper compares the performance of one such 8/9 rate Generalized Maximum Transition Run (GMTR) code with a normal 16/17 rate RLL(0,k) code. The sensitivity of the comparison is considered for two idealized magnetic dipulse shapes, for two idealized signal sampling techniques, and for two idealized noise environments. Comparison of a blended Lorentzian and Gaussian dipulse to a pure Lorentzian show generally similar gross effects, but the blended dipulse shows the onset of high density effects at lower channel densities. Comparison of the ideal minimum bandwidth discrete time equivalent sampler to the ideal whitened matched filter sampler shows negligible differences. The GMTR code in Additive White Gaussian Noise (AWGN) achieves net coding gains from 0.2 to 1.7 dB on user densities from 2 to 3 depending on the sequence detector target. In a media noise model the GMTR code is shown to achieve significant coding gains with the EEPR4 or MLSD detector targets View full abstract»

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  • Error propagation evaluation for RLL-constrained DFE read channels

    Publication Year: 1998 , Page(s): 147 - 152
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    Decision feedback equalization (DFE) is a promising low-cost solution for signal detection in magnetic recording channels. In terms of the bit error rate after detection, (0,k)-DFE and MDFE (Multilevel Decision Feedback Equalization) are comparable to (0,k)-PR4ML. Error propagation, however, is one of the major concerns for all DFE approaches. In this paper, an analysis of error propagation for RLL-constrained DFE at all stages of data processing, including RLL decoder and error correction, is performed. To evaluate error propagation, a Markov chain is constructed that explicitly models any type of RLL constraints. From this model, a Markov chain, describing the error distribution inside the bursts, is derived and a relation between these chains and error propagation decay rate is established. Performance of interleaved ECC (Error Correction Code) is also evaluated. The results obtained are compared with those from simulation. By using the newly developed model, a special technique of equalizer design, aimed to reduce error propagation, is analyzed. The comparison between (0,k)-DFE and MDFE in terms of the bit error rate after ECC is also provided View full abstract»

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  • A reduced complexity EPR4 post-processor

    Publication Year: 1998 , Page(s): 135 - 140
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB)  

    A reduced-complexity Extended Partial Response Class 4 (EPR4) detector implemented as a post-processor following a Partial Response Class 4 (PR4) Viterbi detector is described. Previous work showed that a post-processor architecture eliminates the speed bottleneck associated with an EPR4 Viterbi detector while providing comparable performance. The post-processor uses EPR4 metrics to detect and correct minimum distance EPR4 error-events in the binary sequence at the output of a PR4 Viterbi detector. In the new approach, the complexity is greatly reduced without sacrificing performance by considering only those EPR4 error-events deemed most-likely based on their PR4 metrics View full abstract»

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  • On timing recovery from full-wave-rectified magnetic signals

    Publication Year: 1998 , Page(s): 91 - 93
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    Fullwave rectified magnetic readback signals have a frequency component at the bit frequency, which can be utilized for timing. Feedforward timing can provide quick bit resync when recovering from thermal asperities, since it doesn't depend on a sync field. To be usable, the timing phase must vary little with the binary data, and the timing signal amplitude range must be reasonable. We compute the phase and amplitude distributions for all periodic patterns of length 9, as well as for PRBS patterns. We conclude that the lower the signal ISI, the smaller the timing phase shift. A rate 8/9 code reduces the timing shift to 2% for PR4, 5% for EPR4. Uncoded PRBS signals produce less than 2% timing shift View full abstract»

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  • A comparison of detection methods in the presence of nonlinearities

    Publication Year: 1998 , Page(s): 98 - 103
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    In this paper we evaluate the detectability of nonlinear signals characteristic of high-density, magnetic recording channels read by a magneto-resistive (MR) head. We first introduce a signal model which performs nonlinear superposition of experimentally-collected MR-head transition responses. Feeding signals synthesized from this model through a detection simulator, we compare the performance of Decision Feedback Equalization (DFE), RAM DFE, Partial Response Maximum-likelihood detection with PR4, EPR4, and E2PR4 targets, and Fixed Delay Tree Search with Decision Feedback (FDTS/DF) in the presence of time and amplitude nonlinearities. Signals are generated at a variety of signal-to-noise ratios (SNRs) and densities with runlength constraints of (0,3) and (1,7). We found that the most detrimental nonlinearities come from amplitude asymmetry characteristic of poorly biased MR heads, and such nonlinearities cause a loss of between 0.5 and 1 orders of magnitude in bit error rate. We found that of the schemes, FDTS/DF provided the great robustness against all nonlinearities in the presence of RLL(1,7) coding, and EPR4ML and E2PR4ML preformed the best with RLL(0,3) coding View full abstract»

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  • ECC performance of interleaved RS codes with burst errors

    Publication Year: 1998 , Page(s): 75 - 79
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    In this paper, we describe a computationally efficient way of calculating the probability of decoding error when a Reed Solomon code is utilized to record data over a channel that produces correlated symbol errors. We assume that the channel errors can be described by a Markovian model with a small number of states. A simple modification of the transition probability matrix for this Markov model allows one to compute (using a desk top computer with readily available software) the performance of these codes with and without interleaving. Examples are given illustrating the efficacy of this technique View full abstract»

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  • On coding and decoding for high-order partial response systems

    Publication Year: 1998 , Page(s): 80 - 84
    Cited by:  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    High-data-rate signal processing for hard disk drives is discussed. A recording channel is equalized as a partial response (PR) (1+D)(1-D3), where D is a delay operator. Furthermore, 1/(1+D) pre-coding scheme is used, and the resulting response is given as (1-D3), which achieves three-bit interleaving. The working speed of each Viterbi detector in interleaving PR channels is reduced to one third of the original bit-frequency. The performance of the reduced two-state Viterbi detector in the interleaving PR channel is compared with the conventional two-state Viterbi detector of the PR4 system. As a result, the proposed system improves the signal-to-noise ratio by about 3.0 db compared with the baseline PR4 maximum system. Finally, it is shown that the Error Coding (ECC) scheme for the interleaving needs a reversed hierarchy of ECC and channel coding View full abstract»

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  • Practical MTR-FDTS (τ=2) read channel for the >200 Mbit/sec Era

    Publication Year: 1998 , Page(s): 118 - 123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB)  

    This paper presents an architecture for a fixed-delay tree search with feedback (FDTS/DF) channel which uses a maximum transition run-length code. The critical timing path in this new detector is comparable to that of a decision feedback detector. The forward filter consists of a first-order all-pass filter cascaded with a fourth-order Bessel filter. Timing and gain recovery are also discussed View full abstract»

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  • Using additive white binary noise to marginalize read channels

    Publication Year: 1998 , Page(s): 178 - 180
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Optimization of bit error rate (BER) is typically not a part of disk drive burn-in, due to the large amount of time required to measure bit error rates accurately. In this paper, theoretical calculations, numerical simulations, and experimental results are used to show that additive white binary noise can be used to marginalize the performance of a read channel. As measurements of the larger BERs due to marginalization are much faster than normal BER measurements, this technique makes practical the use of BER based optimization during drive burn-in View full abstract»

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  • Simplified EPR4 detection

    Publication Year: 1998 , Page(s): 129 - 134
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    A new detector implementation for the extended class 4 partial response channel is presented. This implementation uses two, interleaved ternary 1-D detectors followed by a post-processor to detect the recorded data. The post-processor consists of a sequence check followed by a determination of the N most-likely paths through the two 1-D detectors, if necessary. This system is shown via simulation to perform as well as the standard EPRI maximum likelihood detector View full abstract»

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  • Dual-DFE read/write channel IC for hard-disk drives

    Publication Year: 1998 , Page(s): 172 - 177
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    The channel IC described here achieves data rates of 380 Mb/s at performance levels that improve in various directions upon the state of the art. It accomplishes these feats in a mature 1 μm CBiCMOS technology at a readmode power consumption of only 800 mW. The paper discusses some of the underlying architectural concepts View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology