Vadim B. Minuhin

Texture noise and its impact on recording performance at high recording density

Mechanical texture and its impact on recording performance at high recording density have been studied experimentally in this paper. We found that texture noise has a negligible effect on the recording performance in modern disks, even at high density. Texture noise can well be explained by a band pass modulation model. Experimental evidence shows that texture caused amplitude modulation can appear as jitter, which proves statements from the modulation theory as suggested by V. Minhuin [J. Appl. Phys. April 1999],.

Model of media noise generation based on modulation theory

A random profile of transitions in magnetization on thin-film media causes fluctuations of transition-region widths and locations. The readback transducer reacts to an averaged derivative of magnetization, and this results in modulation of magnetization derivative pulses, in shape and amplitude as well as in position (jitter). Due to bandwidth limitations in the readback transducer the high-frequency sideband of the modulation is almost totally suppressed. Thus, readback filtration converts a double-sideband write-cycle modulation into a single-sideband readback modulation.

A general solution for the field of polygonal electromagnet

A general solution for the field of a two-dimensional polygonal electromagnet is presented. The solution is applicable to magnetic recording head models of finite size and arbitrary polygonal configuration. It uses a combination of analytic and numerical techniques. Analytic procedures are based on mixed boundary conditions and a succession of conformal mappings starting with the Schwartz-Christoffel (S-C) transformation. A concept of an idealized winding allows any magnetostatic problem to be reduced to an electrostatic problem of two equipotential shims on the plane of conformal mapping. The result of the analytic solution is a parametric formula for the field vector that can be easily obtained for any model by an inspection of its configuration. This formula contains S-C constants and parameters of unknown values. These difficulties are resolved by numerical procedures. >

Wavelength response of ring-type head with arbitrary gap depth

In 1953 Westmijze found analytic solutions for the fields and wavelength responses of ring-type-head models with zero and infinite gap depths and demonstrated that the wavelength responses for these two extreme cases are substantially different. A model two-dimensional electromagnet that is equivalent to a more general ring-type-head model that takes into consideration a final gap-depth value is considered. It is shown that the Westmijze head models are actually two specific cases of this more general model. Using the theory of complex analytic functions, the gap between the two Westmijze models is bridged and an analytic solution for the wavelength response of a ring-type head with an arbitrary gap depth is derived. Graphs of the responses calculated for several gap depths are presented. These graphs illustrate that the gap depth has no practical effect on wavelength response as long as the ratio of pole thickness to gap size exceeds 0.5. However, further decrease of this ratio causes considerable changes in wavelength responses. >

Modulation in video tape recorders

This paper presents the theory of pulse-frequency modulation, used for signal transmission in analog video recorders. The paper demonstrates that signal processing in recorders is of the discrete-time type, with the sampling exceeding the Nyquist rate and with restoration of the analog video output from samples in the filter-demodulator.

Extension of media noise modulation theory (square-wave recording)

Media noise is treated as the random pulse modulation of averaged magnetization derivative. The modulation is of several types simultaneously: pulse position, shape, width, and amplitude. The theory of such modulations is presented. Bandwidth limitation in a readback transducer results in the transformation of these modulations into a single sideband modulation that mixes all types together.

Adaptive. Analog, Continuous Time Time-domain Equalization For Sampled Channels In Digital Magnetic Recording

A practical, low-cost, adaptive, analog, continuous time time-domain equalizer has been implemented in integrated sampled read/write channels. The equalizer is an IIR filter and is the generalization of a conventional analog transversal equalizer. Active frequency-domain filters are used as delay elements and filtration is completed before sampling. The equalizer has more degrees of freedom than DSP FIR filters and outperforms them. Theory of the generalized transversal equalization is presented.

Usage of laplace transform for analysis of magnetic heads

In the two-dimensional approximation the derivative of a complex head potential is, within a constant factor of unit magnitude, the Laplace image of the harmonic sensitivity of the head. This relationship provides an opportunity to use Laplace transform formalism for head analysis. The application of this formalism has resulted in simple analytical expressions for the wavelength response of both a thin ring head with finite pole pieces and a thin probe head with a fine winding.

Modulation noise in thin-film metallic media: elements of pulse/transition modulation theory

This paper is a mathematical preliminary to a pulse/transition modulation theory in magnetic recording. Equations are given for single-tone pulse modulations of different types (pulse position, width, shape). The theory is applied to noise generation in thin-film metallic media. As longitudinal bit size becomes comparable to the grain size, medium noise manifests itself as significant errors in the traditional mapping of write current to media magnetization. Thus, noise has a character of random multidimensional modulation of pulse parameters of the magnetization derivative. Transition jitter in recording is followed by the transformation of double-sideband recording modulation into single-sideband readback modulation, because of the bandwidth limitation in the readback transducer. Readback output becomes modulated 50% in pulse amplitude and 50% in pulse position. The fluctuation of transition length in recording causes pulse shape modulation. This amounts to simultaneous pulse-width and pulse-amplitude modulations acting against each other, so that virtually no modulation sidebands are generated. The compensation process is hidden in the recording cycle and is not visible in the frequency domain of the readback signal. Therefore, the traditional technique of media noise measurement with a spectrum analyzer is flawed, because the analyzer is blind to pulse shape modulation, which is the dominant source of sampling errors in practical channels.

Superposition in inductive and magnetoresistive readback

This letter demonstrates that the physics of linear readback in various recording-reproducing systems is different from that of communication systems and conventional linear filters, in which superposition is described by the convolution integral. In a linear system of magnetic readback with inductive heads, superposition is described by the correlation (not convolution) between two vector entities-the derivative of media magnetization and the sensitivity function of the readback head. More generally, superposition in all linear magnetic readback with heads of any type is described by the correlation between two scalar entities-the distribution of magnetic charges in the recorded media and the scalar sensitivity function of the readback head with respect to moving charges.