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Class of PARTIAL RESPONSE Systems for Increasing Storage Density in Magnetic Recording

IP.com Disclosure Number: IPCOM000035993D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 34K

Publishing Venue

IBM

Related People

Patel, AM: AUTHOR [+2]

Abstract

In a digital magnetic recording channel, the density of magnetic transitions on the medium and the width of the readback pulse are related to the achievable linear density for a given head, disk, and flying height combination. Pulse-slimming equalizer and/or run-length limiting codes are commonly used for increasing linear density. More recently, the class IV partial response technique (PR4) has been investigated. However, the width of the readback pulse, equalized for the PR4 channel, is about the same as that in the case of (1,7) code for a given net linear density. Higher linear density with PR4 will require further equalization. This equalization, in general, results in loss of signal-noise ratio.

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Class of PARTIAL RESPONSE Systems for Increasing Storage Density in Magnetic Recording

In a digital magnetic recording channel, the density of magnetic transitions on the medium and the width of the readback pulse are related to the achievable linear density for a given head, disk, and flying height combination. Pulse- slimming equalizer and/or run-length limiting codes are commonly used for increasing linear density. More recently, the class IV partial response technique (PR4) has been investigated. However, the width of the readback pulse, equalized for the PR4 channel, is about the same as that in the case of (1,7) code for a given net linear density. Higher linear density with PR4 will require further equalization. This equalization, in general, results in loss of signal-noise ratio.

The PR4 polynomial is given by P(D) = 1-D2 . In this article, we present a class of partial response systems which are extensions of (1-D), with PR4 as the first extension. The higher extensions have the potential for providing significant increase in storage density for a given head/media combination.

EXTENDED PARTIAL RESPONSE SYSTEMS: The extended partial response systems are represented by the set of polynomials Pn(D), given by P
(D) = (1+D)n (1-D) n = 0, 1, 2, ... where D is the delay operator, and n defines a specific extension. In these systems, when n = 2, the shape of the spectral response resembles a typical magnetic-recording-channel transfer function (Fig.
1). Furthermore, a system with a higher value of n fits the spectrum associated with a wider readback pulse. The readback pulse is sampled with n+2 clocks within its natural width, 2W, and the non-zero sample values are the n+1 binomial coefficients in the expression (1+D)n .

For example, consider the P2(D) system. In this, the readback pulse is sampled with four clocks (4T) within its natural pulse width, 2W, as shown in Fig.
2. The pulse will be equalized, if necessary, to obtain the desired ..0,1,2,1,0,... sample values. The unit pulse response for this system has the sample values
..0,1,1,-1,-1,0... corresponding to the polynomial P2(D)...