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Quasi Baseband Equalization and Detection

IP.com Disclosure Number: IPCOM000060958D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Melas, CM: AUTHOR

Abstract

In magnetic recording channel equalization and detection, no equalizer is a perfect match for channel response. To increase recorded data density and to enhance signal-to-noise ratio in a magnetic readback system, quasi baseband equalization, also called quasi-PR1 (QPR1) equalization, is proposed as a better match for overall channel response because the passband of an ideal PR1 equalizer extends to DC. PR1 equalization introduces intersymbol interference (ISI) and bit coding redundancy because actual channel response does not extend to DC. However, such penalties can be overcome with prudent and coding of data and selection of low frequency alteration. In the present configuration, input data is encoded in 4/8 code at rate 3/4.

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Quasi Baseband Equalization and Detection

In magnetic recording channel equalization and detection, no equalizer is a perfect match for channel response. To increase recorded data density and to enhance signal-to-noise ratio in a magnetic readback system, quasi baseband equalization, also called quasi-PR1 (QPR1) equalization, is proposed as a better match for overall channel response because the passband of an ideal PR1 equalizer extends to DC. PR1 equalization introduces intersymbol interference (ISI) and bit coding redundancy because actual channel response does not extend to DC. However, such penalties can be overcome with prudent and coding of data and selection of low frequency alteration. In the present configuration, input data is encoded in 4/8 code at rate 3/4. Thus, 6 input bits are translated into 8 output bits so that each byte will have exactly 4 "1's" and 4 "0's". Note that a "1" means positive flux and a "0" means negative flux, unlike the conventional flux change coding where a "1" is a flux change and a "0" is no flux change. If data bits are encoded as +1, -1, or 0 and the detection threshold is set to 0.5, noise has to be absolute value 0.5 before an error occurs. In baseband transmission, the levels are +1 and -1, and the detection threshold is at 0. Therefore, the quasi baseband system proposed provides twice the noise immunity of a conventional magnetic readback system. In the 4/8 code, there are 70 code words. To decrease distortion introdu...