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Missing Bit Detection in Surface Analysis Testing

IP.com Disclosure Number: IPCOM000044678D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Ball, AJ: AUTHOR [+2]

Abstract

Two retriggerable single shots are triggered at positive and negative thresholds, respectively, of a read-back nominally sinusoidal waveform from a magnetic disk surface being tested. The single-shot outputs, which are one and a half times the nominal period of the waveform in duration, are applied to a NAND gate. If either input falls, the NAND gate output indicates a "missing bit", which is indicative of a defect in the medium. A suitable circuit is shown in Fig. 1. The read-back signal from the disk surface is applied to an input terminal and its positive and negative excursions compared with threshold levels set by positive and negative digital-to-analog converters. Fig. 2, Fig. 3 and Fig. 4 illustrate the operation of the circuit on various types of input waveform.

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Missing Bit Detection in Surface Analysis Testing

Two retriggerable single shots are triggered at positive and negative thresholds, respectively, of a read-back nominally sinusoidal waveform from a magnetic disk surface being tested. The single-shot outputs, which are one and a half times the nominal period of the waveform in duration, are applied to a NAND gate. If either input falls, the NAND gate output indicates a "missing bit", which is indicative of a defect in the medium. A suitable circuit is shown in Fig. 1. The read-back signal from the disk surface is applied to an input terminal and its positive and negative excursions compared with threshold levels set by positive and negative digital-to-analog converters. Fig. 2, Fig. 3 and Fig. 4 illustrate the operation of the circuit on various types of input waveform. In the case of Fig 2, a nominal sine-wave input is shown and above and below it the outputs of single- shot SS1 and SS2. These outputs both remain high so that the NAND output remains low. In Fig 3, an acceptable but distorted waveform is shown in which the first (negative) peak of the input waveform is of larger amplitude than nominal, which causes early firing of SS2, at the negative threshold. A low amplitude second negative peak follows, which just reaches the negative threshold and causes late retriggering of SS2. Since the duration of the single- shot output overlaps by at least one half bit period, the time shifts introduced by these distort...