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Detector for Eliminating Readback Errors from Disk File

IP.com Disclosure Number: IPCOM000051825D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Goretski, JA: AUTHOR [+5]

Abstract

Detector 10 eliminates readback errors from magnetic disk 12 and particularly from unwanted signal peaks caused by (1) shouldering due to low data density (as from the outer track on disk 12), (2) signal pickup from adjacent magnetic tracks due to track misregistration or high track density, and (3) general noise at frequencies close to the channel frequencies. Detector 10 accomplishes this by using the following algorithm: Zero crossings in the differentiated signal from disk 12 will be called a data peak if (1) the signal is above a prescribed threshold after a prescribed time interval and (2) the sign of the peak (or sign of the slope after zero crossing) has reversed from the previous data peak.

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Detector for Eliminating Readback Errors from Disk File

Detector 10 eliminates readback errors from magnetic disk 12 and particularly from unwanted signal peaks caused by (1) shouldering due to low data density (as from the outer track on disk 12), (2) signal pickup from adjacent magnetic tracks due to track misregistration or high track density, and (3) general noise at frequencies close to the channel frequencies. Detector 10 accomplishes this by using the following algorithm: Zero crossings in the differentiated signal from disk 12 will be called a data peak if (1) the signal is above a prescribed threshold after a prescribed time interval and (2) the sign of the peak (or sign of the slope after zero crossing) has reversed from the previous data peak.

Magnetic disk 12 is driven in direction 14, for example, and previously written data on disk 12 is detected using transducer 16. The overall function of the file read channel shown in the drawing is to detect data peaks from the readback signals detected by transducer 16, and the channel must first amplify the readback signal provided by transducer 16 to a usable level. This amplification is done by differential preamplifier 18, producing the signal A. The signal A is then differentiated and maintained at a constant level as signal B by the AGC and filter circuit 20. The differentiated signal B is then fed into detector 10 which digitizes (puts out a pulse) for each data peak of signal A.

Comparator 22 and single shot 24 perform a detection of zero crossings of the differentiated signal B. The input signal B which is applied between input a and input b, is first amplified by a three-state differential amplifier contained in comparator 22, and the output of comparator 22 is amplitude limited and is fed to single shot 24 which triggers whenever the polarity of its inputs is reversed. The output of single-shot 24 is the signal N Phi A, and it will be observed from Fig. 2 that the signal N Phi A rises at the existence of a data peak in the signal A and falls at a time interval later, at the minus peak of the differentiated signal B.

The detector 10 performs a thresholding function, and for this purpose the differentiated signal B is fed to thresholding circuits in parallel with the zero- crossing circuits 22 and 24. The first of the threshold circuits is the amp...