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Switchable Time-Domain Filter

IP.com Disclosure Number: IPCOM000061543D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Jaworski, RC: AUTHOR [+2]

Abstract

The data channel in a disk drive includes a time-domain filter. The optimum value of time delay used for data read at the outer radius of the disk is usually not the optimum value for data read at the inner radius. At the inner radius, shifted bits due to intersymbol interference, are the major contributor to the soft error rate. Therefore, excess time-domain filter delay will only aggravate the situation by forcing data bits into adjacent variable frequency oscillator (VFO) windows. However, at the outer diameter, high disk resolution and wider bit spacing are the major contributors to the soft error rate in the disguise of extra bits. Additionally, excess system noise will aggravate the problem by "riding" on the flat waveform between two data bits, thereby influencing the differentiator/zero-crossing detector.

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Switchable Time-Domain Filter

The data channel in a disk drive includes a time-domain filter. The optimum value of time delay used for data read at the outer radius of the disk is usually not the optimum value for data read at the inner radius. At the inner radius, shifted bits due to intersymbol interference, are the major contributor to the soft error rate. Therefore, excess time-domain filter delay will only aggravate the situation by forcing data bits into adjacent variable frequency oscillator (VFO) windows. However, at the outer diameter, high disk resolution and wider bit spacing are the major contributors to the soft error rate in the disguise of extra bits. Additionally, excess system noise will aggravate the problem by "riding" on the flat waveform between two data bits, thereby influencing the differentiator/zero-crossing detector. A switchable time-domain filter circuit allows the use of two values of time delay. One value can be optimized for the inner radii such that it eliminates extra bits without inducing additional bit shift. The second time delay can be optimized for the outer radii or the remainder of the data band where intersymbol interference is not as severe and high resolution extra-bits are the prominent cause of recoverable or soft errors. The +Iw REDUCE line 10 in the drawing is used to toggle the two values of time delay. The +Iw REDUCE line 10 is controlled by the file microprocessor (not shown). The state of the line is dependant up...