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Method of Optimizing Multitrack, Magnetic Write Head

IP.com Disclosure Number: IPCOM000035238D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Kahwaty, VN: AUTHOR [+2]

Abstract

Dynamic range differs greatly across the tracks of a multitrack, magnetic write head, particularly increasing at write current beyond the write saturation point. The differences are compounded by variations among heads as manufactured, variations among magnetic tapes as manufactured, and shifts in the write characteristics of the heads and tapes caused by wear. Ideally, each track of a head should have the same dynamic range to simplify signal detection. A typical approach to the problem of variance in dynamic range has been the use of read equalization, and less than optimum dynamic range. Unfortunately, read equalization is also known to have the undesirable side effect of reducing signal to noise ratio (SNR).

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Method of Optimizing Multitrack, Magnetic Write Head

Dynamic range differs greatly across the tracks of a multitrack, magnetic write head, particularly increasing at write current beyond the write saturation point. The differences are compounded by variations among heads as manufactured, variations among magnetic tapes as manufactured, and shifts in the write characteristics of the heads and tapes caused by wear. Ideally, each track of a head should have the same dynamic range to simplify signal detection. A typical approach to the problem of variance in dynamic range has been the use of read equalization, and less than optimum dynamic range. Unfortunately, read equalization is also known to have the undesirable side effect of reducing signal to noise ratio (SNR). Another approach would be to select for use only heads having low, relatively constant dynamic ranges across their tracks, but such approach would significantly reduce manufacturing yields and ignore the variances caused by wear. The problem thus presented is how to reduce differences in dynamic range across the tracks of a multitrack, magnetic write head without the previously described associated problems.

The aforementioned problem is solved by adjusting the write current to produce the same dynamic range across all tracks in a magnetic head. Adjustment of the write current begins whenever a new tape cartridge is inserted in a tape drive. First, a small amount of tape at the beginning of the cartridge is AC erased prior to passing over the write head. Next, the tracks are simultaneously written with all 1's for a short time at F/2 frequency and the maximum write current for the particular head design. (F is the frequency corresponding to the maximum permissible linear data density.) The write head is shut off and the read peak-resolver circuit is switched on after a short delay to allow the read preamplifiers to recover. The read signal is compared to a series of different voltage levels from Vmin/2 to Vmax, resulting in a number of bits of data for each track equal to the number of voltage levels....