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Bit Displacement Compensation for High Density Recording

IP.com Disclosure Number: IPCOM000076732D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Hahs, WR: AUTHOR

Abstract

Standard magnetic recording systems which employ double- or triple-frequency recording exhibit a phase shift of the data bits when information is encoded. In these systems, a fixed current write-driver is used to record the information on the magnetic medium, depending on such parameters as the head-to-medium spacing, the type of magnetic medium used, etc. A system employing a fixed current write-driver is optimum for a single-recording frequency only; the remaining recording frequencies suffer from lower readback signals and bit displacement. These defects are observed when the medium is overdriven during higher density recording.

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Bit Displacement Compensation for High Density Recording

Standard magnetic recording systems which employ double- or triple- frequency recording exhibit a phase shift of the data bits when information is encoded. In these systems, a fixed current write-driver is used to record the information on the magnetic medium, depending on such parameters as the head-to-medium spacing, the type of magnetic medium used, etc. A system employing a fixed current write-driver is optimum for a single-recording frequency only; the remaining recording frequencies suffer from lower readback signals and bit displacement. These defects are observed when the medium is overdriven during higher density recording.

In the present system, the write current is varied incrementally depending on the density of the bit pattern. The current is selected at a point where the maximum readback voltage is obtained. As the current increases beyond this point, the readback signal decreases and phase shift (bit displacement) occurs. Fig. 1 is a graph of the readback voltage versus write current for the recording frequencies. The dashed line illustrates the selected operating point of the write current for the various frequencies.

Fig. 2 illustrates a circuit which passes a selected current through the magnetic head winding based on the recording density of the data pulses. A five-position shift register 2 examines the bit pattern during each single-bit interval. The center trigger T3 operates as the information trigger; the first two and the last two positions of the shift register determine the bit pattern before and after the bit in T3.

The output from position T3 turns on the DATA or DATA lines through binary flip-flop 7 and cause transistors 12 or 13 in write-driver 9 to become conductive, depending on whethe...