Browse Prior Art Database

Tri Bit Servo Detection

IP.com Disclosure Number: IPCOM000086205D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 75K

Publishing Venue

IBM

Related People

Lewkowicz, J: AUTHOR [+2]

Abstract

The circuits depicted in the drawings describe methods which improve and enhance the detection of tri-bit servo data on magnetic recording media. U.S. Patent 3,691,543 describes a basic tri-bit servo detection scheme to which this publication is directed.

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Tri Bit Servo Detection

The circuits depicted in the drawings describe methods which improve and enhance the detection of tri-bit servo data on magnetic recording media. U.S. Patent 3,691,543 describes a basic tri-bit servo detection scheme to which this publication is directed.

Fig. 1 depicts a section of a flexible magnetic media with servo tracks positioned on both longitudinal edges of the magnetic media. Data information is positioned within the area ordered by the servo tracks. As a rotating head, not shown, sweeps a slant track across the magnetic media, the information recorded in the servo tracks are used for head track alignment.

Fig. 2 shows how the tri-bit servo pattern is recorded on tape. Basically there are "A" transitions, "B" transitions, and "SYNC" transitions. The magnetic particles in each of the transitions are aligned in different domains. The center line of a data track is the boundary between track 10 and track 12. When the head, not shown, is on track, its path coincides with the center line.

Referring to Fig. 3, the tri-bit servo signal after being read by the rotating head and amplified appears as is shown. Fig. 3A depicts the situation whereby the head is on track. Fig. 3B depicts the situation whereby the head is partially off track, while Fig. 3C depicts the situation where the head is between tracks. The sync bit in the servo readback signal is used for timing to gate on detector circuits for detecting the amplitude of A and B pulses.

When the servo data is recorded in the servo zone of Fig. 1, transitions of equal strength are recorded on opposite sides of the data track center line and at different time intervals between the time the sync transition takes place. During readback, the amplitude difference between the A and B pulses gives a measure of off-track displacement.

Fig. 4 depicts the detection circuitry in block diagram form. For reliability and averaging defects, the servo area contains more than one group of sync, A and B transitions. Reset line 14 to gated peak detectors A (CPDA) and gated peak detector B (CPDB) resets the gated peak detectors to zero. The detectors output will remain at zero until the detectors are enabled by a start line. An uplevel on the start line will allow the detection circuitry to detect the amplitude difference between the A and B transitions, as long as the overall signal amplitude is above the threshold level of amplifier sense means 16.

After the start line is dropped, the detector outputs will remain at their last value until they decay to zero or until they are...