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Browse Prior Art Database

Data Track Following Servo System

IP.com Disclosure Number: IPCOM000087448D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Martin, DH: AUTHOR

Abstract

A data track 12 is followed by a dual-element magnetoresistive (MR) transducer 10 which straddles the track. By means of an automatic gain control (AGC) circuit, a position error signal S is developed which is independent of polarity changes and overall fluctuations in signal strength of data signal D.

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Data Track Following Servo System

A data track 12 is followed by a dual-element magnetoresistive (MR) transducer 10 which straddles the track. By means of an automatic gain control (AGC) circuit, a position error signal S is developed which is independent of polarity changes and overall fluctuations in signal strength of data signal D.

The outputs from MR head 10 are applied to a position error channel and to an AGC channel. In the position error channel, differential amplifier 18 produces the differential signal between elements ab and bc of head 10. High frequency noise is removed from this signal by filter 22, and the differential signal is amplified by variable gain amplifier (VGA) 26. In the AGC channel, the contributions of elements ab and bc are summed by amplifier 16, filtered by filter 20 and amplified by VGA 24 to produce signal GD, where G is the gain of VGA
24.

To generate an AGC signal, the output of amplifier 24 is multiplied by itself in multiplier 28 to full-wave rectify it and then smoothed in low-pass filter and amplifier 30 to produce the mean-square level of the signal. The mean-square level is compared with a reference to produce a gain control signal which is fed back to VGA 24 to control G so as to keep the mean-square level of signal GD a constant. The same gain control signal also determines the gain of VGA 26.

Providing the amplifiers 24 and 26 are identical, the position error S is directly proportional to the root mean-square level of...