Browse Prior Art Database

DC Offset Correction With Fast Recovery Mode in WRITE to READ Recovery Times for Sector Servo Hard Disk Files

IP.com Disclosure Number: IPCOM000047095D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 73K

Publishing Venue

IBM

Related People

Gruver, MR: AUTHOR [+4]

Abstract

The DC offset correction concerns magnetic disk 10 having interlaced data fields and servo fields and circuitry for reading and writing such fields by means of magnetic head 12. The DC offset correction is applied particularly to capacitor 14 (indirectly) from line 16 having an average offset DC voltage thereon so that the output of automatic gain control circuit 18 reduces, as shown in Fig. 4d instead of as shown in Fig. 4e on a change from WRITE mode to READ mode. The alternating servo fields and data fields are shown in Figs. 1 and 2. The circuit includes a common channel for servo information and data information between head 12 and data and servo detection circuitry 20. The common channel includes arm electronics (AE) module 22, amplifier 24 and automatic gain control circuit (AGC) 18.

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DC Offset Correction With Fast Recovery Mode in WRITE to READ Recovery Times for Sector Servo Hard Disk Files

The DC offset correction concerns magnetic disk 10 having interlaced data fields and servo fields and circuitry for reading and writing such fields by means of magnetic head 12. The DC offset correction is applied particularly to capacitor 14 (indirectly) from line 16 having an average offset DC voltage thereon so that the output of automatic gain control circuit 18 reduces, as shown in Fig. 4d instead of as shown in Fig. 4e on a change from WRITE mode to READ mode. The alternating servo fields and data fields are shown in Figs. 1 and 2. The circuit includes a common channel for servo information and data information between head 12 and data and servo detection circuitry 20. The common channel includes arm electronics (AE) module 22, amplifier 24 and automatic gain control circuit (AGC) 18. The data and servo detection circuitry 20 outputs to a central processing unit (CPU) 26 and to voice coil (VC) 28 that controls the movement of the arm carrying head 12 across the magnetic tracks on disk 10. The circuitry includes also comparator 30 inputting from the output of amplifier 24 and outputting to switch 32, integrator 34 inputting from line 36, constituting one of the output lines of AGC 18, and having line 16 as its output, battery 38 connected with line 16 and providing a plus voltage on line 40, battery 42 connected with line 16 and providing a minus voltage on line 44, comparator 46 having lines 36 and 40 as inputs, comparator 48 having lines 36 and 44 as inputs, charge pump 50 having the outputs of comparators 46 and 48 as inputs and providing an output to line 52 connected to point 54 which is the junction also with switch 32, capacitor 14 and control line 56 for amplifier 24. Switch 32 is closed for READ mode and is open for WRITE mode, and the actions of charge pump 50 and arm electronics module 22 are likewise changed for these two modes, this being by signals applied to control lead 58 for pump 50 and control lead 60 for AE module 22. Arm electronics module 22 constitutes an amplifier in READ mode, and in WRITE mode it provides large current transitions in head 12 to write these transitions on disk 10. The file including disk 10 with interlaced data information and servo information and with both types of information passing through the common channel between head 12 and circuitry 20 has unique DC offset requirements. The requirements are particularly strict for certain types of servo encoding in the servo fields. Preferably, it should be possible to read a data field from disk 10 immediately after writing the previous data field; and, in order to achieve this, AGC module 18 must turn off during WRITE mode and then turn back on as soon as possible after the WRITE cycle is complete. In this connection, it should be noted that the servo fields on disk 10 are relatively narrow in order to maximize data density in the...