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Differential Preamplifier for MR Heads Using a Single Power Supply and Ground in a System using Non-Conductive Disk Substrates

IP.com Disclosure Number: IPCOM000014378D
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 4 page(s) / 188K

Publishing Venue

IBM

Abstract

Disclosed is the use of a differential preamplifier in a disk file system having only a single power supply (no second power supply via an invertor is used). This is far less expensive than a traditional scenario where both a positive and negative supply are required so as to hold the common-mode level of the MR head at near ground. Historically this was the case with disk substrates which were conductive (i.e., aluminum) where a possibility existed for a 'conductive asperity' event to destroy the head. Now the use of glass disk substrates has significantly altered this possibility. Disks with glass substrates include a magnetic coating for data storage, and usually a carbon overcoat for physical durability. At least one of the coatings is conductive. Thus, the ability to control the resistance from a conductive asperity on a disk surface to the spindle is possible where the spindle is electrically connected to system ground. A differential amplifier of the disclosed system can then be used with only a single power supply and ground if the common-mode potential of the head is held at a prescribed level above ground which will not result in excessive (destructive) current during a conductive asperity event, given the aforementioned resistance from said conductive asperity on the disk surface to system ground.

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  Differential Preamplifier for MR Heads Using a Single Power Supply and Ground in a System using Non-Conductive Disk Substrates

   Disclosed is the use of a differential preamplifier in a disk file system having only a single power supply (no second power supply via an invertor is used). This is far less expensive than a traditional scenario where both a positive and negative supply are required so as to hold the common-mode level of the MR head at near ground. Historically this was the case with disk substrates which were conductive (i.e., aluminum) where a possibility existed for a 'conductive asperity' event to destroy the head. Now the use of glass disk substrates has significantly altered this possibility. Disks with glass substrates include a magnetic coating for data storage, and usually a carbon overcoat for physical durability. At least one of the coatings is conductive. Thus, the ability to control the resistance from a conductive asperity on a disk surface to the spindle is possible - where the spindle is electrically connected to system ground. A differential amplifier of the disclosed system can then be used with only a single power supply and ground if the common-mode potential of the head is held at a prescribed level above ground which will not result in excessive (destructive) current during a conductive asperity event, given the aforementioned resistance from said conductive asperity on the disk surface to system ground.

   A disk having such an integrated conductive coating (1) should not be involved in an excessively low resistive path to system ground (which will vitiate the destructive results of a conductive asperity event) and (2) should not be involved in an excessively high resistive path to system ground such that a build-up of static surface charge would occur and an electrostatic attraction would be produced to force the head into the disk causing a head crash. To accomplish this, a compromise in the value of said resistive path to system ground must be achieved. The present resistive path to system ground using aluminum disks and grounded spindles is known to be on the order of 100 to 1000 Ohms for the static condition, which is too low to in and of itself protect the head against conductive asperity events. It is also clear that near-infinite resistance would cause a static build-up of charges of opposite polarity on the head and on the disk which, in turn, could result in devastating head crashes. Once an operable range series resistance is determined which would satisfy both the conductive-asperity scenario as well as the static charge build-up scenario, the disclosed invention presents the best mode to accomplish this.

   One method by which to accomplish the desired series resistance would be to manufacture a doughnut-shaped void in the conductive coating media of the disk/substrate assembly relatively close to the (ID) hub wherein when the hub is tightened, enough material would be under and in electrical...