Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2000-07-07
2003-06-24
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C036S06700D, C036S07500A
Reexamination Certificate
active
06583946
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the field of information storage and more particularly relates to hard disk drives.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,831,888 entitled “Automatic Gain Control Circuit” and assigned to Texas Instruments Incorporated, the assignee of the present invention, sets forth generally the description of disk storage for information. Hard disk drives (HDD) are one type of disk storage that is particularly used in personal computers today. The HDD device generally includes a magnetic storage media, such as rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servocontroller, a memory and control circuitry to control the operation of the HDD and to properly interface the HDD to a host or system bus. The following U.S. Patents describe various aspects of HDD devices:
Issued
5,535,067
Frequency Controlled Reference Generator
07/09/96
5,570,241
Single Channel, Multiple Head Servo . . .
10/29/96
5,862,005
Synchronous Detection Of Wide BI-Phase . . .
01/19/99
5,793,559
In Drive Correction Of Servo Pattern . . .
08/11/98
5,719,719
Magnetic Disk Drive With Sensing . . .
02/17/98
5,444,583
Disk Drive Having On-Board Triggered . . .
08/22/95
5,448,433
Disk Drive Information Storage Device . . .
09/05/95
5,208,556
Phase Lock Loop For Sector Servo System
05/04/93
5,642,244
Method and Apparatus For Switching . . .
06/24/97
Prior art
FIG. 1
illustrates a disk/head assembly
12
and a preamplifier
14
. The preamplifier
14
handles both read functions and write functions. Not illustrated in
FIG. 1
, for clarity, is the Read Write (RW) Head. The unshown RW head works through magnetic media and it contains both functions, read and write, with a different portion of the head performing each function. The write function portion of the MR head is inductive and the read function portion of the head acts as a magnetic resistive (MR) element. A write occurs through an inductive element to the magnetic media disk assembly
12
and a read occurs by sensing the magnetic shifts in the disk assembly
12
by using the resistive read element. As explained below, undesirable magnetic or capacitive coupling often occurs between the writer element in the RW head and the reader element because of their close proximity to each other.
Prior art
FIG. 2
depicts a circuit representation the write channel
16
and the read channel
18
of the preamplifier
14
of FIG.
1
. The writer
16
is connected to an inductor
20
. During a write, the preamplifier
14
, through the write channel
18
, drives a current
22
through the inductor
20
of the RW head. In close proximity to the inductor
20
, is a resistive element
24
on the read channel
18
. The value of the resistive element
24
is a function of the magnetic field. Because of the physical closeness of the inductor
20
and the resistive element
24
of the RW head, magnetic or capacitive coupling naturally occurs. This undesirable coupling is represented by the capacitor shown at reference numeral
21
. The concern is that this coupling will change the resistive value in the reader portion of the RW head.
In a personal computer during a typical operation, a read and a write to the RW head do not occur at the same time. Only one function at a time is performed; both do not occur simultaneously. In normal read and write operations, a bias current
26
is maintained through the resistive reader element
24
to keep it ready for the read mode. The RW head is very sensitive to current, particularly in the wrong direction. So, typically a bias current
26
is provided to offset any undesirable effects from magnetic coupling.
At the manufacturer, when formatting the disk/head assembly
12
, all of the RW heads (1 to 12 at present) are written to at the same time. This is known in the industry as the servo track write mode operation or the servo bank write mode operation. In servo bank write mode, when the disk/head assembly
12
is formatted, all RW heads are written to at the same time to write the servo track wedges on the disks. However, unlike the bias current which is maintained on the read portion of the RW head during a normal write operation, the bias current for all the read channel is not turned on during servo bank write mode as the added power dissipation for having the full RW bias on for all heads may exceed the thermal requirements for the preamplifier.
Prior art
FIG. 3
depicts the voltage waveforms of the RW head during servo track mode. The writer voltage is Vw. The reader voltage is Vrmr. If no magnetic coupling existed, when Vw rises, Vrmr would maintain its zero value. However, magnetic (or capacitive) coupling, spikes a voltage on the reader portion of the RW head, which in turn spikes a current. This becomes more of a problem with a new generation of heads because if they have a negative going current, it can greatly upset the magnetic properties of the element and cause it to not read back information from the disk assembly
12
properly. A GMR (Giant Magneto Resistance) RW head is typical of such a newelement having these problems. These heads are extremely sensitive to the negative going currents (voltages). These spikes damage the head, which results in less amplitude output from the head and asymmetric response that yield data bit errors.
It is accordingly an object of this invention to prevent the GMR element in a RW head from becoming upset from its natural state. The negative going current spikes on the reader portion of the head must be eliminated during servo bank write mode when all heads are written to simultaneously.
Other objects and advantages of the invention herein will be apparent to those of ordinary skill in the art having the benefit of the description herein.
SUMMARY OF THE INVENTION
The invention solves the problem of current spikes occurring in the reader portion of a Read Write head of a HDD during servo bank write mode at the HDD manufacturer. During this process when the manufacturer formats the disk assembly, all heads are simultaneously written to. The undesirable current spikes in the read heads are eliminated by providing a relatively small bias current to all read heads during the servo bank write mode. This raises the dc bias level on the reader portion of the RW head to eliminate the negative spikes generated through capacitive or magnetic coupling. The voltage Vrmr appearing on the reader head is prevented from going below zero volts. Thus, the MR element is not upset from its natural state and bit error rates are reduced.
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Holder Regina N.
Mosby April M.
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