Read head protection circuit and method

Details Read head protection circuit and method Read head protection circuit and method

2000-06-22

2003-07-15

Dorvil, Richemond (Department: 2697)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of the amplifier

C360S046000, C360S061000, C360S063000, C360S053000, C360S066000

Reexamination Certificate

active

06594101

ABSTRACT:

TECHNICAL FIELD
This invention relates generally to the field of information storage, and more particularly to a circuit and method for protecting read heads of a hard-disk drive.
BACKGROUND OF THE INVENTION
Hard-disk drives are mass storage devices that typically include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard-disk drive and to properly interface the hard-disk drive to a host system or bus.
FIG. 1
shows an example of a prior art disk drive mass storage system
10
. Disk drive system
10
interfaces with and exchanges data with a host
32
during read and write operations. Disk drive system
10
includes a number of rotating platters
12
mounted on a rotatable base
14
. The platters
12
are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter
12
coupleable to the read/write heads
18
/
20
which transfers data to and from a preamplifier
26
. The preamp
26
is coupled to a synchronously sampled data (SSD) channel
28
comprising a read channel and a write channel, and a control circuit
30
. SSD channel
28
and control circuit
30
are used to process data being read from and written to platters
12
, and to control the various operations of disk drive mass storage system
10
. Host
32
exchanges digital data with control circuit
30
.
Data is stored and retrieved from each side of the magnetic platter
12
by the read head
18
and a write head
20
. The read head comprise of magneto-resistive heads, adapted to read data from or to platters
12
, when current is passed through them. Read/write heads
18
/
20
are coupled to preamplifier
26
that serves as an interface between read/write heads
18
/
20
of disk/head assembly
10
and SSD channel
28
. The preamp
26
provides amplification to the waveform data signals as needed. The platter
12
surfaces are partitioned and formatted into sections as shown, with data storage wedges or sections
22
comprising the majority of the platter surface area, and smaller servo wedges
24
positioned therebetween storing positional information. At specified time intervals during the normal operation of the hard-disk drive system
10
, a sequence called a Servo Bank Write (SBW) sequence is performed during which the write heads
20
write positional data to all of the platter servo wedges
24
simultaneously.
A problem with prior art hard-disk drive designs is the extreme sensitivity of the read heads
18
. When data is being written to platter(s)
12
with write head
20
, a large amount of current, e.g. 40 mA is placed through the write head
20
, which may be coupled back into the read head
18
proximate with write head
20
, possibly damaging or blowing read head
18
. To prevent damage during a write sequence, most prior art designs apply a bias to read head
18
. The risk of read head
18
damage is particularly high during a SBW sequence because all read heads
18
are on simultaneously and thus the bias current is divided equally between the read heads
18
, resulting in the bias current applied to each read head
18
being dependent on the number of read heads
18
connected to the preamp
26
. This relationship is characterized in Equation 1:
Eq. 1:
⁢
 
Ib
head
=
I
biastotal
N
where I
biastotal
is the total bias current applied from the preamplifier
26
to all heads
18
/
20
, Ib
head
is the bias current on one read head
18
, and N is the number of heads in the hard-disk drive system
10
, with N being three in the system
10
shown in FIG.
1
. Thus, in transitioning to SBW mode, the bias current on a read head
18
can potentially drop from I
biastotal
in the read mode to I
biastotal
/N in SBW mode. The decreased bias current may be insufficient to protect read head
18
, resulting in damage to the head
18
.
What is needed is a circuit and method for protecting read heads
18
during a hard-disk drive SBW sequence.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a circuit and method for protecting read heads of a disk drive during a SBW sequence. A feedback loop capacitor of a preamp is controllably coupled to a separate dummy head during a V
bias
mode so the capacitor voltage is both predictable and lower than the voltage of the read head when returning to an I
bias
mode.
The invention comprises a circuit for protecting a read head of a hard-disk drive, comprising a voltage bias circuit selectively coupleable to the read head, a capacitor selectively coupleable to the read head and a dummy head selectively coupleable to the capacitor. The dummy head may comprise an internal resistor. The capacitor is controllably and responsively coupled to the dummy head when the voltage bias circuit is coupled to the read head to prevent coupling a damaging level of current to the read head.
The invention includes a preamplifier for a hard-disk drive storage system having a plurality of platters for storing data and a read head for each the platter for retrieving the data. The preamplifier comprises a read head protection circuit having a voltage bias circuit coupleable to the read head, a capacitor coupleable to the read head and a dummy head coupleable to the capacitor. The capacitor is controllably coupled to the dummy head when the voltage bias circuit is coupled to the read head.
A method of the invention includes protecting a read head of a hard-disk drive storage system, the system comprising a preamplifier circuit having a voltage bias circuit and a capacitor coupleable to the read head, and a dummy head selectively coupleable to the capacitor. The method protects the read head by controllably discharging the capacitor voltage through the dummy head when the voltage bias circuit is coupled to the read head to prevent coupling a damaging level of current to the read head.
Advantages of the invention include protecting read heads
18
of a hard-disk drive system during a servo bank write (SBW) sequence when all of the write heads
20
are in use. The protection circuit and method are an easily implementable and dependable solution protecting read heads from being damaged during the SBW sequence. Preferably, the dummy head resistor discharges the capacitor to a predetermined voltage, rather than leaving the capacitor floating as in the prior art. The voltage is predictable and allows the storage system to remain in the V
bias
mode for a longer amount of time as compared to the prior art. In some circuits, the present invention only requires an additional switch coupling the capacitor to a dummy head of the V
bias
circuit.


REFERENCES:
patent: 6118611 (2000-09-01), Shibasaki et al.
patent: 6388830 (2002-05-01), Matousek et al.
patent: 6469854 (2002-10-01), Gill et al.
patent: 2001/0015867 (2001-08-01), Hatanaka et al.

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