U.S. patent application number 13/333565 was filed with the patent office on 2013-07-11 for distributed temperature detector architecture for head disk interface systems.
The applicant listed for this patent is John Thomas Contreras, Samir Y. Garzon, Rehan Ahmed Zakai. Invention is credited to John Thomas Contreras, Samir Y. Garzon, Rehan Ahmed Zakai.
Application Number | 20130176643 13/333565 |
Document ID | / |
Family ID | 48701435 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130176643 |
Kind Code |
A1 |
Contreras; John Thomas ; et
al. |
July 11, 2013 |
DISTRIBUTED TEMPERATURE DETECTOR ARCHITECTURE FOR HEAD DISK
INTERFACE SYSTEMS
Abstract
Approaches for a distributed temperature detector architecture
in a head disk interface system of a hard-disk drive (HDD). A HDD
may include a read/write head comprising a read element and a write
element and a read/write integrated circuit (IC). The read/write
head may comprise (a) a first temperature sensor that is located
relatively near an air bearing surface (ABS) of the read/write head
and (b) a second temperature sensor that is offset from the ABS.
The read/write IC is configured to detect when the read/write head
makes physical contact with a disk based on a difference in
temperature measured by the first and second temperature sensor.
The first and second temperature sensors form a bridge circuit,
such as a Wheatstone bridge, with a first IC resistor and a second
IC resistor that both reside in the read/write IC, allowing the
temperature of the read/write head to be accurately measured.
Inventors: |
Contreras; John Thomas;
(Palo Alto, CA) ; Zakai; Rehan Ahmed; (San Ramon,
CA) ; Garzon; Samir Y.; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Contreras; John Thomas
Zakai; Rehan Ahmed
Garzon; Samir Y. |
Palo Alto
San Ramon
Sunnyvale |
CA
CA
CA |
US
US
US |
|
|
Family ID: |
48701435 |
Appl. No.: |
13/333565 |
Filed: |
December 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12651161 |
Dec 31, 2009 |
8098450 |
|
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13333565 |
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Current U.S.
Class: |
360/235.4 ;
G9B/5.151; G9B/5.153; G9B/5.229 |
Current CPC
Class: |
G11B 5/6076 20130101;
G11B 5/6005 20130101; G11B 5/607 20130101; G11B 5/6064
20130101 |
Class at
Publication: |
360/235.4 ;
G9B/5.229; G9B/5.153; G9B/5.151 |
International
Class: |
G11B 5/60 20060101
G11B005/60; G11B 5/48 20060101 G11B005/48 |
Claims
1. A hard-disk drive, comprising: a head slider comprising a read
element and a write element disposed on an air bearing surface; a
magnetic-recording disk rotatably mounted on a spindle; a voice
coil motor configured to move the head slider to access portions of
said magnetic-recording disk; and a read/write integrated circuit
(IC) configured to condition write signals sent to the write
element and amplify read signals from the read element, wherein the
head slider comprises (a) a first resistive temperature detector
(RTD) that is located relatively near the air bearing surface and
(b) a second RTD that is offset from the air bearing surface,
wherein the read/write IC is configured to detect when the head
slider makes physical contact with the magnetic-recording disk
based on a difference in temperature measured by the first RTD and
the second RTD, and wherein the first RTD and the second RTD
comprised within the head slider form a bridge circuit with a first
IC resistor and a second IC resistor comprised within the
read/write IC, and wherein a common mode voltage of the bridge
circuit is used to measure the temperature of the head slider while
a differential mode voltage of the bridge circuit is used to
measure a low-frequency signal from a first path of the bridge
circuit to detect physical contact between the head slider and the
disk and to measure a high-frequency signal from a second path of
the bridge circuit to measure disk topography features.
2. The hard-disk drive of claim 1, wherein the temperature measured
by the first RTD or the second RTD is based on an amount of voltage
across the first RTD or the second RTD respectively.
3. The hard-disk drive of claim 1, wherein the first RTD and the
second RTD provide the same amount of resistance.
4. The hard-disk drive of claim 1, wherein the bridge circuit is a
Wheatstone bridge type circuit.
5. (canceled)
6. The hard-disk drive of claim 1, wherein the first temperature
sensor and the second temperature sensor are physically located
within the read/write head such that temperatures changes due to
the ambient environment, a thermal fly height control (TFC), or the
write signals to the write element affect the first temperature
sensor and the second temperature sensor equally.
7. The hard-disk drive of claim 1, wherein the bridge circuit
comprises two arms which have an equal amount of resistance.
8. The hard-disk drive of claim 1, wherein the bridge circuit
comprises two arms, and wherein noise generated by the two arms is
cancelled out by the bridge circuit.
9. A head-gimbal assembly (HGA), comprising: a head slider
comprising a read element and a write element disposed on an air
bearing surface; and a suspension coupled to the head slider,
wherein the head slider comprises (a) a first resistive temperature
detector (RTD) that is located relatively near the air bearing
surface and (b) a second RTD that is offset from the air bearing
surface, and wherein conductive paths within the head slider are
adapted to cause the first RTD and the second RTD to form a bridge
circuit with a first IC resistor and a second IC resistor comprised
within a read/write IC, wherein a common mode voltage of the bridge
circuit is used to measure the temperature of the head slider while
a differential mode voltage of the bridge circuit is used to
measure a low-frequency signal from a first conductive path of the
bridge circuit to detect physical contact between the head slider
and the disk and to measure a high-frequency signal from a second
conductive path of the bridge circuit to measure disk topography
features.
10. The head-gimbal assembly (HGA) of claim 9, wherein the
read/write IC is configured to detect when the head slider makes
physical contact with the magnetic-recording disk based on a
difference in temperature measured by the first RTD and the second
RTD.
11. The head-gimbal assembly (HGA) of claim 9, wherein the first
RTD and the second RTD provide the same amount of resistance.
12. The head-gimbal assembly (HGA) of claim 9, wherein the bridge
circuit is a Wheatstone bridge type circuit.
13. The head-gimbal assembly (HGA) of claim 9, wherein the first
temperature sensor and the second temperature sensor are physically
located within the read/write head such that temperatures changes
due to the ambient environment, a thermal fly height control (TFC),
or the write signals to the write element affect the first
temperature sensor and the second temperature sensor equally.
14. The head-gimbal assembly (HGA) of claim 9, wherein the bridge
circuit comprises two arms which have an equal amount of
resistance.
15. A head-arm assembly (HAA), comprising: a head slider comprising
a read element and a write element disposed on an air bearing
surface; and a suspension coupled to the head slider; and an arm
adapted to support the suspension, wherein the head slider
comprises (a) a first resistive temperature detector (RTD) that is
located relatively near the air bearing surface and (b) a second
RTD that is offset from the air bearing surface, and wherein
conductive paths within the head slider are adapted to cause the
first RTD and the second RTD to form a bridge circuit with a first
IC resistor and a second IC resistor comprised within a read/write
IC, wherein a common mode voltage of the bridge circuit is used to
measure the temperature of the head slider while a differential
mode voltage of the bridge circuit is used to measure a
low-frequency signal from a first conductive path of the bridge
circuit to detect physical contact between the head slider and the
disk and to measure a high-frequency signal from a second
conductive path of the bridge circuit to measure disk topography
features.
16. The head-arm assembly (HAA) of claim 15, wherein the read/write
IC is configured to detect when the head slider makes physical
contact with the magnetic-recording disk based on a difference in
temperature measured by the first RTD and the second RTD.
17. The head-arm assembly (HAA) of claim 15, wherein the first RTD
and the second RTD provide the same amount of resistance.
18. The head-arm assembly (HAA) of claim 15, wherein the bridge
circuit is a Wheatstone bridge type circuit.
19. The head-arm assembly (HAA) of claim 15, wherein the first
temperature sensor and the second temperature sensor are physically
located within the read/write head such that temperatures changes
due to the ambient environment, a thermal fly height control (TFC),
or the write signals to the write element affect the first
temperature sensor and the second temperature sensor equally.
20. The head-arm assembly (HAA) of claim 15, wherein the bridge
circuit comprises two arms which have an equal amount of
resistance.
Description
CLAIM OF PRIORITY AND RELATED APPLICATION DATA
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/651,161, entitled "Fly-Height Management in
a Hard Disk Drive (HDD)," invented by Peter Baumgart et al., filed
on Dec. 31, 2009, the disclosure of which is incorporated by
reference in its entirety for all purposes as if fully set forth
herein.
[0002] This application is related to U.S. patent application Ser.
No. ______, attorney docket number HGST.P060, entitled "Balanced
Embedded Contact Sensor with Low Noise Architecture," invented by
Samir Garzon et al., filed on the same day herewith, the disclosure
of which is incorporated by reference in its entirety for all
purposes as if fully set forth herein.
FIELD OF THE INVENTION
[0003] Embodiments of the invention relate to a distributed
temperature detector architecture for use in a head disk interface
system of a hard-disk drive (HDD).
BACKGROUND OF THE INVENTION
[0004] A hard-disk drive (HDD) is a non-volatile storage device
that is housed in a protective enclosure and stores digitally
encoded data on one or more circular disks having magnetic surfaces
(a disk may also be referred to as a platter). When an HDD is in
operation, each magnetic-recording disk is rapidly rotated by a
spindle system. Data is read from and written to a
magnetic-recording disk using a read/write head which is positioned
over a specific location of a disk by an actuator.
[0005] A read/write head uses a magnetic field to read data from
and write data to the surface of a magnetic-recording disk. As a
magnetic dipole field decreases rapidly with distance from a
magnetic pole, the distance between a read/write head and the
surface of a magnetic-recording disk must be tightly controlled. An
actuator relies on suspension's force on the read/write head to
provide the proper distance between the read/write head and the
surface of the magnetic-recording disk while the magnetic-recording
disk rotates. A read/write head therefore is said to "fly" over the
surface of the magnetic-recording disk. When the magnetic-recording
disk stops spinning, a read/write head must either "land" or be
pulled away onto a mechanical landing ramp from the disk
surface.
[0006] Resistor temperature detector (RTD) architectures have been
used in the prior art to determine when the read/write head makes
physical contact with the magnetic-recording disk based upon the
temperature of the read/write head. RTD architectures in the prior
art have been implemented using a single temperature sensor that
measures temperature based on the amount of voltage across a single
temperature sensor. However, prior art approaches exhibit an
unsatisfactory amount of noise, which complicates accurate
measurements.
SUMMARY OF THE INVENTION
[0007] Approaches described herein teach a distributed temperature
sensing architecture for a head-disk interface (HDI) system. The
distributed temperature sensing architecture comprises two
different resistive temperature detectors within a head slider
which form a bridge circuit with resistors within the read/write
integrated circuit (IC). The bridge circuit of an embodiment allows
the affect of noise generated at the head slider to be cancelled at
the read/write integrated circuit (IC). As a result, accurate
temperature measurements of the head slider may be obtained,
thereby enabling embodiments to detect physical contact between the
head slider and the magnetic-recording disk with greater precision
than prior approaches.
[0008] In an embodiment of the invention, a hard-disk drive (HDD)
comprises a head slider that includes a read element and a write
element disposed on an air bearing surface of the head slider. The
HDD may further include a magnetic-recording disk rotatably mounted
on a spindle and a voice coil motor configured to move the head
slider to access portions of said magnetic-recording disk.
Additionally, the HDD may include a read/write integrated circuit
(IC) configured to condition write signals sent to the write
element and amplify read signals from the read element.
[0009] The head slider may comprises (a) a first resistive
temperature detector (RTD) that is located relatively near the air
bearing surface and (b) a second RTD that is offset from the air
bearing surface. The read/write IC can be configured to detect when
the head slider makes physical contact with the magnetic-recording
disk based on a difference in temperature measured by the first RTD
and the second RTD.
[0010] In an embodiment, the first RTD and the second RTD comprised
within the head slider form a bridge circuit with a first IC
resistor and a second IC resistor comprised within the read/write
IC. The formed bridge circuit from the head and integrated circuit
(IC) has the characteristics like a Wheatstone bridge circuit which
allows the affect of eliminating intrinsic signals from the head
slider's environment and components to be cancelled at the head
slider and read/write IC.
[0011] Embodiments discussed in the Summary of the Invention
section are not meant to suggest, describe, or teach all the
embodiments discussed herein. Thus, embodiments of the invention
may contain additional or different features than those discussed
in this section.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiments of the invention are illustrated by way of
example, and not by way of limitation, in the figures of the
accompanying drawings and in which like reference numerals refer to
similar elements and in which:
[0013] FIG. 1 is a plan view of an HDD according to an embodiment
of the invention;
[0014] FIG. 2 is a plan view of a head-arm-assembly (HAA) according
to an embodiment of the invention;
[0015] FIG. 3 is an illustration of a read/write circuit within an
HDD according to an embodiment of the invention;
[0016] FIG. 4 is an illustration of bridge circuit comprising
resistors residing within both the head slider and the read/write
IC according to an embodiment of the invention; and
[0017] FIG. 5 is an illustration of a temperature sensing
architecture having different filter blocks for signal detection
according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] Approaches for a distributed temperature sensing
architecture for a head-disk interface (HDI) system are described.
In the following description, for the purposes of explanation,
numerous specific details are set forth in order to provide a
thorough understanding of the embodiments of the invention
described herein. It will be apparent, however, that the
embodiments of the invention described herein may be practiced
without these specific details. In other instances, well-known
structures and devices are shown in block diagram form in order to
avoid unnecessarily obscuring the embodiments of the invention
described herein.
Physical Description of Illustrative Embodiments of the
Invention
[0019] Embodiments of the invention may be used to measure the
temperature of the head slider's air-bearing surface (ABS) with
greater precision than prior approaches. Embodiments of the
invention may be incorporated with a hard-disk drive (HDD). In
accordance with an embodiment of the invention, a plan view of a
HDD 100 is shown in FIG. 1. FIG. 1 illustrates the functional
arrangement of components of the HDD including a slider 110b that
includes a magnetic-reading/recording head 110a. Collectively,
slider 110B and head 110a may be referred to as a head slider. The
HDD 100 includes at least one head gimbal assembly (HGA) 110
including the head 110a, a lead suspension 110c attached to the
head 110a, and a load beam 110d attached to the slider 110b, which
includes the head 110a at a distal end of the slider 110b; the
slider 110b is attached at the distal end of the load beam 110d to
a gimbal portion of the load beam 110d. The HDD 100 also includes
at least one magnetic-recording disk 120 rotatably mounted on a
spindle 124 and a drive motor (not shown) attached to the spindle
124 for rotating the disk 120. The head 110a includes a write
element and a read element for respectively writing and reading
information stored on the disk 120 of the HDD 100. The disk 120 or
a plurality (not shown) of disks may be affixed to the spindle 124
with a disk clamp 128. The HDD 100 further includes an arm 132
attached to the HGA 110, a carriage 134, a voice-coil motor (VCM)
that includes an armature 136 including a voice coil 140 attached
to the carriage 134; and a stator 144 including a voice-coil magnet
(not shown); the armature 136 of the VCM is attached to the
carriage 134 and is configured to move the arm 132 and the HGA 110
to access portions of the disk 120 being mounted on a pivot-shaft
148 with an interposed pivot-bearing assembly 152.
[0020] With further reference to FIG. 1, in accordance with an
embodiment of the present invention, electrical signals, for
example, current to the voice coil 140 of the VCM, write signal to
and read signal from the PMR head 110a, are provided by a flexible
cable 156. Interconnection between the flexible cable 156 and the
head 110a may be provided by an arm-electronics (AE) module 160,
which may have an on-board pre-amplifier for the read signal, as
well as other read-channel and write-channel electronic components.
The flexible cable 156 is coupled to an electrical-connector block
164, which provides electrical communication through electrical
feedthroughs (not shown) provided by an HDD housing 168. The HDD
housing 168, also referred to as a casting, depending upon whether
the HDD housing is cast, in conjunction with an HDD cover (not
shown) provides a sealed, protective enclosure for the information
storage components of the HDD 100.
[0021] With further reference to FIG. 1, in accordance with an
embodiment of the present invention, other electronic components
(not shown), including a disk controller and servo electronics
including a digital-signal processor (DSP), provide electrical
signals to the drive motor, the voice coil 140 of the VCM and the
head 110a of the HGA 110. The electrical signal provided to the
drive motor enables the drive motor to spin providing a torque to
the spindle 124 which is in turn transmitted to the disk 120 that
is affixed to the spindle 124 by the disk clamp 128; as a result,
the disk 120 spins in a direction 172. The spinning disk 120
creates a cushion of air that acts as an air-bearing on which the
ABS of the slider 110b rides so that the slider 110b flies above
the surface of the disk 120 without making contact with a thin
magnetic-recording medium of the disk 120 in which information is
recorded. The electrical signal provided to the voice coil 140 of
the VCM enables the head 110a of the HGA 110 to access a track 176
on which information is recorded. Thus, the armature 136 of the VCM
swings through an arc 180 which enables the HGA 110 attached to the
armature 136 by the arm 132 to access various tracks on the disk
120. Information is stored on the disk 120 in a plurality of
concentric tracks (not shown) arranged in sectors on the disk 120,
for example, sector 184. Correspondingly, each track is composed of
a plurality of sectored track portions, for example, sectored track
portion 188. Each sectored track portion 188 is composed of
recorded data and a header containing a servo-burst-signal pattern,
for example, sequenced servo-burst-signal patterns (A,B,C, & D
pattern types) for adjusting the voice coil 140, signal information
that identifies the track 176, and error correction code
information. In accessing the track 176, the read element of the
head 110a of the HGA 110 reads the servo-burst-signal pattern which
provides a position-error-signal (PES) to the servo electronics,
which controls the electrical signal provided to the voice coil 140
of the VCM, enabling the head 110a to follow the track 176. Upon
finding the track 176 and identifying a particular sectored track
portion 188, the head 110a either reads data from the track 176 or
writes data to the track 176 depending on instructions received by
the disk controller from an external agent, for example, a
microprocessor of a computer system.
[0022] Embodiments of the invention also encompass HDD 100 that
includes the HGA 110, the disk 120 rotatably mounted on the spindle
124, the arm 132 attached to the HGA 110 including the slider 110b
including the head 110a.
[0023] With reference now to FIG. 2, in accordance with an
embodiment of the present invention, a plan view of a
head-arm-assembly (HAA) including the HGA 110 is shown. FIG. 2
illustrates the functional arrangement of the HAA with respect to
the HGA 110. The HAA includes the arm 132 and HGA 110 including the
slider 110b including the head 110a. The HAA is attached at the arm
132 to the carriage 134. In the case of an HDD having multiple
disks, or platters as disks are sometimes referred to in the art,
the carriage 134 is called an "E-block," or comb, because the
carriage is arranged to carry a ganged array of arms that gives it
the appearance of a comb. As shown in FIG. 2, the armature 136 of
the VCM is attached to the carriage 134 and the voice coil 140 is
attached to the armature 136. The AE 160 may be attached to the
carriage 134 as shown. The carriage 134 is mounted on the
pivot-shaft 148 with the interposed pivot-bearing assembly 152.
[0024] FIG. 3 is an illustration of a read/write circuit 310 within
an HDD according to an embodiment of the invention. FIG. 3 depicts
hard-disk drive (HDD) 300 which includes enclosure 301 that
contains one or more magnetic platters or disks 302, read elements
304, write elements 305, an actuator arm suspension 306, a
transmission line interconnect 308, a read/write integrated circuit
(IC) 310, a flexible interconnect cable 312, and a disk enclosure
connector 314.
[0025] Electrical signals are communicated between the read/write
elements and read/write integrated circuit 310 over transmission
line interconnect 308. Read/write integrated circuit 310 conditions
the electrical signals so that they can drive write element 305
during writing and amplifies the electrical signal from read
element 304 during reading. Signals are communicated between
read/write integrated circuit 310 and disk enclosure connector 314
over flexible cable 312. Disk enclosure connector 314 conducts
signals with circuitry external to disk enclosure 301. In other
embodiments, read/write integrated circuit (IC) 310 is located
elsewhere than depicted in FIG. 3, such as on flex cable 312 or on
printed circuit board (PCB) within the hard-disk drive.
Distributed Temperature Sensing Architecture
[0026] FIG. 4 is an illustration of a distributed temperature
sensing architecture 400 according to an embodiment of the
invention. Distributed temperature sensing architecture 400 may be
incorporated as part of HDD 100 of FIG. 1. FIG. 4 depicts a head
slider 410, read/write IC 420, and a magnetic-recording disk 430.
Head slider 410 comprises a write element 412, a thermal fly height
control (TFC) 414, and a read element 416. Note that write element
412 and read element 416 are disposed face the air-bearing surface
(ABS) 418 of head slider 410.
[0027] Head slider 410 comprises two different temperature sensors,
namely resistive temperature detector (RTD) 440 and 442. In an
embodiment, RTDs 440 and 442 may each be embodied as a thermistor.
RTDs 440 and 442 may be composed of, but not limited to, metallic
(e.g., NiFe) and semiconductor materials. RTDs 440 and 442 may
measure temperature based on the amount of voltage across the
corresponding resistive temperature detector. Changes in
temperature cause a change in the amount of resistance provided by
a resistive temperature detector. A small increase in temperature
will result in an increase in voltage across a resistive
temperature detector. Thus, the amount of voltage across a
resistive temperature detector may be used to identify the
temperature associated with that resistive temperature detector. In
FIG. 4, RTD 440 and RTD 442 may each provide the same amount of
resistance for a given temperature.
[0028] As shown in FIG. 4, RTD 440 is located on or proximate to
air bearing surface 418 while the position of RTD 442 is offset
from air bearing surface 418 or embedded within head slider 410.
When physical contact is made between head slider 410 and
magnetic-recording disk 430 when magnetic-recording disk 430 is
rotating, the resulting friction causes an increase in temperature
within head slider 410 originating at the point of contact. The
change in temperature resulting from the physical contact will be a
gradient as a function of distance from the point of contact.
[0029] The particular distance which RTD 442 should be offset from
air bearing surface 418 should be equal to a distance where RTD 442
does not measure the full effect of the change in temperature
resulting from friction caused by physical contact between head
slider 410 and magnetic-recording disk 430, but still within close
enough proximity to detect changes in temperature due to TFC 414 or
write signals to write element 412. For example, in one embodiment,
a distance of a few hundred microns may exist between RTD 442 and
air bearing surface 418.
[0030] As RTD 440 is in close proximity to air bearing surface 418,
when physical contact is made between a portion of head slider 410
(which most likely will be at write element 412), RTD 440 will
detect an increase in temperature due to the resulting friction
from the physical contact. Since RTD 442 is offset from air bearing
surface 418, when physical contact is made between a portion of
head slider 410 and magnetic-record disk 430, RTD 442 will not
detect an increase in temperature due to the resulting friction
from the contact of the same magnitude as RTD 440.
[0031] Thus, in an embodiment, read/write IC 420 may be configured
to detect when head slider 410 makes physical contact with
magnetic-recording disk 430 based on a difference in temperature
measured by temperature sensor 440 and temperature sensor 442.
[0032] However, given the physical location of RTDs 440 and 442 in
head 410 slider, changes in temperature due to the ambient
environment or caused by the thermal fly height control (TFC) or
the write signals to the write element will affect temperature
sensors 440 and 442 equally. Thus, an increase in temperature that
is measured by both temperature sensors 440 and 442 may be
attributed to these causes, rather than a physical contact between
head 410 slider and magnetic-recording disk 430. Using the relative
difference between the temperatures measured by RTD 440 and RTD 442
as a means to detect physical contact between head slider 410 and
disk 430 removes or reduces any noise or inaccurate introduced or
caused by temperature changes that affect both RTD 440 and RTD 442
substantially equally, such as heating caused by TFC 414, write
element 412, self-heating, and/or lasers used to warm disk 430.
Using a Distributed Bridge
[0033] In an embodiment, RTDs 440 and 442 may form a bridge circuit
with two resistors located within read/write IC 420. For example,
FIG. 4 depicts RTDs 440 and 442 in a bridge circuit with IC
resistor 422 and IC resistor 424 that reside in read/write IC 420
according to an embodiment of the invention.
[0034] The distributed bridge circuit formed by RTDs 440 and 442
(located within head slider 410) and IC resistors 422 and 424
(located within read/write IC 420) form a Wheatstone bridge type
circuit. In such an embodiment, equal current should flow on both
arms of the Wheatstone bridge absent a temperature change detected
by one or more of RTDs 440 and 442. Thus, in the Wheatstone bridge
circuit, both arms of the circuit should provide the same amount of
resistance.
[0035] In an embodiment, RTDs 440 and 442 provide low levels of
noise, e.g., the signal-to-noise ratio for RTDs 440 and 442 may be
about 30 dB. Indeed, the noise level of RTDs 440 and 442 is low
enough where, in certain implementations, the circuit architecture
itself becomes the biggest noise contributor. Advantageously, noise
in the Wheatstone bridge circuit originating at head slider 410 and
carried by both arms of the circuit bridge will be cancelled at the
read/write IC 420. As a result, accurate temperature measurements
of head slider 410 may be obtained, thereby enabling embodiments to
detect physical contact between the head slider and the
magnetic-recording disk with greater precision.
[0036] In an embodiment employing a Wheatstone bridge type circuit,
read/write IC 420 may measure the differential-mode voltage of the
Wheatstone bridge circuit to identify the relative temperature
difference between RTD 440 and RTD 442. This relative difference
between measured temperatures can be used to identify when head
slider 410 makes physical contact with magnetic-recording disk 430,
since once such contact is made RTD 440 will measure a higher
temperature than RTD 442. By read/write IC 420 measuring the
common-mode voltage of the Wheatstone bridge circuit, read/write IC
420 may identify changes in temperature due to the ambient
environment, a thermal fly height control (TFC), or the write
signals to the write element, since such temperature changes affect
both RTDs 440 and 442 equally.
Filtering for Signal Detection
[0037] FIG. 5 is an illustration of a temperature sensing
architecture having different filter blocks for signal detection
according to an embodiment of the invention. RTDs 440 and 442
residing in head slider 410 are depicted in FIG. 5 as well as
resistors 422 and 424 residing in read/write IC 420. FIG. 5 also
depicts low noise buffer amplifier 510. Low noise buffer amplifier
510 may be a DC coupled amplifier, as no high pass filtering is
required.
[0038] In FIG. 5, the half bridge circuit that includes RTDs 422
and 424 can be tuned by placing switch FETs on different
resistances such that resistance imbalances in RTDs 440 and 442 is
zeroed at low noise buffer amplifier 510. One skilled in the art
can add such switches for a zero-offset scheme.
[0039] The differential mode of the bridge circuit may be used to
monitor the fly height of head slider 410. Filter block 520
measures a low-frequency signal response from the bridge circuit to
detect physical contact between head slider 410 and disk 430 with
great sensitivity. Filter block 522 measures a high-frequency
signal response from the bridge circuit to measure disk topography
features, such as asperities.
[0040] The common mode of the bridge circuit may be used to monitor
the temperature of head slider 410. Filter block 524 may be used to
measure the temperature of head slider 410 using the common mode
voltage of the bridge circuit.
[0041] In the foregoing specification, embodiments of the invention
have been described with reference to numerous specific details
that may vary from implementation to implementation. Thus, the sole
and exclusive indicator of what is the invention, and is intended
by the applicants to be the invention, is the set of claims that
issue from this application, in the specific form in which such
claims issue, including any subsequent correction. Any definitions
expressly set forth herein for terms contained in such claims shall
govern the meaning of such terms as used in the claims. Hence, no
limitation, element, property, feature, advantage or attribute that
is not expressly recited in a claim should limit the scope of such
claim in any way. The specification and drawings are, accordingly,
to be regarded in an illustrative rather than a restrictive
sense.
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