Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of the amplifier
Reexamination Certificate
2000-02-25
2003-04-15
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of the amplifier
C360S046000
Reexamination Certificate
active
06549357
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of information storage, and more particularly to a method and apparatus for increasing the bandwidth of a differential amplifier for a disk drive read head.
BACKGROUND OF THE INVENTION
In general, mass storage devices, such as hard disk drives, include 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 servo circuit, and control circuitry to control the operation of the hard disk drive and to properly interface the hard disk drive to a host system or bus.
FIG. 1
provides one example of a prior art disk drive mass storage system
30
. Disk drive system
30
interfaces and exchanges data with a host
32
during read and write operations. Disk drive system
30
includes a disk/head assembly
12
, a preamplifier
14
, a synchronously sampled data (SSD) channel
10
, and a control circuit
11
. Disk/head assembly
12
and preamplifier
14
are used to magnetically store data. SSD channel
10
and control circuitry
11
are used to process data that is being read from and written to disk/head assembly
12
and to control the various operations of disk drive mass storage system
30
. Host
32
exchanges digital data with control circuitry
11
.
Disk/head assembly
12
includes a number of rotating platters used to store data that is represented as magnetic transitions on the magnetic platters. Read/write heads
13
of disk/head assembly
12
are used to store and retrieve data from each side of the magnetic platters. Read/write heads
13
may comprise any type of available read/write heads such as magneto-resistive heads. Preamplifier
14
serves as an interface between read/write heads
13
of disk/head assembly
12
and SSD channel
10
, and provides amplification to the waveform data signals as needed.
SSD channel
10
is used during read and write operations to exchange analog data signals with disk/head assembly
12
through preamplifier
14
and to exchange digital data signals with control circuitry
11
through a data/parameter path
15
. SSD channel
10
includes a write channel
16
, a read channel
18
, a servo control
20
, and a parameter memory
22
. SSD channel
10
may be implemented as a single integrated circuit.
Some of the various circuit modules of read channel
18
may receive operational parameters for enhanced or optimal performance. The operational parameters are generally calculated during burn-in but may be calculated at other times. The operational parameters are designed to account for the various physical and magnetic characteristics of disk drive mass storage system
30
that vary from system to system and influence operational performance. During start-up, the operational parameters are provided to SSD channel
10
from control circuitry
11
through data/parameter path
15
. Parameter memory
22
stores the operational parameters. The various circuit modules of read channel
18
may then access the operational parameters from parameter memory
22
during read operations.
Control circuitry
11
controls the various operations of disk drive mass storage system
30
and to exchange digital data with SSD channel
10
, the pre-amp
14
and host
32
. Control circuitry
11
includes a microprocessor
28
, a disk control
24
, a random access memory (RAM)
26
, and a read only memory (ROM)
29
. Microprocessor
28
, disk control
24
, RAM
26
, and ROM
29
together provide control and logic functions to disk drive mass storage system
30
so that data may be received from host
32
, stored, and later retrieved and provided back to host
32
. ROM
29
includes preloaded microprocessor instructions for use by microprocessor
28
in operating and controlling disk drive mass storage system
30
. ROM
29
may also include the operational parameters, discussed above, that are supplied to parameter memory
22
during start-up. RAM
26
is used for storing digital data received from host
32
before being supplied to SSD channel
10
and received from SSD channel
10
before being supplied to host
32
. RAM
26
may also provide data to microprocessor
28
and store data or results calculated by microprocessor
28
. Disk control
24
includes various logic and bus arbitration circuitry used in properly interfacing disk drive mass storage system
30
to host
32
and for internally interfacing control circuitry
11
to SSD channel
10
and to the pre-amp status register in pre-amp
14
. Depending on the circuit implementation, any of a variety of circuitry may be used in disk control
24
.
In operation, disk drive mass storage system
30
goes through an initialization or start-up routine when power is initially provided. One such routine instructs microprocessor
28
to supply operational parameters, previously stored in ROM
29
, to parameter memory
22
of SSD channel
10
through data/parameter path
15
. The operational parameters are then stored in memory registers of parameter memory
22
for use by read channel
18
during a read operation. Operational parameters may also be stored in the pre-amp status register in pre-amp
14
using bus
15
b.
During read operations, read channel
18
receives analog data signals from read/write heads
13
of disk/head assembly
12
through preamplifier
14
. Read channel
18
conditions, decodes, and formats the analog data signal and provides a digital data signal in parallel format to control circuitry
11
through data/parameter path
15
. Read channel
18
includes any of a variety of circuit modules such as an automatic gain control circuit, a low pass filter, a variable frequency oscillator, a sampler, an equalizer, such as a finite impulse response filter, a maximum likelihood, partial response detector, a deserializer, and a synchronization field detection circuit. Read channel
18
provides the digital data signal to disk control
24
through data/parameter path
15
. Disk control
24
provides various digital logic control and arbitration circuitry between SSD channel
10
, host
32
, RAM
26
, microprocessor
28
, and ROM
29
during both read and write operations.
The bandwidth of the system is typically limited by the lead inductance associated with the magneto-resistive read/write head. The limited bandwidth is attributable to a pole caused by the combination of the resistance and lead inductance of the magneto-resistive read/write head, which causes a roll off in the system's frequency response.
One approach to increasing the bandwidth of a hard disk drive is to introduce a zero at a frequency corresponding to the pole due to the lead inductance of the magneto-resistive element. One method of locating such a compensating zero was introduced in a prior application, U.S. application Ser. No. 09/211,938 filed Dec. 15, 1998 by Bernard R. Gregoire et. al. In that application, an adjustable impedance boosting circuit was described that improved over the prior techniques by providing an adjustable compensating zero. That invention had several important technical advantages. Varying the impedance of the variable impedance load in proportion to the actual value of the magneto-resistive element facilitates adjustable compensation for a pole caused by the lead inductance of the magneto-resistive element. This prior invention provided a method and apparatus for approximating a compensating zero that is responsive to variations in the actual value of the magneto-resistive element. The peak-limiting circuit prevents peaks in the frequency response by rolling off the gain of the variable impedance load at a selected frequency.
SUMMARY OF THE INVENTION
While the previously described prior invention provided an adjustable impedance boosting circuit that adjusted a compensating zero for variations in the actual value of the magneto-resistive element for a given head, it is desirable to further adjust the response of the impedance boosting circuit. Adjusting the impedance response is needed to allow further bandwidth improvement des
Brady W. James
Holder Regina N.
Kapadia Varsha A.
Petersen Bret J.
Telecky , Jr. Frederick J.
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