Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
2000-06-22
2004-05-11
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S046000, C330S051000
Reexamination Certificate
active
06735034
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to the field of information storage, and more particularly to a circuit and method for timing amplifier stages of a multi-stage reader amplifier for hard disk drive devices.
BACKGROUND OF THE INVENTION
Hard disk drives are mass storage devices that 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 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 a head
16
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 platters
12
by heads
16
which comprise a read head
18
and a write head
20
at the tip thereof. The read
18
and write
20
heads comprise magneto-resistive heads adapted to read or write data from/to platters
12
when current is passed through them. Heads
16
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. A preamp
26
may comprise a single chip containing a reader amplifier
27
, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp
26
may comprise separate components rather than residing on a single chip.
FIG. 2
shows a reader amplifier
27
of the prior art comprising input amplifier stage
12
coupled in series to middle amplifier stage
14
which is coupled to output amplifier stage
16
. The reader amplifier
27
chain of amplifiers
12
,
14
,
16
is utilized to obtain the desired amount of gain.
A problem with reader amplifiers
27
of the prior art is that at certain transitional times in operation, all amplifiers
12
,
14
,
16
are turned off and then turned on at once, resulting in an excursion in the output signal
34
as shown in FIG.
3
. The excursion may be +/−40 mV or greater, for example. Such transitional times occur for various reasons in a hard disk drive system. In a disk drive system having multiple platters
12
written to and read by multiple heads
16
, head
16
communication with reader amplifier
27
is often multiplexed. When heads
16
are changed, an excursion may be seen in the output signal
34
. Another excursion generating transitional time is the read head changing from an idle state to a read state. Often, a reader amplifier
27
will operate in an idle mode to save power. Because the internal transistors of amplifiers
12
,
14
, and
16
are typically bipolar, there is a temporary saturation effect when turning on the transistors of middle stage
14
and output stage
16
. When this occurs, it takes a certain amount of time for the FETs to recover and arrive back into a non-saturated state. In this case it results in a 6 &mgr;s recovery time. The excursion shown between time t
1
and the time t
2
reflects the spike in the output signal on the reader amplifier output when the reader amplifier
27
is switched from one head
16
to another, or from idle mode to read mode, for example. Another factor contributing to the excursion is ringing of the voltage supply from each amplifier stage
12
,
14
, and
16
suddenly simultaneously drawing current from the voltage supply.
What is needed is a circuit and method for eliminating or minimizing excursions in the output signal of a reader amplifier
27
.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a reader amplifier circuit and method with improved recovery time when changing from one mode to another, minimizing the excursion on a reader amplifier output signal. A chain of amplifier stages is turned on in a staggered fashion to avoid saturation of transistors in the second and third stages and reduce ringing on the voltage supply. The last output stage is turned on gradually with an RC circuit, reducing ringing and minimizing the excursion of the output signal.
In one embodiment, disclosed is a method of timing the enabling of amplifier stages of a multi-stage reader amplifier for a hard disk drive system. The reader amplifier includes a first stage, second stage and third stage coupled in series. The first stage is adapted to receive an input signal and the third stage is adapted to generate an output signal. The method includes the steps of powering the first stage, delaying the enabling of the second stage, and delaying the enabling of the third stage, wherein excursions on the third stage output signal are reduced.
Also disclosed is a method of timing the enabling of stages of a multi-stage reader amplifier of a hard disk drive system in a reader amplifier having a first stage, a second stage and a third stage coupled in series. The method includes the steps of powering the first stage, waiting a first predetermined time interval, enabling the second stage, waiting a second predetermined time interval, and enabling the third stage so that excursions of the third stage output signal are reduced.
Further disclosed is a reader amplifier circuit for a hard disk drive system, including a first amplifier stage adapted to receive an input signal and a second amplifier stage coupled to the first amplifier stage. A third amplifier stage is coupled to the second amplifier stage and is adapted to generate an output signal. A logic circuit successively enables the second and third amplifier stages such that excursions of the output signal are reduced.
Advantages of the invention include reducing the recovery time after mode transitions and head switch transitions. Saturation of successive amplifier stage transistors is avoided, reducing excursions in the reader amplifier output signal. Ringing on the voltage supply is minimized by staggering the start-up of the chain of amplifiers of the reader amplifier. An additional feature includes delaying the start of the third output stage with an RC circuit, rather than an abrupt turn on.
REFERENCES:
patent: 5070538 (1991-12-01), Milberger et al.
patent: 5357207 (1994-10-01), Ash
patent: 5446601 (1995-08-01), Fukuta
patent: 6380804 (2002-04-01), Ross
patent: 2001/0015867 (2001-08-01), Hatanaka et al.
Bloodworth Bryan
Emerson Paul Merle
Iroaga Echere
Manjrekar Ashish
Brady W. James
Hudspeth David
Rodriguez Glenda P
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
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