Servo controller and servo control method

Details Servo controller and servo control method Servo controller and servo control method

2002-07-03

2003-03-25

Tokar, Michael (Department: 2819)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

C360S025000, C360S051000, C360S065000, C360S067000, C360S077070, C360S077080, C324S076520, C324S076530, C324S076540, C324S076550, C324S076820, C341S139000, C341S155000

Reexamination Certificate

active

06538834

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a servo controller and a method for controlling a servo. More particularly, it relates to a servo controller that controls an embedded servo by providing servo sections in a data recording surface of a recording medium, such as a magnetic disk.
FIG. 1
is a schematic block diagram of a prior art servo controller
50
. The servo controller
50
reads data from a recording medium, such as a magnetic disk.
The servo controller
50
includes an automatic gain control (AGC) circuit
1
, a D/A converter
2
, a filter circuit
3
, an A/D converter
4
, a servo processing circuit
5
, and an AGC circuit controller
6
.
The AGC circuit
1
receives an input signal IN, which includes data read by a recording medium by a read head (not shown). The AGC circuit
1
sets its gain based on an AGC voltage SG
1
supplied from the D/A converter
2
, amplifies the input signal IN based on the gain, and sends an amplified data signal SG
2
to the filter circuit
3
.
The filter circuit
3
, including a low-pass filter, eliminates unnecessary high frequency components in the amplified data signal SG
2
so to generate a filtered signal SG
3
, and provides the filtered signal SG
3
to the A/D converter
4
. The A/D converter
4
converts the filtered data signal SG
3
to a digital data signal SG
4
, and provides the digital data signal SG
4
to the servo processing circuit
5
and the AGC circuit controller
6
.
The servo processing circuit
5
servo-controls the read position of the read head based on the digital data signal SG
4
. The servo processing circuit
5
includes a discrete Fourier transform (DFT) operational circuit (not shown). The DFT operational circuit performs a discrete Fourier transform on the digital data signal SG
4
to generate phase data PD. The phase data PD is used to servo-control the read position of the read head.
In addition to the digital data signal SG
4
, the AGC circuit controller
6
is provided with a target value PA, which is pre-stored in a register, or the like. The target value PA generates the filtered data signal SG
3
so that its amplitude is substantially equal to the full-scale range of the input level of the A/D converter
4
. The AGC circuit controller
6
compares the digital data signal SG
4
and the target value PA, integrates the error component to generate an integral signal SG
5
, and sends the integral signal SG
5
to the D/A converter
2
.
The D/A converter
2
converts the integral signal SG
5
to an analog signal, and provides the AGC circuit
1
with the AGC voltage SG
1
.
The A/D converter
4
, the servo processing circuit
5
, and the AGC circuit controller
6
are operated in accordance with a clock signal CLK, which is generated by a PLL circuit.
Servo sections are locally defined in each track of a recording medium, such as a magnetic disk.
FIG. 2
illustrates one of the servo sections. The servo section includes an R/W recovery segment
7
, a servo mark segment
8
, an AGC segment
9
, and a phase detection segment
10
.
FIG. 3
is a diagram illustrating the waveform of the signal IN in the servo section. Although the signal IN of the servo section actually has a Lorentz waveform, the signal IN is illustrated as having a sin wave for the sake of brevity.
With reference to
FIG. 3
, when the servo section is read, the R/W recovery segment
7
is read during a first time period t
1
. The signal IN has a predetermined amplitude and frequency during the first time period t
1
. Then, the servo mark segment
8
is read during a second time period t
2
. The signal IN has a continuous null level during the second time period t
2
.
In comparison to the R/W recovery segment
7
, the signal IN has a lower frequency and a greater amplitude when the AGC segment
9
is read during a third time period t
3
. When the phase detection segment
10
is read during a fourth time period t
4
, the frequency and amplitude of the signal IN are the same as the frequency and amplitude of the signal IN when the AGC segment
9
is read.
FIG. 4
is a combined timing and waveform chart of the AGC voltage SG
1
when the servo section is read.
When the read head starts reading the R/W recovery segment
7
, the AGC circuit controller
6
calculates the error between the digital data signal SG
4
, which corresponds to the input signal IN, and the target value PA. Based on the digital integral signal SG
5
generated by the AGC circuit controller
6
, the D/A converter
2
supplies the AGC circuit
1
with the AGC voltage SG
1
.
If the amplitude of the input signal IN of the R/W recovery segment
7
is small and the error between the digital data signal SG
4
and the target value PA is large, the level of the AGC voltage SG
1
increases. As a result, the digital data signal SG
4
becomes the target value PA.
When the servo mark segment
8
is read and the input signal IN has a continuous null level, the digital data signal SG
4
is accordingly generated at a continuous, null level. This fixes the integral signal SG
5
and the AGC voltage SG
1
.
Then, when the reading of the AGC segment
9
is started, the error between the digital data signal SG
4
, which corresponds to the input signal IN, and the target value PA is recalculated by the AGC circuit controller
6
. The D/A converter
2
then supplies the AGC circuit
1
with the AGC voltage SG
1
in accordance with the integral signal SG
5
of the D/A converter
2
.
When the reading shifts from the servo mark segment
8
to the AGC segment
9
, the amplitude of the read signal IN becomes greater than that when the R/W recovery segment
7
is read. Thus, the amplitude of the filtered data signal SG
3
, which is generated by the filter circuit
3
, exceeds a target value.
As a result, the AGC circuit controller
6
gradually decreases the AGC voltage SG
1
until the digital signal SG
4
converges to the target value PA. In a state in which the amplitude of the filtered data signal SG
3
is substantially equal to the full-scale range of the A/D converter
4
, the reading of the phase detection segment
10
is started.
The signal IN has the same frequency and amplitude when the phase detection segment
10
and the AGC segment
9
are read. Thus, the phase detection segment
10
is read in a state in which the A/D converter
4
is provided from the beginning with the substantially full-scale range, filtered data signal SG
3
. Thus, the reading of the phase information stored in the phase detection segment
10
is guaranteed, and servo-control, which corrects the read position, is immediately performed.
In this manner, the servo controller
50
amplifies the input signal IN, which corresponds to the data read from the recording medium. The servo controller
50
then extracts the filtered data signal SG
3
, including a fundamental wave from the amplified data signal SG
2
. Further, the servo controller
50
performs the discrete Fourier transform on the digital data signal SG
4
, which is the converted filtered data signal SG
3
, to obtain the phase data PD. Based on the phase data PD, the servo controller
50
performs phase servo to position the read head.
However, when the servo section is read, the AGC voltage SG
1
is shifted whenever the read segment is changed to provide the A/D converter
4
with the substantially, full-range filtered data signal SG
3
. Therefore, whenever the read segment of the servo section changes, time is required for the amplitude of the filtered data signal SG
3
to substantially converge to the full-scale range input level of the A/D converter
4
. As a result, it is difficult to compress the servo section and shorten the read time.
When starting the reading of the phase detection segment
10
, to provide the A/D converter
4
with the substantially, full-scale range filtered data signal SG
3
from the beginning, the AGC segment
9
must have a sufficient amount of sample data and data storage space.
Further, as the density and reading speed of the recording medium increase, the high-speed rotation of the recording medium causes the inpu

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