Spindle servo system for adjusting rotational speed in optical disk player

A spindle servo system roughly adjusts a rotational speed of a spindle motor for rotationally driving an optical disk at a specified speed in an optical disk player for reproducing digital data composed of run length limited codes and synchronizing signals, wherein the run length limited codes are restricted between a minimum run length and a maximum run length, and wherein the synchronizing signals are composed of a maximum bit pattern with a run length longer than the maximum run length and an additional bit pattern disposed just before or after the maximum bit pattern with a run length longer than the minimum run length and shorter than the maximum run length, the spindle servo system. The spindle servo system includes a pickup detector for reading the digital data from the optical disk; pattern detecting means for detecting a synchronizing signal composed of the maximum bit pattern and the additional bit pattern from the digital data read by the pickup detector; period detecting means for detecting a period of the synchronizing signal, the period including the maximum bit pattern and the additional bit pattern detected by the pattern detector; and motor for controlling the rotational speed of the spindle motor to maintain the period detected by the period detector at a predetermined value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a spindle servo system for adjusting a 
rotational speed of a spindle motor in a disk player, and more 
particularly, to a spindle servo system for rough adjustment of the 
spindle speed. 
2. Description of the Related Art 
In a player for reproducing digitally recorded data from an optical disk 
such as a CD (compact disk), the rotational speed of a spindle motor for 
rotationally driving the optical disk is controlled by a spindle servo so 
that the rotational speed of the optical disk is adjusted to a specified 
speed. In a CD, this specified speed at which the linear velocity of the 
tracks is fixed. In the spindle servo, rough adjustment is normally 
carried out first. That is, a read signal read from the optical disk by a 
pickup is compared with a slice level to convert it into a binary signal 
of "1" or "0". A maximum period or a maximum inversion internal (it is a 
pit portion of a synchronizing signal and is called as a maximum run 
length) of the binary signal is detected and the spindle motor is driven 
so that the maximum period or the maximum inversion interval thereof 
becomes equal to a predetermined reference value. When the maximum 
inversion interval or the maximum period thereof becomes equal to the 
predetermined reference value and the rough adjustment is locked, fine 
adjustment is carried out. The synchronizing signal recorded in the 
optical disk is sampled to compare its phase with that of a reference 
oscillation signal to drive the spindle motor in accordance with the 
result of comparison of the phases. 
A recent proposal was to adopt "14T-4T," for example, as a synchronizing 
signal pattern to be used for rough adjustment of the spindle servo in a 
digital video disk (DVD). Here, (T) denotes a unit bit length, (14T) is a 
bit length of a maximum bit pattern longer than a maximum run length of 
digital data, i.e., the maximum inversion interval, and (4T) denotes an 
additional inversion interval of an additional bit pattern whose length is 
shorter than the maximum run length and longer than the minimum run length 
of the digital data. It is noted that (-) is used not as a symbol of 
subtraction but as a symbol that (4T) follows (14T). However, descriptions 
such as (14T+4T) are made in embodiments described later where (+) is used 
to mean that (14T) is added with (4T). 
There has been a problem in the DVD in that the period of 18T of the 
synchronizing signal pattern of 14T -4T described above is shorter than 
the maximum period of 22T (11T-1T) within the data. Thus, the spindle 
servo of the method of detecting the maximum period of the binary signal 
cannot be applied to it. For synchronizing signal patterns in this 
section, the servo control section has been adapted to output a control 
voltage of 0 V to a spindle motor driving circuit to decelerate the 
rotation of the spindle when a maximum value of a run length of a bit 
pattern detected within a certain section in reading a signal recorded in 
the disk is 15T and over, and to output a control voltage of 5 V to the 
spindle motor driving circuit to accelerate the rotation of the spindle 
motor when the maximum value is 13T and below. Further, the servo control 
section has been adapted to output a control voltage of 2.5 V to the 
spindle motor driving circuit to maintain the rotation of the spindle 
motor when the maximum value is 14T. 
However, because the slice level in binarizing the signal read from the 
disk is set so that a DC component of the binary signal, zero for example, 
is based on the output binary signal, the slice level fluctuates subtly 
corresponding to the binary signal even if the spindle motor rotates 
adequately. For example, the synchronizing signal pattern detected with 
respect to 14T-4T described above may become a pattern of 13T-5T or of 
15T-3T. As a result, problems occur in stabilizing the spindle servo 
because the fluctuating synchronizing signal pattern causes acceleration 
or deceleration of the spindle motor. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed to a spindle servo system of 
an optical disk player that substantially obviates one or more of the 
problems due to limitations and disadvantages of the related art. 
An object of the present invention to provide a spindle servo system which 
can roughly adjust the rotational speed of the spindle motor adequately to 
a specified value in a player for reproducing digital data on an optical 
disk in which synchronizing signal patterns composed of a minimum bit 
pattern and an additional bit pattern are recorded together with digital 
data. 
Additional features and advantages of the invention will be set forth in 
the description which follows, and in part will be apparent from the 
description, or may be learned by practice of the invention. The 
objectives and other advantages of the invention will be realized and 
attained by the structure particularly pointed out in the written 
description and claims hereof as well as the appended drawings. 
To achieve these and other advantages and in accordance with the purpose of 
the present invention, as embodied and broadly described, the spindle 
servo system roughly adjusts a rotational speed of a spindle motor for 
rotationally driving an optical disk at a specified speed in an optical 
disk player for reproducing digital data composed of run length limited 
codes and synchronizing signals, the run length limited codes restricted 
between a minimum run length and a maximum run length, the synchronizing 
signals composed of a maximum bit pattern with a run length longer than 
the maximum run length and an additional bit pattern disposed just after 
the maximum bit pattern with a run length longer than the minimum run 
length and shorter than the maximum run length, the spindle servo system. 
The spindle servo system includes pickup means for reading the digital 
data from the optical disk; pattern detecting means for detecting a 
synchronizing signal composed of the maximum bit pattern and the 
additional bit pattern from the digital data read by the pickup means; 
period detecting means for detecting a period of the synchronizing signal, 
the period including the maximum bit pattern and the additional bit 
pattern detected by the pattern detecting means; and motor control means 
for controlling the rotational speed of the spindle motor to maintain the 
period detected by the period detecting means at a predetermined value. 
In another aspect, the spindle servo system roughly adjusts a rotational 
speed of a spindle motor for rotationally driving an optical disk at a 
specified speed in an optical disk player for reproducing digital data 
composed of run length limited codes and synchronizing signals, the run 
length limited codes restricted between a minimum run length and a maximum 
run length, the synchronizing signals composed of a maximum bit pattern 
with a run length longer than the maximum run length and an additional bit 
pattern disposed just before the maximum bit pattern with a run length 
longer than the minimum run length and shorter than the maximum run 
length, the spindle servo system. The spindle servo system includes pickup 
means for reading the digital data from the optical disk; pattern 
detecting means for detecting a synchronizing signal composed of the 
additional bit pattern and the maximum bit pattern from the digital data 
read by the pickup means; period detecting means for detecting a period of 
the synchronizing signal, the period including the additional bit pattern 
and the maximum bit pattern detected by the pattern detecting means; and 
motor control means for controlling the rotational speed of the spindle 
motor to maintain the period detected by the period detecting means at a 
predetermined value. 
According to one aspect of the present invention, in an optical disk player 
for reproducing digital data from an optical disk in which the digital 
data composed of run length limited codes that meet with the restriction 
of a minimum run length and a maximum run length and synchronizing signals 
whose one period is a pattern composed of a maximum bit pattern having a 
run length longer than the maximum run length and an additional bit 
pattern disposed just after the maximum bit pattern and having a run 
length which is longer than the minimum run length and shorter than the 
maximum run length are recorded, an inventive spindle servo system for 
roughly adjusting a rotational speed of a spindle motor for rotationally 
driving the optical disk to a specified speed comprises pattern detecting 
means for detecting the pattern composed of the maximum bit pattern and 
the additional bit pattern from the read signal read from the optical disk 
by pickup means; period detecting means for detecting a period made up by 
the maximum bit pattern and the additional bit pattern detected by the 
pattern detecting means; and motor control means for adjusting the 
rotational speed of the spindle motor so that the value of period detected 
by the period detecting means becomes equal to a predetermined value. 
According to another aspect of the present invention, in an optical disk 
player for reproducing digital data from an optical disk in which the 
digital data composed of run length limited codes that meet with the 
restriction of a minimum run length and a maximum run length and 
synchronizing signals whose one period is a pattern composed of a maximum 
bit pattern having a run length longer than the maximum run length and an 
additional bit pattern disposed just before the maximum bit pattern and 
having a run length which is longer than the minimum run length and 
shorter than the maximum run length are recorded, an inventive spindle 
servo system for roughly adjusting a rotational speed of a spindle motor 
for rotationally driving the optical disk to a specified speed comprises 
pattern detecting means for detecting the pattern composed of the 
additional bit pattern and the maximum bit pattern from the read signal 
read from the optical disk by pickup means; period detecting means for 
detecting a period made up by the additional bit pattern and the maximum 
bit pattern detected by the pattern detecting means; and motor control 
means for adjusting the rotational speed of the spindle motor so that the 
value of period detected by the period detecting means becomes equal to a 
predetermined value. 
According to the present invention, the period of the synchronizing signal 
composed of the maximum bit pattern and the additional bit pattern 
detected respectively from the signal read from the optical disk is 
obtained to perform spindle servo control corresponding to that period. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory and are 
intended to provide further explanation of the invention as claimed.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Reference will now be made in detail to the preferred embodiments of the 
present invention, examples of which are illustrated in the accompanying 
drawings. 
FIG. 1 shows an optical disk player having a spindle servo system according 
to the present invention. A discoid optical disk 1 set in the optical disk 
player is a CLV type disk which contains information signals, which are 
digital data recorded at a fixed linear velocity and rotationally driven 
by a spindle motor 2. The digital data recorded in the optical disk 1 is 
read optically by a pickup 3. The read signal, which is an RF signal 
outputted from the pickup 3, is an analog signal indicating a quantity of 
a reflected potion received from the optical disk 1 of an optical beam 
irradiated in the pickup 3. It is amplified by an RF amplifier 4 and is 
then binarized by a binarizing circuit 5. The output signal of the RF 
amplifier 4 is also digitized by an A/D converter 20 and is then supplied 
to a signal reproducing system. 
The binarizing circuit 5 comprises a comparator 6 and a slice level control 
circuit 7. The comparator 6 compares the output level of the RF amplifier 
4 with a threshold value of the slice level set by the slice level control 
circuit 7. The slice level control circuit 7 controls the slice level so 
that the DC level of the output signal of the comparator 6 becomes 0. 
Connected to the output of the binarizing circuit 5 are a maximum inversion 
interval detecting circuit 8 and an additional inversion interval 
detecting circuit 9. The maximum inversion interval detecting circuit 8 
measures an interval from a time of rise to a time of the next fall of the 
output signal of the binarizing circuit 5 or an interval from a time of 
fall to a time of the next rise individually by counting clock pulses from 
a counter, and outputs a maximum value of the measured interval as a value 
of maximum inversion interval. The maximum inversion interval detecting 
circuit 8 also supplies a detected signal indicating when the maximum 
value is detected to the additional inversion interval detecting circuit 9 
as the maximum value is detected. The additional inversion internal 
detecting circuit 9 is provided to detect an inversion interval that 
follows the maximum inversion interval detected by the maximum inversion 
interval detecting circuit 8. That is, it measures an interval from a time 
of fall to a time of next rise of the output signal of the binarizing 
circuit 5 or an interval from a time of rise to a time of next fall 
corresponding immediately to the detected signal from the maximum 
inversion interval detecting circuit 8 individually by counting clock 
pulses from a counter. The additional interval detecting circuit 9 then 
outputs the measured interval as a value of additional inversion interval. 
The value of maximum inversion interval from the maximum inversion interval 
detecting circuit 8 and the value of additional inversion interval from 
the additional inversion interval detecting circuit 9 are supplied to a 
period detecting circuit 10. The period detecting circuit 10 operates as a 
comparison circuit and generates a control voltage which indicates an 
error between the values of maximum inversion interval and of additional 
inversion interval and a reference value. A data storage circuit 11, in 
which a relationship between the period and the error is stored beforehand 
as data is connected to the period detecting circuit 10, and the period 
detecting circuit 10 generates the control voltage by making reference to 
the stored data. The control voltage of the period detecting circuit 10 is 
supplied to a motor driving circuit 12 for driving the spindle motor 2. 
The reference value is 14T+4T. Here, (14T) denotes a bit length of a 
maximum bit pattern longer than a maximum run length of digital data, 
i.e., a maximum inversion interval, and (4T) denotes an additional 
inversion interval of an additional bit pattern which follows the maximum 
bit pattern. Its length is shorter than the maximum run length and longer 
than the minimum run length of the digital data. The period of the 
synchronizing signal is 18T. 
The operation of the spindle servo system in accordance with the present 
invention will now be explained. The pickup 3 reads the recorded signal 
composed as a train of pits on the optical disk 1 and the read signal is 
amplified by the RF amplifier 4 and is then binarized by the binarizing 
circuit 5. The output signal of the binarizing circuit 5 becomes a high 
level when a pit portion of the optical disk 1 is read and becomes a low 
level when a land portion is read. The maximum inversion interval 
detecting circuit 8 detects a maximum inversion interval of the read 
signal corresponding to the output signal of the binarizing circuit 5, 
which changes. The output signal indicating the value of maximum inversion 
interval detected by the maximum inversion interval detecting circuit 8 is 
supplied to the period detecting circuit 10. Because the maximum inversion 
interval detecting circuit 8 generates a detected signal when the maximum 
inversion interval is detected, the additional inversion interval 
detecting circuit 9 operates corresponding to the detected signal and 
detects an inversion interval, which follows the maximum inversion 
interval detected by the maximum inversion interval detecting circuit 8. 
The output signal of the additional inversion interval detecting circuit 9 
indicating the value of additional inversion interval detected is also 
supplied to the period detecting circuit 10. 
As an example, assume that the detected value of maximum inversion interval 
is `A` and the detected value of additional inversion interval as `B`. The 
period detecting circuit 10 determines to which domain the period "A+B" 
belongs. The relationship between the control voltages and the periods 
shown in Table 1 is stored in the data storage circuit 11. In each period 
shown in Table 1, `A` corresponds to a value before `+`, `B` corresponds 
to a value after `+`, and `*` shows that it may take any value. 
TABLE 1 
______________________________________ 
Control 
Voltage 
0 v 2.5 V 5 V 
______________________________________ 
A + B 12T and below +* 
13T + 5T 16T and over+* 
13T + 4T and below 
14T + 4T 15T + 2T and below 
13T + 6T and over 
15T + 3T 15T + 4T and over 
14T + 3T 14T + 1T 14T + 5T 
14T + 2T 
14T + 6T and over 
______________________________________ 
Accordingly, the period detecting circuit 10 operates as shown in FIG. 2 
every time "A+B" is supplied. The determination is made as to whether 
"A+B" belongs to a domain of control voltage of 0 V (Step S1), whether 
"A+B" belongs to a domain of control voltage of 2.5 V (Step S2), and 
whether "A+B" belongs to a domain of control voltage of 5 V (Step S3). As 
a result, when "A+B" belongs to the domain of control voltage of 0 V, the 
period detecting circuit 10 supplies the control voltage of 0 V to the 
motor driving circuit 12 to decelerate the rotation of the spindle motor 2 
because the rotational speed of the optical disk 1 is fast (Step S4), when 
"A+B" belongs to the domain of control of 2.5 V, the period detecting 
circuit 10 supplies the control voltage of 2.5 V to the motor driving 
circuit 12 to maintain the present rotational speed of the spindle motor 2 
because the rotational speed of the optical disk 1 is adequate (Step S5), 
and when "A+B" belongs to the domain of control voltage of 5 V, the period 
detecting circuit 10 supplies the control voltage of 5 V to the motor 
driving circuit 12 to accelerate the rotational speed of the spindle motor 
2 because the rotational speed of the optical disk 1 is slow (Step S6). 
Determining all of the steps of S1 through S3 is not necessary as 
determining two of the steps is sufficient. If Steps S1 and S2 yield "NO", 
for example, "A+B" belongs to the domain of control voltage of 5 V. 
The motor driving circuit 12 rotates the spindle motor 2 corresponding to 
the control voltage supplied from the period detecting circuit 10. 
Accordingly, the spindle motor 2 is decelerated when "A+B" belongs to the 
domain of control voltage of 0 V and is accelerated when "A+B" belongs the 
domain of control voltage of 5 V. Because the operation is repeatedly 
carried out, the rotational speed of the optical disk 1 which is 
rotationally driven by the spindle motor 2 is maintained at a fixed linear 
velocity. 
FIGS. 3A through 3C show binary signals obtained with respect to the read 
signal of the synchronizing signal pattern. FIG. 3A shows a case when the 
center level of the read signal coincides with the slice level and a 
binary signal of 14T-4T is obtained. FIG. 3B shows the case when the slice 
level fluctuates to the level lower than the center level of the read 
signal and a binary signal of 15T-3T is obtained. FIG. 3C shows a case 
when the slice level fluctuates to the level higher than the center level 
of the read signal and a binary signal of 13T-5T is obtained. Accordingly, 
even if the synchronizing signal pattern is not correctly detected as 
shown in FIGS. 3B and 3C, the period detecting circuit 10 generates the 
control voltage of 2.5 V and the present rotational speed of the spindle 
motor 2 is maintained by using the spindle servo system of the present 
embodiment described above. The present invention detects the control 
target of the spindle motor adequately as the period of 18T of the 
synchronizing signal pattern. That is, it brings about an effect that the 
control of the spindle is not disturbed even if the slice level 
fluctuates. The signal (VCO CK) in FIGS. 3A through 3C denotes a clock 
pulse indicating the unit bit length T. 
Also, in Table 1, while the domain of the control voltage of 2.5 V is the 
domain to which the period "A+B" basically belongs when it is equal to 
18T. Periods of 14T+1T, 14T+2T, and 14T+6T and over are also included in 
that domain. Further, while the domain of the control voltage of 0 V is 
the domain to which the period "A+B" basically belongs when it is 17T and 
below, and 13T+6T and over is also included in that domain. While the 
domain of the control voltage of 5 V is the domain to which the period 
"A+B" basically belongs when it is 19T and over, 15T+2T and below is also 
included in that domain. Such periods are included because an additional 
bit pattern may have been detected erroneously due to a defect or flaw in 
the disk. 
Although the control voltages of only three voltages of 0 V, 2.5 V and 5 V 
are generated according to Table 1 described above, the present invention 
is not confined only to those three values. That is, a number of values of 
control voltages may be increased to five, for example, as shown in Table 
2. 
TABLE 2 
______________________________________ 
Control 
Voltage 
0 V 1.25 V 2.5 V 3.75 V 5 V 
______________________________________ 
A + B 12T and 13T+*except ST 
13T + ST 
14T + 5T 
16T and 
below+* 14T + 3T 14T + 4T 
15T +* over+* 
15T + 3T 
except 3T 
14T + 1T 
14T + 2T 
14T + 6T 
and over 
______________________________________ 
In this case, respective domains of control voltages of 1.25 V and 3.75 V 
are added. While the control voltage of 1.25 V is a voltage that 
decelerates the rotation of the spindle motor 2 by the motor driving 
circuit 12, it decelerates a little and not as much as control voltage of 
0 V . Further, while the control voltage of 3.75 V is a voltage that 
accelerates the rotation of the spindle motor 2, it accelerates a little 
and not as much as the case of the control voltage of 5 V. The spindle 
motor may be driven and adjusted accurately to a desired speed by 
multi-valuing the control voltages to five or so. 
FIG. 4 shows another embodiment of the present invention. In the present 
embodiment, a period of a synchronizing signal recorded in the optical 
disk 1 is 4T+14T. That is, the additional bit pattern is positioned just 
before the maximum bit pattern in the optical disk 1. In FIG. 4, the same 
components with those shown in FIG. 1 are denoted by the same reference 
numerals. An inversion interval detecting and holding circuit 13 is 
connected to the output of the binarizing circuit 5 together with the 
maximum inversion interval detecting circuit 8. The inversion interval 
detecting and holding circuit 13 measures an interval from a time of rise 
to a time of next fall or an interval from a time of fall to a time of 
next rise of the output signal of the binarizing circuit 5 individually by 
counting clock pulses by a counter, holds the measured interval values 
sequentially, and outputs the inversion interval value just before the 
maximum inversion internal as a value of additional inversion interval 
when the detected signal is supplied from the maximum inversion interval 
detecting circuit 8. Each output of the maximum inversion interval 
detecting circuit 8 and the inversion interval detecting and holding 
circuit 13 is output to the period detecting circuit 10. Assuming that the 
detected value of maximum inversion interval is `A` and that the detected 
value of additional inversion interval is `B`, the period detecting 
circuit 10 is operated in the same manner with the case shown in FIG. 1. 
The other mechanisms are also the same with those in FIG. 1. 
It is noted that although the synchronizing signal pattern has been 
composed of the bit pattern of the maximum run length of 14T and the bit 
pattern of the additional run length of 4T in the embodiments described 
above, the present invention is not confined only to that. That is, the 
synchronizing signal pattern may be composed of a bit pattern having a run 
length longer than the maximum run length of digital data and a bit 
pattern added to it, whose length is above the minimum run length and 
below the maximum run length. 
As described above, according to the inventive spindle servo system of the 
optical disk player, the period of the synchronizing signal composed of 
the maximum bit pattern and the additional bit pattern each detected from 
the read signal is obtained to carry out the spindle servo control 
corresponding to that period, so that the rotational speed of the spindle 
motor may be roughly adjusted adequately to a specified speed and the 
rotational speed of the disk may be stabilized even when the slice level 
fluctuates in the player for reproducing data from the optical disk such 
as DVD. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the spindle servo system of optical disk 
player of the present invention without departing from the spirit or scope 
of the invention. Thus, it is intended that the present invention cover 
the modifications and variations of this invention provided they come 
within the scope of the appended claims and their equivalents.