Synchronization holding circuit in scanning of laser disk player

A synchronization holding circuit in scanning of a laser disk comprising a signal detection circuit, a signal processing circuit, an error detection circuit, a speed control circuit, a locking detection circuit, a microcomputer, and a switching circuit, wherein a user can get information on a location of a currently scanned laser disk by displaying a video signal on a monitor only when the horizontal synchronous signals and phase horizontal synchronous signals of the video signal are synchronized simultaneously and also an eyestrain phenomenon can be removed.

BACKGROUND OF THE INVENTION 
The present invention relates to a laser disk player and, more 
particularly, to a synchronization holding circuit used in scanning within 
a laser disk player which holds coincidentally the synchronization of each 
line during a scan mode. The laser disk player is classified as a constant 
linear velocity (hereinafter, referred to as CLV) system and a constant 
angular velocity (hereinafter, referred to as CAV) system according to 
methods of recording video and audio information onto a laser disk. 
In the CAV system, the same amount of video and audio information are 
recorded on inner and outer tracks and the speed of revolution is 
maintained at 1800 rpm at both innermost and outermost tracks when the 
video and audio information is detected by an optical pickup. In the CAV 
system, since a horizontal synchronizing signal and a color burst 
synchronizing signal are arranged coaxially the horizontal synchronization 
agrees with the color burst synchronization and advantageously images are 
not destroyed even in the scan mode. But, both of the innermost and the 
outermost tracks should be recorded with the same amount of information, 
thereby resulting in wasted disk space. 
The CLV system has been introduced to solve such problems. In the CLV 
system, the amount of information recorded in the outermost track is as 
much as three times more than that in the innermost track. The innermost 
track revolves at a speed of 1800 rpm, while the outermost one revolves at 
a speed of 600 rpm when the information stored on the laser disk is 
detected by the optical pickup. 
FIG. 1 shows a circuit diagram of a conventional laser disk player 
employing the conventional CLV system. In FIG. 1, if a user presses a 
playback key (not shown in FIG. 1) for initially driving of a laser disk 
1, a MICOM (microcomputer) 2 supplies power to a spindle motor 3 and a 
pickup driving servo system 4 for rotating a turntable 5 and locates an 
optical pickup 6 in the inner or outer track of the laser disk 1. 
The location of the optical pickup 6 is determined by the starting point of 
the information, where a frequency generating sensor 7 detects rotational 
speed of the spindle motor 3 and provides such a sensed signal to a 
time-based controller 8. The time-based controller 8 recognizes the 
current rotational speed of the spindle motor 3 by this sensed signal and 
controls a spindle motor servo system 9 to maintain normal speed of the 
spindle motor 3. The time-based controller 8 is controlled by the sensed 
signal which is supplied from the frequency generation sensor 7 only 
during the initial driving of the spindle motor 3, while the time-based 
controller 8 is controlled by another signal which is supplied from an 
adder 16 in the next step if the speed of the spindle motor 3 is beyond a 
predetermined value. 
Particularly, the spindle motor 3 revolves at the speed of 1800 rpm when 
the optical pickup 6 detects the information stored on the inner track of 
the laser disk 1, while revolving at the speed of 600 rpm when the optical 
pickup 6 detects the information stored on the outer track of the laser 
disk 1 so as to detect the information stored on the laser disk 1 safely. 
Next, audio and video signals detected by the optical pickup 6 are 
respectively provided to an audio processor 10 and a video processor 11, 
and they are applied to a speaker and a monitor (which are not shown in 
FIG. 1) after signal processing in the audio processor 10 and the video 
processor 11. 
Subsequently, a horizontal synchronizing signal detector 12 separates a 
horizontal synchronizing signal out of the video signal which comes from 
the video processor 11, while a color burst synchronizing signal detector 
13 separates a color burst synchronizing signal in the burst signal 
interval of the video signal. Then, the horizontal synchronizing signal is 
compared with a reference horizontal synchronizing signal of 15.734 KHz in 
a horizontal synchronizing error detector 14. The color burst 
synchronizing signal is also compared with a reference color burst 
synchronizing signal of 3.58 MHz in a color burst synchronizing error 
detector 15. The error signals which are provided from the horizontal and 
color burst synchronizing error detectors 14 and 15 are added by the adder 
16 and the output of the adder 16 is provided to the time-based controller 
8. Then, the time-based controller 8 controls the speed of the spindle 
motor 3 in response to the summed error signal which is provided from the 
adder 16. Thus, the spindle motor 3 can maintain the constant speed, so 
that the optical pickup 6 can accurately detect the information stored on 
the laser disk 1. 
In this CLV system, if a user presses scan switches SCAN+ or SCAN- of the 
MICOM 2 for scan mode, the MICOM 2 not only rotates the spindle motor 3 at 
a constant speed, but also radially moves the optical pickup 6 to the 
inner or outer side of the laser disk 1 to execute the scan mode. In the 
CLV system, however, the horizontal synchronizing signals are not arranged 
in one line on the laser disk 1 since the amount of the information on the 
outer side of the laser disk 1 is as much as about three times more than 
that on the inner side. 
In the scan mode, therefore, the synchronization of video signals to be 
displayed on a screen do not agree with each other, so the video signal is 
not displayed on the screen. In order to solve this problem, random access 
memories are employed. In other words, the random access memory, first, 
stores the information corresponding to one field of the video signal and 
next applies the information to the monitor to prevent the non-displaying 
mode on the screen. But, this method is not practical since the cost of 
the random access memory is very expensive. In addition, images on the 
screen are not clear since the video signal corresponding to only one 
field is applied to the monitor. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a synchronization holding 
circuit for scanning within a laser disk player which displays a 
predetermined color signal on the monitor until the color burst and 
horizontal synchronizing signals are respectively synchronized by stopping 
the optical pickup after holding the scan mode for a predetermined time 
period in the CLV system, and provides the video signals to the monitor 
only when the color burst and horizontal synchronizing signals agree with 
each other so that the video signal does not appear on the screen, thereby 
preventing user eyestrain. 
According to the present invention, there is provided a synchronization 
holding circuit used in scanning of a laser disk in a laser disk player, 
comprising: a signal detection circuit for detecting audio and video 
signals by moving an optical pickup according to the control of a micom; a 
signal processing circuit connected to the signal detection circuit for 
processing the detected audio and video signals; an error detection 
circuit connected to the signal processing circuit for detecting the 
errors of the audio and video signals provided from the signal processing 
circuit; a speed control circuit connected to the error detection circuit 
for controlling the speed of the laser disk with respect to the output of 
the error detection circuit; a locking detection circuit connected to the 
signal processing circuit for providing a locking signal when horizontal 
and phase synchronous signals of the video signal agree with respective 
reference signals within a predetermined range in the scan mode, the MICOM 
being connected to the locking detection circuit for moving the optical 
pickup for a predetermined time and for stopping the optical pickup after 
the predetermined time so as to provide a switching signal in accordance 
with the locking signal or in accordance with stop or pause mode; and a 
switching circuit located between the MICOM and the signal processing 
circuit for providing the video signals or color-back signals according to 
the switching signal of the MICOM.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be now described in more detail with reference 
to the accompanying drawings. 
FIG. 2 shows a synchronization holding circuit used in a scan mode of a 
laser disk player according to the present invention. In FIG. 2, the 
synchronization holding circuit includes a signal detection circuit 100, a 
signal processing circuit 200, an error detection circuit 300, a speed 
control circuit 400, a locking detection circuit 500, and a switching 
circuit 600, where the signal detection circuit 100, signal processing 
circuit 200, error detection circuit 300, and speed control circuit 400 
are similar to those of the conventional one. 
To describe in more detail, the signal detection circuit 100 is to detect 
audio and video signals which are stored on a laser disk 1 and comprises 
an optical pickup 6 for detecting information of the laser disk 1 by an 
optical signal and a pickup driving servo system 4 connected to the 
optical pickup 6 for moving the optical pickup 6 at a constant speed on a 
straight line under the control of a MICOM 2. 
The signal processing circuit 200 connected to the signal detector 100 for 
processing the audio and video signals comprises an audio processor 10 and 
a video processor 11 for processing video signals to be applied to the 
optic pickup 6. The error detection circuit 300 is to detect errors of the 
horizontal and color burst synchronizing signals of the video signals 
applied from the signal processor 100 and comprises horizontal and color 
burst synchronizing signal detectors 12 and 13 and horizontal and color 
burst synchronizing error detectors 14 and 15 respectively for comparing 
the horizontal and color burst synchronizing signals with their respective 
reference signals and providing their differences as error signals. The 
outputs of the horizontal and color burst synchronizing error detectors 14 
and 15 are provided to an adder 16. 
The speed control circuit 400 for controlling the rotation speed of the 
laser disk 1 comprises a turntable 5 for mounting the laser disk 1, a 
spindle motor 3, a frequency generation sensor 7 for generating a 
predetermined frequency corresponding to the rotation of a driving axis of 
the spindle motor 3, and a time-based controller 8. The output of the 
adder 16 in the error detection circuit 300 is applied to the time-based 
controller 8 and then the time-based controller 8 provides a control 
signal for an initial speed of the spindle motor 3 according to a 
frequency signal of the frequency generation sensor 7. 
Therefore, if the speed of the spindle motor 3 reaches a predetermined 
value, the time-based controller 8 provides the control signal according 
to the output of the adder 16 instead of the frequency generation sensor 
7. The speed control circuit 400 also includes a spindle motor servo 
system 9 for controlling the speed of the spindle motor 3 according to the 
control signal of the time-based controller 8. 
The locking detection circuit 500 provides a locking signal when the 
horizontal and color burst synchronizing signals agree with their 
respective reference signals and comprises horizontal and color burst 
synchronizing signal locking detectors 21 and 22. In addition, the locking 
detection circuit 500 includes a locking signal detector 23 which operates 
as an AND gate only when the locking signals of the horizontal and color 
burst synchronizing signal locking detectors 21 and 22 are applied 
simultaneously. Next, the locking detection circuit 500 is connected to 
the MICOM 2 which moves or stops the optical pickup 6 in normal or scan 
modes and provides a switching signal according to the locking signal or a 
stop or pause mode of the laser disk 1. 
The MICOM 2 is connected to a switching circuit 600 for providing the video 
signals or color-back signal of the signals processing circuit 200 
according to the switching signal of the MICOM 2. The switching circuit 
600 comprises first and second switches 24 and 20, first and second color 
signal generators 25 and 26. The first switch 24 is usually not connected 
to the first and second color signal generators 25 and 26 respectively, 
but when the MICOM 2 provides a switching signal, the switch 24 is 
electrically connected to the first or second color signal generator 25 or 
26 respectively. The first color signal generator 25 displays a bright 
color in the stop or pause modes and the second color signal generator 26 
displays a dark color in the scan mode. In the switching circuit 600, the 
first switch 24, the MICOM 2, and the video signal processor 11 are 
connected to the second switch 20. The second switch 20 is to provide 
either the output of the video signal processor 11 or the output of the 
first switch 24 to a monitor (not shown in FIG. 2) according to the 
switching control signal of the MICOM 2. 
According to this invention constructed as above, the synchronization 
holding circuit of the laser disk player normally operates similarly to 
the conventional one. To describe in more detail, the optical pickup 6 
detects the information stored on the laser disk 1 and provides them to 
the signal processing circuit 200 according to the control of the MICOM 2, 
moving at a constant speed when the laser disk 1 rotates. The signal 
detected by the optical pickup 6 is processed in the audio processor 10 
and the video processor 11. The audio signal processed by the audio 
processor 10 is provided to a speaker and the video signal processed by 
the video processor 11 is provided to the second switch 20, where the 
second switch 20 is connected to the video signal processor 11 and 
provides the video signal to the monitor, since scan keys SCAN+ and SCAN- 
of the MICOM 2 are not activated. On the other hand, the error of the 
horizontal and color burst synchronizing signals out of the video signal 
are detected by the error detection circuit 300 and the detected errors 
are applied to the speed control circuit 400. Thus, the speed control 
circuit 400 controls the spindle motor 3 and maintains the predetermined 
rotation speed. 
If the user wants to execute the scan modes of the laser disk player, then 
the user presses the scan keys SCAN+ or SCAN- which are connected to the 
MICOM 2. The MICOM 2 moves the optical pickup 6 outwardly or inwardly on 
the laser disk 1 in response to activating the scan key SCAN+ or SCAN-. 
However, if the optical pickup 6 is continuously moved as mentioned above, 
the synchronizing signals will no longer stay in phase with each other. In 
the case of the CLV system, system the video signal will not be displayed 
on the screen. 
However, the circuit according to the present invention provides the output 
of the video processor 11 to the monitor through the second switch 20 only 
when the horizontal and color burst synchronizing signals are identified 
with each other in such a manner that the video signal appears on the 
screen only when the optical pickup 6 is moved for a constant time for 
scan mode and subsequently stopped according to the control of the MICOM 
2, as follows: 
##STR1## 
In the scan mode, the MICOM 2 controls the first switch 24 to be connected 
to either the first color signal generator 25 or the second color signal 
generator 26, since the video signals detected by the optical pickup 6 for 
a scan time t1 when the optical pickup 6 is moving are not synchronized 
and thus the video signal appears on the screen. Also, the MICOM 2 
controls the first switch 24 to be connected to the second switch 20 so 
that the predetermined color signal is displayed on the monitor and the 
user becomes free from the eyestrain caused by the non-display phenomenon 
of the screen. 
The MICOM 2 stops the optical pickup 6 after completion of the scan time t1 
and subsequently detects the synchronization of the horizontal and color 
burst synchronizing signals of the displayed video signal. Since the laser 
disk 1 continuously rotates and the optical pickup 6 stops, the horizontal 
and color burst synchronizing signals are synchronized with each other at 
a certain point in time when the displayed video signal is detected. 
Judgement as to whether the horizontal and color burst synchronizing 
signals are synchronized or not is determined by comparing the outputs of 
the horizontal and color burst synchronizing signal detector 12 and 13 
with respective reference signals in the horizontal and color burst 
synchronizing signal locking detectors 21 and 22 respectively. 
If the horizontal and color burst synchronizing signals are within a 
predetermined range of the reference signals, respectively, the horizontal 
and color burst synchronizing signal locking detectors 21 and 22 
respectively provide locking signals. Next, the locking signal detector 23 
determines whether the locking signals of the horizontal and color burst 
synchronizing signal locking detectors 21 and 22 respectively are provided 
at the same time or not, so that if the locking signals are provided at 
the same time, the locking signal detector 23 provides a final locking 
signal. Thus, the final locking signal is provided when the horizontal and 
color burst synchronizing signals are synchronized with the reference 
signals, that is, the video signal is displayed on the screen. 
The MICOM 2 which receives this locking signal, then, controls the first 
switch 24 to disconnect both the first and second color signal generators 
25 and 26 respectively. Even though the first switch 24 is connected to 
the first and second color signal generators 25 and 26 respectively, the 
mode of the present invention is not changed. Also, the MICOM 2 controls 
the second switch 20 to connect to the video processor 11, so that the 
video signal on the screen is provided to the monitor, so that the user 
can watch the screen in the scan mode. 
By repeating this step, the monitor displays a predetermined color of the 
first or second color signal generator 25 or 26 respectively when the 
video signal recorded on the laser disk 1 can no longer be read, while the 
monitor displays the video signal when they can be read from the laser 
disk 1 and the horizontal and color burst synchronizing signals agree with 
the reference signals respectively so that the video signal is provided 
clearly to the user. 
On the other hand, when the laser disk player is in the stop or pause mode, 
the MICOM 2 controls the first and second switches 20 and 24 respectively 
so that the predetermined color outputs of the first or second color 
signal generators 25 or 26 respectively are supplied to the monitor, 
thereby protecting the eyes of the user from the eyestrain. At this time, 
the output color of the first color signal generator 25 may be bright, 
while that of the second color signal generator 26 is dark. The bright 
color is displayed in the stop or pause modes, while the dark color is 
displayed in the scan mode, so that the eyes of the user can be protected. 
As mentioned up to now, the present invention protects the eyes of the user 
and informs the user of the scanning position of the currently scanned 
laser disk by displaying the video signal on the monitor only when the 
video signal is synchronized, while displaying the predetermined color 
signal provided from the color signal generator on the monitor when the 
video signal disappears due to the lack of synchronization of the video 
signal to provide the clear screen to the user. 
The present invention is in no way limited to the embodiment described 
hereinabove. Various modifications of the disclosed embodiment as well as 
other embodiments of the invention will become apparent to persons skilled 
in the art upon reference to the description of the invention. It is, 
therefore, contemplated that the appended claims will cover any such 
modifications or embodiments as fall within the true scope of the present 
invention.