JPH0335432A - Focus servo circuit - Google Patents

Abstract

PURPOSE:To suppress the large distortion of servo caused by the scratch of a disk when focus offset is impressed by muting the focus offset when the scratch is detected. CONSTITUTION:The output of a focus offset generating circuit 6 is set so that the jitter of an RF signal 13 can be made minimum. Then, focus control is executed at the time of normal operation. When it is assumed there is the scratch on the disk, the drop-out of the signal caused by the scratch appears in the RF signal 13 and this is detected by a scratch detecting circuit 12. Then, time to mute the focus offset is determined by a pulse width determining circuit 15. Such an output pulse is inputted to a focus offset mute circuit 7 and during the period of this pulse, the output of the focus offset generating circuit 6 is muted. Thus, since the offset is removed when the scratch is detected, stable focus control is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for reproducing optical discs, such as a compact disc player or a laser disc player.

[Prior Art] Conventionally, in order to accurately focus a laser beam onto an optical disk surface, an optical disk player uses a focus servo device having an astigmatism lens and a four-part light detector, as is well known. In the optical pink amplifier used in such disc playback devices, the relationship between the displacement in the focus direction near the focal point of the objective lens and the focus error signal is the second one.
Point A in Figure 0 as shown in the figure is the ideal operating point of the focus servo, and operating at this point provides the highest stability against scratches and the like.

However, the optimum operating point of the focus servo for reading recorded information on the disk with the minimum shifter does not necessarily match the ideal operating point of the focus servo described above, and the optimum operating point of the focus servo for reading this information is, for example, B It looks like a point, and in order to operate the servo at this point, press B.
Since the DC gain of the phase servo loop is large compared to the voltage at the point, no abnormality will occur to the focus servo during normal operation.

[Problem to be solved by the invention]

However, such a focus offset is a direct current disturbance to the ideal focus servo, so if the disc is scratched, the focus error signal obtained from the disc will include the above-mentioned focus servo/soto signal. As a result, noise components due to scratches are also applied, which greatly disturbs the focus servo and makes it difficult to read disc information normally.

The present invention has been made to improve the above-mentioned problems.

[Means to solve the problem]

The focus servo circuit according to the present invention includes a means for reading out the recorded information by irradiating a disk on which information is recorded in a spiral track with a laser beam, and a means for reading out the recorded information by irradiating a disk with information recorded in a spiral track, and a means for detecting reflected light from the disk and transmitting the laser beam to the disk. A focus servo device for upward focusing includes means for adding an offset signal to a focus servo signal, a flaw detection means for detecting the presence or absence of scratches on the disk, and on/off control of application of the offset signal according to the output of the flaw detection means. It is characterized by:

[Effect]

Therefore, focus error control is normally performed in a state where an offset optimal for information reproduction is added to the focus error signal as in the conventional case, and when a flaw is detected, the offset is removed, so that stable focus control is performed.

〔Example〕

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 1 shows an embodiment of the present invention.

In the figure, the reflected light of the light beam irradiated on the optical disk is applied as an optical signal to a four-split optical detector l arranged in a square shape, photoelectrically converted, and converted into the obtained pressure, which is then transmitted to a focus error amplifier 4. is subtracted by , and becomes the focus error signal. -Focus Offset Lifestyle Circuit 6
The DC focus offset signal generated is added to the focus error signal via the switch 7 in the focus offset addition circuit 5. This added signal is sent to the phase compensation circuit 8. The signal passes through the actuator drive circuit 9, moves the focus actuator IO, is input to the FF amplifier 11, is added, and is converted into an RF signal. RF signal 1
3 is led to an RF decoder 14, where the recorded data is demodulated, and is also applied via a flaw detection circuit 12 to a pulse width determining circuit 15 such as a one-shot multivibrator, and its output controls a switch 7.

In the above configuration, the focus offset generation circuit 6
The output of the RF signal 13 is centered so that the shifter of the RF signal 13 is minimized, and during normal operation, focus control is performed centering on, for example, point B in FIG.

Now, assuming that there is a scratch on the disk, a dropout of the optical signal due to the scratch appears in the RF signal 13. This dropout is detected by a flaw detection circuit 12, and a pulse width determination circuit 15 determines the time to mute the focus offset. The output pulse of the pulse width determining circuit 15 is input to the focus offset muting circuit 7, and the output of the focus offset generating circuit 6 is muted during the period of this pulse.

Note that the longer the duration of the scratches detected by the scratch detection circuit, the longer
The pulse width determining circuit 15 may be provided with a function to lengthen the time for adjusting the focus offset.

〔Effect of the invention〕

By muting the focus offset when a scratch is detected as described above, it is possible to suppress large disturbances in the servo caused by the disk scratch when the focus offset is being applied.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a diagram for explaining its operation. 1...Focus error signal 4...Focus error amplifier 5...Focus offset addition circuit 6...Focus offset generation circuit 7...Focus offset neat circuit 8...Phase compensation circuit 9...・Actuator drive circuit IO...Focus actuator 11...RF amplifier 12...Flaw detection circuit 13...RF double signal 4...RF decoder 15...Pulse width determination circuit

Claims (1)

[Claims] A means for reading out the recorded information by irradiating a disk with information recorded on a spiral track with a laser beam, and a focus servo device for detecting reflected light from the disk and converging the laser beam on a recorded image on the disk. , a focus servo comprising: means for adding an offset signal to a focus servo signal; flaw detection means for detecting the presence or absence of scratches on the disk; and on/off control of application of the offset signal according to the output of the flaw detection means. circuit.