JPH0337828A - Automatic focus pull-in circuit - Google Patents

Abstract

PURPOSE:To prevent a focus setting operation on the surface of a disk performed and to eliminate an error in checking after focus pull-in operation by using a level comparator and a window comparator. CONSTITUTION:When the focus setting is performed, a ramp waveform is generated from a ramp generation circuit 6, and a lens approaches a disk. When it approaches a focal point, the level of a sum light quantity signal (b) is increased, and it exceeds the comparison level V3 of the level comparator LCOMP 10, and a controller CONT 11, the level of which exceeds the comparison level V1 of the window comparator WCOMP 9, and makes the output of the comparator 9 change, and when it further approaches the focal point, a focusing error signal (a) decreases its level again, which makes the output of the WCOMP 9 change, and the CONT 11 checks the output of the LCOMP 10 again afterwards, then, the pull-in operation is completed. And the gain of a switch 12 is set at a value so that the comparison levels V1 and V2 (P-P value) of the WCOMP 9 can go to the allowable maximum value of the signal (a), and error detection is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic focusing circuit in an optical disc device.

[Prior art] Conventionally, the automatic focus side i-focus system in an optical disc device has a fourth
It is configured as shown in the figure.

In the same figure, automatic focus retraction is controlled by the loop switch (
With SW) 7 open (OFF), a ramp signal is generated from the ramp generation circuit 6, and a lens (not shown) is brought close to the disk by the actuator 5 through the equalizer 3 and driver 4.

After the total light amount signal exceeds the comparison voltage of the level comparator lO and the autofocus error signal a exceeds the comparison voltage of the window comparator 9, the controller 11 such as the CPU executes a loop when it enters the window again. The switch (SW) 7 is closed (ON), and then the output of the level comparator 10 is checked again to complete the pull-in operation.

5 shows signal waveforms at various points in the circuit of FIG. 4, (a) shows the focus error signal, and the dotted line shows the comparison voltage level V of the window comparator 9.
1, V2 is shown. Further, (b) shows the waveform of the total light amount signal, and the dotted line similarly shows the comparison voltage level V3 of the level comparator 10. Further, (c) is the output waveform of the focus error signal (a) from the window comparator 9, and (d) is the total light amount signal (b).
) is the output waveform from the level comparator 10.

In addition, (e) is the waveform of the loop SW 0N10FF control signal output from the controller 11,
A pull-in operation is performed at the falling edge of the signal, and the loop S
W7 is turned ON.

[Problems to be Solved by the Invention] However, in the conventional total light amount signal level comparator 10, it is difficult to set the comparison level V3. For example, if the comparison level V3 is set to the level shown by the dotted line in Figure 5, Due to the modulated signal due to the signal track, there is a possibility that an error may occur in the check after the pull-in (section di in FIG. 5d).

Also, if you lower the comparison level v3 to remove this effect,
There was a problem in that the amount of light reflected from the disk surface was caught on the comparison level, causing a pull-in operation on the disk surface.

In addition, such an optical disk device requires a detection system to detect when the focus deviates from an allowable value during focus control, and an error detection circuit is required in addition to the circuit shown in Figure 4. .

[Means and effects for solving the problem] According to the present invention, the comparator comparison level of the total light amount signal is made lower than the lowest value of the total light amount signal modulated by the track,
In addition, the comparison level of the window comparator for the focus error signal is determined by the P-P value (Peak to
By widening the focus more than the peak (Peak), an automatic focus pull-in circuit was created that does not pull in on the disk surface and does not cause errors in checking after pull-in.

In addition, by making the gain of the focus error signal input to the window comparator variable, or by making the comparison level of the window comparator variable before and after automatic focus acquisition,
It can be used in common with the error detection circuit, and the conventional error detection circuit can be omitted.

[Embodiment] FIG. 1 is a drawing that best represents the features of an embodiment of the present invention, in which a is a focus error signal, b is a total light amount signal, 3 is an equalizer, 4 is a driver, 5 is an actuator, and 6 is a Lamp generation circuit, 7 is loop SW, e is loop SW ON
10 FF control signal, 9 is window comparator, 10 is level comparator, 11 is CP
A controller such as U, 12 a gain switch, and 13 a control signal for controlling the gain switch.

Moreover, FIG. 2 shows signal waveforms at various points in the circuit of FIG. It shows. Further, (b) shows the waveform of the total light amount signal, and the dotted line similarly shows the comparison voltage level v3 of the level comparator 10. Further, (c) is the output waveform of the focus error signal (a) from the window comparator 9, and (d) is the output waveform of the total light amount signal (b) from the level comparator 10. Further, (e) is the waveform of the loop SW 0N10FF control signal output from the controller 11, and when the signal falls, a pull-in operation is performed and the loop SW7 is turned on.

The operation of the above circuit will be explained below.

First, when focusing, the loop SW7 is in an open state (OFF), a ramp waveform is generated from the ramp generation circuit 6, and the equalizer 3. The actuator 5 is driven through the driver 4 to bring the lens (not shown) closer to the disk.

When the lens approaches the disk surface, the level of the total light amount signal begins to rise due to reflection from the disk surface. The comparison level v3 of the level comparator 10 is set to a level at which no modulation signal from the track is applied after focusing, so the output of the level comparator 10 changes depending on the amount of light reflected from the surface of the disk (see Figure 2 d). 62 copies). Upon receiving this change signal, the controller 11 outputs the focus error signal a from the window comparator 9 (second
Go see Figure C).

However, the gain switch 12 is controlled by the controller 11.
During retraction (in this embodiment, until the tracking loop (loop 5W7) is closed), the figure 8 waveform (FIG. 2 a) caused by the reflection of the focus error signal a on the disk surface does not reach the comparison level of the wind comparator 9. Since the gain is set, the output of the window comparator 9 does not change as shown in FIG. 2(c), and the controller 11 again checks the output of the level comparator 10 (FIG. 2d). Therefore, the loop SW7 is turned on by the controller 11 on the surface of the disk, and the focal point is not pulled in.

Then, as the lens approaches the disc and approaches the focal point,
Since the level of the total light amount signal S rises again and exceeds the comparison level V3 of the level comparator 10, the controller 11 goes to check the output of the window comparator 9. This time, the focus error signal a also exceeds the comparison level V1 of the wind comparator 9, changing the output of the wind comparator 9, and when it approaches the in-focus point again, the focus error signal a decreases in level, and the wind comparator Since the output of SW 9 is being changed, the controller 11 closes the loop SW7.

The controller 11 then returns to the comparator 10
Check the output (Fig. 2d) to confirm complete retraction and complete the retraction operation.

After the above-mentioned pull-in operation is completed, the controller 11 increases the gain of the gain switch 12 and operates the window comparator 9 as an error detection means for detecting that the focus error signal a exceeds the allowable value. In other words, by setting the gain of the gain switch 12 to such a gain that the comparison levels Vl and V2 of the window comparator 9 become the maximum allowable value of the focus error signal, it can be used as an error detection means.

FIG. 3 is a diagram showing an example of the gain switch 12,
A resistor R1 of an appropriate value is connected between the window comparator 9 and the focus error signal a input to the comparator 9.
R2 and a switch 5W14 are provided. By turning on and off the switch 5W14 using the control signal 13 output from the controller 11,
The gain of the focus error signal a can be switched and inputted to the window comparator 9.

Further, in the above-described embodiment, the same effect can be obtained by adding a circuit for changing the window level of the window comparator instead of the gain switch.

[Effects of the Invention] As explained above, the level comparator circuit has a comparison level set to a lower level than the lower limit value modulated by the track of the total light amount signal, and the level of the focus error signal is lower than the level due to reflection on the disk surface. By using a window comparator whose wind level is set to a high level, a focus pull-in circuit can be realized that does not cause pull-in on the disk surface and does not cause errors in checking after pull-in.

Also, should the gain of the focus error signal be made variable?

By making the level of the window comparator variable, it is also possible to obtain the effect that the circuit can be shared with the error detection system.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention. FIG. 2 is a timing chart of each part of the circuit of FIG. 1. FIG. 3 is a circuit diagram of a gain switch embodying the present invention. FIG. 4 is a block diagram of a conventional circuit. FIG. 5 is a timing chart of each part of the conventional circuit shown in FIG. In Figures 2 and 5, a) is the focus error signal, b) is the total light amount signal, C) is the window comparator output, and d
) is the level comparator output, and e) is the loop SW control signal. a...Focus error signal b...Total light amount signal 3...Equalizer 4...Driver 5...Actuator 6...Lamp generation circuit 7...Loop 5W e-"Loop SW 0N10FF:] l-CI-
Signal 9...Window comparator 10...Level comparator 11...Controller 12...Gain switch 13...Signal 14 that controls the gain switch
...Gain switch switching 5W Vl...Window comparison level 1 ■2...Window comparison level 2 V3...Level converter cooler 1 0 comparison level

Claims (3)

[Claims] (1) An automatic focus pull-in circuit for an optical disc device, which has a level comparator for a total light amount signal from the optical disc and a window comparator for a focus error signal,
setting the comparison level of the level comparator to be lower than the lowest value of the total light amount signal modulated by the track;
Further, the automatic focus pull-in circuit is characterized in that the comparison level of the window comparator is wider than the P-P value of the focus error signal level due to reflection on the surface of the optical disk. (2) The automatic focus pull-in circuit according to claim 1, wherein the comparison level of the window comparator is made variable before and after the automatic focus pull-in is completed. (3) The automatic focus pull-in circuit according to claim 1, wherein the gain of the focus error signal input to the window comparator is made variable before and after the automatic focus pull-in is completed.