JPS6240623A - Focus control circuit for optical disk reproducting device - Google Patents

Abstract

PURPOSE:To make it unnecessary to execute an adjusting work with a simple constitution and to eliminate the offset error of a servo-system by using the level of a search signal of the time when the focused point of a focus search operation is detected as the reference DC signal of the servo-stystem. CONSTITUTION:An output signal from the detecting areas (a)-(d) of a photo- disk 11 is supplid to subtracting circuit 12 and a focus error signal FE corresponding to a shift from the focused point position of an objective lens is outputted. This error signal FE is applied to one terminal of an adding circuit 20 and to the other terminal of this circuit 20, a focus search signal FS from an oscillating circuit 19 is outputted from a holding circuit 21 for holding it and applied. Also, the output of the circuit 20 is provided to changeover switch 13 and the signal FS is applied to the other of the switch 13. Moreover, then the focus OK signal FOK of an H level is generated from a focused point detecting circuit 18, the level of the signal FS is held by the circuit 21 and the switch 13 is controlled by the signal FOK. Also, the level of the signal FS is used as the reference DC signal of a servo-system and the offset error of the servo-system is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a focus control circuit for an optical disc playback device, and in particular to a focus control circuit for eliminating the influence of a DC offset component in the focus servo loop.1.
Regarding this.

[Technical Background of the Invention] As is well known, in an optical disc playback device such as a compact disc player or a video disc player, when reading an information signal from a disc, first,
Performs a focus search to forcibly move the objective lens of the optical pickup in the focus direction from its initial position, and then controls the objective lens to be held at the focus position when the objective lens reaches the vicinity of the focus position. I am trying to switch to focus servo.

FIG. 4 shows such a conventional focus control means. That is, 11 is a photodetector that receives a laser beam that is irradiated onto the disk and reflected through an objective lens (not shown). This photodetector 11 has four light receiving areas ad.
It is configured in a so-called four-part type.

and a light receiving area a of the photodetector 11.

The signals output from b, c, and d are current-added and supplied to a subtracting circuit 12 consisting of an operational amplifier opt, resistors R1 to R4, and capacitors C1 and C2, so that the signal can be adjusted from the focal point position of the objective lens. A focus error signal FE corresponding to the deviation is generated.

This focus error signal is transmitted to one fixed contact 13a of the changeover switch 13, a common contact 13b1, and a phase compensation circuit 14.
It is supplied to a focus actuator coil 16 that moves the objective lens in the focus direction via an amplification drive circuit 15, and a focus servo that controls the objective lens to maintain it at the focused position. It is done.

Also, the light receiving area a of the photodetector 11.

The signals obtained by adding up the currents of the signals output from b, c, and d are supplied to an adder circuit 17 and added together to generate an RF multiplied signal. This RF multiplied signal is supplied to a demodulation/reproduction circuit system (not shown) for reproduction operation, and is also supplied to the in-focus point detection circuit 18. Further, the focus error signal FE is also supplied to the focused point detection circuit 18.

The other fixed contact 13c of the changeover switch 13
A triangular wave-like focus search signal FS of, for example, about IHz is supplied to the oscillation circuit 19.

Here, the changeover switch 13 is connected to the in-focus point detection circuit 18.
The switching operation is performed by the output of the in-focus point detection circuit 18. When an L level signal is generated from the in-focus point detection circuit 18, the common contact tab is connected to the fixed contact 13c, and the in-focus point detection circuit 1
When an H level signal (focus OK signal FOK) is generated from 8, the common contact 13b is switched to be connected to the fixed contact 13a.

Here, when reproduction of the disc is requested, the output of the focused point detection circuit 18 is at the L level as shown in FIG. 5(a), so the focus search signal FS output from the oscillation circuit 19 is Changeover switch 13. The signal is supplied to the focus actuator coil 16 via the phase compensation circuit 14 and the amplification drive circuit 15, and the objective lens is forcibly moved from the initial position in the focus direction.

When the objective lens reaches the vicinity of the in-focus position, the subtraction circuit 12 generates a focus error signal FE as shown in FIG. 5(b), and along with this,
The RF multiplied signal level output from the adder circuit 17 gradually increases as shown in FIG. 5(C).

In this way, when the focus error signal FE reaches the O level, which corresponds to a state of no focus error, and the RF multiplied signal level exceeds a predetermined level, the focused point detection circuit [8] as shown in FIG. As shown in a), a focus OK' signal FOR of H level is generated. Then, the common contact 13b of the changeover switch 13' is connected to the fixed contact 13a, and focus servo is performed based on the i or less focus error signal FE.

[Problems of Background Art] However, the following problems occur in the conventional focus control means as described above. That is, the signal supplied to the focus actuator coil 16 during focus servo is a signal having a constant base DC level for holding the objective lens from the light position to the vicinity of the focused position, and the signal supplied to the focus actuator coil 16 is adjusted to the above-mentioned optical axis error signal FE. is added.

That is, the signal supplied to the focus actuator coil 16 during focus servo includes a constant DC component.

Therefore, the output of the amplification drive circuit 15 naturally includes a DC offset component.

This means that the focus servo system is stable with an offset error.

Therefore, conventionally, it has been considered to apply a DC voltage to the phase compensation circuit 14 or the amplification drive circuit 15 to correct the DC offset component, but the value of the DC offset generated in the focus servo system is However, since it differs depending on the device, there is a problem in that adjustment work is difficult.

[Object of the Invention] The present invention has been made in consideration of the above circumstances, and provides an extremely good optical disc playback device that has a simple configuration, does not require adjustment work, and does not cause offset errors in the focus servo system. The purpose is to provide a focus control circuit.

[Summary of the Invention] In other words, the focus control circuit of the optical disc playback device according to the present invention maintains the level of the focus search signal when the in-focus point is detected in the focus search operation state, and By adjusting the level of the search signal in the focus direction and using the base or DC signal as a base or DC signal, you can easily
This is to prevent offset errors from occurring in the focus servo system.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 4 are indicated by the same symbols, and only the different parts will be explained here. That is, the focus error signal FE output from the subtraction circuit 12 is supplied to one input terminal of the addition circuit 20. The other input terminal of the adder circuit 20 is supplied with the output of a hold circuit 21 that holds the focus search signal FS output from the oscillation circuit 19.

Further, the output end of the adder circuit 20 is connected to the fixed contact 13a of the changeover switch 13. The hold circuit 21 holds the level of the focus search signal FS when the focus OK signal FOK of H level is generated from the in-focus point detection circuit 18.

The operation of the above configuration will be described below with reference to the timing diagram shown in FIG.

First, when disc playback is requested, the output of the focused point detection circuit 18 is at the L level, as shown in FIG. 2(a). For this reason, from the oscillation circuit 19 as shown in FIG.
A focus search signal FS as shown in b) is generated, and the objective lens is forcibly moved from the initial position in the focus direction.

When the objective lens reaches the vicinity of the in-focus position, the subtraction circuit 12 generates a focus error signal FE as shown in FIG. The RF multiplied signal level
As shown in Figure (d), the number increases sequentially.

In this way, when the focus OK signal FOK of H level is generated from the focused point detection circuit 18, the level of the focus search signal FS at this time is held in the hold circuit 21, and the common contact 13b of the changeover switch 13 is switched and connected to the fixed contact 13a. For this reason,
Based on the signal obtained by adding the signal output from the hold circuit 21 and the focus error signal by the addition circuit 20,
Focus servo will now be performed.

Therefore, according to the configuration of the above embodiment, the level of the focus search signal FS when the focus OK signal FOK is generated from the in-focus point detection circuit 18 is set as a reference DC signal, and the focus error signal FE is added to this reference DC signal. Since the focus servo is performed by adding , the DC offset error that occurs in the conventional case can be avoided.

FIG. 3 shows a second embodiment of the invention.

That is, the focus error signal FE output from the subtraction circuit 12 is sent to the addition circuit 23 via the switch 22.
is supplied to one input end of the . In addition, this addition circuit 23
A triangular wave-shaped focus search signal FS obtained by converting the pulse signal output from the pulse generation circuit 24 by a digital-to-analog converter (hereinafter referred to as a D/A converter) 25 is supplied to the other input terminal of the . .

The output end of the adder circuit 23 is connected to the input end of the phase compensation circuit 14. Further, the D/A converter 25 functions to hold the value when the focus OK signal FOK of H level is generated from the in-focus point detection circuit 18.

Here, since the output of the in-focus point detection circuit 18 is at the L level in a state where reproduction of the disc is requested, the switch 22
is in an off state, and the objective lens is forcibly moved in the focus direction from the initial position by the focus search signal FS output from the D/A converter 25.

Then, when the focus OK signal FOK of H level is generated from the focused point detection circuit 18, the D/A converter 25
holds the focus search signal FS at that time, and the switch 22 is turned on.

Therefore, focus servo is performed based on a signal obtained by adding the focus search signal FS held by the D/A converter 25 and the focus error signal FE in the adder circuit 23.

Therefore, even with the above configuration, the focus search signal FS when the focus OK signal FOK is generated can be used as the reference DC signal, and the DC offset error of the focus servo system can be prevented. be.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] Therefore, as described in detail above, according to the present invention, an extremely good optical disc playback device that has a simple configuration, does not require adjustment work, and does not cause offset errors in the focus servo system. A focus control circuit can be provided.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing an embodiment of the focus control circuit of an optical disc playback device according to the present invention and a timing diagram for explaining its operation, and FIG. FIGS. 4 and 5 are a block diagram showing a conventional focus control means and a timing chart for explaining its operation, respectively. 11... Photodetector, 12... Subtraction circuit, I
3... Selector switch, 14... Phase compensation circuit, 15
... Amplification drive circuit, 1B... Focus actuator coil, 17... Addition circuit, 18... Focused point detection circuit, 19... Oscillation circuit, 20... Addition circuit, 2
1...Hold circuit, 22...Switch, 23...
-Addition circuit, 24...Pulse generation circuit, 25...D
/A converter. Applicant's representative Patent attorney Takehiko Suzue 2nd attorney

Claims (1)

[Claims] A focus search means that reads information signals recorded on a disc through an optical pickup, generates a focus search signal when reproduction of the disc is requested, and moves the objective lens of the optical pickup in the focus direction. and in-focus point detection means for detecting that the objective lens has reached the vicinity of the in-focus position in the operating state of the focus search means; generates a focus error signal corresponding to the deviation of the objective lens, and generates a signal obtained by adding the focus error signal and a reference DC signal of a predetermined level corresponding to when the objective lens is at the focused point position, and outputs a signal from the focused point detecting means. and a focus servo means for holding the objective lens at a focal point position in a state in which a detection signal is generated, wherein a detection signal is generated from the focal point detection means when the focus search means is in operation. The focus servo means is characterized by comprising a holding means for holding the level of the focus search signal when the focus search signal is held, and the level of the focus search signal held by the holding means is used as a reference DC signal for the focus servo means. A focus control circuit for an optical disc playback device.