JPH0442443A - Focusing servo circuit for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To surely perform focusing search by detecting the reflectance of a delivered optical disk, deciding the gain of a focusing servo circuit based on the reflectance, and after that, taking a focusing search mode. CONSTITUTION:This circuit is equipped with a means 22 which detects the peak level of a focusing error signal ef, and gain control means 12, 12A which set the gain of the focusing servo circuit at an appropriate value by the peak level setting means 22. The level change of the focusing error signal ef based on the reflectance of the optical disk can be detected before performing the focusing search by applying a focusing drive signal which moves an objective lens 16 upward/downward for one or two times and detecting the peak level of the focusing error signal ef outputted when the focusing drive signal is applied, thereby, the gain control of the focusing servo circuit can be performed. In such a way, it is possible to surely perform focus setting when the next focusing search is performed.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention particularly relates to a focus servo circuit for an optical recording/reproducing device that can write data on the recording surface of an optical disc and read the data.

[Summary of the invention]

The focus circuit in the optical recording/reproducing apparatus of the present invention includes a peak value detection means for detecting the reflectance of an optical disk carried in, and a gain setting means for appropriately determining the gain of the focus servo circuit based on the reflectance, Since the focus search mode is set after the servo circuit reaches an appropriate gain, focus search can be performed reliably. [Prior Art] Since the recording media formed on the recording surface of the optical disk are different between a writable optical disk, a normal optical disk, or a write-once optical disk, the reflectance of light irradiated onto the recording surface is also different for each. This will vary greatly depending on the optical disc. If the reflectance differs, the output of the detector that detects this reflected light will naturally change, and for example, the output level of the focus error signal detected by the detector will change. Furthermore, if the loop gain of the focus servo circuit changes, the stability of the focus servo circuit will be impaired. Furthermore, when the output level of the focus detection signal changes depending on the reflectance, the focus error signal often becomes
C offset may occur and focus search etc. may not be performed accurately.

[Problems to be solved by the invention]

Therefore, it has been proposed to detect the reflected light from the optical disc and set the level of the focus error signal based on the amount of reflected light, but this method takes a long time to initially bring the focus into focus. There is a problem with becoming. [Means for Solving the Problems] The present invention has been made to solve these problems, and includes means for detecting the peak level of a focus error signal, and a focus servo circuit using the peak level detection means. It is equipped with a gain control means for setting the gain to an appropriate value. In the focus search mode, the above two means operate quickly, and then control is performed so that the focus search signal is provided as a gentle slope signal. 1 Effect J: Before performing a focus search, a focus drive signal for forcibly moving the objective lens up and down is applied once or twice. Then, by detecting the peak level of the focus error signal output when this focus drive signal is applied, a change in the level of the focus error signal based on the reflectance of the optical disc is detected, and gain control of the focus servo circuit is performed. . At this point, the gain of the focus servo circuit is set to be appropriate, so it becomes possible to reliably bring the focus into focus the next time a focus search is performed. [Embodiment J] Fig. 1 is a block diagram showing an embodiment of the focus servo circuit of the present invention, and numeral 10 indicates a detector for detecting reflected light of a light beam irradiated onto an optical disc. The light-receiving surface is divided into four parts A, B, C,
The focus detection unit 1 detects the amount of light of each spot imaged on D.
1, a focus error signal ef is generated. Reference numeral 12.12A indicates a gain control amplifier gain control circuit that controls the gain of the focus servo circuit, and the gain is set to an appropriate value by a control section 20, which will be described later. Reference numeral 13 indicates a switch circuit for focus pull-in, and a drive signal for focus gain control and a drive signal for focus search are supplied to the b contact side. This drive signal is then supplied to the drive coil 15 of the focus actuator via the drive circuit 14, and by moving the objective lens 16, changes the distance from the recording surface of the optical disk. Reference numeral 21 denotes a signal generator that generates a sawtooth drive signal in response to a control signal from the control unit 20;
It is configured by a counter, etc. 22 surrounded by a dashed line indicates a peak level detection unit that detects the peak level of the focus error signal and inputs it into the control unit (CPU) 20, which includes positive and negative rectifier diodes D,...
D, , capacitor ClICm5, reset switch S, , S, and an A/D converter. Next, the operation of the focus servo circuit of the present invention will be explained in a second manner.
This will be explained with reference to the waveform diagram in the figure. When an optical disk is loaded into the optical disk recording and reproducing apparatus, first, a control signal is supplied from the control section 20 to the signal generator 21 to generate a drive signal as shown in FIG. 2A. (The switch circuit 13 is connected to the b contact.) This drive signal is transmitted from the detector lO in order to forcibly drive the objective lens 16 to approach the recording surface of the disk during the short T3 period and T2 period. As the objective lens 16 moves, a focus error signal as shown in ef of FIG. 2 is detected. The level of this focus error signal ef changes depending on the reflectance of the inserted optical disc, and its positive and negative peak levels P and P- are respectively held in capacitors C, , C, of the peak level detection section 22. Ru. The voltage held in the capacitors C+ and C- is taken into the control section 20 via the A/D converter, and the control section 20 controls the gain control amplifier 1 so that this value becomes a predetermined level.
2 gain control section 12A. In other words, the output side of the gain control amplifier 12 is controlled to have a constant peak level no matter what reflectance an optical disk is inserted. Next, when this gain control ends, period T3
Then, the signal generator 21 is controlled so that the sawtooth focus search drive signal A is outputted again.
The objective lens 16 moves relatively slowly during this period T3 and approaches the recording surface side of the disk. Therefore, the focus error signal ef is output from the focus detection section 11 as in the previous time. By detecting a time point P at which the focus error signal ef passes the 0 level indicating the in-focus position using the control section 20 (for example, by turning on the reset switches S), the switch circuit 13 is switched to the a contact point. If you select , the focus servo circuit becomes a closed loop at this point, and the focus servo is applied.Although not shown in the diagram, after the focus servo is applied, the tracking servo and spindle servo function next. By the way, in the case of the present invention, the drive signal periods T, , T, for performing gain control in the above embodiment are
is set to be extremely short compared to the period T during which the focus search is performed, thereby shortening the focus search period and ensuring that a stable focus search is performed. In order to perform gain control, a drive signal that rapidly moves the objective lens is applied twice, and the gain control is performed based on the average peak level, but it is also possible to perform gain control using a single drive signal. It is. [Effects of the Invention 1] As explained above, the focus servo circuit of the present invention includes means for applying a drive signal that moves the objective lens for an extremely short period immediately before performing a focus search, and Appropriate gain control of the focus servo circuit is performed from the signal that detects the peak value of the focus error signal when As a result, focus pull-in is shortened and appropriate gain control is performed, which has the effect of stably operating the focus servo circuit.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram showing the operation of an optical recording/reproducing bag orcus search according to an embodiment of the present invention. In the figure, 11 is a focus detection section, 12 is a gain control amplifier, 16 is an objective lens, 21 is a drive signal generation section, and 22 is a peak level detection section.

Claims (1)

[Claims] In an optical recording and reproducing device capable of recording data by irradiating a laser beam and reproducing data by a reflected light of the laser beam, a peak level detection means for detecting a peak level of the reflected light; gain control means for setting the gain of the focus servo circuit to an appropriate value based on the loop gain of the focus servo circuit, and after applying a focus drive signal with a short period to set the focus servo circuit to an appropriate loop gain, A focus servo circuit for an optical recording/reproducing device, characterized in that it is configured to be supplied with a search signal.