JPH0640390B2 - Focus servo timing control device for optical recording / reproducing apparatus - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a focus servo timing control device in an optical recording / reproducing apparatus, and particularly when an optical disc is mistakenly loaded into the reproducing apparatus upside down. The present invention relates to a focus servo timing control device in an optical recording / reproducing device in which focus servo is not performed.

[Technical Background of the Invention and Problems Thereof] Recently, in the field of audio equipment, a digital recording / reproducing system using a PCM (pulse code modulation) technique is being adopted in order to achieve reproduction with high fidelity.

Audio equipment that uses this digital recording / playback method, in principle, exhibits significantly superior characteristics compared to those of the conventional analog recording / playback method, without the audio characteristics depending on the characteristics of the recording medium. It has been known.

Among such digital audios, one using a disc as a recording medium is called a DAD system, and an optical type is generally used as its recording / reproducing system.

The optical disc reproducing device is required to be able to satisfy various advanced control functions and performances which cannot be found in the conventional reproducing device.

Taking a CD (Compact Disc) system as an example, this is a thin metal film that forms pits (irregularities with different reflectances) corresponding to digital PCM data on a transparent resin disk with a diameter of 12 cm and a thickness of 1.2 mm. About 500 discs with the CLV (constant linear velocity) system
~ 200r. p. It is rotationally driven at a variable rotation speed of m, and is reproduced linearly or in a tracking manner from the inner circumference side to the outer circumference side by an optical pickup having a semiconductor laser and a photoelectric conversion element built-in.

This disc has a track pitch of 1.6 μm,
An enormous amount of information that can be reproduced in stereo for about 1 hour on one side is also digitized and recorded together with address data in the program area (radius 25 to 58 mm), and each song number and start address are associated with each other. The table of contents (TOC) shown is the lead-in area (radius 2
3-25 mm) and digitized.

In such an optical disc reproducing apparatus, some extremely advanced servo technology is used in order to quickly catch a target track and pick it up correctly without losing the information on the order of micron or omission of reading. ing.

Of these various servo techniques, focus servo is adopted to accurately irradiate the focus of the laser beam of the pickup on the track surface of the optical disc.

In other words, the depth of focus of the objective lens that focuses the laser beam on the optical disc reflection surface is usually only about ± 1.9 μm, and it is almost impossible to focus on the pit when the optical disc is loaded into the playback device. I can't expect.

Even if it happens to be in focus at a certain moment, the distance between the lens and the optical disc will constantly change due to the surface wobbling caused by the warp of the optical disc and the mechanism accuracy, so the depth of focus will change at the next moment. Will fall out of.

Therefore, in the optical disc reproducing device, the objective lens is attached to a bobbin with a drive coil such as a voice coil of a speaker, and this is moved in the optical axis direction by a servo circuit,
The distance between the lens and the optical disc is constantly adjusted so that the pit surface of the optical disc is within the depth of focus.

In addition, in order for the focus servo circuit to start operating,
The distance between the lens and the reflecting surface of the optical disc must be close to the depth of focus to some extent.

In other words, if the focus is greatly out of focus, the laser light emitted to the optical disc will be scattered and cannot be caught by the light receiving element, and no focus error signal will be output and the servo cannot be applied. Is.

Therefore, immediately after the optical disc is loaded, the focus search circuit is operated to oscillate the oscillating circuit of 1 to 2 Hz to vibrate the objective lens up and down.

When the objective lens approaches the depth of focus due to this vibration,
Since the focus error signal begins to be output, immediately after the focus error signal is detected, the focus servo system is activated to bring the objective lens into the depth of focus, and at the same time, the operation of the focus search circuit is stopped.

FIG. 3 is a circuit diagram of a focus servo timing control device in such a conventional optical recording / reproducing device.

In this device, a signal (RF signal) obtained by summing the outputs of the four-divided detector 1 of the optical pickup is amplified by an amplifier 2, passed through a high-pass filter 3 and a direct current component is cut off, and this signal is comparator 4. In comparison with the variable voltage constant voltage power source 5, the focus servo ON signal is output when the voltage exceeds the determination level.

This focus servo ON signal is supplied to the focus servo system to start the operation of the focus servo.

By the way, in such a conventional focus servo timing control device in an optical recording / reproducing apparatus,
When the optical disc is mistakenly loaded inside out on the reproducing device, a signal very similar to the PF signal may be output depending on the type of the label surface. Therefore, the focus servo ON signal is output from the comparator 4. As a result, the focus servo starts to operate, and as a result, there are problems that the focus search does not stop forever, the disk motor rotates at high speed, and the like.

[Object of the Invention] The present invention has been made in order to solve the drawbacks in the focus servo timing control device in such a conventional optical recording / reproducing apparatus, and in the case where the optical disc is mistakenly loaded inside out in the reproducing apparatus. Another object of the present invention is to provide a focus servo timing control device in an optical recording / reproducing device in which the focus servo is not operated.

SUMMARY OF THE INVENTION That is, in order to achieve the above-mentioned object, the present invention passes an RF signal output from an optical pickup for reproducing an optical disc through a high-pass filter so that its output reaches a predetermined determination level. A first signal generating means for outputting a signal when the optical disk reaches the focus error signal and a focus error signal output from the optical pickup are input, and the focus error signal is a focus error signal obtained from one surface of the optical disc. Second signal generating means for generating a signal when a predetermined judgment level set in advance is reached between the peak level of the signal and the peak level of the focus error signal obtained from the other surface; And a third signal generating means for outputting a focus servo ON signal when the respective output signals of the second signal generating means are inputted together. It is characterized by becoming.

According to the actual measurement results, in a normal optical disc, the peak level of the focus error signal on the front surface and the peak level of the focus error signal on the back surface are more than doubled, so that the judgment level is in the middle of both peak levels. By setting, it is possible to reliably determine the front and back.

Therefore, in the focus servo timing control device in the optical recording / reproducing apparatus of the present invention, even if the first signal generating means outputs the focus servo ON signal, the second signal generating means keeps a constant judgment level. Focus servo
Since the ON signal is not generated, even when the optical disc is loaded inside out, the noise component on the back surface does not generate the focus servo ON signal.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a focus servo timing control device in the optical recording / reproducing apparatus of the present invention.

In the figure, 1 is a four-division detector of an optical pickup, 2 is an amplifier, 3 is a high-pass filter, 4 is a comparator, 5 is a constant voltage power source, and the above configuration is the conventional optical system shown in FIG. It has the same structure as the focus servo timing control device in the recording / reproducing device.

Further, 6 is a focus error signal generator for generating a focus error signal from the output of the 4-division detector 1, and 7 is an output of the focus error signal generator 6 compared with a constant voltage power source 8 of variable voltage, and a level higher than a judgment level. It is an amplitude level determiner that outputs a signal when The voltage of the constant voltage power source 8 is set to an intermediate potential between the peak level of the focus error signal on the front surface and the peak level of the focus error signal on the back surface of the optical disk.

Reference numeral 9 denotes a D-type flip-flop circuit. This clear signal is, for example, in the case of "L" clear, a signal which becomes "H" level at the same time when the laser of the optical pickup is turned on through the delay circuit 10. Input to the clear terminal CL. An AND circuit 11 inputs the output signal of the comparator 4 and the output signal of the flip-flop circuit 9 and supplies the logical product thereof to the focus servo system as a focus servo ON signal.

Next, the operation of the focus servo timing control device in the optical recording / reproducing apparatus of this embodiment will be described.

FIG. 2 shows a case where an optical disc is properly loaded in the optical disc reproducing device using the focus servo timing control device in the optical recording and reproducing device (A) and a case where the optical disc is loaded inside out (B). 3 is a timing chart showing a power supply, a focus search signal, and signals in each part of FIG. 1 in the circuit of FIG. 1.

First, a case (A) in which the optical disc is properly loaded in the optical disc reproducing apparatus will be described.

The optical disc is loaded into the optical disc player,
When the power is turned on and the focus search signal is supplied to the focus servo system (the figure shows an example in which the focus servo is intentionally not turned on in the first cycle), the amplifier 2 starts focusing A low-frequency signal associated with the search is output, and when the objective lens is in focus, a signal (a) in which the RF signal is superimposed is output.

This signal (a) is passed through a high-pass filter 3 to remove low-frequency components and a signal (b) is obtained. A comparator 4 detects this RF signal and outputs a binary signal (c).

On the other hand, the focus error signal (d) output from the focus error signal generator 6 is compared with the determination level of the constant voltage power supply 8 by the amplitude level determination device 7.

Here, since the peak level of the focus error signal on the front side of the optical disc is higher than the determination level, the amplitude level determiner 7 outputs a binary signal (e) if the optical disc is properly loaded. To be done. Since the delay circuit 10 outputs the signal (g), the flip-flop circuit 9 outputs the signal (f) and the AND circuit 11 outputs the focus servo ON signal (h). Become.

On the other hand, in the case of the optical disc loaded inside out in the reproducing apparatus (B), the signals (a) to (c) are output as in the case of being loaded correctly, but from the back side of the optical disc. Since the peak level of the focus error signal (d) is lower than the determination level, no signal is output from the amplitude level determiner 7, and in this case, the focus servo ON signal is output from the AND circuit 11. Not done.

The present invention is not limited to the optical disc reproducing apparatus using the optical pickup based on the so-called astigmatism method, but is also an optical disc using the optical pickup based on other methods such as the critical angle detection method and the knife edge method. The same can be applied to the reproducing device.

[Advantages of the Invention] As described above, according to the present invention, when the optical disc is mistakenly loaded inside out, the focus servo
Since the ON signal is not supplied to the focus servo system, the inconvenience that the focus search does not stop or the disk motor rotates at high speed is solved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a focus servo timing control device in an optical recording / reproducing apparatus of the present invention, FIG. 2 is a timing chart showing signals in respective parts, and FIG. 3 is a conventional optical system. It is a circuit diagram showing a configuration of a focus servo timing control device in the recording and reproducing apparatus. 1 ... 4-division detector 2 ... Amplifier 3 ... High-pass filter 4 ... Comparator 5, 8 ... Constant voltage power supply 6 ... Focus error signal generator 7 ... Amplitude level judgment device 9 ... Flip flop Circuit 10 ... Delay circuit 11 ... AND circuit

Claims (1)

[Claims] 1. A first signal generating means for outputting an RF signal outputted from an optical pickup for reproducing an optical disc through a high pass filter and outputting the signal when the output reaches a predetermined judgment level. And a focus error signal output from the optical pickup is input, and the focus error signal is obtained from the peak level of the focus error signal obtained from one surface of the optical disc to the focus error signal obtained from the other surface. The second signal generating means for generating a signal when a predetermined judgment level is reached up to the peak level of the signal and the respective output signals of the first and second signal generating means are inputted together. And a third signal generating means for outputting a focus servo ON signal when the optical recording / reproducing apparatus is used. Kasusabo timing control apparatus.