JPH0330927B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recorded information reproducing apparatus, and more particularly to a recorded information reproducing apparatus comprising a servo loop for controlling the relative position between an information detection point of a pickup and a recording track on a recording disk. .

One example of such a servo loop for relative position control is a tracking servo device for an optical information reproducing device, a schematic block of which is shown in FIG. The figure shows an example of a three-beam pick-up, in which a pair of pick-up spot lights 1 and 2 generate and detect a tracking error signal, and spot light 3 serves as an information detection point for detecting recorded information. . As shown in the figure, when the center of the spot light 3, which is the information detection point, is located on the center line of the recording track 4, the two spot lights 1 and 2 are located on the center line of the recording track 4, as shown in the figure. It appears to be on both side edges of the track 4.

Therefore, if spot light 3 deviates in the direction perpendicular to the track, the amount of reflected light from both spot lights 1 and 2 will increase or decrease accordingly, so a tracking error signal can be obtained by using the difference between the amounts of both reflected light. become. Therefore, photoelectric conversion elements 5 and 6 are provided to generate signals corresponding to the amounts of reflected light of both spot lights 1 and 2, respectively, and both outputs are input to a differential amplifier 7 to become a tracking error signal. . The error signal is used to control the loop gain.
The signal is inputted to an equalizer via a VCA (voltage controlled amplifier) 8, subjected to appropriate compensation, and then supplied via an amplifier 10 to a coil 12 for driving a tracking mirror 11. This rotation of the tracking mirror 11 causes the pickup information detection point 3 to be biased in a direction perpendicular to the track, thereby enabling tracking control.

Furthermore, changes in reflectance and transmittance of each component of the optical system,
Further, an adder 13 and an LPF (reducing filter) 14 are provided so that the loop gain of the tracking servo system is not affected by changes in the intensity of the light source and always maintains a constant sensitivity. That is, the output sum of the photoelectric conversion elements 5 and 6 for tracking error detection is obtained by the adder 13, and this output sum is
VCA8 is generated by the low frequency (DC) component that has passed through LPF14.
The gain is now controlled. By doing so, sensitivity fluctuations of the servo loop due to changes in the various parameters described above are controlled to a constant level, so that stable servo operation is possible.

If the recording disc is recorded using the CAV (constant angular velocity) recording method, assuming that the same recording frequency is recorded on the entire surface of the disc, the recorded signal will vary depending on the radial position of the disc. The spatial frequencies of the signals are different, and the signals recorded on the outer tracks have lower spatial frequencies.

Note that the spatial frequency refers to the repetition frequency of brightness and darkness (contrast) per unit length on a recording track. Therefore, in a CAV recording disk, under the same recording frequency, the average amount of reflected light increases as the outermost track approaches, and reaches the maximum amount of reflected light on the outermost track.

How this fact affects the error detection sensitivity of the tracking servo loop shown in FIG. 1 will be explained using FIG. 2. Figure A shows a recording track 4-1 along the radial direction of the recording disk.
~ 4-5 is shown, the left side is the inner circumference of the track, the right side is the outer circumference of the track, all signals of the same frequency are recorded, and the spatial frequency becomes smaller toward the outer circumference. . Curve B shows the change in the amount of light reflected by the tracking error detection spot lights 1 and 2 when the pickup is moved from the inner circumference of the track to the outer circumference in a direction perpendicular to the track when the tracking servo loop is off, and curve 1-1 is the reflected light amount of spot light 1, curve 2-1
is that of Spotlight 2. C is a tracking error signal waveform obtained by spotlights 1 and 2 under the same conditions as B, and is the output of the differential amplifier 7.

That is, as the outermost circumference of the recording track approaches, the average value of the amount of reflected light from spot lights 1 and 2 gradually increases toward the maximum amount of reflected light, and the amplitude of the tracking error signal (Figure C) decreases. I will do it. In the method shown in Figure 1,
Naturally, the output level of LPF 14 also increases as you move toward the outer track, but this increase in level causes
Since this acts to reduce the gain of the VCA 8, the amplitude of the tracking error signal further decreases, which is extremely disadvantageous. Such a phenomenon occurs not only due to a change in the spatial frequency but also due to a change in the shape of the pits forming the recording track.

An object of the present invention is to provide a recorded information reproducing device that is capable of always maintaining a constant sensitivity and performing stable servo operation without being adversely affected by changes in the spatial frequency or pit shape on the recording disk. It is to provide.

A recorded information reproducing device according to the present invention is a recorded information reproducing device including a servo loop that uses the difference between a pair of detection signals obtained from a detection means for detecting information recorded on a recording disk as an error signal,
It is characterized by a means for generating a first signal according to the signal level of at least one of a pair of detection signals, and a means for generating a second signal according to the reproduction information signal level obtained from the detection means. and means for controlling the gain of the servo loop according to the difference between the difference signal between the first and second signals and a predetermined reference signal.

The present invention will be explained below using the drawings.

FIG. 3 is a circuit block diagram of an embodiment of the present invention. Portions equivalent to those in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted. In this example, adder 13
The output is attenuated to 1/2 by the attenuator 18 and becomes one input of the subtraction differential amplifier 15. on the other hand,
The reflected light from the information detection spot light 3 is converted into an electric signal by the photoelectric conversion element 16, and is converted into an electric signal by the differential amplifier 15.
As another input, the difference with the output of the attenuator 18 is obtained. This difference signal is level-compared with a reference voltage 19 in the differential amplifier 17, and the comparison output is passed through the LPF 14 and becomes a gain control signal for the VCA 8.

FIG. 4 is a diagram for explaining the operation of the circuit shown in FIG. 3. Similar to FIG. 2A, FIG. The right side shows the outer periphery. A solid line 3-1 in FIG. -2
shows the change in the amount of reflected light of the spot light 3 during normal playback while the tracking servo loop is on.
Figures C and D show waveforms corresponding to Figures B and C, respectively.

In other words, if the tracking servo loop is on and playback is performed from the inner circumference to the outer circumference, Figure B
As shown by the dashed line 3-2, the amount of light reflected by the spot light 3 gradually increases. This shows a change corresponding to a change in the peak level of spotlights 1 and 2 (indicated by the dashed line 2-2 in Figure C). On the other hand, the output change of the adder 13 is the sum of the (1-1) level and the (2-1) level, and the output change of the 1/2 attenuator 18 corresponding to 1/2 is the chain line 1- 2. Therefore, if the level of the photoelectric converter 16 corresponding to the amount of reflected light indicated by the chain line 3-2 in Figure B is made to match the level indicated by the chain line 2-2 in Figure C, the differential output from the differential amplifier 15 will be as shown in Figure C. Dashed lines 1-2 and 2
-2, and this level difference change decreases as the pickup moves from the inner circumference to the outer circumference. As a result, the gain of the VCA 8 is controlled to increase as the movement moves, so that the tracking error no longer decreases and the amplitude is corrected as shown by the chain line, as shown in D. In this example, since the differential amplifier 17 compares the voltage with a predetermined voltage 19, the servo loop gain is controlled so that the tracking error level is at a constant level.

In this embodiment, the dashed line 1-2 in FIG.
The amount shown in is obtained by halving the output sum of the amount of reflected light from spot lights 1 and 2. However, since the problem is when the tracking servo loop is in the on state, the amount shown by spot light 1 can be obtained as an alternative. It is also possible to use the output level of either one of the amounts of reflected light (existing on the dashed-dotted line 2-2 in FIG. 4C). In addition, for ease of understanding, the configuration has been explained in which the output sum is halved, but the attenuation amount of the output sum is determined comprehensively by parameters such as the gain of each photoelectric conversion element. It will be done.

As described above, according to the present invention, it is possible to suppress all influences caused by variations in optical characteristics (reflectance and transmittance) of recording disks and pickups, changes over time, changes in spatial frequency on the disk, pit shape, etc. Constant servo characteristics can always be obtained, making stable tracking servo possible.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a conventional tracking servo loop, FIG. 2 is a diagram explaining the operation of the block in FIG. 1, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. FIG. 3 is a diagram illustrating the operation of the blocks in the figure. Explanation of symbols of main parts, 1, 2... Spot light for tracking error detection, 3... Spot light for information detection, 4... Recording track, 5, 6, 16...
...Photoelectric conversion element, 7, 15...Differential amplifier, 13
... Adder, 17 ... Comparator, 19 ... Reference voltage, 11 ... Tracking mirror.

Claims (1)

[Claims] 1. Three light beams forming a single reading spot and a pair of auxiliary spots at positions sandwiching the reading spot are applied to a CAV optical disk on which information signals are recorded in the form of a track by rotating at a constant angle. a detection means for obtaining a single read signal and a pair of auxiliary signals by emitting the reflected light and receiving the reflected light by three light receivers; and an error signal for using a level difference between the pair of auxiliary signals as a tracking error signal. a generating means, a tracking control means for shifting the optical beam in the radial direction of the optical disk in accordance with the tracking error signal to follow a track, and adjusting the tracking error signal to a gain corresponding to the gain control signal. and variable amplification means for amplifying the amplified signal and supplying the amplified signal to the tracking control means, the optical disc performance apparatus detecting a difference between the level of the read signal and the level of at least one of the pair of auxiliary signals. , comprising means for generating a gain control signal that changes according to the level of the difference, and means for transmitting the gain control signal to the variable amplification means, and the gain of the variable amplification means decreases as the level difference decreases. An optical disc performance device characterized in that its size increases according to