JPS63193332A - Focusing servo circuit for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To perform normal focusing servo which reflectance an optical disk has, by dividing a focusing error signal by the peak value of a light quantity signal to automatically eliminate the influence of the reflectance of the used optical disk. CONSTITUTION:A peak value SP of a light quantity signal S proportional to the reflectance of a used optical disk 5 is held by a peak holding circuit 14 in a first focusing driving period when an objective lens 4 as the focusing means is driven in one direction before the focus leading-in operation. A focusing error signal FE which has information of focusing and is proportional to the reflectance of the optical disk 5 is divided by this held peak value SP, and focusing servo is performed, based on the resultant signal. The focus leading-in operation is performed in second and subsequent focusing driving periods following the first focusing driving period. Thus, the influence of the reflection factor of the used optical disk 5 is automatically eliminated, and normal focusing servo is performed whichever reflectance the optical disk 5 has.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a focus servo circuit for an optical recording/reproducing device, and particularly to one compatible with a plurality of types of optical disks having different reflectances.

B1 Summary of the Invention The present invention provides a focus servo circuit for an optical recording/reproducing device compatible with multiple types of optical discs having different reflectances.
By dividing the focus error signal by the peak value of the light intensity signal, the influence of the reflectance of the optical disk used is eliminated, the focus servo gain is kept constant, and normal focus servo is performed for optical disks of any reflectance. It was made so that it could be done.

C1 Prior Art Optical disks have been known as optical recording media. In a focus servo circuit in a device for reproducing or recording/reproducing this optical disc, for example, a photodetector receives reflected light from the disc due to laser light from a laser diode, and forms a focus error signal according to the focus state. Based on this focus error signal, the objective lens of the optical system is moved in the vertical direction (
Focus servo is performed by controlling the drive in the direction perpendicular to the disk surface. In such focus servo circuits, it is common to use a variable resistor (volume) to adjust the gain to obtain a good eye pattern and to adjust the level of the light amount signal proportional to the reflectance of the disk. There is.

D1 Problems to be solved by the invention By the way, optical discs can be divided into playback-only types that can only be played back, write-once types that can only be recorded once, and erasable types that can be erased and recorded many times. It is broadly divided into If you try to play back such discs, especially multiple types of discs with different reflectances, on one device, the amount of light incident on the photodetector will change, which will change the level of the focus error signal and light amount signal, making it impossible to play back normal discs. Since focus servo cannot be performed, it is necessary to adjust the gain of focus servo. This adjustment may be performed using a variable resistor, but frequent adjustment is cumbersome and impractical.

It is common practice to vary the light intensity level of the laser beam during recording and playback. As stated,
2. Description of the Related Art A device is known in which the light intensity level is switched between recording and reproduction, and the gain of a control circuit for focus control is also switched. However, such devices are designed to solve problems between recording and playback, and are not intended for multiple types of optical discs with different reflectances, so they do not solve the problems mentioned above. It cannot be solved.

The present invention was proposed in view of the above circumstances, and it automatically eliminates the influence of the reflectance of the optical disc used, makes it possible to keep the gain of the focus servo constant, and works with optical discs of any reflectance. It is an object of the present invention to provide a focus servo circuit for an optical recording/reproducing device that can perform normal focus servo even when the optical recording/reproducing device is used.

Means for Solving the E1 Problem The focus servo circuit of the optical recording and reproducing apparatus according to the present invention is capable of recording and recording on a plurality of types of optical discs having different reflectances.
In a focus servo circuit of an optical recording and reproducing apparatus that performs reproduction, prior to a focus pull-in operation, during a first focus drive period in which the focus adjustment means is driven in one direction,
The peak value of the light amount signal proportional to the reflectance of the optical disc used is held, and the focus error signal, which contains focus information and is proportional to the reflectance of the optical disc, is divided by this held peak value, and based on this signal, The present invention is characterized in that focus servo is performed and a focus pull-in operation is performed in one focus drive period after the second focus drive period following the first focus drive period.

F8 Effect According to the present invention, the influence of the reflectance of the optical disc used is eliminated by dividing the focus error signal by the peak value of the light amount signal.

G. Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a focus servo circuit of an optical recording/reproducing apparatus according to the present invention. In this FIG. 1, the laser light from the laser diode 1 is
Polarizing beam splitter 2° 1/4 wavelength plate 3. The light then reaches the optical disc 5 via the objective lens 4, which is a focus adjustment means.

Further, the reflected light from the optical disk 5 is reflected by the objective lens 4, the quarter wavelength plate 3. Polarizing beam splitter 2. The light then enters the photodetector 7 via the detection lens 6 and is detected. The photodetector 7 has a light-receiving area divided into four parts, and the detection outputs PA and Pc from the areas 7A and 7C are sent to the summing amplifier 8, and the detection outputs Pg and pH from the areas 7B and 7D are sent to the summing amplifier 9. Each is supplied. Each output from the summing amplifier 8.9 is supplied to the NX amplifier 10 and the summing amplifier 11, respectively, and the subtracting amplifier 10 corresponds to the difference signal (Pa + Pc) (Pa + pn) of each output of the summing amplifier 8.9. A focus error signal Ft is outputted from the addition amplifier 11, and a sum signal (P
A scene signal S corresponding to a + Pc ) + (Pg +p, ) is output. The focus error signal F is a signal that has focus information and is proportional to the reflectance R of the optical disc 5. Further, the light amount signal S is a signal proportional to the reflectance R of the optical disc 5.

The focus error signal F is supplied to a division circuit 12, and the light amount signal S is supplied to a division circuit 13. The light amount signal S is also supplied to a peak hold circuit 14, and the peak value S of the light amount signal S is held. As will be described in detail later, this peak hold operation is performed during a first focus drive period T□ in which the objective lens 5 is driven in one direction (for example, in the direction of arrow A in the figure) prior to the focus pull-in operation. A peak value S of the scene signal S held by the peak hold circuit 14.

are respectively supplied to the division circuits 12 and 13, and the division circuit 12 generates a focus error signal F! based on the peak value S! The division circuit 13 performs a division process of the scene signal S by the peak value SP. As a result, the influence of the reflectance R of the optical disc 5 is eliminated, and a signal with a constant range or level can be obtained.

Focus error signal F from the divider circuit 12.

A signal based on is supplied to the phase compensation circuit 15, and
The signal is supplied to a double-wave rectifier circuit 16. The rectified output from the double wave rectifier circuit 16 is supplied to the comparator 17 and the reference value vR^
compared to This comparison output is then supplied to the falling edge detection circuit 18, and the falling portion of the pulse signal is detected.
The detection output is supplied to the timing generation circuit 19.

Depending on which, the zero-crossing point of the focus error signal Ft is detected, that is, the optimum focus point is detected.

On the other hand, based on the light amount signal S from the division circuit 13, ((1 is supplied to the comparator 20 (focus OK comparator) and compared with the reference value V□, and the comparison output is supplied to the timing generation circuit 19. .

In the triangular wave generating circuit 21, the generation timing of the triangular wave signal W is controlled by the timing generating circuit 19, and the triangular wave signal W is supplied to the selected terminal 22A of the changeover switch 22. Further, the output from the phase compensation circuit 15 is supplied to the selected terminal 22B of the changeover switch 22. This changeover switch 22 is controlled by the timing generation circuit 19 described above. Then, the signal obtained at the selection terminal 22C of the changeover switch 22 is supplied to the focus coil 24 via the drive amplifier 23, and is sent to the objective lens 24.
is driven in a direction perpendicular to the signal recording surface of the optical disc 5, that is, in the direction of the arrow AB in the figure.

Next, the operation of the focus servo circuit having the above-described configuration will be explained, focusing on the focus pull-in operation.

First, a triangular wave signal W as shown in FIG. As a result, the objective lens 4 is moved to the direction indicated by the arrow A in FIG.
Driven in direction B.

That is, the objective lens 4 is moved in the direction of arrow A during the first focus drive period T, and in the second focus drive period T.
In the focus drive period TF1, in the direction of arrow B,
Furthermore, in the third focus drive period TF2, the lenses are driven again in the direction of arrow A. As a result, the subtraction amplifier 10 outputs a focus error signal F7 called a so-called figure-eight curve as shown in FIG. 2(CB), and the addition amplifier 11 outputs a light amount signal S as shown in FIG. 2(C). Output. Here, in the focus error signal Fz and the light amount signal S, a small amplitude signal change and a large amplitude signal change appear one after the other, respectively.
The small amplitude portion corresponds to reflection on the surface of the optical disk 5, and the large amplitude portion corresponds to reflection on the signal recording surface of the disk 5. Focus servo is of course performed on the signal recording surface.

Further, as shown in FIG. 2(D), the peak hold circuit 14 holds the peak value SP of the light quantity signal S, and supplies the peak value SP to the dividing circuits 12 and 13, respectively. The above peak value SP is the second and third peak value SP for the same disk.
Focus drive period TF! 1st place in I TF2
Since the value is the same as the focus drive period TFI, the peak value holding operation is substantially performed in the first focus drive period T1.

Here, the following relationship holds between the focus error signal F□ and the reflectance R of the optical disc 5: FzoCR−・=+11, and between the light amount signal S and the reflectance R, S and R・...The relationship (2) holds true, and the peak value S of the above light amount signal S
The following relationship holds between P and the reflectance R: Sr QCR-.
From the formula, F(/SP = const, --(41) is derived, and from the above formulas (2) and (3), S/Sp
= const, --+51 is derived. Equation (4) above means that the output of the dividing circuit 12 is constant regardless of the magnitude of the reflectance R, which eliminates the influence of the reflectance R and makes it possible to keep the servo gain constant. can. Of course, the output of the division circuit 12 actually contains servo information depending on the focus state, so it becomes a signal within a certain range. Further, the above equation (5) means that the output of the dividing circuit 13 is constant regardless of the magnitude of the reflectance R.

The focus pull-in operation is performed during the first focus drive period T.
This is performed during the second focus drive period 'I'rt following □ or the third focus drive period TF3. That is, when the level of the signal based on the light amount signal S from the division circuit 13 exceeds the reference value V□, the output of the comparator 20 becomes high level. On the other hand, a signal based on the focus error signal F from the divider circuit 12, which is shown enlarged in FIG. I get the output. This rectified output is supplied to the comparator 17, and from the comparator 17 as shown in FIG.
A pulse signal as shown in C) is output.

Then, the falling portion of the pulse signal is detected by the falling detection circuit 18, and its detection output is supplied to the timing generation circuit 19. From the timing generation circuit 19,
At the time when the output of the comparator 20 becomes high level and the detection output from the falling detection circuit 18 is supplied (
(timing), that is, when the optimum focus point is detected, a control signal is sent to the selector switch 22, and the switch 22 is switched to the selected terminal 22B side. Thereby, the signal based on the focus error signal Ft from the divider circuit 12 is transmitted to the phase compensation circuit 15. Changeover switch 22. The signal is supplied to the focus coil 24 via the drive amplifier 23, and normal focus servo is started. When the timing generation circuit 19 performs the focus pull-in operation during the second focus drive period T, even if the outputs of the falling detection circuit 1B and the comparator 20 are supplied, the timing generation circuit 19 does not perform the focus pull-in operation during the first focus drive period T□. In the case where the changeover switch 22 is not changed and the focus pull-in operation is performed in the third focus drive period TF3, similarly, the first and second focus drive periods T
At v + + T F *, control is performed so that the changeover switch 22 is not switched.

In this way, by dividing the focus error signal Ft and the light amount signal S by the peak value S of the light amount signal S, the influence of the reflectance R of the optical disc 5 used is eliminated, and the range is constant or the level is constant. I'm getting a signal. Therefore, the focus servo gain can be kept constant, and normal focus servo can be performed for optical discs of any reflectance.

In addition to the triangular wave signal, the focus pull-in operation uses
It is also possible to use a sawtooth signal or a sine wave signal or the like. Furthermore, instead of driving the objective lens 4, the entire optical pink amplifier may be driven to perform focus servo.

Further, FIG. 4 shows a specific configuration example of the division circuits 12, 13 and peak hold circuit 14 in the focus servo circuit of this embodiment shown in FIG. This fourth
In the figure, an input terminal 31 to which the focus error signal F is supplied is connected to a multiplexer 33 via each resistor 32, and the multiplexer 33 is connected via an inverting amplifier circuit 36 consisting of an operational amplifier 34 and a resistor 35. and is connected to the output terminal 37. Further, the input terminal 41 to which the light quantity signal S is supplied is connected to a multiplexer 43 via each of the resistors 42.
3 is an inverting amplifier circuit 4 consisting of an operational amplifier 44 and a resistor 45.
6 to the output terminal 47. Further, the input terminal 41 is connected via an operational amplifier 151 to a peak hold circuit consisting of a diode 52 and a capacitor 53. A reset transistor 54 is connected between the diode 52 and the capacitor 53, and a reset pulse RP is connected to the base of the transistor 54.
Resetting is performed by supplying the . The capacitor 53 is connected to a latch circuit 56 via an A/D converter (analog/digital converter) 55.

The launch circuit 56 is supplied with a latch pulse LP from, for example, a micro combinator at the end of the first focus driving period Tv, and the optical M signal S9 peak (of the direct SP) accumulated as an electric charge in the capacitor 53 is The output signal U is latched.The output from the launch circuit 56 is supplied to the multiplexers 33 and 43, respectively, to perform switching control.

That is, by switching each input resistance of the operational amplifiers 34 and 44, the gain is switched, and an operation equivalent to division is performed.

H5 Effects of the Invention In the focus servo circuit of the optical recording/reproducing apparatus according to the present invention, by dividing the focus error signal by the peak value of the light amount signal, the influence of the reflectance of the optical disc used is automatically eliminated, and the I'm trying to get a signal.

Therefore, the focus servo gain can be kept constant, and normal focus servo can be performed for optical discs of any reflectance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the focus servo circuit of an optical recording/reproducing apparatus according to the present invention, FIG. 2 is a time chart for explaining the operation of the focus servo circuit of the above embodiment, and FIG. FIG. 4, which is also a waveform diagram, is a circuit diagram showing a specific configuration example of the division circuit and peak hold circuit portions in the focus servo circuit of the above embodiment. 1...Laser diode 4...Objective lens 5...Optical disk 7...Photodetector 12...Divider circuit 14...Peak hold circuit 19...Timing generation circuit 21...Triangular wave generation circuit 22... Selector switch 24... Focus coil

Claims (1)

[Claims] Recording and recording on multiple types of optical discs with different reflectances.
In a focus servo circuit of an optical recording and reproducing apparatus that performs reproduction, prior to a focus pull-in operation, during a first focus drive period in which the focus adjustment means is driven in one direction, a peak value of a light amount signal proportional to the reflectance of the optical disc used is detected. is held, and a focus error signal having focus information and proportional to the reflectance of the optical disk is divided by this held peak value, and focus servo is performed based on this signal, and the first focus is A focus servo circuit for an optical recording/reproducing device, characterized in that a focus pull-in operation is performed during one focus drive period after a second focus drive period following a drive period.