JPH0548532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical recording and reproducing apparatus that records and reproduces signals by irradiating a recording medium with a beam of light.

[Background of the invention]

In an optical recording/reproducing device, an optical head used to record and reproduce signals on an optical recording medium (hereinafter referred to as a disk) narrows a laser beam into a minute spot and accurately places it on the information track of the disk. It is necessary to focus the light on For this reason, the optical head is equipped with a focus and tracking error detection device, and using this detection signal, a focus and tracking servo circuit performs well-known focus and tracking control.

FIG. 2 is a schematic diagram showing a general optical head in an optical recording/reproducing apparatus.

In Fig. 2, 1 is a semiconductor laser, 2 is a collimating lens, 3 is a diverging beam, 4 is a parallel beam, 5 is a polarizing beam splitter, 5a is a polarizing reflective surface, and 6 is a 1/2
4 wavelength plates, 7 objective lens, 8 disk, 9 information track, 10 reflected light, 11 parallel light, 1
2 is a convex lens, 13 is a mirror, 14 is a concave lens,
15, 16 and 17, 18 are two-divided light receiving elements, respectively.

As shown in FIG. 2, a semiconductor laser 1 serving as a light source
Divergent light 3 emitted from the collimator lens 2 converts the divergent light 3 into parallel light 4. After the parallel light 4 passes through a polarizing beam splitter 5 and a quarter-wave plate 6,
The light is focused by the objective lens 7 and illuminated onto the information track 9 of the disk 8. The reflected light 10 from the disk 8 is converted into parallel light 1 again by the objective lens 7.
After passing through the 1/4 wavelength plate 6, it is reflected by the polarization reflecting surface 5a of the polarization beam splitter 5. After this parallel light 11 passes through a convex lens 12, the light flux is split into two by a mirror 13, and one passes through a concave lens 14 and enters two-split light receiving elements 15 and 16. A focus error signal is generated from the output signals of the two-split light receiving elements 15 and 16. The other of the light beams split into two by the mirror 13 enters the two-split light receiving elements 17 and 18, and a tracking error signal is generated from this output signal. These error signals are used as control signals for driving the objective lens 7 in the x direction, which is the optical axis direction, and in the y direction, which is the radial direction of the disk 8.

FIG. 3 is a block diagram showing a general signal recording/reproducing system in an optical recording/reproducing apparatus.

In FIG. 3, 19 is a video signal, 20 is a recording modulation circuit, 21 is a laser drive circuit, and 22 is a
This is the REC/PLAY switching signal.

In an optical recording and reproducing device, when recording a signal, a disk 8 coated with a photosensitive material is rotated, and a minute spot on which the laser beam is focused to φ1 μm or less by the aforementioned focus control is placed on the disk 8. By irradiating light and modulating the intensity of the optical output of the semiconductor laser 1 using the video signal 19 to be recorded via the recording modulation circuit 20 and the laser drive circuit 21, irregularities or refractive index, etc. are created on the disk 8.
Records changes in optical properties such as reflectance in real time.

During playback, the REC/PLAY switching signal 22 is
The mode is switched to PLAY/MODE, the output of the semiconductor laser 1 is set to an optical output weaker than that during recording, and changes in the optical characteristics of the disk 8 are detected by light reflected from the disk 8 to reproduce information.

In such an optical recording/reproducing device, in order to increase the recording density, guide tracks are provided in advance on the disk 8 in a concentric circle or a spiral shape.
Information is written on a predetermined track while applying tracking control so as to follow the guide track, and information is reproduced from the track.

Therefore, as a generally well-known method for tracking control, the reflected light from the disk 8 is used, and a tracking servo circuit is used to adjust the irradiation position of the minute spot light onto the disk 8 relative to the guide track. There is a method of performing tracking control by detecting the amount of deviation as a tracking error signal and controlling the irradiation position so that the tracking error signal becomes zero.

However, this tracking control method was developed for playback-only devices (such as video disk playback devices) that read video signal information from a video disk or the like on which video signal information has been recorded in advance, so it is When attempting to apply this method to an optical recording/reproducing apparatus that requires tracking control both during recording and during reproduction, the following problems arose.

In other words, in an optical recording/playback device, the amount of light irradiated onto the disk during recording requires 5 to 10 times the amount of light compared to the amount during playback, so the amount of light reflected from the disk is also different during recording and playback. However, there was a problem that the tracking servo loop gain also changed and the tracking accuracy deteriorated significantly, or the tracking servo loop gain became too high and caused oscillation. Further, although the above description has been made regarding an optical recording and reproducing device capable of only recording and reproducing, it is also possible to optically erase information if the photosensitive material is appropriately selected. Even in such erasing, tracking control is necessary, and the amount of light irradiated to the disk is different from that during recording and playback.
A similar problem will occur.

Further, what has been described above regarding tracking control also applies to focus control, and even in this case, there are problems such as a significant deterioration in focus accuracy and oscillation.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and therefore, an object of the present invention is to always perform stable and accurate tracking control and focus control even during recording, playback, or erasing. An object of the present invention is to provide an optical recording and reproducing device.

[Summary of the invention]

In the present invention, in order to achieve the above-mentioned object,
The amount of reflected light that changes during recording, playback, or erasing is detected by a polygonal line approximation circuit, and the gain of each amplifier in the focus and tracking servo circuits is automatically changed according to the change in the amount of light. A constant servo loop gain is always obtained regardless of time, playback, or erasing.

[Embodiments of the invention]

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

FIG. 1 is a block diagram showing a focus servo circuit and a tracking servo circuit in one embodiment of the present invention.

In FIG. 1, 23, 24, 25, and 32 are differential amplifiers, 26 is a polygonal line approximation circuit, and 2
7 and 33 are gain control circuits, 28 and 34 are compensation amplifier circuits, 29 and 35 are loop switch circuits, 30 and 36 are drive circuits, 31 is a focus control coil, and 37 is a tracking control coil. be.

The outputs from the two-split light receiving elements 15 and 16 shown in FIG. 2 are input to a differential amplifier 23, respectively, as shown in FIG. 1, and a focus error signal is obtained as an output signal of the difference. The focus error signal is supplied to a drive circuit 30 via a gain control circuit 27, a compensation amplifier circuit 28, and a loop switch circuit 29, respectively. Then, the focus control coil 31 is driven in accordance with this focus error signal, and focus control is performed so that the diameter of the laser spot on the disk 8 is approximately φ1 μm or less.

On the other hand, the two-split light receiving elements 17 and 1 shown in FIG.
As shown in FIG. 1, the outputs from 8 are respectively input to differential amplifiers 32, and a tracking error signal is obtained as an output signal of the difference. The tracking error signal is sent to a gain control circuit 33, a compensation amplifier circuit 34,
The signals are supplied to a drive circuit 36 via loop switch circuits 35, respectively. Then, according to this tracking error signal, the tracking control coil 37
is driven, and tracking control is performed so that the laser spot on the disk 8 follows a guide track provided on the disk 8 in advance.

Each of the aforementioned circuits that perform focus control (collectively referred to as a focus servo circuit) and each of the aforementioned circuits that perform tracking control (collectively referred to as a tracking servo circuit) are a focus servo loop, A tracking servo loop is configured, and in this embodiment, the following control is performed so that the gain of each servo loop is always constant.

That is, as shown in FIG.
The outputs from 5 and 16 are input to a differential amplifier 24 as a sum signal, and further input to a polygonal line approximation circuit 26 via a differential amplifier 25. Here, this sum signal voltage is converted into a desired voltage and characteristic as described later, and the gains of the gain control circuits 27 and 33 are controlled by the output voltage of the polygonal line approximation circuit 26.

FIG. 4 is a graph showing an example of the required gain with respect to the sum signal voltage of the gain control circuits 27 and 33 when the gain during reproduction is used as a reference. That is,
This graph shows that in order to keep the servo loop gains of the focus servo circuit and the tracking servo circuit always constant with respect to the sum signal voltage, the gains of the gain control circuits 27 and 33 are as follows:
When the gain during reproduction (in the figure, P indicates reproduction) is 0 dB, how many dB is required is plotted against the sum signal voltage.

As shown in FIG. 4, gain control circuits 27 and 33
The required gain of is almost inversely proportional to the sum signal voltage. Since the amount of laser light increases during recording, the sum signal output also increases, but since the laser output is variable depending on the recording position on the disk, the sum signal voltage during recording also varies and varies from about 4 to 4. 8V
It will be about. Therefore, during recording, the gains of the gain control circuits 27 and 33 are approximately -13 to - during reproduction.
A gain of about 20dB is required.

FIG. 5 is a circuit diagram showing a specific example of the polygonal line approximation circuit 26 and gain control circuits 27 and 33 for obtaining the above characteristics.

In FIG. 5, A is the output of the differential amplifier 25 shown in FIG. 1, that is, the sum signal. Furthermore, since the gain control circuits 27 and 33 are circuit-wise identical, only one circuit is shown in the figure. Therefore, when using the gain control circuit 27, B is the first
The output of the differential amplifier 23 shown in the figure, ie, the focus error signal, is the input to the compensation amplifier circuit 28. Moreover, when using the gain control circuit 33,
B is the output of the differential amplifier 32 shown in FIG.
The tracking error signal C is an input to the compensation amplifier circuit 34. In addition, 38a and 38b are diodes, 39, 40, 41, 42, and 4, respectively.
6 is a resistor, 43 and 44 are differential amplifiers, 45 is a transistor, 47 is a Zener diode, and 48 is a current controlled amplifier.

Also, Figure 6 shows the sum signal voltage Vin in Figure 5.
FIG. 7 is a graph showing the relationship between the sum signal voltage Vin and the control current Ic in FIG. 5. FIG.

As shown in FIG. 5, the bending point voltage Vs of the bending line approximation circuit 26 is determined by diodes 38a and 38b, the sum signal voltage is Vin, and the resistor 3
9 is R ₁ , resistor 40 is R ₂ , resistor 41 is R ₃ , resistor 4
2 as R ₄ , when Vin≦R ₁ +R ₂ /R ₂ Vs, the amplification degree G is G=-(1/R ₁ +R ₂ +1/R ₃ )R ₄ When Vin>R ₁ +R ₂ /R ₂ Vs, the amplification degree G is G = -R ₄ /R ₃ , which is inverted by the differential amplifier 44 and the sixth
A control voltage Vc as shown in the figure is obtained. this voltage
A Zener diode 47, a resistor 46, and a transistor 45 convert Vc into a control current Ic. If the voltage of the Zener diode 47 is Vz and the resistor 46 is _R5 , then Ic=Vz-Vc- _VBE / _R5 , and the control current Ic at this time has characteristics as shown in FIG. If this control current Ic is used as the control current of the current control amplifier 48 (for example, BA6110 manufactured by ROHM Co., Ltd.), the desired characteristics as shown in FIG. Also, it is possible to control the servo loop gains of the focus servo circuit and the tracking servo circuit so that they are always constant regardless of changes in the amount of light.

In the above description, a case has been described in which two light-receiving elements are used for focus and tracking error detection, but the present invention is not limited to this, and a plurality of light-receiving elements may be used.

〔Effect of the invention〕

As explained above, according to the present invention, a change in the amount of reflected light is detected by a polygonal line approximation circuit, and the gain of each amplifier in the focus and tracking servo circuits is automatically changed according to the change in the amount of light.
Since the servo loop gain is always constant regardless of whether it is recording, reproducing or erasing, stable and accurate focus and tracking control can always be obtained in any state. Another feature is that the gain is automatically controlled in response to variations in the disc and changes in the amount of light during recorded/unrecorded trick playback.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a focus and tracking servo circuit in one embodiment of the present invention;
Fig. 2 is a schematic diagram showing a general optical head, Fig. 3 is a block diagram showing a general signal recording/reproducing system, and Fig. 4 shows the required gain for the sum signal voltage of the gain control circuit in Fig. 1. Graph showing actual measurement examples, 5th
The figure is a circuit diagram showing a specific example of the polygonal line approximation circuit and the gain control circuit in Figure 1, Figure 6 is a graph showing the relationship between the sum signal voltage Vin and the control voltage Vc in Figure 5, and Figure 7 is a graph showing the relationship between the sum signal voltage Vin and the control voltage Vc in Figure 5. Sum signal voltage in figure
3 is a graph showing the relationship between Vin and control current Ic. 1... Semiconductor laser, 8... Disk, 15,
16, 17, 18... 2-split light receiving element, 23, 2
4, 25, 32... Differential amplifier, 27, 33...
Gain control circuit, 26... broken line approximation circuit.

Claims (1)

[Scope of Claims] 1. means for irradiating a light beam for recording and reproducing signals on a recording medium having a guide track; a plurality of focus light receiving elements for receiving reflected light beams from the recording medium and outputting signals; a focus servo means for controlling the focus of the light beam irradiated by a signal from the focus light receiving element; a plurality of tracking light receiving elements for receiving the light beam reflected by the recording medium and outputting a signal; and the tracking light receiving element. a tracking servo means for tracking the light beam irradiated by a signal from a focusing light receiving element to the guide track, wherein the focusing light receiving element and the tracking light receiving element It has an addition means for adding and outputting signals from some or all of the parts, and a polygonal line approximation circuit whose gain is switched according to the output signal level of the addition means, and the polygonal line approximation circuit has a An optical recording and reproducing apparatus characterized in that the gains of the amplifiers of the focus servo means and the tracking servo means are changed depending on the output signal. 2. In the optical recording and reproducing apparatus according to claim 1, the amplifier is a current control amplifier, and the output of the polygonal line approximation circuit is input to a voltage/current conversion circuit, and the voltage/current conversion circuit is An optical recording/reproducing device characterized in that the gain of the current-controlled amplifier is changed depending on the current value of the circuit.