JPH04117634A - Light quantity controller - Google Patents

Abstract

PURPOSE:To attain the precise control of a light quantity on the face of a recording medium by detecting a reflected light of the recording medium irradiated by a light source, correcting an error signal by the use of the output signal of the reflected light, and correcting the attenuation of the light quantity on the face of the recording medium. CONSTITUTION:This controller is equipped with a photodetecting means 2 arranged proximately to a light source 1 where an information recording medium 5 is irradiated with luminous flux, a means 12 which compares the photodetecting signal with a reference quantity and outputs the error signal a means 14 which drives the light source 1 to emit a prescribed light quantity based on the error signal, and a means 7 which detects the reflected light of the recording medium 5 irradiated from the light source 1. Then, the error signal is corrected by the use of the output signal of the means 7, and the attenuation of the light quantity on the face of the recording medium 5 is corrected. Thus, the attenuation of the light quantity caused by dust, etc., can be corrected and the light quantity on the recording medium 5 can be precisely controlled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a light amount control device for controlling the light amount of a light source, particularly for controlling the light amount of a semiconductor laser used as a light source for recording or reproducing light flux in an optical disk device or the like. The present invention relates to a suitable light amount control device.

[Prior Art] Conventionally, there are several types of optical disk devices, such as read-only devices and rewritable devices. In all of these devices, information is optically recorded or reproduced by irradiating a light beam from a light source such as a semiconductor laser onto an optical disk. For example, when performing reproduction, a constant amount of light is emitted from a light source, and information is reproduced from the reflected light. In this case, if the light intensity of the light source fluctuates, errors will occur in the reproduced data, so the light intensity of the light source is required to be constant.

Therefore, in the past, a light sensor was provided near the light source, and the light intensity was controlled to be constant by applying negative feedback based on the received light signal.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional light amount control device, dust and the like float in the optical path between the light source and the disk, which causes the light to attenuate on the disk surface and reduce the amount of light on the disk surface. There was a problem that could not be controlled accurately.

The present invention has been made to solve these problems, and its purpose is to provide a light amount control device that can accurately control the amount of light on the surface of a recording medium without being affected by dust or the like. .

[Means for Solving the Problems] In order to achieve the above object, a light detection means is placed near a light source that irradiates a light beam onto an information recording medium, and this detection signal is compared with a reference value, and the error signal is detected. a means for outputting
A light amount control device comprising means for driving the light source so that the amount of light becomes a predetermined amount of light based on the error signal, means for detecting reflected light of the recording medium irradiated from the light source, and an output of the means A light amount control device is provided, comprising means for correcting the error signal using a signal and correcting light amount attenuation on the medium surface of the recording medium.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the light amount control device of the present invention. Note that this embodiment is an example in which the present invention is implemented in a read-only optical disk device.

In FIG. 1, 1 is a semiconductor laser that emits a laser beam, and 2 is a photodiode placed close to the semiconductor laser 1. In FIG. The semiconductor laser 1 and the photodiode 2 are housed in a laser unit 3, and the photodiode 2 is designed to detect the laser beam at a position as close as possible to the semiconductor laser 1. Reference numeral 4 denotes an optical system composed of an optical lens, a prism, a mirror, a condensing lens, etc. for collimating the laser beam. A laser beam from the semiconductor laser 1 is guided onto the optical disk 5 by an optical system 4, and is imaged as a minute spot on the disk surface. Further, the light reception signal of the photodiode 2 is amplified by the amplifier 6 and output to the differential amplifier 12.

7 is a photodiode that receives the laser beam reflected from the optical disk 5 via the optical system 4; 8 is an amplifier that amplifies the light reception signal of the photodiode 7; 9 is an amplifier that removes high-frequency noise components and adjusts the amount of light by the optical system 4; This is a filter whose cutoff frequency is set so that only attenuated components pass through.

Further, 10 is a switch for selecting the output of the filter 9 or the ground level, and the switching is controlled by a control section (not shown). When the switch 10 selects the output of the filter 9, it is time to correct the light amount of the semiconductor laser 1, and when the switch 10 selects the ground level, it is time to perform light amount control similar to the conventional one. 11 is a differential amplifier that generates a difference signal between the output of the switch 10 and a reference value. These photodiode 7, amplifier 8, filter 9, switch 10
, the differential amplifier 11 constitutes a light amount correction circuit for the semiconductor laser 1, as will be described in detail later.

12 is a differential amplifier that generates a difference signal between the output of the amplifier 6 and the output of the differential amplifier 11; 13 is a filter having phase compensation characteristics and high-frequency attenuation characteristics to stabilize the servo loop; 14 is a filter 13 This is a driver that drives the semiconductor laser 1 based on the output of the semiconductor laser 1.

Next, the operation of this embodiment will be explained. First, when reproducing information, a laser beam having a predetermined light intensity is irradiated from the semiconductor laser 1 . This laser beam is received by a photodiode 2, and the received light signal is sent to an amplifier 6. on the other hand,
The laser beam is corrected into a parallel beam by the optical system 4, and after being narrowed down to a minute spot, it is irradiated onto the optical disk 5.

The light irradiated onto the optical disc 5 is reflected on its surface,
A portion of the light is guided to the photodiode 7 by a mirror in the optical system 4. In addition, the reflected light from the optical disc 5 is
The information is reproduced by the received signal guided to the reproduction optical system in the optical system 4. The light reception signal from the photodiode 7 is amplified by an amplifier 8 and then input to a filter 9, and the signal from which high-frequency noise components have been removed is sent to a switch 10. Here, when the switch 10 is tilted to the b side, that is, when an instruction is given to select the output of the filter 9, the output signal of the filter 9 is input to the differential amplifier 11. The output of the filter 9 is transferred to the optical disc 5 by the photodiode 7.
Since this is a signal obtained by receiving reflected light from the optical system 4, it is a signal reflecting attenuation of the amount of light due to dust or the like within the optical system 4. Therefore,
When the differential amplifier 11 compares the output of the filter 11 with the reference value, the difference signal becomes a signal corrected for the attenuation of the light amount.
This correction signal is output to the differential amplifier 12 as a reference signal.

The differential amplifier 12 outputs to the filter 13 the difference between the current light amount value of the semiconductor laser 1 from the amplifier 6 and the reference value whose attenuation has been corrected. The filter 13 performs phase compensation as described above and outputs the signal to the driver 14, and the driver 14 drives the semiconductor laser 1 based on the signal. As a result, since the light reflected from the optical disk 5 is used to correct the attenuation of the light amount of the optical system 4, the amount of light on the optical disk 5 can be accurately controlled. On the other hand, when the switch 10 is tilted to the a side, the ground level is output to the differential amplifier 11.

In this case, the differential amplifier 11 outputs the reference value input to the other terminal as it is to the differential amplifier 12, so the differential amplifier 12 outputs a difference signal between this reference value and the output of the amplifier 6. Since this reference value has not been corrected for light intensity attenuation, it is controlled in the same way as the conventional one.

Other embodiments are shown in FIGS. 2 and 3, respectively. The embodiment shown in FIG. 2 is an example in which the differential amplifier 12 calculates the difference between the output of the switch 10 and the output of the amplifier 6, and then the differential amplifier 11 compares the difference signal with a reference value. Further, in the embodiment shown in FIG. 3, after the differential amplifier 11 calculates the difference between the output of the amplifier 6 and the reference value, the differential amplifier 12 calculates the difference signal and the switch 1.
This is an example of comparing outputs of 0. In each of these embodiments, the connection of the differential amplifiers 11 and 12 is changed, and basically, the amount of reflected light from the optical disk 5 received by the photodiode 7 is used in the same way as the embodiment shown in FIG. Optical system 4
This is to correct the light intensity attenuation. Therefore, even in the embodiments shown in FIGS. 2 and 3, there is an effect that the amount of light on the optical disk 5 can be accurately controlled in exactly the same way as the example shown in FIG.

FIG. 4 shows yet another embodiment. Although the above embodiments were all examples using analog circuits, this embodiment is an example in which the light amount control device is configured by a digital circuit.

Incidentally, in FIG. 4, the same parts as in the above embodiment are given the same reference numerals.

In FIG. 4, 15 is an A/D converter that converts the output of the amplifier 6 into a digital signal, and 16 is an A/D converter that converts the output of the amplifier 8 into a digital signal. 17 is a digital signal processor (hereinafter abbreviated as DSP);
The amount of light is controlled according to a predetermined control program. DS
The P17 internally includes arithmetic units such as adders and multipliers, a memory for storing data, a memory for storing control programs such as the order of calculations, and an input/output device for interfacing with external circuits. Also, 18 is DSP
This is a D/A converter that converts the output of No. 17 into an analog signal.

Next, the operation of this embodiment will be explained using FIG. 5. First, laser light from a semiconductor laser is received by a photodiode 2, and the received light signal is amplified by an amplifier 6. Then, the output signal of the amplifier 6 is digitized by the A/D converter 15 and input to the DSP 178. On the other hand, the optical disc 5
The light reflected from the photodiode 7 is received by the photodiode 7, and the received light signal is amplified by the amplifier 8. After the output of the amplifier 8 is digitized by the A/D converter 16, it is also converted to a DSP.
17.

In the DSP 17, as shown in FIG.
At Sl, the input of the A/D converter 15 is stored as data 0 in the internal storage area. Next, in S2, it is determined whether or not to perform light intensity attenuation correction, and if correction is to be performed, the input signal of the A/D converter 16 is stored as data 1 in an internal storage area in S3.

In S4, the high-frequency noise component of data 1 is removed and the optical system 4
The light amount attenuation component is extracted and stored in the storage area as data 2 in the same way. On the other hand, if light amount correction is not to be performed, data 2 is set to 0 in S5. The determination as to whether or not to perform the light amount correction in S2 is made by a control section (not shown).

In S6, the DSP 17 subtracts data 2 obtained in step 84 from a pre-stored reference value (Ref) to calculate data 3. This data 3 is also stored in the storage area in the same way. In addition, in this case, when data 3 is 0,
Since data 3 is the same as the reference value, there is no need to increase or decrease the amount of light.

In S7, data 0, which is the output of the amplifier 6, is subtracted from data 3 to calculate data 4. Next, in S8, phase compensation and high-frequency attenuation filtering processing is performed to stabilize the control loop, and data 5 is obtained. get. Then, in S9, this data 5 is output as an error signal to the D/A converter 18, and the driver 14 drives the semiconductor laser 1 based on this data 5.
to drive.

In this embodiment, as in the previous embodiment, the reflected light from the optical disk 5 is received, and the received light signal is used to correct the light intensity attenuation of the optical system 4. In exactly the same way, the amount of light can be precisely controlled. Furthermore, although the embodiment using an analog circuit has fluctuations due to temperature changes and changes over time, this embodiment has the advantage of being able to improve these problems. Furthermore, when changing the specifications, this embodiment has the advantage of being able to handle the changes by simply changing programs such as arithmetic processing, without changing the hardware.

Note that the present invention is applicable not only to a read-only optical disk device but also to a read-only optical disk device.
The present invention is applicable to all optical disk devices such as writable optical disk devices, such as write-once optical disk devices and rewritable magneto-optical disk devices.

[Effects of the Invention] As explained above, the light amount control device of the present invention has the effect of being able to correct the light M attenuation of the light flux irradiated to the recording medium, that is, the light amount attenuation caused by dust floating in the optical system leading to the medium. be. Therefore, since the amount of light on the recording medium can be accurately controlled to a desired amount of light, the reliability of reproduced data or recorded data can be improved, contributing to improved performance of the apparatus.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the light amount control device of the present invention, Figs. 2, 3, and 4 are block diagrams showing other embodiments, and Fig. 5 is shown in Fig. 4. 3 is a flowchart showing the operation of the embodiment. 1: Semiconductor laser 2, 7 = photodiode 4; Optical system 5: Optical disk 6.8: Amplifier lO; Switch 11.12: Differential amplifier 14: Driver 1.5.16: A/D converter 17: DSP

Claims (1)

[Scope of Claims] A light detection means disposed close to a light source that irradiates a light beam onto an information recording medium, a means for comparing this detection signal with a reference value and outputting an error signal, and a means for comparing this detection signal with a reference value and outputting an error signal thereof; a means for driving the light source so that the light amount becomes a predetermined light amount based on the light source; A light amount control device comprising means for correcting the error signal and correcting light amount attenuation on the medium surface of the recording medium.