JPH03256235A - Optical recorder - Google Patents

Abstract

PURPOSE:To keep an amplitude of a regenerative signal constant without using an AGC circuit by feeding back an amplitude level of the regenerative signal direct to a laser driving circuit and adjusting an irradiating light quantity of a laser beam. CONSTITUTION:A detecting signal including a high frequency modulation component, outputted from a photodetector 2 is amplified with an appropriate gain through a gain changeover circuit 14. A gain is changed multistepwise via a register 15 by a microprocessor 16 to be set at an appropriate value. By inserting the circuit 14, an adjusting width of the irradiating light quantity of the laser beam can be diminished by reducing previously an amplitude varying width of the detecting signal accordingly. Then, an automatic light quantity control circuit 18 to be incorporated into the laser driving circuit 13 is operated, and driving electric power is supplied to a laser light source 1 based on a comparison result between a reference voltage and a monitor voltage to perform a servo control in order to make the amplitude level of the regenerative signal always constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording device, and particularly to a technique for controlling the amplitude of a reproduced signal to be constant.

[Conventional technology]

An optical recording device irradiates a reflective medium with a laser beam and reads out information recorded on the medium by changing the amount or deflection angle of the reflected light. Therefore, the amplitude level of the reproduced signal constantly fluctuates due to changes in the reflectance of the medium surface, changes in the reflection angle due to warping of the medium, or the shape of information pits formed on the medium surface. Conventionally, automatic gain adjustment circuits (AGC) have been used to correct this fluctuation and keep the amplitude constant.
circuit) is added.

FIG. 5 shows an information reproducing system of an optical recording device equipped with the AGC circuit according to FIG. As shown in the figure, a laser drive circuit 101 drives a laser light source 102 to irradiate an information recording medium 103 with a laser beam. Generally, when reproducing information, a laser beam having a constant light intensity at a sufficiently smaller level than when writing information is irradiated. The light reflected by the information recording medium 103 is received by the photodetector 104. The detection signal output from photodetector +04 is sent to AGC circuit +0
After the gain is adjusted by 5, the signal is input to the high frequency amplifier lo6.

The high frequency amplifier 106 selectively amplifies only the high frequency AC component in a specific band included in the detection signal and outputs a reproduced signal. At this time, the AGC circuit 105 constantly monitors the amplitude level of the reproduced signal and operates to maintain the amplitude level constant by adjusting the gain according to fluctuations in the amplitude level. The reproduced signal is input to a demodulation circuit 107, and information included in the reproduced signal is output as pulse data. The demodulation circuit 107 performs binary conversion according to the magnitude of the amplitude of each peak included in the reproduced signal, and outputs pulse data. Therefore, in order to perform accurate binary conversion, it is necessary to keep the amplitude level of the reproduced signal constant, and the AGC circuit 105 is used for this purpose.

[Problem that the invention seeks to solve]

However, since the AGC circuit is an amplifier with a variable gain, it has a complicated structure and is expensive. In addition, when a low reflectance medium is used, or when reflected light is attenuated due to deterioration over time, clouding of the objective lens due to dust, etc., or scratches or stains on the surface of the medium, circuit noise cannot be ignored and the S/N ratio deteriorates. There was a problem. Furthermore, since analog AGC circuits have high sensitivity and poor linearity, there is a problem that operation becomes unstable unless an automatic gain adjustment loop is constantly formed and controlled.

[Means for solving problems]

An object of the present invention is to maintain the amplitude of a reproduced signal constant without using an AGC circuit which has the various problems mentioned above.

In order to achieve the above object, an optical recording device according to the present invention includes a laser light source for irradiating a laser beam onto a reflective medium on which information is recorded, and a laser beam that is modulated and reflected according to the information recorded on the reflective medium. It is equipped with a photodetector that photoelectrically converts the signal and outputs a detection signal containing a high-frequency modulation component. A high frequency amplifier is connected to the photodetector, and outputs an output signal, that is, a reproduced signal, having a predetermined amplitude level by selectively amplifying the high frequency modulation component included in the detection signal. Furthermore, a laser drive circuit for driving a laser light source in response to the amplitude level of the reproduced signal is connected to the high frequency amplifier.

This laser drive circuit operates to adjust the amount of laser beam irradiation so as to cancel out fluctuations in the amplitude level of the reproduced signal, thereby keeping the amplitude level constant.

Preferably, the laser drive circuit includes a monitor unit that receives a laser beam emitted from a laser light source and outputs a monitor voltage corresponding to the amount of light, and drives the laser drive circuit based on the result of comparing the monitor voltage with a reference voltage according to the amplitude level of the reproduced signal. and automatic light amount control means for supplying power to the laser light source.

Also preferably, a gain switching circuit is connected between the photodetector and the high frequency amplifier. This gain switching circuit roughly adjusts the amplitude level of the reproduced signal by switching the gain according to the reflection characteristics of the reflection medium and amplifying the detection signal.

More preferably, the optical recording device according to the present invention stores the amplitude level of the reproduced signal at the time when the amplification operation of the high frequency modulation component is interrupted, and starts the laser drive circuit based on the stored amplitude level when the amplification operation is resumed. It is equipped with a return means to do so.

[For production]

According to the present invention, the laser drive circuit drives the laser light source in direct response to the amplitude level of the reproduced signal.

The amplitude level is maintained constant by adjusting the amount of laser beam irradiation so as to cancel out the fluctuations in the amplitude level.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic perspective view showing the overall optical configuration of an optical recording device according to the present invention.

As shown in the figure, the optical recording apparatus according to the present invention includes a laser light source 1 for irradiating a laser beam, a photodetector 2 for receiving and detecting the reflected laser beam, and a laser beam irradiated from the laser light source 1. It has a monitoring photodiode 3 for monitoring. A laser beam emitted from a laser light source 1 is incident in the optical axis direction of an objective lens 7 via a collimator lens 4, a polarizing beam splitter 5, and a mirror 6, and is selected by irradiating a reflective medium 8 on which information is recorded. playback and recording of information. The information recording medium 8 is composed of, for example, an optical disc.

At this time, the objective lens 7 is driven in the vertical and horizontal directions by the actuator 9 to perform focusing and tracking. A portion of the emitted laser beam is separated by a polarizing beam splitter 5 and received by a monitoring photodiode 3 before proceeding to an objective lens 7.

Further, the laser beam reflected by the information recording medium 8 and traveling backward is separated from the incident light by the polarizing beam splitter 5 and received by the photodetector 2. The photodetector 2 photoelectrically converts the reflected laser beam and outputs a corresponding detection signal.

Next, the electrical configuration of the optical recording apparatus according to the present invention will be explained in detail with reference to FIG. As shown, laser light source 1
A laser beam emitted from the information recording medium 8 is irradiated with the laser beam. A photodetector 2 is arranged to receive a laser beam modulated and reflected according to information recorded on the medium 8. The photodetector 2 photoelectrically converts the reflected laser beam and outputs a detection signal containing a high frequency modulation component according to the information.

For example, when information is recorded in the form of a pit string, such as on an optical disk, the light intensity of a laser beam is modulated and reflected according to the reflectance of each pit. Furthermore, in the case of a magneto-optical disk, modulation and reflection regarding the deflection angle of the laser beam is performed depending on the magnetization direction of the information recording domain array. A high frequency amplifier 10 is connected to the photodetector 2 . The high frequency amplifier 10 receives the detection signal I7 and selectively amplifies only the high frequency modulation component thereof, thereby outputting an AC output signal, that is, a reproduction signal having a predetermined amplitude level. High frequency amplifier 1
A demodulation circuit 11 is connected to the demodulation circuit 11, which converts each peak value of the peak sequence of the AC reproduction signal into binary values and outputs the corresponding pulse data. The pulse data is then used to read information recorded on the medium 8.

Further, an amplitude detection circuit 12 is connected to the high frequency amplifier 10, and detects the amplitude level of the AC reproduction signal.

Then, a reference voltage proportional to the detected amplitude level is output. A laser drive circuit 13 is connected to the amplitude detection circuit 12 . The laser drive circuit 13 drives the laser light source 1 in response to a reference voltage proportional to the amplitude level of the reproduced signal, and automatically adjusts the amount of laser beam irradiation.

Preferably, a gain switching circuit 14 is inserted between the photodetector 2 and the high frequency amplifier 10. The gain switching circuit I4 is for switching the gain according to the reflection characteristics of the information recording medium 8 and amplifying the detection signal. For example, if the information recording medium 8 is an optical disk, the gain is set to 1, and if the information recording medium 8 is a magneto-optical disk, the gain is set to 3 because the reflectance is about 30% compared to an optical disk.
Switch to double. In this manner, the amplitude level of the reproduced signal is roughly adjusted by adjusting the gain according to the light reflection characteristics of the information recording medium. A register 15 is connected to the gain switching circuit 14 and temporarily stores the gain to be set in the gain switching circuit 14. A microprocessor 16 is connected to the register I5, and stores an appropriate gain value in the register 15 depending on the type of information recording medium mounted on the optical recording apparatus. For example, Xl72
．． The value 0 of Xl, X2, etc. is selectively stored to perform substantially semi-fixed switching. This makes it possible to avoid complicating circuits and storage means.

FIG. 3 is a block diagram showing the detailed circuit configuration of the laser drive circuit 13. The laser drive circuit 13 has a monitor means for receiving a part of the laser beam emitted from the laser light source 1 made of a laser diode or the like and outputting a monitor voltage according to the amount of the light. The monitoring means is composed of a monitoring photodiode 3 for receiving a laser beam and outputting a corresponding photocurrent, and a current-voltage conversion circuit 17 for converting the photocurrent into a current-voltage and outputting a corresponding monitor voltage. . The laser drive circuit 13 further includes an automatic light amount control circuit 18, whose negative input terminal receives a monitor voltage supply, whose positive input terminal receives a reference voltage supply, and whose output terminal constitutes the laser light source 1. connected to the anode terminal of the laser diode. The automatic light amount control circuit 18 supplies a driving current to the laser diode based on the result of comparing the reference voltage and the monitor voltage.

Next, the operation of the information reproducing system of the optical recording apparatus shown in FIGS. 2 and 3 will be explained in detail. A detection signal containing a high frequency modulation component outputted by the photodetector 2 is adjusted to an appropriate gain by a gain switching circuit 14. The gain is switched in multiple stages by the microprocessor 16 via the register 15 and set to an appropriate value. That is, when the amount of reflected light of the laser beam is small, a relatively large gain is set, and when the reflectance is large, a relatively small gain is set.
The output level of the detection signal amplified by j( is roughly adjusted so that it is close to the target value. This gain switching circuit 14 simply has the function of switching the gain in multiple stages, so it is not a conventional AGC circuit. It is inexpensive and has a simple structure compared to the above.If such a gain switching circuit 14 is not used, the amplitude fluctuation range of the detection signal becomes large, and if the laser drive circuit is controlled according to this large fluctuation range, the laser light source 1, there is a risk that excessive light emission may occur, and there is a risk that information recorded on the information recording medium 8 may be destroyed.

Therefore, by inserting the gain switching circuit 14, the range of amplitude variation of the 1 2 detection signal is reduced in advance, thereby making it possible to reduce the range of adjustment of the amount of laser beam irradiation. However, the gain switching circuit is not necessarily required when only information recording media guaranteed to always have a constant reflectance are handled.

The detection signal roughly adjusted in advance by the gain switching circuit 14 is amplified by the high frequency amplifier 10. High frequency amplifier I
O has a function of selectively amplifying only the high frequency modulation component included in the detection signal. As a result, an AC reproduction signal having a predetermined amplitude level is output. The AC reproduction signal is input to the demodulation circuit 11, which performs binary conversion according to the individual peak levels of the peak sequence included in the reproduction signal, outputs pulse data, and reads out the information recorded on the medium 8.

Since the binary conversion in the demodulation circuit 11 is performed based on the difference between the individual peak levels, it is necessary to keep the amplitude level of the reproduced transmission constant. For this reason, the reproduced signal is input to the amplitude detection circuit (2), and the amplitude level of the reproduced signal is detected.Then, a reference voltage proportional to the amplitude level is output.Furthermore, the laser drive circuit 13 is The amount of light irradiated by the laser beam is adjusted so as to cancel out fluctuations in the amplitude level.As a result, the amplitude level of the reproduced signal can be kept constant.Specifically, the automatic light amount control built in the laser drive circuit 13 Circuit 18 (APC circuit) operates,
Drive power is supplied to the laser light source 1 based on the result of comparing the reference voltage and the monitor voltage, and servo control is performed so that the amplitude level of the reproduced signal is always constant.

FIG. 4 is a circuit block diagram showing another embodiment of the present invention. In FIG. 4, the same reference numerals are given to the same components as in the embodiment shown in FIG. 2, and detailed explanation thereof will be omitted. In the embodiment shown in FIG. 4, the amplitude detection circuit 12 is not directly connected to the laser drive circuit i3. Instead, an A/D converter 17 is inserted between the amplitude detection circuit 12 and the microprocessor 16, and a D/A converter 18 is inserted between the microprocessor 16 and the laser drive circuit 13. The A/D converter 17 outputs the reference tl(
(TIIiLl:) 3 4 Convert it to the corresponding digital data and microprocessor 1
Supply to 6. The microprocessor 16 temporarily holds such digital data and supplies it to the D/A converter 18 as needed. The D/A converter 18 converts the digital data back into a reference voltage and supplies it to the laser drive circuit 13.

Next, the operation of the embodiment shown in FIG. 4 will be explained in detail. There are cases where the reading operation of the optical recording device is temporarily stopped and the information writing operation is started. At this time, the high frequency modulation component amplification operation of the information reproducing system shown in FIG. 4 is interrupted. The microprocessor 16 temporarily stores the amplitude level of the reproduced signal at the time of interruption as digital data. Subsequently, when the information write operation is completed and the information read operation begins, the high frequency amplification operation is resumed. At this time, the amplitude level temporarily stored in the microprocessor 16 is given to the laser drive circuit 13 as an initial value based on the stored digital data. As a result, the laser drive circuit 13 can be started quickly. On the other hand, conventional AGC circuits have a problem in that when this operation is interrupted, the state after recovery becomes temporarily unstable for a while.

A preferred embodiment of the present invention has been described above in detail using an information reproducing system as an example. However, the present invention is not limited thereto, and can be widely applied to cases in which the amplitude level of an output signal obtained by selectively amplifying a high frequency signal component included in a detection signal is maintained constant.

〔Effect of the invention〕

As described above, according to the present invention, the amplitude level of the reproduced signal is directly fed back to the laser drive circuit 13 to control the amount of irradiation light of the laser beam so that the amplitude level of the reproduced signal is constant. There is. Therefore, there is an effect that the expensive and complicated AGC circuit as in the prior art can be removed. Furthermore, since the present invention is a method for controlling the amount of laser beam irradiation, even if there is a risk that the amplitude level of the reproduced signal will decrease due to attenuation of the amount of reflected light, it is possible to increase the amount of laser beam irradiation as desired by the city. It is possible to maintain the amount of reflected light of "f", and it is possible to maintain the information +'l:6 S/N ratio of the L system.

Furthermore, in general, in optical recording devices, servo signals for forcing and tracking the laser beam spot are also obtained from the reflected light, but this servo signal can also be maintained at an appropriate level by the above-mentioned stabilizing effect on the amount of reflected light. can.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing the overall optical configuration of an optical recording device according to the present invention, FIG. 2 is a circuit block diagram showing an embodiment of the optical recording device according to the present invention, and FIG. FIG. 2 is a detailed circuit block diagram of the laser drive circuit shown in FIG. 2, FIG. 4 is a circuit block diagram showing another embodiment of the optical recording device according to the present invention, and FIG. FIG. 1... Laser light source 2... Photodetector 3...
・Monitoring photodiode 8...information recording medium 】0...high frequency amplifier 11...demodulation circuit 12...amplitude detection circuit 13...laser drive circuit]4...gain switching circuit 16...・Microprocessor 18...Automatic light amount control circuit

Claims (1)

[Claims] 1. A laser light source for irradiating a laser beam onto a reflective medium, a photodetector that photoelectrically converts the laser beam modulated and reflected by the reflective medium and outputs a detection signal containing a high frequency modulation component; A high-frequency amplifier that inputs a detection signal and selectively amplifies its high-frequency modulation component to output an output signal having a predetermined amplitude level, and a high-frequency amplifier that drives a laser light source in response to the amplitude level of the output signal to fluctuate the amplitude level. An optical device comprising a laser drive circuit for keeping the amplitude level constant by adjusting the amount of laser beam irradiation so as to cancel out the amplitude. 2. The laser drive circuit includes a monitor means that receives a laser beam emitted from a laser light source and outputs a monitor voltage according to the amount of light, and a monitor voltage that is based on the result of comparing the monitor voltage with a reference voltage according to the amplitude level of the output signal. 2. The optical device according to claim 1, further comprising automatic light amount control means for supplying driving power to the laser light source. 3. It has a gain switching circuit connected between the photodetector and the high-frequency amplifier to roughly adjust the amplitude level of the output signal by switching the gain according to the reflection characteristics of the reflecting medium and amplifying the detection signal. The optical device according to claim 1. 4. According to claim 1, further comprising a return means for storing the amplitude level of the output signal at the time when the amplification operation of the high frequency modulation component was interrupted and starting the laser drive circuit based on the stored amplitude level when the amplification operation is resumed. The optical device described. 5. The optical device outputs an output signal for information reproduction by irradiating a laser beam onto a reflective medium on which information is recorded and selectively amplifying a high frequency modulation component according to the information. optical device.