JP2009016018A - Optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device capable of generating a monitor signal which is hardly affected by noise even when the power ratio of a mark and a space increases during high-fold speed recording. <P>SOLUTION: A monitor amplifier 6 which extracts laser light emission power as an electric signal is provided with a function of switching gains. Then a large monitor gain is selected for a low-power light emission period corresponding to super-power light emission and then a signal having a large signal amplitude can be transmitted to a signal processing unit even in the low-power light emission period. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus that performs recording and reproduction of an optical disc such as a CD (Compact Disc) and a DVD (Digital Video Disc), and more particularly to a control circuit for an optical disc apparatus that is suitable for high-speed recording on a disc.

  As a medium for recording information data on an optical disc, for example, there are CD and DVD. In recent years, recording / reproduction has been accelerated, and conventionally only the reproduction speed has been the rotational speed limit of the disk, but nowadays the recording speed has become the same as the reproduction speed.

  When recording information on a CD or DVD medium, a mark is formed by irradiating the medium with a high-power laser beam, and a space is formed with a low-power laser beam. When information is reproduced from the recorded medium, the disk is irradiated with a relatively low power laser beam, and the information is read from the difference in reflection of light between the mark and the space.

  In order to perform the reproduction and recording operations stably, control is performed so that the power of the laser beam is constant. This is called APC (Automatic Power Control). A part of the laser light irradiated to the disk is branched and extracted for monitoring, this optical signal is converted into an electric signal, voltage amplified and extracted as a monitor signal, and the voltage value of the monitor signal becomes a desired value. That is, control is applied so that the laser emission power becomes a desired value.

  For example, Japanese Unexamined Patent Application Publication No. 2006-323947 (hereinafter referred to as Patent Document 1) describes conventional techniques related to the operation of APC.

During the recording operation, as described above, the laser light has a high power state and a low power state. In general, the high power portion and low power portion of the monitor signal are sampled and extracted, and control is performed so that each power has a desired value. On the other hand, during the reproduction operation, control is performed so that the light emission is constant and low power. Usually, control is performed so that the low power during recording and the power during reproduction are the same.
JP 2006-323947 A

  While the reproduction power is constant, the recording power increases with the recording speed. The recording power for forming the mark generally increases as the recording speed increases. For this reason, the ratio of mark power to space power is small during low-speed recording, but this ratio increases as the speed increases. For example, in the case of DVD-R, which is a write-once DVD, the reproduction power is 0.7 mW, whereas the power required for high-speed recording is on the order of several tens of mW, which is several tens of times the reproduction power. .

  When the laser emission power is extracted and transmitted as an electrical signal as a monitor signal, the amplitude that can be extracted from the monitor amplifier is limited. For this reason, if the voltage of the high power part at the time of recording is suppressed to a constant value, the signal level of the read power becomes small at high speed. If a small signal is transmitted, it becomes susceptible to noise, and as a result, accurate power control becomes difficult.

  An object of the present invention is to provide an optical disc apparatus capable of generating a monitor signal that is not easily affected by noise even when the power ratio between a mark and a space is increased in high-speed recording.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  The optical disk apparatus according to the present invention includes a light source capable of irradiating a pulsed laser beam having a high light intensity and a pulsed laser beam having a low light intensity, and a monitor amplifier for extracting an electric signal correlated with the light intensity of the laser light. The gain of the monitor amplifier can be switched, and the gain of the monitor amplifier becomes relatively larger than the gain at the time of irradiation of the pulsed laser light having the high light intensity during the irradiation of the pulsed laser light having the low light intensity. It is characterized by.

  The optical disc apparatus further includes a pulse generation circuit for generating the pulsed laser light having the high light intensity and the pulsed laser light having the low light intensity, and the pulsed laser light and the light intensity having the high light intensity. A pulse driver circuit for controlling switching of low-pulsed laser light and switching of the gain of the monitor amplifier may be provided.

  Further, the optical disc apparatus may include a level comparison circuit that compares the internal voltage level in the monitor amplifier with reference to a predetermined voltage level and controls the monitor amplifier.

  The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

  The optical disk apparatus according to the present invention increases the monitor amplitude in a relatively low power period (during recording space and reproduction) even when the mark power and space power ratio increases as in high-speed recording. Therefore, it is resistant to noise and stable power control is possible. Further, since it is not necessary to increase the power supply voltage of the monitor amplifier, it is effective for reducing power consumption.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit configuration diagram showing a configuration of a control circuit of the optical disc apparatus according to the first embodiment of the present invention. In the present embodiment, the control circuit of the optical disk apparatus includes a pulse generation circuit 1, a pulse driver circuit 2, a laser diode driver circuit 3, a laser diode 4 operating as a light source, a monitor diode 5, a monitor amplifier 6, an APC circuit 7, and an FFC ( (Flexible Flat Cable) 8.

  The laser diode driver circuit 3, the laser diode 4, the monitor diode 5, and the monitor amplifier 6 are components mounted on a so-called pickup. The pulse generation circuit 1, the pulse driver circuit 2, and the APC circuit 7 are mounted on a substrate. The pickup has a movable structure for accessing a specific position of the disk, and a line for transmitting a signal between the movable pickup and a substrate (not movable) on which a signal processing circuit such as the APC circuit 7 is mounted. Is FFC8.

  A data signal to be recorded on the disk is converted (encoded) into a signal that can be easily recorded on the disk by the pulse generation circuit 1.

  The signal output from the pulse generation circuit 1 is output via the pulse driver circuit 2 that drives the pulse signal, and is transmitted via the FFC 8 to the pickup on which the laser diode driver circuit 3 is mounted. Two analog signals from the APC circuit 7 are supplied to the laser diode driver circuit 3, and current amplification is performed while controlling the analog information with signals from the pulse driver circuit 2. The laser diode driver circuit 3 supplies a current for causing the laser to emit light to the laser diode 4. The emission intensity of the laser diode 4 changes according to the current supplied from the laser diode driver circuit 3. Laser light 9 emitted from the laser diode 4 is irradiated onto an optical disk (not shown) as a recording medium, and data is recorded and reproduced.

  The optical system is configured such that a part 10 of the optical signal output from the laser diode 4 is irradiated onto the monitor diode 5, and the optical signal is converted into an electrical signal by the monitor diode 5. This electric signal is amplified by the monitor amplifier 6.

  One of the pulse signals input from the pulse driver circuit 2 to the laser diode driver circuit 3 is supplied to the monitor amplifier 6, and the gain of the monitor amplifier 6 is switched by this signal. The output of the monitor amplifier 6 is transmitted from the pickup to the APC circuit 7 on the substrate via the FFC 8.

  In the APC circuit 7, the signal levels at different times are detected by the two detection circuits (first DET11 and second DET12), and the first power control circuit 13 and the second power are set so that the detected levels have predetermined values. Analog signals from the control circuit 14 to the laser diode driver circuit 3 are controlled.

  FIG. 2 is a circuit diagram showing the configuration of the laser diode driver circuit 3 of FIG. Terminals 20 and 21 are input terminals for analog signals supplied from the APC circuit 7, terminals 22 and 23 are input terminals for pulse signals supplied from the pulse driver circuit 2, and terminal 30 is an output terminal of the laser diode driver circuit 3. The laser diode 4 is connected to the terminal 30. The signals at the terminals 20 and 21 are supplied to the first current amplifier 24 and the second current amplifier 25, respectively. Signals supplied to the terminals 22 and 23 are configured to control the switches 26 and 27.

  The laser diode driver circuit of FIG. 2 includes a current amplifier 24 and a subsequent switch 26, a current amplifier 25 and a subsequent switch 27, an adder circuit 28 for adding signals from the two switches, and a current driver 29 subsequent to the adder circuit. Is done. The signal input from the terminal 20 is amplified by the current amplifier 24, turned on / off by the switch 26 and supplied to the adder circuit 28, and the signal input from the terminal 21 is amplified by the current amplifier 25 and turned on / off by the switch 27. Thus, a signal path to be supplied to the adder circuit 28 is provided. Various power modes can be set by the operation of the switches 26 and 27. For example, the two switches are turned off when the laser is not emitted, and the switch 26 is turned on and the switch 27 is turned off during reproduction. When the recording power is high, the two switches are turned on. When the recording power is low, the same switch operation as that during reproduction is performed.

  FIG. 3 is a circuit diagram showing the configuration of the monitor amplifier according to the present embodiment. In FIG. 3, terminals 40 and 46 are a signal input terminal and an output terminal of the monitor amplifier 6, and a terminal 47 is a control signal input terminal for gain switching. The monitor diode 5 is connected to the terminal 40. The monitor amplifier 6 is composed of a two-stage amplifier including a front-stage amplifier (amplifier 41) and a rear-stage amplifier (amplifier 44), and outputs a voltage having a reverse polarity to the power to be monitored.

  The monitor diode 5 is connected to the negative input of the amplifier 41 constituting the preceding amplifier, and the resistor 42 is connected from the output of the amplifier 41 to the negative input. The positive input of the amplifier 41 is connected to the reference voltage Vref, and the current flowing through the monitor diode 5 is converted into a voltage by the resistor 42. The output of the previous amplifier is supplied to the negative input terminal of the amplifier 44 via the resistor 43, and the output of the amplifier 44 is connected to the negative input terminal of the amplifier 44 via the resistor 45. When the gain of the amplifier 44 is sufficiently large, the gain of the post-stage amplifier is represented by (− (resistance value of the resistor 45) / (resistance value of the resistor 43)).

  In the above configuration, when the gain of the monitor amplifier is switched, one of the resistance values of the resistor 42, the resistor 43, and the resistor 45 may be switched. In FIG. 3, the resistance of the resistor 45 is switched in response to the input of the pulse driver.

  In general, the monitor amplifier is composed of an integrated circuit. A general feature of an integrated circuit is that the absolute accuracy of a resistor is not good, but the specific accuracy (relative accuracy) of a certain resistor is good. By utilizing this and preparing two resistors and selectively using them, it is possible to easily switch the gain ratio accuracy. At this time, instead of switching the resistance value that determines the gain, two amplifiers having different gains may be prepared and the output may be switched.

  In general, a monitor amplifier is often adjusted for conversion gain. That is, if the monitor sensitivity with respect to the power applied to the disk is adjusted to a constant value, the power applied to the disk can be converted from the output voltage of the monitor amplifier, and the operating power can be adjusted as a whole. For this purpose, even in a general monitor amplifier, a component corresponding to the resistor 43 is often a semi-fixed resistor outside the integrated circuit. In this case, a configuration may be adopted in which the component is switched to a component corresponding to the resistor 45. In this way, gain adjustment and accurate gain switching are possible. The same applies to the present invention.

  The above is the outline of the circuit configuration, and a more detailed operation will be described with reference to the drawings.

  FIG. 4 is a characteristic diagram showing the relationship between the current (Ild) of the laser diode 4 and the light emission power (Pld) of the laser diode 4. In the figure, when the input current to the laser diode 4 exceeds the threshold current (Ith), the laser diode 4 starts to emit light. Generally, at the time of recording, it is necessary to make the light emission power into a pulse waveform, which is realized by switching the current to the laser diode 4 at high speed.

  For DVD-R high-speed recording, a castle type recording waveform is generally used. However, here, for the sake of simplicity, description will be made with binary values of P1 (low power) and P2 (high power).

  A mark is formed at a high power (P2), while a mark is not formed at a low power (P1), resulting in a space. This low power (P1) is generally controlled to be the same value as the power (Read Power) during reproduction. During recording, high power (P2) and low power (P1) are repeated, but during reproduction, low power (P1) continues. In the example of FIG. 4, the laser current I1 at the time of low power and the current at the time of high power is (I1 + I2). When the temperature changes, the laser current and power characteristics shown in FIG. 4 change. Therefore, the laser current is changed and controlled so as to obtain a constant power.

  5A and 5B show waveforms of each part, where FIG. 5A shows two signals from the pulse driver circuit 2, FIG. 5B shows the current of the laser diode 4, FIG. 5C shows the emission power of the laser diode 4, and FIG. The output of the monitor amplifier 6 is shown.

  Two signals (SW1, SW2) from the pulse driver circuit shown in (a) are signals for controlling the two switches 26, 27 of the laser diode driver circuit 3, and generate two power states of low power and high power. This is a control signal. In these, the current I1 in FIG. 4 is controlled by the switch 26 (here, always High), and the current I2 is controlled by the switch 27. When the power is low, the current I1 is supplied to the laser diode 4, and when the power is high, the current (I1 + I2) is supplied. As a result, the current shown in (b) flows through the laser, and the emission waveform shown in (c) is obtained. The output of the monitor amplifier shown in (d) is output with a reverse polarity with respect to the power.

  As shown in FIG. 1, since a part of the laser emission is supplied to the monitor diode 5, information proportional to the laser emission waveform is supplied to the monitor diode 5. The monitor amplifier 6 operates to amplify the current of the monitor diode 5. However, when there is no gain switching as in the prior art, the current of the monitor diode is simply amplified. The output waveform 6 is as shown in FIG. On the other hand, what is indicated by a broken line is an operation waveform of a conventional circuit in which the gain of the monitor amplifier 6 is not switched. While the voltage at the time of low power of the conventional circuit is V1 ′, in the present invention, the gain of the monitor amplifier is controlled to be high at the time of low power light emission, so that it will be indicated by the solid line voltage V1. A large voltage waveform.

  The monitor signal output from the monitor amplifier 6 and transmitted to the substrate via the FFC 8 is a signal level at the detection circuit (first DET11, second DET12) of the APC circuit 7 where the low power part and the high power part are, for example, sampled by a sample hold circuit. Is detected. A loop for controlling the laser diode current is configured so that the signal level becomes a predetermined value, and control is automatically performed so as to have a constant light emission power. In the present invention, as shown in FIG. 5D, a large signal can be transmitted even during low power emission.

  In general, an analog amplifier circuit such as the monitor amplifier 6 has a limited voltage value that can be output while maintaining linearity. However, since the power required for recording increases as the speed increases, it is necessary to reduce the gain of the monitor amplifier 6 in order to transmit within a limited voltage. On the other hand, since the low power at the time of recording is generally set to a constant power required at the time of reproduction, if the gain of the monitor amplifier 6 is reduced, it will be reduced accordingly. As a result, in the case of the conventional method, the signal level becomes small, so that it is easy to receive crosstalk from other signals on the FFC or on the signal processing board, resulting in an error in the detected signal. Thus, stable power control becomes difficult.

  On the other hand, in the present invention, the gain can be improved and transmitted as a large signal during the low power period during recording and during reproduction, so that the influence of interference from other signals can be reduced and stable power control is possible. It becomes. Also, when control is performed so that the low power during recording and the power during playback are the same, the gain for the low power during recording and the power during playback is increased in the same way. APC operates stably.

  By adopting the above configuration and operation, it is possible to obtain a large monitor gain during a low power emission period corresponding to light emission with space power, and to transmit it to the signal processing unit with a large signal amplitude even during the low power emission period.

(Second Embodiment)
FIG. 6 is a circuit configuration diagram showing the configuration of the control circuit of the optical disc apparatus according to the second embodiment of the present invention. FIG. 7 is a circuit diagram showing the configuration of the monitor amplifier and its peripheral circuits in the second embodiment of the present invention. In the first embodiment, a gain switching operation is performed based on a control signal from the outside (pulse driver circuit 2). In the present embodiment, a level comparison circuit 52 that detects a signal level is provided, and the above detection is performed. The gain is switched according to the output of the circuit. In the following description, the same reference numerals are given to components that operate in the same manner as in the first embodiment, and detailed description thereof is omitted.

  In the monitor amplifier 61, a level comparison circuit 52, which is a peripheral circuit, is added to the output destination of the amplifier 41, which is a previous stage amplifier. A comparison voltage 51 is applied to one input terminal of the level comparison circuit 52.

  The comparison voltage 51 and the output of the amplifier 41 are level-compared. Then, the signal from the level comparison circuit 52 is input to the gain switching control input terminal 47. A gain switching function can be realized by switching the value of the resistor 45 using the signal input to the gain switching control input terminal 47. In this embodiment, the resistor 43 may be controlled.

  FIG. 8 shows waveforms at various parts in FIG. FIG. 8H shows the output waveform of the pre-stage amplifier. This signal is input to the level comparison circuit, and the output of the comparison voltage 51 is compared with the voltage. The output signal of the comparison circuit shown in FIG. 8 (i) outputs a High pulse at a level higher than the comparison voltage, and the gain of the monitor amplifier is switched by this output signal. ), The gain in the low power period increases.

  In this embodiment, since the power ratio between high power and low power at the time of recording is large, the amplitude difference of the comparison circuit input also increases, so that the amplitude is not erroneously detected.

  In the embodiment of FIG. 7, since the monitor gain switching signal can be self-generated, there is no need to supply a special switching signal from another, which is advantageous for downsizing and cost reduction of the apparatus.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention can be mainly applied to a control circuit of an optical disc apparatus that performs high-speed recording, but is not necessarily limited thereto. As long as it is necessary to control the light emitting module in the high power state and the low power state, the present invention is applicable not only to the optical disc apparatus.

FIG. 2 is a circuit configuration diagram showing a configuration of a control circuit of the optical disc apparatus according to the first embodiment of the present invention. It is a circuit diagram which shows the structure of the laser diode driver circuit in connection with the 1st Embodiment of this invention. 1 is a circuit configuration diagram of a monitor amplifier according to a first embodiment of the present invention. It is a graph showing the characteristic of the laser diode in connection with this invention. It is a wave form diagram for demonstrating the operation | movement of the 1st Embodiment of this invention. It is a circuit block diagram which shows the structure of the control circuit of the optical disk apparatus in connection with the 2nd Embodiment of this invention. It is a circuit block diagram of the monitor amplifier in connection with the 2nd Embodiment of this invention. It is a wave form diagram for demonstrating the operation | movement of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pulse generation circuit, 2 ... Pulse driver circuit, 3 ... Laser diode driver circuit, 4 ... Laser diode, 5 ... Monitor diode, 6 ... Monitor amplifier, 7 ... APC circuit, 8 ... FFC, 11 ... 1st DET, 12 ... 2nd DET, 13 ... 1st power control circuit,
14 ... second power control circuit, 24 ... first current amplifier, 25 ... second current amplifier,
26 ... switch, 27 ... switch, 28 ... adder circuit, 29 ... current driver,
DESCRIPTION OF SYMBOLS 41 ... Amplifier, 42 ... Resistance, 43 ... Resistance, 44 ... Amplifier, 45 ... Resistance, 51 ... Comparison voltage, 52 ... Level comparison circuit

Claims (3)

A light source capable of irradiating pulsed laser light with high light intensity and pulsed laser light with low light intensity;
In an optical disc apparatus including a monitor amplifier that takes out as an electrical signal correlated with the light intensity of the laser light,
The gain of the monitor amplifier is switchable, and the gain of the monitor amplifier is relatively larger than the gain at the time of irradiation of the pulsed laser light having the high light intensity during the irradiation of the pulsed laser light having the low light intensity. An optical disc apparatus characterized by comprising: The optical disc apparatus according to claim 1,
Furthermore, a pulse generation circuit for generating the pulsed laser light having the high light intensity and the pulsed laser light having the low light intensity;
An optical disc apparatus comprising a pulse driver circuit for controlling switching of the pulsed laser light having a high light intensity and the pulsed laser light having a low light intensity and switching of the gain of the monitor amplifier. The optical disc apparatus according to claim 1,
An optical disk apparatus further comprising a level comparison circuit for comparing the internal voltage levels in the monitor amplifier with reference to a predetermined voltage level and controlling the monitor amplifier.

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