JPH02108248A - Output controller for laser light emitting element - Google Patents

Abstract

PURPOSE:To attain the emission of a laser light emitting element with an optimum writing power by holding the bottom value of the high frequency component of the output signal of an output detecting means at the time of writing, passing through a low frequency component and outputting it to a low frequency driving circuit part. CONSTITUTION:A laser beam emitted from an LD 1 by a writing data signal 24 is monitored by a PD 2, the signal is bottom-held through an amplifier 4 with a high frequency bottom circuit BH 5 and a low frequency component only is transmitted. The signal is integrated by an integrator 8 so that the difference in the set bottom voltage can become 0 with a differential amplifier 7 and the LD 1 is driven through an amplifier 9. On the other hand, the peak value of the writing current from an amplifier 13 at the time of writing is peak-held with a peak holding circuit PH 6. The output is stored through an A/D converter 10, the difference in a peak setting data signal 23 for a writing power occurs through a D/A converter 11 by a differential amplifier 12 and the LD 1 is controlled through a current driving amplifier 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output control device for a light emitting element such as a laser diode used in a write-once (write-once type) or erasable optical disk memory device.

[Prior Art] In the laser diode used in such an optical disk device, the applied current is ■. The power 20 of the output light with respect to P varies greatly, temperature changes are large, and the laser diode itself generates heat, deteriorates, and changes over time. Therefore, in order to emit light with a constant power and prevent damage to the laser itself, automatic power control (hereinafter referred to as
APC (abbreviated as Auto Power Control) is carried out. In the case of a writable optical disc device, it is necessary to perform the above-mentioned APC and modulate with a high frequency (500 KH2 to IOM) lz) at the time of writing. Further, the laser light power is normally about 1 mW at the medium surface when reading data, and 5 to 10 mW at the peak during data writing and erasing.

[Problems to be Solved by the Invention] In these conventional laser output controls, APC is performed at a low frequency, and when writing at a high frequency, a modulation current with a constant peak is added to the low frequency APC and the laser output is There is a method of superimposing it on a diode and injecting an offset of the APC due to the high frequency component. However, this method has the disadvantage that the laser diode (hereinafter abbreviated as LD) is unstable as described above, so that the write power is likely to fluctuate and the LD is likely to deteriorate or be destroyed.

In addition, the low frequency component of the amount of light emission changes depending on the duty of the pulse during writing, which poses a problem that accurate control is difficult.

Furthermore, in order to prevent damage to the LD and to prevent it from being affected by duty, it is known to hold the light intensity voltage at its peak and apply APC, but this method also has problems with transient response at the start of writing. there were. In addition, the bottom level of the light amount waveform during writing cannot be controlled, and the servo state of focus and track changes between writing and other times, resulting in servo instability.

Therefore, the present invention performs APC in all peak and bottom states during data reading, erasing, and writing.
It is an object of the present invention to propose an output control device for a laser emitting element such as an LD, which can reduce deterioration of the laser emitting element such as an LD and protect it from destruction, and at the same time stabilize focus and track servos.

Another object of the present invention is to propose an output control device for a laser light emitting element that enables the laser light emitting element to emit light with optimal write power from the initial stage of writing.

[Means for Achieving the Object] A laser light emitting element output control device of the present invention for achieving the above object is a device that controls the drive of a laser light emitting element of an optical disk device in which data can be written by light amount feedback control. A first laser drive circuit section that drives the light emitting element in a low frequency range, a second laser drive circuit section that drives the light emitting element in a high frequency range during data writing, and a second laser drive circuit section that drives the output of the light emitting element. An output detection means for detecting is connected between the detection means and the first laser drive circuit section, receives the output of the output detection means, holds the bottom value of the high frequency component of this output signal, and detects the low frequency component. It is characterized by comprising a control circuit section that allows the component to pass through and outputs it to the first laser drive circuit section.

According to this configuration, the high frequency component of the output of the output detection means during writing is held at the bottom, thereby stabilizing the laser output power on the bottom side.

In order to achieve another object, the present invention provides a device for controlling the drive of a laser light emitting element of an optical disk device in which data can be written using light amount feedback control, in which a first laser light emitting element for driving the light emitting element in a low frequency range is provided. a second laser drive circuit section that drives the light emitting element in a high frequency range during data writing; an output detection means that detects the output of the light emitting element; a control circuit unit connected between the second laser drive circuit unit, which receives the output of the output detection means, holds the peak value of the output signal as a digital value, and outputs the peak value to the second laser drive circuit unit; It is characterized by having the following.

With this configuration, it is possible to receive the output of the output detection means and hold the peak value of this output signal as a digital value, to hold the peak level at the time of the latest write, and to write at the optimum power from the time of writing start. I can do things.

[Examples] Examples according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an overall diagram of a control system of a power control device according to an embodiment. In the same figure, 1 is an LD (=laser).
The package includes an LD light emitting section 1a and an internal bin photodiode lb for optical monitoring. FIG. 2 is a diagram showing the configuration of an optical head to which the control device of FIG. 1 is applied. In Fig. 2, numeral 31 is a 4-split detector, for servo,
Used for reading data. 36 is an optical disk medium. The laser beam exiting the LD assembly 1 passes through a collimating lens 32, a circular correction prism and beam splitter 33, and an objective lens 34, and is irradiated onto a disk surface 36. The reflected light from the disk 36 includes data information, tracking information, focus information, and the like. This reflected light passes through the condensing lens 34 and then passes through the beam splitter 3.
3, and is irradiated onto the detector 31 by the focus/track error detection optical systems 35a and 35b. A circuit for tracking and focusing is shown in FIG. 4, and this circuit will be described later.
2 in the figure is an external bin photodiode for externally monitoring the light amount of the LDI.

The laser beam emitted from the LD assembly 1 is transmitted to the optical system 32.
．． 33 and enters the external photodiode 2 for monitoring. A photocurrent corresponding to the amount of light emitted from the LD generated by the photodiode 2 is converted into a voltage by a resistor 3, and then converted by a light amount-voltage conversion normalization amplifier 4 into a voltage value normalized by the amount of light on the medium surface. It is assumed that the gain of this normalized amplifier 4 is adjusted for each head in FIG. 2 according to the efficiency of the optical system and variations in the characteristics of the photodiode 2. The output of the normalization amplifier 4 is connected to a high frequency bottom hold circuit (BH) 5 and a peak hold circuit PH6. BH5 is the write frequency (1 in 500
12 or more), the bottom component of the input signal is held and this bottom component is output. Furthermore, at low frequencies below the writing frequency, the input signal is passed through as is. This BH circuit is composed of, for example, a hold circuit using a capacitor that integrates the output signal of the amplifier 4, and the time constant of this capacitor is set such that the bottom value is held in the capacitor in the high frequency region, and is quickly discharged in the low frequency region. Set it so that

Therefore, the output of BH5 is the write frequency (500KH
, and above), it is the bottom component of the input signal, and at low frequencies below the writing frequency, it is the input signal itself. Regarding the bottom setting data, almost the same data is set when reading and writing, and when erasing, relatively thick data is set in order to increase the power of the LDI (see (Fig. 3)). f)).

The output of BH5 is input to a differential amplifier (DIF) 7.

The other input of DIF7 is the LD during read, erase, and write.
This is a bottom setting data signal which is data for setting the power of I. This setting data 21 is subjected to DA conversion by a DA converter 19 and input to the DIF 7. D.I.
F7 outputs the difference (error voltage) between the amount of light monitored by the diode 2 and the amount of light preset from the outside. The output of DIF7 is connected to an integrating amplifier (INT)8. The output of INT8 is the integral value of the voltage of DIF7. The output of the INT8 passes through a current drive amplifier 9 and drives the diode of the LD light emitting section 1a at a low frequency. INT8 takes a value such that the integrated value of the voltage of DIF7 is such that the light amount of LDl is controlled so that the output of DIF7 becomes zero, while the LD on/off control signal 8a is input to INT8. There is. This on/off control signal not only turns the LD ON10FF, but also forces the integral amount of INT8 to protect the LDI when the internal monitor photodiode output exceeds a certain level, as described later. It works to make it zero. Actually, I
The amount of charge of a capacitor (not shown) in the NTS is made zero, and the output of the amplifier 9 is made zero.

The PH6 output, which is the peak value of the externally monitored light intensity of the LDI, is digitized and stored in the AD converter (AD) 10, and then transferred to the DA converter (DA) 1.
1 and is input to a differential amplifier (DIF) 12. A
DIO and DAII are controlled by the write power gate signal 22 so that they are operated only during writing. D.I.
Another input to the FI2 is a write power peak setting data signal 23 for setting the peak light amount during writing. This data (digital value) is sent to the DA converter 20
The signal is converted into an analog signal via the DIF 12, and is input to the DIF 12. The output of the DIF 12 is converted into a current by a current drive amplifier 13, switched by a write data signal 24, and applied to the LD issuing section 1a. Note that the operation of PH6 is similar to BH5 in circuit terms, although there is a difference in whether a peak component or a bottom component is extracted.

The LD ion off control signal input to INT8 will be explained. The output of the bin photodiode ib in the LD assembly l is converted into a voltage by a resistor 14, and then converted into a voltage value normalized to the amount of light by a differential normalization amplifier 15, similar to the amplifier 4 described above. Ru. The output of the amplifier 15 is input to a comparator (CMP) 16. CMP1
The other input of 6 is the LD set by resistor 26.
power restriction level 16a. photodiode l
If the amount of light monitored by b exceeds this limit, the CM
The output of P16 is inverted and the flip-flop (F, /F
) 17 is reversed. The output of F/F 17 is connected to AND gate 18, and when the amount of light exceeds the limit level,
It functions to turn off the LDI.

According to the timing chart of FIG. 3, the voltages, currents, and waveforms of each part of the embodiment of FIG. 1 will be explained.

- mode When reading data, the light amount-voltage signal output from the amplifier 4 has a low frequency. Therefore, this low frequency signal passes through BH5 and is input to DIF7. In DIF7, the output of DIF7, which is the difference between this input and the power setting voltage (bottom setting data 21) at the time of reading, is integrated by INT8 so that it becomes O volts, and the LDI is driven by the drive amplifier 9 (Fig. 3). (see (g)). In the read mode, the write power gate signal 22 is off, but a digital peak hold value is held in a buffer (not shown) of the DA converter 11. Since the write data 24 is also off, there is no current output from the drive amplifier 13, as shown in FIG. 3(h).

Write mode data When writing data, the data of the bottom setting data 21 is set to be the same as when reading. The output of the drive amplifier 13 is an on/off current that is switched in accordance with the write data signal 24 (see (h) in FIG. 3 in the write mode). The laser light emitted from the LDI with the write data signal is monitored by the photodiode 2, and the signal passes through the amplifier 4 and is monitored as a voltage.
5, the high frequency components are bottom held and only the low frequency branch components are passed. Therefore, even when writing, D
IF7. INT8. Amplifier 9 operates almost in the same way as when reading.

At the time of writing, the peak value of the write current from the amplifier 13 is determined by the digital peak held voltage at PH6 detected at the last write or during test light emission when the power is turned on.

The write power gate signal 22 is PH6 after the start of writing.
It turns on after the time has passed until it reaches a stable point, and then it turns on until the end of the write ((d) in Figure 3).
). In ADIO and DAll, during this time, the digital peak hold voltage is rewritten with the latest peak data. After the write is completed, the peak value is held as a digital value until the next write.

Erase mode゛Tell me.

During erasing, the bottom power is set by the bottom setting data signal. At the same time, the write data signal 24 is turned on with direct current (continuous "1"). Erase power is usually at the same level as write power, or slightly higher. At this time, the weight increase relative to the write power is determined as follows. APC is performed so that a current flows due to the output of the drive amplifier 13, and the increased current flows through the drive amplifier 9 to provide erase power (see (g) and (h) in FIG. 3). The current change on the drive amplifier 9 side is a little delayed compared to the amplifier 13 side because of the INT8, but by doing the above, only the difference between the erase power level and the write power level becomes a slow response, and the constant of integration By selecting , you can follow it without any problems.

FIG. 4 is a servo circuit diagram for tracking and focusing. In the figure, numeral 31 is the four-split detector shown in Fig. 1, numerals 102 to 105 are summing amplifiers that add the two outputs of the Deichiku 31, and numerals 106 to 109 pass the low frequency component, but the bottom component is removed in the high frequency band. Hold B
In the H circuit, 110 is a differential amplifier (DIF) for focus error signals, and 111 is a differential amplifier (DIF) for track error signals. Reference numerals 112 and 113 are variable gain amplifiers, respectively, which amplify the focus error signal and the track error signal. The data input to the amplifiers 112 and 113 is data for changing the gains of these amplifiers. 118 and 119 are coil drive amplifiers, respectively, and each of them is a coil drive amplifier for focusing.
20. Drive the track coil 121.

In write mode, the data 114 and 115 for changing the gain are changed according to information on the reflectance of the medium and the read/brace level, instead of the conventional linear AGC, in order to apply servo only at the bottom power level. , select from several types of gains.

The embodiment described above provides the following effects.

(2): When data is written, the power of the LDI is controlled by holding the peak value, thereby preventing damage and deterioration of the LD due to power overflow, and also preventing write errors due to power drop.

■: In the peak hold circuit, AD and DA conversion (10, 11) are equipped with a digital memory function for the peak hold value, so that the peak level at the latest write is held and the optimum level is maintained from the start of the write. I was able to light it with power.

(2): It is said that when writing data, when the LDI is at high power, the focus and track servo signals are easily distorted. In particular, this effect is large for media of the hole type (bit forming type).

However, in the embodiment of FIG. 1, by providing a bottom hold circuit, the bottom power during writing is also stabilized.

In addition, in combination with sub-circuits as shown in Figure 4,
Stable focus servo and track servo are possible that are not affected by changes in power during writing. moreover,
As explained in connection with FIG. 4, the amplifier is capable of varying several types of gain depending on the reflectance of the medium and the level difference between reading and erasing, so expensive linear AGC ( (auto gain control).

In addition, we propose the following modification example.

■: When in erase mode In the explanation, if there is no effect on the delay in current change on the amplifier 9 side, for example, when the optical disc is rotating at a low speed, no current flows on the amplifier 13 side during erasing, and only on the amplifier 9 side. You can go there.

(2): In the embodiment shown in FIG. 1, a diode 2 for external monitoring was used to eliminate power fluctuations due to returned light. If the influence of the returned light is small, the diode 2 may be used as the diode and the diode 1b.

[Brief explanation of drawings]

FIG. 1 is an overall view of a laser diode output control device according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of an optical head to which the control device of the embodiment of FIG. 1 is applied, and FIG. FIG. 1 is a diagram for explaining the operation of the embodiment, and FIG. 4 is a circuit diagram of a servo circuit to which the control device of the embodiment of FIG. 1 is applied. In the figure, 1... Semiconductor laser assembly, 1a... Semiconductor laser light emitting unit, lb... Built-in bin photodiode for optical monitoring, 2... External bin photodiode for optical monitoring, 3... Photocurrent Electron positive conversion resistor, 4... Light amount-voltage standardization amplifier, 5... High frequency bottom hold circuit,
6...Peak hold circuit, 7...Differential amplifier, 8
... Integrating amplifier, 8a... LD on/off control signal, 9... Current drive amplifier, 10... AD converter, 11... DA converter, 12... Differential amplifier, 13. ... Current drive amplifier, 14... Photocurrent-voltage conversion resistor, 15... Light amount-voltage standardization amplifier, 16... Comparator, 17... Flip-flop, 18... AND gate, 19 ...DA converter, 20.-DA converter, 21.. Bottom power setting data signal, 22.. Write power gate signal, 23.. Write power setting data signal, 24..
・Write data signal, 25...LD ion off signal,
31... Quadrant detector, 32... Collimating lens, 33... Perfect circle correction prism and beam splitter, 34... Objective lens, 35a, 35b... Focus/track error detection optical system, 36...・・Disk, 102-105-・Additional amplifier, 106-109・
...High frequency bottom hold circuit, 110...Differential amplifier, 111...Differential amplifier, 112.113...Variable gain amplifier, 114.115...Data for variable gain, 116,117... Phase compensation circuit, 118.1
．． 1.9...Coil drive amplifier, 120...
- Focus coil, 121... Track coil. Figure 2

Claims (4)

[Claims] (1) A device that controls the drive of a laser light emitting element of an optical disk device in which data can be written by light intensity feedback control, comprising: a first laser drive circuit unit that drives the light emitting element in a low frequency range; , a second laser drive circuit section that drives the light emitting element in a high frequency range, an output detection means that detects the output of the light emitting element, and a second laser drive circuit section that is connected between the detection means and the first laser drive circuit section. and a control circuit section that receives the output of the output detection means, holds the bottom value of the high frequency component of the output signal, passes the low frequency component, and outputs it to the first laser drive circuit section. An output control device for a laser light emitting element, characterized by: (2) The first laser drive circuit section has a threshold value setting means that can be set from the outside, and based on a difference signal between the output signal from the control circuit section and the threshold value set in this setting means, 2. The output control device for a laser light emitting element according to claim 1, wherein the apparatus controls the drive of a laser light emitting element. (3) Output control of the laser emitting device according to claim 2, wherein the threshold value set in the threshold value setting means is set according to data reading, data writing, and data erasing. Device. (4) In a device that controls the drive of a laser light emitting element of an optical disk device capable of writing data by light intensity feedback control, a first laser drive circuit unit that drives the light emitting element in a low frequency range; , a second laser drive circuit section that drives the light emitting element in a high frequency range, an output detection means that detects the output of the light emitting element, and a connection between the output detection means and the second laser drive circuit section. and a control circuit section that receives the output of the output detection means, holds the peak value of this output signal as a digital value, and outputs it to the second laser drive circuit section. output control device. (5) The second laser drive circuit section has a threshold value setting means that can be set from the outside, and based on a difference signal between the output signal from the control circuit section and the threshold value set in this setting means, 5. The output control device for a laser light emitting element according to claim 4, wherein the apparatus controls the drive of a laser light emitting element.