JPH05299738A - Laser-diode control circuit and optical-disk driving device - Google Patents

Abstract

PURPOSE:To keep a modulation factor always definite and to perform a high-quality data playback operation by a method wherein the superposition period and the superposition stop period of a high-frequency current are controlled, the amplitude of the high-frequency current is adjusted during the superposition period on the basis of the detected output of a photodetector and the value of a DC current is adjusted during the superposition stop period. CONSTITUTION:A laser diode 1 is driven by means of a laser-diode driving current I (LD) in which a high-frequency current Ih supplied from a high-frequency current source 3 is superposed on a DC current Ib supplied from a variable current source 2. In addition, a means which controls the following so as to be operated by means of a high-frequency current ON/OFF signal SS is installed: a period during which the superposition of the high-frequency current is stopped; and a period during which the high-frequency current is superposed. In addition, the following are installed: a first adjustment means which adjusts the amplitude of the high-frequency current on the basis of the detected output of a photodetector 6 during the superposition period of the high-frequency current: and a second adjustment means which adjusts the value of the DC current Ib on the basis of the detected output of the photodiode 6 during the superposition stop period of the high-frequency current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode control circuit and an optical disk drive device in an electronic device having a semiconductor laser as a light source for an optical disk device, a laser printer, an optical card drive device, etc., and more particularly to an optical disk drive device and the like. In order to reduce the noise caused by the laser diode, the so-called high-frequency current superposition method has been improved in the laser diode drive control method that superimposes a high-frequency current so that the degree of modulation can be improved even when the laser diode characteristics change due to temperature, etc. The present invention relates to a laser diode control circuit and an optical disk drive device that are kept constant and enable stable operation.

[0002]

2. Description of the Related Art In an electronic device equipped with a laser diode as a light source, such as an optical disk drive device,
A so-called high frequency current superposition method has been conventionally known as a laser diode drive control method for reducing noise caused by the laser diode (for example, 198).
Academic Journal "Optics" Vol. 14, No. 5, No. 37, published in October 1993
"Reduction of laser noise in laser-mounted video disc player by high-frequency current superposition method" on pages 7-384).
The laser diode control circuit based on the high frequency current superposition method has the following configuration.

FIG. 6 is a functional block diagram showing an example of the main configuration of a laser diode control circuit according to the conventional high frequency current superposition method. In the figure, 1 is a laser diode (LD), 2 is a variable current source, 3 is a high frequency current source, 4 is a differential amplifier, 5 is an amplifier, 6 is a photodetector, 7 is a reference voltage source, C is a capacitor, and , I
h is a high frequency current output from the high frequency current source 3, Ib is a direct current output from the variable current source 2, I (LD) is a drive current of the laser diode 1, and Vref is a voltage of the reference voltage source 7.

As shown in FIG. 6, in the conventional laser diode control circuit, in the laser diode 1, the high frequency current Ih supplied from the high frequency current source 3 is superimposed on the direct current Ib supplied from the variable current source 2. It is driven by the laser diode drive current I (LD). In this case,
The frequency of the high frequency current Ih is set to a value that reduces the noise of the laser diode 1, for example, a value of 600 MHz or higher.

The average light emission power of the laser diode 1 is detected by the photodetector 6 and input to the negative terminal of the differential amplifier 4 via the amplifier 5. The differential amplifier 4 compares the output of the photodetector 6 with a reference voltage Vref corresponding to the target light emission power of the laser diode 1, and the variable current source 2 of the variable current source 2 makes the average light emission power equal to the target light emission power. Adjust the output voltage. Here, the relationship between the drive current of the laser diode 1 and the light emission power will be described.

FIG. 7 is a characteristic diagram showing an example of the relationship between the laser diode drive current and the light emission power in the laser diode control circuit. The horizontal axis of the figure shows the laser diode drive current I (LD), the vertical axis shows the light emission power P, and and show the characteristics changed by the temperature and the like.

In FIG. 7, the amplitude of the high frequency current Ih supplied from the high frequency current source 3 is indicated by Ip. Also,
Ib is a direct current supplied from the variable current source 2,
Ib 'is the regulated DC current.

Pa represents the average light emission power of the laser diode 1 when the high frequency current is superimposed, and corresponds to the value of the light emission power detected by the photodetector 6 in the circuit of FIG. 6 described above. Pb is the light emission power of the laser diode 1 when the amplitude Ip of the high frequency current (Ih) is "0".

In the above literature, the scale showing the modulation depth of the high frequency superimposed current is called the modulation degree and is defined as the modulation degree M = Pa / Pb × 100 (%). Then, it is stated that the noise of the laser diode is reduced by setting the modulation degree M to 120% or more.

By the way, the drive current of the laser diode −
The characteristics of the light emission power change depending on the temperature and the like. Therefore, in the laser diode control circuit shown in FIG. 6, the average emission power Pa of the laser diode when the high frequency current is superposed is set.
Controls the laser diode to be constant even if the characteristics of the laser diode change due to temperature or the like.

However, since the amplitude Ip of the high frequency current (Ih) is a constant value, even if the average light emission power Pa is controlled to a constant value, the modulation degree M is affected by the change in the characteristics of the laser diode. Will end up. For example, in FIG. 7, when the characteristic is, in the laser diode control circuit of FIG. 6, the value of the amplitude Ip of the high frequency current (Ih) is adjusted so that the average light emission power of the laser diode becomes Pa.

Further, when the characteristic is, in the laser diode control circuit of FIG. 6, similarly, the direct current Ib is I so that the average light emission power of the laser diode becomes Pa.
It is adjusted to the value of b ', but in this case, the value of the amplitude Ip of the high frequency current (Ih) is constant. Therefore, the emission power Pb of the laser diode 1 when the amplitude Ip of the high frequency current (Ih) is set to "0" changes to Pb ', resulting in a change in the modulation degree M.

As described above, in order to reduce the noise of the laser diode, it is necessary to secure an appropriate modulation factor. However, in the conventional laser diode control circuit,
There is a problem that the modulation degree M fluctuates due to changes in the characteristics of the laser diode due to temperature changes and the like, and noise cannot be sufficiently reduced. In the optical disc drive device, the noise of the laser diode causes the quality of the reproduced data to deteriorate, so that in the worst case, there is a disadvantage that the data cannot be reproduced.

[0014]

SUMMARY OF THE INVENTION The present invention solves such inconvenience in the conventional laser diode control circuit by the high frequency current superposition method, and always modulates even if the characteristics of the laser diode change due to temperature or the like. It is an object of the present invention to provide a laser diode control circuit and an optical disk drive device capable of reproducing high quality data while keeping the degree constant.

[0015]

According to the present invention, firstly, a laser diode, a direct current output from a variable current source and a high frequency current output from a high frequency current source are superimposed on the laser diode. In the laser diode control circuit for applying and detecting the light emission power of the laser diode by a photodetector, means for controlling a period for stopping the superposition of the high frequency current and a period for superimposing the high frequency current, and the high frequency current Based on the output of the photodetector detected during the superposition period, the first adjusting means for adjusting the amplitude of the high frequency current, and based on the output of the photodetector detected during the period during which the superposition of the high frequency current is stopped, the DC And a second adjusting means for adjusting the value of the current.

Secondly, in the first laser diode control circuit, the first adjusting means allows the first reference signal source and the output of the photodetector during the high frequency current superposition period to pass therethrough, thereby superimposing the high frequency current. During the period of stopping
A first sample-hold circuit that holds the value of the immediately preceding output; and a first differential amplifier that compares the output of the first reference signal source with the output of the first sample-hold circuit, The amplitude of the high frequency current output from the high frequency current source is adjusted based on the output of the first differential amplifier.

Thirdly, in the above-mentioned first laser diode control circuit, the second adjusting means compares the second reference signal source with the output of the second reference signal source and the output of the photodetector. The second differential amplifier and the second differential amplifier that passes the output of the second differential amplifier during the superimposing period of the high-frequency current and holds the value of the immediately preceding output during the period in which the superimposing of the high-frequency current is stopped. And a sample and hold circuit, and adjusts the value of the direct current output from the variable current source based on the output of the second sample and hold circuit.

Fourthly, in the first laser diode control circuit, the first adjusting means allows the output of the photodetector during the superimposing period of the high frequency current to pass through the first reference signal source to superimpose the high frequency current. During the period of stopping
A first sample-hold circuit that holds the value of the immediately preceding output; and a first differential amplifier that compares the output of the first reference signal source with the output of the first sample-hold circuit, The amplitude of the high frequency current output from the high frequency current source is adjusted based on the output of the first differential amplifier.

Fifth, in the above-mentioned first laser diode control circuit, the second adjusting means compares the second reference signal source with the output of the second reference signal source and the output of the photodetector. The second differential amplifier and the second differential amplifier that passes the output of the second differential amplifier during the superimposing period of the high-frequency current and holds the value of the immediately preceding output during the period in which the superimposing of the high-frequency current is stopped. And a sample and hold circuit, and adjusts the value of the direct current output from the variable current source based on the output of the second sample and hold circuit.

Sixthly, in the optical disk drive device including the above-mentioned first laser diode control circuit and irradiating the laser beam spot outputted by the laser controlled by the laser diode control circuit onto the optical disk, superposition of high frequency current is performed. The stop period is set so as to correspond to the period during which the laser beam spot passes through the non-information area on the optical disc.

[0021]

According to the present invention, the average light emission power Pa and the high frequency power are changed even if the characteristics of the laser diode are changed in order to keep the modulation constant even when the characteristics of the laser diode are changed by temperature. The amplitude Ip of the high frequency current (Ih) and the direct current I are set so that the emission power Pb when the amplitude Ip of the current (Ih) is set to “0” is always maintained at a constant value.
Both b are adjusted. Therefore, the first adjusting means for adjusting the amplitude Ip of the high frequency current based on the output of the photo detector detected during the superimposing period of the high frequency current, and the output of the photo detector detected during the period during which the superimposing of the high frequency current is stopped. Second adjusting means for adjusting the value of the direct current Ib is provided.

[0022]

First Embodiment A laser diode control circuit according to the present invention will be described in detail with reference to the drawings. This embodiment corresponds to the inventions of claims 1 to 3.

FIG. 1 is a functional block diagram showing an embodiment of the main configuration of the laser diode control circuit of the present invention. Reference numerals in the figure are the same as those in FIG. 6, 11 is a second differential amplifier, 12 is a first sample-hold circuit, 13 is a second sample-hold circuit, and 14 is a sample-hold circuit.
Is an inverter, R1 and R2 are resistors, and SS
Indicates a high frequency current on / off signal, Vref (a) indicates a first reference voltage, and Vref (b) indicates a second reference voltage.

Also in the laser diode control circuit of the present invention, as in the prior art example shown in FIG. 6, the laser diode 1 supplies the direct current Ib supplied from the variable current source 2 to the high frequency current Ih supplied from the high frequency current source 3. Are driven by the superposed laser diode drive current I (LD). In the present invention, means for controlling the period for which the superposition of the high frequency current is stopped and the period for superposing the high frequency current (the means for operating by the high frequency current ON / OFF signal SS), and the photodetector 6 detected during the superposition period of the high frequency current. DC current (Ib) based on the output of the first detector that adjusts the amplitude (Ip) of the high-frequency current based on the output of the photodetector 6 and the output of the photodetector 6 detected during the period when the superposition of the high-frequency current is stopped.
And a second adjusting means for adjusting the value of.

The operation of the laser diode control circuit shown in FIG. 1 is as follows. The high frequency current Ih output from the high frequency current source 3 is a high frequency current ON / OFF signal S.
While being turned on and off by S, when the high frequency current Ih is turned on, the amplitude Ip of the second differential amplifier 11 is adjusted by the output of the second differential amplifier 11. The photodetector 6 detects the light emission power of the laser diode 1 and outputs a signal corresponding to the light emission power via the amplifier 5.

When the high frequency current on / off signal SS indicates the high frequency current on state, the first sample hold circuit 12 passes the detection output of the photodetector 6 and indicates the high frequency current off state. when,
The detection output immediately before the photodetector 6 is held. On the other hand, the second sample-hold circuit 13 passes the detection output of the photodetector 6 when the high-frequency current on / off signal SS indicates the high-frequency current off, contrary to the first sample-hold circuit 12. When the high frequency current is turned on, the photodetector 6
The detection output immediately before is held.

The second differential amplifier 11 corresponds to the output of the first sample and hold circuit 12 and the first target emission power Pa of the laser diode 1 when the high frequency current is superposed.
The reference voltage Vref (a) is compared with the reference voltage Vref (a) of FIG. The (first) differential amplifier 4 compares the output of the second sample hold circuit 13 with the second reference voltage Vref (b) corresponding to the target average light emission power Pb when the high frequency current is not superimposed. , And provides an adjustment signal to the variable current source 2 according to the comparison result.

As described above, in the laser diode control circuit of the present invention, the high frequency current ON / OFF signal SS is appropriately turned on and off to correspond to the average light emission power of the laser diode 1 in the high state of the high frequency current. The detection output of the photodetector 6 is sampled by the first sample hold circuit 12, and the amplitude Ip of the high frequency current Ih is adjusted so that this value matches the target value.
Further, the detection output of the photodetector 6 corresponding to the average light emission power of the laser diode 1 when the high frequency current is off is sampled by the second sample and hold circuit 13, and the variable current source is adjusted so that this value matches the target value. The direct current Ib supplied from 2 is adjusted.

FIG. 2 is a characteristic diagram showing an example of the relationship between the laser diode drive current and the light emission power in the laser diode control circuit of the present invention. The horizontal axis, the vertical axis, and the reference numerals in the figure are the same as those in FIG. 7.

For example, when the characteristic changes from to, the value of the amplitude Ip of the high frequency current (Ih) is Ip '.
And the DC current Ib is adjusted to Ib '. By comparing FIG. 2 with FIG. 7 showing the conventional example, the average emission power Pa of the laser diode when the characteristic is
It is common in that it is maintained at Pa even if the characteristic changes to.

However, the emission power P of the laser diode 1 when the amplitude Ip of the high frequency current (Ih) is set to "0"
In FIG. 7, b changes from Pb to Pb ′, but in FIG. 2 showing the case of the present invention, the value b is always a constant value even if the characteristic changes from (to the contrary, from). Therefore, the modulation factor M is unchanged. Thus, by adjusting both the amplitude Ip of the high frequency current (Ih) and the direct current Ib, the average light emission power Pa and the high frequency current (I
The light emission power Pb when the amplitude Ip of h) is set to “0” can always be kept at a constant value.

FIG. 3 is a timing chart showing an example of the signal of each part of FIG. 1 and the emission power of the laser diode. The code | symbol attached to each signal waveform respond | corresponds to the code | symbol position of FIG.

FIG. 3 shows a state in which the average light emission power when the high frequency current (Ih) is on and the light emission power when it is off are adjusted to the target values Pa and Pb, respectively. As is apparent from FIG. 3, by maintaining the target values Pa and Pb of the emission power, the modulation degree M during superposition of the high frequency current is kept constant, and an appropriate noise reduction effect of the laser diode can be obtained. ..

Therefore, it is possible to reproduce high quality data and improve the reliability of reproduced information. The values of the first reference voltage Vref (a) and the second reference voltage Vref (b) are
It may be set so that a desired modulation degree can be obtained.

[0035]

Second Embodiment Another embodiment of the laser diode control circuit of the present invention will be described. This embodiment provides claim 4
And corresponds to the invention of claim 5.

FIG. 4 is a functional block diagram showing another embodiment of the essential structure of the laser diode control circuit of the present invention. Reference numerals in the figure are the same as those in FIG.

When the embodiment of FIG. 4 is compared with the embodiment of FIG. 1 described above, the positional relationship between the second differential amplifier 11 and the first sample and hold circuit 12 and the (first) differential The positional relationship between the amplifier 4 and the second sample hold circuit 13 is interchanged. That is, in the embodiment of FIG. 1, the detection output of the photodetector 6 is sampled and held and then compared with the first reference voltage Vref (a) or the second reference voltage Vref (b).

On the other hand, in the circuit of FIG. 4, the detection output of the photodetector 6 is first compared with the first reference voltage Vref (a) or the second reference voltage Vref (b),
The comparison result is sampled and held at a predetermined timing. And the basic operation is as shown in FIG.
Is the same as that of the above, and the effect is also the same.

As shown in FIG. 4, the differential amplifier (11,
It is possible to adjust the amplitude Ip of the high frequency current Ih and the direct current Ib even with a circuit in which the positions of 4) and the sample hold circuit (12, 13) are interchanged. As mentioned above, this second
In the embodiment of the present invention, after comparing the detection output of the photodetector 6 and the reference voltage, the comparison result is sampled and held, so that the high-frequency current (Ih) has an average light emission power in the on state and an emission power in the off state. Are adjusted to target values Pa and Pb, respectively.

[0040]

Third Embodiment A third embodiment of the present invention will be described. This embodiment is an optical disk drive device corresponding to the invention of claim 6. This embodiment is characterized in that the timing for temporarily turning off (stopping) the superposition of the high frequency current is set in order to appropriately adjust the amplitude Ip of the direct current Ib and the amplitude Ip of the high frequency current Ih.

FIG. 5 is a time chart for explaining the off timing of the high frequency current superimposition in the optical disk drive device provided with the laser diode control circuit of the present invention.

Gap Gap on Track of Disk
Is provided at the boundary between the ID part and the DATA part, or the boundary between sectors, as shown in FIG. 4, and there is no data to be reproduced in this area. Therefore,
In the gap part Gap, it is not necessary to superimpose a high frequency current.

Therefore, in the third embodiment, the off timing of the high frequency current superimposition is made to coincide with the timing at which the light spot passes through the gap Gap on the track, and the second timing is applied while the high frequency current superimposition is off. The sampling operation of the sample hold circuit 13 is performed to hold the detection output of the photodetector 6. In this way, the light spot changes the off timing of the high frequency current to the gap portion Ga.
According to the timing of passing through p, the ID part and DATA
In the section, it becomes possible to always superimpose the high frequency current.

Therefore, the reproduction sequence of information does not become out of order. That is, there is no inconvenience of interrupting the reproduction of information in order to adjust the amplitude Ip of the high frequency current Ih.

[0045]

According to the first and second aspects of the present invention, the photodetector corresponding to the average light emission power of the laser diode 1 in the ON state of the high frequency current is appropriately turned on and off by turning on and off the high frequency current ON / OFF signal SS. The detection output 6 is sampled by the first sample hold circuit 12, and the amplitude Ip of the high frequency current Ih is adjusted so that this value matches the target value, so that the modulation degree is always kept constant. Therefore, the appropriate noise reduction effect of the laser diode is always obtained, and the reliability of the reproduced information is improved.

In the first and third aspects of the invention, the detection output of the photodetector 6 corresponding to the average light emission power of the laser diode 1 when the high frequency current is in the off state is sampled by the second sample hold circuit 13, and this value is detected. The direct current Ib supplied from the variable current source 2 is adjusted so that the current value Ib matches the target value. Therefore, similarly, an appropriate noise reduction effect of the laser diode is always obtained, so that the reliability of the reproduction information is improved.

In the fourth aspect of the invention, as in the second aspect of the invention, the amplitude Ip of the high frequency current Ih is adjusted, so that the modulation degree is always kept constant. Therefore, the same effect as the invention of claim 2 is obtained.

In the fifth aspect of the invention, as in the third aspect of the invention, since the direct current Ib is adjusted, the modulation degree is always kept constant. Therefore, the same effect as the invention of claim 3 is obtained.

According to the sixth aspect of the present invention, the off timing of the high frequency current can be matched with the timing at which the light spot passes through the gap portion Gap.
In the section A, it is possible to always superimpose the high frequency current, and there is no inconvenience of interrupting the reproduction of information in order to adjust the amplitude Ip of the high frequency current Ih. Therefore, an appropriate noise reduction effect of the laser diode is always obtained, and the reliability of reproduced information is improved.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of a main configuration of a laser diode control circuit of the present invention.

FIG. 2 is a characteristic diagram showing an example of the relationship between the laser diode drive current and the light emission power in the laser diode control circuit of the present invention.

FIG. 3 is a timing chart showing an example of signals of respective parts of FIG. 1 and emission power of a laser diode.

FIG. 4 is a functional block diagram showing another embodiment of the main configuration of the laser diode control circuit of the present invention.

FIG. 5 is a time chart for explaining an off timing of superimposing a high frequency current on an optical disk drive device including the laser diode control circuit of the present invention.

FIG. 6 is a functional block diagram showing an example of a main configuration of a laser diode control circuit according to a conventional high frequency current superposition method.

FIG. 7 is a characteristic diagram showing an example of a relationship between a laser diode drive current and a light emission power in a laser diode control circuit.

[Explanation of symbols]

 1 Laser diode (LD) 2 Variable current source 3 High frequency current source 4 Differential amplifier 5 Amplifier 6 Photodetector 7 Reference voltage source 11 Second differential amplifier 12 First sample and hold circuit 13 Second sample and hold circuit 14 Inverter

Claims (6)

[Claims] 1. A laser diode, a direct current output from a variable current source and a high frequency current output from a high frequency current source are superimposed and applied to the laser diode, and the light emission power of the laser diode is applied by a photodetector. In the laser diode control circuit configured to detect, based on the output of the photodetector detected in the superimposing period of the high frequency current, means for controlling the period of stopping the superimposing of the high frequency current and the period of superimposing the high frequency current. First adjusting means for adjusting the amplitude of the high frequency current, and second adjusting means for adjusting the value of the direct current based on the output of the photodetector detected during the period in which the superposition of the high frequency current is stopped, A laser diode control circuit comprising: 2. The laser diode control circuit according to claim 1, wherein the first adjusting means allows the first reference signal source and the output of the photodetector during the superposition period of the high frequency current to pass therethrough, and stops the superposition of the high frequency current. A first sample-and-hold circuit that holds the value of the immediately preceding output, and a first differential that compares the output of the first reference signal source and the output of the first sample-and-hold circuit. A laser diode control circuit comprising: an amplifier; and adjusting the amplitude of a high frequency current output from the high frequency current source based on the output of the first differential amplifier. 3. The laser diode control circuit according to claim 1, wherein the second adjusting means compares the second reference signal source with the output of the second reference signal source and the output of the photodetector. The output of the second differential amplifier is passed during the superimposing period of the differential amplifier and the high frequency current, and during the period in which the superimposing of the high frequency current is stopped,
A second sample and hold circuit for holding the value of the immediately preceding output; and adjusting the value of the direct current output from the variable current source based on the output of the second sample and hold circuit. Laser diode control circuit. 4. The laser diode control circuit according to claim 1, wherein the first adjusting means allows the first reference signal source and the output of the photodetector during the superposition period of the high frequency current to pass therethrough, and stops the superposition of the high frequency current. A first sample-and-hold circuit that holds the value of the immediately preceding output, and a first differential that compares the output of the first reference signal source and the output of the first sample-and-hold circuit. A laser diode control circuit comprising: an amplifier; and adjusting the amplitude of a high frequency current output from the high frequency current source based on the output of the first differential amplifier. 5. The laser diode control circuit according to claim 1, wherein the second adjusting means compares the second reference signal source with the output of the second reference signal source and the output of the photodetector. The output of the second differential amplifier is passed during the superimposing period of the differential amplifier and the high frequency current, and during the period in which the superimposing of the high frequency current is stopped,
A second sample and hold circuit for holding the value of the immediately preceding output; and adjusting the value of the direct current output from the variable current source based on the output of the second sample and hold circuit. Laser diode control circuit. 6. An optical disk drive apparatus comprising the laser diode control circuit according to claim 1, wherein a laser beam spot emitted by a laser controlled by the laser diode control circuit is irradiated onto the optical disk, and superposition of a high frequency current is stopped. An optical disk drive device, wherein a period is set corresponding to a period during which the laser beam spot passes through a non-information area on the optical disc.