JP2006338701A - Optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk drive which has an optical pickup incorporating a circuit to cancel the amplitude margins of the high frequency current to superpose on the drive current at room temperature to improve the temperature characteristics of the laser diode. <P>SOLUTION: The circuit is built to use the thermistor 11a provided in advance for detecting the ambient temperature of the laser diode and also used for improving the control precision of the light emitting power of the laser diode, by connecting it between the superimposing current amplitude adjusting terminal 7a of the high frequency current superimposing modular circuit 78 and ground instead of a resistor. When the resistance of the thermistor 11a drops as the temperature rises, the superimposing modular circuit 78 increases the amplitude of the high frequency current it outputs. Accordingly, the amplitude margin of the superimposing current can be canceled at room temperature in the temperature characteristics of the laser diode, making it possible to set the superimposing current amplitude smaller that much. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an optical disc apparatus for reproducing information recorded on an optical disc or recording / reproducing information on an optical disc, and more particularly, by irradiating a laser beam on an optical disc,
The present invention relates to drive control of laser light of an optical pickup that writes information to and reads information from an optical disc.

As conventionally known, an optical disc apparatus is provided with an optical pickup that optically writes information to an optical disc and optically reads information recorded on the optical disc. Driven by a laser drive circuit. This laser drive circuit receives part of the laser light emitted from the laser diode using a photodiode, and automatically controls the drive current of the laser diode based on the output signal of this photodiode. Is used, and the light emission power of the laser diode is controlled to be constant.

The reflected light when the optical disk is irradiated with the laser light returns to the laser diode, so that noise, so-called scoop noise, is generated in the laser diode. When the laser diode emits laser light with a wavelength of, for example, 660 nm, the laser light is irradiated onto the recording surface of the optical disc, but the reflected light returns to the laser diode, and scoop noise occurs in the laser diode. .

Therefore, in order to reduce scoop noise, a high-frequency superposition module circuit that superimposes a high-frequency current on the drive current of the laser diode is integrated into an IC and mounted on the optical pickup. When such a high-frequency superposition module circuit is used, for example, a laser beam having a wavelength of 660 nm is swung from a wavelength of about 650 nm to about 670 nm, thereby reducing the influence of the return light amount.

FIG. 3 is a diagram for explaining an example of the relationship (IL characteristic) between the drive current supplied to the laser diode and the light emission power of the laser diode. In FIG. 3, L1 shows the relationship between the drive current and the light emission power when the temperature of the laser diode is 20 ° C., for example, and L2 shows the relationship between the drive current and the light emission power when the temperature of the laser diode is 70 ° C., for example. Ith
1 is a drive current threshold value (for example, 40.9) when the temperature of the laser diode is 20 ° C., for example.
5th), and Ith2 represents a drive current threshold (for example, 63.00 mA) when the temperature of the laser diode is 70 ° C., for example. S1 is a laser diode temperature of, for example, 20 ° C.
The high frequency current superimposed in FIG. 3 indicates the high frequency current, and S2 indicates the high frequency current superimposed when the temperature of the laser diode is 70 ° C., for example.

As shown in FIG. 3, when the amplitude of the high-frequency current S1 exceeds the threshold value Ith1 (in the direction of decreasing with the drive current), the high-frequency current S1 indicated by the hatched portion is not supplied to the laser diode, but when the amplitude is below the threshold value Ith1 (drive) Since the high-frequency current S1 is supplied to the laser diode, the laser diode performs a switching operation. That is, the laser diode does not emit light when the amplitude of the high-frequency current S1 exceeds the threshold value Ith1, and emits light when the amplitude of the high-frequency current S1 becomes the threshold value Ith1 or less. However, when the amplitude of the high-frequency current S2 is less than or equal to the threshold value Ith2, the high-frequency current S2 is supplied to the laser diode and the laser diode emits light. However, since the amplitude of the high-frequency current S2 does not exceed the threshold value Ith2, the laser diode The laser diode remains lit and the laser diode cannot switch.

Further, as shown in FIG. 3, the relationship between the drive current and the light emission power is shifted depending on the temperature as shown by L1 and L2, and the inclination is increased in the direction of falling. When this inclination is indicated by L2, for example, the laser diode cannot perform the switching operation as described above.

Therefore, if the amplitude of the superimposed high-frequency current is increased, the laser diode can be switched even if the relationship between the drive current and the light emission power shifts depending on the temperature or the inclination increases in the direction of falling. Although possible, there is a concern about the adverse effect of unnecessary radiation caused by this switching operation and data destruction of a rewritable optical disk such as DVD-RW or DVD-RAM.

In a rewritable optical disc, when a laser beam is irradiated onto a crystalline portion during recording, the crystalline portion becomes amorphous (amorphous), and the amorphous portion corresponds to data. A pit to be carved is engraved. And at the time of reproduction, the pit is read in a state where the high frequency current is superimposed on the laser beam, but the peak of the emission power of the laser beam is as large as, for example, 5 mW to 6 mW. When light is applied, the crystalline part gradually becomes amorphous. For example, an amorphous material having a length of 3T has a length of 3.
If 5T or 4T becomes longer, data cannot be read accurately. In other words, this rewritable optical disc causes data destruction, and therefore the smaller the amplitude of the superimposed high-frequency current, the better.

FIG. 4 is a circuit diagram showing a part of a temperature detection processing circuit included in a high-frequency superposition module circuit and a thermistor included in an optical pickup circuit unit of an optical pickup and a control circuit unit of a servo control unit in a conventional optical disk device. is there.

In the optical pickup circuit unit 41, the high-frequency superposition module circuit 78 is a circuit that generates a high-frequency current and superimposes it on a drive current of a laser diode (not shown) (a drive current from a laser diode drive circuit not shown). The circuit configuration is such that the amplitude of the high-frequency current can be set by the resistance value of an external resistor R3 connected between the superimposed amplitude adjustment terminal 7a of this circuit and the ground. The thermistor 11a is included in a temperature monitoring circuit (not shown) that detects and monitors the temperature related to the laser diode, and detects the temperature related to the laser diode.

In the control circuit section 42, an operational amplifier 13a is connected to a connection point with one end of the thermistor 11a, a positive input terminal (non-inverting input terminal) and a negative input terminal (inverting input terminal) connected to an output terminal. A having an input terminal connected to the output terminal of the operational amplifier 13a
/ D conversion circuit 13b. The resistor R4 is a pull-up resistor having one end connected to, for example, a 5V voltage line and the other end connected to the + input terminal of the operational amplifier 13a.

The output voltage (analog voltage) of the operational amplifier 13a is given to the input terminal of the A / D conversion circuit 13b and converted into a digital signal by the A / D conversion circuit 13b. This digital signal is
This is input to a servo control unit (not shown), whereby the servo control unit controls the laser diode drive circuit to control the light emission power of the laser diode to be constant.

That is, when the temperature related to the laser diode rises, the thermistor 11a that senses this temperature also rises in its own temperature, and the resistance of the thermistor 11a becomes smaller. As a result, the potential at the + input terminal of the operational amplifier 13a is lowered, the potential at the output terminal of the operational amplifier 13a is lowered, and the voltage applied to the input terminal of the A / D conversion circuit 13b is lowered as compared with before. As a result, a digital signal indicating that the temperature has increased from before is output from the A / D conversion circuit 13b, and a servo control unit (not shown) that has input this digital signal controls the laser diode drive circuit. Then, a large drive current is supplied to the laser diode so that the light emission power of the laser diode becomes constant.
JP 2004-253032 A JP-A-11-213428

Thus, when the temperature of the laser diode rises, the laser diode can be switched at a high temperature by increasing the amplitude of the high frequency current superimposed on the drive signal of the laser diode. Since the high-frequency superposition module circuit 78 determines the amplitude of the high-frequency current by connecting the resistor R3 having a fixed resistance value to the superposition amplitude adjustment terminal 7a, the high-frequency current cannot be increased even if the temperature rises.

For example, as shown in FIG. 3, the relationship between the drive current and the light emission power is shifted depending on the temperature, or the inclination is increased in the direction of falling, as indicated by L1 and L2. For example, when the inclination is indicated by L2 at 70 ° C., the laser diode cannot perform the switching operation because the amplitude of the high-frequency current S2 does not exceed the threshold value Ith2.

Therefore, in such a conventional optical disc apparatus, when the amplitude of the high-frequency current is increased so that the amplitude of the high-frequency current can exceed the threshold even at a high temperature, this results in an increase in the amplitude of the high-frequency current even at room temperature. There arises a problem of adversely causing data destruction of a rewritable optical disc.

In the prior art disclosed in Patent Document 1, in a laser driving device that constitutes a light source unit of an optical head device, a laser (laser diode) and a laser driving circuit, and a high frequency generation circuit that generates a high frequency current for the laser driving current A laser drive current monitor circuit, a photodetector for monitoring the laser light output, a selection means for selecting whether or not to superimpose a high frequency current on the laser drive current, and a laser light output And a control circuit for controlling the amplitude of the high-frequency current based on the current value of the laser drive current or the detected value of the laser light output when the high-frequency current is superimposed and not superimposed. It has been.

However, the high-frequency generation circuit uses a high-frequency superposition module circuit configured so that the amplitude of the high-frequency current can be set by the resistance value of an external resistor connected between the superposition amplitude adjustment terminal and the ground. In order to make the amplitude of the high-frequency current variable, the amplitude of the high-frequency current is controlled based on the current value of the laser drive current or the detected value of the laser light output when the high-frequency current is superimposed or not. Therefore, the circuit configuration tends to be complicated to change the amplitude of the high-frequency current. In short, since this prior art is not a circuit configuration using a high-frequency superposition module circuit, the circuit configuration tends to be complicated.

In the prior art disclosed in Patent Document 2, the CPU of the sub-processor uses high-frequency amplitude temperature-dependent characteristic data corresponding to the temperature detected by the thermistor, and superimposes the amplitude change defined by the amplitude data on the drive signal of the laser diode. I am letting.

However, this prior art also uses a high frequency superposition module circuit configured so that the amplitude of the high frequency current can be set by the resistance value of an external resistor connected between the superposition amplitude adjustment terminal and the ground. Instead, the amplitude of the high-frequency current is controlled based on the high-frequency amplitude temperature-dependent characteristic data corresponding to the temperature detected by the thermistor, so that the circuit configuration tends to be complicated to change the amplitude of the high-frequency current. . In short, since this prior art is not a circuit configuration using a high frequency superposition module circuit, the circuit configuration tends to be complicated.

The present invention has been made in order to solve the above-described problems. An optical circuit having a circuit capable of canceling an amplitude margin of a high-frequency current superimposed on a drive current at room temperature in a temperature characteristic of a laser diode. An object of the present invention is to provide an optical disc apparatus provided with a pickup.

In order to achieve the above object, the invention of claim 1 is directed to a laser diode that emits laser light to an optical disc, a laser diode driving circuit that supplies a driving current to the laser diode, and a high-frequency current to generate the laser diode. The circuit is configured to superimpose on the drive current, and is configured so that the amplitude of the high-frequency current can be set by the resistance value of an external resistor connected between the superimposed amplitude adjustment terminal of the circuit and the ground. In an optical disc apparatus provided with an optical pickup having a high frequency superposition module circuit, in combination with a thermistor provided in advance for detecting the ambient temperature of the laser diode in order to increase the control accuracy of the light emission power of the laser diode, The thermistor is externally connected between the superposition amplitude adjustment terminal of the high frequency superposition module circuit and the ground. On behalf of the resistor to the circuit configuration of connecting, when the resistance value of the thermistor by the temperature rise is reduced, the high-frequency superimposing module circuitry to provide an optical disk apparatus characterized by increasing the amplitude of the high-frequency current to be output.

In this configuration, if a thermistor is connected instead of an external resistor between the superposition amplitude adjustment terminal of the high frequency superposition module circuit and ground, the ambient temperature rises when the laser diode rises in temperature, and this temperature rise As a result, the temperature of the thermistor itself also rises. As a result, the resistance value of the thermistor decreases, and the high frequency superposition module circuit increases the amplitude of the high frequency current to be output.

According to this configuration, when the temperature of the laser diode rises, the amplitude of the high-frequency current superimposed on the drive current of the laser diode increases. Therefore, the laser diode can be reliably manufactured even at a high temperature without increasing the amplitude of the high-frequency current at room temperature. Switching can be prevented, data destruction of the rewritable optical disk can be prevented, and effective against EMI. That is,
The margin of the superposed amplitude (the amplitude of the high-frequency current superimposed on the drive current of the laser diode) at room temperature in the temperature characteristics of the laser diode can be canceled, and the superposed amplitude value can be set small at this temperature. Therefore, data destruction of the rewritable optical disc can be prevented and effective against EMI. In addition, since the circuit that can be canceled is used in combination with a conventionally used component (in this case, a thermistor), the circuit configuration is not complicated and the cost is not increased.

According to a second aspect of the present invention, a laser diode that emits laser light to an optical disk, a laser diode driving circuit that supplies a driving current to the laser diode, and a circuit that generates a high-frequency current and superimposes the driving current on the laser current An optical pickup having a high-frequency superposition module circuit configured so that the amplitude of the high-frequency current can be set by a resistance value of an external resistor connected between the superposition amplitude adjustment terminal of the circuit and the ground In the optical disc apparatus comprising: a temperature detecting element whose resistance value changes in accordance with a temperature change provided in advance for detecting the ambient temperature of the laser diode in order to increase the control accuracy of the light emission power of the laser diode. In combination, the temperature detection element is connected between the superposition amplitude adjustment terminal of the high frequency superposition module circuit and the ground. To provide an optical disk apparatus characterized in that the circuit configuration to connect on behalf of the resistance of the serial external.

In this configuration, if a circuit configuration is used in which a temperature detection element is connected between the superposition amplitude adjustment terminal of the high frequency superposition module circuit and the ground instead of an external resistor, the ambient temperature rises when the temperature of the laser diode rises. The high frequency superposition module circuit increases the amplitude of the high frequency current to be output, based on the resistance value of the temperature detection element when the temperature rise is detected.

According to this configuration, when the temperature of the laser diode rises, the amplitude of the high-frequency current superimposed on the drive current of the laser diode increases. Therefore, the laser diode can be reliably manufactured even at a high temperature without increasing the amplitude of the high-frequency current at room temperature. Switching can be prevented, data destruction of the rewritable optical disk can be prevented, and effective against EMI. That is,
The margin of the superposed amplitude (the amplitude of the high-frequency current superimposed on the drive current of the laser diode) at room temperature in the temperature characteristics of the laser diode can be canceled, and the superposed amplitude value can be set small at this temperature. Therefore, data destruction of the rewritable optical disc can be prevented and effective against EMI. In addition, since the circuit that can be canceled is used in combination with a conventionally used component (in this case, a thermistor), the circuit configuration is not complicated and the cost is not increased.

According to a third aspect of the invention, in the second aspect of the invention, the temperature detecting element is a thermistor whose resistance value decreases as the temperature rises, and when the resistance value of the thermistor decreases due to a temperature rise, the high frequency superposition module circuit Increases the amplitude of the high-frequency current to be output.
When the temperature of the laser diode rises, the amplitude of the high-frequency current superimposed on the drive current of the laser diode can be easily realized by using a thermistor provided in advance.

As described above, according to the present invention, a laser diode that emits laser light to an optical disk, a laser diode drive circuit that supplies a drive current to the laser diode, and a high-frequency current that is generated with respect to the drive current. A high-frequency superposition module circuit configured so that the amplitude of the high-frequency current can be set by a resistance value of an external resistor connected between the superposition amplitude adjustment terminal of the circuit and the ground; In the optical disk device having the optical pickup, the thermistor is used in combination with a thermistor provided in advance for detecting the ambient temperature of the laser diode in order to increase the control accuracy of the light emission power of the laser diode. Instead of the external resistor between the superimposed amplitude adjustment terminal of the superimposed module circuit and the ground When the resistance value of the thermistor decreases due to a temperature rise, the high-frequency superposition module circuit increases the amplitude of the high-frequency current that is output, so that even at high temperatures without increasing the amplitude of the high-frequency current at room temperature. Laser diode switching can be surely performed, data destruction of a rewritable optical disk can be prevented, and effective against EMI. That is, the margin of the amplitude of the high-frequency current superimposed on the laser diode drive current at room temperature in the temperature characteristics of the laser diode can be canceled, and the superimposed amplitude value can be set small at this temperature. Therefore, data destruction of the rewritable optical disc can be prevented and effective against EMI. Also,
Since the circuit that can be canceled is used in combination with a conventionally used component (in this case, a thermistor), the circuit configuration is not complicated and the cost is not increased.

According to the present invention, a laser diode that emits laser light to the optical disc;
A laser diode driving circuit for supplying a driving current to the laser diode, and a circuit for generating a high-frequency current and superimposing the driving current on the laser diode, and an external connection connected between the superimposed amplitude adjustment terminal of the circuit and the ground In order to increase the control accuracy of the light emission power of the laser diode in an optical disc apparatus including an optical pickup having a high frequency superposition module circuit configured so that the amplitude of the high frequency current can be set by a resistance value of a resistor In combination with a temperature detection element whose resistance value changes in accordance with a temperature change provided in advance for detecting the ambient temperature of the laser diode, the temperature detection element is connected to a superposition amplitude adjustment terminal of the high frequency superposition module circuit. Since the circuit is configured to connect in place of the external resistor between the ground, the laser diode is warm. When it rises, the amplitude of the high-frequency current superimposed on the drive current of the laser diode increases, which makes it possible to reliably switch the laser diode even at high temperatures without increasing the amplitude of the high-frequency current at room temperature. It is possible to prevent possible data destruction of the optical disc and to be effective against EMI. That is, the margin of the superposed amplitude (the amplitude of the high-frequency current superimposed on the drive current of the laser diode) at room temperature in the temperature characteristics of the laser diode can be canceled, and the superposed amplitude value can be set small at this temperature. Therefore, data destruction of the rewritable optical disc can be prevented and effective against EMI. In addition, since the circuit that can be canceled is performed in combination with a conventionally used component (in this case, a temperature detection element), the circuit configuration is not complicated and the cost is not increased.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration related to a laser drive system of an optical pickup in an optical disc apparatus according to an embodiment of the present invention.

In FIG. 1, an optical disc apparatus 1 includes a spindle motor 14 that rotates an optical disc 2.
And an optical pickup 3 for optically writing and reading information to and from the optical disc 2, and an RF signal which is a reproduction signal read by the optical pickup 3 at the time of reproduction, and is recorded on the optical disc 2 at the time of recording. A signal processing unit 12 that applies a modulation signal obtained by modulating the signal to the optical pickup 3 and a servo control unit 13 that controls the optical pickup 3 and the spindle motor 14 are provided.

The optical pickup 3 includes a laser diode (hereinafter referred to as LD) 5 that emits laser light to the optical disc 2, an LD drive circuit 6 that drives the LD 5, and a high-frequency superposition that generates a high-frequency current that is superimposed on the drive current of the LD 5. A high-frequency superposition module circuit 78 comprising a circuit 7 and an amplitude control circuit 8 for controlling the amplitude of the high-frequency current; a current monitoring circuit 9 for monitoring the drive current of the LD 5; and a light detection circuit for detecting and monitoring the light output of the LD 5 10, and LD
5 is provided with a temperature monitoring circuit 11 that detects and monitors the temperature according to 5.

The high frequency superposition module circuit 78 has the frequency and amplitude of the high frequency current as parameters, a frequency setting terminal (not shown) for setting the frequency, and a superposition for adjusting the amplitude of the high frequency current superimposed on the drive current. It has an amplitude adjustment terminal 7a (FIG. 2). For example, if a 6.8 kΩ resistor is connected between the frequency setting terminal and the ground, the frequency of the high frequency current is 300 MHz, and if a 3.9 KΩ resistor is connected between the superimposed amplitude adjusting terminal 7a and the ground, the amplitude of the high frequency current is It becomes 50 mA in pp. In addition, since these numerical values are examples, they are not limited to these.

The servo control unit 13 performs focus servo control and tracking servo control by performing current control on the coil of each actuator that moves the objective lens 4 of the optical pickup 3 in the vertical and horizontal directions with respect to the recording surface of the optical disc 2. In addition, the rotation of the spindle motor 14 is controlled, or the driving mechanism of a sled (not shown) for moving the optical pickup 3 with respect to the radial direction of the optical disc 2 is controlled.

By the way, a high frequency superposition module circuit 78 is mounted on the optical pickup 3 in order to reduce scoop noise generated by the LD 5. This high frequency superposition module circuit 78
Is effective in reducing the scoop noise, but because the LD 5 is switched at high speed, it can be rewritten by unnecessary radiation or the peak power of the laser beam (DVD-RW or DVD).
-There is a concern about adverse effects that cause data destruction of RAM. If these concerns are taken into consideration, the superposition amplitude can be reduced. However, since the following parameters must be considered, it is possible to easily reduce the amplitude of the high-frequency current superimposed on the drive current of the LD 5. Can not.

The parameters include LD threshold value Ith, LD differential efficiency, LD temperature characteristics, high frequency superposition module circuit variation, superposition amplitude setting resistance variation, and power supply fluctuation to the high frequency superposition module circuit. The LD threshold value Ith is, for example, Ith1 or Ith2 in FIG.
Say something like that. The differential efficiency of the LD is, for example, a place where the line L1 indicating the drive current / light emission power characteristic (IL characteristic) in FIG. 3 is bent in the drive current direction and the waveform of the high-frequency current S1 does not break the line L1. This refers to the differential efficiency of the IL characteristic for preventing the occurrence of. The temperature characteristics of LD are the characteristics of drive current and light emission power due to temperature change (I-
L characteristic) and also the deviation of linearity of the drive current / light emission power characteristic (IL characteristic). The variation in the superimposing amplitude setting resistance means the variation in the resistance value of the resistor connected to the superimposing amplitude adjusting terminal of the high frequency superimposing module circuit. The fluctuation of the power supply to the high frequency superposition module circuit refers to the fluctuation of the power supply voltage supplied to the high frequency superposition module circuit.

In this embodiment, a circuit capable of canceling the margin of the LD temperature characteristic among these parameters is provided. Since the differential efficiency of the IL characteristic deteriorates due to the temperature characteristics of the LD, the amplitude of the high-frequency current cannot exceed the threshold value Ith at high temperatures unless the amplitude of the high-frequency current at room temperature is designed in consideration of this. Therefore, a state where the LD cannot be switched occurs. Therefore, if the amplitude of the high-frequency current is increased so that the amplitude of the high-frequency current can exceed the threshold value Ith even at a high temperature, this results in an increase in the amplitude of the high-frequency current at room temperature.
Or adversely causing data destruction of the rewritable optical disc.

In order to avoid this problem, if the superposition amplitude is increased along with the temperature change, the LD can be reliably switched even at a high temperature without increasing the amplitude of the high-frequency current at normal temperature. The commercially available high frequency superposition module circuit is integrated into an IC, and the amplitude level of the high frequency current is set by an external resistor. Therefore, the resistance value of the resistor may be varied along with the ambient temperature. The optical pickup is equipped with a thermistor for detecting the temperature of the laser diode in order to improve the accuracy of laser beam power control. If this thermistor is used, the amplitude of the high-frequency current can be varied with the temperature. Note that the temperature detection element is not limited to the thermistor, and any temperature detection element whose resistance value varies with temperature may be used.

FIG. 2 is a circuit diagram showing a part of the high-frequency superposition module circuit and thermistor included in the optical pickup circuit unit of the optical pickup and part of the temperature detection processing circuit included in the control circuit unit of the servo control unit in the present embodiment. .

In the optical pickup circuit unit 21, the high frequency superimposing module circuit 78 is a circuit including the high frequency superimposing circuit 7 and the amplitude control circuit 8 described above, and the thermistor 11 a is included in the temperature monitoring circuit 11 that detects and monitors the temperature related to the LD 5. , A thermistor for detecting the temperature of LD5. In the control circuit unit 22, a positive input terminal (non-inverted input terminal) is connected to a connection point between the superimposed amplitude adjustment terminal 7 a of the high frequency superimposing module circuit 78 and one end of the thermistor 11 a, and a negative input terminal (inverted input). And an A / D converter circuit 13b having an input terminal connected to the output terminal of the operational amplifier 13a via a resistor R1.

One end of the resistor R1 is grounded via the resistor R2, whereby the output voltage of the operational amplifier 13a is divided by the resistor R1 and the resistor R2, and this divided voltage (analog voltage) is A / A.
The signal is given to the input terminal of the D conversion circuit 13b and converted into a digital signal by the A / D conversion circuit 13b. This digital signal is input to the servo control unit 13 shown in FIG. 1, so that the servo control unit 13 controls the LD drive circuit 6 so that the light emission power of the LD 5 becomes constant even if the temperature changes. To control.

That is, in the control of the light emission power, when the temperature of the LD 5 increases, the temperature of the thermistor 11a that senses this temperature also increases, and the resistance of the thermistor 11a decreases. As a result, the potential at the + input terminal of the operational amplifier 13a is lowered, the potential at the output terminal of the operational amplifier 13a is also lowered, and the voltage applied to the input terminal of the A / D conversion circuit 13b is lowered than before. As a result, the A / D conversion circuit 13b outputs a digital signal indicating that the temperature has risen more than before, and the servo control unit 13 that has input the digital signal controls the LD drive circuit 6 to control the LD5. A large drive current is supplied to the LD 5 so that the light emission power of the LD 5 becomes constant.

Further, as described above, when the resistance of the thermistor 11a decreases due to an increase in the temperature of the LD 5, the potential of the superimposed amplitude adjustment terminal 7a of the high-frequency superimposed module circuit 78 decreases,
In the high frequency superposition module circuit 78, the amplitude control circuit 8 performs control so that the amplitude of the high frequency current generated by the high frequency superposition circuit 7 is increased. As a result, the high frequency superposition circuit 7 has a high frequency with a larger amplitude than before. Output current. This high frequency current is superimposed on the drive signal from the LD drive circuit 6 and applied to the LD 5.

As described above, when the temperature of the LD 5 rises, the amplitude of the high-frequency current superimposed on the drive signal of the LD 5 is increased, so that the LD 5 can perform a switching operation even at a high temperature, and the scoop noise can be reduced. By the way, for example, as shown in FIG. 3, the relationship between the drive current and the light emission power is shifted depending on the temperature, and the inclination is increased in the direction of falling, as indicated by L1 and L2.

In the conventional optical disc apparatus, when the inclination is indicated by L2 at 70 ° C., for example, the amplitude of the high-frequency current S2 does not exceed the threshold value Ith2, and thus the LD 5 cannot perform the switching operation. In the apparatus, for example, even when the temperature becomes 70 ° C. and the relationship between the drive current and the light emission power is indicated by L2, the amplitude of the high-frequency current S2 is the threshold value Ith2.
LD5 can perform a switching operation because it is increased to a level slightly exceeding
As a result, the margin of the superposed amplitude (the amplitude of the superposed high-frequency current) due to the LD temperature characteristic can be canceled, and the superposed amplitude value can be set small at room temperature.

Therefore, this embodiment is effective for preventing data destruction and EMI of a rewritable optical disk. Further, in the present embodiment, since the parts currently used (in this case, the thermistor) are used in combination, the circuit configuration is not complicated and the cost is not increased.

1 is a block diagram showing a configuration related to a laser drive system of an optical pickup in an optical disc apparatus according to an embodiment of the present invention. In the said embodiment, it is a circuit diagram which shows a part of temperature detection processing circuit contained in the high frequency superimposition module circuit and thermistor contained in the optical pick-up circuit part of an optical pick-up, and the control circuit part of a servo control part. It is a figure for demonstrating an example of the relationship (IL characteristic) of the drive current supplied to a laser diode, and the light emission power of a laser diode. FIG. 11 is a circuit diagram showing a part of a temperature detection processing circuit included in a high-frequency superposition module circuit and a thermistor included in an optical pickup circuit unit of an optical pickup and a control circuit unit of a servo control unit in a conventional optical disc apparatus.

Explanation of symbols

1 optical disk device 3 optical pickup 5 LD (laser diode)
6 LD drive circuit 7a Superimposed amplitude adjustment terminal 11a Thermistor (temperature detection element)
78 High frequency superposition module circuit

Claims (3)

A laser diode that emits laser light to an optical disc, a laser diode drive circuit that supplies a drive current to the laser diode, and a circuit that generates a high-frequency current and superimposes the drive current on the laser diode. In an optical disc apparatus provided with an optical pickup having a high frequency superposition module circuit configured to be able to set the amplitude of the high frequency current by a resistance value of an external resistor connected between an amplitude adjustment terminal and ground,
In order to increase the control accuracy of the light emission power of the laser diode, a thermistor provided in advance for detecting the ambient temperature of the laser diode is used in combination, and the thermistor is grounded with the superimposed amplitude adjustment terminal of the high-frequency superposition module circuit. An optical disc characterized in that the high frequency superposition module circuit increases the amplitude of the high frequency current to be output when the resistance value of the thermistor decreases due to a temperature rise. apparatus. A laser diode that emits laser light to an optical disc, a laser diode drive circuit that supplies a drive current to the laser diode, and a circuit that generates a high-frequency current and superimposes the drive current on the laser diode. In an optical disc apparatus provided with an optical pickup having a high frequency superposition module circuit configured to be able to set the amplitude of the high frequency current by a resistance value of an external resistor connected between an amplitude adjustment terminal and ground,
In order to improve the control accuracy of the light emission power of the laser diode, the temperature detection is performed in combination with a temperature detection element whose resistance value changes according to a temperature change provided in advance for detecting the ambient temperature of the laser diode. An optical disc apparatus characterized by having a circuit configuration in which an element is connected between a superposition amplitude adjustment terminal of the high frequency superposition module circuit and a ground instead of the external resistor. The temperature detection element is a thermistor whose resistance value decreases as the temperature rises, and when the resistance value of the thermistor decreases due to temperature rise, the high frequency superposition module circuit increases the amplitude of the high frequency current to be output. The optical disc apparatus according to claim 2.

Images