JP2008217898A - Optical disk device and temperature detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably detect the temperature of a laser diode for an optical disk device by a simple constitution. <P>SOLUTION: In the package of the laser diode, provided are a photodiode 26 for detecting the amount of light emitted from the laser diode 25, a current supply means 32 supplying a forward current to the photodiode 26, a voltage drop detection means 12 detecting forward voltage drop when the forward current flows through the photodiode 26, and a temperature calculation means 12 calculating the temperature of the laser diode 25 on the basis of a conversion coefficient indicating a relation between the forward voltage drop and a temperature when the forward current flows through the photodiode 26 and the detected forward drop voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disk device and a temperature detection method, and is suitable for application to temperature detection of a laser diode.

  Conventionally, a laser diode has been widely used as a light source of laser light in an optical disc apparatus.

The laser diode generates heat as the laser beam is emitted. However, the wavelength and output of the laser beam change due to the influence of the generated heat, and the laser diode itself is damaged due to excessive heat generation. Therefore, as shown in FIG. 1, a temperature detection element 3 made of a thermistor or the like is disposed in the vicinity of the laser diode 2 on the circuit board 1 of the optical pickup, and the temperature of the laser diode 2 is detected by the temperature detection element 3. An optical disc apparatus configured as described above has been proposed (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-339757 (FIG. 1b)

  However, in the optical disk apparatus having the above-described configuration, the temperature detection element 3 detects the ambient temperature in the vicinity of the laser diode 2 and the heat transmitted through the circuit board 1, so that the temperature of the laser diode 2 itself is accurately determined. There was a problem that could not be detected. Further, since the temperature detecting element 3 is necessary, there is a problem that the configuration of the optical disk apparatus becomes complicated.

  The present invention has been made in consideration of the above points, and intends to propose an optical disc apparatus and a temperature detection method capable of reliably detecting the temperature of a laser diode with a simple configuration.

  In order to solve such a problem, in the optical disc apparatus of the present invention, a photodiode for detecting the amount of light emitted from the laser diode provided in the package of the laser diode, and a current supply means for supplying a forward current to the photodiode A voltage drop detecting means for detecting a forward voltage drop when a forward current flows through the photodiode, and a conversion indicating a relationship between the forward voltage drop and the temperature when the forward current flows through the photodiode. The optical disk apparatus is provided with temperature calculation means for calculating the temperature of the laser diode based on the coefficient and the detected forward voltage drop.

  Then, the forward voltage drop is normalized using the reference forward voltage drop when a forward current is passed while the photodiode is at a predetermined reference temperature, and the temperature of the laser diode is calculated.

  By applying a forward current to a photodiode provided in a laser diode package and having a low thermal resistance with the laser diode, and detecting the temperature of the laser diode based on the forward voltage drop at that time The temperature of the laser diode can be accurately detected with a simple configuration.

  Then, by normalizing the forward voltage drop using the reference forward voltage drop, it is possible to correct variations in individual characteristics of the photodiode, and to detect the temperature of the laser diode with a simple configuration with higher accuracy. .

  In the temperature detection method of the present invention, a forward current is supplied to a photodiode provided in a laser diode package for detecting the amount of light emitted from the laser diode, and the forward current flows through the photodiode. The temperature of the laser diode is detected based on the conversion coefficient indicating the relationship between the forward voltage drop and the temperature when a forward current is passed through the photodiode and the detected forward voltage drop. Was calculated.

  By applying a forward current to a photodiode provided in a laser diode package and having a low thermal resistance with the laser diode, and detecting the temperature of the laser diode based on the forward voltage drop at that time The temperature of the laser diode can be accurately detected with a simple configuration.

  According to the present invention, a forward current is passed through a photodiode provided in a laser diode package and having a low thermal resistance with the laser diode, and the temperature of the laser diode is detected based on the forward voltage drop. By doing so, it is possible to realize an optical disc apparatus and a temperature detection method capable of accurately detecting the temperature of the laser diode with a simple configuration.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Overall Configuration of Optical Disc Device In FIG. 2, reference numeral 10 denotes an optical disc device to which the present invention is applied as a whole, and the whole is controlled by the control unit 12. When the optical disk device 10 receives a reproduction or recording instruction or the like from an external device (not shown) with the optical disk 100 loaded, the control unit 12 controls the drive unit 13 and the signal processing unit 14, thereby the optical disk 100. The information recorded on the optical disc 100 is read out, or information supplied from an external device is recorded on the optical disc 100.

  In practice, the drive unit 13 rotates the optical disc 100 at a desired rotational speed by the spindle motor 15 based on the control of the control unit 12, and the sled motor 16 moves the optical pickup 17 greatly in the tracking direction which is the radial direction of the optical disc 100. Further, the biaxial actuator 18 finely moves the objective lens 19 in two directions, ie, a focus direction and a tracking direction, which are directions in which the objective lens 19 approaches or separates from the optical disc 100.

  In parallel with this, the signal processing unit 14 irradiates a desired track of the optical disc 100 with a light beam from the objective lens 19 by the optical pickup 17.

  At this time, the optical pickup 17 condenses the emitted light beam using the objective lens 19 and irradiates the recording layer of the optical disc 100 with the focal point being focused, and also reflects the reflected light beam reflected by the focused recording layer. The light is received by the objective lens and photoelectrically converted, and various detection signals are generated and supplied to the signal processing unit 14.

  The driving unit 13 drives the biaxial actuator 18 based on the focus error signal and tracking error signal supplied from the signal processing unit 14. The signal processing unit 14 performs predetermined signal processing on the reproduction signal supplied from the optical pickup 17 and outputs the processed signal to the outside via the control unit 12.

  Further, in the optical disc apparatus 10, the amount of laser light emitted from the laser diode of the optical pickup 17 is detected by the photodiode, and the laser light is adjusted by adjusting the laser driving current supplied to the laser diode based on the detected amount of light. Is controlled to be constant (so-called APC (Automatic Power Control) control).

  Here, the package in which the laser diode is sealed contains a photodiode (so-called rear monitor) that is generally used for detecting the amount of emitted light in the APC control described above.

  That is, FIG. 3 shows a can-type laser package 20 used in the optical disk apparatus 10 according to the present invention, which is formed in a metal can shape on a substantially disc-shaped heat sink 21 formed of a material having a low thermal resistance such as a copper alloy. A cap 22 is attached. At the upper end of the cap 22, a transmission hole 22A for transmitting laser light is opened, and a disk-like window member 23 made of, for example, glass is attached so as to cover the transmission hole 22A. The inner space is sealed by the heat sink 21 and the window member 23.

  An inverted L-shaped laser mount 24 is suspended from the upper surface of the heat sink 21, and a laser diode 25 is attached to the attachment surface 24 </ b> A at the end of the laser mount 24. The laser mount 24 is also formed of a material having a small thermal resistance. As a result, the laser package 20 efficiently transfers the heat generated by the laser diode 25 to the heat sink 25 via the laser mount 24, and further the heat sink 25. Through this, it escapes to the chassis (not shown) of the optical pickup in which the laser package 20 is installed.

  The installation direction of the laser diode 25 is determined so that the emitted laser light passes through the window member 23. Further, the above-described photodiode 26 for detecting the amount of emitted light is attached below the laser diode 25 on the upper surface of the heat sink 21.

  Three leads 27 are attached to the lower surface of the heat sink 21. As shown in FIG. 4, the cathode of the laser diode 25 and the cathode of the photodiode 26 are connected to the ground lead 27A, the anode of the laser diode 25 is connected to the lead 27B, and the anode of the photodiode 26 is the lead. 27C.

  The leads 27A and 27B are connected to a laser driver (not shown) of the drive unit 13 (FIG. 2), and the control unit 12 controls the laser driver to generate a laser drive current, and the leads 27A and 27B. By supplying to the laser diode 25 via the laser diode, laser light is emitted from the laser diode 25.

Here, the accuracy of the amount of emitted light detected by the photodiode 26 in the laser package 20 is relatively low, and a read-only optical disc apparatus does not require strict control of the amount of emitted light. To execute APC control.

  However, in the recording / reproducing optical disk apparatus 10 that requires strict control of the amount of emitted light, it is necessary to control the amount of emitted light with higher accuracy than the photodiode 26, and therefore, a beam splitter (not shown) installed on the optical path. The outgoing light beam is separated at a predetermined light quantity ratio, and the outgoing light quantity is detected by a separately provided photodiode (not shown) to execute the APC control, and the photodetector 26 is not actually used for the APC control.

(2) Temperature Detection of Laser Diode According to the Present Invention In this optical disk apparatus 10, by detecting the temperature of the laser diode 25 using the photodiode 26 in the laser package 20 described above, a separate temperature detection element is not provided. High-precision temperature detection is realized with a simple configuration.

  That is, the photodiode is a PN junction type semiconductor having sensitivity to light, but has an electrical characteristic equivalent to that of a normal junction type silicon diode.

  FIG. 5 shows Vf (forward voltage drop) / If (forward current) curves for the silicon diode SiD, the two types of Schottky diodes SkD1 and SkD2, and the two types of photodiodes PD1 and PD2, respectively. It can be seen that the characteristics of PD2 and PD2 are similar to those of the silicon diode SiD.

  In the photodiode, Vf changes according to the temperature change. FIG. 6 shows a Vf / If curve when the temperature of the photodiode is changed, and it can be seen that Vf decreases as the temperature of the photodiode increases.

  Further, as shown in FIG. 3, since the photodiode 26 is attached to the heat sink 21 for releasing the heat of the laser diode 25, the thermal resistance between the photodiode 26 and the laser diode 25 is extremely small and sufficient. Therefore, as shown in FIG. 6, Vf of the photodiode 26 reflects the temperature of the laser diode 25 well.

  Accordingly, in a state where the light emission of the laser diode 25 is stopped so that the photodiode 26 does not generate a detection current, a measurement current having a constant forward current is supplied to the photodiode 26, and based on Vf at that time. The temperature of the laser diode 25 can be detected.

  In practice, however, individual photodiodes have variations in characteristics. For example, FIG. 7 shows a Vf / If curve for each of six photodiodes of the same type. In the state of If = 8.0 [mA], a variation of about 15 [mV] appears in Vf. This variation corresponds to ± 5 ° C. Therefore, when Vf is simply converted to temperature, there is a problem that an error due to variation in characteristics occurs.

  However, since each Vf / If curve shown in FIG. 7 draws almost the same curve in the region of If> 4.0 [mA], it is practically sufficient to normalize at a predetermined reference temperature. Temperature detection based on Vf can be performed with accuracy. FIG. 8 shows an example of a Vf / If curve when Vf of If = 5 [mA] is normalized at a reference temperature of 25 ° C. and measured at 55 ° C., and variation in Vf is suppressed to about several [mV]. Since this variation corresponds to about ± 0.5 ° C., the temperature of the laser diode 25 can be measured with practically sufficient accuracy.

  That is, the temperature of the photodiode 26 is changed in a state where a predetermined measurement current is supplied to the photodiode 26, and Vf−temperature for obtaining the temperature from Vf based on the relationship between the temperature and Vf at this time. A conversion coefficient is calculated.

  The calculation of the Vf-temperature conversion coefficient may be performed for one photodiode in advance, and the Vf-temperature conversion coefficient obtained as a result may be applied to all the optical disc apparatuses 10. Also, the measurement mode may be performed on the photodiode 26 alone on the test apparatus or in a state where the optical pickup 17 and the optical disk apparatus 10 are assembled. The Vf-temperature conversion coefficient calculated in this way is stored in a storage unit (not shown) such as a non-volatile memory.

  Further, for each optical disk device 10, the above-described measurement current is passed in a state where the photodiode 26 is kept at a predetermined reference temperature, and Vf at this time is stored in the storage unit of the control unit 12 as a reference Vf.

  When detecting the temperature of the photodiode 26 during the operation of the optical disk device 10, the control unit 12 first controls the drive unit 13 to stop the light emission of the laser diode 25, and then controls the current mirror circuit 32. At the same time, the measurement current is supplied to the photodiode 26, and at the same time, the output of the operational amplifier 33 is digitally converted to a measurement Vf. Further, the value obtained by subtracting the reference Vf from the measurement Vf is multiplied by the Vf-temperature conversion coefficient to obtain the detected temperature of the photodiode 26.

  Next, a circuit configuration for detecting the temperature of the laser diode using the photodiode described above will be described. As shown in FIG. 9, the anode of the photodiode 26 is connected to the temperature detection unit 31 in the signal processing unit 14.

  The temperature detector 31 has a current mirror circuit in which the emitters of the transistors Q1 and Q2 are connected to the power source Vcc via the mirror specific resistances R1 and R2, respectively, and the collector of the transistor Q1 and the bases of the transistors Q1 and Q2 are connected. 32 is formed, and the collector of the transistor Q 2 is connected to the anode of the photodiode 26.

  The bases of the transistors Q1 and Q2 are connected to the control unit 12, and the control unit 12 applies a control signal to the bases of the transistors Q1 and Q2, thereby causing the photodiode 26 to move from the current mirror circuit 32 in a certain order. A measurement current consisting of a directional current can be passed, or the measurement current can be stopped.

  The anode of the photodiode 26 is also connected to the + input terminal of the operational amplifier 33. The output terminal and the -input terminal of the operational amplifier 33 are connected to form a voltage follower circuit. The anode of the photodiode 26 is connected to the control unit 12 via the voltage follower circuit. Based on the output of the operational amplifier 33, Vf of the photodiode 26 is detected.

  Actually, if the laser diode 25 emits light when detecting the Vf of the photodiode 26, the photodiode 26 generates a detection current corresponding to the amount of received light of the laser beam, so that Vf can be detected accurately. Disappear. Therefore, the control unit 12 controls the driving unit 13 to stop the light emission of the laser diode 25 when detecting the Vf of the photodiode 26. Then, as soon as the detection of Vf is completed, the light emission of the laser diode 25 is resumed.

  Further, as described above, in order to correct the variation in characteristics of the photodiode 26, it is necessary to measure the reference Vf at the reference temperature in advance and store it in the control unit 12.

  For example, after the optical disk device 10 is completed, the temperature of the laser package 20 or the optical pickup 17 is adjusted to a reference temperature (for example, 25 ° C.), and the laser diode 25 is turned off. A measurement current is passed, and the reference Vf at that time is digitally converted and stored in a nonvolatile memory (not shown) of the control unit 12.

  When detecting the temperature of the photodiode 26 during the operation of the optical disk device 10, the control unit 12 first controls the drive unit 13 to stop the light emission of the laser diode 25, and then sets the current mirror circuit 32. At the same time, the measurement current is supplied to the photodiode 26, and at the same time, the output of the operational amplifier 33 is digitally converted to the measurement Vf, and the value obtained by subtracting the reference Vf from the measurement Vf is multiplied by the Vf-temperature conversion coefficient. 26 detected temperatures are calculated.

(3) Operation and Effect In the above configuration, in the optical disc apparatus 10, a current mirror circuit as a current source that allows a measurement current in the forward direction to flow through the photodiode 26 originally provided for detecting the amount of light emitted from the laser diode 25. 32, and the control unit 12 measures a measurement Vf that is a forward voltage drop of the photodiode 26 when the measurement current is supplied.

  Then, the measured Vf is normalized using a reference Vf that is a forward drop voltage at a reference temperature that has been measured in advance, and is further multiplied by a Vf-temperature conversion coefficient to obtain a detected temperature of the photodiode 26. .

  The photodiode 26 is sealed close to the inside of the laser package 20 together with the laser diode 25, and both are installed with a very low thermal resistance via the heat sink 21 and the laser mount 24. The temperature of the photodiode 26 is very close to the temperature of the laser diode 25 without being affected by the ambient temperature, the air flow inside the optical disc apparatus 10, or the like.

  Furthermore, since the electrical characteristics of the photodiode are almost the same as those of the junction type silicon diode, the forward voltage drop reflects the temperature of the photodiode itself, and the characteristic variation of each photodiode is used as a reference Vf. By correcting by normalization, the temperature of the laser diode 25 can be accurately detected based on the measurement Vf.

  Further, since the photodiode 26 provided for detecting the amount of emitted light is used as the temperature detection means of the laser diode 25, the temperature of the laser diode can be detected accurately with a simple configuration without providing a separate temperature detection means. It can be carried out.

  According to the above configuration, a forward measurement current is passed through the photodiode 26 provided in the laser package 20 to detect the amount of light emitted from the laser diode 25, and the measurement Vf, which is a forward voltage drop at that time, is used. By detecting the temperature of the laser diode 25, it is possible to accurately detect the temperature of the laser diode with a simple configuration.

(4) Other Embodiments In the above-described embodiment, the current mirror circuit 32 is provided as the current source of the measurement current. However, the present invention is not limited to this, and the laser drive supplied from the drive unit 13 is performed. A current is allowed to flow through the photodiode 26, and the forward voltage drop at that time may be set as the measurement Vf.

  That is, in FIG. 10 in which the same reference numerals are assigned to the parts corresponding to those in FIG. 9, the anode of the photodiode 26 is driven through an FET (Field Effect Transistor) 42 as switching means provided in the temperature detection unit 41. Connected to the unit 13. The gate of the FET 42 is connected to the control unit 12, and the control unit 12 controls the gate voltage of the FET 42 so that the laser drive current supplied from the drive unit 13 flows as a measurement current to the photodiode 26. The measurement current can be stopped.

  In a normal laser light irradiation state, the control unit 12 stops supplying the gate voltage to the FET 42 and closes the FET 42, so that the laser drive current does not flow to the photodiode 26.

  On the other hand, when detecting the temperature of the laser diode 25, the control unit 12 controls the drive unit 13 to reduce the current value of the laser drive current to the above-described measurement current value, and then gates the FET 42. A voltage is supplied to open the FET 42.

  As a result, the drive unit 13 is connected to both the laser diode 25 and the photodiode 26, but the forward voltage drop of the laser diode 25 is larger than the forward voltage drop of the photodiode 26 (for example, the laser diode 25). The forward drop voltage of the photodiode 26 is about 0.7 [V] while the forward drop voltage of the photodiode 26 is about 2 [V], and the laser drive current supplied from the drive unit 13 (that is, measurement) Current) flows only to the photodiode 26, thereby turning off the laser diode 25 and allowing a measurement current to flow to the photodiode 26.

  By adopting such a configuration, it is possible to accurately detect the temperature of the laser diode with a simpler configuration by omitting the current mirror circuit 32 as a current source of the measurement current shown in FIG.

  Further, in the above-described embodiment, the case where the photodiode 26 is not used for APC control has been described. However, the present invention is not limited to this, and the photodiode 26 is used for both APC control and temperature detection. May be. In this case, the anode of the photodiode 26 is connected to the emitted light amount detection unit 30 together with the temperature detection unit 31 in the signal processing unit 14. The emitted light quantity detection unit 30 performs signal processing such as amplification on the detection current supplied from the photodiode 26 to generate an emitted light quantity signal, and supplies this to the control unit 12.

  The present invention can be widely applied to various optical disk devices.

It is a basic diagram with which it uses for description of the conventional temperature detection method using a temperature detection element. It is a block diagram which shows the whole structure of an optical disk device. It is a basic diagram which shows the structure of a laser package. It is a block diagram which shows the connection state of a laser package. It is a characteristic curve figure which shows the Vf / If curve of various diodes. It is a characteristic curve figure which shows the Vf / If curve of the photodiode according to a temperature change. It is a characteristic curve figure with which it uses for description of the dispersion | variation in the characteristic of a photodiode. It is a characteristic curve figure which shows the Vf / If curve after normalization. It is a block diagram which shows the structure of a temperature detection part. It is a block diagram which shows the structure of the temperature detection part by other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Circuit board, 2 ... Laser diode, 3 ... Temperature detection element, 10 ... Optical disk apparatus, 12 ... Control part, 13 ... Drive part, 14 ... Signal processing part, 15 ... Spindle motor, 16... Thread motor, 17... Optical pickup, 18... Biaxial actuator, 19... Objective lens, 30. 33: operational amplifier, 42: FET, 100: optical disk.

Claims (4)

A photodiode provided in a laser diode package for detecting the amount of light emitted from the laser diode;
Current supply means for supplying a forward current to the photodiode;
A voltage drop detecting means for detecting a forward voltage drop when the forward current flows through the photodiode;
The temperature at which the temperature of the laser diode is calculated based on the conversion coefficient indicating the relationship between the forward voltage drop and the temperature when the forward current flows through the photodiode and the detected forward voltage drop An optical disc apparatus comprising: a calculating means. The temperature calculation means normalizes the forward voltage drop using a reference forward voltage drop when the forward current flows in a state where the photodiode is at a predetermined reference temperature, and calculates the temperature of the laser diode. The optical disc apparatus according to claim 1, wherein: The current supply means comprises a laser diode drive means for driving current to the laser diode,
2. The optical disk apparatus according to claim 1, further comprising a connecting unit that connects a laser diode driving unit to the photodiode when detecting the forward current of the photodiode. Provided in the laser diode package, supplying a forward current to the photodiode for detecting the amount of light emitted from the laser diode,
Detecting the forward voltage drop when the forward current flows through the photodiode;
Calculating the temperature of the laser diode based on the conversion coefficient indicating the relationship between the forward voltage drop and the temperature when the forward current is passed through the photodiode, and the detected forward voltage drop. The temperature detection method characterized by this.

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