JPH07262593A - Optical disk device - Google Patents

Abstract

PURPOSE:To quicken write/read switching operation and to correctly perform servo control with the simple constitution of the device by controlling the reverse bias voltage of a photodetector for information reproduction comparing with the time of reading at the time of writing and limiting the characteristic of frequency response. CONSTITUTION:The photodetector of an optical pickup 27 is composed of 2X2 arranged photodiodes A-D and, amplifiers 12A-12D together with feedback resistors 13A-13D compose a current/voltage converter circuit 29. A matrix circuit 10 performs the addition/subtraction processing of outputted voltage signals to which the circuit 29 converts the output current signals of respective PDs, forms a reproducing signal RF and a servo signal SB and sends them to a signal decoder and a servo circuit. A transistor 32 controls the reverse bias voltages of diodes A-D by means of a changeover signal VC at the time of writing and limits the characteristic of frequency response more compared with it at the time of reading. Consequently, writing operation is changed to reading operation in a short time using the simplified constitution of the device and tracking and focusing control are correctly performed at the time of writing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, and more particularly to an optical disk device capable of improving frequency characteristics of a reproducing system.

[0002]

2. Description of the Related Art In an optical disk device, a light beam is applied to an optical disk through an objective lens and reflected light is received by a photodetector (PD) from the optical disk. Based on the light receiving result, for example, the biaxial actuator of the optical pickup can be controlled to perform tracking control and focus control. As a result, it is possible to write an information signal to the optical disc at the time of recording or read the information signal recorded on the optical disc at the time of reproducing.

In the conventional optical disk device 1 shown in FIG.
It has four photodetectors A to D. These photodetectors A to D are, for example, photodiodes. The photodetectors A to D are integrally held to form one light receiving element, and are arranged in the optical pickup. The four photodetectors A to D are preferably arranged in a square shape with their light-receiving surfaces adjacent to each other, and the cathodes of the four photodetectors A to D are commonly connected. As shown in FIG. 6, the cathodes of the photodetectors A to D are fixed reverse bias power sources Vr.
Connected to the photo detectors A to D
The anodes of are connected to amplifier circuits (I-VAMP) 3A to 3D via resistors 2A to 2D, respectively.

The circuit including the resistors 2A to 2D, the amplifier circuits 3A to 3D, and the matrix amplifier circuit 5 is a processing circuit for performing low frequency signal processing. The amplifier circuits 3A to 3D are current-voltage conversion circuits having feedback resistors 4A to 4D, respectively. When the reflected light from the optical disk is received by the photodetectors A to D, the amplifier circuits 3A to 3D convert the currents of the photodetectors A to D into current-voltage and output them. The amplifier circuits 3A to 3D limit the band so that the gain is reduced on the high frequency side, and the photodetectors A to D receive the results of the amplification circuit 3A.
3D to 3D convert the low frequency component into a current voltage and output it.

The matrix amplifier circuit 5 is composed of the amplifier circuit 3
The servo signals SB are generated by amplifying the output signals of A to 3D and subjecting them to addition and subtraction processing. This servo signal S
B is a tracking error signal and a focus error signal. Based on this servo signal SB, the biaxial actuator of the optical pickup is subjected to tracking control and focus control.

On the other hand, an amplifier circuit (I-VAMP)
6 and the capacitors 8A to 8D are high frequency signal processing circuits. The amplifier circuit (I-VAMP) 6 includes an amplifier circuit 3A.
A current-voltage conversion circuit having a feedback resistor 7 similarly to 3D. The anode of each photodetector A to D is connected to one end of a capacitor 8A to 8D. The other ends of the capacitors 8A to 8D are commonly connected to the input end of the amplifier circuit 6, so that the photodetection results of the photodetectors A to D are converted into current-voltage in the form of a sum signal.

The amplifying circuit 6 has frequency characteristics set so that a sufficient gain can be obtained in the high frequency region as compared with the amplifying circuits 3A to 3D, whereby the photodetectors A to A obtained in the form of a sum signal. Regarding the light receiving result of D, the high frequency region side is selectively output. A reproduction signal RF is obtained through the amplifier circuit 6, and the reproduction signal RF is processed by a predetermined signal processing circuit to reproduce a desired information signal.

As described above, the conventional optical disc apparatus 1 shown in FIG. 6 detects the servo signal SB and the reproduction signal RF by limiting the received light results of the photodetectors A to D to the high frequency band and the low frequency band, respectively. Then, it is possible to write a desired information signal to the optical disc and read the information signal from the optical disc. That is, when the signal processing circuit system using the band division of FIG. 6 is adopted, when the electric signal (information signal) from the optical disc is read out (during reproduction), the servo signal in which the low frequency band is important and the high frequency An RF signal that requires a frequency band in the range is divided by photodetectors A to D by a method such as band division.

When the method of the signal processing circuit using the band division of FIG. 6 is adopted, the laser diode emits pulses during the recording (writing) of the information signal on the optical disk, and the photodiodes A to D are Even in response to the pulse emission of the laser diode, the frequency band handled by the servo signal processing circuit (the circuit including the resistors 2A to 2D, the amplification circuits 3A to 3D, and the matrix amplification circuit 5) is low, so that the photodiodes A to D However, it hardly responds to the pulsed light emission of the laser diode and operates stably in the circuit.

[0010]

However, in the optical disc apparatus 1 of FIG. 6, when the information signal is written on the optical disc, the data input from the host computer or the like is modulated by a certain modulation method. The frequency band of the information signal actually written on the optical disc changes according to this modulation method.
If the optical disc device 1 adopts a modulation method in which the frequency band of the information signal to be actually written extends from the low band to the high band, the frequency characteristics of the optical disc can be effectively utilized to make the information signal of high density on the optical disc. Can be recorded.

When the modulation system is adopted so that the frequency band of the information signal to be actually written extends from the low band to the high band, the frequency band of the reproduction signal RF extends to the frequency band of the servo signal SB. . Therefore, when the light receiving results of the photodetectors A to D are processed with band limitation, it becomes difficult to reliably separate the reproduction signal RF and the servo signal SB. That is, in order to achieve a high recording density of the information signal of the optical disk, some modulation methods require an RF signal from a low frequency band, and a signal for band division as shown in FIG. It has become impossible to employ a processing system, and the signals of the photodetectors A to D must be processed by a circuit having a wide frequency characteristic from low frequency band to high frequency band.

In this case, the signal processing circuit of the optical disk device 11 shown in FIG. That is, the signals from the photodetectors A to D are processed by the amplifier circuits (I-VAMP) 12A to 12D in which the frequency band from the low band to the high band is guaranteed,
The matrix amplification circuit 10 takes a matrix to generate a reproduction signal RF and a servo signal SB. In the optical disk device 11 of FIG. 7, the anodes of the photodetectors A to D are respectively amplified by an amplifier circuit (I-VAMP).
Connect to 12A to 12D. The amplifier circuits 12A to 12D form a current-voltage conversion circuit having feedback resistors 13A to 13D, respectively.

In the optical disk device 21 shown in FIG. 7, when a laser diode emits a light beam in a pulsed manner to write an information signal on the optical disk, the light quantity of the reflected light rapidly changes in accordance with the rapid and large light quantity change of the light beam. It changes greatly, and the currents of the photodetectors A to D also change abruptly and greatly. That is, if the light beam is pulsed, it is difficult for the outputs of the amplifier circuits 12A to 12D to accurately trace the pulse.
The waveform corresponds to a slew rate of 2A to 12D. Therefore, in the matrix circuit 10, if the matrix of the outputs of the amplifier circuits 12A to 12D is taken and the servo signal SB is created, the variations in the slew rate of the amplifier circuits 12A to 12D will be included as an error. That is, the output signal waveforms of the amplifier circuits 12A to 12D are changed and input according to the transfer characteristics of the amplifier circuits 12A to 12D.

Thus, the amplifier circuit 12A as shown in FIG.
When the frequency band of 12 to 12D is widely selected from the low band to the high band and arithmetic processing is performed by the matrix circuit 10, variations in the transfer characteristics of the amplifier circuits 12A to 12D are superimposed on the servo signal SB. Therefore, it becomes difficult to obtain a correct servo signal SB during writing, and it becomes difficult to correctly perform tracking control and focus control of the biaxial actuator of the optical pickup. As a method of solving this problem, a method of switching the frequency band of the amplifier circuits 12A to 12D between recording and reproduction by making the reproduction signal RF unnecessary at the time of writing is conceivable, but the circuit is complicated. Is difficult.

Further, the frequency band of the amplifier circuits 12A to 12D is widely selected from the low band to the high band and the matrix circuit 1 is selected.
When an information signal is written to the optical disc in the case where the arithmetic processing is performed with 0, if a pulse signal of high power at the time of writing is input, saturation occurs in the circuit. That is, when the currents of the photodetectors A to D change abruptly and largely, the reproduction signal RF also changes abruptly and largely. In the signal processing circuit for processing the reproduction signal RF, the input side of the reproduction signal RF is set. The circuit saturates. As a result, there is also a problem that it may take time to return from the write operation to the next read.

The present invention has been made in view of the above problems, and has a simple structure, and can switch from a writing operation to a reading operation in a short time, and can further properly perform tracking control and focus control during writing. The purpose is to provide a device.

[0017]

SUMMARY OF THE INVENTION In the present invention, the above object is to write an information signal to an optical disc by the intensity of light and read the information signal from the optical disc by using a photodiode to reflect the reflected light from the optical disc. In an optical disk device that receives light and reproduces the information signal recorded based on the light reception result of the photodiode, the reverse bias of the photodiode is set so as to limit the frequency response characteristic of the photodiode when writing, as compared with when reading. This is achieved by an optical disk device including a reverse bias voltage control means for controlling the voltage.

In the present invention, preferably, the frequency response characteristic of the photodiode is lowered to a frequency band required for servo processing. In the present invention, the reverse bias voltage control means is preferably a transistor.
In the present invention, preferably, the reverse bias voltage control means is an analog switch.

[0019]

According to the above-mentioned structure, the frequency response characteristic of the photodiode is limited and the reproduction system frequency characteristic is switched at the time of writing and at the time of reading by a simple constitution of only controlling the reverse bias voltage of the photodiode. be able to.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
These aspects are not limited.

FIG. 1 shows a signal processing circuit of a preferred embodiment of the optical disk device of the present invention, and FIG. 2 shows a preferred embodiment of the optical disk device of the present invention. Figure 2
In the configuration of the optical disc device 21 shown in FIG. 2, the parts denoted by the same reference numerals as those in the above-mentioned conventional example have the same configuration, and therefore, the duplicate description will be omitted.

Write Once
Alternatively, a rewritable optical recording device has a method of modulating light and recording the intensity of light on an optical disc. Further, in the magneto-optical recording apparatus, a method of emitting light in pulses in recording has been considered in order to achieve high density.

The optical disk device 21 of FIG. 2 is an optical recording device, for example, a so-called Write On (Write On) device.
ce) type optical disk device. The optical disk device 21 writes a desired information signal on the optical disk 23 or reads and outputs the information signal written on the optical disk 23 according to a command output from the host computer 22. The spindle motor 24 of the optical disk device 21 checks and holds the optical disk 23, and rotates the optical disk 23 at a predetermined rotation speed. The optical pickup 27 is arranged at a certain distance from the optical disc 23. Optical pickup 2
Although not shown, a laser diode (LD) and a photodetector (PD) are arranged at 7. The laser diode is driven by the laser diode driver 28.

The controller 25 is an interface circuit with the host computer 22, and is a control circuit of the optical disk device 21. The controller 25 responds to commands from the host computer 22 by the servo circuit 2
6. Output the control signal SC to the signal decoder 30 and the laser driver 28. When the control signal SC is applied to the servo circuit 26, the servo circuit 26 is driven to cause the optical pickup 27 to seek a predetermined recording track.

The optical pickup 27 is the optical disc 23.
Can be moved in the radial direction. When controlled by a laser diode driver (LD driver) 28, the laser diode of the optical pickup 27 emits a light beam from the laser diode and irradiates the optical disc 23 with this light beam via a predetermined objective lens. The objective lens of the optical pickup 27 receives the reflected light of the optical disc 23 and guides the reflected light to the above-mentioned light receiving element. Optical pickup 2
A servo circuit 26 can move this objective lens in the focus direction and the tracking direction. Servo circuit 26
Can perform tracking control and focus control of the objective lens by moving the objective lens in the focus direction and the tracking direction based on the servo signal SB.

The light receiving element of the optical pickup 27 shown in FIG. 1 is composed of four photodiodes A to D. These four photodiodes A to D are preferably arranged in the field. Amplifier circuit 12 of FIG.
The A to 12D and the feedback resistors 13A to 13D form the current-voltage conversion circuit 29 of FIG. Output signals of the four photodiodes A to D in FIG. 1 are output to a current-voltage conversion circuit (I-VAMP) 29, and the current-voltage conversion circuit (I-VAMP) 29 outputs the output current signal as a voltage signal. Convert to. The matrix circuit 10 performs addition / subtraction processing (matrix processing) on the voltage signal of the current-voltage conversion circuit 29 to produce a reproduction signal RF and a servo signal SB. The reproduction signal RF of FIG. 2 is sent to the signal decoder 30, and the servo signal SB is sent to the servo circuit 26.

The servo circuit 26 of FIG. 2 generates a tracking signal and a focus signal with reference to this servo signal SB. As a result, the servo circuit 26 seeks the optical pickup 27 to a desired recording track on the basis of the servo signal SB, and then the optical pickup 27.
The objective lens is tracking-controlled and focus-controlled by the biaxial actuator. The address data and the clock are generated from the reproduction signal RF.

Writing Mode In this way, when the optical pickup 27 is moved to a desired recording track and a writing command is input from the host computer 22, the controller 2
Reference numeral 5 modulates the write data transferred from the host computer 22 by a predetermined modulation method.

The controller 25 outputs a control signal SC to the laser diode driver 28 to set the entire operation mode to the write operation mode, and the modulated data D
The ATA is output to the laser diode driver 28. As a result, the laser diode driver 28 switches the light amount of the light beam emitted from the optical pickup 27 to the write mode light amount. The laser diode driver 28 drives the laser diode of the optical pickup 27 according to the modulated data DATA, and irradiates the optical disc 23 with a light beam having a large amount of light intermittently or with a strong or weak light, thereby generating a desired information signal. Is recorded on the optical disc 23.

That is, the write data DATA is sent from the controller 25 to the laser diode driver 28 and is converted into light intensity through the laser diode of the optical pickup 27. The light from the optical pickup 27 hits the optical disc 23, and the light reflectance changes in a strong light portion due to a thermal reaction.

Read Mode On the other hand, when a read command is input from the host computer 22, the controller 25
The control signal SC is output to the laser diode driver 28 to reduce the light quantity of the light beam, and the signal decoder 30
Then, the control signal SC is output to and the entire operation mode is switched to the reading mode.

That is, at the time of reading, the optical pickup 27 causes the laser diode to emit DC light and hits the optical disk 23. Light reflected from the optical disk 23 is converted into an electric signal by the photodetector of the optical pickup 27 and transferred to the host computer 22 through the amplifier circuits 12A to 12D of FIG. 1, the matrix 10, and the signal decoder 30 and controller 25 of FIG. To do.

The signal decoder 30 binarizes the reproduction signal RF to obtain serial data, decodes this serial data by a predetermined decoding method, and outputs it. As a result, the controller 25 sequentially captures and accumulates the reproduction data DATA output from the signal decoder 30, and then outputs the reproduction data DATA at a predetermined timing in response to a request from the host computer 22.

As shown in FIG. 1, the cathodes of the photodetectors A to D are commonly connected to the emitter of the transistor 32, and the collector of the transistor 32 is connected to the power supply VCC. The transistor 32 limits the frequency response characteristic of the photodiode when writing, as compared with when reading,
It is a reverse bias voltage control means for controlling the reverse bias voltage of the photodiode.

In the read mode and the write mode, the controller 25 of FIG. 1 outputs the predetermined switching signal VC of FIG. 2 to the optical pickup 27, thereby switching or limiting the frequency characteristic of the photodetector at the time of reading and writing. To do.

The transistor 32 of FIG. 2 receives the switching signal VC at its base, whereby this switching signal VC
The photodetectors A to D are reverse biased with a reverse bias voltage determined by.

Next, referring to FIG. FIG. 3 shows changes in the time characteristics of each value when the reverse bias voltage of the photodiode is controlled. FIG. 3A shows the amount of light emitted from the laser diode, and FIG. 3B shows the reverse bias voltage of the photodetector. FIG. 3C shows the frequency characteristic of the photodetector. As shown in FIG. 3A, during the write mode period TW, the optical disk device 21 of FIG. 2 has the light amount L of the light beam emitted from the optical pickup 27 in accordance with the write data DATA of FIG.
Is raised from the light amount PR at the time of reading to the light amount PW at the time of writing. On the other hand, the optical disk device 21 of FIG.
During the read mode period TR of FIG. 3A, the light quantity of this light beam is held at the light quantity PR at the time of reading.

The controller 25 of FIG. 2 switches the base voltage VC of the transistor 32 of FIG.
In the period TW of this writing mode, the photo detector A
The bias voltage VD of D to D is held at the reverse bias voltage Vrs at the time of writing. Further, the controller 25 switches the base voltage VC of the transistor 32 of FIG. 1 to hold the bias voltage VD of the photodetectors A to D at the reverse bias voltage Vrr at the time of reading in the period TR of the reading mode.

The rise time tr and the fall time tf, which are the response times (frequency response characteristics) of the photodetectors A to D, are determined by the junction capacitance Cj of the photodetectors A to D and the load resistance R1. The junction capacitance Cj changes according to the reverse bias voltage Vr applied to the photo detectors A to D. The rising time tr and the falling time tf can be expressed by the following equations.

[0040]

[Equation 1]

The junction capacitance Cj can be expressed by the following equation.

[0042]

[Equation 2]

Here, A is a constant, Vd is a diffusion potential of about 0.5 to 0.9 V, Vr is a reverse bias voltage, and Z is Z.
Is a constant with a value of 1/2 to 1/3.

Therefore, the frequency characteristic of the photodiode with respect to the reverse bias voltage of the photodiode is shown in FIG.
It changes like.

As shown in FIG. 4, the photodetectors A to D are characterized in that the frequency response characteristic F improves as the reverse bias voltage VD increases. By utilizing this characteristic, as shown in FIG. 3C, in the optical disc device 21, as compared with the reverse bias voltage Vrr at the time of reading,
The reverse bias voltage VD is switched or lowered or controlled so that the reverse bias voltage Vrs at the time of writing is lowered or limited.

As shown in FIG. 3C, the frequency band of the photodetector required for signal processing of the reproduction signal RF is fr.
Let r be the frequency band of the photodetector required for the servo signal SB and fss be the frequency band (frr >> fss).
Then, as shown in FIG. 3B, the reverse bias voltages of the photodetectors corresponding to them are set to Vrr and Vrs, respectively.

At this time, during the writing period TW, the reproduction signal RF is not necessary and only the servo signal SB needs to be obtained. Therefore, the frequency band frs obtained during the writing period TW in FIG. The reverse bias voltage Vrs at the time of writing in FIG. 3B is set low so that the band is necessary for detecting the servo signal SB in FIG. On the contrary,
The frequency band frr obtained in the reading period TR is
The reverse bias voltage Vrr at the time of reading is set so as to be in a band necessary for detecting the reproduction signal RF of FIG. 2 (a wide frequency band from a low band to a high band).

As a result, even when the amount of light reflected from the optical disk 23 in FIG. 2 changes abruptly and largely during writing, the photodetectors A to D output the light amount detection results obtained by averaging the amount of light. Practically, for example, the light amount PW of the writing period TW is equal to the reading period TR.
The light amount PR is about 10 times or more, but when averaged, the light amount in the writing mode is about 3 to 4 times the light amount in the reading mode.

Thus, at the time of writing, the signal from the photodetector is unnecessary as the reproduction signal RF, and only the servo signal SB is necessary. In other words, as the photodetector, only the low frequency band is required as shown in FIG. 3C, so if the frequency band of the photodetector can be set low during writing, the electric signal obtained from the photodetector is a pulse signal. Instead of an averaged signal. Therefore, it is possible to eliminate the influence of the pulse emission of the laser diode on the servo signal SB. Moreover, as the current-voltage conversion circuit 29 of FIG. 2, it is not necessary to handle the pulse signal at the time of writing, and an inexpensive amplifier having a small dynamic range can be used.

Therefore, each of the amplifier circuits 12A to 12D forming the current-voltage conversion circuit 29 can effectively avoid a rapid and large current change of the photodetectors A to D due to the intensity of light from the laser diode at the time of writing, so that the photodetector A can be effectively prevented. The currents D to D can be correctly converted to current and output. As a result, even when the matrix circuit 10 uses the broadband current-voltage conversion circuit 29 to perform arithmetic processing to generate the reproduction signal RF and the servo signal SB, the reverse bias voltage is simply switched or controlled. Therefore, the correct servo signal SB can be obtained.

A reproduction signal R is selected by selecting a certain modulation method.
Even when the frequency band of F is selected to extend to the frequency band of the servo signal SB, stable tracking control and focus control can be performed during recording, and desired information signals can be recorded at higher density.

Since the averaged value can be output as the light reception result,
In the optical disk device 21, the current-voltage conversion circuit 29 having a small dynamic range can be adopted, and the overall configuration can be simplified. Also, the reproduction signal RF of the next stage
In the processing circuit (signal decoder 30) of 1, the circuit saturation can be effectively avoided, and the optical disk device 21 can switch from the writing operation to the reading operation in a short time.

In the embodiment shown in FIGS. 1 and 2, as the reverse bias voltage control means for controlling the reverse bias voltage of the photodiode at the time of writing so as to limit the frequency response characteristic of the photodiode as compared with the time of reading. The case where the transistor 32 is provided between the power supply VCC and the photodetectors A to D, and the base voltage VC of the transistor 32 is switched to switch the reverse bias voltage VD is described. However, the present invention is not limited to this, and as shown in FIG. 5, a reverse bias voltage for controlling the reverse bias voltage of the photodiode so as to limit the frequency response characteristic of the photodiode at the time of writing as compared with the time of reading. As a control means, a reverse bias voltage V is selected by a selection circuit 37 using an analog switch.
You may switch D.

The optical disk device 36 of FIG. 5 has a selection circuit 37 in place of the transistor 32 of the embodiment of FIG.
Reverse bias power supplies Vrs and Vrr for writing and reading are connected to the selection circuit 37, respectively. The optical disk device 36 switches the contact of the selection circuit 37 with a switching signal SEL output from the controller 25,
As a result, the reverse bias voltage V
Switch D. Even if the reverse bias voltage VD is switched by using the selection circuit 37 in this way, the same effect as that of the embodiment of FIG. 2 can be obtained.

In the embodiment shown in FIGS. 2 and 5, the servo signal SB and the reproduction signal R are produced by using four photodetectors.
F is detected. However, the present invention can be widely applied when various methods are applied to detect the servo signal SB and the reproduction signal RF.

Further, in the above-mentioned embodiment, the case where the present invention is applied to the write-once type optical recording device has been described, but the present invention is not limited to this, and the rewritable (Rewable) is used.
It can also be applied to an optical recording device such as a writeable optical disk device and an optical disk device such as a magneto-optical disk device.

[0057]

As described above, according to the optical disk device of the present invention, it is possible to switch from the write operation to the read operation in a short time with a simple structure, and also to perform the tracking control and the focus control correctly at the time of writing. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a signal processing circuit of a preferred embodiment of an optical disk device of the present invention.

FIG. 2 is a block diagram showing the overall configuration of a preferred embodiment of the optical disk device of the present invention.

FIG. 3 is a signal waveform diagram when controlling the reverse bias of the photodiode in the embodiment of FIG.

FIG. 4 is a characteristic curve diagram showing the relationship between frequency characteristics and reverse bias voltage.

FIG. 5 is a block diagram showing another preferred embodiment of the optical disk device of the present invention.

FIG. 6 is a block diagram showing a signal processing circuit of a conventional optical disc device.

FIG. 7 is a block diagram showing a signal processing circuit of another conventional optical disc device.

[Explanation of symbols]

1, 11, 21, 36 Optical disk device 3A to 3D, 6, 12A to 12D Amplifier circuit 5, 10 Matrix amplifier circuit 8A to 8D Capacitor 23 Optical disk 25 Controller 26 Servo circuit 27 Optical pickup 28 Laser diode driver 29 Current-voltage conversion circuit 30 Signal Decoder 32 Transistor (Reverse Bias Voltage Control Means) 37 Selection Circuit (Reverse Bias Voltage Control Means) A to D Photo Detectors

Claims (4)

[Claims] 1. When an information signal is written on an optical disk by the intensity of light and the information signal is read from the optical disk, the reflected light from the optical disk is received by a photodiode and recorded based on the light receiving result of the photodiode. An optical disc device for reproducing an information signal is provided with a reverse bias voltage control means for controlling a reverse bias voltage of the photodiode at the time of writing so as to limit the frequency response characteristic of the photodiode as compared with the time of reading. Optical disk device. 2. The optical disk device according to claim 1, wherein the frequency response characteristic of the photodiode is lowered to a frequency band required for servo processing. 3. The optical disk device according to claim 1, wherein the reverse bias voltage control means is a transistor. 4. The optical disk device according to claim 1, wherein the reverse bias voltage control means is an analog switch.