JP4544093B2 - Optical pickup device and optical disk device - Google Patents

Description

  The present invention relates to an optical pickup device that receives signal light, such as an optical disk device, and more particularly to removal of an offset component due to unnecessary light other than originally necessary signal light generated in a light receiving element.

  2. Description of the Related Art There is an optical disk device that records and reproduces information signals on and from a disk-shaped recording medium such as an optical disk and a magneto-optical disk. Such an optical disk device is moved in the radial direction of the disk-shaped recording medium and the disk-shaped recording medium An optical pickup for irradiating the medium with laser light is provided. In such an optical pickup, in general, laser light emitted from a light emitting element is transmitted through a light separating element such as a beam splitter, and is condensed by an objective lens to be applied to a recording layer of a disk-shaped recording medium. A spot is formed. The laser beam condensed on the recording layer of the disk-shaped recording medium is reflected and incident again on the light separation element, and the optical path is converted by the light separation element and incident on the light receiving element.

  The disc-shaped recording medium includes a multi-layer type in which a plurality of recording layers are provided. Particularly in a single-sided multi-layer disc-shaped recording medium that emits light from one surface, for example, the first recording Even when a laser beam is focused on a layer (a layer on which information is recorded or reproduced) and a spot is formed, the laser beam is also reflected by another recording layer adjacent to the first recording layer, This may become stray light and enter the light receiving element. Such stray light causes problems such as degradation of RF signal quality and servo signal offset, and also due to environmental changes such as interference of laser light reflected by each layer of the disk-shaped recording medium and temperature changes. It also causes a variation in device characteristics.

Thus, a proposal for such a stray light canceling method has been made (see, for example, Patent Document 1). In this method, the second light receiving element is arranged at a position not on the optical axis of the signal light, and the photocurrent and the dark current due to the stray light received by the second light receiving element are arranged on the optical axis of the signal light. By subtracting from the received light current of the first light receiving element, unnecessary current is removed from the received light current of the first light receiving element.
JP-A-10-49906 (page 6, FIG. 3)

  As shown in FIG. 10, an example of the arrangement of the stray light canceling light receiving element (detector) by the above-described known method is provided on both sides of the main beam detector 60 divided into four parts for receiving the reflected light from the optical disk (not shown). The two divided side beam detectors 61A are arranged, and two stray light canceling detectors 62A and 62B for canceling the stray light entering these side beam detectors 61B are arranged outside the side beam detectors 61A and 61B. . That is, in order to remove stray light, the same stray light canceling detector is required in a one-to-one correspondence. For this reason, light receiving for stray light cancellation is performed more than when a light receiving element for detecting signals (side beam detectors 61A and 61B) is used alone. Since wiring is also required for the element, the wiring length of the input portion becomes long and the high frequency characteristics are deteriorated. In addition, there is a problem that the size of the semiconductor substrate is increased because one pair of light receiving elements for detecting signals and one pair of light receiving elements for detecting dark current and stray light (stray light canceling detectors 62A and 62B) are required.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to use stray light from a current obtained by receiving signal light without impairing high-frequency characteristics and without increasing the number of light receiving elements. An object of the present invention is to provide an optical pickup device capable of removing or reducing an unnecessary output voltage (offset voltage) such as a current, and an optical disk device using the optical pickup device.

In order to solve the above-described problems and achieve the object of the present invention, an optical pickup device of the present invention is an optical pickup device that detects signal light from a multilayer optical disk having a plurality of recording layers, and the light applied to the optical disk Is a detection light-receiving element that detects signal light that is return light reflected by the first recording layer of the plurality of recording layers, and a detection light-receiving element that is disposed at a position away from the optical axis of the signal light. In order to cancel the offset component of the received light signal, the light for irradiating the optical disc is detected for detecting stray light that is return light reflected by another recording layer different from the first recording layer of the plurality of recording layers. The light receiving current output from the light receiving element and the canceling light receiving element is input to the first operational amplifier to be converted into a voltage, and the converted voltage is input to the second operational amplifier to obtain the electric current. Comprising a reference voltage generating means for generating and outputting a reference voltage to adjust the level.
Further, the reference voltage output from the reference voltage generating means is input to the first input terminal of the third operational amplifier, and the received light current output from the detection light receiving element is input to the second input of the third operational amplifier. The light receiving current from the detection light receiving element is converted into a voltage by inputting to the terminal, and the difference voltage between the converted voltage corresponding to the light receiving current from the detection light receiving element and the reference voltage is output from the third operational amplifier. Current / voltage conversion means for outputting from the terminal is provided.

The optical disk apparatus of the present invention is an optical disk apparatus including an optical pickup device that receives a return light from an optical disk when a laser beam is irradiated onto a multilayer optical disk having a plurality of recording layers and obtains a received light signal. . This optical pickup device includes a light receiving element for detecting signal light that is return light reflected by a first recording layer of a plurality of recording layers, and a light receiving element for detection that is separated from the optical axis of the signal light. In order to cancel the offset component of the light reception signal of the light receiving element for detection, the light applied to the optical disk is reflected by another recording layer different from the first recording layer among the plurality of recording layers. A canceling light-receiving element that detects stray light that is return light, and a light-receiving current output from the canceling light-receiving element is input to the first operational amplifier to convert it into a voltage, and the voltage converted voltage is converted into a second calculation. Reference voltage generating means is provided for generating and outputting a reference voltage by adjusting the voltage level by inputting to the amplifier. In addition, the reference voltage is input to the first input terminal of the third operational amplifier, the light reception current output from the detection light receiving element is input to the second input terminal of the third operational amplifier, and the light reception current is calculated. Current / voltage conversion means for converting the voltage into a voltage and outputting a difference voltage between the converted voltage and the reference voltage from the output terminal of the third operational amplifier .

  Further, in the present invention, when one or more of the area, the photosensitivity, and the dark current of the detection light-receiving element and the cancellation light-receiving element are different, the reference voltage of the reference voltage is determined based on the difference in characteristics of the light-receiving elements. Reference voltage adjusting means for setting the level to an optimum value is provided.

  Thus, in the present invention, in addition to the light receiving element for detecting signal light, a canceling light receiving element is disposed at a position not on the optical axis of the signal light, and a photocurrent due to dark current or stray light is signaled from this light receiving element. Focusing on the generation of the same amount as the light receiving element for light detection, after converting the light receiving current of the light receiving element for cancellation into a voltage, the voltage level is adjusted to the reference voltage, and the light receiving element for signal light detection When converting the received light current into a voltage, an unnecessary output voltage such as a stray light current is obtained from the current obtained by receiving the signal light by subtracting the reference voltage from the received light voltage of the light receiving element for signal light detection. (Offset voltage) can be removed or reduced. Therefore, the conversion circuit for converting the voltage of the light receiving currents of the signal detecting and canceling light receiving elements can be separated, so that the wiring length of the input section can be shortened and the high frequency characteristics can be prevented from being impaired. .

  In addition, even if there are multiple light receiving elements for signal light detection, an unnecessary output voltage (offset voltage) such as current due to stray light can be obtained from the current obtained from each light receiving element for signal light detection using the same reference voltage. Since it can be removed or reduced, only one light receiving element for cancellation is required, and the semiconductor substrate on which the light receiving element is formed is not enlarged.

According to the present invention, in addition to the light receiving element for detecting signal light, a canceling light receiving element is disposed at a position not on the optical axis of the signal light, and a photocurrent caused by dark current or stray light is transmitted from the light receiving element to the signal light. Focusing on the generation of the same amount as the light receiving element for detection, after converting the light receiving current of the light receiving element for cancellation into a voltage, the voltage level is adjusted to be a reference voltage, and the light receiving element for signal light detection When converting the received light current to a voltage, the output voltage (offset component) is removed from the received light voltage obtained by receiving the signal light by subtracting the reference voltage from the received light voltage of the light receiving element for detecting the signal light. It can be removed or reduced. Therefore, it is possible to separate the conversion circuits that convert the received light currents of the light receiving elements for signal detection and cancellation, so that the wiring length of the input section can be shortened and the high frequency characteristics are prevented from being impaired. Can do.
Further, even if there are a plurality of light receiving elements for signal light detection, unnecessary output voltage (offset component) is removed or reduced from the voltage obtained from each light receiving element for signal light detection using the same reference voltage. Therefore, only one light-receiving element for canceling is required, and it is possible to prevent the semiconductor substrate on which the light-receiving element is formed from becoming large, and this does not hinder downsizing of the apparatus.
Furthermore, when the area, light sensitivity, and dark current of the light receiving element for detection and the light receiving element for cancellation are different, the light sensitivity of the light receiving element is determined by setting the reference voltage to an optimum value based on the difference in characteristics of these light receiving elements. Even if the dark current and the area are not equal, the offset component included in the light reception signal of the detection light receiving element can be canceled.

  Detect signal light for the purpose of removing or reducing unnecessary output voltage (offset voltage) such as current due to stray light from current obtained by receiving signal light without deteriorating high-frequency characteristics and without increasing the number of light receiving elements In addition to the light receiving element for signal, a light receiving element for cancellation is placed at a position not on the optical axis of the signal light, and the photocurrent due to dark current or stray light from this light receiving element is the same amount as the light receiving element for signal light detection When the light receiving current of the canceling light receiving element is converted into a voltage, the voltage level is adjusted to a reference voltage, and the light receiving current of the light receiving element for detecting signal light is converted into a voltage. This is realized by subtracting the reference voltage from the light receiving voltage of the light receiving element for detecting signal light.

  FIG. 1 is a circuit diagram showing a configuration of a stray light cancellation circuit of the optical pickup device according to the first embodiment of the present invention. The stray light cancellation circuit includes a light receiving element (detector) 1 for receiving stray light, a current-voltage conversion amplification circuit 2 that converts a light reception current of the light reception element 1 into a voltage, and an amplification circuit 3 for adjusting the output voltage level of the current-voltage conversion amplification circuit 2. , A light receiving element (detector) 4 for receiving signal light, and a current-voltage conversion amplifier circuit 5 that converts a light receiving current of the light receiving element 4 into a voltage and cancels an offset component.

  FIG. 2 is a block diagram showing a schematic configuration of an optical system of the optical pickup device shown in FIG. The optical pickup device includes a laser diode 11, a lens 12, a beam splitter 13, an objective lens 14, a condensing lens 15, and a semiconductor substrate 20. The optical pickup device has two layers on one side that irradiates light from one surface such as a DVD. The optical disk 30 is irradiated with laser light, and the return light is received by the light receiving element of the semiconductor substrate 20. In the figure, reference numeral 51 indicates return of signal light, and reference numeral 52 indicates stray light that is reflected light from another layer.

  FIG. 3 is an enlarged cross-sectional view of the portion a of FIG. A light receiving element 1 for receiving stray light and a light receiving element 4 for receiving signal light are formed on a semiconductor substrate 20, and both elements are separated by a separation layer 18. Signal light 51 for reading information from the optical disc 30 is incident on the light receiving element 4 for receiving signal light, and stray light 52 is incident on the light receiving element 4 and the light receiving element 1 for receiving stray light.

  Next, the operation of this embodiment will be described. The light receiving element 1 for receiving stray light receives stray light, and inputs the received light current to the non-inverting input terminal (−) of the operational amplifier 201 of the current-voltage conversion amplifier circuit 2. The operational amplifier 201 converts the input light receiving current into a voltage at an amplification factor determined by the resistor 202 and outputs the voltage to the amplifier circuit 3. The operational amplifier 301 of the amplifier circuit 3 amplifies the input light reception voltage at an amplification factor determined by the resistor 302 to obtain a reference signal 300 of a predetermined level, and then the inverting input terminal (+) of the operational amplifier 501 of the current-voltage conversion amplifier circuit 5. Output.

When the light receiving element 4 for receiving the signal light receives the signal light, it outputs the received light current to the non-inverting input terminal (−) of the operational amplifier 501 of the current-voltage conversion amplifier circuit 5. The operational amplifier 501 converts the received light current into a received light voltage at an amplification factor determined by the resistor 502, and outputs this to a later amplifier (not shown). However, since the reference voltage 300 is input to the inverting input terminal (+) of the operational amplifier 501 at this time, the reference voltage 300 is subtracted from the light reception voltage of the light receiving element 4 when the operational amplifier 501 converts the current voltage. Is done. The reference voltage 300 is obtained by converting the light receiving current of the light receiving element 1 into a voltage and adjusting the level thereof, and is a voltage reflecting the light receiving current caused by stray light and the dark current of the element. The received light current and the dark current of the element due to stray light, which is an included offset component, are canceled, and only the signal current is converted into a voltage and output.

  According to the present embodiment, the reference of the operational amplifier 501 that converts the light receiving current of the light receiving element 4 for receiving signal light into a voltage after changing the level by changing the light receiving current of the light receiving element 1 for receiving stray light into a voltage. By using it as the voltage 300, it is possible to cancel offset components such as a received light current due to stray light and a dark current of the element contained in the light receiving element 4 for receiving signal light.

  Further, since the current / voltage conversion circuits 5 and 2 of the light receiving element 4 for receiving signal light and the light receiving element 1 for detecting stray light are separately provided, the current / voltage conversion circuit can be arranged as close as possible to each element. The wiring length of the input part can be shortened and good high frequency characteristics can be obtained.

  FIG. 4 is a circuit diagram showing the configuration of the stray light cancellation circuit of the optical pickup device according to the second embodiment of the present invention. The stray light cancellation circuit of the present embodiment has substantially the same configuration as that of the first embodiment, except that the light receiving element 1 for receiving stray light has a structure for receiving signal light, as shown in FIG. Compared with the light receiving element 4, the area is 1/3, and the light receiving element 1 and the light receiving element 4 have different area sizes.

  Next, the operation of this embodiment will be described. Since the area sizes of the light receiving element 1 and the light receiving element 4 are different, the amount of current and dark current due to stray light included in the light receiving current of the light receiving element 1 is different from the amount of current and dark current due to stray light of the light receiving element 4. Therefore, the value of the resistor 203 that determines the amplification factor of the operational amplifier 201 of the current-voltage conversion amplifier circuit 2 is tripled compared to the value of the resistor 502 that determines the amplification factor of the operational amplifier 501 of the current-voltage conversion amplifier circuit 5. Thus, the level of the reference signal 300 is adjusted. As a result, the amplification factor of the operational amplifier 201 is three times the amplification factor of the operational amplifier 501, so that the output light reception voltage of the current-voltage conversion amplification circuit 2 is the same as the case where the area sizes of the light receiving element 1 and the light receiving element 4 are the same. Equivalent value. Therefore, as in the first embodiment, the current-voltage conversion amplifier circuit 5 receives the signal light by using the received light current of the light receiving element 4 for receiving the signal light as the reference voltage 300 of the operational amplifier 501 that converts the received light into a voltage. The light receiving current due to the stray light contained in the light receiving element 4 and the dark current of the element are subtracted.

  According to the present embodiment, even if the area sizes of the light receiving element 1 and the light receiving element 4 are different, the level of the reference signal 300 is adjusted by changing the amplification factor of the current-voltage conversion amplifier circuit 2, and the light receiving element 1 and the light receiving element 4 is set to the same level as when the area size is the same, the offset components such as the received light current due to the stray light contained in the light receiving element 4 for receiving the signal light and the dark current of the element by the current-voltage conversion amplification circuit 5 are obtained. Can be canceled.

  In the above example, the areas of the light receiving element 1 and the light receiving element 4 are different from each other. However, in addition to the area, the photosensitivity and the dark current are different, that is, the characteristics of the light receiving element 1 and the light receiving element 4 are different. Even in a different case, the offset component included in the light receiving element 4 for receiving the signal light can be similarly canceled by adjusting the level of the reference signal 300 optimally.

  FIG. 6 is a circuit diagram showing the configuration of the stray light cancellation circuit of the optical pickup device according to the third embodiment of the present invention. In the stray light cancellation circuit of this embodiment, the configuration of the reference voltage generation circuit including the light receiving element 1, the current-voltage conversion amplification circuit 2 and the amplification circuit 3 for generating the reference voltage 300 is the same as that of the first embodiment. However, as shown in FIG. 7, in addition to the light receiving element 4 for receiving signal light, there is a light receiving element 6 for receiving signal light, and accordingly, a current-voltage conversion amplification circuit 7 is provided. In FIG. 7, light receiving elements 4 and 6 are arranged on both sides of the light receiving element 1 with separation layers 21 and 22 therebetween. Therefore, the reference voltage 300 is supplied not only to the operational amplifier 501 of the current-voltage conversion amplifier circuit 5 but also to the operational amplifier 701 of the current-voltage conversion amplifier circuit 7. Therefore, similarly to the current-voltage conversion amplifier circuit 5, the current-voltage conversion amplifier circuit 7 also subtracts the light reception current due to stray light contained in the light receiving element 6 for receiving signal light and the dark current of the element.

  According to this embodiment, even if there are two light receiving elements for receiving signal light, the light receiving elements 4 and 6 for receiving signal light are included by the reference voltage 300 generated by the common reference voltage generating circuit. It is possible to cancel an offset component including a light receiving current due to stray light and a dark current of the element. As a result, the number of the light receiving elements 1 and 6 for receiving the signal light and the number of the light receiving elements 1 for offset component cancellation may be one and the reference voltage generating circuit associated therewith may be one. The offset components of the light reception current and the dark current of the element due to stray light contained in the plurality of light receiving elements 4 and 6 for receiving signal light can be canceled without increasing.

  FIG. 8 is a circuit diagram showing the configuration of the stray light cancel circuit of the optical pickup device according to the fourth embodiment of the present invention. The stray light cancellation circuit of the present embodiment is substantially the same as that of the third embodiment, but when the area sizes of the light receiving elements 1, 4, and 6 are different, the operational amplifier 501 and the current-voltage conversion of the current-voltage conversion amplification circuit 5 are used. Each of the reference voltages 300 supplied to the operational amplifier 701 of the amplifier circuit 7 must be an optimum value determined by the area size ratio of the light receiving elements. In the present embodiment, this is performed by the resistors 505 and 705.

  Although this embodiment has the same effect as the third embodiment, in particular, the size of the light receiving elements 1, 4, and 6 can be set freely, so that the degree of freedom in design increases and the semiconductor substrate is made smaller. be able to. Also in this case, not only when the areas are different, but also when the photosensitivity and dark current are different, that is, when the characteristics of the light receiving element 1 and the light receiving element 4 are different, by adjusting the level of the reference signal 300 optimally, The offset component included in the light receiving current of the light receiving elements 4 and 6 for receiving the signal light can be similarly canceled.

  FIG. 9 is a block diagram showing a configuration of an optical disc apparatus equipped with an optical pickup device according to the fifth embodiment of the present invention. The optical disc apparatus accesses a single-sided dual-layer optical disc 30 such as a DVD or a Blu-ray disc by an optical pickup 42, records and reproduces data, and a spindle motor 41 as a driving means for rotationally driving the optical disc 30; The optical pickup 42 for reading / writing data from / to the optical disc 30, the driver 43 for driving the spindle motor 41 and moving the optical pickup 42, and the movement of the spindle motor 41 and the optical pickup 42 are controlled via the driver 43. Driver controller 44, amplifier 45 that generates a focus error signal, tracking error signal, RF signal, etc. based on various signals output from optical pickup 42, demodulation and error correction processing based on the output signal from amplifier 45, etc. Perform predetermined processing A signal processor 46, a signal processor 46, a D / A converter 47 for D / A converting signals from the control unit 50 and inputting the signals to the input / output unit 48, operation information of the device, etc. The input / output unit 48 for displaying the operation state of the optical signal, the signal recorded on the optical disc 30 is received as a reproduction signal, the data is modulated by the signal processing unit 46, the laser light source in the optical pickup 42 is driven, and the driver control unit 44 A recording control circuit 49 for outputting servo information, and a control unit 50 for controlling the servo as a whole by outputting a focus error signal and tracking error signal to the driver control unit 44. Here, the optical pickup 42 has the same configuration as that of the first to fourth embodiments described above.

  According to the present embodiment, the optical pickup 42 has the configuration described in the first to fourth embodiments. Therefore, the optical pickup 42 is output from the optical pickup 42 when the multilayer optical disc 30 is reproduced. Since the reproduction signal is a high-quality reproduction signal from which the offset component is removed or reduced, a high-quality reproduction signal can be obtained, and the servo signal quality is high, so that stable servo can be performed.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect.

1 is a circuit diagram illustrating a configuration of a stray light cancellation circuit of an optical pickup device according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of an optical system of the optical pickup device illustrated in FIG. 1. It is an expanded sectional view of the part a of FIG. It is the circuit diagram which showed the structure of the stray light cancellation circuit of the optical pick-up apparatus which concerns on the 2nd Embodiment of this invention. FIG. 5 is a cross-sectional view showing a configuration of the light receiving element shown in FIG. 4 on a semiconductor substrate. It is the circuit diagram which showed the structure of the stray light cancellation circuit of the optical pick-up apparatus which concerns on the 3rd Embodiment of this invention. It is sectional drawing which showed the structure on the semiconductor substrate of the light receiving element shown in FIG. It is the circuit diagram which showed the structure of the stray light cancellation circuit of the optical pick-up apparatus which concerns on the 4th Embodiment of this invention. It is the block diagram which showed the structure of the optical disk apparatus carrying the optical pick-up apparatus which concerns on the 5th Embodiment of this invention. It is the top view which showed the example of arrangement | positioning of the light receiving element (detector) for the conventional stray light cancellation, and the light receiving element for signal light reception.

Explanation of symbols

1, 4, 6... Light receiving element (detector), 2, 5, 7... Current-voltage conversion amplifier circuit, 3... Amplifier circuit, 11... Laser diode, 12. ...... Objective lens, 15 ... Condensing lens, 18, 21, 22 ... Separation layer, 20 ... Semiconductor substrate, 30 ... Optical disk, 42 ... Optical pickup, 201, 301, 501, 701 ... Operational amplifier , 202, 203, 204, 302, 304, 502, 504, 505, 702, 704, 705... Resistance.

Claims (8)

An optical pickup device for detecting signal light from a multilayer optical disc having a plurality of recording layers,
A light-receiving element for detection that detects signal light, which is return light reflected by a first recording layer of the plurality of recording layers, which is irradiated onto the optical disc;
In order to cancel the offset component of the light reception signal of the light receiving element for detection, which is arranged at a position away from the optical axis of the signal light, the light irradiated on the optical disk is a first recording of the plurality of recording layers. A light-receiving element for cancellation that detects stray light that is return light reflected by another recording layer different from the layer,
The light receiving current output from the canceling light receiving element is converted to a voltage by inputting it to the first operational amplifier, and the converted voltage is input to the second operational amplifier to adjust the voltage level to adjust the reference voltage. A reference voltage generating means for generating and outputting
The reference voltage is input to the first input terminal of the third operational amplifier, and the light receiving current output from the detection light receiving element is input to the second input terminal of the third operational amplifier to detect the detection. A current / voltage converting means for converting a light receiving current from the light receiving element into a voltage, and outputting a difference voltage between the converted voltage and the reference voltage from an output terminal of the third operational amplifier ;
An optical pickup device comprising:   2. The optical pickup device according to claim 1, wherein a plurality of the detection light-receiving elements and the third operational amplifier are provided in one-to-one correspondence.   When one or more of the area, photosensitivity, and dark current of the detection light-receiving element and the cancellation light-receiving element are different, the reference light-emitting element is based on the difference in characteristics between the detection light-receiving element and the cancellation light-receiving element. The optical pickup device according to claim 1, further comprising reference voltage adjusting means for setting the voltage level of the voltage to an optimum value. The reference voltage adjusting means is
The optical pickup device according to claim 3, wherein the voltage level of the reference voltage is set to an optimum value by adjusting an amplification factor of the reference voltage generation unit.   4. The optical pickup device according to claim 3, wherein the reference voltage adjusting unit sets the voltage level of the reference voltage input to the third operational amplifier to an optimum value in the current / voltage conversion unit. An optical disc device including an optical pickup device that receives a return light from the optical disc when a multi-layer optical disc including a plurality of recording layers is irradiated with laser light and obtains a received light signal,
The optical pickup device is:
A light receiving element for detection that detects signal light, which is return light reflected by the first recording layer of the plurality of recording layers, which is irradiated onto the optical disc;
In order to cancel the offset component of the light reception signal of the light receiving element for detection, which is arranged at a position away from the optical axis of the signal light, the light irradiated on the optical disk is a first recording of the plurality of recording layers. A light-receiving element for cancellation that detects stray light that is return light reflected by another recording layer different from the layer,
The light receiving current output from the canceling light receiving element is converted to a voltage by inputting it to the first operational amplifier, and the voltage level is adjusted by inputting the voltage converted voltage to the second operational amplifier to obtain a reference. A reference voltage generating means for generating and outputting a voltage;
The reference voltage is input to the first input terminal of the third operational amplifier, and the light receiving current output from the detection light receiving element is input to the second input terminal of the third operational amplifier to detect the detection. A current / voltage converting means for converting a light receiving current from the light receiving element into a voltage, and outputting a difference voltage between the converted voltage and the reference voltage from an output terminal of the third operational amplifier ;
An optical disc apparatus comprising: The optical disc apparatus according to claim 6 , wherein a plurality of the detection light receiving elements and the third operational amplifier are provided in a one-to-one correspondence. When the detection light receiving element and the canceling light receiving element have different areas, photosensitivity, and dark current, a reference voltage adjusting unit that optimizes the voltage level of the reference voltage based on a difference in characteristics of the light receiving elements. The optical disc apparatus according to claim 6 or 7, further comprising:

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