Abstract:
According to an embodiment of the present invention, a semiconductor device used in an optical disk device driving an optical disk, includes: an optical pickup device detecting an optical signal irradiated to the optical disk and converting the detected optical signal into an electric signal to output the electric signal; and a light amount detecting circuit amplifying the electric signal output from the optical pickup device, the optical pickup device including a plurality of light receiving elements different in receiving sensitivity and the light amount detecting circuit including at least one amplifier or two or more amplifiers of the same amplifying characteristics.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a light-receiving semiconductor device, an optical pickup device, and an optical disk device. In particular, the invention relates to a light-receiving semiconductor device having different receiving sensitivities. 
         [0003]    2. Description of Related Art 
         [0004]    Up to now, a CD-ROM (Compact Disk Read Only Memory) or the like has been used as a recording medium typified by an optical disk. In recent years, various kinds of recording media have been developed along with an increase in recording capacity of electronic data. For example, a DVD-ROM (Digital Versatile Disk Read Only Memory) having a large recording capacity has been used in place of existing CD-ROMs. An optical pickup for reading data recorded on such an optical disk has been developed. 
         [0005]    In the optical pickup used in CD/DVD (Compact Disk/Digital Versatile Disk) and the like, disk laser light is irradiated to write/read information. As for the write/read processing, laser light power is large during writing data and is small during reading data. Accordingly, a light receiving element that receives laser light for writing/reading data should detect both of strong light and weak light with high accuracy. Meanwhile, high-speed response is required of the light receiving element along with an increase in recording speed. 
         [0006]    Japanese Unexamined Patent Application Publication No. 2001-209959 discloses an example of the optical pickup circuit. In the optical pickup circuit, a photocurrent from one light receiving element is supplied to an amplifier capable of switching an amplification factor. The amplifier switches its amplification factor to a small amplification factor at the time of detecting strong light and to a large amplification factor at the time of detecting weak light. 
         [0007]    The above optical pickup circuit switches a gain to a low gain when receiving strong light and to a high gain when receiving weak light to thereby detect a signal without decreasing an S/N ratio. 
         [0008]    As shown in  FIG. 8 , in the case of switching an amplification factor of the amplifier, an amplification factor of an operational amplifier for amplifying a signal is inversely proportional to a frequency band, resulting in a problem in that high-frequency response characteristic reduces as the large amplification factor is increased for detecting a signal of weak light. 
         [0009]    In addition, Japanese Unexamined Patent Application Publication No. 2000-258244 discloses an in-vehicle optical sensor that detects weak current. In the optical sensor, a light-receiving surface of a light receiving element is split, and a car air conditioner is controlled in accordance with a received light amount of each light receiving region. 
         [0010]    The conventional optical pickup circuit detects strong light and weak light during reading/writing data in this way and thus has a problem in that both of high detection accuracy relative to an incident light intensity and high-speed response characteristic are difficult to realize. 
       SUMMARY OF THE INVENTION 
       [0011]    According to an aspect of the present invention, a light-receiving semiconductor device used in an optical disk device driving an optical disk includes a light-receiving unit including a plurality of light receiving elements different in receiving sensitivity and detecting an optical signal irradiated to the optical disk and converting the detected optical signal into an electric signal to output the electric signal; and an amplifying unit including at least one amplifier or two or more amplifiers of the same amplifying characteristics and amplifying the electric signal output from the light-receiving unit. 
         [0012]    According to another aspect of the invention, an optical pickup device includes a light-emitting unit irradiating light to the optical disk; and a light-receiving semiconductor device described above. 
         [0013]    According to a preferred embodiment of the present invention, it is possible to provide a light-receiving semiconductor device, an optical pickup device, and an optical disk device which can attain high detection accuracy relative to incident light intensity and high-speed response characteristic. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0015]      FIG. 1  is a schematic diagram of a configuration example of an optical disk device according to the present invention; 
           [0016]      FIG. 2  is a schematic diagram of a specific example of the configuration of an optical pickup device and a light amount detecting circuit according to the first embodiment of the present invention; 
           [0017]      FIG. 3  is a schematic diagram of a configuration example of a light receiving element of the optical pickup device according to the first embodiment of the present invention; 
           [0018]      FIGS. 4A and 4B  are schematic diagrams of a circuit configuration example of the optical pickup device and the light amount detecting circuit according to the first embodiment of the present invention; 
           [0019]      FIG. 5  is a schematic diagram of a schematic example of the configuration of an optical pickup device and a light amount detecting circuit according to a second embodiment of the present invention; 
           [0020]      FIG. 6  is a schematic diagram of a circuit configuration example of the optical pickup device and the light amount detecting circuit according to the second embodiment of the present invention; 
           [0021]      FIGS. 7A and 7B  are schematic diagrams of a configuration example of a light receiving element of the optical pickup device according to the second embodiment of the present invention; and 
           [0022]      FIG. 8  is a graph of a relation between a frequency and gain of an amplifier of a conventional optical pickup circuit. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
         [0024]    A semiconductor device according to the present invention is a light-receiving semiconductor device preferably used in a CD/DVD player, a ROM, a recording medium, or the like and used for an optical disk device. 
         [0025]    Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. 
       First Embodiment 
       [0026]    Referring first to  FIG. 1 , the overall configuration of an optical disk device according to a preferred embodiment of the present invention is described.  FIG. 1  shows a main part of the optical disk device of the preferred embodiment. 
         [0027]    As shown in  FIG. 1 , an optical disk device  1  of the preferred embodiment includes an optical pickup device  10 , an optical output control circuit  11 , a light amount detecting circuit  12 , and a control circuit  13 . 
         [0028]    The optical pickup device  10  includes a light emitting element, an optical element, and a light receiving element. The light emitting element is composed of a laser diode, a light-emitting diode, or the like and functions as a light-emitting unit for emitting laser light. The optical element is composed of a convex-lens half mirror (not shown) and the like and has a function of guiding laser light emitted from the light emitting element to a recording surface of the optical disk  2 . The light receiving element functions as a light-receiving unit that receives reflected light from the optical disk  2 . 
         [0029]    The optical output control circuit  11  controls an amount of light emitted from the light emitting element. The optical output control circuit  11  executes control such that an amount of light emitted from the light emitting element becomes constant in accordance with an amount of reflected light that is incident on the light receiving element, during reading data from the optical disk  2 . Further, the optical output control circuit  11  controls an emitted light amount in the light emitting element during writing data to the optical disk  2 . 
         [0030]    The light amount detecting circuit  12  is composed of an A/D converter circuit and the like, and detects an amount of light emitted from the light receiving element. Receiving reflected light from the optical disk  2 , the light amount detecting circuit  12  converts an analog signal output from the light receiving element into a digital signal and outputs the resultant signal to the control unit  13  in the form of digital data corresponding to a reflected light amount. 
         [0031]    The control unit  13  is composed of a CPU  131 , a memory  132 , an interface  133 , and the like, and controls operations of the optical disk device  1 . The CPU  131  executes computations or process for controlling each block of a read/write device for the optical disk. The memory  132  stores data necessary for operations of the CPU  131 . The interface  133  receives/transmits data from/to a host device  3  that uses an optical disk device as an external storage device. 
         [0032]    Referring next to  FIGS. 2 to 4B , the detailed configuration of the optical disk device  1  according to a first embodiment the present invention is described. 
         [0033]    In the optical pickup device  10  of the first embodiment, one light receiving element is provided and a light-receiving surface thereof is split into plural light receiving regions at different area ratios. These plural light receiving regions output photocurrent in accordance with the area ratios. In this case, the area ratios are set to ensure a uniform output amount of the photocurrent. Hence, photocurrents of a uniform amount are output to a same amplifier provided in the light amount detecting circuit  12 , and the amplifier amplifies the currents with the same gain. 
         [0034]    A schematic diagram of  FIG. 2  shows a specific example of the configuration of the optical pickup device  10  and the light amount detecting circuit  12 .  FIG. 2  illustrates a main part of the optical pickup device  10  and the light amount detecting circuit  12 . 
         [0035]    As shown in  FIG. 2 , the light receiving element of the optical pickup device  10  has large-area light receiving regions  301  and small-area light receiving regions  302 . The plural light receiving regions  301  and plural light receiving regions  302  are radially-arranged. More specifically, the split light receiving regions  301  and  302  are alternately arranged along the circumference. For example, an area of the large-area light receiving region  301  may be set 10 times larger than an area of the small-area light receiving region  302 . 
         [0036]    The light amount detecting circuit  12  has switches  311  and  312 , and an amplifier  32 . The switches  311  and  312  are connected to a non-inverting terminal of the amplifier  32 . The switch  311  is connected to each of the split large-area light receiving regions  301 , and an output signal of the large-area light receiving region  301  is input to the amplifier  32 . The switch  312  is connected to each of the split small-area light receiving regions  302 , and an output signal of the small-area light receiving region  302  is input to the amplifier  32 . The switches  311  and  312  are turned ON/OFF in accordance with a control signal from the control unit  13 . 
         [0037]    A schematic diagram of  FIG. 3  shows a specific example of the configuration of the optical pickup device  10  and the light amount detecting circuit  12 .  FIG. 3  is a schematic sectional view of the optical pickup device  10  and the light amount detecting circuit  12 . 
         [0038]    As shown in  FIG. 3 , the light receiving region  301  of the light receiving element and the amplifier  32  of the light amount detecting circuit  12  are formed on a silicon substrate  41 . The light receiving region  301  includes a P-type layer and an N-type layer formed on the P-type layer. The silicon substrate  41  is secured in a predetermined position of a lead frame  420  and connected to the lead frame  420 . The silicon substrate  41  is connected to lead frames  421  and  422  with bonding wires  431  and  432 . The light receiving region  301  and the amplifier  32  are molded with transparent resins  441  and  442 . 
         [0039]      FIGS. 4A and 4B  are schematic diagrams of a specific example of the circuit configuration of the optical pickup device  10  and the light amount detecting circuit  12 . 
         [0040]      FIG. 4A  shows the configuration at the time of reading data. During reading data, a power of light emitted from the light emitting element is small, so a power of light incident on the light receiving element is small. In this case, the control unit  13  turns ON the switch  311  and turns OFF the switch  312  under control in accordance with a control signal generated based on reading operations. Thus, the large-area light receiving region  301  is selected and connected to the non-inverting terminal of the amplifier  32 . The light receiving region  301  outputs photocurrent in accordance with a received light amount, and the photocurrent is input to the amplifier  32 . 
         [0041]      FIG. 4B  shows the configuration at the time of writing data. A power of light emitted from the light emitting element for writing data is generally larger than a power for reading data, so a power of light incident on the light receiving element is large. In this case, the control unit  13  turns OFF the switch  311  and turns ON the switch  312  under control based on a control signal generated in accordance with writing operations. Hence, the small-area light receiving region  302  is selected and connected to the non-inverting terminal of the amplifier  32 . The light receiving region  302  outputs photocurrent in accordance with a received light amount and the photocurrent is input to the amplifier  32 . 
         [0042]    During either the read operations or the write operations, light is almost uniformly incident on the entire light receiving element, so the received light amount for read or write operations is determined based on an area ratio between the light receiving regions  301  and  302 . Accordingly, the light receiving element outputs photocurrent in accordance with the area ratio between the light receiving regions  301  and  302  during reading or writing data. In other words, light that is almost uniformly incident on the entire light receiving element can diverge into photocurrents in accordance with the area ratio between the light receiving regions  301  and  302 . The light split based on the area ratio between the light receiving regions  301  and  302  is output to the amplifier  32 . 
         [0043]    For example, an area of the large-area light receiving region  301  can be set 10 times as large as that of the small-area light receiving region  302 . In this case, an output amount of the large-area light receiving region  301  during reading data is 10 times larger than an output amount of the small-area light receiving region  302  during writing data. Therefore, provided that a power of light emitted from the light emitting element for reading data is 1/10 of a power for writing data, the light emitting element outputs the same amount of light in read/write operations, and the output light can be input to the amplifier  32 . 
         [0044]    As described above, in the optical disk device  1  of this embodiment, even if a received light power differs between reading operations and writing operations, photocurrents of the same amount can be output by splitting the light-receiving surface of the light receiving element into the light receiving regions  301  and  302 . As a result, an amount of signal current input to the amplifier  32  that detects a signal can be kept constant. 
         [0045]    Therefore, even if a level of light incident on the light receiving element varies, the input signal level of the amplifier  32  is constant, so the amplifier  32  of the same characteristics can be used, and the same output characteristics of the amplifier can be attained. Accordingly, it is unnecessary to set an amplification factor ratio of the amplifier, the device can be designed with more emphasis on high-speed response characteristic without being limited by trade-off between a gain and a frequency band. Thus, it is possible to realize both of high detection accuracy relative to incident light intensity of a wider range and a high-speed response characteristic. 
         [0046]    Incidentally, this embodiment describes one light receiving element the light-receiving surface of which is split into plural light receiving regions at different area ratios. Here, the plural light receiving regions are each referred to as “light receiving element” in some cases. In such cases, it is assumed that one light receiving element is split into plural light receiving elements. 
       Second Embodiment 
       [0047]    In the first embodiment, the light-receiving surface of one light receiving element is split into plural light receiving regions. A second embodiment of the present invention describes an example where effects similar to the first embodiment are obtained by changing the number of light receiving elements. That is, in the second embodiment, plural light receiving element groups different in the number of elements are provided, and the plural light receiving element groups output photocurrent in accordance with the number of elements. At this time, the number of elements in each group is determined such that the same amount of photocurrent is output. 
         [0048]    Further, in the second embodiment, photocurrents output from each light receiving element group are input to different amplifiers. These amplifiers are set to have the same characteristics, making it possible to amplify output signals of each light receiving element group with the same gain. 
         [0049]    A schematic description about the second embodiment is given below with reference to  FIGS. 5 and 6 .  FIG. 5  is a schematic diagram of the configuration of the optical pickup device and the light amount detecting circuit.  FIG. 6  is a schematic diagram of a circuit configuration example of the optical pickup device and the light amount detecting circuit. 
         [0050]    As shown in  FIG. 5 , the optical pickup device  10  includes plural light receiving elements. More specifically, the plural light receiving elements are divided into light receiving element groups  303  having more elements and light receiving element groups  304  having fewer elements. The light receiving element groups  303  and  304  are radially-arranged each group. More specifically, the light receiving element groups  303  and  304  are alternately arranged along the circumference. For example, the number of light receiving element groups  303  having more elements may be set 10 times larger than the number of light receiving element groups  304  having fewer elements. 
         [0051]    The light amount detecting circuit  12  includes the amplifiers  321  and  322  with the same gain, and non-inverting terminals of the amplifiers  321  and  322  are connected to the light receiving element group  303  having more elements and the light receiving element group  304  having fewer elements. Output signals of the light receiving element groups  303  and  304  are input to the amplifiers  321  and  322 . 
         [0052]    A schematic diagram of  FIG. 6  shows a schematic example of the circuit configuration of the optical pickup device  10  and the light amount detecting circuit  12 . 
         [0053]    As shown in  FIG. 6 , a power of light emitted from the light emitting element for reading data is small, so a power of light incident on the light receiving element is small. In this case, the control unit  13  drives the light receiving element group  303  having more elements and the amplifier  321  based on a control signal generated according to reading operations. Thus, the light receiving element group  303  having more elements outputs a photocurrent in accordance with a received light amount, and the photocurrent is input to the amplifier  321 . 
         [0054]    In general, a power of light emitted from the light emitting element for writing data is generally larger than a power of light four reading data, so a power of light incident on the light receiving element is large. In this case, the control unit  13  drives the light receiving element group  304  having fewer elements and the amplifier  322  based on a control signal generated according to writing operations. Hence, the light receiving element group  304  having fewer elements outputs photocurrent in accordance with a received light amount, and the photocurrent is output to the amplifier  322 . 
         [0055]    Plural light receiving elements output photocurrents in accordance with the numbers of the light receiving element groups  303  and  304  during the reading or writing operations. Output currents of the light receiving element groups  303  and  304  are input to the amplifiers  321  and  322  which are different albeit the same characteristics. 
         [0056]    For example, the light receiving element group  303  having more elements may include elements 10 times as many as the light receiving element group  304  having fewer elements. At this time, an output current amount of the light receiving element group  303  having more elements for reading data is 10 times larger than that of the light receiving element group  304  having more elements for reading data. Therefore, provided that a power of light emitted form the light emitting element for reading data is 1/10 of that for writing data, the light emitting element can output the same amount of current during reading/writing data, and the current can be input to the amplifiers  321  and  322  of the same characteristics. 
         [0057]    As described above, even in the second embodiment, similar to the first embodiment, the numbers of light receiving elements belonging to the light receiving element groups  303  and  304  are set as appropriate to thereby output the same amount of photocurrents. Hence, the amplifier  32  can be used to attain the same amplifier output characteristics. Hence, high detection accuracy relative to an incident light intensity in a wide range and high-speed response characteristic can be both attained. 
         [0058]    Further, in the second embodiment, the light receiving element groups  303  and  304  are provided with the amplifiers  321  and  322 , respectively, so the plural amplifiers are necessary. In contrast, in the first embodiment, the plural light receiving regions  301  and  302  are switched with the switches  311  and  312  and output currents are input to the single amplifier  32 . Thus, the number of amplifiers in the first embodiment can be reduced to ½ of that of the second embodiment, making it possible to downsize the circuit. 
       Other Embodiments 
       [0059]    In the first and second embodiments, the different light receiving regions  301  and  302  or light receiving element groups  303  and  304  are radially-arranged but may be arranged in the other form without any particular limitations. For example, as shown in  FIG. 7A , small-area light receiving regions  402  can be concentrically arranged around the center of large-area light receiving region  401 . Alternatively, as shown in  FIG. 7B , light receiving element groups  411  having more elements and light receiving element group  412  having fewer elements may be arranged in a stripe shape. 
         [0060]    Incidentally, in the first embodiment, an area ratio among split regions of a single light receiving element is changed, and switches are connected to a single amplifier to selectively input a photocurrent, but plural light receiving regions in different area ratios may be connected to amplifiers. Incidentally, in the second embodiment, plural light receiving element groups are connected to amplifiers, but plural light receiving element groups may be connected to a single amplifier connected to a switch to selectively input a photocurrent. 
         [0061]    It is apparent that the present invention is not limited to the above embodiment that may be modified and changed without departing from the scope and spirit of the invention.