JP2007036623A - Photoelectric-current amplifier circuit and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric-current amplifier circuit that can be achieved in a small scale and is capable of selectively amplifying one or more photoelectric-currents respectively obtained from a plurality of light-receiving elements. <P>SOLUTION: The photoelectric-current amplifier circuit is provided with a plurality of the light-receiving elements 351, 352, an amplifier circuit 364 in which an input and an output are connected with a gain resistor 360, and element selection switches 353, 354 provided for each light-receiving element and connected between the corresponding light-receiving element and the input of the amplifier circuit. The gain resistor 360 supplies a photoelectric-current of the corresponding light-receiving element via the element selection switch to be turned on. The amplifier circuit 364 amplifies the photoelectric-current flowing in the gain resistor 360 to a voltage signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photocurrent amplifier circuit and an optical pickup device using the photocurrent amplifier circuit, and more particularly to a technique for realizing a photocurrent amplifier circuit on a small scale.

  In recent years, optical disc media such as CD (Compact Disk) and DVD (Digital Versatile Disk) have been widely used for recording large-capacity digital information represented by video and audio. As is well known, laser light having different wavelengths depending on the type of the medium is used for reading and writing information to and from these various optical disk media (hereinafter simply referred to as media).

  Conventionally, a miniaturized optical pickup device corresponding to both a CD and a DVD typically includes a two-wavelength semiconductor laser element serving as a light source and a single optical system shared by lasers of both wavelengths. With. Then, through the optical system, the reflected light from the medium projected to different positions for each wavelength according to the separation of the emission points of the lasers of the respective wavelengths is obtained by photoelectric conversion by the light receiving element provided for each wavelength. Amplifies and outputs electrical signals.

As a light-receiving amplifier element suitable for such an optical pickup device, a light-receiving amplifier element that switches a pre-stage amplifier provided corresponding to a light-receiving element for each wavelength and outputs one output is well known (for example, Patent Document 1). (See FIGS. 3 and 4).
Japanese Patent Laid-Open No. 2004-22051

  However, according to the conventional light receiving amplifier element, there is a problem that it is difficult to reduce the scale of the circuit because a pre-stage amplifier is provided in the light receiving element for each wavelength.

  This problem can be solved by reducing the size of the three-wavelength optical pickup device that can handle the BD (Blu-ray Disk) with a larger storage capacity in addition to the CD and DVD, in addition to reducing the size of the optical pickup device with the current function. Especially if you want to.

  The present invention has been made in view of the above problems, and provides a photocurrent amplifier circuit that selectively amplifies one or more photocurrents obtained from a plurality of light receiving elements and can be realized on a small scale. The purpose is to do.

  In order to solve the above problems, the photocurrent amplifier circuit of the present invention includes a plurality of light receiving elements that generate a photocurrent according to the amount of received light, and an element selection that is provided in each light receiving element and connected in series with the corresponding light receiving element. A switch, and an amplifier circuit that amplifies a photocurrent flowing through the corresponding light receiving element via each element selection switch.

  Each circuit including the light receiving element and a corresponding element selection switch is connected in parallel to the input of the amplifier circuit, and the amplifier circuit is an operational amplifier in which an output and the input are connected by a gain resistor. The photocurrent flowing from the light receiving element corresponding to the gain resistor via the element selection switch may be amplified to a voltage signal.

  According to this configuration, since the photocurrent flowing through the element selection switch that is turned on can be selectively amplified by the single amplifier circuit, one or more of the photocurrents generated in the plurality of light receiving elements can be selectively selected. A photocurrent amplifier circuit that amplifies the current is realized on a small scale.

  The photocurrent amplifier circuit further includes a current supply switch provided between each light receiving element and connected between a connection point between the corresponding light receiving element and the element selection switch and a power source. May be turned on while the corresponding element selection switch is turned off.

  According to this configuration, since the photocurrent generated in the light receiving element in which the corresponding element selection switch is turned off, that is, the undesired light receiving element, is directly supplied from the power supply via the corresponding current supply switch, Leakage from the element selection switch in which the current is off and amplification as an error is substantially eliminated, and the accuracy of the voltage signal obtained as a result of amplification is increased.

  Further, the photocurrent amplifier circuit is further provided in each light receiving element, and a first constant current circuit connected in parallel with the corresponding light receiving element, and the same amount of current as the first constant current circuit, And a second constant current circuit that flows through the element selection switch.

  According to this configuration, the first constant current circuit supplies an idle current that is added to the photocurrent of the corresponding light receiving element to the corresponding element selection switch. As a result, as long as the element selection switch is turned on, even if the photocurrent from the corresponding light receiving element is interrupted, the element selection switch always operates in the active region without entering the blocking region. Good response characteristics are exhibited.

  Further, since the second constant current circuit supplies the idle current, the idle current does not flow through the gain resistor and does not affect the voltage signal obtained as a result of amplification.

  Each element selection switch may be a plurality of transistors connected in Darlington.

  According to this configuration, as a result of increasing the current amplification factor of each element selection switch, the base current for turning on the element selection switch is reduced. Since this base current is added to the photocurrent of the light receiving element and amplified, the accuracy of the voltage signal obtained as a result of amplification is increased by reducing this addition.

  Further, the present invention can be realized not only as such a photocurrent amplifier circuit but also as an optical pickup device including such a photocurrent amplifier circuit.

  According to the photocurrent amplifier circuit of the present invention, since only the photocurrent flowing through the element selection switch that is turned on can be selectively amplified by the single amplifier circuit, the photocurrent generated in a plurality of light receiving elements can be reduced. A photocurrent amplifier circuit that selectively amplifies one or more is realized on a small scale.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a circuit diagram showing an example of a photocurrent amplifier circuit according to the first embodiment of the present invention.

  This photocurrent amplifier circuit includes light receiving elements 351 and 352, NPN transistors 353 and 354 as element selection switches, PNP transistors 355, 356, and 362 constituting an operational amplifier 364, NPN transistors 357 and 358, and constant current sources 359 and 363. , And a non-inverting input resistor 361 and a gain resistor 360.

  NPN transistors 353 and 354, which are element selection switches, are alternatively turned on to interrupt the photocurrent generated by the light receiving elements 351 and 352 connected in series. A circuit composed of the NPN transistor 353 and the light receiving element 351 and a circuit composed of the NPN transistor 354 and the light receiving element 352 are connected in parallel to the inverting input of the operational amplifier 364.

  The gain resistor 360 is a feedback resistor inserted in the negative feedback path of the operational amplifier 364 and supplies the photocurrent from the output of the operational amplifier 364. The operational amplifier 364 amplifies the photocurrent flowing through the gain resistor 360 into a voltage signal and outputs the voltage signal.

  As an example, this photocurrent amplifier circuit may be used in a light receiving unit in a miniaturized optical pickup device capable of reading and writing information or reading information using light having different wavelengths for CDs and DVDs.

  FIG. 2 is a diagram schematically illustrating an example of a typical configuration of such an optical pickup device. The optical pickup device includes a semiconductor substrate 10 and an optical system 20 that is shared by CDs and DVDs. In FIG. 2, a medium 30 is further depicted.

  On the semiconductor substrate 10, a light emitting unit 11 and light receiving units 14a and 14b are formed. The optical system 20 includes an objective lens 21 and a hologram element 22.

  The light emitting unit 11 is, for example, a two-wavelength semiconductor laser device, and emits infrared laser light for CD and red laser light for DVD from light emitting points 12 and 13 that are provided apart from each other. In FIG. 2, the optical paths of the infrared laser beam and the red laser beam are indicated by solid lines and broken lines.

  The light of each wavelength emitted from the light emitting unit 11 is reflected by the medium 30 through the objective lens 21, and then is divided in the radial direction of the medium by the hologram element 22, and the light receiving units 14a and 14b have different positions for each wavelength. Are projected onto the light receiving elements 15a and 16a and the light receiving elements 15b and 16b.

  As is well known, the projection spot diameter and light amount imbalance of each divided reflected light are used for focusing and tracking control, and the total light amount of each reflected light is used for reading information.

  The photocurrent amplifier circuit shown in FIG. 1 is provided, for example, in each of the light receiving portions 14a and 14b in this optical pickup device. Assuming that the light receiving elements 351 and 352 are for CD and DVD, respectively, in the light receiving unit 14a, the light receiving elements 351 and 352 are the light receiving elements 15a and 16a, respectively. In the light receiving unit 14b, the light receiving elements 351 and 352 are These are the light receiving elements 15b and 16b, respectively.

  For CD, the NPN transistor 353 is turned on and the NPN transistor 354 is turned off, and for DVD, the NPN transistor 353 is turned off and the NPN transistor 354 is turned on. As a result, the photocurrent from one of the light receiving elements for CD and DVD flows to the gain resistor 360 while the photocurrent from the other light receiving element is cut off, so that the desired photocurrent is correctly amplified. Is done.

  According to this configuration, since only the photocurrent flowing through the gain resistor 360 through the element selection switch that is turned on can be selectively amplified by the operational amplifier 364, one or more of the photocurrents generated in the plurality of light receiving elements are selected. The photocurrent amplifier circuit that amplifies the signal can be realized on a small scale.

Here, the NPN transistor 353 and 354 is an element selection switch, its base - Note that giving emitter voltage V _BE and the reference voltage V _ref and the upper limit voltage or lower of the base voltage obtained by adding the need to be turned on .

This is because, for the NPN transistors 357 and 358 constituting the differential section of the operational amplifier 364, the base-emitter voltages V _BE are normally equal, and the base current of the NPN transistor 358 is extremely small. If the voltage drop is ignored, the base voltages of both are equal to the reference voltage V _ref . At this time, the collector voltages of the NPN transistors 353 and 354 are also equal to the base voltage of the NPN transistor 357 and become the reference voltage V _ref .

  Since this relationship always holds regardless of the amount of photocurrent generated in the light receiving element, if the base voltage exceeding the above-described upper limit voltage is applied to turn on the NPN transistors 353 and 354, all the photocurrents are converted to the NPN transistor 353, This is because the current is supplied from the base current of 354 and a correct amplification result cannot be obtained.

  Therefore, in the application of this circuit, it is necessary to turn on the NPN transistors 353 and 354, which are element selection switches, under the above-described base voltage conditions.

(Second Embodiment)
FIG. 3 is a circuit diagram showing an example of a photocurrent amplifier circuit according to the second embodiment of the present invention.

  This photocurrent amplifier circuit is configured by adding NPN transistors 403 and 405 which are current supply switches to the photocurrent amplifier circuit (see FIG. 1) according to the first embodiment.

The NPN transistors 403 and 405 that are current supply switches are controlled to be turned on during a period in which the NPN transistors 353 and 354 that are corresponding element selection switches are turned off. Directly supplied from the power supply voltage _Vcc .

According to this configuration, a photocurrent generated when light strikes a light receiving element whose corresponding element selection switch is turned off, that is, an undesired light receiving element, is directly supplied from the power supply via the corresponding current supply switch. Therefore, the element selection switch in which the photocurrent is turned off is substantially leaked and is not amplified as an error, and the accuracy of the voltage signal _Vout obtained as a result of amplification is increased.

(Third embodiment)
FIG. 4 is a circuit diagram showing an example of a photocurrent amplifier circuit according to the third embodiment of the present invention.

  This photocurrent amplifying circuit is similar to the photocurrent amplifying circuit according to the second embodiment (see FIG. 3) in that a constant current source 463 and NPN transistors 454, 457, 461, and 462 constituting the first current mirror circuit. , And PNP transistors 459 and 460 constituting a second current mirror circuit.

  In the first current mirror circuit, the same current as the current flowing from the constant current source 463 to the NPN transistor 462 flows through the NPN transistors 454, 457, and 461. Here, the NPN transistors 454 and 457 are an example of a first constant current circuit.

  In the second current mirror circuit, the same current as the current flowing through the PNP transistor 459 flows through the PNP transistor 460. This current is the same as the current flowing through the NPN transistor 461, that is, the current flowing through the constant current source 463. Here, the PNP transistor 460 is an example of a second constant current circuit.

  In this configuration, the NPN transistors 454 and 457 that are the first constant current circuits are the photocurrents of the corresponding light receiving elements 351 and 352, respectively, if the corresponding NPN transistors 353 and 354 that are the element selection switches are turned on. The idle current added to is supplied.

  As a result, as long as the element selection switch is turned on, even if the photocurrent from the corresponding light receiving element is interrupted, the element selection switch always operates in the active region without entering the blocking region. Good response characteristics are exhibited.

Further, since the PNP transistor 460, which is the second constant current circuit, supplies this idle current directly from the power supply voltage _Vcc to the input of the amplifier circuit, this idle current does not pass through the gain resistor 360, The voltage signal _Vout obtained as a result of amplification is not affected.

(Fourth embodiment)
FIG. 5 is a circuit diagram showing an example of a photocurrent amplifier circuit according to the fourth embodiment of the present invention.

  This photocurrent amplifier circuit includes NPN transistors 353 and 354, which are element selection switches in the photocurrent amplifier circuit according to the third embodiment (see FIG. 4). The NPN transistors 509 and 510 are replaced.

According to this configuration, as a result of increasing the current amplification factor of each element selection switch, the base current for turning on the element selection switch is reduced. Since this base current is amplified by being added to the original photocurrent of the light receiving element, a photocurrent closer to the original photocurrent is amplified by reducing this addition, and the voltage signal V obtained as a result of amplification is amplified. _Increases the accuracy of _out .

(Modification)
For the sake of convenience, the description has been given assuming that the number of light receiving elements is two, but it is of course possible to provide a structure in which an element selection switch is provided for each of three or more light receiving elements. Even in such a case, only the photocurrent flowing through the element selection switch to be turned on can be selectively amplified by a single operational amplifier, so that the effect of realizing a photocurrent amplifier circuit on a small scale can be obtained. .

  The configuration with three light receiving elements, for example, is a compact three-wavelength optical pickup device that can handle BDs that can record and read larger amounts of information using blue-violet laser light in addition to CD and DVD. Therefore, the utility value is extremely high.

  Further, the application to the optical pickup device has been described as an example in which the effect of miniaturization is remarkable, but the photocurrent amplifier circuit of the present invention can be obtained from a plurality of light receiving elements in addition to the optical pickup device. Needless to say, it can be widely used as an amplifier circuit that selectively amplifies one or more of the photocurrents.

  The photocurrent amplifier circuit according to the present invention can be widely used as an amplifier circuit that selectively amplifies one or more of photocurrents obtained from a plurality of light receiving elements, and in particular, a plurality of types using a plurality of lights having different wavelengths. It is suitable for use in a light receiving unit in a miniaturized optical pickup device capable of reading / writing information from / into an optical disc medium.

1 is a circuit diagram illustrating an example of a photocurrent amplifier circuit according to a first embodiment. FIG. It is a figure which shows typically an example of the typical structure of an optical pick-up apparatus. It is a circuit diagram which shows an example of the photocurrent amplifier circuit which concerns on 2nd Embodiment. It is a circuit diagram which shows an example of the photocurrent amplifier circuit which concerns on 3rd Embodiment. It is a circuit diagram which shows an example of the photocurrent amplifier circuit which concerns on 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Light-emitting part 12, 13 Light-emitting point 14a, 14b Light-receiving part 15a, 15b, 16a, 16b Light-receiving element 20 Optical system 21 Objective lens 22 Hologram element 30 Medium 351,352 Light-receiving element 353,354 NPN transistor 355,356 PNP Transistors 357, 358 NPN transistor 359 Constant current source 360 Gain resistor 361 Non-inverting input resistor 362 PNP transistor 363 Constant current source 364 Operational amplifier 403, 405 NPN transistor 454, 457 NPN transistor 459, 460 PNP transistor 461, 462 NPN transistor 463 Constant current Source 505, 506, 509, 510 NPN transistor

Claims (6)

A plurality of light receiving elements that generate a photocurrent according to the amount of light received;
An element selection switch provided in each light receiving element and connected in series with the corresponding light receiving element;
An amplifying circuit for amplifying a photocurrent flowing through a corresponding light receiving element via each element selection switch. Each circuit composed of the light receiving element and the corresponding element selection switch is connected in parallel to the input of the amplifier circuit,
The amplifier circuit is an operational amplifier in which an output and the input are connected by a gain resistor, and amplifies a photocurrent flowing from a light receiving element corresponding to the gain resistor via the element selection switch into a voltage signal. The photocurrent amplifier circuit according to claim 1. The photocurrent amplifier circuit further includes:
Provided in each light receiving element, provided with a current supply switch connected between the connection point between the corresponding light receiving element and the element selection switch, and the power supply,
The photocurrent amplifier circuit according to claim 1, wherein each current supply switch is turned on during a period in which the corresponding element selection switch is turned off. The photocurrent amplifier circuit further includes:
A first constant current circuit provided in each light receiving element and connected in parallel with the corresponding light receiving element;
The photocurrent amplifier circuit according to any one of claims 1 to 3, further comprising: a second constant current circuit that causes the same amount of current as the first constant current circuit to flow through the element selection switch. 5. The photocurrent amplifier circuit according to claim 1, wherein each element selection switch is a plurality of transistors connected in a Darlington connection. An optical pickup device capable of reading and writing information to or reading information from a plurality of types of optical disc media using a plurality of lights having different wavelengths,
A photocurrent amplifier circuit according to any one of claims 1 to 4, comprising:
A plurality of light receiving elements in the photocurrent amplifier circuit receive light of different wavelengths, respectively.

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