JP2009088585A - Integrated circuit for photodiode and optical pickup equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an integrated circuit for photodiodes adaptive to a plurality of kinds of optical disks for which photodiodes different from each other need to be used, the circuit having reduced circuit scale. <P>SOLUTION: The integrated circuit for photodiodes includes the plurality of photodiodes A and (a) receiving laser beams, an amplifier circuit 1 which amplifies output signals of the respective photodiodes A and (a), and a switch 41 which changes connections between the respective photodiodes A and (a) and the amplifier circuit 1. Consequently, the integrated circuit for the photodiodes can be provided which is adaptive to a plurality of kinds of optical disks for which photodiodes A and (a) different from each other need to be used, the circuit having reduced circuit scale. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an integrated circuit for photodiodes, and more particularly to an integrated circuit for photodiodes suitable for use in amplification of an output signal of a photodiode. The present invention also relates to an optical pickup provided with such an integrated circuit for photodiodes.

  An optical recording / reproducing apparatus that records and reproduces data on an optical disc such as a CD, DVD, or Blu-ray disc includes an optical pickup. The optical pickup includes a laser diode that is a light source and an integrated circuit for photodiodes, and the integrated circuit for photodiodes includes a photodiode that receives a laser beam reflected by an optical disk. The photodiode is an element that converts a received laser beam into an electric signal, and information recorded on the optical disk can be read by referring to the output signal.

  However, since the output signal of the photodiode is very weak, an amplifier circuit is required to output it to the outside. Therefore, such an amplifier circuit (light receiving amplifier) is also mounted on the photodiode integrated circuit. Patent Document 1 shows an example of such an amplifier circuit.

By the way, one of optical recording / reproducing apparatuses whose demand has been increasing in recent years is a CD (Compact Disc) / DVD / BD (Blu-ray Disc (registered trademark)) compatible recorder. The photodiode integrated circuit of this optical recording / reproducing apparatus includes eight CD photodiodes and twelve DVD / BD photodiodes in order to perform recording / reproduction of CD / DVD / BD. Along with this, 20 amplifier circuits are also provided.
JP 2000-332546 A

  However, the conventional optical recording / reproducing apparatus has a problem that the circuit scale of the photodiode integrated circuit becomes too large because it is necessary to mount as many as 20 amplifier circuits in the photodiode integrated circuit. Such a problem is not limited to a CD / DVD / BD compatible recorder, and may inevitably occur in an integrated circuit for photodiodes corresponding to a plurality of types of optical disks that need to use different photodiodes. is there.

  Therefore, an object of the present invention is to provide a photodiode integrated circuit corresponding to a plurality of types of optical discs that require different photodiodes, and having a reduced circuit scale.

  Another object of the present invention is to provide an optical pickup provided with such an integrated circuit for photodiodes.

  In order to achieve the above object, an integrated circuit for photodiodes according to the present invention includes a plurality of photodiodes that receive a laser beam, an amplification circuit that amplifies an output signal of each photodiode, each of the photodiodes, and the amplification. And a switch for switching connection with a circuit.

  According to this, since the switch for switching the connection between the photodiode and the amplifier circuit is provided, it is possible to reduce the circuit scale of the integrated circuit for photodiodes corresponding to a plurality of types of optical disks that need to use different photodiodes. It becomes possible.

  In the photodiode integrated circuit, the amplifier circuit includes a differential amplifier circuit, and each photodiode is connected to one input terminal of the differential amplifier circuit, and the other input terminal of the differential amplifier circuit is a reference. Voltage sources may be connected to each other, and the voltage value of the bias voltage of each photodiode may be set based on the voltage value of the reference voltage source. According to this, the differential amplifier circuit can appropriately amplify the output signal of each photodiode.

  Further, an integrated circuit for photodiodes according to another aspect of the present invention includes a photodiode that receives a laser beam for a first type optical disc, a photodiode that receives a laser beam for a second type optical disc, A plurality of circuits each including an amplifier circuit that amplifies an output signal of each photodiode; a switch that switches connection between each photodiode and the amplifier circuit; and the first type and the second type optical disc. The apparatus includes: a selection receiving unit that receives one of the selections; and a switch control unit that controls a switch in each circuit in accordance with the content of the selection received by the selection receiving unit. According to this, a plurality of photodiodes for various optical disks can be switched at a time.

  An optical pickup according to the present invention includes at least one of the above-described photodiode integrated circuits. According to this, it becomes possible to reduce the circuit scale of the integrated circuit for photodiodes included in the optical pickup.

  As described above, according to the present invention, it is possible to provide a photodiode integrated circuit corresponding to a plurality of types of optical discs that need to use different photodiodes, and having a reduced circuit scale. It becomes possible.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, FIG. 1 is a diagram showing an example of the appearance of a PDIC (photodiode integrated circuit) 100 included in an optical pickup used in an optical recording / reproducing apparatus for recording / reproducing an optical disc. The PDIC 100 shown in the figure is used for a CD / DVD / BD compatible recorder among optical recording / reproducing apparatuses, and includes 20 photodiodes (A, B, C, D, E1, E2, E3, E4, etc.). F1, F2, F3, F4, a, b, c, d, e1, e2, f1, f2). Each photodiode is disposed in any one of the light receiving portions R-1 to R-6. Hereinafter, BD and DVD are referred to as a first type optical disk, and CD is referred to as a second type optical disk.

  The light receiving parts R-1 to R-3 are used for recording / reproducing of the first type optical disc. The light receiving unit R-1 includes four photodiodes A, B, C, and D, and receives the main beam MB reflected by the first type optical disk. The light receiving unit R-2 includes four photodiodes E1, E2, E3, and E4, and receives the sub beam SB1 reflected by the first type optical disk. The light receiving unit R-3 includes four photodiodes F1, F2, F3, and F4, and receives the sub beam SB2 reflected by the first type optical disk.

  The light receiving parts R-4 to 6 are used for recording / reproducing of the second type optical disk. The light receiving unit R-4 is composed of four photodiodes a, b, c, and d, and receives the main beam MB reflected by the second type optical disk. The light receiving unit R-5 includes two photodiodes e1 and e2, and receives the sub beam SB1 reflected by the second type optical disk. The light receiving unit R-6 includes two photodiodes f1 and f2, and receives the sub beam SB2 reflected by the second type optical disk.

  2 and 3 are diagrams showing an internal circuit configuration of the PDIC 100. FIG. 2 and 3 show the internal circuit configuration of one PDOC 100 in the two diagrams, and the lower part of FIG. 2 and the upper part of FIG. 3 are actually connected. Since there are many parts that are similar to each other in the circuit configuration of each photodiode, the following description will be made by paying attention to the photodiode A and the photodiode a.

  The I / V circuit 40 shown in FIG. 2 is a circuit that outputs the intensity of the laser beam received by the photodiode A and the photodiode a as a voltage signal. In addition to the photodiode A and the photodiode a, the operational amplifier 10 and the resistor 16 are provided. , A switch 41, a limiter circuit 42, a switch 43, and a resistor 44. Among these, the operational amplifier 10 and the resistor 16 constitute the amplifier circuit 1.

  The photodiode A receives the laser beam reflected by the first type optical disk and performs photoelectric conversion. On the other hand, the photodiode a receives the laser beam reflected by the second type optical disc and performs photoelectric conversion. In one example, these photodiodes are configured to include a PN diode, a reverse bias power source, and a resistor, and the voltage across the resistor fluctuates when a laser beam strikes the PN diode. This voltage fluctuates up and down with a predetermined voltage value (bias voltage) as a reference, and becomes an output of these photodiodes. The voltage value of the bias voltage is set based on a voltage value of a reference voltage source Vs (described later), and here, it is assumed that both are 1.65V.

  As shown in FIG. 2, the amplifier circuit 1 has a configuration in which a photodiode is connected to the inverting input terminal (−) of the operational amplifier 10 and a reference voltage source Vs is connected to the non-inverting input terminal (+) of the operational amplifier 10. is doing. The amplifier circuit 1 also includes a feedback circuit that connects the output terminal of the operational amplifier 10 and the inverting input terminal (−). This feedback circuit includes a resistor 16. With these configurations, the amplifier circuit 1 forms a so-called inverting amplifier circuit.

  The inverting input terminal (−) of the operational amplifier 10 is connected to the photodiode A when the recording / playback target medium is the first type optical disk by the operation of the switch 41 (details will be described later) according to the control from the outside. The photodiode a is connected when the medium to be recorded and reproduced is the second type optical disk. On the other hand, a power supply Vs having a predetermined voltage is connected to the non-inverting input terminal (+) of the operational amplifier 10. The amplifier circuit 1 including the operational amplifier 10 and the resistor 16 performs an amplification process on the output signal of the photodiode. As a result, an output corresponding to the intensity of the laser beam received by any one of the photodiodes is obtained as the output of the amplifier circuit 1.

  The control unit 50 controls the switch 41 and the switch 43 according to an instruction from the outside. Of these, the control of the switch 43 makes it possible to incorporate the resistor 44 into the feedback circuit and thereby control the gain of the amplifier circuit 1. The control of the switch 41 will be described together with the detailed description of the operation of the switch 41.

  When the amplitude of the signal output from the operational amplifier 10 exceeds a predetermined maximum value, the limiter circuit 42 clips the excess amplitude and outputs it to the subsequent stage.

  The output signal of the limiter circuit 42 is output from the terminals VA / Va and also input to the synthesis circuit 60. An output signal from the terminal VA / Va is used as a servo signal for detecting defocusing of the light spot or deviation from the track in a control circuit (not shown).

  In addition to the output signal of the limiter circuit 42, the output signal of the limiter circuit is similarly input to the combining circuit 60 from the photodiodes B, C, and D or the photodiodes b, c, and d. These output signals are combined and output from the terminal VRFP and the terminal VRFN. Note that the output signals of the terminal VRFP and the terminal VRFN are out of phase with each other. The signal output in this way is used as a data signal indicating recorded data in a control circuit (not shown).

  Hereinafter, the operation of the switch 41 will be described in detail with reference to FIG. 4 showing a part of the I / V circuit 40 of FIG. 2 in more detail. In the following description, the operation of the amplifier circuit 1 will be described first, and then the switch 41 will be described.

  As shown in FIG. 4, the operational amplifier 10 includes a differential amplifier circuit 20 and a source follower circuit 30, and these are connected in cascade. That is, the output Vin of the photodiode A or a is first supplied to the differential amplifier circuit 20, and the output of the differential amplifier circuit 20 is further supplied to the source follower circuit 30.

  The differential amplifier circuit 20 is connected to P-channel MOS transistors 21 and 22 connected in a current mirror, N-channel MOS transistors 23 and 24 connected in series to the transistors 21 and 22, respectively, and sources of the transistors 23 and 24. The constant current source 25 is used. The gate of the transistor 23 is connected to the photodiode A or a via the switch 41, and the gate of the transistor 24 is connected to the reference voltage source 14 (= reference voltage source Vs). In the present embodiment, as described above, the reference voltage source 14 generates a voltage (here, 1.65 V) having the same value as the bias voltage of the photodiode 2. The output of the differential amplifier circuit 20 is taken out from the connection point between the transistor 21 and the transistor 23.

  The source follower circuit 30 includes an N-channel MOS transistor 31 to which the output of the differential amplifier circuit 20 is supplied to the gate, and a constant current source 32 connected to the source of the transistor 31. The output of the source follower circuit 30 is extracted from the source of the transistor 31 and becomes the output Vout of the amplifier circuit 1. The transistor 31 is a so-called depletion type MOS transistor. That is, the threshold voltage Vth of the transistor 31 is zero or a negative value.

  Note that a power supply voltage Vdd is supplied to the sources of the transistors 21 and 22 and the drain of the transistor 31.

  Here, the voltage amplification degree of the amplifier circuit 1 is appropriately set by adjusting the resistance value of the resistor 16 and the internal resistance value of the photodiode 2. However, when the output voltage of the photodiode A or a is a bias voltage value of 1.65V, the output voltage of the source follower circuit 30 (source voltage of the transistor 31) is about 1.65V regardless of the voltage amplification degree. It becomes.

  When the threshold voltage of the transistor 31 is Vth, the gate voltage of the transistor 31 is given by Vout + Vth. In this embodiment, since the transistor 31 is a depletion type, Vth ≦ 0. Therefore, the gate voltage of the transistor 31 is substantially the same as or lower than the source voltage. For example, if the threshold voltage Vth is approximately 0V, the gate voltage of the transistor 31 is substantially equal to the voltage of the output Vout. As a result, for example, if the voltage of the output Vout is about 1.65V, the gate voltage of the transistor 31 is also about 1.65V.

  As a result, the source-drain voltage of the transistors 21 and 22 constituting the current mirror circuit is increased compared to the conventional case. That is, when an enhancement type transistor is used as the transistor 31, the gate voltage of the transistor 31 becomes higher than the voltage of the output Vout by the threshold voltage, and as a result, the source-drain voltage of the transistors 21 and 22 is lowered, resulting in a dynamic range. Becomes narrower. For this reason, in order to ensure a sufficient dynamic range, it is necessary to increase the power supply voltage Vdd as described above.

  On the other hand, in the present embodiment, since a depletion type transistor is used as the transistor 31, a sufficient dynamic range can be secured even if the power supply voltage Vdd is relatively low. For example, when the power supply voltage Vdd is 3.3 V, the maximum amplitude of the source-drain voltage of the transistors 21 and 22 (the maximum amplitude of the signal that can be output by the differential amplifier circuit 20) is about 1.65 V. (= 3.3V-1.65V (voltage value of the bias voltage of the photodiode 2)), and sufficient amplitude is ensured. In this case, the upper limit value of the dynamic range of the amplifier circuit 1 is 3.3V.

  The switch 41 is a switch for switching the connection between the photodiode A or a and the amplifier circuit 1. When a user instructs recording or reproduction of the first type optical disk or the second type optical disk using an operation unit (not shown), the operation content is transmitted from the operation unit to the control unit 50 (FIG. 2). The control unit 50 accepts selection of one of the first type and the second type optical disks based on the transmitted operation content (selection accepting unit). Then, the switch 41 in the I / V circuit 40 is controlled according to the contents of the received selection (switch control means). Specifically, when selection of the first type optical disk is accepted, the switch 41 is controlled so that the photodiode A is connected to the amplifier circuit 1. On the other hand, when the selection of the second type optical disk is accepted, the switch 41 is controlled so that the photodiode a is connected to the amplifier circuit 1.

  Note that the control unit 50 controls not only the switch 41 corresponding to the photodiodes A and a but also the switches corresponding to other photodiodes. That is, when the selection of the first type optical disk is accepted, the photodiodes (photodiodes A, B, C, D, E1, E2, E3, E4, F1, etc.) that receive the laser beam for the first type optical disk are received. F2, F3, and F4) control the switches so that they are connected to the corresponding amplifier circuits. On the other hand, when the selection of the second type optical disc is accepted, photodiodes (photodiodes a, b, c, d, e1, e2, f1, f2) that receive the laser beam for the second type optical disc are: The switches are controlled so as to be connected to the corresponding amplifier circuits.

  As a result of the switch control as described above, it becomes possible to amplify the output signals of a plurality of photodiodes respectively corresponding to a plurality of types of optical disks with a single amplifier circuit. Therefore, a reduction in the circuit scale of the integrated circuit for photodiodes corresponding to a plurality of types of optical disks that require the use of different photodiodes can be realized.

  In the first embodiment, an example of an amplifier circuit using a two-stage operational amplifier in which the first stage is a differential amplifier circuit and the next stage is a source follower circuit has been described. However, the present invention is not limited to a differential amplifier circuit. The present invention can also be applied to an amplifier circuit including the first amplification unit.

  Here, the overall configuration of the optical pickup 101 including the PDIC 100 will be described with reference to FIG. 5 which is a schematic diagram showing the configuration of the optical pickup 101.

  As shown in FIG. 5, the optical pickup 101 includes a laser light source 102, a diffraction grating 103 that divides the laser beam from the laser light source 102 into a plurality, and a collimator lens that collimates the laser beam emitted from the diffraction grating 103. 104, a mirror 105 that guides the parallel laser beam to the optical disc 200, a quarter-wave plate 110 that converts the laser beam reflected by the mirror 105 into circularly polarized light and enters the objective lens 106, and 1 An objective lens 106 for converging the laser beam incident from the quarter-wave plate 110 onto the disk surface, a beam splitter 107 for guiding the light reflected by the optical disk 200 and further reflected by the mirror 105 to the PDIC 100 side, and from the beam splitter 107 An anamorphic lens 108 for converging the reflected light; And a PDIC100 for receiving the reflected light is converged by Namo Fick lens 108. The PDIC 100 includes 20 photodiodes as described above, and each photodiode receives the reflected light, performs photoelectric conversion, and outputs a voltage signal corresponding to the intensity of the reflected light.

  The position of the objective lens 106 with respect to the optical disc 200 is controlled with high accuracy by the objective lens driving device 109. Specifically, by driving the objective lens 106 in the focus direction, focus correction is performed to focus the beam spot on the recording surface of the optical disc 200, and by driving in the tracking direction, the beam spot is applied to the track of the optical disc 200. Tracking correction to follow is performed. Further, the tilt angle corresponding to the warp of the disk is corrected by rotating the objective lens 106 in the tracking direction with the tangential direction as the rotation axis.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, the configuration of the differential amplifier circuit is not limited to the configuration shown in FIG. 4 and may have a different circuit configuration.

It is a figure which shows the example of an external appearance of PDIC concerning embodiment of this invention. It is a figure which shows the internal circuit structure of PDIC concerning embodiment of this invention. It is a figure which shows the internal circuit structure of PDIC concerning embodiment of this invention. It is a circuit diagram which shows the circuit concerning embodiment of this invention in detail. It is a schematic diagram which shows the structure of an optical pick-up provided with PDIC concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Amplifier circuit 10 Operational amplifier 14 Reference voltage source 16,44 Resistance 20 Differential amplifier circuit 21,22 P channel MOS transistor 23,24 N channel MOS transistor 31 Depletion type transistor 25,32 Constant current source 30 Source follower circuit 40 I / V Circuits 41 and 43 Switch 42 Limiter circuit 50 Control unit 60 Synthesis circuit 100 PDIC
DESCRIPTION OF SYMBOLS 101 Optical pick-up 102 Laser light source 103 Diffraction grating 104 Collimating lens 105 Mirror 106 Objective lens 107 Beam splitter 108 Anamorphic lens 109 Objective lens drive device 110 1/4 wavelength plate 200 Optical disk A, B, C, D, a, b, c, d, E1, E2, E3, E4, F1, F2, F3, F4, e1, e2, f1, f2 Photodiode

Claims (4)

A plurality of photodiodes for receiving a laser beam;
An amplifier circuit for amplifying the output signal of each photodiode;
A switch for switching the connection between each photodiode and the amplifier circuit;
An integrated circuit for a photodiode, comprising: The amplifier circuit includes a differential amplifier circuit;
Each photodiode is connected to one input terminal of the differential amplifier circuit, and a reference voltage source is connected to the other input terminal of the differential amplifier circuit, respectively.
The voltage value of the bias voltage of each photodiode is set based on the voltage value of the reference voltage source,
The integrated circuit for photodiodes according to claim 1. Photodiode for receiving laser beam for first type optical disc, photodiode for receiving laser beam for second type optical disc, amplification circuit for amplifying output signal of each photodiode, and each photodiode A plurality of circuits each including a switch for switching connection between the amplifier circuit and the amplifier circuit;
Selection accepting means for accepting selection of one of the first type and the second type of optical disc;
Switch control means for controlling the switches in each circuit according to the content of the selection received by the selection receiving means;
An integrated circuit for a photodiode, comprising:   An optical pickup comprising the photodiode integrated circuit according to claim 1.

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