JP2008187403A - Current/voltage conversion circuit, photo detector circuit, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current/voltage conversion circuit whose circuit scale can be reduced by simplifying a circuit. <P>SOLUTION: This current/voltage conversion circuit for converting currents flowing to a light receiving element PD1 into a voltage is provided with a differential amplifier 40 having an input node N1 to which a reference voltage source VB is connected, an input node N2 to which the light receiving element PD1 is connected and an output node N3; a plurality of amplifiers 41a to 41c for outputting a voltage corresponding to currents Ix to be input to the output node N3; and a plurality of feedback resistances RT1 to RT3. The amplifiers 41a to 41c are respectively provided with voltage conversion parts 42a to 42c for detecting the change of currents to be input to the output node N3, and for generating a voltage corresponding to the current change; and emitter/follower circuits 43a to 43c for inputting the voltage generated by the voltage conversion part 42a to 42c. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a current-voltage conversion circuit, a photodetector circuit, and an optical disc apparatus.

  2. Description of the Related Art Conventionally, optical disk apparatuses that reproduce data recorded on an optical disk such as a CD (Compact Disc) and a DVD (Digital Versatile Disk) are widely known.

  In this optical disk apparatus, data recorded on the optical disk is read by a photodetector circuit (PD) having a current-voltage conversion circuit that receives light reflected from the optical disk by a light receiving element and converts a current flowing through the light receiving element into a voltage. Is performed as follows.

  First, a light beam emitted from a laser light source is irradiated onto the recording surface as a beam spot. The light receiving element of the photodetector circuit receives the reflected light of the irradiated light beam from the optical disk and outputs a current corresponding to the received light intensity. In the photodetector circuit, the light receiving element is connected to a current-voltage conversion circuit, and generates and outputs a voltage corresponding to the current flowing through the light receiving element. Then, the electrical signal output from the photodetector circuit is processed by the signal processing circuit, thereby reproducing the data stored on the optical disc.

  By the way, since the optical disk apparatus generally needs to support about 7 to 8 types of optical disks, the conventional current-voltage conversion circuit is configured to be able to variably control the conversion rate when performing current-voltage conversion. (For example, refer to Patent Document 1).

  Here, a conventional current-voltage conversion circuit will be specifically described with reference to the drawings. FIG. 3 is a configuration diagram of a conventional current-voltage conversion circuit. In order to facilitate understanding, the current-voltage conversion circuit in FIG. 3 uses two types of conversion rates when performing current-voltage conversion.

  As shown in FIG. 3, the current-voltage conversion circuit 100 includes a first current-voltage conversion unit including a first differential amplifier 101a, a first current supply circuit 102a, a first emitter follower circuit 103a, and a feedback resistor RT100a; A second current-voltage conversion unit including a differential amplifier 101b, a second current supply circuit 102b, a second emitter follower circuit 103b, and a feedback resistor RT100b is provided, and the first current-voltage conversion unit and the second current are controlled by a control circuit (not shown). One of the outputs of the voltage converter is selected and output from an output stage (not shown). In this way, the current-voltage conversion circuit 100 changes the conversion rate when performing current-voltage conversion. In addition, the current-voltage converter not selected for output from the output stage stops the operation of the current supply circuit (the first current supply circuit 102a or the second current supply circuit 102b) in order to stop the operation, The operation of the current source (first constant current source I100a or second constant current source I100b) is stopped. The current supply circuits 102a and 102b are constituted by current mirror circuits, and the operation of the current supply circuits 102a and 102b is stopped by opening the bases of the PNP transistors Q102a and Q102b with a switch or the like. Capacitors C100a and C100b are phase compensation capacitors.

  A specific operation of the current-voltage conversion circuit 100 configured as described above will be described. Here, the first current-voltage conversion unit is set to the operating state, the second current-voltage conversion unit is set to the non-operating (stopped) state, and the output from the first current-voltage conversion unit is selected and output in the output stage. Shall.

  In the first current-voltage converter, the first differential amplifier 101a has a reference voltage source VB having a reference voltage Vc connected to the input node N100 and a light receiving element PD100 connected to the input node N101. A change occurs in the emitter voltage of the transistor Q103a in the first emitter follower circuit 103a in accordance with the flowing current. The first differential amplifier 101a receives a current corresponding to the voltage difference between the voltage at the input node N100 and the emitter voltage of the transistor Q103a from the output node N102a. The current input to the output node N102a is supplied from the first current supply circuit 102a. The first emitter follower circuit 103a is connected to the output node N102a, and receives a voltage obtained by subtracting the voltage drop caused by the first current supply circuit 102a from the power supply voltage Vcc. The first emitter follower circuit 103a performs output according to the input voltage. The output of the first emitter follower circuit 103a is output via an output stage.

On the other hand, in the second current-voltage converter, the operation of the second constant current source I100b of the second differential amplifier 101b is stopped by the control circuit, and the PNP transistor Q102b of the second current supply circuit 102b is turned off. Thus, the current supply to the output node N102b of the second differential amplifier 101b is stopped. The operation of the constant current source I101b of the second emitter follower circuit 103b is also stopped by the control circuit.
JP 2000-269762 A

  However, in the above-described conventional current-voltage conversion circuit, a plurality of differential amplifiers 101a and 101b (a number of differential amplifiers corresponding to variable conversion rates) are required for the light receiving element PD100. Since the NPN transistors of the differential amplifiers 101a and 101b need to be increased in size for low noise and high gain, the circuit scale of the current-voltage conversion circuit has been increased. In addition, phase compensation capacitors C100a and C100b are required for each of the output nodes N102a and N102b, which further increases the circuit scale of the current-voltage conversion circuit. Further, since it is necessary to provide wiring from the outputs of the differential amplifiers 101a and 101b to the emitter follower circuits 103a and 103b for each of the differential amplifiers 101a and 101b, the circuit scale is further increased.

  SUMMARY OF THE INVENTION In order to solve the above-described problems, the present invention provides a current-voltage conversion circuit capable of simplifying the circuit and reducing the circuit scale, a photodetector circuit including the current-voltage conversion circuit, and an optical disc apparatus. And

  In order to solve the above-described problem, according to a first aspect of the present invention, in the current-voltage conversion circuit for converting the current flowing through the light receiving element into a voltage, a reference voltage source is connected to the first input node, and the second input node A differential amplifier to which the light receiving element is connected; a plurality of amplifiers for outputting a voltage corresponding to a current input to an output node of the differential amplifier; outputs of the plurality of amplifiers; A plurality of feedback resistors provided between the input node and the input node; and the amplifier detects a change in current input to the output node of the differential amplifier and generates a voltage corresponding to the current change. A voltage conversion unit; and an emitter follower circuit that inputs a voltage generated by the voltage conversion unit, and a voltage corresponding to a current input to an output node of the differential amplifier is applied to the emitter follower circuit. And outputting from.

  According to a second aspect of the present invention, in the first aspect of the present invention, the voltage converter has a base connected to an output node of the differential amplifier, and an emitter connected to an input of the emitter follower circuit. A PNP transistor, and a resistor and a switch connected in series between an input of the emitter follower circuit and a power supply voltage source, and controls the switch to control one of the plurality of amplifiers. An amplifier is selected, and a voltage corresponding to the output of the differential amplifier is output from the emitter follower circuit of the selected amplifier.

  According to a third aspect of the present invention, in the photodetector circuit including a current-voltage conversion circuit that converts the current flowing through the light receiving element into a voltage, the current-voltage conversion circuit has a reference voltage source connected to the first input node. A differential amplifier in which the light receiving element is connected to a second input node; a plurality of amplifiers that output a voltage corresponding to a current input to an output node of the differential amplifier; and outputs of the plurality of amplifiers; A plurality of feedback resistors provided between the differential amplifier and a second input node of the differential amplifier, and the amplifier detects a change in the current input to the output node of the differential amplifier. A voltage conversion unit that generates a corresponding voltage; and an emitter follower circuit that inputs the voltage generated by the voltage conversion unit, and that corresponds to a current input to an output node of the differential amplifier. The voltage and outputs from the emitter follower circuit.

  According to a fourth aspect of the present invention, there is provided an optical disc apparatus for reproducing data recorded on an optical disc, a light receiving element that receives reflected light from the optical disc, and a current voltage that converts a current flowing through the light receiving element into a voltage. A conversion circuit and a signal processing circuit for reproducing data recorded on the optical disk based on an output from the current-voltage conversion circuit, the current-voltage conversion circuit having a reference voltage source connected to a first input node; A differential amplifier in which the light receiving element is connected to a second input node; a plurality of amplifiers that output a voltage corresponding to a current input to an output node of the differential amplifier; and outputs of the plurality of amplifiers and the difference A plurality of feedback resistors provided between the second input node and the second input node of the dynamic amplifier, and the amplifier detects a change in current input to the output node of the differential amplifier. And a voltage conversion unit that generates a voltage corresponding to the current change, and an emitter follower circuit that inputs the voltage generated by the voltage conversion unit, and a current that is input to the output node of the differential amplifier. Is output from the emitter follower circuit.

  The current-voltage conversion circuit of the present invention includes a plurality of amplifiers that output a voltage corresponding to the current of the output node of the differential amplifier. These amplifiers detect a current change of the output node and detect the current change. A voltage conversion unit that generates a voltage corresponding to the voltage and an emitter follower circuit that inputs the voltage generated by the voltage conversion unit are provided, and a voltage corresponding to the current input to the output node of the differential amplifier is supplied from the emitter follower circuit. Since output is performed, it is not necessary to provide a plurality of differential amplifiers connected to the light receiving element, and only one phase compensation capacitor is required, and the circuit can be simplified and the circuit scale can be reduced.

  The optical disk apparatus according to the present embodiment includes a photodetector circuit that converts reflected light from a disk into a voltage, and a signal processing circuit that reproduces data recorded on the optical disk based on an output from the current-voltage conversion circuit. .

  Here, the photodetector circuit includes a light receiving element that receives reflected light from the disk, and a current-voltage conversion circuit that converts a current flowing through the light receiving element into a voltage, and is configured by a semiconductor integrated circuit. COB (chip) on board) or the like.

  The current-voltage conversion circuit includes a differential amplifier in which a reference voltage source is connected to a first input node, a light receiving element is connected to a second input node, and a current input to an output node of the differential amplifier. A plurality of amplifiers for outputting voltages, and a plurality of feedback resistors respectively provided between outputs of the plurality of amplifiers and a second input node of the differential amplifier.

  The amplifier has a voltage converter that detects a change in the current input to the output node, generates a voltage corresponding to the current change, and an emitter follower circuit that inputs the voltage generated by the voltage converter. A voltage corresponding to the current input to the output node of the differential amplifier is output from the emitter follower circuit.

  As described above, the current-voltage conversion circuit according to the present embodiment responds to the current input to the output node of the differential amplifier without providing a current supply circuit configured by a current mirror circuit between the collector and base of the NPN transistor. Can be output from the amplifier.

  As a result, the differential amplifier that receives the input from the light receiving element can be shared, and the circuit can be simplified. In addition, since the differential amplifier is shared, only one phase compensation is required, and the circuit scale can be reduced. Further, the signal level of the output voltage can be increased as compared with the conventional current-voltage conversion circuit, and the SN ratio can be prevented from deteriorating.

  The voltage converter is connected in series between a PNP transistor having a base connected to the output node of the differential amplifier, an emitter connected to the input of the emitter follower circuit, and the input of the emitter follower circuit and the power supply voltage source. A resistor and a switch, and controls the switch to select one of the plurality of amplifiers, and a voltage corresponding to the output of the differential amplifier from the emitter follower circuit of the selected amplifier. Is output.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical disc apparatus 1 of the present embodiment.

  As shown in FIG. 1, an optical disc apparatus 1 according to this embodiment includes a CD laser diode 2 that emits a laser beam that is an optical signal for CD, and a DVD laser that emits a laser beam that is an optical signal for DVD. A diode 3, an optical system 4, a photodetector circuit 5 that receives laser light reflected from an optical disk 6 such as a CD or a DVD and converts it into an electrical signal, a servo motor 7 for controlling the rotation of the optical disk 6, and an optical system A front monitor photodetector circuit 10 for converting the laser beam dispersed through 4 into an electrical signal, a process for generating a control signal for emitting laser beams from the laser diodes 2 and 3, and from each of the photodetector circuits 5 and 10. A DSP 11 that performs various signal processing such as output signal processing and processing for generating a control signal to the servomotor 7, and the optical disc apparatus 1 And the like controller 12 that controls the body. The optical system 4 includes lenses 20, 21, 25 to 27, a prism 22, a splitter 23, and a reflection mirror 24.

  In the optical disc apparatus 1, when the recording data is received by the controller 12 via the interface, the controller 12 controls the DSP 11, and the laser beam modulated in accordance with the recording data is used for the laser diode 2 for CD or the DVD. The light is emitted from the laser diode 3.

  Laser light emitted from the CD laser diode 2 enters the splitter 23 via the lens 21 and the prism 22. Similarly, the laser beam emitted from the DVD laser diode 3 enters the splitter 23 via the lens 20 and the prism 22.

  The laser light incident on the splitter 23 is split by the splitter 23 in the direction of the reflection mirror 24 and the direction of the front monitor photodetector circuit 10. The direction of the laser light dispersed in the direction of the reflection mirror 24 is changed by reflection by the reflection mirror 24, collimated by the lens 25, condensed by the lens 27, and irradiated onto the optical disk 6.

  The laser light irradiated to the optical disk 6 and reflected by the optical disk 6 is received by the photodetector circuit 5 through the lenses 25 and 26, the reflection mirror 24, the splitter 23, and the lens 27. Further, when reading data written on the optical disk 6, laser light for reading is emitted from the laser diode 2 for CD or the laser diode 3 for DVD. Thereafter, the split laser beam is received by the front monitor photodetector circuit 10 and the laser beam reflected by the optical disc 6 is received by the photodetector circuit 5 through the same path as described above.

  The laser beam received by the photodetector circuit 5 is converted into an electrical signal by the photodetector circuit 5 and transmitted to the DSP 11 (corresponding to an example of a signal processing circuit). The DSP 11 reads data recorded on the optical disc 6 based on the electrical signal transmitted from the photodetector circuit 5, and performs control such as focus servo and tracking servo. The laser light received by the front monitor photodetector circuit 10 is converted into an electrical signal by the front monitor photodetector circuit 10 and transmitted to the DSP 11. The DSP 11 detects the intensity of the laser beam emitted from each of the laser diodes 2 and 3 based on the electric signal transmitted from the front monitor photodetector circuit 10 and determines the intensity of the laser beam emitted from each of the laser diodes 2 and 3. adjust.

  Next, the current-voltage conversion circuit 30 provided in the photodetector circuit 5 will be specifically described with reference to the drawings. The photodetector circuit 5 is housed in a COB (chip on board) package. Note that a transparent mold package or the like can be used instead of the COB package as the package. FIG. 2 is a diagram showing a specific configuration of the current-voltage conversion circuit 30 in the present embodiment.

  The current-voltage conversion circuit 30 includes a current-voltage conversion unit 31 that converts a current flowing through the light receiving element PD1 into a voltage, and an output stage 32 that selects and outputs one of a plurality of outputs of the current-voltage conversion unit 31. I have. Note that the light receiving element PD1 includes a photodiode or the like.

  The current-voltage converter 31 has a reference voltage source VB connected to the first input node N1, a light receiving element PD1 connected to the second input node N2, and a voltage difference between the first input node N1 and the output nodes N4a to N4c. A differential amplifier 40 having an output node N3 for inputting a current Ix according to the output, a plurality of amplifiers 41a to 41c for outputting a voltage according to the current Ix inputted to the output node N3 of the differential amplifier 40, and A plurality of feedback resistors RT1 to RT3 provided between the outputs of the plurality of amplifiers 41a to 41c and the second input node N2 of the differential amplifier 40, respectively.

  The differential amplifier 40 includes NPN transistors Q1 and Q2, a first constant current source I1 having a current value Ia, a second constant current source I2 having a current value Ib, and a third current source I3 having a current value Ic. The Here, the constant current sources I1 to I3 are set so that the current value Ib = current value Ia / 2 + current value Ic.

  The base of NPN transistor Q1 is connected to first input node N1, its collector is connected to power supply voltage source VA having power supply voltage Vcc, and its emitter is connected to one end of constant current source I1. The base of the NPN transistor Q2 is connected to the second input node N2, its collector is connected to the output node N3, and its emitter is connected to one end of the constant current source I1. The other end of the constant current source I1 is connected to the ground GND. The second constant current source I2 is connected to the output node N3 of the differential amplifier 40 and the power supply voltage source VA, and the third current source I3 is connected to the output node N3 of the differential amplifier 40 and the ground GND.

  Each of the amplifiers 41a to 41c has the same configuration, detects a change in the current input to the output node N3 of the differential amplifier 40, and generates a voltage corresponding to the current change. And emitter follower circuits 43a to 43c for inputting voltages generated by the voltage converters 42a to 42, respectively, and a voltage corresponding to the current Ix input to the output node N3 of the differential amplifier 40 is used as the emitter follower circuit. Output from 43a to 43c.

  The voltage converters 42a to 42c have the same configuration, the base is connected to the output node N3 of the differential amplifier 40, the emitter is connected to the inputs of the emitter follower circuits 43a to 43c, and the collector is connected to the ground GND. PNP transistors Q3a to Q3c, and resistors R1a to R1c and switches SW1a to SW1c connected in series between the inputs of the emitter follower circuits 43a to 43c and the power supply voltage source VA, respectively.

  Each of the emitter follower circuits 43a to 43c has the same configuration, and includes NPN transistors Q4a to Q4c whose bases are connected to the outputs of the voltage conversion units 42a to 42c and whose collectors are connected to the power supply voltage source VA. Switches SW2a to SW2c and constant current sources I4a to I4c are provided in series between the emitters of the NPN transistors Q4a to Q4c and the ground GND, respectively. The emitters of NPN transistors Q4a-Q4c are connected to output nodes N4a-N4c of amplifiers 41a-41c.

  The output stage 32 includes differential amplifiers 45a to 45c connected to output nodes N4a to N4c of the amplifiers 41a to 41c, respectively, and an emitter follower circuit 46 that outputs a differential output of the differential amplifiers 45a to 45c. It has.

  The differential amplifiers 45a to 45c have the same configuration, and are connected in series between the NPN transistors Q5a to Q5c and the NPN transistors Q6a to Q6c, and these NPN transistors Q5a to Q5c, Q6a to Q6c and the ground GND. The switches SW4a to SW4c, constant current sources I5a to I5c, and a constant current source I6 are provided. Each of the differential amplifiers 45a to 45c is operated by setting a state of the switches 4a to 4c to a short-circuited state by a control circuit (not shown), and is inactivated by being opened. The differential amplifiers 45a to 45c share the constant current source I6.

  The emitter follower circuit 46 includes an NPN transistor Q7 and a constant current source I6 connected to the emitter of the NPN transistor Q7, and outputs a voltage corresponding to the differential output of each of the differential amplifiers 45a to 45c. Output to node N5.

  Here, each of the amplifiers 41a to 41c in the current-voltage conversion unit 31 amplifies the voltage of the output node N3 of the differential amplifier 40 with different amplification factors by the feedback resistors RT1 to RT3, and is controlled by a control circuit (not shown). One amplifier among the amplifiers 41a to 41c is set in an operating state, and the other amplifiers are controlled in a stopped (non-operating) state.

  For example, when the output from the amplifier 41a is selected, the control circuit (not shown) controls the first switch SW1a and the second switch SW2a of the amplifier 41a to be in a short circuit state, and the first switches SW1b, SW1c and the second switches SW2b and SW2c are controlled to be in an open state.

  A voltage corresponding to the current Ipd flowing through the light receiving element PD1 is output from the output node N4a of the amplifier 41a. That is, when the current Ipd flowing through the light receiving element PD1 is input, the differential amplifier 40 receives the current Ix corresponding to the voltage difference between the first input node N1 and the output node N4a from the output node N3. This current Ix causes a current Ida to flow between the emitter and collector of the PNP transistor Q3a, generating a voltage across the resistor R1a. Emitter follower circuit 43a outputs a voltage corresponding to the base voltage of NPN transistor Q4a to output node N4a. The output of the emitter follower circuit 43a is input to the second input node N2 by the feedback resistor R1a.

  Since the current-voltage conversion circuit 30 in the present embodiment is configured as described above, the circuit scale can be reduced. That is, in the conventional current-voltage conversion circuit 100 shown in FIG. 3, it is necessary to increase the size of the NPN transistors of the differential amplifiers 101a and 101b in order to achieve low noise and high gain. This led to an increase in circuit scale. However, in the current-voltage conversion circuit 30 according to this embodiment, it is not necessary to provide a plurality of differential amplifiers, and the sizes of the transistors Q5a to Q5c and Q6 to Q6c do not need to be increased due to circuit characteristics. Therefore, the circuit scale in the current-voltage conversion circuit can be reduced.

  Here, the dynamic range of the output voltage in the above-described conventional current-voltage conversion circuit 100 (see FIG. 3) will be described.

In the conventional current-voltage conversion circuit 100, the lower limit of the output voltage is the reference voltage Vc, and the upper limit voltage Vomax is determined by the operating range of the current supply circuit configured by a current mirror. The operating range of the current supply circuit is determined by the range in which the PNP transistors Q102a and Q102b can operate in the active region. For example, the minimum collector-emitter voltage Vce at which the PNP transistors Q102a and Q102b can operate in the active region is 0.3V, the voltage Va across the resistors R100a and R100b is 0.2V, and the emitter follower circuits 103a and 103b. When the base-emitter voltage Vbe of the NPN transistors Q103a and Q103b is 0.8V and the voltage Vcc of the power supply voltage source VA of the current-voltage conversion circuit (hereinafter referred to as "power supply voltage Vcc"), the upper limit voltage Vomax is Is obtained by the following equation (1).
Vomax = Power supply voltage Vcc−Vbe−Vce−Va
= Vcc-0.3-0.8-0.2 = Vcc-1.3 (V)
It becomes.

  Thus, since the upper limit voltage Vomax of the output in the current-voltage conversion circuit is limited by the value of Vcc-1.3 (V), the dynamic range is Vc to Vcc-1.3 (V). It becomes a range.

Therefore, when the power supply voltage Vcc of the current-voltage conversion circuit is 5 (V), the dynamic range Vrange of the output voltage is assumed that the reference voltage Vc is 1.6 (V).
Vrange = 5 (V) -1.3 (V) -1.6 (V) = 2.1 (V)
However, when the power supply voltage Vcc is 3.3 (V),
Vrange = 3.3 (V) -1.3 (V) -1.6 (V) = 0.4 (V)
As a result, the level of the output signal is reduced and the SN ratio is deteriorated.

As described above, in the conventional current-voltage conversion circuit 100, the upper limit voltage Vomax of the output is limited to Vcc-1.3V. However, in the current-voltage conversion circuit 30 in the present embodiment, since there is no current supply circuit configured by a current mirror circuit between the power supply voltage source VA and the input of the emitter follower circuit 43a, the ratio of the voltage drop of the feedback resistor R1a Thus, the amplitude of the output voltage is determined. Therefore, the upper limit voltage Vomax is reached when the PNP transistor Q3a does not pass current and there is no voltage drop across the resistor R1a. That is, the upper limit voltage Vomax depends on the base-emitter voltage Vbe of the NPN transistor Q4a in the emitter follower circuit 43a.
Therefore, if the voltage Vbe = 0.8V,
Upper limit voltage Vomax = Vcc-0.8 (V)
It becomes.

  Therefore, compared with the conventional current-voltage conversion circuit 100, the upper limit voltage Vomax can be increased by the collector-emitter voltage Vce (about 0.5 (V)) of the transistors Q102a and 102b of the current supply circuits 102a and 102b. The dynamic range can be improved.

Here, when the voltage Vcc of the power supply voltage source VA is 5 V,
Upper limit voltage Vomax = 5 (V) −0.8 (V) = 4.2 (V)
Dynamic range Vrange = 5 (V) −0.8 (V) −1.6 (V) = 2.6 (V)
It becomes.
If the voltage Vcc of the power supply voltage source VA is 3.3 V,
Upper limit voltage Vomax = 3.3 (V) −0.8 (V) = 2.5 (V)
Dynamic range Vrange = 3.3 (V) −0.8 (V) −1.6 (V) = 0.9 (V)
It becomes.
Therefore, the level of the output voltage can be increased as compared with the conventional current-voltage conversion circuit 100, and the SN ratio can be prevented from deteriorating. Thus, the current-voltage conversion circuit 30 in the present embodiment has a circuit configuration that can sufficiently withstand use at Vcc = 3.3.

  As described above, according to the current-voltage conversion circuit 30 in the present embodiment, a configuration in which a plurality of differential amplifiers are not provided as in the conventional current-voltage conversion circuit 100 has a configuration in which a single differential amplifier is provided. The circuit scale of the current-voltage conversion circuit can be reduced. Further, at the output node N3 of the differential amplifier 40, the bases of the PNP transistors Q3a to Q3c of the amplifiers 41a to 41c are bundled and wired as a single line, so that the phase compensation required for each amplifier in the conventional circuit can be made by one capacitor. It becomes possible to compensate by C1. In addition, the level of the output voltage can be increased as compared with the conventional current-voltage conversion circuit 100, and deterioration of the SN ratio can be prevented.

  Note that the output from the current-voltage converter 31 is selected by the output stage 32, and a voltage corresponding to the output of the current-voltage converter 31 is output from the current-voltage converter circuit 30. For example, when the switches SW1a and SW2a are short-circuited and the amplifier 41a and the emitter follower circuit 43a are in the operating state, the control circuit of the current-voltage conversion circuit 30 selects the differential amplifier 45a by short-circuiting the switch SW3a. Then, the operation state is set, and a voltage corresponding to the output of the amplifier 41a is output. On the other hand, the control circuit of the current-voltage conversion circuit 30 sets the switches SW1b, SW1c, SW2b, SW2c to the open state, sets the amplifiers 41b, 41c to the non-operating state, sets the switches SW3b, SW3c to the open state, and sets the differential amplifiers 45b, 45c to the non-open state. As an operating state, voltage output corresponding to the output of the amplifier 41a is not hindered, thereby reducing power consumption.

  As mentioned above, some of the embodiments of the present invention have been described in detail with reference to the drawings. However, these are merely examples, and the present invention is variously modified and improved based on the knowledge of those skilled in the art. It is possible to carry out the invention.

1 is a diagram showing an overall configuration of an optical disc apparatus according to an embodiment of the present invention. It is a figure which shows the specific structure of the current-voltage conversion circuit concerning one Embodiment of this invention. It is a figure which shows the structure of the conventional current-voltage conversion circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 5 Photo detector circuit 10 Front monitor photo detector circuit 30 Current voltage converter circuit 31 Current voltage converter 32 Output stage 40 Differential amplifier 41a-41c Amplifier 42a-42c Voltage converter 43a-43c Emitter follower circuit 45a-45c Differential amplifier 46 Emitter-follower circuit PD1 Light-receiving element

Claims (4)

In the current-voltage conversion circuit that converts the current flowing through the light receiving element into a voltage,
A differential amplifier having a reference voltage source connected to a first input node and the light receiving element connected to a second input node;
A plurality of amplifiers that output a voltage corresponding to a current input to an output node of the differential amplifier;
A plurality of feedback resistors respectively provided between outputs of the plurality of amplifiers and a second input node of the differential amplifier;
The amplifier detects a change in current input to the output node of the differential amplifier, generates a voltage corresponding to the current change, and an emitter follower that inputs the voltage generated by the voltage converter. A voltage corresponding to the current input to the output node of the differential amplifier is output from the emitter follower circuit. The voltage converter is
A PNP transistor having a base connected to an output node of the differential amplifier and an emitter connected to an input of the emitter follower circuit;
A resistor and a switch connected in series between the input of the emitter follower circuit and a power supply voltage source;
The switch is controlled to select one of the plurality of amplifiers, and a voltage corresponding to the output of the differential amplifier is output from an emitter follower circuit of the selected amplifier. 2. The current-voltage conversion circuit according to 1. In a photodetector circuit having a current-voltage conversion circuit that converts a current flowing through a light receiving element into a voltage,
The current-voltage conversion circuit is
A differential amplifier having a reference voltage source connected to a first input node and the light receiving element connected to a second input node;
A plurality of amplifiers that output a voltage corresponding to a current input to an output node of the differential amplifier;
A plurality of feedback resistors respectively provided between outputs of the plurality of amplifiers and a second input node of the differential amplifier;
The amplifier detects a change in current input to the output node of the differential amplifier, generates a voltage corresponding to the current change, and an emitter follower that inputs the voltage generated by the voltage converter. A photodetector circuit that outputs a voltage corresponding to a current input to an output node of the differential amplifier from the emitter follower circuit. In an optical disc apparatus for reproducing data recorded on an optical disc,
A light-receiving element that receives reflected light from the optical disk, a current-voltage conversion circuit that converts a current flowing through the light-receiving element into a voltage, and reproduces data recorded on the optical disk based on an output from the current-voltage conversion circuit Signal processing circuit,
The current-voltage conversion circuit is
A differential amplifier having a reference voltage source connected to a first input node and the light receiving element connected to a second input node;
A plurality of amplifiers that output a voltage corresponding to a current input to an output node of the differential amplifier;
A plurality of feedback resistors respectively provided between outputs of the plurality of amplifiers and a second input node of the differential amplifier;
The amplifier detects a change in current input to the output node of the differential amplifier, generates a voltage corresponding to the current change, and an emitter follower that inputs the voltage generated by the voltage converter. A voltage corresponding to the current input to the output node of the differential amplifier is output from the emitter follower circuit.

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