JP4770651B2 - CURRENT / VOLTAGE CONVERSION CIRCUIT, PHOTODETECTOR CIRCUIT HAVING THE SAME AND OPTICAL DISC DEVICE - Google Patents

Description

  The present invention relates to a current-voltage conversion circuit that converts a voltage signal into an electric signal, a photodetector circuit including the current-voltage conversion circuit, and an optical disc apparatus.

  Conventionally, there are optical disc apparatuses such as a CD (Compact Disc) drive and a DVD (Digital Versatile Disc) drive. This optical disc apparatus reads and writes data from and on an optical disc by irradiating the optical disc with laser light through an optical system.

  In this type of optical disc apparatus, it is generally performed to monitor the intensity of the laser beam when reading / writing data from / to the optical disc and adjust the laser beam intensity to an appropriate level.

  For this reason, in an optical disc apparatus, a photodetector circuit that converts laser light into an electrical signal is used to monitor the intensity of the laser light.

  The photodetector circuit includes a photodiode that receives an optical signal that is laser light, and a current-voltage conversion circuit that converts a current signal flowing through the photodiode by the optical signal into a voltage signal and outputs the voltage signal.

  This current-voltage conversion circuit is used for optical transmission and optical communication such as an optical transmission system and an optical interconnection in addition to an optical disk device (see, for example, Patent Document 1).

  Here, a specific configuration of a conventional general current-voltage conversion circuit will be described with reference to the drawings. FIG. 4 is a diagram showing a configuration of a conventional current-voltage conversion circuit 100. As shown in FIG.

  As shown in FIG. 4, the current-voltage conversion circuit 100 includes a photodiode PD100, an operational amplifier AMP100 that is a differential amplifier, a feedback resistor Rf, a capacitor Cf, and a reference voltage Vc. Here, the capacitance Cp shown in FIG. 4 is a junction capacitance component of the photodiode PD100, a wiring capacitance component of the photodiode PD100 and other elements, a capacitance component of the feedback resistor Rf, an input capacitance component of the operational amplifier AMP100, and other parasitic capacitances. It is formed by components.

The photodiode PD100 receives laser light when reading / writing data from / to the optical disk and converts it into a current signal. The current signal Iin from the photodiode PD100 is input to the operational amplifier AMP100, and current-voltage conversion is performed by the operational amplifier AMP100. That is, the current signal Iin by the photodiode PD100 is converted into a voltage signal _{V 0} by the operational amplifier AMP100 is output.

Here, the transfer function of the voltage signal V ₀ with respect to the current signal Iin of the photodiode PD100 is represented by the following formula (1), where A = (A ₀ × ωc) / (s + ωc).

上記（１）よりω_０とＱは、以下の式（２）及び式（３）で示される。

From the above (1), ω ₀ and Q are expressed by the following equations (2) and (3).

従って、電流電圧変換回路100における周波数帯域特性を広げるためには、容量Ｃｐの容量値をできるだけ小さくする必要がある。

Therefore, in order to widen the frequency band characteristics in the current-voltage conversion circuit 100, it is necessary to make the capacitance value of the capacitor Cp as small as possible.

  By the way, in the photo detector circuit, it is necessary to switch the sensitivity in accordance with the mode of the optical disc apparatus. As a mode of the optical disc apparatus, there are a mode for writing data to the optical disc (write mode), a mode for reading data from the optical disc (read mode), and the like.

  Therefore, in the current-voltage conversion circuit of the photodetector circuit, the feedback resistor is switched by a transistor switch such as an NMOS transistor. Note that the method of adjusting the sensitivity of the current-voltage conversion circuit by switching the feedback resistor with a switch in this way is a known technique as shown in the prior art described in Patent Document 1, for example.

More specifically, as in the current-voltage conversion circuit 100 ′ shown in FIG. 5, more specifically, between the input and output of the operational amplifier AMP100, the feedback resistor Rf-n and the NMOS transistor Nn (here, n = 1, 2). In other words, the sensitivity of the current-voltage conversion circuit 100 ′ is switched by controlling the ON / OFF of the NMOS transistor N-n.
JP 2005-135528 A

Incidentally, the NMOS transistor N-1 to ON, in the case of the other NMOS transistor N-2 to OFF, indicating the relationship between the current signal Iin and the voltage signal _{V 0} in equation (4) and (5). Note that R _ON is the ON resistance of the NMOS transistor N-1.

そして、ＮＭＯＳトランジスタＮ−１のＯＮ抵抗は、ＮＭＯＳトランジスタＮ−１のドレイン−ソース間電圧Ｖｄｓ≒０Ｖとした場合、次式（６）で表される。

The ON resistance of the NMOS transistor N-1 is expressed by the following equation (6) when the drain-source voltage Vds of the NMOS transistor N-1 is approximately 0V.

ここで、
Ｖｔｈ：ＮＭＯＳトランジスタＮ−１の閾値電圧
Ｃｏｘ：ＮＭＯＳトランジスタＮ−１のゲート酸化膜容量
μｎ：ＮＭＯＳトランジスタＮ−１の電子の移動度
Ｖｇｓ−１：ＮＭＯＳトランジスタＮ−１のゲート−ソース間電圧
Ｌ：ＮＭＯＳトランジスタＮ−１のゲート長
Ｗ：ＮＭＯＳトランジスタＮ−１のゲート幅
である。

here,
Vth: threshold voltage of NMOS transistor N-1 Cox: gate oxide film capacitance of NMOS transistor N-1 μn: electron mobility of NMOS transistor N-1 Vgs-1: gate-source voltage of NMOS transistor N-1 L : Gate length of NMOS transistor N-1 W: gate width of NMOS transistor N-1.

  As shown in FIG. 5, when the NMOS transistor N-1 is ON and the NMOS transistor N-2 is OFF, the gate-to-gate voltage Vg-1 of the NMOS transistor N-1 becomes the power supply voltage Vcc, and the NMOS transistor N- The gate voltage Vg-2 of 2 is the ground voltage GND.

  At this time, when a variation in the power supply voltage Vcc, a variation in the reference voltage Vc, or the like occurs, the gate-source voltage (Vgs-1) varies, and accordingly, the ON resistance of the NMOS transistor N-1 also varies. End up.

For example, if the feedback resistor sum and Rf, as shown in the equation (5), so that the feedback resistance due to variations in R _ON varies.

There is no problem if the ON resistance of the NMOS transistor N-1 can be made sufficiently small (Rf-1 >> R _ON ) with respect to the feedback resistance, but the transimpedance value in the photodetector circuit is 1K to 100KΩ, and the NMOS transistor N-1 In order to realize this, the size (gate width W) of the NMOS transistor N-1 must be considerably increased.

  However, when the size of the NMOS transistor N-1 is increased, the parasitic capacitance (parasitic capacitance such as source-drain-back gate capacitance, source-drain-gate capacitance, etc.) of the NMOS transistor also increases.

  Therefore, the capacitance value of the capacitor Cp shown in FIG. 4 is increased, and as a result, the frequency characteristics of the current-voltage conversion circuit are deteriorated. In addition, since the back gate is connected to the ground voltage GND in order to reduce the capacitance generated in the source (capacitance between the back gate and the well), the value of the threshold voltage Vth of the NMOS transistor N-1 is reduced due to the back gate effect. As a result, the ON resistance of the MOS is further increased. The same can be said for the NMOS transistor N-2 in the ON state.

  Thus, with the conventional configuration, it has been impossible to design a current-voltage conversion circuit that suppresses variations in transimpedance against fluctuations in the power supply voltage Vcc, fluctuations in the reference voltage Vc, etc., and has a wide frequency band characteristic. .

  Accordingly, an object of the present invention is to provide a current-voltage conversion circuit that suppresses variations in transimpedance and has a wide frequency band characteristic, and a photodetector circuit and an optical disk circuit including the current-voltage conversion circuit.

The invention described in claim 1 includes an amplifier that converts an input current signal into a voltage signal based on a reference voltage and outputs the voltage signal, and a feedback resistor and a transistor switch are connected in series between the input and output of the amplifier. In a current-voltage conversion circuit in which a pair is connected in parallel, a first constant current source and a resistor are connected in series between a power supply voltage of the amplifier and the reference voltage, and a second constant current source and a transistor are connected. Are connected in series, and a differential amplifier that outputs a voltage according to the difference between the voltage of the resistor and the output voltage of the transistor is provided, and the voltage that is the output of the differential amplifier is connected via a switch. The voltage applied to the control input of the transistor switch and the output of the differential amplifier is applied to the control input of the transistor.

  The invention according to claim 2 is the invention according to claim 1, characterized in that the size of the transistor switch is larger than the size of the transistor.

According to a third aspect of the present invention, there is provided an amplifier that converts an input current signal into a voltage signal based on a reference voltage and outputs the voltage signal, and a feedback resistor and a transistor switch are connected in series between the input and output of the amplifier. In a photodetector circuit including a current-voltage conversion circuit in which connected sets are connected in parallel, the current-voltage conversion circuit includes a first constant current source and a resistor in series between a power supply voltage of the amplifier and the reference voltage. The second constant current source and the transistor are connected in series , and provided with a differential amplifier that outputs a voltage corresponding to a difference between the voltage of the resistor and the output voltage of the transistor , the voltage which is the output of the differential amplifier via a switch applied to the control input of the transistor switch, and control the voltage the is the output of the differential amplifier of the transistors Characterized in that it applied to the force.

According to a fourth aspect of the present invention, in the optical disc apparatus that reads and writes data from and to the optical disc by irradiating the optical disc with the laser beam through the optical system, the laser beam that is spectrally separated through the optical system. The photo detector circuit includes an amplifier that converts an input current signal into a voltage signal based on a reference voltage and outputs the voltage signal. Between the input and output of the amplifier, a feedback resistor and A current-voltage conversion circuit in which a set of transistor switches connected in series is connected in parallel, and the voltage-current circuit includes a first constant current source and a resistor connected in series between the power supply voltage of the amplifier and the reference voltage And the second constant current source and the transistor are connected in series, and the voltage of the resistor and the output voltage of the transistor Provided a differential amplifier for outputting a voltage corresponding to the difference, the voltage the is the output of the differential amplifier via a switch applied to the control input of the transistor switch, and is the output of the differential amplifier The voltage is applied to a control input of the transistor.

  According to the first, third, and fourth aspects of the present invention, the amplifier includes an amplifier that converts the input current signal into a voltage signal based on the reference voltage and outputs the voltage signal. In a current-voltage conversion circuit in which a set of switches connected in series is connected in parallel, a first constant current source and a resistor are connected in series between the power supply voltage of the amplifier and the reference voltage, and a second constant A current amplifier and a transistor are connected in series, and a differential amplifier is provided that outputs a voltage corresponding to the difference between the voltage of the resistor and the output voltage of the transistor. Since it is applied to the control input of the transistor and to the input of the transistor, it depends on the fluctuation of the transimpedance power supply voltage Vcc and the fluctuation of the reference voltage Vc in the current-voltage conversion circuit. It is possible to suppress the sound. Therefore, a wide frequency band characteristic can be obtained regardless of the fluctuation of the power supply voltage Vcc and the fluctuation of the reference voltage Vc. In addition, the size of a transistor conventionally used as a transistor switch can be reduced, and a broadband voltage-current conversion circuit can be designed by reducing the parasitic capacitance.

  According to the second aspect of the present invention, since the size of the transistor switch is larger than the size of the transistor, the ON resistance of the transistor switch can be reduced.

  The photodetector circuit in this embodiment is provided in an optical disc apparatus that reads and writes data from and on an optical disc by irradiating the optical disc with laser light through an optical system. In addition, this optical disc apparatus is configured to be able to read and write data to both a CD (Compact Disc) and a DVD (Digital Versatile Disc).

  The photodetector circuit includes a photodiode that receives an optical signal that is laser light, and a current-voltage conversion circuit that converts a current signal flowing through the photodiode into a voltage signal and outputs the voltage signal.

  This current-voltage conversion circuit includes an amplifier that converts an input current signal into a voltage signal and outputs the voltage signal. A pair of feedback resistors and transistor switches connected in series is connected in parallel between the input and output of the amplifier. By controlling the ON and OFF states of the transistor switch, it is possible to adjust the sensitivity to the current signal flowing through the photodiode.

  In addition, the first constant current source and the resistor are connected in series between the power supply voltage of the amplifier and the reference voltage, and the second constant current source and the transistor are connected in series, so that the voltage of the resistor And a differential amplifier that outputs a voltage corresponding to the difference between the output voltage of the transistor and the output of the transistor is applied to the control input of the transistor switch via the switch and to the input of the transistor. ing.

  As a result, the current-voltage conversion characteristics can be improved regardless of the fluctuation of the power supply voltage Vcc and the fluctuation of the reference voltage Vc.

  Hereinafter, embodiments 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 according to 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 first photodetector circuit 5 that receives a laser beam reflected from an optical disk 6 such as a CD or a DVD and converts it into an electrical signal, and a servomotor 7 that controls the rotation of the optical disk 6; , A front monitor photodetector circuit 10 which is a second photodetector circuit for converting the laser beam dispersed through the optical system 4 into an electric signal, and a control signal for emitting the laser beam from each of the laser diodes 2 and 3. Generation processing, processing of output signals from the photo detector circuits 5 and 10, generation processing of control signals to the servo motor 7, etc. And a controller 12 for controlling the entire optical disc apparatus 1 and the like.

  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 to modulate the laser beam modulated according to the recorded data to the laser diode 2 for CD or the DVD. The light is emitted from the laser diode 3.

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

  On the other hand, the laser light split by the splitter 23 toward the front monitor photodetector circuit 10 is received by the front monitor photodetector circuit 10.

  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 light emitted from each of the laser diodes 2 and 3 based on the electrical signal transmitted from the front monitor photodetector circuit 10, and determines the intensity of the laser light emitted from each of the laser diodes 2 and 3. adjust.

  The laser light irradiated to the optical disk 6 and reflected by the optical disk 6 is received by the first photodetector circuit 5 through the lenses 25 and 26, the reflection mirror 24, the splitter 23, and the lens 27. When reading data written on the optical disk 6, a laser beam 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 through the same path as described above, and the laser beam reflected by the optical disc 6 is received by the first photodetector circuit 5.

  Here, the front monitor photodetector circuit 10 including the current-voltage conversion circuit 30 which is a characteristic part of the present invention will be specifically described with reference to the drawings. FIG. 2 is a schematic configuration diagram of the front monitor photodetector circuit 10 in the present embodiment, and FIG. 3 is a diagram showing transimpedance characteristics when the power supply voltage Vcc is changed in the current-voltage conversion circuit 30 in the front monitor photodetector circuit 10.

  As shown in FIG. 2, the front monitor photodetector circuit 10 includes a photodiode PD1 and a current-voltage conversion circuit 30.

  As shown in FIG. 2, the current-voltage conversion circuit 30 is an amplifier that uses the power supply voltage Vcc and the ground voltage GND as power supplies, converts a current signal flowing through the photodiode PD1 into a voltage signal based on the reference voltage Vc, and outputs the voltage signal. A first set including an operational amplifier AMP1 and a feedback resistor Rf1-1 and a drain-source of the NMOS transistor N1-1 connected in series between the input and output (inverted input terminal and output terminal) of the operational amplifier AMP1, and feedback The second set in which the resistor Rf1-2 and the drain-source of the NMOS transistor N1-2 are connected in series is connected in parallel, and the NMOS transistors N1-1 and N1-2 are turned on and off. By controlling the above, the sensitivity of the current-voltage conversion circuit 30 is switched. The reference voltage Vc is connected to the non-inverting input terminal of the operational amplifier AMP1. The sources of the NMOS transistors N1-1 and N1-2 are connected to the inverting input terminal of the operational amplifier AMP1 and the photodiode PD1, and the drains of the NMOS transistors N1-1 and N1-2 are respectively connected to the feedback resistors Rf1-1 and Rf1-1. Connected to Rf1-2.

  Here, in order to facilitate understanding, two pairs of feedback resistors and NMOS transistors as transistor switches are connected in series, but these groups are increased according to the bandwidth for which sensitivity adjustment is desired. be able to. The NMOS transistors N1-1 and N1-2 are controlled based on a signal output from the DSP 11 by the controller 12 controlling the DSP 11. That is, the sensitivity of the current-voltage conversion circuit 30 is switched by the controller 12.

  Further, in the current-voltage conversion circuit 30, the same voltage is generated at the control inputs (gate terminals) of the NMOS transistors N1-1 and N1-2 to control the NMOS transistors N1-1 and N1-2 to the ON state. A first constant current source I1 and a second constant current source I2 that are constant current characteristics, an operational amplifier AMP2 that is a differential amplifier, and an NMOS transistor N2 are provided, and an output voltage V2 of the operational amplifier AMP2 switches the switches SW1 and SW2. To the control inputs of the NMOS transistors N1-1 and N1-2. The switches SW1 to SW4 are controlled by a signal output from the DSP 11 by the controller 12 controlling the DSP 11, whereby the ON and OFF states of the NMOS transistors N1-1 and N1-2 are controlled.

  The first constant current source I1 has one end connected to the power supply voltage Vcc and the other end connected to one end of the resistor R2 and the inverting input terminal of the operational amplifier AMP2. The second constant current source I2 has one end connected to the power supply voltage Vcc and the other end connected to the drain of the NMOS transistor N2 and the non-inverting input terminal of the operational amplifier AMP2.

  The other end of the resistor R2 and the source of the NMOS transistor N2 are connected to the reference voltage Vc. The output terminal of the operational amplifier AMP2 is connected to the gate terminal of the NMOS transistor N2 and to one end of the switches SW1 and SW2.

  The other end of the switch SW1 is connected to one end of the switch SW4 and the gate terminal of the NMOS transistor N1-1, and the other end of the switch SW2 is connected to one end of the switch SW3 and the gate terminal of the NMOS transistor N1-2. The other ends of the switches SW3 and SW4 are connected to the ground voltage GND.

  As described above, the first constant current source I1 and the resistor R2 are connected in series between the power supply voltage Vcc and the reference voltage Vc, and the second constant current source I2 and the NMOS transistor N2 are connected in series. The operational amplifier AMP2 outputs a voltage corresponding to the difference between the voltage of the resistor R2 and the voltage of the NMOS transistor N2, and the output of the operational amplifier AMP2 is output to the NMOS transistors N1-1 and N1-2 via the switches SW1 to SW4. And is applied to the gate terminal which is the input of the NMOS transistor N2.

  Therefore, feedback is applied to control the gate voltage of the NMOS transistor N2 so that the output voltage V2 of the operational amplifier AMP2 is equal to the voltage V1 generated in the resistor R2 and the drain-source voltage of the NMOS transistor N2. Become.

  Further, since the first constant current source I1 and the second constant current source I2 have the same constant current characteristics, the currents flowing through the NMOS transistor N2 and the resistor R2 are equal, and therefore the NMOS transistor N2 is turned on. The resistance is the same as the resistance R2.

  The NMOS transistors N1-1, N1-2, and N2 have the same size (gate width W). As a result, the NMOS transistors N1-1 and N1-2 receive the output voltage V2 via the switches SW1 and SW2. These ON resistances when turned ON are the same as the resistance R2.

  Further, since the ON resistance of the NMOS transistor N2 depends on the resistance value of the resistor R2, and does not depend on the power supply voltage Vcc, the NMOS transistor N1-1 even when the power supply voltage Vcc fluctuates. , N1-2 can be made constant.

  In addition, the drain-source voltage of the NMOS transistor N2 is generated by connecting the source of the NMOS transistor N2 and the other end of the resistor R2 to the reference voltage Vc of the operational amplifier AMP1, so that it does not depend on the reference voltage Vc. Even when the reference voltage Vc fluctuates, the ON resistances of the NMOS transistors N1-1 and N1-2 can be made constant. Therefore, in the current-voltage conversion circuit 30, variations in transimpedance can be suppressed.

  As described above, the series connection of the first constant current source I1 and the resistor R2 and the series connection of the second constant current source I2 and the NMOS transistor N2 are arranged between the power supply voltage Vcc and the reference voltage Vc. The voltage according to the difference between the voltage applied to the resistor R2 and the voltage applied to the NMOS transistor N2 is applied from the operational amplifier AMP2 to the base of the NMOS transistor N2 so that the voltage applied to the resistor R2 and the voltage applied to the NMOS transistor N2 are the same. Since the output of the operational amplifier AMP2 is used for the ON / OFF control of the NMOS transistors N1-1 and N1-2, the NMOS transistor N1- is controlled regardless of the fluctuation of the power supply voltage Vcc and the fluctuation of the reference voltage Vc. The ON resistances of N1 and N1-2 can be set to a certain constant value.

  Further, by making the size of the NMOS transistors N1-1 and N1-2 n times as large as the NMOS transistor N2 (n> 1), the ON resistance of the NMOS transistors N1-1 and N1-2 is reduced to R2 / n. It can be a resistance value. That is, since the size of the NMOS transistors N1-1 and N1-2 is larger than that of the NMOS transistor N2, the ON resistance of the NMOS transistors N1-1 and N1-2 can be reduced.

  FIG. 3 shows transimpedance characteristics with respect to fluctuations in the power supply voltage Vcc in the current-voltage conversion circuit 30. As shown in FIG. 3, in the current-voltage conversion circuit 30 according to the present embodiment, the transimpedance has a constant value with respect to fluctuations in the power supply voltage Vcc. Note that the transimpedance characteristics with respect to fluctuations in the reference voltage Vc are similar to the transimpedance characteristics with respect to fluctuations in the power supply voltage Vcc.

  In the conventional current-voltage conversion circuit, the ON resistance ratio of the transimpedance Rf is suppressed to about 1% because the ON resistance of the NMOS transistor which is a transistor switch fluctuates due to the fluctuation of the power supply voltage Vcc and the fluctuation of the reference voltage Vc. Although it was necessary to use the gate voltage control method in this embodiment, even if the ratio of the ON resistance to Rf is increased to about 10%, the variation of the power supply voltage Vcc of the transimpedance and the reference The influence due to the fluctuation of the voltage Vc can be suppressed.

  Therefore, the current-voltage conversion characteristics can be improved regardless of the fluctuation of the power supply voltage Vcc and the fluctuation of the reference voltage Vc.

  In addition, the size of the NMOS transistor conventionally used as a transistor switch can be reduced to less than half, and a broadband voltage-current conversion circuit can be designed by reducing the parasitic capacitance.

  Further, since feedback is applied so as to be equal to the resistance R2, the ON resistance is also affected by variations in the threshold voltage Vth, the gate length L, and the temperature, which are causes of variations in the ON resistance of the NMOS transistors N1-1 and N1-2. It becomes constant without dispersion.

It is a schematic block diagram of an optical disk device. It is a schematic block diagram of a front monitor photodetector circuit. It is a figure which shows the transimpedance characteristic of a current-voltage converter. It is a block diagram of the conventional current-voltage conversion circuit. It is a block diagram of the conventional current-voltage conversion circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 5,10 Photodetector circuit 30 Current voltage conversion circuit AMP1, AMP2 Operational amplifier (differential amplifier)
I1 first constant current source I2 second constant current source R1-1, R2-2 feedback resistor R2 resistor N1-1, N1-2 NMOS transistor (transistor switch)
N2 NMOS transistor PD1 Photodiode SW1 to SW4 Switch Vcc Power supply voltage Vc Reference voltage GND Ground potential

Claims (4)

An amplifier that converts an output current signal into a voltage signal based on a reference voltage and outputs the voltage signal,
Between the input and output of this amplifier, in a current-voltage conversion circuit in which a set of feedback resistors and transistor switches connected in series is connected in parallel,
Between a power supply voltage and the reference voltage of the amplifier, both when a resistance between the first constant current source arranged in series connection,
A second constant current source and a transistor are connected in series ;
A differential amplifier that outputs a voltage corresponding to a difference between the voltage of the resistor and the output voltage of the transistor ;
Applying the voltage, which is the output of the differential amplifier, to the control input of the transistor switch via a switch ;
And a voltage that is an output of the differential amplifier is applied to a control input of the transistor. The current-voltage conversion circuit according to claim 1, wherein a size of the transistor switch is larger than a size of the transistor. An amplifier that converts an output current signal into a voltage signal based on a reference voltage and outputs the voltage signal,
In the photodetector circuit having a current-voltage conversion circuit in which a set of feedback resistors and transistor switches connected in series is connected in parallel between the input and output of this amplifier,
The current-voltage conversion circuit is
Between a power supply voltage and the reference voltage of the amplifier, both when a resistance between the first constant current source arranged in series connection,
A second constant current source and a transistor are connected in series ;
A differential amplifier that outputs a voltage corresponding to a difference between the voltage of the resistor and the output voltage of the transistor ;
Applying the voltage, which is the output of the differential amplifier, to the control input of the transistor switch via a switch ;
A photodetector circuit, wherein the voltage which is an output of the differential amplifier is applied to a control input of the transistor. In an optical disc apparatus that reads and writes data from and to the optical disc by irradiating the optical disc with laser light through an optical system,
A photodetector circuit for converting the laser beam dispersed through the optical system into an electrical signal;
The photodetector circuit includes an amplifier that converts an input current signal into a voltage signal based on a reference voltage and outputs the voltage signal. A pair of feedback resistors and transistor switches connected in series is connected in parallel between the input and output of the amplifier. Current voltage converter circuit,
The current-voltage conversion circuit is
Between a power supply voltage and the reference voltage of the amplifier, both when a resistance between the first constant current source arranged in series connection,
A second constant current source and a transistor are connected in series ;
A differential amplifier that outputs a voltage corresponding to a difference between the voltage of the resistor and the output voltage of the transistor ;
Applying the voltage, which is the output of the differential amplifier, to the control input of the transistor switch via a switch ;
An optical disc apparatus characterized by applying the voltage, which is an output of the differential amplifier, to a control input of the transistor.

Images