JPH11213427A - Current-voltage conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offset an output voltage level by providing a current source which synthesizes to output a current value of a prescribed level against the light receiving current of a photodetector or inserting a resistance between a power supply voltage and the input of the light receiving current in an operation amplifier. SOLUTION: A feedback resistance R is inserted between the output and the inverted input of an operation amplifier 21, with a reference voltage Vref inputted against noninverted input. In addition, a current source Si obtainable from a DC power line VCC is also inputted against the inverted input of the amplifier 21. In other words, an offset current iOFS obtainable from the current source Si is synthesized against the light receiving current iPD of a photodiode PD. In the case where a current-voltage conversion circuit is so constituted, regardless of the presence/absence of the light receiving current iPD, the offset current iOFS that is always outputted by the current source Si is inputted against the inverted input of the operation amplifier 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-voltage conversion circuit for converting an output current of a photodiode into a voltage.

[0002]

2. Description of the Related Art For example, in a reproducing apparatus or a recording / reproducing apparatus corresponding to an optical disk or a magneto-optical disk, a light receiving signal (light receiving current) generated by a laser reflected light received by a photodetector (photodiode) of an optical pickup.
, A reproduction RF signal is generated or a servo error signal for tracking servo or focus servo control is generated. Normally, the light receiving current of the photodetector is converted into a voltage by a current-voltage conversion circuit formed by an operational amplifier or the like, amplified, and supplied to a required function circuit unit at a subsequent stage.

FIG. 6 is a circuit diagram showing an example of a current-to-voltage conversion circuit for performing current-to-voltage conversion on a light-receiving current obtained by a photodiode forming such a photodetector.

In this figure, a photodiode PD is assumed to form a photodetector. In this case, a light-receiving current iPD obtained by the photodiode PD
Are connected so as to be input to the inverting input of the operational amplifier 21 by the polarity shown by the arrow in the figure. The operational amplifier 21 converts the light receiving current iPD of the photodiode PD into a voltage, amplifies the voltage, and outputs it as a light receiving signal voltage Vo. In this case, the feedback resistance R
Are connected as shown in the figure, and the reference voltage Vref is inputted to the non-inverting input.

Here, as the reference voltage Vref, a reference voltage commonly used in a system such as a disk device including the current-voltage conversion circuit shown in FIG. 1 is also used. .

In general, a reference value commonly used in a system is set to a center value of a power supply voltage. That is, 0 (V) is set in the case of the dual power supply system, and n / 2 in the case of the single power supply of n (V).
(V) is set. This is because the dynamic range on the plus side and the minus side of the signal are equally obtained, which is advantageous for the amount of error in the processing by various controls and the like and the drive signal.

Here, the light receiving signal voltage Vo in the current-voltage conversion circuit shown in FIG. 6 is expressed by the following equation: Vo = R · iPD + Vref (1)

[0008]

However, the light receiving current iPD from the photodiode PD forming the photodetector is a signal of a level in a region only on either the plus side or the minus side with respect to the reference voltage Vref. It is. Therefore, regarding the current-voltage conversion circuit,
When a reference voltage commonly used in the system is used for the reference voltage Vref as described above, the dynamic range of the light reception signal voltage Vo expressed by the above (Equation 1) is always 1 / the power supply voltage level. It is less than 2 and cannot be obtained sufficiently. this is,
This can lead to an increase in an error rate relating to signal processing, and is disadvantageous in terms of, for example, S / N.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a sufficient dynamic range as an output voltage of a current-voltage conversion circuit in consideration of the above-mentioned problems.

For this reason, in a current-voltage conversion circuit formed with a current-voltage converter for converting the output current of the photodiode element into a voltage and outputting the voltage,
Offset means for offsetting the output voltage of the voltage converter by a predetermined level with respect to a reference voltage corresponding to the center value of the power supply voltage is provided.

According to the above configuration, the output voltage of the current-to-voltage converter formed by, for example, an operational amplifier or the like is offset. Here, for example, when the offset level is not given, If it is assumed that the output voltage of the current-voltage converter appears in the positive side region, the offset level is given by shifting the reference level to the negative side so that the current
It is possible to obtain a state where the output voltage of the voltage converter swings with reference to a level near the center of the power supply voltage level.

[0012]

Embodiments of the present invention will be described below. Here, it is assumed that the current-voltage conversion circuit of the present embodiment is provided in an optical disk reproducing device as a CD player. Therefore, first, the configuration of the main part of the optical disk reproducing apparatus of the present embodiment will be described with reference to the block diagram of FIG.

The disk D inserted in the reproducing apparatus shown in FIG. 1 is loaded into the disk driver 1 and driven for reproduction. The disk driver 1 shown in FIG. 1 includes a loading mechanism for loading and unloading a disk, a spindle motor 2 as a disk rotation driving mechanism, and an optical pickup mechanism 3. The disk is driven by the spindle motor 2, for example, into a CLV (Constant). Linear Veroci
The laser beam is emitted from the optical pickup mechanism 3 in a state where the optical disk is rotated by the ty (constant linear velocity) method, and a detection signal corresponding to the reflected light is obtained, so that the information from the disk D is read.

For this reason, the optical pickup mechanism 3 includes a laser diode as a laser output unit, an optical system including a polarizing beam splitter and an objective lens, and an optical system for detecting reflected light. A photodetector and the like are mounted. The objective lens provided in the optical pickup mechanism 3 is held by a biaxial mechanism, for example, so as to be displaceable in the radial direction of the disk and in the direction in which the optical disk comes into contact with and separates from the disk. Although not shown here, a thread mechanism for transporting the optical head 3 itself in the radial direction of the disk is also provided.

A light-receiving signal (light-receiving current), which is detection information of light reflected from the disk by the photodetector of the optical pickup mechanism 3, is supplied to a current-to-voltage converter 4 where current-to-voltage conversion is performed. Then, it is output to the RF matrix amplifier 5 as a light receiving signal voltage.

The RF matrix amplifier 5 amplifies the light-receiving signal voltage input from the current-voltage converter 4
By performing various arithmetic processes, a reproduction RF signal, a focus error signal, a tracking error signal, and the like are generated. The outputs of these RF matrix amplifiers 5 are supplied to a binarization circuit 6 and a servo circuit section 9.

The binarization circuit 6 binarizes the reproduced RF signal input from the RF matrix amplifier 5 to obtain
The signal is output to the FM decoding / signal processing circuit 7. In the EFM decoding / signal processing circuit 7, the input binarized EF
The M signal is subjected to EFM demodulation processing, error correction processing, and other necessary signal processing to decode information read from the disk into audio data. Further, based on the input EFM signal, extraction of subcode and address data, extraction of rotation speed information, and the like are performed, and the information is supplied to the controller 8 and the servo circuit unit 9.

The audio signal data output from the EFM decoding / signal processing circuit 7 is converted into an analog audio signal by the D / A converter 10 and supplied to the audio signal output terminal 11 as a reproduced audio signal.

The servo circuit section 9 calculates the focus, tracking, thread, and spindle from the focus error signal and tracking error signal supplied from the RF matrix amplifier 5 and the spindle error signal supplied from the EFM decoding / signal processing circuit 7. Of the disk drive 1 to execute the servo operation related to the disk reproduction operation. Controller 8
Is provided with a microcomputer, a RAM, and the like, and controls various playback operations of the playback device.

Here, the photodetector provided in the optical pickup mechanism 3 has a configuration shown in FIG. In this figure, six photodetectors A, B, C, D, E, and F are shown, and the light receiving signals of the photodetectors A, B, C, and D are used for generating a reproduction RF signal and controlling focus servo. Used to generate a focus error signal. The light receiving signals of the photo detectors E and F are used to generate a focus error signal for tracking control. Specifically, to generate a reproduced RF signal, an arithmetic operation represented by (A + B + C + D) is performed on the light receiving signals of the photodetectors A, B, C, and D, and (A + C)-( B + D). In addition, a calculation represented by (E−F) is performed on the tracking error signal. Such arithmetic processing is performed by the RF matrix amplifier 5 described above.

The circuit diagram of FIG. 3 has a configuration including the current-voltage converter 4 and the RF matrix amplifier 5 shown in FIG. 1 for generating reproduced RF signals from the photodetectors A, B, C, and D. Are extracted and shown.
Note that the configuration shown in this figure is merely a basic configuration, and the configuration of the current-voltage conversion circuit according to the present embodiment described later is modified based on the configuration shown in FIG.

When the configuration shown in this figure corresponds to FIG. 1, the photodetectors A, B, C, D (and the resistors R1, R2,
The capacitor C) belongs to the optical pickup mechanism 3, and a circuit composed of [op-amp 21, feedback resistor R, (resistor R 2)] and [op-amp 22, feedback resistor R, (resistor R 3)] corresponds to the current-voltage converter 4. I do. Then, an amplifier circuit composed of [the operational amplifier 23 and the feedback resistor R4] belongs to the RF matrix amplifier.

In FIG. 3, a photodetector (photodiode) is connected to a power supply line via a resistor R1.
The cathode sides of A, C, B, and D are connected. Note that, for example, a capacitor C for removing noise is inserted between the power supply line and the ground. Here, the anodes of the photodetectors A and C are connected to the non-inverting input of the operational amplifier 21, and the anodes of the photodetectors B and D are
It is connected to the non-inverting input of the operational amplifier 22.
The operational amplifier 21 operates based on the reference voltage Vref input to the non-inverting input, and operates based on the photodetectors A,
The light-receiving current input from C to the inverting input is subjected to current-voltage conversion and output as a light-receiving signal voltage Vo. Thereby, the photodetectors A and C are output from the operational amplifier 21.
With respect to the received light signal, the light receiving signal voltage Vo of the component represented by the term (A + C) is obtained.

Similarly, the operational amplifier 22 operates on the basis of the reference voltage Vref input to the non-inverting input. Here, the light receiving current input from the photodetectors B and D to the inverting input is the current. -Voltage conversion,
It is output as a light receiving signal voltage Vo. As a result, the light receiving signal voltage Vo of the component represented by the term (B + D) is obtained from the operational amplifier 22 for the light receiving signals of the photodetectors A and C.

The light receiving signal voltages Vo of the operational amplifier 21 and the operational amplifier 22 are input to the inverting input of the operational amplifier 23 via the resistors R2 and R3, respectively. That is, a signal component represented by (A + C) + (B + D) = (A + B + C + D) is input to the inverting input of the operational amplifier 23 as a light receiving signal of the photodetectors A, C, B, and D. (A + B
+ C + D) as described above,
The reproduced RF signal RFO is obtained by amplifying each light receiving signal voltage Vo of the operational amplifier 21 and the operational amplifier 22 in the operational amplifier 23.

Although not shown here, for example, each light receiving signal voltage Vo of the operational amplifier 21 and the operational amplifier 22 is branched and supplied to a non-inverting input and an inverting input of the operational amplifier for generating a focus error signal. For example, the operation of (A + C)-(B + D) is performed by the operational amplifier, and a focus error signal is obtained. The circuit configuration for generating a tracking error signal based on the light receiving signals of the photodetectors E and F will not be described here, but, for example, as is obvious from the above configuration, the circuit configuration has been described earlier (EF). , The photodetectors E and F
A signal obtained by current-to-voltage conversion of each light receiving current may be supplied to the non-inverting input and the inverting input of the operational amplifier.

In the circuit configuration shown in FIG. 3, the reference voltage V input to the non-inverting input of each operational amplifier is
ref is set to the center value of the power supply voltage supplied to the system shown in FIG.

Next, a description will be given of a first example of the configuration of the current-voltage conversion circuit, which is a feature of the embodiment of the present invention. The current-voltage conversion circuit here is provided in the current-voltage conversion unit 4 shown in FIG.

FIG. 4 shows a configuration corresponding to a circuit portion including the operational amplifier 21 shown in FIG. 3 as the current-voltage conversion circuit of the present embodiment. In the current-voltage conversion circuit in this case, the cathode of the photodiode PD is connected to the ground, and the anode is connected to the inverting input of the operational amplifier 21. Then, a connection configuration is adopted in which the feedback resistor R is inserted between the output terminal of the operational amplifier 21 and the inverting input, and the reference voltage Vref is input to the non-inverting input. And, for the above connection form,
The current source Si obtained from the DC power supply line VCC is also configured to be input to the inverting input of the operational amplifier 21. That is, the offset current iOFS obtained by the current source Si
Is combined with the light receiving current iPD of the photodiode PD. Note that the photodiode P here
D uses the photodetectors A and C shown in FIG.
They are collectively shown as one photodiode.

When the current-voltage conversion circuit is configured in this manner, the offset current iOFS always output from the current source Si is input to the inverting input of the operational amplifier 21 regardless of the presence or absence of the light receiving current iPD. Will be.
Therefore, the light receiving signal voltage Vo output from the operational amplifier 21 is represented by the following expression: Vo = R ＝ (iPD−iOFS) + Vref (Equation 2) First, FIG.
When comparing with (Equation 1) representing the light receiving signal voltage Vo of the current-voltage conversion circuit shown in (1), {R · (iPD−iOFS) + Vref} − {R · iPD + Vref} = − R · iOFS (Equation 3), and the light receiving signal voltage Vo is given an offset of a level represented by −R · iOFS. Therefore, the dynamic range of the light receiving signal voltage Vo can be increased by setting iOFS of the current source Si so that a state where the light receiving signal voltage Vo oscillates around an appropriate reference level can be obtained.

FIG. 5 shows a second example of the configuration of the current-voltage conversion circuit according to the present embodiment. In this figure, the same parts as those in FIG. In this case, an offset resistor ROFS having a predetermined value is inserted between the DC power supply line VCC and the inverting input of the amplifier 1 instead of the current source Si shown in FIG. In this configuration, the offset resistor ROF
The offset current iOFS input to the inverting input of the amplifier 1 by S is represented by the following expression: iOFS = (Vcc-Vref) / ROFS (Equation 4). Therefore, if the above (Equation 4) is substituted into the above (Equation 2), the light receiving signal voltage Vo of the current-voltage conversion circuit shown in FIG. 4 is given by: Vo = R ｛ΔPD− (VCC−Vref) / ROFS｝ + Vref (Expression 5) And (Equation 5):
First, as for the conventional example, (Equation 1) representing the light receiving signal voltage Vo of the current-voltage conversion circuit shown in FIG. 6 is expressed by a-b By calculating b, it can be seen that an offset level represented by ab = −R (VCC−Vref) / ROFS (Expression 6) can be obtained in the light receiving signal voltage Vo. In this case, as can be seen from the above (Equation 6), the offset level of the light receiving signal voltage Vo depends on the power supply voltage of the DC power supply line VCC.

In the first and second examples,
The current-to-voltage conversion circuit (the operational amplifier 21) for performing the current-to-voltage conversion for the photodetectors A and C has been described as an example. However, as a matter of course, the photodetectors B and D of the operational amplifier 22 shown in FIG. Current-
The same configuration is adopted on the current-voltage conversion circuit side for performing voltage conversion. Further, in the case of a CD player, the same configuration as that of the first and second examples should be provided to the current-voltage conversion circuit that performs the current-voltage conversion for the photodetectors E and F.

The present invention is not limited to the first and second examples described above. For example,
In the first and second examples, the reference voltage V
The description has been given on the assumption that the reference voltage ref supplies a reference voltage commonly used in the system. However, the reference voltage Vref of the operational amplifier forming the current-voltage conversion circuit is the same as the reference voltage Vref used in the above-mentioned system. By adjusting the reference voltage level itself after being independent of the voltage, the light reception signal voltage Vo can also be adjusted.
Can be shifted.

Further, the disk device on which the current-voltage conversion circuit of the present invention is mounted is not limited to a CD player, but a recording or reproducing device having a structure for reading a signal from a recording medium by optical means. The present invention can be applied to an apparatus.

[0035]

As described above, according to the present invention, in a current-voltage conversion circuit for converting a light receiving current of a photodetector into a voltage, for example, a current value of a predetermined level is combined with a light receiving current of the photodetector and output. A current source is provided, or a resistor is inserted between a power supply voltage and a light-receiving current input to an operational amplifier to shift the output voltage level by a predetermined level from the reference voltage level to offset the output voltage level. .

The photodetector current of the photodetector is a signal on either the plus or the minus side. In the above configuration, by taking into account the setting of the offset level with respect to the reference voltage level, the output voltage of the current-voltage conversion circuit is considered. The reference level can be set to a level close to the center value of the power supply voltage. As a result, the dynamic range of the output voltage of the current-voltage conversion circuit can be expanded, and accordingly, the occurrence of errors in the signal processing at the subsequent stage becomes stronger, and the characteristics such as S / N are improved. This has the effect that the reliability of the information read out from is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of an optical disc reproducing apparatus provided with a current-voltage conversion circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a photodetector mounted on the optical disc reproducing device shown in FIG.

FIG. 3 shows an optical disc reproducing apparatus according to the present embodiment.
FIG. 2 is a circuit diagram showing a basic configuration of a circuit for generating a reproduction RF signal.

FIG. 4 is a circuit diagram illustrating a configuration of a current-voltage conversion circuit according to the present embodiment.

FIG. 5 is a circuit diagram illustrating a configuration of a current-voltage conversion circuit according to the present embodiment.

FIG. 6 is a circuit diagram showing a configuration of a current-voltage conversion circuit as a conventional example.

[Explanation of symbols]

1 disk driver, 2 spindle motor, 3 optical pickup mechanism, 4 current-voltage / voltage converter, 5R
F matrix amplifier, 6 binarization circuit, 7 EFM decoding / signal processing circuit, 8 controller, 9 servo circuit section, 10 converter, 21, 22, 23 operational amplifier, iPD light receiving current, iOFS offset current, A,
B, C, D, E, F photodetector, C capacitor, D disk, PD photodiode (photodetector), R feedback resistor, R1, R2, R3, R4
Resistance, ROFS offset resistance, Si current source, Vo
Light receiving signal voltage, Vref reference voltage, VCC DC power supply line

Claims (3)

[Claims] 1. A current-voltage conversion circuit formed by including a current-voltage converter for converting an output current of a photodiode element into a voltage and outputting the voltage, wherein an output voltage of the current-voltage converter is A current-to-voltage conversion circuit comprising offset means for offsetting a reference voltage corresponding to a center value of a power supply voltage by a predetermined level. 2. A current source according to claim 1, wherein said offset means is a current source provided so as to synthesize and output a current value of a predetermined level with respect to an output current of a photodiode element. A voltage conversion circuit; 3. The offset means is inserted between a power supply voltage and an input of an output current of the photodiode element in the current-voltage converter,
2. The current-voltage conversion circuit according to claim 1, wherein the current-voltage conversion circuit is a resistor having a predetermined resistance value.