JP3096933B2 - Drive device for optical information recording medium and signal reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for an optical information recording medium suitable for a magneto-optical disk or a write-once optical disk and a method for reproducing a signal from the optical information recording medium. -Voltage conversion circuit for obtaining a reproduced data signal and a control signal from a reflected light signal or a transmitted light signal
And its operation .

[0002]

2. Description of the Related Art FIG. 3 shows a conventional light-to-voltage conversion circuit of this type. Hereinafter, the configuration and operation of the circuit will be described with reference to the drawings.

In FIG. 3, reference numerals 1 to 4 denote photodetectors, generally called photodiodes, which output a current corresponding to the intensity of light. Reference numeral 5 denotes a power supply for applying an operation bias to the photodetectors 1 to 4. Reference numerals 6 to 9 denote capacitors for passing high frequency components of the output current of the photodetector, a resistor 10 and an operational amplifier 11 convert a current of high frequency components passed through the capacitors 6 to 9 to a voltage, The output terminal. On the other hand, 12 to 15 are resistors, 16 to 19 are operational amplifiers, and 20 to 23 are resistors.
And the resistor 20, the operational amplifier 17 and the resistor 21, the operational amplifier 1
8 and a resistor 22, and an operational amplifier 19 and a resistor 23 constitute a current-voltage conversion amplifier. 24 to 29 are resistors,
30 is an operational amplifier and 32 is its output terminal.

The high-frequency components of the currents output from the photodetectors 1 to 4 pass through the capacitors 6 to 9 and are input to the inverting input terminal of the operational amplifier 11, where they are converted into a voltage by the operational amplifier 11 and the resistor 10. Becomes a data reproduction signal proportional to the light of the high-frequency component input to the photodetectors 1 to 4,
Output from the output terminal 31. The low frequency component is cut off by the capacitors 6 to 9 and flows to the resistors 12 to 15,
The voltage is converted by the operational amplifiers 16 to 19 and the resistors 20 to 23. The outputs of the operational amplifiers 16 and 17 and the operational amplifiers 18 and
The output of 19 is input to the operational amplifier 30 through the resistors 24 to 27 in reverse polarity, and the difference voltage between them is output from the output terminal 32.

In an optical disk drive pickup,
The 1-4 photodetectors are called 4D sensors. The sum of these outputs becomes a main signal called an FM signal in a video disc player and an EFM signal in a digital audio player. FIG. 4 shows the relationship between the arrangement of the 4D sensor and the light beam. 4A shows a case where a focus shift occurs in a certain direction, FIG. 4B shows a case where the focus shift is zero, and FIG. 4C shows a case where a focus shift occurs on the side opposite to the case of FIG. 4D sensor and light beam spot 6
2 is shown. The sum of two sensors arranged on the diagonal line of the 4D sensor (the sum of the photodetectors 1 and 2 and the photodetector 3
And the sum of 4), the difference between them ((3 + 4)-(1 + 2))
4 (a), a positive control signal is obtained in FIG. 4 (b), and a negative control signal is obtained in FIG. 4 (c). That is, main signals and control signals can be extracted from the photodetectors 1 to 4 called 4D sensors, and this is an important role of the pickup.

In FIG. 3, if the capacitance values of the capacitors 6 to 9 are C and the resistance values of the resistors 12 to 15 are R, fc = 1
The cutoff frequency fc represented by / (2πRC) is determined.
The current signal having a frequency higher than fc is output from the operational amplifier 11.
, A main signal appears at the terminal 31, and a current signal having a frequency lower than fc appears at the terminal 32 as a control signal via the operational amplifiers 16 to 19 and 30.

Next, another example of a conventionally known light-to-voltage conversion circuit will be described with reference to FIG. In this figure, 51 to 56 denote operational amplifiers, 57 to 71 denote resistors, and other elements corresponding to those in FIG. 3 are denoted by the same reference numerals. An operational amplifier 51 and a resistor 57,
Operational amplifier 52 and resistor 58, operational amplifier 53 and resistor 5
9, a current-voltage conversion amplifier is constituted by the operational amplifier 54 and the resistor 60, the operational amplifier 55 and the resistor 61, and the operational amplifier 56 and the resistor 62, and converts the output current of the photodetectors 1 to 4 into a voltage. Outputs of the operational amplifiers 51 to 54 are connected to inverting input terminals of the operational amplifier 55 via resistors 63 to 66, and the operational amplifiers 55 to 5
4 are summed and output from the output terminal 31 as a main signal. On the other hand, operational amplifiers 51 and 5 connected to the photodetectors 1 and 2 arranged on the diagonal line of the 4D sensor
Output of the operational amplifier 56 via resistors 67 and 68, respectively.
And the outputs of the operational amplifiers 53 and 54 connected to the photodetectors 3 and 4 arranged on the other diagonal line of the 4D sensor via resistors 69 and 70, respectively. It is connected to the other input terminal, the difference signal between them is taken by the operational amplifier 56, and the output terminal 32
Is output as a control signal.

[0008]

In the circuit of FIG. 3, there is no problem when the signal band of the main signal and the control signal band use completely different bands, but when the same frequency band is desired to be used. There is a disadvantage that it is difficult to set a band. In particular, in the case of a digital audio disc, since the main signal contains many low-frequency components, unless the low frequency of the main signal is passed, the error rate in data identification of the reproduced signal is deteriorated. Therefore, the necessary bands of the main signal and the control signal overlap, and it becomes difficult to separate the band of the main signal and the control signal in the method of FIG.

On the other hand, in the circuit shown in FIG. 5, since the signals obtained at the terminals 31 and 32 include DC to high-frequency signals, only the necessary band needs to be used thereafter. The signal band can be set arbitrarily. However, this circuit has a problem that, due to a large number of operational amplifiers and voltage setting resistors used, noise mixed into the output terminal 31 of high frequency components and a DC offset of a control signal obtained at the output terminal 32 are large. There is. That is, the noise mixed in the output 31 is the photodetector 1
Shot noises generated in the operation amplifiers 4 to 4 and the operational amplifiers 51 to 56
, The thermal noise of the conversion resistors 57 to 62, and the thermal noise of the control signal conversion resistors 67 to 70 are mainly problems. The DC offset of the control signal is caused by the dark current of the photodetectors 1 to 4 and the operational amplifier 57. This is because an offset of ~ 62 is mainly a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a circuit type which enables the control signal and the sum signal to overlap the band, and reduces the noise of the sum signal output and the DC offset of the control signal.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a drive device for an optical information recording medium , in order to achieve the above object.
Is the intensity of the reflected light or transmitted light from the optical information recording medium.
Multiple optical detectors that detect and output current according to the intensity of light
Output signal from the sum of the outputs of the photodetectors.
And a control signal is obtained from the difference between the outputs of the photodetectors.
Drive device for optical information recording media with voltage conversion circuit
Wherein the light-to-voltage conversion circuit comprises the plurality of light detection
And the resistors connected to each of the plurality of photodetectors
And each of the photodetectors is connected to the inverting input terminal via the resistor.
Connected operational amplifiers, each of the photodetectors and their connected
A subtraction circuit for subtracting a voltage between the applied resistors;
And a capacitor inserted in parallel.
The voltage of the sum signal of the photodetector is obtained from the output of the operational amplifier,
A voltage serving as a control signal can be obtained from the output of the subtraction circuit.
And features. As for the signal reproduction method,
The reflected light intensity or transmitted light intensity from the
Detected by photodetectors and reproduced from the sum of outputs from each photodetector
Obtain a data signal and generate a control signal from the difference between the outputs of the photodetectors.
In the obtained signal reproducing method, the plurality of photodetectors,
A resistor connected to each of the plurality of photodetectors;
Each of the photodetectors is connected to an inverting input terminal via a resistor.
Operational amplifiers, each of the photodetectors and the resistors connected thereto.
A subtraction circuit for subtracting a voltage between the resistors;
Light-to-voltage conversion circuit having a capacitor inserted in a column
Using a drive device provided with
Is R, and the capacitance value of each capacitor is C, fc
= Higher than the cutoff frequency fc expressed by 1 / (2πRC)
Through the operational amplifier to generate a sum signal.
A reproduction data signal which is a voltage, and the cutoff frequency fc
A lower frequency current signal is passed through the subtraction circuit to
It is characterized in that a control signal which is a voltage of a signal is obtained.

[0012]

[Function] When the output current of each photodetector is connected to the inverting input terminal of the operational amplifier via a resistor and the voltage of the sum signal of the photodetector is obtained by the feedback resistance of the operational amplifier, the sum signal includes DC to high-frequency signals. Therefore, the bands of the sum signal and the control signal overlap. And a resistor for the resistor
When capacitors are inserted in parallel, the resistance value of each
Frequency higher than the cutoff frequency determined by the capacitance value of the capacitor
The wave number current signal flows into the operational amplifier and is summed.
Output, so a very wide band from DC to high frequency
A sum signal can be obtained. Therefore, the data of the reproduction signal
The error rate in identification can be reduced. If the number of operational amplifiers and voltage setting resistors is two , six operational amplifiers
The noise mixed into the sum signal and the DC offset of the control signal can be reduced as compared with the case where the amplifier and the resistor for setting the voltage are used.

[0013]

An embodiment of the present invention will be described with reference to FIG.
In FIG. 1, 1-4 are photodetectors, 41 is an operational amplifier for obtaining a sum signal, 42 is a feedback resistor for setting its voltage,
33 to 36 are resistors provided between the photodetectors 1 to 4 and the inverting input terminal of the operational amplifier 41;
Capacitors connected in parallel to both ends of
Is a resistor connected to the output terminals of the photodetectors 1 to 4, 48 is an operational amplifier for obtaining a control signal, 49 is a feedback resistor for setting its voltage, and corresponds to FIGS. 3 and 5 described above. Elements have the same reference numbers.

As described above, in the photo-voltage conversion circuit of the present embodiment, the photodetectors 1-4 are connected to the inverting input terminal of the operational amplifier 41 via the parallel circuit of the resistors 33-36 and the capacitors 37-40. The reference voltage is connected to the non-inverting input terminal of the operational amplifier 41. As the operational amplifier 41, one having particularly good high-frequency characteristics is used. Also, photodetectors 1 and 2 (see FIG. 4) arranged diagonally to each other and one input terminal of an operational amplifier 48 for obtaining a control signal are connected via resistors 43 and 44, and The other input terminals of the operational amplifier 48 are connected to the other photodetectors 3 and 4 (see FIG. 4) arranged through the resistors 45 and 46. The resistors 43 to 47 are resistors 33 to 36
Is set higher than

The cutoff frequency fc of the circuit of FIG.
Assuming that the resistance values of 3-36 are R and the capacitance values of capacitors 37-40 are C, fc = 1 / (2πRC). A current signal having a frequency higher than the cutoff frequency fc flows through the resistors 33 to 36, is converted into a voltage, is amplified by an amplifier including an operational amplifier 41 and a feedback resistor 42, and is output from the output terminal 31 as a sum signal as a main signal. Is output. Further, a current signal having a frequency lower than the cutoff frequency fc flows through the resistors 43 to 46, and a difference signal ((3 + 4) − (1)
+2)) is amplified by an amplifier including an operational amplifier 48 and a feedback resistor 49, and output from the output terminal 32 as a difference signal as a control signal. By appropriately selecting the values of R and C, it becomes possible to reproduce the sum signal in the low frequency band.

Further, since the capacitors 37 to 40 are connected in parallel with the resistors 33 to 36, the reproduction of the sum signal in the high frequency band is also improved. That is, when the internal junction capacitance of the photodetectors (photodiodes) 1 to 4 is large, the photodetectors 1 to 4
4 does not flow through the resistors 33 to 36 and does not flow through the feedback resistor 42 of the operational amplifier 41, and the high-frequency characteristics of the sum signal output 31 deteriorate. Therefore, if the capacitors 37 to 40 are connected in parallel to the resistors 33 to 36, the cutoff frequency becomes as shown in the above equation, and it is possible in principle to reproduce even the high frequency components of the sum signal. Therefore, by using the operational amplifier 41 having excellent high-frequency characteristics and appropriately selecting the value of the feedback resistor 42, it is possible to effectively reproduce a sum signal of high-frequency components.

As described above, according to the circuit of this embodiment, a sum signal of a very wide band from DC to high frequency can be obtained, so that the error rate in data identification of the reproduced signal can be reduced as compared with the circuit of FIG. Can be reduced.

The circuit of the present embodiment includes an operational amplifier 41
Since the number of feedback resistors 41 for setting the voltage is two, noise mixed in the sum signal and DC offset of the control signal are reduced as compared with the circuit of FIG. 5 using six operational amplifiers and feedback resistors. can do. FIG. 2 shows a comparison between the control signal output offset and the sum signal output noise measured for the circuit according to the present invention, the conventional circuit shown in FIG. 3, and the conventional circuit shown in FIG. As is clear from the figure,
The circuit of the present invention has the lowest sum signal input conversion noise as compared with other circuits, and can reduce the focus signal input conversion offset by almost one digit as compared with the conventional circuit of FIG.

[0019]

[0020]

As described above, according to the present invention,
The output current of each photodetector is connected to the inverting input terminal of the operational amplifier via a resistor, and the voltage of the sum signal of the photodetector is obtained by the feedback resistance of the operational amplifier. Rutotomoni can wrap,
Since a capacitor was inserted in parallel with the resistor,
Determined by the resistance of each resistor and the capacitance of each capacitor
A current signal with a frequency higher than the cutoff frequency is supplied to the operational amplifier.
Flows, and sums signals in a very wide band from DC to high frequency.
Error rate in data identification of the reproduced signal
Can be reduced. Also, the number of operational amplifiers and voltage setting resistors has been reduced to two, so there are six operational amplifiers and voltage setting resistors.
The noise mixed in the sum signal and the DC offset of the control signal can be reduced as compared with the case where a fixed resistor is used .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a light-to-voltage conversion circuit according to an embodiment.

FIG. 2 is a table showing the effects of the present invention.

FIG. 3 is a circuit diagram of a light-to-voltage conversion circuit according to a conventional example.

FIG. 4 is an explanatory diagram showing a relationship between a configuration of a photodetector and a light beam spot.

FIG. 5 is a circuit diagram of another light-to-voltage conversion circuit according to a conventional example.

[Explanation of symbols]

 1-4 Photodetector 31 Output terminal of sum signal 32 Output terminal of control signal 33-36, 43-47 Resistance 37-40 Capacitor 41,48 Operational amplifier 42,49 Feedback resistance for voltage setting

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 00-7/013 G11B 7/09

Claims (2)

(57) [Claims] A plurality of photodetectors for detecting the intensity of reflected light or transmitted light from an optical information recording medium and outputting a current corresponding to the intensity of light; A drive device for an optical information recording medium comprising a light-to-voltage conversion circuit for obtaining a reproduced data signal and obtaining a control signal from the difference between the outputs of the respective photodetectors; A detector, a resistor connected to each of the plurality of photodetectors, an operational amplifier connected to the inverting input terminal of each of the photodetectors via the resistor, and each of the photodetectors connected thereto. A subtraction circuit for subtracting the voltage between the resistors,
And a capacitor inserted into the optical information recording medium, wherein a voltage of a sum signal of a photodetector is obtained by an output of the operational amplifier, and a voltage serving as a control signal is obtained by an output of the subtraction circuit. apparatus. 2. The method according to claim 1, wherein the intensity of light reflected from the optical information recording medium
The excess light intensity is detected by a plurality of photodetectors, and the
A reproduction data signal is obtained from the sum of outputs, and the output of each photodetector is obtained.
A signal reproduction method for obtaining a control signal from a difference between the plurality of photodetectors and a plurality of photodetectors.
Resistors connected to each other, and each of the photodetectors via the resistors.
Are connected to the inverting input terminal and
Subtraction circuit to subtract the voltage between the output and the resistor connected to it
And a capacitor inserted in parallel with the resistor.
A drive device provided with a light-to-voltage conversion circuit having
The resistance value of each resistor is R, and the capacitance of each capacitor is
When the quantity value is C, it is expressed by fc = 1 / (2πRC)
A current signal having a frequency higher than the cutoff frequency fc.
The read data signal, which is the voltage of the sum signal,
And a current signal having a frequency lower than the cutoff frequency fc is obtained.
A control signal which is a voltage of the difference signal is obtained through the subtraction circuit.
A signal reproducing method characterized by: