JPH08161830A - Optical reproducing device - Google Patents

Abstract

PURPOSE: To hardly receive an adverse effect caused by crosstalk from adjacent tracks by deciding a threshold for an AGC amplifier and controlling the amplification of an electric signal from an optical head. CONSTITUTION: A desired track on an optical disk 10 is irradiated with a light beam, and reflected light from the optical disk 10 is detected and converted into the electric signal by the optical head 1. When an amplitude of the electric signal from the optical head 1 is more than the theshold, this amplitude of the electric signal is amplified to a prescribed value by an AGC amplifier 2, an when the amplitude is less than the threshold, this amplitude is not amplified to the prescribed value. Consequently, by setting the threshold to a proper value, the electric signal from the desired track is amplified to a prescribed amplitude, but the electric signals from the adjacent tracks are not amplified to that amplitude. By this method, an adverse effect caused by adjacent crosstalk can hardly be exerted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing device such as an optical disk device, and more particularly to an AGC (Auto Gain Control) amplifier provided in the optical reproducing device.

[0002]

2. Description of the Related Art When reproducing information from an optical disc, a desired track of the optical disc is irradiated with a light beam from an optical head, and reflected light from the optical disc is detected and converted into an electric signal. The electric signal is input to the AGC amplifier and amplified to a predetermined amplitude. As a result, the waveform equalization and the waveform shaping in the subsequent stage can be normally performed without being affected by the difference in reflectance between the individual optical disks. As a result, the information can be reproduced accurately.

As shown in FIG. 7, the AGC amplifier includes a variable gain amplifier 51 and a control voltage generation circuit 52 for controlling the gain of the variable gain amplifier 51 so that the amplitude of the output signal of the variable gain amplifier 51 becomes constant. Is equipped with.

When the amplitude of the output signal of the variable gain amplifier 51 is small, the control voltage generation circuit 52 supplies the control voltage for increasing the gain of the variable gain amplifier 51 to the variable gain terminal T.
When the amplitude of the output signal of the variable gain amplifier 51 is large, the control voltage generation circuit 52
A control voltage for reducing the gain of 1 is applied to the variable gain terminal T. As a result, regardless of the reflectance of the optical disc,
An output signal with a substantially constant amplitude is obtained.

[0005]

However, in the above-described conventional configuration, there is a problem that not only the signal from the track from which information is reproduced, but also the signal from the adjacent track may be detected. Have

For example, in the case of an optical disc conforming to the ISO / IEC13549 standard, as shown in FIG.
The position of the pre-formatting section 11 of the n-th track is the position of the pre-formatting section 12 of the (n-1) th track on both sides and the pre-formatting section 13 of the (n + 1) th track.
It is out of position.

When the nth track of this optical disk is reproduced, a strong preformat signal 11a from the preformat section 11 of the nth track is reproduced, as shown in FIG.
In addition, the pre-format section 1 of the (n-1) th track
Weak crosstalk signal 12a from 2 and the (n + 1) th
The weak crosstalk signal 13a from the track preformat section 13 is detected as an electric signal.

When this is input to the above AGC amplifier, as shown in FIG.
The amplitudes of the output signals 12b and 13b corresponding to a and 13a are the same as those of the output signal 1 corresponding to the preformatted signal 11a.
It is almost the same as the amplitude of 1b. As a result, even unnecessary crosstalk signals 12a and 13a are detected.

Further, in the above-mentioned conventional structure, the gain of the AGC amplifier becomes maximum when the electric signal of zero level continues. Even if the pre-formatted signal 11a is input in this state, it takes time for the AGC to start functioning, so that the amplitude of the output signal 11b of the AGC amplifier becomes too large for a while. .

Further, when the electric signal of excessive level continues, the gain of the AGC amplifier becomes minimum. Even if the pre-format signal 11a is input in this state, it takes time until the AGC starts to function similarly to the above, so that the amplitude of the output signal 11b of the AGC amplifier becomes too small for a while. Have

[0011]

In order to solve the above-mentioned problems, an optical reproducing apparatus according to the invention of claim 1 irradiates a desired beam of an optical recording medium with a light beam and reflects it from the optical recording medium. An optical head that detects light and converts it into an electrical signal, and, if the amplitude of the electrical signal from the optical head is greater than or equal to a threshold value, amplifies the amplitude of the electrical signal to a predetermined value. It is characterized in that an amplifying means that does not amplify the amplitude of the signal to a predetermined value is provided.

In order to solve the above-mentioned problems, an optical reproducing apparatus according to a second aspect of the present invention is the optical reproducing apparatus according to the first aspect, wherein the amplifying means controls the electric signal from the optical head to a control voltage. A variable gain amplifier that amplifies with a gain proportional to
A control voltage generation circuit that outputs a control voltage so that the amplitude of the output signal of the variable gain amplifier has a predetermined value, and a limiter circuit that limits the control voltage from the control voltage generation circuit to a predetermined voltage or less Is characterized by.

In order to solve the above-mentioned problems, an optical reproducing apparatus according to a third aspect of the present invention is the optical reproducing apparatus of the second aspect, wherein the amplifying means further sets a control voltage arbitrarily. Is provided with a control voltage setting means for

[0014]

According to the structure of the first aspect, the information recorded on the desired track of the optical recording medium is read by the optical head and converted into an electric signal. Among the electric signals from the optical head, the electric signal from the track located at the center of the light beam is stronger than the electric signal from the track adjacent to the track (that is, the crosstalk signal). If a threshold of the electric signal amplitude is set in the middle of the amplitude of the electric signal from the track located at the center of the light beam and the amplitude of the electric signal from the adjacent track, the desired track can be obtained by the amplifying means. The electrical signals from the are amplified to a predetermined amplitude, but the electrical signals from adjacent tracks are not amplified to that amplitude. This makes it less likely to be adversely affected by crosstalk from adjacent tracks.

According to another aspect of the present invention, the control voltage generating circuit outputs the control voltage for amplifying the amplitude of the electric signal from the track located at the center of the light beam to a predetermined value, and the adjacent track. Outputs a control voltage for amplifying the amplitude of the electric signal from 1 to a predetermined value. Since the electric signal from the track located at the center of the light beam is stronger than the electric signal (that is, the crosstalk signal) from the track adjacent to that track, the latter control voltage is larger than the former control voltage. Therefore, if the limiter circuit limits the latter control voltage to a predetermined voltage or less, the gain of the variable gain amplifier with respect to the electric signal from the adjacent track can be reduced. This makes it possible to easily realize the optical reproducing device according to the first aspect.

According to the structure of claim 3, in addition to the operation of claim 2, the control voltage can be arbitrarily set by the control voltage setting means. When the electric signal from the optical head is too large or too small, the control voltage becomes zero or maximum. However, by setting the control voltage to an appropriate initial value by the control voltage setting means, the response of the amplifying means Can be faster.

Further, by fixing the control voltage to an arbitrary voltage by the control voltage setting means, the amplifying means can be used as an amplifier having an arbitrary fixed gain.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, the optical disk apparatus of this embodiment irradiates a desired beam on an optical disk 10 (optical recording medium) with a light beam, detects reflected light from the optical disk 10, and converts it into an electric signal. Optical head 1 and optical head 1
AGC amplifier 2 (amplifying means) for amplifying the electric signal from the
Based on the waveform equalizer 3 that performs waveform equalization of the output signal from the AGC amplifier 2, the waveform shaper 4 that shapes the waveform of the output signal from the waveform equalizer 3, and the output signal from the waveform shaper 4. And a pre-format signal detection block 5 for detecting a pre-format signal.

As shown in FIG. 2, the AGC amplifier 2 has a variable gain amplifier 21 whose gain changes in proportion to the control voltage applied to the variable gain terminal T, and the amplitude of the output signal of the variable gain amplifier 21 is almost the same. A control voltage generation circuit 22 that outputs a control voltage for controlling the gain of the variable gain amplifier 21 so as to be constant, and a control voltage generation circuit 22 that limits the gain of the variable gain amplifier 21 to a predetermined value or less. And a limiter circuit 23 for limiting the control voltage to a predetermined value or less.

In the above structure, when reproducing information from the optical disc 10, a light beam is emitted from the optical head 1 to a desired track of the optical disc 10, and reflected light from the optical disc 10 is detected and converted into an electric signal.

For example, the ISO / IEC13 shown in FIG.
When the nth track of the optical disc 10 conforming to the 549 standard is reproduced, as shown in FIG. 9B, in addition to the strong preformat signal 11a from the preformat section 11 of the nth track, the (n-1) th track The weak crosstalk signal 12a from the track preformat section 12 and the weak crosstalk signal 13a from the (n + 1) th track preformat section 13 are detected as electrical signals and input to the AGC amplifier.

Since the pre-formatted signal 11a is strong,
The control voltage generation circuit 22 outputs a control voltage smaller than a predetermined value to the limiter circuit 23 so as to reduce the gain of the variable gain amplifier 21. Therefore, the control voltage is applied to the variable gain terminal T of the variable gain amplifier 21 without being limited by the limiter circuit 23. as a result,
The preformat signal 11a is amplified to a predetermined amplitude by the variable gain amplifier 21 and output as the output signal 11b.

On the other hand, the crosstalk signals 12a, 1
Since 3a is weak, the control voltage generation circuit 22 outputs a control voltage larger than a predetermined value to the limiter circuit 23 so as to increase the gain of the variable gain amplifier 21. Therefore, the control voltage is limited to a predetermined value by the limiter circuit 23 and applied to the variable gain terminal T of the variable gain amplifier 21. As a result, the crosstalk signals 12a and 13a are not amplified to a predetermined amplitude by the variable gain amplifier 21. Therefore, the output signals 12b and 13b having an amplitude smaller than that of the output signal 11b are output.

Output signals 11b to 13 from the AGC amplifier
b is input to the preformat signal detection block 5 through the waveform equalizer 3 and the waveform shaper 4. Output signal 11
Since b has a predetermined amplitude, waveform equalization and waveform shaping are normally performed. Therefore, the preformatted signal 1
1a is detected. On the other hand, since the output signals 12b and 13b are smaller than the predetermined amplitude, waveform equalization and waveform shaping are not normally performed. Therefore, the crosstalk signals 12a and 13
a is not detected. That is, it is possible to take out only the pre-format signal 11a from the nth track which is the track being reproduced. As a result, the information of the preformatted portion of the desired track can be accurately reproduced regardless of the magnitude of the reflectance of the optical disk 10 and without being affected by the crosstalk from the adjacent tracks.

The control voltage generating circuit 22 is, for example, as shown in FIG. 4, a full-wave rectifying circuit 31 for converting an output signal from the variable gain amplifier 21 into a DC voltage, and a full-wave rectifying circuit 31. Comparator 32 which compares the DC voltage of Vref with the reference voltage (Vref), and outputs high if the DC voltage is higher than Vref, and outputs low if the DC voltage is lower than Vref.
A transistor 34 that is turned on / off according to the output level of the comparator 32, a capacitor 37 that is charged when the transistor 34 is turned on, and a resistor 36 that is connected in parallel to the capacitor 37.

In the above configuration, the variable gain amplifier 2
The output signal from 1 is converted into a DC voltage by the full-wave rectifier circuit 31. The comparator 32 outputs high if the DC voltage from the wave rectifier circuit 31 is higher than Vref, and outputs low if it is lower than Vref. When the output of the comparator 32 is high, the transistor 34 is turned on, the collector current flows, the capacitor 37 is charged, and the voltage across the capacitor 37 rises. Since the voltage across the capacitor 37 is applied to the variable gain terminal T of the variable gain amplifier 21 as a control voltage, the gain of the variable gain amplifier 21 increases. If the output of the comparator 32 is low, the transistor 34 is turned off,
The electric charge of the capacitor 37 is discharged through the resistor 36,
The voltage across capacitor 37 drops. as a result,
The gain of the variable gain amplifier 21 decreases.

The response speed of the AGC amplifier 2 is the product of the capacitance value of the capacitor 37 and the resistance value of the resistor 36 (that is,
Charge / discharge time constant). The capacitance value of the condenser 37 is set to 0.01 μF, for example. Also,
The target amplitude of the output of the AGC amplifier 2 can be determined by the value of Vref.

The limiter circuit 23 is specifically composed of, for example, a Zener diode 23 'connected between the variable gain terminal T of the variable gain amplifier 21 and a common terminal (not shown).

As a result, the upper limit of the control voltage applied to the variable gain terminal T is limited to the Zener voltage of the Zener diode 23 '.

When the variable gain amplifier 21 has the gain-control voltage characteristic shown in FIG. 5, the maximum gain of the AGC amplifier 2 is set to 10 dB by using the Zener diode 23 'having a Zener voltage of V _1. be able to. Similarly, the maximum gain of the AGC amplifier 2 can be set to 30 dB or 50 dB by using the Zener diode 23 'having a Zener voltage of V ₂ or V ₃ .
In this way, the maximum gain of the AGC amplifier 2 can be easily set by changing the Zener voltage.

When the AGC amplifier 2 has the gain-input voltage characteristic shown by the characteristic line L1 in FIG. 6, if the zener diode 23 'having the zener voltage V ₂ is used, the gain-input voltage characteristic is obtained. Changes from the characteristic line L1 to L2. That is, the gain of the AGC amplifier 2 increases as the input voltage decreases, and saturates at 30 dB when the input voltage becomes 40 mV or less.

Preformatted signal 1 from optical head 1
It is assumed that the amplitude of 1a is in the range A of 40 to 200 mV.
In this input voltage range A, the gain of the AGC amplifier 2 changes from about 24.9 dB to about 10.9 dB, so that the amplitude of the output signal 11b is about 700 mV regardless of the amplitude of the preformat signal 11a. .

On the other hand, it is assumed that the amplitudes of the crosstalk signals 12a and 13a from the optical head 1 are in the range B of 2 mV to 10 mV. In this input voltage range B, the gain of the AGC amplifier 2 is fixed at about 30 dB, so that the output signal 1
The amplitudes of 2b and 13b are the crosstalk signals 12a and 13a.
Varies from approximately 63.2 mV to approximately 316 mV.

That is, the amplitudes of the output signals 12b and 13b are smaller than the amplitude of the output signal 11b. Therefore, waveform equalization and waveform shaping are not normally performed as described above. Therefore, the crosstalk signals 12a and 13a are not detected by the preformat signal detection block 5.

The amplitude of the output signal 11b is 700 mV.
However, it is not limited to Vre so that the waveform of the output signal 11b is equalized and Vre is adjusted so that the waveform is shaped normally.
By setting f, the Zener voltage may be set so that the waveforms of the output signals 12b and 13b are equalized and the amplitude is not normally shaped.

In addition to the above AGC amplifier 2,
If a means (control voltage setting means) for setting the control voltage regardless of the output level is added, the AGC amplifier 2 is desired even if the level of the electric signal from the optical head 1 is zero or excessive. The gain can be set to. As a result, even if the preformat signal 11a is input to the AGC amplifier 2 after the level of the electric signal is zero or excessive, the output signal 11b having an appropriate amplitude can be obtained.

The above-mentioned means for setting the control voltage regardless of the output level of the AGC amplifier 2 is specifically, for example,
As shown in FIG. 4, a switch 41 (switching means),
It is composed of a D / A converter 42 (arbitrary voltage generation means) and a microcomputer 43 (control means).

The microcomputer 43 uses the preformatted signal 1
Before a predetermined signal such as 1a is input, the AGC amplifier 2
To output a control voltage that sets
Instruct the A converter 42. For example, when it is assumed that a signal with an amplitude of about 70 mV is input, to automatically adjust the output to about 700 mV, the AGC amplifier 2
To output the voltage that sets the gain of about 20 dB.
/ Instructs the A converter 42.

Then, switch 41 is turned on,
The voltage generated by the D / A converter 42 is applied to the capacitor 37 to forcibly set the potential of the variable gain terminal T to a desired value. After that, by turning off the switch 41, the initial value of the gain of the AGC amplifier 2 can be set.

Further, even if the AGC amplifier 2 goes into a runaway state for some reason, it is possible to restore the normal state by returning the gain to the initial value.

Furthermore, when the switch 41 is turned on, the gain of the AGC amplifier 2 becomes constant, so that the AGC amplifier 2 can be used as an amplifier that can be fixed to an arbitrary gain. This makes it possible to perform an evaluation test of the amplitude of the input signal by monitoring the output of the AGC amplifier 2.

In the above embodiments, the present invention has been described by exemplifying the optical disk device which reproduces information from the optical disk 10, but the information is reproduced on various optical recording media such as optical tapes and optical cards. The present invention can be applied to an optical reproducing device and an optical reproducing / recording device for reproducing / recording information.

[0044]

As described above, the optical reproducing apparatus according to the invention of claim 1 irradiates a desired beam on the optical recording medium with a light beam, detects the reflected light from the optical recording medium, and converts it into an electrical signal. If the amplitude of the electrical signal from the optical head to be converted and the optical head is equal to or greater than the threshold value, the amplitude of the electrical signal is amplified to a predetermined value,
When the amplitude of the electric signal is less than the threshold value, an amplifying unit that does not amplify the amplitude of the electric signal to a predetermined value is provided.

According to this, the electric signal from the desired track is amplified to a predetermined amplitude, but the electric signal from the adjacent track is not amplified to that amplitude. As a result, there is an effect that it is less likely to be adversely affected by crosstalk from adjacent tracks.

As described above, the optical reproducing apparatus according to the invention of claim 2 is the optical reproducing apparatus of claim 1, wherein the amplifying means comprises a gain proportional to the control voltage of the electric signal from the optical head. A variable gain amplifier that amplifies with a control voltage generation circuit that outputs a control voltage so that the amplitude of the output signal of the variable gain amplifier becomes a predetermined value, and the control voltage from the control voltage generation circuit is limited to a predetermined voltage or less. A limiter circuit is provided.

According to this, the control voltage generating circuit outputs the control voltage for amplifying the amplitude of the electric signal from the track located at the center of the light beam to a predetermined value, and
The control voltage for amplifying the amplitude of the electric signal from the adjacent track to a predetermined value is output. Since the electric signal from the track located at the center of the light beam is stronger than the electric signal (that is, the crosstalk signal) from the track adjacent to that track, the latter control voltage is larger than the former control voltage. Therefore, if the limiter circuit limits the latter control voltage to a predetermined voltage or less, the gain of the variable gain amplifier with respect to the electric signal from the adjacent track can be reduced. Thereby, there is an effect that the optical reproducing device of claim 1 can be easily realized.

As described above, the optical regenerator according to the invention of claim 3 is the optical regenerator of claim 2, wherein the amplifying means further comprises a control voltage for arbitrarily setting the control voltage. This is a configuration including setting means.

According to this, in addition to the effect of claim 2, the control voltage can be arbitrarily set by the control voltage setting means. When the electric signal from the optical head is too large or too small, the control voltage becomes zero or maximum. However, by setting the control voltage to an appropriate initial value by the control voltage setting means, the response of the amplifying means There is an effect that can be made faster.

Further, by fixing the control voltage to an arbitrary voltage by the control voltage setting means, it is possible to use the amplifying means as an amplifier having an arbitrary fixed gain.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical disc device according to the present invention.

2 is a block diagram showing a configuration of an AGC amplifier in the optical disc device of FIG.

FIG. 3 is an explanatory diagram showing an operation of the optical disc device of FIG.

FIG. 4 is a circuit diagram showing an example of the AGC amplifier of FIG.

5 is a graph showing a gain-control voltage characteristic of a variable gain amplifier in the AGC amplifier of FIG.

6 is a graph showing a gain-input voltage characteristic of the AGC amplifier of FIG.

FIG. 7 is a block diagram showing a configuration of a conventional AGC amplifier.

8 is an explanatory diagram showing an operation of an optical disc device including the AGC amplifier of FIG.

[Explanation of symbols]

1 Optical Head 2 AGC Amplifier (Amplifying Means) 10 Optical Disk (Optical Recording Medium) 11 Preformatting Section 11a Preformatting Signal (Electrical Signal) 11b Output Signal 21 Variable Gain Amplifier 22 Control Voltage Generating Circuit 23 Limiter Circuit 41 Switch (Switching Means) 42 D / A converter (arbitrary voltage generation means, control voltage generation means) 43 Microcomputer (control means)

Claims (3)

[Claims] 1. An optical head for irradiating a desired track of an optical recording medium with a light beam, detecting reflected light from the optical recording medium and converting it into an electric signal, and the amplitude of the electric signal from the optical head is not less than a threshold value. In the case of, the amplitude of the electric signal is amplified to a predetermined value,
An optical regenerator comprising: an amplification unit that does not amplify the amplitude of the electric signal to a predetermined value when the amplitude of the electric signal is less than a threshold value. 2. The variable gain amplifier for amplifying an electric signal from an optical head with a gain proportional to a control voltage, and the control voltage so that the amplitude of an output signal of the variable gain amplifier has a predetermined value. 2. The optical regenerator according to claim 1, further comprising a control voltage generating circuit for outputting and a limiter circuit for limiting the control voltage from the control voltage generating circuit to a predetermined voltage or less. 3. The optical regenerator according to claim 2, wherein said amplifying means further comprises control voltage setting means for setting a control voltage arbitrarily.