JPH10188291A - Signal reader for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimumly set a slice level and to reproduce always correct data by setting a cut-off frequency lower, reducing slice level variation by reducing DC level variation of a reading signal output, and making the slice level follow a the peak value and the bottom value of a reading signal. SOLUTION: A cut-off frequency is set to a frequency of 10 times as much as the number of disk rotations or less, signal level variation of a reading signal output is made small, and slice level variation is made small. Also, a peal level and a bottom level of a reading signal are detected by a peak detection and bottom detection section 30, and the prescribed value between both values is given to a sample-and-hold circuit 31. Therefore, a slice level B generated by a slice level signal generation section 32 follows to variation of a reading signal A, and is made an added value of an error signal C, and a data detector 14 receiving a slice level signal B outputs correct reproduced data from the reading signal A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical disk signal reading device.

[0002]

2. Description of the Related Art As an optical disk medium (recording medium of an optical disk device), for example, a CD (compact disk),
MO (magneto-optical disk), DVD (digital video disk) and the like. These disks have a recording surface formed on an optically transparent substrate such as polycarbonate, and data is read and written through the transparent substrate.

FIG. 6 is a conceptual diagram of this type of optical disk device. The optical disk device is an optical disk medium (CD,
MO, DVD, etc.) 1 and an optical disk drive (a portion surrounded by a broken line) 20. Optical disk drive 2
0 is about 1 μm in diameter while rotating the optical disc medium 1.
The information is recorded or reproduced by irradiating a minute laser beam spot condensed to m or less.

The optical disk medium 1 is rotated at a predetermined speed by a motor 2 controlled by a rotation control system 3. Optical pickup 4 arranged close to the surface of optical disk medium 1
Irradiates the optical disc medium 1 with a light beam from a light emitting source such as a laser diode. At this time, the optical pickup 4
It is fed in the radial direction of the optical disk medium 1 by the drive motor 5 controlled by the drive motor control system 6.

In such an operation, the optical disk medium 1 is irradiated with a light beam from the optical pickup 4 controlled by the pickup control system 8, and the reflected light enters the signal processing system 7 via the optical pickup 4 and is converted into a digital signal. Converted to data. Drive controller 9 is bus 1
0, it is connected to a rotation control system 3, a drive motor control system 6, and a pickup control system 8, and exchanges data with an external device (not shown) via a drive interface. The drive controller 9 and the signal processing system 7 are connected via a signal line and exchange data and control signals.

The present invention relates to a signal processing system 7 having the configuration shown in FIG. FIG. 7 is a block diagram showing a configuration example of a conventional apparatus, and shows a configuration of the signal processing system 7 of FIG. The reflected light from the optical disk medium 1 in FIG. 6 is converted into an electric signal by the photodetector 4A constituting the optical pickup 4, and the signal is amplified by the preamplifier 11.

The output of the preamplifier 11 is superimposed on and fluctuates with a DC (direct current) component caused by the birefringence of the optical disk medium or a signal state from a no-signal state. In order to remove this DC component, the output of the preamplifier 11 enters the AC coupling unit 12, and only a signal component having a predetermined frequency or higher is passed. Here, the cutoff frequency of the AC coupling unit 12 is a high frequency of about 50 kHz or less.

The output (read signal) of the AC coupling unit 12 enters the AGC circuit and the equalizer 13, where the amplitude is automatically made constant and the noise component is removed by a filter. Thus, the output (read signal A) of the AGC circuit and the equalizer 13 is a signal having no noise component. The output A of the AGC circuit and the equalizer 13 enters one input of the data detector 14.

A slice level signal B is input to the other input of the data detector 14. Then, the data detector 14 compares the output A of the AGC circuit and the equalizer 13 with the slice level signal B and converts it into binary data of “0” and “1”. Data detector 14
Outputs binary output data.

On the other hand, a binary data signal is output from the data detector 14 to the phase comparator 15,
5 is a phase difference Δθ between the reference clock and the binary data.
And outputs the phase difference Δθ to the slice level signal generation unit 16 as an error signal C. The slice level signal generator 16 receives the reference voltage 17 and the error signal from the phase comparator 15, and outputs a value obtained by correcting the reference voltage value with the error signal C as the slice level signal B of the data detector 14. That is, in the case of the conventional apparatus, the read signal is first compared with the reference voltage, and thereafter, the slice level is moved based on the error signal C, and the read signal A is compared with the slice level B. The reference voltage 17 is generated by a reference voltage generation circuit (not shown).

The data detector 14 compares the output A of the AGC circuit and the equalizer 13 with the slice level signal B, converts the signal detected by the photodetector 4A into binary data, and outputs it as output data.

FIG. 8 is a time chart showing the operation of the conventional device, showing the operation of generating a binarized output of the data detector 14. (A) shows slice level B and read signal A
This shows a state in which the relationship is the same. The output data is generated every time the read signal A falls below the slice level B.

In the case (b), the slice level B is initially set.
Indicates the lower side of the read signal, and the output data is output ahead of the reference clock. At this time, the phase difference (phase shift amount) Δθ between the reference clock and the output data is calculated by the phase comparator 15 in FIG. 7 and is provided as the error signal C to the slice level signal generator 16.

Upon receiving the error signal C, the slice level signal generator 16 corrects the reference voltage 17 with the error signal, and sets the slice level B to a normal position with respect to the read signal A so that the slice level B is at a normal position. Correct B upward.

In the case (c), the slice level B is initially set.
Represents the upper side of the read signal, and the output data is output with a delay with respect to the reference clock. At this time, the phase difference (phase shift amount) Δθ between the reference clock and the output data is calculated by the phase comparator 15 in FIG. 7 and is provided as the error signal C to the slice level signal generator 16.

When the slice level signal generator 16 receives the error signal C, it corrects the reference voltage 17 with the error signal, and sets the slice level B to a normal position with respect to the read signal A. Correct B downward.

[0017]

In the above-described conventional apparatus, the cutoff frequency of the AC coupling unit 12 is set to 50.
Since the frequency is set to be as high as about kHz, the DC level of the output greatly fluctuates as shown by f12 in FIG. 5B (FIG. 5 is an explanatory diagram of the effect of the present invention). The read signal waveform f10 and the slice level f11 also change in synchronization with the change in the DC level.

The slice level f11 has a plurality of stable points. If the change in the slice level is faster than the change in the signal waveform, the slice level may be stabilized at an incorrect position. FIG. 9 is an explanatory view of the conventional device during normal operation,
(A) shows the relationship between the read signal A and the slice level B,
(B) shows output data, and (c) shows a reference clock.

In the case of normal operation, slice level B
Is stable at the correct position, the binarized output data is generated at the correct timing as shown in FIG. At this time, the interval between the output pulses changes in the order of 5T, 2T, 2T, and so on.

FIG. 10 is an explanatory view of the conventional apparatus at the time of abnormal operation. In this case, the slice level B is stabilized at an erroneous position as shown in FIG. Such a state is likely to occur when there is a defect in the medium or when the amplitude is shifted when the slice level B is quickly followed. One of the causes of such a phenomenon is that the capacitor of the AC coupling unit 12 is made smaller and its cutoff frequency is set higher. For this reason, the binarized output data is generated as shown in (b), and the interval between the output pulses at this time is 6T, 4T, 6T..., Which is completely different from the normal case. Correct data cannot be reproduced.

The present invention has been made in view of such problems, and has as its object to provide a signal reading apparatus for an optical disk capable of always reproducing correct data.

[0022]

According to the present invention, there is provided an optical disk signal reading apparatus for reading information recorded on an optical disk medium, comprising: a rotating unit for rotating the optical disk; and information from the optical disk. Optical information detection means for detecting and outputting an output signal, and passing only a signal component having a predetermined frequency or more of the output signal,
AC coupling means for generating a read signal; slice level signal generating means for generating a slice level signal from a peak value and a bottom value of the read signal; and a data output means for obtaining a data output from the read signal and the slice level signal. And a data output means.

According to the configuration of the present invention, the cut-off frequency is set lower than in the prior art, so that the fluctuation of the DC level of the read signal output is reduced to reduce the fluctuation of the slice level, and the data reproducing means is used. By causing the slice level to follow based on the peak value and the bottom value of the read signal, the slice level is always set to be optimal, and thereby correct data can always be reproduced.

In this case, a holding means for holding a slice level signal generated by the slice level signal generating means is provided. According to the configuration of the present invention, by holding the output of the slice level following means by the holding means, the slice level after synchronization is kept constant, and the output data of 2
Value conversion can be performed stably.

Further, the cutoff frequency of the AC coupling means is in the range of 1/10 to 80 times the rotation frequency of the rotation means. According to the configuration of the present invention, by setting the cut-off frequency of the AC coupling means in the range of 1/10 to 80 times the rotation frequency, only the signal component of a predetermined frequency or less is effectively removed to obtain the read signal. You can only get.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The same thing as FIG.
The same reference numerals are given. In the figure, reference numeral 4A denotes a photodetector for photoelectric conversion, which is one of the components of the optical pickup 4 (see FIG. 6). As the photodetector 4A, for example, a photodiode or the like is used.

Reference numeral 11 denotes a preamplifier that receives the output of the photodetector 4A and amplifies the signal, and 12 denotes an AC coupling unit for removing a DC component. The AC coupling unit 1
The cut-off frequency of 2 is set to a frequency of about five times the rotation speed of the optical disk (specifically, for example, about 300 Hz), which is much lower than about 50 kHz of the conventional apparatus. This is because the fluctuation of the DC component after passing through the AC coupling unit 12 is largely suppressed. The cutoff frequency of the AC coupling unit can be set to an appropriate value by changing the circuit constant of the time constant circuit including the capacitor C and the resistor R.

Numeral 13 denotes an AGC circuit comprising an AGC circuit for making the amplitude of the read signal passed through the AC coupling unit 12 constant and a filter for removing noise contained in the read signal.
C and equalizer. The AGC and equalizer 13
From the read signal A, which is waveform-shaped and has little noise.
Is output.

A data detector 14 compares the output (read signal A) of the AGC circuit and the equalizer 13 with the slice level B to convert an analog signal into a binary signal. Reference numeral 15 denotes a phase comparator which receives the binarized data output from the data detector 14, calculates a phase difference Δθ from the reference clock, and outputs it as an error signal C.

Reference numeral 30 denotes a peak detection and bottom detection unit that receives the output of the AGC circuit and the equalizer 13 and detects the peak value and the bottom value. Reference numeral 31 denotes a sample and hold circuit that samples and holds the output of the peak detection and bottom detection unit 30. The sample and hold circuit 31 holds the output of the peak detection and bottom detection unit 30 when the reference clock and the read signal A are synchronized.

Reference numeral 32 denotes the sample and hold circuit 3
1 is a slice level signal generation unit that receives the output of the phase comparator 15 and the output of the phase comparator 15 and causes the slice level B to follow the read signal A based on the peak value and the bottom value of the read signal A and the error signal C. The operation of the device configured as described above will be described below.

The reflected light from the optical disk medium 1 (see FIG. 6) is converted into an electric signal by a photodetector 4A constituting the optical pickup 4, and the signal is amplified by a preamplifier 11. The output of the preamplifier 11 fluctuates by superimposing a DC (direct current) component caused by the birefringence of the optical disc medium or a signal state from a no-signal state to a signal state. In order to remove this DC component, the output of the preamplifier 11 is A
The signal enters the C-coupling unit 12, and only a signal component having a frequency equal to or higher than a predetermined frequency is passed. Here, the cut-off frequency of the AC coupling unit 12 is about 1 of the rotation speed of the optical disc.
The frequency is set to be about 0 times or less, which is lower than that of the conventional device. For this reason, the frequency component of the read signal passing through the AC coupling unit 12 is equal to or higher than the frequency. By setting the cutoff frequency of the AC coupling unit 12 to be lower, the fluctuation of the DC level of the read signal passing through the AC coupling unit 12 can be significantly reduced.

The output (read signal) of the AC coupling unit 12 enters the AGC circuit and the equalizer 13, where the amplitude is automatically made constant and the noise component is removed by the filter. Thus, the output (read signal A) of the AGC circuit and the equalizer 13 is a signal having no noise component. The output A of the AGC circuit and the equalizer 13 enters one input of the data detector 14.

A slice level signal B is input to the other input of the data detector 14. Then, the data detector 14 compares the read signal A with the slice level signal B, and converts the read signal A into binary data of “0” and “1”. The data detector 14 outputs binarized output data.

On the other hand, a binary data signal is output from the data detector 14 to the phase comparator 15,
5 is a phase difference Δθ between the reference clock and the binary data.
And outputs the phase difference Δθ as an error signal C to the slice level signal generator 32. The slice level signal generator 32 receives the output of the sample and hold circuit 31 and the error signal C from the phase comparator 15, and adds the error signal C to the output of the sample and hold circuit 31 as a slice level signal B. Output.

According to the present invention, the peak level and the bottom level of the read signal are detected by the peak detection / bottom detection section 30, and a predetermined level between the peak value and the bottom value is output, and the sample and hold is performed. It is given to the circuit 31. Therefore, the slice level B generated by the slice level signal generator 32 follows the fluctuation of the read signal A and becomes a value to which the error signal C is added. From A, correct reproduction data can be generated as output data.

As described above, according to this embodiment, the cutoff frequency is set lower (50
By setting (kHz → 10 times or less the frequency of the rotation speed of the optical disk), the fluctuation of the DC level of the read signal output is reduced to reduce the fluctuation of the slice level, and the slice level tracking means (peak detection and bottom detection unit) 30), the data reproducing means (data detector 1)
By causing the slice level in 4) to follow based on the peak value and the bottom value of the read signal, the slice level is always set to be optimal, whereby correct data can always be reproduced. According to the present invention, the slice level B can be generated slowly, so that the slice level is not set faster than the read signal or set to an inappropriate stable position unlike the conventional apparatus.

In the above-described embodiment, the case where the cutoff frequency is set to be equal to or less than ten times the rotation frequency has been described. Hereinafter, an example in which this frequency range is set in more detail will be described. For example, in a disk having a storage capacity of 640 M, there is a high possibility that a signal waveform is distorted due to AC coupling with respect to DC fluctuation at intervals of a re-mink (resynchronization signal into which a signal is converted). If the distortion of the signal waveform at the rimming interval increases, the slice level must fluctuate greatly. If the slice level does not properly follow the large fluctuation, an error occurs in data reproduction.

Therefore, the signal waveform distortion at the remink interval needs to be within a predetermined range. If the distortion of the signal waveform at the remink interval is considered by its attenuation rate, the attenuation rate needs to be experimentally within -10%. This can be represented by the following equation: 0.9 ≦ exp {− (t / T)} (1) Here, t indicates the rimming interval S, and T indicates the time constant of AC coupling. From equation (1), t ≦ (1/10) T (2)

The cutoff frequency ν _cut of the AC coupling is expressed by the following equation. ν _cut = 1 / T (3) In addition, the re-mink interval is a maximum of 800 for one round of the optical disc.
Since it is about one-half, t is represented by the following equation.

T = (1/800) · (1 / ν) (4) Here, ν indicates the rotation frequency of the optical disk. here,
By substituting equations (3) and (4) into equation (2),
The following relationship is derived.

80ν ≧ ν _cut (5) That is, if the rotation frequency of the optical disk is 80 times or less,
It can be said that the distortion of the signal waveform at the rimming interval is within an allowable range.

AC coupling cut-off frequency ν
_{The cut} and the time constant of the AC coupling have a relationship as shown in the above-mentioned equation (3). However, if T is too large, the fluctuation in the changing portion of the signal waveform becomes too large. but a range not too much larger, i.e., if indicated by the rotational frequency of the optical disc (1/10) range [nu ≦ [nu _cut is preferred.

From the above, (1/10) ν ≦ ν _cut ≦ 80
Within the range of ν, the distortion of the signal waveform is set within a predetermined range, which is preferable for obtaining an appropriate slice level.

In this case, by providing a holding means (sample and hold circuit 31) for holding the output of the slice level tracking means, the output of the slice level tracking means is held by the holding means, and after the synchronization is established. Keep the slice level constant,
Output data can be stably binarized.

FIG. 2 is a circuit diagram showing an embodiment of the slice level generating section, which is a combination of the peak detection and bottom detecting section 30 and the slice level signal generating section 32 shown in FIG. In this embodiment, the sample and hold circuit 31 is omitted, but when the output of the peak detection and bottom detection unit 30 is stable, the sample and hold circuit 31 is not always necessary.

In FIG. 2, reference numeral 21 denotes a peak hold circuit that receives a signal from the AGC circuit and the equalizer 13 and holds a peak value, and 22 denotes a bottom hold that receives a signal from the AGC circuit and the equalizer 13 and holds a bottom value. Circuit. The peak hold circuit 21 and the bottom hold circuit 22 can be realized by using an existing technology such as a peak rectifier circuit using a diode and an operational amplifier.

VR is a resistance voltage divider connected between the output of the peak hold circuit 21 and the output of the bottom hold circuit 22, and 23 is a buffer amplifier for inputting a divided voltage signal of the resistance voltage divider VR. The buffer amplifier 23 is an impedance conversion amplifier having high input impedance and low output impedance characteristics. These peak hold circuits 2
1, the bottom hold circuit 22, the resistor voltage divider VR, and the buffer amplifier 23 constitute the peak detection and bottom detection unit 30 in FIG.

Reference numeral 24 denotes a buffer amplifier 2
3 is an addition amplifier that receives the error signal C from the phase comparator 15 and adds it to the other input to generate a slice level signal B. The summing amplifier 24 constitutes the slice level signal generator 32 in FIG. The operation of the circuit thus configured will be described as follows.

When the optical pickup 4 (see FIG. 6) reads a signal from the optical disc medium 1, the output of the AGC circuit and the equalizer 13 (read signal A) rises as shown by f1 in FIG. The output of the peak hold circuit 21 receiving this read signal rises as shown by f2 in FIG. 3, and the output of the bottom hold circuit 22 becomes f2 in FIG.
Stand up as shown in 3.

As a result, the signal (the signal at the point K in FIG. 2) taken out from the resistive voltage divider VR is always between f2 and f3, as shown at f4 in FIG. The addition amplifier 24 adds the signal at the K point and the error signal C to generate a slice level signal B. Therefore, the slice level B is always a value obtained by adding the error signal C to the level approximately at the middle of the read signal A. Since the slice level B is always generated after the read signal A, there is no problem that the slice level B is set before the read signal A. Further, since the error signal C is also taken into account, output data is not output earlier than or delayed with respect to the reference clock. That is,
According to this embodiment, output data can be stabilized, and a phase correction operation equivalent to that of the conventional device shown in FIG. 8 is also performed.

FIG. 4 is a circuit diagram showing another embodiment of the slice level creating section. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, the peak detection and bottom detection unit 30 shown in FIG. 1, the sample and hold circuit 31, and the slice level signal generation unit 32 are combined.

The sample and hold circuit 31 comprises a switch SW and a capacitor C1. The output of the buffer amplifier 23 is connected to the switch SW,
The other end of the switch SW is connected to a capacitor C1. The switch SW is initially turned on (closed), and is turned off after synchronization. As a result, the output of the buffer amplifier 23 after synchronization is held in the capacitor C1, and the slice level B is stabilized.

According to this embodiment, the output of the slice level tracking means (peak detection and bottom detection unit 30) is held by the hold means (sample and hold circuit 31), so that the slice after synchronization is obtained. The level can be kept constant and the binarization of the output data can be performed stably.

FIG. 5 is an explanatory diagram of the effect of the present invention.
(A) shows an operation waveform according to the present invention, and (b) shows an operation waveform of a conventional example. In the figure, f10 is the read signal A
, F11 indicates the slice level B, and f12 indicates the DC level fluctuation at the output of the AC coupling unit 12.

In (a), the reference clock creation area 1
Is an area for creating a reference clock for phase comparison. The address is confirmed for each sector, and a reference clock is created. The next reference clock creation area 2 is an area for creating a reference clock for data reproduction. This is followed by a data reading area.

The DC level shown in (b) fluctuates greatly as shown by f12 because the cutoff frequency of the AC coupling unit 12 is as high as 50 kHz or less. On the other hand, in the present invention, since the cut-off frequency of the AC coupling unit 12 is as low as 10 times or less the rotation speed of the optical disk, the variation is small as indicated by f12 in FIG. Therefore, since the fluctuation of the slice level f11 is small, the binarization in the data detector 14 can be performed stably.

It is needless to say that the present invention can be applied to any optical disk medium of the edge recording type such as CD, MO and DVD.

[0059]

As described in detail above, claim 1 is as follows.
According to the invention described above, in an optical disk signal reading device for reading information recorded on an optical disk medium, a rotation unit for rotating the optical disk, and an optical information detection unit for detecting information from the optical disk and outputting an output signal An AC coupling unit that passes only a signal component having a frequency equal to or higher than a predetermined frequency of the output signal and generates a read signal; and a slice level signal generation unit that generates a slice level signal from a peak value and a bottom value of the read signal. A data output means for obtaining a data output from the read signal and the slice level signal, thereby setting a cut-off frequency to be lower than in the prior art and reducing a change in the DC level of the read signal output. To reduce the fluctuation of the slice level, and By follow based on the level on the peak value and the bottom value of the read signal, to set the slice level is always to optimize, thereby, always the correct data can be reproduced.

In this case, by providing the holding means for holding the slice level signal generated by the slice level signal generating means, the output of the slice level following means is held by the holding means, so that after the synchronization is established. The slice level can be kept constant, and the output data can be stably binarized.

The cut-off frequency of the AC coupling means is in the range of 1/10 to 80 times the rotation frequency of the rotating means. /
By setting the range from 10 times to 80 times, it is possible to obtain only a read signal by effectively removing only a signal component below a predetermined frequency.

As described above, according to the present invention, it is possible to provide an optical disk signal reading apparatus capable of always reproducing correct data.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing one embodiment of a slice level creation unit.

FIG. 3 is an explanatory diagram of an operation waveform.

FIG. 4 is a circuit diagram showing another embodiment of a slice level creation unit.

FIG. 5 is an explanatory diagram of an effect of the present invention.

FIG. 6 is a conceptual diagram of a configuration of an optical disk device.

FIG. 7 is a block diagram illustrating a configuration example of a conventional device.

FIG. 8 is a time chart showing the operation of the conventional device.

FIG. 9 is an explanatory diagram of a conventional device during normal operation.

FIG. 10 is an explanatory diagram of an abnormal operation of the conventional device.

[Explanation of symbols]

 Reference Signs List 4A Photodetector 11 Preamplifier 12 AC coupling unit 13 AGC circuit and equalizer 14 Data detector 15 Phase comparator 30 Peak detection and bottom detection unit 31 Sample and hold circuit 32 Slice level signal generation unit

Claims (3)

[Claims] 1. An optical disk signal reader for reading information recorded on an optical disk medium, comprising: a rotating unit for rotating the optical disk; an optical information detecting unit for detecting information from the optical disk and outputting an output signal; An AC coupling unit that passes only a signal component of a predetermined frequency or more of the output signal and generates a read signal; a slice level signal generation unit that generates a slice level signal from a peak value and a bottom value of the read signal; A signal reading device for an optical disk, comprising: a data output unit for obtaining a data output from a read signal and the slice level signal. 2. The optical disk signal reading device according to claim 1, further comprising a holding means for holding a slice level signal generated by said slice level signal generating means. 3. The cut-off frequency of the AC coupling means is 1/1 / the rotation frequency of the rotation means.
2. The optical disk signal reading device according to claim 1, wherein the signal is in a range of 10 to 80 times.