JPH08315510A - Signal reproducing apparatus and optical disk signal reproducing apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] The data is not affected by the low frequency component of the modulation code.
An object of the present invention is to provide a signal reproducing device capable of detecting data. [Structure] The signal reproducing apparatus of this example has an input terminal 5 and a comparator.
Lator 1, signal detection circuit 2, delay circuit 3, switch 4,
Capacitor C, resistor R₁, Resistor R₂, Output terminal 6
It is composed of The switch 4 is supplied to the control terminal 4D
Delay circuit output S _FiveIs controlled based on the output level of
It When the recorded signal is reproduced, the movable contact 4A of the switch 4
The constant contacts 4C are connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium on which data having a low frequency component is recorded, and more particularly to a signal reproducing apparatus and an optical disk reproducing apparatus for reproducing signals of an optical disk.

[0002]

2. Description of the Related Art Digital data of "1" and "0" is recorded on a magneto-optical disk and a write-once optical disk.
However, if "1" or "0" continues continuously for a long time, the data becomes meaningless. Therefore, in recent years, in a magneto-optical or write-once type optical disk for recording digital data, in order to improve the recording linear density and enable higher density recording, it is necessary to modulate the digital data using a modulation code. I have to.

This modulation code includes NRZ (Non Re
turn to Zero), NRZI (Non Re)
turn to Zero Inverse). The NRZ becomes high level only at the position corresponding to "1", and returns to low level at "0".
NRZI is a method of inverting the signal level only when it is "1". Here, in the data series, the number of consecutive same bits of "1" or "0" is called a run, and the length of the number of consecutive same bits is a run length (Ru).
n Length). The width with the maximum run length is called the maximum inversion width T-MAX, and the width with the minimum run length is called the minimum inversion width T-MIN.

In NRZ and NRZI, the maximum inversion width T-MAX is infinite, and it can be seen that this is a modulation method in which self-synchronization is difficult to take. Moreover, since it is not DC-free, it is not used in magneto-optical recording. For magneto-optical recording, RLL (Run Length Limited)
The method is adopted. The RLL method is the maximum inversion width T
A modulation scheme in which MAX is finite. here,
When RLL (d, k) is used, the minimum run is d and the maximum run is k.

In NRZ and NRZI, assuming that the interval of 1-bit data is T, the minimum inversion width T-MIN is 1T.
On the other hand, in the RLL (1,7) method, the minimum inversion width T-MIN is 4 / 3T. Here, considering reproduction waveform interference, it is advantageous that the minimum inversion width T-MIN is large and the distance between the marks is large. Therefore, RLL
The (1,7) method is advantageous.

Further, in NRZ and NRZI, the maximum inversion width T-MAX is infinite, whereas in RLL.
In the (1,7) method, the maximum inversion width T-MAX is 8T. Here, the maximum inversion width T-MAX is related to the ease of self-synchronization and is preferably smaller. Therefore, R
The LL (1,7) method is advantageous. For this reason, the RLL (1,7) method is adopted as the modulation method in the high density and high data rate disk.

The reproduction of the pits of the magneto-optical disk is
It is performed using the polar car effect. The polar Kerr effect is a magnetic rotation effect in which the direction of magnetization is added to reflected light with respect to incident light. That is, linearly polarized light is made incident on the perpendicular magnetization film, and the rotation of the polarization plane of the reflected light is detected to read the magnetization state of the film, that is, the recording state. However, noise called light intensity fluctuation noise occurs. The light amount fluctuation noise is caused by the fluctuation of the light amount of the laser light or the fluctuation of the reflectance of the medium, and is proportional to the light amount incident on the photodetector.

Further, noise called media noise is generated. Although media noise depends on the recording medium and the structure of the medium, there are generally polarized noise and non-polarized noise. The deflective noise may be due to the characteristic fluctuation of the recording medium or due to the birefringence of the substrate, and is treated like a signal. The non-deflecting noise is noise generated by fine irregularities on the surface of the disc.
In this way, noise is generated in the reproduction signal of the optical disc due to the fluctuation of the reflectance of the recording medium.

Magneto-optical recording is thermo-magnetic recording that utilizes the change in magnetism associated with the temperature rise of the magnetic medium due to laser light irradiation. It is known that as the temperature rises, the spontaneous magnetization of the magnetic material suddenly becomes zero near the Curie temperature. This is because at temperatures above the Curie temperature, magnetic order disappears and paramagnetism occurs. At this time, by applying a magnetic field of an appropriate magnitude from the outside, the magnetization of the magnetic material can be easily aligned with the direction of the applied magnetic field. That is,
Recording is performed by locally heating the magnetic body by laser irradiation and aligning only the region where the temperature rises to near the Curie temperature with the direction of the external magnetic field. Therefore, the recording area is limited to the laser irradiation area, and conversely, the recording area can be made as small as possible by narrowing the laser spot. Therefore, considering magneto-optical recording as thermo-magnetic recording utilizing the energy of laser light, the recording sensitivity of magneto-optical recording varies depending on the energy conversion rate from optical energy to thermal energy and the state of thermal diffusion in the disk medium. . In this way, noise is generated in the reproduction signal of the optical disc due to the fluctuation of the recording sensitivity.

Further, in order to surely record and reproduce information by following the disk surface without being influenced by surface wobbling or track wobbling of a magneto-optical disk, a focusing tracking servo is used in a magneto-optical optical pickup. . Focus control is performed using a focusing error signal which is an error signal for focus detection. This focusing error signal makes it possible to determine whether or not the pit on the disc is in focus. Further, tracking control is performed using a tracking error signal which is an error signal of tracking control. With this tracking error signal, it can be determined whether or not the spot is tracing on the track. However, when these controls are not proper, a focusing error and a tracking error occur. The focusing error and the tracking error become noise of the reproduced signal. As described above, the reproduction signal of the optical disk has low-frequency noise due to residual errors of the focus and tracking servos.

In order to prevent data detection error due to these noises, it is necessary to remove this noise. In order to remove low-pass noise, a low-pass cutoff filter, that is, a high-pass filter has been conventionally used.

[0012]

However, when the high pass filter is used, the low pass component of the modulation code is also removed together with the noise, and there is a disadvantage that the detection error increases.
It is an object of the present invention to solve such an inconvenience and, in particular, to provide a signal reproducing apparatus capable of detecting data without being affected by the low frequency component of the modulation code.

[0013]

SUMMARY OF THE INVENTION A signal reproducing apparatus of the present invention, in a signal reproducing apparatus for reproducing a signal of a recording medium in which data having a low frequency component is recorded, blocks a low frequency component of a reproduction signal. First high-pass filter, a second high-pass filter having a higher cut-off frequency than the first high-pass filter for cutting low-frequency components of the reproduction signal, and binarizing the analog signal Comparator, a low-pass filter having complementary characteristics to the first high-pass filter for extracting a low-pass component of its output, a signal detection circuit for detecting the presence or absence of a reproduced signal, and a signal detection circuit thereof Of the second high-pass filter is supplied to the input of the comparator when the signal is not detected by the output of the delay circuit, and when the signal is detected, the first circuit is provided.
The output of the high pass filter and the output of the low pass filter are added and controlled so as to be supplied to the input of the comparator.

The optical disc signal reproducing apparatus of the present invention is a first optical disc signal reproducing apparatus for reproducing a signal of an optical disc in which data having a low frequency component is recorded, for cutting off the low frequency component of the reproduction signal. High-pass filter, a second high-pass filter having a higher cut-off frequency than the first high-pass filter for cutting low-frequency components of the reproduction signal, and a comparator for binarizing the analog signal. , A low-pass filter having complementary characteristics to the first high-pass filter for extracting the low-pass component of its output, a signal detection circuit for detecting the presence or absence of a reproduced signal, and delaying the output of the signal detection circuit The output of the delay circuit supplies the output of the second high-pass filter to the input of the comparator when the signal is not detected, and the output of the delay circuit causes the output of the first high-pass filter to be detected when the signal is detected. It adds the output of the force and a low-pass filter and controls to supply to the input of the comparator.

[0015]

According to the present invention, the following operations are performed.
The input reproduction signal is supplied to the first high pass filter and the signal detection circuit. The first high pass filter passes the high frequency component of the reproduced signal and outputs the comparator input. The comparator input is supplied to the comparator. The comparator compares the threshold value with a predetermined threshold value, binarizes the comparator input, and outputs the comparator output. The output of the comparator is supplied to the switch via a low pass filter.

The signal detection circuit detects the presence or absence of a recorded signal from the reproduction signal and outputs the signal detection circuit output. That is, a high level signal is output when a recorded signal is present when the recording signal is reproduced, and a low level signal is output when there is no signal when there is no signal. The output of the signal detection circuit is supplied to the delay circuit. The output of this signal detection circuit is delayed by the delay circuit and becomes the output of the delay circuit. The delay circuit output is supplied to the control terminal of the switch. The switch is
When the delay circuit output is high level, the low pass filter is connected to the comparator. The switch also connects the second high pass filter to the comparator when the delay circuit output is low. Thus, the switch
It is controlled based on the output level of the delay circuit output supplied to the control terminal.

First, when the recording signal is reproduced, the low-pass filter is connected to the comparator, so that the following is performed. Since the first high-pass filter and the low-pass filter are complementary filters having the same cut-off frequency, the first high-pass filter operates so as to pass frequencies higher than the cut-off frequency. To do. Further, the low pass filter operates so as to pass a frequency lower than the cutoff frequency. The reproduction signal has the HPF from which the components in the lower frequency range than the cutoff frequency are removed by the first high-pass filter.
It is output as output. This removes low-pass noise, but at the same time removes low-pass components of the signal.

Therefore, a low-pass filter is used to output L from the output of the comparator as a signal component in a range lower than the cutoff frequency.
Extract the PF output and add the LPF output to the HPF output. This makes it possible to obtain a signal in which the low-frequency signal component is reproduced. In order to perform such an operation correctly, it is an important condition that the reproduced signal and the comparator output have the same amplitude. This condition is not satisfied when the reproduced signal is no signal. That is, since the amplitude of the reproduced signal is smaller than the amplitude of the output of the comparator, the positive feedback loop of the comparator, the low pass filter, and the adder diverges. To prevent this, the positive feedback loop of the comparator, low pass filter, and adder is turned off when there is no signal.
At this time, the positive feedback loops of the comparator, the low pass filter, and the adder are turned off, and the cutoff frequency of the first high pass filter is made higher than that during recording signal reproduction.

That is, when there is no signal, the following occurs. Here, since the cutoff frequency of the second high-pass filter at the time of no signal is higher than the cut-off frequency of the first high-pass filter at the time of reproducing the recording signal, the cutoff frequency of the second high-pass filter at the time of no signal becomes Even if noise is mixed, this noise can be prevented from passing through the second high pass filter.

The cutoff frequency of the first high-pass filter during reproduction of the recording signal is relatively low. That is, the time constant is set large. However, if the time constant is large, the time until the waveform response stabilizes at the start of reproduction of the recording unit of the comparator input becomes long, so the delay time of the delay circuit is also made large.

As described above, by making the time constant of the second high-pass filter smaller than that of the first high-pass filter, damage to the preamble can be suppressed and the clock generation can be stabilized. .

Further, according to the present invention, the following operation is performed in the optical disc signal reproducing apparatus. The reproduction signal input by reproducing the optical disc is supplied to the first high pass filter and the signal detection circuit. The first high pass filter passes the high frequency component of the reproduced signal and outputs the comparator input. The comparator input is supplied to the comparator. The comparator compares the threshold value with a predetermined threshold value, binarizes the comparator input, and outputs the comparator output. The output of the comparator is supplied to the switch via a low pass filter.

The signal detection circuit detects the presence or absence of a recorded signal from the reproduction signal and outputs the signal detection circuit output. That is, a high level signal is output when a recorded signal is present when the recorded signal is reproduced, and a low level signal is output when there is no signal when there is no signal. The output of the signal detection circuit is supplied to the delay circuit. The output of this signal detection circuit is delayed by the delay circuit and becomes the output of the delay circuit. The delay circuit output is supplied to the control terminal of the switch. The switch is
When the delay circuit output is high level, the low pass filter is connected to the comparator. The switch also connects the second high pass filter to the comparator when the delay circuit output is low. Thus, the switch
It is controlled based on the output level of the delay circuit output supplied to the control terminal.

First, when the recording signal is reproduced, the low-pass filter is connected to the comparator, so that the following is performed. Since the first high-pass filter and the low-pass filter are complementary filters having the same cut-off frequencies, the first high-pass filter operates so as to pass frequencies higher than the cut-off frequency. To do. Further, the low pass filter operates so as to pass a frequency lower than the cutoff frequency. The reproduction signal has the HPF from which the components in the lower frequency range than the cutoff frequency are removed by the first high-pass filter.
It is output as output. This removes low-pass noise, but at the same time removes low-pass components of the signal.
Therefore, the low pass filter extracts the LPF output from the comparator output as a signal component in the low frequency range below the cutoff frequency, and adds the LPF output to the HPF output. This makes it possible to obtain a signal in which the low-frequency signal component is reproduced.

In order to perform such an operation correctly, it is an important condition that the reproduced signal and the comparator output have the same amplitude. This condition is not satisfied when the reproduced signal is no signal. That is, since the amplitude of the reproduced signal is smaller than the amplitude of the output of the comparator, the positive feedback loop of the comparator, the low pass filter, and the adder diverges. To prevent this, the positive feedback loop of the comparator, low pass filter, and adder is turned off when there is no signal. At this time, the positive feedback loops of the comparator, the low pass filter, and the adder are turned off, and the cutoff frequency of the first high pass filter is made higher than that during recording signal reproduction.

That is, when there is no signal, it becomes as follows. Here, since the cutoff frequency of the second high-pass filter at the time of no signal is higher than the cut-off frequency of the first high-pass filter at the time of reproducing the recording signal, the cutoff frequency of the second high-pass filter at the time of no signal becomes Even if noise is mixed, this noise can be prevented from passing through the second high pass filter.

The cutoff frequency of the first high-pass filter during reproduction of the recording signal is relatively low. That is, the time constant is set large. However, if the time constant is large, the time until the waveform response stabilizes at the start of reproduction of the recording unit of the comparator input becomes long, so the delay time of the delay circuit is also made large.

As described above, by making the time constant of the second high-pass filter smaller than the time constant of the first high-pass filter, damage to the preamble of the data obtained by reproducing the optical disc is prevented. It is possible to suppress and stabilize the clock generation.

[0029]

EXAMPLE An example in which the present invention is applied to an optical disk reproducing apparatus will be described. First, the configuration of an optical disc reproducing apparatus to which this example is applied will be shown. FIG. 8 is a block diagram showing the basic configuration of the optical disc reproducing apparatus to which this embodiment is applied. The optical disk reproducing device includes an optical disk 100 and an optical disk drive 101. Optical disc drive 101
Records and reproduces information by irradiating a laser beam spot while rotating the optical disc. The optical disc drive 101 includes a spindle motor 102, a rotation control system 103, an optical pickup 104, a coarse movement motor 105,
It comprises a coarse movement motor control system 106, a signal processing system 107, a pickup control system 108, and a drive controller 109.

The optical pickup 104 reproduces the information recorded on the optical disc. The optical pickup 104 is
It has a function of detecting the shake of the surface due to the rotation of the disk and the shake of the track in the radial direction of the disk, and automatically adjusting the shake so that it is always within a certain error. The coarse movement motor 105 largely moves the optical pickup 104 near the target position of the optical disc at high speed. The coarse movement motor 105 is also used in cooperation with the motor in the optical pickup 104 to cause the laser light to follow the shake of the track on the disk.

The drive controller 109 controls the operation of each part of the optical disc reproducing apparatus. The drive controller 109 controls each control system according to an instruction from an external drive interface to perform a target operation. That is, according to the control signal of the drive controller 109, the rotation control system 103 rotates the spindle motor 102 and the optical disc 100. Further, in response to a control signal from the drive controller 109, the coarse movement motor control system 106 moves the coarse movement motor 105 to move the optical pickup 104 in the radial direction of the optical disc 100.

The signal processing system 107 also performs signal processing on the information reproduced by the optical pickup 104 and supplies it to the drive controller. The drive controller outputs information to the external interface. Signal processing system 10
Reference numeral 7 is composed of a reproduction signal demodulation circuit and an error correction circuit. The pickup control system 108 includes a tracking drive circuit and a focusing drive circuit.
The pickup control system 108 is the drive controller 1
The tracking servo and focusing servo of the optical pickup 104 are controlled by the control signal of 09 and the control signal of the signal processing system 107.

The optical disk reproducing apparatus having the above structure operates as follows. Drive controller 1
In response to the control signal from 09, the rotation control system 103 rotates the spindle motor 102 and the optical disc 100. Further, in response to a control signal from the drive controller 109, the coarse motion motor control system 106 causes the coarse motion motor 10 to
5 to move the optical pickup 104 to the optical disc 100.
Move in the radial direction.

The pickup control system 108 controls the tracking servo and the focusing servo of the optical pickup 104 by the control signal of the drive controller 109 and the control signal of the signal processing system 107. The optical pickup 104 reproduces the information recorded on the optical disc. The optical pickup 104 detects the shake of the surface accompanying the rotation of the disk and the shake of the track in the disk radial direction, and reproduces the information while automatically adjusting the shake so that it is always within a certain error.

The signal processing system 107 includes an optical pickup 10
The information reproduced in 4 is subjected to signal processing such as demodulation and error correction, and is supplied to the drive controller. The drive controller outputs information to the external interface.
Such a signal processing system 1 in the optical disc reproducing apparatus
Before or after 07, or drive controller 1
The signal reproducing device of this example is provided in the subsequent stage of 09.

This embodiment will be described below. FIG.
2 is a block diagram showing the configuration of this embodiment, and FIG. 2 is a signal waveform diagram of each part of this embodiment. First, the configuration of this example will be described. The signal reproducing apparatus of this example comprises an input terminal 5, a comparator 1, a signal detecting circuit 2, a delay circuit 3, a switch 4, a capacitor C, a resistor R ₁ , a resistor R ₂ and an output terminal 6.

In FIG. 1, the input terminal 5 is a capacitor C.
Is connected to one side of the signal detection circuit 2 and to the input side of the signal detection circuit 2. The other side of the capacitor C is connected to the input side of the comparator 1 and the movable contact 4 of the switch 4 is connected.
A is connected. The output side of the comparator 1 is the output terminal 6
And to one side of resistor R ₁ .

The output side of the signal detection circuit 2 is connected to the input side of the delay circuit 3. The output side of the delay circuit is connected to the control terminal 4D of the switch 4. Fixed contact 4B of switch 4
Is connected to one side of the resistor R ₂ . The other side of resistor R ₂ is grounded. The fixed contact 4C of the switch 4 is connected to the other side of the resistor R ₁ .

The signal detection circuit 2 comprises, for example, a high pass filter and an envelope detector. The signal detection circuit 2 detects the presence or absence of a recorded signal from the reproduction signal S ₁ and generates a signal detection circuit output S ₄ . That is, a high level signal is output when the recorded signal exists, and a low level signal is output when the recorded signal does not exist. The envelope detector is a circuit that detects the envelope of a high frequency signal.

The signal detection circuit output S ₄ is supplied to the delay circuit 3. The signal detection circuit output S4 is being delayed by the delay circuit 3, the delay circuit output S _5. Switch 4
Includes a movable contact 4A, a fixed contact 4B, a fixed contact 4C, and a control terminal 4D. The switch 4 connects between the movable contact 4A and the fixed contact 4C during reproduction of the recorded signal, that is, when the delay circuit output S ₅ is at a high level. Further, the switch 4 supplies the delay circuit output S supplied to the control terminal 4D so that the movable contact 4A and the fixed contact 4B are connected when there is no signal, that is, when the delay circuit output S ₅ is at a low level. Controlled based on ₅ output levels.

First, during reproduction of the recorded signal, the movable contact 4A and the fixed contact 4C are connected, so that FIG. 1 can be expressed as shown in FIG. FIG. 3 is a block diagram showing the configuration at the time of reproducing the recording signal of the present embodiment. The configuration of FIG. 3 is as follows. In FIG. 3, the input terminal 5 is connected to one side of the capacitor C. The other side of the capacitor C is connected to the input side of the comparator 1. The output side of the comparator 1 is connected to the output terminal 6 and is also connected to one side of the resistor R ₁ . The input side of the comparator 1 is connected to the other side of the resistor R ₁ .

Further, FIG. 3 can be rewritten as shown in FIG. FIG. 4 is a block diagram for explaining the functions of C and R _{1 in} this embodiment. The configuration of FIG. 4 is as shown below. The capacitor C in FIG. 3 is a high pass filter (HPF), and the resistor R ₁ is a low pass filter (LPF).
Function respectively. Therefore, it can be configured as follows. In FIG. 4, the input terminal 5 is a high-pass filter 7
(C) is connected to one side. The other side of the capacitor C is connected to one addition input terminal of the adder 9. The output terminal of the adder 9 is connected to the input side of the comparator 1. The output side of the comparator 1 is connected to the output terminal 6 and the input side of the low pass filter 8 (R ₁ ). The output side of the low pass filter 8 (R ₁ ) is connected to the other addition input terminal of the adder 9. The capacitor C is the first
, And the resistor R ₁ constitutes a low pass filter.

FIG. 5 shows C and R of FIG.₁For explaining the function of
It is a waveform diagram of each part of the block diagram. High pass filter 7
And the low-pass filter 8 both have a cutoff frequency of 1 / (2
πR ₁C) Comprised of filters with complementary characteristics of [Hz]
It That is, the high pass filter 7 has a cutoff frequency of 1 /
(2πR₁C) Pass frequencies higher than [Hz]
Works like. The low pass filter 8 has a cutoff frequency of 1
/ (2πR₁C) Pass frequencies lower than [Hz]
Works like.

Playback signal input S₁Is the high pass filter 7
By 1 / (2πR₁C) Lower frequency components than [Hz] are removed
HPF output S left₆Becomes This allows the low range noise
Is removed, but at the same time the low frequency components of the signal are also removed.
I will end up. Therefore, the low pass filter 8 is used to
Data output S₃From 1 / (2πR ₁C) Lower than [Hz]
LPF output S as the signal component of₇Is extracted and LPF output
S₇HPF output S₆By adding to
A signal in which the signal component is reproduced can be obtained.

In order to properly perform such an operation, it is an important condition that the amplitudes of the reproduction signal input S ₁ and the comparator output S ₃ are equal. This condition is not satisfied when the reproduction signal input S ₁ has no signal. That is, since the amplitude of the reproduction signal input S ₁ is smaller than the amplitude of the comparator output S ₃ , the positive feedback loop of the comparator 1, the low pass filter 8 and the adder 9 diverges. To prevent this, the positive feedback loop of the comparator 1, the low-pass filter 8 and the adder 9 is turned off when there is no signal. That is, the movable contact 4A and the fixed contact 4B of the switch 4 are connected.

At this time, the positive feedback loop of the comparator 1, the low-pass filter 8 and the adder 9 is turned off, and the cut-off frequency of the high-pass filter 7 is made higher than that during the reproduction of the recording signal. That is, it is an important condition that R ₂ in FIG. 1 is smaller than R ₁ .

That is, when there is no signal, the block diagram of FIG. 1 can be rewritten as shown in FIG. FIG. 6 is a block diagram of this embodiment when there is no signal. The structure of the block diagram of FIG. 6 is as follows. In FIG. 6, the input terminal 5 is connected to one side of the capacitor C. The other side of the capacitor C is connected to the input side of the comparator 1 and also to one side of the resistor R ₂ . Resistor R ₂
The other side of is grounded. The output side of the comparator 1 is connected to the output terminal 6. Capacitor C and resistor R ₂
Constitutes a second high pass filter.

Further, FIG. 6 can be rewritten as shown in FIG. FIG. 7 is a block diagram for explaining the functions of C and R _{2 in} this embodiment. The configuration of FIG. 7 is as shown below. The capacitor C and the resistor R ₂ in FIG. 6 function as a high pass filter (HPF). Therefore, it can be configured as follows. In FIG. 7, the input terminal 5 is connected to one side of the high pass filter 10 (C, R ₂ ). The other side of the high-pass filter 10 is the comparator 1
Connected to the input side of. The output side of the comparator 1 is connected to the output terminal 6.

Here, the cutoff frequency 1 / (2πR ₂ of the high-pass filter 10 (C, R ₂ ) when there is no signal in FIG.
C) [Hz] is the cutoff frequency 1 / (2πR ₁ C) of the high-pass filter 7 (C) at the time of reproducing the recording signal in FIG.
Configured higher than [Hz]. By doing so, even if noise is mixed in the high-pass filter 10 (C, R ₂ ) when there is no signal, this noise is
It is possible to prevent passing through 0 (C, R ₂ ).

Further, the cutoff frequency 1 / (2πR ₁ C) [H of the high-pass filter 7 during reproduction of the recording signal in FIG.
z] is determined by the band of low frequency noise and is relatively low. That is, the time constant R ₁ C is set large. This is because if the time constant R ₁ C is made small, the operation of the positive feedback loop becomes unstable due to fluctuations in the reproduced signal amplitude and noise, which is not desirable.

However, if the time constant R ₁ C is large, it takes a long time for the waveform response to stabilize at the beginning of the recording section 21 of the comparator input S _{2 in} FIG. Therefore, it is necessary to increase the delay time Td of the delay circuit 3.
A preamble for reproducing clock generation is recorded in the first part of the recording unit 21, and if this is heavily damaged, clock generation becomes unstable. Therefore, by making R ₂ smaller than R ₁ , that is, making the time constant R ₂ C smaller than the time constant R ₁ C, damage to the preamble can be suppressed and clock generation can be stabilized.

The signal reproducing apparatus of this embodiment having the above-described structure operates as follows. The reproduction signal S ₁ input to the input terminal 5 is supplied to the capacitor C and the signal detection circuit 2. The capacitor C passes the high frequency component of the reproduction signal S ₁ and outputs the comparator input S ₂ . The comparator input S ₂ is supplied to the comparator 1. The comparator 1 compares it with a predetermined threshold value, binarizes the comparator input S ₂ , and supplies the comparator output S ₃ to the output terminal 6. The comparator output S ₃ is supplied to the fixed terminal of the switch 4 via the resistor R ₁ .

The signal detection circuit 2 detects the presence or absence of a recorded signal from the reproduction signal S ₁ and outputs the signal detection circuit output S ₄ . That is, a high level signal is output when a recorded signal is present when the recording signal is reproduced, and a low level signal is output when there is no signal when there is no signal.

The signal detection circuit output S ₄ is supplied to the delay circuit 3. The signal detection circuit output S4 is delayed by Td by the delay circuit 3, the delay circuit output S _5. The delay circuit output S ₅ is supplied to the control terminal 4D of the switch 4. Switch 4, when the delay circuit output S ₅ of high level, between the movable contact 4A- fixed contacts 4C are connected. The switch 4 may, when the delay circuit output S ₅ of low level, between the movable contact 4A- fixed contact 4B is connected. In this way, the switch 4 is controlled based on the output level of the delay circuit output S ₅ supplied to the control terminal 4D.

First, when the recording signal is reproduced, the movable contact 4A and the fixed contact 4C of the switch 4 are connected. Therefore, FIG. 1 appears as in FIG. Further, FIG. 3 can be rewritten as in FIG.

In FIG. 4, the cutoff frequencies of the high-pass filter 7 and the low-pass filter 8 are both 1 / (2πR ₁
C) [Hz], the high pass filter 7 has a cutoff frequency of 1 / (2πR ₁ C) [H]
z] to pass frequencies higher than that of z]. Further, the low-pass filter 8 has a cutoff frequency of 1 / (2πR ₁
C) Operates to pass frequencies lower than [Hz].

Playback signal S₁By the high-pass filter 7.
1 / (2πR₁C) Low frequency components below [Hz] are removed
HPF output S₆Is output as. This makes it low
Band noise is removed, but at the same time the low frequency components of the signal are also removed
Will be done. Therefore, the low-pass filter 8
Comparator output S₃From 1 / (2πR ₁C) [Hz]
LPF output S as a low-frequency signal component₇Extract and LP
F output S₇HPF output S₆Add to. This allows
A signal in which the low-frequency signal component is reproduced can be obtained.

In order to perform such an operation correctly, it is an important condition that the amplitudes of the reproduction signal S ₁ and the comparator output S ₃ are equal. This condition is not satisfied when the reproduced signal S ₁ is no signal. That is, the reproduction signal S
_Since the amplitude of ₁ is smaller than the amplitude of the comparator output S ₃ , the positive feedback loop of the comparator 1, the low pass filter 8 and the adder 9 diverges.

To prevent this, the positive feedback loop of the comparator 1, the low-pass filter 8 and the adder 9 is turned off when there is no signal. That is, the movable contact 4A and the fixed contact 4B of the switch 4 are connected. At this time, the positive feedback loops of the comparator 1, the low-pass filter 8 and the adder 9 are turned off, and the cut-off frequency of the high-pass filter 7 is made higher than that during recording signal reproduction. That is, FIG.
It is an important condition to keep R ₂ of R smaller than R ₁ .

That is, when there is no signal, the block diagram of FIG. 1 can be rewritten as shown in FIG. Further, FIG. 6 can be rewritten as in FIG. Here, the cut-off frequency 1 / (2πR ₂ C) [Hz] of the high-pass filter 10 (C, R ₂ ) when there is no signal in FIG. 7 is the cut-off frequency of the high-pass filter 7 (C) when reproducing the recording signal in FIG. Since the frequency is higher than 1 / (2πR ₁ C) [Hz], even if noise is mixed in the high-pass filter 10 (C, R ₂ ) when there is no signal, this noise causes the high-pass filter 10 (C, R ₂ ).
₂ ) can be prevented from passing through.

Further, the cutoff frequency 1 / (2πR ₁ C) [H of the high-pass filter 7 during reproduction of the recording signal in FIG.
z] is relatively low. That is, the time constant R ₁ C is set large. However, if the time constant R ₁ C is large, the time until the waveform response stabilizes at the beginning of the recording unit 21 of the comparator input S _{2 in} FIG.
The delay time Td of is also increased. Thus, R ₂ is replaced by R ₁
By making the time constant R ₂ C smaller than the time constant R ₁ C, the damage to the preamble can be suppressed and the clock generation can be stabilized.

[0062]

According to the present invention, in the signal reproducing apparatus for reproducing the signal of the recording medium in which the data having the low frequency component is recorded, the first signal for cutting off the low frequency component of the reproduction signal is provided.
High-pass filter, a second high-pass filter having a higher cut-off frequency than the first high-pass filter for cutting low-frequency components of the reproduction signal, and a comparator for binarizing the analog signal. , A low-pass filter having complementary characteristics to the first high-pass filter for extracting the low-pass component of the output, a signal detection circuit for detecting the presence or absence of a reproduced signal, and an output of the signal detection circuit. It has a delay circuit for delaying, and the output of the delay circuit supplies the output of the second high-pass filter to the input of the comparator when no signal is detected,
At the time of signal detection, the output of the first high-pass filter and the output of the low-pass filter are added and controlled to be supplied to the input of the comparator. Therefore, the high-pass filter removes low-pass noise, The low-pass component of the signal lost at that time is positively fed back to the low-pass component of the signal extracted from the binarized data and added to reduce the low-pass component of the signal lost by the first high-pass filter. The range component can be reproduced. In addition, the cutoff frequency of the high-pass filter is set higher than the predetermined frequency when no signal is detected, and the addition amount of the low-pass component is set to zero. By switching the frequency to a predetermined frequency and setting the addition amount to a predetermined value, the settling time of positive feedback can be shortened. As a result, it is possible to stably detect data without being affected by the low frequency component of the modulation code.

Further, according to the present invention, in the above-mentioned signal reproducing apparatus, the time constant of the second high pass filter is made smaller than the time constant of the first high pass filter. Sometimes, even if noise is mixed in the second high-pass filter, the noise is not passed and the noise is not reproduced.

Further, according to the present invention, in the above-mentioned signal reproducing apparatus, the delay time of the output signal of the signal detection circuit by the delay circuit is the waveform response based on the time constant of the first high pass filter from the time of signal detection. Since it is a time until it stabilizes, stable clock generation can be performed without damaging the preamble for reproducing clock generation recorded at the beginning of the recording signal.

Further, according to the present invention, in the optical disc signal reproducing apparatus for reproducing the signal of the optical disc in which the data having the low frequency component is recorded, the first high frequency band for cutting off the low frequency component of the reproduction signal is provided. A pass filter, a second high pass filter having a cut-off frequency higher than that of the first high pass filter for cutting off the low frequency component of the reproduced signal, a comparator for binarizing an analog signal, and its output Low-pass filter having a complementary characteristic to the first high-pass filter for extracting the low-frequency component of the signal, a signal detection circuit for detecting the presence or absence of a reproduced signal, and a delay circuit for delaying the output of the signal detection circuit The output of the delay circuit supplies the output of the second high-pass filter to the input of the comparator when the signal is not detected, and the output of the first high-pass filter and the low-pass filter when the signal is detected. Since by adding the output of the motor is controlled so as to supply to the input of the comparator, the data error is reduced, it is possible to perform high density recording.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a signal reproducing apparatus and an optical disk reproducing apparatus of the present invention.

FIG. 2 is a signal waveform diagram of each part of the block diagram of FIG. 1 of one embodiment of the signal reproducing apparatus and the optical disk reproducing apparatus of the present invention.

FIG. 3 is a block diagram showing a configuration of a signal reproducing apparatus and an optical disk reproducing apparatus according to an embodiment of the present invention when reproducing a recorded signal.

FIG. 4 is a block diagram showing a configuration for explaining the functions of C and R ₁ when reproducing a recording signal in an embodiment of the signal reproducing apparatus and the optical disk reproducing apparatus of the present invention.

5 is a signal waveform diagram of each part of the block diagram of FIG. 4 of one embodiment of the signal reproducing apparatus and the optical disk reproducing apparatus of the present invention.

FIG. 6 is a block diagram showing a configuration of a signal reproducing apparatus and an optical disk reproducing apparatus according to an embodiment of the present invention when there is no signal.

FIG. 7 is a block diagram showing a configuration for explaining the functions of C and R ₁ when there is no signal in one embodiment of the signal reproducing apparatus and the optical disk reproducing apparatus of the present invention.

FIG. 8 is a block diagram showing a configuration of an optical disc reproducing device applied to an embodiment of the signal reproducing device and the optical disc reproducing device of the present invention.

[Explanation of symbols]

1 Comparator 2 Signal Detection Circuit 3 Delay Circuit 4 Switch 5 Input Terminal 6 Output Terminal C Capacitor R ₁ Resistor R ₂ Resistor 7 High Pass Filter 8 Low Pass Filter 9 Adder

Claims (4)

[Claims] 1. A signal reproducing apparatus for reproducing a signal of a recording medium on which data having a low-frequency component is recorded, and a first high-pass filter for cutting off a low-frequency component of the reproduction signal, and a reproduction signal. Second high-pass filter that has a higher cut-off frequency than the first high-pass filter for cutting off the low-pass component of, a comparator that binarizes the analog signal, and the low-pass component of its output is extracted. A first low-pass filter having a complementary characteristic to the first high-pass filter, a signal detection circuit for detecting the presence or absence of a reproduced signal, and a delay circuit for delaying the output of the signal detection circuit, The output of the delay circuit supplies the output of the second high pass filter to the input of the comparator when no signal is detected, and the output of the first high pass filter and the low pass filter when a signal is detected. of By adding the force signal reproducing apparatus and controls to supply to the input of the comparator. 2. The signal reproducing apparatus according to claim 1, wherein the time constant of the second high pass filter is smaller than the time constant of the first high pass filter. Signal reproduction device. 3. The signal reproducing apparatus according to claim 1, wherein the delay time of the output signal of the signal detecting circuit by the delay circuit is a waveform response based on the time constant of the first high pass filter from the time of detecting the signal. A signal reproducing device characterized in that it takes time for the temperature to stabilize. 4. An optical disc signal reproducing apparatus for reproducing a signal of an optical disc in which data having a low frequency component is recorded, and a first high pass filter for blocking a low frequency component of a reproduction signal, and a reproduction signal. Second high-pass filter that has a higher cut-off frequency than the first high-pass filter for cutting off the low-pass component of, a comparator that binarizes the analog signal, and the low-pass component of its output is extracted. A first low-pass filter having a complementary characteristic to the first high-pass filter, a signal detection circuit for detecting the presence or absence of a reproduced signal, and a delay circuit for delaying the output of the signal detection circuit, The output of the delay circuit supplies the output of the second high pass filter to the input of the comparator when no signal is detected, and the output of the first high pass filter and the low pass when the signal is detected. It adds the output of the filter disc signal reproducing apparatus characterized by controlling to supply to the input of the comparator.