JPH06162514A - Signal reproducing device - Google Patents

Abstract

PURPOSE:To reduce an error rate by accurately detecting a mark edge while demodulating the modulated codes, which are recorded by a mark edge method, by a difference voltage detection. CONSTITUTION:This device is provided with a limiter circuit 20 which limits amplitude voltages so that a VL/Vpp value becomes approximately 1.1 where Vpp is a maximum amplitude voltage value of a maximum frequency signal read out of an information recording medium and VL is an amplitude voltage value which is to be limited. By obtaining a difference voltage from the signals whose upper and lower portions are limited through the circuit 20, a mark edge is detected with high precision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing device for reading and reproducing digital data recorded on, for example, an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art As a method for demodulating digital data recorded on an optical disk, there is an amplitude detecting method as shown in FIG. In this method, the recording surface of the disk is irradiated with detection light, and pit detection and read data based on the magnetization direction in the magneto-optical recording film are obtained from the returned light. In Fig. 8 current /
The read data a after voltage conversion is shown. In the amplitude detection method, a threshold value b is set by a comparator, and a change in the amplitude of read data is detected with reference to this threshold value b. For example, a level higher than the threshold value b is set to "1".
The low level is set to "0" and the digital data c is demodulated.

However, in this amplitude detection method, when the entire level of the signal waveform of the read data a changes, the relative level between the change point of the signal amplitude and the threshold value b changes and the threshold value b is changed. It becomes impossible to perform accurate demodulation based on the standard. In particular, in an optical memory device using a magneto-optical disk, data is written using the heat of the laser spot, so the signal waveform of the read data may vary due to variations in the duty ratio due to light diffusion on the disk recording surface and distortion of the pit shape. The level of is likely to fluctuate, and thus an error in the reproduced data is likely to occur.

Another method for demodulating read data is a difference detection method. FIG. 9 is a diagram showing this difference detection method. In this difference detection method, the voltage of the read data a is sampled for each clock signal by using the clock signal from the modulation code having the self-clocking property, and the absolute value of (Vn-Vn-1) is obtained from the sampling voltage ( n = 1,
2, 3 ...). When this absolute value is larger than a predetermined threshold value, it is determined that there is a pit or a conversion point of the magnetization direction. According to this method, even if the voltage level of the read data varies, the demodulation accuracy is higher than that of the amplitude detection method.

[0005]

On the other hand, in an optical memory device or the like, RLL (1,7) or RLL (2,7) is used.
Using a modulation code having a minimum run length of 1 or more (one or more “0” existing between “1” and “1”),
A mark edge recording method is employed in which the presence or absence of pits or the magnetization direction in the magneto-optical recording film is reversed every time there is a code "1". When the data recorded by this mark edge recording method is demodulated by the above-mentioned difference detecting method, there are cases where the reversal position of the presence or absence of pits or the reversal position of the magnetization direction, that is, the mark edge portion cannot be accurately detected. In other words, if there is a voltage fluctuation in the read data from the recording medium, the original pit or the conversion point of the magnetization direction may not be accurately reproduced.

FIGS. 7A to 7C show waveforms when the read data recorded with the mark edge is demodulated by the difference detection method. FIG. 7A shows a change in voltage of read data from the recording medium. This is read data from a magneto-optical disk, for example, and the code "1"
Is the change point of the magnetization direction in the magneto-optical recording film. This recorded content is originally an RLL (1,7) modulation code of "1000001000001010". The voltage of the waveform of FIG. 7A is sampled by the self-clock, and the sampled differential voltage (Vn-Vn) is sampled in the same manner as shown in FIG.
When the absolute value of (-1) is taken, the waveform is as shown in FIG. In the read data shown in FIG. 7A, the waveform has a large rounding at the reversal points (a), (b), and (c) of the recording state, and each of (a), (b), and (c). The fluctuation range of the signal strength in the part of is different. This difference is due to the length of the pit size on the recording surface.

Therefore, looking at the change in the absolute value of the differential voltage shown in FIG. 7B, for example, in the portions shown in (d) and (e),
The differential voltage changes over a long period of time. This is because the waveform becomes a large curve at the positions of (a) and (b) in (A) of the figure, and the fluctuation of the voltage is long. In FIG. 7C, the differential voltage shown in FIG. 7B is waveform-shaped by the comparator, and this becomes the demodulated data. However, since the differential voltage continues to change for a long time in the portions (d) and (e) in FIG. 6B, the portions (f) and (g) shown in FIG.
The signal of "1" appears for a longer time than it should in the area, and the change point of the magnetization direction in the magneto-optical film cannot be accurately detected. Therefore, in FIG.
You will get demodulated data that is completely different from the original data of "10".

The present invention solves the above-mentioned conventional problems, and provides a signal reproducing apparatus capable of reproducing data accurately when demodulating data such as mark edge recording by a difference detection method. It is an object.

[0009]

SUMMARY OF THE INVENTION The present invention is directed to a difference detecting section for detecting a difference in signal intensity of read data obtained by detecting return light of light irradiated on an information recording medium on which digital data is recorded. In the signal reproducing device in which the conversion point of the recorded state of the data is detected by the output from the difference detecting section, the signal limiting section for limiting the signal strength of the read data is provided, and the signal limiting section is passed. It is characterized in that the difference detection unit detects a difference in signal intensity from the data.

Further, in the above, the limit width between the upper limit and the lower limit of the intensity of the read data limited by the signal limiting unit is less than or equal to the maximum value of the change width of the signal intensity at the conversion point of the highest frequency signal of the read data. It is preferable that

[0011]

In the above means, the signal intensity of the read data obtained based on the return light from the recording medium is regulated to a predetermined limit width by the signal limiting section, and the signal intensity of the signal after this limitation is controlled by the difference detecting section. Detect the difference between. By limiting the upper and lower limits of the signal strength by the signal limiter, even if there is a round in the signal strength of the read data, the upper limit of the change in this rounded portion is cut, and the conversion point of the data can be detected with high accuracy. Become.

Further, by determining the limit width of the signal strength based on the highest frequency signal, the detection accuracy of the data conversion point can be made extremely high.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 and 2 are block diagrams showing a circuit configuration as an embodiment of the present invention, FIG. 1 is a circuit diagram showing a front stage portion of the circuit, and FIG. 2 is a circuit diagram showing a rear stage portion of the circuit. The circuit on the front stage side shown in FIG. 1 includes, for example, a DC removing capacitor 11 into which read data read from a magneto-optical disk (not shown) is input after current / voltage conversion, and an RF for amplifying the input signal. An amplifier 12, a noise filter 13 that removes noise components included in the amplified signal, a waveform equalizer 14 that emphasizes the waveform of the input signal in the amplitude direction, and an output from the waveform equalizer 14 are input. And a differential amplifier 15 to be operated.

The signal from the waveform equalizer 14 is positively input to the differential amplifier 15. Also the differential amplifier 1
The output from the circuit 5 is bypassed via the switch S1 and is negatively input via the low-pass filter circuit (indicated by LPF in the figure) 16. In this differential amplifier 15, in order to generate a self-clock signal, the offset component of the input signal that has passed through the waveform equalizer 14 is removed, and a zero point is set for the input waveform. That is, in this circuit, the switch S1 is turned on only when the prepit portion recorded intermittently on the recording surface of the magneto-optical disk is read, and the negative feedback path passing through the low-pass filter circuit 16 is formed. Then, the (low frequency component) is removed, and the zero point of the highest frequency signal included in the read signal from the prepit portion is set.

The subsequent stage of the differential amplifier 15 is branched into a self-clock signal generation path (A) and a reproduction signal difference detection path (B). The self-clock signal generation path (A) is provided with a comparator 17 and an edge detection circuit 18 that detects rising and falling portions of a pulse signal whose waveform has been shaped by the comparator 17. The output of the differential amplifier 15 is positively input to the comparator 17, and the negative input portion is grounded. With this configuration,
The switch S1 is turned on, the offset component passing through the low-pass filter 16 is removed by the differential amplifier 15, and the signal with the zero point set is input to the comparator 17, which detects the input waveform above 0V. Then, the waveform is shaped and a rectangular wave is generated. Then, the rising edge of this rectangular wave is detected by the edge detection circuit 18 connected to the subsequent stage, and a pulse signal of a predetermined pitch is generated.

A PL after the edge detection circuit 18 is provided.
An L (Phase Lock Loop) circuit 19 is connected. The PLL circuit 19 compares the phase of the waveform of the output signal of the edge detection circuit 18 with the phase of the waveform of the output signal of the frequency divider 23, and outputs a voltage value according to the phase difference. A low-pass filter circuit (LP) that removes the DC component contained in the output signal from the phase comparison unit 21.
F) 22 and a voltage controlled oscillator (VCO)
lled oscillator) 24 and a frequency divider 23 having a predetermined frequency division ratio. In this PLL circuit 19, when the pulse signal from the edge detection circuit 18 is input, the PLL circuit 19 enters a lock state according to the frequency of this input signal, whereby a self-clock signal is generated and given to the demodulator 29 in the subsequent stage. .

On the other hand, in the difference detection path (B), as shown in FIG. 2, a limiter circuit 20, which will be described in detail later, and a delay circuit 2 connected to one output side of the limiter circuit 20.
5, a differential amplifier 26 to which the output from the limiter circuit 20 is positively input and an output from the delay circuit 25 is negatively input, and an absolute value circuit 27 for obtaining the absolute value of the signal output from the differential amplifier 26. And a comparator 28 to which the output from the absolute value circuit 27 is positively input and the variable voltage VX is negatively input, and the output from the comparator 28 is given to the demodulator 29.

FIG. 3 is an explanatory diagram showing a detailed configuration of the limiter circuit, and FIG. 4 shows the maximum value based on the maximum value Vp of the change width of the signal strength of the highest frequency signal and the self-clock signal given to the demodulator 29. FIG. 5 is an explanatory diagram showing a relationship between a differential voltage Vpp when a frequency signal is sampled and a voltage limit value VL in the limiter circuit 20. FIG. 5 shows a voltage in RLL (1,7) modulation with a minimum pit length of 0.64 μm. It is a characteristic view which shows the relationship between the limit variable (alpha) and S / N ratio. In FIG. 4, Fi (chain line) represents a signal waveform in the previous stage of the limiter circuit 20, Fo (solid line) represents a signal that has passed through the limiter circuit 20, the vertical axis represents the amplitude voltage, and the horizontal axis represents time. Further, in FIG. 5, the horizontal axis represents the voltage limiting variable α, and the vertical axis represents the S / N.
The ratio is shown.

In the limiter circuit 20 shown in FIG. 3, a resistor R is connected to the input side, and a diode D1 having a cathode connected to an upper limit power supply voltage V1 for upper limit,
This is a so-called diode limiter circuit provided with a diode D2 whose anode is connected to the lower limit power supply voltage V2 for the lower limit. The upper limit voltage of the signal input to the limiter circuit 20 is limited by the upper limit power supply voltage V1 and the voltage drop of the diode D1, and the lower limit voltage is limited by the lower limit power supply voltage V2 and the voltage drop of the diode D2. Here, the relationship between the difference voltage value Vpp sampled by the self-clock signal at the conversion point of the maximum frequency signal shown in FIG. 4 and the limit value VL which is the limit width between the upper limit and the lower limit of the voltage to be limited is shown. Show. The ratio of both voltage values is represented by a voltage limiting variable α as shown in Equation 1.

[0020]

## EQU1 ## α = VL / Vpp

The limit value VL of the voltage to be limited above.
The upper limit voltage value VL1 of is, when the voltage drop in the diode D1 is Vf1,

[0022]

[Formula 2] VL1 = V1-Vf1

Similarly, the lower limit voltage value VL2 of the limit value VL of the voltage to be limited is defined as follows: when the voltage drop value at the diode D2 is Vf2,

[0024]

[Expression 3] VL2 = V2-Vf2

Therefore, the absolute value of the limiting voltage value VL obtained by the absolute value circuit 27 via the differential amplifier 26 is

[0026]

[Expression 4] VL = | VL1 + VL2 |

In the limiter circuit 20 shown in this embodiment, it is preferable that the value of α be set to approximately 1 or less, preferably 1.1 or less. That is, the RL with the minimum pit length of 0.64 μm recorded on the magneto-optical disk or the like.
L (1, 7) Error rate when the modulation codes demodulated almost 10 ^{- 6} but it is desirable that below the upper limit of the S / N ratio required to secure this error rate as shown in FIG. 5 Is about 20 dB. Therefore, from the diagram of FIG. 5, in the demodulation of the RLL (1,7) modulation code having the minimum pit length of 0.64 μm, the voltage limiting variable α required to keep the error rate below the above value is 1.1. It turns out that: Therefore, it is a condition for the error rate to be equal to or less than the appropriate value that α is approximately 1 or less, preferably 1.1 or less.

Thus, the smaller the voltage limiting variable α, the better the S / N ratio is as follows. When a conversion point such as Kerr rotation angle (magnetization direction in the magneto-optical recording film) is detected by the differential voltage, the error rate depends on how large the difference between the differential voltage and the judgment voltage can be taken with respect to the noise voltage. It is determined. Therefore, when the Kerr rotation angle or the like is not converted, the error rate decreases as the difference voltage approaches zero, and conversely at the conversion point such as the Kerr rotation angle, the error rate decreases as the difference voltage increases. If the variable α is reduced as described above, the differential voltage at the time of no conversion can be reduced. At the same time, the differential voltage at the conversion point is also reduced, but at the same time, the influence of noise is reduced, and as a result, the S / N ratio can be improved.

The minimum pit length of 0.64 μm RLL (1,
7) When demodulating the modulation code, the error rate is about 10
^- conditions to be ⁶ or less, as shown in FIG. 5 α = (Vpp /
VL) is 1 or less, preferably 1.1 or less, but considering that the differential voltage at the time of non-conversion is close to zero as described above and the differential voltage at the conversion point is made as large as possible, In FIG. 4, when the maximum value Vp of the level change width of the highest frequency signal is set and the voltage limit value VL is Vp or less, a considerably good error rate can be obtained.

The operation of the signal reproducing apparatus having the above configuration will be described with reference to FIGS. 6 (A) to 6 (C).
FIGS. 6A to 6C are signal waveforms obtained in the portions shown in FIGS. 2A to 2C, respectively. In this embodiment, the read data input to the RF amplifier 12 shown in FIG. 1 is the same as that shown in FIG. 7A, and is recorded by the RLL (1,7) modulation code having the minimum pit length of 0.64 μm. The data of "10000010000010101" is reproduced.

First, the operation of the self-clock signal generation path (A) will be described. When the pit information of the minimum pitch length recorded in the pre-pit area of the magneto-optical disk is read out, the RF amplifier 1 is passed through the capacitor 11
The noise component is removed from the amplified signal by the noise filter 13 and is equalized by the waveform equalizer 14. The signal from the waveform equalizer 14 is input to the differential amplifier 15. When the pit information is read, the switch S1 is closed and the output of the differential amplifier 15 is the low-pass filter circuit 1.
The signal is negatively input to the differential amplifier 15 via 6. As a result, the offset component of the signal is removed, the zero point is set, and the signal is output as the 0V reference.

The signal output from the differential amplifier 15 is compared with 0 V in the comparator 17 and waveform-shaped to obtain a rectangular wave. The rectangular wave is input to the edge detection circuit 18, and a pulse signal synchronized with the rising portion of each rectangular wave is generated. This pulse signal is output to the PLL circuit 19. In the PLL circuit 19, the output signal from the VCO 24 is frequency-divided by the frequency divider 23 at a predetermined frequency division ratio, and the signal waveform output from the edge detection circuit 18 in the phase comparison unit 21 and the frequency divider 13 are output. The phase of the output waveform is compared, and the voltage corresponding to the phase difference between the two is VCO.
An oscillation output corresponding to this input voltage is obtained. This becomes a self-clock signal, and the demodulator 2
Given to 9. In the demodulator 29, the difference detection path (B)
The differential voltage given by is sampled by this self-clock.

Next, the operation of the difference detection path (B) will be described. The read signal shown in FIG. 7A read from the magneto-optical disk is input to the limiter circuit 20. In the present embodiment, the limiter circuit 20 limits the upper limit value and the lower limit value of the input signal by the limit width so that the variable α becomes 1 or less, preferably 1.1 or less. The signal waveform (a) after this limit is shown in FIG. The signal output from the limit circuit 20 is input to the delay circuit 25, where it is delayed for a predetermined time, and then applied to the differential amplifier 26 by minus flow. The differential amplifier 26 outputs a differential voltage that is the difference between the signal directly applied from the limiter circuit 20 and the delayed signal. The absolute value circuit 27 takes the absolute value of the differential voltage. The waveform shape of the output signal (b) from the absolute value circuit 27 is shown in FIG.
It shows in (B).

The output signal (b) shown in FIG. 6B is waveform-shaped by the comparator 28 to obtain a signal (c) shown in FIG.
It shows in (C). As is clear from the figure, the signal (c)
Is "10000010000010101" having the same code as the data recorded on the magneto-optical disk. That is, in this embodiment, the read signal is amplitude-limited by the limiter circuit 20 to have the waveform (a) shown in FIG. 6A, but this waveform does not cause a rounded change in the conversion point of the signal. Therefore, as shown in FIGS. 6B and 6C, the mark edge is accurately detected. This data signal is sampled in the demodulator 29 based on the self-clock signal, and the RLL (1,7) modulation code is demodulated.

As described above in detail, in the present embodiment, α is about 1 or less, preferably 1.1 by the limiter circuit 20.
The input signal is limited so that the influence of the rounding of the signal waveform existing when the signal is read from the magneto-optical disk is prevented. Therefore, even when the data written by the mark edge recording method is reproduced, it is possible to accurately reproduce the data without being adversely affected by thermal diffusion or the like.

[0036]

As described above, according to the present invention, when the modulation code recorded by the mark edge method is reproduced by the differential voltage method, the conversion point such as the Kerr rotation angle can be accurately detected, and the error rate can be improved. Highly accurate reproduction with low

[Brief description of drawings]

FIG. 1 is a block diagram showing a latter part of a circuit configuration as an embodiment of the present invention.

FIG. 2 is a block diagram showing a front stage portion of the circuit configuration shown in FIG.

FIG. 3 is an explanatory diagram showing a detailed configuration of a limiter circuit.

FIG. 4 is an explanatory diagram showing a relationship between a difference voltage value at a conversion point in a maximum frequency signal and a limit value of a voltage to be limited.

FIG. 5: RLL (1,7) with a minimum pit length of 0.64 μm
FIG. 6 is a characteristic diagram showing a relationship between a voltage limiting variable α and S / N when reproducing a modulation code.

6A to 6C are waveform diagrams showing signal waveforms obtained in the portions shown in FIGS. 2A to 2C, respectively.

7A to 7C are explanatory diagrams showing signal waveforms read from a magneto-optical disk or the like by a difference detection method in a conventional device.

FIG. 8 is an explanatory diagram of a reading method by amplitude detection.

FIG. 9 is an explanatory diagram of a reading method by differential voltage detection.

[Explanation of symbols]

 11 Capacitor 12 RF Amplifier 13 Noise Filter 14 Waveform Equalizer 15, 26 Differential Amplifier 16 Low Pass Filter Circuit 17, 28 Comparator 18 Edge Detection Circuit 19 PLL Circuit 20 Limiter Circuit 25 Delay Circuit 27 Absolute Value Circuit 29 Demodulator D1, D2 Diode R Resistance (A) Self-clock generation path (B) Differential voltage detection path

Claims (2)

[Claims] 1. A difference detection unit for detecting a difference in signal intensity of read data obtained by detecting return light of light irradiated on an information recording medium on which digital data is recorded,
In the signal reproducing device in which the conversion point of the recorded state of the data is detected by the output from the difference detecting section, a signal limiting section for limiting the signal strength of the read data is provided, and the data passing through the signal limiting section is subjected to the above-mentioned operation. A signal reproducing apparatus characterized in that a difference in signal strength is detected by a difference detecting section. 2. The limit width between the upper limit and the lower limit of the intensity of the read data limited by the signal limiting unit is equal to or less than the maximum value of the change width of the signal intensity at the conversion point of the highest frequency signal of the read data. The signal reproducing device according to claim 1.