JPH03178038A - Optical recording and reproducing system - Google Patents

Abstract

PURPOSE:To adaptably compensate deterioration of recording and reproducing characteristics by providing a recording system with a waveform equalization means for performing an adapting operation to form a feedback loop from a reproducing system. CONSTITUTION:A waveform equalizer 5 capable of varying a frequency characteristic in accordance with a tap coefft. signal with an input of a regenerative signal is provided, and an optimum tap coefft. of the waveform equalizer 5 is compared by a recording power control circuit 7 with a tap coefft. for an ideal data by reference signal E from a reference signal circuit 9, and an error signal as their difference is outputted as a recording power control signal C. In this case, for generating a multivalued pulse group, a pulse amplitude of each tap is decided in accordance with the polarity and size of the error signal with a center of a preset average amplitude level. By this method, the deterioration of the recording and reproducing characteristics due to characteristic variations of an optical disk medium and a head and changes with the lapse of time, etc., can adaptably by compensated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording/reproducing method in an optical disk device.

[Conventional technology]

Conventional optical recording and reproducing systems will be described below, taking as an example a magneto-optical disk which is a particularly erasable type of optical recording and reproducing disk.

Conventionally, in magneto-optical disk drives, information is recorded using thermomagnetic recording, in which a recording medium made of a magnetic thin film is irradiated with focused laser light in accordance with an information data string, and information is recorded as changes in magnetization on the recording medium. be exposed. Therefore, the distribution of heat caused by the recording laser spot focused on the recording medium moving at the linear velocity V can be considered to be the shape of the recording pit directly recorded on the recording medium.

FIG. 6 is a diagram for explaining recording pit formation by a conventional recording method, and shows recording current, recording pits, and reproduction signals. The recording pit shape is created by heat flow in the direction of travel of the recording laser spot, and by the laser-driven rectangular recording current (
(recording power) shows a so-called waveform. The size of the recording pit also occurs depending on the level of recording power. Therefore, the recording medium has an optimum recording power, and it is necessary to adjust the recording power between the recording medium and the head in advance.

On the other hand, a method for reading information is, for example, when a linearly polarized laser beam is irradiated onto a magnetic recording pattern, the effect of rotating the plane of polarization of the reflected light or transmitted light (called the magnetic Kerr effect and magnetic Faraday effect, respectively) For example, when using the magnetic Kerr effect, the rotation angle θ of the polarization plane of the reflected light differs depending on the direction of recording magnetization, so that the reflected light can be detected by the photodetector. Before entering the light, it is passed through an analyzer and information corresponding to the direction of magnetization is read out as changes in the amount of light. That is, in the conventional method for reading information in such a magneto-optical disk device, the area where the magnetization has changed on the surface of the recording medium becomes a bright or dark area (hereinafter referred to as a recording edge). This is basically equivalent to a method in which a reproduced signal is read out by detecting a change in the amount of light reflected from a recording pit in a reflectance change type optical disk device.

To identify the reproduction of digital information, a slice level is set near the midpoint of the read signal amplitude as shown in FIG.
The recording pit information is pulsed from the recording pit string. At the same time, detect the peak values corresponding to "0°" and "1°" of the readout waveform, and determine the "O" and "l" patterns from the timing relationship between the pit information and the reproduced clock determined by various modulation methods. and performs information reproduction of the source data.

[Problem to be solved by the invention]

As described above, thermomagnetic recording is used as a method for recording information in conventional magneto-optical disk devices. Therefore, in a system where the linear velocity is constant, the optimum recording power must be set experimentally in advance.

Therefore, it has not been possible to deal with changes in recording media, semiconductor lasers, etc. over time. Therefore, there is a drawback that the SN ratio decreases and there is no recording/reproducing margin.

Furthermore, if the recording power is higher than the optimum recording power when the recording density is high, thermal interference between recording pits will increase.
There is a possibility that recording pits may be connected and a recording error may occur. Furthermore, if the recording power is lower than the optimum recording power, the reproduction SN ratio will be low and the pit error rate will deteriorate.

This can be seen from the fact that when the recorded pits have a waveform as shown in FIG. 6, jitter and peak shift occur at the time of slicing the reproduced signal. When the recording power deviates from the optimum value in this way, the shape of the recording pit deviates from the optimum shape, causing distortion of the reproduced signal.

On the other hand, due to the medium interchangeability that is a feature of magneto-optical disks,
Recording and reproducing conditions differ, such as individual variations in characteristics of the head and recording medium, and non-uniformity in recording medium film characteristics. As a result, there are drawbacks such as the inability to fully demonstrate the device performance, which places great restrictions on increasing the recording density, resulting in a drawback that the applications of the optical disk device are narrowed.

The purpose of the present invention is to improve the above-mentioned drawbacks and provide an optical recording and reproducing method that can adaptively control recording and reproducing conditions, keep the reproduced signal stable and of good quality, and improve recording density. There is a particular thing.

[Means to solve the problem]

The present invention relates to an optical recording/reproduction method in which a laser is used as a light source and a pit train is used to perform recording and reproduction, and the present invention provides a recording pulse modulation means for inputting an information data sequence and a recording control signal and converting it into a data sequence of a multi-value pulse group; a writing device that receives the output from the pulse modulation device as an input and records information data on a recording medium; a reading device that reads the information data on the recording medium and outputs a reproduction signal; and a tap that receives the reproduction signal as an input. a waveform equalization means whose frequency characteristic is variable according to the coefficient signal; an error extraction means for extracting an error signal from the output of the 1111 waveform equalization means and a preset reference determination level; and an output of the error extraction means. Equalizer control means receives a signal and outputs the tap coefficient signal that controls the frequency characteristics of the waveform equalization means, and converts and outputs the recording control signal from each tap coefficient signal of the equalizer control means. It is particularly important to include a recording control means.

[Effect]

According to the present invention, since a feed-hack loop from the reproduction system is formed in the recording system, the optimum recording power can always be obtained. Therefore, it becomes possible to record with a stable recording focus and a good shape.

Further, by providing a waveform equalization means that performs an adaptive operation, it becomes possible to adaptively compensate for deterioration in recording and reproducing characteristics due to variations in characteristics of optical disk media and heads, changes over time, and the like.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, a case of binary data using a recording/reproducing method called mark length recording will be described as an example.

This optical recording and reproducing method includes a recording pulse modulation circuit 1 which inputs an information data string and a recording control signal and converts it into a data string of a multivalued pulse group, and an output from this recording pulse modulation circuit 1 which inputs an information data string and a recording control signal. a writing device 2 for recording information data on the recording medium 3; a reading device 4 for reading the information data on the recording medium 3 and outputting a reproduction signal; A waveform equalizer 5, a reference signal circuit 9 that outputs a preset reference signal and a reference determination level, and a waveform equalizer 5.
an error extraction circuit 8 that extracts an error signal from the output of the output and a reference determination level preset by the reference signal circuit 9; and the output signal of the error extraction circuit 8 is input to control the frequency characteristics of the waveform equalizer 5. an equalizer control circuit 6 that outputs a tap coefficient signal to be used, and a recording power control circuit 7 that converts and outputs a recording control signal from the reference signal from the reference signal circuit 9 and each tap coefficient signal of the equalizer control circuit 6. It is configured.

Next, the operation of this embodiment will be explained.

The recording pulse modulation circuit 1 converts the information data string A modulated according to the encoding rule into a data string B of a group of multivalued pulses. In order to determine the characteristics of the recording pulse modulation circuit 1,
For example, it is constructed from four recording taps, a multiplication circuit and an addition circuit. That is, the time width of each pulse of the multivalued pulse train B is fixed to 1/4 of the time width T corresponding to the mark length,
The amplitude is calculated from the recording control signal C input to each recording tap.

FIG. 2(a) shows an information data string A, and FIG. 2(a) shows a data string B converted into a multilevel pulse group. At this time, the recording power control circuit 7 that determines the recording control signal C of each recording tap uses the output signal of the equalizer control circuit 6 that outputs each tap control signal that optimizes the frequency characteristics of the waveform equalizer 5. Use.

That is, the recording power control circuit 7 compares the optimal tap coefficient of the waveform equalization 235 with the tap coefficient for ideal data based on the reference signal E from the reference signal circuit 9, and uses the difference signal as the recording power control signal. Output as C. At this time, if a symmetrical 7-tap transversal filter is used as the waveform equalizer 5, an error signal of 4 taps from the center tap will be output, for example.

At this time, the recording pulse modulation circuit 1 uses the input error signal for four taps to generate a multi-value pulse group in order to bring the recording power closer to the optimum power according to its polarity and magnitude, and increases or decreases the recording power. conduct. That is, to generate a multivalued pulse group, the pulse amplitude of each tap is determined based on the polarity and magnitude of the error signal around a preset average amplitude level. Regarding the time width of each tap of the multi-value pulse group, as mentioned above, the pulse width T of the mark length is 4
1/1 will be allocated. Recording of the converted data string B generated in this manner onto the recording medium 3 is performed by a writing device 2 including an optical head and a laser drive circuit.

Information data on the recording medium 3 is read by a readout device 4 including an optical head and a reproduction amplifier system for outputting as a reproduction signal. With this reproduced signal F as input, the waveform equalizer 5 whose frequency characteristics can be varied according to the tap coefficient signal from the equalizer control circuit 6 reproduces 13
The signals are optimally equalized and output as the signal G.

The error extraction circuit 8 extracts an error No. 13 I from the signal G and the reference determination level II preset in the reference signal circuit 9 and sends it to the equalizer control circuit 6.

FIG. 3 shows an example of a seven-tap configuration of a typical transversal filter as the waveform equalizer 5.

Here, Z-1 means a delay element, and Co.

C1, . . . , Cb mean multiplier coefficients (tap coefficients), and the operation results are respectively added by an adder. The delay time involved in the calculation of each tap is completed within the time that can be absorbed by the delay element.

Next, an algorithm for determining frequency characteristics by adjusting tap coefficients when a transversal filter is used as the waveform equalizer 5 will be described. In order to minimize the intersymbol interference included in the output signal of the transversal filter, the equalizer control circuit 6 adjusts the frequency characteristics of the transversal filter so that the reproduced signal and the error component are uncorrelated. MSE (Mean 5quar
eError) method.

M Z F (Modified Zero Force
A number of algorithms are known, such as the ing) method.

As an example, the MSE method will be explained. The transversal filter control circuit repeatedly calculates the correlation between the signal of each tap of the transversal filter and the error component, and subtracts a minute amount proportional to the correlation from each tap coefficient. If the vector whose elements are each tap coefficient at time j is C(j), the coefficient of each tap is c
(j+1)=C(j)−αΣE(j)H(j)...(
1) The second term on the right side of equation (1), which is controlled by the relational expression 0, is proportional to the correlation. Here, α is a predetermined positive constant. As a result, the correlation between the error signal and the reproduced signal gradually decreases.

In addition, as a simple method, Σ in the second term can be omitted and further E (
j) There is also a method of using only the sign of H(j).

In this case, the circuit that provides C(j) in the above equation can be easily constructed by using an amplifier down counter and switching increase/decrease depending on the sign of E(j)H(j).

At this time, the correlated component is thermal interference related to recording and reproduction.

This reflects various types of interference, such as code amount interference and crosstalk from adjacent tracks.

In order to form a feedback loop from the reproduction signal in the recording circuit as in this embodiment, the optical recording power of each tap of the multilevel pulse group is adjusted to minimize the magnitude of the error signal for recording control. The information data is recorded onto the recording medium using the optimum recording power.

FIG. 4 shows the formation of recording pits according to this embodiment. A recording current, which is a laser drive current, modulates an information data string by the above-mentioned multi-value pulse group. In this way, by increasing the recording power of the leading pulse, thermal recording on the recording film is improved and the recording pits have an ideal shape that reflects the shape of the focused beam.

Therefore, the reproduced signal also reflects only the waveform interference, and ideal reproduction is possible.

FIG. 5 shows another example of conversion of recorded data according to the method of the present invention. FIG. 5(a) shows an information data string, and FIG. 5(b) shows a data string converted to a multi-value pulse group. show.

In the embodiment described above, the time width of each tap of the multilevel pulse group was fixed to 1/4 of the time width T of the mark length. However, since thermal recording is used for recording, a variable time width method may be used as long as the time width x light pulse intensity is the same. Therefore, a method was adopted in which pulse train recording was performed by making the time width of the first tap of the multivalued pulse group one quarter of the time width T of the mark length, and making the other three taps smaller than one quarter. That is, as shown in the figure, the pulse width can be set in advance for each tap, and the optical recording power of each tap of the multi-level pulse group can be optimally controlled in the same manner as in the previous embodiment using feedback from the reproduction side. It becomes possible. According to this, since the time width of the first pulse is larger than the other pulses, the time width×light pulse intensity can be increased, and the edge of the recording focus can be recorded more clearly than in the embodiments described above.

In the above example, 4-tap pulse modulation was used, but
Settings can be made as finely as the circuit scale and cost allow, and accurate optimal recording power control is possible.

In addition, in the present invention, the r1 dynamic setting of the optimal recording pinot can be set even when recording data, but in order to improve the reliability of the data itself, it is set between preamble 1υ1 before the recording data area. This can also be done by providing a power setting area (sector or track).

〔Effect of the invention〕

As explained above, the optical recording and reproducing method of the present invention forms a feed bank loop from the reproducing side in the recording system.
It becomes possible to constantly optimize recording and reproducing characteristics. Therefore, it is possible to apply the present invention to systems in which the linear speed of the disk changes.

Also, variations in characteristics of optical disk media and heads.

Since it becomes possible to adaptively compensate for deterioration in recording and reproduction characteristics due to changes over time, etc., stable and high-quality recording and reproduction is always possible. In this way, optimum recording and reproduction can be performed at all times, so that high recording density of information can be stably realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the optical recording and reproducing method of the present invention, FIG. 2 is a diagram for explaining an example of data conversion related to the optical recording and reproducing method of the present invention, and FIG. , a diagram for explaining a configuration example of a transversal filter according to the optical recording and reproducing method of the present invention, FIG. 4 is a diagram for explaining recording pit formation according to the optical recording and reproducing method of the present invention, and FIG. FIG. 6 is a diagram for explaining another example of data conversion according to the optical recording/reproducing method of the present invention. FIG. 6 is a diagram for explaining recording pitch formation by a conventional recording method. l...Recording pulse modulation circuit 2...Writing device 3...Recording medium 4...Reading device 5...Waveform equalizer 6... Equalizer control circuit 7... Recording power control circuit 8... Error extraction circuit 9... Reference signal circuit type G

Claims (1)

[Claims] (1) In an optical recording and reproducing method that uses a laser as a light source and performs recording and reproducing using a pit train, the recording pulse modulation means converts an information data train and a recording control signal into a data train of a multivalued pulse group as input, and the recording pulses. a writing device that receives the output from the modulation device as an input and records information data on a recording medium; a reading device that reads the information data on the recording medium and outputs a reproduction signal; and a tap coefficient that receives the reproduction signal as an input. a waveform equalization means whose frequency characteristics are variable according to the signal; an error extraction means for extracting an error signal from the output of the waveform equalization means and a preset reference judgment level; and an output signal of the error extraction means inputted. equalizer control means for outputting the tap coefficient signal for controlling the frequency characteristics of the waveform equalization means; and recording control means for converting and outputting the recording control signal from each tap coefficient signal of the equalizer control means. An optical recording and reproducing method characterized by having the following.