JPH10188286A - Laser erasing power setting method for recording and reproducing device of phase change disk, and recording and reproducing device for phase change disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily set erasing power and to optimize laser power by storing each power when a reproduced signal mark level exceeds or does not exceed a threshold value respectively, and setting the erasing power by using the stored value. SOLUTION: After a mark is recorded in a track (a), a value obtained by experiment is defined as an initial value of erasing power Pe, then a laser is emitted, a signal is reproduced from a track (a), it is compared with a reference value by a discriminating circuit 3, and the result is latched by a latch circuit 4, sent to a system control circuit 5 to discriminate whether a level is H (high level) or L (low level). Then respective values of erasing power Pe when an output of the discriminating circuit 3 is changed from L to H and from H to L increasing minute quantity of erasing power Pe are stored, and erasing power Pe to be set is calculated. When the range between both values is divided and erasing power Pe is set, a weighted average value by division ratio of α/β is defined as the erasing power Pe value, so that an optimum value can be obtained by selecting α and β adequately.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing apparatus for a phase change type disc, and more particularly to a method and an apparatus for setting a laser erasing power in such a recording / reproducing apparatus.

[0002]

2. Description of the Related Art A recording method in an optical recording / reproducing apparatus can be classified into two types, write-once recording and rewritable recording, according to the type of recording film (recording medium) of a disk to be used. Can be further divided into magneto-optical recording and phase change recording.

An optical recording / reproducing apparatus to which the present invention is applied performs recording / reproducing by a phase change recording method, and has a reflectance depending on whether a recording film is in a crystalline state or an amorphous state. They use things that change.

When a signal is recorded on a disk using this type of recording / reproducing apparatus, a recording system circuit as shown in FIG. 10 is used. This circuit converts a data bit string into an encoder 1
After being encoded by 1 and amplified by the drive amplifier 12, it is supplied to the optical head 13, converted into light (laser), and projected onto a disk.

[0005] When reproducing a signal recorded on a disk, a reproduction system circuit as shown in FIG. 11 is used.
This circuit is a circuit for projecting a laser beam for reading onto a disk surface, receiving a signal modulated by a signal recorded on the disk surface with the optical head 21, decoding and outputting the signal.

The optical head 21 converts the received optical signal into an electric signal and sends it to the amplifier 22. The amplifier 22 amplifies the weak signal sent from the optical head 21 and sends it to the waveform equalizer 23. The waveform equalizer 23 outputs the reproduced signal to the waveform shaper 24 excluding intersymbol interference. The signal shaped by the waveform shaper 24 is sent to the discriminator 26, and the discriminated binary (mark / space) signal is sent to the decoder 27,
Output the decoded signal.

The signal recording and reproduction in the optical recording / reproducing apparatus have been briefly described above. However, since the system configuration of the optical recording / reproducing apparatus is not directly related to the present invention, detailed description is omitted. Next, recording and erasing of signals in this type of recording / reproducing apparatus will be briefly described.

In recording using a phase change (transition) of a recording film on a disk, first, the entire recording film is heated and sufficiently crystallized, and the recording film is irradiated with a laser beam to thereby heat the recording film. It is recorded by making it amorphous. The crystallization temperature is, for example, 400 ° C., and the amorphization temperature is, for example, 600 ° C. By associating the crystalline state with a space (logic "0") and the amorphous state with a mark (logic "1"), a signal can be recorded by irradiating the recording film of the disk with laser light to cause a phase change. Can be.

FIG. 6 shows an emission waveform of the laser. In the figure, (a) is a clock signal, and the repetition period is T. (B) is a test signal to be recorded on the disk, which is a data signal having a mark length of 8T. (C) is a laser emission waveform at the time of recording. (D) is a laser emission waveform when DC emission is performed as the output power Pe of the laser diode (laser light source).

FIG. 7 shows a reproduced waveform when the power Pe is gradually increased. In FIG. 7, a signal La is a signal level at which the recording film is in an amorphous state, and Lt is a reproduced signal in the discrimination circuit. Lc, which is a threshold value when compared with the threshold value by the comparator, represents a signal level at which the recording film becomes in a crystalline state.

In FIG. 1, (a) is a latch pulse sent from the system control circuit to the latch circuit to latch the mark / space signal discriminated by the discrimination circuit described later with reference to FIG. (B) is a reproduced signal waveform immediately after the 8T mark is recorded. As shown, the mark is at the signal level La in the amorphous state, and the space is at the signal level Lc in the crystalline state. In this state, when the reproduced signal is compared with the threshold Lt by the comparator of the discrimination circuit, the mark (high level H) and the space (low level L) can be clearly distinguished, and accurate reading can be performed.

When the mark signal is erased by slightly increasing the power Pe, as shown in FIG. 3C, the 8T mark disappears by half, the mark level becomes lower than the threshold value Lt of the comparator, and the mark signal is output to the output of the discrimination circuit. Will not be detected. Further, when the power Pe is increased, the mark is completely erased as shown in FIG. 3D, and the recorded signal is lost.

When the power Pe is further increased, as shown in FIG. 1E, the recording medium of the disk starts to change from a crystalline state to an amorphous state, and its value approaches the threshold value Lt of the comparator in the discrimination circuit. If the power Pe is further increased, the traced portion becomes completely amorphous, and as shown in FIG.
When compared with, the whole becomes a mark signal.

As is clear from the above description, the erasing power for erasing the signal on the disk must not be too low, but must not be too high. It is necessary to measure the power required to make the recorded signal completely disappear, and to set the erasing power to that power.

[0015]

In recent years, with the shortening of the recording wavelength, the recording has been more susceptible to the influence of the ambient environment temperature and the unevenness of the sensitivity of the disk during recording. Laser recording is used for the drive of the phase change disk and the drive of the magneto-optical (MO) disk. Therefore, the optimum recording cannot be performed by the recording method in which the recording power is fixed regardless of the ambient environment temperature and the sensitivity of the disk. Sometimes.

As one countermeasure against this, there is a method of setting the optimum recording power by performing test writing on a disk to be recorded before recording.
This is performed in recording on an MO disk. However, to apply this to a phase change disk, it is necessary to optimize not only the recording power Pw but also the erasing power Pe.

This is because the erasing ratio of the MO disk monotonically increases with the erasing power as shown in FIG.
This is because, as shown in FIG. 9, the phase-change disk has an upwardly convex characteristic with respect to the erasing power.

This situation will be described in more detail with reference to FIG. 8. As shown in FIG. 8, the erasing ratio of an MO (magneto-optical) disk starts at a certain point when the erasing power Pe is increased from zero. Erasure begins and the erasure ratio increases logarithmically.
In this case, the point where the erasing ratio is 40 dB or more is selected as a point having no practical problem.

In contrast, the erasing ratio of a phase change disk is generally as shown in FIG. 9. When the erasing power Pe is increased from zero, the erasing ratio sharply increases from a certain point, and thereafter becomes constant. When the erasing power Pe is further increased, the erasing ratio sharply decreases. Therefore, a range where the erase ratio is 25 dB or more is selected as a range where there is no practical problem, and the erase power P
Set e to a value within this range.

In the above description, the data signal recorded on the disk is traced by a laser emitting DC (direct current), the data signal is erased, and a new signal is written after erasing. In this method, an operation for erasing and an operation for recording are required.

On the other hand, the recording method described below is
By overwriting a new data signal on an old data signal recorded on the disk, the old signal can be erased and a new signal can be written.

5A shows a clock pulse having a period T, FIG. 5B shows a test recording signal including 2T marks and spaces, and FIG. 5C shows a laser emission waveform at the time of recording 2T data. In this laser waveform, Pw represents the power for amorphizing the phase change disk, that is, the recording power, and Pe represents the power for crystallizing the phase change disk, that is, the erasing power.

(D) shows a test recording signal composed of a repetition of a 7T mark and space, and (e) shows a laser emission waveform at the time of recording 7T data. Similarly, in this laser emission waveform, Pw is the power for amorphizing the phase change disk, and Pe is the power for crystallizing the phase change disk.

5 (c) and 5 (e), the emission waveform of the laser shows an erasing power P with respect to 0 mW shown by a dotted line.
e, on which a binary signal that changes between Pe and Pw is superimposed.

Comparing the light emission waveform of (c) and the light emission waveform of (e), the light emission waveform of the laser is different between the case of the data signal of the mark space of 2T and the case of the data signal of the mark space of 7T. It has a wavy shape. By emitting light with different waveforms according to the recording signal, direct overwrite (direct overwriting) can be performed on the phase change disk.

In this case, recording on the phase change disk is performed in the following procedure. 1. A repetitive signal of 2T mark space as shown in (b) is recorded. 2. Measure the carrier level of the repetitive signal in the 2T mark space. 3. Next, a repetition signal of a 7T mark space is recorded on the signal of the 2T mark space. The carrier level of a repetitive signal in a 4,2T mark space is measured. 5. The erasure ratio of a 2T mark / space repetitive signal is obtained from the carrier level difference measured in the above items 2 and 4.

The above items 1 to 5 are repeated by changing Pe from 0 to a power at which the erase ratio deteriorates. In general, the erasing ratio of a phase-change disk is as shown in FIG. 9. When the erasing power Pe is increased from zero, the erasing ratio sharply increases from a certain point and then becomes constant. The erasure ratio drops sharply. Therefore, a range where the erasing ratio is 25 dB or more is selected as a range having no practical problem, and the erasing power Pe is set to a value within this range.

In the above method, for one measurement point,
Two recording operations are required. That is, recording of a 2T mark / space repetition signal and recording of a 7T mark / space repetition signal.

The present invention overcomes the drawbacks of the recording / reproducing apparatus according to the conventional measuring method and requires only one recording operation and one measuring pattern for one measuring point. It is an object of the present invention to provide a recording / reproducing apparatus that requires only one erasing operation.

[0030]

According to one aspect of the present invention, there is provided an erasing power setting method including the following steps. That is, a first step of recording a test signal on a certain track on the disk, a second step of setting a predetermined laser output power Pe of a magnitude that does not erase the recorded test signal as an initial value, A third step of causing the laser to emit DC light with power Pe to trace the track, reproduce a signal from the track, and compare the mark level of the reproduced signal with a predetermined threshold level; If not, the power Pe is increased by a small amount and the third step is repeated, and when the mark level exceeds the threshold, the power Pe at that time is increased.
A step of storing the power Pe as a first storage value, increasing the power Pe by a small amount, causing the laser to emit DC light with the increased power Pe, tracing the track, reproducing a signal from the track, and reproducing the signal. A sixth step of comparing the mark level of the obtained signal with a predetermined threshold level, a seventh step of repeating the sixth step if the mark level exceeds the threshold level, and a step of repeating the sixth step if the mark level exceeds the threshold level. If not, the power Pe at that time is set to the second
An erasing power setting method for a phase-change disk, the method comprising: setting an erasing power based on the first and second stored values.

In the above method, the eighth step of setting the erasing power based on the first and second stored values may be performed by calculating a simple averaging of the first and second stored values. It can be a step of determining power.

In the above method, the eighth step of setting the erasing power based on the first and second stored values may be performed by calculating a weighted average of the first and second stored values. The step may be a step of determining an erasing power.

According to a second aspect of the present invention, there is provided the following recording / reproducing apparatus. That is, an optical head that records a signal on a recording medium on a disk, and that can read the recorded signal, compares the mark level of the read signal with a predetermined threshold, and the mark level is higher than the threshold. A discrimination circuit for discriminating whether it is low or low, and a system control circuit having a circuit for generating a power control signal to be sent to the optical head based on an output of the discrimination circuit, comprising: The system control circuit sets, as an initial value of the power Pe, a predetermined value of such a magnitude that the recorded test signal does not disappear, and as long as the mark level of the reproduced signal does not exceed the threshold level, the power Pe Is sent to the optical head after a slight increase, and when the mark level exceeds a threshold value, the power Pe at that time is stored as a first storage value, and the power Pe is further stored. Increased small amount, the increased power Pe sent to the optical head, when the mark level is lower than the threshold level, and stores the power Pe at that time as a second stored value,
There is provided a recording / reproducing apparatus for a phase change disk, wherein an erasing power is set based on the first and second stored values.

In the above apparatus, the means for setting the erasing power based on the first and second stored values includes a circuit for calculating a simple average or a weighted average of the first and second stored values. be able to.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a phase change disk recording / reproducing apparatus according to the present invention will be described with reference to FIG. FIG. 1 shows only a reproduction system circuit, and includes an optical head 1, a reproduction amplifier 2, a discrimination circuit 3, a latch circuit 4, and a system control circuit.

The data signal recorded on the disk is read by the optical head 1 and the read signal is amplified by the reproducing amplifier 2 and compared with the reference value by the comparator of the discrimination circuit 3 to determine whether the state of the signal is mark or space. Decide. The output of the discrimination circuit 3 is latched by a latch circuit 4 and a system control circuit 5 determines whether the signal level is H (high) or L (low).
Tell At this time, the value latched by the latch circuit is latched based on the latch control signal sent from the system control circuit 5.

The system control circuit 5 checks the state of the signal sent from the latch circuit 4 and issues a laser power control signal for the optical head. Next, the operation of this reproduction system circuit will be described with reference to FIG.

In step S0, the operation starts, and in step S1, a mark of about 8T is recorded on one track a. At this time, the condition for the length of the mark may be anything as long as the latch timing is not severe. When the track a is read as it is, the output of the comparator becomes H.

After the mark is recorded, the flow advances to step S2 to set an initial value of the erasing power Pe. This initial value setting is based on the approximate value P1 which has been previously examined by experiments.
And substitute this value for Pe. The value of P1 can be any value as long as the recorded signal will not disappear.

In step S3, the laser is caused to emit DC light with the above erasing power Pe, and the track a is traced using the laser light. Proceeding to step S4, the signal is reproduced from the track a, compared with the reference value by the comparator of the discrimination circuit, and the comparison result is latched in the latch circuit 4,
The latched value is sent to the system control circuit.

Proceeding to step S5, the system control circuit 5
Determines whether the output of the comparator sent from the latch circuit 4 is H (high level) or L (low level).
If L, the process proceeds to step S6, the erasing power Pe is increased by a small amount ΔP, and the process returns to step S3.

While the output of the comparator is L, the operations of steps S3 to S6 are repeated. When the output of the comparator becomes H, the process proceeds to step S7, and the erase power Pe at that time is stored as Pe (low).

In step S8, the erasing power Pe is set to Δ
Increase by P. The laser emits DC light again with the power Pe to trace the track a. Proceeding to step S10, a signal is reproduced from the track a, and the output of the comparator is determined in step S11. If the output is H, the process returns to step S8, and steps S8 to S11 are repeated to further increase the power Pe. .

When the output from the comparator is determined to be L in step S11, the process proceeds to step S12, and Pe at that time is stored as Pe (high). Proceeding to step S13, Pe to be set is calculated. This calculation is a simple averaging of Pe (low) and Pe (high),
That is, Pe = (Pe (high) + Pe (low)) / 2.

In the setting of the erasing power, Pe (h
FIG. 3 and FIG. 4 show the relationship between (high) and Pe (low). As described above, Pe (low) is the power Pe at the point where the output of the comparator changes from L to H.
Pe (high) is the value of the power Pe when the erasure is not performed as a result of increasing the power Pe.

The erasing powers are Pe (low) and Pe (hi).
gh), and FIG. 3 shows a case where the value is determined by simply taking an average value. FIG.
Indicates a case where the point between Pe (low) and Pe (high) is selected to be divided into α and β. In this case, the weighted average value by α and β is {β * Pe (low) + α * Pe (high)} / (α
+ Β). Here, by appropriately selecting the values of α and β, an optimal value can be set as the erasing power.

[0047]

Since the recording / reproducing apparatus of the present invention includes the above-described erasing power setting circuit, the erasing power can be easily set, and the laser power can be easily optimized by the system control circuit.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a reproducing system circuit of a recording / reproducing apparatus according to the present invention.

FIG. 2 is a flowchart of an erasing power setting operation of the recording / reproducing apparatus of the present invention.

FIG. 3 is an erasing characteristic diagram of a phase change recording medium.

FIG. 4 is an erasing characteristic diagram of a phase change recording medium.

FIG. 5 is a waveform diagram of a test recording waveform.

FIG. 6 is a waveform diagram of a test recording waveform.

FIG. 7 is an explanatory diagram of recording and erasing of a phase change disk.

FIG. 8 is a characteristic diagram showing an erasing ratio of an MO disk.

FIG. 9 is a characteristic diagram showing erasing characteristics of a phase change disk.

FIG. 10 is a block diagram of a recording system circuit of the phase change disk recording / reproducing apparatus.

FIG. 11 is a block diagram of a reproducing system circuit of the phase change disk recording / reproducing apparatus.

[Explanation of symbols]

1. Optical head, 2. Reproduction amplifier, 3. Discrimination circuit (comparator), 4. Latch circuit, 5. System control circuit

Claims (5)

[Claims] 1. A first step of recording a test signal on a certain track on a disk, and a second step of setting a predetermined laser power Pe of a magnitude that does not erase the recorded test signal as an initial value. A third step of causing the laser to emit DC light with the power Pe, tracing the track, reproducing a signal from the track, and comparing a mark level of the reproduced signal with a predetermined threshold level; If the mark level does not exceed the threshold, the power Pe is increased by a very small amount and the third step is repeated.
a fifth step of storing e as a first storage value; and increasing the power Pe by a small amount.
A sixth step of causing the laser to emit DC light, tracing the track, reproducing a signal from the track, and comparing the mark level of the reproduced signal with the predetermined threshold level; and when the mark level exceeds the threshold level. Then, a seventh step of repeating the sixth step, and if the mark level does not exceed the threshold level, the power Pe at that time is stored as a second storage value, and the first and second storage values are stored. And setting an erasing power based on the erasing power. 8. 2. The method according to claim 1, wherein an erasing power is set based on the first and second stored values.
Is a step of determining an erasing power by calculating a simple averaging of the first and second stored values. 3. The method according to claim 1, wherein an erasing power is set based on said first and second stored values.
The step of determining the erasing power by calculating a weighted average of the first and second stored values. 4. A signal is recorded on a recording medium on a disk,
An optical head capable of reading a recorded signal; a discrimination circuit for comparing a mark level of the read signal with a predetermined threshold to discriminate whether the mark level is higher or lower than the threshold; and the discrimination circuit. And a system control circuit having a circuit for generating a power control signal to be sent to the optical head based on the output of the phase change disk. As the initial value of Pe, a predetermined value is set so that the recorded test signal does not disappear, and the control signal obtained by increasing the power Pe by a small amount while the mark laser of the reproduction signal does not exceed the threshold level. Is sent to the optical head, and when the mark laser exceeds the threshold value, the power Pe at that time is stored as a first storage value, and the power Pe is further stored. The control signal of the increased power is sent to the optical head by a small amount, and when the mark level becomes lower than the threshold level, the power Pe at that time is stored as a second stored value, and the first and second power values are stored. A recording / reproducing apparatus for a phase change disk, wherein the erasing power is set based on the stored value of 2. 5. The apparatus according to claim 4, wherein the means for setting the erasing power based on the first and second stored values comprises a simple averaging or a weighted average of the first and second stored values. Recording / reproducing apparatus for a phase change disk, including a circuit for calculating a phase change disk.