JPH0562191A - Optical memory device - Google Patents

Abstract

PURPOSE:To achieve the large capacity and the high yield of an optical memory device. CONSTITUTION:A modulation is executed, by means of a both-edge modulation circuit 18, so as to provide information on both ends at the front and the rear of a recording pit. The number of sectors per turn is controlled, by means of a Z-CAV format device 27, so as to be increased from the inner circumference toward the outer circumference of a disk. A driving pulse to a semiconductor laser 10 is corrected by means of a driving-pulse correction circuit 19 in such a way that the length of the recording pit does not become long. In addition, the characteristic of a cosine equalizer 24 is changed over between the central part and the outer circumference of the disk, and the compensation of a reproduced waveform is kept good.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical memory device, and more particularly to improvements for large capacity and high speed.

[0002]

2. Description of the Related Art FIG. 1 shows a recording system of an optical memory device.
The pit position recording method shown in (a) and FIG. 1 (b)
The double-edge recording method shown in FIG.

The pit position recording system is also called an inter-mark recording system. As can be seen from FIG. 1A, one mark corresponds to one modulation bit 1, and the modulation bit 1 is "1". Only when, mark 2 is written. At the time of reading, the peak position of the reproduction signal 3 is detected and the read information 4 is obtained.

On the other hand, the double-edge recording method is also called a mark length recording method. As can be seen from FIG. 1B, one modulation bit 1 is associated with each of the leading edge and the trailing edge of the mark, and modulation is performed. The recording data 5 is inverted every time when “1” comes to the bit 1 and the mark 6 is written while the recording data 5 is “1”. At the time of reading, the read signal 7 is second-order differentiated and its zero-cross point is detected to obtain the read information 4 corresponding to the leading edge and the trailing edge of the played signal 7.

Therefore, the double-edge recording method is suitable for high-density recording because one mark has 2-bit information as compared with the pit position recording method.

Next, as a disk format, FIG.
The CAV format shown in (a) and the Z-CAV format are known.

In the CAV format, the recording area of the disk 8 is divided in the circumferential direction into several areas, that is, sectors 9
When setting, track 1
The number of sectors per cycle is constant.

On the other hand, since the Z-CAV format has a higher linear velocity on the outer circumference of the track, the number of sectors per one circumference of the track is increased from the inner circumference to the outer circumference.

Therefore, the Z-CAV format is
It can be said that it is more suitable for high-density recording than the CAV format.

However, in the conventional optical memory device, there is no example in which both the double-edge recording system and the Z-CAV format are adopted at the same time, and there is a limit to increase in capacity and speed.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, it is an object of the present invention to provide an optical memory device suitable for large capacity and high speed.

[0012]

In order to achieve the above object, the optical memory device of the present invention according to claim 1 is configured so that information is recorded / reproduced on / from an optical disk of a recording medium by an optical head using a semiconductor laser or the like as a light source. In an optical memory device to be performed, both edge modulators that give information to the front and rear ends of a recording pit and a recording area of an optical disc are divided into a plurality of zones in a radial direction, and one zone is formed from an inner zone to an outer zone. A Z-CAV format device for supporting the Z-CAV format for increasing the number of sectors per hit is provided.

In this case, a second aspect of the present invention is characterized in that the optical disc according to the first aspect is an optical disc having a concentric groove.

According to a third aspect of the present invention, between the reproducing circuit for obtaining the reproduced signal from the information written by the double-edge modulation and the demodulating circuit for demodulating the reproduced signal according to the first aspect,
It is characterized by comprising a cosine equalizer whose characteristics change from the inner circumference to the outer circumference of the disk.

According to a fourth aspect of the present invention, in the first aspect, the drive pulse width of the light source is set shorter than the length of the recording data obtained by the double-edge modulator, and the predetermined time is set longer on the inner circumference of the optical disc. , And a drive pulse setting device for switching to shorten the outer circumference.

According to a fifth aspect of the present invention, in the first aspect, the length of the recording data obtained by the double-edge modulator is compared with a set time, and when the length is short, the drive pulse width of the light source is made shorter than the recording data by a predetermined time. In the case of a long drive pulse, a drive pulse setting device for chopping the rear part of the drive pulse at an interval shorter than the drive pulse width is provided.

According to a sixth aspect of the present invention, in the fifth aspect, the drive pulse setting device controls the chopping frequency so that the chopping frequency is increased on the inner circumference and decreased on the outer circumference.

According to a seventh aspect of the present invention, in the first aspect, the drive pulse width of the light source is set to be the same as the length of recording data obtained by the double-edge modulator, and the power of the drive pulse is maximized at the front end of the drive pulse. It is characterized in that it is provided with a drive pulse setting device that decreases as it goes to the rear end.

According to an eighth aspect of the present invention, in the first aspect, the drive pulse width of the light source is set shorter than the length of the recording data obtained by the double-edge modulator, and the power of the drive pulse is maximized at the front end of the drive pulse. It is characterized in that it is provided with a drive pulse setting device that decreases as it goes to the rear end.

[0020]

In the structure of claim 1, the both-edge recording system and the Z-CAV format are simultaneously adopted to realize a large capacity and high speed.

In the structure of claim 2, when the Z-CAV format is used, the clock of the circuit for reading the ID (track and sector information) is switched when accessing the track where the number of sectors is switched. In an optical disc having a spiral groove, the reading of the ID may fail, and thus it takes time to access or the access algorithm becomes complicated, but this does not occur in an optical disc having a concentric circle groove.

In the structure of claim 3, the shortest mark length recorded becomes smaller than the light spot when aiming at the highest recording density in the double-edge recording method, and read information longer than the mark length is obtained during reproduction and demodulation. However, using a cosine equalizer to compensate the reproduced waveform eliminates this problem. However, since the Z-CAV format is adopted, the transfer rate increases from the inner circumference to the outer circumference of the disc, and a cosine equalizer having a constant characteristic loses the compensation effect or the reproduced waveform is distorted. The characteristics are switched between the inner and outer circumferences to always perform good compensation.

When the driving pulse width of the light source is kept the same as the recording data by the double edge recording method, the heating time is longer than that of the pit position recording method and the pit can be written larger than expected. , The position of the rear end of the pit is displaced from the ideal position. Especially in the case of a long pit, the rear part of the pit spreads and distorts into a teardrop shape,
The displacement is large. Further, by adopting the Z-CAV format, the inner circumference of the disk has a longer time corresponding to the pits than the outer circumference, so that the positional deviation is large. Therefore,
In the fourth aspect, the width of the drive pulse is made shorter than the recording data to shorten the heating time, but further, it is further shortened at the inner circumference than at the outer circumference of the disc so that the pit is not written large. In claim 5, the driving pulse width is shortened when it is short due to the length of the recorded data, but when it is long, the amount of heat applied by chopping the rear part of the pulse is reduced without changing the pulse width so that the pit is not written large. To According to the sixth aspect, the number of times of chopping is increased on the inner circumference of the disk to reduce the heating amount, and pit enlargement on the inner circumference of the disk is prevented. In claim 7, the drive pulse width is not shortened, but the power is adjusted to reduce the heating amount at the pulse rear part. According to the eighth aspect, in addition to the power adjustment, the pulse width is shortened to reduce the heating amount at the pulse rear part.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. First, with reference to FIG. 3, a configuration example of an optical head in a magneto-optical memory device utilizing magneto-optical properties in the optical memory device will be described. In FIG. 3, the light emitted from the semiconductor laser 10 is converted into parallel light 12 by a collimator lens 11,
The parallel light 12 passes through a polarization beam splitter 13 and then enters an objective lens 14 to form a light spot on a magneto-optical disk (hereinafter referred to as a disk) 15 having concentric circular grooves. The reflected light from the disk 15 is reflected by the polarization beam splitter 13 and passed to the focus servo system, the track servo system, and the reproducing system.

Next, referring to FIG. 4, an example of the structure of the recording system and the reproducing system for the optical head will be described. 4, in the recording system, the input data 15 corresponding to the modulation bit 1 of FIG.
Is temporarily stored in the buffer memory 16, and the data 17 read from this is converted into recording data 5 (see FIG. 1A) having information on the front and rear edges by the double-edge modulation circuit 18. This recording data 5 is input to the drive pulse correction circuit 19 and given to the semiconductor laser 10 of the optical head as a drive pulse 20. In the reproduction system, the optical signal from the optical head is converted into an electric signal by the photoelectric conversion element 21 to become a reproduction signal 7 (see FIG. 1B), which reproduction signal 7 passes through the amplifier 22 and the low-pass filter 23 to equalize the cosine. After the waveform is compensated by the device 24, it is input to the second-order differentiation circuit 25. The read data circuit 26 detects the zero-cross point of the second-order differentiated signal, and the read data 4 is demodulated. The Z-CAV formatter 27 is in the system control system, and in this embodiment, the disk is divided into three zones in the radial direction as shown in FIG. 2B, and the number of sectors per track is equal to the inner circumference. There are more intermediate zones than zones, and more peripheral zones than intermediate zones. A clock signal and a control signal corresponding to each zone of the Z-CAV format are given to the recording system and the reproducing system.

Next, the cosine equalizer 24 will be described with reference to FIGS. FIG. 5 is a basic circuit diagram of the cosine equalizer, and FIG. 6 is a diagram showing a state of waveform compensation. The basic circuit 41 includes a resistor 29, a variable resistor 31, a delay line 32, and a differential amplifier 33. Composed of. When the reproduction signal before waveform compensation is input to the input terminal 28, it is divided into two at the branch point 30,
One of them is multiplied by K (0 ≦ K ≦ 1) through the variable resistor 31 and input as a time starting point signal 37 to the inverting input terminal of the differential amplifier 33 without time delay. The other passes through the delay line 32 and τ
6 is delayed by the time, and the amplitude remains unchanged.
Is input to the non-inverting input terminal of the differential amplifier 33 as
Since the delay line 32 is present and the input impedance of the differential amplifier 33 is very large, the light is totally reflected at the non-inverting input terminal and returns to the branch point 30. This totally reflected signal is then multiplied by K through the variable resistor 31 and input to the inverting input terminal of the differential amplifier 33. This reflected wave is the reflected delay signal 3 shown in FIG.
6 and the time starting point signal 37 which is not delayed is the delay line 32.
It is delayed by 2τ for the round trip. Here, since the parallel resistance value of the combined resistance of the resistance 29 and the variable resistance 31 matches the characteristic impedance of the delay line 32, no reflection occurs. As a result, at the output terminal 34 of the differential amplifier 33, a signal 40 corresponding to the addition of the delay signal 35, the inverted time origin signal 38, and the inverted reflected delay signal 39 is obtained. This signal 40 has sharper rise and fall time changes than the original reproduction signal, and therefore the zero cross points before and after the second-order differential detection are shifted inward of the pulse, and waveform compensation is applied.

The characteristic of the cosine equalizer 41 described above can be expressed by the following equation (1), and it can be seen that the characteristic can be changed by two variables τ and K. Note that v _i (t) is the input and v _i (t) is
_o (t) is the output.

[0028]

[Number 1] _{v 0 (t) = v i} (t) -K {v i (t + τ) -v i (t-τ)} ... formula (1)

In FIG. 7, four 41A to 41D having different delay times τ in the basic circuit 41 shown in FIG. 5 are arranged in parallel, and one of these outputs v _{OA to} v _OD is signal selector. An example in which the cosine equalizer 24 shown in FIG. 4 is realized by the configuration selected by 42 is shown. Signal selector 42
Uses a 2-bit control signal from the Z-CAV format device to select a circuit having a larger delay time toward the inner circumference of the disk. Note that τ _A <τ _B <τ _C <τ _D
There is.

FIG. 8 shows another example of the structure of the cosine equalizer 24. Six delay lines 32 of the same delay time τ are connected in cascade.
, Six buffer amplifiers 43, two three-input signal selectors 44 and 45, two gain K attenuators 46 and 47, and a three-input operational amplifier 48. The input signal v _i is the buffer amplifier 43 as it is.
, And is input as v ₁ to one inverting input terminal of an operational amplifier 48 through one attenuator 46. Further, the input signal v _i is delayed by τ, 2τ, 3τ respectively, passes through the buffer amplifier 43, and is input to the signal selector 44 as v ₂ , v ₃ , and v ₄ , and any one of them is selected and the non-operation of the operational amplifier 48 is stopped. Input to the inverting input terminal. Further, the input signal v _i is delayed by 2τ, 4τ, 6τ respectively, passes through the buffer amplifier 43, and is input to the signal selector 45 as v ₃ , v ₅ , v ₆ , and any one of them is selected and passed through the other attenuator 47. Operational amplifier 48
Input to the inverting input terminal of. Two signal selectors 4
4 and 45, depending on the content of the 2-bit control signal from the Z-CAV format device, select each v ₂ and v ₃ when the "00", respectively when the "01" v ₃
And v ₅ are selected, and when “10”, v ₄ and v _{6 are selected.}
Select.

[0031] Therefore, when the control signal is "00", the output v ₀ of the operational amplifier _{48, v 0 = -Kv 1 + v} 2 -K
_{v 3 = v i (t +} τ) -K {v i (t) + v i (t + 2
τ)}, and operates as a cosine equalizer with delay time τ.

When the control signal is "01", v ₀
= −Kv ₁ + v ₃ −Kv ₅ = v _i (t + 2τ) −K {v _{i
(T) + v i (τ} + 4)} , and the delay time operates at 2.tau.

When the control signal is "10", v ₀ = -K
v ₁ + v ₄ −Kv ₆ = v _i (t + 3τ) −K {v _i (t) +
v _i (t + 6τ)}, and the delay time is 3τ. In this way, three types of cosine equalizers of τ, 2τ, and 3τ are realized, and the inner periphery of the disk is switched to a larger delay time by the control signal.

Next, claim 4 of the drive pulse correction circuit 19
An embodiment according to will be described with reference to FIGS. In this embodiment, as shown in FIG. 9, the pulse width of the drive pulse 20 for the semiconductor laser is set shorter than the pulse width of the recording data 5 by a predetermined time T ₁ . This required time T
_As shown in FIG. 10, ₁ corrects the deviation amount of the reproduction pulse width from the ideal value for obtaining the target reproduction pulse width. As shown in FIG. 11, the time T ₁ is set longer as the inner circumference of the disc is changed, but it may be changed continuously or stepwise according to the track radius. FIG. 12 shows a concrete circuit example. The delay times are τ ₁ , τ ₂ , and
τ ₃ (where τ ₁ <τ ₂ <τ ₃ ) three delay lines 49,
50, 51, four 3-input AND gates 52, one 4-input OR gate 53, and two inverters 54, 5
5 is used, T ₁ = 0 with a 2-bit control signal being “00” on the outer circumference side of the disk, and “1” on the inner circumference side of the disk.
1 ”is T ₁ = τ ₃ , and“ 1 ”is nearer to the inner circumference in the middle.
0 "as T ₁ = τ ₂ , and in the middle part near the outer circumference is“ 0 ”.
1 ”is set as T ₁ = τ ₁ .

Next, claim 5 of the drive pulse correction circuit 19
An embodiment according to will be described with reference to FIGS. If the drive pulse width is not corrected, as shown in FIG.
When the recording data 5 is short, the pit length is slightly longer than the ideal, but when the recording data 5 is long, the pit length becomes too long and the rear part of the pit spreads to form a teardrop shape. Therefore, as shown in FIG.
Is shorter than the predetermined value T ₀ , the width of the drive pulse 20 is T
_When it is shortened by _{1 and} is longer than T ₀ , the drive pulse width is made the same as the recording data length, but the rear part of the driving pulse 20 is chopped at a frequency higher than the recording data 5. As a result, the pit length and shape approach the ideal one. 14
An example of the relationship between the input data, the recording data and the drive pulse is shown in FIG. In this example, 2-7 RLL is used as the modulation method, and the number of "0" s between "1" and "1" is 2 to 7, so that the driving pulse is 6 as shown in FIG. It becomes a kind. A concrete circuit configuration example is shown in FIG.
6, a comparison circuit 57, and two delay lines 5 having a delay time T _1.
8, 59, three AND gates 60 to 62, and two OR gates 63 and 64. The timing chart of the signals of each part of this circuit is as shown in FIG.
That is, the counter 56 is the length or the pulse width T of the "H" portion of the recording data 5 is detected by the clock 65, the output Q _A to Q _D is some predetermined value T of the comparison circuit 57 the counter 56
Determine if less than or greater than ₀ . When 0 <T <T ₀ , the output S1 of the comparison circuit 57 becomes “H”, and T ₀
When <T, S2 becomes “H”. In this example, T ₀ =
There are four. Then, a signal S3 obtained by delaying the comparison output S1 by T ₁ and a signal S4 obtained by delaying the comparison output S2 by T ₁ are created, and driven by logical processing of these signals S3, S4, the clock 65 and the comparison outputs S1, S2. The pulse 20 is generated, and as shown in FIG. 16, when T <T ₀ , the drive pulse 20 becomes shorter than the recording data 5 by T ₁ ,
_{When 0} <T, the rear part of the drive pulse 20 is chopped at the clock frequency.

In the circuit of FIG. 15, the number of chopping pulses can be changed by changing the predetermined value T ₀ .
Therefore, as an embodiment according to a sixth aspect, switching control is performed by a control signal from the Z-CAV format device so that T ₀ is small at the inner circumference of the disk and large at the outer circumference according to the track to be accessed.

Next, an embodiment according to claim 7 of the drive pulse width correction circuit 19 will be described with reference to FIGS. FIG. 17 shows a first circuit example. With respect to the recording data 5 as shown in FIG. 18, a pattern generator 67 generates a digital signal having a waveform 66 shown in FIG. 18, and the output thereof is outputted by a D / A converter 68. It is converted into an analog signal and used as a drive pulse for the semiconductor laser through the current drive circuit 69. FIG. 19 shows a waveform example a generated by the pattern generator 67.
~ E are shown. By using the circuit shown in FIG. 17, the drive pulse according to claims 4 and 5 can be generated depending on how the pattern is formed.

FIG. 20 shows a second circuit example, and FIG. 21 shows the signal waveform of each part. Reference numerals 70, 72 and 77 are operational amplifiers. The recorded data 5 becomes “H” at the portion where the pit is written, and is input to the bases of the transistors 71 and 80, and its inverted data 86 is input to the base of the transistor 81. V ₁ is a voltage for determining the rising current of the pulse, the transistor 71 is off when the recording data 5 is “L”, and the collector 73 thereof is V ₁ . When it is "H", it turns on and becomes zero volt. The analog switch 84 is closed when the inverted data 86 is “H”, and the operational amplifier 7
The voltage of the positive input terminal 75 of 7 becomes a predetermined value V ₂ . Then, when the recorded data 5 becomes “H”, as shown in FIG. 21, the positive input terminal of the operational amplifier 77 lowers from V ₂ to V ₁ ,
After that, it rises to V _{2 with a} time constant determined by the capacitor 74 and the resistor 76. Operational amplifier 77 and transistor 7
9. The constant current source of the pulse current I _P is constituted by the resistor 78 and the resistor 78, and the pulse current I _P is switched by the circuit composed of the transistors 80 and 81 and the resistors around the transistors 80 and 81. Then, the recorded data 5 is “H” and the inverted data 86 is “L”.
At this time, the transistor 80 is turned off, the transistor 81 is turned on, and the pulse current I _P flows into the semiconductor laser 82. In the opposite case, the current does not flow into the semiconductor laser 82 and the resistor 8
I _P flows to 6. The circuit 83 is an APC (Automatic Powe
r Control) circuit, which monitors the optical output of the semiconductor laser 82 with a photodiode (not shown) and controls the bias current I _b so as to obtain a constant output. From the above, as shown in FIG. 21, when the recording data 5 is “L”, the bias current I _b flows in the semiconductor laser 82, and when the recording data 5 is “H”, I _b + I _P1 at the rising edge thereof.
Flows and decreases with the lapse of time to become I _b + I _p2 . However, I _P1 > I _p2 , I _P1 is determined by V ₂ −V ₁ , and I _p2 is determined by V ₂ .

Next, claim 8 of the drive pulse correction circuit 19
An example according to FIG. 22 will be described. That is, the drive pulse 20 whose width is shorter than that of the recording data 5 and whose amplitude gradually decreases is generated. As an example of the circuit, in the circuit of FIG. 17, the pattern generator 67 is caused to generate a digital pattern having a waveform corresponding to a drive pulse. Alternatively, FIG.
It can also be generated using a 0 circuit.

[0040]

According to the present invention, the double-edge recording method and Z
-By adopting the CAV format simultaneously, a large capacity and high speed of the optical memory device can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a double-edge recording method.

FIG. 2 is an explanatory diagram of a Z-CAV format.

FIG. 3 is a diagram showing a configuration example of an optical head.

FIG. 4 is a diagram showing a configuration example of a recording system and a reproduction system.

FIG. 5 is a diagram showing a basic configuration of a cosine equalizer.

FIG. 6 is a diagram showing how the waveform is compensated.

FIG. 7 is a diagram showing an embodiment of a cosine equalizer.

FIG. 8 is a diagram showing another embodiment of the cosine equalizer.

FIG. 9 is a diagram showing input / output signals of the drive pulse correction circuit according to claim 4;

FIG. 10 is an explanatory diagram of the predetermined time T ₁ .

FIG. 11 is a diagram showing an example of a relationship between a predetermined time T ₁ and a track radius.

FIG. 12 is a diagram showing an example of a circuit configuration.

FIG. 13 is a diagram showing input / output signals of a drive pulse correction circuit according to claim 5;

FIG. 14 is a diagram showing an example of the relationship between input data and drive pulses.

FIG. 15 is a diagram showing a circuit configuration example.

FIG. 16 is a timing chart thereof.

FIG. 17 is a diagram showing a circuit configuration of an embodiment of a drive pulse correction circuit according to claim 7;

FIG. 18 is a diagram showing the input / output signals.

FIG. 19 is a diagram showing an example of a waveform generated by a pattern generator.

FIG. 20 is a diagram showing another circuit configuration.

FIG. 21 is a view showing signal waveforms of respective parts.

FIG. 22 is a diagram showing an example of input / output signals of the drive pulse correction circuit according to claim 8;

[Explanation of symbols]

 18 Double-edge modulation circuit 19 Drive pulse correction circuit 24 Cosine equalizer 27 Z-CAV format device

Claims (8)

[Claims] 1. An optical memory device for recording / reproducing information on / from an optical disc of a recording medium by an optical head using a semiconductor laser or the like as a light source. The recording area is divided into a plurality of zones in the radial direction, and the Z-CAV format corresponding to the Z-CAV format increases the number of sectors per rotation from the inner zone to the outer zone.
An optical memory device comprising: a CAV format device. 2. The optical memory device according to claim 1, wherein the optical disk is a concentric groove optical disk. 3. The characteristic according to claim 1, between a reproduction circuit that obtains a reproduction signal from information written by both-edge modulation and a demodulation circuit that demodulates from the reproduction signal, the characteristics change from the inner circumference to the outer circumference. An optical memory device comprising a switching cosine equalizer. 4. The drive pulse width of the light source according to claim 1, which is shorter than a length of recording data obtained by the both edge modulators by a predetermined time, and the predetermined time is longer in an inner circumference of the optical disc and in an outer circumference thereof. An optical memory device comprising a drive pulse setting device for switching to shorten. 5. The method according to claim 1, wherein the length of the recording data obtained by the double-edge modulator is compared with a set time, and when it is short, the drive pulse width of the light source is shorter than the recording data by a predetermined time, and when it is long Is equipped with a drive pulse setting device for chopping the rear part of the drive pulse at intervals shorter than the drive pulse width. 6. The drive pulse setting device according to claim 5, wherein the number of choppings is large on the inner circumference of the optical disc,
An optical memory device characterized in that it is controlled so as to be reduced in the outer circumference. 7. The drive pulse width of the light source according to claim 1, wherein the drive pulse width is set to be the same as the length of recording data obtained by the both-edge modulator, and the power of the drive pulse is maximized at the front end of the drive pulse and set at the rear end. An optical memory device comprising a drive pulse setting device that decreases as time goes by. 8. The drive pulse width of the light source according to claim 1, wherein the drive pulse width is set shorter than the length of recording data obtained by the both edge modulators, and the power of the drive pulse is maximized at the front end of the drive pulse and set at the rear end. An optical memory device comprising a drive pulse setting device that decreases as time goes by.