JPH0658741B2 - Signal recording / reproducing device - Google Patents

Description

The present invention relates to signal recording capable of forming pits with little distortion when a binary digital signal is recorded by a laser on an optical recording medium such as an optical disk. The present invention relates to a playback device.

[Conventional technology]

The recordable optical disk drive device is capable of increasing the capacity by about two digits as compared with the magnetic disk device, and is attracting attention as a code data recording device or a coded document file information recording device.

The structure of the recording system of the optical disk device is shown in FIG. In the figure, binary data is input from an input terminal 1 and converted by a modulator 2 into a transmission path code in which the number of "0" s or "1" s is limited. It is output to the recording circuit 3 in the form of an RZ code (Return To Zero) having a positive polarity at 1 ”or an NRZI code (Non Return To Zero Inverted) at which the polarity is inverted at a bit“ 1 ”. The recording circuit 3 supplies a predetermined recording current to a laser diode (hereinafter referred to as LD) 4 in a section where a normal input signal has a positive polarity. The light beam from the LD 4 is condensed on the rotating disk 6 by an optical system 5 such as a lens,
Pits 7 are formed on the disk surface by melting sputtered or vapor-deposited metal.

At the time of reproduction, a reproduction current is passed through the LD 4 to focus the light on the track of the disc. In the track, since the reflectance is different between the pit portion and the other portion (hereinafter referred to as the land portion), a reproduction signal is obtained by photoelectrically converting the reflected light with a photodetector. For the reproduced signal, a demodulation clock is created by the level discrimination circuit, and the data is demodulated using the clock. At this time, if the phase of the reproduced data phase pulse exceeds a predetermined demodulation time width (hereinafter referred to as TW) of the transmission path code, the data becomes error data. In order to reduce the error probability of the reproduced data, it is necessary to reduce the phase shift (hereinafter referred to as jitter) of the reproduced signal.

There are various causes of jitter generation, but as the important jitter in the NRZ recording system, the change in the shape of the recording pit is extremely large. One of the reasons for this is a variation in the luminous efficiency of the LD or a characteristic change due to temperature.

FIG. 3 is a diagram showing that the LD drive current vs. optical power characteristic of the disk surface changes due to temperature change.

At the time of recording, the LD is driven so that the disc surface power is PW at the portion where the pits are to be formed and at the land portion it is PR, and at the time of reading, the LD is driven so that the disc surface power is at the PR. Read power PR on this disc surface
The recording power PW must be constant regardless of the temperature. However, the characteristics of the LD change depending on the temperature, and when the temperature is low, the driving current characteristics of the LD are as shown by the curve A. Therefore, at the time of recording, the IB-IP
Must be applied to the LD. On the other hand, the drive current characteristic at high temperature is as shown by curve B, and IB at low temperature is
-It is necessary to change the current value of IP to IB'-IP '. Further, the characteristics of the curve A and the curve B are also different for each LD, so that it is difficult to always set the power on the disc surface to PR-PW at the time of recording, and the pits may be changed according to the change in the recording power on the disc surface. , The reproduced waveform will have jitter.

For this reason, the recording device currently employs the RZ recording method in which the jitter of the reproduced waveform is unlikely to increase even if the size of the pit changes.

Next, the RZ recording method and the NRZ recording method will be described with reference to FIG. 4 by taking MFM (Modified FM) modulation, which is a typical digital recording, as an example.

Input binary data a is MFM modulated and
As shown in (b), 1 bit becomes a 2-bit data string b. M
When RZ recording the FM data b, a recording signal d of time τ1 is created corresponding to the logic “1”. On the other hand, in the case of NRZ recording, a signal that is inverted by logic "1" is created and used as the recording signal e. The figure (c) shows the channel clock c.
Indicates.

Next, the advantages and disadvantages of the RZ recording method and the NRZ recording method will be described.

(1) Regarding changes in recording pits In RZ recording, as shown in FIG. 4 (d), the recording current time is recorded at τ1. As described above, even if a large pit or a small pit is formed on the disc according to the fluctuation of τ1 hour, the reproduced waveform is
If the detection time (T ') from the leading edge of a pit to the leading edge of the next pit does not change with respect to a predetermined value, waveform jitter does not occur. However, during recording, since a series of data is recorded under the same environmental conditions, there is no change between pits during recording during the same recording.

On the other hand, in the NRZ recording, the recording current time is recorded as τ2 as shown in FIG. 8E, and when the recording pit length changes for τ2 hours, the flow of the land portion between the pits changes. That is, in the NRZ reproduction method, both the time τ2 from the leading edge to the trailing edge of the pit of the reproduced waveform and the time τ3 from the trailing edge to the leading edge of the next pit become demodulation jitter, and the pit shape change occurs. Immediate increase in jitter. As described above, the RZ method is a method in which the jitter does not relatively increase with respect to the change in the pit shape. Therefore, by supplying a sufficient recording current for forming the pit at the time of recording, the LD of the LD due to the temperature change described above is recorded. It is possible to sufficiently deal with the characteristic change.

On the other hand, in the NRZ method, since the recording pit length and the length of the land portion both have information, it is necessary to control the LD drive current so that pits are always formed optimally for recording jitter.

(2) Regarding LD power Actually used LD is currently 20mW, wavelength 780nm
The standard is about 830 nm, and it is necessary to use the LD within this rated power during recording and reproduction. However, the recording power on the disk surface is generally required to be about 10 mW, and in this case, it is necessary to sufficiently collect the amount of light emitted by the LD with a lens or the like. However, LD
In order to collect about 50% of the emitted light amount on the disk surface, the structure of the optical head actuator such as the lens of the optical system becomes strict, which causes problems in mass productivity and cost.

In order to mass-produce the optical head actuator, it is necessary to simplify the optical elements, but as a result, the power on the disk surface becomes only about 10 to 20% of the emitted light amount of the LD. For this reason, in the recording means, a method that requires less recording power than the LD is desired. Comparing RZ recording and NRZ recording in this regard, in RZ recording, the period during which the recording current flows in the LD is τ1, and τ1
Is sufficiently smaller than the original data bit section T, the average current becomes small. On the other hand, in the NRZ recording, a current is applied to the LD according to the bit interval of the data, and in the peculiar pattern of the original data, the current flow time is longer than the rest period, and the LD power may exceed the rating. .

(3) Regarding data recording capacity On the other hand, the light spot of the LD is determined by the wavelength and the numerical aperture of the objective lens, and the pit length of about 1 μm is the limit. Considering the capacity of the RZ signal and the NRZ signal when considering a device in which the limit minimum pit length is determined to be 1 μm, the shortest pit length of the RZ signal (see (d) in the same figure) is shown in FIG. For the bit length T of T / 2
Corresponds to the section. In this case, the linear recording density S per unit length is Becomes On the other hand, in the NRZ signal (see (e) in the figure), the shortest pit length is equal to the section of the original data bit length T, S = 25.4K (BPI), and the capacity is double that in recording the RZ signal.

The increase in capacity means a decrease in the bit unit price of the device, and if the same storage capacity is sufficient, the device can be downsized by reducing the disk diameter.
The effect is very large.

[Problems to be solved by the invention]

The conventional signal recording device is configured as described above, and it is difficult for reproduction jitter to occur due to fluctuations in the recording pit width.
The recording system of the RZ signal has been mainly adopted at the expense of the small device capacity due to the small recording current power of the LD. However, the cost performance of the device is determined by the capacity, and therefore it is desirable to perform recording by the NRZ method, but when performing NRZ recording, use of a high power LD that can withstand the power consumption of the LD And an optical actuator with less loss of light quantity, a recording power control system with less fluctuation in recording pit width, and selection of used disks and LDs are required, making mass production difficult and increasing device cost. There was a problem.

The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a signal recording / reproducing apparatus which requires less LD power and less fluctuation in recording pit width in a method of recording an NRZ signal. It is a thing.

[Means for solving problems]

A signal recording / reproducing apparatus according to the present invention is a signal recording / reproducing apparatus for irradiating an optical recording medium with a laser beam to form a recorded area and an unrecorded area corresponding to a bit polarity of a transmission path code. And a modulator that converts the polarity into a transmission path code consisting of a combination of a limited number of types, and the inversion interval of the transmission path code corresponding to any of the polarities of the output signals of the modulators. The laser is driven by a repeating pulse signal according to the type of the recording medium to form a recording area having a length corresponding to the inversion interval time of the transmission path code on the optical recording medium, and the leading edge and the trailing edge of the recording area are formed. A device for obtaining reproduction information based on both positions of the recording area and a laser driving condition for forming a leading edge of the recording area and a laser driving condition for forming a trailing edge of the recording area. Drive the laser, In serial unrecorded area is obtained by so as to interrupt the laser drive for the recording area forming.

[Action]

The signal recording / reproducing apparatus according to the present invention changes the laser driving conditions for forming the leading edge and the trailing edge of the recording area on the medium, and interrupts the laser driving for forming the recording area in the unrecorded area. Since it is controlled like this,
Regardless of the length of the recording area, the forming conditions of the leading edge and the trailing edge of the formed recording area can be controlled to be constant.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. The block configuration of this embodiment is similar to that of the conventional one shown in FIG.
In this embodiment, the modulator 2 converts the input signal into an NRZ transmission path code, and the recording circuit 3 uses a plurality of repetitive pulse signals whose number corresponds to each inversion interval of a predetermined polarity of the NRZ code. It drives the LD4.

FIG. 1 is a diagram for explaining the operation of a signal recording apparatus according to an embodiment of the present invention. FIG. 1 (a) is an MFM modulated signal with an input data interval T, FIG. 1 (b) is an NRZI signal, Same figure (c)
Is a recording signal in this embodiment. Further, FIG. 3D shows the shape of the pit formed by the apparatus of this embodiment.
(e) and (f) show the signals of each part of the demodulation system.

Next, the operation will be described.

The recording signal by the apparatus of this embodiment is composed of a plurality of pulse trains with respect to the conventional recording current waveform, and the pulse width of each signal is τ4. However, only the last pulse is τ5.
When recording is performed with such a repetitive pulse train, the shape of the recording pits becomes as shown in FIG. 9D, and the recording pits in the conventional RZ recording system are formed to be continuous. Since the LD is driven by such a repetitive pulse signal, NRZ recording can be performed with low power consumption.
The power will not exceed the rating. Further, since the LD is driven with a large current in each pulse period, the occurrence of jitter due to variations in the characteristics of the LD and temperature changes is eliminated.

On the other hand, the reproduction signal waveform corresponding to the above-mentioned recording pit shape is as shown in FIG.
It has a dip (rise) every period of / 2. But,
This dip portion does not rise to the level of (V1 + V2) / 2 with respect to the peak levels V1 and V2 of the reproduction signal d, and therefore, the waveform shown in FIG. be able to. N in the waveform
The bit period of the RZ signal has a value of ± K with respect to the bit period of the MFM data, T, 1.5T or 2T. However, K is represented by K = T / 2− (τ6 + τ7 + τ5). Among them, τ6 and τ7 are signals of the first pulse signal of the repetitive pulse signal corresponding to the section of the predetermined polarity of the transmission path code depending on the spot diameter on the disk surface and the recording current value when the repetitive pulse signal is recorded. The pit length is formed in the front and back of the section and the signal section of the last pulse signal. If recording is performed by such a repetitive pulse signal (since there is no risk of exceeding the LD power consumption rating), the recording current value can have a sufficiently large value, and the spot diameter is determined by the device. And τ7 can be controlled relatively easily. Therefore, by controlling only the signal period τ5 of the last pulse signal of the repetitive pulse signals, the value of K can be made extremely small, and the pit protrusion (jitter) due to the LD spot diameter and the storage current value can be prevented. It can be easily eliminated, and the influence of jitter in NRZ recording can be eliminated more completely.

FIG. 5 shows another embodiment of the present invention, in which the same effect as that of FIG. 1 is obtained by changing the recording current value according to the pulse position so that the jitter amount K shown in FIG. I try to make it smaller. In FIG. 5, similarly to τ6 in FIG. 1, the current value of the recording pulse is usually set to I1, and only the last is set to I2. In this case, the pulse width is all common with τ4. In this way, the recording current value is
By increasing or decreasing from I1 to I2,
The position of the trailing edge of the recording pit changes, and the length of the pit formed by the protrusion as shown in FIG. In this case, K = T / 2− (τ6 + τ7 + τ4), and it is possible to reduce K by controlling τ7, that is, by controlling the current value I2.

FIG. 6 shows still another embodiment of the present invention, in which the recording pits with small waveform jitter are similar to those in FIGS. 1 and 5 by changing the phase of only the last pulse of the recording pulses. Is to be configured. In FIG. 6, a to c are signals similar to those in FIG. In FIG. 1, the recording current value is changed only for the last pulse, whereas in FIG. 6, the recording current values are all the same and only the last pulse changes its phase from T / 2 phase to τ8. It was made. By doing so, it is possible to obtain the same effect as that obtained by the device of FIG.

As described above, according to this embodiment, the laser is current-driven by a plurality of repeating pulse signals whose number depends on the type of the inversion interval of the transmission path code.
The fluctuation in the recording pit pattern due to the change in the characteristics of the LD, which is a problem in the Z recording method, that the power consumption of the LD is large, and that is a problem in the method of recording by reducing the recording current is eliminated. An LD having a low power rating can be used, the cost can be reduced by simplifying the optical actuator, the influence of jitter due to the characteristic change of the LD can be eliminated, and a large-capacity optical disk device by NRZ recording can be constructed at low cost.

Further, in this embodiment, the frequency of the repetitive pulse signal is set to an integral multiple of the clock frequency of the recording signal, so that the circuit can be easily constructed.

Furthermore, in the present embodiment, in the repetitive pulse signal corresponding to each inversion interval, the reproduced waveforms of the leading edge portion of the first recording pit and the trailing edge portion of the last recording pit are demodulation information. Since only the corresponding pulse signal has a different pulse width, recording phase, or recording current value from the other pulse signals, it is possible to reduce the jitter due to the spot diameter on the disk surface and the recording current.

〔The invention's effect〕

As described above, according to the signal recording / reproducing apparatus of the present invention, the signal recording / reproducing in which the optical recording medium is irradiated with the laser beam to form the recorded area and the unrecorded area corresponding to the bit polarity of the transmission path code In the device, a modulator for converting a binary digital signal into a transmission path code composed of a combination of limited kinds of polarity inversion intervals, and one of the polarities of output signals of the modulator, The laser is driven by a repeat pulse signal according to the type of the reversal interval of the transmission path code, and a recording area having a length corresponding to the reversal interval time of the transmission path code is formed on the optical recording medium, and the recording is performed. A device for obtaining reproduction information based on the positions of both the leading edge and the trailing edge of the area, the laser driving condition for forming the leading edge of the recording area and the laser for forming the trailing edge of the recording area. Laser with different driving conditions Since the laser drive for forming the recording area is interrupted in the unrecorded area while driving, it is possible to form the recording area with the correct position and length on the optical recording medium, and the reproduction detection is performed. There is an effect that a signal recording / reproducing apparatus having an improved error rate and an improved recording density in a recording medium, that is, a recordable data capacity can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing signals in a signal recording device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a recording system of an optical disc device, and FIG. 3 is a diagram showing drive current versus disc surface power according to temperature of a laser diode. Figure 4 shows changes in characteristics, and Figure 4 shows MF.
Explanatory diagrams of the RZ signal and NRZ signal in M modulation, FIGS. 5 and 6 are diagrams showing signals in another embodiment of the present invention. 2 ... Modulator, 3 ... Recording circuit, 4 ... Laser diode, 6 ... Disk (optical recording medium).

Claims (6)

[Claims] 1. A signal recording / reproducing apparatus for irradiating an optical recording medium with a laser beam to form a recorded area and an unrecorded area corresponding to a bit polarity of a transmission path code, wherein a binary digital signal is inverted in polarity. Depending on the type of the inversion interval of the transmission line code, the modulator converts the transmission line code into a combination of a certain limited type of intervals and the polarity of the output signal of the modulator. A laser is driven by a repeated pulse signal to form a recording area having a length corresponding to the inversion interval time of the transmission path code on the optical recording medium, and the positions of both the leading edge and the trailing edge of the recording area are formed. A device for obtaining reproduction information based on the above, wherein the laser is driven under different laser driving conditions for forming the leading edge of the recording region and for forming the trailing edge of the recording region. , In the above unrecorded area The signal recording and reproducing apparatus being characterized in that so as to interrupt the laser drive for the recording area forming. 2. The signal recording / reproducing apparatus according to claim 1, wherein the cycle of the repeating pulse signal is an integral multiple of the clock cycle of the transmission path code. 3. A pulse signal corresponding to the leading edge or trailing edge of each inversion interval of the predetermined polarity of the transmission path code, of the repeating pulse signal, having a pulse width different from other pulse signals of the repeating pulse signal. The signal recording / reproducing apparatus according to claim 1, further comprising: 4. A pulse signal corresponding to a leading edge or a trailing edge of each inversion interval of the predetermined polarity of the transmission path code in the repeating pulse signal has a phase different from other pulse signals of the repeating pulse signal. The signal recording / reproducing apparatus according to claim 1, wherein 5. A pulse signal corresponding to a leading edge or a trailing edge of each inversion cycle having a predetermined polarity of the transmission path code in the repeating pulse signal has a different current value from other pulse signals of the repeating pulse signal. The signal recording / reproducing apparatus according to claim 1, characterized in that it has. 6. The signal recording / reproducing apparatus according to claim 1, wherein the driving of the laser for forming the recording area is performed during a time shorter than the inversion interval time.