JP2009289302A - Optical recording pulse generation method, its device, and information recording/reproducing device - Google Patents

Abstract

A laser diode driving time setting pulse that is accurate and accurate to recording data is obtained regardless of the recording clock frequency.
According to an embodiment of the present invention, first and second recording data are input to first and second pulse delay circuits, and a delay amount is set for each of the first and second pulse delay circuits. The second control signal is inputted, the latch circuit is set and reset by the first and second delay pulses obtained from the first and second delay circuits, and the output of the latch circuit is used as the laser diode driving time. Output as a setting pulse.
[Selection] Figure 9

Description

  The present invention relates to an optical recording pulse generation method, an apparatus therefor, and an information recording / reproducing apparatus, and is particularly effective when an information recording is performed on an optical disk recording apparatus using a short pulse laser beam.

  As a medium suitable for information recording, reproduction and erasure (repeated recording), there is an optical disk. In particular, digital versatile disc (DVD) systems are widely used for video recording, and high-quality (or high-density) DVD (so-called HD DVD) systems and Blu-ray Disc (BD) systems are also available as large-capacity and developed standards. Is realized. In an information recording apparatus that realizes these systems, there is a demand for a pulse generator that can accurately obtain pulses of various widths.

  For example, Patent Document 1 discloses a pulse generator for a laser diode drive pulse. In this apparatus, a laser diode drive pulse is controlled in the time axis direction using a delay line. The reason for controlling in the time axis direction is that it is necessary to adjust the pulse length according to the length of the mark to be recorded, and that it is less susceptible to thermal interference according to the length of the land just before. (This is because if the length of the land just before is short, the accumulated heat of the mark just before is not sufficiently dissipated and is subject to thermal interference).

  In the above-mentioned Patent Document 1, a laser diode driving pulse generating unit that generates a laser diode driving pulse according to recording data, and a time axis so that the pulse generated by the laser diode driving pulse generating unit has an appropriate length for a recording mark. Waveform adjusting means for adjusting and outputting in the direction. The waveform adjusting means includes a first delay circuit that delays the laser drive pulse in units of clocks, and a second delay circuit that delays the laser drive pulse with a delay time shorter than that of the first delay circuit. 1 and the output of the second delay circuit are combined and output.

Patent Document 2 discloses a technique for improving the rising edge of a recording waveform by using relaxation oscillation of a semiconductor laser diode.
JP 2001-209958 A JP 2002-123963 A

  In the prior art, a recording clock pulse is used to obtain a laser diode drive pulse. For this reason, the accuracy of the clock pulse greatly affects the output timing and pulse width of the laser diode drive pulse. For this reason, the relationship between the recording data and the laser diode drive pulse may shift.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording pulse generating method, an apparatus thereof, and an information recording / reproducing apparatus capable of obtaining an accurate laser diode driving time setting pulse faithful to recording data irrespective of the recording clock frequency. is there.

  In order to solve the above-mentioned problem, as a method for generating a laser diode driving time setting pulse, recording data is input to first and second pulse delay circuits, and the first and second pulse delay circuits are respectively input. Inputting first and second control signals for setting a delay amount; setting and resetting a latch circuit using first and second delay pulses obtained from the first and second delay circuits; The driving method includes outputting the output of the latch circuit as the laser diode driving time setting pulse.

  According to the above means, since the recording data is directly used and the laser diode driving time setting pulse is generated at the timing of the recording data, it is independent of the recording clock frequency.

  Embodiments of the present invention will be described below with reference to the drawings. First, the apparatus and signal waveforms which are the premise of the present invention will be described with reference to FIGS.

<Recording using short pulses>
FIG. 1 schematically shows an example of an optical recording apparatus to which the present invention is applied. In this optical recording apparatus, a semiconductor laser diode 20 such as a laser diode is used as a short-wavelength laser light source. The wavelength of the emitted light is, for example, in the violet wavelength band in the range of 400 nm to 410 nm.

  The light emitted from the semiconductor laser diode 20 is converted into parallel light by the collimator lens 21 and sequentially passes through the polarization beam splitter 22 and the λ / 4 plate 23. Then, the light enters the objective lens 24. Thereafter, the light passes through the substrate of the optical disc 1 and is focused on the target information recording layer. Reflected light from the information recording layer of the optical disc 1 passes through the objective lens 24 and the λ / 4 plate 23, is reflected by the polarization beam splatter 22, passes through the condenser lens 25, and enters the photodetector 26. .

  The light receiving part of the photodetector 26 is usually divided into a plurality of parts, and a current corresponding to the light intensity is output from each light receiving part. The output current is converted into a voltage by an unillustrated I / V amplifier (current-voltage conversion amplifier), and then an arithmetic circuit 27 reproduces user information and an HF signal, and a beam spot by a light source on the optical disc 1 A focus error signal and a track error signal for controlling the position are processed. The arithmetic circuit 27 is controlled by a controller (CTR).

  The objective lens 24 can be driven in the vertical direction and the disc radial direction by an actuator 28. The actuator 28 is controlled by a servo driver (SD). Then, the beam spot position is controlled by the servo driver (SD) so as to follow the information track on the optical disc 1.

  The optical disk 1 is a recordable disk on which information can be written, and information is recorded by light emitted from the semiconductor laser diode 20. The amount of light (light intensity) of the emitted light EL of the semiconductor laser diode 20 can be controlled by a semiconductor laser drive circuit (LD drive circuit) 29, and when the information is recorded on the optical disc 1, the emitted light EL of the semiconductor laser diode 20 is a relaxation oscillation pulse. Is emitted. The LD drive circuit 29 is controlled by the controller CTR. The recording pulse at the time of recording information on the optical disc 1 will be described in detail later.

<Optical disk structure>
FIG. 2 shows an example of a cross-sectional structure of the optical disc 1 used in the optical recording apparatus. For example, a recording layer 13 which is a phase change recording film is formed on a substrate 11 made of polycarbonate via a protective layer 12 made of a dielectric. A protective layer 12 made of a dielectric is further formed thereon, and a conductive reflective layer 14 is further formed thereon. Furthermore, another substrate 11 made of polycarbonate is formed on this with an adhesive layer 15 in between.

  In terms of the overall structure, the optical disc 1 is obtained by bonding two discs each having an information recording layer including a recording film on at least one substrate in opposite directions. The thickness of one substrate is about 0.6 mm, for example, and the entire thickness of the optical disc 1 is about 1.2 mm.

  In this embodiment, an example of an optical disk having four information recording layers is shown. However, the present invention is also applied to an optical disk having five or more information recording layers, such as providing interface layers above and below the recording layer 13. Is applicable. In this embodiment, the information recording layer is a single layer. However, the present invention can also be applied to an optical disc having two or more information recording layers. Furthermore, in the present embodiment, a disk-shaped optical disk is used as a recording medium. However, the present invention can also be applied to, for example, a card-shaped recording medium.

<Structure of semiconductor laser diode>
FIG. 3 shows an example of the light emitter structure of the semiconductor laser diode 20. In FIG. 3, only the semiconductor chip portion that is a light emitter of the semiconductor laser diode 20 is shown, but this chip portion is usually fixed to a metal block that becomes a heat sink, and further includes a base, a cap with a glass window, and the like. Composed.

  Here, description will be made using only the semiconductor chip portion directly related to laser emission. As an example, the semiconductor laser chip is a micro block having a thickness (up and down direction in the figure) of 0.15 mm, a length (L in the figure) of 0.5 mm, and a lateral width (depth direction in the figure) of about 0.2 mm. . The upper end 31 and the lower end 32 of the laser chip are electrodes, respectively, the upper end 31 is a − (minus) electrode, and the lower end 32 is a + (plus) electrode.

  The central active layer 33 emits laser light, and an upper clad layer 34 and a lower clad layer 35 are formed above and below with the active layer 33 interposed therebetween. The upper clad layer 34 is an n-type clad layer having many electrons, and the lower clad layer 35 is a p-type clad layer having many holes.

A forward voltage is applied from the electrode 32 to the electrode 31 between the electrode 32 and the electrode 31. As a result, when a current flows from the electrode 32 toward the electrode 31, many holes and electrons excited in the active layer 33 are recombined, and light corresponding to the energy lost at that time is emitted. The material of the upper clad layer 34 and the lower clad layer 35 is selected so that the refractive index of the upper clad layer 34 and the lower clad layer 35 is lower than the refractive index of the active layer 33 (for example, 5% lower). The light wave travels left and right in the drawing while reflecting the boundary with the cladding layers 34 and 35 in the active layer 33.

  The left and right end faces in the figure are mirror surfaces M, and the active layer 33 itself forms an optical resonator. The light wave that travels left and right in the active layer 33 and is reflected by the mirror surfaces at the left and right ends is amplified in the active layer 33 and finally emitted from the right end (and left end) of the figure as laser light. At this time, the resonator length of the semiconductor laser diode 20 is the length L in the left-right direction in the drawing.

  The semiconductor laser diode 20 is controlled by a laser drive current generated by the LD drive circuit 29. The light emitted from the semiconductor laser diode 20 is generated as a recording pulse used for recording on the optical disc 1 by a laser driving current from the LD driving circuit 29.

<Emission light of semiconductor laser diode>
FIG. 4A shows a waveform of a laser driving current applied in a conventional recording method in which light emitted from the semiconductor laser diode 20 is obtained as a normal recording pulse, and FIG. 4B shows a laser shown in FIG. The intensity waveform of the emitted light of the semiconductor laser diode 20 obtained by applying the drive current is shown. FIG. 4C shows the waveform of the laser drive current applied in the recording method of this embodiment in which the light emitted from the semiconductor laser diode 20 is obtained as a short pulse using relaxation oscillation, and FIG. The intensity waveform of the emitted light of the semiconductor laser diode 20 obtained by applying the laser driving current shown in FIG.

  The laser drive current is controlled as a pulse that transitions between two levels of the bias current Ibi and the peak current Ipe shown in FIGS. 4 (A) and 4 (C). In some cases, the bias current Ibi is further controlled by being subdivided into two levels or three levels, but here the bias current Ibi and the peak current Ipe are each at a single level for the sake of simplicity of explanation. The case where it is is demonstrated.

  In the case of generating a normal recording pulse, the LD drive circuit 29 causes the threshold current to start the laser oscillation of the semiconductor laser diode 20 (that is, the emitted light intensity starts to increase rapidly) as shown in FIG. First, a bias current Ibi set to a level slightly higher than Ith is generated to drive the semiconductor laser diode 20. Thereafter, at time A, a peak current Ipe for obtaining a desired recording power is applied, and after a peak current Ipe is applied for a certain period of time, it is again reduced to the bias current Ibi at time B. The time change of the emitted light intensity of the semiconductor laser diode 20 at this time is shown in FIG.

  As shown in FIG. 4B, until the time A driven by the bias current Ibi, the intensity of the emitted light is very low power at which data cannot be recorded on the optical disc 1, but the peak current Ipe is applied. The emitted light intensity is raised to the recording power, and this level is maintained until the drive current is lowered to the bias current Ibi level at time B. After time B, the emitted light intensity becomes low power again. Thus, the semiconductor laser diode 20 is controlled so that a normal recording pulse is emitted during the period from time A to time B.

  When the emitted light intensity is observed in more detail, when the emitted light intensity is raised toward the recording power at time A, the emitted light intensity rises momentarily and decreases before it stabilizes at the recording power as a steady state. Is observed (dotted line circle in the figure). This is a relaxation oscillation of the emitted light intensity generated in the semiconductor laser diode 20. In normal recording pulse generation, control is performed to minimize this relaxation oscillation.

  In this way, relaxation oscillation is a transient oscillation phenomenon that occurs when a laser drive current suddenly increases from a certain level to a certain level that greatly exceeds the threshold current Ith in a semiconductor laser. The relaxation vibration is reduced every time the vibration is repeated, and the vibration is eventually reduced.

  In the optical recording apparatus according to the present embodiment, this relaxation vibration is actively used for recording. Specifically, one of the heads of relaxation oscillation pulses obtained by relaxation oscillation is used as a short pulse. In this case, as shown in FIG. 4C, the LD drive circuit 29 first generates a bias current Ibi set to a level lower than the threshold current Ith of the semiconductor laser diode 20 to drive the semiconductor laser diode 20.

  After that, at time A, the laser drive current is suddenly raised to the peak current Ipe at a rise time earlier than the normal recording pulse generation, and after a shorter time than the normal recording pulse generation, again at time C. Is lowered to the bias current Ibi. The time change of the emitted light intensity of the semiconductor laser diode 20 at this time is shown in FIG.

  As shown in FIG. 4D, the semiconductor laser diode 20 does not start laser oscillation until time A when it is driven by the bias current Ibi lower than the threshold current Ith. There is a certain amount of light emission. Thereafter, with a sharp increase in applied current at time A, relaxation oscillation starts, and the emitted light intensity increases rapidly. Thereafter, light emission by relaxation oscillation continues until time C at which the applied current is returned to the threshold current or less again. In this example, the time C is reached at the timing when the second pulse of the relaxation oscillation is generated, and the recording pulse generation is completed.

  In this way, the short pulse due to relaxation oscillation increases the emitted light intensity in a very short time compared to a normal recording pulse, and the emitted light intensity decreases at a constant period determined by the structure of the semiconductor laser. have. Therefore, by using a pulse due to relaxation oscillation as a recording pulse, it is possible to obtain a short pulse having a short rise / fall time and a strong peak intensity, which cannot be obtained with a normal recording pulse. .

  As a generally known relationship, there is the following relationship between the laser resonator length L of the semiconductor laser and the relaxation oscillation period T.

T = k · {2 nL / c} (1)
Where k is a constant, n is the refractive index of the active layer of the semiconductor laser,
c is the speed of light (3.0 × 10 ⁸ (m / s)). Therefore, it can be seen that the LD resonator length L and the relaxation oscillation period T, and hence the relaxation oscillation pulse width, are in a proportional relationship.

  For this reason, if it is desired to increase the relaxation oscillation pulse width, the laser resonator length L should be increased, and if it is desired to reduce the relaxation oscillation pulse width, the laser resonator length L may be decreased. That is, it can be said that the relaxation oscillation pulse width can be controlled by the laser resonator length L.

<Relaxation vibration>
FIG. 5 shows the measurement result of the relaxation oscillation waveform of the emitted light intensity obtained when the laser resonator length L of the semiconductor laser diode 20 is 650 μm. It can be seen that the relaxation oscillation pulse width is about 81 ps at the full width at half maximum. From the above equation (1), it is known that the laser resonator length L and the relaxation oscillation pulse width are in a proportional relationship. Therefore, the conversion equation of the laser resonator length L and the obtained relaxation oscillation pulse width (FWHM) Wr. The following relationship is obtained.

Wr (ps) = L (μm) /8.0 (μm / ps) (2)
Next, data recording on the optical recording medium in the optical recording apparatus according to the present embodiment will be described. The optical disc 1 is a rewritable disc such as DVD-RAM, DVD-RW, HDDVD-RW, or HDDVD-RAM, and uses a phase change material for the recording layer. In the phase change type optical disc, data bits are recorded and erased by controlling the intensity of pulsed laser light focused on the recording layer.

  Recording means forming an amorphous mark in a region initialized to a crystalline state of the recording layer. The amorphous mark is formed by melting the phase change material and quenching immediately thereafter. For this purpose, a relatively short and high-power pulsed laser beam is condensed on the phase change recording layer, and the local temperature is raised to a temperature exceeding the melting point Tm of the phase change material to cause local melting. Must be generated. Thereafter, when the recording pulse is interrupted, the molten local region is rapidly cooled, and a solid amorphous mark is formed through a melting-quenching process.

  On the other hand, the recorded data bit is erased by recrystallizing the amorphous mark. Crystallization is now achieved by local annealing. By condensing the laser beam on the recording layer and controlling it to a level slightly lower than the recording power, the local temperature of the phase change recording layer is raised to the crystallization temperature Tg or higher, and the temperature is lower than the melting point Tm. keep.

  At this time, by maintaining the local temperature between the crystallization temperature Tg and the melting point Tm for a certain period of time, the amorphous mark can be phase-changed into a crystalline state. In this way, the recording mark can be erased.

  Note that the time required for crystallization at this time to be maintained between the crystallization temperature Tg and the melting point Tm is called crystallization time. For reproducing the recorded data bit, the information recording layer is irradiated with a DC laser beam having a low power that does not cause a phase change of the recording layer, that is, a reproducing power.

<Recrystallization ring by melting and quenching process of phase change material>
The optical recording apparatus according to this embodiment is characterized in that a recording pulse used for recording a data bit is a short pulse by relaxation oscillation.

  When the amorphous mark formed by the normal recording pulse is formed through the melting-quenching process of the phase change material as described above, a recrystallization ring is formed at the peripheral portion of the amorphous mark as shown in FIG. A region (recrystallization ring) is produced. This is because the region once melted at the peripheral portion of the amorphous mark is recrystallized by passing through the temperature region between the crystallization temperature Tg and the melting point Tm in the cooling process for the crystallization time or longer. Although this has the effect of reducing the size of the amorphous mark (self-sharpening effect) as a result, the jitter (fluctuation) of the reproduced signal at the mark periphery, thermal interference between the front and rear marks on the track, In some cases, the mark formed on the adjacent track may be partially erased (cross erase).

  On the other hand, an amorphous mark formed by a short pulse obtained by relaxation oscillation as in the optical recording apparatus according to the present embodiment does not cause a recrystallization ring at the periphery of the amorphous mark as shown in FIG. By irradiating a high-power laser beam in a short time as a short pulse, the phase change layer is melted immediately after the laser beam irradiation, and the irradiation is terminated before the melted region significantly spreads to the peripheral part due to heat conduction. Thus, only the melted part immediately after laser beam irradiation is made into an amorphous mark.

  As described above, in an amorphous mark that does not cause a recrystallization ring due to a short pulse, jitter at the peripheral edge of the mark is reduced, mark deformation or edge shift due to thermal interference between front and rear marks on the track, and adjacent tracks. There is an advantage that the cross-erasing of the mark formed on the substrate does not occur.

  Of course, recording with a short pulse has the advantage of improving the quality of the recording mark as described above, and since it can record the mark in a short time, it is needless to say that it is suitable for high transfer rate recording. .

  In optical discs, there is a strong demand for high transfer rates along with an increase in capacity, and double-speed standards have already been issued for HDDVD-R and HDDVD-RW against the standard 1x speed (linear speed 6.61 m / s). ing. In the future, it is expected that higher speeds such as 4 times speed and 8 times speed will be expected.

  In order to achieve a high transfer rate, it is necessary to record the recording mark at a high speed, that is, in a short time. In the phase change type disc, this means that the amorphous mark is recorded with a short pulse. For example, in HDDVD, the channel clock rate is 518.4 Mbps at 8 × speed, and the time corresponding to one channel bit is 1.929 ns.

  The pulse width required for a short pulse in the optical recording apparatus according to the present embodiment is a pulse width that does not cause a recrystallization ring when an amorphous mark is formed. The region that becomes the recrystallization ring when the amorphous mark is formed is a region that is once melted at the periphery of the amorphous mark as described above, that is, the region that exceeds the melting point of the phase change material. At this time, only the region slightly exceeding the melting point is recrystallized.

This is because a region where the temperature has been raised to a temperature greatly exceeding the melting point has a large temperature decrease gradient and is cooled relatively steeply, and thus becomes amorphous. This is because the temperature gradient δT / δx and the heat flow density q (W / m ² ) are well known (Fourier's heat conduction law) q = K · δT / δx This is because the heat flow from the high temperature region to the low temperature region increases. Here, K (W / m · K) is the thermal conductivity, and x is the distance in the direction of thermal conduction (interface normal vector direction) at the interface having a temperature difference.

  In the case of recording with a short pulse, high-power laser light is irradiated so that the central portion of the light spot exceeds the melting point immediately after laser light irradiation.

<Comparison of temperature distribution on recording tracks>
FIG. 7A shows the temperature distribution on the recording track in the case of recording with a short pulse, and FIG. 7B shows the temperature distribution on the recording track in the case of recording with a normal recording pulse. In FIG. 7A and FIG. 7B, the upper portion is the melting point excess region on the track immediately after the recording pulse irradiation, the middle portion is the melting point excess region at the end of the recording pulse, and the lower portion is the temperature in the AA ′ cross section. Represents the distribution. Originally, the recording beam spot (the region indicated by the broken line in FIG. 7A) moves in the vertical direction in the figure during pulse irradiation, but in this example, it is assumed that it does not move for the sake of simplicity of explanation. did.

  In any recording pulse, the region beyond the melting point at the center of the light spot is enlarged by heat transfer immediately after the pulse irradiation until the end of the pulse. However, in the case of a short pulse, since the pulse irradiation time is short, it hardly expands.

  In the case of recording with a short pulse, the temperature distribution in the cross section including the center of the light spot at the end of the pulse has almost the same Gaussian distribution as that immediately after the light beam irradiation, and the temperature is steep before and after the boundary between the melting point and the melting point. It is a slope. For this reason, a region to be recrystallized, that is, a region slightly exceeding the melting point (in the figure, a region having a temperature between the melting point Tm and the temperature Tm2) has almost no spread in the planar direction. Therefore, if the light intensity (laser power) becomes zero within a time period in which expansion of the region above the melting point at the center of the light spot due to heat transfer is negligible, the recrystallization ring is limited to a very narrow region.

  On the other hand, in the case of mark formation by a normal recording pulse, a laser beam having a relatively low power is irradiated for a long time, so that the region exceeding the melting point at the center of the light spot gradually expands (FIG. 7B) ). At this time, the temperature distribution in the cross section including the center of the light spot is no longer a Gaussian distribution, but has a shape having a gentler temperature gradient (lower stage in FIG. 7B).

  For this reason, the region to be recrystallized has a relatively large extent in the plane direction. The broken line in the middle of FIG. 7B indicates the recrystallization limit, and the inside of this broken line is an area where an amorphous mark is formed. Thus, a normal recording pulse is accompanied by a large recrystallization ring during mark formation.

The width in the planar direction of the recrystallization ring is considered to be substantially the same as the diffusion distance in the planar direction of the melting point region during the pulse irradiation time. As a general phase change material,
When the thermal conductivity K = 0.005 J / cm / s / ° C. and the specific heat C = 1.5 J / cm ³ / ° C., the thermal diffusion distance within the pulse irradiation time can be estimated. Since heat is considered to diffuse by the distance Lx = (Kt / C) ^1/2 during time t, the recrystallization ring region is 10% or less of the shortest mark length of 0.204 μm of HD DVD-RW. In other words, in order to be limited to a range of 10.2 nm or less in one direction, the pulse irradiation time is 0.44 ns. This can be said to be a pulse width required for a short pulse.

  As described above, since the equation (2) is obtained as the relationship between the laser resonator length L of the semiconductor laser and the obtained relaxation oscillation pulse width Wr, a pulse width of 440 ps or less is used for recording with a short pulse. It was found that it was necessary to use a semiconductor laser having a resonator length of 3520 μm or less.

  On the other hand, from the viewpoint of reducing the recrystallization ring, the shorter the pulse irradiation time, the better. However, in reality, it is difficult to give energy for raising the temperature of the phase change material above the melting point. That is, it is necessary to irradiate laser light with extremely high power in a short time. Therefore, in reality, it may be considered that the pulse irradiation time is required to be about 50 ps or more. This corresponds to the necessity of a semiconductor laser having a laser resonator length of 400 μm or more when the relationship of the expression (2) is used.

  As can be seen from equation (2), when the relaxation oscillation pulse is used for recording information on the optical disc 1, the relaxation oscillation pulse width is uniquely determined when the laser resonator length of the semiconductor laser diode 20 used in the optical recording apparatus is determined. become. As described above, when the pulse width is short, the phase change material is heated to the melting point or higher by irradiating with a high-power laser beam, but the laser beam is irradiated with the maximum power of the semiconductor laser diode 20. Even if it does not reach the melting point or higher. In such a case, it is useful to irradiate the relaxation oscillation pulse of the laser light a plurality of times.

<Other examples of relaxation oscillation pulses>
FIG. 8 shows a relaxation oscillation waveform of the emitted light intensity obtained when the laser driving current for the semiconductor laser diode 20 is controlled so that the relaxation oscillation pulse is generated three times. By generating the relaxation oscillation pulse three times, the irradiation energy by the pulse (time integration value by the pulse in the figure) is increased, so that the phase change material can be raised above the melting point. However, as can be seen from the figure, the second and third pulse intensities gradually decrease compared to the first relaxation oscillation pulse. For this reason, irradiation of a plurality of pulses more than this is not very effective.

  Thus, in the optical recording apparatus that records data on the optical recording medium using the relaxation oscillation pulse of the semiconductor laser diode 20, it is necessary to adjust the number of relaxation oscillation pulses according to the laser resonator length. . Even when a laser with a low rated output of the semiconductor laser is used, it is useful to use a plurality of relaxation oscillation pulses.

<Recording pulse generator that specifies pulse width in absolute time regardless of recording clock frequency>
In this apparatus, the fine adjustment of the leading and trailing edges of the output pulse can be performed by switching the delay line, and the width of the output pulse is a simple strategy. The delay amount and width for the mark portion of the input pulse (NRZI) can be freely specified.

  In the following, an embodiment of a recording pulse generating apparatus for designating a pulse width in absolute time regardless of the recording clock frequency will be described. FIG. 9 is a block diagram of a main part of a recording pulse generator to which the present invention is applied. It consists of pulse delay circuits 101A and 101B and an RS latch 103.

  The recording data itself as input is input to the first and second pulse delay circuits 101A and 101B. Further, first and second control signals for setting delay amounts are input to the first and second pulse delay circuits 101A and 101B, respectively. The first and second control signals are output from a central processing unit (CPU) described later.

  The latch circuit 103 is set and reset by the first and second delay pulses Pa and Pb obtained from the first and second delay circuits 101A and 101B. The output pulse of the latch circuit 103 is used as a laser diode drive time setting pulse.

  Now, as an example of a conventional conventional circuit, a ring oscillator is placed in a portion corresponding to a pulse delay circuit, and frequency division is performed. Then, the recording pulse is taken out from the RS latch using the divided output pulses. However, in this method, the pulse width is limited by the frequency division number, and there is a possibility that the frequency division is more than necessary. Also, in the recording mode with different double speeds, high resolution is required at low double speeds, and low resolution is acceptable at high double speeds, resulting in non-uniform resolution. It becomes. This circuit solves this.

  The same input is connected to each of the pulse delay circuits 101A and 101B. In addition to this input, the CPU set value from the signal bus 102 is input as a control signal to the pulse delay circuits 101A and 101B.

  From these inputs, the pulse delay circuits 101A and 101B respectively generate a delay pulse Pa having a pulse delay time Ta and a delay pulse Pb having a pulse delay time Tb. Pa and Pb are respectively input to the input S and the input R of the latch circuit 103, and a signal having a pulse width (Tb−Ta) and a delay amount Ta is obtained as an output from the output terminal Q. The obtained output pulse is a simple strategy, and is used as a pulse specifying a pulse width and a delay amount with respect to a mark portion of the input pulse.

  FIG. 10 shows an embodiment of the pulse delay circuits 101A and 101B in detail. Since both have the same configuration, the pulse delay circuit 101A will be representatively described. Terminals M1, M2,... Mx (x: integer) and x terminals are placed at intervals having a certain delay time Td in order from the input P (record data), and one terminal is provided for the output of the circuit. N is placed. The terminals M1, M2,... Mx and the terminal N are in a switch relationship with each other, and a delay line connecting any one of the terminals N and the terminals M1, M2,... Mx with a setting value (control signal) from the CPU. Can be switched. For example, in FIG. 10, it is assumed that Td = 10 ps. In this configuration, if it is desired to generate a delay of 20 ps, it can be realized by connecting the terminal M2 and the terminal N according to a set value from the CPU.

  The desired minimum delay time unit Td and the number x of the terminals M on the input side can be determined, and Td is not limited to a fixed value but can be set to different values. With this configuration, it is possible to generate a signal having an arbitrary delay with respect to the signal from the input P.

<Description of operation>
FIG. 11 shows the relationship between the recording data and the signal waveform of each part of the circuit of FIG. In FIG. 11, (b) is recording data, (c) and (d) are delay pulses Pa and Pb, and (e) are output pulses. FIG. 11A shows marks and spaces formed on the track. In this example, two output pulses correspond to the mark a1, but one output pulse may be used depending on the mark length.

  As described above, the delay time Ta is set in the pulse delay circuit 101A for the input P as the recording data, and the delay time Tb is set in the pulse delay circuit 101B. An arbitrary output Q can be obtained from these waveforms. The setting of the delay time is set by a control signal and can be arbitrarily changed as necessary.

  Since the delay pulses Pa and Pb output from the pulse delay circuits 101A and 101B are input to the set and reset terminals of the latch circuit 103, an output pulse having a pulse width (Tb−Ta) is obtained from the latch circuit 103. This output pulse is used as a laser diode drive time setting pulse.

<Configuration example of information recording / reproducing apparatus (optical disc drive)>
FIG. 12 is a block diagram showing a configuration example of an information recording / reproducing apparatus (optical disc drive) to which the present invention is applied. This information recording / reproducing apparatus (optical disk drive) has the same basic configuration as that of the optical recording apparatus of FIG. The optical disc 1 has grooves concentrically or spirally. The concave portion of the groove is called a land, the convex portion is called a groove, and one round of the group or land is called a track.

  User data is recorded as recording marks along this track (groove only or groove and land). The recording mark is formed by irradiating the track with intensity-modulated laser light. At the time of data reproduction, laser light having a lower read power than that at the time of recording is irradiated along the track, and a change in the intensity of reflected light from the recording mark on the track is detected. The intensity change of the reflected light is converted into an electric signal by the photodetector. Erasing the recorded data is realized by irradiating a laser beam of erase power stronger than the read power along the track and crystallizing the recording layer.

  The optical disk 1 is rotationally driven by a spindle motor 63. A rotation angle signal is provided from a rotary encoder 63 a provided in the spindle motor 63. For example, when the spindle motor 63 makes one rotation, the rotation angle signal is generated by 5 pulses. The spindle motor control circuit 64 determines the rotation angle and rotation speed of the spindle motor 63 by using this rotation angle signal.

  Information is recorded on and reproduced from the optical disk 1 by the optical head 65. The optical head 65 is connected to a feed motor 67 through a gear and a screw shaft, and this feed motor 67 is controlled by a feed motor control circuit 68. When the feed motor 67 is rotated by a feed motor drive current from the feed motor control circuit, the optical head 65 moves in the radial direction of the optical disc 1.

  The optical head 65 is provided with an objective lens 70 supported by a wire or a leaf spring (not shown). The objective lens 70 can be moved in the focusing direction (the optical axis direction of the lens) by driving the driving coil 72, and can be moved in the tracking direction (the direction orthogonal to the optical axis of the lens) by driving the driving coil 71. It is.

  The laser modulation control circuit 75 outputs a write signal (laser element drive pulse) to a laser diode (laser diode) based on recording data supplied from the host device 94 via the interface circuit 93 during information recording (mark formation). ) 79.

  Each FM-PD 95 constituted by a photodiode branches a part of the laser beam generated by the laser diode 79 by a certain ratio by a half mirror 96, detects a received light signal proportional to the amount of light, that is, the irradiation power, and detects the detected signal. The laser modulation control circuit 75 is supplied. The laser modulation control circuit 75 controls the laser diode 79 so as to emit light with the reproduction laser power, the recording laser power, and the erasing laser power set by the CPU 90 while referring to the light reception signal of the FM-PD 95.

  The laser diode 79 generates laser light in accordance with the drive pulse supplied from the laser modulation control circuit 75. Laser light emitted from the laser diode 79 is irradiated onto the optical disc 1 through the collimator lens 80, the half prism 81, and the objective lens 70. The reflected light from the optical disk 1 is guided to the photodetector 84 through the objective lens 70, the half prism 81, the condenser lens 82, and the wavelength selection prism 101, and through the cylindrical lens 83.

  The photodetector 84 is composed of, for example, four-divided photodetection cells, and detection signals from these photodetection cells are output to the RF amplifier 85. The RF amplifier 85 processes a signal from the light detection cell, a focus error signal FE indicating an error from the in-focus position, a tracking error signal TE indicating an error between the beam spot center of the laser beam and the track center, and the light detection cell. A reproduction signal that is a full addition signal of the signals is generated.

  The focus error signal FE is supplied to the focus control circuit 87. The focus control circuit 87 generates a focus drive signal according to the focus error signal FE. The focus drive signal is supplied to the drive coil 71 in the focusing direction. As a result, focus servo is performed in which the laser light is always just focused on the recording film of the optical disc 1.

  The tracking error signal TE is supplied to the track control circuit 88. The track control circuit 88 generates a track drive signal according to the tracking error signal TE. The track drive signal output from the track control circuit 88 is supplied to the drive coil 72 in the tracking direction. As a result, tracking servo is performed in which the laser beam always traces the track formed on the optical disc 1.

  By performing the focus servo and the tracking servo, a change in reflected light from a recording mark or the like is reflected in the full addition signal RF of the output signal of each light detection cell of the light detector 84. The recording mark is a mark corresponding to the recording information and is formed on the track of the optical disc 1. Therefore, the full addition signal RF is supplied to the data reproduction circuit 78. The data reproduction circuit 78 reproduces recorded data based on the reproduction clock signal from the PLL circuit 76.

  When the objective lens 70 is controlled by the track control circuit 88, the feed motor 67, that is, the optical head 65 is controlled by the feed motor control circuit 68 so that the objective lens 70 is positioned in the vicinity of a predetermined position in the optical head 65. .

  A spindle motor control circuit 64, a feed motor control circuit 68, a laser control circuit 73, a PLL circuit 76, a data reproduction circuit 78, a focus control circuit 87, a track control circuit 88, an error correction circuit 62, and the like are executed by a CPU 90 via a bus 89. Be controlled. The CPU 90 comprehensively controls the recording / reproducing apparatus in accordance with an operation command provided from the host apparatus 94 via the interface circuit 93. Further, the CPU 90 uses the RAM 91 as a work area, appropriately refers to the parameters for each device recorded in the nonvolatile memory NV-RAM 99, and performs a predetermined operation according to a control program including the program according to the present invention recorded in the ROM 92. .

<Laser modulation circuit 75>
Next, FIG. 13 is a block diagram showing a configuration example of the laser modulation control circuit 75 in more detail. The laser modulation circuit can be roughly classified into three parts, that is, a shape generation unit, an APC calculation unit, and a control unit. The waveform generator is a part that generates a recording waveform from the recording clock and recording data and switches the current source corresponding to the recording waveform. The APC calculation unit is a part that controls the current to the laser diode 79 so that the irradiation power commanded from the CPU 90 is obtained during recording and reproduction. The control unit is a part that interprets a control signal from the signal bus 89 and controls the laser modulation control circuit.

  Further, when classified into different functional blocks, a recording pulse output unit 75A, a bias current output unit 75B that outputs a constant bias current between the recording pulses, and a reproduction current output unit 75C that obtains a constant irradiation power during reproduction. And a high-frequency superimposing unit 75D that superimposes a high-frequency signal on the constant bias current between the recording pulses. The high frequency superimposing unit 75D is controlled so that the current values at the start and end of the high frequency signal coincide with the constant bias current value (this function will be described in more detail later). Further, an erasing current output unit for obtaining power at the time of erasing may be provided. The bias current output unit 75B may also serve as a reproducing current output unit and an erasing current output unit.

  The APC calculation unit is attached to the reproduction current output unit 75C and the bias current output unit 75B.

  At the time of reproduction, the received light signal from the monitor light detector 95 is input to the sample hold circuit (S / H) 7506 for holding the state at the time of reproduction via the LPF 7503 for noise removal and sampled. . On the other hand, in the reading APC command circuit 7518, reading irradiation power information included in a control signal input from the CPU 90 via the signal bus 89 is set. The comparison amplifier 7523 compares the sample value from the sample hold circuit (S / H) 7506 with the read irradiation power information (APC command value) from the read APC command circuit 7518, and sets the current source 7541 according to the difference. Control. Thereby, the drive current of the laser diode is controlled, and the light emission intensity is controlled so as to match the set reading irradiation power. The reading switch 7545 is turned on mainly during reproduction.

  At the time of recording, the light reception signal from the monitor light detector 95 in the space between the marks is taken into the sample hold circuit (S / H) 7505. On the other hand, in the bias APC command circuit 7516, space portion irradiation power information included in a control signal given from the CPU 90 via the signal bus 89 and the internal bus 7502 is set. The comparison amplifier 7522 compares the sample value from the sample hold circuit (S / H) 7505 with the space portion irradiation power information (APC command value) from the bias APC command circuit 7516, and a current source 7540 according to the difference. To control. Thereby, the drive current of the laser diode is controlled, and the light emission intensity is controlled to coincide with the set space portion irradiation power. The space switch 7545 is turned on between recording pulses (space period).

  At this time, a waveform in which high frequency superposition is averaged is input to the sample-and-hold circuit (S / H) 7505 due to the low-pass filter effect due to the band limitation of the monitor photodetector 95.

  In addition to the comparison amplifier of the laser modulation control circuit 75, the APC calculation may be performed by the calculation of the CPU 90. In that case, the CPU 90 switches the output of the sample hold circuit 7505 or the sample hold circuit 7506 with the input changeover switch 7513 and inputs it to the AD converter 7507 for analog-digital conversion, and obtains the information through the internal bus 7502 and the signal bus 89. Then, the LD drive current is calculated by calculation. The calculated LD drive current value is set in the bias APC command circuit 7516 or APC command circuit 7518 and transmitted to the current source 7540 or the current source 7541 without passing through the comparison amplifier.

  The waveform generation unit includes a PLL circuit 7508, a modulation circuit 7509, and a high frequency superimposing circuit 7548. The PLL circuit 7508 receives the recording clock and generates a timing signal necessary for the modulation circuit 7509. The modulation circuit 7509 interprets the recording data, generates a recording waveform according to the control signal set by the internal bus 7502, and decomposes it into current source control signals indicating ON / OFF of each current source. The current source control signal is supplied to the switches 7543 and 7544, respectively, and each current source output is turned on and off (ON / OFF) in accordance therewith, whereby the intensity of the LD drive current is generated and the intensity modulation of the irradiation power during recording is performed. Achieved.

  The switch 7545 is a current source switch that is turned on mainly during reproduction. The control circuit 7510 performs on / off control according to a recording / reproduction switching signal included in the control signals from the signal bus 89 and the internal bus 7502.

  The high frequency superimposing circuit 7548 outputs a sine wave having an amplitude and a frequency in a range from approximately 100 MHz to 1 GHz. The amplitude and frequency are determined by a control signal set by the internal bus 7502. The switch 7547 controlled by the modulation circuit 7509 controls the output current of the high frequency superimposing circuit 7548, and intermittent high frequency current is superimposed on the diode drive current. The superposition of the high-frequency current is mainly performed only during reproduction.

  The switch 7543 includes differential transistors T1 and T2. The bases of the differential transistors T1 and T2 are connected in common and then grounded via the switch SW1 and the current source Is. The collector of one differential transistor T1 is connected to the power supply line via a load diode D1. The collector of the other differential transistor T2 is connected to the laser diode LD. The bases of the differential transistors T1 and T2 are respectively supplied with first and second control signals whose phases are inverted from the modulation circuit 7509. The switch SW1 is supplied with a peak current timing control signal from the modulation circuit 7509. Further, a current command value for controlling the amount of current is supplied to the current source Is. The current command value is output from the peak APC setting circuit 7515. In the peak APC setting circuit 7515, peak irradiation power information included in a control signal given from the CPU 90 via the signal bus 89 and the internal bus 7502 is set.

<Another example devised in the modulation circuit 75>
The apparatus of the present invention uses short pulses as recording pulses. For this reason, the response of the photoelectric conversion element for monitoring is slow with respect to the pulse, it is difficult to obtain an instantaneous value, and since the pulse duty ratio is small, the average value with respect to the peak power is small, and the SN ratio of the average value is There are problems such as lowering.

  Therefore, the following devices are applied to the recording pulse output unit 75A. FIG. 14 shows a configuration of the recording pulse output unit 75A shown in FIG. The control signal is input to the peak APC setting circuit 7515. The light reception signal of the FM-PD 95 is input to the subtractor 7551. The output of the subtracter 7551 is integrated by an integrator 7552. The output of the integrator 7552 is sampled by the sample hold circuit 7553. The output of the sampling hold circuit 7553 is input to one end of the comparison amplifier 7554. The output of the peak APC setting circuit 7515 is input to the other input terminal of the comparison amplifier 7554. The difference signal output from the comparison amplifier 7554 is used as a control signal for controlling the current amount of the current source Is. As a result, the current amount of the current source Is is drawn so as to be equal to the value set by the peak APC setting circuit 7515.

  At the time of recording, the light reception signal from the FM-PD 95 in the space portion is input to the integrator 7552. The integrator 7552 and the sample-and-hold circuit 7553 are for FM− with respect to laser light having a specific (one or a plurality of types) pulse length or a light intensity capable of providing a specific (one or a plurality of types) recording mark length. The output of the PD 95 is integrated, and the intensity of the drive current is controlled using the integrated value as a target value. That is, the integrator 7552 performs integration for the output period of the integration gate signal generated by the modulation circuit 7509. The output of the integrator 7552 is input to a sample hold circuit (S / H) 7553 and holds the value at the end of the integration gate signal. Needless to say, the target value may be set by averaging two or more integration results.

  Incidentally, since the integrator 7552 integrates the input DC offset, the presence or fluctuation of the DC offset may cause a large output error. Therefore, it is preferable to provide a circuit for removing the input DC offset. An example is shown.

  Basically, a circuit including an integrator 7556 for detecting offset (previous stage) is provided in front of the integrator 7552, and when an integration gate signal is input to the integrator 7556 for offset detection, an integration gate is supplied from the control circuit 7510 (CPU 90). Only while the signal is supplied, the received light signal input from the FM-PD 95 is integrated. When not (when the received light signal is not input), the integrated value is initialized to zero.

  Hereinafter, the output of the integrator 7556 is input to the sample hold circuit (S / H) 7557 and holds the value at the end of the integration gate signal.

  In order to remove the DC offset, the integrator is operated in a state where the LD 79 is not driven prior to recording of information on the optical disc 1 or reproduction of information from the optical disc (mainly during initialization operation after power-on). A sequence in which integration is started at (pre-integrator) 7556 and output of the integration gate signal is stopped after a certain time has elapsed is useful.

  Therefore, the integrator 7556 accumulates the received light signal output (input offset) in a state where the LD 79 is not driven after a lapse of a certain time (10 times or more time constant determined by the integral gain K (7555)). This offset is canceled by the subtracter 7551.

  FIGS. 15A to 15D show recording data, a recording light pulse (short pulse), an integration gate signal, and an integrator output, respectively. Integration is performed only for a specific mark length (ML1). The mark length to be integrated is set by the CPU 90.

  As yet another example, as shown in FIGS. 16 (a) to 16 (f), the recording pulse portion is integrated regardless of the length of the recording pulse, and the average value of the integrated values is observed to record the recording pulse. A method for controlling the current value to be constant is also suitable. FIGS. 16A to 16F respectively show recording data, a recording light pulse, an integration gate signal, an integrator output, an output of a sample-and-hold circuit (S / H) 7553, and an averaged low-pass filter output, for example. It is.

  In this case, it can be easily realized by inserting a circuit for averaging processing, for example, a low-pass filter (LPF) between the sample hold circuit (S / H) 7553 and the comparison amplifier 7554.

<Measures that can reduce power consumption when obtaining sub-nano class pulsed laser light with a low duty ratio>
As described above, the peak switch 7543 has differential transistors T1 and T2 as shown again in FIG. The bases of the differential transistors T1 and T2 are connected in common and then grounded via the switch SW1 and the current source Is. The collector of one differential transistor T1 is connected to the power supply line via a dummy load diode D1. The collector of the other differential transistor T2 is connected to the laser diode LD. Note that the switch SW1 and the current source Is are normally configured by semiconductor elements, but are schematically illustrated here for the sake of simplicity. Further, it is desirable that the current-voltage characteristic of the load diode D1 is close to the characteristic of the laser diode LD.

  An input P is input to the transistor T2, and an input / P (an inverted signal of P) is input to the transistor T1. The inputs P and / P are binary voltage inputs and have a complementary relationship.

  An input S is supplied to the switch SW1. The input S is also a binary voltage input. As shown in FIG. 18, when the voltage is at a high level, a current passes through the switch SW1, and when it is at a low level, the switch SW1 is opened and no current flows.

  However, turning the current on / off by the switch SW1 causes pulsation of the current in the power supply of the drive circuit, and the influence of parasitic inductance (not shown) existing in the power supply and the wiring path on the way becomes remarkable. Therefore, it is known that a high-speed current having a rise time / fall time of about 1 ns cannot be turned on / off.

  Therefore, currents I (current source), ia (laser diode drive current), and ib (current to the dummy load) are obtained from inputs P, / P, and S as shown in FIG. 18 (to LD). When generating current pulses, give inputs in the following order):

That is,
1) Before changing the input P from the Low level to the High level and changing / P (inversion) from the High level to the Low level, the input S is set to the High level (SW1 is turned on), and the current I starts to flow.

continue,
2) Wait for a time for the current I to stabilize, change the input P from the low level to the high level, change / P from the high level to the low level, and flow the current ia to the LD.

Less than,
3) When the necessary pulse width time elapses, the input P is changed from High level to Low level, / P is changed from Low level to High level, and the current ia to the LD is stopped (the current ib is supplied to the dummy load D1). Flowing). At the same time, or after waiting for an elapsed time until the current ia stops, the input S is changed from the High level to the Low level, and the current I is stopped.

  In this way, by using the switch SW1 having a slow rise time, the current I starts to flow first, and subsequently the switching of the current by the transistors T2 (LD drive) and T1 (dummy load) whose changes are fast is caused to occur. Without sacrificing the rise time / fall time of the drive current to, the time during which current flows to the dummy load diode D1 can be reduced.

  For example, when generating a pulse width of 500 ps with a period of 4 ns, when the switch (SW) 5 is not used, a current flows through the dummy load diode D1 for 3.5 ns. For example, although it depends on how long the switch SW1 is raised (margin time), the time for the current to flow through the dummy load diode D1 can be suppressed to about 1 ns, and the power consumption can be suppressed by about 70%.

  Further, such a property is a pulse whose duty ratio (ON time ratio) is smaller than 1: 1 (50:50), for example, about 10% (1: 9), and has a fast rise time in a period of several ns. It is suitable for “sub-nanopulse recording” that requires light emission.

  FIG. 17 shows an example in which NPN transistors are used for the transistors T1 and T2, and the laser diode LD and the dummy load diode D1 are connected to the anode common connection. However, the circuit is configured with the cathode common connection using the PNP transistor. It is also possible to do.

  Needless to say, even if a field effect transistor is used, it can be driven in the same manner. Furthermore, the LD and the dummy load diode D1 do not have to be diodes, and it is also possible to use resistors and other elements as loads.

  According to this circuit and driving method, power consumption can be greatly reduced when obtaining a sub-nano class pulse laser beam with a low duty ratio as compared with the current driving method. Thereby, the heat generation in the light emitting element or its periphery is greatly reduced.

  In “sub-nanopulse (short pulse) recording”, the laser emission time is less than 10% (1%) with respect to the mark length which is one of the recording mark rows recorded on the optical disc (information recording medium). −10%), the average power value at the time of recording the laser beam may be lower than the power at the time of reproduction.

  On the other hand, depending on the material of the optical disk as the recording medium, there is a material with a low difference in reflectance between the mark portion and the space portion. Therefore, in order to improve the apparent contrast, a recording medium has been developed in which the reflectance of the mark portion or the space portion is lowered to about 2% when information recording is performed.

  When a recording method using sub-nanopulses is applied to information recording on such a recording medium, the average amount of light returning to the photodetector in the optical head during recording becomes extremely small. For this reason, the signal quality of the detection signal is remarkably deteriorated, and an operation (focus / tracking servo) in which an error signal is obtained therefrom and the objective lens is kept at a predetermined position of the recording layer may be impossible.

  Therefore, as an information recording / reproducing device that can increase the average light intensity by superimposing high-frequency signals between recording pulses (the period of the space part), and perform focus tracking servo normally while performing recording by sub-nanopulses. Yes.

  As described above, according to the present invention, it is possible to generate a recording waveform that can determine the pulse width and the delay amount regardless of the recording clock frequency. It became easy to generate constant and very short pulses.

  Conventionally, in high-speed recording of information, it has been common to generate and record a waveform having a pulse width proportional to the recording clock frequency. However, in contrast, in sub-nanopulse recording, recording can be performed with a recording pulse (1 ns) having a constant pulse width even if the speed is increased. Therefore, with the conventional method, in order to obtain the desired recording pulse, it is necessary to decompose the recording clock at high resolution at low speed, but at high speed, the recording clock is decomposed at low resolution. It doesn't matter. As described above, it is necessary to change the resolution of the recording clock between the low speed and the high speed, and a circuit design corresponding to this becomes a heavy burden.

  Conventionally, a ring oscillator is placed at a portion corresponding to a pulse delay circuit, phase division is performed, and a recording waveform is generated from each output by an RS latch.

  FIG. 19 shows a circuit diagram of a simplified ring oscillator. As an example, consider the case of recording on an HD DVD by sub-nanopulse recording. When writing 2T of the shortest mark (T is a length as a mark unit), writing can be performed with a pulse of 1T. At 1 × speed, the recording clock frequency is 32.4 MHz, and 1T required for recording is about 16 ns. On the other hand, at 8 × speed, the recording clock frequency is 259.2 MHz, and 1T required for recording is about 2 ns (= 16/8). When a 1 ns recording pulse is generated by a circuit using a 40-division ring oscillator, in the case of 8 × speed, 1T is divided into 40 and 50 ps (= 2 ns / 40), so 1 ns (= 50 × 20) is generated. However, in the case of 1 × speed, if 1T is divided into 40, 400 ps (= 16 ns / 40) is obtained, and thus a 1 ns pulse cannot be generated. Thus, the required resolution varies depending on the double speed.

  In addition, since the number of divisions of the recording clock is limited, there may be a problem that a desired pulse cannot be generated. This circuit solves this.

  In the above description, FIG. 9 shows one circuit as the internal circuit of the modulation circuit 7509. However, a plurality of circuits similar to the circuit shown in FIG. 9 are provided in the modulation circuit 5509, and output pulses having phases corresponding to purposes are generated.

  FIG. 20 shows an example of the inside of the modulation circuit 5509. That is, 101A1 and 101B1 are first and second pulse delay circuits, and 103-1 is a latch circuit. Further, 101A2 and 101B2 are first and second pulse delay circuits, and 103-2 is a latch circuit. Further, 101Am and 101Bm are first and second pulse delay circuits, and 103-m is a latch circuit. Furthermore, 101An and 101Bn are first and second pulse delay circuits, and 103-n is a latch circuit.

  The outputs of the latch circuits 103-1, 103-2, 103-m, and 103-n are distributed by the distributor 104 and supplied to appropriate switches or control terminals shown in FIG. A control signal is given from the CPU to each pulse delay circuit, and a delay amount is set. Therefore, each of the latch circuits 103-1, 103-2, 103-m, 103-n can obtain an output having a desired phase and pulse width. The CPU can also control the selection operation of the distributor 104. The pulse for controlling the laser diode was generated based on the recording data. However, other switches may of course be created based on the clock obtained from the PLL circuit 7508.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a diagram schematically showing an example of an optical recording apparatus to which the present invention is applied. It is a figure which shows the example of the cross-section of the optical disk 1 used with an optical recording device. It is a figure which shows an example of the light-emitting body structure of a semiconductor laser diode. It is explanatory drawing of the drive current and emitted light intensity of a semiconductor laser diode. It is a figure which shows the measurement result of the relaxation oscillation waveform of the emitted light intensity obtained when the laser resonator length L of a semiconductor laser diode is 650 micrometers. It is explanatory drawing of the amorphous mark formed through the melting-rapid cooling process of a phase change material. It is explanatory drawing which compares and compares the temperature distribution on the recording track in the case of recording by a short pulse, and the temperature distribution on the recording track in the case of recording by a normal recording pulse. It is a figure which shows the relaxation oscillation waveform of the emitted light intensity obtained when a laser drive current is controlled to a semiconductor laser diode so that a relaxation oscillation pulse is generated 3 times. It is a block diagram of the principal part of the recording pulse production | generation apparatus with which this invention is applied. It is a figure which shows the specific structural example of pulse delay circuit 101A, 101B of FIG. It is a figure which shows the relationship between recording data and the signal waveform of each part of the circuit of FIG. 1 is a block diagram showing a configuration example of an information recording / reproducing apparatus (optical disc drive) to which the present invention is applied. FIG. 13 is a block diagram illustrating a configuration example of the laser modulation control circuit 75 in FIG. 12 in more detail. It is a figure which shows another example of a structure of the recording pulse output part 75A shown in FIG. It is the wave form diagram shown in order to demonstrate the operation example of the circuit of FIG. FIG. 15 is a waveform diagram shown for explaining another operation example of the circuit of FIG. 14. FIG. 14 is a circuit diagram showing the switch 7543 shown in FIG. 13 together with a laser diode. FIG. 18 is a waveform diagram shown for explaining the operation of the circuit shown in FIG. 17. It is a figure which shows the basic structural example of a ring oscillator. It is a figure which shows the example of an internal structure of the modulation circuit shown in FIG.

Explanation of symbols

101A, 101B ... Pulse delay circuit, 103 ... Latch circuit, 62 ... Error correction circuit, 63 ... Spindle motor, 63A ... Rotary encoder, 64 ... Spindle motor control circuit, 65 ... Optical head, 67 ... Feed motor, 68... Feed motor control circuit, 70... Objective lens, 71 and 72... Drive coil, 75... Laser modulation control circuit, 75 A. High-frequency superimposing unit 76 ... PLL control circuit 78 78 Data reproduction circuit 79 Laser diode 80 Collimator lens 81 Half prism 82 Condensing lens 83 Cylindrical lens 84 Photo detector 85 RF amplifier, 87 ... focus control circuit, 88 ... tracking control circuit, 89 ... signal bus 90 ... Central processing unit, 91 ... RAM, 92 ... ROM, 93 ... Interface circuit, 94 ... Host device, 95 ... Monitor photodetector, 96 ... Half mirror, 99 ... Non-volatile memory, 100 ... Optical disk, 7502 ... Internal bus , 7505705 ... Sample hold circuit, 7506 ... Sample hold circuit, 7507 ... AD converter, 7508 ... PLL circuit, 7509 ... Modulation circuit, 7510 ... Control circuit, 7513 ... Input changeover switch, 7516, 7518 ... APC command circuit, 7520 ... Bias command circuit, 7522, 7523 ... comparison amplifier, 7523 ... comparison amplifier, 7543, 7544, 7545, 7546, 7547 ... switch, 7548 ... high frequency superposition circuit.

Claims (7)

As a generation method of the laser diode drive time setting pulse,
Inputting the recording data to the first and second pulse delay circuits;
Inputting first and second control signals for setting respective delay amounts to the first and second pulse delay circuits;
Performing set / reset of the latch circuit by the first and second delay pulses obtained from the first and second delay circuits;
Outputting the output of the latch circuit as the laser diode drive time setting pulse. An optical recording pulse generating method comprising:   2. The optical recording pulse generation method according to claim 1, wherein the laser diode drive time setting pulse is a pulse for obtaining a short pulse that causes relaxation oscillation of the laser diode.   3. The optical recording pulse generation method according to claim 2, wherein the short pulse strategy is set by the first and second control signals.   2. The optical recording pulse generation method according to claim 1, wherein the laser diode drive time setting pulse is used as an on / off control signal of a switch for supplying a current to the laser diode. First and second pulse delay circuits to which recording data is input;
A control unit for inputting first and second control signals for setting respective delay amounts to the first and second pulse delay circuits;
A latch circuit that is set and reset by first and second delay pulses obtained from the first and second delay circuits;
An optical recording pulse generating device comprising a switch that is switched by an output of the latch circuit to drive a laser diode.   6. The optical recording pulse generation device according to claim 5, wherein the switch outputs a short pulse that causes relaxation oscillation of the laser diode. In an information recording / reproducing apparatus having a laser modulation control circuit for recording and reproducing information to and from an optical disk by an optical head, the optical head giving a recording pulse to a laser diode,
The laser modulation control circuit includes a modulation circuit that outputs a short pulse that causes relaxation oscillation in the laser diode as the recording pulse,
The modulation circuit includes:
First and second pulse delay circuits to which recording data is input;
A control unit for inputting first and second control signals for setting respective delay amounts to the first and second pulse delay circuits;
A latch circuit that is set and reset by first and second delay pulses obtained from the first and second delay circuits;
An information recording / reproducing apparatus comprising a switch that is switched by an output of the latch circuit to drive a laser diode.

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