JPH1049899A - Optical disk driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk driving device which can prevent deterioration in recording data in still operation and improve reliability of recording of an optical disk. SOLUTION: A high-frequency current is superposed on a laser current for driving an LD1 from a high-frequency oscillating circuit 4 through transistors Q5, Q2, Q3 and Q4. At this point, a switch SW3a is switched over in response to the control from a system controller 10. A voltage VSR at the time of still operation, a voltage VVR at the time of normal reproduction, or 0V at other times is applied to the high-frequency oscillating circuit 4, and a high-frequency current having an amplitude corresponding to the voltage is applied to the laser current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk drive for suppressing deterioration of recorded data on an optical disk due to a still operation.

[0002]

2. Description of the Related Art At present, an optical disk is widely used as a recording medium, and there is a tendency that a biodetape is replaced with an optical disk in an application for recording an audio visual (AV) signal. Some optical disks are recordable, such as magneto-optical disks and phase-change optical disks.
The reliability of such recordable optical discs is, for example, Archival Life or Shelf Life (S
judging by shelf life and repetition life such as helf Life).

[0003] Here, the archival life indicates the degree of deterioration of data recorded once. The shelf life indicates the recording / reproducing characteristics after storage, and is generally 10 to 10.
It is said to be more than 15 years. On the other hand, the repeated life
There are a number of times of repetitive recording and a number of times of repetitive reproduction, and indicates how many times the same track can be recorded and reproduced. For example, in the case of a magneto-optical disk, 1 × 10 ⁶ repetitive recordings and 1 × 10 ⁹ repetitive reproductions are each a guide. However, it is said that the repetition life of the phase change optical disk, which has recently begun to spread, is even shorter than that of the magneto-optical disk.

[0004]

By the way, considering the usage situation of general users, the number of times of repetitive recording of the same track is rarely 1 × 10 ⁶ times, but the same track is repeatedly reproduced. Still) operation is performed frequently, and greatly affects the reliability of the optical disk.

[0005] For example, when the rotational speed of the disk is 3600 rpm
In the case of m, the track on which the still operation is performed is 1
6.67 ms × 10 ⁹ times ≒ 4630 hours ≒ 192 days, that is, the recording data deteriorates in about half a year.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide an optical disk drive capable of preventing deterioration of recorded data and improving the reliability of recording on an optical disk in a still operation. And

[0007]

In order to solve the above-mentioned problems of the prior art and achieve the above-mentioned object, an optical disk drive of the present invention detects an optical output from a semiconductor laser, and detects the result of the detection. A semiconductor laser drive device used in an optical disk drive device equipped with an optical pickup that controls the optical output of the semiconductor laser based on a high-frequency current having a smaller amplitude than that during normal reproduction during a still operation. There is a high-frequency current generating means superimposed on the driving laser current.

Also, in the optical disk drive of the present invention, specifically, the high-frequency current generating means includes:
A high-frequency current having a smaller amplitude than during normal reproduction is superimposed on a laser current for driving the semiconductor laser so that the average of the laser light output is substantially the same as during normal reproduction. Increase the time.

In the optical disk drive of the present invention, a high-frequency current having the same amplitude as that of the prior art is superimposed on the laser current during normal reproduction.
/ N characteristic is obtained. Further, at the time of the still operation, the on / off duty cycle of the semiconductor laser is increased to the extent that the reproduction C / N is not deteriorated, thereby effectively suppressing the deterioration of the recording data when the still operation is frequently performed. it can.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical disk drive according to an embodiment of the present invention will be described. First, read stability will be described. The main factors that determine the number of times of repeated reproduction (hereinafter also referred to as read stability) are (1) laser read power, (2) disk temperature, and (3) disk linear velocity. In the case of a magneto-optical disk, an external magnetic field is also one of the factors. Here, regarding the disk temperature of (2), the ambient temperature is 4
Assuming that the internal temperature rise is 5 to 15 ° C. and the internal temperature rise is 10 to 15 ° C., the maximum temperature of the disk may be expected to be 60 ° C. Regarding the linear velocity of (3), it is disadvantageous that the linear velocity is low.
In the V mode, the still state in the user area located at the innermost periphery is the most disadvantageous state. Here, the CAV mode refers to a mode in which the angular velocity is constant, that is, the rotation of the disk is constant.

[0011] Currently, the ISO standard 5.25 "
FIG. 1 shows an example of read stability in a magneto-optical disk. Here, ω = 2400 rpm, and the radius is 30 mm. Note that the read stability refers to the number of reproductions when the C / N of the write data signal becomes 3 dB smaller than the initial value.

Incidentally, the C / N characteristics required for an optical disk drive differ depending on each optical disk drive. Factors that contribute to the C / N characteristics include the disk format (recording density, modulation method, error correction method, etc.), optical system (NA, λ, LD / PD noise), media (sensitivity, disk noise), and recording compensation. and so on. 43 dB or more for 5 ″ 2 × ISO standard, 5 ″ 4
In x, it is standardized as 46 dB or more. Usually, in the design of an optical disk drive, a margin of 3 to 6 dB is usually taken in consideration of variations and compatibility.
3d from the initial C / N as the standard of read stability
It is the number of times when B down.

In FIG. 1, the horizontal axis indicates read power, and the vertical axis indicates read stability. Also, the case where the medium temperature is 40 ° C. and the case where the medium temperature is 60 ° C. are shown. FIG. 1 shows that the lower the media temperature and the lower the read power, the better the read stability. In the case of a magneto-optical disk, there is an external magnetic field dependency, and the read stability is better as the external magnetic field is smaller.

Since the ambient temperature is unambiguously determined for the media temperature, it is important how the internal temperature is reduced. However, there is a limit to lowering the media temperature because improving ventilation and contaminating dust are incompatible.
Also, if the read power is reduced, the reproduction C / N is deteriorated, so that the read power cannot be reduced more than necessary. This is because when the read power is reduced, the signal level is reduced, and the laser noise due to the influence of the return light to the laser is increased. From the above situation, it is conceivable to improve read stability by (1) providing a refuge area, (2) reducing read power, and (3) reducing external magnetic field strength. This is intended to improve read stability while obtaining a stable reproduction signal without lowering the readout stability.

In general, when a semiconductor laser is used for an optical pickup, when the optical disk is irradiated with focused light and a recording signal and a servo signal are obtained from the optical disk, reflected light from the optical disk returns to the laser side to some extent. Scoop noise and mode hopping noise due to interference between the return light and the irradiation light are caused by the amount of light returned to the laser and the optical path length, causing C / N deterioration of the reproduced signal, and these noises are generated by 30 mW. This is remarkable in high-power semiconductor lasers of the class.

As a method of reducing the noise due to the return light, a high-frequency superposition method is known. This is shown in FIG.
As shown in (a), the laser DC bias current I
_In this method, a high-frequency current having a current amplitude of 2 × (I _R −I _th ) or more is superimposed on _R , and the optical output of the LD 1 at this time has an on / off waveform as shown in FIG. APC (Auto) so that the average power becomes appropriate read power.
Power Control) circuit.

FIG. 3 is a configuration diagram of the high-frequency superposition circuit and the APC circuit. In the circuit shown in FIG.
And still time, the output of the high-frequency oscillation circuit 4 is supplied to the laser diode LD1 via the capacitor C1, the output voltage of the photodiode PD2 for receiving the laser beam from the read power setting voltage V _R and LD1 which is set by the switch SW3b Are controlled by the error amplifier 6 and the current booster 9 so that the DC bias current supplied to the LD 1 is controlled. In FIG. 3,
“5” indicates a current-voltage conversion circuit.

The effect of harmonic superposition is related to the superposition frequency and the duty cycle of the on / off waveform shown in FIG. Regarding the superposition frequency, there is an optimum value in each optical system according to the return light amount and the optical path length described above,
Generally, 200 to 500 MHz is used for optical disks.

As for the on / off duty cycle, it is generally said that the shorter the duty cycle in the ON (LD1 emission) section has a higher frequency superimposing effect, the shorter the duty cycle is. , APC
When the circuit controls the average power to be constant, the peak value of the emission power increases. FIG. 4 shows the difference in peak value due to the difference in duty cycle. FIG.
(A) is a case where the ON section of LD1 is 46.5%,
FIG. 4B shows a case where the ON section of LD1 is 38.0%. In this case, the peak value of the optical power shown in FIG. 4B is larger than the peak value of the optical power shown in FIG.

The read power in the read stability graph shown in FIG. 1 is the average power, but when the average power is the same, it is expected that the read stability characteristic will deteriorate as the peak power due to the high frequency superposition increases. In particular, at present, the characteristics are 1 to 2 more than magneto-optical disks.
The effect is great for phase-change optical discs with orders of magnitude worse.

Hereinafter, an optical disk drive according to an embodiment of the present invention will be described in detail. This optical disk drive ensures read stability without lowering the read power (without deteriorating the C / N of reproduced data) even on a phase change optical disk having a lower read stability than a magneto-optical disk. Is what you do.

More specifically, when a still operation is performed, the high frequency superimposition level is changed, the on / off duty cycle is increased until the reproduction C / N is not degraded, and the peak value of the light emission power is increased. Decrease. At this time, the average power is kept constant by the APC circuit.

FIG. 5 is a specific circuit configuration diagram of a laser light output control circuit including a harmonic superimposing circuit in the optical disk drive 1 of the present embodiment. In FIG. 5, the transistors Q1, Q2, Q3, Q4, and Q5 form a differential switching type laser drive circuit. In this differential switching type laser drive circuit, a current mirror circuit is formed by the transistors Q3 and Q4, and a drive current is supplied from the collector of the transistor Q4 to the LD1. Among these transistors, the transistors Q1, Q2, Q3 and Q4 form an LD current booster 9, and the transistor Q5 forms an LD current control circuit 13.

The D output from the recording signal generating circuit 8 is supplied to the base of the transistor Q2, and the inverted D (D bar) output is supplied to the base of the transistor Q1. By the D output and the inverted D output, the transistor Q2 or Q
1 is turned on, and each mode described later is set. When the transistor Q2 is turned on by the D output, the collector current of the transistor Q4 is supplied to LD1, and the APC circuit (A
utomatic Power Control) 14 to voltage DDR described later
V is applied to the base of transistor Q5 to control the collector current of transistor Q4, that is, the current supplied to LD1.

The transistor Q10 has a high frequency oscillation circuit 4
And the transistor Q10
Is connected to a transistor Q9 constituting a buffer. At the time of reading and stilling, the oscillation output of the high-frequency oscillation circuit 4 is supplied to the base of the transistor Q5 via the transistor Q9 and the capacitor C1, whereby the collector current of the transistor Q5 is amplitude-modulated. A high frequency current is superimposed on the current. Here, the transistor Q
10, a modified Colpitts circuit is constituted by the capacitors C1 to C3, the coils L1 and L2, and the resistors R1 to R3, and the oscillation frequency f0 is given by the following equation (1).

F0 = 1 / {2π (L1 × C0) ^1/2 )} (1) In the above equation (1), C0 = C1 // C2 // C3.

The MODON signal applied to the base of the transistor Q10 constituting the high-frequency oscillation circuit 4 becomes high level at the time of reading and still, causing the high-frequency oscillation circuit 4 to oscillate. On the other hand, the MODON signal is at a low level except during the read and the still, and the high-frequency oscillation circuit 4 does not oscillate.

Here, the level of the MODON signal is determined according to the switching operation of the switch SW3a in response to the switching signal S10a from the system controller 10. The switch SW3a is connected to R
￣ terminal, connected to the NR terminal during normal read operation, and connected to the SR terminal during still playback. here,
The R # terminal supplies a ground level voltage, and the SR terminal supplies a voltage approximately twice that of the NR terminal. Therefore, the level of the high-frequency superimposed signal at the time of still reproduction is approximately half the level of the high-frequency superimposed signal in the normal read operation. Therefore, the duty cycle in the ON section of the LD 1 during still reproduction increases, and the peak value of the optical power can be reduced.

FIG. 6A shows an IP (supply current-optical output) curve at the time of still reproduction when a semiconductor laser of a 30 mW class is used, and FIG. 6B shows an I-P curve in a normal read operation. -It is a P curve. FIG. 6 (A), (B)
As shown in, the level of the high-frequency superimposed signal is about half that during still playback compared to normal read operation,
As a result, the duty cycle in the section where the LD1 is on increases, and the peak value of the optical power decreases.

In the example shown in FIG. 6, the threshold current I _th
= 40 mA and the current I _OP = 1 when the light emission output is 30 mW
00 mA, and the differential efficiency is 0.5 [mW / mA].
(30 mW / (100-40) mA). Normally, in an optical disk drive, the optical power (objective lens emission output) that contributes to actual recording / reproduction depends on the characteristics of optical components (transmission / reflectance, spectral ratio, etc.) and filter conditions.
It is said that 40-50% of the original power of the semiconductor laser is reasonable. The ratio between the output of the objective lens and the original power is called the coupling efficiency. Here, as an example, it is assumed that I _th = 40 mA, I _op = 100 mA, coupling efficiency = 40%, and read power (average power of objective lens output) 1.2 mW. At this time, the average original power of the semiconductor laser is 3 mW (1.2 / 0.4), and the laser current is 46 mA (40 + 3 / 0.5).

Next, a case where high frequency superposition is applied will be described. FIG. 6 (A) shows a still time, when the high-frequency superimposed level has a current amplitude of 12 mAp-p, the laser current changes by 40 to 52 mA, and the original power is 0 to 6 mW (the objective output is 0 to 2. 4 mW), and the emission peak value of the objective output becomes 2.4 mW. FIG. 6B shows a normal read operation in which the high-frequency superposition level is set to a current amplitude of 24 mAp-p in order to enhance the high-frequency superposition effect. At this time, the laser current changes by 34 to 58 mA, and the original power becomes 0 to
The power changes by 9 mW (the objective output is 0 to 3.6 mV), the emission peak value of the objective output is 3.6 mW, and the off section of the LD 1 is longer than that in FIG.

When the MODON signal becomes high level and the high-frequency oscillation circuit 4 oscillates, the oscillation output is supplied to the base of the transistor Q5 constituting the LD current control circuit 13 via the buffer transistor Q9 and the capacitor C1. A high-frequency current is superimposed on the collector current of Q4.

The current-to-voltage converter 5 for converting a photocurrent proportional to the optical output from the PD 2 into a voltage supplies the output voltage to the APC circuit 14. In the APC circuit 14,
In each mode (reproduction R, recording W, erasure E) selected by the switch SW under the control of the system controller 10, the light output is compared with the corresponding reference voltage, and the output voltage is compared with the LD current control circuit 13. Is input to the base of the transistor Q5 as DDRV, the collector current of the transistor Q4 is controlled, and the light output in each mode of the LD1 becomes constant.

The operation of each mode of the laser light output control circuit shown in FIG. 5 will be described below. <LD1 off> When the LD1 is turned off and no light is emitted, the recording signal generation circuit 8 outputs D = L (low level),
= H (high level) is output and DDRV = 0. As a result, the transistor Q1 is turned on,
The transistors Q2, Q3, and Q4 are turned off, the collector current of the transistor Q4 does not flow, and the light output of the LD1 is zero. At this time, the switch SW3a is connected to the R # terminal, and the MODON signal = 0 (L).

[0034] When the <playback (read) mode> playback mode, from the recording signal generation circuit 8 D = H, inverted D = L is output in a state of DDRV = V _R. Also,
The switch SW3a is connected to the NR terminal, the MODON signal = V _NR , the high-frequency oscillation circuit 4 oscillates, and the LD1 receives the collector current of the transistor Q4 on which the high-frequency current is superimposed, and outputs a pulsed light. is obtained, the average light output is maintained at P _R.

[0035] <Still mode> For still mode, from the recording signal generation circuit 8 D = H, inverted D = L is output in a state of DDRV = V _R. The switch SW3a is connected to the SR terminal, the MODON signal = V _SR , the high-frequency oscillation circuit 4 oscillates, and the LD1 receives the pulse of the collector current of the transistor Q4 on which the high-frequency current is superimposed. light output is obtained, the average light output is maintained at P _R.

<Recording Mode> From the recording signal generating circuit 8, D = (H → L → H) and inverted D =
(L → H → L) is output and DDRV = V _W , and the light output of the LD 1 is a pulse light emission of the peak light output P _W synchronized with the D and inverted D modulation signals. At this time, the switch SW3a is connected to the R # terminal, and the
N signal = 0. <Erase Mode> From the recording signal generating circuit 8, D = H and D = L inverted. At this time, the switch SW3a is set to R
ＭＯ Terminal is connected, and MODON signal = 0.

As described above, according to the optical disk drive 1, when driving a phase-change optical disk, which is said to be inferior to a magneto-optical disk due to its repetitive recording / reproducing characteristics, it frequently repeats during still reproduction. Reproduction characteristics can be improved. Also, according to the optical disk drive 1,
Since the average optical power at the time of reproduction is not reduced as compared with the related art, the C / N characteristics of the reproduced data can be maintained with high accuracy as in the related art.

The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the case where the Colpitts oscillation circuit is used as the high-frequency oscillation circuit has been described.
Alternatively, a Hartley oscillation circuit may be used as the oscillation circuit.

[0039]

As described above, according to the optical disk drive of the present invention, it is possible to effectively suppress the deterioration of the recording data when the still operation is frequently performed. Further, according to the optical disk drive of the present invention, the average optical power at the time of reproduction is not reduced as compared with the related art, so that the C / N characteristics of the reproduced data can be maintained with high accuracy as in the related art.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between read power and read stability of a semiconductor laser used in an optical disk drive.

FIG. 2 is a diagram showing I in a read operation of a semiconductor laser;
It is a P curve (supply current-light output).

FIG. 3 is a configuration diagram of a high-frequency superposition circuit and an APC circuit;

FIG. 4 shows a difference in peak value due to a difference in duty cycle. FIG.
(B) shows the case where the LD on section is 38.0%.
Is the case.

FIG. 5 is a specific circuit configuration diagram of a laser light output control circuit including a harmonic superimposing circuit in the optical disk drive according to the embodiment of the present invention.

FIG. 6A is an IP (supply current-optical output) curve at the time of still reproduction when a semiconductor laser of a 30 mW class is used, and FIG. 6B is a diagram showing a normal read operation; It is an IP curve.

[Explanation of symbols]

4 ... High frequency oscillation circuit, 5 ... Current-voltage conversion circuit, 8 ... Recording signal generation circuit, 9 ... LD drive circuit, 10 ... System controller, 13 ... LD current control circuit, 14 ... APC
circuit

Claims (4)

[Claims] 1. A semiconductor laser drive device used in an optical disk drive device equipped with an optical pickup that detects an optical output from a semiconductor laser and controls the optical output of the semiconductor laser based on the detection result. An optical disk drive device having a high-frequency current generating means for superimposing a high-frequency current having a smaller amplitude than that during normal reproduction on a laser current for driving the semiconductor laser. 2. The high-frequency current generating means generates a high-frequency current having a smaller amplitude than during normal reproduction so that the average of the laser beam output during still operation is substantially the same as during normal reproduction.
2. The optical disk drive according to claim 1, wherein the light emission time of the semiconductor laser is made longer than that in a normal reproduction by superimposing the laser current on a laser current for driving the semiconductor laser. 3. An optical disk drive according to claim 1, wherein said high-frequency current generating means has a Colpitts oscillation circuit. 4. The optical disk drive according to claim 1, which drives a phase change optical disk.