JP2002312935A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk device, in which the resolution for setting the laser power is secured at the time of recording operation and a jitter deterioration due to the PWM waveform for setting the laser power is prevented at the time of reproduction. SOLUTION: The device is provided with a recording modulation setting means 15 for outputting the PWM waveform setting the recording laser power from a PWM producing circuit 14 and a reproducing modulation setting means 16 for setting the reproducing laser power and also outputting the PWM waveform having the higher low limit of the frequency band, and the low band frequency components of the PWM waveform at the time of reproduction are prevented from leaking to laser beams while securing the setting resolution at the time of recording operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for optimally setting a laser power for recording and reproduction.

[0002]

2. Description of the Related Art Conventionally, there has been known an optical disk apparatus which records and reproduces data on and from an optical disk such as an MD (mini disk) (registered trademark). This means that during recording, high-power laser light is applied to the disk to perform magneto-optical recording, and during reproduction, low-output laser light is applied to the disk, and data recorded on the disk (encoded audio, etc.) The reflected light modulated by the information signal is received by a light receiving element to detect the content of the data.

It is necessary to adjust the laser power in order to compensate for variations in the characteristics of the disk and the like, and pulse width modulation (PW) is required to set the laser power.
A voltage obtained by smoothing the M) waveform is often used.

A conventional optical disk device will be described below.
D will be described as an example with reference to the drawings. FIG. 3 is a block diagram showing a configuration (part) of a conventional optical disk device. In FIG. 3, the optical pickup 31 includes a laser diode 32, a photodiode 33 for signal detection, a photodiode 34 for monitoring, and a resistor 35 for detection. The cathode of the laser diode 32 and the anode of the photodiode 33 The photodiode 34 has a cathode connected to a power supply and an anode grounded via a resistor 35. The laser light emitted from the laser diode 32 is reflected by the disk 36 and received by the photodiode 33. A part of the laser light emitted from the laser diode 32 is
The light is directly received by the photodiode 34 regardless of.

The PNP transistor 37 has an emitter connected to the power supply and a collector connected to the anode of the laser diode 32.

The operational amplifier (OP) 38 performs current-voltage conversion. The inverting input terminal (-) is connected to the cathode of the photodiode 33, and the non-inverting input terminal (+) is connected to DC.
It is connected to a voltage source 39. The DC voltage source 39 is set to, for example, half the power supply voltage. The output terminal 40 and the inverting input terminal of the operational amplifier 38 are connected via a resistor 41.

[0007] Pulse width modulation generation circuit (PWM generation circuit)
Reference numeral 42 outputs a pulse width modulation waveform (hereinafter abbreviated as a PWM waveform) according to the set value of the laser power. The low-pass filter 43 smoothes the PWM waveform output from the pulse width modulation generation circuit 42 and outputs a DC voltage, and is composed of, for example, a resistor and a capacitor. The output voltage of the low-pass filter 43 is proportional to the pulse width of the PWM waveform and equal to the average peak value.

The operational amplifier 44 has a non-inverting input terminal connected to the anode of the photodiode 34 and an inverting input terminal connected to the output of the low-pass filter 43. The output of the operational amplifier 44 is connected to a transistor 37 via a resistor 45.
Connected to the base.

The operation of the conventional optical disk apparatus configured as described above will be described. The laser light emitted from the laser diode 32 irradiates the disk 36, and the reflected light is received by the photodiode 33 and converted into a current. Further, the converted current is current-voltage converted by the operational amplifier 38 and the resistor 41 and output to the terminal 40. At this time, a data signal or a servo signal included in the reflected light from the disk 36 is output to the terminal 40. Normally, the data signal and the servo system signal included in the reflected light are often reproduced by a dedicated photodiode and a current-voltage conversion circuit, respectively.

On the other hand, a part of the laser light emitted from the laser diode 32 is received by the phototransistor 34, so that a voltage proportional to the laser power of the laser diode 32 is output to both ends of the resistor 35. The operational amplifier 44, the resistor 45, and the transistor 37 are configured so that the error between the voltage across the resistor 35 and the output voltage of the low-pass filter 43 becomes zero. Power is controlled.

As described above, the laser power of the laser diode 32 is proportional to the output voltage of the low-pass filter 43.

The laser power for reproduction is low, and the laser power for recording is several times to about ten times that during reproduction.
Therefore, the PW output from the pulse width modulation generation circuit 42
The M waveform has a pulse width that is several times to about ten times as large as that during reproduction during recording.

Here, the operation of the pulse width modulation generation circuit 42 will be described in detail. The PWM waveform output from the pulse width modulation generation circuit 42 is a digital waveform having the carrier frequency f ₁ and the H (high) level ratio is 0 to 10
It changes in 2 ^m steps (m is a positive integer) to 0%. Less than,
This PWM waveform is referred to as an m-bit PWM waveform for convenience. Particularly, the recording laser power needs to be set finely according to the ambient temperature of the apparatus. The larger the value of m, the finer the setting of the PWM waveform, but it is difficult to obtain a desired resolution because of the circuit scale and clock restrictions.

In order to compensate for the above-mentioned drawback, PWM pulse 2
^{With n} (n is a positive integer) period, a method of expanding or reducing the pulse width by one step for 2 ⁿ pulses constituting one period is performed.

According to this method, 2 ⁿ is added for each stage.
An intermediate value of the steps is obtained, and a DC voltage of 2 ^{(m + n)} steps is apparently output as the voltage after smoothing. Hereinafter, this PWM waveform is referred to as a pseudo (m + n) for convenience.
It is referred to as a bit PWM waveform.

As a specific example, the carrier frequency f ₁ = 100
When kHz, m = 4, n = 3, 4 bits (16 steps)
Can be operated as a pseudo 7-bit (128 steps), and the DC voltage after smoothing can be set more precisely. In other words, it can be seen that the setting resolution is improved.

[0017]

The A problem you try the Invention However the aforementioned conventional configuration, in the spectrum of the pulse width modulated waveform, the frequency component appears in the low frequency side of the carrier frequency f _1. In the case of the above specific example, for f ₁ = 100 kHz, _one -half thereof
³ (= 1/8) of a 12.5 kHz component.

There is a problem that the 12.5 kHz component cannot be completely removed by the low-pass filter 43 and the quality of the reproduced signal is degraded via the optical pickup 31.

As a countermeasure for this problem, the carrier frequency f ₁
Or the low-frequency shift of the cutoff frequency of the low-pass filter 43 was considered. However, in the former, the reference clock frequency for operating the pulse width modulation generation circuit 42 becomes too high, and in the latter, the cost increases due to the enlargement of the capacitor. And a new problem such as an operation delay due to an increase in the time constant occurs, and any method cannot fundamentally solve the problem.

An object of the present invention is to solve the above-mentioned conventional problems, and to provide an optical disk apparatus which secures a setting resolution of laser power at the time of recording and prevents jitter deterioration caused by a laser power setting pulse width modulation waveform at the time of reproduction. The purpose is to provide.

[0021]

In order to achieve the above object, an optical disk apparatus according to the present invention comprises: a first pulse width modulation means for outputting a first pulse width modulation waveform for setting a recording laser power; Pulse width modulation means for setting a laser power for use and outputting a second pulse width modulation waveform having a lower limit of a frequency band higher than the first pulse width modulation waveform, and the first or second pulse width. A low-pass filter for smoothing a modulation waveform, a gain conversion circuit for amplifying an output voltage of the low-pass filter with a first gain during recording, and amplifying with a second gain lower than the first gain during reproduction. And a laser light generating circuit for generating a laser power according to the output voltage of the gain conversion circuit and irradiating the disk.

According to this configuration, since the low frequency component does not occur in the spectrum of the pulse width modulation waveform at the time of reproduction, there is a problem that the low frequency component of the pulse width modulation waveform leaks into the reproduction signal to deteriorate the jitter. Can be prevented. In addition, the provision of the gain conversion circuit improves the setting resolution of the reproducing laser power.

Also, in the optical disk device of the present invention, the low-pass filter is set so as to cut off at least the frequency band of the second pulse-modulated waveform. And the response speed required by the system, such as the switching time between recording and reproduction, can be satisfied at the same time.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, taking an example in which the present invention is applied to an MD.

(Embodiment) FIG. 1 is a block diagram showing a configuration of an optical disk device according to an embodiment of the present invention.

In FIG. 1, an optical pickup 1 comprises a laser diode 2, a photodiode 3 for signal detection, a photodiode 4 for monitoring, and a resistor 5 for detection. Is grounded and the photodiode 4
Has a cathode connected to a power supply (Vcc) and an anode grounded via a resistor 5. Laser light emitted from the laser diode 2 is reflected by the disk 6 and received by the photodiode 3. Further, a part of the laser light emitted from the laser diode 2 is directly received by the photodiode 4 irrespective of the disk 6.

The PNP transistor 7 has an emitter connected to the power supply (Vcc) and a collector connected to the laser diode 2.
Connected to the anode.

The operational amplifier (OP) 8 performs current-voltage conversion. The inverting input terminal (-) is connected to the cathode of the photodiode 3 and the non-inverting input terminal (+) is connected to the DC voltage source 9.
It is connected to the. The DC voltage source 9 is, for example, a power source (Vc
The voltage is set to 1/2 of c). The output terminal 10 and the inverting input terminal of the operational amplifier 8 are connected via a resistor 11. Normally, the data signal and the servo signal included in the reflected light are often reproduced by a dedicated photodiode and a current-voltage conversion circuit, respectively.

The operational amplifier (OP) 12 has a non-inverting input terminal (+) connected to the anode of the photodiode 4,
The output is connected to the base of the transistor 7 via the resistor 13.

Pulse width modulation generation circuit (PWM generation circuit)
14 is a pulse width modulation wave corresponding to the set value of the laser power
A shape (hereinafter abbreviated as PWM waveform) is output. Pulse width variation
The tone generation circuit 14 is a pulse generator in a conventional optical disc device.
A PWM waveform basically similar to that of the width modulation generation circuit 42 is output.
Power. Therefore, detailed description is omitted here.
Is a PWM wave output from the pulse width modulation generation circuit 14.
The shape is the carrier frequency f₁Digital waveform
Bell ratio from 0 to 100% 2^mStage (m is a positive integer
(A) is an m-bit PWM waveform that changes to (number). further,
PWM pulse 2 ⁿ(N is a positive integer) cycle
Pulse 2 that makes up the periodⁿOne step pal for each
Increase or decrease the width of the^{(m + n)}Stage
Generates PWM waveform (pseudo (m + n) -bit PWM waveform)
Power.

The laser power for reproduction is low, and the laser power for recording is several times to about ten times as large as that for reproduction.
Therefore, the PW output from the pulse width modulation generation circuit 14
The M waveform has a pulse width that is several times to about ten times as large as that during reproduction during recording.

The recording modulation setting means 15 outputs the recording laser power setting value from the pulse width modulation generation circuit 14 as a pseudo (m + n) -bit PWM waveform. The reproduction modulation setting means 16 causes the pulse width modulation generation circuit 14 to output a reproduction laser power set value as an m-bit PWM waveform.
^The pulse width is not increased or decreased by ⁿ cycles.

The recording / resetting means 17 switches the output of the selector 18 between recording and reproduction. At the time of recording, the output of the recording modulation setting means 15 is input to the pulse width modulation generating circuit 14 via the selector 18; At the time of reproduction, the output of the reproduction modulation setting means 16 is input to the pulse width modulation generation circuit 14 via the selector 18.

The low-pass filter 19 smoothes the PWM waveform output from the pulse width modulation generation circuit 14 and outputs a DC component, and is composed of, for example, a resistor and a capacitor. The output voltage of the low-pass filter 19 is PW
It is proportional to the pulse width of the M waveform and equal to the average peak value. Note that the low-pass filter 19 determines the carrier frequency f of the PWM waveform.
_The cutoff frequency is set as high as possible within a range where ₁ is completely attenuated, and the response to the output change of the pulse width modulation generation circuit 14 due to the switching operation of the recording / resetting means 17 and the like is hastened.

The gain conversion circuit 20 includes a low-pass filter 1
9 is a circuit that amplifies the output voltage at a low gain during reproduction and amplifies it at a high gain during recording. The gain conversion circuit 20 is composed of, for example, a linear amplifier that amplifies with a low gain when a low voltage for reproduction is input and amplifies with a high gain when a high voltage for recording is input. The output of the gain conversion circuit 20 is the operational amplifier 1
2 inverted output terminals.

In the present embodiment, the first pulse width modulation means is constituted by the pulse width modulation generation circuit 14 and the recording modulation setting means 15, and the pulse width modulation generation circuit 14
The reproduction pulse setting means 16 constitutes a second pulse width modulation means.

The operation of the optical disk apparatus thus configured will be described with reference to FIG.

FIG. 2 is a diagram for explaining the operation of the optical disk device according to the embodiment of the present invention. FIG. 2A shows a frequency spectrum of a PWM waveform output from the pulse width modulation generation circuit 14 during recording, and FIG. Is a pulse width modulation generation circuit 14
, The frequency spectrum of the PWM waveform output during reproduction, (3) is the frequency characteristic of the low-pass filter 19,
(4) shows a frequency spectrum of a waveform obtained by smoothing the PWM waveform at the time of recording by the low-pass filter 19. Note that the illustration of the DC component is omitted in each drawing of FIG. Also, each horizontal axis in the figure is frequency, the vertical axis of (3) is gain, and the other vertical axes are frequency spectrum values (peak values).

First, the operation at the time of recording will be described. During recording, the output of the recording modulation setting unit 15 is input to the pulse width modulation generation circuit 14 via the selector 18 by the recording / resetting unit 17 switching the selector 18. The pulse width modulation generation circuit 14 outputs a pseudo (m + n) -bit PWM waveform. In this case, the frequency component f is the low frequency side of the carrier frequency f ₁ as shown in (1) in FIG. 2
a, fb, fc, ... appear.

As a specific example, the carrier frequency f ₁ = 100
When kHz, m = 4, and n = 3, a 4-bit (16 steps) PWM waveform can be operated as a pseudo 7-bit (128 steps), and the setting resolution of the DC voltage after smoothing is improved. In this case, the frequency components fa, fb, fc,
... is 12.5 kHz and its integral multiple.

By attenuating the PWM waveform with the attenuation characteristic as shown in FIG. 2C by the low-pass filter 19, the frequency component of the smoothed voltage at the output of the low-pass filter 19 becomes as shown in FIG. In addition, low frequency components such as the fa component remain in addition to the DC component.

Since a high smoothing voltage for setting the recording laser power is output from the low-pass filter 19, the signal is amplified at a high gain by the gain conversion circuit 20 and input to the inverting input terminal of the operational amplifier 12.

The laser beam emitted from the laser diode 2 irradiates the disk 6, and the reflected light is received by the photodiode 3 and converted into a current. Further, the converted current is current-voltage converted by the operational amplifier 8 and the resistor 11 and output to the terminal 10. At this time, the data signal or servo system signal included in the reflected light from the disk 6 is supplied to the terminal 1.
Output to 0. Normally, data signals and servo signals included in the reflected light are often reproduced by dedicated photodiodes and current-voltage conversion circuits, respectively.
Since both are well-known technologies, the description is omitted.

On the other hand, a part of the laser light emitted from the laser diode 2 is received by the phototransistor 4, so that a voltage proportional to the laser power of the laser diode 2 is output to both ends of the resistor 5. The operational amplifier 12, the resistor 13, and the transistor 7 are configured so that the error between the voltage across the resistor 5 and the output voltage of the gain conversion circuit 20 becomes zero. Power is controlled. Thus, the laser power of the laser diode 2 is proportional to the output voltage of the gain conversion circuit 20.

As is well known, a magnetic field modulation method is employed for MD recording, and the laser power at the time of recording is used to heat the magnetic film of the disk 6 above the Curie point temperature. For this reason, even if a frequency component such as the fa component remains in the recording laser light, the recorded data has almost no influence such as deterioration of jitter. Therefore, by increasing the cutoff frequency of the low-pass filter 19, it is possible to make the response to the output change of the pulse width modulation generation circuit 14 faster.

Next, the operation during reproduction will be described. At the time of reproduction, the recording / resetting means 17 switches the selector 18, so that the output of the reproduction modulation setting means 16 is input to the pulse width modulation generation circuit 14 via the selector 18. The pulse width modulation generation circuit 14 outputs an m-bit PWM waveform (see FIG. 2 (2)). In this case, PWM
Since the pulse width of the waveform is not changed, the frequency component fa of the low frequency side of the carrier frequency f ₁ as shown at the time of recording in the (4) in FIG. 2, fb, fc, ..., etc., it does not at all appear at the time of reproduction.

As a specific example, similarly to the PWM waveform at the time of recording, the carrier frequency f ₁ = 100 kHz, m = 4, n = 3
Then, it is a 4-bit (16 steps) PWM waveform.

Since a low smoothing voltage for reproduction is output from the low-pass filter 19, the signal is amplified at a low gain by the gain conversion circuit 20 and input to the inverting input terminal of the operational amplifier 12. Since the gain at the time of reproduction is low, the change of the smoothed voltage per stage is compressed, and a coarse set resolution can be sufficiently compensated as compared with the case of recording.

Since the following is the same as the case of recording, detailed description is omitted, but the laser power of the laser diode 2 is proportional to the output voltage of the gain conversion circuit 20.

In this case, the laser light includes fa, fb, fc,.
, There is no frequency component such as fa, fb, fc,... Mixed into the reproduced signal output to the terminal 10, and the signal quality does not deteriorate.

As described above, according to the present embodiment, the performance required for recording and the performance required for recording and reproduction are achieved by using the PWM waveform considering the set resolution at the time of recording and the PWM waveform considering the quality of the reproduced signal at the time of reproduction. Can be compatible.

Further, by using the gain conversion circuit 20 having a linear amplification characteristic in which the gain at the time of reproduction is lower than the gain at the time of recording, the setting resolution of the PWM waveform at the time of reproduction can be set as fine as the recording. It is possible.

Note that some or all of the recording modulation setting unit 15, the reproduction modulation setting unit 16, the recording / resetting unit 17, and the selector 18 may be realized by software.

In the present embodiment, the m-bit PWM waveform is output from the pulse width modulation generation circuit 14 at the time of reproduction, but the pseudo (m + p) is output as long as the remaining frequency components after the low-pass filter 19 can be tolerated. The modulation setting means 16 for reproduction may be configured so as to output a bit PWM waveform (p <n).

As a specific example, carrier frequency f ₁ = 100
By setting kHz, m = 4 and p = 1, 4 bits
When the (16 steps) PWM waveform is operated as a pseudo 5 bit (32 steps), f _{1 is used} as a low frequency component.
/ 2 = 50 kHz appears, but the low-pass filter 19
If it is sufficiently attenuated, there is no practical problem as an apparatus. In this case, there is an advantage that the setting resolution of the laser power at the time of reproduction is improved.

Alternatively, using a known technique, the carrier frequency f ₁ may be increased and the number of bits m may be decreased at the same time with respect to the PWM waveform output from the pulse width modulation generation circuit 14 during reproduction. In this case, since the lower limit of the frequency component can be increased without increasing the reference clock frequency for operating the pulse width modulation generation circuit 14, the reproduction signal quality can be improved.

Further, if the coarseness of the set resolution during reproduction can be tolerated, the gain conversion circuit 20 may be omitted.
Even in such a case, the object of the present invention of improving the laser power setting resolution during recording and improving the signal quality during reproduction can be realized.

In the above embodiment, the MD has been described as an example, but it goes without saying that the present invention can be applied to various disks having different laser powers during recording and during reproduction.

[0059]

As described above, the first pulse width modulation means for outputting the first pulse width modulation waveform for setting the recording laser power, the setting of the reproduction laser power and the lower limit of the frequency band are set as described above. A second pulse width modulation means for outputting a second pulse width modulation waveform higher than the first pulse width modulation waveform, a low-pass filter for smoothing the first or second pulse width modulation waveform, and a low-pass filter. A gain conversion circuit that amplifies an output voltage with a first gain during recording and amplifies with a second gain that is lower than the first gain during reproduction, and generates a laser power corresponding to the output voltage of the gain conversion circuit. And a laser light generating circuit for irradiating the disc with the laser power, the laser power setting resolution can be improved during recording, and the low-frequency Thereby preventing the problem of low frequency components of the pulse width modulated waveform to the reproduced signal because components are not generated aggravate leaked jitter.

Further, by providing the gain conversion circuit,
In addition to the above effects, there is an advantage that the setting resolution of the reproducing laser power can be greatly improved.

Further, since the low-pass filter is set so as to cut off at least the frequency band of the second pulse modulation waveform, there is an advantage that switching between recording and reproduction can be performed quickly in addition to the above-mentioned effect.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a frequency spectrum diagram for explaining the operation of the optical disc device.

FIG. 3 is a block diagram showing a configuration of a conventional optical disk device.

[Explanation of symbols]

 Reference Signs List 1 optical pickup 2 laser diode 3, 4 photodiode 5, 11, 13 resistor 6 disk 7 PNP transistor 8, 12 operational amplifier 9 voltage source 14 pulse width modulation generation circuit 15 recording modulation setting means 16 reproduction modulation setting means 17 Recording / resetting means 18 Selector 19 Low-pass filter 20 Gain conversion circuit

Continuation of the front page F term (reference) 5D075 AA03 CD11 5D090 AA01 CC01 CC04 EE13 KK03 5D119 AA12 AA21 BA01 BB05 HA45 HA54 HA68

Claims (5)

[Claims] 1. A first pulse width modulation means for outputting a first pulse width modulation waveform for setting a recording laser power, and a band higher than the first pulse width modulation waveform while setting a reproduction laser power. A second pulse width modulation means for outputting a second pulse width modulation waveform, a low-pass filter for smoothing the first or second pulse width modulation waveform, and a laser power corresponding to an output voltage of the low-pass filter An optical disk device comprising: a laser light generation circuit for generating a laser beam and irradiating the disk. 2. A first pulse width modulation means for outputting a first pulse width modulation waveform for setting a recording laser power, and a band higher than the first pulse width modulation waveform while setting a reproduction laser power. A second pulse width modulation means for outputting a second pulse width modulation waveform, a low-pass filter for smoothing the first or second pulse width modulation waveform, and an output voltage of the low-pass filter, A gain conversion circuit for amplifying with a gain of 1 and amplifying with a second gain which is lower than the first gain during reproduction; and generating a laser power according to an output voltage of the gain conversion circuit to irradiate the disk. An optical disc device comprising: 3. The second pulse width modulation means outputs a second pulse width modulation waveform having a carrier frequency equal to the first pulse width modulation waveform and a lower limit of the frequency band being higher than the first pulse width modulation waveform. 3. The method according to claim 1, wherein
An optical disk device according to claim 1. 4. The pulse width modulation means according to claim 1, wherein said second pulse width modulation means outputs a second pulse width modulation waveform having a carrier frequency equal to said first pulse width modulation waveform and a fixed pulse width. Or the optical disk device according to 2. 5. The optical disk device according to claim 1, wherein the low-pass filter is set to block at least a frequency band of the second pulse modulation waveform.