JPH07129957A - Laser driving circuit - Google Patents

Abstract

PURPOSE:To provide an inexpensive laser driving circuit with simple constitution capable of recording and correcting edge emphasis by adding a small scale circuit. CONSTITUTION:When a mark is formed on a recording medium, a power level of a laser is set to write power at a prescribed voltage of a maximum value control voltage, and the power level of the laser between marks is set to pedestal power at the prescribed voltage of a minimum value voltage. The timing of laser emission at the time of mark formation is taken by respectively inputting a recording signal and an inversion recording signal whose polarities are inversed each other to transistors TR1, TR2. A semiconductor laser LD is driven by the current and the timing corresponding to the set write power and the set pedestal power. Then, a correction circuit to make the power level from the LD into the power level which is larger than the write power corresponding to the difference between the write power level and the pedestal power level when the power level from the LD is changed to the write power is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser drive circuit for controlling the drive of a laser used in a magneto-optical disk device or the like.

[0002]

2. Description of the Related Art Currently, optical recording is performed by utilizing the thermal property of a laser beam. The recording / reproducing of the magneto-optical disk is performed by irradiating the laser beam emitted from the laser to about 1 μm and irradiating it onto the perpendicularly magnetized film surface. The record is
Curry point writing is used. The laser light is emitted while the intensity is modulated according to the information to be recorded. The part where the light spot (laser light) hits is heated. When the temperature of the recording film exceeds (or becomes higher) than the Curie point (the temperature that can be obtained by the material used for the optical disk, etc.), the recording film in that portion becomes non-magnetic. When irradiating with laser light, heating is performed while applying a magnetic field to the outside. When the optical disk rotates and moves out of the position of the light spot, the temperature of the recording film decreases. When the temperature of the recording film decreases, the recording film is magnetized in the direction of the external magnetic field applied when the temperature further decreases below the Curie point. Recording is performed by changing the direction of magnetization in this way.

On an optical disk (optical recording medium), tracks for recording information are formed in a spiral shape or a concentric shape. Tens of thousands of tracks are formed with one track as one track. 0 and 1 on this track
2 types of information units corresponding to are formed and information is recorded. Generally, the magnetization of the tracks of the magneto-optical disc is aligned in one direction (for example, upward) by applying a strong external magnetic field before recording. Then, a mark having a magnetization in the opposite direction (for example, downward) is formed on the track. The recording information is represented by the presence or absence of the mark, the position, the front end (front edge) position, the rear end (rear edge) position of the mark, the mark length, and the like. Particularly, a method in which the edge position of the mark represents information is called mark length recording. Incidentally, the mark has been called a pit or a bit in the past, but recently it is called a mark.

Such marks are formed by utilizing heat as described above. The power of the laser at this time is as shown in FIG. The laser power level when the mark is formed is the write power (Pw), and the laser power level when the mark is not formed is the pedestal power (Pped).
Is. However, the mark is not formed unless the temperature of the recording film is higher than the Curie point. That is, even if the laser power is the write power, the mark is not formed at the front edge portion of the mark because it is not formed unless the temperature of the recording film is higher than the Curie point.
(It becomes thinner or shorter.) Conversely, at the back edge of the mark, the temperature of the recording film does not immediately drop below the Curie point, so the mark formation does not end immediately (thicker. Or it will become long.). Therefore, the mark cannot be formed in an appropriate shape.

Therefore, recording correction by edge enhancement is performed by setting the laser power as shown in FIG. The power level of the laser is set higher than the write power at the portion forming the front edge of the mark and lower than the pedestal power at the portion forming the rear edge of the mark. In this way, the mark is formed in a proper shape. At this time, the amount of laser power when the front edge of the mark is emphasized (the amount of light emitted more than the write power) is called the overshoot amount, and the amount of laser power when the rear edge of the mark is emphasized (pedestal). The amount of light emitted less than the power) is called the undershoot amount. The amount of overshoot and the amount of undershoot are called recording correction amount. This recording correction amount can be determined by the edge enhancement amounts I ₁ and I ₂ and the time constant τ.

In such recording correction, the recording correction amount varies depending on various conditions such as the linear velocity (radial position) of the recording medium at the time of recording, the temperature, and the laser power for recording. Therefore, for example, when the overshoot amount is the amount shown by the solid line in FIG. 5, the time constant τ of the circuit is changed to increase or decrease the overshoot amount as shown by the broken line. The amount of overshoot was optimal. Regarding the amount of undershoot, the optimum amount of undershoot was similarly set.

[0007]

However, the conventional technique requires a circuit for changing the time constant in order to change the recording correction amount. Therefore, there is a problem that the number of circuits increases and the laser driving device becomes expensive. The present invention has been made in view of the above problems, and an object of the present invention is to provide a laser driving device that can perform recording correction by simplifying the configuration.

[0008]

As a result of earnest research, the inventors of the present invention have fixed the time constant of the laser drive circuit, and have set the power level of the laser [write power (first power level) and pedestal power ( It was found that the edge emphasis amount can be changed by changing the second power level)]. By doing so, the power level of the conventional laser [write power (first power level) and pedestal power (second power level)]
The present invention has been accomplished by finding that the configuration is simple because the recording correction amount can be set by the circuit that performs the setting.

That is, in the laser drive circuit of the present invention, firstly, "the laser power level is set to the first power level and the second power smaller than the first power level according to the level of the input signal. In a laser drive circuit for controlling the level to a level, when the power level of the laser changes to the first power level, the power level of the laser corresponds to the difference between the first power level and the second power level. A correction circuit for increasing the power level higher than the first power level is provided (claim 1).

Second, in a laser drive circuit for controlling the power level of a laser to a first power level and a second power level smaller than the first power level according to the level of an input signal. , When the power level of the laser changes to the second power level, the power level of the laser is higher than the second power level corresponding to the difference between the first power level and the second power level. A correction circuit for reducing the power level is provided (Claim 2) ”.

Further, preferably, thirdly, "a laser drive for controlling the laser power level to a first power level and a second power level smaller than the first power level according to the level of an input signal. In the circuit, when the power level of the laser changes to the first power level, the power level of the laser corresponds to a difference between the first power level and the second power level. A first correction circuit for increasing the power level higher than
Correction circuit for setting the power level of the laser to a power level smaller than the second power level corresponding to the difference between the first power level and the second power level when the power level changes to the second power level. And are provided (claim 3) ”.

Preferably, fourthly, "the overshoot amount due to the laser power level higher than the first power level or the undershoot amount due to the laser power level lower than the second power level is edge-emphasized. Is determined according to the amount I, and the edge enhancement amount I
Is (edge emphasis amount I) = (edge emphasis degree) × [(first
Power level)-(second power level)] (claim 4) ”. However, the edge emphasis degree is a constant.

Further, since the correction circuit for generating the overshoot amount and the undershoot amount is one correction circuit, the circuit is not bulky.
preferable. Therefore, preferably, it is preferably composed of "the first correction circuit and the second correction circuit are combined into one correction circuit (claim 5)".

[0014]

The recording correction amount can be set by setting the pedestal power (second power level) and the write power (first power level), which are in the conventional laser drive circuit.
Recording medium linear velocity (or radial position), temperature,
Alternatively, it is possible to easily set the optimum recording correction amount according to various conditions such as the recording correction value recorded in advance on the recording medium.

FIG. 2 is a diagram showing an example of a laser emission waveform at the time of recording correction by the laser driving device of the present invention. The laser power level when forming marks on the recording medium is set to the write power (Pw) (first power level), and the laser power level between the marks is set to the pedestal power (Pped) (second power level). ). The laser power level is Pw> Pped. The recording correction is performed by emphasizing the front edge and the rear edge of the mark. In that case, the power level of the laser at the front edge is higher than the write power (overshoot amount), and the power level of the laser at the rear edge is lower than the pedestal power (undershoot amount). The emphasis amount I of each edge is equal to the front and rear edges, and the emphasis degree is represented by the following equation.

Edge enhancement degree = I / (Pw-Pped) Further, it is represented by a time constant τ (FIG. 2). The edge emphasis degree and the time constant τ are fixed. That is, (Pw-Ppe
By changing d), the edge enhancement amount I changes and the recording correction amount can be set to an appropriate value.

It is preferable that the edge emphasis amount I is the same for both the front and rear edges because one circuit can process it, but it may be different for the front and rear edges. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0018]

1 is a schematic diagram showing an embodiment in which a laser drive circuit of the present invention is used in a magneto-optical disk device. The degree of emphasis of the front edge and the rear edge of the mark at the time of recording correction is expressed by the following equation. Edge emphasis degree = R2 / R1 time constant τ = L / R2 The edge emphasis degree is fixed to R2 / R1 and the time constant τ is fixed to L / R2. The edge emphasis amount I is expressed by the following equation.

(Edge emphasis amount I) = R2 (Pw-Pped) / R1 That is, the recording correction amount is determined by changing the write power (first power level) and the pedestal power (second power level). The write power (first power level) is controlled by the maximum control voltage, and the pedestal power (second power level) is controlled by the minimum control voltage.

When forming marks on the recording medium, the power level of the laser is set to the write power (first power level).
The maximum value control voltage is set to a predetermined voltage value, and the laser power level between the marks is set to the pedestal power (second power level). This is done by setting the voltage value of. The laser emission timing at the time of forming the mark is performed by inputting the recording signal and the inverted recording signal whose polarities are mutually inverted to the differential transistor. Set light power (first
Laser power level), and the semiconductor laser L with a current and timing corresponding to the pedestal power (second power level).
Drive D.

Next, the operation of this laser drive circuit will be described. In this laser drive circuit, the polarities of the inverted recording signal and the recording signal are mutually inverted (when a high level signal is input to one side, a low level signal is input to the other side). There are two types of motion. It should be noted that this input signal may be a binary signal and may not be a signal whose polarities are opposite to each other as in the present embodiment.

First, when the inverted recording signal is a low level signal, T
R1 is turned off. At this time, since the recording signal is a high level signal, TR2 is turned on. Therefore, a current flows through TR2. This current is determined by the voltage of the maximum value control voltage. The voltage-current conversion circuit 11 converts the voltage of the maximum value control voltage into a current to control the constant current source 12. The current flowing through the constant current source 12 controls the current flowing through the TR2 side. At this time, the current flowing between ac is I '. R2 in steady state
Since L and L are parallel, there is a short between a and b. That is, there is a voltage drop of I′R1 between a and c. There is also a voltage drop between the base and emitter of TR3 and TR4. In this way, the potential at point d is determined and the current flowing through the LD is determined. The LD emits light according to the magnitude of this current. The maximum current flowing through the LD is controlled by the constant current source 14. Further, when the steady state is not established, that is, when TR2 is turned on from off, there is a voltage drop of I ′ (R1 + R2) between a and b. Therefore, there is a voltage drop between a and c as compared with the steady state, and the potential at the point c is low, so that the light emission of the LD can be increased. Then, the light emission returns to the steady state with the time constant L / R2. In this way, when the laser light emission (power level) is changed from the pedestal power (second power level) to the write power (first power level), the light emission that is larger than the steady state (write power) is first obtained. It is possible to realize (laser power level) and then to emit less light than the light emission (power level) with a circuit having a simple configuration.

Next, when a high level signal is input to the inverted recording signal, TR1 is turned on, and a low level signal is input to the recording signal, so TR2 is turned off.
In the steady state, since TR2 is off, no current flows between a and c, and the base potential of TR3 becomes the value of the minimum control voltage. In addition, there is a voltage drop between the base and emitter of TR3 and TR4. In this way, the potential at point d is determined and the current flowing through the LD is determined. The LD emits light according to the magnitude of this current. The maximum current flowing through the LD is controlled by the constant current source 14. In addition, when the steady state is not established, that is, TR1 changes from OFF to ON
When R2 goes from on to off, I'is between a and c
Since there is a voltage drop of (R1 + R2), the potential at the base of TR3 is higher than the potential in the steady state,
It is possible to reduce the light emission of the LD. Then, the potential of the pedestal power (second power level) in the steady state is approached with a time constant L / R2. In this way, when the laser emission (power level) is changed from the write power (first power level) to the pedestal power (second power level), the emission (power level) smaller than the pedestal power (second power level) ( It is possible to realize the light emission larger than the light emission (power level) after the light emission is set to the power level with a circuit having a simple configuration.

Since the recording medium records data while rotating, the position where data is recorded (radial position)
Depending on the linear velocity. If the linear velocity is different, the power of the laser light at the time of recording also becomes different, and the recording correction amount also becomes different. Therefore, it is preferable to provide a means for obtaining the radial position and add means for controlling the power of the laser light from the obtained radial position to the laser drive circuit.

Further, the power of the laser light at the time of recording also varies depending on the recording medium and the thermal time constant of the recording medium, and the recording correction amount also varies. In this case, once a mark is formed (trial writing), a means for measuring this mark is provided, and a means for controlling the power of the laser light for forming an optimum mark from the formed mark is laser-driven. It is preferably added to the circuit.

Further, even when the temperature of the recording medium is high or low, the power of the laser light at the time of recording is different and the recording correction amount is also different. Therefore, the power of the laser light is controlled based on this temperature. It is preferable to add a means for doing so to the laser drive circuit. The light intensity of the laser is set to the light power (first power level) and the pedestal power (second power level).
The laser may be controlled by providing a monitor of the amount of laser light in order to check whether or not the laser power level is properly met.

In this case, the power of the laser beam can be controlled by using the control circuit shown in FIG. The set write power (first power level) is controlled by detecting the difference between the write power setting voltage and the power monitor signal voltage from the laser power monitor circuit that detects the power level when the laser emits light, and samples the value. The / hold circuit samples and holds a predetermined write power sample timing signal. The held error voltage value is output to the laser drive circuit (FIG. 1) as the maximum value control voltage by the loop filter circuit, and closed loop control is performed to settle to a predetermined write power setting voltage or light power of the write power. The control of the set pedestal power detects the difference between the pedestal power setting voltage and the power monitor signal voltage from the laser power monitor circuit that detects the power level when the laser emits light, and samples the value.
The hold circuit samples and holds with a predetermined pedestal power sample timing signal. The held error voltage value is output to the laser drive circuit (FIG. 1) as the minimum control voltage by the loop filter circuit, and
Closed loop control is performed to settle to a specified pedestal power setting voltage or pedestal power light amount.

The laser power control is not limited to this method.

[0029]

According to the present invention, since recording correction by edge enhancement can be realized by adding a small-scale circuit to the conventional laser drive circuit, it is possible to provide an inexpensive laser drive circuit with a simple structure.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a laser drive circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a laser emission waveform at the time of recording correction according to an example of the present invention.

FIG. 3 is a schematic diagram showing a laser control operation at the time of recording correction according to the embodiment of the present invention.

FIG. 4 is a waveform diagram of a laser beam used for conventional recording.

FIG. 5 is a waveform diagram of a laser beam subjected to conventional recording correction.

[Explanation of symbols]

12, 13, 14 ... Constant current source 11 ... Voltage / current conversion circuit TR1, TR2, TR3, TR4 ... Transistor element R1, R2, R3, R4 ... Resistor element L ... Inductance element Amp ・ ・ ・ Amplifier LD ・ ・ ・ Semiconductor laser diode ▽ ・ ・ ・ 0V-V ・ ・ ・ Negative power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Ishii 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (5)

[Claims] 1. A laser drive circuit for controlling the power level of a laser to a first power level and a second power level smaller than the first power level according to the level of an input signal. When the power level changes to the first power level, the power level of the laser is increased to a power level higher than the first power level corresponding to the difference between the first power level and the second power level. A laser drive circuit, characterized in that a correction circuit is provided. 2. A laser drive circuit for controlling the power level of a laser to a first power level and a second power level smaller than the first power level according to the level of an input signal. When the power level changes to the second power level, the power level of the laser is set to a power level smaller than the second power level corresponding to the difference between the first power level and the second power level. A laser drive circuit, characterized in that a correction circuit is provided. 3. A laser drive circuit for controlling the power level of a laser to a first power level and a second power level smaller than the first power level according to the level of an input signal. When the power level changes to the first power level, the power level of the laser is increased to a power level higher than the first power level corresponding to the difference between the first power level and the second power level. A first correction circuit for adjusting the power level of the laser corresponding to a difference between the first power level and the second power level when the power level of the laser changes to the second power level. And a second correction circuit for setting a power level smaller than the second power level. 4. An overshoot amount due to a laser power level higher than the first power level or an undershoot amount due to a laser power level lower than the second power level is determined according to the edge emphasis amount I, The edge emphasis amount I is determined by (edge emphasis amount I) = (edge emphasis degree) × [(first power level) − (second power level)]. 3. The laser drive circuit described in 3. However, the edge emphasis degree is a constant. 5. The first correction circuit and the second correction circuit are combined into a single correction circuit.
The laser drive circuit described.