JP2633972B2 - Optical regeneration device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing device such as an optical disk device, and more particularly to a laser driving circuit thereof.

[Conventional technology]

In an optical disk device, laser light emitted from a semiconductor laser is condensed by an objective lens and illuminated on an optical disk as a minute light spot, and information is reproduced by detecting the reflected light. Focus control and tracking control are performed so that the laser can accurately focus on and follow a desired track on the optical disk, and emit a semiconductor laser so that a constant amount of laser light irradiates the optical disk. Light amount control is being performed.

For this emission light amount control, feedback control using a CPU (Central Processing Unit) that controls the entire optical disk device is usually adopted. That is, the amount of emitted light of the semiconductor laser is detected at a constant sampling cycle, compared with a predetermined value, and based on the result, the drive current of the semiconductor laser is increased or decreased by a fixed amount. I try to keep it.

[Problems to be solved by the invention]

By the way, when the focus of the objective lens is just focused on the track on the optical disk at the time of focusing, the reflected light returns to the semiconductor laser as return light, so that the amount of emitted light rapidly increases and exceeds the required range. is there.

However, in the above-described conventional configuration, since the amount of emitted light of the semiconductor laser is detected and controlled at a constant sampling cycle, when a relatively large change in the amount of emitted light occurs, as in the above-described focus pull-in, the amount of emitted light is reduced. It takes time to return the light amount to within the predetermined range, and during this time, there is a problem that the recording / erasing and reproducing operations cannot be performed.

Therefore, in order to quickly return the emitted light amount to within a predetermined range,
It is conceivable to shorten the sampling period. However, if this is done, the CPU must always spend a considerable amount of time for emission control, so that the control efficiency of the CPU of the entire optical disc device is reduced, and the problem cannot be solved.

[Means for solving the problem]

In the optical reproducing apparatus of the present invention, in order to solve the above-mentioned problem, a process of detecting the emitted light amount so that the emitted light amount of the laser becomes substantially constant and performing feedback control of the drive current of the laser every predetermined sampling period. An optical reproducing apparatus that includes a unit and reproduces information by performing focus control so that the laser light is focused on the optical recording medium.
The processing unit is provided with a sampling cycle setting means for shortening the sampling cycle from a normal period during a period from when the focus is pulled until the emitted light amount returns to a predetermined value.

(Operation)

According to the above configuration, the processing unit is provided with the sampling cycle setting means for shortening the sampling cycle from the normal time until the emission light amount returns to the predetermined value from the time of focus pull-in. The increasing amount of emitted laser light can be quickly returned to a predetermined value. In addition, when the fluctuation of the output light amount is not a time of relatively slow focus pull-in, the sampling period is relatively long, so that the time occupied by the processing unit for feedback control is reduced, and the load on the processing unit is reduced. . Thereby, for example, the time that the processing unit can use for performing other control increases, and the processing unit can be effectively used.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5 by taking an optical disk device as an example.

In an optical disc device, laser light emitted from a semiconductor laser as a laser is condensed by an objective lens, irradiates the optical disc as a minute light spot, and information is reproduced by detecting the reflected light. Focus control and tracking control are performed so that the light spot accurately focuses on and follows a desired track on the optical disc, and the semiconductor light source irradiates the optical disc with a constant amount of laser light. The emission light amount control of the laser is performed.

First, focus control of the optical disk device will be described with reference to FIGS.

The focus control unit includes, as shown in FIG.
It is basically composed of 11, a switch circuit 12, a focus actuator drive circuit 13, and a focus actuator 14.

In the above configuration, when the focus is pulled, the oscillation circuit 11 is connected to the focus actuator drive circuit 13 by the switch circuit 12, and the oscillation circuit
11 output signal is the focus actuator drive circuit 13
And is input to the focus actuator 14, whereby the focus actuator 14 is driven up and down. At this time, a so-called S-curve appears in the focus error signal (FES) as shown in the waveform of FIG. 5A, but at the just focus points t ₁ and t ₂ , the objective lens for condensing laser light. (C) because the light is focused on the track on the optical disk and the reflected light returns to the semiconductor laser as return light.
As shown in, the laser power predetermined value P _a, the embodiment has increased by about 30% rapidly.

As in the just focus point t _2, when the focal point enters the operation range of the focus control, the focus sequence circuit (not shown), as shown in FIG. 5 (b), focus-on (Focus ON) signal Is the switch circuit 1
2, the switch circuit 12 is switched, and a focus error signal is input to the focus actuator drive circuit 13. Then, focus control is performed according to the focus error signal.

During focusing control start, but the laser power is increased than the predetermined value P _a, the flow returns to a predetermined value P _a a while the emitted light amount control.

In the optical disk device according to the present invention, in order to shorten the laser power recovery time T (FIG. 5 (c)), a CPU (central processing unit) as a processing unit for controlling the entire optical disk device only at the time of focusing is performed. Most of the processing time of section (2) is allocated to emission light amount control. That is, the sampling period of the amount of light emitted from the semiconductor laser is made shorter than usual at the time of focusing, so that the laser power returns to the predetermined value Pa in _a short time.

Hereinafter, a semiconductor laser drive circuit of an optical disk device according to the present invention will be described with reference to FIGS.

As shown in FIG. 2, the semiconductor laser driving circuit includes a semiconductor laser 1 (laser), a photo sensor 2, an I / V
(Current / voltage) converter 3, A / D (analog signal / digital signal) converter 4, CPU 5 (processing unit), ROM (read-only storage element) 6, D / A (digital signal / analog signal) converter 7. It mainly comprises a V / I (voltage / current) converter 8.

In the above configuration, the semiconductor laser 1 is excited by the drive current _ID output from the V / I converter 8 and oscillates with an output light amount corresponding to the magnitude of the drive current _ID . The emitted light amount is detected by the photo sensor 2. And is converted into a voltage signal S _a which corresponds to light emission amount by the I / V converter 3, is converted further and the voltage signal S _a by the A / D converter 4 into a digital signal D _in CPU 5
Is input to

On the other hand, the CPU 5, ROM 6 to the digital data D _P is stored corresponding to a predetermined amount of emitted light is connected.

Then, the CPU 5 compares the digital signal D _in input from the A / D converter 4 with the digital data D _P stored in the ROM 6.
And drive current I _D so that the difference is zero.
The control output signal D _OUT is output.
The output signal D _OUT is converted into a voltage signal S _b by a D / A converter 7 and then input to a V / I converter 8. A driving current _ID for the voltage signal S _b is output from the V / I converter 8. It is supplied to the semiconductor laser 1. In this way, the amount of emitted light of the semiconductor laser 1 is controlled so as to substantially maintain a predetermined value.

The above-described feedback control operation is executed at every predetermined sampling period.In the present invention, however, the sampling period is not constant, and is set by the sampling period setting means provided in the CPU 5 so that the sampling period is shorter than usual at the time of focus pull-in. Switching.

The switching operation of the sampling period by the sampling period setting means will be described based on the flowchart of FIG.

In step 1 (hereinafter, step is abbreviated as S), the sampling cycle is initially set to the temperature of the semiconductor laser
A relatively long cycle B (for example, about several seconds) is set so that the above-mentioned emission light quantity control can cope with the change in the emission light quantity (FIG. 2). Then, the state of the cycle B is maintained until the focus-on signal becomes active (S2). When the focus ON signal is active, the sampling period is switched to a short period A (S3), until the laser power is substantially a predetermined value P _a by emitted light amount control, the state of the period A is maintained (S4). As a result, the emission light amount control can quickly respond to a sudden increase in the laser power (see FIG. 5) occurring at the start of the focus control. When the period A is shortened, the recovery time T of the laser power is reduced to several milliseconds. It is also possible to do. When the laser power is returned substantially to a predetermined value P _a, the sampling period is returned to the original longer cycle B (S5).

Next, the relationship between the sampling period and the feedback control operation will be described with reference to FIG.

FIG (a) is a diagram showing the relationship between the drive current I _D and the emission light quantity, the emission light intensity of the semiconductor laser 1 (FIG. 2) is currently in a small light emission amount P ₀ than a predetermined light emission amount P ₁ Has become.

Comparative Therefore, CPU 5 takes in the digital signal D _in input in response to the amount of light emitted P ₀ from the A / D converter 4, a digital data corresponding to a predetermined amount of emitted light P ₁ stored in advance in the ROM6 Then, as shown in the relationship between the time and the drive current _{ID in} FIG. 3B, the output signal D _OUT for increasing the drive current _ID by ΔI is output to the D / A converter 7. By repeating a series of operations of inputting data from the A / D converter 4 to the CPU 5, comparing data, and updating data of the D / A converter 7 at a predetermined sampling period Δt, the amount of light emitted from the semiconductor laser 1 is soon. reaches a predetermined light emission amount P _1, within the range of variation ΔP of the emitted light amount corresponding to [Delta] I.

As is apparent from FIG.
Halving the t, time is also halved to return to a predetermined light emission amount P _1. Therefore, as described above, even when the laser power is sharply increased and the emission light amount is increased at the time of focusing, the sampling period Δt is switched from the relatively long period B to the short period A so that the laser can be quickly driven. The power can be reduced to restore the emitted light quantity.
In addition, since the period B can be set to a relatively long time without considering the focus pull-in, the load on the CPU 5 for controlling the amount of emitted light is reduced other than at the time of focus pull-in, and the control of the entire optical disc apparatus is promptly performed. Will be done.

In the above embodiments, the optical disc device as the optical reproducing device has been described, but the present invention can be applied to an optical card device, an optical tape device, and the like.

〔The invention's effect〕

As described above, the optical reproducing device of the present invention includes the sampling period setting means for shortening the sampling period from the normal period until the emission light amount returns to the predetermined value from the focus pull-in to the processing unit. The amount of emitted laser light that rapidly increases due to the return light can be quickly returned to a predetermined value. In addition, when the fluctuation of the output light amount is not a time of relatively slow focus pull-in, the sampling period is relatively long, so that the time occupied by the processing unit for feedback control is reduced, and the load on the processing unit is reduced. . Thereby, for example, there is an effect that the time that the processing unit can use for performing another control is increased, and the processing unit can be effectively used.

[Brief description of the drawings]

1 to 5 show one embodiment of the present invention. FIG. 1 is a flowchart for explaining the switching operation of the sampling period by the sampling period setting means. FIG. 2 is a block diagram of a semiconductor laser drive circuit of the optical disk device. FIG. 3 is an explanatory diagram of the feedback control operation. FIG. 4 is a block diagram showing a focus control unit. FIG. 5 is a waveform showing that the laser power sharply increases at the just focus point. 1 is a semiconductor laser (laser), 2 is a photo sensor, 3 is an I / V converter, 4 is an A / D converter, 5 is a CPU (processing unit), 6 is ROM, 7 is D / A converter, 8 Is a V / I converter.

Claims (1)

(57) [Claims] A processing unit for detecting the emitted light amount so that the emitted light amount of the laser becomes substantially constant and performing feedback control of a driving current of the laser at a predetermined sampling cycle; In the optical reproducing apparatus that reproduces information by performing focus control so that light is condensed into the light, the processing unit performs the sampling in which the sampling cycle is shorter than usual during a period from when the focus is pulled until the amount of emitted light returns to a predetermined value. An optical reproducing device comprising a period setting means.