JPH02278531A - Control circuit for light emitting power of semiconductor laser - Google Patents

Abstract

PURPOSE:To eliminate the error of reproduced power just after a laser is recorded or erased by providing a driving current correcting circuit to correct the holding value of a holding means which holds a driving current when the semiconductor laser is reproduced. CONSTITUTION:When recording or erasing is finished, operation is returned to reproducing and the output current of a recording and erasing power driving circuit 31 is turned OFF, fluctuation is generated in the reproduced power for a semiconductor laser 21. An output signal set to a prescribed value is outputted from a driving current correcting circuit 29 and added to a holding circuit 27 by an adder circuit 28. Then, the laser 21 is emitted by the suitable power. Since the output signal of the circuit 29 gradually goes to be 0 at a speed lower than a control speed, the output of the holding circuit 27 is made suitable for outputting the reproduced power from the laser 21 just before the next recording and erasing. When the output signal of a power detecting circuit 23 corresponds to the reproduced power of the laser 21, the circuits 24 and 27 are not set in a holding mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser emission power control circuit in an optical disk device or the like.

[Conventional technology]

JP-A-62-42339 discloses a semiconductor laser emission power control circuit in a device that records and reproduces (or records, reproduces, and erases) information by condensing a light beam from a semiconductor laser onto an information recording medium using an objective lens. is listed.

In this semiconductor laser emission power control circuit, the rear light of the semiconductor laser 12 is detected by the power detection circuit 1 as shown in FIG.
, h are connected, and the output signal of the power detection circuit 1 is inputted to the first control circuit 4. The second switching circuit 5 is connected to terminals A and C, and the first control circuit 4 controls the first drive so that the output signal of the reproduction power setting circuit 2 and the output signal of the power detection circuit 1 are equal. The circuit 8 drives the semiconductor laser 12. Therefore, the semiconductor laser 12 stably emits light at the reproduction power set by the reproduction power setting circuit 2. At this time, the third switching circuit 10 is open,
The second drive circuit 9 does not operate.

The reproduction value holding circuit 7 holds the output signal of the first control circuit 4 during reproduction immediately before the recording transition.

During recording, the terminals a and b of the second switching circuit 5 are connected, and the first drive circuit 8 receives the output signal of the value holding circuit 7 during reproduction and causes the semiconductor laser 12 to flow the current immediately before the recording transition. At this time, the third switching circuit 10 is closed, the output signal of the recording power setting circuit 11 is input to the second drive circuit 9, and the second drive circuit 9 sets the recording power to the semiconductor laser 12 by the recording power setting circuit 11. A current is applied so that light is emitted with the recording power set. The first switching circuit 3 has terminal g+
h is connected, and the second control circuit 6 outputs an output signal to the first control circuit 4 such that the output signal of the first control circuit 4 becomes equal to the output signal of the value holding circuit 7 during reproduction. At the time of transition from recording to playback, the first switching circuit 3 switches between terminals f and h.
is connected, the second switching circuit 5 has terminals A and C connected, and the third switching circuit 10 is open. Immediately before this, the output signal of the first control circuit 4 is controlled to be equal to the output signal of the value holding circuit 7 during reproduction.

As the reproduction value holding circuit 7, one as shown in FIG. 6 can be considered.

The output signal of the first control circuit 4 is compared in a comparator 13 with the output signal of a digital/analog (D/A) converter 14 at the final stage. When the output signal of the first control circuit 4 is smaller than the output signal of the D/A converter 14 and the output signal of the comparator 13 is at a high level, the up/down counter 15 up-runs the clock from 1 to 1 and performs the first control. Since the output signal of the circuit 4 is larger than the output signal of the D/A converter 14, the comparator 13
When the output signal of is low level, the clock is counted down. The output signal of this up/down counter 15 is D
The D/A converter 14 performs D/A conversion, and the output signal of the D/A converter 14 becomes equal to the output signal of the first control circuit 4. When a control signal is applied to the enable terminal of the up/down counter 15, the up/down counter 15 stops counting and enters a holding mode during recording.

[Problem to be solved by the invention]

In the semiconductor laser emission power control circuit, even if the reproduction value holding circuit 7 accurately retains the output signal of the first control circuit 4 during reproduction immediately before the recording transition, the semiconductor laser 1
When the semiconductor laser 12 emits light at recording power, the semiconductor laser 12 self-heats, so even when the semiconductor laser 12 returns to playback mode, the light emission power fluctuates. This situation is shown in FIG. Since there is a limit to the control speed of the first control circuit 4, an error ΔL in the emission power of the semiconductor laser 12 occurs. This error ΔL is then eliminated depending on the characteristics of the first control circuit 4.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser emission power control circuit which can improve the above-mentioned drawbacks and eliminate errors in reproduction power immediately after recording or erasing of a semiconductor laser.

[Means to solve the problem]

In order to achieve the above object, the invention of claim 1 provides semiconductor laser emission power control in an apparatus that records/reproduces information or records/reproduces/erases information by condensing a light beam from a semiconductor laser onto an information recording medium using an objective lens. A circuit comprising: a holding means for holding a driving current of the semiconductor laser during reproduction during recording or erasing; and a semiconductor for causing a driving current corresponding to a value held by the holding means to flow through the semiconductor laser immediately after recording or erasing. The laser emission power control circuit further comprises a drive current correction circuit for correcting the value held by the holding means. The apparatus includes a correction amount control means for changing the correction amount by the correction circuit in accordance with the error in the reproduction power immediately after the previous recording or erasing.

[For production]

In the first aspect of the invention, the driving current of the semiconductor laser during reproduction is held by the holding means during recording or erasing, and immediately after recording or erasing, a driving current corresponding to the value held by the holding means is passed through the semiconductor laser. The value held by the holding means is then corrected by the drive current correction circuit.

Further, in the second aspect of the invention, the amount of correction by the drive current correction circuit is changed by the correction amount control means in accordance with the error in the reproduction power immediately after the previous recording or erasing.

〔Example〕

FIG. 1 shows an embodiment of the invention.

This embodiment is a semiconductor laser emission power control circuit in an optical disk device that records/reproduces information or records/reproduces/erases information by condensing a light beam from a semiconductor laser onto an information recording medium using an objective lens. , a semiconductor laser 21 is driven by a reproduction power drive circuit 22, and a portion of the light emitted from the semiconductor laser 21 enters a power detection circuit 23, where the amount of light emitted is monitored.

The output signal of this power detection circuit 23 is transmitted to the first holding circuit 2.
4 and is inputted to the control circuit 25 as it is, and an output signal of the reproduction power setting circuit 26 is inputted to the control circuit 25. The control circuit 25 controls the second holding circuit 27. so that the output signal of the power detection circuit 23 and the output signal of the reproduction power setting circuit 26 become equal. The reproduction power drive circuit 22 is controlled through the adder circuit 28, and the reproduction power of the semiconductor laser 21 is controlled to the reproduction power set by the reproduction power setting circuit 26. At this time, the output signal of the drive current correction circuit 29 is 0, and the output signal of the addition circuit 28 is equal to the output signal of the second holding circuit 27.

Next, during recording or erasing, the first holding circuit 24 and the second holding circuit 27 enter the holding state, and the power detection circuit 23 . The output signal of the control circuit 25 is held, and the reproduction power drive circuit 22 receives the output signal of the second holding circuit 27 through the adder circuit 28 and causes the same current as during reproduction to flow through the semiconductor laser 21. Furthermore, the output signal of the recording/erasing power setting circuit 30 is input to the recording/erasing power drive circuit 31, and the recording/erasing power driving circuit 31 superimposes a current corresponding to the output signal of the recording/erasing power setting circuit 30 on the current. The light is then passed through the semiconductor laser 21. At this time, the recording/erasing power drive circuit 31 turns on/off the superimposed current using a modulation signal according to the recording data, and causes the semiconductor laser 21 to emit light with recording power or erasing power.

When recording or erasing is completed and reproduction is resumed, the output current of the recording/erasing power drive circuit 31 is turned off. At this time, the semiconductor laser 21 emits light at approximately the reproduction power, but the reproduction power fluctuates as described above. In order to prevent this fluctuation, an output signal set to a predetermined value is output from the drive current correction circuit 29 and added to the output signal of the second holding circuit 27 in the adder circuit 28, so that the semiconductor laser 21 is properly adjusted. Lights up with regenerated power. In addition, the drive current correction circuit 2
By gradually changing the output signal of 9 to ○ at a speed slower than the control speed (the power control speed of the semiconductor laser 21 during reproduction), the semiconductor laser 21 outputs the reproduction power immediately before the next recording/erasing. The output signal of the second holding circuit 27 becomes appropriate. The first holding circuit 24 and the second holding circuit 24
The holding circuit 27 is no longer in the holding mode after the output signal of the power detection circuit 23 becomes the same output signal according to the reproduction power of the semiconductor two-body laser 21.

Although the above embodiment is an example in which the recording current or the erasing current is superimposed on the reproduction current, variations in the reproduction power can be similarly prevented even if the reproduction current and the recording current or the erasing current are determined independently. can.

FIG. 2 shows another embodiment of the invention.

In this embodiment, the power detection circuit 23 in the above embodiment is
The output signal of the output signal and the output signal of the reproduction power setting circuit 26 are input to the error detection circuit 32, and the error detection circuit 32 detects an error in the reproduction power immediately after recording or erasing. The output signal of this error detection circuit 32 is taken in and held by the third holding circuit 33, and the drive current correction circuit 2
The correction amount of 9 is changed by the output signal of the third holding circuit 33. This makes the reproduction power more accurate immediately after recording or erasing. Also, at this time, the output signal of the drive current correction circuit 29 gradually becomes O at a speed slower than the control speed.

FIG. 3 shows another embodiment of the invention.

In this embodiment, the output signal of the power detection circuit 23 and the output signal of the reproduction power setting circuit 26 are input to the error detection circuit 32 in the embodiment shown in FIG. 2, and the error in the reproduction power immediately after recording or erasing is detected as an error. The output signal of the error detection circuit 32 is A/D converted by an analog/digital (A/D) converter 34 and input to a microcomputer (CPU) 35. The CPU 35 accumulates errors in the reproduction power immediately after recording or erasing the past n times (n is 2 or more), and determines the output value of the drive current correction circuit 29 through the D/A converter 36 according to the accumulated error. This prevents the correction amount of the drive current correction circuit 29 from becoming an abnormal value due to noise or the like.

FIG. 4 shows another embodiment of the invention.

In this embodiment, a fourth holding circuit 37 is provided in the embodiment of FIG. 2, and the output signal of the error detection circuit 32 immediately after recording and the output signal of the error detection circuit 32 immediately after erasing are 3 holding circuit 33
The output signals of the third holding circuit 33 and the fourth holding circuit 37 are respectively taken in and held by the third holding circuit 33 and the fourth holding circuit 37, and are recorded and erased during playback after recording and playback after erasure. The switching signal is input to the drive current correction circuit 29 through the switch element 38. Therefore, the drive current correction circuit 29 adjusts the amount of correction of the reproduction power immediately after recording,
The correction amount of the reproduction power immediately after erasing is determined by the third holding circuit 33.
and the respective output signals of the fourth holding circuit 37, and fluctuations in reproduction power can be corrected more accurately.

Furthermore, in each of the embodiments shown in FIGS. 1 and 3, the amount of correction of the reproduction power immediately after recording and the amount of correction of the reproduction power immediately after erasing can be set independently.

〔Effect of the invention〕

As described above, according to the invention of claim 1, a semiconductor laser emission power control circuit in an apparatus for recording/reproducing information or recording/reproducing/erasing information by condensing a light beam from a semiconductor laser onto an information recording medium using an objective lens. A holding means for holding a driving current of the semiconductor laser during reproduction during recording or erasing, and a semiconductor laser for causing a driving current to flow through the semiconductor laser according to a value held by the holding means immediately after recording or erasing. Since the light emission power control circuit includes a drive current correction circuit that corrects the value held by the holding means, it is possible to eliminate errors in the reproduction power immediately after recording or erasing of the semiconductor laser.

According to the invention of claim 2, in the semiconductor laser emission power control circuit of claim 1, the amount of correction by the drive current correction circuit is changed according to the error in the reproduction power immediately after the previous recording or erasing. Since the control means is provided, more stable reproduction power can be obtained.

[Brief explanation of drawings]

1 to 4 are block diagrams showing each embodiment of the present invention, FIG. 5 is a block diagram showing a conventional semiconductor laser emission power detection circuit, and FIG. 6 is a block diagram showing the conventional semiconductor laser emission power control circuit during reproduction. A block diagram showing an example of a value holding circuit,
FIG. 7 is a timing chart 1 of the semiconductor laser emission power control circuit. 11... Semiconductor laser, 27.33... Holding circuit,
29... Drive current correction circuit, 32... Error detection circuit.

Claims (1)

[Scope of Claims] 1. A semiconductor laser emission power control circuit in an apparatus for recording/reproducing information or recording/reproducing/erasing information by condensing a light beam from a semiconductor laser onto an information recording medium using an objective lens, comprising: Holding means for holding the driving current of the semiconductor laser during reproduction during recording or erasing, and a semiconductor laser emission power control circuit for flowing a driving current to the semiconductor laser according to the value held by the holding means immediately after recording or erasing. A semiconductor laser emission power control circuit comprising: a drive current correction circuit for correcting a value held by the holding means. 2. The semiconductor laser emission power control circuit according to claim 1, further comprising a correction amount control means for changing the correction amount by the drive current correction circuit in accordance with an error in reproduction power immediately after previous recording or erasing. A semiconductor laser emission power control circuit.