JPH04143934A - Laser light quantity control circuit in optical recording/ reproducing device - Google Patents

Abstract

PURPOSE:To extend the service life of a laser by generating a compensation voltage added to a monitor output of the laser light quantity at the time of reproduction and holding a driving circuit in almost the same state equivalently to the time of a recording mode, and preventing an excessive current at the time of switching from a reproducing mode to a recording mode. CONSTITUTION:In a reproducing mode, a laser diode 1A is driven in a low level by a reproducing mode driving circuit, and accordingly, an output of a monitor amplifier 5 is also in a low level in accordance with the light emission quantity, and it is inputted to an error amplifier 10. When said mode is switched to a recording mode in such a state, a reference voltage of the recording mode is supplied to the amplifier 10. In this case, when a difference to the reference voltage of the recording mode is generated due to a delay in which a output of the amplifier 5 is varied from a low level to a high level, the amplifier 10 generates instantaneously an error output of light quantity shortage, and an excessive driving current flows transiently. In order to prevent it, a compensation reference voltage is supplied to the amplifier 10 from a circuit 12 at the time of reproducing mode, and an input level of an operational amplifier 14 of the amplifier 10 is equalized substantially to an input level at the time of recording mode.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser light amount control circuit in an optical recording/reproducing device, and more particularly to a laser light amount control circuit that controls the light amount of a semiconductor laser when recording or reproducing information.

[Conventional technology]

In this type of optical recording/reproducing device, a high-output laser beam is used during recording, and a low-output laser beam is used during reproduction. Therefore, it is necessary to quickly switch the intensity of the laser beam in response to switching between recording and playback modes. Further, it is known that the characteristics of the semiconductor laser itself change depending on the temperature, and the output light fluctuates. For this reason,
The optical recording/reproducing device is equipped with a laser light amount control circuit, and is controlled to operate stably against fluctuations due to laser light output switching and temperature.

Generally, this type of laser light amount control circuit has a drive circuit for high output and a drive circuit for low output depending on the recording mode (including erasing mode) and playback mode, and these drive circuits are Automatic light amount control (hereinafter referred to as AP)
C) loop. This APC loop is equipped with a photodiode that monitors the amount of light emitted from the semiconductor laser, and a comparison means that compares the output from this photodiode with reference values set corresponding to high output and low output. The results are fed back to the drive circuit to control the amount of light from the semiconductor laser to a predetermined value. Regarding such a laser light amount control circuit, for example, Japanese Patent Laid-Open No. 62
-892-48.

[Problem to be solved by the invention]

In the conventional laser light amount control circuit described above, when switching from playback mode to recording mode and starting recording, the APC
Due to the time constant of the loop system, the output signal of the light intensity monitoring photodiode is delayed in tracking the amount of light emitted, so an excessive current momentarily flows through the semiconductor laser. For this reason,
This method has disadvantages in that it deteriorates the semiconductor laser and deteriorates the recording condition on the magneto-optical recording medium at the start of recording, causing errors.

An object of the present invention is to prevent the semiconductor laser from being driven with excessive current transiently when switching from the playback mode to the record mode, thereby extending the life of the semiconductor laser. It is an object of the present invention to provide a laser light amount control circuit in an optical recording/reproducing device that can prevent deterioration of recording marks formed on a magneto-optical disk when switching modes.

[Means to solve the problem]

The laser light amount control circuit in the optical recording and reproducing apparatus of the present invention includes a reproduction mode drive circuit that drives a semiconductor laser at a low level in a reproduction mode that reads information from a storage medium, and a reproduction mode drive circuit that drives a semiconductor laser at a low level in a reproduction mode that reads information from a storage medium. a recording mode driving circuit that is added to the output of the reproduction mode driving circuit to drive the semiconductor laser at a high level during the recording mode in which the recording mode is performed; a light amount detection means that detects the amount of light emitted from the semiconductor laser; playback mode control means for receiving an output from the light amount detection means and controlling the playback mode drive circuit to control the amount of light emitted by the semiconductor laser; and an output from the light amount detection means when in the recording mode. and recording mode control means for controlling the recording mode drive circuit in response to a signal from the semiconductor laser to control the amount of light emitted from the semiconductor laser, wherein the recording mode control means In this case, the recording mode driving circuit is maintained in substantially the same state as in the recording mode. Further, the recording mode control means includes a storage mode reference voltage generation circuit that generates a reference voltage for controlling the recording mode drive circuit when in the recording mode;
a compensation voltage generation circuit that generates a compensation voltage for controlling the recording mode drive circuit when in the reproduction mode; and a compensation voltage generation circuit that selects the compensation voltage when in the reproduction mode according to a mode signal specifying a reproduction and recording mode. and a switch circuit that selects and outputs the reference voltage when in the recording mode, and a comparison circuit that controls the recording mode drive circuit according to the output of the switch circuit and the output of the light amount detection means. may be configured. Furthermore, the recording mode control means includes a comparison circuit that controls the recording mode drive circuit so that the output sum of the output of the switch circuit and the output of the light amount detection means becomes a constant value, and The compensation voltage may be set so that the output sum in the recording mode is equivalently approximately the same value.

〔Example〕

Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a laser light amount control circuit in an optical recording/reproducing apparatus according to the present invention. The semiconductor laser unit 1 has a built-in laser diode IA and a photodiode IB for monitoring the amount of light. The laser diode IA is driven by a reproduction mode driving circuit 2 and a recording mode driving circuit 3. Further, a switch 4 that is closed by an external recording mode signal S is connected between the recording mode drive circuit 3 and the laser diode IA. The output of the light intensity monitoring photodiode IB is supplied via a monitor amplifier 5 and a sample hold circuit 6 to an error amplifier 7 that generates an error output based on a reference voltage that defines the light intensity during playback and the output of the sample hold circuit 6. Ru. The reproduction mode reference voltage generation circuit 8 and the recording mode reference voltage generation circuit 12 generate reference voltages that define the amount of light during reproduction and recording, respectively. The output of the error amplifier 7 passes through a low-pass filter 9 to the regeneration mode drive circuit 2.
sent to. On the other hand, the output of the monitor amplifier 5 is also sent to the error amplifier 10, where an error output is generated from the output of the monitor amplifier 5 and the output voltage from the recording mode reference voltage generation circuit 12, and is passed through the low-pass filter 11 to drive the recording mode. Feedback is sent to circuit 3. The recording mode signal S is supplied to the sample hold circuit 6, the recording mode reference voltage generation circuit 12, and the switch 4.

The sample and hold circuit 6 is placed in a hold state by this signal S. As a result, the APC operation in the playback mode is frozen, so the playback mode drive circuit 2 continues to send out the drive current during playback. Further, the recording mode reference voltage generation circuit 12 generates a reference voltage in the recording mode according to the recording mode signal S. Further, since the switch 4 is turned on by this signal S, the output of the recording mode drive circuit 3 is sent to the laser diode IA.

Next, the error amplifier 10 and the recording mode reference voltage generation circuit 12 will be explained with reference to FIG. The error amplifier 10 is composed of an operational amplifier 14 and a resistor as shown in the figure, and the output of the monitor amplifier 5 and the output of the recording mode reference voltage generation circuit 12 are supplied to the inverting input side of the operational amplifier 14 via the resistor. The operational amplifier 14 generates an error output so that the sum of the two outputs becomes a constant level. The recording mode reference voltage generation circuit 12 includes a potentiometer 15 that generates a reference voltage in the recording mode, a potentiometer 16 that generates a compensation reference voltage higher than the base Ms voltage, and a switch 17 that complementarily switches the outputs of the potentiometers 15 and 16. .18, an amplifier 19 that receives a reference voltage from a switch 17, 18, and an inverter 20 that receives a recording mode signal S and controls the switch 18.
The output of 9 is supplied to the inverting input side of error amplifier 10. Here, switches 17 and 18 are complementary controlled by the recording mode signal, and in recording mode switch 1
7 is closed and switch 18 is opened. Conversely, in playback mode, switch 17 is opened and switch 18 is opened.
is closed.

Here, the switching operation from playback mode to recording mode will be explained. In the reproduction mode, the laser diode IA is driven at a low level by the reproduction mode drive circuit 2, and therefore the output of the monitor amplifier 5 is also at a low level corresponding to the amount of light emitted, and this is input to the error amplifier 10.

When switching to the recording mode in this state, the reference voltage for the recording mode is supplied to the error amplifier 10, and the switch 4 shown in FIG. supplied to In this case, if a difference with the reference voltage in the recording mode occurs due to a delay in the output of the monitor amplifier 5 changing from a low level to a high level, the error amplifier 10 momentarily generates an error output indicating insufficient light quantity. Therefore, as shown in FIG. 4, an excessive drive current transiently flows through the laser diode. In order to eliminate this phenomenon, the present invention supplies a compensation reference voltage to the error amplifier 10 in the reproduction mode. Now, set the output level of monitor amplifier 5 in playback mode to Vmr.
, if the compensation reference voltage output by the recording mode reference voltage generation circuit 12 is Vc, then the operational amplifier 1 of the error amplifier 10
The input level of 4 is (Vmr+Vc). Therefore,
If this input level is made substantially equal to the input level in the recording mode, that is, the output level of the monitor amplifier 5 in the recording mode is Vmw, and the reference voltage output by the recording mode reference voltage generation circuit 12 is Vs. Then, (Vmr
By setting the compensation reference voltage Vc so that +Vc) = (VIllW+VS), it is possible to suppress the phenomenon of transiently overdriving the laser diode IA as shown in FIG.

〔Effect of the invention〕

As explained above, when the present invention has a semiconductor laser drive circuit and an APC system corresponding to the reproduction mode and the recording mode, the APC system for the recording mode adds the amount of laser light to the monitor output during reproduction. By generating a compensation voltage and keeping the drive circuit equivalently in almost the same state as in the recording mode, the output of the error amplifier does not fluctuate transiently when switching from the playback mode to the recording mode. The laser is no longer overdriven, deterioration can be prevented, and distortion of recording marks formed on the magneto-optical disk can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of the error amplifier 10 and recording mode reference voltage generation circuit 12 shown in FIG. 1, and FIG. 3 is an operation of the embodiment of the present invention. FIG. 4 is a waveform diagram of a drive current in a conventional example. 1... Semiconductor laser unit, IA... Laser diode, IB... Photodiode for light intensity monitoring, 2
...Reproduction mode drive circuit, 3...Record mode drive circuit, 4.17.18...Switch, 5...Monitor amplifier, 6...Sample hold circuit, 7.10...
・Error amplifier, 8... Playback mode reference voltage generation circuit, 9.11... Low pass filter, 12... Recording mode reference voltage generation circuit, 14.19... Operational amplifier,
15°6... Potentiometer, 20... Inverter.

Claims (1)

[Claims] 1. A reproduction mode drive circuit that drives a semiconductor laser at a low level during a reproduction mode in which information is read from a storage medium, and a recording mode in which information is written to and erased from the storage medium. a recording mode drive circuit that is added to the output of the playback mode drive circuit to drive the semiconductor laser at a high level; a light amount detection means that detects the amount of light emitted from the semiconductor laser; and the light amount detection means when in the playback mode. a reproduction mode control means for receiving an output from the light quantity detecting means and controlling the reproduction mode drive circuit to control the amount of light emitted from the semiconductor laser; In the laser light amount control circuit in an optical reproducing apparatus, the laser light amount control circuit includes a recording mode control means for controlling a light emission amount of the semiconductor laser by controlling a circuit, wherein the recording mode control means controls the recording mode drive when in the reproduction mode. 1. A laser light amount control circuit in an optical recording/reproducing apparatus, characterized in that the circuit is maintained in substantially the same state equivalently as in the recording mode. 2. In the laser light amount control circuit in an optical recording/reproducing apparatus according to claim 1, the recording mode control means has a storage mode standard that generates a reference voltage for controlling the recording mode drive circuit when in the recording mode. a voltage generation circuit; a compensation voltage generation circuit that generates a compensation voltage for controlling the recording mode drive circuit when in the reproduction mode; and a compensation voltage generation circuit that generates a compensation voltage for controlling the recording mode drive circuit when in the reproduction mode; a switch circuit that selects the compensation voltage and selects and outputs the reference voltage when in the recording mode; and a comparison circuit that controls the recording mode drive circuit according to the output of the switch circuit and the output of the light amount detection means. A laser light amount control circuit in an optical recording/reproducing device, characterized in that the circuit comprises: 3. In the laser light amount control circuit in the optical recording/reproducing apparatus according to claim 2, the recording mode control means controls the laser light amount so that the sum of the output of the switch circuit and the output of the light amount detection means becomes a constant value. Optical recording and reproducing, comprising a comparison circuit that controls a recording mode drive circuit, and wherein the compensation voltage is set so that the output sum in the reproduction mode and the recording mode is equivalently approximately the same value. Laser light amount control circuit in the device.