JPS63273227A - Laser driver circuit - Google Patents

Abstract

PURPOSE:To prevent the record of information from being missed at the time of switching a mode to a recording mode, by setting reference DC power levels equal both in a recording and a reproducing modes, and obtaining a feedback signal by peak holding when information of rectangular waveform shape is superposed on a monitor current signal. CONSTITUTION:A current comparison circuit 5 compares the monitor current signal iM photoelectric-transduced by a photodiode 4 with a reference current from a constant current source 15, and supplies a comparison differential signal SUB to a peak holding circuit 16. The circuit 16 holds the upper limit or the lower limit level of the signal SUB, and supplies it to a current driver circuit 11. By constituting a device in such a way, the signals iM and SUB are formed in the rectangular waveforms corresponding to the information, however, a signal PH is constant in spite of the mode, and a current on a laser diode 2 remains unchanged. Therefore, no change occurs in a DC level at the time of switching the mode to the recording mode, therefore, no missing of the information is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser driver circuit, and can be applied, for example, to a magneto-optical disk device in which the laser power is different in recording mode and reproduction mode.

[Prior Art] In a magneto-optical disk device, information is recorded and reproduced by irradiating a magneto-optical disk with a laser beam. In the recording operation, the temperature of the magneto-optical disk must be raised to just one Curie point to temporarily eliminate the magnetization, which requires a high-output laser beam.

On the other hand, in the reproduction operation, a low output laser beam is irradiated so that the recorded information is not erased in the reproduction operation.

Such control of the output of the laser beam is performed by varying the current flowing through the laser diode depending on the operating mode. That is, in the reproduction mode, only the small current 11 is passed through the laser diode, and in the recording mode, the small current 11 and the large current 12 are switched depending on the logic level of the information, that is, a square wave current is passed through the laser diode. That's what I do.

The square wave current in the recording mode is controlled by a square wave driver circuit, and the DC current in the recording mode and reproduction mode is conventionally controlled by a laser driver circuit 1 shown in FIG.

In FIG. 4, the laser diode 2 has a combined current i generated by the laser driver circuit 1 and the square wave driver circuit 3.
L1+iL2 flows, and a laser beam corresponding to this current is emitted.

This laser beam is received by the photodiode 4, photoelectrically converted, and provided as a monitor current signal LM to the current comparison circuit 5 as a first comparison input. Further, the current comparator circuit 5 is supplied with a reproduction reference current (read power) from a constant current source 7 in the reproduction mode via a switch circuit 6, and is supplied with a recording dark reference current from a constant current source 8 in the recording mode. (light power) is given.

In this way, the current comparator circuit 5 obtains a difference signal SUB between the reference current to be passed and the current actually flowing, and this is given to the average value circuit 9 having an integrating circuit configuration. The average value circuit 9 averages the difference signal SUB and supplies it to the current driver circuit 10, converts it into a current signal, removes the noise component via the integrating circuit 11, and feeds it back to the laser diode 2 via the coil 12. A current of a predetermined value corresponding to the reference current is caused to flow.

Note that the coil 12 prevents the laser driver circuit 1 from being affected by the current of the square wave driver circuit 3.

[Problems to be Solved by the Invention] According to the conventional circuit, the power of the laser diode 2 is automatically controlled to a predetermined value in this way.

However, according to this conventional circuit, in the recording mode, the current flowing through the laser diode 2 is transferred to the average value circuit 9.
In order to swing around the average value obtained in
As shown in the figure, when switching from playback mode to recording mode or from recording mode to playback mode, it takes time for the transition to the predetermined average value level.
The recording level at the time of the transition is the minimum level TH required for recording
In some cases, recording information was given within the time limit and was not recorded accurately.

For example, the information for period T in FIG. 5 is originally recorded, but it is not recorded because it does not exceed the lowest level TH.

Therefore, it is conceivable to make the time constant of the average value circuit 9 faster, but during the period when the rectangular wave current signal is superimposed, the average value output is also converted into a rectangular waveform, making it impossible to obtain a DC signal.

The present invention has been made in consideration of the above points, and it is possible to quickly perform a switching operation of a predetermined power when switching between recording mode and playback mode, and prevent the occurrence of information recording failure, etc. The purpose of this invention is to provide a laser driver circuit that can perform the following steps.

[Means for Solving the Problem] In order to solve the problem, in the present invention, a predetermined DC current signal or a current signal obtained by combining this DC current signal with a rectangular wave-shaped current signal is used as the operating mode. In the laser driver circuit that supplies the predetermined DC current signal to the semiconductor laser flowing in accordance with a ratio axis circuit that compares the reference predetermined DC current signal output from the reference DC current signal;
A peak hold circuit holds the peak value on the side where the upper limit or lower limit peak value of the comparison difference signal is almost equal in each operation mode, and a current driver circuit supplies a current signal to the semiconductor laser according to the hold signal. Feedback control is performed so that a predetermined DC current signal is passed through the semiconductor laser.

[Operation] When a current signal in which rectangular waveform current signals are synthesized flows through the semiconductor laser, the monitor current signal also has a rectangular waveform, and the comparison difference signal also has a rectangular waveform. On the other hand, in a mode in which only a predetermined DC current signal flows through the semiconductor laser, the comparison difference signal has a substantially constant value. However, by holding the signal with a peak hold circuit, a substantially constant signal can be obtained even if the operation mode is different. Therefore,
Regardless of whether or not a rectangular waveform signal is combined with the monitor current signal, the difference between the predetermined DC signal and the actually flowing current can be obtained, and "feedback control" can be performed.

In this way, since the predetermined DC signal level for driving the current driver circuit is the same in each operating mode, the DC level does not change even when the mode is switched, and the composite signal is disturbed during the transition, making it difficult to record and reproduce information. can be prevented from becoming inaccurate.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. In this embodiment, a reference constant current is supplied to the current comparison circuit 5 from a constant current source 15 regardless of the recording mode or reproduction mode.

The current comparator circuit 5 converts these currents into a ratio axis and provides the comparison difference signal SUB to the peak hold circuit 16. The peak hold circuit 16 holds the upper limit or lower limit level of the incoming difference signal SUB, and the current driver circuit 10
give to Note that the peak hold circuit 16 holds the peak value on the side that is approximately at the same level in the recording and reproduction modes.

The subsequent configuration is similar to the conventional circuit described above.

In the above configuration, in the playback mode, the monitor current signal from the photodiode 4 and the current from the constant current source 15 are approximately equal, and the output voltage PH from the peak hold circuit 16 is equal to the period shown in FIG. It becomes a constant value as shown by T1, and the power of the laser diode 2 is kept at a substantially constant value.

In addition, in the recording mode, the photodiode 4 provides a monitor current signal in the form of a rectangular wave according to information as shown in period T2 in FIG. 2(B), and the current comparison circuit 5
However, since the peak hold circuit 16 holds the lower limit peak level and supplies it to the current driver circuit 10 (see FIG. 2(A)), the monitor current signal has a rectangular waveform. Even if there is a signal, a signal having a substantially constant value can be supplied to the current driver circuit 10, and the output current of the laser driver circuit can be kept at a constant value.

Here, since the lower limit peak value is taken instead of the average value of the specific axis output, the hold level is the same in both recording mode and playback mode, and when switching between playback mode and recording mode, the laser diode There is no change in the DC level of the current flowing through 2.

Therefore, according to the embodiment described above, since the DC level does not change when switching modes, it is possible to prevent the current flowing through the laser diode 2 from fluctuating due to changes in the DC level. It is possible to prevent the occurrence of a situation where the threshold level becomes smaller than the threshold level (TH) and is not recorded.

FIG. 3 shows a specific circuit of this embodiment.

In FIG. 3, the current comparator circuit 20 compares the monitor current signal after converting it into a current/voltage, and since this comparator circuit 20 outputs a signal that becomes high in the reproduction mode, the peak hold An upper limit peak hold circuit 21 is applied as a circuit, and its hold signal is applied to a current driver circuit 22, an integrating circuit 23, and a coil 12.
A predetermined current is made to flow through the laser diode 2 through the laser diode 2. Of course, the configuration embodying the above embodiment is not limited to that shown in the drawing.

[Effects of the Invention] As described above, according to the present invention, even in the recording mode,
Even in playback mode, the reference DC power level is made equal, and when rectangular waveform information is superimposed on the monitor current signal, the peak is held to obtain a feedback signal for the reference DC signal. The DC signal hardly changes even when switching between modes, so information can be recorded and reproduced appropriately without disturbing the waveform of the current flowing through the laser light source.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the laser driver circuit according to the present invention, FIG. 2 is a signal waveform diagram of each part thereof, and FIG.
The figure is a connection diagram showing a specific circuit configuration of the above embodiment, FIG. 4 is a block diagram showing a conventional circuit, and FIG. 5 is a signal waveform diagram of each part thereof. 2... Laser diode, 4... Photodiode, 5... Current comparison circuit, 10... Current driver circuit, 15... Constant current source, 16... Peak hold circuit.

Claims (1)

[Claims] The predetermined DC current signal is supplied to a semiconductor laser through which a predetermined DC current signal or a current signal obtained by combining the DC current signal with a rectangular waveform current signal flows depending on the operation mode. In the laser driver circuit, a light receiving element receives the laser beam from the semiconductor laser and outputs a monitor current signal, and compares the monitor current signal with the reference predetermined DC current signal output from the constant current source. A comparison circuit, a peak hold circuit that holds the peak value of the upper limit or lower limit peak value of the comparison difference signal that is approximately equal in each of the above operation modes, and supplies a current signal according to the hold signal to the semiconductor laser. 1. A laser driver circuit comprising: a current driver circuit that performs feedback control to cause the predetermined DC current signal to flow through the semiconductor laser.