JPS61194649A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To deal with even the low output area of output characteristics of a semiconductor laser which has polygonal characteristics by switching and controlling of the by-pass current of a semiconductor laser driving circuit. CONSTITUTION:When the output current Io of a light quantity detector 3 corresponding to a polygonal point becomes equal to the total output current Ipd of the light quantity detector 3, a converted voltage generated by a resistance 7 is applied to an input of a comparing circuit 8 at any time so that it attains to a threshold value Ew. Therefore, when the output of the comparing circuit 8 is '0' while the converted voltage of the resistance 7 is below the threshold value Ew, a multiplexer 93 is triggered with the signal '0' and switched to the side of a low-current attenuator 91. Similarly, when the converted voltage of the resistance 7 is below the threshold value Ew. The output of the comparing circuit 8 is '1' and the multiplexer 93 is triggered to the side of a high- current attenuator 92. Consequently, the light output of the semiconductor laser during reproduction is made constant and a desired light output for recording is obtained over the entire light output range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Summary) In a semiconductor laser drive circuit, by switching and controlling the bypass current, it is possible to cope with the low output region of the output characteristics of a semiconductor laser having corner characteristics.

[Industrial application field]

The present invention relates to a drive circuit for a semiconductor laser used in an optical recording/reproducing device such as an optical disk device or a magneto-optical disk device, and in particular a drive circuit for stabilizing the optical output of a semiconductor laser during information reproduction and recording. Regarding improvements.

That is, semiconductor lasers are widely used as light sources in optical recording/reproducing devices, and the amount of emitted light is converted into electric current and monitored by a light amount detector using a photodiode.

During playback, the output of the light intensity detector is converted into a voltage and fed back negatively to an automatic power control circuit (hereinafter abbreviated as APC circuit) to control the playback current so that the amount of light emitted by the semiconductor laser remains at a constant value. .

This semiconductor laser is also used during recording due to the simplification of the optical system. For recording, a modulation circuit is used in the semiconductor laser to superimpose a recording current on the reproducing current.

However, when the recording current is superimposed on the reproduction current, the output of the light amount detector changes, so if this is done, the APC circuit that acts to keep the amount of light emitted from the semiconductor laser at a constant value.
A modulation circuit that attempts to increase this constant value by using a superimposed current has an irreconcilable contradiction, and it is desired to develop a means for achieving both of these problems.

[Conventional technology]

FIG. 4 shows a block diagram of a conventional semiconductor laser drive circuit. In the figure, 1 is a semiconductor laser, and 3 is a light amount detector, which is usually a photodiode or the like, is formed integrally with the semiconductor laser 1, and is a rear light of the optical output emitted by the current that drives the semiconductor laser 1. It receives the light, outputs a current of 1 pd corresponding to the intensity of the light output, and is used as a laser light intensity monitor of the semiconductor laser 1.

The drive circuit 2 shown in FIG. 1 is composed of an APC circuit 21 that outputs a reproduction current Ib and a modulation circuit 22 that outputs a recording current Iw in FIG. 4, and the modulation circuit 22 includes a switching circuit 221 and a constant current circuit. 222.

Reference numeral 4 denotes a resistor which converts the detection current 1r of the light amount detector 3 flowing through the resistor into a voltage and feeds it back to the APC circuit 21 to form a closed loop circuit 5. -V indicates the applied power supply voltage.

The closed loop circuit 5 constitutes a circuit that supplies a drive current rb for reproducing information to the semiconductor laser l for the light source of the optical disc device, and the APC circuit 21 always keeps the optical output of the semiconductor laser 1 at a constant value during reproduction. The reproduction current 1b is controlled so as to maintain the reproduction current 1b.

221 is a high-speed switching circuit, 222 is a constant current circuit, and M is a modulation signal, which constitutes a modulation circuit 22 that superimposes and supplies an intermittent recording current Iw to a drive current Tb flowing through the semiconductor laser 1 during reproduction.

Normally, the APC circuit 21 does not have good high-frequency characteristics in terms of band, so high-speed modulation cannot be expected. A modulation circuit 22 is configured in parallel to the semiconductor laser 1.

When reproducing information, a predetermined drive current Tb is passed through the semiconductor laser 1 by the APC circuit 21, and when recording information, a high-speed switching circuit 221 is driven by the modulation signal M,
An intermittent constant recording current - is superimposed on the semiconductor laser 1 to flow Ib+1-.

However, in this case, if the APC circuit 21 remains a mere feedback circuit, the detection current Is will also increase in response to the superimposition of the recording current Iw, and the amount of feedback detected by the resistor 4 will increase, so the output of the APC circuit 21 will be Inconsistency occurs because the average value is made to be at the same level as when reproducing information, so in order to solve this problem, a bypass circuit 6 that bypasses the corresponding detection current Is during recording and an attenuation circuit that drives this are provided. A container 10 is provided.

The bypass circuit 6 has a configuration in which a transistor 61 and a resistor 62 and a transistor 63 and a resistor 64 are combined as shown.

When the current 1o flows into one transistor 61, the bypass circuit 6 can allow a current Is = Io of the same value as the current 1° to flow into the other transistor 63. Therefore, depending on the configuration of the constant current circuit (used It is known for that.

FIG. 5 is a current vs. light output characteristic curve of a conventional example, showing the characteristics of a semiconductor laser and a light amount detector. 4 and 5, the optical output when the drive current 1b is applied to the semiconductor laser 1 during reproduction is Pr, and the total detection current Ipd of the light amount detector 3 corresponding to the optical output Pr, that is, in this case, the detection Only the current Ir is converted into a voltage and fed back to the APC circuit 21, and the APC circuit 21 controls the drive current rb so that the optical output Pr during reproduction of the semiconductor laser 1 becomes a constant value.

Further, if the total optical output when a recording current ■- is superimposed and passed through the semiconductor laser l is Pw, and the superimposed detection current of the light amount detector 3 corresponding to the recording current face is Is, then the light amount detector 3
The total detection current 1pd = Ir + Is, and when this total detection current Ipd is converted into voltage by the resistor 4, only the component of the superimposed detection current Is becomes redundant, and the reproduction current rb changes.

Therefore, it can be seen that the current Io flowing through the transistor 1) should be controlled so that only the superimposition detection current Is flows into the transistor 13 of the bypass circuit 6.

By the way, as can be seen from FIG. 2, this superimposition detection current Is is proportional to the recording current 1w. If the coefficient is set to 1/, it is easy to set the output current Io to Iw/k using the attenuator 10.

Therefore, by setting the coefficient 1/k of the attenuator 10 so that the superimposed detection current Is = Io = Iw/k, only the detection current Ir corresponding to the reproduction current Ib flows through the resistor 4, and the contradiction is resolved. resolved.

[Problem that the invention seeks to solve]

Generally, the current vs. light output characteristic of a semiconductor laser is a folded line having one breakpoint as shown in FIG. 5, and the output current characteristic of a light amount detector corresponding to the light output of the semiconductor laser is a linear shape.

Therefore, the current ratio of the detection current Is flowing through the light amount detector 3 in proportion to the recording current I- exhibits different values with the corner point P as a boundary. When the range of change of the recording current 1w is in the increasing direction from the breaking point P, it is only necessary to set one proportionality coefficient.
When a region in the decreasing direction is included from the corner point P, using only one attenuator 10 has the disadvantage that an error occurs in the current value to be branched to the bypass circuit 6, and the modulation waveform is disturbed.

The present invention was created in view of the above-mentioned drawbacks of the conventional art, and an object of the present invention is to provide a circuit in which errors do not occur in branch currents.

[Means to solve the problem]

FIG. 1 shows a diagram explaining the principle of the present invention. In the figure, 1 is a semiconductor laser, and 2 is a drive circuit that supplies a predetermined reproduction current or a recording current superimposed on the reproduction current to the semiconductor laser. 3 is a light amount detector for monitoring the amount of light emitted from the semiconductor laser, 4 is a resistor, and 5 is a loop circuit, which is driven by converting the output current 1r of the light amount detector 3 corresponding to the reproduction current into a voltage using the resistor 4. This is a circuit that feeds back to circuit 2.

6 is a bypass circuit which converts the output current Is of the light amount detector 3 corresponding to the recording current to the total output current Ipd of the light amount detector 3.
=Ir+Is This is a circuit that has a function of branching from Is.

In the semiconductor laser drive circuit configured in this way,
a resistor 7 that converts the total output current Tpd into voltage; and the resistor 7
A comparison circuit 8 is provided for comparing the output voltage of the output voltage with a required threshold value Ew, and means 9 for switching and controlling the branch current of the bypass circuit 6 using the output of the comparison circuit 8, that is, a low current attenuator 81 and a high current attenuation The object of the present invention can be achieved by providing an optical recording/reproducing apparatus characterized in that it is equipped with a multiplexer 82 and a multiplexer 83 for switching and controlling these.

[Effect]

The voltage at which the output current of the light amount detector 3 corresponding to the corner position in the current vs. output characteristic of the semiconductor laser 1 is converted by the resistor 7 is set to a threshold value E-, and the input of the comparator circuit 8 is below the threshold value Ew. In this case, select the low current attenuator 91 and set the threshold E
- In the above case, by switching and controlling the multiplexer 93 to select the high current attenuator 92, it is possible to separately supply drive currents for reproduction and recording without error even in the low optical output region of the semiconductor laser. I can do it.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make the explanation of the configuration and operation easier to understand, the same parts are denoted by the same reference numerals throughout the drawings, and repeated explanation thereof will be omitted.

FIG. 2 shows a detailed illustration of the invention. In the figure, 7
is a resistor used as a means for converting the total output current 1 pd of the light amount detector 3 into a voltage.

Reference numeral 8 denotes a comparator circuit, to which a required threshold value Ew is always applied to one of its input terminals, and a converted voltage generated by the current 1 pd flowing through the resistor 7 is input to the other input terminal.

Reference numeral 9 denotes means for switching and controlling the branch current of the bypass circuit 6, and for example, a low current attenuator 91 and a high current attenuator 92 are provided as means for regulating the branch current, and a multiplexer 93 is used as the switching means. It has become. Multiplexer 93 is controlled by the output of comparison circuit 8.

FIG. 3 is a current versus output characteristic curve of the present invention, which is a characteristic curve illustrating the operating current of the semiconductor laser 1 and the light amount detector 3. In the figure, the characteristics of the semiconductor laser ■ are at the bending point P
The characteristic of the light amount detector 3 is a linear shape. Here, a case will be considered in which the operating range of the recording current includes the breaking point P.

That is, the light quantity detector 3 flows in proportion to the recording current Iw.
The current ratio Is/I- of the output current Is is divided into two parts: 1/I- in the region A before the break point and 1/2 in the region B after the break point.

In FIGS. 2 and 3, the output current of the light amount detector 3 corresponding to the breaking point P is set as IO, and the light amount detector 3 in FIG.
When the total output current of 1 pd = io, the resistor 7
The comparator circuit 8
Always applied to the input.

Therefore, if the output of the comparator circuit 8 is set to "0" when the converted voltage of the resistor 7 is less than the threshold value Ew, the multiplexer 93 is triggered by this signal "0" and connected to the low current attenuator 91. Switch to The low current attenuator 91 is the modulation circuit 2
This is an attenuator configured to convert the output of 2 to Iw/.

Similarly, when the converted voltage of the resistor 7 is equal to or higher than the threshold value Ew,
The output of the comparator circuit 8 becomes “1” and is sent to the multiplexer 93.
, and is switched to be connected to high current attenuator 92. A high current attenuator 92 reduces the output of the modulation circuit 22 to I
The attenuator is set to convert to w/kz.

〔Effect of the invention〕

As explained in detail above, according to the optical recording/reproducing apparatus of the present invention, it is possible to always keep the optical output of the semiconductor laser constant during reproduction and to obtain the desired optical output for recording over the entire optical output range. I can do it.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a detailed explanatory diagram of the present invention, Fig. 3 is a current vs. optical output characteristic curve of the present invention, and Fig. 4 is a block diagram of a conventional semiconductor laser drive circuit. , FIG. 5 shows a current versus light output characteristic curve of a conventional example. In the figure, 1 is a semiconductor laser, 2 is a drive circuit, 3 is a light amount detector, 4 and 7 are resistors, 5 is a loop circuit, 6 is a bypass circuit, 8 is a comparison circuit, and 9 is a means for switching and controlling the branch current. are shown respectively. Figure 3 Senkuro stop of a man's name - γ ear 1 layer Entsuba Tako Pro 17 Figure 4F
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Claims (1)

[Scope of Claims] A drive circuit (2) that supplies a predetermined reproduction current or a recording current superimposed on the reproduction current to the semiconductor laser (1), and a light amount detector that monitors the amount of light emitted from the semiconductor laser (1). a loop circuit (3) that converts the output current (Ir) of the light amount detector (3) corresponding to the reproduction current into a voltage with a resistor (4) and negatively feeds it back to the drive circuit (2); 5) and an output current (Is) of the light amount detector (3) corresponding to the recording current.
and a bypass circuit (6) that branches from the total output current (Ipd) of the light amount detector (3), a resistor (7) that converts the total output current (Ipd) into a voltage. ) and a comparison circuit (8) that compares the output voltage of the resistor (7) with a required threshold (Ew), and the branch of the bypass circuit (6) is provided at the output of the comparison circuit (8). An optical recording/reproducing device characterized in that it is provided with means (9) for switching and controlling current.