JPH04271025A - Apc circuit for laser light source - Google Patents

Abstract

PURPOSE:To always attain the highly accurate APC control for the quantity of emitted laser by eliminating the unbalance of weight that is caused per bit of the output value of a pin monitor by the difference of quantities of light emitted from a laser diode. CONSTITUTION:A varying circuit 7 varies the output gain with a/RD signal so as to secure the same weight per bit of the output value of a pin monitor 6 generated with the light quantity of a laser diode 5 that is decreased in a reproduction state and increased in a record/erasion state. At the same time, the circuit 7 amplifiers and outputs the input voltage received from a resistor R1 in accordance with the varied output gain. The circuit 7 consists of an operational amplifier 7a, received the negative feedback, a resistor R2, the feedback resistors R3 and R4 connected in parallel to each other, and an analog switch 7b which is connected in series to the R3 and turned on and off with the/RD signal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an APC circuit for a laser light source that controls the output power of an optical head of an optical information recording/reproducing apparatus.

0002

[Prior Art] In recent years, instead of using a magnetic head, it has become possible to optically write information and read recorded information using an optical head that focuses laser light and irradiates it onto a recording medium. Optical information recording and reproducing devices that can perform this function have been put into practical use. This optical information recording/reproducing device is capable of recording and reproducing information at a much higher density than with a magnetic head.

By the way, FIG. 4 shows a conventional example of an auto power control (APC) circuit for keeping the laser light emitted by the laser light source of the optical head at a constant level. The CPU 20 has digital/analog (D/
A) Outputting an analog laser emission amount instruction value to the drive circuit 22 via the converter 21. Then, the drive circuit 22 causes a current corresponding to the light emission amount instruction value to flow to the laser diode 23, which is a laser light source. The laser diode 23 is
Light is emitted according to the current output by the drive circuit 22. The laser diode 23 emits light at a higher recording/erasing power during recording/erasing than during reproducing, and emits light at a lower reproducing power during reproducing.

On the other hand, in the pin monitor 24, a current flows according to the amount of light emitted from the laser diode 23, and this current is converted into a voltage by a resistor R7, and this voltage is converted into an analog/
A digital (A/D) converter 25 inputs. The A/D converter 25 converts the input voltage into a digital signal and outputs the CP
Input to U20. The CPU 20 determines the difference between the initially set digital light emission amount instruction value and the current light emission amount detection value obtained from the A/D converter 25. The CPU 20 corrects the light emission amount command value instructed to the A/D converter 21 according to the obtained difference, and performs APC so that the laser diode 23 always emits light at a constant light amount.

[0005] In this way, the APC circuit has two functions:
During recording/erasing, the current flowing from the drive circuit 3 is changed to change the output power of the laser diode 23, and the amount of light emitted is controlled so as not to emit light with more power than necessary.

[0006] In addition to the method of obtaining the recording/erasing power and the reproducing power, as described above, in addition to the method of setting separate light emitting amounts, there is also a method of obtaining the recording/erasing power and the reproducing power, as described in Japanese Patent Laid-Open No. 2-227836. There is also a switching type in which when the reproduction power is emitted, the light is emitted only with the reproduction power, and when the recording/erasing power is emitted, a predetermined power is superimposed on the reproduction power to provide the recording/erasing power.

[0007]

[Problem to be Solved by the Invention] However, in the conventional APC circuit, the amount of laser light emission was detected, and the laser power simply changed by the amount of change, and the output current value of the pin monitor also changed again. . That is, conventional A
In the PC circuit, the current value simply changes in response to changes in operation such as when reproducing power is emitted or when recording/erasing power is emitted. Therefore, since the weight per bit of the output value of the pin monitor is the same when the amount of light emitted by the laser diode is small and large, there is a drawback that APC cannot be applied with high precision when the value is small.

That is, in the APC circuit shown in FIG.
When the laser power is large, such as recording/erasing power,
For example, the laser emission power is 40 mW. Furthermore, in the case of a small reading power, for example, the laser output power is 4.5 mW. Dynamic pin monitor 24
When using within the range, e.g. 4V, e.g. A/
Assuming that the D converter 25 has 8 bits, the weight per bit is 40 [mW]/255 = 0.157 [mW
/bit] …(1).

[0009] Here, when the laser power is large,
The error of 1 bit is 0.157 [mW/bit]/40 [mW
]=0.4%...(2).

[0010] Furthermore, when the laser power is small, 1
The bit error is 0.157 [mW/bit]/4.5 [m
W]=3.5% (3).

Comparing the results of (2) and (3), the error per bit when the laser power is low is about 10 times that when the laser power is high. Therefore, the conventional APC circuit has the drawback that when the laser power, such as the reproduction power, is small, the APC control error increases, and the amount of laser light emission cannot be controlled with high precision.

The present invention has been made in view of the above circumstances, and provides an APC for a laser light source that controls the amount of laser light emitted with high precision regardless of the level of the amount of light emitted by the laser.
The purpose is to provide circuits.

[0013]

[Means for Solving the Problems] In the APC circuit for a laser light source of the present invention, a control means converts a light emission amount instruction value for causing the laser light source to emit light at an appropriate amount of light through a D/A conversion means. a light emission amount detection means for detecting the light emission amount of the laser light source while the driving means supplies a signal corresponding to the light emission amount instruction value to the laser light source so that the laser light source emits light according to the light emission amount instruction value; sends the output signal as a detected value to the control means via the D/A conversion means, and the control means determines the difference between the light emission amount instruction value and the detected value, and determines the light emission amount of the laser light source based on the obtained difference. An APC circuit for a laser light source that maintains a constant value, wherein the light emission amount detection means outputs an output so as to maintain high control accuracy of the APC according to changes in a light emission amount instruction value outputted by the control means. The output gain for the signal to be output is varied, and the value of the signal output by the light emission amount detection means is changed based on the variable output gain.
It includes variable gain/output means for outputting to the conversion means.

[0014]

[Operation] With this configuration, the gain variable/output means outputs a signal outputted by the light emission amount detection means so as to maintain high control accuracy of the APC according to a change in the light emission amount instruction value outputted by the control means. The output gain for the output gain is varied, and the value of the signal output by the light emission amount detection means is changed based on the varied output gain and outputted to the A/D conversion means.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 relate to a first embodiment of the present invention, in which FIG. 1 is an electrical circuit diagram of an APC circuit, and FIG. 2 is a waveform diagram for explaining the operation of the circuit in FIG.

As shown in FIG. 1, an auto power control (APC) circuit 1 is used in an optical information recording/reproducing device capable of recording/erasing or reproducing information by installing an optical disk (not shown). This is a circuit for keeping the laser power of the laser light source installed in the optical head of the device at a constant level. CP as a control means
U2 outputs an analog laser emission amount instruction value to the drive circuit 4 via the digital/analog (D/A) converter 3. The drive circuit 4 is configured to flow a current corresponding to the light emission amount instruction value to a laser diode (LD) 5 as a laser light source. The laser diode 5 emits light in response to the current output from the drive circuit 4. The CPU 2 sets a predetermined light emission amount instruction value that is larger during recording/erasing power emission than during reproduction, and the laser diode 5 emits light with a predetermined recording/erasing power. Also, CPU2
When emitting reproduction power, a predetermined light emission amount instruction value lower than that during recording/erasing is set, and the laser diode 5 emits light at a predetermined reproduction power lower than the recording/erasing power.

On the other hand, a current corresponding to the amount of light emitted from the laser diode 5 flows through the pin monitor (PD) 6 as a means for detecting the amount of light emitted, and this current is converted into a voltage by the resistor R1, and this voltage is used as a gain variable - It is designed to be input to the variable circuit 7 as an output means.

The variable circuit 7 is controlled by the /RD signal from a host computer (not shown) which is a higher-order control means.
The output gain is varied, and the input voltage from the resistor R1 is amplified and output according to the varied output gain. This variable circuit 7 includes a differential amplifier (hereinafter referred to as an operational amplifier) 7a with negative feedback, a resistor R2, a feedback resistor R3 and a feedback resistor R4 connected in parallel, and the feedback resistor R3. connected in series with
and an analog switch 7b which is turned on/off by the /RD signal. In addition, the analog switch 7b is turned off when the /RD signal becomes "0" when the reproduction power is emitted, and when the recording/erase power is emitted.
It is turned on when the /RD signal becomes "1". Therefore, in the operational amplifier 7a, the combined resistance value of the entire feedback resistor changes by turning on/off the analog switch 7b, thereby varying the output gain. In this variable circuit 7, the output value of the pin monitor 6, which is caused by the fact that the amount of light emitted by the laser diode 6 is small during playback and becomes large during recording/erasing, is transmitted to the subsequent analog/digital (A/D) converter 8. This is provided to make the weight per bit the same. Furthermore, the above
The /RD signal may be output from the CPU 2.

The A/D converter 8 receives the output signal of the operational amplifier 7a of the conversion circuit 7, converts it into a digital signal, and outputs it to the CPU 2 as a light emission amount detection value. The CPU 2 calculates the difference between the initially set digital light emission amount instruction value and the current light emission amount detection value obtained from the A/D converter 8. CPU2 is
The light emission amount instruction value instructed to the A/D converter 3 is corrected according to the obtained difference, and APC is performed so that the laser diode 5 always emits light at a constant light amount.

The operation of this embodiment will be explained with reference to FIG. As shown in FIG. 2(a), when the reproduction power is emitted, the /RD signal becomes "0" and the analog switch 7b is turned off. At this time, the laser diode 5
is the reproduction power (for example, 4 at a given laser output power)
．． As shown in FIG. 2(b), the pin monitor 6 converts the amount of light emitted from the laser diode 6 into a current and detects it. For example, the voltage value generated across the resistor R1 is detected by the pin monitor 6. It is set to 0.45V.

On the other hand, as shown in FIG. 2(a), when the recording/erasing power is emitted, the /RD signal becomes "1" and the analog switch 7b is turned on. At this time, the laser diode 5 emits light with recording/erasing power (for example, 40 mW with a predetermined laser emission power), while the pin monitor 6 monitors the amount of light emitted by the laser diode 6, as shown in FIG. 2(b). Convert to current, for example, resistor R
Assume that the voltage value generated across 1 is 4V.

By the way, when the reproduced power is emitted, the analog switch 7b is off, so the gain of the operational amplifier 7b is 1+(R4/R2)...(4), for example, resistor R2=1kΩ, resistor R3=91Ω, resistor R
If 4=9.1kΩ, then from equation (4), 1+(9.1
kΩ/1kΩ)=10.1.

On the other hand, when the recording/erasing power is emitted, the analog switch 7b is on, so the gain of the operational amplifier 7b is 1+{R3·R4/(R3+R4)}/R2
...(5), and the gain of the operational amplifier 7b is, for example, as described above, according to equation (5), 1+{(9.1kΩ+91Ω)/9.1kΩ・91Ω}
/1kΩ=1.09.

Therefore, as shown in FIG. 2(c), the output voltage of the operational amplifier 7a is 0.45V when the reproduction power is emitted.
×10.1=4.54V, and when recording/erasing power is emitted, 4V×1.09=4.36V, which is almost the same.

Here, when the reproduced power is emitted, the output of the operational amplifier 7a is 10.1 times the output of the pin monitor 6, so if the A/D converter 8 is 8 bits, the error per bit is as follows. become that way.

4.5 [mW]×10.1/255=0.18 [mW/
bit], and the error is 0.18 [mW/bit]/(4.5 [mW] x 10.
1)=0.4%...(6) Also, when recording/erasing power is emitted, the output of the operational amplifier 7a is 1.09 times the output of the pin monitor 6, so the error per bit is similarly 40 [mW] x 1.09/255 = 0.17 [ mW/bit] From 0.17 [mW/bit]/(40 [mW] x 1.09
)=0.4%...(7).

In this example, as shown in the results (6) and (7), the errors when emitting the reproduction power and when emitting the recording/erasing power are almost the same. Therefore, in this embodiment, the pin monitor 6 caused by the level of laser emission power
It is possible to eliminate the unbalance of the weight per bit of the output value, and it is possible to APC the amount of laser light emission with high precision both when emitting reproduction power and when emitting recording/erasing power. Moreover, the effects of this embodiment can be obtained with a simple configuration.

FIG. 3 is an electrical circuit diagram according to a second embodiment of the present invention. In this embodiment, the variable circuit 7 of the first embodiment
In place of the operational amplifier 7a, the analog switch 7b and the resistor R5 are connected in series. That is, while the voltage of the resistor R1 is input to the A/D converter 8, the analog switch 7b and the resistor R5 are connected in parallel with the resistor R1, and when recording/erasing power is emitted, / The analog switch 7b is turned on by the RD signal "1", and a resistor R5 is connected in parallel to the resistor R1. Therefore, in this embodiment, when the recording/erasing power is emitted, the combined resistance value of the resistors is lowered, and the voltage value input to the A/D converter is lowered, and when the reproducing power and the recording/erase power are emitted, the combined resistance value of the resistors is lowered. Therefore, the weight per bit in the A/D converter 8 can be made the same. The other configurations and effects are the same as those in the first embodiment, so the same reference numerals are given and the explanations are omitted. Note that in this embodiment, the load resistance value applied to the pin monitor 6 changes depending on whether the read power is emitted and the recording/erase power is emitted, so care must be taken in selecting the resistance value.

As described in Japanese Unexamined Patent Publication No. 2-227836, the present invention employs a switching system in which a predetermined power is superimposed on the reproduction power to obtain the recording/erasing power when the recording/erasing power is emitted. It is also effective for those that perform APC digitally.

[0030]

As described above, according to the present invention, the gain variable/output means adjusts the light emission amount so as to maintain high control accuracy of the APC in accordance with changes in the light emission amount instruction value outputted by the control means. The output gain for the signal output by the detection means is varied, and the value of the signal output by the light emission amount detection means is changed based on the variable output gain and outputted to the A/D conversion means, so that the light emission of the laser light source is This has the effect that the amount of light emitted by the laser light source can always be controlled by APC stably and with high precision regardless of the amount of light emitted.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram of an APC circuit according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the circuit in FIG. 1;

FIG. 3 is an electrical circuit diagram of an APC circuit according to a second embodiment of the present invention.

FIG. 4 is an electrical circuit diagram of a conventional APC circuit.

[Explanation of symbols]

1...APC circuit 2...CPU 3...D/A converter 4...Drive circuit 5...Laser diode 6...Pin monitor 7...Variable circuit 7a...Op amp 7b...Analog switch 8...A/D converter R1~R4...Resistor

Claims (1)

[Claims] 1. The control means sends a light emission amount instruction value for causing the laser light source to emit light at an appropriate amount of light to the driving means via the D/A conversion means, and the driving means corresponds to the light emission amount instruction value. A signal is supplied to the laser light source so that the laser light source emits light according to the light emission amount instruction value, and a signal outputted by the light emission amount detection means that detects the light emission amount of the laser light source is transmitted through the A/D conversion means to emit light. In the APC circuit of the laser light source, the APC circuit of the laser light source sends the amount detected value to the control means, the control means determines the difference between the light emission amount instruction value and the detected value, and adjusts the light emission amount of the laser light source to a constant value based on the determined difference. An output gain that is varied by varying an output gain for a signal output by the light emission amount detection means in accordance with a change in the light emission amount instruction value outputted by the control means so as to maintain high control accuracy of the APC. 1. An APC circuit for a laser light source, comprising variable gain/output means for changing the value of a signal output from a light emission amount detection means based on the above and outputting the signal to an A/D conversion means.