JP2532283B2 - Laser diode control method - Google Patents

Description

DETAILED DESCRIPTION [Overview] Regarding control of a laser diode in a rewritable optical disk device, a laser diode LD is used for the purpose of controlling the current of the laser diode by using both APC and high frequency superposition. , A photodiode PD that supplies a current according to the amount of light emitted from the LD, a basic current source that outputs a current of a predetermined value in the read mode and a current of another predetermined value in the erase / write mode, and a current LD output the current output from the basic current source in response to the switch switching instruction signal.
Current switch circuit, a constant switch circuit that outputs a constant of a predetermined value or a constant of zero according to the constant switch switching instruction signal, and a value that subtracts the constant output by the constant switch circuit from the current value that flows through the PD Current subtraction unit, an adjustment unit that outputs a value according to the difference between the target value and the output of the current subtraction unit, a variable current source that outputs a current according to the output of the adjustment unit, a current switch circuit, and a constant switch. And a high frequency superimposing circuit section for outputting a switching instruction signal to the circuit.

[Industrial applications]

The present invention relates to control of a laser diode in a rewritable optical disc device.

[Conventional technology]

When controlling a laser diode (hereinafter abbreviated as LD) for a rewritable optical disk, there are a low emission power read state and a high power write (erase) state. The S / N of the playback signal deteriorates.

As a countermeasure for this, a method is adopted in which the level is set higher than the low power (outside the LD noise region), and high-speed switching is performed with this power to reduce the effective value power. This is called high frequency superposition.

On the other hand, the light emitting power of the LD changes according to the temperature change. Therefore, control is performed to monitor the light amount of the LD so that the light emission power is constant and to keep the monitor light amount constant (Auto Power
er Control) is performed.

[Problems to be Solved by the Invention]

However, heretofore, there has been no method for achieving both APC and high frequency superimposition.

The present invention was created in view of this point,
In a rewritable optical disk device, the purpose is to control the current flowing through the laser diode by using both APC and high frequency superposition.

[Means for Solving the Problem] FIG. 1 is a diagram for explaining the principle of the present invention. The control method of the laser diode of the present invention is: a laser diode LD, a photo diode PD that supplies a current according to the light emission amount of the laser diode LD, and a write current that outputs a predetermined value of current in the read mode. A basic current source that outputs another predetermined value of current in mode
300 and the basic current source 300 according to the current switch switching instruction signal.
A current switch circuit 310 that causes the current output from the laser diode LD to flow, a constant switch circuit 100 that outputs a constant of a predetermined value or a constant of zero according to a constant switch switching signal, and a current that flows through the photo diode PD. A current subtraction unit 200 that outputs a value obtained by subtracting the constant output from the constant switch circuit 100 from a value, an adjustment unit 210 that outputs a value corresponding to the difference between the target value and the output of the current subtraction unit 200, and an adjustment unit 210 Variable current source 2 that outputs a current according to the output of
20 and a high frequency superimposing circuit section 400.

The sum of the current output from the current switch circuit 310 and the current output from the variable current source 220 is the laser diode LD.
Flowing through.

The high-frequency superimposing circuit 400, in the read mode,
When outputting a high frequency pulsed current switch switching instruction signal and a constant switch switching instruction signal indicating that a constant of zero should be output, and in the erase / write mode and when there is erase / write data. Outputs a constant switch switching instruction signal indicating that a predetermined constant should be output, as well as outputting a current switch switching instruction signal indicating that the current of the basic current source 300 should flow through the laser diode LD. It is configured.

[Action]

Basic current source 300 in erase / write mode
Is a current required for the laser diode to emit light of, for example, 7 mW, and the constant switching circuit 100 uses the photodiode PD when the laser diode LD emits 7 mW.
A constant corresponding to the value of the current flowing through is output. Erase / write mode and erase / write data is 1
In this case, the current output from the basic current source 300 flows through the laser diode LD. Laser diode LD is 7m
When W is emitted, the output of the current subtraction unit 200 becomes zero. The target value is, for example, 1 mW, and therefore the adjustment unit 210
Outputs a value indicating that the current should be increased. The current output from the variable current source 220 also flows through the laser diode LD. Due to the additional current of the variable current source 220, the laser diode LD always emits 8 mW.

In the read mode, the basic current source 300 supplies a current necessary for the laser diode to emit, for example, 2 mW, a high frequency pulsed current switch switching instruction signal is given to the current switch circuit 310, and a constant switch circuit is provided. 100 outputs a constant of zero. In read mode, laser
The diode LD operates so that the average light emission amount is 1 mW.

〔Example〕

 FIG. 2 is a block diagram of one embodiment of the present invention.

In the figure, 1 to 3 are D / A converters, 4 are A / D converters, 5 to 8 are level shift circuits, and 10 to
Reference numeral 16 is a transistor, 17 is a current-voltage converter, 18 is an error integrator, 19 is a switch, R1 to R4 are resistors, LD is a laser diode, and PD is a photo diode. I _th : Current at which laser starts to emit light (threshold power) I ₁ : Current corresponding to read power (1 mW) I ₂ : Current at high frequency superposition (2 mW) I ₃ : minute current corresponding to write power (8mW) I _'1: read power light emission time of the monitor current _I' 2ave: high frequency average of the superposition amount of the monitor current value I _'3: light power component of monitoring current, respectively Show.

The microprocessor applies digital signals to the inputs of D / A converters 1-3. The digital output of the A / D converter 4 is captured by the microprocessor. The level shift circuits 5 to 8 can be considered to correspond to voltage dividers.

D / A converter 3 is set to the monitor current I '3 _{-I' 1} so the transistor 10 is flowed. I _'3 -
I ′ ₁ is a current flowing through the photodiode PD when the laser diode emits 7 mW, for example,
This is represented by I (k). The transistors 11 and 12 form a changeover switch. When the signal a'is at the high level and the signal b'is at the low level, the transistor 11 is turned on, and the signal a '
When the low level b'is high, the transistor 12 is turned on. If transistor 12 is on, I (k)
And the sum of the current flowing out from the current-voltage converter 17 is
It flows to the diode PD. The photo diode PD receives a part of the light emitted from the laser diode LD.

The current-voltage conversion unit 17 converts the current flowing in the photodiode PD when the transistor 12 is off, and subtracts I (k) from the current flowing in the photodiode PD when the transistor 12 is on. The converted value is converted into voltage. The output of the current-voltage converter 17 is sent to the microprocessor via the A / D converter 4. The output of the current-voltage converter 17 is applied to the-input terminal of the error integrator 19. To the + input terminal of the error integrator 18, a value (target value) obtained by converting the current flowing in the photo diode PD into a voltage when the laser diode emits 1 mW is applied. A proportional element may be added to the error integrator 18. The output of the error integrator 18 is applied to the base of the transistor 13 via the switch 19 and the level shift circuit 8. Switch 19
It is turned on when APC is performed and turned off when APC is not performed. The current flowing through the transistor 13 is supplied to the laser diode LD. The sum of the current flowing through the transistor 13 and the current flowing through the transistor 15 flows through the laser diode LD.

When writing data to the optical disk, the digital value for making the laser diode LD emit 7 mW is D
When the data of the optical disk is read by being applied to AC2, a digital value for causing the laser diode LD to emit 2 mW of light is applied to the DAC2. The output of the DAC 2 is applied to the base of the transistor 14 via the level shift circuit 6. The transistors 15 and 16 form a changeover switch. When the signal a is low level and the signal b is high level, the transistor 15 is turned on, and the signal a is high level and the signal b is high level.
When is low, transistor 16 turns on. When the transistor 15 is on, the current flowing through the transistor 14 is supplied to the laser diode LD.

FIG. 3 is a diagram showing a configuration example of a high frequency superposition circuit unit used in the present invention, and FIG. 4 is a diagram showing a waveform of the high frequency superposition circuit unit. In the figure, G ₁ to G ₄ are gates, S ₁ to
S ₇ indicates the waveform of each signal.

When erase / write data is 1, erase / write
When the gate is 1, the signal b'is 0, the signal a'is 1, the signal b is 0, and the signal a is 0. When the erase / write data is 0 and the erase / write gate is 1, the signal b'is 1, the signal a'is 0, the signal b is 1, and the signal a is 0.

When erase / write data is 1, erase / write
When the gate is 0, the signal b'is 1, the signal a'is 0, and the signals b and a invert the state at a constant cycle. The same applies when the erase / write data is 0 and the erase / write gate is 0. The waveform of each part of FIG. 4 is shown.

FIG. 5 is a diagram showing the LD current, its output power, and the modulation state by the write data.

When the write gate is 1 and the write data is 1, the transistor 14 supplies a current corresponding to 7 mW, and
A current corresponding to mW flows through the transistor 15 into the laser diode LD. When the write gate is 1 and the write data is 1, 7mW flowing out from the transistor 10
The current I (k) corresponding to is supplied to the photo diode PD via the transistor 12, so that the photo diode PD
Assuming that a current corresponding to a light emission amount of 7 mW is flowing, the current flowing out from the current-voltage converter 17 becomes zero. Since zero is input to the-input terminal of the error integrator 18 and the target value of 1 mW is input to the + input terminal, the error integrator 18
Tells transistor 13 to increase the current,
Finally, the transistor 13 passes a current corresponding to a light emission amount of 1 mW.

When the write gate is 1 and the write data is 0, the transistor 14 passes a current corresponding to 7 mW, and
A current corresponding to mW flows through transistor 16 and resistor R4 to ground. When the write gate is 1 and the write data is 0, the current I (k) corresponding to 7 mW flowing out from the transistor 10 flows to the ground via the transistor 11, so that the light emission amount of the photodiode PD is zero. Assuming that there is, the current flowing out from the current-voltage converter 17 becomes zero. Zero is input to the-input terminal of the error integrator 18,
Since the target value of 1 mW is input to the + input terminal, the error integrator 18 informs the transistor 13 that the current should be increased.
Finally, the transistor 13 finally supplies a current corresponding to a light emission amount of 1 mW.

When the write gate is 0, the transistor 14 is 2m
Apply a current equivalent to W. The signal a and the signal b are alternately turned on / off repeatedly. When the signal a is on, a current corresponding to 2 mW is supplied to the laser diode LD. When the write gate is 0, the current flowing out of the transistor 10 flows through the transistor 11 to the ground. Assuming that the light emission amount of the photo diode PD is 2 mW, the current flowing out from the current-voltage conversion unit 17 is equivalent to 2 mW. Since the voltage equivalent to 2 mW is input to the-input terminal of the error integrator 18 and the target value of 1 mW is input to the + input terminal, the error integrator 18 instructs the transistor 13 to reduce the current. To do. The current flowing through the transistor 13 is adjusted so that the average light emission amount of the laser diode LD becomes 1 mW.

FIG. 6 is a diagram for explaining the output power of the LD at the time of high frequency superposition. During high frequency superimposition (at the time of reading), APC is applied to the average value, and as shown in Fig. 6, even if the oscillation duty changes, the APC circuit automatically controls the average power to 1 mW. To be done.

FIG. 7 is a diagram showing a processing flow of the microprocessor.

 Reset all DAC1 to DAC3.

 Turn off the APC loop and connect the emission control system.

Set E / WGT = 1 and E / WDT = 1. Transistor 15 turns on.

Check whether the LD has started to emit light. If NO, proceed to. If YES, proceed to.

 Set DAC1 to +1. Return to

Check whether the LD light emission is 2 mW or not. If NO, proceed to. If YES, proceed to.

 Set DAC2 to +1. Return to.

Set DAC2 to register R1 (register in microprocessor) and reset DAC2.

Check whether the LD emission power is the read power (1 mW). If NO, go to and if YES, go to.

 Set DAC1 to +1. Return to

Check whether the LD emission power is the light power (8 mW). If NO, go to and if YES, go to.

 Adds 1 to DAC2. Return to

Set DAC2 to R2 (register in microprocessor).

 Reset DACs 2 and 1.

 Set E / WGT = 0 and E / WDT = 0.

 Turn on APC.

Output of current-voltage converter 17 is read power (1mW)
Is checked, and if NO, proceed to and YES
If, go to.

 Adds 1 to DAC1. Return to

 Set R2 to DAC2.

 Set E / WGT = 1 and E / WDT = 1.

Output of current-voltage converter 17 is read power (1mW)
Is checked, and if NO, proceed to and YES
If, go to.

 Adds 1 to DAC3. Return to

 Set R1 to DAC2.

 Set E / WGT = 0 and E / WDT = 0.

Check if E / WGT (Erase / Write Gate) is at high level. If YES, go to.

 Set R2 to DAC2.

Check if E / WGT is at low level. If YES, go to.

 Set R1 to DAC2. Proceed to.

FIG. 8 is a diagram showing a second embodiment of the present invention. In the figure, 2-1 and 2-2 are D / A converters, 21 and 22 are switches, and 23 is an inverting gate.

In the embodiment of FIG. 8, the value of the register R1 is preset in the D / A converter 2-1 and the D / A converter 2-
The value of register R2 is preset in 2 and E / WGT =
When it is 0, the switch 21 is turned on, and when E / WGT = 1, the switch 22 is turned on. The other structure is the same as that of the embodiment shown in FIG. According to the embodiment of FIG.
The read mode can be switched to the erase / write mode, or the erase / write mode can be switched to the read mode at high speed.

FIG. 9 is a diagram showing an example of the LD unit. In FIG. 9A, the cathode of the laser diode LD and the anode of the photodiode are connected, and the connection point is grounded. Further, in FIG. 9B, the cathode of the photo diode PD and the anode of the laser diode LD are connected, and the connection point is grounded. In the embodiment shown in FIG. 2, the LD unit shown in FIG. 9 (a) is used.

FIG. 10 is a diagram showing an example of a circuit on the LD current supply side when the LD unit of FIG. 9 (b) is used. In the figure, reference numerals 14 'to 16' denote transistors, respectively. In this example, NPN type transistors are used as the transistors 14 'to 16'. The circuit on the PD current detection side is also configured by using NPN type transistors. The read power, write, and
The power and the high frequency superimposed power are examples, and changing the values does not impair the function of the present invention.

〔The invention's effect〕

As is clear from the above description, according to the present invention, the AP
Under the condition that C is applied, write light emission and high frequency superimposition at the time of reading are possible, and stable laser control is possible.

[Brief description of drawings]

1 is a block diagram showing the principle of the present invention, FIG. 2 is a block diagram showing a first embodiment of the present invention, FIG. 3 is a diagram showing a configuration example of a high frequency superimposing circuit section, and FIG. 4 is a high frequency superimposing circuit section. Figure 5 shows the waveform of LD, Figure 5 shows the LD current, its output power, and the modulation status by write data. Figure 6 shows the output power of LD at high frequency superposition. Figure 7 shows the microprocessor's output power. FIG. 8 is a diagram showing a processing flow, FIG. 8 is a diagram showing a main part of a second embodiment of the present invention, FIG. 9 is a diagram showing an example of an LD unit, and FIG. 10 is a diagram showing a third embodiment of the present invention. It is a figure which shows a part. 1 to 3 ... D / A converter, 4 ... A / D converter,
5 to 8 ... Level shift circuit, 10 to 16 ... Transistor, 17 ... Current-voltage converter, 18 ... Error integrator, 19 ... Switch, R1 to R4 ... Resistor, LD ... Laser diode , PD ... Photo diode.

Claims (1)

(57) [Claims] 1. A laser diode (LD), a photo diode (PD) that supplies a current according to the amount of light emitted from the laser diode (LD), and a write current that outputs a predetermined current in the read mode.
In the mode, a basic current source (300) that outputs a current of another predetermined value, and a current switch circuit (310) that causes the current output from the basic current source to flow to the laser diode (LD) according to the current switch switching instruction signal. ) And a constant switch circuit (100) that outputs a constant of a predetermined value or a constant of zero according to the constant switch switching signal, and the constant switch circuit (100) outputs from the current value that flows through the photodiode (PD). Depending on the output of the adjustment unit (210), the current subtraction unit (200) that outputs a value after subtracting a constant, the adjustment unit (210) that outputs a value according to the difference between the target value and the output of the current subtraction unit It is equipped with a variable current source (220) that outputs a fixed current and a high frequency superimposing circuit section (400), and the sum of the current output from the current switch circuit (310) and the current output from the variable current source (220). Flows through the laser diode (LD) In the read mode, the high frequency superposition circuit section (400) outputs a high frequency pulsed current switch switching instruction signal and a constant switch switching instruction indicating that a constant of zero should be output. Current switch switching instruction signal that outputs a signal and indicates that the current of the basic current source (300) should flow to the laser diode (LD) when in erase / write mode and there is erase / write data. And a constant switch switching instruction signal indicating that a predetermined constant should be output. A laser diode control system characterized by the above-mentioned.