JPH05283776A - Laser drive circuit - Google Patents

Abstract

PURPOSE:To enhance a laser in output response from a high power side to a low power side so as to enable data to be surely stored or erased by a method wherein a high-speed rise analog control and a digital closed control are carried out by a high-speed amplifier and a bias setting means respectively. CONSTITUTION:A value detected by a detection means 1 and a target reference value held by a target reference value holding means 5 on a second high power side are compared with each other by an analog control system high-speed amplifier 25 to drive a laser to a high power level at a high speed. When the laser output power produced by this process reaches to a prescribed level, it is held by a sample holding means 27. The output power concerned is compared with the output of a second bias value setting means 9 through a switching value comparing means 29, and the output of the comparing means 29 turns ON a switch 14 connected to a bias value setting means 9 on a second high power side and turns OFF a switch 28 linked to a sample holding means 27 through a flip-flop circuit 23, whereby a laser can be switched in output power at a high speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser drive circuit provided in an optical disk drive or a magneto-optical disk drive in a document file device or a data file device for controlling the output of laser light.

[0002]

2. Description of the Related Art An optical disk information recording device such as an optical disk drive or a magneto-optical disk drive is equipped with a laser drive circuit. FIG. 5 shows a schematic configuration of the laser drive circuit, and FIG. 6 shows an output waveform diagram from the laser drive circuit at that time. In FIG. 5, 2 is a laser lighting command signal, 1 is a monitoring photodiode, 4 is a first storage circuit which is a first target reference value holding means for storing and holding a low power reference voltage PL, and 6 is Clock for counter,
Reference numerals 3 and 7 are comparators, which are first and second target value comparing means, and 8 and 9 are output up by the control from the comparators.
First, the output value is turned down and the output value is kept digital.
An 8-bit up / down counter which is a second bias value setting means, 11 and 12 are 8-bit D / A converters for converting an input digital bias into an analog bias, 13 is a low power side connection switch, and 15 Is a laser drive circuit for oscillating the laser 16, 1
Reference numeral 7 is a modulation circuit, 16 is a laser, 10 is a power switching circuit for switching between low power during reproduction and high power during recording / erasing, 14 is a high power side connection switch, and 5 is a high power reference voltage PH. The second storage circuit is a target reference value holding unit on the second high power side.

The operation of such an apparatus will be described.
First, the laser lighting command signal 2 is activated to drive the laser drive circuit. At this time, since the power switching command 10 for controlling switching between low power (playback mode) and high power (recording / erasing mode) is set on the playback mode side, the up / down counter 8 on the low power side is in an operable state. Becomes The monitor signal from the monitoring photodiode 1 is stored in the first storage circuit 4 and held by the low power reference voltage PL and the comparator 3 on the reproduction mode side.
And the result is sent to the up / down counter 8. The output is converted into an analog signal by the 8-bit D / A converter 11, is sent to the laser drive circuit 15 through the switch 13, and a laser current starts flowing through the laser 16. At this time, the laser output is 3 in FIG.
As in the state of 33 in FIG. 6, it starts increasing stepwise as shown by 2, and stops when it coincides with the command value PL (low power reference voltage PL).

When the power output command 10 shown in FIG. 5 is switched to the high power side (recording / erasing) while the laser output matches the low power reference voltage PL, the up / down counter 8 on the low power side is changed. After stopping, the value is fixed to a specific value (counter value when the laser output matches the low power reference voltage PL), and the high power up / down counter 9 starts operating. In addition to the switch 13 on the low power side, the switch 14 on the high power side is also connected. Therefore, the output voltage of the laser matches the high power reference voltage PH after the reference voltage is switched from the low power reference voltage PL to the high power reference voltage PH and is stepwise increased as in the above-described operation. It stops in the state of 35 of FIG.

[0005]

However, the current for maintaining the high power level PH shown above is not always constant.
That is, as shown in the laser characteristic diagram of FIG. 7, the laser current I1 for outputting the same power P1 increases like I2 and I3 due to the temperature rise and deterioration of the laser element. On the contrary, if the temperature drops, the current will decrease. This is the curve 40 to the curve 4 of the characteristics of the laser.
This is because it changes like 1, 42.

Therefore, in the above laser drive circuit, when the laser output is to be switched from the low power side to the high power side, the difference in the laser output up to the reference value is set at the timing of clock 6 as shown in FIG. A transition period is required to gradually increase in accordance with the resolution of the up / down counter 9, and as shown in FIG. 6, the time required to reach it (from T2 to T3) becomes long.

The switching time from the low power side at the time of reproduction to the high power side at the time of recording / erasing is limited to the time from reading (reproducing) an address for recording to starting recording / erasing at that address. However, in the above-mentioned case, there is a problem that the laser output is insufficient at the start of the recording or erasing operation, resulting in insufficient writing or unerased.

As a countermeasure against this, a method of increasing the clock frequency can be considered, but there is a problem of the time constant of the circuit and a problem of noise generation, and the frequency has an upper limit. The present invention has been made in view of the above circumstances, and provides a laser drive circuit capable of speeding up the response of the laser output from the low power side to the high power to reliably record or erase information. is there.

[0009]

Means for Solving the Problems Detection means for detecting laser output, first or second target reference value holding means for setting and holding a target reference value of laser output, and detection value detected by the detection means. And a target reference value held by the first or second target reference value holding means.
Alternatively, the second target value comparing means and the first or second bias value for setting the digital laser bias value for controlling the laser output based on the comparison result from the first or second target value comparing means. And a target reference value held by the second high power side target reference value holding means in the laser drive circuit for controlling the laser output to the target reference value. A high-speed amplifier of an analog control system that compares the value with the high-speed amplification and raises the power to high power, a sample-hold means that holds the power level generated by the high-speed amplifier when the power level reaches a specified level, and a sample The switching value comparing means for comparing the output of the holding means and the output of the bias value setting means, and the second by the output of the switching value comparing means. A switch coupled to the bias value setting means of the high-power side is turned on, and a flip-flop circuit to turn off the switch that connects to the sample-and-hold means.

[0010]

In the present invention, an analog control system using a high speed amplifier and a sample and hold circuit is added in parallel with the conventional high power digital control system for recording / erasing. Immediately after switching from reproduction to recording / erasing, the analog control system is used to start up at the slew rate of the high-speed amplifier. When the specified power is reached, the hold mode is set and the level is held. Sample as it is
Since the level drops due to the droop characteristic of the hold circuit, when the output of the digital control system becomes equivalent to the output of the analog control system, it switches to the closed loop of the digital control system to keep the laser power level constant during writing or reproduction. keep. By performing the high-speed switching of the laser power in this manner, insufficient writing or unerased data does not occur at the beginning of high-power switching.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An outline of an optical disk device including a laser drive circuit of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of an optical disk device. In the figure,
Reference numeral 48 is an optical disk, 49 is a motor for rotating the optical disk 48, 50 is a pickup for reading information on the optical disk, 51 is a motor servo circuit, and 52 is a pickup 5.
RF / signal circuit which is a signal from 0, 53 is a laser control circuit according to the present invention, 54 is a focus
Servo circuit, 55 is a tracking circuit, 56
Is a linear motor / servo circuit, and 57 is a CPU that controls each circuit within the dotted line.

Next, the laser drive circuit of the present invention will be described with reference to FIGS. FIG. 2 is a conceptual diagram of a laser drive circuit according to an embodiment of the present invention.
The same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. Reference numeral 24 is a switch that is turned on / off by the power switching command 10, and 25 is a target value held by the second storage circuit 5 which is the detection value detected by the monitoring photodiode 1 and the second target reference value holding means. A high-speed amplifier of an analog control system that compares the value with a value and amplifies it at high speed to rise to high power, and 27 is a sample-hold means that holds the power level generated by the high-speed amplifier 25 when it reaches a prescribed level, 28 is a switch for controlling whether or not the output of the sample and hold means 27 is connected to the laser drive circuit 15, and 29 is a comparison between the output of the sample and hold means 27 and the output of the second bias value setting means 9. Switching value comparison means, 21 is a gate circuit, and 23 is triggered by the output of the switching value comparison means 29, and as a result, the switch 14 is turned on. A flip-flop circuit that controls to turn off the switch 28. 30 is an adder.

FIG. 3 is a laser output waveform diagram when the laser drive circuit of the present invention is used. Next, the operation of the laser driving circuit of the present invention will be described with reference to FIGS. still,
Since the basic operation has been described in the above-mentioned conventional example, it will be omitted. When the power switching command changes from low power (playback mode) to high power (recording / erasing mode), the up / down counter 8 stops, but the recording (erasing) output is output from the high-speed amplifier 25 and the sample / hold circuit 27. , Through the switch 28. Immediately after the switching, the reference voltage of the high-speed amplifier 25 becomes the output value of the second storage circuit 5 which is the second target reference value holding means when the switch 24 is turned on, so that the output increases (see FIG. 3). 44), sample and hold circuit 27, and switch 28 to adder 30
In addition, the laser drive circuit 15 drives the laser 16. Then, when the output from the monitoring photodiode 1 also rises and exceeds the output of the second storage circuit 5, the output of the comparator 7 is inverted. And
The sample-hold circuit 27 enters the hold mode, and as shown in FIG. 3, the droop characteristic of the sample-hold circuit slightly lowers the level to a substantially constant level 45.
To maintain. Then, as in the conventional example, the output of the up / down counter 9 rises through the step 41,
On the other hand, when the sample and hold circuit 27 is constant, the switching value comparison means 29 is inverted and the flip-flop circuit 2
Trigger 3. As a result, the output of the switch 28
Is turned off, the switch 14 is turned on, and the gate circuit 21 also receives the comparator 7 and switches to digital closed control. This is the high power steady state 46 shown in FIG. After all, the transition state of a series of optical outputs becomes like the solid line shown in FIG. Further, some of the high-speed amplifiers used here have a slew rate that reaches 300 V / μs, and if they are used at the time constant t1 level shown in the output rise characteristic diagram of FIG. I will have.

[0014]

When the laser drive circuit of the present invention is used,
Since the laser power rises at high speed, recording and erasing can be performed optimally from the specified time. It can also be applied to high-speed recording.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical disk device.

FIG. 2 is a circuit diagram of a laser drive circuit of the present invention.

FIG. 3 is a laser output waveform diagram when the laser drive circuit of the present invention is used.

FIG. 4 is an output rising characteristic diagram.

FIG. 5 is a circuit diagram of a conventional laser drive circuit.

FIG. 6 is a laser output waveform diagram when a conventional laser drive circuit is used.

FIG. 7 is a laser characteristic diagram.

[Explanation of symbols]

1 Monitor Photodiode 3,7 Comparator (Target Value Comparison Means) 4,5 Storage Circuit (Target Reference Value Holding Means) 8,9 Up-Down Counter (Bias Value Setting Means) 14 High Power Side Connection Switch 16 Laser 23 Flip・ Flop circuit 25 High-speed amplifier 27 Sample / hold means 28 Switch 29 Switching value comparison means (comparator)

Claims (1)

[Claims] 1. A detection means for detecting a laser output, a first or second target reference value holding means for setting and holding a target reference value of the laser output, a detection value detected by the detection means and the first Alternatively, the first or second target value comparison means for comparing the target reference value held by the second target reference value holding means and the digital laser bias value for controlling the laser output are the first or second In the laser drive circuit for controlling the laser output to the target reference value, the first or second bias value setting means being set based on the comparison result from the target value comparison means. A high-speed analog control system high-speed amplifier that compares and amplifies the detected value with the target reference value held by the second high-power side target reference value holding means, and raises the power to high power at high speed. And, when the power level generated by the high-speed amplifier reaches a prescribed level, a sample and hold means for holding it, an output of the sample and hold means, and an output of the second high power side bias value setting means. And the switch connected to the bias value setting means on the second high power side is turned on and the switch connected to the sample and hold means is turned off by the output of the switch value comparing means. A laser drive circuit comprising a flip-flop circuit and performing high-speed startup analog control by a high-speed amplifier and digital closed control by a bias value setting means.