JPH0684171A - Laser output control system of optical disk device - Google Patents

Abstract

PURPOSE:To stabilize optical head laser output on write operation and at the same time to reduce time until a reference laser output is reached. CONSTITUTION:In this system for controlling an optical head based on the output of a photo detector corresponding to the optical head, the output value and the reference value of a sample and hold circuit 9 for sampling and holding the output of a photo detector on write operation are compared. The title system is provided with a write current drive circuit 8 for controlling the laser drive current of an optical head 1 according to the comparison result and a read/write control circuit 7 for transmitting a sample and hold signal 33 to the sample and hold circuit and for controlling the flow drive circuit 8 on writing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser output control system for an optical head mounted on an optical disk device.

[0002]

2. Description of the Related Art In a laser diode used in an optical head of an optical disk device, the laser output varies from the solid line to the broken line as shown in FIG. 5 due to the ambient temperature and heat generated by the laser diode itself. The value and slope change. Here, in order to make the laser output P1 constant, the current flowing through the laser diode is changed from I11 to I1.
It should be controlled to 2.

FIG. 6 is a block diagram showing a conventional example of a laser output control system (hereinafter referred to as APF) for stabilizing the laser diode output of an optical head, and FIG. 7 is a diagram showing operation waveforms of FIG. is there. During the read operation, the laser output of the laser diode 2 of the optical head 1 is detected by the photodetector 3. The output of the photodetector 3 is sampled by the sample-and-hold circuit 4, and the read current drive circuit 5 constitutes a feedback circuit using the output of the sample-and-hold circuit 4 as an input signal, so that the input signal level is constant. A drive current is passed through the laser diode 2 of the optical head 1 through the current addition circuit 6 so that

During the write operation, the read / write control circuit 7 outputs the write gate signal 71 and the data signal 72 to the write current drive circuit 8, and the write current drive circuit 8 is shown in FIG. 5 (I2-I11). The current of 1 is passed through the laser diode 2 through the current adding circuit 6. Photodetector 3 has signal 7
Laser outputs P1 and P2 are detected as shown in FIG. Lead /
The write control circuit 7 changes the hold signal level (for example, logic “0”) of the sample / hold signal 73 to the write signal 71.
Is output to the sample and hold circuit 4 immediately before. The sample-and-hold circuit 4 holds (holds) the laser output level P1 of the photodetector 3 immediately before the write operation, and the sample / hold signal 7 after the write operation is completed.
3 returns to the sample signal level (for example, logic "1"), samples the laser output level P1 and reads lead A
Performs PC operation.

[0005]

However, in the conventional optical disk apparatus, the APC operation is only for the laser output of the read operation, and the laser output of the write operation is not performed, and the laser output fluctuation in the write operation causes The write characteristics may change and the read error rate may deteriorate.

[0006]

The present invention relates to a laser output control system for an optical disk device, which controls the laser output of an optical head based on the output of a photodetector mounted on the optical head.
A sample-and-hold circuit that samples and holds the output of the photodetection at the time of a write operation, a write current drive circuit that controls the laser drive current of the optical head according to the output value of the sample-and-hold circuit, And a read / write control circuit for sending a sample and hold signal to the sample and hold circuit and controlling the write current drive circuit.

Further, the write current drive circuit compares a reference value with the output of the sample and hold circuit, and an up / down counter that counts up or down according to the comparison result.
A memory for storing the counter value, a D / A converter for converting the counter value into an analog value, and a current drive circuit for controlling a laser drive current of the optical head based on the converted analog value may be provided. Good.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG. 2 is a block diagram showing a second embodiment of the present invention.
FIG. 3 is a diagram showing a signal waveform of the operation of FIG. 1, and FIG. 4 is a diagram showing an arrangement of a sector format of a rewritable optical disc having a diameter of 13 cm and a double-sided 600 MB according to the ISO format.

During the read operation, the laser output of the laser diode 2 mounted on the optical head 1 is detected by the photodetector 3. The output of the photodetector 3 is sampled by the sample-and-hold circuit 4, and the read current drive circuit 5 constitutes a feedback circuit using the output of the sample-and-hold circuit 4 as an input signal, so that the input signal level is constant. A drive current is passed through the laser diode 2 of the optical head 1 through the current addition circuit 6 so that

During the write operation, the optical disk device recognizes the data in the preformat area shown in FIG. 4, generates the write gate signal and the data signal, and writes various data in the data area shown in FIG. VFO3 of data area
And SYNC are used as a sync signal for data reproduction during data reading. Here, VFO3, which is data at the beginning of the write data and having a constant cycle, is used to perform VFO.
The write APC operation can be performed by detecting the level of the write pulse of the laser output during the write operation of the three data and feeding it back to the write current drive circuit.

First, the read / write control circuit 7 outputs the write gate signal 31, the data signal 32, and the write APC gate signal 35 to the write current drive circuit 8, and the write current drive circuit 8 outputs a preset initial value. The current of (2) is passed through the current adding circuit 6 to the laser diode 2. The photodetector 3 detects the laser outputs P1 and P2 as the signal 36. The read / write control circuit 7 outputs the hold signal level (for example, logic “0”) of the sample / hold signal 34 to the sample and hold circuit 4 immediately before the write gate signal 31.

The sample-and-hold circuit 4 holds (holds) the laser output level P1 of the photodetector 3 immediately before the write operation, and the sample / hold signal 34 outputs the sample signal level (for example, logic) after the write operation is completed. By returning to "1"), the laser output level P1
Is sampled and the signal 37 is output to the read current drive circuit 5, and the APC operation of the laser output level P1 of the read operation is performed.

The read / write control circuit 7 makes a sample / write operation for each pulse within the range of VFO3 of the data signal 32.
The pulse of the hold signal 33 is output to the sample and hold circuit 9 to sample and hold the laser output level P2 of the photodetector 3 during the write operation. The sample and hold circuit 9 uses the sample / hold signal 3
At the timing of following the laser output level P2 of the photodetector 3 by N pulses (N is a natural number) of 3
The write control circuit 7 outputs the write APC gate signal 35 to the write current drive circuit 8.

The write current drive circuit 8 has an active level (for example, logic "1") of the write APC gate signal 35.
The input starts a comparison between the reference level and the level of the output signal 38 of the sample and hold circuit 9, and the result of the comparison makes the level of the output signal 38 of the sample and hold circuit 9 equal to the reference level. As described above, the drive current is increased or decreased to perform the APC operation of the laser output level P2 of the write operation. Then, the write APC gate signal 3
5 returns to the inactive level (for example, logic "0") before the end of the VFO3 data, and the sample and hold circuit 9 holds the laser output level immediately before the write APC gate signal 35 returns to the inactive level. And write the remaining data area.

Next, the embodiment shown in FIG. 2 will be described with reference to FIG. The block diagram shown in FIG. 2 constitutes the write current drive circuit 8 in FIG. Sample and
The output signal 38 of the hold circuit 9 is input to the comparison circuit 22, and if it is lower than the voltage of the reference power supply 21, a count-up (for example, logic “0”) signal is output to the up / down counter 23.

The up / down counter 23 loads a preset initial value at the leading edge of the write gate signal 31, and counts at the trailing edge of each pulse of the data signal 32 while the write APC gate signal 35 is at the active level. Carry out. The output of the up / down counter 23 is D
It is input to the / A converter 24. Current drive circuit 25
Represents the current value determined by the output of the D / A converter 24 as a pulse current in the data signal 32.
Output to.

Thus, the output signal 38 of the sample-and-hold circuit 9 coincides with the voltage of the reference power source 21 by N pulses of the data signal 32, and thereafter, the APC operation starts. Here, the count value of the up / down counter 23 is stored in the memory 26 at the trailing edge of the write gate signal 31, and the count stored in the up / down counter 23 from the memory 26 at the leading edge of the next write gate signal 31. By loading the value, you can
The number of counts until the C operation starts decreases. Also,
By making the memory 26 a non-volatile memory, for example, the previous count value can be loaded from the memory 26 from the first write operation when the optical disk device is powered on.

[0019]

As described above, according to the present invention, the VFO3 data in the data signal is sampled / held by the sample-and-hold circuit, and at the time of the write operation, based on the comparison result of this output value and the reference value. Since the laser drive current of the optical head is controlled, the laser output of the optical head is stabilized and the read error is reduced. Further, by storing the output value of the sample-and-hold circuit in the non-volatile memory, it is possible to shorten the time until the optical head reaches the reference laser output.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

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

FIG. 3 is a diagram showing a signal waveform of an operation in the first embodiment of FIG.

FIG. 4 is a diagram showing an arrangement of sector formats of an optical disc conforming to the ISO format.

FIG. 5 is a block diagram showing a conventional example.

FIG. 6 is a diagram showing a signal waveform of an operation in the conventional example of FIG.

[Explanation of symbols]

 1 optical head 2 laser diode 3 photodetector 4, 9 sample and hold circuit 5 read current drive circuit 6 current adder 7 read / write control circuit 8 write current drive circuit 21 reference power supply 22 comparison circuit 23 up / down counter 24 D / A converter 25 Current drive circuit 26 Memory 31, 71 Write gate signal 32, 72 Data signal 33, 34, 73 Sample / hold signal 35 Write APC gate signal 36, 37, 38, 74, 75 Output signal

Claims (2)

[Claims] 1. A laser output control system of an optical disk device for controlling a laser output of an optical head based on an output of the optical detection record mounted on the optical head, wherein the output of the optical detection record is sampled and held during a write operation. Sample and
A hold circuit, a write current drive circuit for controlling the laser drive current of the optical head based on the output value of the sample and hold circuit, and a sample and hold signal sent to the sample and hold circuit,
A laser output control system for an optical disk device, further comprising: a read / write control circuit for controlling the write current drive circuit. 2. The write current drive circuit compares a reference value with the output of the sample and hold circuit, an up / down counter that counts up or down according to the comparison result, and the counter value. And a D / A converter that converts the counter value into an analog value, and a current drive circuit that controls the laser drive current of the optical head based on the converted analog value. A laser output control method for an optical disk device according to claim 1.