JPH0479028A - Method for laser output setting in optical disk recording - Google Patents

Abstract

PURPOSE:To set an optimum laser output by reading recommended laser output recorded onto a blank disk, executing recording while changing the laser outputs on severage stages higher or lower than this output, and defining the recording laser output of a frame, for which the direct current voltage of an EFM signal at the recording place is closest to a specified value, as the recording laser output of a recording area. CONSTITUTION:When setting the laser output, an analog switch 17 is connected to the correcting side of the laser output by a microcomputer 5 and as a comparing voltage, the 1/2 voltage of a power supply voltage is applied through a buffer 18 and a differential amplifier 19 to a comparator 9. The EFM signal at a TTL level obtained by the comparator 9 is passed through buffers 13 and 14 on one side, turned to a direct current by a low-pass filter 15, converted to a digital value by an A/D converter 16 and inputted to the microcomputer 5, and the recording laser output of the frame, which value is closest to 2.5V, is defined as the laser output in the case of following recording. Thus, the optimum value of the laser output is set.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of setting laser output when recording an optical disc, and in particular, to a laser output calibration area of an optical disc to determine the most suitable laser output for each optical disc or optical disc recording device. Regarding how to use and ask.

[Prior Art] Currently, write-once (WO) optical disc recording and reproducing apparatuses are known that are capable of writing on an optical disc only once using a laser beam.

In this optical disk recording and reproducing apparatus, a laser beam is modulated by an EFM signal and irradiated onto the optical disk to write a pit string, and the laser beam reflected by the pit string is converted into an electric current to reproduce the recording.

The HL logic duty ratio of the EFM signal is 0.5, but
The length of the front f&end of the pit changes depending on the magnitude of the laser power, resulting in asymmetry.

Furthermore, since the edge shape of the waveform changes depending on the performance of the optical pickup when reading the signal, there are cases where the duty ratio of the read signal is not 0.5.

Therefore, a laser output calibration area is provided on an unrecorded optical disc, a recommended laser output for a predetermined wavelength is recorded therein, and the recommended laser output is read and the laser output is set before recording on the optical disc.

[Problems to be Solved by the Invention] The shape of the pits recorded on an optical disc varies depending on each optical disc and optical disc recording/playback device, and the waveform shape of the read signal also changes depending on the optical pickup. There was a problem in that the laser output most suitable for the optical disk recording/reproducing apparatus could not be obtained by the above-mentioned conventional method.

This invention was made to solve the above problems, and the EFM signal is recorded on an optical disc by an optical disc recording and reproducing device, and the optimum laser output is determined from the signal that is read from the recorded EFM signal by the same optical disc recording and reproducing device. The purpose is to provide a method to configure the .

[Means for Solving the Problems] A laser output setting method for optical disc recording according to the present invention includes:
Read the recommended laser output recorded on a blank disc, record the laser output at several levels above and below the read output for several frames, and reproduce the recorded location to obtain a TTL level EPM signal. A direct current is passed through a low-pass filter, and the recording laser output of the frame whose DC voltage is closest to 2.5V is set as the recording laser output of the recording area.

Further, in the laser output setting method for recording on an optical disc, an identification code is recorded in a subcode frame in which each stage of the recording laser output is recorded, and the IJL suitable laser output is confirmed by the identification code.

[Function] Since the TTL level signal obtained by reproducing the pit string of the EFM signal recorded on the optical disk changes to H and L at the edge of the signal read by the optical pickup, the direct current of the TTL level signal When the voltage is 2.5V, the duty ratio is 0°5, and by setting the recording laser output that provides the DC voltage closest to 2.5V,
Good symmetry of the signal recorded and read with that laser power is obtained.

Furthermore, if the laser output is recorded as an identification code during recording, it becomes easy to confirm the laser output during reproduction.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

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

When recording on an optical disc, the optical disc 20 is rotated by a spindle motor 21 while laser light emitted from a laser diode of the optical pickup 1 is focused on the optical disc 20.

At that time, the current supplied to the laser diode of the optical pickup 1 is E F M created by the CD encoder 3.
The @ signal is modulated by the laser current modulator 2, and the strength of the current is controlled by the digital signal set by the microcomputer 5 which is converted into an analog signal by the DA converter 4.

In addition, when reproducing the optical disc 20 recorded in this way, the laser current modulator 2 supplies a constant low current to the laser diode, and the light emitted from the laser diode is transmitted to the optical disc 20 recorded as described above. The reflected light is received by the photodiode of the optical pickup 1, and the current obtained from the photodiode of the optical pickup is converted into a voltage by the I-V converter 6 and amplified by the RF amplifier 7. , the DC component is removed by the capacitor 8 and input to the comparator 9.

When setting the laser output, the analog switch 17 is operated by the microcomputer 5 to calibrate the laser output (
PCA) side, and a voltage (V c c / 2 ) of 1/2 of the power supply voltage is applied to the comparator 9 as a comparison voltage via the buffer 18 and the differential amplifier 19 .

The TTL level EFM signal obtained by the comparator 9 passes through buffers 13 and 14, is converted into DC by a low-pass filter 15, is converted into a digital value by an AD converter 16, and is input to the microcomputer 5. , amplified by an EFM signal amplifier 10, demodulated into 8-bit symbols by an EFM decoder, and an identification code recorded in the subcode frame is identified by a subcode identifier 12 and input to the microcomputer 5.

With such a circuit configuration, the laser output setting method of the present invention is implemented.

First, a recommended laser output recorded in a calibration area of an unrecorded optical disk in a reproduction state is read, and the microcomputer 5 sets several levels of laser output around the recommended laser output.

A predetermined frame in the optical disk calibration area is recorded using the laser output set in this way.

At this time, the laser output is coded and recorded in a subcode frame.

Next, the test area thus recorded is read, but at this time the analog switch is connected to PCAlpl.

The microcomputer 5 is inputted as a DC component or a digital value of the TTL level EFM signal, and the value is 2.
The recording laser output of the frame closest to 5V is set as the laser output for subsequent recording.

Note that the laser output can be easily recognized because the code recorded in the subcode frame is read by the microcomputer 5 at the same time.

FIG. 2 shows in detail the portion of the loop including the analog switch 17 of FIG.

This loop forms the auto-asymmetry circuit of a typical CD player.

That is, when the analog switch 17 is connected to the RECPB side, the TTL level EFM signal obtained by the comparator 9 is connected to the inverters 13 and 14 of the CMO3.
The output impedance is converted by a buffer in which two are connected in series, and the DC component is extracted by a low-pass filter 15 formed by a smoothing circuit of a resistor and a capacitor.

The DC component is impedance-converted by a buffer 18 of an operational amplifier whose output terminal is connected to an inverting input terminal, and then differentially amplified by a differential amplifier 19 whose comparison voltage is 1/2 of the power supply voltage. is input as a comparison voltage.

In this way, the threshold voltage of the comparator 9 is controlled by the average voltage of its output, thereby automatically adjusting the asymmetry of the read signal.

The present invention provides an analog switch 17 in such a conventional auto-asymmetry circuit, opens the loop of the auto-asymmetry circuit, and inputs the DC component of the TTL level BFM signal to the microcomputer as a digital signal using the AD converter 16. It can be implemented by

[Effects of the Invention] As explained above, according to the present invention, an analog switch and a V c c that make the servo loop of an auto-asymmetry circuit used in a CD player an open loop
/2 A simple circuit that adds a reference voltage and an AD converter can set the optimum value of the laser output, reducing errors in reading recorded data.

Furthermore, if the laser output is included as an identification code on the sub-code data when recording at each stage of laser output, it becomes possible to recognize the laser output in a short time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a circuit for carrying out the invention, and FIG. 2 is a circuit diagram showing a portion of the circuit shown in FIG. 1... Optical pickup, 2... Laser flow modulator,
3...CD encoder, 4...DA converter, 5...
・Microcomputer, 6...I-V converter, 7.
...RF amplifier, 8...Capacitor, 9...Comparator, 10...EFM amplifier, 11...EFM decoder, 12...Subcode identifier, 13.14...
・Buffer-15...Low pass filter, 16...
AD converter, 17...analog switch, 18...
Buffer 19... Differential amplifier, 20... Optical disk, 21... Spindle motor.

Claims (1)

[Claims] 1. Read the recommended laser output recorded on a blank disc, record several frames by changing the laser output in several steps above and below the read output, and reproduce the recorded location. A laser output setting method for optical disc recording in which the obtained TTL level EFM signal is converted to DC through a low-pass filter, and the recording laser output of the frame whose DC voltage is closest to 2.5V is the recording laser output of the recording area. 2. The laser output setting method for recording on an optical disc according to claim 1, wherein an identification code is recorded in a subcode frame in which each stage of the recording laser output is recorded.