JP2646474B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording and reproducing on an optical recording medium by a light beam.

[0002]

2. Description of the Related Art In recent years, the development and commercialization of optical recording media have been promoted, and their use has been widespread. In order to perform recording by irradiating the optical recording medium with the light beam of the optical pickup, it is necessary to provide a guide groove (pre-groove) in advance and track the light beam along the guide groove. The level of the light beam at the time of recording is high, which is about 20 times that at the time of reproduction, and the servo control for the focus and tracking signals extracted from the optical pickup is performed by using the same circuit as at the time of reproduction. It was impossible. In order to detect the focus and tracking servo signals during recording of the optical recording / reproducing apparatus, the period during which no pits are formed between the high-level light beams that form the pits irradiating on the optical recording medium is set at the time of low reproduction. A servo signal is detected by sampling and holding the period of the light beam at the reproduction level of the electric signal obtained by detecting the return light of the light beam from the optical recording medium by reflection from the optical recording medium with the same level as the light beam. Was added to the vessel.

FIG. 4 shows the above relationship when an EFM signal, which is a signal format of a CD (compact disk), is recorded. The signals are from 3T (T = data bit interval) to 11T. "H" 3T,
4T is a period during which a pit is formed, and 3T, 4T,
When 5T is a period in which no pit is formed , it is better to reduce the pulse width and increase the level of the light beam in order to form a pit having a high C / N ratio on the optical recording medium. The period of 3T and 4T for forming the pit is 2T and 3T. Accordingly, in the laser drive signal, 2T and 3T of "H" optically record a high-level light beam forming a pit, and 4T and 5T of "L" optically record a low-level light beam as in reproduction without forming a pit. Irradiate the medium.

The return light of the irradiation light beam from the optical recording medium is detected by a photodetector and converted into an electric signal to obtain a detection signal. When the pit of the detection signal is formed at a high level, the pits are not formed yet, so that the amount of return light is high and the level is high. However, when the pits are formed, the amount of return light decreases and the level decreases. When the light beam changes to a low level that does not form pits, the detection signal undershoots under the influence of the high level beam. The servo signal at the time of recording is obtained by sampling and holding the low level period in which the light beam does not form a pit of the detection signal, but is delayed by a predetermined time τ in order to avoid the undershoot, as shown in the sample pulse of FIG. The sample hold is performed by obtaining a constant pulse with the width t2 regardless of the length of the period of the light beam of the low reproduction level.

[0005]

Since the width of the sample pulse is constant irrespective of the pulse width of the recording information signal, the amount of information when the period of the low-level light beam is long is lacking and is detected. The S / N of the servo signal was deteriorated. Further, the time information written in the pre-groove provided for tracking control could not be completely reproduced.

[0006]

According to the present invention, a high-level light beam for recording information on an optical recording medium and a low-level light beam for not recording information are alternately irradiated on the optical recording medium to emit the light beam from the recording medium. an optical pickup unit according to the one-beam method to obtain a detected electric signal return light due to reflection, the high
During the low level period
Clamp circuit that approaches the air signal level and the clamp described above
A predetermined period within the low level period is subtracted from the circuit output.
Sampling the electrical signal during the
Hold this sampled value for the duration of the level
It continued an optical recording and reproducing apparatus comprising means for obtaining a servo signal of the optical pickup.

[0007]

According to the present invention, the electric signal detected by the optical pickup of the one-beam method is clamped to a large amplitude signal during the recording period via the clamp circuit, so that the amplification of the circuit can be increased and the low level signal can be obtained. It is possible to improve the S / N of the reproduction signal level during the period, reduce the occurrence of overshoot and undershoot, and to reliably obtain the focus and tracking servo information of the optical pickup.

[0008]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a main part of FIG. 1, and FIG. 3 is a diagram showing signal waveforms of the main part of FIGS. . The digital audio interface signal input from the terminal 1 of FIG. 1 is applied to the encoder 3 together with the clock generated by the interface circuit 2, and a waveform example is shown in FIG. The synchronized bit clock a is output and applied to the signal correction circuit 4. Recording is performed in the "H" portions 3T and 4T of the signal b.

In recording on an optical recording medium, when a high-level light beam is irradiated in a time shorter than the actual data time, C
Since the recording with good / N can be performed, the signal correction circuit 4 generates the signal c of FIG. 3 suitable for recording by the circuit composed of the shift register and the NAND gate shown in FIG. The period of the signal c corresponding to 3T and 4T of the signal b is 2T, 3
T and the data time width are reduced. The signal c is applied to the laser circuit 5 to control the laser light beam. The optical pickup 6 outputs a high laser light beam from the 2T and 3T recording portions of “H” of the signal c, and outputs “L” 4T,
For the non-recording portions of 5T and 6T, a laser light beam of a reproduction level is output and irradiated on the optical recording medium 7. The optical recording medium 7 is rotated by a spindle motor 8.

The laser light beam emitted from the optical pickup 6 is reflected by the optical recording medium 7 as return light, returns to the optical pickup 6 again, is converted into an electric signal by a photodetector (not shown), and is converted into an electric current. Voltage (I /
V) applied to the conversion circuit 9; The signal waveform converted into a voltage by the I / V conversion circuit 9 is shown in FIG. 3E, and the recording portion which fluctuates greatly from 0V (forms a pit) and does not record near 0V (forms no pit) Consists of parts. The large overshoot in the recording portion of the signal waveform e is at the beginning of the pit formation, and the reflection of the light beam is large until the pit is formed on the optical recording medium. The amplitude of the waveform decreases.

On the other hand, the undershoot at the beginning of the non-recording portion of the signal waveform e is caused by a voltage having a large amplitude corresponding to a high-level light beam of the recording portion. The signal e is applied to the clamp circuit 10 and the signal f extracted from only the portion of the non-recorded portion having a level close to 0 V is applied to the sample hold circuit 11. The sample and hold circuit 11 performs sample and hold of the signal e in order to obtain focus and tracking servo information from a portion where the reproduction level of the signal e is not recorded by light beam irradiation. However, as described above, this part has a large undershoot, so this part must be avoided.

For this purpose, the signal b is converted to a signal correction circuit 4
In addition, the signal d passes through the shift register shown in FIG. The signal d is, as shown in FIG. 3, a portion 3T, 4 of the signal b which is not recorded on the optical recording medium.
In order to avoid an undershoot portion by waveform processing from T and 5T, the rise is delayed for a predetermined time τ and the entire time is adjusted to obtain sample pulses of t1, t1 + T and t1 + 2T. The sample hold circuit 11 converts the output signal f of the clamp circuit 10 to the sample pulse d.
To obtain a focus and / or tracking servo signal in addition to the servo signal detection circuit 13.

[0013]

According to the present invention, since the electric signal detected by the optical pickup of the one-beam method is clamped to the large amplitude signal during the recording period via the clamp circuit, the amplification degree of the circuit can be increased. To improve the S / N of the reproduction signal level during the low level period and overshoot
Influence on the control system due to occurrence of undershoot
It is possible to, the Fuokasu and recording and reproducing operations can be obtained tracking servo information of the optical pickup can be reliably formed.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of an implementation circuit of a main part of FIG. 1;

FIG. 3 is a view showing signal waveforms of main parts in FIG. 1;

FIG. 4 is a diagram showing signal waveforms of main parts according to the related art.

[Explanation of symbols]

Reference Signs List 1 input 2 interface circuit 3 encoder 4 signal correction circuit 5 laser circuit 6 optical pickup 7 optical recording medium 8 spindle motor 9 I / V conversion circuit 10 clamp circuit 11 sample and hold circuit 12 pulse generation circuit 13 servo signal detection circuit

Claims (1)

(57) [Claims] 1. An optical recording medium, wherein a high-level light beam for recording information and a low-level light beam for not recording information are alternately irradiated, and return light due to reflection of the light beam from the recording medium is detected. Optical pickup means by one beam method for obtaining a signal, and clamping of the high level period
To approach the electrical signal level during the low level period.
From the output of the ramp circuit and the clamp circuit,
The electrical signal during the period of removing the predetermined period within the bell period
Sampling during this high level period.
An optical recording / reproducing apparatus comprising means for holding the ringed value and obtaining the servo signal of the optical pickup.