JPH06259789A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the S/N by lengthening the sampling period of a servo signal detecting signal in accordance with the length of a period of unpitting an optical recording medium. CONSTITUTION:A large overshoot of a recording part of a signal waveform (e) converted by an I/V converter 9 is the beginning of pit formation for the reason of that the reflection of a light beam is large before forming a pit in the recording medium 7, and when the pit is formed, the reflection is reduced and the amplitude of a data waveform is reduced. The signal (e) is given to a clamp circuit 10 and a signal (f) made by extracting only a level part nearly at 0V of a nonrecorded part is given to a sample-and-hold circuit 11. In the circuit 11, for the purpose of obtaining focus and servo information from the nonrecorded part irradiated with a light beam at a reproducing level of the signal (e), the part is subjected to sample-and-hold. For this reason, a signal (b) is given to a recording correcting circuit 4 to obtain a signal (d), and its rise is delayed by a prescribed time in waveform processing from the nonrecorded part of the medium with the signal (b), and then a sample pulse is obtained after setting the whole time. Thus, the S/N of the servo signal can be improved.

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 / reproducing on / from an optical recording medium with a light beam.

[0002]

2. Description of the Related Art In recent years, optical recording media have been developed and further commercialized, and are becoming popular. In order to perform recording by irradiating the optical beam of the optical pickup on the optical recording medium, it is necessary to previously provide a guide groove (pre-groove) and track the light beam along the guide groove. The light beam level at the time of recording is high, which is about 20 times that at the time of reproduction, and it is necessary to perform servo control of the focus and tracking servo signals extracted from the optical pickup using the same circuit as during reproduction. It was impossible. In order to detect focus and tracking servo signals at the time of recording by the optical recording / reproducing apparatus, a period during which a pit is not formed between a high-level light beam forming a pit to be irradiated onto an optical recording medium is set to a low level during reproduction. The level of the light beam is the same, and the servo signal is detected by sample-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 reflected from the optical recording medium by the photodetector. I added it to the bowl.

FIG. 4 shows the above relationship when recording an EFM signal which is a signal format of a CD (compact disc). The signal is from 3T (T = data bit interval) to 11T, but the recording signal "H" 3T,
4T is a period for forming a pit, and "L" 3T, 4T,
When 5T is a period in which no pits are formed, it is better to narrow the pulse width and increase the light beam level in order to form pits with high C / N on the optical recording medium. The period of 3T and 4T which forms a pit is 2
It becomes T, 3T. Therefore, the laser drive signal is "H".
2T and 3T irradiate the optical recording medium with a high-level light beam that forms a pit, and "L" 4T and 5T irradiate the optical recording medium with a low-level light beam that is the same as during reproduction without pit formation.

The return light of the irradiation light beam from the optical recording medium is photodetected and converted into an electric signal to obtain a detection signal.
At the high-level rising of the detection signal that forms a pit, the pit is not formed yet, so the return light is high and the level is high. However, when the pit is formed, the return light is reduced and the level is lowered. When the light beam changes to a low level that does not form pits, the detection signal undershoots under the influence of the higher level beam. The servo signal at the time of recording is obtained by sample-holding a low-level period of the detection signal in which the light beam does not form a pit, but is delayed by a predetermined time τ to avoid the undershoot, as shown in the sample pulse of FIG. The sample hold is performed by obtaining a constant pulse with a width t2 regardless of the length 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 detected and detected. The S / N of the servo signal was deteriorated. Further, the time information written in the pregroove provided for tracking control could not be completely reproduced.

[0006]

In order to solve the above problems, an optical recording medium is alternately irradiated with a high-level light beam that forms pits and a low-level light beam that does not form pits. Optical pickup means for detecting return light of reflection of irradiation light from the optical recording medium and outputting an electric signal; and sample holding means for sampling and holding a period of the low-level light beam of the electric signal,
In an optical recording / reproducing apparatus comprising servo detection means for detecting focus and tracking servo signals of the optical pickup from the output of the sample hold means, the width of the sample pulse of the sample hold means is set to the low level. An optical recording / reproducing apparatus characterized in that it is narrower than a light beam period for a predetermined period.

[0007]

With the above-mentioned means, the sample pulse width of the sample hold for detecting the servo signal becomes wider corresponding to the reproduction level period, the sampling period is increased, and the information amount of the servo signal is increased, so that S / N is improved.

[0008]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit example of the main part of FIG. 1, and FIG. 3 is a signal waveform of the main part of FIGS. . The digital audio interface signal input from the terminal 1 of FIG. 1 is added to the encoder 3 together with the clock generated by the interface circuit 2, and the EEM signal b of the CD format shown in FIG. The synchronized bit clock a is output and applied to the recording signal correction circuit 4. Recording is performed at 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 / N can be recorded satisfactorily, the signal correction circuit 4 produces the signal c of FIG. 3 suitable for recording by the circuit composed of the shift register and NAND gate shown in FIG. The signal c has a period of 2T, 3 corresponding to 3T, 4T of the signal b.
T and the data time width are shortened. The signal c is applied to the laser circuit 5 to control the light beam of the laser. The optical pickup 6 outputs a high laser light beam in the 2T and 3T recording portions of the signal c, "H", and the 4T portion of "L".
The non-recorded portions of 5T and 6T output a laser beam of a reproduction level and irradiate 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 and returns to the optical pickup 6, which returns to the optical pickup 6 and is converted into an electric signal by a photodetector (not shown). Voltage (I /
V) Added to the converter 9. The signal waveform converted into a voltage by the I / V converter 9 is shown in FIG. 3e, and a recording portion that greatly deviates from 0V (forms a pit) and a recording portion near 0V (forms no pit) are not recorded. Made of parts. The large overshoot of the recording portion of the signal waveform e is 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 is reduced.

On the other hand, the undershoot at the beginning of the non-recorded portion of the signal waveform e is the influence of the voltage of large amplitude corresponding to the 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 close to 0 V is applied to the sample hold circuit 11. The sample and hold circuit 11 performs sample and hold on the portion to obtain the focus and tracking servo information from the portion which is not recorded by the light beam irradiation of the reproduction level of the signal e. However, since there is a large undershoot in this part as described above, this part must be avoided.

Therefore, the signal b is added to the recording signal correction circuit 4, passes through the shift register shown in FIG. 2, and is added to the pulse generation circuit 12 to obtain the signal d. The above signal d is shown in FIG.
As shown in FIG. 3, a portion 3 of the signal b which is not recorded on the optical recording medium
In order to avoid the above-mentioned overshoot portion by waveform processing from T, 4T, and 5T, the rising edge is delayed by a predetermined time τ and the entire time is adjusted to obtain t1, t1 + T, and t1 + 2T sample pulses. Sample hold circuit 1
In step 1, the output signal f of the clamp circuit 10 is sampled and held by the sample pulse d, and the servo signal for the focusing and tracking is obtained in addition to the servo signal detecting circuit 13.

[0013]

As described above, according to the present invention, the signal sampling period for servo signal detection is lengthened according to the length of the period in which no pit is formed in the optical recording medium, so that the information amount of the servo signal can be increased. , S / N of servo signal can be improved.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing a signal waveform of a main part of FIG.

[Explanation of symbols]

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

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[Procedure amendment]

[Submission date] November 30, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Added

[Correction content]

FIG. 4 is a diagram showing a signal waveform of a main part of a conventional technique.

Claims (1)

[Claims] 1. An optical recording medium is alternately irradiated with a high-level light beam that forms pits and a low-level light beam that does not form pits, and the light beam is returned by reflection from the optical recording medium. Optical pickup means for detecting light and outputting an electric signal, sample and hold means for sampling and holding the low-level light beam period of the electric signal, and focus and tracking of the optical pickup from the output of the sample and hold means. In the optical recording / reproducing apparatus including the servo detecting means for detecting the servo signal, the width of the sample pulse of the sample holding means is narrower than the period of the low-level light beam by a predetermined period. Recording / playback device.