JPH03162719A - Regenerated signal processing circuit for rewrite type optical disk - Google Patents

Abstract

PURPOSE:To eliminate a false pulse due to a failute of erasing which frequently occurs on a rewrite type optical disk by providing a gate means for the false data pulse due to the failure of erasing. CONSTITUTION:A reproduced waveform (b) is inputted to a second gate generating circuit 8 and passes an integrator to obtain a variance slice level (c) and this level (c) is used to slice the voltage of the reproduced waveform, thereby obtaining a second gate signal (j). AND between a data pulse (i) including an error pulse F and the second gate signal (j) is operated to obtain a corrected data pulse (k) where the error pulse is eliminated. Thus, the false pulse is eliminated to accurately reproduce data even in the case of residual of erasing exists.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reproduction signal processing circuit for a rewritable optical disc. [Prior Art] When a bit position recording method is used in an optical disc, when demodulating the recorded information, a method is used in which the reproduced signal of the optical disc is differentiated to find its zero-crossing point and the peak position of the reproduced waveform is detected. This method is described in, for example, Japanese Patent Laid-Open No. 171727/1983.

Figure 5 is a block diagram of a conventionally known reproduction signal processing circuit. The reproduced signal processing circuit shown in this figure is composed of a photodetector 2, a photoelectric converter 3, a differentiating circuit 4, a zero-cross detection circuit 5, a gate creation circuit 6, and an AND circuit 7. Further, FIGS. 6(a) to 6(f) show waveforms of various parts in the conventional reproduced signal processing circuit shown in FIG. FIG. 6 shows a state in which data bits (a) formed on the optical disc 1 are reproduced using the photodetector 2. As shown in FIGS. 5 and 6, the reproduced waveform (b) obtained through the photoelectric converter 3 is input to the differentiating circuit 4, and the differential waveform (b) in which the black dots (shown in FIG. 6) are information points ( c)
is obtained. Next, a zero-crossing point in the differential waveform is detected by a comparator or the like, and a zero-crossing signal (d) is obtained. Furthermore, by using the gate signal (e) created with fixed slice levels S and R (shown in FIG. 6) to remove the noise A (shown in FIG. 6) generated in the zero-crossing signal, the arrow A data pulse (f) whose position is an information point can be obtained.

[Problem to be Solved by the Invention 1] When the reproduced signal from an optical disc does not include an unerased waveform due to unerased pits, such as from a write-once optical disc, a conventional reproduced signal processing circuit can accurately detect the peak position. It is possible to perform detection. That is, as shown in Fig. 6, the true information point always exists between the S level and the R level, and by performing a logical product operation on the gate signal and the zero-crossing signal, an accurate data pulse can be obtained. be able to. However, in rewritable optical discs, due to fluctuations in laser power, etc., the previous data may not be completely erased, or unerased bits may occur. These unerased pits generate unerased components in the reproduced waveform and further induce waveform distortion in the differential waveform, which is a major cause of erroneous data reproduction in conventional reproduced signal processing circuits. The reproduction of such erroneous data will be described in detail below.

FIG. 7 shows waveforms of various parts when unerased pits occur in the conventional method. Here, FIG. 7(1) shows a case where the waveform distortion B of the differential waveform due to the unerased pit A does not reach both the S level and the R level. in this case,
A pseudo-zero-cross signal C occurs on the zero-cross signal, but
Since the gate signal is in the OFF state, no error pulse is generated.

In addition, FIG. 7 (II) shows that the waveform distortion is S level or R level.
This is the case when reaching either level.

When this waveform distortion reaches only the R level (Fig. 7 (I
In the case of Sl, S2 in I), the gate signal (e)
is in the OFF state, and no error pulse occurs on the data pulse (f). However, when the waveform distortion reaches only the S level (in the case of S2 and R2 in FIG. 7 (I!)), the gate signal (e°) becomes the ON state D, and the signal on the data pulse (f°) Error pulse E is generated.

FIG. 3 (III) shows a case where the waveform distortion is of the same magnitude as the waveform of the signal component and reaches both the S level and the R level. In this case as well, the gate signal (e) is in the ON state D, and an error pulse E is generated on the data pulse (f). Therefore, the problem when using the conventional reproduction signal processing method for a rewritable optical disc is when the waveform distortion of the differential waveform due to unerased pits reaches the S level or both the S level and the R level. In this case, an error pulse occurs, resulting in incorrect data reproduction. SUMMARY OF THE INVENTION Therefore, in order to solve the problems of the conventional art, it is an object of the present invention to provide a system in which even if unerased data is generated due to fluctuations in laser power, false pulses caused by this can be removed and data can be reproduced accurately. The purpose is to provide a reproduced signal processing circuit. [Means for Solving the Problems] The wooden invention records and reproduces data by irradiating laser light onto a recording medium that has portions with different reflectances on the disc. In a reproduction signal processing circuit for a rewritable optical disk that performs erasing and overwriting, an amplifying means for converting reflected light from the recording medium into an electric signal, a differentiating means for differentiating an output signal from the amplifying means, and the differentiating means a first gate means for removing zero-crossing signals other than information points using the output signal of the differentiating means; and an output signal from the amplifying means and the output. The second gate means compares the voltage of the signal obtained by integrating the signal and outputs a gate signal for removing pseudo data for removing pseudo data due to unerased data from the recorded data. [Function] The present invention uses a second gate signal (gate signal for removing pseudo data) to remove error pulses caused by unerased pits, and includes a second gate means in a conventional signal processing circuit. In addition, a true data pulse can be obtained by performing an AND operation between the read pulse and the output signal of the second gate means.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In general, unerased pits that occur on rewritable optical discs have the following characteristics.

The occurrence of unerased pits is small in areas where the density of recording pits is high, and more in areas where the density is low. For example 2
In the case of the -7 code, it occurs less in the 1001.10001 code portion and more in other code portions.

Waveform distortion caused by unerased pits becomes larger at the differential waveform stage than at the reproduced waveform stage. Furthermore, when the recording density is increased, the signal amplitude of the differential waveform decreases due to a decrease in waveform resolution in the code portion with a high recording pit density, and a phenomenon is observed where the signal amplitude becomes comparable to the amplitude of waveform distortion. It will be done.

The embodiment of the present invention utilizes the above two characteristics, and performs fluctuation slice using an integrator at the reproduced waveform stage, and a second gate is installed to recognize the position where unerased bits are likely to occur. Generate a signal. Further, after detecting the read pulse, error pulses are removed by performing an AND operation with the gate signal.

Figure 1 shows a second waveform using the fluctuating slice method of the reproduced waveform.
A block diagram of a gate generation circuit is shown. This circuit includes a buffer circuit 1, an integration circuit 2. It is composed of a comparator circuit 3.

FIG. 2 shows waveforms of various parts of the circuit shown in FIG. Here, the reproduced waveform (b) including the unerased waveform B generated due to the unerased pit A generated on the data pit (a) is input to the buffer circuit 1, and its output is sent to the integrator circuit 2 and the converter circuit. 3. Manpower. The reproduced waveform input to the integrating circuit 2 has high frequency components cut off and becomes a variable slice level (C). From this, the second gate signal (d) is generated by comparing the buffer output (b) with the variable slice level (C) using the comparator circuit 3. This second gate signal (d) is
Indicates the position of the information point (indicated by a black dot) when ON, and when OFF
Indicates the position of waveform distortion due to unerased bits.

FIG. 3 is a block diagram showing an entire embodiment of the present invention. In this embodiment, a photodetector 2, a photoelectric converter 3, a Wl branch circuit 4. Zero cross detection circuit 5, first gate creation circuit 6, ^
ND circuit7. It is composed of a second gate creation circuit 8 and a second AND circuit 9.

FIG. 4 shows waveforms of various parts of this embodiment.

Next, the operation of this embodiment will be explained using FIGS. 3 and 4. From the data pit (a) containing the unerased bit A recorded on the optical disc 1, the photodetector 2. Using the photoelectric converter 3, a reproduced waveform (b) including the unerased waveform B is obtained.
The reproduced waveform is differentiated through a differentiating circuit 4, and then becomes a zero-cross signal (e) using a zero-cross detector 5. The position of the black dot in the differential waveform (d) indicates the information position, and corresponds to the position of the black dot in the reproduced waveform. Furthermore, the arrow position of the zero-cross signal corresponds to the black point position of the differential waveform and represents the information position. Furthermore, the zero-crossing signal includes a pseudo zero-crossing signal D due to waveform distortion C caused by the unerased waveform B. On the other hand, by performing fixed slices of S level and R level in the differential waveform, set pulse (f). A reset pulse (g) is obtained. Both pulses are R-S
A gate signal (h) is obtained by manually inputting a logic circuit such as a flip-flop.

Therefore, by performing an AND operation on the zero cross signal (e) and the gate signal (h), a data pulse (i) whose arrow position is the information position is obtained.

However, in the differential waveform (d), the waveform distortion C is S level,
Or, since both the S level and the R level have been reached, a doubtful gate signal E is generated on the gate signal (h), and an error pulse F is generated on the data pulse (i).

This error pulse can be removed using the second gate signal (j). The second gate a(j) manually inputs the reproduced waveform (b) to the second gate generation circuit 8, and performs voltage slices of the reproduced waveform using the fluctuating slice level (c) obtained through the integrator. can get. Furthermore, data pulse (i) including error pulse F
By performing an AND operation with the second gate signal (l), the corrected data pulse (k
) can be obtained. Effects of the Invention As explained above, according to the present invention, in addition to the conventional optical disc playback signal processing circuit, a gate means for pseudo data pulses due to unerased data is provided, so that false data pulses that occur frequently on rewritable optical discs are provided. It is possible to remove spurious pulses due to unerased areas. Further, according to the present invention, it is possible to improve the margin for fluctuations in the laser output power of the optical disk device and the margin for setting the slice level of the gate signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of generating a second gate signal by performing fluctuation slices of a reproduced waveform. FIG. 2 is a waveform diagram of each part to explain the operation of the second gate generation circuit. The figure is a circuit block diagram showing an entire embodiment of the present invention, Figure 4 is a waveform diagram of each part to explain the operation of Figure 3, and Figure 5 is a block diagram to explain a conventional signal processing circuit. , Figure 6 is a waveform diagram of each part to explain the operation of a conventional signal processing circuit, and Figure 7 explains the operation of a conventional reproduced signal processing circuit for three examples when unerased bits occur. This is a waveform diagram of each part. 2... Photodetector, 3... Photoelectric converter, 4... Differential circuit, 5... Zero cross detection circuit, 6... First gate creation circuit, 7... AND circuit, 8. ...Second gate creation circuit, 9...Second AND circuit. (I) A (III) Figure 7

Claims (1)

[Claims] 1) Playback signal processing for a rewritable optical disc in which data is recorded, played back, erased, and overwritten by irradiating a laser beam onto a recording medium on which parts with different reflectances are formed. The circuit includes: an amplifying means for converting reflected light from the recording medium into an electrical signal; a differentiating means for differentiating an output signal from the amplifying means; and a zero-cross detecting means for detecting a zero cross of the signal output from the differentiating means. and a first gate means for removing zero-crossing signals other than information points using the output signal of the differentiating means, and a voltage comparison between the output signal from the amplifying means and a signal obtained by integrating the output signal. 1. A reproduction signal processing circuit for a rewritable optical disc, comprising: a second gate means for outputting a pseudo data removal gate signal for removing pseudo data due to unerased data from previously recorded data.