JPH03150726A - Reproduced signal processing circuit for rewrite type optical disk - Google Patents

Abstract

PURPOSE:To eliminate the pseudo pulses which are frequently produced with a rewrite type optical disk due to the miserasion by providing a gate means for pseudo data pulses caused by the miserasion in addition to a conventional signal processor. CONSTITUTION:A 2nd gate generating circuit 18 produces a 2nd gate with use of the output (h) of an AND circuit 17 which is conventionally used as a reproduced data signal and a reset signal g2 which is used for production of a gate signal. Then a gate is produced after detecting the occurrence of miserasion with use of the signal g2 and a data pulse (h). Thus it is possible to suppress the occurrence of a pseudo data pulse due to the miserasion with use of the 2nd gate signal.

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 bit position recording 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 Application Laid-Open No. 171727/1983.

In such a peak position detection method, the slice circuit for detecting the original peak position of the reproduced signal at the zero crossing point provides a slice level and generates a gate signal by comparing the slice level and the reproduced signal. The gate signal is used to distinguish between an original peak corresponding to recorded information and a pseudo peak caused by noise or the like.

FIG. 4 is a block diagram of a conventionally known reproduction signal processing circuit, and FIG. 5 is a waveform diagram of each part of the reproduction signal processing circuit shown in FIG.

As shown in FIG. 4, the conventional reproduction signal processing circuit includes a photodetector 2, a photoelectric converter 3, a differentiation circuit 4, a zero-cross detection circuit 5, a gate creation circuit 6, and an AND circuit 7. It is configured.

The operation in FIG. 4 will be explained with reference to waveforms (a) to (f) in FIG. 5. On the optical disc 1 shown in FIG.
) is formed, which is reproduced by a laser beam using a photodetector 2. This is passed through a photoelectric converter 3 to obtain a reproduced waveform (b). Here, the center point of each data bit (a) becomes an information point, and the point corresponding to this is the peak position of the reproduced waveform (b) (indicated by a black dot). This is differentiated via a differentiating circuit 4 to obtain a differentiated waveform (C). The information point in this differential waveform is the peak position of the reproduced waveform, that is, the point where the derivative becomes zero, so if the zero-crossing point in the differential waveform is detected with a comparator or the like, the information point can be found in the binarized signal. It becomes possible to take it out as it rises. The above process is performed by the zero cross detector 5, and the output is shown in Figure 5 (
d) Shown in zero cross signal.

[Problem N to be solved by the invention] When using the conventional method as described above, the true It is not an information point, but a zero-crossing signal (d
) a pseudo peak detection pulse is generated. In order to remove such spurious pulses, a level S and a level R are provided for the differential waveform (C), and a gate signal (e) whose cross point position (indicated by a white circle O) is the rising edge and falling edge, respectively is provided. A gate generation circuit 6 is provided to generate . This R
Set the oS level to an appropriate value, and send the zero cross signal (d
), an accurate data pulse (f) can be obtained by generating a logical AND with ^NO circuit 7.

That is, when the reproduced signal does not include waveform distortion due to the influence of unerased data, such as on a write-once optical disc, it is possible to accurately detect the peak position.

However, in rewritable optical discs, there may be a situation where the previous data is not completely erased due to fluctuations in laser output or the like. As shown in FIG. 5(a), when the unerased bit B occurs, it appears as a pseudo peak as shown at C in the reproduced waveform (b), which causes a pseudo pulse E to be generated in the zero-cross signal (d). arise. This pseudo pulse E has a differential waveform (
As shown by the dotted line in C), if the S level is not reached, the gate signal (e) does not turn ON and does not appear in the data pulse (f), but as shown by the solid line D, When the S level is reached, the gate signal (e) is turned ON, a pseudo pulse F is generated in the data pulse (f), and a data error occurs.

When such a pseudo pulse is generated, it can be classified into the following four cases depending on the shape of the differential waveform due to unerased pulses. That is, ■Those who do not reach both S level and R level: ■Those who reach S level but not R level: ■Those who do not reach S level but reach R level: ■S level There are four cases: one in which both the . Among these cases, in the case of ■ and ■, as explained earlier, the gate signal (e) shown in Fig. 5 does not turn ON because the S level is not reached, and the data pulse (f) is not erased. Therefore, even if conventional signal processing methods are used, pseudo pulses can be removed.

On the other hand, in the case of ■ and ■, both reach the S level, so the gate is turned on and a pseudo pulse is generated in the data pulse (f). In the case of waveform distortion (2), it is completely indistinguishable from true data, so it is impossible to remove the pseudo pulses in such cases. Since the peak value is lower than that of the signal, the differential waveform (C) also has a lower peak value in the differential waveform due to unerased bits than in the differential waveform due to true bits. Therefore, if the R level and the S level are set sufficiently large, the waveform distortion (2) will not occur.

For this reason, waveform distortion due to unerased data takes the three forms described above (■■■), and when (■) occurs, it does not normally exist.

Therefore, a problem with conventional signal processing systems is waveform distortion that reaches the S level as shown in (2), and unless this is removed, accurate reproduction data cannot be obtained from rewritable optical discs.

SUMMARY OF THE INVENTION Therefore, in order to solve these conventional problems, it is an object of the present invention to eliminate false pulses caused by unerased pulses due to power fluctuations, etc., and reproduce data accurately. Another object of the present invention is to provide a reproduced signal processing circuit that can expand the margin due to power fluctuations.

[Means for Solving the Problems] In order to achieve such an object, the present invention irradiates a recording medium with different reflectances on a disc with a laser beam, thereby recording and reproducing data. , in a reproduction signal processing circuit of an optical disk device that performs erasing and overwriting, 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 the differentiating means. a first gate means for removing zero crossings other than information points based on the output signal of the differentiating means; and second gate means for removing spurious pulses due to unerased data.

[Function] According to the present invention, generation of pseudo data pulses due to unerased data can be suppressed.

In other words, pseudo pulses (
For example, the pseudo pulse shown in Figure 6 (■) appears in the reproduced data signal, but the ZERO circuit uses the reset signal and data pulse in addition to the conventional circuit to detect the occurrence of unerased data. Since the gate is created by using this second gate signal, generation of pseudo data pulses due to unerased data can be suppressed by using this second gate signal.

【Example] Hereinafter, the present invention will be described in detail based on examples.

FIG. 1 is a block diagram of a reproduced signal processing circuit to which the present invention is applied.
The configuration includes a second gate generation circuit 18 that further generates a second gate using the output (h) of the D circuit 17 and the reset signal (g2) used to generate the gate signal, and eliminates the problem caused by unerased data. pseudo peaks due to waveform distortion,
It is configured to separate correct information peaks.

FIG. 2 is a block diagram showing another embodiment (i.e.
FIG. 3 is a block diagram including a second gate generation circuit for removing unerased parts. FIG. 3 is a waveform diagram of each part of the unerased parts removing circuit shown in FIG. 2.

Next, the operation of the unerased area removing circuit shown in FIG. 2 will be explained with reference to FIGS. 3(b) to 3(j).

By comparing the differential waveform (C) explained earlier in Fig. 4 at the center level, the zero cross signal (d) is obtained.
get. In the differential waveform (C), since the zero cross of the rising part is originally an information point, the zero cross signal (d
) is the peak position (i.e., information point)
shows.

On the other hand, a set signal (g+) and a reset signal (g2) are obtained by comparing the S level and R level shown in FIG. 3(C) with a comparator 29 and a comparator 30, respectively. By inputting these two signals to the set terminal and reset terminal of the flip-flop 31, the gate signal (e) is obtained as the output of the flip-flop 31. As a result, as shown in the unerased section G, in the case of waveform distortion that does not apply to either the S level or the R level (case ◯ in Figure 6), the zero cross signal (d)
The gate signal can be removed by taking the AND of the gate signal (e) and the gate signal (e).

However, in the case of waveform distortion as shown in unerased section H (6th
In the case of Figure ■), in order to reach the S level, a gate signal like the dot shown in gate signal (e) is generated, and as a result, the pseudo pulse L appears as signal M in the read data (f), causing an error. It becomes data.

In this embodiment, a circuit capable of removing such a pseudo data signal M is provided as a flip-flop 33. NO to delay circuit 34
It is configured using a circuit 35. flip flop 33
The input is manually set the reset signal (g2),
The read data signal (f) is operated as a reset input. If the read data signal (f) is accurate, the unerased gate signal (h) output from the flip-flop 33 has exactly the same pulse as the read data signal (f). However, in the case of waveform distortion reaching the S level, as obtained in section H, the unerased gate signal (h) is set by the pseudo data signal M until the next reset signal pulse K is manually applied. , the gate is ON. Therefore, the gate signal N in this unerased signal gate (h) becomes a gate indicating from the beginning of the pseudo pulse M generated in the section H to the end of the next data pulse.

On the other hand, using the delay circuit 34, the read data signal (f)
is delayed by an appropriate time Δ, that is, a delayed read data signal (i) is generated. As for how to set this delay time Δt, as shown in the unerased gate signal (h) in Figure 3 and the delayed read data signal (i) in Figure 3, the true data signal is Remove from gate signal,
Furthermore, the pseudo data pulse M is set to exist within the gate. Thereafter, the NO circuit 35 sends a signal (
A read data signal (j) from which unerased pulses have been removed can be obtained by ANDing h) and signal (i).

[Effect of the Invention J As explained above, according to the present invention, in addition to the conventional optical disc signal processing, by further providing a gate means for pseudo data pulses due to unerased data, erasures that occur frequently on rewritable optical discs can be eliminated. The remaining spurious pulses can be removed.

Further, according to the present invention, it is possible to improve the margin against fluctuations in the laser output power of the optical disc device and to improve the margin for setting the slice level of the gate signal.

[Brief explanation of the drawing]

1 is a block diagram showing a reproduced signal processing circuit according to one embodiment of the present invention, FIG. 2 is a block diagram showing a reproduced signal processing circuit according to another embodiment of the present invention, and FIG. 3 is a block diagram showing a reproduced signal processing circuit according to another embodiment of the present invention. Figure 4 is a block diagram for explaining the conventional signal processing circuit. Figure 5 is the conventional signal processing circuit. Figure 6 is a waveform diagram of each part to explain the operation using waveforms. FIG. DESCRIPTION OF SYMBOLS 11... Optical disk, 12... Photodetector, 13... Photoelectric converter, 14... Differential circuit, 15... Zero cross detection circuit, 16... N1 gate generation circuit, 17... AND circuit, 18... second gate generation circuit. Tsuq 4) 3 flat

Claims (1)

[Scope of Claims] 1) In a reproduction signal processing circuit of an optical disk device that records, reproduces, erases, and overwrites data by irradiating a recording medium having portions with different reflectances on the disc with a laser beam. , an amplifying means for converting reflected light from the recording medium into an electrical signal, a differentiating means for differentiating the output signal from the amplifying means, a zero-cross detecting means for detecting a zero cross in the output signal of the differentiating means, and the differentiating means. a first gate means for removing zero crosses other than information points based on the output signal of the means; and a second gate means for removing pseudo pulses due to unerased recorded data that occur when erasing, recording, and overwriting are performed. A reproduction signal processing circuit characterized by comprising: