JPH02137128A - Reproducing signal processor - Google Patents

Abstract

PURPOSE:To obtain an exact reproducing signal by thinning the waveform of an electric signal, twice differentiating this signal and after that, making the level of this signal uniform. CONSTITUTION:A converting means 4 is provided to convert a reflected light from a recording medium, for which the part of a different reflection factor is formed for information recording on a surface, to the electric signal and a waveform correcting means 6 is provided to thin the waveform of the electric signal from the converting means 4. Then, a twice differentiating means 7 is provided to twice differentiate the signal from the correcting means 6 and a gain control means 8 is provided to made the level of the signal from the twice differentiating means 7 uniform. Further, a binarizing means 9 is provided to detect the zero cross of the signal from the gain control means 8 and to binarize the signal. A phase error to be generated by waveform interference, which is caused by high density recording, and a phase error to be generated by reflection nonuniformity and sensitivity nonuniformity are corrected and the exact demodulation of information is executed. Thus, the exact reproducing signal can be obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a reproduced signal processing device, and particularly to a reproduction signal processing device that demodulates data by irradiating laser light onto portions with different reflectances formed on a plate. The present invention relates to a playback signal processing device that enables accurate playback in a disk device.

(Prior Art) Conventionally, there has been a so-called bit edge recording method as a reproduction signal processing method in an optical disk device.

FIG. 5 shows an example of the configuration of the signal extraction section, in which 1 is an optical disk recording medium, 2 is a rotating shaft hole, 3 is an optical head, 4 is an optical amplifier that converts an optical signal into an electrical signal, and 15 is an optical Slice the signal from the amplifier 4 at a certain level (for example, zero level),
This is a waveform shaping circuit that shapes the waveform and outputs a rectangular wave signal.

In the case of the bit edge recording method, as shown in FIG. 2(b), pits (portions with different reflectances on the medium) are formed on the medium 1 corresponding to the data (FIG. 2(a)), and the bits are The leading edge and trailing edge of correspond to "1". As shown in FIG. 2(C), the output from the optical amplifier 4 is output corresponding to the high and low reflectance areas on the board, and by passing the optical amplifier 5 through the optical amplifier 5, the second A rectangular waveform signal as shown in Figure (d) is obtained. “1” at the rising and falling edges of this signal
is extracted.

(Problem to be solved by the invention) However, the diameter of the laser beam is determined by the oscillation wavelength of the laser and the numerical aperture of the irradiation lens, and the laser emitting elements and lenses for laser irradiation that can be used in general optical disk devices are currently unavailable. In the case of high-density recording, the recording bit length and recording pit interval are smaller than the diameter of the laser beam used to reproduce data.
This causes interference in the reproduced waveform, and when conventional signal processing methods are used, distortion occurs in the extracted electrical signal, resulting in a phase error.

In addition, reflection unevenness and sensitivity unevenness that occur during the manufacturing of optical discs cause zero-level fluctuations in reproduced signals, and in the conventional signal processing method by slicing at a constant level, reflection unevenness and sensitivity unevenness directly become phase errors.

Furthermore, the reproduced signal contains a mixture of positive and negative level signals depending on the data, so when amplified through an amplifier, the zero level of the signal fluctuates, causing a phase error, resulting in an accurate waveform. becomes difficult to obtain.

For example, in a modulation method used for high-density recording such as a 2-78LL code, the fluctuation is very large, and an undesired phase shift occurs. Furthermore, this zero level fluctuation occurs due to reflection unevenness and sensitivity unevenness, resulting in a phase shift.

FIG. 3 shows the output signal waveform of the optical amplifier 4 shown in FIG. 5, and depending on the written data,
The entire signal floats up and down. When the conventional method shown in FIG. 5 is used, a phase shift occurs when sliced at the zero level, as shown in FIG. 2(C).

At the same time, in high-density recording, the laser beam diameter is larger than the pit width P, as shown in Figure 4(b), and the tail of the reproduced waveform usually widens, as shown in Figure 4(C). , interferes with the waveform of adjacent bits. As a result, the peak amplitude decreases, which causes signal detection errors, and the waveform itself is distorted, resulting in a phase shift with respect to the information recording interval A during writing shown in FIG. 4(a). A signal with a reproduction interval B as shown in FIG. 4(d) is reproduced and demodulated. This phenomenon becomes more pronounced as the recording density increases, and becomes a major impediment to changes in recording density.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a reproduced signal processing device that can obtain accurate reproduced signals.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for converting reflected light from a recording medium having portions with different reflectances for recording information on the surface into electrical signals. means, waveform correction means for thinning the waveform of the electrical signal from the conversion means, double differentiating means for differentiating the signal from the correction means twice;
The present invention includes gain control means for aligning the levels of the signals from the differential differentiator, and binarization means for detecting zero crossings of the signals from the gain control means and binarizing them.

[For production]

According to the present invention, with the above configuration, phase errors caused by waveform interference caused by high-density recording, phase errors caused by reflection unevenness, and sensitivity unevenness are corrected, and accurate information is demodulated.

More details are as follows.

The first cause of phase errors in the signal reproduction process of optical disk devices is the fluctuation of the zero level of the reproduced signal due to the uneven ratio of positive and negative levels of the signal. This may be due to reflection unevenness and sensitivity unevenness of the medium, or due to changes in signal components corresponding to data when a modulation method using a non-DC free code such as 2-7 RLL is used. The second cause of phase errors is that high density causes waveform interference, and the information points of the reproduced waveform corresponding to the areas with increased reflectance are reproduced with a wider period than the desired period. This is due to the phenomenon.

Using the signal processing according to the invention, the above-mentioned problems can be solved.

Regarding the first factor, the present invention removes the above-mentioned reflection unevenness, sensitivity unevenness, and DC components and low frequency components contained in the signal waveform due to the non-DC free code by performing differentiation twice. Therefore, it is possible to perform demodulation without being influenced by the influence of reflection unevenness, etc., and phase shift can be eliminated. Regarding the second factor, in the present invention, the reproduced waveform, which has become wider than the original one due to the waveform equalization circuit (waveform thinning circuit) that has been proposed in many conventional techniques, can be thinned to the original value. Create a reproduced waveform with accurate spread width.

Furthermore, by using a gain control circuit, it is possible to eliminate differences in reproduction output amplitude due to differences in reflectance between optical disk media, and in addition, since this circuit is provided after differentiation, it is possible to Similar to that in , it is processed as an alternating current signal, and has the advantage that conventional auto gain control ICs and circuits can be applied as they are.

(Embodiment) FIG. 1 shows an embodiment of a reproduced signal processing device according to the present invention. In the figure, 1 is an optical disk recording medium, 2 is a rotary shaft hole, 3 is an optical head, and 4 is an optical signal processing device. An optical amplifier that converts into an electrical signal, which corresponds to FIG. 5, where 5 is a preamplifier, 6 is a waveform correction circuit, 7 is a two-time differentiator, 8 is an auto gain control circuit, and 9 is a binarization circuit. It is.

According to the configuration shown in FIG. 1, when demodulating pit edge recorded information on the optical disk recording medium 1, the signals at each component have a waveform as shown in FIG. (a) is the signal to be recorded, (b) is the medium 1 based on the signal to be recorded
The upper bit (C) is a reproduction signal output from the optical amplifier 4 and linearly amplified by the preamplifier 5.

In the case of high-density recording, this signal (C) has a phase shift (especially for the smallest bit), so the signal period is larger than the recording signal period (this signal (
If C) is processed by a conventional waveform shaping circuit, the result shown in Fig. 6 (fo
), the waveform correction circuit 6 consists of a filter that has a waveform thinning effect, and
) to output a signal with accurate information intervals as shown in FIG. 6(d).

In the present invention, the information point for binarization in the output signal (d) is taken as the inflection point. That is, the signal (d) becomes a signal having an accurate information period obtained by correcting the deviation of the inflection point (of the signal (C)) caused by the phase shift by thinning. The output signal (d) is input to the twice differentiating circuit 7, and passes through the internal two-stage differentiating circuit, and the first time, a signal (e) is obtained whose peak point is the inflection point of the signal (d). ), obtain the twice differentiated signal (f) (the peak point of the signal (e) is the signal (f
), therefore, the signal (f) is differentiated twice to eliminate the DC component contained in the data signal, which is the floating factor of the zero level, as described above, This results in a signal that does not have zero level floating. Further, the signal (f) is input to the auto gain control circuit 8, where it is controlled so that both signals with a level lower than a certain level and signals with a higher level are at a constant level (zero level does not change). The output signal becomes an output signal in which fluctuation factors such as changes in the reflectance of the output signal are absorbed. The output signal from the auto gain control circuit 8 is further
The input signal is input to the binarization circuit 9 (because the zero level is the information point of the input signal), where it is compared at the zero level, and the recorded signal (
A signal corresponding to FIG. 6(a)) is obtained, and from this, a binary signal (g) whose information point is the rising edge of the signal (fo) is output.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a reproduced signal processing device that can obtain accurate reproduced signals.

[Brief explanation of the drawing]

Figure 's1 is a block diagram of one embodiment of the reproduced signal processing device according to the present invention, Figure 2 is an explanatory diagram illustrating the signal output mode of pit edge recording with the configuration shown in Figure 5, and Figure 3 is a diagram showing the positive component of the signal. An explanatory diagram to explain the fluctuation of the zero level due to the imbalance of negative components, Fig. 4 is an explanatory diagram to explain the phase shift that occurs during high-density recording, and Fig. 5 is a configuration diagram of a conventional signal extraction section. , FIG. 6 is an explanatory diagram showing an aspect of signal processing by an embodiment of the reproduced signal processing device according to the present invention. DESCRIPTION OF SYMBOLS 1... Optical disc recording medium, 3... Optical head, 4... Optical amplifier, 5... Preamplifier, 6... Waveform correction circuit, 7... Double differentiator circuit, 8... Auto gain control circuit, 9...binarization circuit. (0) -r'-Evening 01001000+00 1
01t)) Neotsu wo Nabibuto (====■=
=) (======:)A Figure 2 Figure 1 Figure 3 Figure Figure Figure

Claims (1)

[Claims] 1) Conversion means for converting reflected light from a recording medium having portions with different reflectances for recording information on its surface into an electric signal, and waveform correction for narrowing the waveform of the electric signal from the conversion means. means, twice differentiating means for differentiating the signal from the correcting means twice, gain control means for aligning the levels of the signals from the twice differentiating means, and detecting a zero cross of the signal from the gain controlling means; Value 2
1. A reproduced signal processing device characterized by comprising: value conversion means.