JP3136583B2 - Digital data detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital data detection circuit, and more particularly to a digital data detection circuit capable of reproducing a plurality of types of recording media recorded in different signal formats by the same reproducing apparatus.

[0002]

2. Description of the Related Art A digital audio disk as a recording medium is obtained by digitizing an audio signal and recording the optical signal on the disk at a constant linear velocity and optically at a high density. The signal format has a DC component and a low frequency component as much as possible. The modulation signals (EFM) of the digital audio disk are modulated so that the appearance rates of the "H" and "L" levels per unit time are equal so as to decrease.
Are low frequency components.

In this case, as shown in FIG. 2A, when the reference level of the reproduction signal detected from the digital audio disc does not change in bias, the reproduction signal is compared with a reference value Vth of a constant level. This makes it possible to easily detect digital data "1" and "0" from the reproduced signal. However, depending on the conditions in the manufacturing process of the digital audio disc and the state of the signal detection system such as the wavelength of the semiconductor laser for signal reading, asymmetry in which the reference level of the reproduced signal deviates from the bias 0 level as shown in FIG. Therefore, if the reference value Vth is fixed, digital data cannot be detected accurately.

Therefore, conventionally, as a digital data detecting circuit which varies a reference value for generating digital data from a reproduced signal from a recording medium in accordance with a variation of the reproduced signal, the reproduced signal is compared with a reference value Vth. The output (digital data) of the comparison circuit is input to a low-pass filter circuit via a buffer, and the direct-current component of the digital data is detected by the low-pass filter circuit, and the difference between the detected output and the reference level is calculated. There is known a configuration in which an operational amplifier generates an optimum reference value in accordance with the asymmetry of a reproduction signal input to a comparison circuit. Here, the cutoff characteristic of the low-pass filter of the digital data detection circuit used in the digital audio disc is generally set to 500 Hz or less so as not to affect the signal spectrum.

Further, as disclosed in Japanese Patent Publication No. 1-50994, a comparator for comparing a reproduced signal with a reference value Vth, a positive and negative detection circuit as an output signal input of the comparator, An adding circuit for adding the outputs of the negative detection circuits to each other; a loop filter for averaging the output signals of the adding circuit; and a negative feedback control of the reference value Vth corresponding to the difference between the output of the loop filter and the reference value Vth. There is also known one provided with an operational amplifier.

[0006]

Meanwhile, among recording media, there is a digital video disk for digitizing and recording not only audio but also a video signal, which is recorded at a higher density than a digital audio disk. The signal frequency spectrum also has higher frequency components. When digital data is detected from a reproduced signal from such a high-density recording medium by using the former digital data detection circuit, in order to maintain the reliability of detection, the cutoff frequency of the low-pass filter is signaled. It must be set as high as possible without affecting the low-frequency spectrum. In particular, in order to reduce the influence of the defect on the amplitude fluctuation and the bias fluctuation of the reproduction signal due to the influence of the defect due to the dust or scratch attached to the recording medium surface, the cutoff frequency of the low-pass filter is set high. It is effective.

However, when trying to reproduce a plurality of types of recording media recorded in different signal formats, such as a digital audio disk and a digital video disk, with the same reproducing apparatus, it is necessary to detect digital data accurately. As described above, it is necessary to set the cut-off frequency of the low-pass filtering circuit so as not to affect the low-pass spectrum of the signal, so that the cut-off frequency is adjusted to the recording medium of the signal format whose signal spectrum is the lowest frequency. Must be set. Therefore, when reproducing a recording medium recorded at a higher density in a signal format of a wide spectrum, reliability of detection accuracy of digital data cannot be obtained.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention sets a plurality of cutoff characteristics in low-pass filtering means, and the cutoff characteristic switching means determines the type of the recording medium by the discriminating means. If not, switching to the cut-off characteristic of the lowest cut-off frequency of the plurality of cut-off characteristics set in the low-pass filtering means, and after the type of the recording medium is determined by the determining means, the determination result is corresponded. The cutoff characteristic of the low-pass filtering means is determined.

[0009]

By switching a plurality of cutoff characteristics set in the low-pass filtering means in accordance with the result of discrimination of the type of recording medium, it is possible to reproduce recording media recorded in different signal formats by the same reproducing apparatus. Also, digital data can be detected with high accuracy. Before the type of the recording medium is determined, the cutoff characteristic of the lowest cutoff frequency among the plurality of cutoff characteristics set for the lowpass filtering means is set, so that the reproduction signal based on the cutoff characteristics of the lowpass filtering means is set. Digital data can be detected while preventing adverse effects on the digital data.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of a digital data detection circuit according to the present invention. This digital data detection circuit
Two types of recording media D1 and D having different signal formats
2. For example, the present invention is applied to a reproducing apparatus capable of reproducing a digital audio disk and a digital video disk.
A buffer 3, a low-pass filtering circuit 4 as low-pass filtering means, an operational amplifying circuit 5 as operational amplifying means, a recording medium discriminating circuit 6 as discriminating means, and a cut-off characteristic switching circuit 7 as cut-off characteristic switching means. Have.

The comparator 1 converts a reproduction signal S (S1 or S2) from the recording medium D (D1 or D2) into a reference value Vt.
h to detect and generate digital data. The digital processing circuit 2 demodulates the digital data detected by the comparator 1. The low-pass filtering circuit 4 inputs the digital data detected by the comparator 1 via the buffer 3, and detects a DC component from the input digital data. The low-pass filter circuit 4 can switch a plurality of preset cutoff characteristics (cutoff frequencies) by an external input.
The operational amplifier circuit 5 compares the detection result from the low-pass filter circuit 4 with a predetermined reference level, calculates a reference value Vth according to the difference, and provides the reference value Vth to the comparator 1.

The recording medium discriminating circuit 6 includes a recording medium D (D1
Or the recording medium D being reproduced based on the reproduction signal S (S1 or S2) from the recording medium D1 and the recording medium D2
Is determined. When the type of the recording medium D is not determined by the recording medium discriminating circuit 6 based on the discrimination result of the recording medium discriminating circuit 6, a plurality of cutoff characteristics set in the low-pass filter circuit 4 are provided. After the type of the recording medium D is determined by the recording medium determination circuit 6, the cutoff characteristic of the low-pass filter circuit 4 is determined according to the determination result.

In the digital data detecting circuit configured as described above, when reproducing the recording medium D1, the reproduction signal S1 from the recording medium D1 is input to the comparator 1 and is compared with the reference value Vth to "H". The digital data is detected as an “L” digital data signal, and the digital data is demodulated by the digital processing circuit 2 and input to the low-pass filter circuit 4 via the buffer 3 to detect a DC component.

At this time, immediately after the reproduction of the recording medium D1 is started, a signal indicating undetermined from the recording medium discriminating circuit 6 is input to the cutoff characteristic switching circuit 7, so that the cutoff characteristic switching circuit 7
Thereby, the cutoff characteristic of the low-pass filter circuit 4 is switched to the characteristic of filtering at the lowest cutoff frequency. Thereafter, a signal indicating that the recording medium discriminating circuit 6 is reproducing the recording medium D1 based on the reproduction signal S1 is input to the cutoff characteristic switching circuit 7, whereby the cutoff characteristic switching circuit 7 cuts off the low-pass filter circuit 4. The characteristic is switched to a characteristic of filtering at an optimum cutoff frequency according to the signal format of the recording medium D1.

The signal of the DC component detected by the low-pass filter circuit 4 switched to the characteristic of filtering at the optimum cutoff frequency according to the signal format of the recording medium D1 is input to the operational amplifier circuit 5. The reference value Vt for the comparator 1 is calculated and amplified according to the difference from the reference level.
Since it is given as h, the comparator 1 detects digital data by comparing with the optimum reference value Vth linked to the asymmetry of the reproduction signal S1.

The recording medium D recorded in a signal format having a higher frequency spectrum than the recording medium D1.
Similarly, in the case of reproducing the reproduction signal No. 2, the reproduction signal S2 from the recording medium D2 is input to the comparator 1 and the reference value Vt
The digital data is compared with h and detected as “H” and “L” digital data signals. The digital data is demodulated by the digital processing circuit 2 and input to the low-pass filtering circuit 4 via the buffer 3. A DC component is detected.

At this time, immediately after the reproduction of the recording medium D2 is started, a signal indicating the unidentified state is input from the recording medium discriminating circuit 6 to the cutoff characteristic switching circuit 7.
Thereby, the cutoff characteristic of the low-pass filter circuit 4 is switched to the characteristic of filtering at the lowest cutoff frequency. Thereafter, a signal indicating that the recording medium D2 is being reproduced is input from the recording medium discrimination circuit 6 to the cutoff characteristic switching circuit 7 by the reproduction signal S2, whereby the cutoff characteristic switching circuit 7 cuts off the low-pass filter circuit 4. The characteristic is switched to a characteristic of filtering at an optimum cutoff frequency according to the signal format of the recording medium D2.

The signal of the DC component detected by the low-pass filter circuit 4 switched to the characteristic of filtering at the optimum cutoff frequency according to the signal format of the recording medium D2 is input to the operational amplifier circuit 5. The reference value Vth for the comparator 1 is calculated and amplified according to the reference level and the difference.
Thus, the comparator 1 outputs the reproduced signal S
The digital data is detected by comparing with the optimum reference value Vth linked to the second asymmetry.

Even when a plurality of types of recording media recorded in different signal formats are reproduced by the same reproducing apparatus, an optimum reference value can be set according to each type of recording medium. Any digital data can be detected with high accuracy. Further, when the type of the recording medium is not determined, the cutoff frequency of the low-pass filter is set to be the lowest, so that any type of recording medium that can be reproduced by the reproducing apparatus is determined before the type of the recording medium is determined. Digital data can be detected without adversely affecting the reproduced signal due to the characteristics of the low-pass filtering circuit, and the reliability of digital data detection is improved.

In the above embodiment, the type of the recording medium is determined by using the reproduced signal. However, the type of the recording medium may be determined by using the detected digital data.

[0021]

As described above, according to the present invention, the type of the recording medium is determined, and the cutoff characteristic of the low-pass filter for detecting the DC component from the digital data is switched according to the result of the determination. Accordingly, even when a plurality of recording media recorded in different signal formats are reproduced by the same reproducing device, digital data can be detected with high accuracy. Before the type of the recording medium is determined, the cutoff characteristic of the low-pass filter is set to the cutoff characteristic of the lowest cut-off frequency. Digital data can be detected while preventing digital data from being detected, and the reliability of digital data detection is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital data detection circuit according to the present invention.

FIG. 2 (a) is a signal eye pattern without bias fluctuation,
(B) Signal eye pattern with bias fluctuation

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Comparator (comparison means), 2 ... Digital processing circuit, 3 ... Buffer, 4 ... Low-pass filter circuit, 5 ... Operation amplifier circuit, 6 ... Recording medium discriminating circuit, 7 ... Interruption characteristic switching circuit, D
1, D2: recording medium, S1, S2: reproduced signal.

Claims (1)

(57) [Claims] 1. A comparison means for comparing a reproduction signal from a recording medium with a reference value to generate digital data, and a low-pass filtering means capable of changing a cutoff characteristic for detecting a DC component from an output of the comparison means. An amplifying means for changing a reference value of the comparing means in accordance with a difference between a detection result of the low-pass filtering means and a predetermined reference level; a determining means for determining a type of the recording medium; And a cut-off characteristic switching means for switching a cut-off characteristic of the low-pass filtering means based on a determination result of the means, wherein a reference value for generating digital data from the reproduced signal of the recording medium is set to a change in the reproduced signal. In the digital data detecting circuit, the plurality of cut-off characteristics are set in the low-pass filtering means, and the cut-off characteristic switching means is provided by the discriminating means. When the type has not been determined, switching to the cut-off characteristic of the lowest cut-off frequency of the plurality of cut-off characteristics set in the low-pass filtering means, after the type of the recording medium has been determined by the determining means, A digital data detection circuit for determining a cutoff characteristic of the low-pass filtering means according to a result of the determination.