JPH04289516A - Data slicing circuit for optical disk reproducing device - Google Patents

Abstract

PURPOSE:To make a device immune to dust and flaws as well as fingerprint on an optical disk. CONSTITUTION:The time constant of a low pass filter 2c is set to a small value, and flaws and dust on the optical disk are detected by a defect circuit 2e. If flaws and dust on the optical disk are not detected, the sampling operation is performed in a sampling and holding circuit 2f provided between a subtracting circuit 2d and an EFM comparator 2b; but otherwise, the holding operation is performed in the sampling and holding circuit 2f.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data slicing circuit for an optical disc reproducing device, and more particularly to a data slicing circuit for an optical disc reproducing device, and particularly for a CD player and a CD-R.
The present invention relates to a data slice circuit for an optical disc playback device that shapes the waveform of an RF signal and converts it into a digital signal for OM, CD-V, CD-I, etc.

0002

[Prior Art] In a CD player, a CD recording signal is detected by an optical pickup, a head amplifier performs current-voltage conversion and calculation to create an RF signal, and a digital signal processing circuit demodulates audio sample data. It has become. Incidentally, although digital signals are recorded on a CD, the RF signal output from the head amplifier has an analog waveform due to the frequency characteristics of the optical pickup and head amplifier. Therefore, the CD player is provided with a data slice circuit that shapes the waveform of the RF signal output from the head amplifier to create a binary RF signal (EFM signal).

FIG. 3 shows the configuration of a conventional data slice circuit. The analog RF signal output from the head amplifier is amplified by an RF amplifier 1, and then waveform-shaped by a data slice circuit 2 to create a binary RF signal. RF
The analog RF signal output from the amplifier 1 has fluctuations in low frequency components due to manufacturing variations in CDs, etc., and in order to remove this fluctuation component, the high-pass filter 2 is first applied.
After AC coupling at point a, the signal is input to the non-inverting input terminal of the EFM comparator 2b. A comparison reference voltage Eref is input to the inverting input terminal of the EFM comparator 2b. The EFM comparator 2b compares the output of the high-pass filter 2a with the reference voltage for comparison Eref, and the output of the high-pass filter 2a is the reference voltage for comparison Eref.
It outputs an H level when it is above the level, and an L level when it is below it, converting the analog RF signal into a binary RF signal (
EFM signal) and output to the subsequent digital signal processing circuit 3.

Here, if the output of the high-pass filter 2a does not contain a DC component, the reference voltage for comparison Eref
should be fixed at 0V, but in reality, AC coupling alone cannot completely eliminate asymmetry that occurs due to manufacturing variations in CDs, so the comparison reference voltage Ere
If f is fixed at 0V, accurate waveform shaping cannot be performed. Specifically, when there is a positive DC component in the output of the high-pass filter 2a, the reference voltage for comparison Eref = 0V
Then, the binarized R output from the EFM comparator 2b
When the duty ratio of the F signal becomes greater than 50% and, conversely, there is a negative DC component in the output of the high-pass filter 2a, the duty ratio of the binarized RF signal output from the EFM comparator 2b becomes smaller than 50%. .

For this reason, in FIG. 3, the comparison reference voltage Ere
f is controlled to enable accurate waveform shaping. That is, first, the binary RF signal input to the digital signal processing circuit 3 is taken out via the internal buffer amplifier 3a, and input to the low-pass filter 2c to detect the DC component. Since the probability of occurrence of "0" and "1" in the binary RF signal is 50% each, the comparison reference voltage Eref
is appropriate and the EFM comparator 2b performs accurate waveform shaping, the DC component of the binary RF signal will be VD /2, where VD is the peak value of the binary RF signal.

When the comparison reference voltage Eref is inappropriate and the EFM comparator 2b cannot perform accurate waveform shaping, for example, if the comparison reference voltage Eref is too low, the duty ratio of the binarized RF signal increases and the Value R
The DC component of the F signal becomes larger than VD /2, and conversely,
If the reference voltage Eref is too high, the duty ratio of the binary RF signal becomes small, and the DC component of the binary RF signal becomes smaller than VD /2. Therefore, if the comparison reference voltage Eref is feedback-controlled by the output voltage of the low-pass filter 2c, accurate waveform shaping can be performed by the EFM comparator 2b.

The output voltage of the low-pass filter 2c is subtracted by a predetermined reference voltage Ec in a subtracting circuit 2d, and then applied to the inverting input terminal of the EFM comparator 2b as a comparison reference voltage Eref. The gain of the subtraction circuit 2d is set so that the difference between the output voltage of the low-pass filter 2c and the reference voltage Ec is exactly equal to the DC offset voltage of the output of the high-pass filter 2a.

Briefly explaining the operation of the data slice circuit shown in FIG. 3, when the RF signal that has passed through the high-pass filter 2a has no DC component and the comparison reference voltage Eref is 0V, the binarized RF The DC component of the signal is V
At D/2, the output of subtraction circuit 2d is maintained at 0V. From this state, R output from the high-pass filter 2a
When a + (-) DC component is added to the F signal, the DC component of the binarized RF signal becomes larger (smaller) than VD /2, and the output voltage of the subtraction circuit 2d becomes higher (lower) than 0V.
The comparison reference voltage Eref is modified in a direction that is optimal for the RF signal. As a result, EFM comparator 2b
This means that accurate waveform shaping operations are always performed.

[0009]

By the way, in the data slice circuit configured as shown in FIG. 3, even if the DC component of the RF signal passing through the high-pass filter 2a fluctuates due to the influence of the time constant of the low-pass filter 2c, , the reference voltage for comparison Eref cannot follow immediately and a delay occurs. For this reason, an error will occur in the binary RF signal output from the EFM comparator 2b, but if it is in a normal playback state, the error will be small and will be corrected by the digital signal processing circuit 3, so there will be no problem. .

However, when the CD has scratches, dust, or large stains such as fingerprints, the binary RF
This is problematic because a large error may occur in the signal and cannot be corrected by the digital signal processing circuit 3. CD
When the laser beam of the optical pickup passes through the fingerprint above, the envelope of the RF signal is as shown by the solid lines A and B in Figure 4 (1).
While passing through the fingerprint, the upper envelope A of the RF signal drops. At this time, if the time constant of the low-pass filter 2c is large, the comparison reference voltage Eref
changes as shown by the broken line C, and while passing through the fingerprint, the comparison reference voltage Eref becomes inappropriate, causing a large error in the binarized RF signal. On the other hand, when the time constant of the low-pass filter 2c is small, the comparison reference voltage Eref changes as shown by the dashed line D, and while passing through the fingerprint, the RF
The comparison reference voltage Eref also decreases in proportion to the drop in the upper envelope A of the signal and maintains a proper state, so the error in the binary RF signal becomes smaller.

[0011] Furthermore, when the laser beam of the optical pickup passes through scratches and dust on the CD, the envelope of the RF signal becomes as shown by solid lines a and b in Fig. 4 (2), indicating that the laser beam passes through the scratches and dust. During this period, the RF signal is lost. At this time, if the time constant of the low-pass filter 2c is small, the comparison reference voltage Er
ef changes as shown by the dashed line d, and after passing through scratches and dust, R
Even if the F signal returns to normal, the comparison reference voltage Eref is still inappropriate for a while (see period τ in FIG. 4(2)), so a large error occurs in the binarized RF signal. On the other hand, when the time constant of the low-pass filter 2c is large, the reference voltage for comparison Eref changes as shown by the broken line C, and when the RF signal returns to normal after passing through scratches and dust, the reference voltage for comparison Eref changes as shown by the broken line C.
Since has already become a proper value, the error in the binarized RF signal becomes small.

As a result, in the conventional data slicing circuit, if it is made resistant to errors in one of scratches, dust, and fingerprints, it becomes weaker in the other, and it is not possible to make it resistant to errors in both scratches, dust, and fingerprints. There wasn't.

From the foregoing, it is an object of the present invention to provide a data slice circuit for an optical disk reproducing apparatus that can be made resistant to errors caused by both scratches and dust on the optical disk and fingerprints.

[0014]

[Means for Solving the Problems] In the present invention, AC
A comparator that binarizes the RF signal after the coupling with a predetermined comparison reference voltage, a low-pass filter that extracts the DC component from the binarized RF signal output from the comparator, and a low-pass filter that extracts the DC component from the binarized RF signal output from the comparator. Detects scratches and dust on an optical disc in the data slice circuit of an optical disc playback device, which is equipped with an arithmetic circuit that inputs the output and a predetermined reference voltage, performs a predetermined calculation, generates a reference voltage for comparison, and outputs it to a comparator. A sample between the defect circuit, the low-pass filter, and the comparator that performs a sampling operation when the defect circuit does not detect scratches or dust, and performs a hold operation when the defect circuit detects scratches or dust. - This is achieved by providing a hold circuit and reducing the time constant of the low-pass filter.

[0015]

[Function] According to the present invention, the time constant of the low-pass filter is kept small, and scratches and dust on the optical disc are detected. When scratches and dust on the optical disc are not detected, a filter installed between the low-pass filter and the comparator is The sample/hold circuit performs sampling operation to prevent scratches on the optical disc.
When dust is detected, the sample and hold circuit is caused to perform a hold operation. As a result, when the laser beam of the optical pickup does not pass through scratches or dust on the optical disk, a reference voltage for comparison is formed based on the output of the low-pass filter with a small time constant. The error in the comparator output is reduced even when the laser beam passes through a fingerprint, and when the laser beam of the optical pickup passes through scratches or dust on the optical disk, a reference voltage for comparison based on the previous low-pass filter output is held and output. Therefore, immediately after passing through scratches and dust, RF
When the signal returns to normal, the reference voltage for comparison has already reached a proper value, and the error in the binary RF signal becomes smaller.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram of a data slice circuit for a CD player according to an embodiment of the present invention. In addition, Figure 3
The same components are given the same reference numerals.

1 is an RF amplifier that amplifies an analog RF signal; 2A is a data slice circuit that shapes the RF signal to create a binary RF signal; 2a is a high-pass filter for AC coupling; Removes DC components from the signal. 2b is an EFM comparator, which compares the output of the high-pass filter 2a input to the non-inverting input terminal and the comparison reference voltage Eref' input to the inverting input terminal, so that the output of the high-pass filter 2a becomes the comparison reference voltage Er.
A binary RF signal is created by outputting an H level when it exceeds ef' and an L level when it is below. 3
is a digital signal processing circuit that inputs a binary RF signal and demodulates audio sample data and subcode data, and outputs the input binary RF signal to the outside via a buffer amplifier 3a.

Reference numeral 2c denotes a low-pass filter that inputs the binary RF signal from the buffer amplifier 3a of the digital signal processing circuit 3 and extracts the DC component, and has a small time constant. 2d is a subtraction circuit that subtracts a predetermined reference voltage Ec from the output voltage of the low-pass filter 2c and outputs it as a comparison reference voltage Eref. The gain of the subtraction circuit 2d is determined by the output voltage of the low-pass filter 2c and the reference voltage E.
The difference in c is set to be exactly equal to the DC offset voltage (DC component) of the output of the high-pass filter 2.

A defect circuit 2e receives an RF signal and performs envelope detection to detect scratches and dust on the optical disc. The defect circuit 2e outputs an H-level defect signal while detecting scratches or dust, and outputs an L-level defect signal when not detecting scratches or dust. 2f is a sample/hold circuit provided between the output side of the subtraction circuit 2d and the inverting input terminal of the EFM comparator 2b, which inputs a defect signal from the defect circuit 2e, and performs sampling operation while the defect signal is at L level. The comparison reference voltage Eref inputted from the subtraction circuit 2d is output as is to the EFM comparator 3, and while the defect signal is at H level, a hold operation is performed, and immediately before the defect signal becomes H level, the subtraction circuit 2d is output. Holds and outputs the comparison reference voltage Eref input from.

FIG. 2 is a diagram showing the operation of the data slice circuit, and the following description will be made with reference to this diagram.

When the laser beam of the optical pickup does not pass through scratches or dust on the optical disk, the defect circuit 2e outputs an L-level defect signal (see FIG. 2 (2)). At this time, sample and hold circuit 2
f is the comparison reference voltage Ere output from the subtraction circuit 2d.
f is directly output to the inverting input terminal of the EFM comparator 2b.

Therefore, the comparison reference voltage Eref' input to the inverting input terminal of the EFM comparator 2b changes in accordance with the output voltage of the low-pass filter 2c having a small time constant. As shown on the left side of Figure 2 (1), when the laser beam of the optical pickup passes through the fingerprint on the optical disk, R
The comparison reference voltage Eref' also decreases in proportion to the drop in the upper envelope A of the F signal and maintains a proper state, thereby reducing errors in the binary RF signal.

On the other hand, as shown on the right side of FIG. 2(1), when the laser beam of the optical pickup passes through scratches or dust on the optical disk, the defect circuit 2e outputs an H-level defect signal (FIG. 2(1)). (See 2). At this time, the sample/hold circuit 2f holds and outputs the comparison reference voltage Eref output from the subtraction circuit 2d just before the laser beam passes through the scratches and dust on the optical disk.

Therefore, while the laser beam passes through scratches and dust on the optical disk, the comparison reference voltage Eref' input to the inverting input terminal of the EFM comparator 2b is:
It changes as shown by the solid line E in Figure 2 (1), and R after passing through scratches and dust.
When the F signal returns to normal, the comparison reference voltage Eref
Since has already become a proper value, the error in the binarized RF signal becomes small.

[0025] EFM comparator 2 due to fingerprints, scratches, and dust.
Even if a small error occurs in the binary RF signal output from the digital signal processing circuit 3, the digital signal processing circuit 3 can demodulate correct data by correcting the error.

In the above embodiment, the sample and hold circuit is provided on the output side of the subtraction circuit, but it may also be provided on the output side of the low-pass filter 2c.

[0027]

[Effects of the Invention] According to the present invention, scratches on optical discs,
Between the defect circuit that detects dust, the low-pass filter, and the comparator, sampling operation is performed when the defect circuit is not detecting scratches or dust, and holding operation is performed when the defect circuit is detecting scratches or dust. At the same time, a sample and hold circuit is installed between the low-pass filter and the comparator to detect scratches and dust on the optical disc by reducing the time constant of the low-pass filter. The circuit is configured to perform a sampling operation, and when scratches or dust on the optical disk are detected, the sample/hold circuit is configured to perform a hold operation, so that the laser beam of the optical pickup can detect scratches or dust on the optical disk. When the fingerprint does not pass through, a reference voltage for comparison is formed based on the output of the low-pass filter with a small time constant, so even if the laser beam of the optical pickup passes through the fingerprint on the optical disk, the error in the comparator output is reduced. When the laser beam of the optical pickup passes through scratches or dust on the optical disk, a reference voltage for comparison based on the previous low-pass filter output is held and output, so when the RF signal returns to normal after passing through the scratches or dust. , the reference voltage for comparison has already become a proper value, and the error in the binary RF signal is reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a data slice circuit of a CD player according to an embodiment of the present invention.

FIG. 2 is a diagram showing the operation of the data slice circuit of FIG. 1;

FIG. 3 is a circuit diagram of a data slice circuit of a conventional CD player.

FIG. 4 is a diagram showing the operation of the data slice circuit of FIG. 3;

[Explanation of symbols]

2A Data slice circuit 2a High pass filter 2b EFM comparator 2c Low pass filter 2d Subtraction circuit 2e Defect circuit 2f Sample/hold circuit

Claims (1)

[Claims] [Claim 1] The RF signal after passing through AC coupling,
a comparator that compares with a reference voltage for comparison and converts it into a binary value;
A low-pass filter extracts the DC component in the binary RF signal output from the comparator, and the output of the low-pass filter and a predetermined reference voltage are input, and a predetermined calculation is performed to generate a reference voltage for comparison, which is output to the comparator. In a data slice circuit of an optical disc playback device that is equipped with an arithmetic circuit that detects scratches and dust on the optical disc, when the defect circuit detects scratches and dust between the low-pass filter and the comparator, the defect circuit detects scratches and dust. Data for an optical disc playback device, characterized in that a sample/hold circuit that performs a sampling operation and performs a holding operation when the defect circuit detects scratches or dust is provided, and the time constant of the low-pass filter is made small. slice circuit.