JPH08315369A - Data reproducing circuit - Google Patents

Abstract

PURPOSE: To precisely decode regenerative RF signals with different amplitudes without increasing the circuit scale. CONSTITUTION: This circuit is a data reproducing circuit reproducing two kinds of signals with different reflectances from a disk. The regenerative RF signals with different amplitude levels reproduced from the disk are supplied to an AGC circuit 30, and after they were controlled so that the signal amplitudes became nearly equal levels to be supplied to a time constant variable circuit 38, and the regenerative RF signal Sc with less sag and low-band noise is obtained because of that respective time constants are controlled in a signal section and a non-signal section. The regenerative RF signal is supplied to a signal processing circuit 22, and the recording data are decoded from the regenerated clock data and the address data. Since the signal amplitudes re made equal, the signals are processed by a common circuit system. Since the sag and the noise are less, data decoding processing is made precise, and an error rate is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing circuit for reproducing data from an optical disc whose reflectance differs depending on the region to be reproduced, such as a write-once optical disc. Further, the error rates can be improved by making the respective signal amplitudes substantially the same and selecting appropriate time constants in the signal section and the non-signal section.

[0002]

2. Description of the Related Art Some optical disks, such as a write once read multiple (WORM) optical disk, have different reflectances of laser light between a preformatted area (address area) and a data area. R such as CD and LD
The same applies to an OM type optical disc (ROM disc).

Taking a WORM disk as an example, address data and the like are recorded as unevenness of pits in the preformat area. Since the reflectance in the portion with pits is lower than that in the portion without pits, the reproduction signal level B where the pits are recorded is lower than the reproduction signal level A from the portion without pits as shown in FIG. 6A.

In the data area, since the data recorded portion has a higher reflectance than the unrecorded portion, the reproduced signal level C of the portion where the data is actually recorded is further higher than the level A as shown in FIG. 6A. Get higher Therefore, when the data is reproduced from the disc, the amplitude as shown in FIG. 6A is obtained.

In order to extract or decode the address data, the clock data for reproducing data, and the recording data from the reproduced RF signal (reproduced high frequency signal) Sa having different amplitudes, as shown in FIG. The data reproduction circuit 10 is used.

In the data reproducing circuit 10 shown in FIG. 7,
The RF signal Sa reproduced from the disc is obtained at the terminal 12. The reproduction RF signal Sa is supplied to the waveform equalizer (equalizer) 16 via the preamplifier 14 and is given a cosine descending characteristic. The aperture ratio of the eye pattern is improved by adding the cosine descending characteristic. The waveform-equalized reproduction RF signal Sa is DC-cut by the AC coupling circuit 16. The DC cut, that is, the AC-coupled reproduced RF signal Sa ′ is supplied to the signal processing circuit 20 to demodulate (decode) the reproduced data, and the demodulated data is obtained at the output terminal 28.

In the signal processing circuit 20, as is well known, a waveform shaper as preprocessing for data decoding, a PLL circuit for generating a clock, and further for decoding the waveform-shaped data into binary data. There are comparators, etc., but the details are omitted.

[0008]

By the way, in the conventional data reproduction circuit 10, in order to decode the reproduction RF signal from the pre-formatted area and the reproduction RF signal from the data area, AC coupling using a capacitor is required. (DC cut) processing is performed.

When the time constant τ of the AC coupling circuit 18 is small, a sag as shown in FIG. 6B occurs when the signal rises or falls. Since it is difficult to correctly reproduce the data in the sag portion, the error rate during reproduction is reduced.

In order to avoid this, the time constant τ may be increased to some extent so that the low frequency component of the signal can be passed. However, if this is done, the low-frequency noise component will also pass this time, and in this case too, a malfunction due to noise will occur and the error rate during reproduction will drop.

Therefore, the present invention solves such a conventional problem, and proposes a data reproducing circuit which can avoid the influence of sag and noise on the data reproducing and which has an improved error rate.

[0012]

In order to solve the above-mentioned problems, in the present invention, at least two different reflectances are used.
A data reproducing circuit for reproducing signals of various kinds from a disc, wherein reproduction RF signals reproduced from the disc and having different amplitude levels are supplied to the gain control means so that the signal amplitudes become substantially the same level. After being controlled, it is supplied to the time constant varying means, and the reproduction RF signal without sag is outputted by controlling the respective time constants of the signal section and the non-signal section. .

[0013]

The two types of signals having different reflectances are supplied to the gain control circuit, and the gain control is performed so that the amplitudes of the signals are substantially the same. Reproduction RF signal S
Two types of reproduction RF with different reflectances are used to make the amplitudes of a uniform.
This is because the signal can be processed by one signal processing system.

The reproduction RF signal having a uniform amplitude has its transmission time constant switched between the signal section and the non-signal section. By switching the time constant, the sag generated between the signal section and the non-signal section is reduced, and the influence of the sag on the data reproduction can be avoided. Since the low frequency component is cut by the time constant used in the signal section, malfunction due to noise is reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a case where an example of a data reproducing apparatus according to the present invention is applied to a disk reproducing apparatus using the WORM disk described above will be described in detail with reference to the drawings.

FIG. 1 shows a concrete example of a data reproducing circuit 10 according to the present invention used in a disk reproducing apparatus. Terminal 1
A reproduction RF signal Sa from the WORM disc is supplied to the signal line 2. Since the WORM disc has different reflectances in the preformatted area and the data area as described above,
Playback R having two types of amplitude levels with different amplitude levels
The F signal Sa is obtained (FIG. 2A).

The reproduced RF signal Sa is supplied to the AGC circuit 30 functioning as a gain control means through the preamplifier 14, the waveform equalizer 16 and the AC coupling circuit 18, respectively, and the amplitude levels thereof are almost uniform as described later. It is used as a reproduction RF signal Sb. In this example, since the time constant for AC coupling is selected to be relatively large so that the signal component passes through to the low frequency component, a slight sag occurs in the reproduced RF signal Sb after AC coupling ( FIG. 2C).

The reproduced RF signal Sa is also supplied to the clamp circuit 32. A diode clamp circuit or the like can be used as the clamp circuit 32, and the level of the reproduction RF signal obtained from the preformat area is diode clamped. Reproduction RF signal Sb after diode clamp
Is supplied to the comparator 34 for reference level RE shown in FIG. 2A.
Compared to F. The comparator 34 is adapted to obtain a comparison output when a signal having a level equal to or lower than the reference level REF is inputted, and as a result, FIG.
A pulse Pa shown in is obtained.

This pulse Pa is used as a level control pulse for the AGC circuit 30, and at least the reproduction amplitude level of the preformatted area is controlled by controlling the gain in the section where the control pulse Pa is obtained. The gain is controlled so that it becomes almost the same as the reproduction amplitude level of the area. For example, the section where the control pulse Pa is obtained has the maximum gain, and the section of the data area has the minimum gain, or the gain is controlled so that the input gain is output as it is, so that the reproduced signal amplitudes in the two areas are almost the same. Can be the same (Figure 2
D).

The reason why the signal amplitudes are made substantially the same is that the reproduction R obtained from the preformatted area is used.
This is because both the F signal and the reproduced RF signal obtained from the data area can be processed by the same signal processing system thereafter. Even if the signal amplitude remains unchanged, for example, as shown in FIG. However, in this case, particularly, since the amplitude of the reproduction RF signal in the pre-formatted area is small, the reproduction RF signal is easily affected by noise and the like, which causes a problem that the error rate increases.

The reproduced RF signal Sb having the uniform amplitude is supplied to the time constant variable circuit 38. The time constant variable circuit 38 is configured as a variable high-pass filter including a capacitor and a resistor as shown in FIG. As shown in FIG. 3, in this example, a capacitor C is connected in series with the transmission line, and a parallel circuit of a pair of resistors Rr and Rm is connected between the transmission line and the ground at the subsequent stage of the capacitor C, respectively. Switch 39 selects one of the resistors Rr and Rm. The switch 39 has an electronic switch configuration, and the selection state is controlled by the switching pulse Pb (FIG. 2E).

The switch 39 has a signal section Tr as shown in FIG.
And the no-signal section Tm, and the switching pulse P is such that the resistor Rr is selected in the signal section Tr and the other resistor Rm is selected in the no-signal section Tm.
b is supplied to the switch 39. Therefore, in this example, the control pulse Pa is supplied to the pulse generation circuit 36, and the switching pulse Pb as shown in FIG. 2E is generated based on the control pulse Pa.

Here, the time constant τr when the resistor Rr is selected is τr = CRr (1), and the time constant τm when the resistor Rm is selected is τm = C / Rm ... (2)

The non-signal section Tm is selected so that its time constant is sufficiently larger than that of the signal section Tr, for example, τm = 10τr (3)

As described above, if the time constant m in the no-signal section Tm is selected to be a value sufficiently larger than the time constant τr in the signal section Tr, a sawtooth waveform generated between the signal section and the no-signal section is generated. In addition to effectively suppressing the sag (low-frequency fluctuation component), low-frequency components mixed in the signal section are reduced because the low-frequency component is blocked in the signal section. The output waveform of the time constant variable circuit 38 is shown in FIG. 2F.

A quantizing feedback circuit 40 is provided at the subsequent stage of the time constant variable circuit 38, and the DC component lost at the previous stage is reproduced. FIG. 4 shows a concrete example of the quantization feedback circuit 40.
The discrimination data binarized (quantized) by the binary discrimination circuit (comparison circuit) 44 is cut off by passing through a low-pass filter 46 having a pass band characteristic equivalent to that lost by transmitting through the transmission line in the previous stage. The generated DC component is reproduced.
This reproduced DC component is added to the input reproduced RF signal Sc (FIG. 2F) in the adder 42 to obtain a reproduced RF signal in which the DC component is reproduced.

The quantizing feedback circuit 40 is not necessary when a modulation method is adopted in which data is modulated and recorded so as not to contain a DC component.

The low frequency component is reproduced, and the reproduced RF signal in which the sag is suppressed is supplied to the signal processing circuit 22 and subjected to the same signal processing as described above, whereby the recorded data is finally decoded. .

By thus making the amplitudes the same, the decoding processing of address data and the like and the decoding processing of the recorded data can be performed in the same signal processing system, so that the overall structure can be simplified, and sag and low Data can be accurately decoded from the reproduced RF signal by processing it into a reproduced RF signal having a small range noise and reproducing the DC component. As a result, the error rate can be greatly improved.

FIG. 5 shows another example of the present invention, which is exactly the same as the configuration of FIG. 1 except that a gain switching circuit 52 is provided in the preceding stage of the AGC circuit 30. The gain switching circuit 52 controls the gain to increase the amplitude of the RF signal reproduced from the preformatted area. After that, gain control is performed by the AGC circuit 30 in the subsequent stage so that the overall signal amplitude becomes substantially constant.
Therefore, the control pulse Pa is given to the gain switching circuit 52 side and is controlled so that the gain is increased in the pre-format area, and the gain is decreased in the data area or is output with the gain as it is. Controlled by.

Thus, if the gain is roughly adjusted in advance by the gain switching circuit 52 and then the final gain control is performed by the AGC circuit 30, a small dynamic range can be used as the AGC circuit 30, which is inexpensive. This has the effect that the AGC circuit 30 can be used.

In the above-mentioned embodiments, the WORM disc is exemplified as a disc for reproducing signals having different reflectances, but the present invention can be applied to a reproducing processing system such as a ROM disc such as a CD or LD.

[0033]

As described above, according to the present invention, when a signal having a different reflectance is reproduced from the disc, the gain is adjusted so as to eliminate the difference in the reproduced signal amplitude due to the difference in the reflectance, and the sag and the low frequency band are adjusted. The data demodulation processing is performed while suppressing noise.

According to this, since the gain is adjusted in advance so as to eliminate the difference in the amplitude of the reproduced signal, the subsequent signal processing system can be a common signal processing system, so that the circuit scale can be reduced. .

In addition, reproduction RF with less sag and low frequency noise
Since the final data is decoded from the signal, the data can be reproduced accurately and the error rate can be greatly improved. Therefore, the present invention
It is extremely suitable to be applied to a disc reproducing device for reproducing signals having different reflectances such as an ORM disc.

[Brief description of drawings]

FIG. 1 is a system diagram of essential parts showing an example of a data reproducing circuit according to the present invention.

FIG. 2 is an explanatory diagram of the operation.

FIG. 3 is a connection diagram showing an example of a time constant variable circuit used in a data reproducing circuit.

FIG. 4 is a system diagram showing an example of a quantization feedback circuit.

FIG. 5 is a system diagram of essential parts showing another example of the data reproducing circuit according to the present invention.

FIG. 6 is a waveform diagram according to the description of the present invention.

FIG. 7 is a system diagram showing an example of a conventional data reproducing circuit.

[Explanation of symbols]

 18 AC coupling circuit 32 Clamp circuit 34 Comparator 30 AGC circuit 36 Pulse generation circuit 38 Time constant variable circuit 40 Quantization feedback circuit 52 Gain switching circuit

Claims (5)

[Claims] 1. A data reproducing circuit for reproducing at least two kinds of signals having different reflectances from a disc, wherein a reproducing R having different amplitude levels reproduced from the disc.
The F signal is supplied to the gain control means and controlled so that the signal amplitudes become substantially the same level, and then supplied to the time constant varying means, and the time constants of the signal section and the non-signal section are controlled. As a result, a reproduction RF signal without sag is output. 2. The data reproducing circuit according to claim 1, wherein the two types of signals are a preformatted area signal and a data area signal. 3. The data reproducing circuit according to claim 1, wherein the gain control means is composed of an AGC circuit. 4. A data reproducing circuit according to claim 1, wherein a gain switching circuit is connected to the preceding stage of the gain control means to increase the gain in the preformatted area with respect to the data area. . 5. The time constant changing means is composed of a variable high-pass filter, and a time constant in a non-signal section is made larger than a signal section so that a reproduction RF signal without sag can be obtained. Item 1. The data reproducing circuit according to item 1.