KR100240338B1 - Improved optical disc reproduction system - Google Patents

Abstract

The present invention can accurately detect the pulse width of a pit from a reproduction signal reproduced on an optical disc by using a passive element, remove jitter included in the reproduction signal by using an external oscillation clock, and minimize random error correction failure. The present invention relates to an improved optical disc reproducing system, in which the present invention continuously detects the pulse widths of the upper level section of the input pulse string and the lower level section of the pulse string, respectively, consisting of channel bits having a predetermined arbitrary bit length. A pulse width detection block; Based on the oscillation clock from the external oscillator, it detects the amount of jitter included in the pulse signal consisting of the upper level section and the lower level section provided by the pulse width detection block, and the detected jitter is within the preset tolerance range. A pulse width correction block which removes this when the signal is generated and generates a corresponding flag signal when the detected jitter size exceeds a preset tolerance range; And demodulating the detected pulse signal provided from the pulse width correction block into the data string of the original signal before channel coding, and detecting the error in the demodulated n-bit data string having a plurality of data patterns, And a demodulation block for performing error correction on each of the n-bit data strings demodulated based on the flag signal and the error detection result.

Description

Improved optical disc playback system

The present invention relates to an optical disc reproducing system, and more particularly, to an improved optical disc reproducing system suitable for detecting and eliminating jitter which is a random error mixed in a reproduction signal read out from an optical disc.

As is well known, an optical disc system is a reproduction type that can only reproduce recorded information, and additional recording types and information which a user can record once and then read (play) the recorded information whenever necessary, but cannot record again. There is an erase recording type that can arbitrarily perform writing and erasing.

On the other hand, optical disc systems such as CDs and DVDs are modulated, that is, channel coded, according to a pre-defined principle before recording digital data on optical discs. When converted to a single non-return to inverted (NRZI) code waveform, the waveform width is limited in length. That is, in CD to EFM (Eight to Fourteen Modulation), it has 9 limited pulse widths from 3T to 11T.

At this time, a technique of adding a parity bit or a check bit having an arbitrary length to the user information bit or interleaving a code in a predetermined order is used for error checking during reproduction when recording digital data on an optical disc. In conventional CD, CIRC, which combines Reed Solomon code and interleaving technique, is mainly used as an error checking technique.

Accordingly, in an optical disc reproducing system such as a CD player or a DVD player, error detection and error correction are performed on data reproduced on the optical disc using a code such as CIRC.

On the other hand, the types of errors (deformation or distortion of digital data) generated from signals reproduced on an optical disc include random errors and burst errors. Random errors such as system instability, line noise, etc. are intermittent errors. The burst error refers to an error in which adjacent bits are continuously concentrated due to a physical defect of an optical disc, an instability of a playback mechanism, or the like. Here, the present invention relates in particular to the improvement of error detection due to jitter, which is one of the main causes of random errors.

That is, jitter, which is one of the main causes of the random error, can be regarded as the shaking on the time axis caused by the defect of the optical disc, the instability of the drive system, or the like. As an example, the original signal data recorded on the optical disc is shown in FIG. 3A. Assume that the reproduction output may appear as shown in FIG. 3B when temporal instability (i.e., jitter) occurs in the digital signal on the optical disc. At this time, small jitter is compensated by using the data PLL, and large jitter is compensated in the error detection / correction step.

On the other hand, optical discs, which have recently been widely studied for their use as mass storage media, require inevitably high speeds and densities for this purpose. As the trend of noise increases, the ratio of noise is gradually increased. In response to the increase in density, a stronger error correction capability that can more reliably cope with errors such as jitter during data restoration is required.

Accordingly, the present invention has been devised in view of the above-mentioned point, and uses a passive element to accurately detect the pulse width of the pit in the reproduction signal reproduced on the optical disc, and use the external oscillation clock to detect the jitter contained in the reproduction signal. It is an object of the present invention to provide an improved optical disc reproducing system capable of eliminating and minimizing a failure of correcting a random error.

In order to achieve the above object, the present invention provides a level amplification and waveform equalization of a reproduction signal read from an optical disc through an optical pickup, and the waveform equalized reproduction signal is subjected to waveform shaping based on a predetermined threshold value, and then to any predetermined value. In an optical disc reproducing system which reconverts to a channel bit having a bit and detects a pulse width of a pulse signal converted into the channel bit to perform demodulation and error detection / correction to an original signal before channel coding, a predetermined arbitrary bit length A pulse width detection block for continuously detecting pulse widths of an upper level section of an input pulse string and a lower level section of a pulse string each having the channel bits; Based on the oscillation clock from the external oscillator, the amount of jitter included in the pulse signal consisting of the upper level section and the lower level section provided by the pulse width detection block is detected, and the detected jitter size is a preset tolerance. A pulse width correction block that removes it when within range and generates a corresponding flag signal when the detected jitter magnitude exceeds the predetermined tolerance range; And demodulating the detected pulse signal provided from the pulse width correction block into a data string of an original signal before channel coding, and detecting an error in the demodulated n-bit data string having a plurality of data patterns. An improved optical disc reproducing system comprising a demodulation block for performing error correction of each demodulated n-bit data string based on a flag signal from a correction block and the error detection result.

1 is a block diagram of an improved optical disc reproducing system according to a preferred embodiment of the present invention;

2 is a detailed block diagram of the pulse width detection block shown in FIG. 1;

3 is a diagram illustrating a case where random error occurs due to jitter as an example;

4 is a characteristic graph showing an example in which the output characteristics of a capacitor change due to jitter.

* Description of the symbols for the main parts of the drawings *

102: disk 104: optical pickup

106: RF amplification and equalization block 108: data slicer

110: pulse width detection block 112: pulse width correction block

114: demodulation block 210: high pulse detection block

212,214,232,234: Buffer 216,236: A / D Converter

230: low pulse detection block

The above and other objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of an improved optical disc reproducing system according to a preferred embodiment of the present invention.

As shown in the figure, the optical disc reproducing system of the present invention comprises an optical pickup 104, an RF amplification and equalization block 106, a data slicer 108, a pulse width detection block 110, a pulse width correction block 112 ) And demodulation block 114. Also, reference numeral 102 denotes a disc.

Referring to Fig. 1, the optical pickup 104 is composed of a semiconductor laser, an optical sensor, an optical system made of concave lenses, and the like, although detailed illustrations in the same drawing are omitted. Digital data (additional information, video, audio, text, etc.) recorded (or recorded) is read. That is, an intermediate frequency (RF) signal is generated by converting an optical signal reflected in another phase into an electrical signal depending on the presence or absence of a pit (or mark) recorded on the surface (that is, a track) of the optical disc.

In addition, in the RF amplification and equalization block 106, the level amplification is performed to sufficiently process the reproduction signal output from the optical pickup 104 in the next stage, and the waveform equalization is performed using a filter. The equalized reproduction signal is provided to the data slicer 108 of the next stage. In this case, as a filter for waveform equalization of the reproduction signal, for example, a transversal filter, a CR filter, or the like can be used.

Next, the data slicer 108 converts the waveform-equalized playback signal into channel data before recording on the optical disc, i.e., shaping the waveform based on a predetermined threshold value, and the waveform-shaped playback signal is the NRZI data before recording. It is restored to a shape almost similar to the waveform. In this case, when the optical disc reproducing system is a CD player, the reproduction signal will be a pulse signal having a pulse width of 3T-11T, wherein each pulse is not exactly a pulse having a width of 3T-11T, but some time. A pulse with jitter that is an error.

On the other hand, the pulse width detection block 110 detects the width of each pulse signal by inputting the pulse signal provided from the data slicer 108, that is, a pulse string having a width of 3T-11T. More specifically, time data of the upper level H section and the lower level L section of the input pulse string is detected and provided to the pulse width correction block 112 of the next stage.

At this time, in detecting a limited type of pulse width, the clock of the digital device must be made very high in order to detect the pulse width in a precise time unit. However, conventionally, pulse widths can be detected relatively easily by using digital elements such as counters and timers, but there is a problem that the accuracy thereof is somewhat reduced. Accordingly, in the present invention, the pulse width is detected using a passive element composed of a resistor and a capacitor, that is, the time data of the pulse width is precisely detected by using a difference in discharge voltage with time.

As such, a detailed operation of the pulse width detection block 110 for accurately detecting the pulse width according to the present invention will be described later in detail with reference to FIG. 2.

FIG. 2 is a detailed block diagram of the pulse width detection block 110 shown in FIG. 1 and includes a high pulse detection block 210 and a low pulse detection block 230.

As shown in the figure, the high pulse detection block 210 is composed of an inverter 212, a switch SW1, a capacitor C1, a resistor R1, a buffer 214, and an A / D converter 216. The low pulse detection block 230 includes a buffer 232, a switch SW3, a capacitor C3, a resistor R3, a buffer 234, and an A / D converter 236.

Here, the high pulse detection block 210 detects the time data (pulse width) of the high level (H) section (that is, the section other than the pit) of the pulse train provided by the data slicer 108 of FIG. The pulse width correction block 112 of FIG. 1 is provided to the pulse width correction block 112 of FIG. 1. In the low pulse detection block 230, the time data of the low level (L) section (that is, the pit section) of the pulse train provided by the data slicer 108 Pulse width) is detected and provided to the pulse width correction block 112 of FIG.

That is, as an example, when the pulse string currently input is a low level (L) section, the output of the inverter 212 becomes a high level and the output of the buffer 232 becomes a low level, wherein the contact switching control signal is a high level. In this case, it is assumed that each of the switches SW1 and SW3 is designed to be turned on, and the switch SW1 is turned on and the switch SW3 is turned off. Therefore, if the capacitor C1 and the resistor R1 are designed to be sufficiently charged to the saturation voltage Vsat even within the minimum pulse section 3T, the switch SW1 is turned on at the low level of the input pulse and the saturation voltage ( The voltage of Vsat) will be charged. Then, when the high level of the pulse comes, the switch SW1 is turned off and the capacitor C1 starts to discharge through the resistor R1. At this time, the predetermined time is the time until the next low level of the pulse comes, that is, the time width of the high level of the current pulse. Therefore, the discharge time varies depending on the width of the high level (3T-11T in the case of CD) and accordingly the high level is detected by detecting the voltage level of the capacitor C1 detected just before the next low level comes through the buffer 214. The width of the section can be detected as a voltage.

On the other hand, in contrast to the above, when the pulse string currently input is the high level (H) section, the output of the buffer 232 is turned high to turn on the switch SW3. As a result, the capacitor C3 starts charging and sufficiently charges to the saturation voltage Vsat. Then, when the low level of the pulse train comes, the switch SW3 is turned off and the capacitor C3 starts discharging through the resistor R3. Similarly, the width of the low level section can be detected as a voltage by detecting the voltage level of the capacitor C3 detected just before the next high level comes.

At this time, the voltage waveform discharged through the capacitor (C1 or C3), as an example has an output as shown in Figure 4, as can be seen from the figure, if the pulse width is short (t1) discharge time is small detection The voltage level that is made is higher than the long pulse width t2.

Next, the A / D converter 216 converts the discharge residual pressure of the capacitor C1 described above into digital data through the buffer 214, which is a voltage having a width information of a high level section as a line ( Through L21 to the pulse width correction block 112 of FIG. Similarly, the A / D converter 236 also converts the above-described discharge voltage of the capacitor C3 into the digital data through the buffer 234, which is a voltage having the width information of the low-level section as a line L23. Is provided to the pulse width correction block 112 of FIG.

Referring to FIG. 1, the pulse width correction block 112 first calculates pulse width time data from the discharge voltage data supplied to the lines L21 and L23. The high and low pulses of the respective pulses are expressed using the following equation. The width can be obtained.

[Equation 1]

Vc = Vsat * e ^{-t / RC} (where Vc is the voltage input to the A / D converter through the buffer)

Therefore, the width of the pulse obtained as described above is not completely consistent with nT (3T-11T for CD), which is the pulse width at the time of recording, and if the pulse width obtained by the calculation of the above equation is τ, it can be expressed as the following equation. Has jitter.

[Formula 2]

τ = nT ± Jitter

Referring back to FIG. 1, the pulse width correction block 112 is input with an oscillation clock CLK provided from an oscillator (e.g., a crystal oscillator) not shown, which is a pulse of the correct width without jitter. To provide a basic timing T from which (3T-11T) can be made.

At this time, in the pulse width correction block 112, a threshold value for jitter processing is set, and the amount of jitter included in the original signal component, that is, whether the time error value exceeds the preset allowable range is checked first. Then, if the time error is within the preset allowable range, the jitter of the corresponding pulse signal is removed based on the oscillation clock provided by the oscillator, not shown, and then the jitter-removed pulse signal, for example, the EFM signal, is removed through line L11. To demodulation block 114.

That is, when the pulse width provided from the pulse width detection block 110 is referred to as τ, and the detected pulse is referred to as nT (n = 3-11 in the case of CD), and the preset threshold is referred to as Jmax, the pulse width correction block At 112, jitter removal is performed as in the following equation.

[Equation 3]

On the other hand, if the time error value included in the original signal component exceeds the preset allowable range, the pulse width calibration block 112 corrects the value of nT closest to the corresponding pulse signal to demodulate the block through the line L11. At the same time, a flag signal is generated on the line L13 and provided to the demodulation block 114. That is, the pulse signal on the current line L11 provides a flag signal via the line L13 to the demodulation block 114 to indicate that the jitter is not a signal completely removed but a signal having an error.

Therefore, in the demodulation block 114, the pulse signal provided by the pulse width correction block 112 through the line L11, for example, the 14-bit channel coded EFM signal is demodulated into the original 8-bit data, that is, the EFM inputted serially. The signals are latched in parallel by 14 bits and demodulated into 8-bit data strings having 256 data patterns. For example, a CIRC decoder is used to perform error detection and correction of 8-bit demodulated data strings, that is, burst errors and random data. Error is detected and error correction is performed.

On the other hand, in the case of detecting an error in the demodulation block 114, a random error that appears intermittently, such as jitter, often fails to be detected. If such a random error detection fails, error correction is not performed. As a result, degradation (deterioration of image quality or sound quality, etc.) may occur in the reproduction signal.

However, in the present invention, especially when jitter occurs, a small jitter error is first removed, and a flag signal for informing when the jitter is large and not completely removed is provided to the CIRC decoder of the demodulation block, so that the decoder detects the jitter error. Even if a failure occurs, the effective jitter removal can be performed based on the flag signal provided by the pulse width correction block. That is, when performing error correction in the demodulation block, the failure rate of error correction for random error (jitter) can be minimized.

As described above, according to the present invention, the pulse width of the pit is precisely detected from the reproduction signal reproduced on the optical disc using a passive element composed of a capacitor and a resistor, and the jitter included in the reproduction signal is removed using an external oscillation clock. In the case of jitter having a large time error, a corresponding flag signal is provided as an error correction block to minimize error correction of random errors, thereby realizing an optical disc reproducing system that can reliably cope with random errors such as jitter.

Claims (10)

Level pickup and waveform equalization of the reproduction signal read out from the optical disc through the optical pickup, waveform shaping the waveform equalized reproduction signal based on a predetermined threshold value, and then reconverting it to a channel bit having a predetermined random bit. An optical disc reproducing system that detects a pulse width of a pulse signal converted into channel bits, demodulates to an original signal before channel coding, and performs error detection / correction. A pulse width detection block for successively detecting pulse widths of an upper level section of an input pulse string and a lower level section of a pulse string each consisting of the channel bits having a predetermined bit length; Based on the oscillation clock from the external oscillator, the amount of jitter included in the pulse signal consisting of the upper level section and the lower level section provided by the pulse width detection block is detected, and the detected jitter size is a preset tolerance. A pulse width correction block that removes it when within range and generates a corresponding flag signal when the detected jitter magnitude exceeds the predetermined tolerance range; And Demodulating the detected pulse signal provided from the pulse width correction block into a data string of an original signal before channel coding, detecting an error in the demodulated n-bit data string having a plurality of data patterns, and correcting the pulse width. And an demodulation block for performing error correction of each demodulated n-bit data string based on a flag signal from a block and the error detection result. 2. The improved optical disc reproducing system as set forth in claim 1, wherein said detected pulse signal is an EFM signal. The pulse width detection block of claim 1, wherein the pulse width detection block comprises: A high pulse detection block which detects an upper level section value of the input pulse string by using first charge / discharge means charged and discharged according to the level change of the input pulse string, and converts the detected upper level section value by A / D; And A low pulse detection block for detecting a lower level interval value of the input pulse string and performing A / D conversion using the second charge / discharge means charged and discharged according to the level change of the input pulse string. Improved optical disc playback system characterized in that the configuration. 4. The improved optical disc reproducing system as set forth in claim 3, wherein each of said first and second charging and discharging means is a capacitor. 4. The apparatus of claim 3, wherein the high pulse detection block is: An inverter for inverting the level of the input pulse string to generate an inverted pulse signal; A first switch switched in response to an output pulse signal from the inverter; A first capacitor that charges an externally provided voltage when the first switch is turned on and discharges the charged voltage when the first switch is turned off; A first buffer for buffering the discharge output provided from the first capacitor; And Improved optical disc playback, characterized in that the first A / D converter for generating the upper level interval value of the input pulse string by A / D conversion of the discharge output having a linear voltage characteristics provided through the first buffer system. 4. The low pulse detection block of claim 3, wherein: A second buffer for buffering the input pulse train signal; A second switch switched in response to an output pulse signal from the second buffer; A second capacitor which charges an externally provided voltage when the second switch is turned on and discharges the charged voltage when the second switch is turned off; A third buffer for buffering the discharge output provided from the second capacitor; And Improved optical disc playback comprising a second A / D converter to A / D conversion of the discharge output having a linear voltage characteristic provided through the third buffer to generate a lower level interval value of the input pulse train system. 2. The improved optical disc reproducing system according to claim 1, wherein the oscillator is a crystal oscillator. 2. The improved optical disc reproducing system according to claim 1, wherein the lower level sections are each pit section. 2. The improved optical disc reproducing system according to claim 1, wherein the pulse width correction block approximates an arbitrary channel bit value closest when the jitter included in the pulse signal exceeds the predetermined tolerance range. . 2. The improved optical disc reproducing system as set forth in claim 1, wherein each demodulated data string is composed of 8 bits of data.

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