KR20000034470A - Adaptive equalizer of a dvd reproducing apparatus - Google Patents

Abstract

PURPOSE: An adaptive equalizer of a DVD reproducing apparatus is provided to stop an update of an equalization coefficient temporarily in a case where a detected envelope is less than a reference value. CONSTITUTION: An adaptive equalizer of a DVD reproducing apparatus comprises a prefilter(402) which removes a noise comprised in a reproduction signal. An analog-to-digital converter(404) converts an output of the pre filter into a digital signal. A feed forward equalizer(406) filters data from the analog-to-digital converter(404) according to an updated equalization coefficient, and a determination part(408) determines an output of the feed forward equalizer into three levels. An error detecting part(410) compares an output of the determination part with an output of the feed forward equalizer to detect an error. An envelope detecting part(412) receives the reproduction signal to detect an envelope of the reproduction signal, and a comparison part(414) compares the detected envelope value with a reference value. An equalization coefficient updating part(416) receives an error value of the error detecting part(410) and an output of the analog-to-digital converter(404), and updates the equalization coefficient when the detected envelope value is equal to or more than the reference value. The equalization coefficient updating part(416) stops a coefficient update when the detected envelope value is less than the reference value.

Description

ADAPTIVE EQUALIZER FOR A DVDR

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer of a DVD player, and more particularly, to detects an envelope of a reproduced signal and to temporarily hold an update of the equalization coefficient. ) Equalizer of a playback apparatus.

In general, methods for increasing information storage capacity in optical storage media such as DVDs include shortening the wavelength of the light source, improving optical sensitivity and recording method of the disk media, improving data efficiency and reducing error rate by signal processing, and the like. have. The PRML (Partial Responce Maximum Likelihood) technique is applied to a DVD as a technique for improving recording density by signal processing. The PRML is a combination of two technologies, PR and ML. PR utilizes the intersymbol interference generated in the channel to increase the transmission rate in the limited band. ML refers to restoring data using the Viterbi algorithm, which transmits correlations between each data and selects the most likely data column when restoring the original data column from that data column. To improve the error rate.

As shown in FIG. 1, the system for recording and reproducing the encoded data on the optical disc includes an optical disc 102, a spindle motor 104, an optical pickup 106, a laser driver 108, a precoder 110, and a phase. It consists of a synchronous loop (PLL: 112), a data phase synchronous loop (DATA PLL: 114), a delay unit (DELAY: 116), a Viterbi decoder 118, an equalizer 120, and the data on the optical disc 102. ), The recorded data is reproduced, and the reproduced data (REPRODUCTION DATA) is output.

Referring to Fig. 1, an optical disc 102 of a medium for recording information is rotated at a predetermined speed by a spindle motor 104. As shown in FIG. The optical pickup 106 is located adjacent to the optical disk 102. The optical pickup 106 has a laser source so that the optical power of the laser can be changed during recording or erasing to adjust the temperature of the portion where the beam is focused. . By temperature control, the surface of the optical disc is able to transition to a crystalline and amorphous state, and information recording of " 1 " and " 0 " is possible. At the time of reproduction, the optical pickup 106 irradiates a low output beam to read information from the optical disc by the difference in the amount of reflection depending on the state of the media.

In FIG. 1, the data recording portion includes a precoder 110 and a laser driver 108 to record data on the optical disc 102. The data reproduction portion includes a PLL 112, a DATA PLL 114, and a delay circuit 116. In FIG. ), An equalizer 120 and a Viterbi decoder 118 reproduce data from the optical disc 102. The wobble pit is engraved on the optical disc 102 in advance. The wobble pit uses a periodic signal for the spindle servo, and the wobble signal and the reference clock are used in the PLL circuit 112. Phase-locked phase is generated between them to generate a data clock signal. This clock signal is processed by the data PLL 114 and provided to the Viterbi decoder 118 via the delay unit 116. In the Viterbi decoder 118, a transition path for the most probable data value is determined based on the data sampled by synchronizing the reproduction signal with the clock CLOCK, and the signal value is determined based on the transition path. .

The adaptive equalizer 120 is designed to reduce inter-symbol interference (ISI) which affects the sampling instant during decoding, and is a general equalization scheme and a partial response using a linear equalizer or a decision feedback equalizer. In the general equalization method, the Nyquist evaluation is satisfied by using zero enhancement or least-square error method so that the intersymbol interference becomes "0" at the sampling time around, and the PR method approximates the reproduction waveform. By choosing the equalizer to be a partial response of, we can reduce the noise increase, which is a disadvantage of the general equalization method.

However, in the conventional DVDR equalizer, the RF waveform does not exhibit normal characteristics at the beginning of the DVDR operation, and thus the envelope is not normal. Therefore, it is necessary to hold the equalization coefficient updater so as not to change the equalizer coefficient if the envelope is detected at the beginning of the equalizer operation and the envelope is lower than the reference value.

Accordingly, the present invention has been proposed to meet the above necessity, and adapts the DVD playback apparatus to pause the updating of the equalization coefficient when the envelope is detected and compared with a reference value when the equalizer is lower than the reference value. The purpose is to provide an equalizer.

In order to achieve the above object, the apparatus of the present invention comprises a DVD recorder / player for recording data on an optical disc and reproducing the recorded data, the apparatus comprising: a prefilter for removing noise included in a reproduction signal; An analog-to-digital converter for converting the analog output of the prefilter to digital; A feedforward equalizer for filtering data output by the analog-to-digital converter according to an updated equalization coefficient; A decision unit which receives the output of the feedforward equalizer and determines three levels; An error detection unit for detecting an error by comparing the output of the determination unit with the output of a feed forward equalizer; An envelope detector for detecting an envelope by receiving a reproduction signal; A comparison unit for comparing the detected envelope with a predetermined reference value; And if the envelope detected according to the output of the comparator is smaller than the reference value, the coefficient update is paused. If the envelope is greater than or equal to the reference value, the error detection unit receives the error value and the output of the analog-digital converter to update the equalization coefficient. And an equalization coefficient updating unit provided to the feedforward equalizer.

1 is a block diagram showing a recording / reproducing portion of a general DVD (DVD);

2 is a channel block diagram when applying PRML to a DVD.

3 is a conceptual diagram of a DVD channel when NRZI and PR-1 are applied;

4 is a graph showing PR-1 characteristics;

5 is a block diagram illustrating an adaptive equalizer of a DVD according to the present invention.

* Explanation of symbols for main parts of the drawings

402: prefilter 404: analog-to-digital converter

406: feed forward equalizer 408: decision unit

410: error detector 412: envelope detector

414: comparison unit 416: equalization coefficient update unit

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

First, the PR-1 characteristic used in the DVD adaptive equalizer will be described schematically. The partial response (PR) characteristic can be expressed by Equation 1 below, where "D" is a delay operator and D =. e ^jwT .

As shown in FIG. 2, the entire channel of the optical disc includes a recording process and a playback process, as shown in FIG. 2, the encoder 119, the precoder 110, the optical disc drive unit 108, the equalizer 120, and a low pass filter (LPF). 122, an analog-to-digital converter (A / D: 124), a Viterbi decoder 126, and a demodulator 128. Since the optical disk channel characteristic has a low pass filter characteristic, PR (1,1) or PR (1,2,1) having similar characteristics are used, and PR (1,1) has a characteristic as shown in Equation 2 below. Has

PR (1,1): f1,1 = 1 + D = 1 + e ^-jwt

In FIG. 2, the precoder 110 is configured to have an inverse characteristic of the PR, and the precoder 110 for the PR (1,1) has a characteristic as shown in Equation 3 below.

Equation 3 is an NRZI characteristic used in recording encoding to increase optical detection capability in an optical disc system. 2 is simplified to model PR (1,1) as shown in FIG. 3. In FIG. 3, input "a _K " is data modulated by EFM, (1,7) RLL, etc., and "b _K " is NRZI of a _K. And a _K is binary data of 1 or 0, and the precoder 110 converting to NRZI calculates the previous output through the delay element 304 and the exclusive OR 302 or modulo 2, as shown in Equation 4 below. I can express it.

b _K = a _K + b _K-1

The equalizer 4 is transmitted to the recording / playback channel. The equalizer is configured so that the total characteristic of the channel is (1 + D), and the original channel output data is 0,1, by (1 + D). It has a value of 2. As shown in FIG. 4, the PR-1 characteristic may be represented by a graph of a frequency response characteristic and an impulse response characteristic.

Meanwhile, as shown in FIG. 5, the adaptive equalizer according to the present invention includes a prefilter 402, an analog-to-digital converter (A / D) 404, a feedforward equalizer (FFE) 406, and a determination unit 408. , An error detector 410, an envelope detector 412, a comparator 414, and an equalization coefficient updater 416.

Referring to FIG. 5, the feedforward equalizer 406 may be expressed as Equation 5 below.

y (k) = X ^t (k) W (k) = W ^t (k) X (k)

Here, X is a filter input vector of Nx1, and W is a filter coefficient (ie, equalization coefficient) vector of Nx1. y is the filter output and t is the transpose of the vector.

The output value of the feedforward filter 406 is determined by the determination unit 408 at three levels. The determined value and the feedforward filter output value are input to the error detection unit 410 and calculated as shown in Equation 6 below to obtain an error value (e). ) Is obtained.

e (k) = d (k) -y (k)

The error value obtained by the error value detector 410 is fed back to the equalization coefficient updater 416 and calculated as shown in Equation 7 to be used to calculate a new equalization coefficient W.

W (k + 1) = W (k) + ue (k) X (k)

That is, the equalization coefficient updater 416 receives the error value of the error value detector 410, receives the input vector X from the feedforward filter 406, and calculates the equalized value by calculating with a predetermined scaling constant u. The coefficients are updated and the coefficients are automatically adjusted so that the overall channel response is 1 + D.

In this case, when the envelope detected by the envelope detector 412 is higher than the reference value, the equalization coefficient is updated according to the above process. However, when the envelope detected by the envelope detector 412 is higher than the reference value, the equalization coefficient updater 416 is held to update the equalization coefficient. The operation is paused. That is, the envelope detector 412 detects the envelope from the reproduced RF signal, and the comparator 414 determines whether the envelope is below the reference level and outputs a high or low signal. The equalization coefficient updater 416 pauses the update when the detected envelope is lower than the reference value according to the output of the comparator 414, and updates the equalization coefficient according to Equation 7 above. .

As described above, in the present invention, after detecting the envelope of the RF signal reproduced by the DVD playback apparatus, the equalization coefficient is updated when the detected envelope is at least a reference value, thereby making the unstable playback signal at the beginning of the DVDR operation. It is possible to prevent the equalization coefficient from being incorrectly updated by

Claims (1)

In a DVD playback apparatus for playing back data recorded on an optical disc, A prefilter 402 for removing noise included in the reproduction signal; An analog-to-digital converter (404) for converting the analog output of the prefilter to digital; A feedforward equalizer 406 for filtering data output by the analog-to-digital converter according to an updated equalization coefficient; A decision unit 408 which receives the output of the feed forward equalizer and determines the level as three levels; An error detection unit 410 for detecting an error by comparing the output of the determination unit with the output of a feed forward equalizer; An envelope detector 402 for receiving an reproduction signal and detecting an envelope; A comparison unit (414) for comparing the detected envelope with a predetermined reference value; And If the envelope detected according to the output of the comparator is smaller than the reference value, the coefficient update is paused. If the envelope is greater than or equal to the reference value, the coefficient update is paused. The error value of the error detector and the output of the analog-digital converter are received to update the equalization coefficient. And an equalization coefficient updating unit (416) provided to the feedforward equalizer.