KR20000004654A - Equalizer for digital vcr - Google Patents

Abstract

PURPOSE: Equalizer for digital VCR(video cassette recorder) is provided which enable optimum equalizing property by moving center of weight according to the property of regeneration signal. CONSTITUTION: An equalizer(210) comprises: a feed-forward filter(211) for filtering an inputted digital regeneration signal to output the regeneration signal having (1-D) delay characteristic, a level determining unit(212) for receiving a filter output outputted from the feed-forward filter to determine 3-levels, an error detection unit(213) for computing difference between 3 level signal outputted from the level determining and the filter output from the feed-forward filter and generating an error value, a weight update unit(214) for updating a weight according to the error value from error detection unit and previous weight and for moving center of weight according to control of a weight center control unit, a delay(215) for delaying the updated weight for a given time and outputting it to the feed-forward filter, and a weight center control part(260) for setting the center of weight of the digital regeneration signal depending on regeneration property of equalized data and providing it to the weight update unit.

Description

EQUALIZER FOR A DIGITAL VCR

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer for reproducing a magnetically recorded signal of a digital VCR, and more particularly, to an equalizer of a digital VRL for optimizing equalization characteristics of data to be reproduced.

With the development of computer, communication, broadcasting, home appliances, etc., the quality of information provided to general users is getting higher and higher, and this information can be characterized by multimedia, visualization, stereoscopic, and independence.

In particular, digital media use technology is based on this trend and has a great impact on the future of information society.

As the information age flows, the demand for high-speed data transmission and storage is rapidly increasing.

The storage of digital data has mainly used a magnetic recording method and is used early by providing a lot of data storage capacity at a low price.

Currently, the magnetic recording apparatus used early is an analog method using RLL (Run Length Limited) and peak detection.

The equalization process of the conventional PR4 channel will be described with reference to FIG. 1.

The input code string of the magnetic recording / reproducing apparatus is recorded after passing through a precoder 100 composed of a 2-bit delayer 102 and a MOD2 adder 101. That is, the magnetic channel 110, the equalizer 111, and the playback encoder 112 are composed of 1 / (1-D ² ) to match the characteristics before passing through a player having the characteristics of (1-D ² ) during playback. It is precoded to have a delay characteristic.

The regeneration process consists of a delay characteristic of (1-D ² ), so that it can be decomposed into (1-D) and (1 + D). Here, (1-D) is replaced with the differential characteristic by the magnetic channel 110 and the equalizer 111 of the reproduction system, and (1 + D) is replaced by the 1-bit delay 121 and the adder 122. Consisting of a configured playback encoder 112.

Therefore, the playback process has a delay characteristic of (1-D ² ) consisting of (1-D) and (1 + D) signals, and the recording signal is 1 in the precoder 100 for accurate playback. Precode to have delay delay of / (1-D ² ).

The magnetic recording signal precoded and recorded on the magnetic recording tape is reproduced by the head provided in the magnetic channel 110, reproduced and amplified through the rotary transformer, and has a (1-D) delay characteristic through the equalizer 111. The reproducing encoder 112 is input to have a (1 + D) delay characteristic and thus has a delay characteristic of (1-D ² ) during reproduction.

The ternary waveforms (1,0, -1) passing through the reproduction encoder 112 of (1 + D) are identified as binary waveforms (1,0) by the data detector 113 to enable reproduction of the recording signal. .

That is, the data detector 113 generates three levels of reproduction signals output from the reproduction encoder 112 at two levels.

In other words, the data detector 113 corresponds to the first level of the playback signal output from the playback encoder 112 to one level, the zero level of the playback signal to the zero level, and the -1 level of the playback signal. 0 and 1 level equalization signals are generated in correspondence with 1 level reproduction signals.

In such a PR4 detection method, the high frequency component emphasized in the equalization circuit can be suppressed by the (1 + D) circuit which is the reproducing encoder 112.

In the magnetic recording / reproduction channel, the reproduction signal is a differential form of magnetic recording, so the step response h (t) for determining the characteristics of the magnetic recording channel is modeled by a Lorentzian function of Equation 1 below.

Here, PW ₅₀ is the width of the pulse at which the maximum output value of h (t) corresponds to 50%, which is determined according to the recording density.

However, the conventional analog magnetic recording and reproducing apparatus of the PR4 channel has a simple system implementation and effective timing recovery. However, as the recording density increases, the inter symbol interference (ISI) is deepened, making it difficult to detect.

That is, the recording density for recording the magnetic recording signal on the magnetic recording tape becomes gradually higher, which makes it difficult to detect data during analog magnetic recording and reproduction of the above-described PR4 channel.

Therefore, in recent years, the PRLM (Partial Response Maximum Likelihood) technology has been introduced.

The PRLM technology generates and transmits artificial interference so that interference can be easily removed when detecting data.

The configuration and operation of the digital VLC equalizer to which the PRLM technology is applied will be described below with reference to FIG. 2.

As shown in FIG. 2, a conventional digital equalizer equalizer includes a weight updater 135 and a weight updater for updating a weight by inputting a digital reproduction signal converted into a digital signal by the A / D converter 150. Delay 136 delays the weight updated in the predetermined time, and provides the weight update unit 135 from the A / D converter 150 in accordance with the weight output from the smoker 135 A feed forward filter 132 for feed forward filtering the output digital reproduction signal and outputting the reproduction signal, and a level determination unit for determining a three-level signal with the reproduction signal output from the feed forward filter 132 as an input; 133, and a level signal whose level is determined by the level determining unit 133 is compared with a reproduction signal of a next clock output from the feed forward filter 132. Detecting the call, and is composed of an error detection section 134 to output to the weight update unit 135 so as to update the weights in the weight update unit 135.

On the other hand, the reproduction signal output from the feed forward filter 132 is input to the timing recovery unit consisting of the timing recovery unit 140, the D / A converter 141, and the VCO 142 is used for timing recovery, The recovered clock is input to the A / D converter 150.

The operation of the conventional equalizer configured as described above will be described.

The A / D converter 150 receives an analog reproduction signal as an input and accurately digitizes and restores timing to supply a digital signal to the equalizer 130.

In this case, the timing restoration is performed by the timing restoration unit 140, the D / A converter 141, and the VCO 142.

The A / D converter 150 is input to the equalizer 130 to equalize the digitized signal by the timing recovery to have a PR4 characteristic.

The digital reproduction signal output from the A / D converter 150 is output after feedforward filtering by the feedforward filter 132, and the filter output signal y (k) output from the feedforward filter 132. Is the sum of the values obtained by multiplying the filter coefficients after the input digital reproduction signal x (k) is delayed at sampling time intervals, as shown in Equation 2 below.

Equation (2) can be briefly expressed internally of the vector as shown in Equation (3).

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

In Equation 3 above, t is a vector or matrix transpose, and the N-dimensional column vectors W and x (k) are defined by Equation 4 below.

W = [w ₀ , w ₁ , w ₂ , w _3, ⃛w _n-1 ] ^t

X (k) = [(k), x (k-1), ⃛, x (k-N + 1)] ^t

The output of the equalizer 130, that is, the output y (k) of the feedforward filter 132 is determined by the level determiner 133 as a three-level signal d (k) and the error detector 134. ) Is entered.

That is, the output y (t) of the feedforward filter 1320 is input to the level determiner 133 in order to update and determine the weight w shown in the above equation.

The three-level signal d (k) whose level is determined by the level determiner 133 is the feedforward filter to a subsequent sampling clock by a sampling time interval in the error detector 134, as shown in Equation 5 below. An output signal of 132 and its difference is calculated and output as an error signal e (k).

Where W _nw is the updated new weight value and W _old is the previous weight value.

The error signal e (k) output from the error detector 134 is input to the weight updater 135 and used for weight update as shown in Equation 5 above.

That is, the weight updater 135 outputs the digital reproduction signal x (k) output from the A / D converter 150 and the previous weight W _{old that} is delayed and output from the delay unit 136. The weight is updated according to the error signal e (k) output from the detector 134, and then output to the feedforward filter 132 through the delayer 136 to be used as the updated new weight W _nw . To print it out.

The data y (k) equalized and output from the equalizer 130 is inputted to a Viterbi detector, which is a data detector, so as to effectively search for a desired signal.

On the other hand, as shown in Equation 5 above, in order to filter and converge the digital reproduction signal, it is necessary to update the weight to update the new weight. However, since the scaling factor (μ) is fixed, the weight is updated only by the error value (e). Is done.

This conventional weight updater will be described in detail with reference to FIG. 3.

The weight updater 135 may include a first matrix multiplier 200 configured to perform matrix multiplication by receiving an input digital reproduction signal x (k) and a scaling factor μ; A second matrix multiplier (210) receiving the output of the first matrix multiplier (200) and an error value (e (k)) and multiplying the multiplier to output the multiplier; A matrix adder 220 for adding the output of the second matrix multiplier 210 and a previous weight value W _old to output the sum; The matrix is receiving the output of adder 220 to delay it consists of a delay unit 230 for outputting (W _old).

First, the first matrix multiplier 200 receives a reproduction signal x (k) and a scaling factor μ from the A / D converter 150 to multiply and output the multiplied signal.

The output of the first matrix multiplier 200 is applied to the second matrix multiplier 210 to perform multiplication with the error value e (k) detected by the error detector 134, and the result is a matrix adder ( 220).

Therefore, the matrix adder 220 is output from the output of the second matrix multiplier 210 and the delayer 230, and receives and adds the previous weight value W _old .

Accordingly, the delay unit 230 receives the delay and provides one delay to the feed forward filter 132 and the matrix adder 220.

The timing recovery unit 140 recovers timing for synchronizing the output of the received signal, that is, the equalizer 130, and the received signal is band-limited to | f | = R / 2, and the low-frequency received signal is represented by Equation 6 below. It is expressed as

Where n (t) is white Gaussian noise, h (t) is channel impulse coherence, and when the low-pass received signal is equal to Equation 6, the output of equalizer 130 for the sampling phase τ is It is expressed as Equation 7.

In Equation 7, W _i is an equalizer coefficient.

In addition, the error equation, which is differentiated from Equation 7 for the sampling phase τ and approximated, is

Equation 8 is approximated by Equation 9, and the result of Equation 9 is used to adjust the phase of the clock by passing the loop filter.

z _k = -Λ _k = e _k (y _{k + 1} -y _k-1 )

In Equation 9 e _k Means equalizer output error, y _k Is the output of equalizer 130.

Timing error signal z _k When is used as the input of the PLL's secondary rope filter, it is used to provide the timing position by the following equation (10).

Δ _{k + 1} = Δ _k + βz _k

Τ _{k + 1} = Τ _k + αz _k + Δ _{k + 1}

Where α and β are loop filter gains.

The digital signal y (k) reproduced by the equalizer 130 is input to the data detector 220 so that only a desired reproduction signal is effectively searched for and output.

However, such an equalizer has a problem in that the characteristic of the reproduction signal is deteriorated by the updated weight when the center of the weight is incorrectly set during the weight update.

In other words, the equalization characteristics are not optimal and the characteristics of the reproduction signal deteriorate and the reliability of the system is deteriorated.

Accordingly, an object of the present invention is to provide an equalizer of a digital VRL having an optimal equalization characteristic by moving the center of weight according to the characteristics of a reproduction signal in order to improve the above problem.

In order to achieve the above object, the present invention, a feed forward filter for filtering the input digital reproduction signal to output a reproduction signal having a delay characteristic of (1-D); A level determination unit which determines three levels by inputting the filter output output from the feedforward filter; An error detector for generating an error value by calculating a difference between a three-level signal output from the level determiner and a filter output output from the feedforward filter; A weight updater for updating a weight according to an error value output from the error detector and a previous weight, and moving a weight center under the control of a weight center controller; A delayer for delaying the updated weight outputted from the weight updater for a predetermined time and outputting the delayed weight to the feedforward filter; According to the reproduction characteristics of the equalized data, the weight center of the digital reproduction signal is set and provided to the weight update unit.

1 is a structural diagram of a PR4 channel used for general magnetic recording and reproduction;

2 is a block diagram of a conventional DVCR equalizer.

3 is a block diagram of an equalizer according to the present invention.

4 is a detailed configuration diagram of the weight center control unit of FIG. 3.

Fig. 5 is a waveform diagram for explaining reproduction signal characteristics by an equalizer.

6 is a view for explaining the movement of the weight center according to the weight center value and the reproduction signal characteristic.

7 is a diagram for explaining a track structure.

Explanation of symbols on the main parts of the drawings

200: A / D converter 210: equalizer

211: feed forward filter 212: level determination unit

213: error detection unit 214: weight update unit

215: delay 220: data detector

230: timing recovery unit 240: D / A converter

250: VCO 260: weight center control unit

261: register 262: arithmetic unit

263: center weight determiner 264: signal detector

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

The equalizer 300 according to the present invention includes a feedforward filter 211, a level determiner 212, an error detector 213, a weight updater 214, a delayer 215, and the like. The weight center controller 260 is configured.

The feedforward filter 211 filters the input digital reproduction signal x and outputs a reproduction signal y having a delay characteristic of (1-D).

The level determiner 212 determines three levels by inputting the filter output y output from the feedforward filter 211.

The error detector 213 generates an error value e by calculating a difference between a three-level signal output from the level determiner 212 and a filter output y output from the feedforward filter 211. do.

The weight updater 214 updates the weight according to the error value e output from the error detector 213 and the previous weight w _OLD , and also sets the weight center set by the weight center controller 260. Update weights by value.

The delay unit 215 delays the updated weight output from the weight update unit 214 for a predetermined time and outputs the delayed weight to the feedforward filter 211.

The weight center controller 260 controls the weight update of the weight update unit by optimally setting the center data of the weight to be updated. As shown in FIG. 4, the weight center controller 260 receives an equalized reproduction signal k to receive a F0 track. A signal detector 264 for detecting data of the camera; A register 261 for providing a digital reproduction signal (x) currently applied to the signal detection unit (264) and data of the F0 track detected by the signal detection unit (264) to the operation unit (262) when the FO track is detected by the signal detection unit (264); An operation unit 262 which receives the output of the register 261 and obtains a difference between the digital reproduction signal x and the data of the F0 track; The center weight determination unit 263 determines a center of weight based on the difference value obtained by the calculation unit 262.

The operation of the digital VAL equalizer according to the present invention configured as described above will be described with reference to the accompanying drawings.

First, the digital reproduction signal x converted and input into a digital signal by the A / D converter 200 is feedforward filtered by the feedforward filter 211, and has a reproduction signal y having a delay characteristic of (1-D). Will be printed).

The signal output from the feedforward filter 211 needs to be leveled to update the weight of the equalizer.

That is, the signal y output from the feedforward filter 211 is determined by the level determiner 212 to three levels.

The signal d determined as three levels by the level determiner 320 is input to the error detector 213 to calculate a difference from the output y of the feedforward filter and output as an error signal e.

That is, the error detector 213 subtracts the output y of the filter from the three-level signal d output from the level determiner 212, as shown in Equation 6 below, and outputs the error signal e. Detect.

As such, the error value e output from the error detector 213 is input to the weight updater 340 to update the weight by the above equation (5).

That is, the weight updater 340 updates the error value e output from the error detector 330 and the previous weight value output from the delayer 350 by matrix multiplication and addition processing. Occurs weights.

The updated weight is used as a coefficient in feedforward filtering of the digital reproduction signal input from the A / D converter 200 after being delayed by the delay unit 350.

Meanwhile, the weight center controller 260 determines the center weight of the weight updater 214, which will be described in detail with reference to FIGS. 4 to 6.

First, as shown in FIG. 5A, the most ideal reproduction signal output from the data detector 220 has the same width L1 and L2 from the center island of the mountain signal.

The reproduction signal of the correct F0 track of this signal has a constant height of the mountain as shown in Fig. 5C, in which case the center weight is located at the center of the weight values as shown in Fig. 6A.

Accordingly, the reproduction characteristic of the reproduced signal is corrected so that the weight updater 214 performs the weight update by the center weight thereof.

However, when the update is performed because the center of the weight is set incorrectly, the reproduction signal characteristics output from the data detector 220 have the widths L1 and L2 from the center islands of the signals forming the mountains as shown in FIG. 5B. It will be done differently.

As shown in Fig. 5D, the reproduction signal of the FO track is different in height from neighboring mountains (a, b) by α.

This means that the playback signal is not correct and has deteriorated.

Therefore, it is necessary to shift the center of weight in order to uniformly adjust the height of its peaks a and b.

Accordingly, the signal detecting unit 254 receives the equalized reproduction signal k applied from the data detector 220 and detects the reproduction data of the FO track when the codeword of 1000101110, which represents the FO track, is continued for a predetermined number or more times. Is supplied to the register 261.

At this time, the signal detection unit 264 has a table of codewords of 1000101110, which are data values of the FO track, and detects the data of the FO track by comparing them with codewords of 1000101110, which represent an input FO track.

The F0 track is a track inserted between the F1 track and the F2 track as shown in FIG. 7 when data is recorded on each track of the recording medium, and about 140 codewords of 1000 101110 are recorded.

The register 261 stores the digital reproduction data applied from the A / D converter 200 and outputs the data stored by the detection signal of the register 261 to the calculation unit 262 and the signal detection unit 264. Data of the FO track detected from the "

The operation unit 262 receives the digital generation data (x) and the data of the FO track output from the register 261 and obtains a difference between the two signals, which is a neighboring mountain (as shown in FIG. 5D). The difference α between the heights p and g with a and b is obtained.

The difference α is applied to the center weight determiner 263 to determine the center of the weight. As shown in FIG. 6B, the center of the weight is positioned by the position corresponding to the difference α calculated from the center to the left or the right. It will be moved.

When the center of the weight is determined in this way, the weight of the weight is provided to the weight updater 214 so that the correct weight can be updated by this value.

As described above, when the weight of the digital VLC according to the present invention is not correct, the digital weight is reset based on the data value of the FO track to update the weight by the center of the set weight. It has the effect of achieving an optimal equalization characteristic.

Claims (3)

A feedforward filter for filtering an input digital reproduction signal and outputting a reproduction signal having a delay characteristic of (1-D); A level determination unit which determines three levels by inputting the filter output output from the feedforward filter; An error detector for generating an error value by calculating a difference between a three-level signal output from the level determiner and a filter output output from the feedforward filter; A weight updater for updating a weight according to an error value output from the error detector and a previous weight, and moving a weight center under the control of a weight center controller; A delayer configured to delay the updated weight outputted from the weight updater for a predetermined time and output the delayed weight to the feedforward filter; And a weight center controller configured to set the weight center of the digital reproduction signal according to the reproduction characteristic of the equalized data and provide the weight center to the weight update unit. The method of claim 1, wherein the weight center control unit A signal detector which receives the equalized reproduction signal and detects data of the F0 track; A register for providing a digital reproduction signal currently applied and data of the F0 track detected by the signal detection unit to the calculation unit when the FO track is detected by the signal detection unit; An operation unit receiving the output of the register to obtain a difference between the digital reproduction signal and the data of the F0 track; And a center weight determination unit for determining a center of weight based on the difference value obtained by the calculation unit. The method of claim 2, wherein the signal detection unit A digital V equalizer having a table of codewords of FO tracks and detecting data of the FO tracks in comparison with codewords of input FO tracks.