KR100311488B1 - adaptive equalizer - Google Patents

Abstract

An adaptive equalizer suitable for an optimized equalizer implementation is provided using a modified least mean squares (LMS) algorithm, which is an equalizer symmetric and an equalizing coefficient. The adaptive equalizer includes an A / D converter for oversampling an analog signal of a predetermined band by n times and converting the digital signal of the A / D converter into a digital signal, and an A / D converter for multiplying the digital signal of the A / D converter by a factor of n times oversampling taps and a modified LMS algorithm. An adaptive equalizer for outputting the equalized values, and a result detector for receiving equalized values output from the adaptive equalizer, removing error bits, and outputting only the recovered data. Therefore, this adaptive equalizer can effectively reduce the number of multipliers necessary for the reduction of hardware due to the reduction of the number of equalizer taps, that is, the redundancy calculation.

Description

{Adaptive equalizer}

The present invention relates to an adaptive equalizer and more particularly to a method and apparatus for adaptive equalizer that is optimized for an equalizer implementation using a modified least mean squares (LMS) algorithm which is an equalizer symmetric and an equalizing coefficient. Lt; / RTI >

A typical adaptive equalizer reads data recorded on a compact disc (CD) / digital versatile disc (DVD) using an optical pickup device and oversamples it in an A / D converter before transmitting it to the next- , And is used to remove redundant sampling data used in oversampling in the A / D converter to restore the data to original data. The reason for performing the oversampling in the A / D converter is to remove the distortion component of the frequency signal generated between the adjacent channels during data reading.

1 is a block diagram illustrating an adaptive equalizer in accordance with the prior art.

1, the conventional adaptive equalizer includes an A / D converter 10 for oversampling a predetermined band (for example, 20 MHz) of an analog signal provided from a receiver filter (not shown) and converting the analog signal into a digital signal, An adaptive equalizer 11 for outputting the digital signal of the A / D converter 10 as an equalized value according to an oversampling tap number and an LMS algorithm coefficient value, And a result detector 15 for receiving equalized values of positive (+) / negative (-) and removing error bits and outputting only recovered data.

The adaptive equalizer 11 and a quantizer 13 for quantizing the output of the output of the equalizer 12 to the positive / negative level, the equalization value (y _k), and quantized values ( ({Epsilon} _ {k}) of the adder 14 and outputs the error value ({epsilon} _ {k}) according to the LMS algorithm And an LMS algorithm 15 for providing the updated coefficient value omega_ {k + 1} ^ {i} to the equalizer 12 according to the number of taps.

The conventional adaptive equalizer configured as described above first reads the data of the adjacent channel according to the loading state of the disc and the loading position of the optical pickup when reading the data recorded on the disc to the optical pickup apparatus, An analog signal is oversampled through an A / D converter 10, converted into a digital signal, and then applied to an equalizer 12. In this case, when the equalizer 12 is a fixed equalizer, a symmetrical low pass filter having symmetry about the center of the sampling frequency band can be used.

The equalization factor in the next equalizer 12 is updated every clock by the LMS algorithm 15 with another input and this clock corresponds to the sampling frequency of the A / D converter 10. [

The equalization value y _k of the equalizer 12 is then _multiplied by a quantization value And these values are respectively added to the error value {epsilon} _ {k} via the adder 14 and then applied to the LMS algorithm 15.

The LMS algorithm 15 is also referred to as an encoded LMS algorithm.

Where {omega} `_ {k} ^ {i} represents the ith coefficient when t = k and {x}` _ {k} ^ {i} } _ {ki}. β is the increase / decrease value of the equalization coefficient that determines the convergence speed, {epsilon} _ {k} is the equalization value (y _k ) and the quantization value ), That is, an error value.

Also, Equation (1) satisfies 0? I <N and N means the number of equalizer tapes.

In Equation (1), the following LMS can be used to eliminate hardware complexity.

Therefore, if the updated coefficient value omega_ {k + 1} ^ {i} is provided to the equalizer 12 according to Equation 1 or Equation 2, the new equalization value y _k , And the quantized value in the allowable frequency band through the quantizer 13 is output to the original data after the error bit is removed again through the result detector 16. [

Since the conventional adaptive equalizer operates at a high speed of 2x or higher speed in the CD / DVD system, a multiplier corresponding to each equalizer tap number is necessary to equalize the sampling frequency according to oversampling, and the convergence speed corresponding to the reduction of the error value, As shown in FIG.

In addition, the conventional adaptive equalizer has a problem in that when the tilt is severely generated according to the loading state of the disc and the loading position of the optical pickup, it is difficult to equalize the read data and the bit error rate (BER) increases.

Accordingly, the present invention has been made to solve all of the problems expected in the conventional adaptive equalizer, and it is an object of the present invention to provide an adaptive equalizer employing a modified LMS algorithm in consideration of symmetry and frequency characteristics of an equalizer Thereby reducing the complexity of the hardware, reducing the error value, reducing the convergence speed, and improving the equalization performance.

1 is a block diagram illustrating an adaptive equalizer in accordance with the prior art;

Figure 2 is a block diagram illustrating a first embodiment of an adaptive equalizer according to the present invention;

3 is a block diagram illustrating a second embodiment of an adaptive equalizer according to the present invention.

4 is a detailed block diagram illustrating the 3T symmetric equalizer of FIG. 3;

DESCRIPTION OF THE REFERENCE NUMERALS

10: A / D converter 11, 21, 31: adaptive equalizer

12: equalizer 13, 23, 33: quantizer

14, 24, 34, 38: adder 15: LMS algorithm

16: result detector 22: symmetry equalizer

25, 35: modified LMS algorithm 32: 3T symmetric equalizer

36: counter 37: multiplier

According to an aspect of the present invention, there is provided an adaptive equalizer including an A / D converter for oversampling an analog signal of a predetermined band by n times and converting the analog signal into a digital signal, a digital signal of the A / An adaptive equalizer for outputting the equalized values according to the number of oversampling taps and the modified LMS algorithm, and an adaptive equalizer outputting the equalized values output from the adaptive equalizer to remove error bits and output only recovered data And the result detector.

Hereinafter, a preferred embodiment of the adaptive equalizer according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating a first embodiment of an adaptive equalizer in accordance with the present invention.

Referring to FIG. 2, the adaptive equalizer includes an A / D converter 10 for oversampling an analog signal in the 40 MHz band by n times and converting the analog signal into a digital signal, and an A / D converter 10 for multiplying the digital signal of the A / An adaptive equalizer 21 for outputting an equalized value according to the number of oversampling taps and a coefficient value of the modified LMS algorithm, and an adaptive equalizer 21 for receiving an equalized value output from the adaptive equalizer 21, And a result detector 16 for outputting only the recovered data.

The adaptive equalizer 21 includes a symmetric equalizer 22 for equalizing and outputting a specific coefficient by zeroing so that only the left or right value is updated at the center of the n-times oversampling frequency, ) and a quantizer 23 for quantizing the output value output by positive / negative level, the equalization value (y _k) of the quantizer value ( ({Epsilon} _ {k}) of the adder, and outputs the error value ({epsilon} _ {k} And a modified LMS algorithm 25 for providing the updated coefficient value omega_ {k + 1} ^ {i} to the symmetric equalizer 22 according to the number of taps.

The adaptive equalizer according to the first embodiment of the present invention thus oversamples an analog signal of the 40 MHz band through the A / D converter 10 at least six times the signal band, converts the analog signal into a digital signal, 22).

The equalization factor in the next symmetric equalizer 22 is updated every clock by the modified LMS algorithm 25 with another input and this clock corresponds to the sampling frequency of the A / D converter 10. [

The equalization value y _k of the symmetric equalizer 22 is then _multiplied by a quantization value And these values are added to the error value {epsilon} _ {k} via adder 24 and applied to the modified LMS algorithm 25, respectively.

The modified LMS algorithm 25 is also referred to as an encoded LMS algorithm.

Where {omega} `_ {k} ^ {i} is the ith coefficient when t = k and {x}` _ {k} ^ {i} is the ith input signal when t = k, {Epsilon} _ {k} is the difference between the equalization value (y _k ) and the quantization value ( _t ) when t = k ).

Wherein the input coefficient i satisfies any of the following conditions: 0? I <N / 2 or N / 2? I <N where N is the number of taps of the equalizer, 0, 1, 2, --- and alpha is an integer).

If the updated coefficient value omega_ {k + 1} ^ {i} is provided to the symmetric equalizer 22 according to the Equation 3, the new equalized value y _k is output , The quantized value in the allowable frequency band through the quantizer 23 is output to the original data (40 MHz) after the error bit is removed again through the result detector 26.

Actually, according to the first embodiment, since the input coefficient changes only from 0 to N / 2 or N / 2 to N, it can drive the LMS to have symmetry like a fixed equalizer, so that the convergence speed And the number of equalizer taps can be reduced by half.

FIG. 3 illustrates a second embodiment of the adaptive equalizer according to the present invention. The adaptive equalizer 31 includes a 3T symmetric equalizer 31 for updating the coefficient value of the n-times oversampling frequency by 3? 32, the quantizer 33 for quantizing the output of the output of the 3T symmetry equalizer 32 to the positive / negative level, the equalization value (y _k), and quantized values ( ({Epsilon} _ {k}) of the adder 34 and outputs the error value ({epsilon} _ {k}) to the modified LMS algorithm And a modified LMS algorithm 35 for providing the 3T symmetric equalizer 32 with a coefficient value omega_ {k + 1} ^ {i} updated at intervals of 3 alpha according to the number of equalizer taps.

The 3T symmetric equalizer 32 also includes a counter 36 for updating and outputting the input value x _k at intervals of 3T (where T is an inverse number of the oversampling frequency) intervals according to the external clock frequencies ck _{1 to} ck ₆ , And a multiplier 37 for outputting the updated output value of the counter 36 with the equalization coefficient values {omega} `_ {0}, {omega}` _ {3}, {omega} `_ {6} And an adder 38 for adding an output value of the multiplier 37 and outputting an equalization value y _k .

Since the adaptive equalizer according to the second embodiment of the present invention has up to six bit signals in one cycle in the case of an analog signal of the 40 MHz band, the analog signal is converted into a signal band And then applied to the 3T symmetric equalizer 22 and the modified LMS algorithm 35. The 3S symmetric equalizer 22 and the modified LMS algorithm 35 are shown in FIG.

The equalization factor in the next 3T symmetry equalizer 22 is updated every 3 留 intervals by the modified LMS algorithm 25 with another input and this clock corresponds to the sampling frequency of the A / D converter 10 .

The equalization value y _k of the 3T symmetric equalizer 22 is then _multiplied by a quantization value And these values are added to the error value {epsilon} _ {k} via adder 24 and applied to the modified LMS algorithm 25, respectively.

The modified LMS algorithm 25 satisfies Equation 3 and i has 0 and 3 or 3 and 6 when the input coefficient i satisfies 0? I <7.

This is the input value (x _k), the counter 36 is composed of first through 6 D flip-flop (36-1~36-6) according to the external clock frequency (ck ₁ ~ck ₆₎ As shown in Figure 4 And the update output value is updated by the first to third multipliers 37 by the equalization coefficient values {omega} `_ {0}, {omega}` _ {3}, {omega} `_ {6}), and these multiplied values are all added up by the adder 38 and output as an equalization value y _k .

Therefore, if the above condition of the input coefficient is satisfied, the function of the equalizer is performed by only two multipliers, so that the redundant operation due to the n-times oversampling can be reduced, and the hardware complexity can be reduced.

As described above in detail, the adaptive equalizer according to the present invention can effectively reduce the number of multipliers necessary for the reduction of hardware due to the reduction of the number of equalizer taps, that is, the computation of the redundancy.

Also, the present invention reduces the convergence speed corresponding to the reduction of the error value by the modified LMS algorithm, and dramatically improves the performance of the equalizer.

Therefore, it is apparent that the adaptive equalizer of the present invention is not limited to the embodiments shown in the present invention, and various modulation changes are possible within the scope of the technical idea of the present invention.

Claims (7)

An A / D converter for oversampling an analog signal of a predetermined band by n times and converting the analog signal into a digital signal; a quantizer for quantizing and outputting an output value of the symmetric equalizer to a positive / negative level, a symmetric equalizer for performing an equalization output by stuffing a specific coefficient to 0 so that only the left or right value is updated at a center value of the n-times oversampling frequency, The equalization value (y _k ) and the quantization value ( ({Epsilon} _ {k}) of the adder according to the modified LMS algorithm based on the number of equalizer taps, and outputs the error value {epsilon} _ {k} And a modified LMS algorithm for providing the updated coefficient value (omega_ {k + 1} ^ {i}) to the symmetric equalizer so that the digital signal of the A / D converter is multiplied by n times oversampling taps and the modified LMS algorithm An adaptive equalizer for outputting an equalized value according to a coefficient value; And And a result detector for receiving an equalized value output from the adaptive equalizer, removing an error bit, and outputting only recovered data. 2. The adaptive equalizer of claim 1, wherein the modified LMS algorithm satisfies the following equation and an input coefficient. Where {omega} `_ {k} ^ {i} is the ith coefficient when t = k and {x}` _ {k} ^ {i} is the ith input signal when t = k, {Epsilon} _ {k} is the difference between the equalization value (y _k ) and the quantization value ( _t ) when t = k ). 3. The adaptive equalizer of claim 2, wherein the input coefficient i satisfies 0? I <N / 2 or N / 2? I <N. 4. The adaptive equalizer of claim 3, wherein the input coefficient i satisfies i =? N (where n = 0, 1, 2, --- and? Is an integer). 2. The adaptive equalizer of claim 1, wherein the adaptive equalizer comprises: a 3T symmetric equalizer for updating a coefficient value of the n-times oversampling frequency by 3 alpha intervals and outputting an equalization output; and a quantization unit for quantizing the output value of the 3T symmetric equalizer T y, the equalization value y _k and the quantization value y _k ({Epsilon} _ {k}) of the adder and outputs the error value ({epsilon} _ {k}) to the equalizer tap number And a modified LMS algorithm for providing the 3T symmetric equalizer with a coefficient value (omega_ {k + 1} ^ {i}) updated at 3α intervals. Article as claimed in 5, wherein a counter for updating and outputting the 3T symmetry equalizer input values (x _k) to 3T (where T is the number of over-sampling frequency Station) intervals according to the external clock frequency (ck ₁ ~ck _6), A multiplier for multiplying the updated output value of the counter by the equalization coefficient values {omega} `_ {0}, {omega}` _ {3}, and {omega} `_ {6} And outputting an equalization value y _k . 6. The adaptive equalizer of claim 5, wherein i has 0 and 3 or 3 and 6 when the input coefficient i satisfies 0? I <7.