JPH04330818A - Tap interval mixing type automatic equalizer - Google Patents

Abstract

PURPOSE:To prevent the degradation of equalizing characteristic due to the phase deviation of the input signal of an automatic baud interval type equalizer, and to realize the automatic equalizer whose operational amounts are less than those of an automatic fractional interval type equalizer. CONSTITUTION:An adding tap 5 is moreover added to the tap 3 of the automatic baud interval type equalizer, and the constitution of the automatic fractional interval type equalizer can be partially obtained. The additional number or additional position of the adding tap 5 is set so that the prescribed equalizing characteristic can be obtained by the minimum operational amounts at the time of an initial leading-in. A performance which is almost equivalent to the automatic fractional interval type equalizer can be realized by the small number of the taps, so that the operational amounts can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic equalizer that automatically equalizes digitized signals.

[0002] Conventional automatic equalizers employ a Baud period interval type automatic equalization system consisting of a delay element with a delay of a Baud period and a tap, or a delay element and a tap with a delay of an integer fraction of a Baud period. A fractional period interval type automatic equalization method consisting of the following is used.

FIG. 4 is a block diagram of a Baud period interval type automatic equalizer. Delay element 2 with Baud period delay (T)
2 are connected in cascade, and each delay element 22
a tap 24 that multiplies the output signal of the coefficient by a coefficient, and each tap 24
and a tap corrector 26 that evaluates the output signal of the adder 25 and corrects the coefficients of each tap 24 in order to perform optimal equalization.

FIG. 5 shows that the delay amount is half the baud period (T/2
) is a block diagram of a fractional period interval type automatic equalizer using a delay element 27. A delay element group 28 in which delay elements 27 having a delay of 1/2 of a baud period are connected in cascade, a tap 29 that multiplies the output signal of each delay element 27 by a coefficient, and an adder 30 that adds the outputs of each tap 29. Then, the output signal of the adder 30 is evaluated to perform optimal equalization, and each tap 29 is
The tap corrector 31 corrects the coefficients of the tap corrector 31.

[0005]

[Problems to be Solved by the Invention] In the above-mentioned baud period interval type automatic equalizer, in order to sample at the baud rate period, the baud frequency is set to 1/1 of the baud frequency as shown in the output spectrum diagram of FIG.
An alias occurs due to aliasing near the frequency of 2. When the phases of the input signal and the automatic equalizer match, the Nyquist criterion is satisfied, but if the phases of the input signal and the automatic equalizer do not match, the fundamental component and the folded component cancel each other out. In addition, the signal component is attenuated around a frequency that is 1/2 of the baud frequency. The automatic equalizer amplifies this attenuated signal in order to equalize the signal components, but it also amplifies the noise components at the same time, resulting in deterioration of the equalization characteristics. Therefore, there is a problem in that control is required to accurately match the phase of the automatic equalizer.

On the other hand, the fractional period interval type automatic equalizer, which is a method for solving this problem, does not require controlling the phase of the automatic equalizer because aliasing does not occur. The problem is that the number is increasing.

[0007]

[Means for Solving the Problems] In the tap interval mixing type automatic equalizer of the present invention, there is a delay in the sampling period when the input signal is a digital signal sampled at a sampling period corresponding to an integer fraction of the baud period. A delay element group having a plurality of delay elements connected in cascade, and an output signal from an output terminal corresponding to a baud period interval among the output terminals of each delay element in the delay element group are extracted and multiplied by a coefficient. A baud interval tap that outputs a multiplication result, and an addition that extracts an output signal from each output terminal of the delay element output terminal other than the delay element output terminal that is input to the baud interval tap, multiplies it by a coefficient, and outputs a multiplication result. a selector that selects and adds one or more outputs of the tap and the additional tap; an adder that adds each output signal of each of the baud interval taps and the output signal of the selector and outputs the addition result; Evaluates the output signal of the adder and outputs a correction signal for modifying the coefficient of the baud interval tap and the coefficient of the additional tap selected by the selector, and also outputs a correction signal for modifying the coefficient of the baud interval tap and the additional tap selected by the selector at the time of initial pull-in. The present invention is characterized by comprising a corrector that outputs a signal to the selector to find the optimum value while changing at least one of the tap position and the number of additional taps to be selected.

[0008]

[Operation] In the present invention, in order to eliminate the influence of aliasing, by adding the minimum necessary additional taps to the baud-spaced automatic equalizer, it is possible to calculate fractional Characteristics equivalent to interval type automatic equalizers can be achieved. In addition, by monitoring the quality of the output signal of the adder with a corrector during the initial pull-in of the automatic equalizer, and outputting a signal to the selector to control at least one of the number of additional taps and the position of the additional taps, The number and location of additional taps selected by the selector are determined.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention for controlling the position of one additional tap. Delay element 1 has a delay amount (T/2) that is half the baud period. These delay elements 1
Eight of them are connected in cascade to form the delay element group 2. The output of each delay element 1 is connected to every other tap 3. At tap 3, each tap coefficient is multiplied, and tap 3
The adder 6 adds the signals as output signals. On the other hand, the output signals of the respective delay elements 1 not connected to the tap 3 are input to the selector 4, and one of them is selected. Selector 4
The output signals of are multiplied by a tap coefficient at an additional tap 5 and added at an adder 5. The modifier 7 evaluates the output signal of the adder 6 and modifies the coefficient of the tap 3 so that the equalization characteristic is optimal, and also selects one of the signals input to the selector 5. , modify the tap coefficient.

FIG. 2 is a block diagram of an embodiment of the present invention for controlling the number of additional taps. The delay element 8 has a delay amount (T/2) that is half the baud period. These delay elements 8
Eight pieces are connected in cascade to form the delay element group 9. The output of each delay element 8 is connected to every other tap 10. At the taps 10, the signals are multiplied by tap coefficients, and the signals are added together at the adder 13 as output signals of the taps 10. On the other hand, the output signal of each delay element 8 that is not connected to the tap 10 is connected to the additional tap 11. The output signals of the additional taps 11 are input to the selector 12, taken in from the center taps of the taps 10 in order of proximity, and added. The number of additional taps 11 to be included is determined by the output signal of the modifier 14. The output signal of the selector 12 is added to the output signal of each tap 11 in an adder 13. The modifier 14 evaluates the output signal of the adder 13 and modifies the coefficient of the tap 8 so that the required equalization characteristics can be obtained with the minimum number of taps.
Multiply and correct the tap coefficient. No calculation is performed for additional taps 11 that are not selected by the selector 12.

FIG. 3 is a block diagram of an embodiment of the present invention for controlling the location and number of additional taps. The delay element 15 has a delay amount (T/2) that is half the baud period. Eight of these delay elements 15 are connected in series to form a delay element group 16. The output of each delay element 15 is connected to every other tap 17.
connected to. At the taps 17, the signals are respectively multiplied by tap coefficients, and added by an adder 20 as output signals of the taps 17. On the other hand, the output signal of each delay element 15 that is not connected to the tap 17 is connected to the additional tap 18. The output signal of the additional tap 18 is input to the selector 19. In the selector 19, the output signals of one or more additional taps 18 are selected based on the signal from the corrector 21, added, and output. The output signal of the selector 19 is sent to the adder 20
is added together with the output signal of tap 17. Corrector 21
Now, by evaluating the output signal of the adder 20, the coefficient of the tap 15 is corrected, and the position and number of taps to be selected by the selector 19 are determined so that the required equalization characteristics can be obtained with the minimum number of additional taps. At the same time, the additional tap 18 selected by the selector 19 is multiplied and the tap coefficient is corrected. No calculation is performed for additional taps 18 that are not selected by the selector 19.

Next, an example of the operation of this embodiment will be explained with reference to FIG. If the selector 19 does not select any of the output signals of the additional taps 18, it operates as a baud-spaced automatic equalizer, and if all the output signals of the additional taps 18 are selected, it operates as a fractional-spaced automatic equalizer. operates as The present invention operates as an automatic equalizer in which a portion of the Baud period interval type automatic equalizer is replaced with a fractional period interval type automatic equalizer.

In the corrector 21, the tap coefficients of the tap 17 and the additional tap 18 are constantly corrected using the maximum slope method from the output signal of the adder 20. On the other hand, the positions and numbers of the additional taps 18 to be selected by the selector 19 are determined by searching for all combinations of the positions and numbers of the additional taps 18 to be selected by the selector 19 at the initial pull-in of the automatic equalizer. , find and set a combination that provides the required equalization characteristics with the least number of additional taps. At this time, the additional taps 18 that have not been selected stop their subsequent calculations. Thereby, the amount of calculations during normal operation can be reduced.

Additional tap 18 selected by selector 19
FIG. 1 shows a method in which the number of taps is fixed to one and only the position of the additional tap 18 is controlled by the corrector 21.

In the selector 19, the additional tap 18 is
FIG. 2 shows a system in which the additional taps 18 are selected preferentially in the order of distance from the center tap, and only the number of selected additional taps 18 is controlled by the corrector 21.

[0016] Also, the amount of delay is 1/3 or 1/4 of the baud period.
The equalizer of the present invention can also be configured using a delay element.

[0017]

As explained above, in the present invention, by replacing a part of the baud period interval type automatic equalizer with a fractional period interval type automatic equalizer, the input signal, which is a drawback of the baud period interval type, can be improved. This also has the effect of reducing deterioration in equalization characteristics that occurs when the phases of the automatic equalizers do not match.

Furthermore, since the number of taps can be reduced compared to the fractional cycle interval type automatic equalizer, there is an effect that the amount of multiplication processing for multiplying tap coefficients and addition processing for adding up the outputs of the taps can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a method for controlling the position of an added tap in the present invention.

FIG. 2 is a block diagram of an embodiment of a method for controlling the number of added taps in the present invention.

FIG. 3 is a block diagram of an embodiment of a method for controlling the number and position of added taps in the present invention.

FIG. 4 is a block diagram of a baud period interval type automatic equalizer.

FIG. 5 is a block diagram of a fractional period interval type automatic equalizer.

FIG. 6 is a spectral diagram of an output signal of a Baud periodic automatic equalizer.

[Explanation of symbols]

1 Delay element 2 Delay element group 3 Tap 4 Selector 5 Additional tap 6 Adder 7 Modifier 8 Delay element 9 Delay element group 10 Tap 11 Additional tap 12 Selector 13 Adder 14 Modifier 15 Delay element 16 Delay element group 17 Tap 18 Additional tap 19 Selector 20 Adder 21 Modifier 22 Delay element 23 Delay element group 24 Tap 25 Adder 26 Modifier 27 Delay element 28 Delay element group 29 Tap 30 Adder 31 Modifier

Claims (3)

[Claims] 1. A delay element group comprising a plurality of cascade-connected delay elements each having a delay of a sampling period, the input signal being a digital signal sampled at a sampling period corresponding to an integer fraction of a baud period, and the delay element A baud interval tap that takes out an output signal from an output terminal corresponding to the baud period interval among the output terminals of each of the delay elements in the group, multiplies it by a coefficient, and outputs the multiplication result, and inputs the output signal to the baud interval tap. a selector that takes out one output signal from each output of the delay element output terminals other than the delay element output terminal; an additional tap that multiplies the output signal of the selector by a coefficient and outputs a multiplication result; an adder that adds each output signal of the interval tap and the output signal of the additional tap and outputs the addition result; and an adder that evaluates the output signal of the adder and corrects the coefficient of the baud interval tap and the coefficient of the additional tap. and a corrector that outputs a correction signal for finding the optimum value while changing the tap addition position during initial pull-in to the selector. Equalizer. 2. A delay element group comprising a plurality of cascade-connected delay elements having a delay of a sample period whose input signal is a digital signal sampled at a sample period corresponding to an integer fraction of a baud period, and the delay element A baud interval tap that takes out an output signal from an output terminal corresponding to the baud period interval among the output terminals of each of the delay elements in the group, multiplies it by a coefficient, and outputs the multiplication result, and inputs the output signal to the baud interval tap. an additional tap that extracts an output signal from each output terminal among the delay element output terminals other than the delay element output terminal, multiplies it by a coefficient, and outputs a multiplication result; and a selector that selects additional taps in order of proximity to the center tap and adds them. an adder that adds each output signal of each of the baud interval taps and the output signal of the selector and outputs the addition result; and an adder that evaluates the output signal of the adder and calculates the coefficient of the baud interval tap and the selector. and a corrector that outputs a correction signal for correcting the coefficient of the additional tap selected in the selector, and outputs a signal for finding the optimum value while changing the number of additional taps at the time of initial pull-in to the selector. A mixed tap interval automatic equalizer. 3. A delay element group comprising a plurality of cascade-connected delay elements having a delay of a sample period whose input signal is a digital signal sampled at a sample period corresponding to an integer fraction of a baud period, and the delay element A baud interval tap that takes out an output signal from an output terminal corresponding to the baud period interval among the output terminals of each of the delay elements in the group, multiplies it by a coefficient, and outputs the multiplication result, and inputs the output signal to the baud interval tap. an additional tap that extracts an output signal from each output terminal among the delay element output terminals other than the delay element output terminal, multiplies it by a coefficient, and outputs a multiplication result; a selector that selects one or more additional taps and performs addition; an adder that adds each output signal of each of the baud interval taps and an output signal of the selector and outputs the addition result; and an adder that evaluates the output signal of the adder and selects the coefficient of the baud interval tap and the selector. a corrector that outputs a correction signal for correcting the coefficient of the additional tap that has been selected, and outputs a signal to the selector for finding the optimum value while changing the position and number of the additional tap during initial pull-in. A mixed tap interval automatic equalizer.