JPS59160335A - Decision system for convergence of bridged tap equalizer - Google Patents

Abstract

PURPOSE:To obtain resistance to a noise by deciding the convergence of an equalizer by ANDing the repetitive frequency of a tap coefficient with a pattern detection signal. CONSTITUTION:A signal (e.g. AMI code sequence) applied to an input terminal 2-1 is led to an output terminal 2-2 through a correcting signal adding circuit 2-9 and an identifying circuit 2-3, and part of this signal is applied to a pattern detecting circuit 2-5. This pattern detecting circuit 2-5 when detecting specific patterns of 0, + or -1, 0, and 0 sends the pattern detection signal to one input terminal of an AND circuit. The signal from an error polarity detector 2-4, on the other hand, is applied to the other terminal of said AND circuit and ANDed with said pattern detection signal. Consequently, a tap coefficient counter 2-6 counts up or down according to the value of the AND between the error polarity signal (repetitive frequency of tap coefficient) and pattern detection signal to reach convergence.

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a convergence determination method for an automatic equalizer, and in particular, convergence determination for waveform distortion contained in a signal is resistant to noise, can be performed reliably, and is performed using a simple circuit. The present invention relates to a convergence determination method for a bridged tap equalizer that can be realized and that can accurately and quickly equalize waveform distortion based on pulse reflection of a branch line (bridged tap line) of a metallic line as a waveform distortion.

(Prior Art) FIG. 1 is a block diagram of a conventional array of automatic waveform equalizers for distortion contained in a signal. Figure 1 shows the signal input/output terminal 1-
1, 1-2, auxiliary waveform adder 1-, ? , identification circuit 1-
4. Error polarity determination circuit 1-5, time T delay circuit 1-
6, tap coefficient update circuit 1-7, D/A converter 1-8,
It is composed of multiple low-pass filters l-9.

In the system shown in Figure 1, when the equalizer adjusts, the tag coefficient is increased or decreased by utilizing the fact that the value of the automatically controlled tap coefficient increases or decreases around a constant value. . However, it is known that the repeating increase/decrease of the tap coefficient occurs even when the isolator is in a diverging state, and is also caused by noise, so it has the disadvantage that it cannot be guaranteed whether the isolator has converged or not. had.

(Object of the Invention) An object of the present invention is to provide a convergence judgment method capable of eliminating convergence judgment errors caused by conventional noise or instability of the circuit itself.

(Summary of the Invention) In order to achieve the above object, the present invention performs tap coefficient control only when a predetermined specific pattern is detected. It is characterized in that the convergence determination of the isolator is performed as a logical product with the tangent detection signal. Actual below
This will be explained in detail based on an example.

(Embodiment of the Invention) FIG. 2 is a block diagram showing one embodiment of the present invention, and is an example in which the order of the feedback digital filter is 2nd order, that is, 2 taps. Input/output tJ terminal 2-1゜2-2, discriminator 2-3, error polarity detector 2-4, pattern detector 2-
5, a coefficient counter 2-6, a D/A converter 2-7, a filter 2-8, and a correction signal addition circuit 2-9.

The operation will be explained using a signal obtained by adding a distorted waveform component to the AMI code string (0, ±1.0.0) as an example of an input signal.

FIG. 3(a) shows an AMI code string (o,
Examples of t, o, o) are shown below. In FIG. 3(a), the horizontal axis 3-1 indicates progress of time. The vertical axis 3-2 shows the amplitude of the waveform, 3-3 shows the input waveform including distortion, and 3-4 shows the discrimination level. -T on time axis 3-1, 0. T, 2T, 3T
is the identification timing time in the identification circuit 2-3.

The identification circuit 2-3 is configured to operate as shown in FIG.
As shown in b), it is determined as (0, +1.+1.O) and shifted in order at each time T, and the delay device 2-10.2 of time T
-11 and is output to the pattern detector 2-5. The pattern detector 2-5 detects a specific/main turn (in this example, 0.±1,
0°0) and a signal that violates the bipolar violation law (in this column, 0.+1.+1,0 and 0,-
1. -1.0 and O, +1, O, +1 and 0. -1.0
゜-1) is corrected and generates one word for the specific turn detection.

On the other hand, the error polarity detector 2-5 detects the polarity of the input signal at the timing time.

FIG. 3(c) shows the output of the error polarity detector 2-4.

The iP turn detection signal is output to each tap of the digital filter and ANDed with the error polarity signal. The tap coefficient counter 2-6 counts up or down depending on the result of ANDing the error polarity signal and the turn detection signal. Tap coefficient counter 2-
The precision of 6 is selected to be the same as the number of quantization bits of the D/A converter 2-7.

The correction signal is obtained by adding the logical product of the output of the delay device 2-10. The signal is converted into an analog signal by a low-pass filter 2-8, and the signal is band-limited by a low-pass filter 2-8. The band-limited correction signal is sent to the adder 2-9.
is added to the input signal containing distortion.

FIG. 4 shows the convergence process of the tap coefficients obtained by seven simulations of the system described above. In Figure 4, 4-
1 is the tag coefficient of the ■th tap, and 4-2 is the tap coefficient of the second tap. The horizontal axis 4-3 is the number of updates of the tap coefficients, the vertical axis 4-4 is the coefficient value, and the broken line 4-5 is the base point at which the tap coefficients of the isolator enter a convergence state. In this example, approximately 3
By updating the tap coefficients five times, a transition is made to the convergence state. When the equalizer enters the convergence state, each tap coefficient repeats increases and decreases at a constant value. Also, at this stage, the distorted wave components of the input signal are mostly corrected.
can reliably detect the specific/mother turn. Convergence determination of the tap coefficients is performed by counting increases and decreases of a constant value in the convergence process of the tap coefficients, and generating a coefficient convergence signal when a predetermined value is reached. Therefore, by determining the convergence of the equalizer by considering both the Flaj coefficient convergence signal and the nosoturn detection signal, it is possible to reliably determine the convergence state of the equalizer.

In addition, in the above description, the case where the control operation of the automatic isolator is in the initial stage of system operation, that is, in the training stage has been described. On the other hand, even when the training phase has ended and the system has returned to normal operation, it may be necessary to further change the state of the isolator. This is the case when the characteristics of the system change over time. In the training state, the equalization operation needs to be performed as quickly as possible, whereas during normal operation, the equalization operation is required to be performed more slowly.

As a method to achieve this, the tap coefficients are updated only when a specific turn that is stochastically included in the signal is detected and the number of times it is detected reaches a preset number of times. You can achieve it. This is done by setting a guard time for updating the tap coefficients.

Next, the signal may contain noise, causing the equalization operation to appear to be completed only once. On the other hand, if the counter stops before reaching the number of up and down cycles that have been set in advance, the count up to that point will be reset to zero. Malfunctions caused by noise can be reduced.

(Effects of the Invention) As explained above, in the present invention, the convergence determination of the equalizer is performed by the AND of the convergence signal of the tap coefficient and the turn detection signal, which is resistant to noise and reliable. It is possible to determine the convergence of the equistopper.

In the above description, for simplicity, a case has been described in which 2±1.0 on the AMI sequence is used as the specific pattern, but the present invention is also applicable to any other code format or code sequence. Furthermore, it is clear that the present invention is also applicable to cases where the distortion component included in the signal is not caused by a branch line (bridged tap line).

The present invention is very effective in determining the convergence of an automatic equalizer for waveform distortion that equalizes the transmission distortion caused by reflection in Dinotal subscriber line transmission. The method for converging can be widely used.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a general example of a conventional decision feedback type automatic equalizer, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 shows the operation of the circuit shown in FIG. Explanatory diagram,
FIG. 4 is an explanatory diagram showing the convergence process of tap coefficients obtained by simulation of the circuit shown in FIG. 2. 2-1.2-2... Input/output terminal, 2-3... Identification circuit, 2-4... Error polarity determination circuit, 2-5... Pattern detector, 2-6... tap coefficient update counter,
2-7... Color converter, 2-8... Ronos filter, 3-1... Time axis, 3-2... Waveform amplitude, 3-3
...Input waveform, 3-4...m different level, 4-1.
4-2...Tap coefficient, 4-3 Coefficient update count. l Epiphytic growth of sea urchins in 1982 q,! l Leopard Application No. 033743
No. 2 Name of the invention Convergence judgment method for Sirinot tap stopper: Relationship with the supplementary case Patent application Person I J.
Location (〒] +) 5) Toranomon l]-, Minato-ku, Tokyo
No. 12 Address (〒105) 1-7-12-5 Toranomon, Minato-ku, Tokyo 7-J Elephant in Toriichi "Figure 1" and "Figure 2" in the drawing (contents of j Valley 011-) As shown in the attached sheet, the mouth surface "'硲10..l隨hi" 2 pieces of foil 1. Figure 1 of the attack.

Claims (1)

[Claims] A convergence determination method for a decision feedback automatic equalizer consisting of a digital signal identification circuit, a digital filter for generating a correction signal, and a control circuit for controlling tag coefficients of the digital filter. It has a pattern detection circuit and a control circuit that performs the tap coefficient control only when a specific pattern is detected, and the tap coefficient control circuit 1 is composed of an up/down counter and a flip/flip circuit, Alas,
When two conditions are satisfied: the number of <υ returns of pull-down reaches a set value and the specific pattern detection circuit is outputting, it is determined that the equalizer has converged, and a determination output is generated. A method for determining convergence of a 7-nod tap equalizer.