JPS61285831A - Decision feedback type automatic equalizer - Google Patents

Abstract

PURPOSE:To equalize correctly an input pulse signal including a forward interference component independently of the quantity of backward interference component by eliminating the forward interference component from the signal obtained by eliminating the backward interference component of an input pulse signal by a decision feedback equalizer. CONSTITUTION:A pulse a1 with distorted waveform is fed to an input terminal. A discriminator 3 compares the output of an adder 2 with a threshold value at a timing 0 to decide whether '1' to '0'. The output pulse (b) of the discriminator 3 is subjected to the multiplication of coefficients C<(1)>, C<(2)> by multipliers 5-1, 5-2 via delay elements 4-1, 4-2 having a delay time T, becomes signals b1,b2, which are returned to the adder 2. Thus, the backward interference component is eliminated from the input pulse a1 by timing points T, 2T, 3T. The output of the adder 2 is retarded by a time equal to the basic period T of the input pulse by the delay element 7-1 and the result is fed to an adder 8. On the other hand, a multiplier 6-1 multiplies a coefficient C<(-1)> with the output pulse (b) of the discriminator 3 to form a signal b3. The adder 8 subtracts the forward interference component b3 from the input pulse signal extracted by the backward interference component.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a decision feedback type automatic equalizer, and more specifically, the present invention determines the level of an input pulse signal, performs certain processing on the determined signal, and processes the input pulse signal. The present invention relates to an equalizer that automatically obtains pulses of an equalized waveform by detecting a distortion component (interference waveform) of and subtracting it from an input pulse signal.

[Background of the invention]

When obtaining a reproduced pulse from a pulse signal whose waveform has been distorted by transmission, the five characteristics of the transmitter are equalized by a five equalizer, and then the decision feedback equalizer is used to eliminate interference at the time of pulse identification. Circuits that remove waveform components are known.

When the speed (baud rate) of the pulse signal increases, a so-called forward interference component occurs, in which the pulse signal does not become O at a point before the pulse period from the point of identification of the pulse signal.

A known method for removing this forward interference component is to place a transversal filter in front of a decision feedback equalizer, remove the forward interference component, and then use a decision feedback equalizer to remove the rear interference component. [Collection of lectures from the 1980 National Conference on IEICE Nα4
75 “Configuration of digital signal processing automatic equalization LSI J)
. However, since the above-mentioned equalizer first identifies a signal containing backward interference and then creates a pseudo forward interference component, if the backward interference component is large, the pulses may not be identified correctly. There is a problem that arises.

[Purpose of the invention]

Therefore, an object of the present invention is to realize an automatic equalizer that can correctly equalize an input pulse signal including a forward interference component, regardless of the magnitude of the backward interference component.

[Summary of the invention]

In order to achieve the above object, the present invention removes the forward interference component from a signal obtained by removing the backward interference component of the input pulse signal using a decision feedback equalizer. is not affected by the forward interference component due to the configuration of the decision feedback equalizer, and the front interference component is extracted from the signal excluding the rear interference component, so the front interference component is extracted from the signal excluding the rear interference component. The circumferential component of interference can be correctly removed.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of an automatic equalizer according to the present invention. FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in FIG. Note that this embodiment shows an example of the simplest configuration for simplicity of explanation.

A distorted waveform pulse containing a forward interference component and a backward interference component such as a□ is applied to the input terminal. These waveforms are ideally located at timing points n T (n=Oe
It is desirable that the interference component be 0 at ±T, 2T, -). This input signal a1 is subjected to an adder 2 from which a feedback signal (pseudo rear interference component), which will be described later, is subtracted.

The discriminator 3 compares the output of the adder with a threshold value at timing point O and determines '1' or 'OPI'. In addition.

When the input signal is a bipolar code, the polarity is further identified, but the description will be made assuming a unipolar case.

The output pulse b of the discriminator is applied to series-connected delay elements 4-1 and 4-2 having a delay time T. The output of each delay element 4-1 and 4-2 is outputted to a multiplier 5, respectively.
-1 and 5-2 are multiplied by coefficients CD), (), and (z), resulting in signals b□ and b2. These coefficients are determined so as to create a pseudo interference component at the identification timing point nT, as will be explained later. These pseudo-generated backward interference components are added to the adder 2 as a feedback signal 6 Therefore, 2 For example, when there are continuous input pulses of positive polarity, the input pulse a in FIG.
The process becomes like (frozen), and the timing is T.

The backward interference component is removed at 2T and 3T.

The output of the adder 2 is further delayed by a delay element 7-1 by a time equal to the fundamental period T of the input pulse, and then added to the adder 8. - The multiplier 6-1 multiplies the output pulse b of the discriminator 3 by a coefficient C (-1), which will be explained later,
Let it be signal b3. This b3 is a signal with a level equal to the forward interference component h0 at timing point -T of the input pulse.

The adder 8 subtracts the artificially created forward interference component b3 from the input pulse signal from which the backward interference component has been removed.

The second discrimination circuit 9 discriminates whether the input pulse signal is 1'' or ROII from the equalized waveform after removing the forward and backward interference components from the adder 8, and outputs the discrimination output pulse from the output terminal 10. Occur.

The adder circuit 11 uses the above-mentioned coefficients C'' and C(1).

Coefficient control circuit (not shown) that determines
This is to obtain the signal θ for driving the discriminator, that is, the error signal of the input/output signal of the discriminator.

Since these coefficient control circuits are generally known, their detailed configuration will be omitted, but in principle they are realized by a circuit that performs the calculation of the following equation. In other words, the level of the input pulse signal is
, when the level of the error signal is e and the update step width is Δ, c,, 1==c m+Δ・SGN (8-+-t)'
Xm+z+1 ”'(')C14,=C,+Δ・S
GN (am-2)" x, -, -1-j = (2).Here, SGN (
e) represents the polarity of the error signal e. i = −1 in the above formula
, j = 1, 2 is the embodiment shown in FIG. This is a formula for obtaining coefficients G (1) and C (2) for removing components.

FIG. 3 is a block diagram showing the structure of another embodiment of the automatic equalizer according to the present invention. This embodiment is effective when forward and backward interference needs to be considered over a long time slot, and in terms of configuration, there are more delay elements 4-1 to 4-k than in the embodiment shown in FIG. Except for the case where the delay time of the delay means 7 is long, this is substantially the same as in FIG. 1, and blocks having the same functions are given the same numbers.

〔Effect of the invention〕

As described above, according to the present invention, since the forward interference cancellation operation is performed using the signal after the backward interference cancellation,
It is possible to realize an automatic equalizer that can equalize forward interference even for inputs having backward interference of % or more. Also,
Since the filter coefficient control information is extracted from the equalization error extracted after the forward and backward interferences are removed, it is possible to prevent errors from spreading between the forward interference cancellation system and the backward interference cancellation system.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an automatic equalizer according to the present invention;
FIG. 2 is a waveform diagram for explaining the operation of the above embodiment, and FIG. 3 is a configuration diagram of another embodiment of the automatic equalizer according to the present invention. 1...Input terminal, 2,8.11...Adder, 3,9
... Discriminator, 4, 7... Delay element, 5, 6... Multiplier. Early 1st S-t Φ-2 2nd Suo Eco':l:l.

Claims (1)

[Claims] 1. A first adder that subtracts a first feedback signal from an input pulse signal, a first identification circuit that determines the output of the first adder, and the first identification circuit. a digital circuit that extracts the backward interference signal in the input pulse signal from the output of the circuit and generates the first feedback signal and the forward interference signal in the input pulse signal; and the output of the first adder is input to the digital circuit. a delay means for delaying the pulse signal by an integral multiple of the period of the pulse signal; a second adder for subtracting the forward interference signal from the output of the delay means; and an equalized output signal for determining the output of the second adder. A decision feedback type automatic equalizer configured to include a second discrimination circuit. 2. In the automatic equalizer described in item 1, the digital circuit includes a plurality of cascade-connected delay elements, a coefficient circuit that multiplies the input and output of each of the plurality of delay elements by a coefficient,
A decision feedback type automatic equalizer comprising means for controlling the coefficients based on a difference signal between the input and output of the second discrimination circuit.