JPS5813036A - Nonlinear distortion removing circuit - Google Patents

Abstract

PURPOSE:To hold a perturbing signal at a low level and to prevent the disturbance of a received signal, by detecting the perturbing signal on the basis of its correlation with a perturbation effect, when performing parameter control in a perturbing method in a nonlinear compensating circuit. CONSTITUTION:The input and output characteristics of the nonlinear distortion correcting circuit 1 composed of an odd-function input and output characteristic circuit 10, a variable phase shifter 11, a variable attenuator 12, and an adder 13 are inverse to those of a nonlinear element 4, and the phase shifter 11 is already set to the best conditions. As an input signal passes through the element 4, the degree of deformation at this time is extracted at a part through a band- pass filter 20 and a full-wave rectifying circuit 21, and is decreased by selecting the value of the attenuator 12 adequately. When a switch 38 is placed at a side (b), the extent of perturbation varies linearly with the mean value of the deformation of the input signal and when the deformation of the input signal is eliminated, the extent of the perturbation is reduced, preventing the signal from being disturbed carelessly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nonlinear distortion removal circuit, and particularly to a nonlinear distortion removal circuit using a traveling wave tube amplifier (hereinafter abbreviated as TWT).

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As you can see, multi-level quadrature amplitude modulation (QAN) will be used.One problem at this time is the nonlinear distortion of the transmission amplifier (TWT), and this distortion distorts the QAM signal. It is characterized by a 0-width saturation characteristic (AM/AM conversion) where the signal is distorted, and a 0(x) characteristic (AM/PM conversion) with a phase rotation of the output corresponding to the input level X. Therefore, this type of distortion is It is generally possible to compensate to the extent of Kana 9 with a relatively simple circuit.

Now, if we consider the case where band limiting of the transmitted signal is not performed in front of the TWT, it is possible to separate the nonlinear effects from the effects of band limiting, so we can accurately observe this distortion on both the transmitting and receiving sides. can do.

Based on this idea, various preset type nonlinear distortion compensation circuits have been proposed in the past, but an automatic tracking type circuit that automatically guides the circuit to the most desirable operating state has been proposed in a document published by the Communication Systems Study Group of the Institute of Electronics and Communication Engineers. C87J1-201
1.T by automatic tracking complex synthesis bridistorshin
The precedent can be seen in Study 1 of WT nonlinear compensation.

The present invention uses a perturbation method to control the parameters of a nonlinear compensation circuit, similar to those described in the previous literature.

However, the effect of perturbation is determined by the correlation between this and the perturbation signal]
[Detection] makes it possible to use very low-level perturbation signals, so that the above parameter control can be carried out without the perturbation signal disturbing the signals that should be received. be.

According to this invention, a nonlinear distortion correction circuit that passes an input signal through an odd function input/output characteristic circuit and a variable complex coefficient circuit and adds it to the input signal to generate a complex composite distortion characteristic is placed before or after the nonlinear element. 1. In a method for canceling nonlinear distortion, a change extraction circuit extracts a change from the original frequency characteristic of the input signal after passing through the nonlinear distortion correction circuit and the nonlinear element, and the variable complex coefficient an oscillator that perturbs the change extraction circuit, and a correlator that correlates the output of the change extraction circuit with the output of the oscillator;
; and], it is possible to obtain a nonlinear distortion removal circuit characterized in that the distortion of the nonlinear element is canceled out by the nonlinear distortion correction circuit.

Next, the present invention will be explained in detail with reference to seven drawings.

FIG. 1 shows a block diagram of a conventionally commonly used nonlinear distortion correction circuit, and FIG. 2 is an explanatory diagram of the operation of the circuit shown in FIG.

FIG. 1 shows an odd function input/output characteristic circuit 10 (for example, a cubic nonlinear element) and a variable phase shifter 1 constituting a variable complex coefficient circuit.
1. It consists of a variable attenuator 12 and an adder 13.

Let the input X to the input terminal 100 be the vector 200 in FIG. The output of variable attenuator 12 is vector 208 in FIG.
As shown in FIG. 204, 205 and 206. The relative length of the vector 208 to the vector 200 depends on the characteristic f(x) of the Hiroki function input/output characteristic circuit 10, but in general K
f(x)z (ax-)-bx”-)-cx”--・-
)a (b, cx0), the vector 208 will grow relatively as the input X becomes larger. Therefore, it increases in input/output range. Figure 3 shows the input/output 4I41k t yj of the circuit in Figure 1, and one song I.
i! A curve 301 indicates an amplitude characteristic, and a curve 302 indicates a phase i characteristic. This characteristic has the form of an inverse characteristic of the input/output characteristic of TWT.The problem is how to choose parameters α and φ to obtain an arbitrary TWT%
If we are to say whether we can approximate the inverse characteristics of gender, then it becomes K.

Now, for the input X, due to the nonlinear distortion of TWT] f(x)=X+W −I
Suppose that is output. This is a good approximation of the actual nonlinear distortion. Here da is =. , 6j is a complex number. Also, compared to the first term, the second term of foo is usually 1xl)Iv-1xl''-xl.

When λ is applied to the signal Xt-TWT, its output is as described above: f=X+!・IXII・X When this signal is passed through a nonlinear distortion correction circuit with the characteristic g(萄=X+ζ・1x:3・X (ξ=α・e), the output 0
is 1゜Co=X+111XILX+ξi(X+v lxlm-
x)x.

(X+1FIXl"・X)) zX+vlXI"-X+ξIXII-X=X+(亨+ξ
) IEI laziness・X E: c, −x== (Da + ξ month X 1 year old・X.

According to this formula, if Schiff = -ξ, then E = 0.

Therefore, let's rewrite ξ as follows.

, ξMida±ξ櫨ξ− is a parameter indicating how far ξ is currently deviating from its optimal value. ζ to ζ0・Lu in ω. When a perturbation of 1 is added, ξ=-da ± ξ纏+ξ. -8ゑnω,t.

Assuming that the degree of deformation of the input signal due to this shift is E, ζ becomes ξ4=Q or IE (411) in the vicinity.
- 1ElzlE, l±β・5inae@t (ξ−之0)
changes in the form of Here, IE61-β is a constant. Therefore, the IEI and the perturbation signal ζ, ·s1nω. Calculating the correlation value with t = ±ξ.・gi・β. From the above equation, which shows that the general polarity is the same as the polarity of the ξ reef, it can be seen that ξ can be controlled by increasing or decreasing it in the opposite direction to the polarity of the obtained correlation value. Therefore, since the integral for finding the general and the integral for control can be used in common, ξ can be controlled in the following manner.

The above is the principle of the present invention. FIG. 4 is an equivalent baseband block diagram of one embodiment of the present invention, and is a specific example of the principle of p1 ahead. The block 1 in FIG. 1 is a simplified version of the nonlinear distortion correction shown in FIG. This example is for simplicity.

It is assumed that the variable phase shifter 11 has already been optimally set, and the remaining variable attenuator 12 is controlled for the attenuator ξ. Block 4 is a nonlinear element such as a TWT. Block 2 is a change extraction circuit that detects the afE of deformation of the input signal. Since we are detecting out-of-band radiation generated by the nonlinear element 4 detected by the rectifier circuit 21, we set the value of the variable attenuator 12 of the nonlinear distortion correction circuit 1 appropriately. This out-of-band radiated power is reduced by selecting . 31 is the perturbation ζ・
・An oscillator that generates sinω·t, 33 is an integrator for control, and 34 is a polarity inversion circuit. The adder 32 is for adding a perturbation signal. O30 is a correlator for finding the correlation value R between the perturbation signal and the output of the change extraction circuit.
0 and an integrator 301. However, this integrator 301 may be omitted. In this embodiment, the loop switch 38 has two modes for each operation. First, when the switch 311 is turned to the (a) side, it operates according to the principle explained earlier. When it is turned to the o (') side, the perturbation amount ζ- changes in proportion to the average value of Ill. is given in the form of the attenuation amount J of the low-frequency F wave filter 36 and the attenuator 35, the multiplier 37: IIe, 1 ξ, any Ill. As a result, the control progresses and IEI→0
When , the amount of perturbation is correspondingly small,
This eliminates the possibility of inadvertently causing disturbance to the signal.

FIG. 5 is a professional diagram of another embodiment of the present invention, in which the nonlinear distortion correction circuit 1 corrects up to 5th order distortion, and the parameters to be controlled are those for 3rd order distortion. Variable attenuator 12, phase shifter 11. Variable attenuator 1 for fifth-order distortion
5. There are four phase shifters 16. Therefore, four of the same control circuits as the control circuit 3 shown in FIG. 4 are used. In other words, since the outputs of the four 09 change extraction circuits 2, 33/, 3#, and 3#, are used in common, the output signals of the oscillator 31 in the block 3 need to be made into four orthogonal functions. For example, (sin%
t, come, t, I in2@@t, C
GI@2%1) 1k ill, (11n%t.

5ln2as6t, 5ins*, t, 5tn4aslt
) etc.

Control in the same way: 1--Compensate for higher-order nonlinearity by increasing the number of paths 1 Automatically and easily
1. As explained above, according to the present invention, nonlinear distortion caused by TWT etc. can be automatically and accurately compensated using a high-order nonlinear compensation circuit.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional nonlinear distortion correction circuit, Fig. 2 is an explanatory diagram of the operation of the circuit shown in Fig. 1, Fig. 3 is an input/output characteristic diagram of the circuit shown in Fig. 1, FIG. S is a block diagram of an embodiment of the present invention. 1... Nonlinear distortion correction circuit, 2... Change extraction circuit, 3... Control circuit, 4...
TWT%30... Phase #i5 I Concave #53 Figure

Claims (1)

[Claims] A nonlinear distortion correction circuit that passes an input signal through an odd function input/output characteristic circuit and a variable complex coefficient circuit and adds it to the input signal to generate a complex composite distortion characteristic is placed before or after the nonlinear element to cancel out the nonlinear distortion. In the method, a change extraction circuit extracts a change from the original frequency characteristic of the previous input signal after passing through the nonlinear distortion correction circuit and the nonlinear element, and perturbs the variable complex coefficient. an oscillator; and a correlator that takes a correlation between the output of the change extraction circuit and the output of the oscillator, and the distortion of the nonlinear element is adjusted to the nonlinear 1. A nonlinear distortion removal circuit characterized in that the distortion is canceled by a distortion correction circuit.