JP5160344B2 - Predistorter - Google Patents

Description

  The present invention relates to a predistorter for adding a distortion compensation value to an input signal in advance in order to compensate for distortion of an output signal from a compensated circuit such as a signal amplifier.

Conventionally, as a memory effect countermeasure distortion compensation technique of an amplifier, a method based on a Volterra series (see, for example, Patent Document 1 and Patent Document 2), a method based on a memory polynomial (for example, There is a method for Doherty amplifier (for example, see Patent Document 4).
JP 2004-320598 A JP 2007-282066 A JP 2004-320329 A JP 2007-243549 A JP 2006-093947 A Toshio Nojima and Yasuo Yamao, “Radio Circuit Technology for Mobile Communications”, p. 61, IEICE, 2007

  In Patent Document 1 and Patent Document 2, a coefficient of a polynomial subjected to Volterra series expansion is estimated, and an inverse distortion characteristic (distortion compensation characteristic) generated by Volterra series expansion using the coefficient is used for a predistorter. In the memory effect countermeasure distortion compensation technique based on Volterra series expansion, the degree of the polynomial is sufficiently large, and sufficient distortion compensation can be performed when an appropriate term is selected. However, in the method based on the Volterra series, the number of terms increases even if the order is small, so that the calculation time for estimating the coefficient becomes long. Further, the method based on the Volterra series has a problem that sufficient distortion compensation cannot be performed unless an appropriate term is selected and unnecessary unnecessary terms are deleted. Furthermore, although the method based on the Volterra series can perform ideal distortion compensation if an appropriate term can be selected from a polynomial, there is also a problem in determining whether an appropriate term should be selected.

  In other words, the Volterra series expansion used in the distortion compensation method based on the Volterra series does not model the distortion characteristics of the amplifier (or distortion compensation characteristics that are the inverse characteristics of the distortion characteristics), but simply to the amplifier. It is only an expression expressing all combinations of input signals with different sampling times. Such a distortion compensation method based on the Volterra series has a large number of terms, so the amount of calculation required for coefficient estimation is enormous, and as a result, it takes a long time to update the coefficient estimation value. There was a problem of not being able to follow the fluctuations of Therefore, it is not realistic to obtain all the coefficients of the Volterra series. For the purpose of calculating the coefficients with realistic calculation amount and calculation time, a memory polynomial that models an amplifier instead of the Volterra series has been proposed. Yes.

  On the other hand, in Patent Document 3, a coefficient of a polynomial called a memory polynomial is estimated, and a distortion compensation value generated by the memory polynomial using the coefficient is used for a predistorter. Here, the memory polynomial is a polynomial obtained by adding a distortion compensation polynomial defined by a past input signal to a distortion compensation polynomial obtained by modeling a distortion compensation value of a conventional amplifier that does not take a memory effect countermeasure into consideration. This memory polynomial has a smaller number of terms than the aforementioned Volterra series when the order of the polynomial is the same, and the amount of calculation can be greatly reduced. However, the method based on the memory polynomial is not sufficient in the amount of distortion compensation compared with the memory effect countermeasure distortion compensation technique based on the Volterra series, and there is a problem in compensation accuracy.

  The method for the Doherty amplifier is a memory effect countermeasure distortion compensation technique using a model specialized for the Doherty amplifier. In addition to the lookup table used in the conventional distortion compensation, a synthesis ratio lookup table is provided. This is necessary, and since it is necessary to sequentially estimate the characteristics of the element amplifiers constituting the Doherty amplifier and the characteristics of the synthesis ratio from the input / output signals, there is a problem that convergence is slow.

  Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide a predistorter that can calculate a distortion compensation value with a small amount of calculation and has high distortion compensation accuracy.

  In order to achieve the above object, the predistorter according to the present invention appropriately models a compensated circuit and compensates for distortion based on a distortion compensation polynomial calculated therefrom.

  Specifically, the predistorter according to the present invention stores a distortion compensation polynomial expressed by Equation 1 or Equation 2, generates a predistortion compensation signal in which an input signal is distortion-compensated by the distortion compensation polynomial, A distortion compensation unit for outputting to the compensation circuit is provided.

  Since the predistorter according to the present invention appropriately models the compensated circuit and estimates the distortion compensation polynomial from the distortion characteristics of the model, the distortion compensation value can be calculated with a smaller amount of calculation than the method using the Volterra series, Distortion compensation can be performed with the same accuracy as the method using the Volterra series.

  Therefore, the predistorter according to the present invention can calculate the distortion compensation value with a small amount of calculation, and can increase the accuracy of the distortion compensation.

  The predistorter according to the present invention receives the input signal and the output signal of the compensated circuit, calculates a coefficient of the distortion compensation polynomial stored in the distortion compensation unit, and applies the polynomial coefficient to the distortion compensation polynomial A calculation unit is further provided.

  Therefore, in the predistorter according to the present invention, the polynomial coefficient calculation unit calculates the coefficient of the distortion compensation polynomial from the input signal and the output signal, and applies it to the distortion compensation polynomial of the distortion compensation unit. Therefore, the distortion compensation value can be calculated with a small amount of calculation, and the accuracy of distortion compensation can be increased.

  The polynomial coefficient calculation unit of the predistorter according to the present invention may calculate a coefficient of the distortion compensation polynomial from the input signal and the output signal by a least square method.

  In order to accurately obtain the coefficients of the distortion compensation polynomial at one time, a predistortion compensation signal that covers all of the assumed amplitude (or power) of the input signal, an input signal, and an output corresponding to the input signal It is necessary to calculate the coefficient of the distortion compensation polynomial using the pair with the signal using the least square method, and the calculation amount becomes enormous. That is, in order to accurately calculate the coefficient of the distortion compensation polynomial, it is necessary to use a very large number of sampled input signals and output signals. Further, the coefficient of the distortion compensation polynomial of the amplifying device also changes with temperature, humidity, and aging.

  Therefore, the polynomial coefficient calculation unit of the predistorter according to the present invention multiplies the input signal by a value obtained by substituting the input signal into the distortion compensation polynomial to generate an input replica signal, and the distortion A value obtained by substituting the output signal into the compensation polynomial and the output signal are multiplied to generate an output replica signal, and the distortion compensation polynomial is set such that an error between the input replica signal and the output replica signal is minimized. It is preferable to update the coefficient.

  Therefore, the predistorter according to the present invention can update the coefficient of the distortion compensation polynomial with the passage of time while compensating for the distortion of the compensated circuit.

  The present invention can calculate a distortion compensation value with a small amount of calculation, and can provide a predistorter with high distortion compensation accuracy.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiment described below is an example of the configuration of the present invention, and the present invention is not limited to the following embodiment. In the present specification and drawings, the same reference numerals denote the same components.

  FIG. 2 is a block diagram illustrating the configuration of the predistorter 301 of this embodiment. The predistorter 301 receives the distortion compensation unit 11 that performs distortion compensation of the input signal X with a distortion compensation value and outputs the distortion to the compensated circuit 401, the input signal X and the output signal Y of the compensated circuit 401, and a distortion compensation polynomial. And a polynomial coefficient calculation unit 13 for calculating the coefficient. For example, the compensated circuit 401 is an amplifier. In the following description, the compensated circuit 401 is described as an amplifier.

  FIG. 3 is a block diagram illustrating the distortion compensation unit 11 of the predistorter 301. The distortion compensation unit 11 stores a distortion compensation polynomial that can be expressed by Equation 1 or Equation 2. The distortion compensation unit 11 generates a predistortion compensation signal A obtained by compensating the distortion of the input signal X with the distortion compensation polynomial, and outputs the signal to the compensated circuit 401.

  The polynomial coefficient calculation unit 13 calculates a coefficient of a distortion compensation polynomial by a coefficient calculation method described later. Further, the polynomial coefficient calculation unit 13 outputs the calculated coefficient to the distortion compensation unit 11. The distortion compensator 11 generates a predistortion compensation signal A using this coefficient. Further, the distortion compensation unit 11 periodically updates the coefficient of the distortion compensation polynomial.

とおく。ここで、ｊは要素増幅器５１３の番号であり、Ｊは要素増幅器５１３の全個数である。また、ｄは入力信号の正規化先行時間、または正規化遅延時間を表し、Ｄ１_ｊはｊ番目の要素増幅器の最大正規化先行時間、Ｄ２_ｊはｊ番目の要素増幅器の最大正規化遅延時間、ｋは次数であり、Ｋ_ｊはｊ番目の要素増幅器の歪成分の最大次数を表す。 (Modeling of amplifier circuit and estimation of distortion characteristics)
First, the distortion characteristics of the amplifier circuit are modeled. FIG. 1 is a diagram modeling an amplifier circuit including a plurality of amplifiers. Input signal X is input and output signal Y is output. Here, a discrete time signal obtained by sampling the input signal X with a period T _s is x (nT _s ), and a discrete time signal obtained by sampling the output signal Y with a period T _s is y (nT _s ) to simplify the notation. Therefore, each is represented by x (n) and y (n). Also, x (n) and y (n) are complex signals having a real component and an imaginary component, and multiplication and addition for x (n) and y (n) indicate complex multiplication and complex addition, respectively. . Each of the distortion characteristics of the element amplifier 513 constituting the amplifier circuit

far. Here, j is the number of the element amplifier 513, and J is the total number of element amplifiers 513. Further, d represents a normalization leading time of the input signal, or a normalization delay time, D1 _j is a maximum normalization leading time of the _jth element amplifier, D2 _j is a maximum normalization delay time of the jth element amplifier, k is the order, and K _j represents the maximum order of the distortion component of the j-th element amplifier.

とおく。ここで、ｒは入力信号の正規化先行時間、または正規化遅延時間を表し、Ｒ１_ｊはｊ番目の要素増幅器に対する合成する比率において関係する入力信号の最大正規化先行時間、Ｒ２_ｊはｊ番目の要素増幅器に対する合成する比率において関係する入力信号の最大正規化遅延時間、ｌは次数であり、Ｌ_ｊはｊ番目の要素増幅器に対する合成する比率において関係する入力信号の最大次数から１次高い次数を表す。 The ratio of combining the element amplifiers 513 is a function (combining polynomial) 512 of the amplitude value of the input signal X.

far. Here, r represents the normalization leading time of the input signal, or the normalization delay time, R1 _j is the maximum normalization leading time of the input signal related in the combining ratio with respect to the jth element amplifier, and R2 _j is the jth The maximum normalized delay time of the input signal related in the combining ratio with respect to the element amplifier of L, l is the order, and L _j is the first order higher than the maximum order of the input signal related in the ratio of combining with the j-th element amplifier. Represents.

At this time, the output of the amplifier circuit is

Here, Formula 5 is arranged. First, the same terms for different amplifiers (different j)

Next, if the term of r = d of Formula 6 is put together,

Equation 7 is

further,

That is, in order to estimate the distortion characteristic of an amplifier circuit that can be modeled as shown in FIG. 1, complex coefficients h ′ _{d, k} , h ′ _{r, d, l} , and h ′ _{r, d, l, k} are calculated. It ’s fine. The coefficients h ′ _{d, k} , h ′ _{r, d, l} , and h ′ _{r, d, l, k} are calculated by applying the input signal X and the output signal Y to the model of Equation 9 and using the least squares method. May be used.

For example, in Equation 5, J = 2, R1 = 40, R2 = 40, D1 = 50, D2 = 50, L = 3, K = 5 (here, R1 _j , R2 _j , D1 _j , D2 _j , L _j , and K _j are different from each other even if j is the same number, and are abbreviated as R1, R2, D1, D2, L, and K, respectively.) The number is
2 × (2 × 40 + 1) × (2 × 50 + 1) × 3 × 5 = 245430
In Equation 9, which rearranges Equation 5, the number of coefficients is
(2 × 50 + 1) × (5 + 3-1) + (2 × 50 + 1) × (2 × 40) × 2
+ (2 × 50 + 1) × (2 × 40) × 2 × 4 = 81507
It becomes street.

通りである。 On the other hand, in the Volterra series having the same delay number 50, leading number 50, and polynomial order 5,

Street.

Therefore, the number of coefficients obtained in the stage of Equation 5 is compared to the Volterra series.
245430/101340875 ≒ 1/413
It becomes. Furthermore, in the case of Equation 9, the number of coefficients to be obtained is compared to the Volterra series.
81507/101340875 ≒ 1/1243
Thus, if the method of the present invention is used, the characteristic of the amplifier can be calculated by calculating the coefficient of about 1/243 of the Volterra series. The amount of calculation for solving the simultaneous equations used to calculate the coefficients is proportional to the cube of the number of terms, so the amount of calculation is compared to the case where the Volterra series is used.
(81507/101340875) ³ ≒ 1/1922070104
Reduced to

となり、線形であるのが理想的である。但し、Ｇは増幅装置の利得を表す実数定数である。ここでは、以降の議論を簡単にする目的で、Ｇ＝１とおくこととする。 (Distortion compensation method)
Next, a distortion compensation method for the amplifier circuit based on the model of FIG. 1 will be described. The relationship between the input and output signals of the entire amplifier is

Ideally, it should be linear. Here, G is a real constant representing the gain of the amplifier. Here, G = 1 is set for the purpose of simplifying the following discussion.

However, in an actual amplifying device, when the amplitude (or power) of the input signal increases, the relationship between the input and output signals is not linear but nonlinear as expressed by Equation 5 or Equation 9. In order to compensate the distortion of the amplifier circuit based on the model of FIG. 1, a distortion compensation polynomial in which the input signal X and the output signal Y are interchanged in Equation 5 or Equation 9, which is a distortion characteristic polynomial expressing the model of FIG.

Similar to the arrangement from Equation 5 to Equation 9,

The complex coefficients w ′ _{d, k} , w ′ _{r, d, l} , and w ′ _{r, d, l, k} in Equation 13 are estimated using the least square method, and the input signal X is compensated according to the distortion compensation polynomial. That's fine. In calculating the coefficients w ′ _{d, k} , w ′ _{r, d, l} and w ′ _{r, d, l, k} by the least square method, the coefficients w ′ _{d, k} , w ′ _{r, d, l} , And a set of x (n) and y (n) obtained by sampling more input signals X and output signals Y than the total number of w ′ _{r, d, l, k} .

  That is, for the purpose of linearizing the input / output relationship of the amplifier using the coefficient of Equation 13 obtained using the least square method, the nonlinear distortion characteristic (distortion value) of the amplifier provided in the preceding stage of the amplifier. In a predistorter 301 that generates a reverse distortion characteristic (distortion compensation characteristic) for the input signal X, a predistortion compensation signal A in which a distortion compensation value is given in advance to the input signal X is generated and input to an amplifying apparatus. At this time, in order to obtain a predistortion compensation signal A in which the output signal Y of the amplification device becomes y (n) = x (n), the predistorter 301 uses the distortion compensation polynomial expressed by Equation 1 as the input signal X A distortion compensation value is given in advance to generate a predistortion compensation signal A and input to the amplifying apparatus.

A predistortion compensation signal A that gives an inverse distortion characteristic (distortion compensation characteristic) that compensates for a non-linear distortion given by a mathematical expression 5 or 9, which is a distortion characteristic polynomial expressing the model of FIG. In order to obtain (n), the coefficient w ′ _{j, r, d, l, k} , which satisfies the relationship of Expression 12 or Expression 13 in which x (n) and y (n) are replaced in Expression 5 or 9, Alternatively, the coefficients w ′ _{d, k} , w ′ _{r, d, l} , and w ′ _{r, d, l, k} may be obtained.

ここで、Ｔは行列の転置を表す。 (Calculation method of distortion compensation polynomial coefficients)
Here, a method for obtaining the coefficient of the distortion compensation polynomial using Expression 13 will be described. However, here, for simplicity of expression, Da = 0, R1 = 0, and D1 = 0. A coefficient vector in which all the coefficients w ′ _{d, k} , w ′ _{r, d, l} and w ′ _{r, d, l, k} are arranged is set as in Expression 14.

Here, T represents transposition of the matrix.

但し、

歪補償多項式の係数を推定する際に使用する異なるｎに対する数式１３の個数はＮ（Ｎ≧Ｑ＋１）であり、数式１３をＮ個まとめると数式１５は数式１７の連立方程式となる。

Here, in order to obtain the coefficients w ₀ , w ₁ ,..., W _Q of the distortion compensation polynomial in Expression 13, Q + 1 or more Expressions 13 in different n are required. Here, when Expression 13 is expressed as a matrix, Expression 15 is obtained.

However,

The number of Equations 13 for different n used for estimating the coefficient of the distortion compensation polynomial is N (N ≧ Q + 1), and when Equation 13 is put together, Equation 15 becomes the simultaneous equations of Equation 17.

但し、Ｈは表列の複素共役転置を表す。このようにして得られた係数ｗ_０、ｗ_１、・・・、ｗ_Ｑをａ（ｎ）に適用し、ｘ（ｎ）に応じた歪補償値を算出すれば歪補償ができる。 The coefficients w ₀ , w ₁ ,..., W _Q are obtained by solving the simultaneous equations of Expression 17 or Expression 19. In order to solve the simultaneous equations of Expression 17 or 19, the sweeping method may be used, or Expression 20 may be used by using the least square method.

However, H represents the complex conjugate transpose of a table row. If the coefficients w ₀ , w ₁ ,..., W _Q obtained in this way are applied to a (n) and a distortion compensation value corresponding to x (n) is calculated, distortion compensation can be performed.

  The distortion compensation unit 11 receives the coefficient calculated by the polynomial coefficient calculation unit 13 and applies it to the distortion compensation polynomial. The predistorter 301 generates a predistortion compensation signal A from the input signal X using a distortion compensation polynomial to which this coefficient is applied. Since the distortion compensation polynomial stored in the distortion compensation unit 11 is obtained by appropriately modeling the compensated circuit 401 and obtained from the distortion characteristics of the model, the predistorter 301 can calculate the distortion compensation value with a small amount of calculation. The accuracy of distortion compensation can be increased.

(Update algorithm)
Next, an update algorithm for updating the coefficient of the distortion compensation polynomial over time will be described.

  When updating the coefficient of the distortion compensation polynomial while compensating for distortion of the amplifier circuit, the signal input to the amplifier circuit is not x (n), but y (n), which is the output signal Y of the amplifier circuit, is changed to x (n). This is a predistortion compensation signal A that can be expressed by Formula 2 in which distortion compensation is performed so as to be close, that is, a ′ (n). Formula 2 plays the role of Formula 1 described so far when performing distortion compensation while updating the coefficient of the distortion compensation polynomial.

も成立する。 At this time, if distortion compensation of the amplifier circuit is accurately performed, y (n) = x (n) is established.

Also holds.

とおくと、誤差

が得られる。この誤差ｅ（ｎ）が零になるように歪補償多項式の係数を更新する。 If the distortion compensation of the amplifier circuit is not sufficient, y (n) = x (n) is not satisfied,

Error

Is obtained. The coefficient of the distortion compensation polynomial is updated so that this error e (n) becomes zero.

That is, the coefficients w ′ _{d, k} (i), w ′ _{r, d, l} (i), and w ′ _r satisfying the condition y (n) = x (n) that makes the input / output relationship of the entire amplifier circuit linear. _{, D, l, k} (i) satisfies Expression 13. Here, the coefficients w ′ _{d, k} , w ′ _{r, d, l} , and w ′ _{r, d, l, k} are all arranged as w ₀ , w _{1 ,.} because represented, i-th coefficient _w 0 obtained _{updates, w 1, ···,} w _Q each _{w 0 (i), w 1} (i), ···, w Q (i) and In other words, the coefficients w ₀ (i), w ₁ (i),..., W _Q (i) satisfying the condition y (n) = x (n) that makes the input / output relationship of the entire amplifier circuit linear 13 is satisfied. Accordingly, w ₀ (i), w ₁ (i),..., W _Q (i) may be obtained so that a ′ (n) and a ″ (n) match.

とおく。但し、ｉ≧０である。なお、数式２４の係数ｗ（ｉ）の初期値としては、ｗ（０）＝（１，０，…，０）^Ｔを用いるか、同じ被補償部に対して十分な取り込み点数Ｎのときに数式１７、数式１９、または数式２０を用いて予め求めておいた係数ｗをｗ（０）＝ｗとして用いるか、同じ被補償部に対して十分に更新回数を確保して予め求めておいた係数の行列ｗ（∞）をｗ（０）＝ｗ（∞）として用いればよい。 Here, the update of w ₀ (i), w ₁ (i),..., W _Q (i) will be described.

far. However, i ≧ 0. As the initial value of the coefficient w (i) in Expression 24, w (0) = (1, 0,..., 0) ^T is used, or when the number of capture points N is sufficient for the same compensated portion. The coefficient w obtained in advance using Equation 17, Equation 19, or Equation 20 is used as w (0) = w, or is obtained in advance by ensuring a sufficient number of updates for the same compensated portion. The coefficient matrix w (∞) may be used as w (0) = w (∞).

また、行ｘ_ｎ（ｉ）を構成するベクトルｘ１_ｎ（ｉ）、ｘ２_ｎ（ｉ）およびｘ３_ｎ（ｉ）はそれぞれ数式２６、数式２７及び数式２８で表せる。

また、行ｙ_ｎ（ｉ）を構成するベクトルｙ１_ｎ（ｉ）、ｙ２_ｎ（ｉ）およびｙ３_ｎ（ｉ）はそれぞれ数式３０、数式３１及び数式３２で表せる。

但し、Ｎは歪補償値を推定する際に使用する入出力信号の取り込み点数、Ｍは次の多項式係数の更新時に用いる入出力信号の取り込み開始までのサンプリング間隔数である。 Here, if placed with Da = 0, R1 = 0, D1 = 0 for simplicity of _{representation, w 0 (i), w} 1 (i), the input signal X corresponding to the ··· _w Q (i) And the matrix of the output signal Y can be expressed as Equation 25 and Equation 29, respectively.

Further, the vectors x1 _n (i), x2 _n (i), and x3 _n (i) constituting the row x _n (i) can be expressed by Expression 26, Expression 27, and Expression 28, respectively.

Further, the vectors y1 _n (i), y2 _n (i), and y3 _n (i) constituting the row y _n (i) can be expressed by Expression 30, Expression 31, and Expression 32, respectively.

Here, N is the number of input / output signal capture points used when estimating the distortion compensation value, and M is the number of sampling intervals until the start of input / output signal capture used when updating the next polynomial coefficient.

とおくと、連立方程式

によりｗ（ｉ）を更新すればよい。但し、μは０＜μ≦１．０を満たす。 Also,

Then, simultaneous equations

The w (i) may be updated by However, μ satisfies 0 <μ ≦ 1.0.

  Specifically, the polynomial coefficient calculation unit 13 generates an input replica signal in which the predistortion compensation signal A is estimated by multiplying the input signal X by a value obtained by substituting the input signal X into the distortion compensation polynomial. The polynomial coefficient calculation unit 13 generates an output replica signal in which the predistortion compensation signal A is estimated by multiplying the output signal Y by a value obtained by substituting the output signal Y into the distortion compensation polynomial. The coefficient of the distortion compensation polynomial is updated so that the error between the input replica signal and the output replica signal is minimized.

  The predistorter 301 in FIG. 2 calculates a ′ (i (N + M) + n) of the predistortion signal A in the distortion compensation unit 11 using w (i) calculated in the distortion compensation coefficient calculation unit 13. To the compensated circuit 401. Since the distortion-compensated predistortion compensation signal A is input, the compensated circuit 401 obtains y (i (N + M) + n) of the output signal Y.

Here, the calculation amount necessary for the distortion compensation method is compared between the present invention and the conventional method. For example, in Equation 13, the number of coefficients when J = 2, R1 = 40, R2 = 40, D1 = 50, D2 = 50, L = 3, and K = 5 is the same as in the distortion estimation.
(2 × 50 + 1) × (5 + 3-1) + (2 × 50 + 1) × (2 × 40) × 2
+ (2 × 50 + 1) × (2 × 40) × 2 × 4 = 81507
It becomes street.

通りである。 On the other hand, in the Volterra series having the same delay number 50, leading number 50, and polynomial order 5,

Street.

Therefore, in Equation 13, the number of coefficients to be calculated is 81570 / 101340875≈ 1/1243 compared to the Volterra series.
Thus, if the method of the present invention is used, the characteristic of the amplifier can be calculated by calculating the coefficient of about 1/243 of the Volterra series. Since the amount of calculation of the simultaneous equations used when obtaining the coefficients is proportional to the cube of the number of terms, the amount of calculation is (81507/1013875) ³ ≈ 1/1192070104 compared to the case where the Volterra series is used.
Reduced to

(Example)
FIG. 4 shows the experimental results of distortion compensation of a class E Doherty amplifier circuit as the compensated circuit 401. In the graph of FIG. 4, the horizontal axis indicates the frequency [MHz], and the vertical axis indicates the power logarithmically. FIG. 4A shows the spectrum of the output signal Y of the amplifier circuit without distortion compensation. FIG. 4B shows the spectrum of the output signal Y of the amplifier circuit that has been subjected to distortion compensation by the predistorter of the distortion compensation method of Patent Document 5. FIG. 4C shows a spectrum of the output signal Y of the amplifier whose distortion is compensated by the predistorter 301 of FIG.

  In FIG. 4, each of the four portions with high power located at the center of the horizontal axis is one signal carrier wave of 3GPP / W-CDMA, which is an international standard for mobile phones, and in FIG. It can be seen that a CDMA signal carrier is input to the amplifier.

  As an evaluation value of the amplifying device, the adjacent channel leakage power ratio, which is the ratio of the average power in the signal carrier band and the average power in a certain frequency range centered around ± 5 MHz and ± 10 MHz from the center frequency of the signal carrier. (Adjacent Channel Leakage Power Ratio: ACLR) (for example, see Non-Patent Document 1). For example, in W-CDMA which is a cellular phone standard, an average power of a signal carrier bandwidth of 3.84 MHz, an average of 3.84 MHz band centered on a frequency separated by ± 5 MHz and ± 10 MHz from the center frequency of the signal carrier. ACLR is defined by the power ratio. In W-CDMA, ACLRs that are ± 5 MHz and ± 10 MHz away from the center frequency of the signal carrier are determined to be −45 dB or less and −50 dB or less, respectively, with respect to the mobile phone base station. Here, the effect of the amplification device and the distortion compensation method will be described using this ACLR.

  In FIG. 4A, which is the output result of the amplifier circuit when there is no distortion compensation, ACLRs at frequencies that are ± 5 MHz and ± 10 MHz away from the center frequency of the signal carrier are −35.94 dB and −37.27 dB, respectively. . In FIG. 4 (b), which is a result of distortion compensation of the amplifying apparatus of FIG. 4 (a) by the distortion compensation method of Patent Document 5 that cannot compensate for the memory effect, frequencies separated by ± 5MHz and ± 10MHz from the center frequency of the signal carrier. The ACLRs in the graph are −44.92 dB and −44.67 dB, respectively, and the improvements compared to FIG. 4A remain at 8.98 dB and 7.40 dB, respectively. On the other hand, in FIG. 4 (c), which is the result of distortion compensation of the amplifying device of FIG. 4 (a) by the distortion compensation method of the present invention that can compensate for the memory effect, it is ± 5MHz and ± 10MHz away from the center frequency of the signal carrier. The ACLRs at the frequencies are −54.86 dB and −54.94 dB, respectively, and the improvements compared to FIG. 4A are increased to 18.92 dB and 17.67 dB, respectively. Therefore, the distortion compensation method of the present invention can perform distortion compensation with higher accuracy than the conventional distortion compensation method that cannot compensate for the memory effect.

  The predistorter according to the present invention can be applied to a power amplifier of a radio transmitter used in a mobile communication base station or the like.

It is the figure which modeled the amplifier circuit comprised with the some amplifier. It is a block diagram explaining the structure of the predistorter which concerns on this invention. It is a block diagram explaining the distortion compensation part of the predistorter concerning this invention. It is a figure explaining the experimental result which carried out distortion compensation of the class E Doherty amplifier circuit as a compensated circuit. (A) is the spectrum of the output signal Y of the amplifier circuit without distortion compensation. (B) is a spectrum of the output signal Y of the amplifier circuit that has been subjected to distortion compensation by the predistorter of the conventional distortion compensation method. (C) is a spectrum of the output signal Y of the amplifier subjected to distortion compensation by the predistorter according to the present invention.

Explanation of symbols

301: Predistorter 11: Distortion compensation unit 13: Polynomial coefficient calculation unit 401: Compensated circuit 511: Delay element 512-j: Amplitude value function (j is a natural number)
513: Element amplifier 514: Multiplier 515: Adder X: Input signal Y: Output signal A: Predistortion compensation signal

Claims (4)

Stores the distortion compensation polynomial represented by Equation 1 or Equation 2, and generates a predistortion compensation signal distortion compensation input signal in the distortion compensation polynomial predistorter including a distortion compensator that outputs to the compensation circuit There,
The distortion compensation polynomial represents the compensated circuit,
A plurality of element amplifiers represented by Equation 3,
The same number as the element amplifier, and the amplitude value function expressed by Formula 4;
A multiplier for multiplying the output of the element function by the output of the amplitude value function corresponding to the element function;
An adder for adding all the outputs of the multiplier;
A predistorter, wherein the complex coefficient of the distortion compensation polynomial is determined by a coefficient ν of Formula 3 and a coefficient f of Formula 4 .

Here, j is the number of the element amplifier, and J is the total number of element amplifiers. Further, d represents a normalization leading time of the input signal, or a normalization delay time, D1 _j is a maximum normalization leading time of the _jth element amplifier , D2 _j is a maximum normalization delay time of the jth element amplifier, k is the order, and K _j represents the maximum order of the distortion component of the j-th element amplifier. ν _{j, d, k} are coefficients.

r represents the normalized lead time of the input signal, or normalized delay time, R1 _j is the maximum normalized lead time of the input signal related in the combining ratio with respect to the jth element amplifier, and R2 _j is the jth element amplifier The maximum normalized delay time of the input signal related in the combining ratio with respect to, l is the order, and L _j represents the order higher than the maximum order of the input signal related in the combining ratio for the j-th element amplifier. f _{j, r, l} are coefficients.

  2. The apparatus according to claim 1, further comprising a polynomial coefficient calculation unit that receives the input signal and the output signal of the compensated circuit, calculates a coefficient of the distortion compensation polynomial stored in the distortion compensation unit, and applies the coefficient to the distortion compensation polynomial. The predistorter described.   The predistorter according to claim 2, wherein the polynomial coefficient calculation unit calculates a coefficient of the distortion compensation polynomial from the input signal and the output signal by a least square method.   The polynomial coefficient calculation unit generates an input replica signal by multiplying the input signal by a value obtained by substituting an input signal into the distortion compensation polynomial, and obtained by substituting an output signal into the distortion compensation polynomial. A value is multiplied by the output signal to generate an output replica signal, and a coefficient of the distortion compensation polynomial is updated so that an error between the input replica signal and the output replica signal is minimized. Item 4. The predistorter according to Item 2 or 3.

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