JP2007189535A - Distortion compensation amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively compensate the nonlinear distortion of an A-D converter by saving an effort and time. <P>SOLUTION: An analog signal outputted from a power amplifying part 4 is supplied as a feedback signal FB to the A-D converter 7 and converted into a digital signal FB' and also supplied to an A-D correcting part 11. An adding part 14 of the A-D correcting part 11 eliminates nonlinear distortion caused by a nonlinear characteristic of the A-D converter 7 from the digital feedback signal FB' and the digital feedback signal FB' is supplied to a distortion part 8 for extracting nonlinear distortion caused by a nonlinear characteristic of the power amplifying part 4. The A-D correcting part 11 stores data of an inverse characteristic of the nonlinear characteristic of the A-D converter 7 as correction data into the correction table 13 of the A-D correcting part 11, reads correction data stored in an address Ad corresponding to the level of a feedback signal FB detected by a control part 12 from the correction table 13 and supplies the correction data to the adding part 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a distortion compensation amplifying apparatus used in a nonlinear distortion compensation apparatus for an amplifier.

  In wireless devices such as transmitters in mobile wireless communication systems, digitization has progressed, and accompanying this, it has become an important problem to compensate for nonlinear distortion of the power amplification unit. As one of the compensation methods, A predistortion method is known. As an example, one used for compensation of nonlinear distortion of a power amplifying unit of a transmitter has been proposed (see, for example, Patent Document 1).

  FIG. 9 is a block diagram showing a conventional example of a nonlinear distortion compensator for a power amplification unit using a predistortion system, where 1 is an input terminal, 2 is a predistorter, and 3 is a D / A (digital / analog). Converter, 4 is a power amplifier, 5 is a power detector, 6 is a distortion compensation table, 7 is an A / D (analog / digital) converter, and 8 is an ACLR (Adjacent Channel Leakage Power Ratio). ) Detection unit, 9 is a control unit.

  In the figure, a digital signal input from an input terminal 1 is supplied to a predistorter 2 and a power detection unit 5. In the predistorter 2, based on the amplitude / phase distortion compensation signal from the distortion compensation table 6, the supplied digital signal is processed to compensate for nonlinear distortion in the power amplification unit 4. In this compensation processing, by controlling the amplitude and phase of the digital signal so as to cancel the nonlinear distortion generated in the power amplification unit 4, the nonlinear distortion due to the nonlinear characteristic opposite to the nonlinear characteristic of the power amplification unit 4 is previously obtained. Processing (predistortion processing).

  In the distortion compensation table 6, amplitude / phase compensation data corresponding to the power of the input digital signal is registered, and the compensation data is associated with the amplitude of the input digital signal.

  The input digital signal from the input terminal 1 is supplied to the power detection unit 5 to detect the power, and the amplitude / phase compensation data corresponding to the detected power is read from the distortion compensation table 6 to obtain the amplitude / The phase distortion compensation signal is supplied to the predistorter 2.

  The digital signal predistorted by the predistorter 2 in this way is converted into an analog signal by the D / A converter 3 and then power amplified by the power amplifier 4 and output (in the case of a transmitter). Is converted to a radio frequency signal, then amplified and transmitted from the antenna). In the power amplifying unit 4, distortion (that is, non-linear distortion) is generated in the analog signal to be amplified due to the nonlinear characteristic. However, since the predistorter 2 performs predistortion processing, the power amplifying unit 4 Is compensated (cancelled).

  By the way, the non-linear characteristics of the power amplifying unit 4 change due to environmental changes such as ambient temperature or aging, and the non-linear distortion generated in the power amplifying unit 4 changes accordingly. For this reason, it is necessary to adjust the amplitude / phase compensation data in the distortion compensation table 6 in accordance with environmental changes and aging. As the adjustment means, an A / D converter 7, a distortion detector 8, and a controller 9 are used. A reasonable feedback circuit is provided.

  The analog signal output from the power amplifying unit 4 is appropriately converted to an intermediate frequency as a feedback signal and then supplied to the A / D converter 7 where it is converted into a digital signal and supplied to the distortion detecting unit 8. . In the distortion detection unit 8, nonlinear distortion is detected from the supplied digital feedback signal, and the control unit 9 changes the amplitude / phase compensation data in the distortion compensation table 6 in accordance with the detected nonlinear distortion change. .

  Here, in the power amplifying unit 4, the analog signal supplied thereto is amplified. Due to the non-linear characteristic of the power amplifying unit 4, the analog signal is out of the frequency band (that is, from this frequency band). If an unnecessary signal component due to nonlinear distortion occurs in the upper and lower bands), and the nonlinear distortion remains in the analog signal output due to a change in the nonlinear characteristic of the power amplifier 4, the unnecessary signal is outside the frequency band of the analog signal. An ingredient will be produced. The distortion detector 8 analyzes the spectrum of the feedback signal, and uses the spectrum power outside the signal band of the analog signal to be amplified by the power amplifier 4 as a nonlinear distortion component (unnecessary signal component) due to the nonlinear characteristics of the power amplifier 4. To detect. The control unit 9 processes the unnecessary signal component detected by the distortion detection unit 8 as a nonlinear distortion component, and creates an adjustment amount of the amplitude / phase compensation data stored in the distortion compensation table 6. The inverse characteristic that compensates for the nonlinear characteristic of the power amplifying unit 4 is represented by an nth power series. The control unit 9 represents an inverse characteristic that compensates for the nonlinear characteristic of the power amplifying unit 4 by updating the coefficient of each term of the power series by the perturbation method according to the nonlinear distortion component detected by the distortion detecting unit 8. Thus, the amplitude / phase compensation data for each power of the input digital signal detected by the power detection unit 5 is created based on the power series updated in this way, and the amplitude / phase compensation data of the distortion compensation table 6 is generated using the compensation data. Update phase compensation data. Alternatively, the control unit 9 creates an adjustment amount of the amplitude / phase compensation data using the updated power series and the amplitude / phase compensation data of the distortion compensation table 6 and the like. The amplitude / phase compensation data may be adjusted.

In this way, even if the nonlinear characteristic of the power amplifying unit 4 changes due to environmental changes or changes over time, the amplitude / phase compensation data of the distortion compensation table 6 is adjusted accordingly. As a result, in the power amplifying unit 4, the analog signal is amplified with the nonlinear distortion effectively suppressed.
JP 2001-203539 A

  By the way, in the conventional technique, when the level of the feedback signal is low, the nonlinear distortion of the power amplifying unit 4 is correctly detected by the quantization noise and nonlinear characteristics of the A / D converter 7 constituting the feedback circuit. There was a problem that could not. That is, when the A / D converter 7 is used up to a strong part (non-linear part) such as its nonlinear characteristic, nonlinear distortion occurs in the output feedback signal of the A / D converter 7, and this nonlinear When the distortion is detected by the distortion detector 8, the amplitude / phase compensation data in the distortion compensation table 6 is updated even though non-linear distortion does not appear in the output signal of the power amplifier 4. . For this reason, the output signal of the predistorter 2 includes predistortion that cannot cancel the non-linear distortion generated in the power amplifying unit 4, and the non-linear distortion remains in the output signal of the power amplifying unit 4. Will do.

  As an example of the non-linear part of the characteristics of the A / D converter, there is a non-linear characteristic in a low level (low amplitude) region. In order to eliminate such non-linear distortion due to non-linear characteristics, an AGC (automatic gain control) circuit 10 is provided on the input side of the A / D converter 7 of the feedback circuit as shown in FIG. It is conceivable that this feedback signal is converted by the A / D converter 7 in a linear region exceeding the nonlinear region of the characteristic.

  However, since the non-linear characteristics of the A / D converter are different for each A / D converter to be used, even if compensation is performed, the power amplifying unit 4 having a non-linear distortion compensation circuit as shown in FIG. 10 is used. It is not easy to verify and compensate the characteristics of the A / D converter 7 for each product. Even if the AGC circuit 10 is used, since the AGC circuit is an analog circuit, it is necessary to verify the characteristics of the AGC circuit, and the number of parts increases.

  Further, when the A / D converter 7 having sufficient linear characteristics is used, the A / D converter 7 handles a feedback signal including a minute nonlinear distortion generated in the power amplification unit 4. The characteristics of the A / D converter 7 are also required to be linear over a wide range, and it is necessary to use an expensive A / D converter with high resolution.

  An object of the present invention is to provide a distortion compensation amplifying apparatus capable of solving such problems, saving labor and time, and effectively compensating for non-linear distortion of an A / D converter.

  In order to achieve the above object, the present invention includes an amplifying unit, a predistorter that gives a signal input to the amplifying unit a characteristic opposite to the nonlinear characteristic of the amplifying unit, and an output signal of the amplifying unit. An A / D converter that performs A / D conversion using the feedback signal as a feedback signal, a distortion detection unit that detects distortion included in the output signal of the amplification unit based on the output signal of the A / D converter, and the distortion detection A control unit that controls the characteristics of the prodistorter so that distortion detected by the unit is reduced; and a first level that detects the level of the analog signal input to the A / D converter as an input level A correction unit comprising: means; second means for generating correction data according to the input level; and third means for adding the correction data to the digital signal output from the A / D converter. The correction data is a nonlinear characteristic of the A / D converter. Is characterized in that the inverse characteristic data of the.

  According to the present invention, since the non-linear characteristic of the A / D converter in use can be compensated for, it is not necessary to verify the characteristics of the A / D converter in use, and labor and time for that can be saved. In addition, it is possible to use an inexpensive A / D converter with low resolution.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a first embodiment of a distortion compensation amplifying apparatus according to the present invention, in which 11 is an A / D correction unit, 12 is a control unit, 13 is a correction table, and 14 is an addition unit. Parts corresponding to those in FIG. 9 are denoted by the same reference numerals and redundant description is omitted.

  In the figure, the digital information signal input from the input terminal 1 and processed by the predistorter 2 is converted to an analog information signal by the D / A converter 3 and is not shown as appropriate as in the conventional example shown in FIG. The frequency is converted by a mixer or the like, amplified by the power amplification unit 4, and supplied to the A / D converter 7 and the A / D correction unit 11 as a feedback signal FB. In the A / D converter 7, the supplied analog feedback signal FB is converted into a digital feedback signal FB ′ and supplied to the A / D correction unit 11.

  The A / D correction unit 11 includes a control unit 12, a correction table 13, and an addition unit 14. The correction table 13 includes from the minimum level (negative maximum value) to the maximum level (positive maximum value) of the analog feedback signal FB from the power amplifying unit 4 and hence from the input side of the A / D converter 7. The correction data for each level is stored at addresses corresponding to the respective levels. It should be noted that these levels may be used as addresses. In the following, in order to simplify the description, the levels are used as addresses, and correction data corresponding to these levels is read from the correction table 13. Note that the control unit 12 may (temporarily) include another A / D converter in order to convert these levels into addresses. The A / D converter may have a low sampling rate and resolution as long as linearity is sufficient.

  FIG. 2 is a flowchart showing a specific example of the correction operation of the A / D correction unit 11, and the operation of the A / D correction unit 11 will be described using this flowchart.

  The control unit 12 sequentially detects the level of the supplied feedback signal FB (step 100), reads the correction data DF of the address Ad from the correction table 13 as the address Ad, and supplies it to the adder unit 14. (Step 101). In the adder 14, the correction data DF read from the correction table 13 is added to the digital feedback signal FB ′ from the A / D converter 7 as an offset value (step 102), thereby the feedback signal. Non-linear distortion due to the non-linear characteristic of the A / D converter 7 of FB ′ is corrected.

  The correction data DF in the correction table 13 is created by inputting a test signal from the input terminal 1. A specific example of the operation of creating the correction table 13 by the control unit 12 in the A / D correction unit 11 at this time will be described with reference to the flowchart shown in FIG.

When creating the correction table 13, a digital test signal is input from the input terminal 1, whereby an analog test signal AT is output from the power amplifier 4 as a feedback signal, and the A / D converter 7 is nonlinear. The characteristic acquisition routine is entered (step 200). The analog test signal AT from the power amplification unit 4 is supplied to the A / D converter 7 and the control unit 12 of the A / D correction unit 11, and the test signal AT is digitally converted by the A / D converter 7. It is converted into a test signal DT and supplied to the control unit 12 of the A / D correction unit 11. The level of the test signal AT is sequentially switched at equal intervals from the minimum value to the maximum value within the possible level range of the analog information signal output from the power amplifier 4 (step 201), and the level is switched. Each time, the control unit 12 captures the level of the test signal AT at this time and the value (digital value) of the output test signal DT of the A / D converter 7 corresponding to the level (this capture timing is hereinafter referred to as a sample point). ) And save (step 202). Here, the level of the test signal AT captured by the control unit 12 at the sample point is hereinafter referred to as an analog sample value, and the digital value of the test signal DT from the A / D converter 7 captured by the control unit 12 at the sample point. Is hereinafter referred to as a digital sample value. Note that there is a time difference corresponding to the processing time of the A / D converter 7 between the analog sample value captured by the control unit 12 and the digital sample value corresponding to the analog sample value captured by the control unit 12. In 12, the analog sample value and the digital sample value are stored in association with each other. As described above, the analog sample value and the digital sample value that are associated with each other are hereinafter referred to as a pair of the analog sample value and the digital sample value. Thus, the level of the test signal AT is reduced from the minimum level in the above level range. When pairs of analog sample values and digital sample values at all sample points when switching to the maximum level are acquired, the nonlinear characteristic acquisition routine of the A / D converter 7 ends (step 203).

  The captured series of digital sample values correspond to the characteristics of the power amplification unit 4 and the A / D converter 7, that is, the nonlinear characteristics thereof, and the captured series of analog sample values are the values of the power amplification unit 4. Although it is influenced by the nonlinear characteristic, it is not influenced by the characteristic of the A / D converter 7. Therefore, by taking the difference between the analog sample value and the digital sample value that make a pair, the difference data represents a portion due to the influence of the non-linear characteristic of the A / D converter 7, and the A / D converter 7 is data corresponding to the non-linear distortion according to 7. Therefore, by obtaining such differential data between the analog sample value and the digital sample value for each sample point, the nonlinear distortion due to the nonlinear characteristic of the A / D converter 7 is not affected by the nonlinear characteristic of the power amplifier 4. Inverse characteristic data for correction is obtained (step 204). The difference data cancels out non-linear distortion due to the non-linear characteristic of the power amplifying unit 4. Therefore, the difference data is data of the inverse characteristic of the non-linear characteristic of the A / D converter 7.

  Note that one of the sample values for obtaining the difference data is a digital value and the other is an analog value. However, when obtaining these difference data, the level of the analog sample value is not shown in the other A / D. The detected value of this level is detected by a converter and the like, and the detected value at this level is converted into a digital value when converted by an ideal A / D converter having a linear characteristic (for example, calibrated using a table or the like), and this converted digital The difference between the value and the digital sample value is obtained. The difference data at each sample point obtained in this way is associated with the converted digital value at the corresponding sample point, and this becomes the data of the reverse characteristic.

  In this way, when data of inverse characteristics (that is, data consisting of the correspondence between the level (converted digital value) of the analog test signal AT for each sample point and the difference data) is obtained, next, between the sample points, Data interpolation is performed to obtain a series of difference data at finer sample points (step 205). Thereby, inverse characteristic data with high accuracy of the nonlinear characteristic of the A / D converter 7 is obtained. The difference data of each sample point including the interpolation sample point in the inverse characteristic data obtained in this way is used as the correction data DF, and the level of the analog test signal AT corresponding to this is used as the address Ad. And the address Ad are stored in the correction table 13 (step 206).

  Operations of the first embodiment other than those described above are the same as those of the prior art shown in FIG.

  As the test signal AT, a tone signal having a frequency slightly deviated from an integer multiple (including 0) of the sampling frequency of the A / D converter 7 can be used. The power amplifying unit 4 can be supplied through by changing the connection. Further, when passing through, a filter that allows only the test signal AT to pass may be passed.

  In addition, the control unit 12 uses the digital PLL and DDS from the test signal DT from the A / D converter 7 instead of detecting the level of the analog test signal, so that the test signal DT has the same amplitude and the same phase. A simple tone signal may be reproduced and its level detected.

  As described above, in the first embodiment shown in FIG. 1, it is possible to effectively suppress the influence due to the non-linear characteristics of the A / D converter without taking time and effort for the user. As a result, even in the nonlinear distortion compensation device of the power amplification unit 4, the amplitude / phase compensation data stored in the distortion compensation table 6 is not affected by the nonlinear characteristic of the A / D converter 7. Thus, a signal in which nonlinear distortion is effectively suppressed can be obtained.

  FIG. 4 is a block diagram showing the main part of the second embodiment of the distortion compensation amplifier according to the present invention, in which 15 is a control unit, 16 is a coefficient table, 17 is a calculation unit, 18 is an addition unit Parts corresponding to those in the previous drawings are denoted by the same reference numerals and redundant description is omitted.

  In the figure, the A / D correction unit 11 includes a control unit 15, a coefficient table 16, a calculation unit 17, and an addition unit 18, and the feedback signal FB from the power amplification unit 4 and the A / D are transmitted to the control unit 15. A digital feedback signal FB ′ from the D converter 7 is supplied. The coefficient table 16 stores coefficient data of an arithmetic expression for obtaining correction data for nonlinear distortion due to nonlinear characteristics of the A / D converter 7 in the digital feedback signal FB ′ from the A / D converter 7. Yes.

  Here, this arithmetic expression will be described.

FIG. 5 shows the relationship between the analog sample value L of the feedback signal FB that is the basis of such an arithmetic expression and the digital sample value SD of the digital feedback signal FB ′ output from the corresponding A / D converter 7. The analog sample value L ₀ is the minimum level of the feedback signal FB, the analog sample value L _N is the maximum level of the feedback signal FB, and the analog sample values (levels) L ₀ , L ₁ , L at N + 1 sample points _{2, ......, L N-1} , L N digital sample values corresponding to these respective (digital _{value) SD 0, SD 1, SD} 2, ......, show the SD _N-1, SD _N. Thus, in the second embodiment, digital sample values SD are determined for N + 1 analog sample values (levels) L from the minimum level to the maximum level of the feedback signal FB. However, the digital sample value SD _X at the level L _X between these sample points is the N + 1 analog sample values L _i (where i = 0, 1, 2,..., N− 1) and the digital sample value SD _i are obtained by a linear interpolation method, and a coefficient of an arithmetic expression f (L _X ) (= SD _X ) = α · L _X + β for this purpose α and β are stored in the coefficient table 16.

Therefore, for example, as shown in FIG. 5, when obtaining the digital sample value SD _X for the level L _X between the analog sample values L ₁ and L ₂ , the control unit 15 obtains the level of the feedback signal FB fetched at that time. Is determined as L _X, it is determined at which position of the analog sample value L shown in FIG. 5 this level L _X is, and from this determination, the analog sample value above this level L _X is set to L ₁ , determining the analog sample value and L _2. Based on the determined analog sample values L ₁ and L ₂ , the coefficient table 16 is searched for the coefficients α and β for obtaining the digital sample value SD _X for the level L _X between the analog sample values L ₁ and L ₂ . Are read out and supplied to the calculation unit 17.

At this time, the calculation unit 17 calculates the coefficients α and β read from the coefficient table 16 and supplied based on the level L _X supplied from the control unit 15 as an arithmetic expression f (L _X ) = α · L _X. + by fitting the β seeking digital sample values SD _X for this level L _X, further, the digital sample values the level L _X is subtracted from the SD _X creates the correction data DF, and sends to the adder 18.

In the adder 18, the digital value of the digital feedback signal FB ′ from the A / D converter 7 with respect to this level L _X of the feedback signal FB (this is almost equal to the digital sample value SD _X obtained by the above equation). Correction data DF from the calculation unit 17 is added to the digital feedback signal FB ′, thereby compensating for non-linear distortion due to non-linear characteristics of the A / D converter 7 included in the digital value at this time of the digital feedback signal FB ′. Will be.

Here, an arithmetic expression between the analog sample values L ₀ and L ₁ by a coefficient stored in the coefficient table 16, an arithmetic expression between the analog sample values L ₁ and L ₂ ,..., An analog sample value L _N−1 , The arithmetic expression f (L _X ) (= SD _X ) between L _N is now assumed that the detected level L _X is the level between the analog sample values L _i and L _{i + 1} , and the digital with respect to the analog sample value L _i If the sample value is SD _i and the digital sample value for the analog sample value L _{i + 1} is SD _{i + 1} , linear interpolation

Is required. That is, since the analog sample values L _i and L _{i + 1} and the digital sample values SD _i and SD _{i + 1} are known, the digital sample value SD _X can be obtained by substituting the level L _X. The coefficients α and β are stored at an address Ad corresponding to the level between the analog sample values L _i and L _{i + 1 in} the coefficient table 16.

The calculation unit 17 further calculates the digital sample value SD _X thus obtained,

The correction data DF is obtained by performing the above calculation. By the arithmetic processing of Equation 2, nonlinear distortion due to the nonlinear characteristic of the power amplifier 4 is canceled out, and data of the inverse characteristic of the nonlinear characteristic of the A / D converter 7 is obtained.

  The correction data DF is supplied to the adder 18 and added to the digital feedback signal FB ′ from the A / D converter 7, whereby the A / D converter 7 mixed in the feedback signal FB ′. Non-linear distortion due to non-linear characteristics is compensated.

As described above, the coefficient table 16 includes the arithmetic expression f ( ₁₎ between the analog sample values L ₀ and L _1, between L ₁ and L ₂ ,..., Between L _N−1 and L _N. L _x ) coefficients α and β are stored. The calculation unit 17 uses the coefficient coefficients α and β with respect to the calculation formula f (L _X ) of the above formula 1 of the coefficient table 16 for the level L _X of the captured feedback signal FB, and uses the calculation formula f (L _{X of} this formula 1 ) performs by the arithmetic processing is to use a digital sample values SD _X for this level L _X.

  The coefficients α and β of the above formula 1 registered in the coefficient table 16 are input from the input terminal 1 (FIG. 1) and output from the power amplifier 4 as in the first embodiment shown in FIG. 1. It is created using the signal AT. The test signal AT is also a signal that changes from the minimum level that can be taken by the feedback signal FB when the power amplifier 4 is used to the maximum level. This will be described with reference to the flowchart shown in FIG.

When the test signal AT is supplied, the control unit 15 takes in the level L _i . This level L _i is an analog sample value that is first taken in, and is i = 0 (step 300 in FIG. 6), and is the level (analog sample value) L ₀ in FIG. 5 (step 301 in FIG. 6). Next, the control unit 7 takes in the digital value (digital sample value) SD _i of the digital test signal DT from the A / D converter 7 for this level L _i (L ₀ ). Since the digital value SD _{i in} this case is i = 0, it is the digital value SD ₀ in FIG. 5 (step 302 in FIG. 6).

Next, when the level of the test signal AT changes, the control unit 15 takes in this level as the level _{Li + 1} . At this time, since i = 0, the level L _{i + 1} is the level (analog sample value) L ₁ in FIG. 5 (step 303 in FIG. 6). Then, the digital value (digital sample value) SD _{i + 1} of the digital test signal DT from the A / D converter 7 for the level L _{i + 1} (L ₁ ) is captured. Digital value SD _{i + 1} in this case is a digital value SD ₁ in FIG. 5 (step 304 in FIG. 6).

Then, the control unit 15 obtains the coefficients α and β from the levels L _i and L _{i + 1} and the digital values SD _i and SD _{i + 1 according} to the above equation 1 (step 305 in FIG. 6). α and β are associated with the levels L _i and L _{i + 1} (in this case, the levels L ₀ and L ₁ ) and stored in the coefficient table 16 (step 306 in FIG. 6).

Here, in the coefficient table 16, if the coefficients α and β obtained for the range of the levels L _{0 to} L ₁ are α ₀ and β ₀ , the coefficient table 16 includes the range of the levels L _{0 to} L _1. address Ad ₀ are assigned, as shown in FIG. 7 (a), the coefficient alpha ₀ according to the address Ad _0, beta ₀ is stored. Further, in the control unit 15, as shown in FIG. 7B, the range of the level range L _{i to} L _{i + 1} (in this case, the level range L _{0 to} L ₁ ) and the adlay Ad (this) in the coefficient table 16 In this case, information indicating a correspondence relationship with the address Ad ₀ ) is held.

Next, the control unit 15 sets the level L _{i + 1} and the digital value SD _{i + 1} as the level L _i and the digital value SD _i (that is, i = 1), and the level L _i and the digital value SD. _i (in this case, level L ₁ , digital value SD ₁ ) is held (step 307 in FIG. 6).

When the test signal AT changes to the next level, the control unit 7 takes in the level at that time as the level L _{i + 1} (the level in FIG. 5 (corresponding to the analog sample value L ₂ )) (step 303 in FIG. 6). further, taking the level L _{i + 1} digital values of the digital test signal DT from the a / D converter 7 for (digital sample value) SD i + _1. Digital value SD _{i + 1} in this case is a digital value SD ₁ in FIG. 5 (step 304 in FIG. 6). Then, the control unit 15 holds the above-mentioned level L _i (= level L ₁ ), digital value SD _i (= SD ₁ ), newly captured level L _{i + 1} (= level L ₂ ), digital From the value SD _{i + 1} (= SD ₂ ), the coefficients α and β are obtained by the above equation 1 (step 305 in FIG. 6), and these coefficients α and β are set to levels L _i and L _{i + 1} (in this case, Are stored in the coefficient table 16 in association with the levels (L ₁ , L ₂ ) (step 306 in FIG. 6). Then, the newly acquired level L _{i + 1} and digital value SD _{i + 1} are set as level L _i and digital value SD _i (that is, i = 2), respectively, and these level L _i and digital value SD _i ( In this case, level L ₂ and digital value SD ₂ ) are held (step 307 in FIG. 6).

In this case, in the coefficient table 16, if the coefficients α and β obtained for the range of the levels L _{1 to} L ₂ are α ₁ and β ₁ , the coefficient table 16 includes the coefficient table 16 in the range of the levels L _{1 to} L ₂ . assigned address Ad _1, as shown in FIG. 7 (a), the coefficient alpha ₁ according to the address Ad _1, beta ₁ is stored. Further, in the control unit 15, as shown in FIG. 7B, the level range L _{i to} L _{i + 1} (in this case, the level range L _{1 to} L ₂ ) and the adlay Ad in the coefficient table 16 (in this case, Information indicating the correspondence with the address Ad ₁ ) is held.

In the same manner, every time the level L of the test signal AT changes, it is set to the level L _{i + 1,} and the output level of the A / D converter 7 is taken into this as the digital value SD _{i + 1} (see FIG. step 303 and 304 6), these to be held level L _i, the coefficient between the digital value SD _i alpha, calculates a beta (step 305 in FIG. 6), associated with a level range L _i ~L _{i + 1} (That is, the address Ad of the coefficient table 16 is assigned) and stored in the coefficient table 16 (step 306 in FIG. 6). Such an operation is repeated until i = N−1 (step 308 in FIG. 6).

In this way, the coefficients α _i and β _i in the above equation 1 are obtained for each level range L _{i to} L _{i + 1} (i = 0, 1, 2,..., N−1). 16 is stored. When the feedback signal FB is supplied from the power amplifier 4 to the A / D converter 7 and the operation of updating the correction data in the distortion compensation table 6 is performed, the control unit 15 detects the level L _{X of the} feedback signal FB. The address Ad _i is determined by determining which level range L _{i to} L _{i + 1} is included in the level range L _X using the table shown in FIG. The coefficients α _i and β _i at the address Ad _i are read from the coefficient table 16 and the calculation unit 17 uses the coefficients α _i and β _i and the level L _X to perform the above equations 1 and 2. , the correction data DF for compensation of nonlinear distortion by the digital value SD _X of the a / D converter 7 for the level L _X, i.e., the correction data DF of inverse characteristic of the nonlinear characteristic of the a / D converter 7 It is intended Mel.

  As described above, also in the second embodiment, the same effect as that of the first embodiment can be obtained.

  FIG. 8 is a block diagram showing the main part of a third embodiment of the distortion compensation amplifier according to the present invention. 19 is a control unit, 20 is a correction table, 21 is an adding unit, 22 is a changeover switch, Parts that are input terminals and that correspond to the previous drawings are assigned the same reference numerals, and redundant description is omitted.

  In the figure, the A / D correction unit 11 includes a control unit 19, a correction table 20, and an addition unit 21, and a feedback signal FB from the A / D converter 7 is supplied to the control unit 15. This is different from the previous embodiment. The correction table 20 stores correction data for non-linear distortion due to non-linear characteristics of the A / D converter 7 with the digital feedback signal FB ′ from the A / D converter 7.

  When the power amplifying unit 4 is in use, the changeover switch 22 is closed to the fixed contact a side on the power amplifying unit 4 side, and the output signal of the power amplifying unit 4 serves as an analog feedback signal FB as an A / D converter. 7 and the control unit 19 of the A / D correction unit 11. The correction table 20 stores correction data similar to the correction table 13 of the A / D correction unit 11 in FIG. The control unit 12 reads the correction data DF from the correction table 13 using the supplied feedback signal FB as the direct address Ad, and supplies the correction data DF to the addition unit 14. In the adding unit 14, the correction data DF read from the correction table 13 is added to the digital feedback signal FB ′ from the A / D converter 7 as an offset value, and thereby the A of the feedback signal FB ′ is added. Non-linear distortion due to the non-linear characteristic of the / D converter 7 is corrected.

  Next, a method for creating correction data in the correction table 20 will be described.

  In this case, the changeover switch 22 is switched to the fixed contact b side, and two types of test signals AT are supplied to the A / D converter 7 from the input terminal 23 via the changeover switch 22. The test signal AT is converted into a digital test signal DT by the A / D converter 7 and supplied to the adding unit 21 of the A / D correction unit 11.

The first test signal AT has a minimum value (negative maximum value) corresponding to the maximum possible range of the feedback signal FB output from the power amplifier 4 when the power amplifier 4 is in use. From the minimum value to the maximum value (positive maximum value) (ramp waveform), and the control unit 19 sequentially detects the level of the test signal DT, and performs A / D conversion from the minimum value. Each time the level changes by a predetermined level corresponding to the resolution of the device 7, the level at that time is sequentially taken as levels L ₀ (minimum value), L ₁ , L ₂ ,..., L _N (maximum value).

On the other hand, in the correction table 20, such level _{L 0, L 1, L 2} , ......, L N every address Ad is Ad _0, Ad _1, Ad _2, ......, it is assigned as Ad _N, the initial state Then, correction data having a value of 0 is stored at each address Ad _i (where i = 0, 1, 2,..., N).

  When the control unit 19 detects a discontinuous change (jumping or stagnation) in the test signal DT with respect to the continuous change in the test signal AT, correction data that eliminates the discontinuity is calculated and the correction table 20 is calculated. Write to. Such a discontinuity is due to an error of each bit weight of the A / D converter 7, and the discontinuous values when the carry of each bit occurs are summed and averaged. The discontinuous value is the level difference itself when jumping, and is an assumed value of how many levels change during the stagnation period if it is a continuous section when stagnation. At both ends of the bit weight interval, linear interpolation is performed so that the correction data becomes ± 1/2 of the discontinuous value, and the correction data is calculated by synthesizing the correction data for each bit.

  Next, a second test signal AT 'is given. The second test signal AT 'is, for example, a plurality of tone signals having an arbitrary frequency.

The digital test signal DT from the A / D converter 7 is supplied to the addition unit 21 of the A / D correction unit 11, and the digital value SD _i and the correction data read from the correction table 20 are added to add a distortion detection unit. 8 is supplied. At this time, the correction data DF having a value of 0 read from the correction table 20 is read from the address Ad _i assigned to the level L _i of the digital value SD _i supplied to the adder 21 at this time.

When the digital test signal DT output from the adder 21 includes non-linear distortion due to non-linear characteristics of the A / D converter 7 other than the bit weight error, the frequency (band) of the test signal DT itself is included. An unnecessary signal component (intermodulation distortion) is included outside. The distortion detection unit 8 extracts this unnecessary signal component, for example, for each order of intermodulation distortion, and supplies it to the control unit 19 of the A / D correction unit 11. The control unit 19 detects a change in non-linear distortion in the digital value SD _i from the unnecessary signal component, like the control unit 9, and obtains correction data ΔDF that can cancel the change, and supplies the correction data ΔDF to the correction table 20. Here, unnecessary signal components are extracted for each power or amplitude level L ₀ ′, L ₁ ′, L ₂ ′,..., L _N ′ of the test signal DT, but the nonlinear characteristic of the A / D converter 7 is It can be represented by M following power series, such level _{L 0 ', L 1',} L 2 ', ......, L N' level L _0, L _1, L ₂ corresponding to, ..., and L _N The coefficients of the power series are calculated without being affected by the noise floor level by the simultaneous equations composed of unnecessary signal components at that time, and a power series representing the inverse characteristic of the nonlinear characteristic of the A / D converter 7 is obtained. It is done. From this power series, the correction data ΔDF for each of the levels L ₀ , L ₁ , L ₂ ,..., L _N is obtained, and the correction data DF in the correction table 20 is corrected.

In this case, the correction data ΔDF is associated with the address Ad _i assigned to the level L _i corresponding to the digital value SD _i from which the defective signal component is extracted in order to obtain the correction data ΔDF. The correction data DF at this time at the address Ad _i is corrected by adding the obtained correction data ΔDF.

In this way, in the correction table 20, the correction data is corrected for each level L ₀ , L ₁ , L ₂ ,..., L _{N of} the test signal AT. Such correction processing of the correction data DF is performed a plurality of times by repeatedly inputting the same test signal AT from the input terminal 23 a plurality of times, and the non-linear distortion caused by the A / D converter 7 in the digital test signal DT is further increased. Correction data DF that can be removed with high accuracy, that is, correction data having a reverse characteristic of the nonlinear characteristic of the A / D converter 7 can be set in the correction table 20.

  As described above, the feedback signal FB from the power amplifying unit 4 is converted by the A / D converter 7 by switching the changeover switch 22 to the fixed contact a side in the state where the highly accurate correction data DF is set in the correction table 20. Non-linear distortion caused by the A / D converter 7 when converted to the digital feedback signal FB ′ can be removed by the A / D correction unit 11.

  As described above, according to the third embodiment, the same effects as those of the first and second embodiments can be obtained, and a plurality of tone signals can be used as test signals to perform spectrum analysis and unnecessary signals. By extracting the components, the accuracy required for the test signal source can be lowered.

  In the above description of each embodiment, the correction data creation process may be performed during the non-transmission period of the power amplifying unit 4. Thereby, it is possible to reliably cope with a change in non-linear distortion due to a change in non-linear characteristic of the A / D converter 7 with time.

  In the embodiment shown in FIGS. 1 and 4, the test signal AT is supplied to the A / D converter 7 and the A / D correction unit 11 via the switch 22 as in the embodiment shown in FIG. The digital feedback signal from the A / D converter 7 may be input to the control units 12 and 15.

  Further, in each of the above-described embodiments, the addition unit in the A / D correction unit 11 adds the correction data to the digital feedback signal FB ′ from the A / D converter 7, whereby the A / D converter 7 Although the nonlinear distortion is compensated, the nonlinear distortion is compensated by changing the conversion characteristic of the A / D converter 7 according to the correction data corresponding to the variation in the bit weight of the A / D converter 7. It can also be. For example, when the A / D converter 7 is a CMOS pipeline type A / D converter, the weight of each stage of the pipeline is calibrated using the correction data. For example, a calibrator terminal is provided in each stage, and a minute analog current or the like is applied through the terminal.

  Furthermore, the A / D correction unit 11 in FIGS. 1, 4 and 8 may be configured by a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or other dynamic reconfigurable device. .

1 is a block configuration diagram showing a first embodiment of a distortion compensation amplifying apparatus according to the present invention. 3 is a flowchart illustrating a specific example of a method for creating a correction table of an A / D correction unit in FIG. 1. 3 is a timing chart showing a specific example of the test operation of the first embodiment shown in FIG. 1. It is a block block diagram which shows the principal part of 2nd Embodiment of the distortion compensation amplification apparatus by this invention. It is a figure for demonstrating the memory | storage data in the table in FIG. It is a flowchart which shows a specific example of the production method of the memory | storage data of the table of 2nd Embodiment shown in FIG. FIG. 5 is a diagram schematically showing storage data of a table in FIG. 4 and data of a control unit in FIG. 4 for reading it. It is a block block diagram which shows 3rd Embodiment of the distortion compensation amplification apparatus by this invention. It is a block block diagram which shows one prior art example of the nonlinear distortion compensation apparatus by the predistortion system of a power amplification part. It is a figure which shows an example of the distortion compensation amplification apparatus used with the prior art shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input terminal 2 Predistorter 3 D / A converter 4 Power amplification part 5 Power detection part 6 Distortion compensation table 7 A / D converter 8 Distortion detection part 9 Control part 11 A / D correction part 12 Control part 13 Correction table 13 14 Addition Unit 15 Control Unit 16 Coefficient Table 17 Calculation Unit 18 Addition Unit 19 Control Unit 20 Correction Table 21 Addition Unit 22 Changeover Switch 23 Test Signal Input Terminal

Claims (1)

An amplification unit;
A predistorter that gives a signal input to the amplifier to a characteristic opposite to the nonlinear characteristic of the amplifier;
An A / D converter for A / D converting the output signal of the amplifier as a feedback signal;
A distortion detection unit that detects distortion included in the output signal of the amplification unit based on the output signal of the A / D converter;
A control unit that controls the characteristics of the prodistorter so that the distortion detected by the distortion detection unit is reduced;
First means for detecting, as an input level, the level of an analog signal input to the A / D converter;
A second means for generating correction data according to the input level;
And a third unit for adding the correction data to the digital signal output from the A / D converter,
The distortion compensation amplifying apparatus, wherein the correction data is data having an inverse characteristic of a nonlinear characteristic of the A / D converter.

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