JP2017220744A - Distortion compensation circuit, distortion compensation method, and transmitter - Google Patents

Abstract

An object of the present invention is to suppress distortion degradation of a signal output from a power amplifier by performing distortion compensation based on the characteristics of the input signal. A power calculator (11) calculates a power value of an input signal. Memory 12 stores a plurality of lookup tables containing compensation coefficients to be multiplied by input signals. The data output unit 13 reads and outputs a compensation coefficient corresponding to the power P calculated by the power calculation unit 11 from one of the plurality of lookup tables. The distortion compensation calculation section 14 multiplies the input signal by the compensation coefficient output from the data output section 13 . The signal analysis unit 16 analyzes signal characteristics of the input signal. Based on the analysis result of the signal analysis unit 16, the control unit 15 determines the lookup table from which the compensation coefficient is read, and notifies the data output unit 13 of the determined lookup table. [Selection drawing] Fig. 1

Description

  The present invention relates to a distortion compensation circuit, a distortion compensation method, and a transmitter.

  As a distortion compensation technique that has been widely adopted in recent years, there is a digital predistortion method (DPD: Digital Predistortion). Distortion compensation by the DPD method compensates for nonlinear distortion generated in the power amplifier. For example, an envelope detection type linearizer device described in Patent Document 1 can be cited. Specifically, the amplitude and phase of the transmission signal input to the power amplifier and the feedback signal obtained by feeding back the signal output from the power amplifier are compared as digital signals, and the nonlinear characteristics of the power amplifier based on the comparison result The distortion compensation coefficient representing the inverse characteristic of is obtained.

  Also, in the field of current mobile communication, OFDM (Orthogonal Frequency Division Multiplex) modulation scheme is adopted in the LTE (Long Term Evolution) downlink to improve frequency utilization efficiency. In OFDMA (Orthogonal Frequency Division Multiple Access), resource scheduling of flexibly allocating resource blocks (Resource Blocks) to user resources in the time domain and the frequency domain is considered in accordance with real-time characteristics. Therefore, transmission power fluctuates in real time and the amount of change is large.

  Under such circumstances, a technique for appropriately compensating for distortion even for a signal having a large variation in transmission power has been proposed. For example, a distortion compensation device (Patent Document 2) that compensates for distortion due to fluctuations in power supply voltage or ambient temperature, or a radio that corrects a coefficient for compensating distortion in consideration of a gain that has changed due to fluctuations in transmission power. A communication device is known (Patent Document 3).

JP 2000-278190 A JP 2003-298429 A JP 2010-278505 A

  By the way, power amplifiers used in mobile communication base stations employ GaN (gallium nitride) transistors in order to achieve higher output and higher efficiency. In the GaN transistor, a so-called Idq drift phenomenon occurs. Thereby, in the GaN transistor, the nonlinear characteristic (AM-AM characteristic, AM-PM characteristic) of the power amplifier is such that the average power of the transmission signal and the signal distribution (CCD: Complementary Distribution Function, PAPR: Paek to Average Ratio), It varies greatly depending on the signal pattern.

  An example is shown in FIGS. As shown in FIGS. 16 and 17, when the average power of the signal is high and there is a signal up to a high amplitude, the characteristics are the same as those during the large signal operation. However, when the average power of the signal is low and the signal is not distributed to a high amplitude, the characteristics are the same as those in the small signal operation. It can be understood that these two characteristics are completely different characteristics. When a signal such as OFDMA in which the transmission power fluctuates in real time is used for a power amplifier having such characteristics, the characteristics of the power amplifier greatly change with respect to fluctuations in the transmission power. There is a problem that it takes time to converge the compensation coefficient, and power leakage to the adjacent channel increases until the compensation coefficient converges.

  In addition, when the average gain of the power amplifier greatly changes depending on the average power and signal distribution of the transmission signal, the nonlinear characteristic of the power amplifier changes due to the gain correction. Therefore, until the distortion compensation coefficient is converged by DPD. Further, there arises a problem that it takes more time.

  Such a problem occurs regardless of fluctuations in the power supply voltage and the ambient temperature, and cannot be solved by the device described in Patent Document 2.

  When the shape of the nonlinear characteristic of the power amplifier (the shape of the AM-AM characteristic or AM-PM characteristic) is approximated before and after the transmission power fluctuates, distortion compensation is possible with the apparatus described in Patent Document 3. However, when the nonlinear characteristics of the power amplifier are different before and after transmission power fluctuation, it is not possible to obtain an optimum distortion compensation coefficient only by correction considering the gain.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress distortion degradation of a signal output from a power amplifier by performing distortion compensation based on characteristics of an input signal. is there.

  A distortion compensation circuit according to an aspect of the present invention includes a power calculation unit that calculates a power value of an input signal, a memory that stores a plurality of lookup tables including a compensation coefficient that is multiplied by the input signal, and the plurality of the plurality of lookup tables. A data output unit that reads out and outputs a compensation coefficient corresponding to the power value calculated by the power calculation unit from any one of the lookup tables, and a distortion that multiplies the input signal by the compensation coefficient output from the data output unit A compensation calculation unit, a signal analysis unit that analyzes signal characteristics of the input signal, and a lookup table for reading a compensation coefficient are determined based on an analysis result of the signal analysis unit, and the determined lookup table is output as the data And a control unit that notifies the unit.

  A distortion compensation method according to one aspect of the present invention calculates a power value of an input signal, analyzes signal characteristics of the input signal, and includes a plurality of compensation coefficients stored in a memory based on the analysis result. A lookup table for reading a compensation coefficient to be multiplied to the input signal is determined from the lookup table, a compensation coefficient corresponding to the calculated power value is read from the determined lookup table, and the readout compensation coefficient is read from the input signal. Multiply by.

  A transmitter according to an aspect of the present invention includes: a distortion compensation circuit that performs distortion compensation calculation on an input signal; and a conversion circuit that converts a signal subjected to distortion compensation calculation by the distortion compensation circuit into a wireless transmission signal. The distortion compensation circuit includes any one of a power calculator that calculates a power value of the input signal, a memory that stores a plurality of lookup tables including a compensation coefficient to be multiplied by the input signal, and the plurality of lookup tables. A data output unit that reads and outputs a compensation coefficient corresponding to the power value calculated by the power calculation unit, a distortion compensation calculation unit that multiplies the input signal by a compensation coefficient output from the data output unit, and Based on the analysis result of the signal analysis unit for analyzing the signal characteristics of the input signal and the signal analysis unit, the lookup table for reading the compensation coefficient is determined. And a control unit which notifies the data output unit, in which comprises a.

  ADVANTAGE OF THE INVENTION According to this invention, distortion degradation of the signal output from a power amplifier can be suppressed by performing distortion compensation based on the characteristic of an input signal.

1 is a circuit diagram schematically showing a configuration of a distortion compensation circuit according to a first exemplary embodiment; 1 is a circuit diagram schematically illustrating a transmitter having a distortion compensation circuit according to a first embodiment; It is a figure which shows the structural example of a look-up table. 3 is a flowchart showing a lookup table determination operation of the distortion compensation circuit according to the first exemplary embodiment; It is a figure which shows the example of a fluctuation | variation with the input amplitude of a digital baseband signal, and the output amplitude of a power amplifier. It is a figure which shows the sampling of input amplitude. It is a figure which shows the example of the input amplitude distribution obtained by sampling input amplitude in a certain period. It is a figure which shows the example of the input amplitude distribution obtained by sampling input amplitude in a certain period. It is a figure which shows the example of the input amplitude distribution obtained by sampling input amplitude in a certain period. It is a figure which shows an example of the determination method of a signal pattern. FIG. 4 is a block diagram schematically showing a configuration of a transmitter having a distortion compensation circuit according to a second embodiment. It is a figure which shows the relationship between the average power and signal pattern of an input side, and a lookup table. 10 is a flowchart showing a lookup table determination operation of the distortion compensation circuit according to the second exemplary embodiment; FIG. 6 is a block diagram schematically illustrating a configuration of a transmitter having a distortion compensation circuit according to a third embodiment. 10 is a flowchart showing a lookup table determination operation of the distortion compensation circuit according to the third exemplary embodiment; It is a figure which shows the nonlinear characteristic (AM-AM characteristic) of a power amplifier. It is a figure which shows the nonlinear characteristic (AM-PM characteristic) of a power amplifier.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

Embodiment 1
A distortion compensation circuit 100 according to the first embodiment will be described. FIG. 1 is a circuit diagram schematically illustrating a configuration of a distortion compensation circuit 100 according to the first embodiment. FIG. 2 is a circuit diagram schematically illustrating a transmitter 1000 including the distortion compensation circuit 100 according to the first embodiment. The transmitter 1000 includes a distortion compensation circuit 100, a quadrature modulation unit 41, a digital / analog converter (DAC) 42, a frequency converter 43, and a power amplifier 45.

  First, the distortion compensation circuit 100 will be described. The distortion compensation circuit 100 includes a power calculation unit 11, a memory 12, a data output unit 13, a distortion compensation calculation unit 14, a control unit 15, and a signal analysis unit 16.

  The power calculator 11 calculates the power P of the digital baseband signals I and Q input to the distortion compensation circuit 100. In the example of FIG. 1, the digital baseband signals I and Q are orthogonal signals and include an I component and a Q component orthogonal to the I component.

  The memory 12 stores a plurality of lookup tables (Look Up Table: hereinafter referred to as LUT). Here, each LUT will be described. FIG. 3 is a diagram illustrating a configuration example of the LUT. As shown in FIG. 3, each LUT table stores a compensation coefficient corresponding to the range of power calculated by the power calculator 11. Between each LUT, a compensation coefficient suitable for the corresponding signal pattern is set in advance as an initial setting at the time of shipment, for example. In each LUT, after the distortion compensation circuit is mounted on the transmission device or the like and the distortion compensation operation is started, for example, as will be described later, the control unit 15 appropriately updates the compensation coefficient stored in each LUT (DAT in FIG. 2). ) Is also possible.

  Returning to FIGS. 1 and 2, the configuration of the distortion compensation circuit 100 will be described. The data output unit 13 reads the compensation coefficient CC corresponding to the power P of the digital baseband signals I and Q calculated by the power calculation unit 11 from the LUT specified by the control unit 15. Then, the data output unit 13 outputs the read compensation coefficient CC to the distortion compensation calculation unit 14.

  The distortion compensation calculation unit 14 outputs a signal obtained by multiplying the digital baseband signals I and Q by the compensation coefficient CC received from the data output unit 13, that is, the digital baseband signals Ic and Qc after distortion compensation calculation.

  The signal analysis unit 16 analyzes the signal characteristics of the digital baseband signals I and Q, and outputs the analysis results (PAT in FIGS. 1 and 2) to the control unit 15.

  Based on the analysis result (PAT in FIGS. 1 and 2), the control unit 15 outputs to the data output unit 13 a control signal CON1 that specifies the LUT that the data output unit 13 uses to read the compensation coefficient.

  Next, the configuration of the transmitter 1000 other than the distortion compensation circuit 100 will be described. The quadrature modulation unit 41 performs quadrature modulation on the digital baseband signals Ic and Qc output from the distortion compensation calculation unit 14 and outputs the result to the DAC 42 as a digital IF (Intermediate Frequency) signal. The DAC 42 converts the digital IF signal into an analog IF signal by digital-analog conversion and outputs the analog IF signal. The frequency converter 43 up-converts (frequency converts) the analog IF signal into an RF (Radio Frequency) signal. The power amplifier 45 amplifies the RF signal of the frequency converter 43 and outputs an output signal OUT.

  Here, the quadrature modulation unit 41, the DAC 42, the frequency converter 43, and the power amplifier 45 are also collectively referred to as a first conversion circuit 40. That is, the first conversion circuit 40 is configured as a circuit that converts the digital baseband signals Ic and Qc output from the distortion compensation circuit 100 into an output signal OUT that is a wireless transmission signal.

  Next, the operation of the distortion compensation circuit 100 will be described. FIG. 4 is a flowchart of the LUT determination operation of the distortion compensation circuit 100 according to the first embodiment.

Step S11
The signal analysis unit 16 determines signal patterns of the digital baseband signals I and Q, and notifies the control unit 15 of the determined signal pattern PAT.

Step S12
Based on the signal pattern PAT, the control unit 15 determines the LUT _i that the data output unit 13 uses for reading the compensation coefficient, and outputs a control signal CON1 that notifies the determined LUT to the data output unit 13.

Step S13
The data output unit 13 determines whether the LUT _i specified by the control signal CON1 is the same as the LUT _{c from} which data is read at that time.

Step S14
If the LUT _i specified by the control signal CON1 is different from the LUT _c that is the source of the data referred to at that time, the data output unit 13 changes the LUT to be referenced to the LUT _i specified by the control signal CON1. Switch.

  Thereafter, the data output unit 13 reads the compensation coefficient CC corresponding to the power value P from the LUTc to be referred to, and outputs the read compensation coefficient CC to the distortion compensation calculation unit 14. The distortion compensation calculation unit 14 multiplies the digital baseband signals I and Q by the compensation coefficient CC and outputs the digital baseband signals Ic and Qc.

  Next, analysis of the digital baseband signals I and Q in the signal analysis unit 16 will be described. In the present embodiment, a method for performing pattern analysis of digital baseband signals I and Q will be described as a specific example of signal analysis.

  First, signal pattern analysis will be described with reference to the drawings. FIG. 5 is a diagram illustrating an example of fluctuations in the input amplitude of the digital baseband signal and the output amplitude of the power amplifier. In FIG. 5, the horizontal axis represents the input amplitude of the digital baseband signal, and the vertical axis represents the value obtained by dividing the output amplitude of the power amplifier by the input amplitude of the digital baseband signal (ie, the gain of the power amplifier). FIG. 5 shows two types of characteristics as an example. In this example, it can be seen that the gain of the power amplifier varies with respect to the input amplitude of the digital baseband signal. However, the aspect of fluctuation of the gain of the power amplifier differs depending on the signal pattern. In FIG. 5, paying attention to the section D1, the characteristic curve L1 has a larger average gain of the power amplifier and a larger fluctuation amount than the characteristic curve L2. That is, it can be seen that the optimum LUT differs depending on the signal pattern. Therefore, it can be said that it is desirable to analyze the signal pattern.

  In this embodiment, the input amplitude is sampled to obtain the distribution of the input amplitude, and the signal pattern is determined using this distribution. FIG. 6 is a diagram illustrating sampling of the input amplitude. As shown in FIG. 6, with respect to the changing input amplitude, for example, the value of the input amplitude is sampled every time Δt to generate a distribution. 7 to 9 are diagrams illustrating examples of the input amplitude distribution obtained by sampling the input amplitude in a certain period. In this example, the peak positions are different in FIGS. 7 to 9, and the peak is the gentlest in FIG. In this way, the signal distribution pattern includes many signals in the low-amplitude region when the signal is uniformly distributed from low to high amplitude, or when signal samples are biased in the low-amplitude region. When there is a mixture of high amplitude signals. In the present embodiment, a signal pattern is determined based on these distributions, and an LUT to be used is determined based on the determined signal pattern.

  A method for determining a signal pattern will be specifically described. In order to determine the LUT to be used, a signal pattern may be determined using a distribution statistic, for example, the peak center value Ap in the input amplitude distribution. In this case, the input amplitude is divided into a plurality of ranges, and it is determined to which range the peak center value (that is, the value of the input amplitude when the slope of the distribution curve (first derivative) becomes 0) belongs. By doing so, the signal pattern can be determined.

  In addition, for example, in the input amplitude distribution, the signal pattern may be determined using the shape of the peak, for example, the area S of the region surrounded by the straight line and the peak at a certain number of samples. In this case, a signal pattern can be determined by setting a range of a plurality of area values and determining which range the calculated area S belongs to.

  In this example, the input amplitude distribution has been described. However, not only such a frequency distribution but also a probability density function corresponding to the frequency distribution may be used. In this case, the signal pattern may be determined based on the center value of the peak in the probability density function or the area surrounded by the line and the peak drawn with a predetermined probability. For example, CCDF (Complementary Distribution Function) or PAPR (Paek to Average Ratio) may be used, and several threshold values are provided for CCDF and PAPR, and signal distribution patterns are distinguished and specified according to the threshold values. Can do.

  The above-described peak center value and peak area value may be used alternatively, or both may be used in combination. FIG. 10 is a diagram illustrating an example of a signal pattern determination method. In this case, if an individual signal pattern is assigned to each element of the matrix formed by a plurality of ranges set for the peak center value Ap and a plurality of ranges set for the area value S, Good.

  As described above, according to this configuration, since the compensation coefficient can be selected based on the characteristics of the input digital baseband signal, particularly the signal pattern, it is possible to perform predistortion type distortion compensation regardless of the signal characteristics.

Embodiment 2
A distortion compensation circuit according to the second embodiment will be described. FIG. 11 is a block diagram schematically illustrating a configuration of a transmitter 2000 including the distortion compensation circuit 200 according to the second embodiment. The transmitter 2000 has a configuration in which the distortion compensation circuit 100 of the transmitter 1000 according to the first embodiment is replaced with a distortion compensation circuit 200.

  The distortion compensation circuit 200 has a configuration in which an average power calculation unit 21 is added to the distortion compensation circuit 100. The average power calculator 21 calculates the average power Pa (also referred to as first average power) of the digital baseband signals I and Q over a predetermined period, and outputs the calculation result to the controller 15.

  The control unit 15 determines the LUT to be used based on the average power Pa on the input side and the signal pattern. FIG. 12 is a diagram illustrating the relationship between the average power and signal pattern on the input side and the LUT. As shown in FIG. 12, the LUT is set as a matrix composed of the average power Pa on the input side and the signal pattern PAT. Thereby, the control unit 15 can determine the LUT to be used based on the average power Pa on the input side and the signal pattern PAT. The matrix shown in FIG. 12 may be stored in a memory (not shown) provided in the control unit 15, for example. The matrix shown in FIG. 12 may be set in advance or may be updated by an external command.

  Next, the operation of the distortion compensation circuit 200 will be described. FIG. 13 is a flowchart of the LUT determination operation of the distortion compensation circuit 200 according to the second embodiment.

Step S21
The average power calculator 21 accumulates the power values of the digital baseband signals I and Q for a certain period and calculates the average power Pa for that period.

Step S22
The signal analysis unit 16 determines the signal patterns of the digital baseband signals I and Q, and notifies the control unit 15 of the determined signal pattern PAT, as in step S11 of FIG.

Step S23
Based on the signal pattern PAT and the average power Pa, the control unit 15 determines the LUT _i that the data output unit 13 uses to read the compensation coefficient, and sends the control signal CON1 that notifies the determined LUT to the data output unit 13. Output to.

Step S24
Similarly to step S13, the data output unit 13 determines whether the LUT _i specified by the control signal CON1 is the same as the LUT _{c from} which data is read at that time.

Step S25
If the LUT _i specified by the control signal CON1 is different from the LUT _c that is the source of the data referred to at that time, the data output unit 13 uses the control signal CON1 to refer to the LUT to be referred to as in step S14. Switch to the specified LUT _i .

  Thereafter, as in the first embodiment, the data output unit 13 reads the compensation coefficient CC corresponding to the power value P from the LUTc to be referred to, and outputs the read compensation coefficient CC to the distortion compensation calculation unit 14. The distortion compensation calculation unit 14 multiplies the digital baseband signals I and Q by the compensation coefficient CC and outputs the digital baseband signals Ic and Qc.

  As described above, according to this configuration, since the LUT to be used is determined by referring not only to the signal pattern of the digital baseband signal but also to the average power, it is possible to realize more precise distortion compensation than in the first embodiment. Understandable.

Embodiment 3
A distortion compensation circuit according to the third embodiment will be described. In the above-described transmitter, depending on the average power and signal distribution of the transmission signal, not only the nonlinear characteristics of the power amplifier but also the average gain may change greatly. In this case, the nonlinear characteristic of the power amplifier changes due to the gain correction. Therefore, in order to speed up the convergence of the distortion compensation coefficient by DPD, first, the average gain may be adjusted to a specified value. In the present embodiment, a distortion compensation circuit capable of performing gain correction in such a case will be described. FIG. 14 is a block diagram schematically illustrating a configuration of a transmitter 3000 including the distortion compensation circuit 300 according to the third embodiment. The transmitter 3000 has a configuration in which the distortion compensation circuit 200 of the transmitter 2000 according to the second embodiment is replaced with a distortion compensation circuit 300.

  The distortion compensation circuit 300 includes a delay circuit 31, a frequency converter 32, an analog-to-digital converter (ADC) 33, an orthogonal demodulation unit 34, an average power calculation unit 35, and a directional coupler. 36 and a variable resistance attenuator (ATT) 44 are added.

  The delay circuit 31 delays the digital baseband signals I and Q according to the control signal CON3 from the control unit 15, and supplies the delayed digital baseband signals Ia and Qa to the control unit 15. Thereby, the control unit 15 controls the delay amount in the delay circuit 31 so that feedback digital baseband signals Ib and Qb, which will be described later, and the delayed digital baseband signals Ia and Qa are synchronized. The average power calculator 21 calculates the average power Pa of the delayed digital baseband signals Ia and Qa over a predetermined period and outputs the calculation result to the controller 15.

  The directional coupler 36 branches the output signal and feeds it back. The frequency converter 32 outputs a feedback analog IF signal obtained by down-converting the output signal OUT fed back from the directional coupler 36. The ADC 33 converts the feedback analog IF signal from the frequency converter 32 into a feedback digital IF signal by analog-digital conversion, and outputs it. The quadrature demodulation unit 34 outputs the feedback digital baseband signals Ib and Qb obtained by demodulating the feedback digital IF signal from the ADC 33 to the control unit 15 and the average power calculation unit 35.

  Here, the frequency converter 32, the ADC 33, the quadrature demodulator 34, and the directional coupler 36 are also collectively referred to as a second conversion circuit 30. That is, the second conversion circuit 30 is configured as a circuit that converts the output signal OUT, which is a radio transmission signal, into feedback digital baseband signals Ib and Qb.

  The average power calculator 35 calculates the average power Pb (also referred to as second average power) of the feedback digital baseband signals Ib and Qb over a predetermined period, and outputs the calculation result to the controller 15.

The variable resistance attenuator 44 attenuates the power of the RF signal by a value specified by the control signal CON2 from the control unit 15. Here, a conversion circuit in which the variable resistance attenuator 44 is added to the first conversion circuit 30 is also referred to as a first conversion circuit 50.

  The controller 15 not only determines the LUT to be used, but also calculates the gain G of the transmitter 3000 by dividing the average power Pb on the output side by the average power Pa on the input side. When the value of the gain G is outside the predetermined range, the control unit 15 controls the amount of attenuation in the variable resistance attenuator 44 by the control signal CON2 so that the gain G is within the predetermined range.

  Further, the control unit 15 compares the average power Pa on the input side and the average power Pb on the output side, or between the delayed digital baseband signals Ia and Qa and the feedback digital baseband signals Ib and Qb. By comparing the amplitudes, the delay amount in the delay circuit 31 can be suitably controlled.

  Further, the amplitude and phase may be compared between the delayed digital baseband signals Ia and Qa and the feedback digital baseband signals Ib and Qb, and the compensation coefficient included in each LUT may be updated based on the comparison result. At this time, various calculation methods can be used for calculating the compensation coefficient. For example, a method using an envelope detection linearizer device described in Patent Document 1 may be used.

  Next, an LUT determination method in the distortion compensation circuit according to the third embodiment will be described. FIG. 15 is a flowchart of the LUT determination operation of the distortion compensation circuit according to the third embodiment.

Step S31
The average power calculator 21 accumulates the power values of the delayed digital baseband signals Ia and Qa for a certain period and calculates the average power Pa for that period.

Step S32
The average power calculator 35 accumulates the power values of the feedback digital baseband signals Ib and Qb for a certain period, and calculates the average power Pb for that period.

Step S33
The control unit 15 calculates the gain G (G = Pb / Pa) of the transmitter 3000.

Step S34
The control unit 15 determines whether the gain G is within a predetermined range.

Step S35
When the gain G is outside the range specified in advance, the control unit 15 controls the variable resistance attenuator 44 so that the gain G falls within the range specified by the control signal CON2.

Step S36
The signal analysis unit 16 determines the signal patterns of the delayed digital baseband signals Ia and Qa, and notifies the control unit 15 of the determined signal pattern PAT, as in step S11 of FIG.

Step S37
Similarly to step S23, the control unit 15 determines the LUT _i used by the data output unit 13 for reading the compensation coefficient based on the signal pattern PAT and the average power Pa, and notifies the determined LUT of the control signal CON1. Is output to the data output unit 13.

Step S38
Similarly to step S13, the data output unit 13 determines whether the LUT _i specified by the control signal CON1 is the same as the LUT _{c from} which data is read at that time.

Step S39
If the LUT _i specified by the control signal CON1 is different from the LUT _c that is the source of the data referred to at that time, the data output unit 13 uses the control signal CON1 to refer to the LUT to be referred to as in step S14. Switch to the specified LUT _i .

  Thereafter, as in the first and second embodiments, the data output unit 13 reads the compensation coefficient CC corresponding to the power value P from the LUTc to be referred to, and outputs the read compensation coefficient CC to the distortion compensation calculation unit 14. The distortion compensation calculation unit 14 multiplies the digital baseband signals I and Q by the compensation coefficient CC and outputs the digital baseband signals Ic and Qc.

  As described above, according to this configuration, the gain of the transmitter can be adjusted, and as a result, the signal quality of the output signal of the transmitter can be further improved. As a result, even when the average power and signal distribution of the transmission signal change suddenly, and not only the nonlinear characteristics of the power amplifier but also the average gain changes significantly, the distortion compensation coefficient converges quickly and the radio characteristics deteriorate. Can be suppressed. Further, by repeatedly executing this control, adaptive control of the LUT that follows changes in temperature and frequency characteristics can be performed.

Other Embodiments The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention. For example, the distortion compensation circuit mounted on the transmitter is not limited to the distortion compensation circuit 100 according to the first embodiment, and similarly using the distortion compensation circuits 200 and 300 according to the second and third embodiments, similarly to the wireless communication apparatus. Can be configured.

In step S37 of FIG. 15, the control unit 15 has been described as determining the LUT _i used by the data output unit 13 for reading the compensation coefficient based on the signal pattern PAT and the average power Pa, similarly to step S23. This is just an example. That is, similarly to step S12 of FIG. 4, the control unit 15 may determine the LUT _i used by the data output unit 13 for reading the compensation coefficient based on the signal pattern PAT.

DESCRIPTION OF SYMBOLS 11 Power calculation part 12 Memory 13 Data output part 14 Distortion compensation calculating part 15 Control part 16 Signal analysis part 21, 35 Average power calculation part 30 2nd conversion circuit 31 Delay circuit 32, 43 Frequency converter 33 ADC
34 Quadrature Demodulator 36 Directional Coupler 40, 50 First Conversion Circuit 41 Quadrature Modulator 42 DAC
44 variable resistance attenuator 45 power amplifier 100, 200, 300 distortion compensation circuit 1000, 2000, 3000 transmitter

Claims (10)

A power calculator for calculating the power value of the input signal;
A memory storing a plurality of lookup tables including a compensation coefficient for multiplying the input signal;
A data output unit that reads and outputs a compensation coefficient corresponding to the power value calculated by the power calculation unit from any of the plurality of lookup tables;
A distortion compensation calculation unit that multiplies the input signal by a compensation coefficient output from the data output unit;
A signal analyzer for analyzing the signal characteristics of the input signal;
A control unit that determines a lookup table for reading a compensation coefficient based on the analysis result of the signal analysis unit and notifies the data output unit of the determined lookup table;
Distortion compensation circuit. The data output unit, when the look-up table notified from the control unit is different from the look-up table from which the compensation coefficient was read before the notification, the look-up table from which the compensation coefficient is read out from the control unit Switch to table,
The distortion compensation circuit according to claim 1. The signal analysis unit samples the input amplitude of the input signal, determines a signal pattern based on the distribution of the input amplitude,
The control unit determines a lookup table for reading a compensation coefficient based on the determined signal pattern.
The distortion compensation circuit according to claim 1 or 2. The signal analysis unit
Determining a signal pattern based on one or both of the peak center value and the peak shape of the input amplitude distribution;
The distortion compensation circuit according to claim 3. A first average power calculating unit that calculates a first average power of the input signal in a certain period and outputs the calculated first average power to the control unit;
The control unit determines a lookup table for reading a compensation coefficient based on the analysis result of the signal analysis unit and the first average power.
The distortion compensation circuit according to any one of claims 1 to 4. The input signal is a digital baseband signal, and the digital baseband signal multiplied by a compensation coefficient in the distortion compensation calculation unit is converted into a wireless transmission signal by a first conversion circuit at a subsequent stage.
The distortion compensation circuit according to claim 1. A delay circuit for delaying the digital baseband signal as the input signal;
A first average power calculating unit that calculates a first average power in a certain period of the digital baseband signal delayed by the delay circuit, and outputs the calculated first average power to the control unit;
A second conversion circuit for converting the wireless transmission signal into a digital baseband signal;
A second average power calculation unit that calculates a second average power in a certain period of the digital baseband signal converted by the second conversion circuit, and outputs the calculated second average power to the control unit; Further comprising
The controller is
Calculating a gain of the first conversion circuit from the first average power and the second average power;
When the gain is outside the predetermined range, the first conversion circuit is controlled so that the gain is within the predetermined range;
The distortion compensation circuit according to claim 6. The control unit controls the delay amount in the delay circuit so that the digital baseband signal delayed by the delay circuit and the digital baseband signal converted by the second conversion circuit are synchronized. ,
The distortion compensation circuit according to claim 7. Calculate the power value of the input signal,
Analyzing the signal characteristics of the input signal;
Based on a result of the analysis, a lookup table for reading a compensation coefficient to be multiplied by the input signal is determined from a plurality of lookup tables including a compensation coefficient stored in a memory,
Read the compensation coefficient corresponding to the calculated power value from the determined lookup table,
Multiplying the input compensation signal by the read compensation coefficient;
Distortion compensation method. A distortion compensation circuit for performing distortion compensation calculation on the input signal;
A conversion circuit that converts a signal subjected to distortion compensation calculation by the distortion compensation circuit into a wireless transmission signal, and
The distortion compensation circuit includes:
A power calculator for calculating a power value of the input signal;
A memory storing a plurality of lookup tables including a compensation coefficient for multiplying the input signal;
A data output unit that reads and outputs a compensation coefficient corresponding to the power value calculated by the power calculation unit from any of the plurality of lookup tables;
A distortion compensation calculation unit that multiplies the input signal by a compensation coefficient output from the data output unit;
A signal analyzer for analyzing the signal characteristics of the input signal;
A control unit that determines a lookup table for reading a compensation coefficient based on the analysis result of the signal analysis unit and notifies the data output unit of the determined lookup table;
Transmitter.

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