Abstract:
Disclosed is a polar modulation transmission circuit wherein distortion components resulting from variations between individual amplifiers are compensated for with few man-hours, and deterioration in signal quality is effectively suppressed. A frequency converter ( 180 ) converts the frequency of an output signal of a high frequency power amplifier ( 170 ) and outputs a frequency domain signal, and a phase compensation unit ( 150 ) measures the power level, for each delay amount, at a low frequency band and high frequency band wherein the detuning frequency from the frequency domain signal is the same, calculates the “unlevel amount” (relative level difference) between the power level of the low frequency band and power level of the high frequency band for each delay amount, and determines the compensation characteristics on the basis of the relationship of the unlevel amount (relative level difference) to the delay amount. Then, the phase compensation unit ( 150 ) compensates for the phase signal by adding to the phase signal the phase compensation amount, in the determined compensation characteristics, that corresponds to the amplitude signal.

Description:
TECHNICAL FIELD 
     The present invention relates to a transmission circuit and a transmission method, which are used in communication devices such as a mobile phone and a wireless LAN, particularly to a polar modulation transmission circuit and a polar modulation transmission method for performing compensation to a phase. 
     BACKGROUND ART 
     In design of the conventional transmission apparatus, generally there is a trade-off relationship between efficiency and linearity. However, in the transmitting apparatus, recently there is proposed a technology in which a balance between the high efficiency and the linearity can be established using polar modulation. 
     As to the conventional polar modulation transmission circuit, for example, Patent Literature 1 discloses a transmission circuit.  FIG. 1  is a block diagram illustrating an example of a configuration of conventional transmission circuit  10  disclosed in Patent Literature 1. In  FIG. 1 , conventional transmission circuit  10  includes amplitude/phase extraction section  11 , phase modulation section  12 , amplifier  13 , output terminal  14 , and amplitude control section  15 . 
     Amplitude/phase extraction section  11  extracts an amplitude signal indicating an amplitude component (for example, √(I 2 +Q 2 )) and a phase signal indicating a phase component (for example, an angle formed by a modulation symbol and an I-axis) from input data. The amplitude signal is input to amplitude control section  15 . Amplitude control section  15  supplies a voltage corresponding to the amplitude signal as a power supply voltage to amplifier  13 . The phase signal is input to phase modulation section  12 . Phase modulation section  12  performs phase modulation of a high-frequency signal based on the input phase signal, and outputs a phase modulation signal obtained by the phase modulation. The phase modulation signal is input to amplifier  13 . Amplifier  13  amplifies the phase modulation signal according to the voltage supplied from amplitude control section  15 . The signal amplified by amplifier  13  is output as a transmission signal from output terminal  14 . An output level of the transmission signal can be controlled by changing an output voltage of amplitude control section  15  to be supplied to amplifier  13 . A method in which the amplitude signal and the phase signal are separated from the input data to perform the modulation using the amplitude signal and the phase signal is called polar modulation or polar coordinate modulation. Transmission circuit  10  that performs the method is also called a polar modulation transmission circuit (or polar coordinate modulation transmission circuit). 
     In the polar modulation transmission circuit, there is known a distortion generated in amplifier  13 . A relationship (AM-AM characteristic) between an output power and the power supply voltage corresponding to the amplitude signal is not linear in amplifier  13 . Additionally, a relationship (AM-PM characteristic) between a phase deviation of input/output and the power supply voltage of amplifier  13  is not constant. Particularly, when the AM-PM characteristic changes, a shape of a spectrum of the output signal becomes asymmetry. As a result, radio performance such as an ACLR (Adjacent Channel Lockage Power Ratio) is degraded in a transmitter. 
     An influence of the AM-PM characteristic on the ACLR will be described below with reference to  FIGS. 2 and 3 . The AM-PM characteristic means a phase characteristic that changes according to power supply voltage Vcc of amplifier  13 .  FIG. 2  illustrates an example of a relationship between power supply voltage Vcc of amplifier  13  and passage phase Ph, namely, the AM-PM characteristic of amplifier  13 . In  FIG. 2 , characteristic  21  indicates the ideal AM-PM characteristic, and characteristic  22  indicates the actual AM-PM characteristic. While the ideal AM-PM characteristic is flat, passage phase Ph varies according to power supply voltage Vcc of amplifier  13  in the actual AM-PM characteristic. 
       FIG. 3  illustrates an example of a spectrum when amplifier  13  has the AM-PM characteristic illustrated in  FIG. 2 . In  FIG. 3 , broken line  31  indicates the spectrum of the ideal AM-PM characteristic indicated by characteristic  21  of  FIG. 2 , and solid line  32  indicates the spectrum of the AM-PM characteristic when passage phase Ph varies according to power supply voltage Vcc as indicated by characteristic  22  of  FIG. 2 . When the AM-PM characteristic is not flat, the ACLR is degraded as illustrated in  FIG. 3 . 
     As described above, in the polar modulation transmission circuit, the relationship (AM-AM characteristic) between the power supply voltage of the amplifier and the output power and the relationship (AM-PM characteristic) between the power supply voltage and the phase deviation of the input/output are compensated in order to maintain quality of the transmission signal. 
     A pre-distortion distortion compensation method is known as a method for compensating a generated distortion component through such compensation (for example, see Patent Literature 2). In a polar modulation transmission circuit described in Patent Literature 2, the AM-AM characteristic and the AM-PM characteristic are previously acquired and stored in a distortion compensation processing circuit, and reverse characteristics of the AM-AM characteristic and the AM-PM characteristic are added to the amplitude signal and the phase signal. By this means, it is possible to compensate the characteristic degradation caused by the distortion generated in the amplifier. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Patent Application Laid-Open No. 2004-266351 
         PTL 2 
         Japanese Patent Application Laid-Open No. 2007-180782 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the high-frequency amplifier used in the actual polar modulation transmission circuit, the AM-AM characteristic and/or the AM-PM characteristic changes individually by an individual variation. Therefore, it is necessary to individually perform the distortion compensation in order to suppress the influence of the individual variation, which results in a problem in that a man-hour is increased. Particularly, it is necessary to provide a demodulator that demodulates the output signal in order to measure the AM-PM characteristic, which results in a problem in that a circuit scale is enlarged. 
     Additionally, when a temperature around the amplifier or the power supply voltage of the amplifier varies, the AM-AM characteristic and the AM-PM characteristic vary. However, when the characteristic variation is compensated in real time, it is necessary to insert a pilot signal in order to measure the change of the AM-PM characteristic. Therefore, it is difficult to compensate the characteristic variation in real time in a system that continuously transmits the signal. 
     An object of the present invention is to provide a polar modulation transmission circuit and a polar modulation transmission method, in which the distortion component caused by the individual variation of the amplifier can be compensated with the small man-hour to effectively suppress the degradation of the signal quality. 
     Solution to Problem 
     A polar modulation transmission circuit of the present invention includes: an extraction section that extracts an amplitude signal and a phase signal from a modulated signal to output the amplitude signal and the phase signal; an amplitude control section that outputs a voltage corresponding to the amplitude signal; a phase compensation section that performs phase compensation by operating on the phase signal with a phase compensation amount corresponding to the amplitude signal; a phase modulation section that performs phase modulation of a high-frequency signal using the phase signal to which the phase compensation is performed, and generates a phase modulation signal; an amplifying section that sets the voltage output from the amplitude control section as a power supply voltage, amplifies the phase modulation signal output from the phase modulation section, and outputs the amplified phase modulation signal; and a conversion section that performs a fast Fourier transform of the output signal of the amplifying section to output a frequency spectrum signal to the phase compensation section, wherein the phase compensation section, using the frequency spectrum signal, determines a compensation characteristic in order to compensate an amplitude-phase characteristic of the amplifying section, and determines the phase compensation amount corresponding to the amplitude signal in the determined compensation characteristic. 
     A polar modulation transmission method of the present invention includes: extracting an amplitude signal and a phase signal from a modulated signal; outputting a voltage corresponding to the amplitude signal as a power supply voltage to an amplifying section; performing phase compensation by operating on the phase signal with a phase compensation amount corresponding to the amplitude signal; performing phase modulation of a high-frequency signal using the phase signal to which the phase compensation is performed; generating a phase modulation signal; amplifying the phase modulation signal with the amplifying section; outputting the amplified phase modulation signal; performing a fast Fourier transform of the output signal of the amplifying section to output a frequency spectrum signal; determining a compensation characteristic in order to compensate an amplitude-phase characteristic of the amplifying section using the frequency spectrum signal; and determining the phase compensation amount corresponding to the amplitude signal in the determined compensation characteristic. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to compensate the distortion component caused by the individual variation of the amplifier, with the small man-hour, to effectively suppress the degradation of the signal quality. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a configuration of a main part of a conventional polar modulation transmission circuit; 
         FIG. 2  is a view illustrating an example of an AM-PM characteristic; 
         FIG. 3  is a view for explaining a relationship between the AM-PM characteristic and an ACLR; 
         FIG. 4  is a view illustrating a configuration of a main part of a polar modulation transmission circuit according to Embodiment 1 of the present invention; 
         FIG. 5  is a view illustrating an example of a spectrum input from a frequency converter; 
         FIG. 6  is a view illustrating a relationship between the ACLR and a delay amount; 
         FIG. 7  is a view illustrating imbalanced amounts at delay amounts τ 1  and τ 2 ; 
         FIG. 8  is a view for explaining a method for determining a shape of the AM-PM characteristic of a compensation characteristic; 
         FIG. 9  is a view for explaining the method for determining a change amount of the shape of the AM-PM characteristic of the compensation characteristic; 
         FIG. 10  is a view illustrating an example of an internal configuration of a variable phase compensation section according to Embodiment 1; 
         FIG. 11  is a view illustrating an example of the compensation characteristic indicated by an amplitude level and a compensation phase amount, which are retained by each of LUTs; 
         FIG. 12  is a view illustrating another example of the internal configuration of the variable phase compensation section according to Embodiment 1; 
         FIG. 13  is a view illustrating still another example of the internal configuration of the variable phase compensation section according to Embodiment 1; 
         FIG. 14  is a view illustrating a configuration of a main part of a polar modulation transmission circuit according to Embodiment 2 of the present invention; 
         FIG. 15  is a view for explaining a method for setting a delay amount in a delay amount setting section; 
         FIG. 16  is a view illustrating a configuration of a main part of a polar modulation transmission circuit according to Embodiment 3 of the present invention; and 
         FIG. 17  is a view illustrating a configuration of a main part of a polar modulation transmission circuit according to Embodiment 4 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention, will be described with reference to the drawings. 
     (Embodiment 1) 
       FIG. 4  illustrates a configuration of a main part of polar modulation transmission circuit (hereinafter simply referred to as a “transmission circuit”)  100  according to the present embodiment of the present invention. 
     Amplitude/phase extraction section  110  inputs modulation data (hereinafter referred to as input data) as data to be transmitted, and extracts an amplitude signal r(t) and a phase signal φ(t) from the input data. Amplitude/phase extraction section  110  outputs the amplitude signal r(t) to amplitude control section  130  and variable phase compensation section  152  of phase compensation section  150 . Amplitude/phase extraction section  110  outputs the phase signal φ(t) to delay adjuster  140 . 
     Power supply (battery)  120  supplies a power supply voltage to amplitude control section  130 . 
     Amplitude control section  130  biases the power supply voltage, which is supplied from power supply (battery)  120 , according to the input amplitude signal r(t) and outputs a voltage corresponding to the input amplitude signal as power supply voltage Vcc to high-frequency power amplifier  170 . 
     Delay adjuster  140  delays the input phase signal φ(t) based on a delay adjusting signal output from phase compensation control section  151  of phase compensation section  150 , which is described below, and outputs the delayed phase signal φ(t) to variable phase compensation section  152  of phase compensation section  150 . 
     Phase compensation section  150  includes phase compensation control section  151  and variable phase compensation section  152 . 
     Phase compensation control section  151  outputs the delay adjusting signal to delay adjuster  140  in order to control a delay amount in delay adjuster  140 . The delay adjusting signal is described later. 
     Using a signal (frequency spectrum signal) in a frequency domain of an output signal of high-frequency power amplifier  170 , which is input from frequency converter  180  described below, phase compensation control section  151  generates a compensation characteristic signal in order to specify a compensation characteristic that compensates an AM-PM characteristic of high-frequency power amplifier  170 . A method for generating the compensation characteristic signal in phase compensation control section  151  is described later. Phase compensation control section  151  outputs the compensation characteristic signal to variable phase compensation section  152 . 
     Based on the compensation characteristic signal from phase compensation control section  151 , variable phase compensation section  152  determines the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . A method for determining the compensation characteristic in variable phase compensation section  152  is described later. 
     Variable phase compensation section  152  includes an adder therein. Variable phase compensation section  152  inputs the amplitude signal r(t), adds a phase compensation amount φr corresponding to the amplitude signal in the determined compensation characteristic to the phase signal φ(t) to perform phase compensation, and outputs a phase signal φ′(t) (=φ(t)+φr) of post-phase compensation to phase modulation section  160 . 
     Phase modulation section  160  performs phase modulation of a high-frequency signal based on the phase signal φ′(t) of the post-phase compensation, and generates a phase modulation signal. Specifically, phase modulation section  160  generates a phase modulation signal (cos(2πfct+φ′(t))) having a carrier frequency fc by performing the phase modulation of the high-frequency signal having a frequency fc. Phase modulation section  160  outputs the phase modulation signal to high-frequency power amplifier  170 . 
     High-frequency power amplifier  170  amplifies the phase modulation signal according to voltage Vcc supplied from amplitude control section  130 . 
     Frequency converter  180  inputs the output signal of high-frequency power amplifier  170 , performs a fast Fourier transform to the output signal to convert the output signal into the signal (frequency spectrum signal) in the frequency domain, and outputs the spectrum to phase compensation control section  151 . 
     In an operation of transmission circuit  100  having the above configuration, operations of phase compensation control section  151  and variable phase compensation section  152  will mainly be described below. 
     As described above, the ACLR is degraded when high-frequency power amplifier  170  does not have the flat AM-PM characteristic. The AM-PM characteristic is a phase characteristic that varies according to power supply voltage Vcc of high-frequency power amplifier  170 . Power supply voltage Vcc varies according to the amplitude signal r(t). In other words, the AM-PM characteristic is a gain characteristic that varies according to the amplitude signal r(t). 
     Furthermore, therefore, in the present embodiment, the AM-PM characteristic is previously compensated according to the amplitude signal r(t). In the present embodiment, in order to compensate a distortion component caused by an individual variation of high-frequency power amplifier  170 , phase compensation control section  151  generates the compensation characteristic signal specifying the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . Based on the compensation characteristic signal, variable phase compensation section  152  determines the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . Variable phase compensation section  152  compensates the phase signal by adding the phase compensation amount corresponding to the amplitude signal in the compensation characteristic to the phase signal. 
     The method for generating the compensation characteristic signal in phase compensation control section  151  will be described. 
     Phase compensation control section  151  generates the delay adjusting signal in order to set the delay amount of delay adjuster  140  to at least two delay amounts different from each other, and outputs the generated delay adjusting signal to delay adjuster  140 . Therefore, the delay amount of delay adjuster  140  is set to at least the two delay amounts different from each other. 
     When the delay amount of delay adjuster  140  is set to the two delay amounts, phase compensation control section  151  sets the delay amount to a first delay amount τ 1  that is smaller than a delay amount τ 0  (reference delay amount) and a second delay amount τ 2  that is larger than the delay amount τ 0  (τ 1 &lt;τ 0 &lt;τ 2 ). As used herein, the delay amount means a time corresponding to a path difference between an AM path through which the amplitude signal travels from amplitude/phase extraction section  110  to high-frequency power amplifier  170  and a PM path through which the phase signal travels from amplitude/phase extraction section  110  to high-frequency power amplifier  170 . The delay amount τ 0  is a delay amount between the AM path and the PM path of transmission circuit  100 , which are previously determined by a sample inspection. 
     The case in which phase compensation control section  151  sets the delay amount of delay adjuster  140  to the first delay amount τ 1  and the second delay amount τ 2  (τ 1 &lt;τ 0 &lt;τ 2 ) to generate the compensation characteristic signal specifying the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  will be described below. 
     Using the spectrum input from frequency converter  180 , phase compensation control section  151  calculates power levels and imbalanced amounts (relative level difference) of a low-frequency band and a high-frequency band, which are separated from a carrier frequency fc onto a low-frequency side and a high-frequency side by the same mistuned frequency. A method for calculating the power level and the imbalanced amount in phase compensation control section  151  will be described below with reference to  FIG. 5 . 
       FIG. 5  is a view illustrating an example of the spectrum when a variation is included in the AM-PM characteristic.  FIG. 5A  illustrates an example of the spectrum in the case of the delay amount τ=τ 1  (&lt;τ 0 ),  FIG. 5B  illustrates an example of the spectrum in the case of the delay amount τ=τ 0 , and  FIG. 5C  illustrates an example of the spectrum in the case of the delay amount τ=τ 2  (&gt;τ 0 ). A broken line of  FIG. 5  illustrates an example of the spectrum in the case of no variation in the AM-PM characteristic and in the case of the delay amount τ=τ 0 . 
     As illustrated in  FIG. 5A  (delay amount τ 1 ), phase compensation control section  151  acquires ACLR  1110  as the power level at a mistuned point of −5 MHz from the carrier frequency, and acquires ACLR  1120  as the power level at a mistuned point of +5 MHz from the carrier frequency. 
     As illustrated in  FIG. 5C  (delay amount τ 2 ), phase compensation control section  151  acquires ACLR  1210  as the power level at the mistuned point of −5 MHz from the carrier frequency, and acquires ACLR  1220  as the power level at the mistuned point of +5 MHz from the carrier frequency. Phase compensation control section  151  uses the ACLR [dBc] as the power level, thereby easily recognizing an influence of the distortion. 
       FIG. 6  illustrates a relationship between ACLRs  1110 ,  1120 ,  1210 ,  1220  and the delay amount. In  FIG. 6 , ACLR characteristic  1310  indicates a relationship between ACLRs  1110  and  1120  of the low-frequency band (ACLR −5) at the mistuned point of −5 MHz from the carrier frequency and the delay amount. In  FIG. 6 , ACLR characteristic  1320  indicates a relationship between ACLRs  1210  and  1220  of the high-frequency band (ACLR +5) at the mistuned point of +5 MHz from the carrier frequency and the delay amount. 
     Phase compensation control section  151  calculates the imbalanced amount at each delay amount from the ACLR characteristics of the low-frequency band and the high-frequency band. As used herein, the imbalanced amount means the relative level difference between the power level (in terms of dBm) of the low-frequency band and the power level (in terms of dBm) of the high-frequency band, and the low-frequency band and the high-frequency baud are separated from the carrier frequency fc by the same mistuned frequency. 
     For example, phase compensation control section  151  calculates a result, in which the power level in the high-frequency band (ACLR +5) is subtracted from the power level in the low-frequency band (ACLR −5), as the imbalanced amount at the delay amounts τ 1  and τ 2 . 
       FIG. 7  illustrates imbalanced amounts  1410  and  1420  at the delay amounts τ 1  and τ 2 . In  FIG. 7 , characteristic  1430  indicates an imbalance characteristic that is obtained when phase compensation control section  151  continuously adjusts the delay amount of delay adjuster  140 . 
     Phase compensation control section  151  changes the delay amount of delay adjuster  140  into at least the first delay amount τ 1  and the second delay amount τ 2  to measure the at least two imbalanced amounts. 
     Using imbalanced amounts  1410  and  1420  corresponding to at least the two delay amounts τ 1  and τ 2 , phase compensation control section  151  generates the compensation characteristic signal for specifying the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . Specifically, phase compensation control section  151  determines [1] a shape of AM-PM in the compensation characteristic and [2] a change amount of the shape of the AM-PM in the compensation characteristic as pieces of information for specifying the compensation characteristic, and includes the pieces of information in the compensation characteristic signal. 
     A method for determining the shape of the AM-PM of the compensation characteristic and a method for determining the change amount of the shape of the AM-PM will be described below. 
     [1] Shape of AM-PM 
     Phase compensation control section  151  determines the shape of the AM-PM of the compensation characteristic, which is used in variable phase compensation section  151 , from the relationship between the delay amounts τ 1  and τ 2  and the imbalanced amounts at the delay amounts τ 1  and τ 2 . The method for determining the shape of the AM-PM characteristic of the compensation characteristic will be described with reference to  FIG. 8 . 
     For example, in the case that the imbalanced amount indicates a positive value when the delay amount τ in delay adjuster  140  is larger than the reference delay amount τ 0 , phase compensation control section  151  determines that a positively-changing shape is used as the shape of the AM-PM of the compensation characteristic. As used herein, the positively-changing shape means a shape in which the PM is increased with increasing AM. 
     On the other hand, in the case that the imbalanced amount indicates a negative value when the delay amount τ in delay adjuster  140  is larger than the reference delay amount τ 0 , phase compensation control section  151  determines that a negatively-changing shape is used as the shape of the AM-PM of the compensation characteristic. The negatively-changing shape means a shape in which the PM is decreased with increasing AM. 
     [2] Change Amount of Shape of AM-PM 
     Phase compensation control section  151  measures the imbalanced amounts at the delay amounts τ 1  and τ 2  in different times, and determines the change amount of the shape of the AM-PM of the compensation characteristic, which is used in variable phase compensation section  152 , based on the sum of absolute values of the imbalanced amounts. The method for determining the change amount of the shape of the AM-PM characteristic of the compensation characteristic will be described with reference to  FIG. 9 . 
     With increasing sum of the imbalanced amounts, phase compensation control section  151  sets the change amount (a value in which the minimum PM value of the AM-PM shape is subtracted from the maximum PM value) of the shape of the AM-PM of the compensation characteristic, which is used in variable phase compensation section  152 , to a larger value. 
     On the other hand, with decreasing sum of the imbalanced amounts, phase compensation control section  151  sets the change amount of the shape of the AM-PM of the compensation characteristic, which is used in variable phase compensation section  152 , to a smaller value. 
     Therefore, using imbalanced amounts  1410  and  1420  corresponding to at least the two delay amounts τ 1  and τ 2 , phase compensation control section  151  determines the pieces of information for specifying the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . At this point, the pieces of information for specifying the compensation characteristic includes [1] the shape of the AM-PM in the compensation characteristic and [2] the change amount of the shape of the AM-PM in the compensation characteristic. Phase compensation control section  151  generates the pieces of information and outputs the pieces of information as the compensation characteristic signal to variable phase compensation section  152 . 
     Next, an internal configuration and an operation of variable phase compensation section  152  will be described below. 
     [Configuration Example # 1 ] 
       FIG. 10  illustrates an example of the internal configuration of variable phase compensation section  152 . Variable phase compensation section  152  of  FIG. 10  includes selection section  1521 , LUT (Look Up Table) group  1522 , and adder  1523 . 
     LUT group  1522  includes LUTs  1522 - 1  to  1522 - 3 . LUTs  1522 - 1  to  1522 - 3  are tables that provide the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170 , and provide different compensation characteristics, respectively. LUTs  1522 - 1  to  1522 - 3  retain amplitude levels and compensation phase amounts while correlating the amplitude levels and the compensation phase amounts, respectively.  FIG. 11  illustrates an example of the compensation characteristic indicated by the amplitude level and the compensation phase amount, which are retained by each of LUTs  1522 - 1  to  1522 - 3 . 
     Although  FIG. 10  illustrates the example in which LUT group  1522  retains the three LUTs, the number of retained LUTs is not limited to three. 
     Selection section  1521  selects the LUT indicating the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the compensation characteristic signal output from phase compensation control section  151 . Variable phase compensation section  152  outputs the phase compensation amount φr corresponding to the amplitude signal from the LUT, which is selected from LUTs  1522 - 1  to  1522 - 3  by selection section  1521 , to adder  1523 . 
     Adder  1523  performs the phase modulation by adding the phase compensation amount φr corresponding to the amplitude signal to the phase signal φ(t), and outputs the phase signal φ′(t) (=φ(t)+φr) of the post-phase compensation to phase modulation section  160 . 
     By this means, the plural LUTs that provide the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170  are previously prepared in LUT group  1522 . As a result, the distortion can individually be compensated even if the AM-PM characteristic is individually changed by the individual variation to individually change the compensation characteristic. 
     Instead of the plural LUTs, variable phase compensation section  152  prepares plural calculating equations that calculate the phase compensation amount, and selection section  1521  may switch the calculating equations according to the compensation characteristic signal. 
     [Configuration Example # 2 ] 
       FIG. 12  illustrates another example of the internal configuration of variable phase compensation section  152 . Variable phase compensation section  152  of  FIG. 12  includes selection section  1524 , multiplier  1525 , and adder  1523 . 
     Selection section  1524  sets a correction factor k 0 , which is multiplied by the amplitude signal in multiplier  1525 , based on the compensation characteristic signal output from phase compensation control section  151 . As described above, phase compensation control section  151  outputs [1] the information on the shape of the AM-PM in the compensation characteristic and [2] the information on the change amount of the shape of the AM-PM in the compensation characteristic as the compensation characteristic signal to variable phase compensation section  152 . Selection section  1524  sets the correction factor k 0 , which compensates the AM-PM characteristic of high-frequency power amplifier  170 , based on the pieces of information. In this case, variable phase compensation section  152  needs not to include LUT group  1522  unlike [Configuration Example # 1 ], so that it is possible to reduce a circuit scale. 
     Multiplier  1525  multiplies the amplitude signal r(t) and the correction factor k 0  to generate the phase compensation amount φr (=k 0 ·r(t)), and outputs the generated phase compensation amount φr to adder  1523 . 
     [Configuration Example # 3 ] 
       FIG. 13  illustrates still another example of the internal configuration of variable phase compensation section  152 . Variable phase compensation section  152  shown in  FIG. 13  includes selection section  1526 , LUT (Look Up Table) group  1522 , multiplier  1527 , and adder  1523 . 
     Selection section  1526  selects the LUT closest to the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the compensation characteristic signal output from phase compensation control section  151 . Variable phase compensation section  152  outputs the phase compensation amount φr corresponding to the amplitude signal from the LUT, which is selected from LUTs  1522 - 1  to  1522 - 3 , to multiplier  1527 . 
     Furthermore, selection section  1526  sets a correction factor k 1 , which corrects an error with the compensation characteristic indicated by the selected LUT, based on the compensation characteristic signal output from phase compensation control section  151 . 
     Multiplier  1527  multiplies the phase compensation amount φr and the correction factor k 1  to generate the phase compensation amount φ′r (=k 1 ·φr), and outputs the generated phase compensation amount φ′r to adder  1523 . 
     By this means, the compensation characteristic provided by the previously-retained LUTs  1522 - 1  to  1522 - 3  can finely be adjusted so as to be matched with the actual compensation characteristic. Therefore, even if LUT group  1522  prepares only the typical LUT that provides the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170 , it is possible to individually perform the distortion compensation to the difference in compensation characteristic, which is caused by the individual variation of high-frequency power amplifier  170 . 
     As described above, in the present embodiment, frequency converter  180  converts the frequency of the output signal of high-frequency power amplifier  170  and outputs the signal in the frequency domain. Phase compensation section  150  controls the delay amount of delay adjuster  140 , and determines the compensation characteristic that compensates the amplitude-phase characteristic of high-frequency power amplifier  170  using the signals in the frequency domains at the different delay amounts. More specifically, in each delay amount, phase compensation section  150  acquires the power levels of the low-frequency band and the high-frequency band, in which the mistuned frequencies are identical, from the signals in the frequency domains at the different delay amounts. Phase compensation section  150  calculates the imbalanced amount (relative level difference) between the power levels of the low-frequency band and the high-frequency band in each delay amount, and determines the compensation characteristic based on the relationship between the imbalanced amount (relative level difference) and the delay amount. Phase compensation section  150  compensates the phase signal by adding the phase compensation amount corresponding to the amplitude signal in the determined compensation characteristic to the phase signal. 
     By this means, even if the relationship (AM-PM characteristic) between power supply voltage Vcc and passage phase Ph is changed by the individual variation of high-frequency power amplifier  170  and the variation in voltage, it is possible to compensate the AM-PM characteristic of high-frequency power amplifier  170  without providing a demodulator that leads to the increase of the circuit scale. As a result, it is possible to effectively compensate the distortion component caused by the individual variation of high-frequency power amplifier  170  by a small man-hour, and suppress the degradation of the signal quality. 
     (Embodiment 2) 
     In the present embodiment, a polar modulation transmission circuit that sets the delay amount of delay adjuster  140  to an optimum value based on [1] the shape of the AM-PM in the compensation characteristic and [2] the change amount of the shape of the AM-PM in the compensation characteristic will be described. 
       FIG. 14  illustrates a configuration of a main part of a polar modulation transmission circuit (hereinafter simply referred to as a “transmission circuit”) according to the present embodiment of the present invention. In the transmission circuit of the present embodiment of  FIG. 14 , the component common to that of  FIG. 4  is designated by the same numeral, and the description is omitted. Transmission circuit  200  of  FIG. 14  differs from transmission circuit  100  of  FIG. 4  in that transmission circuit  200  includes phase compensation section  210  instead of phase compensation section  150 . 
     Phase compensation section  210  includes phase compensation control section  151 , variable phase compensation section  152 , and delay amount setting section  211 . 
     Delay amount setting section  211  sets an optimum value as the delay amount of delay adjuster  140  using the signal (spectrum) in the frequency domain of the output signal of high-frequency power amplifier  170 , which is input from frequency converter  180 . Delay amount setting section  211  generates the delay adjusting signal indicating the set optimum delay amount, and outputs the generated delay adjusting signal to delay adjuster  140 . 
     A method for setting the delay amount in delay amount setting section  211  will be described with reference to  FIG. 15 . 
       FIG. 15  illustrates ACLR characteristic  1310  illustrated in  FIG. 6 . ACLR characteristic  1310  indicates the relationship between the ACLR of the low-frequency band (ACLR −5) at the mistuned point of −5 MHz from the carrier frequency and the delay amount. In ACLR characteristic  1310 , ACLR  1110  indicates the ACLR at the delay amount τ 1  and ACLR  1120  indicates the ACLR at the delay amount τ 2 . As illustrated in  FIG. 15 , it is assumed that P 1  is the power level of ACLR  1110  while P 2  is the power level of ACLR  1120 . 
     At this point, delay amount setting section  211  calculates a delay amount τP low  in the low-frequency band (ACLR −5) between the first delay amount τ 1  and the second delay amount τ 2  based on a reciprocal of a proportion of the power level P 1  with respect to the first delay amount τ 1  to the power level P 2  with respect to the second delay amount τ 2 . 
     Specifically, delay amount setting section  211  sets the delay amount τP low  using an equation 1.
 
τ P   low   =C (τ2−τ1)/ P 1+τ1  (Equation 1)
 
where C=P 1 ·P 2 /(P 1 +P 2 )
 
Thus, as illustrated in  FIG. 15 , the power level indicates a value close to the minimum value in the low-frequency band (ACLR −5) at the delay amount τP low  by calculating the delay amount τP low .
 
     Similarly, delay amount setting section  211  calculates a delay amount τP high  in the high-frequency band (ACLR +5) from the relationship between the ACLR of the high-frequency band (ACLR +5) at the mistuned point of +5 MHz from the carrier frequency and the delay amount. Specifically, delay amount setting section  211  calculates a delay amount τP high  in the high-frequency band (ACLR +5) between the first delay amount τ 1  and the second delay amount τ 2  using equation 2 based on the reciprocal of the proportion of the power level P 1  with respect to the first delay amount τ 1  to the power level P 2  with respect to the second delay amount τ 2 .
 
τ P   high   =C (τ2−τ1)/ P 1+τ1  (Equation 2)
 
     Delay amount setting section  211  sets a median value between the delay amount τP low  and the delay amount τP high  as the optimum delay amount τP in delay adjuster  140 . 
     Delay amount setting section  211  outputs the delay adjusting signal corresponding to the set delay amount Tp to delay adjuster  140 . By this means, the delay amount of delay adjuster  140  is set to the optimum delay amount. 
     As described above, in the present embodiment, delay amount setting section  211  of phase compensation section  210  sets the optimum value as the delay amount of delay adjuster  140  based on the power level P 1  of the first delay amount τ 1  in the low-frequency band and the power level P 2  of the second delay amount τ 2  in the high-frequency baud. 
     By this means, it is possible to correct the path difference (relative delay difference) between the AM path and the PM path. As a result, even if the path difference (relative delay difference) between the AM path and the PM path is changed, it is possible to effectively compensate the path difference (relative delay difference) between the AM path and the PM path with the small man-hour, and suppress the degradation of the ACLR characteristic, which is caused by the relative delay difference. 
     (Embodiment 3) 
     Generally, when an ambient temperature is changed, a characteristic of the high-frequency power amplifier varies in consideration of an operating environment of the transmission circuit. For example, in the high-frequency power amplifier including an HBT (Heterojunction Bipolar Transistor), a relationship (AM-PM characteristic) between the power supply voltage supplied to the power supply voltage of the high-frequency power amplifier and the passage phase varies by the change of the temperature. That is, the passage phase varies by the temperature even if the same power supply voltage is supplied to the high-frequency power amplifier. Because the AM-PM characteristic of the high-frequency power amplifier is degraded by the variation in passage phase, for example, unfortunately a disturbing signal is generated to the adjacent frequency band to degrade the ACLR. Therefore, it is necessary to adaptively perform the temperature compensation according to the temperature change. In the present embodiment, a polar modulation transmission circuit that adaptively performs the temperature compensation according to the temperature change will be described. 
       FIG. 16  illustrates a configuration of a main part of a polar modulation transmission circuit (hereinafter simply referred to as a “transmission circuit”) according to the present embodiment of the present invention. In the transmission circuit of the present embodiment of  FIG. 16 , the component common to that of  FIG. 4  is designated by the same numeral, and the description is omitted. Transmission circuit  300  of  FIG. 16  differs from transmission circuit  100  of  FIG. 4  in that transmission circuit  300  includes phase compensation section  320  instead of phase compensation section  150  and that temperature measuring instrument  310  is added. 
     Temperature measuring instrument  310  measures a temperature around high-frequency power amplifier  170 , and outputs the measurement result to phase compensation section  320 . 
     Phase compensation section  320  includes phase compensation control section  321  and variable phase compensation section  322 . 
     Phase compensation control section  321  outputs the measurement result of the temperature around high-frequency power amplifier  170 , which is input from temperature measuring instrument  310 , as the compensation characteristic signal to variable phase compensation section  322 . 
     Based on the temperature measurement result indicated by the compensation characteristic signal from phase compensation control section  321 , variable phase compensation section  322  determines the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . The internal configuration of variable phase compensation section  322  is identical to that of variable phase compensation section  152  in [Configuration Example # 1 ] to [Configuration Example # 3 ] illustrated in  FIGS. 10 ,  12 , and  13 . Therefore, the configuration diagram of variable phase compensation section  322  is omitted, and only the operation of variable phase compensation section  322  will be described below. 
     [Configuration Example # 1 ] 
     LUT group  1522  includes LUTs  1522 - 1  to  1522 - 3 . LUTs  1522 - 1  to  1522 - 3  are tables that provide the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170 , and correspond to different temperature, respectively. 
     Selection section  1521  selects the LUT indicating the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the temperature measurement result indicated by the compensation characteristic signal from phase compensation control section  321 . 
     [Configuration Example # 2 ] 
     Selection section  1524  sets the correction factor k 0 , which is multiplied by the amplitude signal in multiplier  1525 , based on the temperature measurement result indicated by the compensation characteristic signal output from phase compensation control section  321 . As described above, because phase compensation control section  321  outputs the measurement result of the temperature around high-frequency power amplifier  170  as the compensation characteristic signal to variable phase compensation section  322 , selection section  1524  sets the correction factor k 0  corresponding to the temperature measurement result. In this case, variable phase compensation section  152  needs not to include LUT group  1522  unlike [Configuration Example # 1 ], so that it is possible to reduce a circuit scale. 
     [Configuration Example # 3 ] 
     Selection section  1526  selects the LUT closest to the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the temperature measurement result indicated by the compensation characteristic signal output from phase compensation control section  321 . 
     Variable phase compensation section  322  outputs the phase compensation amount φr corresponding to the amplitude signal from the LUT, which is selected from LUTs  1522 - 1  to  1522 - 3 , to multiplier  1527 . 
     Furthermore, selection section  1526  sets a correction factor k 1 , which corrects the error with the compensation characteristic indicated by the selected LUT, based on the temperature measurement result indicated by the compensation characteristic signal output from phase compensation control section  321 . 
     By this means, it is possible to finely adjust the compensation characteristic provided by the previously-retained LUTs  1522 - 1  to  1522 - 3  so as to be matched with the actual compensation characteristic. As a result, even if LUT group  1522  prepares only the typical LUT that provides the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170 , it is possible to individually perform the distortion compensation to the difference in compensation characteristic, which is caused by the individual variation of high-frequency power amplifier  170 . 
     As described above, in the present embodiment, temperature measuring instrument  310  measures the temperature around high-frequency power amplifier  170 , and phase compensation section  320  corrects the phase compensation amount based on the temperature measurement result. 
     Therefore, even if the relationship (AM-PM characteristic) between power supply voltage Vcc and passage phase Ph is changed by the temperature change of high-frequency power amplifier  170 , it is possible to compensate the AM-PM characteristic of high-frequency power amplifier  170  without providing the demodulator that leads to the increase of the circuit scale. As a result, it is possible to effectively compensate the distortion component caused by the temperature change high-frequency power amplifier  170  by the small man-hour, and suppress the degradation of the signal quality. 
     (Embodiment 4) 
     In the present embodiment, a polar modulation transmission circuit that controls the phase compensation amount according to the signal in the frequency domain obtained by performing the frequency conversion of the output signal of high-frequency power amplifier and the temperature around high-frequency power amplifier  170  will be described. 
       FIG. 17  illustrates a configuration of a main part of a polar modulation transmission circuit (hereinafter simply referred to as a “transmission circuit”) according to the present embodiment of the present invention. In the transmission circuit of Embodiment 4 of  FIG. 17 , the component common to that of  FIGS. 14 and 16  is designated by the same numeral of  FIG. 14 , and the description is omitted. Transmission circuit  400  of  FIG. 17  differs from transmission circuit  200  of  FIG. 14  in that transmission circuit  400  includes phase compensation section  410  instead of phase compensation section  210  and that temperature measuring instrument  310  is further added. 
     Phase compensation section  410  includes phase compensation control section  411 , variable phase compensation section  412 , and delay amount setting section  413 . 
     Similarly to phase compensation control section  151 , using the signals in the frequency domains at the different delay amounts, phase compensation control section  411  controls the delay amount in delay adjuster  140  to generate information in specifying the compensation characteristic that compensates the amplitude-phase characteristic of high-frequency power amplifier  170 . 
     Similarly to phase compensation control section  321 , phase compensation control section  411  includes the measurement result of the temperature around high-frequency power amplifier  170 , which is input from temperature measuring instrument  310 , and the information specifying the compensation characteristic that compensates the amplitude-phase characteristic of high-frequency power amplifier  170  in the compensation characteristic signal. Phase compensation control section  411  outputs the compensation characteristic signal to variable phase compensation section  412 . 
     Based on the compensation characteristic signal from phase compensation control section  411 , variable phase compensation section  412  determines the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170 . The internal configuration of variable phase compensation section  412  is identical to that of variable phase compensation section  152  in [Configuration Example # 1 ] to [Configuration Example # 3 ] illustrated in  FIGS. 10 ,  12 , and  13 . Therefore, the configuration diagram of variable phase compensation section  412  is omitted, and only the operation of variable phase compensation section  412  will be described below. 
     [Configuration Example # 1 ] 
     LUT group  1522  includes LUTs  1522 - 1  to  1522 - 3 . LUTs  1522 - 1  to  1522 - 3  are tables that provide the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170  in each different temperature, provide different compensation characteristics, respectively, and correspond to different temperatures. 
     Selection section  1521  selects the LUT indicating the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the compensation characteristic signal output from phase compensation control section  411 . 
     [Configuration Example # 2 ] 
     Selection section  1524  sets the correction factor k 0 , which is multiplied by the amplitude signal in multiplier  1525 , based on the compensation characteristic signal output from phase compensation control section  411 . As described above, phase compensation control section  411  outputs [1] the information on the shape of the AM-PM in the compensation characteristic, [2] the information on the change amount of the shape of the AM-PM in the compensation characteristic, and the measurement result of the temperature around high-frequency power amplifier  170  as the compensation characteristic signal to variable phase compensation section  412 . Assuming that the compensation characteristic has linearity, selection section  1524  can form the compensation characteristic using the pieces of information. Thus, selection section  1524  forms the compensation characteristic, and sets the correction factor k 0  corresponding to the change amount in the formed compensation characteristic. In this case, variable phase compensation section  412  needs not to include LUT group  1522  unlike [Configuration Example # 1 ], so that it is possible to reduce the circuit scale. 
     [Configuration Example # 3 ] 
     Selection section  1526  selects the LUT closest to the compensation characteristic that compensates the AM-PM characteristic of high-frequency power amplifier  170  from LUTs  1522 - 1  to  1522 - 3  based on the compensation characteristic signal output from phase compensation control section  411 . 
     Variable phase compensation section  412  outputs the phase compensation amount φr corresponding to the amplitude signal from the LUT, which is selected from LUTs  1522 - 1  to  1522 - 3 , to multiplier  1527 . 
     Further, selection section  1526  sets the correction factor k 1 , which corrects the error with the compensation characteristic indicated by the selected LUT, based on the compensation characteristic signal output from phase compensation control section  411 . 
     Therefore, it is possible to finely adjust the compensation characteristic provided by the previously-retained LUTs  1522 - 1  to  1522 - 3  so as to be matched with the actual compensation characteristic. As a result, even if LUT group  1522  prepares only the typical LUT that provides the compensation characteristic compensating the AM-PM characteristic of high-frequency power amplifier  170 , it is possible to individually perform the distortion compensation to the difference in compensation characteristic, which is caused by the individual variation of high-frequency power amplifier  170 . 
     Similarly to delay amount setting section  211 , delay amount setting section  413  sets the delay amount τp as the delay amount of delay adjuster  140  using the signal (spectrum) in the frequency domain of the output signal of high-frequency power amplifier  170 , which is input from frequency converter  180 . Delay amount setting section  413  also corrects the delay amount τp based on the measurement result of the temperature around high-frequency power amplifier  170 , which is input from temperature measuring instrument  310 . By this means, the influence of the path difference between the AM path and the PM path, which varies by the temperature change of high-frequency power amplifier  170 , can be suppressed. Delay amount setting section  413  generates the delay adjusting signal indicating the delay amount τ′p of the post-correction, and outputs the generated delay adjusting signal to delay adjuster  140 . 
     As described above, in the present embodiment, phase compensation section  410  sets the phase compensation amount corresponding to the amplitude signal and the delay amount based on the relationship between the imbalanced amount (relative level difference) and the delay amount and the measurement result of the temperature around high-frequency power amplifier  170 . By this means, it is possible to compensate the distortion with higher accuracy compared with Embodiment 2. 
     The preferred embodiments of the present invention are described above by way of example. However, the present invention is not limited to the embodiments. It is possible to make various changes without departing from the scope of the present invention. 
     The disclosure of Japanese Patent Application No. 2009-161149, filed on Jul. 7, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     Industrial Applicability 
     In the polar modulation transmission circuit and the polar modulation transmission method of the present invention, it is possible to compensate the distortion component caused by the individual variation of the amplifier with the small man-hour to effectively suppress the degradation of the signal quality. For example, the polar modulation transmission circuit and the polar modulation transmission method are suitable to communication devices such as a mobile phone and a wireless LAN. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  200 ,  300 ,  400  transmission circuit 
           110  amplitude/phase extraction section 
           120  power supply (battery) 
           130  amplitude control section 
           140  delay adjuster 
           150 ,  210 ,  320 ,  410  phase compensation section 
           151 ,  321 ,  411  phase compensation control section 
           152 ,  322 ,  412  variable phase compensation section 
           160  phase modulation section 
           170  high-frequency power amplifier 
           180  frequency converter 
           1521 ,  1524 ,  1526  selection section 
           1522  LUT group 
           1522 - 1  to  1522 - 3  LUT 
           1523  adder 
           1525 ,  1527  multiplier 
           211 ,  413  delay amount setting section 
           310  temperature measuring instrument