Abstract:
A polar modulator of the present invention includes: a first function block which generates an amplitude signal and a phase signal; a second function block which adjusts the signal delay between the amplitude signal and the phase signal; a third function block which allows the low frequency component of the amplitude signal to pass therethrough; a fourth function block which modulates the phase of the phase signal; a fifth function block which outputs a modulation voltage, based on the amplitude signal; a sixth function block which modulates the amplitude of the phase signal, based on the modulation voltage; a seventh function block which measures the temperature of at least one function block; and an eighth function block which calculates a compensation amount for the signal delay, based on the measured temperature. The second function block adjusts the signal delay, based on the compensation amount.

Description:
TECHNICAL FIELD 
     The present invention relates to a polar modulator for performing amplitude modulation in communication devices such as mobile phones and wireless LAN devices, and particularly relates to a polar modulator for adjusting the signal delay between an amplitude signal and a phase signal which are generated from an input signal. 
     BACKGROUND ART 
     Communication devices such as mobile phones and wireless LAN devices are required to secure the precision of a transmission signal and operate with a low power consumption. For such communication devices, a transmission circuit that is small in size, operates with high efficiency, and outputs a transmission signal having high linearity, is used. 
     As conventional transmission circuits, for example, there are transmission circuits for generating a transmission signal by using a modulation method such as quadrature modulation (hereinafter, referred to as quadrature modulation circuits). In addition, polar modulation circuits are known as conventional transmission circuits that are small in size and operate with high efficiency as compared to the quadrature modulation circuits. 
     A polar modulation circuit generates an amplitude signal and a phase signal from an input signal, and modulates the amplitude signal and the phase signal separately. Then, the amplitude signal and the phase signal which have been modulated in different paths are inputted to an power amplifier. This results in a problem of increase in modulation distortion due to the signal delay between the amplitude signal and the phase signal. 
     In view of the above, a polar modulator for adjusting modulation distortion due to the signal delay between an amplitude signal and a phase signal is conventionally proposed (see Patent Literature 1 and Patent Literature 2, for example).  FIG. 9  shows a conventional polar modulator  900 . In  FIG. 9 , the polar modulator  900  includes a signal generation unit  901 , a delay adjustment unit  902 , a DAC  903 , a phase modulator  904 , a low-pass filter (LPF)  905 , an amplitude signal driven unit  906 , and a power amplifier (PA)  907 . The signal generation unit  901 , the delay adjustment unit  902 , the DAC  903 , and the phase modulator  904  are implemented on a Radio Frequency Integrated Circuit (RFIC)  910 . These function blocks (electronic components) are arranged on a substrate  920  to form the polar modulator  900 . 
     The signal generation unit  901  generates an amplitude signal and a phase signal from an input signal. The amplitude signal generated by the signal generation unit  901  is subjected to delay adjustment by the delay adjustment unit  902 . Then, the amplitude signal having been subjected to the delay adjustment is inputted as an amplitude-modulated signal to the amplitude signal driven unit  906  through the DAC  903  and the LPF  905 . The amplitude signal driven unit  906  applies, to the power amplifier  907 , a modulation voltage corresponding to the amplitude-modulated signal. Meanwhile, the phase signal generated by the signal generation unit  901  is inputted as a phase-modulated signal to the power amplifier  907  through the phase modulator  904 . The power amplifier  907  modulates the amplitude of the phase-modulated signal inputted from the phase modulator  904  by means of the modulation voltage applied by the amplitude signal driven unit  906 , and outputs the resultant signal as an output signal. The amplitude signal driven unit  906  controls an envelope signal, and thus is referred to as an EMIC (Envelope Management IC). 
     Here, the conventional delay adjustment performed by the delay adjustment unit  902  will be briefly described. Patent Literature 1 discloses a configuration in which the signal delay between an amplitude signal and a phase signal is adjusted based on a transmission power, and further discloses a configuration in which an ACPR (Adjacent Channel Power Ratio) and an EVM (Error Vector Magnitude) are used in order to adjust the signal delay between an amplitude signal and a phase signal. Patent Literature 2 also discloses a configuration in which the signal delay between an amplitude signal and a phase signal is controlled based on an ACPR and an EVM. 
     Thus, the conventional polar modulator  900  adjusts modulation distortion due to the signal delay between an amplitude signal and a phase signal by means of the delay adjustment unit  902  described above. 
     CITATION LIST 
     Patent Literature 
     
         
         [Patent Literature 1] U.S. Pat. No. 6,909,757 
         [Patent Literature 2] U.S. Pat. No. 6,404,823 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, if the temperatures of the function blocks (electronic components) of the polar modulator  900  change, the signal delay between an amplitude signal and a phase signal also changes accordingly. The conventional polar modulator can adjust the signal delay in accordance with a transmission power, but cannot adjust the signal delay in accordance with the changes in the temperatures. Therefore, the conventional polar modulator has a disadvantage in that if the temperatures of the function blocks (electronic components) of the polar modulator change, modulation distortion due to the signal delay between the amplitude signal and the phase signal cannot be adjusted to an optimal state. 
       FIG. 10  shows the characteristics of modulation distortion due to the signal delay between an amplitude signal and a phase signal.  FIG. 10  shows modulation distortion characteristics A (plotted by black circles) when the temperatures of both the power amplifier  907  and the LPF  905  are 20° C., and modulation distortion characteristics B (plotted by white circles) when the temperature of the power amplifier  907  is 80° C. and the temperature of the LPF  905  is 40° C. As shown in  FIG. 10 , it is understood that when the temperatures of the power amplifier  907  and the LPF  905  increase, the characteristics of modulation distortion greatly change from A to B. 
     As indicated by the modulation distortion characteristics A, when the temperatures of both the power amplifier  907  and the LPF  905  are 20° C., if the signal delay is set to 0 ns, the modulation distortion will be −55 dBc, which is an optimal state. If the temperature of the power amplifier  907  increases from 20° C. to 80° C. and the temperature of the LPF  905  increases from 20° C. to 40° C., the characteristics of modulation distortion greatly change from A to B. In this case, since the signal delay is 0 ns, the modulation distortion is −42 dBc, which is far from the optimal state. Moreover, the 3GPP (Third Generation Partnership Project) standards cannot be satisfied. 
     Therefore, an object of the present invention is to provide a polar modulator that adjusts, even when the temperatures of the function blocks (electronic components) of the polar modulator change, modulation distortion due to the signal delay between an amplitude signal and a phase signal to an optimal state by adjusting the signal delay in accordance with the changes in the temperatures. 
     Solution to the Problems 
     In order to attain the above objects, a polar modulator of the present invention includes a plurality of function blocks, and comprises: a first function block configured to generate an amplitude signal and a phase signal from an input signal; a second function block configured to adjust the signal delay between the amplitude signal and the phase signal; a third function block configured to allow the low frequency component of the amplitude signal from the second function block to pass therethrough; a fourth function block configured to modulate the phase of the phase signal from the second function block; a fifth function block configured to output a modulation voltage, based on the amplitude signal from the third function block; a sixth function block configured to modulate the amplitude of the phase signal from the fourth function block, based on the modulation voltage from the fifth function block; a seventh function block configured to measure the temperatures of one or more function blocks of the first to sixth function blocks; and an eighth function block configured to calculate a compensation amount for the signal delay, based on the temperatures of the one or more function blocks measured by the seventh function block. The second function block adjusts delay of at least one of the amplitude signal and the phase signal, based on the compensation amount for the signal delay calculated by the eighth function block. 
     The seventh function block preferably measures the temperature of a ninth function block which is a radio frequency integrated circuit including the first function block, the second function block, the fourth function block, and the eighth function block. 
     The polar modulator of the present invention preferably further includes a tenth function block configured to previously store compensation amounts for the signal delay which correspond to values of the temperatures of the plurality of function blocks. In the calculation of the compensation amount for the signal delay, the eighth function block obtains a compensation amount for the signal delay stored in the tenth function block, based on the temperatures of the one or more function blocks measured by the seventh function. 
     Alternatively, the polar modulator of the present invention preferably further includes a tenth function block configured to previously store temperature compensation coefficients for the plurality of function blocks, the temperature compensation coefficients being equivalent to compensation amounts for the signal delay per unit amount of change in the temperatures. The eighth function block obtains a temperature compensation coefficient stored in the tenth function block, based on the temperatures of the one or more function blocks measured by the seventh function block, and calculates a compensation amount for the signal delay. 
     In addition, at least one of the one or more function blocks whose temperatures are measured by the seventh function block typically includes an analog component. 
     In addition, at least one of the one or more function blocks whose temperatures are measured by the seventh function block is typically the sixth function block. 
     In addition, at least one of the one or more function blocks whose temperatures are measured by the seventh function block is typically the third function block. 
     In addition, at least one of the one or more function blocks whose temperatures are measured by the seventh function block is typically the fifth function block. 
     In order to attain the above objects, a communication device of the present invention includes a transmission circuit configured to generate a transmission signal, and an antenna configured to output the transmission signal generated by the transmission circuit, and the polar modulator according to claim  1  is used for the transmission circuit. 
     The communication device of the present invention preferably further includes a reception circuit configured to process a reception signal received from the antenna, and an antenna duplexer configured to output, to the antenna, the transmission signal generated by the transmission circuit, and output, to the reception circuit, the reception signal received from the antenna. 
     Advantageous Effects of the Invention 
     As described above, according to the present invention, the signal delay between an amplitude signal and a phase signal is adjusted based on temperature information about function blocks (electronic components) in accordance with changes in the temperatures. Therefore, a polar modulator can be realized that can adjust modulation distortion due to the signal delay to an optimal state even when the temperatures of the function blocks (electronic components) of the polar modulator change. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a polar modulator  100  according to a first embodiment of the present invention. 
         FIG. 2  shows the characteristics of modulation distortion due to the signal delay between an amplitude signal and a phase signal, and compensation amounts for the signal delay which are based on change in temperature (increase in temperature). 
         FIG. 3  shows a polar modulator  200  according to a second embodiment of the present invention. 
         FIG. 4  shows the characteristics of modulation distortion due to the signal delay between an amplitude signal and a phase signal, and compensation amounts for the signal delay which are based on change in temperature (increase in temperature). 
         FIG. 5  shows the characteristics of modulation distortion due to the signal delay between an amplitude signal and a phase signal, and compensation amounts for the signal delay which are based on change in temperature (decrease in temperature). 
         FIG. 6  shows a polar modulator  300  according to a third embodiment of the present invention. 
         FIG. 7  shows compensation amounts for the signal delay which correspond to values of the temperatures of function blocks (electronic components). 
         FIG. 8  shows a communication device  400  according to a fourth embodiment of the present invention. 
         FIG. 9  shows a conventional polar modulator  900 . 
         FIG. 10  shows the characteristics of modulation distortion due to the signal delay between an amplitude signal and a phase signal. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  shows a polar modulator  100  according to the first embodiment of the present invention. In  FIG. 1 , the polar modulator  100  includes a signal generation unit  101 , a delay adjustment unit  102 , a DAC  103 , a phase modulator  104 , a low-pass filter (LPF)  105 , an amplitude signal driven unit  106 , a power amplifier (PA)  107 , an ADC  108 , a calculation unit  109 , and a temperature measurement unit  201 . The signal generation unit  101 , the delay adjustment unit  102 , the DAC  103 , the phase modulator  104 , the ADC  108 , and the calculation unit  109  are implemented on an RFIC  110 . These function blocks (electronic components) are arranged on a substrate  120  to form the polar modulator  100 . 
     The signal generation unit  101  generates an amplitude signal and a phase signal from an input signal. The amplitude signal and/or the phase signal generated by the signal generation unit  101  are subjected to delay adjustment by the delay adjustment unit  102 . Then, the amplitude signal outputted from the delay adjustment unit  102  is inputted as an amplitude-modulated signal to the amplitude signal driven unit  106  through the DAC  103  and the LPF  105 . The amplitude signal driven unit  106  applies, to the power amplifier  107 , a modulation voltage corresponding to the amplitude-modulated signal. Meanwhile, the phase signal outputted from the delay adjustment unit  102  is inputted as a phase-modulated signal to the power amplifier  107  through the phase modulator  104 . In this embodiment, it is assumed that the phase modulator  104  includes a DAC. The power amplifier  107  modulates the amplitude of the phase-modulated signal inputted from the phase modulator  104  by means of the modulation voltage applied by the amplitude signal driven unit  106 , and outputs the resultant signal as an output signal. The amplitude signal driven unit  106  controls an envelope signal, and thus is referred to as an EMIC. 
     The configuration and operation of the polar modulator  100  which have been described above are substantially the same as the configuration and operation of the conventional polar modulator  900 . The polar modulator  100  according to the present embodiment further includes the temperature measurement unit  201 , the ADC  108 , and the calculation unit  109 , in addition to the components of the conventional polar modulator  900 . 
     The temperature measurement unit  201  measures the temperature of the power amplifier  107 . Temperature information representing the temperature of the power amplifier  107  measured by the temperature measurement unit  201  is digitally converted by the ADC  108 , and is inputted to the calculation unit  109 . Typically, the temperature information is represented by using a voltage value. 
     The calculation unit  109  calculates a compensation amount for the signal delay between the amplitude signal and the phase signal, based on the temperature information representing the temperature of the power amplifier  107  measured by the temperature measurement unit  201 . Detailed descriptions are given below. 
       FIG. 2  shows the characteristics of modulation distortion due to the signal delay between the amplitude signal and the phase signal, and compensation amounts for the signal delay which are based on change in temperature (increase in temperature).  FIG. 2  shows the modulation distortion characteristics A (plotted by black circles) when the temperatures of both the power amplifier  107  and the LPF  105  are 20° C., and the modulation distortion characteristics B (plotted by white circles) when the temperature of the power amplifier  107  is 80° C. and the temperature of the LPF  105  is 40° C. 
     First, in an initial state, the delay adjustment unit  102  sets the signal delay between the amplitude signal and the phase signal in such a manner that the modulation distortion due to the signal delay under a reference temperature is in an optimal state. In this embodiment, the reference temperature is 20° C., and the delay adjustment unit  102  sets the signal delay at 0 ns to cause the modulation distortion to be in an optimal state (−55 dBc), as indicated by the modulation distortion characteristics A when the temperatures of both the power amplifier  107  and the LPF  105  are 20° C. 
     Then, if the temperature of the power amplifier  107  increases from 20° C. to 80° C., and the temperature of the LPF  105  increases from 20° C. to 40° C., the characteristics of modulation distortion greatly change from A to B. At this time, the temperature measurement unit  201  monitors the temperature of the power amplifier  107 , and measures the temperature of the power amplifier  107 . The temperature measurement unit  201  notifies, via the ADC  108 , the calculation unit  109  of the temperature information representing the measured temperature of the power amplifier  107 . 
     The calculation unit  109  calculates a compensation amount for the signal delay, based on the temperature information representing the temperature of the power amplifier  107  measured by the temperature measurement unit  201 . A compensation amount D [ns] for the signal delay is calculated by using a temperature compensation coefficient K [ns/° C.], a measured temperature Tm [° C.], and a reference temperature Tb [° C.], in accordance with (expression 1) shown below. The temperature compensation coefficient K is equivalent to a compensation amount for the signal delay per unit amount of change in the temperature of a function block (electronic component) from the reference temperature, and is previously determined for each function block (electronic component) in accordance with the characteristics of the function block.
 
 D=K× ( Tm−Tb )  (expression 1)
 
     In the polar modulator  100  according to the present embodiment, the reference temperature Tb is 20 [° C.], and the temperature compensation coefficient K of the power amplifier  107  is −0.2 [ns/° C.]. When the measured temperature Tm of the power amplifier  107  which is measured by the temperature measurement unit  201  is 80 [° C.], the compensation amount D for the signal delay is calculated as −12 [ns]. 
     The delay adjustment unit  102  sets the signal delay at 0 ns in the initial state where the temperatures of both the power amplifier  107  and the LPF  105  are 20° C. Next, the delay adjustment unit  102  adjusts the signal delay from 0 ns to −12 ns, based on the compensation amount D for the signal delay which has been calculated as −12 [ns] by the calculation unit  109 . 
     If the temperature of the power amplifier  107  increases from 20° C. to 80° C. and the temperature of the LPF  105  increases from 20° C. to 40° C. the characteristics of modulation distortion greatly change from A to B. In this case, if the signal delay remained at 0 ns as set in the initial state, the modulation distortion would be −42 dBc. However, as described above, since the delay adjustment unit  102  adjusts the signal delay from 0 ns to −12 ns, the modulation distortion is −47 dBc. 
     As described above, the delay adjustment unit  102  in the polar modulator  100  according to the present embodiment adjusts the signal delay based on the temperature information about the power amplifier  107 . Therefore, although not reaching the optimal state, the modulation distortion due to the signal delay in the whole of the polar modulator  100  is improved to satisfy the 3GPP standards and to become approximate to the optimal state. 
     As described above, according to the polar modulator  100  of the first embodiment of the present invention, even when the temperatures of the function blocks (electronic components) of the polar modulator  100  change, since the signal delay between the amplitude signal and the phase signal is adjusted based on the temperature information about the power amplifier  107  in accordance with a change in the temperature, the modulation distortion due to the signal delay can be approximated to the optimal state. 
     Although in the present embodiment, the signal delay between the amplitude signal and the phase signal is adjusted based on the temperature information about the power amplifier  107 , a function block (electronic component) whose temperature is monitored is not limited to the power amplifier  107 . For example, the temperature of the LPF  105  may be monitored. In the case where the LPF  105  is the main factor for the modulation distortion due to the signal delay between the amplitude signal and the phase signal, if the signal delay is adjusted based on temperature information representing a measured temperature of the LPF  105 , the same effect as described above can be obtained. 
     The temperature information represents a measured temperature of the power amplifier  107  as a voltage value. However, the present invention is not limited thereto. For example, the temperature measurement unit  201  may notify the calculation unit  19  of the amount of change in temperature from a reference temperature to a measured temperature as the temperature information. 
     The delay adjustment unit  102  may adjust the signal delay between the amplitude signal and the phase signal by adjusting the amount of delay of either the amplitude signal or the phase signal, or may adjust the signal delay between the amplitude signal and the phase signal by adjusting the amount of delay of both the amplitude signal and the phase signal. 
     Second Embodiment 
       FIG. 3  shows a polar modulator  200  according to the second embodiment of the present invention. In  FIG. 3 , the polar modulator  200  includes the signal generation unit  101 , the delay adjustment unit  102 , the DAC  103 , the phase modulator  104 , the low-pass filter (LPF)  105 , the amplitude signal driven unit  106 , the power amplifier (PA)  107 , the ADC  108 , the calculation unit  109 , a first temperature measurement unit  201 , and a second temperature measurement unit  202 . The signal generation unit  101 , the delay adjustment unit  102 , the DAC  103 , the phase modulator  104 , the ADC  108 , and the calculation unit  109  are implemented on the RFIC  110 . These function blocks (electronic components) are arranged on the substrate  120  to form the polar modulator  200 . In  FIG. 3 , the components of the polar modulator  200  according to the present embodiment that are the same as those of the polar modulator  100  according to the first embodiment of the present invention are denoted by the same reference characters, and the description thereof is omitted. 
     The polar modulator  200  according to the present embodiment is different from the polar modulator  100  according to the first embodiment of the present invention in that the polar modulator  200  includes the second temperature measurement unit  202 . The polar modulator  100  according to the first embodiment of the present invention measures only the temperature of the power amplifier  107 . The polar modulator  200  according to the present embodiment measures the temperature of the power amplifier  107  by means of the first temperature measurement unit  201 , and also measures the temperature of the LPF  105  by means of the second temperature measurement unit  202 . 
     Temperature information representing the temperature of the power amplifier  107  measured by the first temperature measurement unit  201 , and temperature information representing the temperature of the LPF  105  measured by the second temperature measurement unit  202 , are digitally converted by the ADC  108 , and inputted to the calculation unit  109 . 
     The calculation unit  109  calculates a compensation amount for the signal delay between the amplitude signal and the phase signal, based on the temperature information representing the temperature of the power amplifier  107  measured by the first temperature measurement unit  201  and the temperature information representing the temperature of the LPF  105  measured by the second temperature measurement unit  202 . Detailed descriptions are given below. 
       FIG. 4  shows the characteristics of modulation distortion due to the signal delay between the amplitude signal and the phase signal, and compensation amounts for the signal delay which are based on change in temperature (increase in temperature).  FIG. 4  shows the modulation distortion characteristics A (plotted by black circles) when the temperatures of both the power amplifier  107  and the LPF  105  are 20° C., and the modulation distortion characteristics B (plotted by white circles) when the temperature of the power amplifier  107  is 80° C. and the temperature of the LPF  105  is 40° C. 
     First, as described in the first embodiment of the present invention, the delay adjustment unit  102  sets the signal delay between the amplitude signal and the phase signal at 0 ns in an initial state. 
     Next, a description will be given of the case where the temperature of the power amplifier  107  increases from 20° C. to 80° C., and the temperature of the LPF  105  increases from 20° C. to 40° C. The first temperature measurement unit  201  monitors the temperature of the power amplifier  107 , and measures the temperature of the power amplifier  107 . The first temperature measurement unit  201  notifies, via the ADC  108 , the calculation unit  109  of the temperature information representing the measured temperature of the power amplifier  107 . Similarly, the second temperature measurement unit  202  monitors the temperature of the LPF  105 , and measures the temperature of the LPF  105 . The second temperature measurement unit  202  notifies, via the ADC  108 , the calculation unit  109  of the temperature information representing the measured temperature of the LPF  105 . 
     The calculation unit  109  calculates a compensation amount D PA  for the signal delay that is caused by the power amplifier  107 , based on the temperature information representing the temperature of the power amplifier  107  measured by the first temperature measurement unit  201 . Similarly, the calculation unit  109  calculates a compensation amount D LPF  for the signal delay that is caused by the LPF  105 , based on the temperature information representing the temperature of the LPF  105  measured by the second temperature measurement unit  202 . Each of the compensation amount D PA  for the signal delay that is caused by the power amplifier  107  and the compensation amount D LPF  for the signal delay that is caused by the LPF  105  is calculated in accordance with (expression 1) described in the first embodiment of the present invention. 
     Here, a temperature compensation coefficient K PA  of the power amplifier  107  is −0.2 [ns/° C.], and a temperature compensation coefficient K LPF  of the LPF  105  is +0.3 [ns/° C.]. Therefore, the compensation amount D PA  for the signal delay that is caused by the power amplifier  107  is −12 [ns], and the compensation amount D LPF  for the signal delay that is caused by the LPF  105  is +6 [ns]. 
     Further, a compensation amount D for the signal delay in the whole of the polar modulator  200  is calculated by using the D PA  and D LPF , in accordance with (expression 2) shown below.
 
 D=D   PA   +D   LPF   (expression 2)
 
     Therefore, the compensation amount D for the signal delay in the whole of the polar modulator  200  is calculated as −6 [ns]. 
     In the initial state where the temperatures of both the power amplifier  107  and the LPF  105  are 20° C., the delay adjustment unit  102  sets the signal delay at 0 ns. Next, the delay adjustment unit  102  adjusts the signal delay from 0 ns to −6 ns, based on the compensation amount D for the signal delay which has been calculated as −6 [ns] by the calculation unit  109 . 
     If the temperature of the power amplifier  107  increases from 20° C. to 80° C., and the temperature of the LPF  105  increases from 20° C. to 40° C., the characteristics of modulation distortion greatly change from A to B. In this case, if the signal delay remained at 0 ns as set in the initial state, the modulation distortion would be −42 dBc. However, as described above, since the delay adjustment unit  102  adjusts the signal delay from 0 ns to −6 ns, the modulation distortion is −50 dBc. 
     As described above, the delay adjustment unit  102  in the polar modulator  200  according to the present embodiment adjusts the signal delay, based on the temperature information about the power amplifier  107  and the temperature information about the LPF  105 . Accordingly, the modulation distortion due to the signal delay in the whole of the polar modulator  200  becomes more approximate to the optimal state than that in the polar modulator  100  according to the first embodiment of the present invention which adjusts the signal delay based on only the temperature information about the power amplifier  107 . 
     As described above, according to the polar modulator  200  of the second embodiment of the present invention, even when the temperatures of the function blocks (electronic components) of the polar modulator  200  change, since the signal delay between the amplitude signal and the phase signal is adjusted, based on the temperature information about the power amplifier  107  and the temperature information about the LPF  105 , in accordance with changes in the temperatures, the modulation distortion due to the signal delay can be approximated to the optimal state. 
     The case where the temperatures of the power amplifier  107  and the LPF  105  increase has been described above. Hereinafter, the case where the temperatures of the power amplifier  107  and the LPF  105  decrease will be described.  FIG. 5  shows the characteristics of modulation distortion due to the signal delay between the amplitude signal and the phase signal, and compensation amounts for the signal delay which are based on change in temperature (decrease in temperature).  FIG. 5  shows the modulation distortion characteristics A (plotted by black circles) when the temperatures of both the power amplifier  107  and the LPF  105  are 20° C., and modulation distortion characteristics C (plotted by white circles) when the temperature of the power amplifier  107  is −10° C. and the temperature of the LPF  105  is −20° C. 
     If the temperature of the power amplifier  107  decreases from 20° C. to −10° C. and the temperature of the LPF  105  decreases from 20° C. to −20° C. the first temperature measurement unit  201  notifies, via the ADC  108 , the calculation unit  109  of temperature information representing the measured temperature of the power amplifier  107 . Similarly, the second temperature measurement unit  202  notifies, via the ADC  108 , the calculation unit  109  of temperature information representing the measured temperature of the LPF  105 . 
     The calculation unit  109  calculates a compensation amount D PA  for the signal delay that is caused by the power amplifier  107 , based on the temperature information about the power amplifier  107 , and calculates a compensation amount D LPF  for the signal delay that is caused by the LPF  105 , based on the temperature information about the  105 . Here, the temperature compensation coefficient K PA  of the power amplifier  107  when the temperature decreases is −0.3 [ns/° C.], which is different from the value when the temperature increases. On the other hand, the temperature compensation coefficient K LPF  of the LPF  105  is +0.3 [ns/° C.], which is the same as the value when the temperature increases. 
     According to (expression 1) described in the first embodiment of the present invention, the D PA  for the signal delay that is caused by the power amplifier  107  is −9 [ns], and the compensation amount D LPF  for the signal delay that is caused by the LPF  105  is +6 [ns]. Further, the compensation amount D for the signal delay in the whole of the polar modulator  200  is calculated as −3 [ns] in accordance with (expression 2) described above. 
     In the initial state where the temperatures of both the power amplifier  107  and the LPF  105  are 20° C., the delay adjustment unit  102  sets the signal delay at 0 ns. Next, the delay adjustment unit  102  adjusts the signal delay from 0 ns to −3 ns, based on the compensation amount D for the signal delay which has been calculated as −3 [ns] by the calculation unit  109 . 
     If the temperature of the power amplifier  107  decreases from 20° C. to −10° C. and the temperature of the LPF  105  decreases from 20° C. to −20° C. the characteristics of modulation distortion greatly change from A to C. In this case, if the signal delay remained at 0 ns as set in the initial state, the modulation distortion would be −42 dBc. However, as described above, since the delay adjustment unit  102  adjusts the signal delay from 0 ns to −3 ns, the modulation distortion is −52 dBc. 
     As described above, according to the polar modulator  200  of the second embodiment of the present invention, also when the temperatures of the function blocks (electronic components) of the polar modulator  200  decrease, since the signal delay between the amplitude signal and the phase signal is adjusted, based on the temperature information about the power amplifier  107  and the temperature information about the LPF  105 , in accordance with changes in the temperatures, the modulation distortion due to the signal delay can be approximated to the optimal state. 
     In the present embodiment, the value of the temperature compensation coefficient K PA  of the power amplifier  107  is different depending on whether the temperature of the power amplifier  107  increases or decreases from the reference temperature. On the other hand, the value of the temperature compensation coefficient K LPF  of the LPF  105  is the same regardless of whether the temperature of the power amplifier  105  increases or decreases from the reference temperature. Thus, the temperature compensation coefficients depend on the characteristics of the function blocks (electronic components), and in some cases, the value of the temperature compensation coefficient of a function block (electronic component) may vary depending on the way in which the temperature thereof changes. If the temperature compensation coefficients are minutely set based on the characteristics of the function blocks (electronic components), the signal delay can be adjusted with enhanced accuracy, and thus the modulation distortion due to the signal delay can be approximated to the optimal state. 
     Third Embodiment 
       FIG. 6  shows a polar modulator  300  according to the third embodiment of the present invention. In  FIG. 6 , the polar modulator  300  according to the present embodiment includes the components of the polar modulator  200  according to the second embodiment of the present invention, and further includes a third temperature measurement unit  203  for measuring the temperature of the amplitude signal driven unit  106  and a fourth temperature measurement unit  204  for measuring the temperature of the RFIC  110 . In  FIG. 6 , the components of the polar modulator  300  according to the present embodiment that are the same as those of the polar modulator  200  according to the second embodiment of the present invention are denoted by the same reference characters, and the description thereof is omitted. 
     The calculation unit  109  calculates a compensation amount D PA  for the signal delay that is caused by the power amplifier  107 , based on temperature information representing the temperature of the power amplifier  107  measured by the first temperature measurement unit  201 . Similarly, the calculation unit  109  calculates a compensation amount D LPF  for the signal delay that is caused by the LPF  105 , based on temperature information representing the temperature of the LPF  105  measured by the second temperature measurement unit  202 . Further, the calculation unit  109  calculates a compensation amount D EMIC  for the signal delay that is caused by the amplitude signal driven unit  106 , based on temperature information representing the temperature of the amplitude signal driven unit  106  measured by the third temperature measurement unit  203 . The calculation unit  109  calculates a compensation amount D RFIC  for the signal delay that is caused by the RFIC  110 , based on temperature information representing the temperature of the RFIC  110  measured by the fourth temperature measurement unit  204 . Each of the D PA , D LPF , D EMIC , and D RFIC  is calculated in accordance with (expression 1) described in the first embodiment of the present invention. Further, a compensation amount D for the signal delay in the whole of the polar modulator  300  is calculated by using the D PA , D LPF , D EMIC , and D RFIC , in accordance with (expression 3) shown below.
 
 D=D   PA   +D   LPF   +D   EMIC   +D   RFIC   (expression 3)
 
     As described above, the calculation unit  109  calculates the compensation amount D for the signal delay in the whole of the polar modulator  300 , based on the temperature information about the power amplifier  107 , the LPF  105 , the amplitude signal driven unit  106 , and the RFIC  110 . Then, the delay adjustment unit  102  adjusts the signal delay between the amplitude signal and the phase signal, based on the compensation amount D for the signal delay in the whole of the polar modulator  300  which has been calculated by the calculation unit  109 . Therefore, the modulation distortion due to the signal delay in the whole of the polar modulator  300  becomes more approximate to the optimal state than that in the polar modulator  200  according to the second embodiment of the present invention. 
     When the signal delay between the amplitude signal and the phase signal is adjusted based on temperature information about function blocks (electronic components) of the polar modulator in accordance with changes in the temperatures, the larger the number of function blocks about which the temperature information is obtained, the more the modulation distortion due to the signal delay is approximate to the optimal state. In particular, it is remarkably effective to adjust the signal delay between the amplitude signal and the phase signal based on temperature information about analog components of the polar modulator, such as the power amplifier and the LPF, because the signal delay changes significantly with changes in the temperatures of the analog components. 
     The compensation amount D for the signal delay in the whole of the polar modulator  300  can be represented by the following (expression 4), by using coefficients k1 to k4 which depend on the characteristics of the function blocks (electronic components) of the polar modulator, and temperature information T1 to T4 about the function blocks (electronic components).
 
 D=k 1× T 1+ k 2× T 2+ k 3× T 3+ k 4× T 4  (expression 4)
 
     The polar modulator  300  according to the present embodiment may previously store, in a memory or the like, the above-described (expression 4) and coefficients k1 to k4 which depend on the characteristics of the function blocks (electronic components). The calculation unit  109  can calculate the compensation amount D for the signal delay in the whole of the polar modulator  300 , based on (expression 4) and the coefficients k1 to k4 which are previously stored in a memory or the like and based on the temperature information from the first to fourth temperature measurement units  201  to  204 . 
     In addition, the polar modulator  300  according to the present embodiment may store, in a look-up table, compensation amounts for the signal delay which correspond to values of the temperatures of the function blocks (electronic components).  FIG. 7  shows compensation amounts for the signal delay which correspond to values of the temperatures of the function blocks (electronic components). Calculated results of k1×T1, k2×T2, k3×T3, and k4×T4 in (expression 4) described above are previously stored in the look-up table. In this case, the calculation unit  109  refers to the look-up table shown in  FIG. 7 , based on the temperature information from the first to fourth temperature measurement units  201  to  204 , thereby acquiring compensation amounts for the signal delay which correspond to the measured temperatures of the function blocks (electronic components). If the obtained temperatures of the function blocks are not represented in the look-up table, the calculation unit  109  can calculate the compensation amount D for the signal delay in the whole of the polar modulator  300  by just calculating compensation amounts by linear interpolation and summing the compensation amounts. 
     The compensation amount D for the signal delay in the whole of the polar modulator  300  is calculated by using the coefficients k1 to k4 which depend on the characteristics of the function blocks (electronic components) of the polar modulator. However, the present invention is not limited thereto. For example, functions f1 to f4 which depend on the characteristics of the function blocks (electronic components) may be used. In this case, (expression 4) described above can be represented as the following (expression 4)′.
 
 D=f 1( T 1)+ f 2( T 2)+ f 3( T 3)+ f 4( T 4)  (expression 4)′
 
     Fourth Embodiment 
       FIG. 8  shows a communication device according to the fourth embodiment of the present invention. In  FIG. 8 , the communication device  400  includes a transmission circuit  401 , a reception circuit  402 , an antenna duplexer  403 , and an antenna  404 . One of the above-described polar modulators  100  to  300  according to the first to third embodiments of the present invention is used as the transmission circuit  401 . 
     The antenna duplexer  403  transmits, to the antenna  404 , a transmission signal outputted from the transmission circuit  401 , and prevents the transmission signal from leaking into the reception circuit  402 . Further, the antenna duplexer  403  transmits, to the reception circuit  402 , a reception signal inputted from the antenna  404 , and prevents the reception signal from leaking into the transmission circuit  401 . The transmission signal is outputted from the transmission circuit  401 , and released out into space from the antenna  404  via the antenna duplexer  403 . The reception signal is received by the antenna  404 , and then received by the reception circuit  402  via the antenna duplexer  403 . 
     Since one of the polar modulators  100  to  300  according to the first to third embodiments is used as the transmission circuit  401 , it is understood that the same effect as described in the first to third embodiments can be obtained in the transmission circuit  401 . 
     As described above, according to the communication device  400  of the fourth embodiment, even when the temperatures of the function blocks (electronic components) of the transmission circuit  401  change, since the signal delay between an amplitude signal and a phase signal is adjusted based on temperature information about the function blocks (electronic components) in accordance with changes in the temperatures, modulation distortion due to the signal delay can be adjusted to an optimal state. 
     In addition, since the output of the transmission circuit  401  is not branched out to a directional coupler or the like, it is possible to reduce loss on the path from the transmission circuit  401  to the antenna  404 , and thus possible to reduce power consumption at the time of transmission. This enables the communication device  400  to be used as a wireless communication device for a long time period. The communication device  400  may include only the transmission circuit  401  and the antenna  404 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to, for example, communication devices such as mobile phones and wireless LAN devices, and is particularly useful in the case where, for example, the temperatures of function blocks (electronic components) change. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               100 ,  200 ,  300 ,  900  polar modulator 
               101 ,  901  signal generation unit 
               102 ,  902  delay adjustment unit 
               103 ,  903  DAC 
               104 ,  904  phase modulator 
               105 ,  905  low-pass filter (LPF) 
               106 ,  906  amplitude signal driven unit 
               107 ,  907  power amplifier (PA) 
               108  ADC 
               109  calculation unit 
               110 ,  910  RFIC 
               120 ,  920  substrate 
               201 ,  202 ,  203 ,  204  temperature measurement unit 
               400  communication device 
               401  transmission circuit 
               402  reception circuit 
               403  antenna duplexer 
               404  antenna 
             A, B, C modulation distortion characteristics