Abstract:
Provided is a transmitter apparatus including: a signal conversion section for, in polar modulation, converting input data into an amplitude-component signal and a phase-component signal, and in quadrature modulation, converting input data into an in-phase component signal and a quadrature component signal; a carrier wave generation section for outputting a carrier wave; a mixer section for, in quadrature modulation, generating a quadrature modulation signal; a regulator for, in polar modulation, outputting a supply voltage control signal; and a power amplifier for, in polar modulation, amplifying the supply voltage control signal and superimposing the resultant signal onto the carrier wave, thereby generating a transmission signal, wherein in polar modulation, the carrier wave generation section outputs the carrier wave modulated with respect to phase component, and in quadrature modulation, the carrier wave generation section outputs the carrier wave that is yet to be modulated.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the configuration of a transmitter circuit used in a wireless communication system such as a mobile phone or a wireless LAN. More specifically, the present invention relates to a transmitter circuit that operates with small current consumption and is small in its circuit scale. 
       BACKGROUND ART 
       [0002]    As an example of conventional transmitter circuits, a transmitter circuit that generates a transmission signal by using a quadrature modulation method is known. Since such transmitter circuits using the quadrature modulation method are widely known, the description thereof will be omitted. In addition, as an example of conventional transmitter circuits that operate more efficiently than the circuits using the quadrature modulation method, an EER modulation circuit using an EER (Envelope Elimination and Restoration) modulation method is known. In the EER modulation method, an input signal is divided into a phase-component signal and an amplitude-component signal. First, an oscillation signal generated by an oscillator is multiplied by the phase-component signal, whereby a phase-modulated signal having a constant amplitude is generated. Next, by using a saturation amplifier, the amplitude-component signal is amplified and superimposed onto the phase-modulated signal, whereby a transmission signal is generated. 
         [0003]    In the EER modulation method, there is a feature that a saturation amplifier is used when the amplitude component is superimposed onto the phase-modulated signal. Since the saturation amplifier is operated in a saturation region, a transmission signal can be generated with high power efficiency. 
         [0004]    However, in the EER modulation method, when the output level of a transmission signal is low, the amplifier operates outside the saturation region, whereby power efficiency decreases, or the proportion of power consumption of an amplitude modulation section to power consumption of the entirety of the transmitter becomes large, whereby power efficiency decreases. Therefore, conventionally, there has been proposed a transmitter circuit that linearly operates the amplifier, using the EER modulation method for high level of output and using the quadrature modulation method for low level of output, thereby improving power efficiency. For example, Patent Literature 1 discloses a transmitter circuit  600  shown in  FIG. 7 . Hereinafter, the configuration and the operation of the transmitter circuit  600  will be described. 
         [0005]    An in-phase component signal (I-signal) and a quadrature component signal (Q-signal), which are signals for the quadrature modulation method, are inputted from a baseband section  601  to an interface section  602 . An Rθ conversion section  604  in the interface section  602  switches a modulation method between the quadrature modulation method and the EER modulation method, based on an AGC control signal from the baseband section  601 . In the quadrature modulation method, the Rθ conversion section  604  outputs the I-signal and the Q-signal as they are, without performing signal processing, and in the EER modulation method, the Rθ conversion section  604  performs processing of converting the I-signal and the Q-signal into an amplitude-component signal and a phase-component signal (Rθ conversion processing). The Rθ conversion processing is performed by extraction of phase information by a limiter, and envelope detection. 
         [0006]    In the quadrature modulation method, the I-signal is inputted to a DAC  605 , and in the EER method, the phase-component signal is input to the DAC  605 . In addition, in the quadrature modulation method, the Q-signal is inputted to a DAC  606 , and in the EER method, the amplitude-component signal is inputted to the DAC  606 . An output from the DAC  605  is inputted to a mixer  621  via a baseband filter  625 . 
         [0007]    In the quadrature modulation method, a switch  607  connects the output of the DAC  606  to a Q-component baseband filter  608  in an RF-IC  603 , and in the EER modulation method, the switch  607  connects the output of the DAC  606  to an amplitude modulation circuit  609 . 
         [0008]    In the quadrature modulation method, a switch  610  connects the sum of the I-signal and the Q-signal to an AGC amplifier  611 , and in the EER modulation method, the switch  610  connects only the phase-component signal to the AGC amplifier  611 . In the quadrature modulation method, a switch  612  connects the output of the AGC amplifier  611  to an output buffer  613 , thereby transmitting an output from the AGC amplifier  611 , to an front end not via a power amplifier  614 , and in the EER modulation method, the switch  612  connects the output of the AGC amplifier  611  to the power amplifier  614 , thereby amplifying an output from the AGC amplifier  611 . 
         [0009]    In the quadrature modulation, an input signal is converted into the I-signal and the Q signal. An oscillation signal generated by an oscillator  620  is distributed into two lines by a phase shifter  623 . One of the two signals is outputted to the mixer  621  without shifting the phase of the signal, and the mixer  621  multiplies the signal by the I-signal outputted from the baseband filter  625 . The other one of the two signals is outputted to a mixer  622  after the phase of the signal is shifted, and the mixer  622  multiplies the signal by the Q-signal outputted from the baseband filter  608 . Thereafter, the signals which have been respectively multiplied by the I-signal and the Q-signal are synthesized by the adder  624 , whereby a modulated wave based on the quadrature modulation method is obtained. In the EER modulation method, an input signal is converted into the amplitude-component signal and the phase-component signal. First, an oscillation signal generated by the oscillator  620  is multiplied by the phase-component signal, whereby a phase-modulated signal is generated. Thereafter, the amplitude-component signal is amplified and superimposed onto the phase-modulated signal by the power amplifier  614 , whereby a modulated wave based on the EER modulation method is obtained. That is, the transmitter circuit switches the modulation method such that if the voltage level of a signal is smaller than a predetermined value, the quadrature modulation is performed, and if the voltage level is larger than the predetermined value, the EER modulation is performed. In this way, the conventional transmitter circuit uses the quadrature modulation method and the EER modulation method in a combined manner, thereby realizing reduction in the power consumption. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         [PTL 1] Japanese Patent No. 3979237 
       
     
       SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0011]    However, the phase-modulated signal is strictly required to have a low-noise characteristic. Therefore, in the case where the phase-modulated signal is generated by using the mixer  621  as in the conventional transmitter circuit  600 , the mixer  621  having high performance which is excellent in low-noise characteristic needs to be used. Such a mixer having a low-noise characteristic has high device requirements. Therefore, in general, the circuit scale increases. Moreover, even if the mixer  621  having a low-noise characteristic is used, it is impossible to completely eliminate noise. Therefore, actually, it is necessary to connect an image eliminating filer, which is not shown in  FIG. 7 , to the output of the mixer  621 , thereby eliminating noise. 
         [0012]    As described above, the circuit scale of the conventional transmitter circuit  600  is large because the mixer  621  having high performance and the image eliminating filter are needed, and therefore, there is a limit to improvement in power consumption. Especially in the case of low level of output, the proportion of the power consumption of the power amplifier  614  to the power consumption of the entirety of the transmitter circuit is small. Therefore, even if the power consumption of the power amplifier  614  is reduced by switching the modulation method, this hardly reduces the power consumption of the entirety of the transmitter circuit  600 . 
         [0013]    Therefore, an object of the present invention is to reduce the circuit scale of a transmitter circuit switching a modulation method, and reduce power consumption of the entirety of the circuit, without reducing the quality of a transmission signal. 
       Solution to the Problems 
       [0014]    To achieve the above objects, the first aspect of the present invention is a transmitter circuit that performs two modulation methods of a polar modulation method and a quadrature modulation method, and generates a transmission signal by a designated modulation method, the transmitter circuit comprising: a signal conversion section for, in the polar modulation method, converting input data into an amplitude-component signal and a phase-component signal, and in the quadrature modulation method, converting input data into an in-phase component signal and a quadrature component signal; a carrier wave generation section for outputting a carrier wave corresponding to a designated modulation method; a mixer section for, in the quadrature modulation method, generating a quadrature modulation signal from the carrier wave, the in-phase component signal, and the quadrature component signal; a regulator for, in the polar modulation method, outputting a supply voltage control signal in accordance with the amplitude-component signal; and a power amplifier for, in the polar modulation method, amplifying the supply voltage control signal and superimposing the resultant signal onto the carrier wave, thereby generating the transmission signal, and for, in the quadrature modulation method, amplifying the quadrature modulation signal, thereby generating the transmission signal. In the polar modulation method, the phase-component signal is inputted to the carrier wave generation section, and the carrier wave generation section outputs the carrier wave that has been modulated with respect to phase component. In the quadrature modulation method, the carrier wave generation section outputs the carrier wave that is yet to be modulated. 
         [0015]    According to the second aspect of the present invention based on the first aspect, the carrier wave generation section includes: an oscillation section for generating an oscillation signal corresponding to the designated modulation method; a phase shifter for, in the quadrature modulation method, distributing and phase-shifting the oscillation signal, and outputting the resultant signals as the carrier wave that is yet to be modulated, to the mixer section; and a switch for, in the polar modulation method, outputting the oscillation signal as the carrier wave that has been modulated with respect to phase component, to the power amplifier, and for, in the quadrature modulation method, connecting the oscillation signal to the phase shifter. The oscillation section includes: an oscillator for, in the polar modulation method, generating a high-frequency signal that has been modulated with respect to phase component, based on the phase-component signal inputted to the carrier wave generation section, and for, in the quadrature modulation method, generating a high-frequency signal that is yet to be modulated; and a frequency divider having respective frequency division characteristics corresponding to the polar modulation method and the quadrature modulation method, and the frequency divider switches the frequency division characteristic in accordance with the designated modulation method and frequency-dividing the high-frequency signal, thereby generating the oscillation signal. 
         [0016]    According to the third aspect of the present invention based on the first aspect, the carrier wave generation section includes an oscillation section for generating the carrier wave corresponding to the designated modulation method. In the quadrature modulation method, the carrier wave generation section outputs the carrier wave to the mixer section, and in the polar modulation method, the carrier wave generation section outputs the carrier wave to the power amplifier. The oscillation section includes: an oscillator for, in the polar modulation method, generating a high-frequency signal that has been modulated with respect to phase component, based on the phase-component signal inputted to the carrier wave generation section, and for, in the quadrature modulation method, generating a high-frequency signal that is yet to be modulated; a first frequency divider having a frequency division characteristic corresponding to the polar modulation method; and a second frequency divider having a frequency division characteristic corresponding to the quadrature modulation method, a distribution function, and a phase shifting function. The first frequency divider, in the polar modulation method, frequency-divides the high-frequency signal, thereby generating the carrier wave that has been modulated with respect to phase component, and in the quadrature modulation method, does not operate. The second frequency divider, in the quadrature modulation method, frequency-divides the high-frequency signal, distributes and phase-shifts the resultant signal, thereby generating the carrier wave that is yet to be modulated, and in the polar modulation method, does not operate. 
         [0017]    According to the fourth aspect of the present invention based on the third aspect, the transmitter circuit is a multiband supporting transmitter circuit for generating a transmission signal while switching a band among a plurality of predetermined bands, in accordance with a designation. The carrier wave generation section includes a plurality of the oscillation sections which output the carrier waves respectively corresponding to the plurality of bands. Of the plurality of the oscillation sections, the oscillation section that corresponds to a designated band outputs the carrier wave, and the oscillation sections that do not correspond to the designated band do not output the carrier waves. 
         [0018]    According to the fifth aspect of the present invention based on the fourth aspect, whether or not to output the carrier wave from each of the plurality of oscillation sections is controlled by supply or shutoff of power to the first frequency divider and the second frequency divider included in each of the plurality of oscillation sections. 
         [0019]    The sixth aspect of the present invention is a communication apparatus comprising: the transmitter circuit according to any one of claims  1  to  5 , which generates a transmission signal; and an antenna for outputting the transmission signal generated by the transmitter circuit. 
         [0020]    According to the seventh aspect of the present invention based on the sixth aspect, the communication apparatus further comprises: a receiver circuit for processing a reception signal received from the antenna; and an antenna duplexer section for outputting the transmission signal generated by the transmitter circuit to the antenna, and outputting the reception signal received from the antenna, to the receiver circuit. 
       Advantageous Effects of the Invention 
       [0021]    According to the present invention, it becomes possible to realize a transmitter circuit, switching a modulation method, that has a small circuit scale, without reducing the quality of a transmission signal, thereby reducing the power consumption and the cost of the transmitter circuit or a communication apparatus including the transmitter circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows the configuration of a transmitter circuit according to the first embodiment of the present invention. 
           [0023]      FIG. 2  shows the configuration of a transmitter circuit according to the second embodiment of the present invention. 
           [0024]      FIG. 3  shows the difference between the configurations of the transmitter circuit according to the first embodiment of the present invention and the transmitter circuit according to the second embodiment of the present invention. 
           [0025]      FIG. 4  shows the configuration of a transmitter circuit according to the third embodiment of the present invention. 
           [0026]      FIG. 5  shows the configuration of the transmitter circuit according to the third embodiment of the present invention. 
           [0027]      FIG. 6  shows the configuration of a communication apparatus according to the fourth embodiment of the present invention. 
           [0028]      FIG. 7  shows a conventional transmitter circuit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0029]    Hereinafter, the first embodiment of the present invention will be described. First, a polar modulation method used in the present embodiment will be described. In the EER modulation method used in the conventional transmitter circuit  600 , an oscillation signal outputted by an oscillator is multiplied by a phase-component signal, whereby a phase-modulated signal is generated. Instead, a phase-component signal is inputted to an oscillator, and an oscillation signal including the phase component is directly outputted from the oscillator, whereby a phase-modulated signal can be generated. As used herein, an EER modulation method using this way of generating the phase-modulated signal instead of using the conventional way is, in particular, referred to as a polar modulation method. 
         [0030]      FIG. 1  shows a transmitter circuit  100  according to the present embodiment. With reference to  FIG. 1 , the transmitter circuit  100  includes a signal conversion section  102 , a carrier wave generation section  123 , a mixer section  181 , a regulator  114 , a VGA (variable gain amplifier)  113 , and a power amplifier  115 . The transmitter circuit  100  switches a modulation method between two types, i.e., the quadrature modulation method and the polar modulation method, in accordance with an instruction from the outside. Examples of instructions from the outside include an instruction from a base station. For example, in the case where a communication apparatus including the transmitter circuit  100  communicates with a base station, if the communication condition is bad, the base station can transmit an instruction to increase the output level of a transmission signal, to the communication apparatus. The communication apparatus sends the instruction to the transmitter circuit  100  inside the communication apparatus. In accordance with the instruction, if the output level designated by the instruction is higher than a predetermined threshold value, the transmitter circuit can increase the output level by switching the modulation method from the quadrature modulation method to the polar modulation method. On the other hand, if the output level designated by the instruction is lower than the predetermined threshold value, the transmitter circuit can decrease the output level by switching the modulation method from the polar modulation method to the quadrature modulation method. 
         [0031]    An input signal is inputted to the signal conversion section  102 . When a digital processing section  101  in the signal conversion section  102  has received the instruction to change the output level, the digital processing section  101  switches the modulation method between the quadrature modulation method and the polar modulation method at a timing corresponding to the boundary between unit communication times (time slots). In the case where the instruction is to decrease the output level, the digital processing section  101  converts the input signal into an in-phase component signal (I-signal) and a quadrature component signal (Q-signal) which are signals for the quadrature modulation method, and then outputs the I-signal and the Q-signal. In the case where the instruction is to increase the output level, the digital processing section  101  converts the input signal into an amplitude-component signal and a phase-component signal which are signals for the polar modulation method, and then outputs the amplitude-component signal and the phase-component signal. It is noted that in the case where there is no instruction from the outside, either one of the modulation methods that is set in advance may be used. 
         [0032]    An output from the digital processing section  101  is inputted to DACs (digital analog converters)  103  and  104 . In the quadrature modulation method, the I-signal is inputted to the DAC  103 , and in the polar modulation method, the amplitude-component signal is input to the DAC  103 . In addition, in the quadrature modulation method, the Q-signal is inputted to the DAC  104 , and in the polar modulation method, the phase-component signal is input to the DAC  104 . These inputted signals are converted into analog signals, and the converted signals are outputted to switches  105  and  106 , respectively. 
         [0033]    In the quadrature modulation method, the switch  105  connects the output of the DAC  103  to a mixer  109  (to I-side in  FIG. 1 ), and in the polar modulation method, the switch  105  connects the output of the DAC  103  to the regulator  114  (to r-side in  FIG. 1 ). 
         [0034]    In the quadrature modulation method, the switch  106  connects the output of the DAC  104  to a mixer  110  (to Q-side in  FIG. 1 ), and in the polar modulation method, the switch  106  connects the output of the DAC  104  to an oscillation section  107  in the carrier wave generation section  123  (to θ-side in  FIG. 1 ). In the quadrature modulation method, a switch  108  in the carrier wave generation section  123  connects the output of the oscillation section  107  to a phase shifter  111  in the carrier wave generation section  123  (to Q-side in  FIG. 1 ), and in the polar modulation method, the switch  108  connects the output of the oscillation section  107  to the VGA  113  (to θ-side in  FIG. 1 ). 
         [0035]    That is, in the case where the quadrature modulation method is designated, the signal conversion section  102  outputs the I-signal and the Q-signal. The I-signal and the Q-signal are converted into analog signals by the DACs  103  and  104 , respectively, and then the converted signals are inputted to the mixers  109  and  110 , respectively. The oscillation section  107  in the carrier wave generation section  123  outputs an oscillation signal to the phase shifter  111 . The phase shifter  111  distributes the inputted oscillation signal into two lines. The phase shifter  111  outputs one of the two signals to the mixer  109  without shifting the phase of the signal. The phase shifter  111  shifts the phase of the other one of the two signals by 90 degrees, and outputs the resultant signal to the mixer  110 . The mixers  109  and  110  multiply the inputted signals by the I-signal and the Q-signal, respectively, thereby generating an I-component modulation signal and a Q-component modulation signal, and outputs the I-component modulation signal and the Q-component modulation signal to an adder  112 . The adder  112  combines the I-component modulation signal and the Q-component modulation signal to generate a quadrature modulation signal. In this way, the mixers  109  and  110 , and the adder  112  compose a mixer section for generating a quadrature modulation signal from the carrier wave, the I-signal, and the Q-signal. The quadrature modulation signal is amplified by the VGA  113  in accordance with the transmission output level, and then is inputted to the power amplifier  115 . The power amplifier  115  further amplifies the inputted quadrature modulation signal, thereby generating a transmission signal. It is noted that although the quadrature modulation signal is amplified by the VGA  113  and the power amplifier  115  here, the quadrature modulation signal may be amplified by only one of the VGA  113  and the power amplifier  115 . 
         [0036]    On the other hand, in the case where the polar modulation method is designated, the signal conversion section  102  outputs the amplitude-component signal and the phase-component signal. The amplitude-component signal and the phase-component signal are converted into analog signals by the DACs  103  and  104 , respectively. The converted amplitude-component signal is inputted to the regulator  114 , in which the amplitude-component signal is converted into a supply voltage control signal for the power amplifier  115 , and the supply voltage control signal is inputted to the power amplifier  115 . Meanwhile, the converted phase-component signal is inputted to the oscillation section  107  in the carrier wave generation section  123 . The oscillation section  107  generates a phase-modulated signal including a phase component, based on the phase-component signal. The phase-modulated signal is amplified by the VGA  113  in accordance with the transmission output level, and then is inputted to the power amplifier  115 . The power amplifier  115  amplifies the supply voltage control signal and superimposes the resultant signal onto the inputted phase-modulated signal, thereby generating a transmission signal. It is noted that the DACs  103  and  104  are shared both in the quadrature modulation method and in the polar modulation method, whereby the scale of the transmitter circuit is suppressed. 
         [0037]    According to the present embodiment, the transmitter circuit  100  can switch the modulation method such that if the required output level of a transmission signal is low, the quadrature modulation is performed, and if the required output level is high, the polar modulation is performed. In this way, the quadrature modulation method and the polar modulation method are used in a combined manner, and if the required output level of a transmission signal is low, the operation of the regulator is stopped, using the quadrature modulation method, whereby the power consumption of the entirety of the transmitter circuit is reduced. In addition, in the transmitter circuit  100 , in the polar modulation method, the oscillation section  107  directly generates the phase-modulated signal, based on the phase-component signal. Therefore, in the generation of the phase-modulated signal, it is not necessary to use the mixer, and it is not necessary to take measures for noise caused by the mixer, either. Therefore, it is possible to generate a phase-modulated signal having low noise without using a mixer having high performance that is excellent in low-noise characteristic or using an image eliminating filter. Therefore, it is possible to reduce the circuit scale in comparison with the conventional transmitter circuit and reduce the power consumption, without decreasing the quality of a transmission signal. 
       Second Embodiment 
       [0038]    Hereinafter, a transmitter circuit  200  according to the second embodiment of the present invention will be described with reference to  FIG. 2  and  FIG. 3 . As shown in  FIG. 2 , the transmitter circuit  200  of the present embodiment is obtained by replacing the carrier wave generation section  123  in the transmitter circuit  100  according to the first embodiment with a carrier wave generation section  223 . 
         [0039]      FIG. 3  shows, side-by-side, a part  120  in the transmitter circuit  100  and a part  220  in the transmitter circuit  200  enclosed by dashed lines in  FIG. 1  and  FIG. 2 , respectively, for the purpose of comparing the configurations of the carrier wave generation sections  123  and  223  with each other, in which the internal configurations of the oscillation section  107  and an oscillation section  207  are also shown. 
         [0040]    In the transmitter circuit  100  of the first embodiment, the carrier wave generation section  123  includes the oscillation section  107 , the switch  108 , and the phase shifter  111 . The oscillation section  107  includes an oscillator  121  and a frequency divider  122 . The oscillator  121  generates a higher frequency than the frequency band of a transmission signal. The frequency of an output from the oscillator  121  is decreased by the frequency divider  122 , whereby a carrier wave for modulation signal having a desired frequency is obtained. It is noted that conventionally, such a technique of, in the transmitter circuit, frequency-dividing an output from the oscillator to obtain a modulation wave having a desired frequency is generally used. The frequency divider  122  has respective frequency division characteristics corresponding to the quadrature modulation method and the polar modulation method, and performs frequency division processing, switching the frequency division characteristic in accordance with the modulation method. The destination of an output from the frequency divider  122  is switched by the switch  108  in accordance with the modulation method. 
         [0041]    On the other hand, in the transmitter circuit  200  of the present embodiment, the carrier wave generation section  223  includes only the oscillation section  207 . The oscillation section  207  includes an oscillator  221 , and two frequency dividers  216  and  217 . As in the oscillator  121 , the oscillator  221  generates a higher frequency than the frequency band of a transmission signal. The frequency divider  216  has a frequency division characteristic corresponding to the polar modulation method. Only in the polar modulation method, the frequency divider  216  is supplied with power, and operates. The frequency divider  217  has a frequency division characteristic corresponding to the quadrature modulation method. Only in the quadrature modulation method, the frequency divider  216  is supplied with power, and operates. In addition, the frequency divider  217  also has a signal distributing function and a phase shifting characteristic, as part of the frequency division characteristic. The frequency divider  217  frequency-divides a signal from the oscillator  221 , and then distributes the resultant signal into two lines. The frequency divider  217  outputs one of the two signals to a mixer  209  without shifting the phase of the signal. The frequency divider  217  shifts the phase of the other one of the two signals by 90 degrees, and outputs the resultant signal to a mixer  210 . It is noted that conventionally, such a technique of providing the frequency divider with the signal distributing function and the phase shifting characteristic can be realized without cost. 
         [0042]    The frequency dividers  216  and  217  are obtained by dividing the frequency divider  122  of the first embodiment and moving the function of the phase shifter  111  to one of them. The frequency divider  122  needs to have respective frequency division characteristics corresponding to the quadrature modulation method and the polar modulation method. The circuit scale of the sophisticated frequency divider  122  having such a wide range of frequency division characteristics is large. On the other hand, each of the frequency dividers  216  and  217  has only the frequency division characteristic corresponding to the modulation method that the frequency divider supports. Even the total circuit scale of the two frequency dividers is smaller than the circuit scale of the frequency divider  122  of the first embodiment. Therefore, the present embodiment can reduce the circuit scale in comparison with the first embodiment, thereby reducing the power consumption. 
         [0043]    In addition, in the carrier wave generation section  223 , the switch  108  is not needed, in comparison with the carrier wave generation section  123  of the first embodiment. Since the switch  108  is used for allowing a high-frequency signal to pass, the switch  108  needs to have a frequency characteristic that allows a high-frequency signal to pass, and therefore, the circuit scale thereof is large. In the present embodiment, supply of power to the frequency divider  216  or the frequency divider  217  is switched therebetween, whereby a function of a switch that allows a high-frequency signal to pass is realized, and the switch  108  is not needed. Therefore, the cost can be reduced, and the power consumption is reduced. 
         [0044]    It is noted that the carrier wave generation section  223  needs to include a circuit (not shown) for switching supply of power to the frequency divider  216  or  217  therebetween. However, unlike the switch  108 , the circuit for switching is not a circuit for allowing a high-frequency signal to pass, and therefore, the circuit does not need to have a high function. The scale of the circuit is equal to or smaller than that of a circuit (not shown), included in the carrier wave generation section  123 , for instructing the frequency divider  122  to make switching in accordance with the modulation method in the first embodiment. Therefore, the circuit does not contribute to increase in the circuit scale or the cost, in comparison with the first embodiment. 
       Third Embodiment 
       [0045]    Hereinafter, a transmitter circuit  300  according to the third embodiment of the present invention will be described with reference to  FIG. 4  and  FIG. 5 . As shown in  FIG. 4 , in the present embodiment, a carrier wave generation section  323  is provided in place of the carrier wave generation section  123  of the first embodiment. The carrier wave generation section  323  includes four oscillation sections  351 ,  352 ,  353 , and  354 . The four oscillation sections output respective carrier waves having different frequency bands. That is, the transmitter circuit  300  support a multiband mode. 
         [0046]      FIG. 5  shows a part  320  enclosed by dashed line in  FIG. 4 . In  FIG. 5 , the internal configurations of the oscillation sections  351 ,  352 ,  353 , and  354  are also shown. The oscillation section  351  includes an oscillator  361 , a first frequency divider  371 , and a second frequency divider  372 . Similarly, the oscillation section  352  includes an oscillator  362 , a first frequency divider  373 , and a second frequency divider  374 . The oscillation section  353  includes an oscillator  363 , a first frequency divider  375 , and a second frequency divider  376 . The oscillation section  354  includes an oscillator  364 , a first frequency divider  377 , and a second frequency divider  378 . For example, the oscillation sections  351 ,  352 ,  353 , and  354  respectively support a high-frequency band of 1.9 GHz band, a medium-frequency band of 1.5 GHz band, a low-frequency band of 900 MHz band of a UMTS, and a band of a GSM/EDGE. 
         [0047]    For example, in the case where a high-frequency band of the UMTS method is designated, a carrier wave outputted by the oscillation section  351  is used. In the polar modulation method, the first frequency divider  371  frequency-divides an oscillation signal outputted by the oscillator  361 , while supply of power to the second frequency divider  372  is stopped and the second frequency divider  372  stops its operation. In the quadrature modulation method, the second frequency divider  372  frequency-divides an oscillation signal outputted by the oscillator  361 , while supply of power to the first frequency divider  371  is stopped and the first frequency divider  371  stops its operation. In addition, at this time, supply of power to the other oscillation sections  352 ,  353 , and  354  is stopped, and their operations are stopped. Therefore, the other oscillation sections  352 ,  353 , and  354  do not output carrier waves. In this case, only supply of power to the frequency dividers  373 ,  374 ,  375 ,  376 ,  377 , and  378  which are the frequency dividers in the other oscillators may be stopped. In this way, in the case where only the operations of the frequency dividers in the other oscillators are stopped, since the operations of the other oscillators themselves continue, variation in the oscillation frequencies due to intermittent oscillation can be suppressed. Therefore, even if a band is frequently switched, it is possible to suppress reduction of the quality of a transmission signal. 
         [0048]    Thus, the circuit scale of the transmitter circuit supporting a multiband mode is larger than the circuit scale of the transmitter circuit for a single band as in the second embodiment. However, in comparison among such transmitter circuits supporting a multiband mode, since in the present embodiment, each of the oscillation sections supporting the respective bands individually includes frequency dividers respectively corresponding to the quadrature modulation method and the polar modulation method, it is not necessary to provide a sophisticated frequency divider having a wide range of frequency division characteristics, and a switch for a high-frequency signal, i.e., the switch  108  of the first embodiment. Therefore, the circuit scale of the transmitter circuit of the present embodiment can be reduced. 
         [0049]    In the present embodiment, the transmitter circuit  300  includes the four oscillation sections  351 ,  352 ,  353 , and  354  which respectively support a high-frequency band of 1.9 GHz band, a medium-frequency band of 1.5 GHz band, a low-frequency band of 900 MHz band of the UMTS, and a band of the GSM/EDGE. However, the kinds or the number of supported bands are not limited thereto. The oscillation sections may support other kinds of bands or other number of bands. 
         [0050]    As described above, according to the first to third embodiments, it is possible to provide a transmitter circuit, switching a modulation method between the quadrature modulation method and the polar modulation method, that has a reduced circuit scale, without reducing the quality of a transmission signal, thereby reducing the power consumption of the transmitter circuit. 
         [0051]    In addition, in the first to third embodiments, since the regulators  114 ,  214  and,  314  are not used in the quadrature modulation method, supply of power to the regulators  114 ,  214 , and  314  may be stopped when the quadrature modulation method is performed. In this way, the power consumption is further reduced. 
       Fourth Embodiment 
       [0052]      FIG. 6  is a block diagram showing an example of the configuration of a communication apparatus according to the fourth embodiment of the present invention. The communication apparatus  410  of the fourth embodiment includes a transmitter circuit  400 , a receiver circuit  401 , an antenna duplexer section  402 , and an antenna  403 . The transmitter circuit  400  is the transmitter circuit according to any one of the first to third embodiments. The antenna duplexer section  402  transmits a transmission signal outputted from the transmitter circuit  400 , to the antenna  403 , and prevents the transmission signal from leaking into the receiver circuit  401 . In addition, the antenna duplexer section  402  transmits a reception signal inputted from the antenna  403 , to the receiver circuit  401 , and prevents the reception signal from leaking into the transmitter circuit  400 . 
         [0053]    Therefore, a transmission signal is outputted from the transmitter circuit  400 , and then discharged to the outside from the antenna  403  via the antenna duplexer section  402 . The reception signal is received by the antenna  403 , and then received by the receiver circuit  401  via the antenna duplexer section  402 . It is noted that the communication apparatus  410  may include only the transmitter circuit  400  and the antenna  403 . 
         [0054]    In this way, the communication apparatus  410  according to the present embodiment reduces the power consumption on transmission and reduces the cost of the apparatus by using the transmitter circuits according to the first to third embodiments. In addition, the transmitter circuit according to the present invention is applicable to communication apparatuses such as a mobile terminal or a wireless LAN. 
       INDUSTRIAL APPLICABILITY 
       [0055]    The present invention is useful for transmitter circuits used in, for example, wireless communication systems such as a mobile phone or a wireless LAN, and more particularly, the present invention is useful for reducing the power consumption and reducing the circuit scale. 
       DESCRIPTION OF THE REFERENCE CHARACTERS 
       [0000]    
       
         
           
               100 ,  200 ,  400 ,  300 ,  600  transmitter circuit 
               101 ,  201 ,  301  digital processing section 
               102 ,  202 ,  302  signal conversion section 
               103 ,  104 ,  203 ,  204 ,  303 ,  304  DAC 
               105 ,  106 ,  108 ,  205 ,  206 ,  305 ,  306  switch 
               107 ,  207 ,  351 ,  352 ,  353 ,  354  oscillation section 
               109 ,  110 ,  209 ,  210 ,  309 ,  310  mixer 
               111  phase shifter 
               112 ,  212 ,  312  adder 
               113 ,  213 ,  313  VGA 
               114 ,  214 ,  314  regulator 
               115 ,  215 ,  315  power amplifier 
               121 ,  221 ,  361 ,  362 ,  363 ,  364  oscillator 
               122 ,  216 ,  217 ,  371 ,  372 ,  373 ,  374 ,  375 ,  376 ,  377 ,  378  frequency divider 
               123 ,  223 ,  323  carrier wave generation section 
               181 ,  281 ,  381  mixer section 
               401  receiver circuit 
               402  antenna duplexer section 
               403  antenna 
               410  communication apparatus 
               601  BB section 
               602  interface section 
               603  RF-IC 
               604  Rθ conversion section 
               605 ,  606  DAC 
               607 ,  610 ,  612  switch 
               608 ,  625  baseband filter 
               609  amplitude modulation circuit 
               611  AGC amplifier 
               613  output buffer 
               614  power amplifier 
               620  oscillator 
               621 ,  622  mixer 
               623  phase shifter 
               624  adder