Abstract:
A power amplifying device includes an amplifier that amplifies a signal which is input in accordance with a voltage signal which is supplied to the amplifier, a voltage control section that controls the voltage signal in accordance with a transmission signal, a distortion compensating section that executes a distortion compensating process on the transmission signal by giving a value indicative of a reverse characteristic of the amplifier to the transmission signal in advance and inputs an output signal obtained by executing the distortion compensating process into the amplifier, an amplitude detecting section that detects an amplitude of the transmission signal, and a timing adjusting section that adjusts timings of the output signal and the voltage signal so that a value relating to the distortion compensating process meets a given condition when a detected value of the amplitude of the transmission signal is less than a given value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-68422, filed on Mar. 19, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present invention relates to a power amplifying device and a power amplifying method of performing voltage control and distortion compensation on signals supplied to an amplifier. 
     BACKGROUND 
     A high power efficiency is desired for a power amplifying device used in radio communication. However, the linearity and efficiency of the power amplifying device are characteristics which are incompatible with each other. Accordingly, various distortion compensating methods have been proposed so far in order to make them compatible with each other. 
       FIG. 1  is a configurational diagram illustrating an example of a conventional power amplifying device. In the example illustrated in  FIG. 1 , a transmission signal (I, Q) is supplied to a terminal  1 . The transmission signal is then supplied to a voltage control section  2  and a distortion compensating section  3 . The voltage control section  2  obtains the amplitude of the transmission signal (I, Q) and generates a voltage signal which is based on this amplitude. The voltage signal is then supplied to a power source terminal of a voltage control amplifier  5  via a delay section  4 . 
     The distortion compensating section  3  has a pre-distortion signal generating section  6  and an adaptive control section  7 . The pre-distortion signal generating section  6  generates a pre-distortion signal using, for example, a series type distortion compensation system. The pre-distortion signal is then supplied to an orthogonal modulator  9  via a delay section  8  and is orthogonally modulated. The orthogonally modulated signal of a radio frequency output from the orthogonal modulator  9  is supplied to an input terminal of the voltage control amplifier  5 . 
     The voltage control amplifier  5  performs power amplification on the orthogonally modulated signal by changing its amplification characteristic in accordance with a voltage signal supplied to the power source terminal. An output signal from the voltage control amplifier  5  is output from a terminal  11  via a directional coupler  10 . Part of the orthogonally modulated signal is taken out of the directional coupler  10  and is orthogonally demodulated using an orthogonal demodulator  12 . The obtained demodulated signal (I, Q) is supplied to the coefficient updating section  7  via a filter  13 . 
     The adaptive control section  7  has a pre-distortion signal generating section  14  of the same configuration as the pre-distortion signal generating section  6 , a subtractor  15 , and a coefficient updating section  16 . 
     The pre-distortion signal generating section  14  generates a pre-distortion signal from the demodulated signal and supplies the generated pre-distortion signal to the subtracter  15 , and supplies the demodulated signal to the coefficient updating section  16 . The subtractor  15  subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section  14  from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section  6  to obtain a difference between these signals and supplies the difference to the coefficient updating section  16 . The coefficient updating section  6  calculates distortion compensation coefficients and supplies the calculated distortion compensation coefficients respectively to the pre-distortion signal generating sections  6  and  14  as new distortion compensation coefficients. 
     A technique of storing delay amount information for information on amplitude value and transmission level of an amplitude signal in the form of table data using a polar coordinates modulation system and executing delay adjustment using the information on amplitude signal and transmission level of the amplitude signal as a reference signal is proposed (see, for example, Japanese Laid-open Patent Publication No. 2006-333450). 
     In addition, a technique of improving the responsibility in amplitude of an output signal from an amplifier to a change in control voltage by executing amplitude adjustment on amplitude information which has been subjected to amplitude correction in a steady state using the polar coordinates modulation system is also proposed (see, for example, Japanese Laid-open Patent Publication No. 2006-197537). 
     In the voltage control amplifier  5  that changes the voltage signal supplied to the power source terminal in accordance with the transmission signal, timings of the voltage signal and the transmission signal supplied to the voltage control amplifier  5  are adjusted using the delay section  8 . In general, the timings are adjusted upon adjustment carried out in a factory and after the timings have been adjusted in the factory, a delay amount of the delay section  8  is fixed and is not variably controlled in operation. 
     Therefore, such a problem is caused that in the case that a change occurs in path length characteristic between a path ranging from the voltage control section  2  to the delay section  4  and a path ranging from the distortion compensating section  3 , through the delay section  8 , to the orthogonal modulator  9 , influenced by temperature change and aged deterioration of respective electronic components such as the voltage control section  2 , the delay section  4 , the distortion compensating section  3 , the delay section  8  and the orthogonal modulator  9  making up the power amplifying device, a lag in timing is generated between the voltage signal and the transmission signal to decrease the transmission characteristic. 
     SUMMARY 
     According to an aspect of the embodiments discussed herein, a power amplifying device includes an amplifier that amplifies a signal which is input in accordance with a voltage signal which is supplied to the amplifier, a voltage control section that controls the voltage signal in accordance with a transmission signal, a distortion compensating section that executes a distortion compensating process on the transmission signal by giving a value indicative of a reverse characteristic of an input-to-output characteristic of the amplifier to the transmission signal in advance and inputs an output signal obtained by executing the distortion compensating process into the amplifier, an amplitude detecting section that detects an amplitude of the transmission signal, and a timing adjusting section that adjusts timings of the output signal and the voltage signal so that a value relating to the distortion compensating process executed on the transmission signal meets a given condition when a detected value of the amplitude of the transmission signal is less than a given value. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the embodiments, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a configurational diagram illustrating an example of a conventional power amplifying device; 
         FIG. 2  is a diagram illustrating a configuration of a first embodiment of a power amplifying device; 
         FIG. 3  is a diagram illustrating a configuration of a pre-distortion signal generating section of a series type distortion compensation system; 
         FIGS. 4A-4C  are diagrams illustrating a pre-distortion signal waveform; 
         FIGS. 5A and 5B  are diagrams illustrating a pre-distortion signal waveform; 
         FIG. 6  is a flowchart of an embodiment of a delay adjusting process executed using a power amplifying device; 
         FIG. 7  is a diagram illustrating a configuration of a second embodiment of the power amplifying device; 
         FIG. 8  is a diagram illustrating a configuration of a third embodiment of the power amplifying device; 
         FIG. 9  is a diagram illustrating a configuration of a fourth embodiment of the power amplifying device; 
         FIG. 10  is a diagram illustrating a configuration of a fifth embodiment of the power amplifying device; and 
         FIG. 11  is a diagram illustrating a configuration of a sixth embodiment of the power amplifying device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 2  is a diagram illustrating a configuration of a first embodiment of a power amplifying device. In  FIG. 2 , a transmission signal (I, Q) is supplied to a terminal  21 . The transmission signal is then supplied to a voltage control section  22  and a distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into a function F to generate a voltage signal which is based on the amplitude. In the example illustrated in the drawing, the function F is a function with which a voltage signal is set to a constant value when the amplitude value is less than, for example, a given value α and the voltage signal is set to a value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of a maximum amplitude of the transmission signal). The voltage signal is supplied to a power source terminal of a voltage control amplifier  25  via a delay section  24 . 
     The distortion compensating section  23  has a pre-distortion signal generating section  26 , a delay control section  27 , a pre-distortion signal generating section  28   a , a subtractor  28   b , and a coefficient updating section  28   c . The pre-distortion signal generating section  26  generates a pre-distortion signal using, for example, a series type distortion compensation system. As the pre-distortion signal generating section  26 , a pre-distortion signal generating section of a look-up table system may be also employed. 
     The pre-distortion signal generating section of the series type distortion compensation system has raising parts  80   1  to  80   n  that raise a transmission signal x(t) to 1st, 2nd, 3rd, . . . and n-th powers, multiplying parts  81   1  to  81   n  that multiply outputs from the raising sections  80   1  to  80   n  and coefficients, and an adding part  82  that sums up outputs from the multiplying parts  81   1  to  81   n . A pre-distortion signal y(n) expressed by an equation illustrated at the bottom of  FIG. 3  is generated using the pre-distortion signal generating section  26  configured as mentioned above and is output from the adding part  82 . 
     As the pre-distortion signal generating section  26 , a pre-distortion signal generating section based on a look-up table system, for example, may also be used in which an address is generated from the amplitude of the transmission signal and an increment of the amplitude to gain access to a distortion compensation coefficient table using the address, distortion compensation coefficients may be read out of the distortion compensation coefficient table. Then, the transmission signal and the distortion compensation coefficients are complex-multiplied to generate a pre-distortion signal to which a reverse characteristic of the distortion characteristic of the voltage control amplifier  25  is given. 
     The pre-distortion signal is supplied to an orthogonal modulator  32  via a delay section  31  to be orthogonally modulated. An orthogonally modulated signal of a radio frequency output from the orthogonal modulator  32  is supplied to an input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with a voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. An output signal from the voltage control amplifier  25  is output from a terminal  34  via a directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using an orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  28   a  via a filter  36 . 
     The pre-distortion signal generating section  28   a  has the same configuration as the pre-distortion signal generating section  26 , generates a pre-distortion signal from the demodulated signal, supplies the generated pre-distortion signal to the subtractor  28   b , and supplies the demodulated signal to the coefficient updating section  28   c . The subtractor  28   b  subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section  28   a  from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section  26  to obtain a difference between these signals and supplies the obtained difference to the coefficient updating section  28   c . The coefficient updating section  28   c  calculates distortion compensation coefficients h 1  to h n  using equations (1) and supplies the calculated distortion compensation coefficients h 1  to h n  to the pre-distortion signal generating sections  26  and  28   a  as new distortion compensation coefficients. 
     Next, the equations of generating the distortion compensation coefficients h 1  to h n  will be given. In the equations, x(t) is a transmission signal, r(t) is a modulated signal, e(t) is a difference, μ 1  to μn are coefficients, and n is a degree. 
     
       
         
           
             
               
                 
                   
                     
                       
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     Next, the delay control section  27  will be described. An amplitude converting section  40  in the delay control section  27  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to an amplitude judging section  41 . The amplitude judging section  41  judges whether the amplitude value is less than a given value β and is more than a given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of a maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies a switch-on signal to a switch  42  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on when a transmission signal part of the amplitude is less than the given value β lies in that the amplitude of the pre-distortion signal changes when the transmission signal part of the amplitude is less than the given value β, influenced by a lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     The pre-distortion signal is supplied to the switch  42  from the pre-distortion signal generating section  26  and the switch  42  is turned on when the switch-on signal is being supplied from the amplitude judging section  41 . The switch  42  is turned on to supply the pre-distortion signal to an average amplitude section  43 . The average amplitude section  43  obtains the amplitudes of the pre-distortion signal which is supplied when the switch  42  is turned on and also obtains the average amplitude value of the pre-distortion signal. 
     The average amplitude value of the pre-distortion signal obtained using the average amplitude section  43  is directly supplied to a comparing section  44  and is also supplied to the comparing section  44  via a delay section  45  where the average amplitude value of the pre-distortion signal is delayed by a given time D corresponding to the time to update the distortion compensation coefficient by being subjected to feedback control using the delay section  45 . The comparing section  44  compares the undelayed average amplitude value with the delayed average amplitude and supplies a result of the comparison to a control section  46 . The control section  46  variably adjusts the delay time of the delay section  31  in accordance with the result of comparison. As an alternative, the control section  46  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     (Pre-Distortion Signal Waveform) 
     A situation in which the timing of the transmission signal input into the voltage control amplifier  25  is different from the timing of the voltage signal input into the voltage control amplifier  25  will be discussed. In the above mentioned situation, since a period for which the voltage of the voltage signal is insufficient occurs, the amplitude of the output signal from the voltage control amplifier  25  becomes smaller than a desired amplitude relative to the transmission signal (which is not subjected to pre-distortion) of the amplitude waveform illustrated in  FIG. 4A , and hence notches a 1  to a 5  as illustrated in  FIG. 4B  or notches b 1  to b 5  as illustrated in  FIG. 4C  are formed in the waveform. 
     If the distortion compensation coefficient used in the pre-distortion signal generating section  26  is updated using the coefficient updating section  28  in a state that a signal which is output from the voltage control amplifier  25  having the amplitude smaller than the desired amplitude is fed back, the distortion compensation coefficients corresponding to the notches will be increased so as to compensate for the reductions in amplitude. Accordingly, the variance value of the distortion compensation coefficients will be increased. That is, protrusions c 1  to c 5  illustrated in  FIG. 5A  are generated in the waveform of the pre-distortion signal corresponding to the notches a 1  to a 5  illustrated in  FIG. 4B  in the waveform of the output signal and hence the average value of amplitudes of parts of the pre-distortion signal which are smaller than the maximum amplitude is increased. 
     In addition, protrusions d 1  to d 5  illustrated in  FIG. 5B  are generated in the waveform of the pre-distortion signal corresponding to the notches b 1  to b 5  illustrated in  FIG. 4C  in the waveform of the output signal and hence the average value of amplitudes of parts of the pre-distortion signal which are smaller than the maximum amplitude is increased. 
     Therefore, it may be possible to bring the timing of the transmission signal input into the voltage control amplifier  25  into coincidence with the timing of the voltage signal input into the voltage control amplifier  25  by variably adjusting the delay time of the delay section  31  so that the average amplitude value of the amplitudes of the parts of the pre-distortion signal which are smaller than the maximum amplitude is reduced after the distortion compensation coefficient has been updated. 
     (Flowchart of Delay Adjusting Process) 
       FIG. 6  illustrates a flowchart of one embodiment of a delay adjusting process executed using the power amplifying device. In  FIG. 6 , initialization is executed at S 1 . Next, at S 2 , the control section  46  sets a delay time (timing) of the delay section  31  to T 0  which is a default value (state A). At S 2 , the coefficient updating section  28   c  generates distortion compensation coefficients in the state A to update the distortion compensation coefficients of the pre-distortion signal generating sections  26  and  28   a . The average amplitude section  43  obtains an average amplitude value A at S 3 . 
     At S 4 , the control section  46  sets the delay time (timing) of the delay section  31  to a value T 1  which is prolonged from the value T 0  by a short time Δt (state B). At S 5 , the coefficient updating section  28   c  generates distortion compensation coefficients in the state B to update the distortion compensation coefficients of the pre-distortion signal generating sections  26  and  28   a . At S 6 , the average amplitude section  43  obtains an average amplitude value B. 
     Then, at S 7 , the comparing section  44  compares the average amplitude value A with the average amplitude value B. A&gt;B indicates that the average amplitude value is reduced and hence the timing of the transmission signal is brought into coincidence with the timing of the voltage signal, so that at S 8 , the control section  46  replaces the average amplitude value A with the average amplitude value B and replaces T 0  with T 1  and then returns to S 4  to repeatedly execute the processes from S 4  to S 7 . 
     On the other hand, when at S 7 , A≦B, whether or not execution of the process at S 9  is the first-time execution is judged. When it is judged to be the first-time execution, at S 10 , the sign of the short time Δt is changed to negative and the process returns to S 4  to repeatedly execute the processes at steps S 4  to S 7 . That is, at first, if the delay time (timing) is prolonged from T 0  each time by the short time Δt, then the delay time (timing) will be shortened each time by the short time Δt by executing the process at S 10 . When the execution of the process at S 9  is judged to be a second-time execution or succeeding executions, execution of the process is terminated. 
     Execution of the delay adjusting process allows the generation of distortion compensation coefficients with which the average amplitude value is minimized. Accordingly, a lag in timing between the voltage signal and the transmission signal in the voltage control amplifier may be reduced regardless of temperature change and aged deterioration of the electronic components making up the power amplifying device. 
     Second Embodiment 
       FIG. 7  is a diagram illustrating a configuration of a second embodiment of the power amplifying device. In  FIG. 7 , the same numerals are assigned to the same parts as those in  FIG. 2 . 
     In  FIG. 7 , the transmission signal (I, Q) is supplied to the terminal  21 . The transmission signal is then supplied to the voltage control section  22  and the distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into the function F to generate the voltage signal which is based on the amplitude. In the example illustrated in the drawing, the function F is the function with which the voltage signal is set to the constant value when the amplitude value is less than, for example, the given value α and the voltage signal is set to the value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of the maximum amplitude of the transmission signal). The voltage signal is supplied to the power source terminal of the voltage control amplifier  25  via the delay section  24 . 
     The distortion compensating section  23  includes the pre-distortion signal generating section  26 , a delay control section  50 , the pre-distortion signal generating section  28   a , the subtractor  28   b , and the coefficient updating section  28   c . The pre-distortion signal generating section  26  generates a pre-distortion signal using, for example, a series type distortion compensation system. As the pre-distortion signal generating section  26 , a pre-distortion signal generating section based on a look-up table system may also be employed. 
     The pre-distortion signal is supplied to the orthogonal modulator  32  via the delay section  31  to be orthogonally modulated. The orthogonally modulated signal of the radio frequency output from the orthogonal modulator  32  is supplied to the input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with the voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. The output signal from the voltage control amplifier  25  is output from the terminal  34  via the directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using the orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  28   a  via the filter  36 . 
     The pre-distortion signal generating section  28   a  has the same configuration as the pre-distortion signal generating section  26 , generates the pre-distortion signal from the demodulated signal, supplies the generated pre-distortion signal to the subtractor  28   b , and supplies the demodulated signal to the coefficient updating section  28   c . The subtractor  28   b  subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section  28   a  from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section  26  to obtain the difference between these signals and supplies the obtained difference to the coefficient updating section  28   c . The coefficient updating section  28   c  calculates the distortion compensation coefficients h 1  to h n  using the equations (1), which are the same as those in the first embodiment, and supplies the calculated distortion compensation coefficients h 1  to h n  respectively to the pre-distortion signal generating sections  26  and  28   a  as new distortion compensation coefficients. 
     Next, the delay control section  50  will be described. The amplitude converting section  40  in the delay control section  50  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to the amplitude judging section  41  and an inclination calculating section  51 . The amplitude judging section  41  judges whether the amplitude value is less than the given value β and is more than the given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of the maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies the switch-on signal to the switch  42  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on where the transmission signal part of the amplitude is less than the given value β lies in that the amplitude of the pre-distortion signal changes where the transmission signal part of the amplitude is less than the given value β, influenced by the lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     The inclination calculating section  51  judges whether an inclination where the amplitude of the transmission signal is increased is positive (+) or an inclination where the amplitude of the transmission signal is decreased is negative (−), and supplies a result of the judgment to average amplitude sections  52  and  53 . 
     The pre-distortion signal is supplied to the switch  42  from the pre-distortion signal generating section  26  and the switch  42  is turned on when the switch-on signal is supplied from the amplitude judging section  41 . The switch  42  is turned on to supply the pre-distortion signal to the average amplitude sections  52  and  53 . 
     The average amplitude section  52  obtains amplitudes of a pre-distortion signal obtained when the switch  42  is turned on when the inclination is positive and also obtains the average amplitude value. The average amplitude section  53  obtains amplitudes of a pre-distortion signal obtained when the switch  42  is turned on when the inclination is negative and also obtains the average amplitude value. The average amplitude values obtained respectively using the average amplitude sections  52  and  53  are supplied to a comparing section  54 . 
     When the protrusions c 1  to c 5  illustrated in  FIG. 5A  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4B  are positive and hence the average amplitude value of the amplitudes of the positively inclined parts of the pre-distortion signal is increased, the delay time of the delay section  31  may be changed in a direction in which the average amplitude value is decreased. 
     On the other hand, when protrusions d 1  to d 5  illustrated in  FIG. 5B  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4C  are negative and hence the average amplitude value of the amplitudes of the negatively inclined parts of the pre-distortion signal is increased, the delay time of the delay section  31  may be changed in a direction in which the average amplitude value is increased. 
     The comparing section  54  selects the polarity (positive for the average amplitude section  52  or negative for the average amplitude section  53 ) of the inclination of the average amplitude value which is larger than the other in the average amplitude values of the pre-distortion signals obtained respectively using the average amplitude sections  52  and  53  and supplies the selected polarity to a control section  55 . 
     When the polarity of the inclination is positive, the control section  55  shortens the delay time of the delay section  31  by the short time Δt. On the other hand, when the polarity of the inclination is negative, the control section  55  prolongs the delay time of the delay section  31  by the short time Δt. As an alternative, the control section  55  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     The distortion compensation coefficients with which the average amplitude value is minimized may be generated by repetitively executing the delay adjusting process using the control section  55 . Accordingly, the lag in timing between the voltage signal and the transmission signal in the voltage control amplifier may be reduced regardless of temperature change and aged deterioration of the electronic components making up the power amplifying device. In the second embodiment, since a direction in which the delay time is adjusted is found from the polarity of the inclination, the adjustment time may be reduced. 
     Third Embodiment 
       FIG. 8  is a diagram illustrating a configuration of a third embodiment of the power amplifying device. In  FIG. 8 , the same numerals are assigned to the same parts as those in  FIG. 2 . 
     In  FIG. 8 , the transmission signal (I, Q) is supplied to the terminal  21 . The transmission signal is supplied to the voltage control section  22  and the distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into the function F to generate the voltage signal which is based on the amplitude. In the example illustrated in  FIG. 8 , the function F is the function with which the voltage signal is set to the constant value when the amplitude value is less than, for example, the given value α, and the voltage signal is set to the value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of the maximum amplitude of the transmission signal). The voltage signal is supplied to the power source terminal of the voltage control amplifier  25  via the delay section  24 . 
     The distortion compensating section  23  includes the pre-distortion signal generating section  26 , a delay control section  60 , and the coefficient updating section  29 . 
     The pre-distortion signal generating section  26  may be based on a look-up table system and includes an address generating section  26   a , a distortion compensation coefficient table (a memory)  26   b , and a multiplier  26   c . The amplitude of the transmission signal is supplied from the amplitude converting section  40  in the delay control section  60  to the address generating section  26   a  and the address generating section  26   a  generates the address of the distortion compensation coefficient table  26   b  from the amplitude of the transmission signal supplied thereto and from the increment of the amplitude of the transmission signal. The distortion compensation coefficient table  26   b  is accessed using the address generated by the address generating section  26   a , and a distortion compensation coefficient is read out from the distortion compensation coefficient table  26   b.    
     The multiplier  26   c  complex-multiples the transmission signal x(t) supplied from the terminal  21  and a distortion compensation coefficient h(m) read out from the distortion compensation coefficient table  26   b  to generate a pre-distortion signal y(t) having the reverse characteristic of the distortion characteristic of the voltage control amplifier  25 . m is a value determined from the amplitude of the transmission signal x(t).
 
 y ( t )= h ( m )× x ( t )  (2)
 
     Also in the above mentioned first embodiment, if the pre-distortion signal generating section  26  is based on a look-up table system, the amplitude converting section  40  may be configured to be commonly used by the pre-distortion signal generating section  26  and the delay control section  60  by supplying the amplitude of the transmission signal from the amplitude converting section  40  to the pre-distortion signal generating section  26  as in the case in the third embodiment. 
     The pre-distortion signal is supplied to the orthogonal modulator  32  via the delay section  31  to be orthogonally modulated. The orthogonally modulated signal of the radio frequency output from the orthogonal modulator  32  is supplied to the input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with the voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. The output signal from the voltage control amplifier  25  is output from the terminal  34  via the directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using the orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  29  via the filter  36 . 
     The coefficient updating section  29  obtains an updated portion of the distortion compensation coefficient based on the distortion compensation coefficient read out from the pre-distortion signal generating section  26 , the difference between the transmission signal and the demodulated signal, and the demodulated signal using the equation (3). The coefficient updating section  29  adds the updated portion to the distortion compensation coefficient read out from the distortion compensation coefficient generating section  45  to generate a new distortion compensation coefficient. The coefficient updating section  29  supplies the new distortion compensation coefficient generated to the pre-distortion signal generating section  26  to update the distortion compensation coefficient in the distortion compensation coefficient table. 
     Next, the equation of generating the distortion compensation coefficient h(m) will be given. In the equation, x(t) is a transmission signal, m is a value determined from the amplitude of the transmission signal x(t), e(t) is a difference, r(t) is a demodulated signal, μ is a coefficient, h−(m) is a distortion compensation coefficient before updated, and x′(t) is a previous transmission signal. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     Next, the delay control section  60  will be described. The amplitude converting section  40  in the delay control section  60  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to the amplitude judging section  41 . The amplitude judging section  41  judges whether the amplitude value is less than the given value β and is more than the given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of the maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies the switch-on signal to a switch  62  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on where the transmission signal part of the amplitude is less than the given value β lies in that the amplitude of the pre-distortion signal changes where the transmission signal part of the amplitude is less than the given value β, influenced by the lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     In the third embodiment, unlike the first and second embodiments, the distortion compensation coefficient read out from the distortion compensation coefficient table  26   b  of the distortion signal generating section  26  is supplied to the switch  62 , and the switch  62  is turned on when the switch-on signal is supplied from the amplitude judging section  41 . The switch  62  is turned on to supply the distortion compensation coefficient to a variance calculating section  63 . 
     The variance calculating section  63  obtains the variance (the variance with respect to the distortion compensation coefficients obtained for a given time) of the distortion compensation coefficients obtained when the switch  62  is turned on. The variance value of the distortion compensation coefficients obtained using the variance calculating section  63  is supplied directly to the comparing section  44  and is delayed by the given time D required to update the distortion compensation coefficient by being subjected to feedback control using the delay section  45 , and then is supplied to the comparing section  44 . The comparing section  44  compares the undelayed variance value of the distortion compensation coefficients with the delayed variance of the distortion compensation coefficients and supplies a result of the comparison to the control section  46 . The control section  46  variably adjusts the delay time of the delay section  31  in accordance with the comparison result. The control section  46  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     As described above, when the distortion compensation coefficient of the distortion signal generating section  26  is updated using the coefficient updating section  29  in a state that the signal which is output from the voltage control amplifier  25  having the amplitude smaller than the desired amplitude is fed back, the distortion compensation coefficients corresponding to the notches are increased so as to compensate for the notches which are reduced in amplitude. Accordingly, the variance value of the distortion compensation coefficients is increased. 
     Therefore, the timing of the transmission signal input into the voltage control amplifier  25  may be brought into coincidence with the timing of the voltage signal input into the voltage control amplifier  25  by variably adjusting the delay time of the delay section  31  so that the variance value of the distortion compensation coefficients is decreased. 
     Fourth Embodiment 
       FIG. 9  is a diagram illustrating a configuration of a fourth embodiment of the power amplifying device. In  FIG. 9 , the same numerals are assigned to the same parts as those in  FIG. 7 . 
     In  FIG. 9 , the transmission signal (I, Q) is supplied to the terminal  21 . The transmission signal is supplied to the voltage control section  22  and the distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into the function F to generate the voltage signal which is based on the amplitude. In the example illustrated in the drawing, the function F is the function with which the voltage signal is set to the constant value when the amplitude value is less than, for example, the given value α, and the voltage signal is set to the value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of the maximum amplitude of the transmission signal). The voltage signal is supplied to the power source terminal of the voltage control amplifier  25  via the delay section  24 . 
     The distortion compensating section  23  includes the pre-distortion signal generating section  26 , a delay control section  70 , and the coefficient updating section  29 . 
     The pre-distortion signal generating section  26  is based on a look-up table system and includes the address generating section  26   a , the distortion compensation coefficient table (the memory)  26   b , and the multiplier  26   c . The amplitude of the transmission signal is supplied from the amplitude converting section  40  in the delay control section  60  to the address generating section  26   a , and then the address generating section  26   a  generates the address of the distortion compensation coefficient table  26   b  from the amplitude of the transmission signal supplied thereto and its increment. The distortion compensation coefficient table  26   b  is accessed using the address generated by the address generating section  26   a  and the distortion compensation coefficient concerned is read out from the distortion compensation coefficient table  26   b.    
     The multiplier  26   c  complex-multiples the transmission signal x(t) supplied from the terminal  21  and the distortion compensation coefficient h(m) read out from the distortion compensation coefficient table  26   b  to generate the distortion signal y(t) having the reverse characteristic of the distortion characteristic of the voltage control amplifier  25  using the equation (2) which is the same as that in the third embodiment. 
     Also in the above mentioned second embodiment, if the pre-distortion signal generating section  26  is based on a look-up table system, the amplitude converting section  40  may be configured to be commonly used by the pre-distortion signal generating section  26  and the delay control section  70  by supplying the amplitude of the transmission signal from the amplitude converting section  40  to the pre-distortion signal generating section  26  as in the case in the fourth embodiment. 
     The pre-distortion signal is supplied to the orthogonal modulator  32  via the delay section  31  to be orthogonally modulated. The orthogonally modulated signal of the radio frequency output from the orthogonal modulator  32  is supplied to the input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with the voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. The output signal from the voltage control amplifier  25  is output from the terminal  34  via the directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using the orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  29  via the filter  36 . 
     The coefficient updating section  29  obtains the updated portion of the distortion compensation coefficient based on the distortion compensation coefficient read out from the pre-distortion signal generating section, the difference between the transmission signal and the demodulated signal, and the demodulated signal using the equation (3) which is the same as that in the third embodiment. The coefficient updating section  29  adds the updated portion to the distortion compensation coefficient read out from the distortion compensation coefficient generating section  45  to generate the new distortion compensation coefficient. The coefficient updating section  29  supplies the new distortion compensation coefficient generated to the pre-distortion signal generating section  26  to update the distortion compensation coefficient in the distortion compensation coefficient table. 
     Next, the delay control section  70  will be described. The amplitude converting section  40  in the delay control section  70  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to the amplitude judging section  41  and the inclination calculating section  51 . The amplitude judging section  41  judges whether the amplitude value is less than the given value β and is more than the given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of the maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies the switch-on signal to the switch  62  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on where the transmission signal part of the amplitude value is less than the given value β lies in that the amplitude of the pre-distortion signal changes where the transmission signal part of the amplitude is less than the given value β, influenced by the lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     The inclination calculating section  51  judges whether the inclination at which the amplitude of the transmission signal is increased is positive (+) or the inclination at which the amplitude of the transmission signal is decreased is negative (−) and supplies a result of the judgment to variance calculating sections  72  and  73 . 
     In the fourth embodiment, like the third embodiment, the distortion compensation coefficient read out from the distortion compensation coefficient table  26   b  of the distortion signal generating section  26  is supplied to the switch  62  and the switch  62  is turned on when the switch-on signal is being supplied from the amplitude judging section  41 . The switch  62  is turned on to supply the distortion compensation coefficient to the variance calculating sections  72  and  73 . 
     When the inclination is positive, the variance calculating section  72  obtains the variance of the distortion compensation coefficients obtained when the switch  62  is turned on. When the inclination is negative, the variance calculating section  73  obtains the variance of the distortion compensation coefficients obtained when the switch  62  is turned on. The variance values of the distortion compensation coefficients obtained using the variance calculating sections  72  and  74  are supplied to the comparing section  54 . 
     When the protrusions c 1  to c 5  illustrated in  FIG. 5A  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4B  are positive and hence the variance value of the distortion compensation coefficients of the positively inclined parts is increased, the delay time of the delay section  31  may be changed in a direction in which the delay time is decreased. 
     On the other hand, when the protrusions d 1  to d 5  illustrated in  FIG. 5B  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4C  are negative and hence the variance value of the distortion compensation coefficients of the negatively inclined parts is increased, the delay time of the delay section  31  may be changed in a direction in which the delay time is increased. 
     The comparing section  54  selects the polarity (positive for the variance calculating section  72  or negative for the variance calculating section  73 ) of the inclination of the variance value of the distortion compensation coefficients which is larger in the distortion compensation coefficient variance values obtained respectively using the variance calculating sections  72  and  73  and supplies the selected polarity to the control section  55 . 
     When the polarity of the inclination is positive, the control section  55  shortens the delay time of the delay section  31  by the short time Δt. On the other hand, when the polarity of the inclination is negative, the control section  55  prolongs the delay time of the delay section  31  by the short time Δt. As an alternative, the control section  55  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     The distortion compensation coefficients with which the average amplitude value is minimized may be generated by repetitively executing the delay adjusting process using the control section  55 . Accordingly, the lag in timing between the voltage signal and the transmission signal in the voltage control amplifier may be reduced regardless of temperature change and aged deterioration of the electronic components making up the power amplifying device. In the fourth embodiment, since the direction in which the delay time is adjusted is found from the polarity of the inclination, the time for adjustment may be reduced. 
     Although in the above mentioned embodiment, the pre-distortion signal generating section  26  based on the look-up table system is employed, a pre-distortion signal generating section of a series type distortion compensation system may be used instead. 
     Fifth Embodiment 
       FIG. 10  is a diagram illustrating a configuration of a fifth embodiment of the power amplifying device. In  FIG. 10 , the same numerals are assigned to the same parts as those in  FIG. 2 . 
     In  FIG. 10 , the transmission signal (I, Q) is supplied to the terminal  21 . The transmission signal is then supplied to the voltage control section  22  and the distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into the function F to generate the voltage signal which is based on the amplitude. In the example illustrated in the drawing, the function F is the function with which the voltage signal is set to the constant value when the amplitude value is less than, for example, the given value α, and the voltage signal is set to the value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of the maximum amplitude of the transmission signal). The voltage signal is supplied to the power source terminal of the voltage control amplifier  25  via the delay section  24 . 
     The distortion compensating section  23  includes the pre-distortion signal generating section  26 , the delay control section  27 , the pre-distortion signal generating section  28   a , the subtractor  28   b , and the coefficient updating section  28   c . The pre-distortion signal generating section  26  generates a pre-distortion signal, for example, by a series type distortion compensation system. As the pre-distortion signal generating section,  26 , a pre-distortion signal generating section based on a look-up table system may be used instead. 
     The pre-distortion signal is supplied to the orthogonal modulator  32  via the delay section  31  to be orthogonally modulated. The orthogonally modulated signal of the radio frequency output from the orthogonal modulator  32  is supplied to the input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with the voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. The output signal from the voltage control amplifier  25  is output from the terminal  34  via the directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using the orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  28   a  via the filter  36 . 
     The pre-distortion signal generating section  28   a  has the same configuration as the pre-distortion signal generating section  26 , generates the pre-distortion signal from the demodulated signal, supplies the generated pre-distortion signal to the subtractor  28   b , and supplies the demodulated signal to the coefficient updating section  28   c . The subtractor  28   b  subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section  28   a  from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section  26  to obtain the difference between the signals, and supplies the obtained difference to the coefficient updating section  28   c . The coefficient updating section  28   c  calculates the distortion compensation coefficients h 1  to h n  using the equations (1), which are the same as the equations in the first embodiment, and supplies the calculated distortion compensation coefficients h 1  to h n  respectively to the pre-distortion signal generating sections  26  and  28   a  as new distortion compensation coefficients. 
     A delay control section  90  will be described. A dividing circuit  91  in the delay control section  90  divides a pre-distortion signal A supplied from the pre-distortion signal generating section  26  by a transmission signal B supplied from the terminal  21  (A/B). A value (A/B) corresponding to the distortion compensation coefficient for the transmission signal is obtained by executing the above arithmetic operation and the distortion compensation coefficient corresponding value is supplied to a switch  92 . 
     The amplitude converting section  40  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to the amplitude judging section  41 . The amplitude judging section  41  judges whether the amplitude value is less than the given value β and is more than the given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of the maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies the switch-on signal to a switch  92  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on where the transmission signal part of the amplitude is less than the given value β lies in that the amplitude of the pre-distortion signal changes where the transmission signal part of the amplitude is less than the given value β, influenced by the lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     The distortion compensation coefficient corresponding value is supplied to the switch  92  and the switch  92  is turned on when the switch-on signal is supplied from the amplitude judging section  41 . The switch  92  is turned on to supply the distortion compensation coefficient corresponding value to a variance calculating section  93 . 
     The variance calculating section  93  obtains the variance (the variance with respect to the distortion compensation coefficients obtained for a given time) of the distortion compensation coefficient corresponding values obtained when the switch  62  is turned on. The variance value of the distortion compensation coefficients obtained using the variance calculating section  93  is supplied directly to a comparing section  94  and is delayed by the given time D required to update the distortion compensation coefficient by being subjected to feedback control using a delay section  95  and is then supplied to the comparing section  94 . The comparing section  94  compares the undelayed variance value of the distortion compensation coefficients with the delayed variance of the distortion compensation coefficients and supplies a result of comparison to a control section  96 . The control section  96  variably adjusts the delay time of the delay section  31  in accordance with the comparison result. The control section  96  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     As described above, when the distortion compensation coefficient of the distortion signal generating section  26  is updated using the coefficient updating section  28   c  in a state that the signal which is output from the voltage control amplifier  25  having the amplitude smaller than the desired amplitude is fed back, the distortion compensation coefficients corresponding to the notches are increased so as to compensate for the notches which are reduced in amplitude. Accordingly, the variance value of the distortion compensation coefficient corresponding values is also increased. 
     Therefore, the timing of the transmission signal input into the voltage control amplifier  25  may be brought into coincidence with the timing of the voltage signal input into the voltage control amplifier  25  by variably adjusting the delay time of the delay section  31  such that the variance value of the distortion compensation coefficient corresponding values is decreased. 
     Sixth Embodiment 
       FIG. 11  is a diagram illustrating a configuration of a sixth embodiment of the power amplifying device. In  FIG. 10 , the same numerals are assigned to the same parts as those in  FIG. 2 . 
     In  FIG. 11 , the transmission signal (I, Q) is supplied to the terminal  21 . The transmission signal is then supplied to the voltage control section  22  and the distortion compensating section  23 . The voltage control section  22  obtains the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal (I, Q) and substitutes the obtained amplitude into the function F to generate the voltage signal which is based on the amplitude. In the example illustrated in the drawing, the function F is the function with which the voltage signal is set to a constant value when the amplitude value is less than, for example, the given value α, and the voltage signal is set to the value proportional to the amplitude value when the amplitude value is more than the given value α (α corresponds to, for example, fractions of the maximum amplitude of the transmission signal). The voltage signal is supplied to the power source terminal of the voltage control amplifier  25  via the delay section  24 . 
     The distortion compensating section  23  includes the pre-distortion signal generating section  26 , the delay control section  27 , the pre-distortion signal generating section  28   a , the subtractor  28   b , and the coefficient updating section  28   c . The pre-distortion signal generating section  26  generates a pre-distortion signal, for example, by a series type distortion compensation system. As the pre-distortion signal generating section,  26 , a pre-distortion signal generating section of a look-up table system may be also used. 
     The pre-distortion signal is supplied to the orthogonal modulator  32  via the delay section  31  to be orthogonally modulated. The orthogonally modulated signal of the radio frequency output from the orthogonal modulator  32  is supplied to the input terminal of the voltage control amplifier  25 . 
     The voltage control amplifier  25  changes the amplification characteristic of the orthogonally modulated signal in accordance with the voltage signal supplied to the power source terminal to perform power amplification on the orthogonally modulated signal. The output signal from the voltage control amplifier  25  is output from the terminal  34  via the directional coupler  33 . Part of the orthogonally modulated signal is taken out of the directional coupler  33  and is orthogonally demodulated using the orthogonal demodulator  35 . The obtained demodulated signal (I, Q) is supplied to the pre-distortion signal generating section  28   a  via the filter  36 . 
     The pre-distortion signal generating section  28   a  has substantially the same configuration as the pre-distortion signal generating section  26 , generates the pre-distortion signal from the demodulated signal, supplies the generated pre-distortion signal to the subtractor  28   b , and supplies the demodulated signal to the coefficient updating section  28   c . The subtractor  28   b  subtracts the pre-distortion signal which is generated from the demodulated signal and output from the pre-distortion signal generating section  28   a  from the pre-distortion signal which is generated from the transmission signal and output from the pre-distortion signal generating section  26  to obtain the difference between the signals and supplies the obtained difference to the coefficient updating section  28   c . The coefficient updating section  28   c  calculates the distortion compensation coefficients h 1  to h n  using the equations (1) which are the same as the equations in the first embodiment, and supplies the calculated distortion compensation coefficients h 1  to h n  respectively to the pre-distortion signal generating sections  26  and  28   a  as new distortion compensation coefficients. 
     Next, a delay control section  100  will be described. The dividing circuit  91  in the delay control section  100  divides the pre-distortion signal A supplied from the pre-distortion signal generating section  26  by the transmission signal B supplied from the terminal  21  (A/B). The value (A/B) corresponding to the distortion compensation coefficient for the transmission signal is obtained by executing the above arithmetic operation and the distortion compensation coefficient corresponding value is supplied to the switch  92 . 
     The amplitude converting section  40  obtains the value of the amplitude [(I 2 +Q 2 ) 1/2 ] of the transmission signal supplied from the terminal  21  and supplies the obtained amplitude value to the amplitude judging section  41 . The amplitude judging section  41  judges whether the amplitude value is less than the given value β and is more than the given value α(&lt;β). In the example, the given value β is sufficiently smaller than, for example, the value of the maximum amplitude of the transmission signal, such as, for example, about ⅘ the maximum amplitude of the transmission signal. The amplitude judging section  41  generates and supplies the switch-on signal to the switch  92  when the amplitude value is less than the given value β and more than the given value α. The reason why the switch is set to be turned on where the transmission signal part of the amplitude is less than the given value β lies in that the amplitude of the pre-distortion signal changes where the transmission signal part of the amplitude is less than the given value β, influenced by the lag in timing between the transmission signal in the voltage control amplifier  25  and the pre-distortion signal. 
     An inclination calculating section  101  judges whether the inclination at which the amplitude of the transmission signal is increased is positive (+) or the inclination at which the amplitude of the transmission signal is decreased is negative (−), and supplies a result of the judgment to variance calculating sections  102  and  103 . 
     The distortion compensation coefficient corresponding value is supplied to the switch  92  and the switch  92  is turned on when the switch-on signal is being supplied from the amplitude judging section  41 . The switch  92  is turned on to supply the distortion compensation coefficient corresponding value to the variance calculating sections  102  and  103 . 
     The variance calculating section  102  obtains the variance of the distortion compensation coefficient corresponding values obtained when the switch  92  is turned on when the inclination is positive. The variance calculating section  103  obtains the variance of the distortion compensation coefficient corresponding values obtained when the switch  92  is turned on when the inclination is negative. The variance values of the distortion compensation coefficient corresponding values obtained using the variance calculating sections  102  and  103  are supplied to a comparing section  104 . 
     As described above, when the protrusions c 1  to c 5  illustrated in  FIG. 5A  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4B  are positive and hence the variance value of the distortion compensation coefficient corresponding values of the positively inclined parts is increased, the delay time of the delay section  31  may be changed in a direction in which the delay time is decreased. 
     On the other hand, when the protrusions d 1  to d 5  illustrated in  FIG. 5B  are generated in the waveform of the pre-distortion signal on parts where the inclinations of the amplitudes of the output signal illustrated in  FIG. 4C  are negative and hence the variance value of the distortion compensation coefficient corresponding values of the negatively inclined parts is increased, the delay time of the delay section  31  may be changed in a direction in which the delay time is increased. 
     The comparing section  104  selects the polarity (positive for the variance calculating section  102  or negative for the variance calculating section  103 ) of the inclination of the variance value of the distortion compensation coefficient corresponding values which is larger in the variance values of the distortion compensation coefficient corresponding values obtained respectively using the variance calculating sections  102  and  103  and supplies the selected polarity to a control section  105 . 
     When the polarity of the inclination is positive, the control section  105  shortens the delay time of the delay section  31  by the short time Δt. On the other hand, when the polarity of the inclination is negative, the control section  105  prolongs the delay time of the delay section  31  by the short time Δt. As an alternative, the control section  105  may be configured to variably adjust the delay time of the delay section  24  in place of the delay section  31 . 
     The distortion compensation coefficients with which the average amplitude value is minimized may be generated by repetitively executing the delay adjusting process using the control section  105 . Accordingly, the lag in timing between the voltage signal and the transmission signal in the voltage control amplifier may be reduced regardless of temperature change and aged deterioration of the electronic components making up the power amplifying device. In the sixth embodiment, since the direction in which the delay time is adjusted is found from the polarity of the inclination, the time for adjustment may be reduced. 
     Although in the sixth mentioned embodiment, the pre-distortion signal generating section  26  of the series type distortion compensation system is employed, a pre-distortion signal generating section based on a look-up table system may be used instead. 
     According to the above mentioned first to sixth embodiments, the lag in timing between the voltage signal and the transmission signal supplied to the voltage control amplifier may be reduced. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.