Abstract:
Disclosed are a distortion-correcting receiver and a distortion correction method capable of precisely cancelling inter-modulation secondary distortion even when an input signal is markedly band-limited in a reception processing unit. In the distortion-correcting receiver ( 100 ), the reception processing unit ( 110 ) executes reception processing of the input signal and outputs a received signal. A replica signal generation unit ( 120 ) generates a replica signal of the inter-modulation distortion component of the input signal by use of the input signal. A correction signal generation unit ( 130 ) comprises a frequency property imparting unit ( 131 ) and a weighting unit ( 132 ), adjusts the frequency property and the gain of the replica signal, and generates a correction signal. A correction signal injection unit ( 140 ) adds the reverse-phase signal of the correction signal to the received signal to correct the received signal.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a wireless communication apparatus. More particularly, the present invention relates to a distortion correcting receiver and a distortion correcting method having a function of correcting a secondary inter-modulation distortion. 
       BACKGROUND ART 
       [0002]    There is known, as a wireless device such as a cell phone or one-segment receiver, a receiver using a direct sampling mixer (DSM) (which will be referred to as “direct sampling receiver” below). For example, a structure of a receiver using the DSM is disclosed in patent literature 1. 
         [0003]    In recent years, band widening is required also for the direct sampling receiver. In order to achieve a receiving system with a wider band, a function of canceling a secondary inter-modulation distortion needs to be enhanced. 
         [0004]    The method disclosed in patent literature 2 is well known as one method for canceling a secondary inter-modulation distortion. The method generates a replica signal having the same frequency component as a secondary inter-modulation distortion occurring in a radio frequency (RF) block by square calculation for RF input and a low pass filter processing for removing a high frequency component. Then, an optimal weight is assigned to the replica signal and the weighted replica signal as a correction signal is injected in reverse phase into the RF block output, thereby canceling the secondary inter-modulation distortion. 
         [0005]    The direct sampling receiver has a characteristic that a signal in an output intermediate frequency (IF) band is significantly band-limited by a frequency band. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2004-289793 
       
     
       PTL 2 
       [0000]    
       
         Published Japanese Translation No. 2006-503450 of the PCT International Publication 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    There is a problem that since even when the distortion correcting technique disclosed in patent literature 2 is directly applied to a direct sampling receiver, a secondary inter-modulation distortion occurring in the direct sampling receiver and a correction signal used for canceling the secondary distortion do not have the same magnitude in all the frequency bands, the secondary inter-modulation distortion is difficult to be completely can cell ed. 
         [0009]    In other words, when a receiving system having no band limitation in band frequencies or a narrowband signal is handled, the secondary inter-modulation distortion can be cancelled only by use of the method described in patent literature 2. 
         [0010]    However, in a receiving system that handles a broadband signal such as the direct sampling receiver, the function of accurately canceling a secondary inter-modulation distortion is difficult to achieve without taking into account a frequency dependent characteristic of the secondary inter-modulation distortion. 
         [0011]    It is therefore an object of the present invention to provide a distortion correcting receiver and a distortion correcting method capable of accurately canceling a secondary inter-modulation distortion. 
       Solution to Problem 
       [0012]    One aspect of a distortion correcting receiver according to the present invention comprises a reception processing section that performs a reception processing on an input signal and outputs a received signal, a replica signal generating section that uses the input signal to generate a replica signal of the inter-modulation distortion component of the input signal, a correction signal generating section that has a frequency characteristic assigning section and a weight assigning section and adjusts a frequency characteristic and gain of the replica signal to generate a correction signal, and a correction signal injecting section that adds the anti-phase signal of the correction signal to the received signal to correct the received signal. 
         [0013]    One aspect of the distortion correcting receiver according to the present invention is such that the frequency characteristic assigning section assigns a frequency characteristic of the reception processing section to the replica signal, and the weight assigning section adjusts a gain by weighting the replica signal assigned with the frequency characteristic of the reception processing section, and generates the correction signal. 
         [0014]    One aspect of the distortion correcting receiver according to the present invention is such that the weight assigning section assigns a weight to the replica signal to adjust a gain, and the frequency characteristic assigning section assigns the frequency characteristic of the reception processing section to the weighted replica signal and generates the correction signal. 
         [0015]    One aspect of a distortion correcting method according to the present invention comprises the steps of performing a reception processing on an input signal and outputting a received signal, generating a replica signal of the inter-modulation distortion component of the input signal by use of the input signal, adjusting a frequency characteristic and gain of the replica signal and generating a correction signal, and adding the anti-phase signal of the correction signal to the received signal and correcting the received signal. 
       Advantageous Effects of Invention 
       [0016]    According to the present invention, since a correction signal taking into account a frequency characteristic of a distortion component occurring in a reception processing section is used to cancel the distortion component, an inter-modulation distortion can be accurately cancelled even when an input signal is significantly band-limited in the reception processing section. By this, a broadband receiving system having excellent communication quality can be achieved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a diagram showing a structure of a distortion correcting circuit described in patent literature 2; 
           [0018]      FIG. 2  is a block diagram showing a structure of essential sections in a receiver according to Embodiment 1 of the present invention; 
           [0019]      FIG. 3  is a block diagram showing a structure of essential sections in a receiver according to Embodiment 2 of the present invention; 
           [0020]      FIG. 4  is a diagram showing a structure of a direct sampling receiver; 
           [0021]      FIG. 5  is a block diagram showing a structure of essential sections in a receiver according to Embodiment 3 of the present invention; 
           [0022]      FIG. 6  is a block diagram showing a structure of essential sections in a receiver according to Embodiment 4 of the present invention; 
           [0023]      FIG. 7  is a block diagram showing a structure of essential sections in a receiver according to Embodiment 5 of the present invention; and 
           [0024]      FIG. 8  is a block diagram of a structure of essential sections in a receiver according to Embodiment 6 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Embodiments of the present invention will be described below in detail with reference to the drawings. 
       Embodiment 1 
       [0026]      FIG. 2  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. 
         [0027]    In receiver  100  of  FIG. 2 , a path routing through reception processing section  100  is called main path, and a path routing through replica signal generating section  120  and correction signal generating section  130  is called replica path. 
         [0028]    In the present embodiment, a secondary inter-modulation distortion component occurring in the main path is generated as a correction signal in the replica path and the anti-phase signal of the correction signal is injected into a mix signal in correction signal injecting section  140 , thereby canceling the secondary distortion component. 
         [0029]    Reception processing section  110  performs a reception processing on a signal (input signal) input into receiver  100  and outputs a received signal. At this time, a secondary inter-modulation distortion occurs at the same time in reception processing section  110 . Therefore, the received signal mixed with the secondary inter-modulation distortion is output from reception processing section  110 . 
         [0030]    Replica signal generating section  120  generates a secondary inter-modulation distortion component of the input signal. For example, replica signal generating section  120  is achieved by a square circuit and a low pass filter. The square circuit squares the input signal to generate a signal containing the same frequency components as the secondary inter-modulation distortion occurring in reception processing section  110 . The low pass filter removes a high frequency component from the signal containing the same frequency components as the secondary inter-modulation distortion generated in the square circuit and removes extra signal components other than the replica signal, thereby generating the replica signal of the secondary inter-modulation distortion occurring in reception processing section  110 . 
         [0031]    The square circuit may employ a diode wave detecting circuit. The square circuit may conduct square calculation by acquiring a sum current of an output of in-phase gate input and an output of anti-phase gate input. 
         [0032]    Correction signal generating section  130  has frequency characteristic assigning section  131  and weight assigning section  132 , and adjusts the frequency characteristic and gain of the replica signal to generate a correction signal. 
         [0033]    Specifically, frequency characteristic assigning section  131  assigns the frequency characteristic of reception processing section  110  to the replica signal. Frequency characteristic assigning section  131  needs to assign the same frequency characteristic as that of reception processing section  110 . The frequency characteristic of reception processing section  110  can be specified by simulation in the design stage. For example, various types of filters such as finite impulse response (FIR) type and infinite impulse response (IIR) type are known and a filter closest to the above frequency characteristic is selected from those and its filter coefficient is optimized by simulation to perform approximation of the frequency characteristic equivalent to reception processing section  110 . The permitted approximation characteristic required herein can be found by reverse operation from the distortion characteristic required in the system. 
         [0034]    In a system that handles a broadband signal, a secondary inter-modulation distortion to be cancelled is also broadband. Therefore, the correction signal generated in the replica path needs to be assigned the frequency characteristic so as to have the same magnitude as the received signal output from the main path. The frequency characteristic is assigned in this way so that the secondary inter-modulation distortion can be accurately cancelled. 
         [0035]    Weight assigning section  132  assigns an optimal weight to the replica signal assigned with the frequency characteristic of reception processing section  110  by frequency characteristic assigning section  131  to adjust the gain, thereby generating a correction signal. Specifically, weight assigning section  132  amplifies or attenuates, by assigning a weight, the gain of the replica signal assigned with the frequency characteristic of reception processing section  110  by frequency characteristic assigning section  131  such that the anti-phase signal of the correction signal is added to the received signal at optimal gain in correction signal injecting section  140  in the later stage. 
         [0036]    Weight assigning section  132  can be achieved by use of a variable gain amplifier or a multi-stage current mirror circuit. 
         [0037]    Correction signal injecting section  140  injects (adds) the anti-phase signal of the correction signal output from correction signal generating section  130  to the received signal containing the secondary inter-modulation distortion output from reception processing section  110  thereby to cancel the secondary distortion component from the received signal. 
         [0038]    The received signal with the secondary distortion component cancelled is subjected to a demodulation processing to be demodulated in an AD converter and a digital signal processing section (neither shown) in the later stage. 
         [0039]    As described above, in the present embodiment, reception processing section  110  performs the reception processing on the input signal to output the received signal. Replica signal generating section  120  uses the input signal to generate the replica signal of the inter-modulation distortion component of the input signal. Correction signal generating section  130  has frequency characteristic assigning section  131  and weight assigning section  132 , and frequency characteristic assigning section  131  assigns the frequency characteristic of reception processing section  110  to the replica signal. Weight assigning section  132  adjusts (amplifies or attenuates) the gain of the replica signal assigned with the frequency characteristic of reception processing section  110  to assign an optimal weight, thereby generating a correction signal. Correction signal injecting section  140  adds the anti-phase signal of the correction signal to the received signal to correct the received signal. 
         [0040]    Thereby, since the secondary distortion component is cancelled by use of the correction signal taking into account the frequency characteristic of the secondary distortion component occurring in reception processing section  110 , the secondary inter-modulation distortion can be accurately cancelled even when the input signal is significantly band-limited in reception processing section  110 . 
         [0041]    There has been described above that frequency characteristic assigning section  131  is arranged in front of weight assigning section  132 , but frequency characteristic assigning section  131  may be arranged behind weight assigning section  132 . In this case, weight assigning section  132  assigns a weight to the replica signal to adjust the gain, and frequency characteristic assigning section  131  assigns the frequency characteristic of reception processing section  110  to the weighted replica signal to generate a correction signal. 
         [0042]    As shown in  FIG. 2 , when frequency characteristic assigning section  131  is arranged in front of weight assigning section  132 , frequency characteristic assigning section  131  may be integral with the low pass filter contained in replica signal generating section  120 . 
         [0043]    When frequency characteristic assigning section  131  is arranged behind weight assigning section  132 , frequency characteristic assigning section  131  may be integral with correction signal injecting section  140 . 
       Embodiment 2 
       [0044]    The present embodiment will be described by way of the case in which the receiver described in Embodiment 1 is applied to a direct sampling receiver. 
         [0045]      FIG. 3  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. 
         [0046]    In  FIG. 3 , direct sampling (DSM) receiver  210  is configured of two components including mixer  211  and switched capacitor filter (SCF)  212 . 
         [0047]    Receiver  200  according to the present embodiment has replica signal generating section  220  and correction signal generating section  230  in addition to direct sampling receiver  210 . 
         [0048]    In the following, in receiver  200  of  FIG. 3 , a path routing through mixer  211  and SCF  212  is called main path and a path routing through replica signal generating section  220  and correction signal generating section  230  is called replica path. 
         [0049]    Replica signal generating section  220  generates a secondary inter-modulation distortion component of an input signal. There will be described a case where square circuit  221  and low pass filter (LPF)  222  are used as replica signal generating section  220  in the present embodiment. 
         [0050]    Correction signal generating section  230  has a frequency characteristic assigning section and a weight assigning section, and adjusts the frequency characteristic and gain of the replica signal to generate a correction signal. 
         [0051]    In the present embodiment, the frequency characteristic assigning section employs R filter  231 . The frequency characteristic assigned by R filter  231  is the same as the frequency characteristic assigned in direct sampling receiver  210  arranged in the main path and is assigned to be equivalent to the total frequency characteristic between the main path and the replica path. IIR filter  231  as the frequency characteristic assigning section may approximately assign the frequency characteristic given in SCF  212 . 
         [0052]    The weight assigning section employs current mirror circuit  232 . 
         [0053]    The detailed structure of mixer  211  and SCF  212  configuring direct sampling receiver  210  will be shown in  FIG. 4 . Direct sampling receiver  210  is roughly configured with mixer  211  and SCF  212 . The structure of  FIG. 4  will be described below. 
         [0054]    In SCF  212 , control switches  322 ,  326 ,  323 ,  327 ,  328 ,  329 ,  332 ,  333  are controlled for operating the sampling receiver in association with the timing of LO input switch  312  of mixer  211  in SCF controlling section  336 . In the first period of the LO input, control switches  322 ,  327 ,  328 ,  333  are powered ON and control switches  326 ,  323 ,  329 ,  332  are powered off. 
         [0055]    In the second period of the LO input, control switches  326 ,  323 ,  329 ,  332  are powered ON and control switches  332 ,  327 ,  328 ,  333  are powered OFF, and in the third and subsequent periods of the LO input, the first period and the second period are repeated. 
         [0056]    With the switch changeover operation, a MCR capacity (MCR) of main rotate capacitor  324  and a capacity (MCR) of main rotate capacitor  325  are alternately charged for the sampling output conducted in LO input switch  312  so that the IIR characteristic is assigned. 
         [0057]    Digital to analog converter (DAC)  335  of  FIG. 4  corresponds to correction signal injecting section  140  in Embodiment 1. The anti-phase signal of the correction signal generated in the replica path is input as a precharge voltage into DAC  335  so that the secondary inter-modulation distortion signal occurring in direct sampling receiver  210  can be cancelled. Correction signal injecting section  140  may directly inject the anti-phase signal of the analog correction signal into buffer capacitor  334  not via DAC  335 . The precharge voltage is input into DAC  335  so that the setting of the initial charge of the DSM receiver and the correction of the secondary inter-modulation distortion can be achieved in one circuit at the same time. 
         [0058]    As described above, in the present embodiment, the reception processing section is the direct sampling mixer (DSM) receiver including mixer  211  that samples an input signal and SCF  212  that frequency-converts the signal sampled in mixer  211 , and IIR filter  231  as the frequency characteristic assigning section assigns the same frequency characteristic as the IIR characteristic assigned in direct sampling receiver  210 . By this, since the secondary distortion component is cancelled by the correction signal taking into account the frequency characteristic of the secondary distortion component occurring in direct sampling receiver  210 , the secondary inter-modulation distortion can be accurately cancelled. 
       Embodiment 3 
       [0059]      FIG. 5  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. The constituents in receiver  400  of  FIG. 5  common to those in receiver  200  according to Embodiment 2 are denoted by the same numerals as  FIG. 3 , and an explanation thereof will not be repeated here. Receiver  400  of  FIG. 5  has correction signal generating section  410  instead of correction signal generating section  230  in addition to receiver  200  of  FIG. 3 , and is different from Embodiment 2 in terms of the methods for assigning a frequency characteristic and weight to a replica signal. 
         [0060]    Correction signal generating section  410  has frequency characteristic assigning section  420  configured of DC detecting section  421  and AC detecting section  422 , weight assigning section  430  configured of DC component weight assigning section  431  and AC component weight assigning section  432 , and adder  440 . 
         [0061]    DC detecting section  431  detects a DC component from the replica signal generated by replica signal generating section  220  (square circuit  221  and LPF  222 ) and outputs the detected DC component to DC component weight assigning section  431 . 
         [0062]    AC detecting section  422  detects an AC component from the replica signal generated by replica signal generating section  220  (square circuit  221  and LPF  222 ) and outputs the detected AC component to AC component weight assigning section  432 . 
         [0063]    A specific method for achieving DC detecting section  421  and AC detecting section  422  employs two methods including an analog domain method and a digital domain method. In the digital domain method, a time average among sufficient periods is taken for an input signal to detect a DC component and the DC component is subtracted from the input signal, thereby detecting the DC component and the AC component. The analog domain method is achieved by mounting a low pass filter on DC detecting section  421  and mounting a high pass filter on AC detecting section  422 . 
         [0064]    DC component weight assigning section  431  weights the DC component to adjust the gain of the DC component. 
         [0065]    AC component weight assigning section  432  assigns a weight to the AC component to adjust the gain of the AC component. 
         [0066]    Adder  440  adds the weighted DC component and AC component, respectively, to generate a correction signal. Then, adder  440  outputs the anti-phase signal of the correction signal to DAC  335 . 
         [0067]    The anti-phase signal of the correction signal is injected into DAC  335  (corresponding to the correction signal injecting section) in SCF  212  so that the secondary distortion is cancelled. 
         [0068]    In the zero IF system, such as direct sampling receiver  210 , in which a down-sampled desired wave is converted from 0 Hz to a significantly small frequency area, the frequency component of the signal to be handled is near the DC component. Thus, the frequency characteristic can be assigned mainly for the two frequency components such as a DC component and its nearby component. By this, the circuit size and the number of weighting (gain) parameter deciding steps can be largely reduced as compared with Embodiment 1. 
         [0069]    As described above, in the present embodiment, frequency characteristic assigning section  420  detects the AC component and the DC component from the replica signal, weight assigning section  430  individually assigns a weight to each of the AC component and the DC component, and adder  440  generates the addition result by the weighted AC component and the weighted DC component as a correction signal. By this, as in the zero IF system, since when a desired wave is converted into a frequency area near 0 Hz, the frequency characteristic can be assigned mainly for the two frequency components such as DC component and its vicinity, the circuit size and the number of weighting (gain) parameter deciding steps can be largely reduced as compared with Embodiment 1. 
       Embodiment 4 
       [0070]      FIG. 6  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. The constituents in receiver  500  of  FIG. 6  common to those in receiver  200  according to Embodiment 2 are denoted by the same numerals as  FIG. 3  and an explanation thereof will not be repeated here. Receiver  500  of  FIG. 6  has correction signal generating section  510  instead of correction signal generating section  230  in addition to receiver  200  of  FIG. 3 , and is different from Embodiment 2 in terms of the methods for assigning a frequency characteristic to and weighting a replica signal. 
         [0071]    In Embodiment 4, an adaptive filter as correction signal generating section  510  is employed for assigning a frequency characteristic to a replica signal.  FIG. 6  shows multi-stage FIR type adaptive filter (FIR adaptive filter)  520  as an exemplary adaptive filter. 
         [0072]    The frequency characteristic capable of being assigned in Embodiment 2 is a fixed characteristic set at the time of design, and the characteristic is only applied uniform weight in Embodiment 2. On the other hand, in the present embodiment, since the frequency characteristic can be expressed by the adaptive filter, a filter coefficient is adjusted thereby to assign an arbitrary frequency characteristic. Further, in the present embodiment, the filter coefficient is adjusted so that the weight-assigning processing for the replica signal can be performed in the adaptive filter at the same time. 
         [0073]    The frequency characteristic generated in direct sampling receiver  210  is the IIR characteristic. The frequency characteristic equivalent to the HR characteristic has to be reproduced in the multi-stage FIR adaptive filter. 
         [0074]    Typically, the output signal is added to the input signal again and the IIR characteristic has an infinite response characteristic. Therefore, if the number N of taps can be infinitely increased for expressing recursive characteristics by the feedback of the output signal in the FIR type filter, an arbitrary IIR characteristic can be achieved by the multi-stage FIR characteristic. 
         [0075]    Furthermore, since direct sampling receiver  210  is the zero IF system, the frequency characteristic does not need to be fit in all the frequency areas, and may be fit only in a limited frequency area near the DC component. Thus, the IIR characteristic of the direct sampling receiver can be approximated by a FIR filter having a relatively small number of stages. 
         [0076]    As described above, in the present embodiment, correction signal generating section  510  is configured of multi-stage FIR adaptive filter  520 . Thereby, assignment of frequency characteristics and weights can be achieved by FIR adaptive filter  520 . Since frequency characteristics and weights may be assigned only in a limited frequency area near the DC component in direct sampling receiver  210 , the secondary distortion component can be cancelled by the FIR filter having a relatively small number of stages. 
       Embodiment 5 
       [0077]      FIG. 7  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. The constituents in receiver  600  of  FIG. 7  common to those in receiver  500  according to Embodiment 4 are denoted by the same numerals as  FIG. 6  and an explanation thereof will not be repeated here. Receiver  600  of  FIG. 7  has correction signal generating section  610  instead of correction signal generating section  410  in addition to receiver  500  of  FIG. 6 . The present embodiment is different from Embodiment 4 in that a weighting (gain) parameter used for FIR adaptive filter  520  can be adaptively updated and decided while the least mean square (LMS) algorithm is used to make normal communication. 
         [0078]    Correlation calculating section  611  performs correlation calculation between the corrected signal (output signal) which is output from SCF  212  and which is obtained after adding the anti-phase signal of the correction signal to the received signal, and the replica signal, thereby obtaining a correlation value. 
         [0079]    LMS calculating section  612  uses the correlation value to decide an optimal weight (gain) parameter used for FIR adaptive filter  520 . 
         [0080]    As described above, in the present embodiment, the filter coefficient of FIR adaptive filter  520  is a filter coefficient which is obtained by using the LMS algorithm based on the correlation value between the replica signal and the corrected received signal output from the correction signal injecting section (included in SCF  212 ). As can be seen from the above, the system employed in the present embodiment is a dynamic adaptive system. Thus, a change in characteristics due to a change in temperature can be handled in real-time. The adaptive system can be achieved by adding a circuit much smaller than the structure of Embodiment 4. 
       Embodiment 6 
       [0081]      FIG. 8  is a block diagram showing a structure of essential sections in a receiver according to the present embodiment. The constituents in receiver  700  of  FIG. 8  common to those in receiver  200  according to Embodiment 2 are denoted by the same numerals as  FIG. 3  and an explanation thereof will not be repeated here. Receiver  700  of  FIG. 8  has correction signal generating section  710  instead of correction signal generating section  230  in addition to receiver  200  of  FIG. 3 . 
         [0082]    Correction signal generating section  710  is configured such that the frequency characteristic assigning section configured of IIR filter  231  is deleted from correction signal generating section  230 . 
         [0083]    The internal structure of SCF  212  is already shown in  FIG. 4 . The present embodiment is characterized in that the capacity CF of feedback capacitors  330 ,  331  is set at the same capacity value as the capacity CH of history capacitor  321  in SCF  212 . 
         [0084]    In the direct sampling reception system, the impulse response of the IIR characteristic is decided by the capacity CH of history capacitor  321  and the capacity MCR of main rotate capacitors  324 ,  325 . The IIR characteristic is expressed in the following equation 1. 
         [0000]      IIR1 =a /{MCR+ CH (1 −Z −1)}  (Equation 1)
 
         [0085]    On the other hand, the impulse response of the HR characteristic is decided by the ratio of the capacity CF to the capacity MCR in terms of DAC  335 . The IIR characteristic is expressed in the following equation 2. 
         [0000]      IIR2=MCR/{MCR+ CF (1 −Z −1)}  (Equation 2)
 
         [0086]    Cutoff frequencies of the respective IIR characteristics are obtained as in equation 3-1 and equation 3-2 by the impulse responses, respectively. 
         [0000]        fc 1 =k ·MCR/ CH   (Equation 3-1)
 
         [0000]        fc 2 =k ·MCR/ CF   (Equation 3-2)
 
         [0087]    (k is a constant value) 
         [0088]    Herein, if the capacity CF and the capacity CH are set at the same capacity value, the cutoff frequencies of the two IIR characteristics can be made equal. 
         [0089]    In this way, the capacity CF of feedback capacitors  330 ,  331  and the capacity CH of history capacitor  321  are set at the same capacity value so that the exactly same frequency characteristic as the IIR characteristic assigned in the reception system can be assigned to the replica signal to generate a correction signal. In other words, a new frequency characteristic assigning section does not need to be prepared in order to generate a correction signal for canceling a secondary distortion component. Thus, the secondary distortion component can be cancelled with a smaller circuit structure as compared with Embodiment 2. 
         [0090]    As described above, in the present embodiment, the capacity CF of feedback capacitors  330 ,  331  included in SCF  212  is set at the same value as the capacity CH of history capacitor  321 . By this, since a correction signal can be generated without providing the frequency characteristic assigning section, the secondary distortion component can be cancelled in a smaller circuit structure. 
         [0091]    The disclosure of Japanese Patent Application 2009-067410, filed on March 19, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0092]    The distortion correcting receiver and the distortion correcting method according to the present invention can accurately cancel a secondary inter-modulation distortion in a broadband receiving system. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100 ,  200 ,  400 ,  500 ,  600 ,  700 : Receiver 
           110 : Reception processing section 
           120 ,  220 : Replica signal generating section 
           130 ,  230 ,  410 ,  510 ,  610 ,  710 : Correction signal generating section 
           131 ,  420 : Frequency characteristic assigning section 
           132 ,  430 : Weight assigning section 
           140 : Correction signal injecting section 
           210 : Direct sampling receiver 
           211 : Mixer 
           212 : SCF 
           221 : Square circuit 
           222 : LPF 
           231 : HR filter 
           232 : Current mirror circuit 
           311 : Constant current source 
           312 : LO input switch 
           321 : History capacitor 
           322 ,  323 ,  326 ,  327 ,  328 ,  329 ,  332 ,  333 : Control switch 
           324 ,  325 : Main rotate capacitor 
           330 ,  331 : Feedback capacitor 
           334 : Buffer capacitor 
           335 : DAC 
           336 : SCF controlling section 
           421 : DC detecting section 
           422 : AC detecting section 
           431 : DC component weight assigning section 
           432 : AC component weight assigning section 
           440 : Adder 
           520 : FIR adaptive filter 
           611 : Correlation calculating section 
           612 : LMS calculating section