Abstract:
A receiver has a pre-stage variable gain amplifier configured to amplify an RF signal received by an antenna, a frequency converter configured to convert an output signal of the pre-stage variable gain amplifier into a low frequency signal to output the low frequency signal, a filter unit configured to selectively extract a receiving channel frequency band component from the low frequency signal, a post-stage variable gain amplifier configured to amplify the output signal of the filter unit, a pre-stage amplifier controller configured to adjust a gain of the pre-stage variable gain amplifier so that an output amplitude of the frequency converter approaches a target value, a post-stage amplifier controller configured to adjust a gain of the post-stage variable gain amplifier so that an output amplitude of the post-stage variable gain amplifier approaches a target value, and an adaptive controller configured to detect a receiving status based on the gain of the pre-stage variable gain amplifier and the gain of the post-stage variable gain amplifier, and control a circuit property of at least a portion of a circuit block from the pre-stage variable gain amplifier to the post-stage variable gain amplifier based on the detected result.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-322085, filed on Dec. 13, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a receiver that can be used for reception of analog television broadcasting or digital television broadcasting, for example. 
         [0004]    2. Related Art 
         [0005]    As one-segment broadcasting becomes widespread, a case where small electronic equipment, such as a cellular phone, has a built-in receiver for television (hereinafter, TV) reception has been increased. Most of this kind of the electronic equipment that has a built-in receiver is driven by a battery. It is important to reduce power consumption of the receiver as much as possible. 
         [0006]    There has been proposed a receiver embodied with a semiconductor chip with reduced power consumption (http:/Ipc.watch.impress.co.jp/docs/2007/0214/isscc03.htm). The proposed receiver determines a receiving status automatically, and controls each circuit constant in an analog signal processing circuit of a tuner unit to an optimal value depending on the receiving status. 
         [0007]    However, the apparatus requires several hundred milliseconds to several seconds to determine the receiving status with accuracy, thereby failing to provide good response time. Further, when the receiving status is determined by using a digital demodulated signal, the digital demodulation processing takes time and thus the receiving status cannot be determined promptly. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect of the present invention, A receiver comprising: 
         [0009]    pre-stage variable gain amplifier configured to amplify an RF signal received by an antenna; 
         [0010]    a frequency converter configured to convert an output signal of the pre-stage variable gain amplifier into a low frequency signal to output the low frequency signal; 
         [0011]    a filter unit configured to selectively extract a receiving channel frequency band component from the low frequency signal; 
         [0012]    a post-stage variable gain amplifier configured to amplify the output signal of the filter unit; 
         [0013]    a pre-stage amplifier controller configured to adjust a gain of the pre-stage variable gain amplifier so that an output amplitude of the frequency converter approaches a target value; 
         [0014]    a post-stage amplifier controller configured to adjust a gain of the post-stage variable gain amplifier so that an output amplitude of the post-stage variable gain amplifier approaches a target value; and 
         [0015]    an adaptive controller configured to detect a receiving status based on the gain of the pre-stage variable gain amplifier and the gain of the post-stage variable gain amplifier, and control a circuit property of at least a portion of a circuit block from the pre-stage variable gain amplifier to the post-stage variable gain amplifier based on the detected result. 
         [0016]    According to the other aspect of the present invention, A receiver comprising: 
         [0017]    a pre-stage variable gain amplifier configured to amplify an RF signal received by an antenna; 
         [0018]    a frequency converter configured to convert an output signal of the pre-stage variable gain amplifier into a low frequency signal to output the low frequency signal; 
         [0019]    a filter unit configured to selectively extract a receiving channel frequency band component from the low frequency signal; 
         [0020]    a post-stage variable gain amplifier configured to amplify the output signal of the filter unit; 
         [0021]    a pre-stage amplifier controller configured to adjust a gain of the pre-stage variable gain amplifier so that an output amplitude of the frequency converter approaches a target value; 
         [0022]    a post-stage amplifier controller configured to adjust a gain of the post-stage variable gain amplifier so that an output amplitude of the post-stage variable gain amplifier approaches a target value; and 
         [0023]    an adaptive controller configured to detect a receiving status based on the gain of the pre-stage variable gain amplifier, the gain of the post-stage variable gain amplifier and an output signal amplitude of the post-stage variable gain amplifier, and control a circuit property of at least a portion of a circuit block from the pre-stage variable gain amplifier to the post-stage variable gain amplifier based on the detected result. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a block diagram showing a schematic structure of a receiver according to a first embodiment of the present invention; 
           [0025]      FIG. 2A  is a graph showing an example of a property of an RF filter  12 ,  FIG. 2B  is a graph showing an example of a control property of a pre-stage variable gain amplifier  2 ,  FIG. 2C  is a graph showing an example of a frequency property of an IFBPF  21 , and  FIG. 2D  is a graph showing an example of a control property of a post-stage variable gain amplifier  5 ; 
           [0026]      FIG. 3  is a graph showing a property of a digital value obtained by converting a gain control voltage output from a pre-stage amplifier controller  7  by a second A/D converter  8 ; 
           [0027]      FIG. 4  is a graph showing a property of a digital gain setting value of an IFGCA  22 ; 
           [0028]      FIG. 5  is a graph showing a property of a digital IF signal obtained by converting an IF signal output from the IFGCA  22  by a first A/D converter  6  according to the first embodiment; 
           [0029]      FIG. 6  is a flowchart showing an example of a procedure of interference determination and electric field determination performed by an adaptive controller  10 ; 
           [0030]      FIG. 7  is a graph showing a property of an RF input level Iinrf calculated from an RF part; 
           [0031]      FIG. 8  is a graph showing a property of an RF input level Iinif calculated from an IF signal side; 
           [0032]      FIG. 9  is a graph showing a property of a DU ratio rdu calculated at Step S 5  in  FIG. 6 ; 
           [0033]      FIG. 10  is a table listing control patterns of the adaptive controller  10 ; 
           [0034]      FIG. 11  is a table showing an example of a passing property of the RF filter  12 ; 
           [0035]      FIG. 12  is a view showing in detail a control of a delay point and a control of a shift amount of a center frequency of the RF filter  12 ; 
           [0036]      FIG. 13  is a view showing in detail a control of an operational current of each part inside of the receiver; 
           [0037]      FIG. 14  is a block diagram showing a schematic structure of a receiver according to a second embodiment of the present invention; 
           [0038]      FIG. 15  is a graph showing a property of a digital IF signal obtained by converting an IF signal output from the IFGCA  22  by the first A/D converter  6  according to the second embodiment; 
           [0039]      FIG. 16  is a graph showing a property of the RF input level Iinif calculated from the IF signal side according to the second embodiment; and 
           [0040]      FIG. 17  is a graph showing a property of the DU ratio rdu. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Embodiments according to the present invention will now be explained with reference to the accompanying drawings. 
       First Embodiment 
       [0042]      FIG. 1  is a block diagram showing a schematic structure of a receiver according to a first embodiment of the present invention. The receiver in  FIG. 1  intends to receive TV broadcast waves. The receiver in  FIG. 1  includes a pre-stage variable gain amplifier  2  connected to an antenna  1 , a frequency converter  3  connected to the post-stage of the pre-stage variable gain amplifier  2 , a filter unit  4  connected to the post-stage of the frequency converter  3 , a post-stage variable gain amplifier  5  connected to the post-stage of the filter unit  4 , a first A/D converter (ADC 1 )  6  that converts an output signal from the post-stage variable gain amplifier  5  to a digital value, a pre-stage amplifier controller (RFAGC)  7  that adjusts a gain of the pre-stage variable gain amplifier  2 , a second A/D converter (ADC 2 )  8  that converts an output signal from the pre-stage amplifier controller  7  to a digital value, a post-stage amplifier controller (Ctrl)  9  that adjusts a gain of the post-stage variable gain amplifier  5 , an adaptive controller  10  that optimizes operation of each part in the receiver depending on receiving states, and a digital demodulator  11  that performs demodulation processing based on the digital value output from the first A/D converter  6 . 
         [0043]    The pre-stage variable gain amplifier  2  has a low noise amplifier (LNA)  13  to which a high frequency filter (RF filter)  12  is attached, and a gain control amplifier (RFGCA)  14 . 
         [0044]    The frequency converter  3  has a mixer (MIXER)  15 , and receives a local oscillation signal generated in a divider (DIV)  16 , a voltage-controlled oscillator (VCO)  17 , and a PLL circuit  18 . The divider  16  divides an oscillating signal generated in the VCO  17  and the PLL circuit  18  to generate the local oscillation signal. 
         [0045]    The following describes an operation of the receiver in  FIG. 1 . A broadcast wave signal in an RF (high frequency) band (90 MHz to 770 MHz in the VHF band and the UHF band for TV in Japan) received by the antenna  1  is input to the LNA  13 . The RF filter  12  attached to the LNA  13  passes through only signal components whose frequencies are close to desired frequencies. The LNA  13  amplifies a received signal by about 10 to 20 dB, and supplies it to the RFGCA  14 . 
         [0046]      FIG. 2A  is a graph showing an example of a property of the RF filter  12 , and the horizontal axis represents the frequency and the vertical axis represents the gain. As shown in  FIG. 2A , the RF filter  12  has the passing property of the narrow band where the gain becomes largest at the center frequency. 
         [0047]    The RFGCA  14  controls the gain of an input signal by the gain control voltage supplied from the pre-stage amplifier controller  7 .  FIG. 2B  is a graph showing an example of a control property of the pre-stage variable gain amplifier  2 , and the horizontal axis represents the gain control voltage level and the vertical axis represents the gain. As shown in  FIG. 2B , the gain changes linear depending on the gain control voltage. 
         [0048]    An output signal from the RFGCA  14  is input to the mixer  15 . The mixer  15  mixes the output signal from the RFGCA  14  with the local oscillation signal generated in the divider  16 , generates frequency components of the sum and the difference of both of the signals, and supplies them to the filter unit  4 . 
         [0049]    An intermediate frequency band pass filter (IFBPF)  21  in the filter unit  4  selects only a receiving IF signal (429 kHz bandwidth centered on 500 kHz in the case of one-segment broadcasting) among the output signals from the mixer  15 . Among the components of the sum and the difference generated in the mixer  15 , the component of the sum is removed because it is out of the pass band of the band passing property of the IFBPF  21 , and the image signal component that becomes unnecessary among the components of the difference is removed by using the image rejection function of the IFBPF  21 . 
         [0050]      FIG. 2C  is a graph showing an example of a frequency property of the IFBPF  21 , and the horizontal axis represents the frequency and the vertical axis represents the gain. As shown in  FIG. 2C , since the gain is set only in a received signal band, the IFBPF  21  passes through the signal component only in the received signal band. The IF signal that has passed through the IFBPF  21  is supplied to the post-stage variable gain amplifier  5 . 
         [0051]    A gain of an IF gain control amplifier (IFGCA)  22  in the post-stage variable gain amplifier  5  is controlled by the digital value generated in the post-stage amplifier controller  9 . Accordingly, the IFGCA  22  amplifies the IF signal with a desired amplification degree, and supplies it to the first A/D converter  6 . 
         [0052]      FIG. 2D  is a graph showing an example of the control property of the post-stage variable gain amplifier  5 , and the horizontal axis represents the digital gain setting value of the IFGCA  22  and the vertical axis represents the gain. 
         [0053]    The receiver in  FIG. 1  has two auto gain control (AGC) loops. One is an RFAGC loop. The pre-stage amplifier controller  7  detects an output signal amplitude of the mixer  15 , and compares it with a preset target value. When there is a difference between the output signal amplitude and the preset target value, the pre-stage amplifier controller  7  adjusts the gain control voltage so that the output signal amplitude of the mixer  15  will approach the target value, and supplies it to the RFGCA  14 . The other is an IFGCA  22  loop. The post-stage amplifier controller  9  detects the IF signal output from the IFGCA  22  by using the digital value output from the first A/D converter  6 , generates a digital gain setting value so that a signal amplitude of the IF signal will approach a target value, and supplies it to the IFGCA  22 . 
         [0054]    One of characteristic features in the present embodiment is in that the adaptive controller  10  is provided. Each of the input and output signals to and from the adaptive controller  10  is a digital value, and the adaptive controller  10  performs digital signal processing. The adaptive controller  10  performs delay point control of the RFGCA  14 , a control of the RF filter  12 , a current control of each part in the receiver, for example. 
         [0055]    The input signals to the adaptive controller  10  include a digital value obtained by converting the gain control voltage for the RFGCA  14  that is generated in the pre-stage amplifier controller  7  by the second A/D converter  8 , the digital gain setting value for the IFGCA  22  that is generated in the post-stage amplifier controller  9 , and an IF signal level value obtained by converting the IF signal by the first A/D converter  6 . 
         [0056]    The output signals from the adaptive controller  10  include a signal for increasing and decreasing the operational current of the LNA  13 , the RFGCA  14 , the mixer  15 , and the IFBPF  21 , an RFAGC reference level signal for setting a delay point of the RFGCA  14 , and a signal that sets a passing center frequency of the RF filter  12 . 
         [0057]    The general operation of the adaptive controller  10  will be described hereinafter. The adaptive controller  10  determines the presence of an interference wave and determines the field intensity by using the above-mentioned three kinds of input signals, and generates a signal that controls the operational current of each part inside of the receiver, a signal that controls the delay point of the RFGCA  14 , and a signal that controls the passing center frequency of the RF filter  12 , based on these two determination results. 
         [0058]    The interference wave will be more specifically described hereinafter. An RF signal received in the antenna  1  includes a received wave (which is also called as a desired wave) that is a signal of a receiving channel, and the interference wave that is independent to the receiving channel. When receiving in the UHF band, all broadcast waves other than the receiving channel in 470 to 770 MHz are interference waves. Although the interference wave usually includes a plurality of frequency components, the signal amplitude of each frequency component is added and combined to become one wave. The present embodiment concerns two waves of the received wave and the interference wave. 
         [0059]    In the receiver in  FIG. 1 , the received wave and the interference wave are simultaneously transmitted to the mixer  15 . The received wave and the interference wave are included also in the signal component converted to low frequency conversion by the mixer  15 . Therefore, the pre-stage amplifier controller  7  detects a summing signal of the received wave and the interference wave, to say simply, a signal amplitude of the larger one between the received wave and the interference wave. The RFAGC loop performs a feedback control so that an amplitude value of the larger one between the received wave and the interference wave will become a target amplitude value. 
         [0060]      FIG. 3  is a graph showing a property of the digital value obtained by converting the gain control voltage output from the pre-stage amplifier controller  7  by the second A/D converter  8 . In  FIG. 3 , the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12 , and the vertical axis represents the digital value of the gain control voltage. 
         [0061]      FIG. 3  shows the graphs showing a property corresponding to eleven types of interference waves with different levels. The graph line g 1  illustrated in  FIG. 3  is a case where no interference wave is present. The digital value becomes small as the interference wave increases. 
         [0062]    When the received signal passes through the mixer  15  and the IFBPF  21 , only a low frequency IF band converted wave of the desired received wave included in the received signal is sent to the post-stage side as an IF signal due to a frequency selective property of the IFBPF  21 . Therefore, the component of the interference wave is present before an input part of the IFBPF  21 , and is removed at an output part of the IFBPF  21 . For example, when the interference wave is larger than the received wave, the interference wave is a main component at the input part of the IFBPF  21  and the received wave component is relatively small. In this case, the received wave component of the output part of the IFBPF  21  is also relatively small. Accordingly, the gain of the IFGCA  22  is increased so that the signal amplitude is raised to a target IF signal level. In a state where the interference wave is large, even if the gain of the IFGCA  22  is raised to the maximum, the amplitude of the IF signal output may be smaller than a target value. 
         [0063]      FIG. 4  is a graph showing a property of the digital gain setting value of the IFGCA  22 , and the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12  and the vertical axis represents the digital gain setting value of the IFGCA. The graph line g 2  illustrated in  FIG. 4  is a case where no interference wave is present. The graph line shifts rightward as the interference wave increases. 
         [0064]      FIG. 5  is a graph showing a property of the digital IF signal obtained by converting the IF signal output from the IFGCA  22  by the first A/D converter  6 . In  FIG. 5 , the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12 , and the vertical axis represents the digital IF signal. The graph line g 3  illustrated in  FIG. 5  is a case where no interference wave is present. The level of the digital IF signal hardly changes. The graph line shifts to rightward as the interference wave increases. 
         [0065]    Further, in  FIG. 5 , the level slightly changes near the graph line g 3  due to a quantization error. 
         [0066]    As apparent from  FIGS. 3 to 5 , the graphs change depending on the presence/absence of the interference wave. By using the properties of  FIGS. 3 to 5 , the field intensity also can be determined. 
         [0067]      FIG. 6  is a flowchart showing an example of a procedure of interference determination and electric field determination performed by the adaptive controller  10 . First, by using a gradient grfa of the gain of the pre-stage variable gain amplifier  2  and an intercept grfb of a reference gain in the RFAGC loop, a digital value nrf of the gain control voltage is converted to a gain grf of the pre-stage variable gain amplifier  2 , and an amplitude target value Imix of a RF part in the output part of the mixer  15  is set (Step S 1 ). 
         [0068]    Next, a digital gain setting value nif is converted to a gain gif of the post-stage variable gain amplifier  5  by using a gradient gifa of the gain of the post-stage variable gain amplifier  5  and an intercept gifb of a reference gain in an IFGCA loop (Step S 2 ). 
         [0069]    By deducting the gain grf of the pre-stage variable gain amplifier  2  from the output level Imix of the mixer  15 , the RF input level Iinrf calculated from the RF part is calculated (Step S 3 ). The following equation (1) expresses Iinrf. 
         [0000]        Iinrf=I mix−grf  (1) 
         [0070]    Next, when the sum of the gain grf of the pre-stage variable gain amplifier  2  and the gain gif of the post-stage variable gain amplifier  5  is deducted from a digital IF signal level Iif, the RF input level Iinif calculated from the IF signal side can be calculated (Step S 4 ). The following equation (2) expresses Iinif. 
         [0000]        Iinif=Iif −( grf+gif )  (2) 
         [0071]    When an interference wave is larger than a received wave, Iinrf is strongly affected by the interference wave, while Iinif is not affected by the interference wave. Therefore, when the interference wave is larger than the received wave, the difference between the two RF input levels Iinrf and Iinif is exactly a level difference between the interference wave and the received wave. This level difference is called as a DU ratio (D: desire, U: undesire) and represents as rdu (Step S 5 ). The rdu is expressed by the following equation (3). 
         [0000]        rdu=Iinif−Iinrf=Iif−I mix− gif   (3) 
         [0072]    When the interference wave is present, rdu becomes a negative value. Whether or not the interference wave is present can be determined based on the value of rdu. Specifically, rdu is compared with an interference determination threshold thdu (Step S 6 ). If rdu is smaller than thdu, it is determined that the interference wave is present and a variable bougai is set as “present” (Step S 7 ). On the other hand, if rdu is equal to or larger than thdu, it is determined that no interference wave is present and the variable bougai is set as “absent” (Step S 8 ). 
         [0073]    Meanwhile, the field intensity can be determined by the RF input level Iinrf that includes the interference wave. Specifically, it is determined as a weak electric field in a case where Iinrf is equal to or smaller than a weak electric field threshold thl (Steps S 9  and S 10 ), and it is determined as a strong electric field in a case where Iinrf is larger than a strong electric field threshold thh (Steps S 11  and S 12 ), and otherwise it is determined as a medium electric field (Step S 13 ). Thus, a variable denkai can take three types of values: “weak”, “medium”, and “strong”. 
         [0074]      FIG. 7  is a graph showing a property of the RF input level Iinrf calculated from the RF part, and the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12  and the vertical axis represents Iinrf [dBm]. The graph line g 4  illustrated in  FIG. 7  shows a property when no interference wave is present, and the graph line shifts upward as the interference wave increases. 
         [0075]      FIG. 8  is a graph showing a property of the RF input level Iinif calculated from the IF signal side, and the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12  and the vertical axis represents Iinif [dBm]. The graph line g 5  illustrated in  FIG. 8  shows a property when no interference wave is present, and even if the interference wave increases or decreases, the graph hardly changes. 
         [0076]      FIG. 9  is a graph showing a property of the DU ratio rdu calculated at Step S 5  in  FIG. 6 , and the horizontal axis represents the desired received wave level [dBm] input to the RF filter  12  and the vertical axis represents rdu [dBm]. The graph line g 6  illustrated in  FIG. 9  shows a property when no interference wave is present, and the graph line shifts downward as the interference wave increases. 
         [0077]    The receiver in  FIG. 1  is modeled to perform an operation simulation, thereby arriving at graphs in  FIGS. 3 to 5  and  FIGS. 7 to 9 . 
         [0078]    The adaptive controller  10  not only determines the presence/absence of an interference wave and the strength of a field intensity, but performs a variable control of the delay point of the RFGCA  14  and a variable control of the center frequency of the RF filter  12 . The flowchart in  FIG. 6  also shows a procedure of the variable control of the delay point and the variable control of the center frequency of the RF filter  12  (Step S 14  or later). 
         [0079]      FIG. 10  is a table listing control patterns of the adaptive controller  10 . In  FIG. 10 , the delay point is abbreviated to “DP” and the property of the RF filter  12  is abbreviated to “FIL” 
         [0080]    As shown in  FIG. 10 , the adaptive controller  10  performs a control of an operational current fed into each part in the receiver, a variable control of the delay point of the RFGCA  14 , and a variable control of the center frequency of the RF filter  12 , depending on the presence/absence of an interference wave and the strength of a field intensity determined by the processes of Steps S 1 -S 13  in  FIG. 6 . 
         [0081]    Note that a delay point is an input level at which the gain of the RFGCA  14  begins lowering. When an interference wave is present, it is known that by shifting the delay point to be larger, a received wave can be received even if the received wave is smaller. This is caused by a property that the RFAGC loop responds to the amplitude of the interference wave so that the gain of the pre-stage variable gain amplifier  2  to the mixer  15  is reduced more than needed. 
         [0082]    For example, if a target amplitude of the output of the mixer  15  is (−16 dBm) and a maximum gain by adding the LNA  13  and the RFGCA  14  is 44 dB, the delay point value becomes (−16 dBm−44 dB=−60 dBm). When an interference wave (−55 dBm) and a received wave (−95 dBm) are input, the gain is compressed by (−55 dBm−(−60 dBm)=5 dB) in the RFGCA  14 . The received wave equivalently corresponds to a case where a received wave (−95 dBm−5 dBm=−100 dBm) is input. If a limit of reception capability is (−98 dBm), the reception of the received wave becomes impossible. 
         [0083]    When the target amplitude of the mixer  15  output is increased by 10 dB and is changed to (−6 dBm), the delay point value becomes (−50 dBm). When the interference wave (−55 dBm) and the received wave (−95 dBm) are input same as the above, the gain is not decreased in the RFGCA  14 . The received wave is operated with the maximum gain and is passed with an equivalent signal level (−95 dBm) without any change, and the reception of the received wave becomes possible. 
         [0084]    However, the delay point is not required to be simply enlarged, but to set based on a trade off with the distortion performance of each part inside the receiver. The adaptive controller  10  supplies the RFAGC reference level signal to the pre-stage amplifier controller  7 . The pre-stage amplifier controller  7  generates a gain control voltage for setting a delay point of the RFGCA  14  based on this RFAGC reference level. 
         [0085]    At Step S 14  in  FIG. 6 , the adaptive controller  10  determines whether or not an interference wave is present and the gain grf of the RF part is equal to or less than a predetermined threshold. In a case where the interference wave is present and the gain grf is equal to or less than the predetermined threshold, the delay point (DP) is set as “large” and the center frequency of the RF filter  12  is shifted (Step S 15 ). Otherwise, the delay point is set as “small” and the center frequency of the RF filter  12  is not shifted (Step S 16 ). 
         [0086]    Note that  FIG. 10  shows that in case where the interference wave is present, the delay point is set as “large” and the center frequency of the RF filter  12  is shifted. In practice, the delay point and the center frequency of the RF filter  12  are set in consideration of also the gain grf of the RF part. 
         [0087]    Meanwhile, when the field intensity “weak” or the interference wave is “present”, the operational current is set as “large” (Steps S 17  and S 18 ). When the interference wave is “absent”, determination is made whether or not the field intensity is “strong” (Step S 19 ), if “strong”, the operational current is set as “medium” (Step S 20 ), and if not “strong”, the operational current is set as “small” (Step S 21 ). 
         [0088]    As shown in  FIG. 10 , when the interference wave is determined as “absent”, regardless of the field intensity, the delay point is set as “small” and the center frequency of the RF filter  12  is not shifted. However, when the field intensity is weak, the operational current fed through each part (such as the LNA  13 , the RFGCA  14 , the mixer  15 , and the IFBPF  21 ) in the receiver is increased. The reason for increasing the operational current is in that it is necessary to obtain the amplification performance of low noise, low distortion, and high gain by exhibiting the performance of each part to the maximum extent. 
         [0089]    As describe above, the adaptive controller  10  controls the operational current of each part inside of the receiver, in order to lower the noise and reduce the distortion in each part. 
         [0090]    Meanwhile, when the interference wave is “absent” and the field intensity is medium, the low noise performance or low distortion performance is not required so much in the whole receiver. Accordingly, the operational current can be reduced in the range that degradation of the noise performance and the distortion performance is restricted within about several dBs, in both the LNA  13  and the RFGCA  14  at the pre-stage and the mixer  15  and the IFBPF  21  at the post-stage. Therefore, the operational current is set as “small” in this case. 
         [0091]    Further, when the interference wave is “absent” and the field intensity is strong, since the level of the signal that passes through pre-stage side circuits before the mixer  15  is large, the low distortion performance is required and the operational current is set as “large”. In post-stage side circuits subsequent to the mixer  15 , since proper signal quality can be obtained, “small” is sufficient for the operational current. Accordingly, in the whole receiver, the operational current is set as “medium” 
         [0092]    On the other hand, when the interference wave is determined as “present”, regardless of the field intensity, the operational current of each part in the receiver is increased, the delay point is set as “large”, and the center frequency of the RF filter  12  is shifted. The reason for performing such control is as follows. When the interference wave is present, a large interference wave and a small received wave have to be considered simultaneously. As a result, the performance of low noise and low distortion is required, and therefore, the operational current needs to be increased. 
         [0093]    When a center frequency f 0  of the RF filter  12  is not shifted, the signal passing loss becomes smallest in the case where the frequency of the received wave coincides with the center frequency f 0 , and the receiving sensitivity becomes good. Therefore, when no interference wave is present, the adaptive controller  10  does not shift the center frequency of the RF filter  12 . 
         [0094]    On the other hand, when the interference wave is present, it is advantageous to increase the DU ratio expressing a level difference between the interference wave and the received wave, and it is effective to intentionally shift the center frequency of the RF filter  12  with respect to the frequency of the received wave. 
         [0095]      FIG. 11  is a table showing an example of a passing property of the RF filter  12 , and shows a relation between the amount of frequency deviation from the center frequency and the gain. When the RF filter  12  having the property in  FIG. 11  is used, it is assumed that an interference wave larger by 30 dB than a received wave is present on the level higher by 40 MHz than the received wave. If the center frequency of the RF filter  12  is the same as the frequency of the original received wave, an input DU ratio is (−30 dB), but it will be (−30+(0−(−15))=−15 dB) after passing through the RF filter  12 . 
         [0096]    If the property of the RF filter  12  is changed so that (received frequency minus 20 MHz) becomes a center frequency, the DU ratio after passing through the RF filter  12  is (−30+(−5−(−30))=−5 dB), and is improved by 10 dB. 
         [0097]    Further, if the center frequency of the RF filter  12  is shifted too much, the level of the received wave becomes so small that reception becomes impossible. Due to the frequency relation and the signal level relation between the interference wave and the received wave, since an optimal shift amount differs and cannot be predicted, it is desirable to use together a method of preparing some kinds of candidates for the shift amount and selecting the optimal shift amount by trial and error. 
         [0098]      FIG. 12  is a view showing in detail a control of a delay point and a control of a shift amount of the center frequency of the RF filter  12 , and the horizontal axis represents the interference wave intensity and the vertical axis represents the received wave intensity. The “large” in  FIG. 12  shows that the delay point is enlarged and the center frequency of the RF filter  12  is shifted. The “small” shows that the delay point is lowered and the center frequency of the RF filter  12  is not shifted. As seen from  FIG. 12 , it is understood as a general tendency that the adaptive controller  10  enlarges the delay point and also shifts the center frequency of the RF filter  12  as the interference wave becomes large. 
         [0099]      FIG. 13  is a view showing in detail a control of the operational current of each part inside of the receiver, and the horizontal axis represents the interference wave intensity and the vertical axis represents the received wave intensity. The “strong”, “medium”, and “small” in  FIG. 13  show that the operational current is set large, medium, and small, respectively. As seen from  FIG. 13 , it is understood as a general tendency that the adaptive controller  10  increases the operational current when the received wave intensity is small and when the interference wave intensity is large, decreases the operational current when the received wave intensity is medium, and sets medium the operational current the when received wave intensity is large. 
         [0100]    As described above, in the first embodiment, since the presence/absence of an interference wave is determined by the difference between the RF input level Iinrf calculated from the RF part and the RF input level Iinif calculated from the IF signal side and the field intensity is determined by the signal amplitude of Iinrf, the operational current of each part inside of the receiver, the delay point of the RFGCA  14 , and the center frequency of the RF filter  12  can be controlled so that interference wave resistance becomes high and a reception rate can be improved. 
         [0101]    In the first embodiment, since various kinds of controls are performed by using the signals before being input to the digital demodulator  11 , the time response property is improved. It should be noted that any configuration can be used as the digital demodulator  11 , and various types of conventional digital demodulators  11  can be used without any change, thereby simplifying design variation. 
         [0102]    In addition, power consumption can be reduced by controlling the operational current of each part inside of the receiver. 
       Second Embodiment 
       [0103]    The first embodiment performs the control based on the precondition that an IF signal level fluctuates. On the contrary, the IF signal level may be treated as a specified value. With this arrangement, although the control accuracy in the weak electric field deteriorates, almost the same result is obtained in the final determination so that the control process can be simplified. 
         [0104]      FIG. 14  is a block diagram showing a schematic structure of a receiver according to a second embodiment of the present invention. In  FIG. 14 , the same numerals are given to the components that are common to those in  FIG. 1 , and the following will be described by focusing on differences from  FIG. 1 . In the receiver in  FIG. 14 , the IF signal level is regarded as a specified value, and the digital IF signal output from the first A/D converter  6  is not supplied to the adaptive controller  10 . Other components are common to those in  FIG. 1 , and the adaptive controller  10  also processes with the same procedure as that shown in  FIG. 6  and controls the operational current of each part inside of the receiver, the delay point of the RFGCA  14 , and the center frequency of the RF filter  12 . 
         [0105]      FIG. 15  is a graph, corresponding to  FIG. 5 , showing a property of a digital IF signal obtained by converting an IF signal output from the IFGCA  22  by the first A/D converter  6 . As shown in  FIG. 15 , since an IF signal level is the specified value, it is not affected by an interference wave. 
         [0106]      FIG. 16  is a graph showing a property, corresponding to  FIG. 8 , of the RF input level Iinif calculated from the IF signal side. Although the graph in  FIG. 8  is not affected by the interference wave, the graph in  FIG. 16  is affected by the interference wave affects in the weak electric field. However, influence of the interference wave is little on the whole. 
         [0107]      FIG. 17  is a graph showing property, corresponding to  FIG. 9 , of the DU ratio rdu.  FIG. 17  shows the almost same property as that in  FIG. 9 , and even if the IF signal level is set at the specified value, it is understood that there is almost no substantial influence. 
         [0108]    As described above, in the second embodiment, by setting the IF signal level as the specified value, the operation of the adaptive controller  10  can be simplified and the time response property is improved rather than the first embodiment. 
         [0109]    (Other Modifications) 
         [0110]    The first and the second embodiments illustrate controlling the operational current, the center frequency of the RF filter  12 , and the delay point of the RFGCA  14 . As a modified example, at least one characteristic among the above three characteristics may be controlled. Alternatively, circuit characteristics other than these three characteristics may be controlled. 
         [0111]    The configuration shown in  FIG. 1  or  FIG. 14  is an example, and various modifications can be considered. For example, the LNA  13  and the RFGCA  14  may be provided integrally, or the LNA  13  and the RF filter  12  may be provided separately. 
         [0112]    As a configuration of the mixer  15 , the multiple mixers  15  may be provided. For example, the mixer  15  for an I signal may be provided separately from that for a Q signal which differ in a phase about 90 degrees. 
         [0113]    The IFBPF  21  may be a low pass filter that removes only a high band. A filter for image reduction may be provided separately from the IFBPF  21 . 
         [0114]    The operational current or the like may be controlled by a different procedure from the procedure in  FIG. 6 . A part or all of the receiver in  FIG. 1  may be constituted of one or more semiconductor chips, or may be constituted of a discrete circuit. 
         [0115]    In the embodiments described above, a frequency of the IF signal centered on 500 kHz is taken as an example. As a modified example, an intermediate frequency about 30 MHz to 70 MHz that is used in the TV tuner field for several decades may be used, or zero IF (I signals and Q signals with 0 Hz as the center frequency) may be used. 
         [0116]    Although based on above description, those skilled in the art can figure out additional effects and variations of the present invention, the aspect of the present invention is not limited to the stated each embodiments. Various additions, alterations and partial deletions can be done to the present invention within the conceptualistic thought and purpose of the present invention drawn on the claims and the equivalents.