PATENT ABSTRACT
The present invention provides a phase locked loop circuit including: a voltage controlled oscillator; a variable frequency-dividing circuit; a phase comparing circuit for comparing a phase of the frequency-dividing signal a charge pump circuit; a loop filter; a voltage supplying circuit; a frequency measuring circuit; and a voltage measuring circuit.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a PLL (Phase Locked Loop) circuit which is suitable for being used in a receiver using a synthesizer system, and an IC (Integrated Circuit) for the same. 
         [0003]    2. Description of the Related Art 
         [0004]    When a receiver using a super-heterodyne system is configured so as to use a synthesizer system instead, in general, a local oscillation signal is outputted from a PLL circuit.  FIG. 12  shows an example of such a PLL circuit  30 . In the PLL circuit  30 , an oscillation signal SVCO from a VCO (Voltage Controlled Oscillator)  31  is supplied to a variable frequency-dividing circuit  32 . The variable frequency-dividing circuit  32  frequency-divides the oscillation signal SVCO having an oscillation frequency into a frequency-dividing signal having a frequency of 1/N (N: positive integral number) of the oscillation frequency of the oscillation signal SVCO. The resulting frequency-dividing signal is then supplied to a phase comparing circuit  33 . In addition, an alternating current (A.C.) signal SREF having a reference frequency fREF is supplied to the phase comparing circuit  33 . 
         [0005]    Also, a comparison output signal from the phase comparing circuit  33  is supplied to a loop filter  35  through a charge pump circuit  34 . A direct current (D.C.) voltage VC having a level which changes so as to correspond to a phase difference between the frequency of the output signal from the variable frequency-dividing circuit  32 , and the reference frequency fREF is fetched from the loop filter  35 . Also, the D.C. voltage VC thus fetched is supplied as a control voltage for an oscillation frequency fVCO to the VCO  31 . 
         [0006]    Therefore, in a stationary state, the oscillation frequency fVCO of the VCO  31  is given by Expression (1): 
         [0000]        f VCO= N·f REF   (1) 
         [0007]    where N is a frequency driving ratio. Thus, the changing of the frequency-dividing ratio N makes it possible to change the oscillation frequency fVCO of the VCO  31 . As a result, the oscillation signal SVCO of the VCO  31  (or a frequency-dividing signal thereof) is used as a local oscillation signal, thereby converting a frequency of a received signal. Also, the changing of the frequency-dividing ratio N makes it possible to change the frequency of the received signal. That is to say, it is possible to carry out the signal reception using the synthesizer system. 
         [0008]    Now, in the PLL circuit  30 , in the case of the same setting, the loop characteristics when the oscillation frequency fVCO is the highest frequency, and the loop characteristics when the oscillation frequency fVCO is the lowest frequency largely change from each other. Also, when the loop characteristics change, not only the stability of a feedback loop itself changes, but also a phase noise changes. 
         [0009]    The change in phase noise results in that although the oscillation frequency fVCO of the VCO  31  should be ideally held constant, i.e., held at a value of the oscillation frequency fVCO as indicated by a heavy line in  FIG. 12 , the oscillation frequency fVCO of the VCO  31  changes as indicated by a thin line. Also, the phase noise is an important item in a phase of reception of a digital broadcasting, and thus exerts an influence on the reception of a broadcasting wave signal. Therefore, it is necessary to prevent the loop characteristics from changing even when the oscillation frequency fVCO changes. 
         [0010]    On the other hand, the loop characteristics of the PLL circuit  30  depends on a transfer function G(s) when the PLL circuit  30  is held in a state of an open loop. That is to say, in  FIG. 12 , a signal line extending from the variable frequency-dividing circuit  32  to the phase comparing circuit  33  is cut at a point X, thereby holding the PLL circuit  30  in the open loop state. In this state, the transfer function G(s) about a signal line extending from an input terminal of the phase comparing circuit  33  (an input terminal of the reference signal SREF) to an output terminal of the variable frequency-dividing circuit  32  (an output terminal of the frequency-dividing signal) is given by Expression (2) : 
         [0000]        G ( s )=(ICP/2 n )·( ZP ( s )· K VCO)/ SN    (2) 
         [0011]    where ICP (Inductively Coupled Plasma) is a charge pump current of the charge pump circuit  34 , ZP(s) is an impedance of the loop filter  35 , KVCO is a control sensitivity of the VCO  31  and is given by KVCO=ΔfVCO/ΔVC, and N is a frequency-dividing ratio of the frequency-dividing circuit  32 . 
         [0012]    Therefore, when the frequency-dividing ratio N is changed for the purpose of changing the oscillation frequency fVCO, the transfer function G(s) changes accordingly. As a result, the stability and the phase noise of the PLL circuit  30  change accordingly. In addition thereto, when in a television receiver, a front end circuit is configured in the form of an IC, and the response can be made to television broadcastings of the countries by using one IC, a variability region of the oscillation frequency fVCO of the PLL circuit configured in the form of an on-chip becomes considerably wide, and the variability region of the frequency-dividing ratio N becomes considerably wide. For this reason, the stability and the phase noise of the PLL circuit  30  becomes easy to get worse. 
         [0013]    In order to cope with this situation, it is devised as a first compensation method that reference is made to the frequency-dividing ratio N, and the charge pump current ICP of the charge pump circuit  34  is changed in proportion to the frequency-dividing ratio N thus referred, thereby suppressing the change in transfer function G(s) in Expression (2). This technique, for example, is described in Japanese Patent No. 2,842,847 and Japanese Patent Laid-Open No. 2001-156629. 
         [0014]    In addition, a method in which since the oscillation frequency fVCO of the VCO  31  depends on an output voltage VC of the loop filter  35 , that is, a control voltage VC for the VCO  31 , the control voltage VC is monitored, and the charge pump current ICP is controlled in accordance with the control voltage VC is also devises as a second compensation method. This technique, for example, is described in Japanese Patent Laid-Open No. Hei 11-308101. 
         [0015]    Moreover, the following method is also devised as a third compensation method. That is to say, in a phase of calculation of the charge pump current ICP, the PLL circuit  30  is held in the open loop state once. Also, the oscillation frequency fVCO of the VCO  31  for the control voltage VC is measured with a frequency counter, thereby actually measuring the control sensitivity KVCO. Also, the charge pump current ICP is obtained based on the control sensitivity KVCO obtained from the actual measurement result. This technique, for example, is described in non-patent literary document of “A Fully Integrated 0.13-μm CMOS Digital Low-IF DBS Satellite Tuner Using a Ring Oscillator-Based Frequency Synthesizer,” IEEE JSSC, pp. 967 to 982, Vol. 42, No. 5, MAY 2007. 
         [0016]    According to the first to third compensation methods, the charge pump current ICP is changed so as to correspond to either the frequency-dividing ratio N or the oscillation frequency fVCO in Expression (2). Therefore, the transfer function G(s) can be stabilized. As a result, the loop characteristics of the PLL circuit  30  can be stabilized. 
       SUMMARY OF THE INVENTION 
       [0017]    According to the first to third compensation methods described above, the charge pump current ICP is changed so as to correspond to either the frequency-dividing ratio N or the oscillation frequency fVCO in Expression (2). Therefore, the transfer function G(s) ought to be stabilized. As a result, the loop characteristics of the PLL circuit  30  ought to be stabilized. 
         [0018]    However, in the first and second compensation methods described above, as apparent from Expression (2) as well, attention is paid only to the frequency-dividing ratio N, that is, only to the oscillation frequency fVCO of the VCO  31 , and the charge pump current ICP of the factors with which the loop characteristics of the PLL circuit  30  are determined. In this case, the control sensitivity KVCO of the VCO  31 , and the impedance ZP of the loop filter  35  as other factors with which the loop characteristics are determined are assumed to be constant. 
         [0019]    For this reason, actually, the loop characteristics of the PLL circuit  30  changes due to the dispersion, the temperature change, the temporal change, and the like of the characteristics of the constituent elements of the VCO  31  and the loop filter  35 . 
         [0020]    In addition, when the VCO  31  is configured in the form of on-chip in the IC as in the recent case, a variable-capacitance diode (a so-called varicap) of the VCO  31  is also desired to be configured in the form of an IC. Also, in the front end circuit for receiving the television broadcasting, or the like, a PN (Positive-Negative) junction type variable-capacitance diode having a narrow control range for a capacitance (electrostatic capacitance) is not used as the variable-capacitance diode, but a MOS (Metal Oxide Semiconductor) type variable-capacitance diode having a wide control range for a capacitance is used as the variable-capacitance diode in many cases. 
         [0021]    However, since the MOS type variable-capacitance diode has a non-linear relationship between a control voltage and a capacitance, the control sensitivity KVCO largely changes depending on the control voltage. In particular, when the control voltage is used in the wide range, the non-linearity of the MOS type variable-capacitance diode exerts a large influence on the loop characteristics. That is to say, in such a case, with the existing control method, the loop characteristics can no longer be held constant. 
         [0022]    In addition, a method of adopting a configuration of a capacitor bank is effective when the necessary oscillation frequency range cannot be covered even by using the MOS type variable-capacitance diode in the case where the VCO  31  is configured in the form of the on-chip in the IC. This method is described as follows. That is to say, for example, as shown in  FIG. 13 , series circuits of a capacitor C 0  and a switch circuit S 0 , . . . , and a capacitor Cn and a switch circuit Sn are connected in parallel with an original variable-capacitance diode CD, thereby obtaining a total capacitance C. Also, the switch circuits S 0  to Sn are selectively controlled to be turned ON/OFF, thereby changing the total capacitance C, and the capacitance of the variable-capacitance diode CD is changed, thereby changing the oscillation frequency fVCO. 
         [0023]    In this case, since the capacitances of the capacitors C 0  to Cn have no relation to the control voltage VC of the variable-capacitance diode CD, the control sensitivity KVCO differs depending on the combinations of the capacitors C 0  to Cn. As a result, it becomes more difficult to hold the loop characteristics constant without taking the control sensitivity KVCO into consideration. In addition, even when the control voltage VC for the VCO  31  (the control voltage for the variable-capacitance diode CD) is monitored, the oscillation frequency fVCO cannot be detected. Thus, even if the control sensitivity KVCO is constant, the charge pump current ICP cannot be controlled only with the control voltage VC. 
         [0024]    In that respect, in the case of the third compensation method, the charge pump current ICP can be suitably set because the charge pump current ICP is set based on the actual measurement of the control sensitivity KVCO. However, in the case as well of the third compensation method, it is impossible to cope with the change, in control sensitivity KVCO of the VCO  31 , caused by the ambient temperature. In addition, when the control sensitivity KVCO is measured, the PLL circuit  30  needs to be held in the open loop state once. At this time, since the PLL circuit  30  cannot be used, it is not allowed to use the third compensation method in the front end circuit or the receiver which continuously receives the broadcasting. 
         [0025]    In the light of the foregoing, it is therefore desirable to provide a PLL circuit desired characteristics of which can be held even when a control sensitivity of a VCO disperses due to a manufacture process, and an IC for the same. 
         [0026]    In order to attain the desire described above, according to an embodiment of the present invention, there is provided a PLL circuit including: a VCO; a variable frequency-dividing circuit for frequency-dividing an oscillation signal having an oscillation frequency of the VCO into a frequency-dividing signal having a frequency of (1/N) (N: positive integral number) of the oscillation frequency of the oscillation signal; a phase comparing circuit for comparing a phase of the frequency-dividing signal outputted from the variable frequency-dividing circuit, and a phase of a signal having a reference frequency with each other; a charge pump circuit to which a comparison output signal is supplied from the phase comparing circuit; and a loop filter for fetching a D.C. component from an output signal from the charge pump circuit, supplying the D.C. component thus fetched as a control signal for the oscillation frequency of the VCO to the VCO; a voltage supplying circuit for, in a phase of measurement, supplying a predetermined first control voltage as a control signal for the oscillation frequency of the VCO to the VCO instead of the output signal from the charge pump circuit; a frequency measuring circuit for, in the phase of the measurement, measuring the oscillation frequency of the VCO; and a voltage measuring circuit for, in a phase of use, measuring a magnitude of a second control voltage supplied as a control signal for the oscillation frequency of the VCO to the VCO; in which in the phase of the measurement, a data table representing a relationship between the first control voltage, and a rate of a change in oscillation frequency of the VCO is created by the voltage supplying circuit and the frequency measuring circuit; in the phase of the use, the second control voltage measured by the voltage measuring circuit is converted into a control sensitivity representing the rate of the change in oscillation frequency by referring to the data table; and a magnitude of a charge pump current of the charge pump circuit is controlled by using the control sensitivity as a result of the conversion so that a transfer function in a phase of an open loop becomes constant irrespective of the frequency-dividing ratio N. 
         [0027]    According to another embodiment of the present invention, there is provided an IC for a PLL circuit including: a VCO; a variable frequency-dividing circuit for frequency-dividing an oscillation signal having an oscillation frequency of the VCO into a frequency-dividing signal having a frequency of (1/N) (N: positive integral number) of the oscillation frequency of the oscillation signal; a phase comparing circuit for comparing a phase of the frequency-dividing signal outputted from the variable frequency-dividing circuit, and a phase of a signal having a reference frequency with each other; a charge pump circuit to which a comparison output signal is supplied from the phase comparing circuit; and a loop filter for fetching a D.C. component from an output signal from the charge pump circuit, and supplying the D.C. component thus fetched as a control signal for the oscillation frequency of the VCO to the VCO; in which a voltage supplying circuit for, in a phase of measurement, supplying a predetermined first control voltage as a control signal for the oscillation frequency of the VCO to the VCO instead of the output signal from the charge pump circuit, a frequency measuring circuit for, in the phase of the measurement, measuring the oscillation frequency of the VCO, and a voltage measuring circuit for, in a phase of use, measuring a magnitude of a second control voltage supplied as a control signal for the oscillation frequency of the VCO to the VCO are formed as one-chip IC; in the phase of the measurement, a data table representing a relationship between the first control voltage, and a rate of a change in oscillation frequency of the VCO is created by the voltage supplying circuit and the frequency measuring circuit; in the phase of the use, the second control voltage measured by the voltage measuring circuit is converted into a control sensitivity representing the rate of the change in oscillation frequency by referring to the data table; and a magnitude of a charge pump current of the charge pump circuit is controlled by using the control sensitivity as a result of the conversion so that a transfer function in a phase of an open loop becomes constant irrespective of the frequency-dividing ratio N. 
         [0028]    According to the embodiments of the present invention, even when the control sensitivity of the VCO disperses due to the manufacture process, the desired PLL characteristics can be held. Also, at this time, the trimming or the like needs not to be carried out. In addition, even when the ambient temperature changes, the loop characteristics of the PLL circuit can be controlled so as to be held at the defined value without stopping the operation of the PLL circuit. 
         [0029]    Moreover, even when the measured voltage or the like is not applied from the outside to the PLL circuit operating in the stationary state, the oscillation frequency, control sensitivity or the like of the VCO can be measured. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a block diagram showing an example of a front end circuit to which the present invention can be applied; 
           [0031]      FIG. 2  is a block diagram showing an example of a base-band processing circuit; 
           [0032]      FIG. 3  is a system diagram explaining a part of the front end circuit shown in  FIG. 1 ; 
           [0033]      FIGS. 4A and 4B  are respectively graphs showing examples of measurement of characteristics of a VCO; 
           [0034]      FIG. 5  is a circuit diagram explaining a part of the front end circuit shown in  FIG. 1 ; 
           [0035]      FIG. 6  is a graph explaining the part of the front end circuit shown in  FIG. 1 ; 
           [0036]      FIG. 7  is a block diagram showing a PLL circuit according to an embodiment of the present invention; 
           [0037]      FIGS. 8A and 8B  are respectively graphs showing examples of measurement of characteristics of the PLL circuit shown in  FIG. 7 ; 
           [0038]      FIG. 9  is a block diagram showing a PLL circuit according to another embodiment of the present invention; 
           [0039]      FIG. 10  is a block diagram showing a PLL circuit according to still another embodiment of the present invention; 
           [0040]      FIG. 11  is a block diagram explaining an existing PLL circuit; 
           [0041]      FIG. 12  is a frequency spectrum diagram explaining characteristics of the existing PLL circuit; and 
           [0042]      FIG. 13  is a circuit diagram showing an existing capacitor bank. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     [1] Example of Circuit of Television Receiver 
       [0043]    Firstly, a description will be given with respect to an example of a television receiver to which the present invention can be applied. With the television receiver in this example, television broadcastings of countries can be received irrespective of their broadcasting forms. The television receiver is composed of a front end circuit, and a base-band circuit. 
         [0044]    Also, with the front end circuit, in this example, the frequencies which are used in the television broadcastings of the respective countries are divided into the following three bands: 
         [0045]    (A) 46 to 147 MHz (VL band) 
         [0046]    (B) 147 to 401 MHz (VH band) 
         [0047]    (C) 401 to 887 MHz (U band) 
         [0048]    Thus, in each of the reception bands (A) to (C), the frequency can be changed so as to correspond to the desired channel. 
       [1-1] Example of Front End Circuit 
       [0049]    Referring now to  FIG. 1 , a portion  10  surrounded by a chain line shows a front end circuit. In this case, the front end circuit  10  is configured in the form of one-chip IC. In addition, the front end circuit (IC)  10  has terminal pins T 11  to T 18  for external connection. 
         [0050]    Also, a broadcasting wave signal of a television broadcasting is received at an antenna ANT, and the received signal is selectively supplied to antenna tuning circuits  12 A to  12 C through from the terminal pin T 11  to a switch circuit  11 . In this case, the antenna tuning circuits  12 A to  12 C are provided so as to correspond to the reception bands shown in the items (A) to (C) described above, respectively. In this case, the antenna tuning circuits  12 A to  12 C are configured in such a way that a plurality of tuning capacitors are selectively connected in accordance with digital data, thereby changing the tuning frequency so as to be tuned with a reception signal having the desired frequency (channel). 
         [0051]    Also, the received signals outputted from the tuning circuits  12 A to  12 C, respectively, are supplied to a switch circuit  15  through high frequency amplifiers  13 A to  13 C, and interstage tuning circuits  14 A to  14 C, respectively. In this case, the interstage tuning circuits  14 A to  14 C are also configured similarly to the tuning circuits  12 A to  12 C. However, the tuning capacitors of the interstage tuning circuits  12 A to  12 C, and  14 A to  14 C, and the tuning circuits  12 A to  12 C are built in the IC  10 , and also the IC  10  includes external tuning coils thereof. Moreover, the switch circuit  15  is switched in conjunction with the switch circuit  11 . Therefore, a received signal SRX having the desired reception band is fetched from the switch circuit  15 . Also, the received signal SRX thus fetched is supplied to each of mixer circuits  21 I and  21 Q. 
         [0052]    In addition, a clock signal having a stable frequency (in the range of about 1 to about 2 MHz) is supplied from the outside to a signal forming circuit  36  through the terminal pin T 15 , thereby forming a signal SREF having a reference frequency fREF. The resulting signal SREF is supplied as a reference signal to a PLL circuit  30 . 
         [0053]    Although details of the PLL circuit  30  will be described later, the PLL circuit operates in a stationary phase in the manner as described with reference to  FIG. 11 . In addition, in order to correspond to the reception frequency in the broad range shown in the items (A) to (C) described above, the VCO  31  and a peripheral circuit thereof, for example, are configured as shown in  FIG. 3 . 
         [0054]    That is to say, VCOs  31 A to  31 C having oscillation frequency bands different from one another are provided as the VCO  31 , and an output voltage VC from a loop filter  35  is supplied as a control signal for each of oscillation frequencies of the VCOs  31 A to  31 C to each of the VCOs  31 A to  31 C. Also, oscillation signals of the VCOs  31 A to  31 C are selectively fetched so as to correspond to the reception frequency by a switch circuit  31 S. The oscillation signal thus fetched is supplied as an oscillation signal SVCO of the VCO  31  to a variable frequency-dividing circuit  32 . 
         [0055]    Therefore, the VCOs  31 A to  31 C become selectively valid by the switch circuit  31 S, which results in that an apparent oscillation frequency band for the VCO  31  is widened, thereby making it possible to correspond to the reception frequencies shown in the items (A) to (C) described above. 
         [0056]    It is noted that in the following description, the VCOs  31 A to  31 C, and the switch circuit  31 S are representatively represented by the VCO  31  for brief unless they are especially given notice. 
         [0057]    Also, in this case, as described above, the oscillation frequency fVCO of the VCO  31  is expressed by Expression (1). Therefore, when the frequency-dividing ratio N is controlled by a microcomputer (not shown) for system control, the oscillation frequency fVCO of the VCO  31  can be changed. For example, the oscillation frequency fVCO of the VCO  31  is set in the range of 1.8 to 3.6 GHz in correspondence to the reception band and the reception frequency (reception channel). 
         [0058]    Then, the oscillation signal SVCO, having an oscillation frequency, fetched from the switch circuit  31 S is supplied to the variable frequency-dividing circuit  37  to be frequency-divided into a frequency-dividing signal having a frequency of 1/M (for example, M=2, 4, 8, 16, 32) of the oscillation frequency. The resulting frequency-dividing signal is supplied to a frequency-dividing circuit  38  to be frequency-divided into frequency-dividing signals SL 0 I and SL 0 Q having phases mutually orthogonal. Also, the resulting frequency-dividing signals SL 0 I and SL 0 Q are supplied as local oscillation signals to mixer circuits  21 I and  21 Q, respectively. 
         [0059]    Here, when the frequency of each of the local oscillation signals SL 0 I and SL 0 Q is represented by fL 0 , the frequency fL 0  is given by Expression (3): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           fL 
                            
                           
                               
                           
                            
                           0 
                         
                         = 
                         
                           fVCO 
                           / 
                           
                             ( 
                             
                               2 
                                
                               M 
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           N 
                           · 
                           
                             fREF 
                             / 
                             
                               ( 
                               
                                 2 
                                  
                                 M 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           fREF 
                           · 
                           
                             N 
                             / 
                             
                               ( 
                               
                                 2 
                                  
                                 M 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0060]    Therefore, the changing of the frequency-dividing ratios M and N makes it possible to change the local oscillation frequency fL 0  over a wide range in a predetermined frequency step. For example, the local oscillation frequency fL 0  is set in the range of 28.125 to 900 MHz so as to correspond to the items (A) to (C) described above. 
         [0061]    In addition, a received signal SRX desired to be received is given in brief by Expression (4): 
         [0000]        SRX=ERX ·sin ω RXt    (4) 
         [0062]    where ERX is an amplitude of the received signal, and ωRX is given by 2πfRX where fRX is a central frequency of the received signal SRX. 
         [0063]    Also, an image disturbing signal SUD is given in brief by Expression (5): 
         [0000]        SUD=EUD ·sin ω UDt    (5) 
         [0064]    where EUD is an amplitude of the image disturbing signal SUD, and ωUD is given by 2πfUD where fUD is a central frequency of the image disturbing signal SUD. 
         [0065]    Moreover, the local oscillation signals SL 0 I and SL 0 Q are given by Expression (6): 
         [0000]        SL 0 I=EL 0·sin ω L 0 t    
         [0000]        SL 0 Q=EL 0·cos ω L 0 t    (6) 
         [0066]    where EL 0  is an amplitude of each of the local oscillation signals SL 0 I and SL 0 Q, and ωL 0  is given by 2πfL 0 . 
         [0067]    However, at this time, when ωIF=2πfIF where fIF is an intermediate frequency which, for example, is set in the range of 4 to 5.5 MHz (which is changed depending on the broadcasting systems) is established, in the case of an upper heterodyne system, the central frequency fRX of the received signal SRX, and the central frequency fUD of the image disturbing signal SUD are given by Expression (7): 
         [0000]        fRX=fL 0 −fIF    
         [0000]        fUD=fL 0 +fIF    (7) 
         [0068]    Therefore, signals SIFI and SIFQ outputted and fetched from the mixer circuits  21 I and  21 Q are respectively expressed by Expressions (8) and (9): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         SIFI 
                         = 
                           
                          
                         
                           
                             ( 
                             
                               SRX 
                               + 
                               SUD 
                             
                             ) 
                           
                           × 
                           SL 
                            
                           
                               
                           
                            
                           0 
                            
                           I 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               ERX 
                               · 
                               sin 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             RXt 
                             × 
                             EL 
                              
                             
                                 
                             
                              
                             
                               0 
                               · 
                               sin 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             L 
                              
                             
                                 
                             
                              
                             0 
                              
                             t 
                           
                           + 
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           
                             EUD 
                             · 
                             sin 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           UDt 
                           × 
                           EL 
                            
                           
                               
                           
                            
                           
                             0 
                             · 
                             sin 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           L 
                            
                           
                               
                           
                            
                           0 
                            
                           t 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           α 
                            
                           
                             { 
                             
                               
                                 
                                   cos 
                                    
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         RX 
                                       
                                       - 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                 
                                  
                                 t 
                               
                               - 
                               
                                 cos 
                                 ( 
                                 
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         RX 
                                       
                                       + 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                    
                                   t 
                                 
                                 } 
                               
                               + 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           β 
                            
                           
                             { 
                             
                               
                                 
                                   cos 
                                    
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         UD 
                                       
                                       - 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                 
                                  
                                 t 
                               
                               - 
                               
                                 
                                   cos 
                                    
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         UD 
                                       
                                       + 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                 
                                  
                                 t 
                               
                             
                             } 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       where 
                        
                       
                           
                       
                        
                       α 
                     
                     = 
                     
                       
                         ERX 
                         · 
                         EL 
                       
                        
                       
                           
                       
                        
                       
                         0 
                         / 
                         2 
                       
                     
                   
                   , 
                   
                       
                   
                    
                   
                     
                       and 
                        
                       
                           
                       
                        
                       β 
                     
                     = 
                     
                       
                         EUD 
                         · 
                         EL 
                       
                        
                       
                           
                       
                        
                       
                         0 
                         / 
                         2. 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         SIFQ 
                         = 
                           
                          
                         
                           
                             ( 
                             
                               SRX 
                               + 
                               SUD 
                             
                             ) 
                           
                           × 
                           SL 
                            
                           
                               
                           
                            
                           0 
                            
                           Q 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               ERX 
                               · 
                               sin 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             RXt 
                             × 
                             EL 
                              
                             
                                 
                             
                              
                             
                               0 
                               · 
                               cos 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             L 
                              
                             
                                 
                             
                              
                             0 
                              
                             t 
                           
                           + 
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           
                             EUD 
                             · 
                             sin 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           UDt 
                           × 
                           EL 
                            
                           
                               
                           
                            
                           
                             0 
                             · 
                             cos 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           L 
                            
                           
                               
                           
                            
                           0 
                            
                           t 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             α 
                              
                             
                               { 
                               
                                 
                                   
                                     sin 
                                      
                                     
                                       ( 
                                       
                                         
                                           ω 
                                            
                                           
                                               
                                           
                                            
                                           RX 
                                         
                                         + 
                                         
                                           ω 
                                            
                                           
                                               
                                           
                                            
                                           L 
                                            
                                           
                                               
                                           
                                            
                                           0 
                                         
                                       
                                       ) 
                                     
                                   
                                    
                                   t 
                                 
                                 + 
                                 
                                   
                                     sin 
                                      
                                     
                                       ( 
                                       
                                         
                                           ω 
                                            
                                           
                                               
                                           
                                            
                                           RX 
                                         
                                         - 
                                         
                                           ω 
                                            
                                           
                                               
                                           
                                            
                                           L 
                                            
                                           
                                               
                                           
                                            
                                           0 
                                         
                                       
                                       ) 
                                     
                                   
                                    
                                   t 
                                 
                               
                               } 
                             
                           
                           + 
                         
                       
                     
                   
                   
                     
                       
                           
                          
                         
                           β 
                            
                           
                             { 
                             
                               
                                 
                                   sin 
                                    
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         UD 
                                       
                                       + 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                 
                                  
                                 t 
                               
                               + 
                               
                                 sin 
                                 ( 
                                 
                                   
                                     ( 
                                     
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         UD 
                                       
                                       - 
                                       
                                         ω 
                                          
                                         
                                             
                                         
                                          
                                         L 
                                          
                                         
                                             
                                         
                                          
                                         0 
                                       
                                     
                                     ) 
                                   
                                    
                                   t 
                                 
                                 } 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       where 
                        
                       
                           
                       
                        
                       α 
                     
                     = 
                     
                       
                         ERX 
                         · 
                         EL 
                       
                        
                       
                           
                       
                        
                       
                         0 
                         / 
                         2 
                       
                     
                   
                   , 
                   
                       
                   
                    
                   
                     
                       and 
                        
                       
                           
                       
                        
                       β 
                     
                     = 
                     
                       
                         EUD 
                         · 
                         EL 
                       
                        
                       
                           
                       
                        
                       
                         0 
                         / 
                         2. 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
         [0069]    Also, these signals SIFI and SIFQ are supplied to a low-pass filter  22  having a broader band than a band width (for example, in the range of 6 to 8 MHz) occupied by a video intermediate wave signal and an audio intermediate wave signal. As a result, signal components (and the local oscillation signals SL 0 I and SL 0 Q) of sums of angular frequencies (ωRX+ωL 0 ) and (ωUD+ωL 0 ) are removed from the signals SIFI and SIFQ. Thus, the signals SIFI and SIFQ expressed by Expressions (10) and (11) are fetched from the low-pass filter  22 : 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         SIFI 
                         = 
                           
                          
                         
                           
                             α 
                             · 
                             
                               cos 
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     RX 
                                   
                                   - 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     L 
                                      
                                     
                                         
                                     
                                      
                                     0 
                                   
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               β 
                               · 
                               
                                 cos 
                                  
                                 
                                   ( 
                                   
                                     
                                       ω 
                                        
                                       
                                           
                                       
                                        
                                       UD 
                                     
                                     - 
                                     
                                       ω 
                                        
                                       
                                           
                                       
                                        
                                       L 
                                        
                                       
                                           
                                       
                                        
                                       0 
                                     
                                   
                                   ) 
                                 
                               
                             
                              
                             t 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               α 
                               · 
                               cos 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                           + 
                           
                             
                               β 
                               · 
                               cos 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         SIFQ 
                         = 
                           
                          
                         
                           
                             α 
                             · 
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     RX 
                                   
                                   - 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     L 
                                      
                                     
                                         
                                     
                                      
                                     0 
                                   
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               β 
                               · 
                               
                                 sin 
                                  
                                 
                                   ( 
                                   
                                     
                                       ω 
                                        
                                       
                                           
                                       
                                        
                                       UD 
                                     
                                     - 
                                     
                                       ω 
                                        
                                       
                                           
                                       
                                        
                                       L 
                                        
                                       
                                           
                                       
                                        
                                       0 
                                     
                                   
                                   ) 
                                 
                               
                             
                              
                             t 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               
                                 - 
                                 α 
                               
                               · 
                               sin 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                           + 
                           
                             
                               β 
                               · 
                               sin 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
         [0070]    Also, these signals SIFI and SIFQ are supplied to a complex band-pass filter (polyphase band-pass filter)  24  through an amplitude phase correcting circuit  23  which will be described later. This complex band-pass filter  24  has the following characteristics: 
         [0071]    (a) having frequency characteristics of a band-pass filter, 
         [0072]    (b) giving a phase difference of 90° between the signal SIFI and the signal SIFQ, and 
         [0073]    (c) having two band-pass characteristics having a frequency f 0  and a frequency −f 0 , as central frequencies, symmetric with respect to a zero frequency on a frequency axis, and can select one or both of the two band-pass characteristics based on a relative phase of an input signal. 
         [0074]    Therefore, with the complex band-pass filter  24 , the signal SIFQ lags the signal SIFI by a phase difference of 90° in accordance with the items (b) and (c) described above. As a result, Expression (12) is transformed into Expression (13): 
         [0000]    
       
         
           
             
               
                 
                   SIFI 
                   = 
                   
                     
                       
                         α 
                         · 
                         cos 
                       
                        
                       
                           
                       
                        
                       ω 
                        
                       
                           
                       
                        
                       IFt 
                     
                     + 
                     
                       
                         β 
                         · 
                         cos 
                       
                        
                       
                           
                       
                        
                       ω 
                        
                       
                           
                       
                        
                       IFt 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         SIFQ 
                         = 
                           
                          
                         
                           
                             
                               - 
                               α 
                             
                             · 
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     IFt 
                                   
                                   - 
                                   
                                     90 
                                      
                                     ° 
                                   
                                 
                                 ) 
                               
                             
                           
                           + 
                           
                             β 
                             · 
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   
                                     ω 
                                      
                                     
                                         
                                     
                                      
                                     IFt 
                                   
                                   - 
                                   
                                     90 
                                      
                                     ° 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               α 
                               · 
                               cos 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                           - 
                           
                             
                               β 
                               · 
                               cos 
                             
                              
                             
                                 
                             
                              
                             ω 
                              
                             
                                 
                             
                              
                             IFt 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
         [0075]    That is to say, signal components, α·cos ωIFt, of the signal SIFI and the signal SIFQ are in phase with each other, and signal components, ⊕·cos ωIFt, of the signal SIFI and the signal SIFQ are 180° out-of-phase. 
         [0076]    Also, the signal SIFI and the signal SIFQ are supplied to an amplifier  25  for level correction to be added to each other, and a signal SIF expressed by Expression (14) is fetched from the amplifier  25  for level correction: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         SIF 
                         = 
                           
                          
                         
                           SIFI 
                           + 
                           SIFQ 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           2 
                            
                           
                               
                           
                            
                           
                             α 
                             · 
                             cos 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           IFt 
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             ERX 
                             · 
                             EL 
                           
                            
                           
                               
                           
                            
                           
                             0 
                             · 
                             cos 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           IFt 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
         [0077]    The signal SIF thus fetched is nothing else but an intermediate frequency signal when the signal SRX is received by using the upper heterodyne system. Also, the intermediate frequency signal SIF contains therein no image disturbing signal SUD. It is noted that the amplitude phase correcting circuit  23  is provided in order to correct amplitudes and phases of the signals SIFI and SIFQ so that Expression (14) is sufficiently established, that is, the image disturbing signal SUD becomes minimum. 
         [0078]    Moreover, at this time, even when levels of the signals SIFI and SIFQ are different from each other due to a difference in broadcasting system, the amplifier  25  for level correction corrects the level of the signal SIF so that AGC (Automatic Gain Control) characteristics (especially, a start level of the AGC) or the like which will be described later do not change. 
         [0079]    Also, the intermediate frequency signal SIF is outputted to the terminal pin T 12  through a variable gain amplifier  26  for AGC, and a band-pass filter  27  for cutting and aliasing a D.C. component. 
         [0080]    Therefore, the changing of the frequency-dividing ratios M and N makes it possible to select the desired frequency (channel) in accordance with Expression (3). Also, the intermediate frequency signal SIF outputted to the terminal pin T 12  is demodulated so as to correspond to the broadcasting system, which results in that the desired broadcasting can be viewed and listened. 
         [0081]    Thus, according to the front end circuit  10 , it is possible to respond to the broad frequency range of  46  to  887  MHz stated in the items (A) to (C) with one chip IC. In addition, the front end circuit  10  can be realized with the less number of parts or components without reducing the disturbing characteristics for the broad frequency range. Moreover, it is possible to cope with the difference in broadcasting system between the digital broadcasting and the analog broadcasting, and the difference in broadcasting system between the global areas with one front end circuit  10 . 
         [0082]    In addition, the reception disturbance due to the harmonic or the like of the clock signal is reduced, and as a result, the reception sensitivity is enhanced. Moreover, the entire PLL circuit  30  can be configured in the form of an on-chip in an IC except for capacitors C 11 , C 12  and C 13  in the loop filter  35 . As a result, it is possible to obtain the PLL circuit which has the large resistance against the disturbance, and for which the hindrance occurrence is reduced. In addition, since the tuning circuits  14 A to  14 C are merely connected to the frequency amplifiers  13 A to  13 C, respectively, the load can be lightened and the distortions caused in the frequency amplifiers  13 A to  13 C can be reduced. 
       [1-1-1] Example of AGC 
       [0083]    In a base-band processing circuit (details thereof will be described later) shown in  FIG. 2 , an AGC voltage VAGC is formed, and is then supplied as a control signal for a gain of a variable gain amplifier  26  for AGC to the variable gain amplifier  26  for AGC through the terminal pin T 14 . As a result, the AGC in the intermediate frequency stage is carried out. 
         [0084]    In addition, for example, when the level of the desired received signal SRX is too large, or when the disturbing wave signal having a large level is mixedly contained in the received signal SRX, the AGC in the intermediate frequency stage described above can hardly cope with such a situation. In order to cope with this situation, the signals SIFI and SIFQ outputted from the low-pass filter  22  are supplied to a level detecting circuit  41 . The level detecting circuit  41  detects whether or not each of the levels of the signals SIFI and SIFQ before the AGC is carried out in the variable gain amplifier  26  for AGC exceeds a predetermined value. 
         [0085]    Also, a detection signal from the level detecting circuit  41 , and the AGC voltage VAGC at the terminal pin T 14  are supplied to an addition circuit  42 , and an addition output signal from the addition circuit  42  is supplied to a formation circuit  43 , thereby forming a delay AGC voltage VDAGC. The delay AGC voltage VDAGC is then supplied as a control signal for each of gains of high frequency amplifiers  13 A to  13 C to each of the high frequency amplifiers  13 A to  13 C, thereby carrying out the delay AGC. 
         [0086]    Therefore, the optimal AGC operation can be carried out based on a D/U (Desire to Undesire ratio) between an intensity of a signal desired to be received and each of intensities of many signals undesired to be received. As a result, the desired broadcasting of the digital broadcasting and the analog broadcasting can, even when the digital broadcasting and the analog broadcasting are mixedly broadcasted, be received well. 
       [1-1-2] Example of Voltage for Test Adjustment 
       [0087]    The signals SIFI and SIFQ outputted from the low-pass filter  22  are supplied to a linear detection circuit  44  to be detected and smoothed, thereby obtaining a D.C. voltage V 44  representing each of the levels of the signals SIFI and SIFQ. Also, the resulting D.C. voltage V 44  is outputted to the terminal pin T 13 . 
         [0088]    The D.C. voltage V 44  outputted to the terminal pin T 13  is used in a phase of a test or adjustment of the front end circuit  10 . For example, the D.C. voltage V 44  can be used when the level of the input signal (received signal) is checked over the broad frequency range. That is to say, unlike the output signal obtained through an intermediate frequency filter having a narrow band, the attenuation characteristics of the broad band can be directly checked about a signal line extending from the antenna terminal pin T 11  to each of the mixer circuits  21 I and  21 Q. 
         [0089]    In addition, in the case where the antenna tuning circuits  12 A to  12 C, and the interstage tuning circuits  14 A to  14   c  are adjusted, when an input test signal is supplied to the antenna terminal pin T 11  and the AGC voltage VAGC supplied to the terminal pin T 14  is fixedly set at a predetermined value, the tracking adjustment can be carried out based on a change in D.C. voltage V 44 . Moreover, data used to adjust the functions of the front end circuit  10 , and to measure the characteristics thereof can be stored in a non-volatile memory  51  through the terminal pin T 16 , and thus can be supplied to the corresponding circuits when necessary. 
       [1-1-3] Initialization 
       [0090]    The central frequency and a passband width of the complex band-pass filter  24 , a correction amount in the amplitude phase correcting circuit  23 , and a gain of the amplifier  25  for level correction are made variable and can be set from the outside because they needs to correspond to the broadcasting system of the received television broadcasting. For example, the central frequency of the complex band-pass filter  24  is made variable in the range of 3.8 to 5.5 MHz, and the passband thereof is made variable in the range of 5.7 to 8.0 MHz. 
         [0091]    Also, in a phase of assembly, factory shipment or the like, set values for the amplitude phase correcting circuit  23 , the complex band-pass filter  24 , and the amplifier  25  for level correction are written to the non-volatile memory  51  through the terminal pin T 16 . In addition, data for tracking for the antenna tuning circuits  12 A to  12 C, and the interstage tuning circuits  14 A to  14 C (data used to fine-tune a tuning frequency), and data used to fine-tune the output voltage from the constant voltage circuit  53  are also written to the non-volatile memory  51  through the terminal pin T 16  similarly to the case of the set values. Therefore, the characteristics of the individual circuits can be set so as to correspond to the broadcasting system of the television broadcasting desired to be received. 
         [0092]    Note that, when the signals SL 0 I and SL 0 Q which are supplied from the frequency-dividing circuit  38  to the mixer circuits  21 I and  21 Q, respectively, are reversed from the above case, Expression (14) is transformed into Expression (15): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         SIF 
                         = 
                         
                           SIFI 
                           + 
                           SIFQ 
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             - 
                             2 
                           
                            
                           
                             β 
                             · 
                             cos 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           IFt 
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             EUD 
                             · 
                             EL 
                           
                            
                           
                               
                           
                            
                           
                             0 
                             · 
                             cos 
                           
                            
                           
                               
                           
                            
                           ω 
                            
                           
                               
                           
                            
                           IFt 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
         [0093]    As a result, the image disturbing signal SUD is fetched through the terminal pin T 13 . Therefore, the amplitude phase correcting circuit  23  is adjusted so that the image disturbing signal SUD at this time becomes minimum, and the adjustment data is written to the non-volatile memory  51 . 
       [1-1-4] Operation in Phase of Use 
       [0094]    In the case as well where a power source of a receiver using the IC  10  is turned ON, the set values stored in the non-volatile memory  51  are copied to the buffer memory  52 . Also, the set values thus copied are supplied as default values to the antenna tuning circuits  12 A to  12 C, the interstage tuning circuits  14 A to  14 C, the amplitude phase correcting circuit  23 , the complex band-pass filter  24 , the amplifier  25  for level correction, and the circuit  53 , respectively. 
         [0095]    Also, when a user selects a desired channel, data for the channel selection is supplied from a microcomputer (not shown) for system control to the buffer memory  52  through the terminal pin T 17  to be temporarily stored therein. The data thus stored is supplied to each of the switch circuits  11  and  15 , the antenna tuning circuits  12 A to  12 C, the interstage tuning circuits  14 A to  14 C, and the PLL circuit  30 . As a result, the reception band containing the desired channel (frequency) is selected, and the desired channel is selected in the reception band. 
       [1-1-5] Conclusion 
       [0096]    According to the front end circuit  10  shown in  FIG. 1 , it is possible to receive the television broadcasting in the frequency band of  46  to  887  MHz as shown in the items (A) to (C) described above. Also, at this time, since the central frequency and the passband width of the complex band-pass filter  24  are made variable, it is possible to respond to not only the domestic terrestrial digital broadcasting and terrestrial analog television broadcasting, but also the foreign digital broadcasting and analog television broadcasting. 
       [1-2] Example of Base-band Processing Circuit 
       [0097]      FIG. 2  shows an example of a base-band processing circuit. The base-band processing circuit processes the intermediate frequency signal SIF outputted thereto from the front end circuit  10 , and outputs a color video signal and an audio signal. That is to say, in  FIG. 2 , a portion  60  surrounded by a chain line shows the base-band processing circuit which is configured in the form of an one chip IC. In addition, this IC (base-band processing circuit)  60  has terminal pins T 61  to T 67  for external connection. 
         [0098]    Also, the intermediate frequency signal SIF outputted through the terminal pin T 12  of the front end circuit  10  is supplied to an A/D (Analog to Digital) converter circuit  61  to be A/D-converted into a digital intermediate frequency signal SIF. The resulting digital intermediate frequency signal SIF is then supplied to a filter  62 , thereby removing therefrom unnecessary frequency components. 
         [0099]    Also, at the time of reception of the digital television broadcasting, the digital intermediate frequency signal SIF outputted from the filter  62  is supplied to a demodulation circuit  63 , so that the digital signal in the base-band is demodulated and fetched. The resulting demodulated output signal is supplied to an error correcting circuit  64  to become a data stream for which the error correction is carried out. The resulting data stream is outputted to the terminal pin T 62 . Therefore, when the signal at the terminal pin T 62  is decoded in accordance with the broadcasting system corresponding thereto, it is possible to obtain the original color video signal and audio signal. 
         [0100]    On the other hand, at the time of reception of the analog television broadcasting, the digital intermediate frequency signal SIF outputted from the filter  62  is supplied to a video intermediate frequency filter  71 , thereby fetching therefrom a digital video intermediate frequency signal. After a ghost component is removed from the digital video intermediate frequency signal in a ghost removing circuit  72 , the resulting signal is supplied to a modulation circuit  73  to be demodulated into a digital color video signal. Also, the resulting digital color video signal is supplied to a D/A (Digital to Analog) converter circuit  74  to be D/A-converted into an analog color video signal. The resulting analog color video signal is outputted to the terminal pin T 63 . 
         [0101]    Moreover, at the time of reception of the analog television broadcasting, the digital intermediate frequency signal SIF outputted from the filter  62  is supplied to an audio intermediate frequency filter  81 , thereby fetching therefrom a digital audio intermediate frequency signal. The digital audio intermediate frequency signal thus fetched is supplied to a demodulation circuit  82  to be demodulated into a digital audio signal. Also, the resulting digital audio signal is supplied to a D/A converter circuit  84  to be D/A-converted into audio signals of left- and right-hand channels. These audio signals of the left- and right-hand channels are outputted to the terminal pins T 64  and T 65 , respectively. 
         [0102]    In addition, an AGC voltage VAGC is formed in an AGC voltage forming circuit  91 . The AGC voltage VAGC thus formed is outputted to the terminal pin T 67 , and is then applied to the terminal pin T 14  of the front end circuit  10 . As a result, the AGC in the intermediate frequency stage, and the delay AGC in the high frequency stage are carried out in the manner as described above. 
         [0103]    Moreover, a clock signal having a predetermined frequency is formed in a clock forming circuit  92 . The clock signal thus formed is supplied to each of the corresponding portions of the base-band processing circuit  60 . Also, the clock signal is supplied to the signal forming circuit  36  through the terminal pin T 66 , and the terminal pin T 15  of the front end circuit  10 . 
         [0104]    Therefore, the reception disturbance due to the harmonic or the like of the clock signal is reduced. As a result, the reception sensitivity is enhanced. 
       [2] With Respect to VCO  31  Capable of Being Used in the Present Invention 
     [2-1] With respect to Temperature Characteristics of Oscillation Frequency fVCO and Control Sensitivity KVCO of VCO  31   
       [0105]      FIG. 4A  shows an example of results of measurement of the characteristics of the control voltage VC and the oscillation frequency fVCO of the VCO  31 . Also,  FIG. 4B  shows an example of results of measurement of the characteristics of the control voltage VC and the control sensitivity KVCO (=ΔfVCO/ΔVC) of the VCO  31 . It is noted that in these figures, a heavy line indicates the characteristics when the ambient temperature T is 25° C., and a thin line indicates the characteristics when the ambient temperature T is 90° C. In this case, the ambient temperature T is used as a parameter. 
         [0106]    Also, when the oscillation frequency fVCO is locked at 3,200 MHz in the case of T=25° C in  FIG. 4A , the control voltage VC≅1.06 V is obtained. Also, when the ambient temperature T rises to 90° C., the control voltage VC changes to about 1.15 V. However, according to the measurement results shown in  FIG. 4B , even when there is a change in ambient temperature T, the control sensitivity KVCO does not change so much. Even in the vicinity of a local maximum value, when the control voltage VC is 1.06 V, the control sensitivity KVCO is about 206 MHz/V. When the control voltage VC is 1.15 V, the control sensitivity KVCO is about 220 MHz/V. 
         [0107]    That is to say, when the control sensitivity KVCO for the ambient temperature T is corrected, even if the VCO which has the same correction characteristics of the control sensitivity KVCO irrespective of the ambient temperature T is substituted for the VCO  31 , there is no problem in practical use because the correction error is sufficiently small. Therefore, the characteristics of the control sensitivity KVCO, for example, at T=25° C. are acquired and held. In this case, all that is required is that when the ambient temperature T changes, the control sensitivity KVCO is corrected from the control sensitivity KVCO thus held. 
         [0108]    However, according to the measurement results shown in  FIG. 4B , the control sensitivity KVCO largely changes depending on the control voltage VC. Thus, when the control voltage VC is in the range of 1.0 to 1.5 V, the control sensitivity KVCO becomes local maximum. Therefore, the control sensitivity KVCO, for example, when the control voltage VC is in the range of 1.0 to 1.5 V is supposed, and the charge pump current ICP is set from the control sensitivity KVCO. In this case, when the control voltage VC is out of the range of 1.0 to 1.5 V, the control sensitivity KVCO is low, and the loop gain decreases. As a result, it is impossible to obtain the desired characteristics. 
         [0109]    From the foregoing, in the case where there is a change in ambient temperature T, when the control voltage VC is measured and converted into the control sensitivity KVCO, the charge pump current ICP is calculated from the control sensitivity KVCO, and the resetting is carried out, the loop characteristics can be held constant. 
         [0110]    In other words, a data table, of the control sensitivity KVCO, having the control voltage VC as a variable, that is, a data table about the characteristics complementary to the characteristics shown in  FIG. 4B  is prepared. Also, by referring to the data table, the charge pump current ICP has to be corrected so as to correspond to the change in ambient temperature T. By adopting this process, even when the operation of the PLL circuit  30  is not stopped, the control sensitivity KVCO for the ambient temperature T can be corrected by correcting the charge pump current ICP. 
         [0111]    At this time, the broadcasting can be continuously received because there is no need for stopping the operation of the PLL circuit  30 . In addition, when the PLL circuit  30  is provided with no function of detecting the change in ambient temperature T, the control voltage VC has to be periodically measured, thereby calculating and setting the charge pump current ICP. 
         [0112]    It is noted that even when a MOS type variable capacitance diode is used in the VCO  31  instead of using the variable capacitance diode (the so-called varicap), the oscillation frequency fVCO changes similarly. As a result, it is possible to obtain the same correction method as that in the above case. 
       [2-2] Consideration about That Temperature Change in Control Sensitivity KVCO is Small 
       [0113]    In this paragraph, let us consider that as shown in  FIG. 4B , the temperature change of the control sensitivity KVCO is small. As well known, the oscillation frequency fVCO in an LC type oscillation circuit is given by Expression (16): 
         [0000]        f VCO=1/(2π√( LC )   (16) 
         [0114]    where L is an inductance of a resonance circuit, and C is an electrostatic capacitance of the resonance circuit. 
         [0115]    Therefore, when the VCO  31  is composed of an LC type oscillation circuit having a broad band, an electrostatic capacitance for the resonance becomes the total capacitance C in  FIG. 13 . 
         [0116]    Also, it is thought that the temperature dependency of the oscillation frequency fVCO is mainly caused by a change in electrostatic capacitance C. Moreover, the electrostatic capacitance C includes the capacitance of the variable capacitance diode CD and the capacitances of the capacitors C 0  to Cn (refer to  FIG. 13 ), and a parasitic capacitance of a wiring or the like. In this case, it is thought that the temperature change in electrostatic capacitance C is mainly caused by changes in parasitic capacitances (having a PN junction capacitance) of the variable capacitance diode CD and the capacitors C 0  to Cn. 
         [0117]    However, each of the parasitic capacitances of the variable capacitance diode CD and the capacitors C 0  to Cn essentially has no sensitivity for the control voltage VC. Therefore, the characteristics of the control sensitivity KVCO, as shown in  FIG. 4B , do not change so much depending on the ambient temperature T. 
         [0118]    Although the description has been given so far with respect to the LC type oscillation circuit, the description concerned also applies to a ring oscillator. Therefore, the VCO  31  is by no means limited to the LC type oscillation circuit. 
       [2-3] Example of Configuration of VCO  31   
       [0119]    In consideration of the foregoing, the VCO  31  (VCOs  31 A to  31 C), for example, is configured in the form of an LC type resonance circuit as shown in  FIG. 5 . A resonance capacitance C of this LC type resonance circuit is configured by connecting a variable capacitance diode CD, and four (n=3 in the case shown in  FIG. 13 ) series circuits of a capacitor C 0  and a switch circuit S 0 , . . . , a capacitor C 1  and a switch circuit S 1 , a capacitor C 2  and a switch circuit S 2 , and a capacitor C 3  and a switch circuit S 3  in parallel with one another. It is noted that capacitances of the four capacitors C 0  to C 3  are set in such a way that C 0 =reference value, C 1 =2·C 0 , C 2 =4·C 0 , and C 3 =8·C 0 . 
         [0120]    Therefore, the resonance capacitance C changes from a minimum value to a maximum value in 16 steps as expressed by Expression (17) with the capacitance C 0  as a change unit based on combinations of ON and OFF of the switch circuits S 0  to S 3 : 
         [0000]        C=CD  (minimum value) 
         [0000]        C=CD+C 0 
         [0000]        C=CD+ 2 ·C 0 
         [0000]        C=CD+ 15 ·C 0 (maximum value)   (17) 
         [0121]    In addition, in the individual steps, the capacitance CD of the variable capacitance diode CD can be controlled with the control voltage VC. 
         [0122]    As a result, in each of the VCOs  31 A to  31 C, the necessary oscillation frequency fVCO can be obtained based on the combinations of ON and OFF of the switch circuits S 0  to S 3 , and the change in control voltage VC. 
         [0123]      FIG. 6  shows an example of measurement of a relationship between the control voltage VC and the oscillation frequency VCO. In this case, a combination of connection of the capacitors C 0  to C 3  (a combination of ON and OFF of the switch circuits S 0  to S 3 ) is used as a parameter. In addition, in this case, upper  16  curves (each indicated by a solid line) represent the characteristics of the VCO  31 A, middle  16  curves (each indicated by a broken line) represent the characteristics of the VCO  31 B, and lower  16  curves (each indicated by a solid line) represent the characteristics of the VCO  31 C. 
         [0124]    As apparent from  FIG. 6  as well, it is understood that the oscillation frequency fVCO (in the range of 1,800 to 3,000 MHz) necessary for the VCO  31  can be obtained based on the switching of the VCOs  31 A to  31 C, the combination of the capacitors C 0  to C 3 , and the control for the capacitance of the variable capacitance diode CD. 
         [0125]    In addition, it is also understood that the oscillation frequency fVCO for the control voltage VC has the same tendency as that of the characteristics shown in  FIG. 4A . That is to say, although a gradient of each of the characteristic curves shown in  FIG. 6  represents the control sensitivity KVCO, in any of the characteristic curves, the control sensitivity KVCO becomes local maximum at a center of the control voltage VC. 
       [3-1] First Embodiment of PLL Circuit  30   
       [0126]      FIG. 7  shows a configuration of a PLL circuit  30  according to a first embodiment of the present invention. The PLL circuit  30  of the first embodiment is configured based on the paragraphs [2-1] to [2-3] described above. In this case, the VCO  31  is composed of the VCOs  31 A to  31 C (n=3 in the case of  FIG. 13 ). 
         [0127]    Also, data on the frequency driving ratio N is supplied from a buffer memory  52  to a variable frequency-dividing circuit  32 , and the frequency driving ratio N is then set in the variable frequency-dividing circuit  32 . In addition, a control circuit  300  is provided in the PLL circuit  30 . A band signal SB used to set the reception bands of the items (A) to (C) described above, and the data on the frequency driving ratio N are supplied from the buffer memory  52  to the control circuit  300 . Also, a control signal in accordance with which one of the VCOs  31 A to  31 C is switched over to another one so as to correspond to the reception bands of the items (A) to (C) described above is supplied from the control circuit  300  to the VCO  31 . 
         [0128]    In addition, a control signal in accordance with which the control sensitivity KVCO is controlled is supplied from the control circuit  300  to a charge pump circuit  34 , so that a charge pump current ICP is controlled in the manner as will be described later. In addition, a memory  301  for storing therein the data on the characteristics of the control sensitivity KVCO, for example, shown in  FIG. 4B  is connected to the control circuit  300 . 
         [0129]    Note that, in  FIG. 7 , reference numeral  302  designates a D/A converter circuit, reference numeral  303  designates a frequency counter for detecting (counting) the oscillation frequency fVCO of the VCO  31 , and reference numeral  304  designates an A/D converter circuit. In addition, the control circuit  300  controls switch circuits  311  and  312 . 
         [0130]    With this configuration, for example, when a power source of a receiver is turned ON, the control sensitivity of the VCO  31  is measured. That is to say, the control circuit  300  turns OFF the switch circuit  311 , and turns ON the switch circuit  312 . In addition, the control circuit  300 , for example, selects the VCO  31 A in the VCO  31 . 
         [0131]    Next, predetermined control data is supplied from the control circuit  300  to a D/A converter  302 , and a D/A conversion output signal is supplied from the D/A converter  302  to a loop filter  35 . Also, the loop filter  35  outputs a control voltage VC. The control voltage VC is outputted in order to obtain the control sensitivity characteristics shown in  FIG. 4B , and changes from the lowest voltage up to the highest voltage. That is to say, in the case of the control sensitivity characteristics shown in  FIG. 4B , the control voltage VC changes from 0 V up to 2.5 V as shown in an axis of abscissa of  FIG. 4B . 
         [0132]    Also, since the oscillation frequency fVCO of the VCO  31  changes with the change in control voltage VC, the oscillation frequency fVCO is measured by the frequency counter  303 , and data on the oscillation frequency fVCO thus measured is supplied to the control circuit  300 . 
         [0133]    As a result, the characteristics (for example, the characteristics shown in  FIG. 4A ) representing the relationship between the control voltage VC, and the oscillation frequency fVCO of the VCO  31  can be obtained based on the operation of the control circuit  300 . In this case, the characteristics (for example, the characteristics shown in  FIG. 4B ) representing the relationship between the control voltage VC and the control sensitivity KVCO are calculated from the characteristics representing the relationship between the control voltage VC, and the oscillation frequency fVCO of the VCO  31 . Also, the data on the characteristics concerned is stored in the memory  301 . 
         [0134]    Specifically, an i-th (i=1 to max.) control voltage VC(i) is supplied as the control voltage VC to the VCO  31 , and an oscillation frequency fVCO(i) of the VCO  31  in the i-th control voltage VC(i) is measured. Next, an (i+1)-th control voltage VC(i+1) is supplied as the control voltage VC to the VCO  31 , and an oscillation frequency fVCO(i+1) of the VCO  31  in the (i+1)-th control voltage VC(i+1) is measured. 
         [0135]    In this case, Expression (18) is given as follows: 
         [0000]      Δ VC=VC ( i +1)− VC ( i ) ( VC ( i +1)&gt; VC ( i ))   (18) 
         [0136]    After this, the measurement is repetitively carried out similarly to the above case, and a difference KVCO(i) expressed by Expression (19) is obtained every measurement: 
         [0000]        K VCO( i )= f VCO( i )− f VCO( i +1)   (19) 
         [0137]    By adopting this process, the difference KVCO(i) can be obtained as the control sensitivity KVCO in the control voltage VC(i). 
         [0138]    Therefore, when a set of control voltage VC(i) and control sensitivity KVCO(i) is stored as a data table in the memory  301 , with respect to the VCO  31 , the control sensitivity KVCO for an arbitrary control voltage VC can be known. It is noted that when there is no control voltage corresponding to the data table in this case, the control sensitivity KVCO can be obtained by carrying out the interpolation for the control sensitivities KVCO(i) and KVCO(i+1) of the nearest two points. 
         [0139]    Also, the above processing is carried out with respect to the VCO for formation of the local oscillation frequency used in the actual receiving location (place of destination). It is noted that when there is caused the necessity for forming the local oscillation frequency to be used by another VCO from the reason that, for example, the receiving location is changed, the same processing is carried out again with respect to the another VCO. 
         [0140]    Therefore, data on the characteristics representing the relationship between the control voltage VC and the control sensitivity KVCO is obtained with respect to the VCO, necessary for reception of the broadcasting, of the VCOs  31 A to  31 C, and is then stored in the memory  301 . 
         [0141]    Also, after completion of the measurement of the control sensitivity KVCO, the switch circuit  311  is turned ON and the switch  312  is turned OFF. As a result, the configuration of the normal PLL circuit  30  is obtained and thus the PLL operation starts to be carried out. Also, when the PLL circuit  30  is locked, the magnitude of the control voltage VC at this time is measured and is then converted into the control sensitivity KVCO by referring to the data table described above created in the memory  301  by the A/D converter circuit  304 . 
         [0142]    Also, the charge pump current ICP is controlled so that Expression (12) is established based on the control sensitivity KVCO as the results of the A/D conversion, and the frequency-dividing ratio N corresponding to the oscillation frequency fVCO at this time: 
         [0000]      ICP· K VCO/ N=κ   (20) 
         [0143]    where κ is a predetermined constant value. 
         [0144]    The predetermined constant value κ is a constant value with which the band width of the loop of the PLL circuit  30  is determined, and is determined in the phase of design of the loop of the PLL circuit  30  or based on the previous evaluation. However, the predetermined constant value κ is held as a default value in the non-volatile memory  51  (refer to  FIG. 1 ), and thus can be changed as may be necessary. 
         [0145]    Therefore, since the transfer function G(s) of the PLL circuit  30  becomes constant irrespective of the frequency-dividing ratio N, the loop characteristics of the PLL circuit  30  are stabilized irrespective of the oscillation frequency fVCO of the VCO  31 , in other words, the received frequency. 
         [0146]    Moreover, when the ambient temperature T changes in the phase of reception, the oscillation frequency fVCO of the VCO  31  changes accordingly. At this time, however, as apparent from the characteristic curve at T=25° C. or at T=90° C., for example, shown in  FIG. 4A , the control voltage VC of the VCO  31  changes so as to cancel the frequency change in the characteristic curve. Hereupon, as a result, for example, as shown in  FIG. 4B , the control sensitivity KVCO changes, so that the loop characteristics of the PLL circuit  30  become unstable. 
         [0147]    However, in the PLL circuit  30  of the first embodiment shown in  FIG. 7 , the control circuit  300  fetches the data, corresponding to the control voltage VC at this time, of the data (for example, refer to  FIG. 4B ), representing the control sensitivity KVCO, stored in the memory  301 . The data thus fetched is supplied as the control signal for the charge pump current ICP to the charge pump circuit  34 . As a result, the magnitude of the charge pump current ICP is controlled in accordance with Expression (20) so that the transfer function G(s) of the open loop expressed in Expression (2) becomes constant irrespective of the control sensitivity KVCO. 
         [0148]    Therefore, the loop characteristics of the PLL circuit  30  become stable irrespective of the ambient temperature T because the transfer function G(s) of the PLL circuit  30  becomes constant irrespective of the ambient temperature T. 
         [0149]    As a result, according to the PLL circuit  30  of the first embodiment shown in  FIG. 7 , even when the oscillation frequency fVCO of the VCO  31  is changed in order to change the received frequency, that is, even when the frequency-dividing ration N of the variable frequency-dividing circuit  32  changes, or even when the control voltage VC of the VCO  31  changes, the charge pump current ICP changes in accordance with Expression (20). As a result, the transfer function G(s) when the PLL circuit  30  is held in the open loop state is kept constant. Therefore, the stability of the PLL circuit  30  does not change at all. 
         [0150]    In addition, when the ambient temperature T changes, the oscillation frequency fVCO of the VCO  31  changes accordingly. However, the control sensitivity KVCO changes so as to correspond to the control voltage VC of the VCO  31  at this time, and the charge pump current ICP changes in accordance with Expression (20) so as to correspond to the change in control sensitivity KVCO. As a result, the stability of the PLL circuit  30  does not change at all. 
         [0151]      FIGS. 8A and 8B  show the results of measurement of the distribution characteristics of the phase noise of the PLL circuit  30  of the first embodiment shown in  FIG. 7 . That is to say,  FIG. 8A  shows the results of measurement of the distribution characteristics of the phase noise of the PLL circuit  30  when the charge pump current ICP is changed based only on the oscillation frequency fVCO of the VCO  31 . Also,  FIG. 8B  shows the results of measurement of the distribution characteristics of the phase noise of the PLL circuit  30  when the charge pump current ICP is changed in consideration of the control sensitivity KVCO as well of the VCO  31  according to the embodiment the present invention. 
         [0152]    According to  FIGS. 8A and 8B , it is understood that the reduction of the phase noise in a high frequency range (a portion surrounded by a broken line) is larger in the case where the charge pump current ICP is changed in consideration of the control sensitivity KVCO of the VCO  31  ( FIG. 8B ) than in the case where the charge pump current ICP is changed without consideration of the control sensitivity KVCO of the VCO  31  ( FIG. 8A ). That is to say, the measurement results mean that the phase noise characteristics are improved. Therefore, these frequency ranges can also be used. 
       [3-2] Second Embodiment of PLL Circuit  30   
       [0153]    In a second embodiment shown in  FIG. 9 , a PLL circuit  30  is configured basically, similarly to the case of the PLL circuit  30  of the first embodiment shown in  FIG. 7 . Also, an oscillation signal SVCO, having an oscillation frequency, of a VCO  31  is supplied to a frequency-dividing circuit  305  to be frequency-divided into a frequency-dividing signal having a frequency of 1/m (m: positive integral number) of the oscillation frequency. Also, the resulting frequency-dividing signal is supplied as a count input to a frequency counter  303 . In addition, although not illustrated in the figure, start and stop of a counting operation of the frequency counter  303  are controlled in accordance with a frequency-dividing signal. In this case, a pulse having a frequency of 1 MHz is frequency-divided into this frequency-dividing signal having a frequency of 1/m of 1 MHz. That is to say, the frequency counter  303  counts the number of cycles of the oscillation signal SVCO of the VCO  31  for one cycle time period of the pulse having the frequency of 1 MHz. 
         [0154]    Therefore, in this case, a count value of the counter  303  becomes a frequency at which the oscillation frequency fVCO of the VCO  31  is counted with MHz as a unit. As a result, it is unnecessary to provide processing or a circuit for converting the count value of the frequency counter  303  into a frequency. In addition, it is also unnecessary to use a high-speed frequency counter as the frequency counter  303 . 
       [3-3] Third Embodiment of PLL Circuit  30   
       [0155]    In a PLL circuit  30  of a third embodiment shown in  FIG. 10 , a variable frequency-dividing circuit  32  of the PLL circuit  30  of the third embodiment is configured in the form of a multi-modulus type frequency-dividing circuit, for example, a pulse swallow type frequency-dividing circuit by using a dual modulus pre-scaler. 
         [0156]    That is to say, an oscillation signal SVCO, having an oscillation frequency, of a VCO  31  is supplied to a pre-scaler  321  to be frequency-divided into a frequency-dividing signal having a frequency of 1/Q or 1/(1+Q) of the oscillation frequency. Also, the resulting frequency-dividing signal is supplied to each of a pulse counter  322  having a frequency-dividing ratio P, and a swallow counter  323  having a frequency-dividing ratio S. In this case, the frequency-dividing ratios P and Q are positive integral numbers, respectively, and a relationship of S&lt;P is established between them. 
         [0157]    Also, an output signal from the swallow counter  323  is supplied as a switching signal (modulus control signal) used to switch one of the frequency-dividing ratios Q and (1+Q) over to another one to the pre-scaler  321  through a switch circuit  313 . When the output signal from the swallow counter  323  is “0,” the frequency-dividing ratio is set at the value Q, while when the output signal from the swallow counter  323  is “1,” the frequency-dividing ratio is set at the value (1+Q). 
         [0158]    In addition, an output signal from the pulse counter  322  is supplied as a comparison input signal to a phase comparison circuit  33 , and is also supplied as a reset signal to the swallow counter  323 . Moreover, the control circuit  300  controls the switch circuit  313  and a counter  303 . 
         [0159]    With such a configuration, in a stationary phase, the output signal from the swallow counter  323  is supplied to the pre-scaler  321  through the switch circuit  313 . In addition, the output signal from the swallow counter  323  is held at “1” for a time period for which the input signal is counted up to a value S previously set. On the other hand, the output signal from the swallow counter  323  becomes “0” when the input signal is counted up to the value S, and stops its counting operation. Also, the output signal from the swallow counter  323  is continuously held at “0” until the swallow counter  323  is reset by the output signal from the pulse counter  322 . When being rest by the output signal from the pulse counter  322 , the swallow counter  323  restarts the counting operation. 
         [0160]    Also, when counting the input signal up to a value P previously set, the pulse counter  322  outputs the reset pulse described above, and resets itself. As a result, the pulse counter  322  starts to count the input signal again from the start. 
         [0161]    In addition, the relationship of S&lt;P is established, which results in that while the swallow counter  323  counts the input signal, the pulse counter  322  counts the frequency-dividing output signal having the frequency of 1/(1+Q) of the oscillation frequency from the pre-scaler  321 , and while the swallow counter  323  stops to count the input signal, the pulse counter  322  counts the frequency-dividing output signal having the frequency of 1/Q of the oscillation frequency from the pre-scaler  321 . 
         [0162]    Also, since in the stationary phase, the reset pulse outputted from the pulse counter  322  becomes the frequency-dividing output (having the frequency of 1/N of the oscillation frequency) for the variable frequency-dividing circuit  32 , a total frequency-dividing ratio N in the stationary phase is given by Expression (21): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         N 
                         = 
                         
                           
                             
                               ( 
                               
                                 Q 
                                 + 
                                 1 
                               
                               ) 
                             
                             · 
                             S 
                           
                           + 
                           
                             Q 
                             · 
                             
                               ( 
                               
                                 P 
                                 - 
                                 S 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           QP 
                           + 
                           S 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   21 
                   ) 
                 
               
             
           
         
       
     
         [0163]    Therefore, suitably selecting the values P and Q makes it possible to change the frequency-dividing ratio N “1” at a time. 
         [0164]    In the third embodiment shown in  FIG. 10 , the control signal, for the frequency-dividing ratio, supplied to the pre-scaler  321  is set at “0” by the switch circuit  313 , and thus the frequency-dividing ratio of the pre-scaler  321  is set at the value Q. Therefore, during the frequency-counting, the frequency-dividing signal having the frequency of 1/Q of the oscillation frequency of the oscillation signal SVCO is outputted from the pre-scaler  321  irrespective of the operation of the pulse swallow counter  32 . Also, the frequency-dividing signal is inputted to the pulse counter  322 . 
         [0165]    When the variable frequency-dividing circuit  32  is configured in the form of the pulse swallow type frequency-dividing circuit in the manner as described above, it is unnecessary to specially provide the frequency-dividing circuit having the frequency-dividing ratio Q for the frequency counting. Thus, the frequency-dividing ratio of the pre-scaler  321  is used as the fixed value Q in the phase of measurement of the frequency, which results in that the pre-scaler  321  can be used as the frequency-dividing circuit as well having the frequency-dividing ratio Q. Using the pre-scaler  321  as the frequency-dividing circuit as well having the frequency-dividing ratio Q offers an effect that the output load of the VCO  31  is prevented from being increased. As a result, it is possible to suppress the scale-up of the circuit scale. It is noted that if necessary, a fixed frequency-dividing circuit may be further additionally provided in a subsequent stage. 
       [4] Conclusion 
       [0166]    According to the PLL circuits  30  of the first to third embodiments, even when the control sensitivity KVCO of the VCO  31  disperses due to the manufacture process of the IC  10 , the desired PLL characteristics can be held, and at this time, the trimming or the like needs not to be carried out. 
         [0167]    In addition, even when the ambient temperature T changes, the control voltage VC changes so that no oscillation frequency fVCO of the VCO  31  changes. As a result, even when the control sensitivity UVCO changes, the loop characteristics of the PLL circuit  30  can be controlled so as to be held at the defined value without stopping the operation of the PLL circuit  30 . 
         [0168]    Moreover, even when the measurement voltage or the like is not applied from the outside to the PLL circuit  30  operating in the stationary state, it is possible to measure the oscillation frequency fVCO, the control voltage VC and the control sensitivity KVCO of the VCO  31 . Therefore, when a failure is caused in the PLL circuit  30 , an analysis for the failure can be readily carried out. 
       [5] The Others 
       [0169]    In the above case, in the case where the data table representing the relationship between the control voltage VC and the control sensitivity KVCO of the VCO  31  is created, when the resolutions or the signal levels (analog values) of the D/A counter  302  and the A/D counter  304  are equalized to each other, it is possible to simplify the creation of the data table described above. For example, the A/D converter circuit  304  can be configured in the form of a successive-approximation type A/D converter circuit for carrying out A/D conversion based on a reference voltage generated from the D/A converter circuit  302 . 
         [0170]    In addition, the measurement of the control sensitivity KVCO can be carried out whenever the combination of the capacitors CO to C 3  (in the case shown in  FIG. 5 ) in the VCO  31  is changed. Moreover, the control circuit  300  can be realized in the form of software which is executed by a microcomputer or the like composing a system control circuit. 
         [0171]    Moreover, in the phase of creation of the data table representing the relationship between the control voltage VC and the control sensitivity KVCO of the VCO  31 , an output impedance of the charge pump circuit  34  can be made a high impedance instead of turning OFF the switch circuit  311 . 
         [0172]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2008-089371, filed in the Japan Patent Office on Mar. 31, 2008, the entire content of which is hereby incorporated by reference. 
         [0173]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.