Patent Publication Number: US-9425777-B2

Title: Phase interpolator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-109497, filed on May 27, 2014, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are directed to a phase interpolator. 
     BACKGROUND 
     A trigonometric function computing unit which finds a sine value and a cosine value of numerical data has been known (refer to Patent Document 1). A storage device stores an initial sine value sin θ 0  and an initial cosine value cos θ 0  as initial numerical values θ 0 . The trigonometric function computing unit finds the sine value and the cosine value of the input numerical data by the following expressions, from the initial sine value sin θ 0  and the initial cosine value cos θ 0 , which are stored in the storage device, and differences Δθ(Δθ=θ−θ 0 ) between the input numerical data θ and the initial numerical values θ 0 .
 
sin θ=sin θ 0 ·cos θΔ+cos θ 0 ·sin θΔ
 
cos θ=cos θ 0 ·cos θΔ−sin θ 0 ·sin θΔ
 
     Further, there has been known a sine/cosine arithmetic circuit having an absolute value/sign extraction circuit which outputs an absolute value signal of an input phase angle signal and a positive/negative sign signal of the phase angle signal (refer to Patent Document 2). A sine/cosine approximation arithmetic circuit performs an approximation operation of sine operation results and cosine operation results in a predetermined limited quadrant by using a primary approximation operation expression, based on a predetermined less significant bit in the absolute value signal output by the absolute value/sign extraction circuit. According to three significant bits of the positive/negative sign signal and the absolute value signal which are output by the absolute value/sign extraction circuit, a phase rotation processing circuit replaces the sine operation results and the cosine operation results which are output by the sine/cosine approximation arithmetic circuit, and changes signs to thereby output sine operation results and cosine operation results in a quadrant other than the predetermined limited quadrant. 
     Patent Document 1: Japanese Laid-open Patent Publication No. 11-194926 
     Patent Document 2: Japanese Laid-open Patent Publication No. 2000-112715 
     In recent years, performance, especially a bandwidth, of components such as a central processing unit (CPU) constituting an information processing system such as a server and a computer has been greatly improved. Accordingly, in order to improve the total bandwidth of the whole information processing system, it is necessary to increase the speed of a transmission/reception circuit which transmits/receives data to/from the component such as the CPU. 
     As a method to increase the speed of the transmission/reception circuit, there has been known a method which uses a phase interpolator for the generation of a clock signal of the transmission/reception circuit. Generally, a noise component is superimposed on a data signal that the transmission/reception circuit processes. Here, the use of the phase interpolator for the generation of the clock signal that decides the timing of data processing makes it possible to set the processing timing of the data signal (phase of the clock signal) to an optimum value, and accordingly, can reduce an influence of the noise component superimposed on the data signal. 
     As a method to increase the speed of the transmission/reception circuit, there has been known a method to increase a frequency of a clock signal of the transmission/reception circuit. However, when a frequency of a square-wave clock signal input to a phase interpolator is increased, phase linearity of the phase interpolator deteriorates. When the frequency of the clock signal is increased, the square-wave clock signal is distorted due to an influence of parasitic capacitance or the like existing in a wiring line in the circuit. When the distorted square-wave clock signal is input to the phase interpolator, phase linearity of the phase interpolator deteriorates. 
     SUMMARY 
     A phase interpolator includes: a mixer configured to synthesize phases of a plurality of cosine-wave or sine-wave input signals whose phases are different from each other; and a bias generator configured to output a bias signal in accordance with a phase control signal to the mixer, and the mixer outputs a signal with a phase in accordance with the phase control signal. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration example of a phase interpolator according to a first embodiment; 
         FIG. 2  is a diagram illustrating a configuration example of a bias generator in  FIG. 1 ; 
         FIG. 3  is an explanatory chart of operations of the bias generator and a bias selector in  FIG. 1 ; 
         FIG. 4  is a diagram illustrating a configuration example of a phase interpolator to which four-phase square-wave signals are input; 
         FIG. 5  is a chart illustrating phase characteristics of the phase interpolators; 
         FIG. 6  is a diagram illustrating a configuration example of a bias generator according to a second embodiment; 
         FIG. 7  is a diagram illustrating a configuration example of a phase interpolator according to a third embodiment; 
         FIG. 8  is a diagram illustrating a configuration example of a phase interpolator according to a fourth embodiment; 
         FIG. 9  is a diagram illustrating a configuration example of a phase interpolator according to a fifth embodiment; 
         FIG. 10  is a diagram illustrating a configuration example of a phase interpolator according to a sixth embodiment; and 
         FIG. 11  is a diagram illustrating a configuration example of a phase interpolator according to a seventh embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a diagram illustrating a configuration example of a phase interpolator according to a first embodiment. The phase interpolator is capable of generating a clock signal of a transmission/reception circuit. A noise component is superimposed on a data signal that the transmission/reception circuit processes. By generating the clock signal that decides the timing of data processing, the phase interpolator is capable of setting the processing timing of the data signal (phase of the clock signal) to an optimum value to reduce an influence of the noise component superimposed on the data signal. 
     The phase interpolator has a mixer  101 , a bias generator  102 , and a bias selector  103 . The mixer  101  has a first differential pair  151 , a second differential pair  152 , a third differential pair  153 , a fourth differential pair  154 , a fifth differential pair  155 , a sixth differential pair  156 , a seventh differential pair  157 , an eighth differential pair  158 , current sources  147 ,  148 , and resistors  149 ,  150 . 
     The first differential pair  151  has current sources  111 ,  112 , resistors  113 ,  114 , n-channel field effect transistors  115 ,  116 , and a tail current source  117 . The current source  111  is connected between a power supply potential node and a drain of the n-channel field effect transistor  115 . The resistor  113  is connected to the current source  111  in parallel. The n-channel field effect transistor  115  has a gate connected to a first input terminal CLK_ 0  and a source connected to a ground potential node via the tail current source  117 . The current source  112  is connected between the power supply potential node and a drain of the n-channel field effect transistor  116 . The resistor  114  is connected to the current source  112  in parallel. The n-channel field effect transistor  116  has a gate connected to a second input terminal CLK_ 180  and a source connected to the ground potential node via the tail current source  117 . In each of the current sources  111  and  112 , a current based on a bias signal B 1  flows. In the tail current source  117 , a tail current based on the bias signal B 1  flows. A parallel-connection circuit of the current source  111  and the resistor  113  and a parallel-connection circuit of the current source  112  and the resistor  114  are loads of the first differential pair  151 . 
     The second differential pair  152  has resistors  118 ,  119 , n-channel field effect transistors  120 ,  121 , and a tail current source  122 . The resistor  118  is connected between the power supply potential node and a drain of the n-channel field effect transistor  120 . The n-channel field effect transistor  120  has a gate connected to the first input terminal CLK_ 0  and a source connected to the ground potential node via the tail current source  122 . The resistor  119  is connected between the power supply potential node and a drain of the n-channel field effect transistor  121 . The n-channel field effect transistor  121  has a gate connected to the second input terminal CLK_ 180  and a source connected to the ground potential node via the tail current source  122 . In the tail current source  122 , a tail current based on a bias signal B 3  flows. The resistors  118  and  119  are loads of the second differential pair  152 . 
     The third differential pair  153  has n-channel field effect transistors  123 ,  124  and a tail current source  125 . The n-channel field effect transistor  123  has a drain connected to a first output terminal O_CLK, a gate connected to the drain of the n-channel field effect transistor  115 , and a source connected to the ground potential node via the tail current source  125 . The n-channel field effect transistor  124  has a drain connected to a second output terminal O_CLKX, a gate connected to the drain of the n-channel field effect transistor  116 , and a source connected to the ground potential node via the tail current source  125 . In the tail current source  125 , a tail current based on the bias signal B 1  flows. 
     The fourth differential pair  154  has n-channel field effect transistors  126 ,  127  and a tail current source  128 . The n-channel field effect transistor  126  has a drain connected to the second output terminal O_CLKX, a gate connected to the drain of the n-channel field effect transistor  120 , and a source connected to the ground potential node via the tail current source  128 . The n-channel field effect transistor  127  has a drain connected to the first output terminal O_CLK, a gate connected to the drain of the n-channel field effect transistor  121 , and a source connected to the ground potential node via the tail current source  128 . In the tail current source  128 , a tail current based on the bias signal B 3  flows. 
     The fifth differential pair  155  has current sources  129 ,  130 , resistors  131 ,  132 , n-channel field effect transistors  133 ,  134 , and a tail current source  135 . The current source  129  is connected between the power supply potential node and a drain of the n-channel field effect transistor  133 . The resistor  131  is connected to the current source  129  in parallel. The n-channel field effect transistor  133  has a gate connected to a third input terminal CLK_ 90  and a source connected to the ground potential node via the tail current source  135 . The current source  130  is connected between the power supply potential node and a drain of the n-channel field effect transistor  134 . The resistor  132  is connected to the current source  130  in parallel. The n-channel field effect transistor  134  has a gate connected to a fourth input terminal CLK_ 270  and a source connected to the ground potential node via the tail current source  135 . In each of the current sources  129  and  130 , a current based on a bias signal B 2  flows. In the tail current source  135 , a tail current based on the bias signal B 2  flows. A parallel-connection circuit of the current source  129  and the resistor  131  and a parallel-connection circuit of the current source  130  and the resistor  132  are loads of the fifth differential pair  155 . 
     The sixth differential pair  156  has resistors  136 ,  137 , n-channel field effect transistors  138 ,  139 , and a tail current source  140 . The resistor  136  is connected between the power supply potential node and a drain of the n-channel field effect transistor  138 . The n-channel field effect transistor  138  has a gate connected to the third input terminal CLK_ 90  and a source connected to the ground potential node via the tail current source  140 . The resistor  137  is connected between the power supply potential node and a drain of the n-channel field effect transistor  139 . The n-channel field effect transistor  139  has a gate connected to the fourth input terminal CLK_ 270  and a source connected to the ground potential node via the tail current source  140 . In the tail current source  140 , a tail current based on the bias signal B 3  flows. The resistors  136  and  137  are loads of the sixth differential pair  156 . 
     The seventh differential pair  157  has n-channel field effect transistors  141 ,  142  and a tail current source  143 . The n-channel field effect transistor  141  has a drain connected to the first output terminal O_CLK, a gate connected to the drain of the n-channel field effect transistor  133 , and a source connected to the ground potential node via the tail current source  143 . The n-channel field effect transistor  142  has a drain connected to the second output terminal O_CLKX, a gate connected to the drain of the n-channel field effect transistor  134 , and a source connected to the ground potential node via the tail current source  143 . In the tail current source  143 , a tail current based on the bias signal B 2  flows. 
     The eighth differential pair  158  has n-channel field effect transistors  144 ,  145  and a tail current source  146 . The n-channel field effect transistor  144  has a drain connected to the second output terminal O_CLKX, a gate connected to the drain of the n-channel field effect transistor  138 , and a source connected to the ground potential node via the tail current source  146 . The n-channel field effect transistor  145  has a drain connected to the first output terminal O_CLK, a gate connected to the drain of the n-channel field effect transistor  139 , and a source connected to the ground potential node via the tail current source  146 . In the tail current source  146 , a tail current based on the bias signal B 3  flows. 
     The current source  147  is connected between the power supply potential node and the first output terminal O_CLK. The resistor  149  is connected to the current source  147  in parallel. The current source  148  is connected between the power supply potential node and the second output terminal O_CLKX. The resistor  150  is connected to the current source  148  in parallel. In each of the current sources  147  and  148 , currents based on the bias signals B 1  and B 2  flow. A parallel-connection circuit of the current source  147  and the resistor  149  and a parallel-connection circuit of the current source  148  and the resistor  150  are loads commonly connected to the third differential pair  153 , the fourth differential pair  154 , the seventh differential pair  157 , and the eighth differential pair  158 . 
     The bias generator  102  has a constant current generation circuit  104 , a sin α current generation circuit  105 , a cos α current generation circuit  106 , and a control circuit  107 , and receives a phase control signal CTL. The constant current generation circuit  104  outputs the bias signal B 3  for applying a constant current, to the current sources  122 ,  128 ,  140 ,  146 . In the current sources  122 ,  128 ,  140 ,  146 , the constant current flows. The control circuit  107  controls the sin α current generation circuit  105  and the cos α current generation circuit  106  according to the phase control signal CTL. The sin α current generation circuit  105  outputs a bias signal for applying a current with a sine value sin α. The cos α current generation circuit  106  outputs a bias signal for applying a current with a cosine value cos α. 
     The bias selector  103  has a control circuit  108  and a switch circuit  109  and receives the phase control signal CTL. The control circuit  108  controls the switch circuit  109  according to the phase control signal CTL. The switch circuit  109  outputs the bias signals output by the sin α current generation circuit  105  and the cos α current generation circuit  106 , as the bias signals B 1  and B 2 . 
     An input signal with a cosine wave cos θ is input to the first input terminal CLK_ 0 . An input signal with a cosine wave −cos θ is input to the second input terminal CLK_ 180 . An input signal with a sine wave sin θ is input to the third input terminal CLK_ 90 . An input signal with a sine wave −sin θ is input to the fourth input terminal CLK_ 270 . The four input cosine-wave or sine-wave signals whose phases are different by 90 degrees from one another are input to the four input terminals CLK_ 0  to CLK_ 270  respectively. The mixer  101  synthesizes the phases of the four cosine-wave or sine-wave input signals with the different phases input to the four input terminals CLK_ 0  to CLK_ 270  and outputs a differential signal having a phase according to the phase control signal CTL to the first output terminal O_CLK and the second output terminal O_CLKX. The bias generator  102  outputs the bias signals B 1  to B 3  according to the phase control signal CTL to the mixer  101 . 
     The first differential pair  151  receives the input signals of the first input terminal CLK_ 0  and the second input terminal CLK_ 180 . The second differential pair  152  receives the input signals of the first input terminal CLK_ 0  and the second input terminal CLK_ 180 . The third differential pair  153  receives an output signal of the first differential pair  151  and outputs a signal to the first output terminal O_CLK and the second output terminal O_CLKX. The fourth differential pair  154  receives an output signal of the second differential pair  152  and outputs a signal to the second output terminal O_CLKX and the first output terminal O_CLK. The fifth differential pair  155  receives the input signals of the third input terminal CLK_ 90  and the fourth input terminal CLK_ 270 . The sixth differential pair  156  receives the input signals of the third input terminal CLK_ 90  and the fourth input terminal CLK_ 270 . The seventh differential pair  157  receives an output signal of the fifth differential pair  155  and outputs a signal to the first output terminal O_CLK and the second output terminal O_CLKX. The eighth differential pair  158  receives an output signal of the sixth differential pair  156  and outputs a signal to the second output terminal O_CLKX and the first output terminal O_CLK. 
     The mixer  101  performs the phase synthesis based on an addition theorem of a trigonometric function of the following expression (1). 
     
       
         
           
             
               
                 
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     Here, let us consider synthesizing two signals with a cosine wave cos θ and a sine wave sine whose phases are shifted by 90 degrees. An amplitude of the cosine wave cos θ is multiplied by a weight of a cosine value cos α of a desired shift angle (phase) α, whereby a cos θ·cos α signal is generated. Further, an amplitude of the sine wave sin θ is multiplied by a weight of a sine value sin α of the desired shift angle (phase) α, whereby a sin θ·sin α signal is generated. Thereafter, by adding the cos θ·cos α signal and the sin θ·sin α signal, it is possible to generate a cos(θ−α) signal having a phase shifted from that of cos θ by α is generated as expressed by the expression (1) according to the addition theorem of the triangular function, to output it to the output terminals O_CLK and O_CLKX. That is, it is possible for the signal at the output terminal O_CLK to have the phase shifted by α from the phase of the signal at the input terminal CLK_ 0 . Further, the input signals are the cosine wave and the sine wave, and therefore are less likely to be influenced by parasitic capacitance than a square wave. Therefore, even when frequencies of the input signals are increased, it is possible to prevent the deterioration of phase linearity of the phase interpolator. Hereinafter, details thereof will be described. 
     The first to fourth differential pairs  151  to  154  generate the cos θ·cos α signal for the output terminals O_CLK and O_CLKX. The fifth to eighth differential pairs  155  to  158  generate the sin θ·sin α signal for the output terminals O_CLK and O_CLKX. At the output terminals O_CLK and O_CLKX, the cos θ·cos α signal and the sin θ·sin α signal are added, whereby the cos(θ−α) signal is generated. 
     In each of the tail current sources  117  and  125 , a current I 11  having the cosine weight flows due to the bias signal B 1  being a current with the cosine value cos α, as expressed by the following expression (2). Further, in each of the tail current sources  122 ,  128 ,  140 , and  146 , a constant current I 12  expressed by the following expression (2) flows. 
     
       
         
           
             
               
                 
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     Here, β is β of each of the input-stage transistors  115 ,  116 ,  120 ,  121 ,  123 ,  124 ,  126 ,  127 ,  133 ,  134 ,  138 ,  139 ,  141 ,  142 ,  144 ,  145  of the differential pairs  151  to  158 . α is a desired shift angle. k is an arbitrary constant. 
     First, an operation of the first differential pair  151  will be described. In the tail current source  117  of the first differential pair  151 , the current I 11  expressed by the expression (2) flows. Therefore, in each of the input-stage transistors  115  and  116  of the first differential pair  151 , a bias current I 11 /2 which is a half of the current I 11  flowing in the tail current source  117  flows. Here, mutual conductance g m  of the transistors  115  and  116  in saturated operation is expressed by the following expression (3).
 
[expression 3]
 
 g   m =√{square root over (2β I   dr )}  (3)
 
     Here, I dr  is a drain current of the transistors  115  and  116 . Therefore, mutual conductance g m1  of the input-stage transistor  115  of the first differential pair  151  has a value correlated with the desired shift angle α as expressed by the following expression (4). Further, since the cosine wave cos θ is input to the gate of the transistor  115 , a drain current i o1  flowing in the transistor  115  has a value equal to a square root of the cosine value cos α of the desired shift angle α multiplied by the cosine wave cos θ, as expressed by the following expression (4). Further, a voltage v o1  of the drain of the transistor  115  has a value equal to an output impedance Z o1  of the first differential pair  151  multiplied by the current i o1 , as expressed by the following expression (4). 
     
       
         
           
             
               
                 
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     Incidentally, in the current sources  111  and  112  being the loads connected to the first differential pair  151 , a current I 11 /2 which is a half of the current I 11  flowing in the tail current source  117  flows. This has an advantage that, even when a value of the desired shift angle α is changed, a current value of the current sources  111  and  112  being the loads also changes according to a change of the tail current, and therefore an output operating point does not fluctuate. 
     Next, an operation of the second differential pair  152  will be described. In the tail current source  122  of the second differential pair  152 , the current I 12  expressed by the expression (2) flows. Therefore, in the input-stage transistor  121  of the second differential pair  152 , a bias current I 12 /2 flows, and mutual conductance g m2  of the input-stage transistor  121  of the second differential pair  152  has a value equal to a square root of the arbitrary constant k as expressed by the following expression (5). Therefore, a drain current i o2  and a drain voltage v o2  of the transistor  121  have values expressed by the following expressions (5) respectively. 
     
       
         
           
             
               
                 
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                           · 
                           cos 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Here, Z o2  is an output impedance of the second differential pair  151 . Note that values of the output impedance Z o1  of the first differential pair  151  and the output impedance Z o2  of the second differential pair  152  are equal, that is, Z o1 =Z o2 . 
     Next, an operation of the third differential pair  153  will be described. In the tail current source  125  of the third differential pair  153 , the same current I 11  as that of the tail current source  117  of the first differential pair  151  flows. Therefore, mutual conductance g m3  of the input-stage transistor  123  of the third differential pair  153  has the same value as that of the mutual conductance g m1  of the input-stage transistor  115  of the first differential pair  151 , as expressed by the following expression (6). Further, since a gate voltage of the input-stage transistor  123  of the third differential pair  153  is equal to the drain voltage v o1  of the input-stage transistor  115  of the first differential pair  151 , a drain current i o3  of the input-stage transistor  123  of the third differential pair  153  has a value proportional to a value equal to the cosine weight cos α of the desired shift angle α multiplied by the cosine wave cos θ, as expressed by the following expression (6).
 
[expression 6]
 
 g   m3   =g   m1 =√{square root over ( k (1+cos α))}
 
 i   o3   =−g   m3   ·v   o1   =Z   o1   ·k ·(1+cos α)·cos θ  (6)
 
     Next, an operation of the fourth differential pair  154  will be described. In the tail current source  128  of the fourth differential pair  154 , the same current I 12  as that of the tail current source  122  of the second differential pair  152  flows. Therefore, mutual conductance g m4  of the input-stage transistor  127  of the fourth differential pair  154  has the same value as that of the mutual conductance g m2  of the input-stage transistor  121  of the second differential pair  152  as expressed by the following expression (7). Further, since a gate voltage of the input-stage transistor  127  of the fourth differential pair  154  is equal to the drain voltage v o2  of the input-stage transistor  121  of the second differential pair  152 , a drain current i o4  of the input-stage transistor  127  of the fourth differential pair  154  has a value proportional to the cosine wave cos θ, as expressed by the following expression (7).
 
[expression 7]
 
 g   m4   =g   m2   =√{square root over (k)} 
 
 i   o4   =−g   m4   ·v   o2   =−Z   o2   ·k ·cos θ  (7)
 
     Here, since the drain of the input-stage transistor  123  of the third differential pair  153  and the drain of the input-stage transistor  127  of the fourth differential pair  154  are connected by the first output terminal O_CLK, the third differential pair  153  and the fourth differential pair  154  add the current i o3  of the third differential pair  153  and the current i o4  of the fourth differential pair  154  to output, to the first output terminal O_CLK, a current i o3 +i o4  proportional to cos θ·cos α as expressed by the following expression (8). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           
                             i 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               3 
                             
                           
                           + 
                           
                             i 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               4 
                             
                           
                         
                         ⁢ 
                           
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Z 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                               · 
                               k 
                               · 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     cos 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                                 ) 
                               
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                           - 
                           
                             
                               
                                 Z 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                               · 
                               k 
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             · 
                             k 
                             · 
                             cos 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             α 
                             · 
                             cos 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Next, operations of the fifth differential pair  155  to the eighth differential pair  158  will be described. In each of the tail current sources  135  and  143 , a current I 13  expressed by the following expression (9) flows due to the bias signal B 2  having the weight of the sine value sin α. Further, in each of the current sources  140  and  146 , the constant current I 12  expressed by the following expression (9) flows. 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       I 
                       13 
                     
                     = 
                     
                       
                         k 
                         β 
                       
                       ⁢ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             sin 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                         
                         ) 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       I 
                       12 
                     
                     = 
                     
                       k 
                       β 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     Here, β is β of each of the input-stage transistors  115 ,  116 ,  120 ,  121 ,  123 ,  124 ,  126 ,  127 ,  133 ,  134 ,  138 ,  139 ,  141 ,  142 ,  144 ,  145  of the differential pairs  151  to  158 . α is the desired shift angle. k is the arbitrary constant. 
     First, the operation of the fifth differential pair  155  will be described. In the tail current source  135  of the fifth differential pair  155 , the current I 13  expressed by the expression (9) flows due to the bias signal B 2 . Therefore, in the input-stage transistor  133  of the fifth differential pair  155 , a bias current I 13 /2 flows. Therefore, mutual conductance g m5  of the input-stage transistor  133  of the fifth differential pair  155  has a value correlated with the desired shift angle α as expressed by the following expression (10). Further, since the sine wave sine is input to the gate of the input-stage transistor  133  of the fifth differential pair  155 , a drain current i o5  of the input-stage transistor  133  has a value equal to a square root of the weight of the sine value sin α of the desired shift angle α multiplied by the sine wave sin θ, as expressed by the following expression (10). Further, a drain voltage v o5  of the input-stage transistor  133  has a value equal to an output impedance Z o5  of the fifth differential pair  155  multiplied by the drain current i o5  as expressed by the following expression (10). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       g 
                       
                         m 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         5 
                       
                     
                     = 
                     
                       
                         
                           2 
                           ⁢ 
                           
                             β 
                             · 
                             
                               
                                 I 
                                 13 
                               
                               2 
                             
                           
                         
                       
                       = 
                       
                         
                           
                             β 
                             · 
                             
                               I 
                               13 
                             
                           
                         
                         = 
                         
                           
                             k 
                             ⁡ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   sin 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   α 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       i 
                       
                         o 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         5 
                       
                     
                     = 
                     
                       
                         
                           - 
                           
                             g 
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               5 
                             
                           
                         
                         · 
                         
                           v 
                           in 
                         
                       
                       = 
                       
                         
                           
                             - 
                             
                               
                                 k 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     1 
                                     + 
                                     
                                       sin 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       α 
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                           · 
                           sin 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       v 
                       
                         o 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         5 
                       
                     
                     = 
                     
                       
                         
                           Z 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             5 
                           
                         
                         · 
                         
                           i 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             5 
                           
                         
                       
                       = 
                       
                         
                           
                             - 
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 5 
                               
                             
                           
                           · 
                           
                             
                               k 
                               ⁡ 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     sin 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                                 ) 
                               
                             
                           
                           · 
                           sin 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     Note that, in each of the current sources  129  and  130  being the loads connected to the fifth differential pair  155 , a current I 13 /2 which is a half of the current I 13  flowing in the tail current source  135  flows. Consequently, even when the value of the desired shift angle α is changed, a current value of the current sources  129  and  130  being the loads also changes according to a change of the tail current, and therefore, an output operating point does not fluctuate. 
     Next, the operation of the sixth differential pair  156  will be described. In the tail current source  140  of the sixth differential pair  156 , the current I 12  expressed by the above expression (9) flows. Therefore, in the input-stage transistor  139  of the sixth differential pair  156 , a bias current I 12 /2 flows, and mutual conductance g m6  of the input-stage transistor  139  of the sixth differential pair  156  has a value equal to a square root of the arbitrary constant k as expressed by the following expression (11). Therefore, a drain current i o6  and a drain voltage v o6  of the input-stage transistor  139  of the sixth differential pair  156  have values expressed by the following expressions (11) respectively. 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         g 
                         
                           m 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           6 
                         
                       
                       = 
                       
                         
                           
                             2 
                             ⁢ 
                             
                               β 
                               · 
                               
                                 
                                   I 
                                   12 
                                 
                                 2 
                               
                             
                           
                         
                         = 
                         
                           
                             
                               β 
                               · 
                               
                                 I 
                                 12 
                               
                             
                           
                           = 
                           
                             k 
                           
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                       i 
                       
                         o 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         6 
                       
                     
                     = 
                     
                       
                         
                           - 
                           
                             g 
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               6 
                             
                           
                         
                         · 
                         
                           v 
                           in 
                         
                       
                       = 
                       
                         
                           
                             k 
                           
                           · 
                           sin 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       v 
                       
                         o 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         6 
                       
                     
                     = 
                     
                       
                         
                           Z 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             6 
                           
                         
                         · 
                         
                           i 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             6 
                           
                         
                       
                       = 
                       
                         
                           
                             Z 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               6 
                             
                           
                           · 
                           
                             k 
                           
                           · 
                           sin 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     Here, Z o6  is an output impedance of the sixth differential pair  156 . Note that a value of the output impedance Z o5  of the fifth differential pair  155  is equal to a value of the output impedance Z o6  of the sixth differential pair  156  and is also equal to the value of the output impedance Z o1  of the first differential pair  151 , that is, Z o5 =Z o6 =Z o1  holds. 
     Next, the operation of the seventh differential pair  157  will be described. In the tail current source  143  of the seventh differential pair  157 , the same current I 13  as that of the tail current source  135  of the fifth differential pair  155  flows. Therefore, mutual conductance g m7  of the input-stage transistor  141  of the seventh differential pair  157  has the same value as that of the mutual conductance g m5  of the input-stage transistor  133  of the fifth differential pair  155  as expressed by the following expression (12). Further, since a gate voltage of the input-stage transistor  141  of the seventh differential pair  157  is equal to the drain voltage v o5  of the input-stage transistor  133  of the fifth differential pair  155 , a drain current i o7  of the input-stage transistor  141  of the seventh differential pair  157  has a value proportional to a value equal to the sine value sin α of the desired shift angle α multiplied by the sine wave sin θ, as expressed by the following expression (12).
 
[expression 12]
 
 g   m7   =g   m5 =√{square root over ( k (1+sin α))}
 
 i   o7   =−g   m7   ·v   o5   =Z   o5   ·k ·(1+sin α)·sin θ  (12)
 
     Next, the operation of the eighth differential pair  158  will be described. In the tail current source  146  of the eighth differential pair  158 , the same current I 12  as that of the tail current source  140  of the sixth differential pair  156  flows. Therefore, mutual conductance g m8  of the input-stage transistor  145  of the eighth differential pair  158  has the same value as that of the mutual conductance g m6  of the input-stage transistor  139  of the sixth differential pair  156  as expressed by the following expression (13). Further, since a gate voltage of the input-stage transistor  145  of the eighth differential pair  158  is equal to the drain voltage v o6  of the input-stage transistor  139  of the sixth differential pair  156 , a drain current i o8  of the input-stage transistor  145  of the eighth differential pair  158  has a value proportional to the sine wave sin θ, as expressed by the following expression (13).
 
[expression 13]
 
 g   m8   =g   m6   =√{square root over (k)} 
 
 i   o8   =−g   m8   ·v   o6   =−Z   o6   ·k ·sin θ  (13)
 
     Here, since the drain of the input-stage transistor  141  of the seventh differential pair  157  and the drain of the input-stage transistor  145  of the eighth differential pair  158  are connected by the first output terminal O_CLK, the seventh differential pair  157  and the eighth differential pair  158  add the current i o7  of the seventh differential pair  157  and the current i o8  of the eighth differential pair  158  to output, to the first output terminal O_CLK, a current i o7 +i o8  proportional to sin θ·sin α, as expressed by the following expression (14). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     14 
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           
                             i 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               7 
                             
                           
                           + 
                           
                             i 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               8 
                             
                           
                         
                         ⁢ 
                           
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Z 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   5 
                                 
                               
                               · 
                               k 
                               · 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     sin 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                                 ) 
                               
                               · 
                               sin 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                           - 
                           
                             
                               
                                 Z 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   6 
                                 
                               
                               · 
                               k 
                               · 
                               sin 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             · 
                             k 
                             · 
                             sin 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             α 
                             · 
                             sin 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     At the first output terminal O_CLK, the output current i o3 +i o4  of the third differential pair  153  and the fourth differential pair  154  and the output current i o7 +i o8  of the seventh differential pair  157  and the eighth differential pair  158  are added, and a current proportional to cos(θ−α) flows according to the addition theorem of the trigonometric function as expressed by the expression (1). As described above, the mixer  101  is capable of outputting the signal with the cosine wave cos(θ−α) according to the phase α indicated by the phase control signal CTL. 
     The loads of the first differential pair  151  are the parallel-connection circuits of the current sources  111 ,  112  in which the current proportional to the tail current of the first differential pair  151  flows and the resistors  113 ,  114 . The loads of the fifth differential pair  155  are the parallel-connection circuits of the current sources  129 ,  130  in which the current proportional to the tail current of the fifth differential pair  155  flows and the resistors  131 ,  132 . Parallel-connection circuits of the current sources  147 ,  148  in which the current proportional to the sum of the tail current of the third differential pair  153  and the tail current of the seventh differential pair  157  flows and the resistors  149 ,  150  are connected to the first output terminal O_CLK and the second output terminal O_CLKX respectively. 
     In the tail current sources  117 ,  122 ,  125 ,  128 ,  135 ,  140 ,  143 ,  146  of the first to eighth differential pairs  151  to  158 , the currents I 11 , I 12 , I 13  proportional to reciprocals of respective βs of the input-stage transistors of the first to eighth differential pairs  151  to  158  flow. βs of the input-stage transistors of the first to eighth differential pairs  151  to  158  are all equal. That is, the input-stage transistors of the first to eighth differential pairs  151  to  158  are mutually equal in channel kind, channel width, and channel length. 
       FIG. 2  is a diagram illustrating a configuration example of the bias generator  102  in  FIG. 1 . First, the structure of the constant current generation circuit  104  will be described. A p-channel field effect transistor Ma has a source connected to the power supply potential node and a gate and a drain connected to the ground potential node via a current source  201 . In the current source  201 , a current I ref  flows. A p-channel field effect transistor Mb has a source connected to the power supply potential node and a gate connected to the gate of the transistor Ma. The transistors Ma and Mb constitute a current mirror circuit, and their current mirror ratio (size ratio) is Ma:Mb=1:k/β. An n-channel field effect transistor Mc has a drain and a gate connected to a drain of the transistor Mb and a source connected to the ground potential node. An n-channel field effect transistor Md has a drain connected to a node N 3 , a gate connected to the gate of the transistor Mc, and a source connected to the ground potential node. The transistors Mc and Md constitute a current mirror circuit, and their current mirror ratio (size ratio) is Mc:Md=1:1. A drain current I d  of the transistor Mb and a drain current I d  of the transistor Md are the same current. The node N 3  outputs the bias signal B 3  in  FIG. 1 . 
     Next, the structures of the sin α current generation circuit  105  and the cos α current generation circuit  106  will be described. The control circuit  107  outputs a first control signal S 1  according to the phase control signal CTL. A p-channel field effect transistor M 1  has a source connected to the power supply potential node and a gate and a drain connected to the ground potential node via a current source  202 . In the current source  202 , a current I a  flows. A p-channel field effect transistor M 2  has a source connected to the power supply potential node and a gate connected to the gate of the transistor M 1 . The transistors M 1  and M 2  constitute a current mirror circuit, and their current mirror ratio (size ratio) is controlled to M 1 :M 2 =1:m according to the first control signal S 1 . m is a coefficient proportional to the desired shift angle α, and m=s·α. s is an arbitrary constant Concretely, by changing a size of a channel width (number of parallel connections) of the transistor M 2  according to the first control signal S 1 , the current mirror ratio is changed. 
     An n-channel field effect transistor M 3  has a drain and a gate connected to a drain of the transistor M 2  and a source connected to the ground potential node. An n-channel field effect transistor M 4  has a drain connected to a drain of a p-channel field effect transistor M 5 , a gate connected to the gate of the transistor M 3 , and a source connected to the ground potential node. The transistors M 3  and M 4  constitute a current mirror circuit, and their current mirror ratio (size ratio) is controlled to M 3 :M 4 =1:m according to the first control signal S 1 . 
     The p-channel field effect transistor M 5  has a source connected to the power supply potential node and a gate and the drain connected to the drain of the transistor M 4 . A p-channel field effect transistor M 6  has a source connected to the power supply potential node, a gate connected to the gate of the transistor M 5 , and a drain connected to the ground potential node via a current source  203 . In the current source  203 , a current I b  flows. The transistors M 5  and M 6  constitute a current mirror circuit, and their current mirror ratio (size ratio) is M 5 :M 6 =1:½. 
     A p-channel field effect transistor M 7  has a source connected to the power supply potential node and a gate and a drain connected to the ground potential node via the current source  203 . A p-channel field effect transistor M 8  has a source connected to the power supply potential node, a gate connected to the gate of the transistor M 7 , and a drain connected to a node N 2 . The transistors M 7  and M 8  constitute a current mirror circuit, and their current mirror ratio (size ratio) is M 7 :M 8 =1:1. A current source  204  is connected between the power supply potential node and the node N 2 , and the current I b  flows therein. The node N 2  is an output terminal of the cos α current generation circuit  106  in  FIG. 1  and outputs the cos α current. Details thereof will be described later. 
     A p-channel field effect transistor M 9  has a source connected to the power supply potential node, a gate connected to the gate of the transistor M 5 , and a drain connected to the ground potential node via a current source  205 . In the current source  205 , the current I b  flows. The transistors M 5  and M 9  constitute a current mirror circuit, and their current mirror ratio (size ratio) is M 5 :M 9 =1:⅙. 
     A p-channel field effect transistor M 10  has a source connected to the power supply potential node and a gate and a drain connected to the ground potential node via the current source  205 . A p-channel field effect transistor M 11  has a source connected to the power supply potential node, a gate connected to the gate of the transistor M 10 , and a drain connected to a node N 1 . The transistors M 10  and M 11  constitute a current mirror circuit, and their current mirror ratio (size ratio) is controlled to M 10 :M 11 =1:m according to the first control signal S 1 . A current source  206  is connected between the power supply potential node and the node N 1  and a current I c  flows therein. The node N 1  is an output terminal of the sin α current generation circuit  105  in  FIG. 1  and outputs the sin α current. Details thereof will be described later. 
     Here, ratios of the currents I a , I b , and I c  to the drain current I d  of the transistor Mb are as expressed by the following expression (A1).
 
 I   a   :I   b   :I   c   =I   d   :s   2   ·I   d   :s   3   :I   d   (A1)
 
     cos α and sin α can be expressed by the following expressions (15) when expressed up to a second term of the Taylor series of the trigonometric function. 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     15 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       α 
                     
                     ≅ 
                     
                       1 
                       - 
                       
                         
                           1 
                           2 
                         
                         ⁢ 
                         
                           α 
                           2 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       α 
                     
                     ≅ 
                     
                       α 
                       ⁡ 
                       
                         ( 
                         
                           1 
                           - 
                           
                             
                               1 
                               6 
                             
                             ⁢ 
                             
                               α 
                               2 
                             
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     First, an operation of the constant current generation circuit  104  will be described. The current mirror ratio of the transistors Ma and Mb is 1:k/β, and therefore, when the reference current I ref  flows in the current source  201  by a band gap reference circuit or the like, the drain current I d  of the transistor Mb becomes a current proportional to the reciprocal of β and k as expressed by the following expression (16). Here, k and β have the same values as those of the aforesaid k and β. In the node N 3 , the current I d  flows. The current I d  corresponds to the bias signal B 3  in  FIG. 1 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     16 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     d 
                   
                   = 
                   
                     
                       
                         k 
                         β 
                       
                       ⁢ 
                       
                         I 
                         ref 
                       
                     
                     ∝ 
                     
                       k 
                       β 
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
     Next, the sin α current generation circuit  105  and the cos α current generation circuit  106  will be described. In the current source  202 , the current I a  flows. Since the current mirror ratio of the transistors M 1  and M 2  is 1:m and the current mirror ratio of the transistors M 3  and M 4  is 1:m, a drain current I 1  of the transistor M 4  is expressed by the following expression (17). Since the current I 1  also flows in the drain of the transistor M 5  and the current mirror ratio of the transistors M 5  and M 6  is 1:½, a drain current I 2  of the transistor M 6  is expressed by the following expression (17). Further, a drain current I 3  of the transistor M 7  becomes a current equal to the current I b  from which the current I 2  is subtracted as expressed by the following expression (17). Further, since the current mirror ratio of the transistors M 7  and M 8  is 1:1, the current I 3  also flows in the drain of the transistor M 8 . Further, an output current I 4  of the node N 2  becomes a current equal to the sum of the current I 3  and the current I b  as expressed by the following expression (17). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     17 
                   
                   ] 
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
             
               
                 
                   
                     I 
                     1 
                   
                   = 
                   
                     
                       
                         m 
                         2 
                       
                       · 
                       
                         I 
                         a 
                       
                     
                     = 
                     
                       
                         
                           s 
                           2 
                         
                         · 
                         
                           α 
                           2 
                         
                       
                       ⁢ 
                       
                         I 
                         a 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     2 
                   
                   = 
                   
                     
                       
                         1 
                         2 
                       
                       · 
                       
                         I 
                         1 
                       
                     
                     = 
                     
                       
                         
                           s 
                           2 
                         
                         · 
                         
                           1 
                           2 
                         
                       
                       ⁢ 
                       
                         α 
                         2 
                       
                       ⁢ 
                       
                         I 
                         a 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     3 
                   
                   = 
                   
                     
                       
                         I 
                         b 
                       
                       - 
                       
                         I 
                         2 
                       
                     
                     = 
                     
                       
                         I 
                         b 
                       
                       - 
                       
                         
                           
                             s 
                             2 
                           
                           · 
                           
                             1 
                             2 
                           
                         
                         ⁢ 
                         
                           α 
                           2 
                         
                         ⁢ 
                         
                           I 
                           a 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     4 
                   
                   = 
                   
                     
                       
                         I 
                         b 
                       
                       + 
                       
                         I 
                         3 
                       
                     
                     = 
                     
                       
                         I 
                         b 
                       
                       + 
                       
                         I 
                         b 
                       
                       - 
                       
                         
                           
                             s 
                             2 
                           
                           · 
                           
                             1 
                             2 
                           
                         
                         ⁢ 
                         
                           α 
                           2 
                         
                         ⁢ 
                         
                           I 
                           a 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Here, since a ratio of the currents I a  and I b  is I a :I b =I d :s 2 ·I d , the current with the cosine value cos α approximated up to the second term of the Taylor series flows as the current I 4 , as expressed by the expression (15). The node N 2  corresponds to the output terminal of the cos α current generation circuit  106  in  FIG. 1  and outputs the current I 4  with the cosine value cos α. 
     Further, since the current mirror ratio of the transistors M 5  and M 9  is 1:⅙, a drain current I 5  of the transistor M 9  is expressed by the following expression (18). Further, a drain current I 6  of the transistor M 10  becomes a current equal to the current I b  from which the current I 5  is subtracted as expressed by the following expression (18). Further, since the current mirror ratio of the transistors M 10  and M 11  is 1:m, a drain current I 7  of the transistor M 11  is expressed by the following expression (18). Further, an output current I 8  of the node N 1  becomes a current equal to the sum of the current I 7  and the current I c  as expressed by the following expression (18). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     18 
                   
                   ] 
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
             
               
                 
                   
                     I 
                     5 
                   
                   = 
                   
                     
                       
                         1 
                         6 
                       
                       · 
                       
                         I 
                         1 
                       
                     
                     = 
                     
                       
                         
                           s 
                           2 
                         
                         · 
                         
                           1 
                           6 
                         
                       
                       ⁢ 
                       
                         α 
                         2 
                       
                       ⁢ 
                       
                         I 
                         a 
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     6 
                   
                   = 
                   
                     
                       
                         I 
                         b 
                       
                       - 
                       
                         I 
                         5 
                       
                     
                     = 
                     
                       
                         I 
                         b 
                       
                       - 
                       
                         
                           
                             s 
                             2 
                           
                           · 
                           
                             1 
                             6 
                           
                         
                         ⁢ 
                         
                           α 
                           2 
                         
                         ⁢ 
                         
                           I 
                           a 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     7 
                   
                   = 
                   
                     
                       m 
                       · 
                       
                         I 
                         5 
                       
                     
                     = 
                     
                       
                         
                           2 
                           · 
                           α 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           I 
                           b 
                         
                       
                       - 
                       
                         
                           
                             s 
                             3 
                           
                           · 
                           
                             1 
                             6 
                           
                         
                         ⁢ 
                         
                           α 
                           3 
                         
                         ⁢ 
                         
                           I 
                           a 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     I 
                     8 
                   
                   = 
                   
                     
                       
                         I 
                         c 
                       
                       + 
                       
                         I 
                         7 
                       
                     
                     = 
                     
                       
                         I 
                         c 
                       
                       + 
                       
                         
                           s 
                           · 
                           α 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           I 
                           b 
                         
                       
                       - 
                       
                         
                           
                             s 
                             3 
                           
                           · 
                           
                             1 
                             6 
                           
                         
                         ⁢ 
                         
                           α 
                           3 
                         
                         ⁢ 
                         
                           I 
                           a 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Here, since the ratio of the currents I a , I b , and I c  is I a :I b :I c =I d :s 2 ·I d :s 3 ·I d , the current with the sine value sin α approximated up to the second term of the Taylor series flows as the current I 8 , as expressed by the expression (1). The node N 1  corresponds to the output terminal of the sin α current generation circuit  105  in  FIG. 1  and outputs the current I 8  with the sine value sin α. 
     Next, concrete examples of the currents I a , I b , and I c  will be described. As described above, the ratio of the currents I a , I b , and I c  is I a :I b :I c =I d :s 2 ·I d :s 3 ·I d . Hereinafter, an example where the currents I a , I b , and I c  are expressed by the following expressions (19) will be described.
 
[expression 19]
 
 I   a   =I   d  
 
 I   b   =s   2   ·I   d  
 
 I   c   =s   3   ·I   d   (19)
 
     In this case, the output current I 4  of the node N 2  becomes a current proportional to (1+cos α) as expressed by the following expression (20) by applying the approximation of the expression (15). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     20 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           I 
                           4 
                         
                         = 
                           
                         ⁢ 
                         
                           
                             I 
                             b 
                           
                           + 
                           
                             I 
                             b 
                           
                           - 
                           
                             
                               
                                 s 
                                 2 
                               
                               · 
                               
                                 1 
                                 2 
                               
                             
                             ⁢ 
                             
                               α 
                               2 
                             
                             ⁢ 
                             
                               I 
                               a 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               s 
                               2 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                           + 
                           
                             
                               s 
                               2 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                           - 
                           
                             
                               
                                 s 
                                 2 
                               
                               · 
                               
                                 1 
                                 2 
                               
                             
                             ⁢ 
                             
                               α 
                               2 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             s 
                             2 
                           
                           ⁢ 
                           
                             
                               I 
                               d 
                             
                             ⁡ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 1 
                                 - 
                                 
                                   
                                     1 
                                     2 
                                   
                                   ⁢ 
                                   
                                     α 
                                     2 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         ≅ 
                           
                         ⁢ 
                         
                           
                             s 
                             2 
                           
                           ⁢ 
                           
                             
                               I 
                               ref 
                             
                             · 
                             
                               k 
                               β 
                             
                           
                           ⁢ 
                           
                             ( 
                             
                               1 
                               + 
                               
                                 cos 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 α 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   20 
                   ) 
                 
               
             
           
         
       
     
     Further, the output current I 8  of the node N 1  becomes a current proportional to (1+sin α) as expressed by the following expression (21) by applying the approximation of the expression (15). 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   
                     [ 
                     
                       expression 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       21 
                     
                     ] 
                   
                 
                 
                   
                       
                   
                 
               
               
                 
                   
                     
                       
                         
                           
                             I 
                             8 
                           
                           = 
                             
                           ⁢ 
                           
                             
                               I 
                               c 
                             
                             + 
                             
                               
                                 s 
                                 · 
                                 α 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 I 
                                 b 
                               
                             
                             - 
                             
                               
                                 
                                   s 
                                   3 
                                 
                                 · 
                                 
                                   1 
                                   6 
                                 
                               
                               ⁢ 
                               
                                 α 
                                 3 
                               
                               ⁢ 
                               
                                 I 
                                 a 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                           ⁢ 
                           
                             
                               
                                 s 
                                 3 
                               
                               · 
                               
                                 I 
                                 d 
                               
                             
                             + 
                             
                               
                                 
                                   s 
                                   3 
                                 
                                 · 
                                 α 
                               
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 I 
                                 d 
                               
                             
                             - 
                             
                               
                                 
                                   s 
                                   3 
                                 
                                 · 
                                 
                                   1 
                                   6 
                                 
                               
                               ⁢ 
                               
                                 α 
                                 3 
                               
                               ⁢ 
                               
                                 I 
                                 d 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                           ⁢ 
                           
                             
                               s 
                               3 
                             
                             · 
                             
                               
                                 I 
                                 d 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   α 
                                   - 
                                   
                                     
                                       1 
                                       6 
                                     
                                     ⁢ 
                                     
                                       α 
                                       3 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                           ⁢ 
                           
                             
                               s 
                               3 
                             
                             · 
                             
                               
                                 I 
                                 d 
                               
                               ⁡ 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     α 
                                     ⁡ 
                                     
                                       ( 
                                       
                                         1 
                                         - 
                                         
                                           
                                             1 
                                             6 
                                           
                                           ⁢ 
                                           
                                             α 
                                             2 
                                           
                                         
                                       
                                       ) 
                                     
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           ≅ 
                             
                           ⁢ 
                           
                             
                               s 
                               3 
                             
                             ⁢ 
                             
                               
                                 I 
                                 ref 
                               
                               · 
                               
                                 k 
                                 β 
                               
                             
                             ⁢ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   sin 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   α 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
                 
                   
                     ( 
                     21 
                     ) 
                   
                 
               
             
           
         
       
     
     Next, an example where the currents I a , I b , and I c  are expressed by the following expressions (22) will be described. 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     22 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       I 
                       a 
                     
                     = 
                     
                       
                         1 
                         
                           s 
                           2 
                         
                       
                       ⁢ 
                       
                         I 
                         d 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       I 
                       b 
                     
                     = 
                     
                       I 
                       d 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       I 
                       c 
                     
                     = 
                     
                       s 
                       · 
                       
                         I 
                         d 
                       
                     
                   
                 
               
               
                 
                   ( 
                   22 
                   ) 
                 
               
             
           
         
       
     
     In this case, the output current I 4  of the node N 2  is expressed by the following expression (23), and by applying the approximation of the expression (15), it becomes a current proportional to (1+cos α). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     23 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           I 
                           4 
                         
                         = 
                           
                         ⁢ 
                         
                           
                             I 
                             b 
                           
                           + 
                           
                             I 
                             b 
                           
                           - 
                           
                             
                               
                                 s 
                                 2 
                               
                               · 
                               
                                 1 
                                 2 
                               
                             
                             ⁢ 
                             
                               α 
                               2 
                             
                             ⁢ 
                             
                               I 
                               a 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             I 
                             d 
                           
                           + 
                           
                             I 
                             d 
                           
                           - 
                           
                             
                               1 
                               2 
                             
                             ⁢ 
                             
                               α 
                               2 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             I 
                             d 
                           
                           ⁡ 
                           
                             ( 
                             
                               1 
                               + 
                               1 
                               - 
                               
                                 
                                   1 
                                   2 
                                 
                                 ⁢ 
                                 
                                   α 
                                   2 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         ≅ 
                           
                         ⁢ 
                         
                           
                             
                               I 
                               ref 
                             
                             · 
                             
                               k 
                               β 
                             
                           
                           ⁢ 
                           
                             ( 
                             
                               1 
                               + 
                               
                                 cos 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 α 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   23 
                   ) 
                 
               
             
           
         
       
     
     Further, the output current I 8  of the node N 1  is expressed by the following expression (24) and becomes a current proportional to (1+sin α) by applying the approximation of the expression (15). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     24 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           I 
                           8 
                         
                         = 
                           
                         ⁢ 
                         
                           
                             I 
                             c 
                           
                           + 
                           
                             
                               s 
                               · 
                               α 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               I 
                               b 
                             
                           
                           - 
                           
                             
                               
                                 s 
                                 3 
                               
                               · 
                               
                                 1 
                                 6 
                               
                             
                             ⁢ 
                             
                               α 
                               3 
                             
                             ⁢ 
                             
                               I 
                               a 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             s 
                             · 
                             
                               I 
                               d 
                             
                           
                           + 
                           
                             
                               s 
                               · 
                               α 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                           - 
                           
                             
                               s 
                               · 
                               
                                 1 
                                 6 
                               
                             
                             ⁢ 
                             
                               α 
                               3 
                             
                             ⁢ 
                             
                               I 
                               d 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           s 
                           · 
                           
                             
                               I 
                               d 
                             
                             ⁡ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 α 
                                 - 
                                 
                                   
                                     1 
                                     6 
                                   
                                   ⁢ 
                                   
                                     α 
                                     3 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           s 
                           · 
                           
                             
                               I 
                               d 
                             
                             ⁡ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   α 
                                   ⁡ 
                                   
                                     ( 
                                     
                                       1 
                                       - 
                                       
                                         
                                           1 
                                           6 
                                         
                                         ⁢ 
                                         
                                           α 
                                           2 
                                         
                                       
                                     
                                     ) 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         ≅ 
                           
                         ⁢ 
                         
                           
                             
                               sI 
                               ref 
                             
                             · 
                             
                               k 
                               β 
                             
                           
                           ⁢ 
                           
                             ( 
                             
                               1 
                               + 
                               
                                 sin 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 α 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   24 
                   ) 
                 
               
             
           
         
       
     
     Here, the Taylor series of the trigonometric function of cos α and sin α are expressed by the following expressions (25). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     25 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       cos 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       α 
                     
                     = 
                     
                       1 
                       - 
                       
                         
                           1 
                           
                             2 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           2 
                         
                       
                       + 
                       
                         
                           1 
                           
                             4 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           4 
                         
                       
                       - 
                       
                         
                           1 
                           
                             6 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           6 
                         
                       
                       + 
                       … 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       sin 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       α 
                     
                     = 
                     
                       α 
                       - 
                       
                         
                           1 
                           
                             3 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           3 
                         
                       
                       + 
                       
                         
                           1 
                           
                             5 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           5 
                         
                       
                       - 
                       
                         
                           1 
                           
                             7 
                             ! 
                           
                         
                         ⁢ 
                         
                           α 
                           7 
                         
                       
                       + 
                       … 
                     
                   
                 
               
               
                 
                   ( 
                   25 
                   ) 
                 
               
             
           
         
       
     
     In the above, the example of the circuits which generate the currents up to the second term of the Taylor series of the trigonometric function is presented, but the circuits can be circuits which generate currents of higher-order Taylor series of the trigonometric function. 
       FIG. 3  is an explanatory chart of operations of the bias generator  102  and the bias selector  103  in  FIG. 1  and illustrates the sine value sin α output by the sin α current generation circuit  105  and the cosine value cos α output by the cos α current generation circuit  106 . 
     First, a method how the bias selector  103  outputs the cos α current will be described. sin α in a range of α=0° to 45° and cos α in a range of α=45° to 90° are in line symmetry with respect to a 45° axis. For example, cos 60°=sin 30° and cos 75°=sin 15°. That is, in the range of 45°≦α&lt;90°, cos α=sin(90°−α) holds. Therefore, in the range of 0°≦α&lt;45°, the cos α current generation circuit  106  generates the current with the cosine value cos α, and the bias selector  103  outputs this current with the cosine value cos α. On the other hand, in the range of 45°≦α&lt;90°, the sin α current generation circuit  105  generates a current with a sine value sin(90°−α) (=cos α) and the bias selector  103  outputs this current with the sine value sin(90°−α) (=cos α). That is, only the range of 0°≦α&lt;45° is used. 
     Next, a method how the bias selector  103  outputs the sin α current will be described. cos α in the range of α=0° to 45° and sin α in the range of α=45° to 90° are in line symmetry with respect to the 45° axis. For example, sin 60°=cos 30° and sin 75°=cos 15°. That is, in the range of 45°≦α&lt;90°, sin α=cos(90°−α) holds. Therefore, in the range of 0°≦α&lt;45°, the sin α current generation circuit  105  generates the current with the sine value sin α, and the bias selector  103  outputs this current with the sine value sin α. On the other hand, in the range of 45°&lt;α&lt;90°, the cos α current generation circuit  106  generates a current with a cosine value cos(90°−α) (=sin α) and the bias selector  103  outputs this current with the cosine value cos(90°−α) (=sin α). That is, only the range of 0°≦α&lt;45° is used. 
     First, a case where the range of the shift angle α is “0≦α&lt;45°” will be described. The control circuit  107  in  FIG. 2  outputs the first control signal S 1  for setting m (=s·α) corresponding to the angle α when the angle α indicated by the phase control signal CTL is 0°≦α&lt;45°. Consequently, the sin α current generation circuit  105  outputs the sin α current, and the cos α current generation circuit  106  outputs the cos α current. In this case, the bias selector  103  outputs the current with the sine value sin α as the bias signal B 2 , and outputs the current with the cosine value cos α as the bias signal B 1 . 
     Next, a case where the range of the shift angle α is “45°&lt;α&lt;90°” will be described. The control circuit  107  in  FIG. 2  outputs the first control signal S 1  for setting m (=s·(90°−α)) corresponding to an angle (90°−α) when the angle α indicated by the phase control signal CTL is 45°&lt;α&lt;90°. Consequently, the sin α current generation circuit  105  outputs the sin(90°−α) (=cos α) current, and the cos α current generation circuit  106  outputs the cos(90°−α) (=sin α) current. In this case, the bias selector  103  outputs the current with the cosine value sin(90°−α) (=cos α) as the bias signal B 1 , and outputs the current with the sine value cos(90°−α) (=sin α) as the bias signal B 2 . 
     Next, a case where the shift angle α is “45°” will be described. When α is 45°, sin α=cos α holds. Here, when the approximation orders of the Taylor series of sin α and cos α generated by the sin α current generation circuit  105  and the cos α current generation circuit  106  are the same, approximation accuracy of sin α is higher than that of cos α. Therefore, the sin α current generation circuit  105  is higher in accuracy than the cos α current generation circuit  106 . Therefore, the control circuit  107  in  FIG. 2  outputs the first control signal S 1  for setting m (=s·α) corresponding to the angle α when the angle α indicated by the phase control signal CTL is 45°. Consequently, the sin α current generation circuit  105  outputs the sin α current. In this case, the bias selector  103  outputs the current with the sine value sin α and the current with the cosine value sin α (=cos α) as the bias signals B 1  and B 2 . 
     As described above, the bias generator  102  does not generate sin α nor cos α in the range of 45°&lt;α&lt;90° and generates sin α and cos α only in the range of 0°≦α&lt;45°. That is, since, owing to the first control signal S 1 , a size change range of the transistors M 2 , M 4 , and M 11  is the narrow range of 0°≦α&lt;45°, the maximum number of parallel connections of each of the transistors M 2 , M 4 , and M 11  becomes small, which can reduce areas of the transistors M 2 , M 4 , and M 11 . That is, it is possible to reduce a circuit scale of the bias generator  102 . 
     Next, in order to explain the effect of the phase interpolator in  FIG. 1 , a phase interpolator in  FIG. 4  will be described.  FIG. 4  is a diagram illustrating a configuration example of a phase interpolator to which four-phase square-wave signals are input. Current polarity changing circuits  401  to  404  receive a 0° square-wave signal φ 0 , a 90° square-wave signal φ 1 , a 180° square-wave signal φ 0 X, and a 270° square-wave signal  41 X respectively. The current polarity changing circuit  401  has field effect transistors  411 ,  412  and current sources  413 ,  414 , and receives the 0° square-wave signal φ 0  to output a triangular-wave signal to a capacitor  406 . A voltage level correction circuit  405  is connected to the capacitor  406 . The current polarity changing circuits  402  to  404  operate similarly to the current polarity changing circuit  401 . At an output terminal CSO, the output signals of the current polarity changing circuits  401  to  404  are synthesized. By controlling currents flowing in the current sources  413 ,  414  of each of the current polarity changing circuits  401  to  404 , it is possible to give weights to the 0° square-wave signal φ 0 , the 90° square-wave signal φ 1 , the 180° square-wave signal φ 0 X, and the 270° square-wave signal φ 1 X. Consequently, the output terminal CSO is capable of outputting a signal with a desired phase. 
     However, when frequencies of the square-wave input signals φ 0 , φ 1 , φ 0 X, φ 1 X are increased, the square-wave input signals φ 0 , φ 1 , φ 0 X, φ 1 X are distorted due to an influence of parasitic capacitance or the like existing in input wiring lines. When the distorted square-wave signals φ 0 , φ 1 , φ 0 X, φ 1 X are input to the phase interpolator, phase linearity of the phase interpolator deteriorates. 
       FIG. 5  is a chart illustrating a phase characteristic of the phase interpolator according to this embodiment. A characteristic  502  is a phase characteristic of the phase interpolator in  FIG. 4 , and because of the above reason, its phase linearity deteriorates. A characteristic  501  is the phase characteristic of the phase interpolator of this embodiment in  FIG. 1  and almost matches ideal phase linearity. In this embodiment, by using the cosine wave or the sine wave instead of the square wave, it is possible to prevent the deterioration of the phase linearity even when the frequency of the signal is increased. 
     Second Embodiment 
       FIG. 6  is a diagram illustrating a configuration example of a bias generator  102  according to a second embodiment. Hereinafter, differences of this embodiment ( FIG. 6 ) from the first embodiment ( FIG. 2 ) will be described. A control circuit  107  outputs a first control signal S 1 , a second control signal S 2 , and a third control signal S 3  according to a phase control signal CTL. A size of a transistor M 6  is controlled according to the second control signal S 2 . That is, a current mirror ratio of a transistor M 5  and the transistor M 6  is controlled according to the second control signal S 2 . A size of a transistor M 11  is controlled according to the third control signal S 3 . That is, a current mirror ratio of a transistor M 10  and the transistor M 11  is controlled according to the third control signal S 3 . 
     When a desired shift angle α is 0°&lt;α&lt;90°, the size of the transistor M 6  is controlled to ½ of of a size of the transistor M 5 , and the size of the transistor M 11  is controlled to m times a size of the transistor M 10 . Further, as a size ratio m of each of transistors M 2 , M 4 , M 11 , a value proportional to the desired shift angle α is selected as in the first embodiment. In this case, an operation in this embodiment is the same as that of the first embodiment. 
     When the desired shift angle α is 00, a size of the transistor M 2  is controlled to the same size as that of a transistor M 1  (M 1 :M 2 =1:1), and a size of the transistor M 4  is controlled to the same size as that of a transistor M 3  (M 3 :M 4 =1:1). Further, the sizes of the transistors M 6  and M 11  are set to 0. That is, gates of the transistors M 6  and M 11  are disconnected from gates of the transistors M 5  and M 10  respectively. The transistor M 6  becomes off, a drain current I 2  of the transistor M 6  becomes 0, and an output current I 4  of a node N 2  becomes a current proportional to (1+cos 0°). Further, the transistor M 11  becomes off, a drain current I 7  of the transistor M 11  becomes 0, and an output current I 8  of a node N 1  becomes a current proportional to (1+sin 0°) 
     Consequently, whatever value the angle α indicated by the phase control signal CTL has, a voltage in the bias generator  102  is not fixed to a power supply potential or a ground potential, and consequently, a response of an output to the phase control signal CTL becomes quick. 
     Incidentally, the transistors whose sizes are controlled are not limited to the aforesaid transistors M 6  and M 11 . When the desired shift angle α is 0°, a gate of a transistor M 7  or M 8  instead of the transistor M 6  may be disconnected, and a gate of a transistor M 9  or the transistor M 10  instead of the transistor M 11  may be disconnected. 
     As described above, a current mirror ratio of a current mirror circuit of the transistors M 1  and M 2  and a current mirror ratio of a current mirror circuit of the transistors M 3  and M 4  are controlled according to the first control signal S 1 . 
     Further, a current mirror circuit of the transistors M 5  and M 6  and so on is connected to a subsequent stage of the current mirror circuit of the transistors M 1  and M 2  and the current mirror circuit of the transistors M 3  and M 4 , and its current mirror ratio is controlled according to the second control signal S 2  in order to generate a current with a cosine value cos α. 
     Further, a current mirror circuit of the transistors M 10  and M 11  and so on is connected to a subsequent stage of the current mirror circuit of the transistors M 1  and M 2  and the current mirror circuit of the transistors M 3  and M 4 , and its current mirror ratio is controlled according to the third control signal S 3  in order to generate a current with a sine value sin α. 
     Third Embodiment 
       FIG. 7  is a diagram illustrating a configuration example of a phase interpolator according to a third embodiment. In this embodiment ( FIG. 7 ), the resistors  118 ,  119 ,  136 ,  137  are deleted from the first embodiment ( FIG. 1 ). Hereinafter, differences of this embodiment ( FIG. 7 ) from the first embodiment ( FIG. 1 ) will be described 
     A drain of a transistor  116  and a drain of a transistor  120  are connected to each other and are connected to a power supply potential node via a parallel-connection circuit of a current source  111  and a resistor  113 . A drain of a transistor  115  and a drain of a transistor  121  are connected to each other and are connected to the power supply potential node via a parallel-connection circuit of a current source  112  and a resistor  114 . 
     A drain of a transistor  134  and a drain of a transistor  138  are connected to each other and are connected to the power supply potential node via a parallel-connection circuit of a current source  129  and a resistor  131 . A drain of a transistor  133  and a drain of a transistor  139  are connected to each other and are connected to the power supply potential node via a parallel-connection circuit of a current source  130  and a resistor  132 . 
     A first differential pair  151  and a second differential pair  152  are commonly connected to a first load. The first load is the parallel-connection circuits of the current sources  111 ,  112  and the resistors  113 ,  114 . A fifth differential pair  155  and a sixth differential pair  156  are commonly connected to a second load. The second load is the parallel-connection circuits of the current sources  129 ,  130  and the resistors  131 ,  132 . 
     The output loads of the first differential pair  151  and the second differential pair  152  become common, and the output loads of the fifth differential pair  155  and the sixth differential pair  156  become common. Since the loads become common, a circuit scale can be reduced. 
     Next, operations of the first differential pair  151  to a fourth differential pair  154  will be described. A tail current I 11  expressed by the following expression (26) flows in each of tail current sources  117  and  125 . Further, a tail current I 12  expressed by the following expression (26) flows in each of tail current sources  122  and  128 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     26 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       I 
                       11 
                     
                     = 
                     
                       
                         k 
                         β 
                       
                       ⁢ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             cos 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             α 
                           
                         
                         ) 
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       I 
                       12 
                     
                     = 
                     
                       k 
                       β 
                     
                   
                 
               
               
                 
                   ( 
                   26 
                   ) 
                 
               
             
           
         
       
     
     Mutual conductance g m1  of the input-stage transistor  115  of the first differential pair  151  has a value correlated with a cosine value cos α of a desired shift angle α as expressed by the following expression (27). Since a cosine wave cos θ is input to a gate of the input-stage transistor  115  of the first differential pair  151 , a drain current i o1  of the input-stage transistor  115  has a value equal to a square root of the cosine value cos α of the desired shift angle α multiplied by the cosine wave cos θ as expressed by the following expression (27). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     27 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       g 
                       
                         m 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     = 
                     
                       
                         
                           2 
                           ⁢ 
                           
                             β 
                             · 
                             
                               
                                 I 
                                 11 
                               
                               2 
                             
                           
                         
                       
                       = 
                       
                         
                           
                             β 
                             · 
                             
                               I 
                               11 
                             
                           
                         
                         = 
                         
                           
                             k 
                             ⁡ 
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   cos 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   α 
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       i 
                       
                         o 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     = 
                     
                       
                         
                           - 
                           
                             g 
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                         · 
                         
                           v 
                           in 
                         
                       
                       = 
                       
                         
                           
                             - 
                             
                               
                                 k 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     1 
                                     + 
                                     
                                       cos 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       α 
                                     
                                   
                                   ) 
                                 
                               
                             
                           
                           · 
                           cos 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         θ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   27 
                   ) 
                 
               
             
           
         
       
     
     The current I 12  expressed by the above expression (26) flows in the tail current source  122  of the second differential pair  152 . Therefore, since a bias current I 12 /2 flows in the input-stage transistor  121  of the second differential pair  152 , mutual conductance g m2  of the input-stage transistor  121  of the second differential pair  152  has a value equal to a square root of an arbitrary constant k as expressed by the following expression (28). Further, a drain current i o2  of the input-stage transistor  121  of the second differential pair  152  is expressed by the following expression (28). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     28 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       g 
                       
                         m 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     = 
                     
                       
                         
                           2 
                           ⁢ 
                           
                             β 
                             · 
                             
                               
                                 I 
                                 12 
                               
                               2 
                             
                           
                         
                       
                       = 
                       
                         
                           
                             β 
                             · 
                             
                               I 
                               12 
                             
                           
                         
                         = 
                         
                           k 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     i 
                     
                       o 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                   = 
                   
                     
                       
                         - 
                         
                           g 
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                       
                       · 
                       
                         v 
                         in 
                       
                     
                     = 
                     
                       
                         
                           k 
                         
                         · 
                         cos 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       θ 
                     
                   
                 
               
               
                 
                   ( 
                   28 
                   ) 
                 
               
             
           
         
       
     
     Output nodes of the first differential pair  151  and the second differential pair  152  are connected to the common load. Therefore, drain voltages v o1  of the input-stage transistor  115  of the first differential pair  151  and the input-stage transistor  121  of the second differential pair  152  are equal, and they have a value equal to a current i o1 +i o2  being the sum of the current i o1  and the current i o2 , multiplied by an output impedance Z o1 , as expressed by the following expression (29). 
     
       
         
           
             
               
                 
                   [ 
                   
                     
                       e 
                       ⁢ 
                       xpression 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     29 
                   
                   ] 
                 
               
               
                 
                   ( 
                   29 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           v 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             Z 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           · 
                           
                             ( 
                             
                               
                                 i 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                               + 
                               
                                 i 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   2 
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             Z 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           · 
                           
                             ( 
                             
                               
                                 
                                   
                                     - 
                                     
                                       
                                         k 
                                         ⁡ 
                                         
                                           ( 
                                           
                                             1 
                                             + 
                                             
                                               cos 
                                               ⁢ 
                                               
                                                   
                                               
                                               ⁢ 
                                               α 
                                             
                                           
                                           ) 
                                         
                                       
                                     
                                   
                                   · 
                                   cos 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 θ 
                               
                               + 
                               
                                 
                                   
                                     k 
                                   
                                   · 
                                   cos 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 θ 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             · 
                             
                               k 
                             
                           
                           ⁢ 
                           
                             
                               ( 
                               
                                 
                                   - 
                                   
                                     
                                       1 
                                       + 
                                       
                                         cos 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         α 
                                       
                                     
                                   
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                             · 
                             cos 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           θ 
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Next, operations of the third differential pair  153  and the fourth differential pair  154  will be described. The same current i 11  as that of the tail current source  117  of the first differential pair  151  flows in the tail current source  125  of the third differential pair  153 . Therefore, mutual conductance g m3  of an input-stage transistor  124  of the third differential pair  153  has the same value as that of the mutual conductance g m1  of the input-stage transistor  115  of the first differential pair  151  as expressed by the following expression (30). Further, since a gate voltage of the input-stage transistor  124  of the third differential pair  153  is equal to the drain voltage v o1  of the input-stage transistor  115  of the first differential pair  151 , a drain current i o3  of the input-stage transistor  124  of the third differential pair  153  is expressed by the following expression (30). 
     
       
         
           
             
               
                 
                   [ 
                   
                     
                       e 
                       ⁢ 
                       xpression 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     30 
                   
                   ] 
                 
               
               
                 
                   ( 
                   30 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           g 
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             g 
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                           = 
                           
                             
                               k 
                               ⁡ 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     cos 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           i 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             - 
                             
                               g 
                               
                                 m 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 3 
                               
                             
                           
                           · 
                           
                             v 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               
                                 Z 
                                 
                                   o 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   1 
                                 
                               
                               · 
                               
                                 k 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     1 
                                     + 
                                     
                                       cos 
                                       ⁢ 
                                       
                                           
                                       
                                       ⁢ 
                                       α 
                                     
                                   
                                   ) 
                                 
                               
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                           - 
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ⁢ 
                             k 
                             ⁢ 
                             
                               
                                 
                                   1 
                                   + 
                                   
                                     cos 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                               
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     The same current I 12  as that of the tail current source  122  of the second differential pair  152  flows in the tail current source  128  of the fourth differential pair  154 . Therefore, mutual conductance g m4  of an input-stage transistor  127  of the fourth differential pair  154  has the same value as that of the mutual conductance g m2  of the input-stage transistor  121  of the second differential pair  152  as expressed by the following expression (31). Further, since a gate voltage of the input-stage transistor  127  of the fourth differential pair  154  is equal to the drain voltage v o1  of the input-stage transistor  115  of the first differential pair  151 , a drain current i o4  of the input-stage transistor  127  of the fourth differential pair  154  is expressed by the following expression (31). 
     
       
         
           
             
               
                 
                   [ 
                   
                     expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     31 
                   
                   ] 
                 
               
               
                 
                   ( 
                   31 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           g 
                           
                             m 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             4 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             g 
                             
                               m 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           = 
                           
                             k 
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           i 
                           
                             o 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             4 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             - 
                             
                               g 
                               
                                 m 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 4 
                               
                             
                           
                           · 
                           
                             v 
                             
                               o 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ⁢ 
                             k 
                             ⁢ 
                             
                               
                                 
                                   1 
                                   + 
                                   
                                     cos 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     α 
                                   
                                 
                               
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                           - 
                           
                             
                               Z 
                               
                                 o 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 1 
                               
                             
                             ⁢ 
                             
                               k 
                               · 
                               cos 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θ 
                           
                         
                       
                     
                   
                 
               
               
                 
                     
                 
               
             
           
         
       
     
     Since an output node of the third differential pair  153  and an output node of the fourth differential pair  154  are connected by output terminals O_CLK and O_CLKX, an output current of the output terminals O_CLK and O_CLKX is a current i o3 +i o4  being the sum of the current i o3  of the third differential pair  153  and the current i o4  of the fourth differential pair  154  as expressed by the following expression (32), and as in the first embodiment, it becomes a current proportional to cos θ·cos α. This also applies to the fifth differential pair  155  to an eighth differential pair  158 . 
     
       
         
           
             
               
                 
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     Fourth Embodiment 
       FIG. 8  is a diagram illustrating a configuration example of a phase interpolator according to a fourth embodiment. In this embodiment ( FIG. 8 ), the current sources  111 ,  112 ,  129 ,  130 ,  147 ,  148  are deleted from the first embodiment ( FIG. 1 ). Hereinafter, differences of this embodiment ( FIG. 8 ) from the first embodiment ( FIG. 1 ) will be described. 
     A drain of a transistor  115  is connected to a power supply potential node via a resistor  113 . A drain of a transistor  116  is connected to the power supply potential node via a resistor  114 . A drain of a transistor  133  is connected to the power supply potential node via a resistor  131 . A drain of a transistor  134  is connected to the power supply potential node via a resistor  132 . A first output node O_CLK is connected to the power supply potential node via a resistor  149 . A second output node O_CLKX is connected to the power supply potential node via a resistor  150 . Loads of first to eighth differential pairs  151  to  158  are the resistors. The resistors being the loads of the first to eighth differential pairs  151  to  158  have resistance values proportional to βs of input-stage transistors of the first to eighth differential pairs  151  to  158  respectively. 
     According to this embodiment, the loads of the first to eight differential pairs  151  to  158  do not include current sources, and accordingly, parasitic capacitance components in output nodes of the first to eighth differential pairs  151  to  158  are smaller and a band becomes wider. Further, it is possible to make an output range of the output terminals O_CLK and O_CLKX wider. 
     Fifth Embodiment 
       FIG. 9  is a diagram illustrating a configuration example of a phase interpolator according to a fifth embodiment. In this embodiment ( FIG. 9 ), the resistors  118 ,  119 ,  136 ,  137  are deleted from the fourth embodiment ( FIG. 8 ). Hereinafter, differences of this embodiment ( FIG. 9 ) from the fourth embodiment ( FIG. 8 ) will be described. 
     A drain of a transistor  115  and a drain of a transistor  121  are connected to each other and are connected to a power supply potential node via a resistor  114 . A drain of a transistor  116  and a drain of a transistor  120  are connected to each other and are connected to the power supply potential node via a resistor  113 . A gate of a transistor  123  and a gate of a transistor  126  are connected to each other and are connected to a mutual connection point of the drains of the transistors  116  and  120 . A gate of a transistor  124  and a gate of a transistor  127  are connected to each other and are connected to a mutual connection point of the drains of the transistors  115  and  121 . 
     A drain of a transistor  133  and a drain of a transistor  139  are connected to each other and are connected to the power supply potential node via a resistor  132 . A drain of a transistor  134  and a drain of a transistor  138  are connected to each other and are connected to the power supply potential node via a resistor  131 . A gate of a transistor  141  and a gate of a transistor  144  are connected to each other and are connected to a mutual connection point of the drains of the transistors  134  and  138 . A gate of a transistor  142  and a gate of a transistor  145  are connected to each other and are connected to a mutual connection point of the drains of the transistors  133  and  139 . 
     A first differential pair  151  and a second differential pair  152  are commonly connected to a first load. The first load is the resistors  113  and  114 . A fifth differential pair  155  and a sixth differential pair  156  are commonly connected to a second load. The second load is the resistors  131  and  132 . 
     The output loads of the first differential pair  151  and the second differential pair  152  are common, and the output loads of the fifth differential pair  155  and the sixth differential pair  156  are common. Since the loads become common, it is possible to reduce a circuit scale. 
     Sixth Embodiment 
       FIG. 10  is a diagram illustrating a configuration example of a phase interpolator according to a sixth embodiment. In this embodiment ( FIG. 10 ), the resistors  113 ,  114 ,  118 ,  119 ,  131 ,  132 ,  136 ,  137 ,  149 ,  150  are deleted from the first embodiment ( FIG. 1 ) and current sources  1001  to  1004  are added thereto. Hereinafter, differences of this embodiment ( FIG. 10 ) from the first embodiment ( FIG. 1 ) will be described 
     A drain of a transistor  115  is connected to a power supply potential node via a current source  111 . A drain of a transistor  116  is connected to the power supply potential node via a current source  112 . A drain of a transistor  120  is connected to the power supply potential node via the current source  1001 . A drain of a transistor  121  is connected to the power supply potential node via the current source  1002 . In each of the current sources  1001  and  1002 , a current according to a bias signal B 3  flows. 
     A drain of a transistor  133  is connected to the power supply potential node via a current source  129 . A drain of a transistor  134  is connected to the power supply potential node via a current source  130 . A drain of a transistor  138  is connected to the power supply potential node via the current source  1003 . A drain of a transistor  139  is connected to the power supply potential node via the current source  1004 . In each of the current sources  1003  and  1004 , a current according to the bias signal B 3  flows. 
     A first output terminal O_CLK is connected to the power supply potential node via a current source  147 . A second output terminal O_CLKX is connected to the power supply potential node via a current source  148 . 
     According to this embodiment, loads of first to eighth differential pairs  151  to  158  are the current sources. Since the current sources high in output resistance are the output loads of the differential pairs  151  to  158 , it is possible to increase voltage gains of the differential pairs  151  to  158 . 
     Seventh Embodiment 
       FIG. 11  is a diagram illustrating a configuration example of a phase interpolator according to a seventh embodiment. In this embodiment ( FIG. 11 ), the current sources  1001  to  1004  are deleted from the sixth embodiment ( FIG. 10 ). Hereinafter, differences of this embodiment ( FIG. 11 ) from the sixth embodiment ( FIG. 10 ) will be described 
     A drain of a transistor  115  and a drain of a transistor  121  are connected to each other and are connected to a power supply potential node via a current source  112 . A drain of a transistor  116  and a drain of a transistor  120  are connected to each other and are connected to the power supply potential node via a current source  111 . A gate of a transistor  123  and a gate of a transistor  126  are connected to each other and are connected to a mutual connection point of the drains of the transistors  116  and  120 . A gate of a transistor  124  and a gate of a transistor  127  are connected to each other and are connected to a mutual connection point of the drains of the transistors  115  and  121 . 
     A drain of a transistor  133  and a drain of a transistor  139  are connected to each other and are connected to the power supply potential node via a current source  130 . A drain of a transistor  134  and a drain of a transistor  138  are connected to each other and are connected to the power supply potential node via a current source  129 . A gate of a transistor  141  and a gate of a transistor  144  are connected to each other and are connected to a mutual connection point of the drains of the transistors  134  and  138 . A gate of a transistor  142  and a gate of a transistor  145  are connected to each other and are connected to a mutual connection point of the drains of the transistors  133  and  139 . 
     Output loads of a first differential pair  151  and a second differential pair  152  are common, and output loads of a fifth differential pair  155  and a sixth differential pair  156  are common. Since the loads become common, it is possible to reduce a circuit scale. 
     Note that the above-described embodiments all only present concrete examples in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be embodied in various forms without departing from its technical idea or its main features. 
     By using a cosine wave or a sine wave instead of a square wave, it is possible to prevent deterioration of phase linearity even when a frequency of a signal is increased. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.