Patent Abstract:
Provided is a reference current circuit able to reduce temperature dependence of the reference current even in a case of using a resistor with extremely low temperature-dependent resistance. The reference current circuit comprises a non-inverting amplifier circuit  110  receiving a temperature-compensated reference voltage V BG  and generating a voltage V out1  at an output point; a current source circuit  120  composed of a transistor Q 1  connected to the output point via a resistor and a transistor Q 2  receiving a voltage equal to a voltage V BE1  generated across terminals of Q 1  and generating a corresponding current. The circuit  110  (i) includes a third transistor Q 3 , a voltage V BE3  generated across terminals of which has the same temperature characteristic as the voltage V BE1 , and (ii) is configured such that V out1  is a sum of (a) a temperature-compensated voltage component based on V BG  and (b) a voltage component equal-to-the voltage V BE3 .

Full Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a reference current circuit which generates a bias current provided to an analogue circuit. 
     (2) Description of the Related Art 
       FIG. 4  shows a structure of a conventional reference current circuit. 
     A reference current circuit  400  includes anon-inverting amplifier circuit  410  and a current source circuit  120 . 
     The non-inverting amplifier circuit  410  is composed of an amplifier circuit OP 40 , a resistor R 1 , and a resistor R 2 . The amplifier circuit OP 40  includes an inverting input terminal, a non-inverting input terminal, and an output terminal; the resistor R 1  is inserted in a wiring connecting the inverting input terminal and a ground terminal; and the resistor R 2  is inserted in a wiring connecting the output terminal and the inverting input terminal. The non-inverting input terminal of the amplifier circuit OP  40  receives input of a reference voltage V BG  which is independent of a temperature T and a power supply voltage Vdd. In other words, the reference voltage V BG  is temperature-compensated. 
     The current source circuit  120  is composed of a resistor R 3 , a transistor Q 1 , and a transistor Q 2 . One terminal of the resistor R 3  is connected to the output terminal of the amplifier circuit OP 40 ; a collector and a base of the transistor Q 1  are connected to the other terminal of the resistor R 3 , while an emitter of the transistor Q 1  is grounded; and a base of the transistor Q 2  is connected to the collector and the base of the transistor Q 1 . 
     In general, a bandgap reference circuit is often used as a reference voltage circuit  500  which outputs the reference voltage V BG .  FIG. 5  shows one example of such a bandgap reference circuit. The reference voltage circuit  500  is composed of an amplifier circuit OPS, a resistor R 1   a , a transistor Q 1   a , a resistor R 2   a , a resistor R 3   a , and a transistor Q 2   a . The resistor R 1   a  is inserted in a wiring connecting an on-inverting input terminal and an output terminal of the amplifier circuit OPS; a base and a collector of the transistor Q 1   a  are grounded; the resistor R 2   a  is inserted in a wiring connecting an inverting input terminal and the output terminal of the amplifier circuit OPS; the resistor R 3   a  is inserted in a wiring connecting the inverting input terminal and an emitter of the transistor Q 2   a ; and a base and a collector of the transistor Q 2   a  are grounded. 
     In the following, an outline of a principle which generates a reference current with low temperature dependence will be described in relation to the reference current circuit  400  structured as above. 
     The following equation holds for the non-inverting amplifier circuit  410 . 
     
       
         
           
             
               
                 
                   
                     V 
                     BG 
                   
                   = 
                   
                     
                       
                         R 
                         1 
                       
                       
                         
                           R 
                           1 
                         
                         + 
                         
                           R 
                           2 
                         
                       
                     
                     · 
                     
                       V 
                       
                         out 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4.1 
                   ) 
                 
               
             
           
         
       
     
     The following equation is derived from the equation (4.1). 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       out 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       4 
                     
                   
                   = 
                   
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             R 
                             2 
                           
                           
                             R 
                             1 
                           
                         
                       
                       ) 
                     
                     · 
                     
                       V 
                       BG 
                     
                   
                 
               
               
                 
                   ( 
                   4.2 
                   ) 
                 
               
             
           
         
       
     
     Here, V BG  is a reference voltage which is independent of the temperature T and the power supply voltage Vdd; and R 1  and R 2  are resistances with a positive temperature coefficient. When the temperature is T, the following equations hold. 
     
       
         
           
             
               
                 
                   ∂ 
                   
                     V 
                     BG 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
             , 
             
               
                 
                   ∂ 
                   
                     R 
                     1 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               
                 
                   
                     ∂ 
                     
                       R 
                       2 
                     
                   
                   
                     ∂ 
                     T 
                   
                 
                 &gt; 
                 0 
               
             
           
         
       
     
     Since the ratio of R 1  and R 2  remains the same regardless of temperature change, the equation (4.2) indicates that an output voltage V out4  is temperature-independent. 
     Also, the following equation can be found for the current source circuit  120 .
 
 V   out4   =R   3   ·I   ref4   +V   BE   (4.3)
 
     The equation (4.3) leads to the following equation. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       4 
                     
                   
                   = 
                   
                     
                       
                         V 
                         
                           out 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                       
                       - 
                       
                         V 
                         BE 
                       
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   4.4 
                   ) 
                 
               
             
           
         
       
     
     By partially differentiating both sides of the equation (4.4) by the temperature T, the following equation can be obtained. 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         I 
                         
                           ref 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                       
                     
                     
                       ∂ 
                       T 
                     
                   
                   = 
                   
                     
                       
                         - 
                         
                           1 
                           
                             R 
                             3 
                           
                         
                       
                       · 
                       
                         
                           ∂ 
                           
                             V 
                             BE 
                           
                         
                         
                           ∂ 
                           T 
                         
                       
                     
                     - 
                     
                       
                         
                           
                             V 
                             
                               out 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               4 
                             
                           
                           - 
                           
                             V 
                             BE 
                           
                         
                         
                           R 
                           3 
                           2 
                         
                       
                       · 
                       
                         
                           ∂ 
                           
                             R 
                             3 
                           
                         
                         
                           ∂ 
                           T 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4.5 
                   ) 
                 
               
             
           
         
       
     
     Also, based on the following inequality 
     
       
         
           
             
               
                 ∂ 
                 
                   V 
                   BE 
                 
               
               
                 ∂ 
                 T 
               
             
             &lt; 
             0 
           
         
       
     
     and “V out4 &gt;V BE ”, in the right side of the equation (4.5), the first term is positive, while the second term is negative. Thus, by adjusting each parameter such that the right side of the equation (4.5) becomes 0, a reference current I ref4  with low temperature-dependence is generated. This is how the temperature characteristic of the transistor Q 1  is compensated by the temperature characteristic of the resistor R 3 . 
     However, in recent years, in the field of semiconductor integrated circuits, temperature dependences of resistances are becoming extremely low as miniaturization of resistors progresses. Also, there are limits to actual adjustment ranges when adjusting each parameter. Thus, with the above-mentioned conventional structure, it is becoming increasingly difficult to reduce temperature dependence of a reference current. 
     Non-Patent Document 1: Fundamentals of Analogue LSI Design, by Kajiro Watanabe and Tetsuo Nakamura, Ohmsha, 2006, pp. 149-151. 
     SUMMARY OF THE INVENTION 
     The present invention was conceived in view of the above problem, and aims to provide a reference current circuit able to reduce temperature dependence of a reference current even in a case where a resistor with an extremely low temperature-dependent resistance value is used. 
     In order to achieve the above-stated aim, the present invention provides a reference current circuit comprising a voltage generating circuit operable to generate, from a reference voltage which is temperature-compensated, a predetermined voltage at an output point, and a current source circuit including a current mirror composed of (i) a first semiconductor device connected to the output point via a resistor and (ii) a second semiconductor device which, as a result of receiving a voltage equal to a voltage across terminals of the first semiconductor device, generates a current corresponding to the received voltage. Here, the voltage generating circuit (i) includes a third semiconductor device, a voltage across terminals of which has a temperature characteristic identical to the temperature characteristic of the voltage across the terminals of the first semiconductor device, and (ii) is configured such that the predetermined voltage is a sum of (a) a temperature-compensated voltage component which is based on the reference voltage and (b) a voltage component equal to the voltage across the terminals of the third semiconductor device. 
     According to the above structure, the temperature dependence of the reference current is able to be reduced even in a case where an extremely low temperature-dependent resistor is used. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate a specific embodiment of the invention. In the drawings: 
         FIG. 1  shows a structure of a reference current circuit of a first embodiment of the present invention; 
         FIG. 2  shows a structure of a reference current circuit of a second embodiment of the present invention; 
         FIG. 3  shows a structure of a reference current circuit of a third embodiment of the present invention; 
         FIG. 4  shows a structure of a conventional reference current circuit; 
         FIG. 5  shows a structure of a reference voltage circuit; 
         FIG. 6  shows a structure of a modification example of the first, second or third embodiment; 
         FIG. 7  shows a structure of a modification example of a temperature-compensated circuit of the second or third embodiment; and 
         FIG. 8  shows a structure of a modification example using a MOS transistor of the temperature-compensated circuit of the second or third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, embodiments of the present invention will be described with reference to the drawings. 
     First Embodiment 
       FIG. 1  shows a structure of a reference current circuit of a first embodiment of the present invention. 
     A reference current circuit  100  includes anon-inverting amplifier circuit  110  and the current source circuit  120  which receives input from the non-inverting amplifier circuit  110 . 
     The non-inverting amplifier circuit  110  is composed of an amplifier circuit OP 10 , a resistor R 1 , a resistor R 2 , and a transistor Q 3 . The amplifier circuit OP 10  has an inverting input terminal, a non-inverting input terminal, and an output terminal; the resistor R 1  is inserted in a wiring connecting the inverting input terminal and a ground terminal; and the resistor R 2  and the transistor Q 3  which functions as a temperature-compensating element are inserted in a wiring connecting the output terminal and the inverting input terminal. The non-inverting input terminal of the amplifier circuit OP 10  receives input of a reference voltage V BG  which is independent of the temperature T and the power supply voltage Vdd. In other words, the reference voltage V BG  is temperature-compensated. 
     Since the structures of the current source circuit  120  and the reference voltage circuit  500  are the same as those described in the prior art, their descriptions are omitted here. 
     Next, with regard to the above-structured reference current circuit  100  of the first embodiment, an outline of a-principle which generates a reference current with low temperature-dependence in a case where a temperature coefficient of resistance is substantially 0. 
     The following equation holds for the non-inverting amplifier circuit  110 . 
     
       
         
           
             
               
                 
                   
                     V 
                     BG 
                   
                   = 
                   
                     
                       
                         R 
                         1 
                       
                       
                         
                           R 
                           1 
                         
                         + 
                         
                           R 
                           2 
                         
                       
                     
                     · 
                     
                       ( 
                       
                         
                           V 
                           
                             out 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         - 
                         
                           V 
                           
                             BE 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   1.1 
                   ) 
                 
               
             
           
         
       
     
     Based on the equation (1.1), an output voltage V out1  of the non-inverting amplifier circuit is derived as follows: 
                     V     out   ⁢           ⁢   1       =         (     1   +       R   2       R   1         )     ·     V   BG       +     V     BE   ⁢           ⁢   3                 (   1.2   )               
where, V BG  is a reference voltage which is independent of the temperature T and the power supply voltage Vdd; and R 1 , R 2 , and R 3  are resistances whose temperature coefficients are substantially 0. When the temperature is T, the following equations hold.
 
     
       
         
           
             
               
                 
                   ∂ 
                   
                     V 
                     BG 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
             , 
             
               
                 
                   ∂ 
                   
                     R 
                     1 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               
                 
                   
                     ∂ 
                     
                       R 
                       2 
                     
                   
                   
                     ∂ 
                     T 
                   
                 
                 = 
                 0 
               
             
           
         
       
     
     Accordingly, although the first term in the right side of the equation (1.2) is independent of the temperature, V BE3  is temperature-dependent. Also, the following equation holds for the current source circuit  120 .
 
 V   out1   =R   3   ·I   ref1   +V   BE1   (1.3)
 
     Based on the equations (1.2) and (1.3), the following equation can be obtained. 
     
       
         
           
             
               
                 
                   R 
                   3 
                 
                 · 
                 
                   I 
                   
                     ref 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                 
               
               + 
               
                 V 
                 
                   BE 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
             = 
             
               
                 
                   ( 
                   
                     1 
                     + 
                     
                       
                         R 
                         2 
                       
                       
                         R 
                         1 
                       
                     
                   
                   ) 
                 
                 · 
                 
                   V 
                   BG 
                 
               
               + 
               
                 V 
                 
                   BE 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
               
             
           
         
       
     
     Hence, the following equation can be derived. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             R 
                             1 
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           
                             R 
                             1 
                           
                           · 
                           
                             R 
                             3 
                           
                         
                       
                       · 
                       
                         V 
                         BG 
                       
                     
                     + 
                     
                       
                         
                           V 
                           
                             BE 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                         - 
                         
                           V 
                           
                             BE 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       
                         R 
                         3 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1.4 
                   ) 
                 
               
             
           
         
       
     
     Here, when V BE3  and V BE1  are equal or substantially equal, the second term in the right side of the equation (1.4) can be considered 0. That is to say, the following holds. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   ≈ 
                   
                     
                       
                         
                           R 
                           1 
                         
                         + 
                         
                           R 
                           2 
                         
                       
                       
                         
                           R 
                           1 
                         
                         · 
                         
                           R 
                           3 
                         
                       
                     
                     · 
                     
                       V 
                       BG 
                     
                   
                 
               
               
                 
                   ( 
                   1.5 
                   ) 
                 
               
             
           
         
       
     
     Here, when the resistance is expressed as follows; 
     
       
         
           
             
               f 
               ⁡ 
               
                 ( 
                 R 
                 ) 
               
             
             ≡ 
             
               
                 
                   R 
                   1 
                 
                 + 
                 
                   R 
                   2 
                 
               
               
                 
                   R 
                   1 
                 
                 · 
                 
                   R 
                   3 
                 
               
             
           
         
       
     
     since R 1 , R 2 , and R 3  are resistances with temperature coefficients of substantially 0, the following equation holds. 
     
       
         
           
             
               
                 ∂ 
                 
                   f 
                   ⁡ 
                   
                     ( 
                     R 
                     ) 
                   
                 
               
               
                 ∂ 
                 T 
               
             
             = 
             0 
           
         
       
     
     Partially differentiating both sides of the equation (1.5) by the temperature T yields the following: 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         I 
                         
                           ref 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                     
                       ∂ 
                       T 
                     
                   
                   = 
                   
                     
                       
                         
                           
                             ∂ 
                             
                               f 
                               ⁡ 
                               
                                 ( 
                                 R 
                                 ) 
                               
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                         · 
                         
                           V 
                           BG 
                         
                       
                       + 
                       
                         
                           f 
                           ⁡ 
                           
                             ( 
                             R 
                             ) 
                           
                         
                         · 
                         
                           
                             ∂ 
                             
                               V 
                               BG 
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                       
                     
                     = 
                     0 
                   
                 
               
               
                 
                   ( 
                   1.6 
                   ) 
                 
               
             
           
         
       
     
     The equation (1.6) indicates that a reference current I ref1  is independent of the temperature T. 
     Consequently, the structure shown in  FIG. 1  is capable of reducing the temperature-dependence of the reference current I ref1 . 
     As described above, the temperature characteristic of the transistor Q 1  can be cancelled by inserting, on a negative feedback circuit of the non-inverting amplifier circuit  110 , the transistor Q 3  whose temperature characteristic is the same as that of the transistor Q 1 . In other words, the temperature dependence of the reference current I ref1  can be eliminated or reduced. 
     Note that while the transistors Q 1  and Q 2  are used in the current source circuit  120  of the first embodiment, MOS transistors M 1  and M 2  can be used as is the case with a current source circuit  121  shown in  FIG. 6 . In this case, it is preferable that MOS transistors with the same temperature characteristic as the MOS transistor M 1  be used in place of the transistor Q 3 . 
     Also, while an NPN bipolar transistor is used as the transistor Q 3  included in the non-inverting amplifier circuit  110 , the transistor Q 3  can be a diode-connected PNP bipolar transistor or a P-N junction diode, or can further be any device or a circuit of a similar temperature characteristic, as there are no particular limitations. 
     Second Embodiment 
       FIG. 2  shows a structure of a reference current circuit of a second embodiment of the present invention. 
     A reference current circuit  200  includes a temperature-compensating circuit  210 , a voltage follower  220  which receives output from the temperature-compensating circuit  210  as input, and the current source circuit  120  which receives output from the voltage follower  220  as input. 
     The temperature-compensating circuit  210  is composed of a transistor Q 4  and a resistor R 4 . The transistor Q 4  receives input of the reference voltage V BG  from an emitter thereof, and a collector and a base of the transistor Q 4  are connected to each other. The resistor R 4  is inserted in a wiring connecting a power supply terminal and the collector of the transistor Q 4 . 
     The voltage follower  220  is composed of an amplifier circuit OP 20  which includes an inverting input terminal, a non-inverting input terminal, and an output terminal. The collector and the base of the transistor Q 4  are connected to the non-inverting input terminal of the amplifier circuit OP 20 , and the output terminal and the inverting input terminal of the amplifier circuit OP 20  are connected to each other. 
     Since the structures of the current source circuit  120  and the reference voltage circuit  500  are the same as those described in the prior art, their descriptions are omitted here. 
     Next, with regard to the above-structured reference current circuit  200  of the second embodiment, an outline of the principle which generates a reference current with low temperature-dependence in a case where a temperature coefficient of resistance is substantially 0. 
     An output voltage V TC  of the temperature-compensating circuit  210  can be expressed as follows:
 
 V   TC   =V   BG   +V   BE4   (2.1)
 
     Accordingly, an output voltage V out2  of the voltage follower  220  can be expressed as follows:
 
 V   out2   =V   BG   +V   BE4   (2.2)
 
     Also, for the current source circuit  120 , the following equation holds, as is the case with the first embodiment.
 
 V   out2   =R   3   ·I   ref2   +V   BE1   (2.3)
 
     Based on the equations (2.2) and (2.3), the following equation can be obtained.
 
 R   3   ·I   ref2   +V   BE1   =V   BG   +V   BE4 
 
     Thus, the following equation can be derived. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                   = 
                   
                     
                       
                         V 
                         BG 
                       
                       + 
                       
                         V 
                         
                           BE 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                       
                       - 
                       
                         V 
                         
                           BE 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   2.4 
                   ) 
                 
               
             
           
         
       
     
     Here, when V BE4  and V BE1  are equal or substantially equal, the following equation holds. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                   = 
                   
                     
                       V 
                       BG 
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   2.5 
                   ) 
                 
               
             
           
         
       
     
     Here, V BG  is a reference voltage which is independent of the temperature T and the power supply voltage Vdd; and R 3  is a resistance whose temperature coefficient is substantially 0. Accordingly, when the temperature is T, the following equations hold. 
     
       
         
           
             
               
                 
                   ∂ 
                   
                     V 
                     BG 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
             , 
             
                 
             
             ⁢ 
             
               
                 
                   ∂ 
                   
                     R 
                     3 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
           
         
       
     
     Partially differentiating both sides of the equation (2.5) by the temperature T yields the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         I 
                         
                           ref 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     
                       ∂ 
                       T 
                     
                   
                   = 
                   
                     
                       
                         
                           1 
                           
                             R 
                             3 
                           
                         
                         · 
                         
                           
                             ∂ 
                             
                               V 
                               BG 
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                       
                       - 
                       
                         
                           
                             V 
                             BG 
                           
                           
                             R 
                             3 
                             2 
                           
                         
                         · 
                         
                           
                             ∂ 
                             
                               R 
                               3 
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                       
                     
                     = 
                     0 
                   
                 
               
               
                 
                   ( 
                   2.6 
                   ) 
                 
               
             
           
         
       
     
     The equation (2.6) indicates that a reference current I ref2  is independent of the temperature T. 
     Consequently, the structure shown in  FIG. 2  is capable of reducing temperature dependence of the reference current I ref2 . 
     As described above, the temperature characteristic of the transistor Q 1  can be cancelled by inserting, on the temperature-compensating circuit  210 , the transistor Q 4  whose temperature characteristic is the same as that of the transistor Q 1 . In other words, the temperature dependence of the reference current I ref2  can be eliminated or reduced. 
     Note that while the transistors Q 1  and Q 2  are used in the current source circuit  120  of the second embodiment, the MOS transistors M 1  and M 2  can be used as with the current source circuit  121  shown in  FIG. 6 . In this case, it is preferable that MOS transistors with the same temperature characteristic as the MOS transistor M 1  be used in place of the transistor Q 4 . 
     Also, while the resistor R 4  is used in the temperature-compensating circuit  210 , a PNP bipolar transistor whose base receives input of a bias voltage VBIAS can be used alternatively, as is the case with the temperature-compensating circuit  211  shown in  FIG. 7 . Additionally, as shown in  FIG. 8 , the temperature-compensating circuit  210  can be replaced with a temperature-compensating circuit  212  which employs MOS transistors M 3  and M 4 . 
     Third Embodiment 
       FIG. 3  shows a structure of a reference current circuit of a third embodiment of the present invention. 
     A reference current circuit  300  includes the temperature-compensating circuit  210 , an inverting amplifier circuit  320 , an inverting amplifier circuit  330 , and the current source circuit  120 . The inverting amplifier circuit  320  receives output from the temperature-compensating circuit  210  as input; the inverting amplifier circuit  330  receives output from the inverting amplifier circuit  320  as input; and the current source circuit  120  receives output from the inverting amplifier circuit  320  as input. 
     The temperature-compensating circuit  210  is composed of the transistor Q 4  and the resistor R 4 . The emitter of the transistor Q 4  is grounded, and the collector and the base of the transistor Q 4  are connected to each other. The resistor R 4  is inserted in a wiring connecting a power supply terminal and the collector of the transistor Q 4 . 
     The inverting amplifier circuit  320  is composed of an amplifier circuit OP 30 , a resistor R 6 , and a resistor R 7 . The amplifier circuit OP 30  has an inverting input terminal, a non-inverting input terminal, and an output terminal, and the non-inverting input terminal of the amplifier circuit OP 30  is connected to a ground terminal; the resistor R 6  is inserted in a wiring connecting the inverting input terminal of the amplifier circuit OP 30  and the output terminal of the temperature-compensating circuit  210 ; and the resistor R 7  is inserted in a wiring connecting the output terminal and the inverting input terminal of the amplifier circuit OP 30 . 
     The inverting amplifier circuit  330  is composed of an amplifier circuit OP 31 , a resistor R 8 , and a resistor R 9 . The amplifier circuit OP 31  has an inverting input terminal, a non-inverting input terminal, and an output terminal, and the non-inverting input terminal of the amplifier circuit OP 31  receives input of the reference voltage V BG ; the resistor R 8  is inserted in a wiring connecting the inverting input terminal of the amplifier circuit OP 31  and the output terminal of the amplifier circuit OP 30 ; and the resistor R 9  is inserted in a wiring connecting the output terminal and the inverting input terminal of the amplifier circuit OP 31 . 
     Since the structures of the current source circuit  120  and the reference voltage circuit  500  are the same as those described in the prior art, their descriptions are omitted here. 
     Next, with regard to the above-structured reference current circuit  300  of the third embodiment, an outline of the principle which generates a reference current with low temperature dependence in the case where a temperature coefficient of resistance is substantially 0. 
     Output of the temperature-compensating circuit  210  is a voltage V BE4 , a base-emitter voltage of the transistor Q 4 . 
     Next, assume that an output voltage of the inverting amplifier circuit  320  is V 320 , the following equation holds. 
     
       
         
           
             
               
                 
                   
                     V 
                     320 
                   
                   = 
                   
                     
                       - 
                       
                         
                           R 
                           7 
                         
                         
                           R 
                           6 
                         
                       
                     
                     · 
                     
                       V 
                       
                         BE 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                     
                   
                 
               
               
                 
                   ( 
                   3.1 
                   ) 
                 
               
             
           
         
       
     
     Furthermore, an output voltage V out3  of the inverting amplifier circuit  330  can be expressed as follows: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           V 
                           
                             out 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                         = 
                         
                           
                             
                               
                                 
                                   R 
                                   8 
                                 
                                 + 
                                 
                                   R 
                                   9 
                                 
                               
                               
                                 R 
                                 8 
                               
                             
                             · 
                             
                               V 
                               BG 
                             
                           
                           - 
                           
                             
                               
                                 R 
                                 9 
                               
                               
                                 R 
                                 8 
                               
                             
                             · 
                             
                               V 
                               320 
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               
                                 
                                   R 
                                   8 
                                 
                                 + 
                                 
                                   R 
                                   9 
                                 
                               
                               
                                 R 
                                 8 
                               
                             
                             · 
                             
                               V 
                               BG 
                             
                           
                           - 
                           
                             
                               
                                 R 
                                 9 
                               
                               
                                 R 
                                 8 
                               
                             
                             · 
                             
                               ( 
                               
                                 
                                   - 
                                   
                                     
                                       R 
                                       7 
                                     
                                     
                                       R 
                                       6 
                                     
                                   
                                 
                                 · 
                                 
                                   V 
                                   
                                     BE 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     4 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3.2 
                   ) 
                 
               
             
           
         
       
     
     Here, if R=R 6 =R 7 =R 8 =R 9 , V out3  can be expressed as:
 
 V   out3 =2 ·V   BG   +V   BE4   (3.3)
 
     Also, for the current source circuit  120 , the following equation can be found, as is the case with the first embodiment.
 
 V   out3   =R   3   ·I   ref3   +V   BE1   (3.4)
 
     Based on the equations (3.4) and (3.5), the following equation can be found.
 
 R   3   ·I   ref3   +V   BE1 =2 ·V   BG   +V   BE4 
 
     Hence, the equation can be rearranged as follows: 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       3 
                     
                   
                   = 
                   
                     
                       
                         2 
                         · 
                         
                           V 
                           BG 
                         
                       
                       + 
                       
                         V 
                         
                           BE 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                       
                       - 
                       
                         V 
                         
                           BE 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   3.5 
                   ) 
                 
               
             
           
         
       
     
     Here, when V BE4  and V BE1  are equal or substantially equal, the following equation can be derived. 
     
       
         
           
             
               
                 
                   
                     I 
                     
                       ref 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       3 
                     
                   
                   = 
                   
                     
                       2 
                       · 
                       
                         V 
                         BG 
                       
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   ( 
                   3.6 
                   ) 
                 
               
             
           
         
       
     
     Here, V BG  is a reference voltage which is independent of the temperature T and the power supply voltage Vdd; and R 3  is a resistance with a temperature coefficient of substantially 0. Accordingly, when the temperature is T, the following equations hold. 
     
       
         
           
             
               
                 
                   ∂ 
                   
                     V 
                     BG 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
             , 
             
                 
             
             ⁢ 
             
               
                 
                   ∂ 
                   
                     R 
                     3 
                   
                 
                 
                   ∂ 
                   T 
                 
               
               = 
               0 
             
           
         
       
     
     Partially differentiating both sides of the equation (3.6) by the temperature T yields the following: 
     
       
         
           
             
               
                 
                   
                     
                       ∂ 
                       
                         I 
                         
                           ref 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           3 
                         
                       
                     
                     
                       ∂ 
                       T 
                     
                   
                   = 
                   
                     
                       
                         
                           2 
                           
                             R 
                             3 
                           
                         
                         · 
                         
                           
                             ∂ 
                             
                               V 
                               BG 
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                       
                       - 
                       
                         
                           
                             2 
                             · 
                             
                               V 
                               BG 
                             
                           
                           
                             R 
                             3 
                             2 
                           
                         
                         · 
                         
                           
                             ∂ 
                             
                               R 
                               3 
                             
                           
                           
                             ∂ 
                             T 
                           
                         
                       
                     
                     = 
                     0 
                   
                 
               
               
                 
                   ( 
                   3.7 
                   ) 
                 
               
             
           
         
       
     
     The equation (3.7) indicates that a reference current I ref3  is independent of the temperature T. 
     Consequently, the structure shown in  FIG. 3  is capable of reducing temperature dependence of the reference current I ref3 . 
     As described above, the temperature characteristic of the transistor Q 1  can be cancelled by using, on the temperature-compensating circuit  210 , the transistor Q 4  whose temperature characteristic is the same as that of the transistor Q 1 . In other words, the temperature dependence of the reference current I ref3  can be eliminated or reduced. 
     Note that while in the above description, the resistance values are assumed to be R=R 6 =R 7 =R 8 =R 9 , the resistance values can be R 6 =R 9  and R 7 =R 8 . 
     Also, while the transistors Q 1  and Q 2  are used in the current source circuit  120  of the third embodiment, the MOS transistors M 1  and M 2  can be used as is the case with the current source circuit  121  shown in  FIG. 6 . In this case, it is preferable that MOS transistors with the same temperature characteristic as the MOS transistor M 1  be used in place of the transistor Q 4 . 
     In addition, while the resistor R 4  is used in the temperature-compensating circuit  210 , a PNP bipolar transistor whose base receives input of a bias voltage VBIAS can be used alternatively, as is the case with the temperature-compensating circuit  211  shown in  FIG. 7 . Additionally, as shown in  FIG. 8 , the temperature-compensating circuit  210  can be replaced with the temperature-compensating circuit  212  which employs the MOS transistors M 3  and M 4 . 
     Also, a resistor can be connected between the non-inverting input terminal of the inverting amplifier circuit  320  and the ground terminal. 
     While the embodiments of the present invention have been described in detail as above, the present invention is not limited to the above-described embodiments. The inverting amplifier circuit  110  of the first embodiment, the temperature-compensating circuit  210  and the voltage follower  220  of the second embodiment, and the temperature-compensating circuit  210  and the inverting amplifier circuits  320  and  330  of the third embodiment, respectively, can be considered to be a voltage generating circuit whose output voltage V out  satisfies a relational expression “V out =α×V BG +V BE ”. Any voltage generating circuit which satisfies the above relational expression can achieve, regardless of the circuit structure, effects equivalent to those achieved by the above-mentioned embodiments. It should be noted here that α is an arbitrary coefficient which has an extremely low temperature dependence, and V BE  is a voltage across terminals of a semiconductor device which is equivalent, in temperature characteristic, to a semiconductor device included in the current source circuit  120 . Here, the semiconductor device can be a diode-connected bipolar transistor, a P-N junction diode, or a diode-connected MOS transistor. Also, the voltage across the terminals can be, for instance in a case of a bipolar transistor, a base-emitter voltage (this can also be referred to as a collector-emitter voltage due to the diode-connection). 
     Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.

Technology Classification (CPC): 6