# Patent

## Title
Constant voltage circuit

## Abstract

An inverse temperature characteristic generating circuit decreases an output voltage Vout by a voltage VGS, and supplies the resultant voltage as a voltage VA to a temperature characteristic generating circuit. The temperature characteristic generating circuit includes a differential amplification circuit that receives a terminal voltage VAP between resistances R22 and R23 and an emitter voltage VAM of a bipolar transistor T21, and outputs a control signal VC. When the terminal voltages VAP and VAM are equal to each other, an operation of a circuit is stable. The temperature characteristic of the voltage VA during the stable operation, and the temperature characteristic of the voltage VGS are inverse to each other and therefore cancel each other, so that the constant voltage Vout independent of temperature is output. In addition, the output terminal is not connected via a resistance to a ground, so that low current consumption can be easily achieved.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-291170 filed in Japan on Nov. 8, 2007, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a constant voltage circuit for generating a constant voltage, and more particularly, to a technique for a circuit capable of generating a constant voltage independent of temperature.
2. Description of the Related Art
FIG. 11 is a diagram showing a configuration of a conventional constant voltage circuit capable of generating a constant voltage independent of temperature. A series circuit of a constant current source 54 and a reference voltage circuit 51, the source and drain of an NPN transistor 53, the power source and ground ends of a differential amplification circuit 52, and a series circuit of resistances R51 and R52, are each connected between an output terminal 50 for outputting an constant voltage Vout and a ground. The constant current source 54 applies a constant current to the reference voltage circuit 51, which in turn generates a predetermined reference voltage VR5 independent of temperature. The reference voltage VR5 is input to the inverting input of the differential amplification circuit 52. The series circuit of the resistances R51 and R52 is a resistor-divider circuit for dividing the constant voltage Vout to generate a fractional voltage VM. The fractional voltage VM is input to the non-inverting input of the differential amplification circuit 52. The differential amplification circuit 52 amplifies a voltage difference between the input reference voltage VR5 and the fractional voltage VM and outputs the result to the gate of the NPN transistor 53.
In the circuit of FIG. 11, when the constant voltage Vout increases, the fractional voltage VM may become higher than the reference voltage VR5, so that the output level of the differential amplification circuit 52 increases. Therefore, the NPN transistor 53 increases a current that flows from the output terminal 50 to the ground so as to decrease the constant voltage Vout. When the constant voltage Vout decreases, the fractional voltage VM may become lower than the reference voltage VR5, so that the output level of the differential amplification circuit 52 decreases. Therefore, the NPN transistor 53 decreases a current flowing from the output terminal 50 to the ground so as to increase the constant voltage Vout. Specifically, the constant voltage Vout is controlled so that the reference voltage VR5 is equal to the fractional voltage VM, thereby making it possible to cause the constant voltage Vout to be independent of temperature and proportional to the predetermined reference voltage VR5 that is independent of temperature.
(Patent Document 1) Japanese Unexamined Patent Application Publication No. H08-185232
However, in the circuit of FIG. 11, the temperature-independent reference voltage VR5 has a fixed voltage value for each set of manufacturing conditions, i.e., the voltage value cannot be freely set. Therefore, in order to allow the constant voltage Vout to be freely set, the series circuit of the resistances R51 and R52 for generating the fractional voltage VM that is input to one of the inputs of the differential amplification circuit 52, needs to be provided as a circuit having a current path different from that of the constant current source 54 that supplies a current to the reference voltage circuit 51 that generates the reference voltage VR5. Therefore, when the current consumption of the constant voltage circuit is reduced, the current consumption of the three circuits, i.e., the constant current source 54, the series circuit of the resistances R51 and R52, and the differential amplification circuit 52, needs to be reduced, and therefore, it is difficult to design low current consumption. Particularly, the current consumption of the series circuit of the resistances R51 and R52 is large since it is connected between the output terminal 50 of the constant voltage Vout and the ground. Therefore, an additional circuit configuration is required to design low current consumption, resulting in a non-negligible influence on manufacturing cost. Also, the circuit scale of the constant current source 54 or the reference voltage circuit 51 needs to be increased so as to cause the circuit reference voltage VR5 to be independent of temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a constant voltage circuit for generating a constant voltage independent of temperature that can be easily designed to have low current consumption while suppressing an increase in circuit scale.
According to a first aspect of the present invention, a constant voltage circuit is provided for outputting a constant voltage from an output terminal thereof. The constant voltage circuit comprises an output voltage control circuit for receiving a control signal and controlling a voltage of the output terminal in accordance with the control signal, a temperature characteristic generating circuit for generating the control signal, and an inverse temperature characteristic generating circuit for decreasing the voltage of the output terminal by a predetermined voltage and supplying the resultant voltage to the temperature characteristic generating circuit. The temperature characteristic generating circuit includes a first and a second diode property element having a first terminal and a second terminal, where a forward current flows from the first terminal to the second terminal, and the second terminal is grounded, a first resistance provided between a voltage input end via which the voltage supplied from the inverse temperature characteristic generating circuit is input thereto, and the first terminal of the first diode property element, a second and a third resistance provided the voltage input end and the first terminal of the second diode property element, where the second and third resistances are connected in series, and a differential amplification circuit for receiving a first terminal voltage between the second and third resistances, and a second terminal voltage of the first terminal of the first diode property element, and outputting the control signal. The temperature characteristic generating circuit has predetermined temperature characteristic with respect to the supplied voltage under conditions such that the first and second terminal voltages are equal to each other. The inverse temperature characteristic generating circuit has inverse temperature characteristic that cancel the predetermined temperature characteristic possessed by the temperature characteristic generating circuit with respect to the predetermined voltage by which the voltage of the output terminal is decreased.
In the first aspect of the present invention, the inverse temperature characteristic generating circuit decreases the voltage of the output terminal by a predetermined voltage and supplies the resultant voltage to the temperature characteristic generating circuit. The temperature characteristic generating circuit receives the voltage supplied from the inverse temperature characteristic generating circuit and outputs a control signal to the output voltage control circuit. The temperature characteristic generating circuit includes a configuration in which the first resistance and the first diode property element are connected and a configuration in which the second and third resistances and the second diode property element are connected, between the voltage input end to which the supplied voltage is input and the ground. The constant voltage circuit further includes the differential amplification circuit that receives the first terminal voltage between the second and third resistances, and the second terminal voltage between the first resistance and the first diode property element, and outputs a control signal. The inverse temperature characteristic generating circuit, the temperature characteristic generating circuit, and the output voltage control circuit constitute a feedback loop. When the first and second terminal voltages are equal to each other, an operation of the circuit is stable. Here, the temperature characteristic of the supplied voltage that satisfies conditions such that the first and second terminal voltages are equal to each other is inverse to the temperature characteristic of the predetermined voltage by which the supplied voltage is decreased, so that both the temperature characteristics are canceled. Therefore, a constant voltage independent of temperature is output from the output terminal. In addition, as is different from the conventional art, an output terminal and a ground are not connected via a resistance. Therefore, as compared to the conventional art, current consumption is reduced. Thus, it is easy to design a circuit with low current consumption. Also, it is not necessary to add a circuit that eliminates temperature dependency, as is different from the conventional art, so that the circuit scale can be reduced as compared to the conventional art.
According to a second aspect of the present invention, a constant voltage circuit is provided for outputting a constant voltage from an output terminal thereof. The constant voltage circuit comprises a temperature characteristic generating circuit for controlling a voltage of the output terminal, and an inverse temperature characteristic generating circuit for decreasing the voltage of the output terminal by a predetermined voltage and supplying the resultant voltage to the temperature characteristic generating circuit. The temperature characteristic generating circuit includes a first and a second diode property element having a first terminal and a second terminal, wherein a forward current flows from the first terminal to the second terminal, and the second terminal is grounded, a first resistance provided between a voltage input end via which the voltage supplied from the inverse temperature characteristic generating circuit is input thereto, and the first terminal of the first diode property element, a second and a third resistance provided the voltage input end and the first terminal of the second diode property element, wherein the second and third resistances are connected in series, and a differential amplification circuit for receiving a first terminal voltage between the second and third resistances, and a second terminal voltage of the first terminal of the first diode property element, wherein the differential amplification circuit has an output connected to the output terminal. The temperature characteristic generating circuit has predetermined temperature characteristic with respect to the supplied voltage under conditions such that the first and second terminal voltages are equal to each other. The inverse temperature characteristic generating circuit has inverse temperature characteristic that cancel the predetermined temperature characteristic possessed by the temperature characteristic generating circuit with respect to the predetermined voltage by which the voltage of the output terminal is decreased.
In the second aspect of the present invention, the inverse temperature characteristic generating circuit decreases the voltage of the output terminal by a predetermined voltage and supplies the resultant voltage to the temperature characteristic generating circuit. The temperature characteristic generating circuit receives the voltage supplied from the inverse temperature characteristic generating circuit and controls the voltage of the output terminal. The temperature characteristic generating circuit includes a configuration in which the first resistance and the first diode property element are connected and a configuration in which the second and third resistances and the second diode property element are connected, between the voltage input end to which the supplied voltage is input and the ground. The constant voltage circuit further includes the differential amplification circuit that receives the first terminal voltage between the second and third resistances, and the second terminal voltage between the first resistance and the first diode property element, and has the output connected to the output terminal. The inverse temperature characteristic generating circuit and the temperature characteristic generating circuit constitute a feedback loop. When the first and second terminal voltages are equal to each other, an operation of the circuit is stable. Here, the temperature characteristic of the supplied voltage that satisfies conditions such that the first and second terminal voltages are equal to each other is inverse to the temperature characteristic of the predetermined voltage by which the supplied voltage is decreased, so that both the temperature characteristics are canceled. Therefore, a constant voltage independent of temperature is output from the output terminal. In addition, the constant voltage independent of temperature can be set to have an arbitrary voltage value, but not a voltage value fixed for each set of manufacturing conditions.
According to the present invention, a constant voltage circuit capable of generating a constant voltage independent of temperature can be easily designed to have low current consumption and a small circuit scale.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a configuration of a constant voltage circuit according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a specific exemplary circuit configuration of the constant voltage circuit of FIG. 1.
FIG. 3A is a graph showing a relationship between temperature and an output constant voltage Vout. FIG. 3B is a graph showing a relationship between a supplied voltage VA and its temperature dependency during a stable operation.
FIGS. 4A to 4C are diagrams showing other specific exemplary circuit configurations of the constant voltage circuit of FIG. 1.
FIG. 5 is a diagram showing another specific exemplary circuit configurations of the constant voltage circuit of FIG. 1.
FIGS. 6A to 6C are diagrams showing other specific exemplary circuit configurations of the constant voltage circuit of FIG. 1.
FIG. 7 is a block diagram showing a configuration of a constant voltage circuit according to a second embodiment of the present invention.
FIG. 8 is a diagram showing a specific exemplary circuit configuration of the constant voltage circuit of FIG. 7.
FIGS. 9A to 9C are diagrams showing other specific exemplary circuit configurations of the constant voltage circuit of FIG. 7.
FIG. 10 is a diagram showing another specific exemplary circuit configurations of the constant voltage circuit of FIG. 7.
FIG. 11 is a diagram showing a configuration of a conventional constant voltage circuit.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that like parts including terminals, etc. and their voltages are indicated by the same reference symbols throughout the specification unless otherwise specified.
First Embodiment
FIG. 1 is a block diagram showing a configuration of a constant voltage circuit according to a first embodiment of the present invention. The constant voltage circuit of FIG. 1 receives an input voltage Vin at an input terminal 10a, and outputs a constant voltage Vout from an output terminal 10b. The input terminal 10a and the output terminal 10b are connected to each other via a resistance R. A series circuit of a temperature characteristic generating circuit 11 and an inverse temperature characteristic generating circuit 12, and an output voltage control circuit 13 are each connected between the output terminal 10b and a ground. A voltage output end of the inverse temperature characteristic generating circuit 12 is connected to a voltage input end of the temperature characteristic generating circuit 11 at a terminal VA. The constant voltage Vout is input as a power supply voltage to the output voltage control circuit 13.
The inverse temperature characteristic generating circuit 12 generates a potential difference (Vout−VA) between the constant voltage Vout and a voltage VA, decreases the constant voltage Vout by the voltage (Vout−VA), and supplies the voltage VA via the voltage output end to the temperature characteristic generating circuit 11. The temperature characteristic generating circuit 11 receives the voltage VA supplied from the inverse temperature characteristic generating circuit 12 at the voltage input end, generates a control signal VC based on the supplied voltage VA, and outputs the control signal VC to the output voltage control circuit 13. The output voltage control circuit 13 receives the control signal VC and controls the voltage of the output terminal 10b in accordance with the control signal VC.
FIG. 2 is a diagram showing a specific exemplary circuit configuration of the constant voltage circuit of FIG. 1.
In FIG. 2, the temperature characteristic generating circuit 11 comprises PNP bipolar transistors T21 and T22 that have bases and collectors are grounded. The PNP bipolar transistors T21 and T22 serve as first and second diode property elements in the present invention, respectively. A first the resistance R21 is connected between the emitter of the PNP bipolar transistor T21 and the voltage input end to which the voltage VA is input. Second and third resistances R22 and R23 are connected in series between the emitter of the PNP bipolar transistor T22 and the voltage input end. The temperature characteristic generating circuit 11 further comprises a differential amplification circuit 211 that receives a first terminal voltage VAP of a terminal between the second and third resistances R22 and R23 and a second terminal voltage VAM of the emitter of the PNP bipolar transistor T21. The differential amplification circuit 211 receives the voltage Vout as a power supply voltage, the first terminal voltage VAP at a non-inverting input terminal thereof, and the second terminal voltage VAM at an inverting input terminal thereof. The differential amplification circuit 211 outputs the control signal VC.
Also, the inverse temperature characteristic generating circuit 12 comprises a PNP transistor M21 that has a source connected to the output terminal 10b via which the constant voltage Vout is supplied thereto, and a gate and a drain that are connected together and connected to the voltage output end. Specifically, the inverse temperature characteristic generating circuit 12 decreases the constant voltage Vout by a gate-source voltage VGS of the PNP transistor M21 and outputs the result as the supplied voltage VA. The output voltage control circuit 13 has an NPN transistor M22 that has a drain connected to the output terminal 10b via which the constant voltage Vout is supplied thereto, a source that is grounded, and a gate at which the control signal VC is received.
In the configuration of FIG. 2, the inverse temperature characteristic generating circuit 12 that receives the constant voltage Vout and outputs the voltage VA, the temperature characteristic generating circuit 11 that receives the voltage VA and outputs the control signal VC, and the output voltage control circuit 13 that receives the control signal VC and determines the voltage level of the constant voltage Vout constitute a feedback loop. Thereby, the first terminal voltage VAP and the second terminal voltage VAM are caused to have the same voltage level, so that the constant voltage Vout and the voltage VA each become constant, resulting in a stable operation.
When a high input voltage VIN is input via the input terminal 10a, the constant voltage Vout and the voltage VA become higher than a voltage level at which an operation is stable, so that the first terminal voltage VAP becomes higher than the second terminal voltage VAM. In this case, the voltage level of the control signal VC output from the differential amplification circuit 211 becomes high, so that the NPN transistor M22 increases a current flowing from the output terminal 10b to the ground so as to decrease the constant voltage Vout. As a result, the voltage VA also decreases.
On the other hand, when a low input voltage VIN is input via the input terminal 10a, the constant voltage Vout and the voltage VA becomes lower than a voltage level at which an operation is stable, so that the first terminal voltage VAP becomes lower than the second terminal voltage VAM. In this case, the voltage level of the control signal VC output from the differential amplification circuit 211 becomes low, so that the NPN transistor M22 decreases a current flowing from the output terminal 10b to the ground so as to increase the constant voltage Vout. As a result, the voltage VA also increases.
In other words, the constant voltage Vout is controlled by the output voltage control circuit 13 so that the voltage VA supplied from the inverse temperature characteristic generating circuit 12 to the temperature characteristic generating circuit 11 becomes the voltage level at which an operation is stable.
Here, the inverse temperature characteristic generating circuit 12 has temperature characteristic with respect to the predetermined voltage VGS that decreases the constant voltage Vout. Specifically, when temperature is high, the predetermined voltage VGS is low. When temperature is low, the predetermined voltage VGS is high. Thus, the inverse temperature characteristic generating circuit 12 has negative temperature characteristic.
On the other hand, the temperature characteristic generating circuit 11 has predetermined temperature characteristic with respect to the supplied voltage VA that satisfies conditions such that the first terminal voltage VAP is equal to the second terminal voltage VAM. In other words, the level of the supplied voltage VA when a circuit operation is stable (stable operation) varies depending on temperature. Here, it is assumed that when temperature is high, the supplied voltage VA during the stable operation is high, and when temperature is low, the supplied voltage VA during the stable operation is low (i.e., positive temperature characteristic). This temperature characteristic can be achieved by appropriately setting circuit parameters of the temperature characteristic generating circuit 11. The setting of the circuit parameters will be described below.
It is also assumed in this embodiment that the negative temperature characteristic possessed by the inverse temperature characteristic generating circuit 12 are arranged to cancel the positive temperature characteristic possessed by the temperature characteristic generating circuit 11. Specifically, when temperature is high, the supplied voltage VA during the stable operation is high. In this case, the voltage VGS that decreases the constant voltage Vout is low. Therefore, the changes cancel each other, so that the controlled constant voltage Vout does not change. On the other hand, when temperature is low, the supplied voltage VA during the stable operation is low. In this case, the voltage VGS that decreases the constant voltage Vout is high. Therefore, these changes cancel each other, so that the controlled constant voltage Vout does not change. Thus, as shown in FIG. 3A, the positive temperature dependency of the voltage VA and the negative temperature dependency of the voltage VGS cancel each other, so that the constant voltage Vout does not have temperature dependency. Thus, according to this embodiment, it is possible to achieve a constant voltage circuit that generates a constant voltage independent of temperature.
Also, the circuit configuration of FIG. 2 does not have a configuration in which an output terminal of a constant voltage is connected to a ground via a resistance, as is different from the conventional art. Therefore, as compared to the conventional art, current consumption is reduced, i.e., it is easy to design a circuit with low current consumption. Also, it is not necessary to add a circuit that eliminates temperature dependency, as is different from the conventional art, so that the circuit scale can be reduced as compared to the conventional art.
Here, a method for setting circuit parameters of the temperature characteristic generating circuit 11 so that the positive temperature characteristic of the temperature characteristic generating circuit 11 are canceled by the negative temperature characteristic of the inverse temperature characteristic generating circuit 12, will be described using the following expressions.
The constant voltage Vout is represented by:




  
    
      
        
          V
          out
        
        =
        
          
            
              
                
                  R
                  2
                
                +
                
                  R
                  3
                
              
              
                R
                3
              
            
            ⁢
            Δ
            ⁢
            
              
            
            ⁢
            V
          
          +
          
            V
            
              BE
              ⁢
              
                
              
              ⁢
              2
            
          
          +
          
            V
            GS
          
        
      
    
    
      
        (
        1
        )
      
    
  




where ΔV represents a potential difference between the first terminal voltage VAP and the emitter voltage of the PNP bipolar transistor T22, A1 represents the area of the emitter of the PNP bipolar transistor T21, VBE1 represents the base-emitter voltage of the PNP bipolar transistor T21, A2 represents the area of the emitter of the PNP bipolar transistor T22, VBE2 represents the base-emitter voltage of the PNP bipolar transistor T22, and R1, R2 and R3 represent the resistance values of the first to third resistances R21, R22 and R23, respectively.

The temperature dependency of the constant voltage Vout is represented by differentiating expression (1) with respect to temperature T.




  
    
      
        
          
            ∂
            
              V
              out
            
          
          
            ∂
            T
          
        
        =
        
          
            
              
                
                  R
                  2
                
                +
                
                  R
                  3
                
              
              
                R
                3
              
            
            ⁢
            
              
                
                  ∂
                  Δ
                
                ⁢
                
                  
                
                ⁢
                V
              
              
                ∂
                T
              
            
          
          +
          
            
              ∂
              
                V
                
                  BE
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              ∂
              T
            
          
          +
          
            
              ∂
              
                V
                GS
              
            
            
              ∂
              T
            
          
        
      
    
    
      
        (
        2
        )
      
    
  




Note that R1, R2 and R3 in expression (2) can be assumed to satisfy the following.




  
    
      
        
          
            ∂
            
              R
              1
            
          
          
            ∂
            T
          
        
        =
        
          
            
              ∂
              
                R
                2
              
            
            
              ∂
              T
            
          
          =
          
            
              
                ∂
                
                  R
                  3
                
              
              
                ∂
                T
              
            
            =
            0
          
        
      
    
    
      
        (
        3
        )
      
    
  




On the right side of expression (2), the sum of the first term and the second term indicates the temperature characteristic of the temperature characteristic generating circuit 11, and the third term indicates the temperature characteristic of the inverse temperature characteristic generating circuit 12. Each term has the following sign.




  
    
      
        
          
            
              
                
                  R
                  2
                
                +
                
                  R
                  3
                
              
              
                R
                3
              
            
            ⁢
            
              
                
                  ∂
                  Δ
                
                ⁢
                
                  
                
                ⁢
                V
              
              
                ∂
                T
              
            
          
          >
          0
        
        ,
        
          
            
              ∂
              
                V
                
                  BE
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            
              ∂
              T
            
          
          <
          0
        
        ,
        
          
            
              ∂
              
                V
                GS
              
            
            
              ∂
              T
            
          
          <
          0
        
      
    
    
      
        (
        4
        )
      
    
  




The sum of the terms on the right side of expression (2) needs to be zero so as to eliminate the temperature dependency of the constant voltage Vout.
ΔV in expressions (1) and (2) is represented by the following.




  
    
      
        
          Δ
          ⁢
          
            
          
          ⁢
          V
        
        =
        
          
            
              V
              
                BE
                ⁢
                
                  
                
                ⁢
                1
              
            
            -
            
              V
              
                BE
                ⁢
                
                  
                
                ⁢
                2
              
            
          
          =
          
            
              kT
              q
            
            ⁢
            ln
            ⁢
            
              
            
            ⁢
            
              
                
                  I
                  1
                
                ⁢
                
                  A
                  1
                
              
              
                
                  I
                  2
                
                ⁢
                
                  A
                  2
                
              
            
          
        
      
    
    
      
        (
        5
        )
      
    
  
  
    
      
        
          
            
              ∂
              Δ
            
            ⁢
            
              
            
            ⁢
            V
          
          
            ∂
            T
          
        
        =
        
          
            k
            q
          
          ⁢
          ln
          ⁢
          
            
              
                I
                1
              
              ⁢
              
                A
                1
              
            
            
              
                I
                2
              
              ⁢
              
                A
                2
              
            
          
        
      
    
    
      
        (
        6
        )
      
    
  




I1 and I2 in expressions (5) and (6) are represented by the following.





  
    
      
        
          I
          1
        
        =
        
          
            1
            
              R
              1
            
          
          ⁢
          
            (
            
              
                V
                ⁢
                
                  
                
                ⁢
                A
              
              -
              
                V
                
                  BE
                  ⁢
                  
                    
                  
                  ⁢
                  1
                
              
            
            )
          
        
      
    
    
      
        (
        7
        )
      
    
  
  
    
      
        
          I
          2
        
        =
        
          
            1
            
              
                R
                2
              
              +
              
                R
                3
              
            
          
          ⁢
          
            (
            
              
                V
                ⁢
                
                  
                
                ⁢
                A
              
              -
              
                V
                
                  BE
                  ⁢
                  
                    
                  
                  ⁢
                  2
                
              
            
            )
          
        
      
    
    
      
        (
        8
        )
      
    
  




Therefore, the circuit parameters of the temperature characteristic generating circuit 11 are set by the second term and the third term of expression (2), and VGS, VBE1, and VBE2, and design values R1, R2, R3, A1, A2, VA, which are known for each set of manufacturing conditions.
Note that, as shown in FIG. 3B, the supplied voltage VA during the stable operation has positive temperature characteristic when it is higher than a predetermined voltage VA0, and negative temperature characteristic when it is lower than the voltage VA0. Under manufacturing conditions that are assumed by the present inventors, the voltage VA has positive temperature characteristic when it is about 1.2 V or more, for example. In this case, the constant voltage Vout output by the constant voltage circuit of this embodiment is 1.2+VGS or more.
The circuit configuration of the constant voltage circuit of this embodiment is not limited to that shown in FIG. 2. Various configurations may be contemplated.
For example, the inverse temperature characteristic generating circuit 12 may include a plurality of PNP transistors each of which has a gate and a drain connected together as with the PNP transistor M21 and which are connected in series, so that the constant voltage Vout may be decreased by a voltage corresponding to the total sum of the gate-source voltages of the PNP transistors. Alternatively, a resistance may be connected in series to the PNP transistor M21 so as to decrease the constant voltage Vout.
Also, the PNP bipolar transistors T21 and T22 of the temperature characteristic generating circuit 11 may be replaced with another kind of elements. For example, NPN bipolar transistors T23 and T24 are provided in a circuit configuration of FIG. 4A. PNP transistors M23 and M24 are provided in a circuit configuration of FIG. 4B. NPN transistors M25 and M26 are provided in a circuit configuration of FIG. 4C. Diodes D21 and D22 are provided in a circuit configuration of FIG. 5. With these circuit configurations, an operation similar to that of this embodiment can be achieved. Specifically, any element that has a diode property that allows a forward current to flow from a first terminal thereof to a second terminal thereof can be used instead of the PNP bipolar transistors T21 and T22, where the second terminal is grounded. In the case of the PNP bipolar transistors T21 and T22, the emitter corresponds to the first terminal and the grounded base and collector correspond to the second terminal.
Further, the output voltage control circuit 13 may include an NPN bipolar transistor T25 as shown in FIG. 6A or may include a PNP bipolar transistor T26 or a PNP transistor M26 as shown in FIGS. 6B and 6C. Note that, in the case of FIGS. 6B and 6C, in the differential amplification circuit 211 of the temperature characteristic generating circuit 11, the first terminal voltage VAP is input to the inverting input terminal and the second terminal voltage VAM is input to the non-inverting input terminal.
Also, in the circuit configurations of FIGS. 4A to 4C and FIG. 5, the output voltage control circuit 13 may include an NPN bipolar transistor T25 as shown in FIG. 6A. In the differential amplification circuit 211 of the temperature characteristic generating circuit 11, if the first terminal voltage VAP may be input to the inverting input terminal and the second terminal voltage VAM may be input to the non-inverting input terminal, the output voltage control circuit 13 may include a PNP bipolar transistor T26 or a PNP transistor M26 as shown in FIG. 6B or 6C.
As described above, according to this embodiment, the temperature characteristic of the supplied voltage VA during the stable operation in which the first and second terminal voltages VAP and VAM are equal to each other and the temperature characteristic of the voltage VGS that decreases the constant voltage Vout so as to generate the supplied voltage VA cancel each other, so that a constant voltage circuit capable of generating a constant voltage independent of temperature can be achieved. In addition, the output terminal of a constant voltage is not connected via a resistance to a ground. Therefore, as compared to the conventional art, current consumption is reduced, resulting in a circuit that can be easily designed to have low current consumption. Also, as is different from the conventional art, it is not necessary to add a circuit for eliminating temperature dependency, so that the circuit scale can be made smaller than in the conventional art.
Second Embodiment
FIG. 7 is a block diagram showing a configuration of a constant voltage circuit according to a second embodiment of the present invention. The constant voltage circuit of FIG. 7 outputs a constant voltage VR from an output terminal 30. A series circuit of a temperature characteristic generating circuit 31 and an inverse temperature characteristic generating circuit 32 is connected between the output terminal 30 and a ground. A voltage output end of the inverse temperature characteristic generating circuit 32 is connected to a voltage input end of the temperature characteristic generating circuit 31 at a terminal VA.
The inverse temperature characteristic generating circuit 32 generates a potential difference (VR−VA) between the constant voltage VR and a voltage VA, decreases the constant voltage VR by the voltage (VR−VA), and supplies the voltage VA via the voltage output end to the temperature characteristic generating circuit 31. The temperature characteristic generating circuit 31 receives the voltage VA supplied from the inverse temperature characteristic generating circuit 32 at the voltage input end, generates a voltage based on the supplied voltage VA, and outputs the voltage to the output terminal 30. Thus, the output of the temperature characteristic generating circuit 31 is the constant voltage VR.
FIG. 8 is a diagram showing a specific exemplary circuit configuration of the constant voltage circuit of FIG. 7.
In FIG. 8, the temperature characteristic generating circuit 31 comprises PNP bipolar transistors T41 and T42 that have bases and collectors that are grounded. The PNP bipolar transistors T41 and T42 serve as first and second diode property elements in the present invention, respectively. A first the resistance R41 is connected between the emitter of the PNP bipolar transistor T41 and the voltage input end to which the voltage VA is input. Second and third resistances R42 and R43 are connected in series between the emitter of the PNP bipolar transistor T42 and the voltage input end. The temperature characteristic generating circuit 31 further comprises a differential amplification circuit 411 that receives a first terminal voltage VAP of a terminal between the second and third resistances R42 and R43 and a second terminal voltage VAM of the emitter of the PNP bipolar transistor T41. The differential amplification circuit 411 receives a voltage VD as a power supply voltage, the first terminal voltage VAP at a non-inverting input terminal thereof, and the second terminal voltage VAM at an inverting input terminal thereof. The differential amplification circuit 411 has an output connected to the output terminal 30.
Also, the inverse temperature characteristic generating circuit 32 comprises a PNP transistor M41, having a source connected to the output terminal 30 via which the constant voltage VR is supplied thereto, and a gate and a drain that are connected together to the voltage output end. Thus, the inverse temperature characteristic generating circuit 32 decreases the constant voltage VR by a gate-source voltage VGS of the PNP transistor M41 and outputs the result as the supplied voltage VA.
In the configuration of FIG. 8, the inverse temperature characteristic generating circuit 32 that receives the constant voltage VR and outputs the voltage VA, and the temperature characteristic generating circuit 31 that receives the voltage VA and outputs the constant voltage VR constitute a feedback loop. Thereby, the first terminal voltage VAP and the second terminal voltage VAM are caused to have the same voltage level, so that the constant voltage Vout and the voltage VA each become constant, resulting in a stable operation.
When the power supply voltage VD of the differential amplification circuit 411 is applied, then if the constant voltage VR and the voltage VA become higher than a voltage level at which an operation is stable, the first terminal voltage VAP becomes higher than the second terminal voltage VAM. In this case, the differential amplification circuit 411 decreases the constant voltage VR. As a result, the voltage VA also decreases. On the other hand, when the power supply voltage VD of the differential amplification circuit 411 is applied, then if the constant voltage VR and the voltage VA are lower than the voltage level at which an operation is stable, the first terminal voltage VAP becomes lower than the second terminal voltage VAM. In this case, the differential amplification circuit 411 increases the constant voltage VR. As a result, the voltage VA also increases.
The constant voltage VR is controlled by the temperature characteristic generating circuit 31 so that the voltage VA supplied from the inverse temperature characteristic generating circuit 32 to the temperature characteristic generating circuit 31 becomes the voltage level at which an operation is stable.
Here, the inverse temperature characteristic generating circuit 32 has temperature characteristic with respect to the predetermined voltage VGS that decreases the constant voltage VR. Specifically, when temperature is high, the predetermined voltage VGS is low. When temperature is low, the predetermined voltage VGS is high. Thus, the inverse temperature characteristic generating circuit 32 has negative temperature characteristic.
On the other hand, the temperature characteristic generating circuit 31 has predetermined temperature characteristic with respect to the supplied voltage VA that satisfies conditions such that the first terminal voltage VAP is equal to the second terminal voltage VAM. In other words, the level of the supplied voltage VA when a circuit operation is stable (stable operation) varies depending on temperature. Here, it is assumed that when temperature is high, the supplied voltage VA during the stable operation is high, and when temperature is low, the supplied voltage VA during the stable operation is low (i.e., positive temperature characteristic). This temperature characteristic can be achieved by appropriately setting circuit parameters of the temperature characteristic generating circuit 31. The setting of the circuit parameters may be performed in a manner similar to that described in the first embodiment. Note that the constant voltage Vout in each expression of the first embodiment is replaced with the constant voltage VR.
It is also assumed in this embodiment that the negative temperature characteristic possessed by the inverse temperature characteristic generating circuit 32 are arranged to cancel the positive temperature characteristic possessed by the temperature characteristic generating circuit 31. In other words, when temperature is high, the supplied voltage VA during the stable operation is high. In this case, the voltage VGS that decreases the constant voltage VR is low. Therefore, the changes cancel each other, so that the controlled constant voltage VR does not change. On the other hand, when temperature is low, the supplied voltage VA during the stable operation is low. In this case, the voltage VGS that decreases the constant voltage VR is high. Therefore, these changes cancel each other, so that the controlled constant voltage VR does not change. Thus, the positive temperature dependency of the voltage VA and the negative temperature dependency of the voltage VGS cancel each other, so that the constant voltage VR does not have temperature dependency. Thus, according to this embodiment, it is possible to achieve a constant voltage circuit that generates a constant voltage independent of temperature.
Note that the power supply voltage VD (not the constant voltage VR) is input to the differential amplification circuit 411, so that the constant voltage VR can be freely set within the range of lower than the power supply voltage VD.
The circuit configuration of the constant voltage circuit of this embodiment is not limited to that shown in FIG. 8. Various configurations may be contemplated.
For example, the inverse temperature characteristic generating circuit 32 may include a plurality of PNP transistors each of which has a gate and a drain connected together as with the PNP transistor M41 and which are connected in series, so that the constant voltage VR may be decreased by a voltage corresponding to the total sum of the gate-source voltages of the PNP transistors. Alternatively, a resistance may be connected in series to the PNP transistor M41 so as to decrease the constant voltage VR.
Also, the PNP bipolar transistors T41 and T42 of the temperature characteristic generating circuit 31 may be replaced with another kind of elements. For example, NPN bipolar transistors T43 and T44 are provided in a circuit configuration of FIG. 9A. PNP transistors M42 and M43 are provided in a circuit configuration of FIG. 9B. NPN transistors M44 and M45 are provided in a circuit configuration of FIG. 9C. Diodes D41 and D42 are provided in a circuit configuration of FIG. 10. With these circuit configurations, an operation similar to that of this embodiment can be achieved. Specifically, any element that has a diode property that allows a forward current to flow from a first terminal thereof to a second terminal thereof can be used instead of the PNP bipolar transistors T41 and T42, where the second terminal is grounded. In the case of the PNP bipolar transistors T41 and T42, the emitter corresponds to the first terminal and the grounded base and collector correspond to the second terminal.
As described above, according to this embodiment, the temperature characteristic of the supplied voltage VA during a stable operation in which the first and second terminal voltages VAP and VAM are equal to each other and the temperature characteristic of the voltage VGS that decreases the constant voltage VR so as to generate the supplied voltage VA cancel each other, so that a constant voltage circuit capable of generating a constant voltage independent of temperature can be achieved. In addition, the output terminal of a constant voltage is not connected via a resistance to a ground. Therefore, as compared to the conventional art, current consumption is reduced, resulting in a circuit that can be easily designed to have low current consumption. Also, as is different from the conventional art, it is not necessary to add a circuit for eliminating temperature dependency, so that the circuit scale can be made smaller than in the conventional art. Further, as compared to the first embodiment, the voltage level of a constant voltage can be freely set.
According to the present invention, a constant voltage circuit capable of generating a constant voltage independent of temperature can be easily designed to have low current consumption and a small circuit scale. Therefore, such a constant voltage circuit can be useful for a reduction in power consumption or circuit area of an LSI.

## Claims

1. A constant voltage circuit for outputting a constant voltage from an output terminal thereof, comprising:
an output voltage control circuit for receiving a control signal and controlling a voltage of the output terminal in accordance with the control signal;
a temperature characteristic generating circuit for generating the control signal; and
an inverse temperature characteristic generating circuit for decreasing the voltage of the output terminal by a predetermined voltage and supplying the resultant voltage to the temperature characteristic generating circuit,
wherein the temperature characteristic generating circuit includes:
a first and a second diode property element having a first terminal and a second terminal, wherein a forward current flows from the first terminal to the second terminal, and the second terminal is grounded;
a first resistance provided between a voltage input end via which the voltage supplied from the inverse temperature characteristic generating circuit is input thereto, and the first terminal of the first diode property element;
a second and a third resistance provided the voltage input end and the first terminal of the second diode property element, wherein the second and third resistances are connected in series; and
a differential amplification circuit for receiving a first terminal voltage between the second and third resistances, and a second terminal voltage of the first terminal of the first diode property element, and outputting the control signal,
wherein the temperature characteristic generating circuit has predetermined temperature characteristic with respect to the supplied voltage under conditions such that the first and second terminal voltages are equal to each other, and

the inverse temperature characteristic generating circuit has inverse temperature characteristic that cancel the predetermined temperature characteristic possessed by the temperature characteristic generating circuit with respect to the predetermined voltage by which the voltage of the output terminal is decreased.

2. The constant voltage circuit of claim 1, wherein
the first and second diode property elements are each a PNP bipolar transistor having an emitter as the first terminal and a base and a collector as the second terminal.

3. The constant voltage circuit of claim 1, wherein
the inverse temperature characteristic generating circuit includes a PNP transistor having a source connected to the output terminal, and a gate and a drain connected together to the voltage input end of the temperature characteristic generating circuit.

4. The constant voltage circuit of claim 1, wherein
the output voltage control circuit includes an NPN transistor having a drain connected to the output terminal, a source grounded, and a gate for receiving the control signal.

5. A constant voltage circuit for outputting a constant voltage from an output terminal thereof, comprising:
a temperature characteristic generating circuit for controlling a voltage of the output terminal; and
an inverse temperature characteristic generating circuit for decreasing the voltage of the output terminal by a predetermined voltage and supplying the resultant voltage to the temperature characteristic generating circuit,
wherein the temperature characteristic generating circuit includes:
a first and a second diode property element having a first terminal and a second terminal, wherein a forward current flows from the first terminal to the second terminal, and the second terminal is grounded;
a first resistance provided between a voltage input end via which the voltage supplied from the inverse temperature characteristic generating circuit is input thereto, and the first terminal of the first diode property element;
a second and a third resistance provided the voltage input end and the first terminal of the second diode property element, wherein the second and third resistances are connected in series; and
a differential amplification circuit for receiving a first terminal voltage between the second and third resistances, and a second terminal voltage of the first terminal of the first diode property element, wherein the differential amplification circuit has an output connected to the output terminal,
wherein the temperature characteristic generating circuit has predetermined temperature characteristic with respect to the supplied voltage under conditions such that the first and second terminal voltages are equal to each other, and

the inverse temperature characteristic generating circuit has inverse temperature characteristic that cancel the predetermined temperature characteristic possessed by the temperature characteristic generating circuit with respect to the predetermined voltage by which the voltage of the output terminal is decreased.

6. The constant voltage circuit of claim 5, wherein
the first and second diode property elements are each a PNP bipolar transistor having an emitter as the first terminal and a base and a collector as the second terminal.

7. The constant voltage circuit of claim 5, wherein
the inverse temperature characteristic generating circuit includes a PNP transistor having a source connected to the output terminal, and a gate and a drain connected together to the voltage input end of the temperature characteristic generating circuit.