Abstract:
A temperature detector circuit using a MOS transistor capable of reducing manufacture variation of a mobility and realizing stable output characteristics which are not affected by temperature dependency may be offered. In one example, the temperature detector circuit includes a pair of depression type transistors to output a voltage which is proportional to temperature from a connecting point of a source of a first transistor and a drain of a second transistor. The transistors are the same conducted type of current and are formed in different channel size, which are connected between power supplies in series, and have a configuration in which first transistor&#39;s gate and source are connected each other and a first transistor&#39;s drain is connected with a second power supply and second transistor&#39;s gate and drain are connected each other and a second transistor&#39;s source is connected with a first power supply.

Description:
This application is a Continuation of application Ser. No. 11/487,400, filed Jul. 17, 2006, now U.S. Pat. No. 7,400,208 the application of which is herein incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a temperature detector circuit and an oscillation frequency compensation device using it, and more particularly to a MOS-transistor-based temperature detector circuit which has stable output characteristics and an oscillation frequency compensation device including such temperature detector circuit. 
   2. Discussion of the Background 
     FIG. 1  illustrates an example of a background temperature detector circuit using a bipolar transistor with commonly connected base and collector.  FIG. 2  illustrates an example of a background temperature detector circuit using a Darlington connection of bipolar transistors. 
   The background temperature detector circuit of  FIG. 1  drives the bipolar transistor by a constant current to use a temperature dependency of forward direction voltage for temperature detection. This is of the same kind as a method of using a temperature dependency of forward direction voltage in a so-called PN junction diode. Further, a series connection of two or more of this circuit in  FIG. 1  is also known. 
   In  FIG. 2 , this circuit has a configuration of Darlington connection with two or more bipolar transistors in order to raise its output sensitivity. This circuit realizes a high sensitivity temperature sensor having two or more Darlington connections and a constant current power supply to the sensor. This kind of circuit may be formed on a single substrate by using a CMOS (complementary metal oxide semiconductor) manufacture process. 
     FIG. 3  illustrates an example of a background temperature detector circuit having MOS (metal oxide semiconductor) transistors with commonly connected gate and drain in a state of diode connection. The background temperature detector circuit of  FIG. 3  uses a temperature dependency of a MOS-transistor threshold for temperature detection. The background temperature detection circuit drives the MOS transistors by a constant current and uses a voltage between the gate and a source for temperature detection. 
   The temperature dependency of voltage between a gate and a source of a MOS transistor having diode connection is known to change with values of the driving constant current. Specifically, the temperature dependency of threshold is dominantly effective in a minute current domain, resulting in a negative temperature inclination of voltage between the gate and the source. However, the temperature dependency of electron mobility is dominantly effective in a domain above a certain current, resulting in a positive temperature inclination of the voltage. 
   As illustrated in  FIG. 3 , the background temperature detection circuit includes a temperature detection section  81 , a constant voltage generating section  82 , a constant current circuit  832 , and a P-type MOS transistor  831 . In the temperature detection section  81 , a MOS transistor  811  has the diode connection and is driven in a minute current domain to make the temperature dependency of threshold dominantly effective. To increase output sensitivity, the temperature detection section  81  is provided with a plurality of series-connected MOS transistors  812   1 - 812   m  which have diode connection. 
     FIG. 4  illustrates an example of a background semiconductor integrated circuit for temperature detection. This circuit includes a first circuit block  97  and a second circuit block  98 . The first circuit block  97  generates a reference voltage without temperature dependency. The second circuit block  98  generates an output voltage which has a temperature dependency with a similar configuration to the first circuit block  97 . An output Vs 1  of the first circuit block  97  and an output Vs 2  of the second circuit block  98  may be compared in this circuit. In the first circuit block  97 , MOS transistors  912  and  914  having different thresholds form a current mirror circuit which outputs a voltage determined based on a difference between the thresholds of these MOS transistors  912  and  914 . In the first circuit block  97 , a channel conductance of the MOS transistor  912  and a MOS transistor  913  is made equivalent to a channel conductance of the transistor  914  and a MOS transistor  915 . On the other hand, in the second circuit block  98 , a channel conductance of MOS transistors  916  and  917  is intentionally made different from a channel conductance of MOS transistors  918  and  919 . 
   Since the output Vs 2  of the second circuit block  98  may be a reference voltage with temperature dependency, it can be used as a temperature sensing element. This reference voltage Vs 2  is divided so that it can be detected at a predetermined temperature by using resistances  920  and  921  and an operational amplifier  99  that outputs an output voltage Vs 3 . A comparator  910  compares Vs 1  and Vs 3  to detect a predetermined temperature, and an output buffer  911  outputs a resultant signal. 
   SUMMARY OF THE INVENTION 
   A novel temperature detector circuit and a novel oscillation frequency compensation device using a MOS transistor capable of reducing manufacture variation of a mobility characteristic and realizing stable output characteristics which are not affected by temperature dependency is offered. In one example, the temperature detector circuit includes a pair of depression type transistors to output a voltage which is proportional to temperature from a connecting point of a source of a first transistor and a drain of a second transistor. The transistors are the same conductivity type of current and are formed in different channel size, which are connected between power supplies in series, and have a configuration in which first transistor&#39;s gate and source are connected to each other and a first transistor&#39;s drain is connected with a second power supply and the second transistor&#39;s gate and drain are connected to each other and a second transistor&#39;s source is connected with a first power supply. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  illustrates an example of a background temperature detector circuit using a bipolar transistor; 
       FIG. 2  illustrates an example of a background temperature detector circuit using bipolar transistors with a Darlington connection; 
       FIG. 3  illustrates an example of a conventional temperature detector circuit including a MOS transistor; 
       FIG. 4  illustrates an example of a background semiconductor integrated circuit for temperature detection; 
       FIG. 5  illustrates an example configuration of a temperature detector circuit according to an example embodiment of the present invention; 
       FIG. 6A  illustrates an example configuration of a temperature detector circuit according to another example embodiment of the present invention; 
       FIG. 6B  illustrates an example configuration of a temperature detector circuit including a Wilson current mirror circuit according to another example embodiment of the present invention; 
       FIG. 6C  illustrates an example configuration of a temperature detector circuit including a cascode current mirror circuit according to another example embodiment of the present invention; 
       FIG. 6D  illustrates an example configuration of a temperature detector circuit including a cascode current mirror circuit corresponding to a low-voltage operation according to another example embodiment of the present invention; 
       FIG. 7  illustrates an example configuration of a temperature detector circuit according to another example embodiment of the present invention; 
       FIG. 8A  illustrates an example configuration of a temperature detector circuit according to another example embodiment of the present invention; 
       FIG. 8B  illustrates an example configuration of a temperature detector circuit according to another example embodiment of the present invention; and 
       FIG. 9  illustrates a configuration of a clock generator or a real-time clock which includes the temperature detector circuit of  FIGS. 8A and 8B . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, particularly to  FIG. 5 , an illustration showing a configuration of an embodiment of the present invention as a temperature detector circuit. 
     FIG. 5  illustrates an example configuration of a temperature detector circuit according to an embodiment of the present invention. Depression type N channel transistors M 1  and M 2  are connected in series between the second power supply terminal Vdd and the first power supply terminal Vss. A drain of the transistor M 1  is connected to the high-voltage terminal Vdd, and a source of the transistor M 2  is connected to the low-voltage terminal Vss. The gate and the source of the transistor M 1  and the gate and the drain of the transistor M 2  have a common connection to output voltage Va. In the above-mentioned configuration, when power supply voltage is high enough, the transistor M 1  may operate in a satiety region, and the transistor M 2  may operate in a variable resistor domain. 
   To the voltage Va, currents I 1  and I 2  which penetrates the transistors M 1  and M 2 , respectively, are sought by the following formulas: 
                     I   1     =       1   2     ⁢     μ   n     ⁢     C   ox     ⁢     A   1     ⁢            V     t   ⁢           ⁢   1            2         ;   and                   I   2     =       μ   n     ⁢     C   ox     ⁢     A   2     ⁢     {         (       V   a     -     V     t   ⁢           ⁢   2         )     ⁢     V   a       -       V   a   2     2       }         ,               
where μ n  is a surface mobility of electron, C ox  is a gate capacity per unit area, A 1  and A 2  are channel width W/channel length L (i.e., an aspect ratio) of the transistors M 1  and M 2 , V t1  and V t2  are threshold of the transistors M 1  and M 2 . If the formula explaining the output of the temperature sensor include the mobility μ n  or the gate capacity C ox , a calculated value may change with the variations of μ n  or C ox , or output characteristics may be influenced by the change of the mobility μ n  due to temperature change. It is desirable to eliminate these, if possible, and it is preferable to reduce influences by variations in a process.
 
   In the above-mentioned formulas, a value calculated by multiplying by the mobility μ n , the gate capacity C ox  per unit area, and the aspect ratios A 1  and A 2  of a channel is generally called a channel conductance. If the same type transistors (e.g., P-MOS) are formed in adjacent areas on a semiconductor board with the same physical and electric conditions, their element values, such as the mobility μ n , the gate capacity C ox , and the threshold may be substantially equal in each transistor. Where I 1 =I 2 , V t2 =−|V t1 |=V td , a next formula holds: 
   
     
       
         
           
             
               V 
               a 
             
             = 
             
               
                 ( 
                 
                   1 
                   - 
                   
                     
                       
                         
                           A 
                           2 
                           2 
                         
                         + 
                         
                           
                             A 
                             1 
                           
                           ⁢ 
                           
                             A 
                             2 
                           
                         
                       
                     
                     
                       A 
                       2 
                     
                   
                 
                 ) 
               
               ⁢ 
               
                 V 
                 td 
               
             
           
           , 
         
       
     
   
   where Vtd is a threshold of a depression type transistor. A 1  and A 2  are channel width W/channel length L (i.e., an aspect ratio) of the transistors M 1  and M 2 . An inclination of the A 1  and A 2  may be controlled by adjusting the size. The temperature inclination of Va may be given by a following formula: 
   
     
       
         
           
             
               ⅆ 
               
                 V 
                 a 
               
             
             
               ⅆ 
               t 
             
           
           = 
           
             
               ( 
               
                 1 
                 - 
                 
                   
                     
                       
                         A 
                         2 
                         2 
                       
                       + 
                       
                         
                           A 
                           1 
                         
                         ⁢ 
                         
                           A 
                           2 
                         
                       
                     
                   
                   
                     A 
                     2 
                   
                 
               
               ) 
             
             ⁢ 
             
               
                 
                   ⅆ 
                   
                     V 
                     td 
                   
                 
                 
                   ⅆ 
                   t 
                 
               
               . 
             
           
         
       
     
   
   An absolute value of output voltage Va and the conditional expression of a temperature inclination are determined only by a threshold and an aspect ratio of a channel of a depression type transistor, and may not be affected by a mobility characteristic. 
   It is known generally that a temperature inclination of a mobility is nonlinear, and that a temperature inclination of a threshold may be linear of about −1 to −2 mV/° C. As a realistic value, if the aspect ratio of M 1  and M 2  is 1:8, then the value of output voltage Va may be |2×V td | and a temperature inclination may be given by −2 times of the temperature inclination of a same threshold. 
   It is greatly effective that an output characteristic may be simply set up using the aspect ratio. For example, an output sensitivity may be secured by the Darlington connection etc. using a bipolar transistor in conventional technology, the detection means of this example embodiment simply need to change the aspect ratio of both transistors to secure the output sensitivity. Further, it is not necessary to verify a current domain where a transistor operates at this time. 
   Thus, in the circuit of this embodiment, since the temperature detector circuit is composed of one kind of depression type transistor, a mobility characteristic may not intervenes when determining an output voltage and output characteristics, just a threshold of the depression type transistor and an accuracy of the ratio may determine the output voltage and the output characteristics. For this reason, there are few elements changed with manufacture variation, and a stable output is obtained. It is not necessary to limit the range of the current value which penetrates the inside of a detector circuit to a specific domain, and a temperature detection means which has high design flexibility may be offered. 
     FIGS. 6A to 6D  illustrate another example configuration of a temperature detector circuit according to an embodiment of the present invention. As for the above-mentioned embodiment, it is ideally desirable for a back gate of the transistor M 1  to be Va potential. However, in a CMOS process using P-type substrate base, it generally becomes Vss potential in the example, and errors may be produced in output voltage due to a base bias effect of the transistor M 1 . In such a case, it may be a configuration that includes current which penetrates the transistor M 1  as a current mirror to the transistor M 2 . 
   An exemplary circuit in  FIG. 6A  has a configuration including a series connection of a depression type N channel transistor M 1  and a P channel transistor M 3  between power supplies, a series connection of a depression type N channel transistor M 2  and a P channel transistor M 4  between power supplies, a gate and a sauce source of the transistor M 1  and a sauce source of the M 2  to a low power supply terminal Vss, a sauce source of the transistors M 3  and M 4  which constitute a current mirror to a high power supply terminal Vdd, a gate of the transistors M 3  and M 4  to a drain of the M 3  and M 1 , and a gate and a drain of the transistor M 2  and a drain of the transistor M 4  to an output terminal a. 
   In this example, using a current ratio of a current mirror enables set up an output voltage and a temperature inclination without using an aspect ratio of a channel like the former example. 
   For example, if aspect ratios of the transistors M 1  and M 2  are in equal and a current ratio is 1:α, then next formula about an output voltage Va holds:
 
 V   a =(1−√{square root over (1+α)}) V   td  
 
   Further, a temperature inclination of Va is given by a following formula: 
   
     
       
         
           
             
               ⅆ 
               
                 V 
                 a 
               
             
             
               ⅆ 
               t 
             
           
           = 
           
             
               ( 
               
                 1 
                 - 
                 
                   
                     1 
                     + 
                     α 
                   
                 
               
               ) 
             
             ⁢ 
             
               
                 
                   ⅆ 
                   
                     V 
                     td 
                   
                 
                 
                   ⅆ 
                   t 
                 
               
               . 
             
           
         
       
     
   
   An output voltage Va and output characteristics are determined only by a threshold and an aspect ratio of a channel of a depression type transistor, and may not be affected by a mobility characteristic. 
   According to this example, although the number of elements and current paths of a detection means increase, it may respond even if a base bias effect influences, and it enables set up an output voltage and output characteristics using a ratio of a current mirror or an aspect ratio of a channel. 
   In this example, a function of the current mirror is produced by only using the transistors M 3  and M 4 . In the circuit in  FIG. 6A , the voltage between source-drains of both transistors is not in agreement in many power-supply-voltage conditions, and there is a problem that a current ratio of the current mirror is not reproduced correctly. In this case, output voltage may separate from a theoretical formula, or may include power-supply-voltage dependability. When using this example embodiment in a wide power-supply-voltage range, it is effective to change the configuration of a current mirror into circuits shown in  FIGS. 6B to 6D . 
     FIG. 6B  illustrates a configuration of a temperature detector circuit which includes a Wilson current mirror circuit. It is realizable only by adding one P channel transistor M 5  to the circuit in  FIG. 6A . A threshold of the transistor M 5  may cause a little gap to remain in the voltage between sauce source-drains of transistors M 3  and M 4 , a slight error may occur in output voltage, and the minimum operation voltage may rise by the threshold of the P channel transistor. 
     FIG. 6C  illustrates a configuration of a temperature detector circuit which includes a cascode current mirror circuit. In this circuit, a P channel transistor M 6  is connected between a transistor M 3  and a high power supply terminal Vdd, and a P channel transistors M 7  is connected between a transistor M 4  and the high power supply terminal Vdd, and a common connection of a gate of M 6  and M 7  is connected with a source terminal of the transistor M 3 . According to this circuit, since the voltage between source-drains in the transistor pair of right and left of a current mirror circuit is kept in high accuracy, a current ratio may be reproduced correctly and the accuracy of the output voltage may improve. However, the rise of the minimum operation voltage is the same level in  FIG. 6B . 
     FIG. 6D  illustrates a configuration of a temperature detector circuit which includes a cascode current mirror circuit corresponding to low-voltage operation. A common connection of a gate of transistors M 6  and M 7  is connected with a drain terminal of a transistor M 3 . A constant voltage generated in another circuit such as a circuit  20  shown in this  FIG. 6D  is input into gates of transistors M 3  and M 4 . According to this example, a current ratio may be kept in high accuracy in a wide power-supply-voltage range, and a rise of the minimum operation voltage may also be controlled. 
     FIG. 7  illustrates another example configuration of a temperature detector circuit according to an embodiment of the present invention. This example amplifies an output signal of the temperature detection means in former examples using an amplification circuit  31  which includes resistors R 31  and R 32  and an operational amplifier  30  so as to raise an output sensitivity to temperature. In former examples, since the temperature detection means may set up output sensitivity by using an aspect ratio of a channel, arbitrary sensitivity setup may be possible theoretically. However, a setup of an extreme aspect ratio may cause the influence of a processing accuracy in a manufacturing process to be imbalanced between transistors, and an assumed characteristic may not be acquired. 
   In such a case, an output sensitivity at the rate of amplification set up by resistance may be realized by using the circuit of this example which set up the aspect ratio of a temperature detection means as a suitable value. 
   For example, if a large aspect ratio of the channel is taken as 1:100 in former examples in  FIG. 6A to 6D , sensitivity may increase about 9 times as converted value as a threshold, but accuracy may fall. For this reason, using the circuit in  FIG. 7 , controlling the rate of amplification of the temperature detection means as twice (i.e. 1:8 as an aspect ratio), the amplification circuit  31  may amplify 4.5 times. 
   The circuit shown in  FIG. 7  may have a configuration with a variable resistor or a trimming means as a part of resistance, and that adjusts the rate of amplification. 
   Otherwise, it is also possible to change the connection place of R 32  in giving DC-offset as fixed potential other than Vss or in combining the known addition circuit. 
     FIG. 8A  illustrates another example configuration of a temperature detector circuit according to an embodiment of the present invention.  FIG. 8B  also illustrates another example configuration of a temperature detector circuit as an application of the example in  FIG. 8A . The example in  FIG. 8A  is the temperature detector circuit including the temperature detection means of former example which has output voltage Va′ and the reference voltage Vref prepared independently, comparing both outputs Va′ and Vref through an A/D converter  41 , and outputting the comparing result as digital data. In this example, the input reference voltage Vref may be, for example, voltage generated using a well-known reference voltage generating circuit, or a fixed potential provided physically. Further, when the reference voltage has a little temperature dependency, it may increase the rate of amplification of the circuit means which includes a configuration of former example in  FIG. 7  according to the accuracy of the reference voltage, and errors due to the temperature dependency of the reference voltage Vref may be set as the level which does not cause a problem substantially. 
   For example, when using a depression type transistor which has a condition that V td =−0.3 V and the temperature dependency of a threshold is −1.2 mV/° C. setting about 4 times of output sensitivity, an output value Va′ may be about 1.2 V, and a temperature inclination may be 4.8 mV/° C.=4000 ppm/° C. in normal temperature. When comparing the reference voltage which has a range of ±100 ppm/° C. fluctuation with this, it may be a calculation which changes from normal temperature to ±40° C. with an error of 1° C. 
   Further, when having a configuration in  FIG. 8B , a next formula holds: 
   
     
       
         
           
             V 
             a 
             ′ 
           
           = 
           
             
               
                 
                   
                     R 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     31 
                   
                   + 
                   
                     R 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     32 
                   
                 
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   32 
                 
               
               ⁢ 
               
                 V 
                 a 
               
             
             - 
             
               
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   31 
                 
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   32 
                 
               
               ⁢ 
               
                 
                   V 
                   bias 
                 
                 . 
               
             
           
         
       
     
   
   Therefore, it may be possible to increase only a temperature inclination without changing an output value in normal temperature, for example, it may also be possible for ±80° C. change with an error of 1° C. at 8000 ppm/° C. Although Vbias in  FIG. 8B  may be a form of a buffer output here, it also may be given with a regulator output or a fixed power supply, and it may be used together with other addition circuits. 
     FIG. 9  illustrates a configuration of a clock generator or a real-time clock which includes a temperature detector circuit of a former example in  FIGS. 8A and 8B . This example is a clock generator or a real-time clock equipped with a means which compensates oscillation frequency using a digital output of the temperature detector circuit in  FIGS. 8A and 8B . It is known that oscillation frequency of a clock generator or a real-time clock using a piezoelectric vibrator may be fluctuated based on temperature. 
   As a general method of rectifying this oscillation frequency, there is a method in which oscillation capacity is changed according to acquired temperature information with a temperature detector circuit, in addition, there is another method in which time information is compensated with adjusting frequency divider. In a real-time clock, since it may be driven full-time in a equipment, it is important that it has low consumption current. The temperature detector circuit in  FIGS. 8A and 8B  uses MOS transistors which run in low consumption current. Thus, when using a configuration of this embodiment in a real-time clock and a clock generator equipped with a correction means for temperature, whole consumption current may be controlled in low. 
   Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein. 
   This patent specification is based on Japanese patent application, No. JPAP2005-206581 filed on Jul. 15, 2005 in the Japan Patent Office, the entire contents of which are incorporated by reference herein.