Abstract:
A comparing detector circuit capable of operating regardless of input voltages thereto includes a first pair of transistors to which first and second input signal voltages are input for functioning as a buffer; a second pair of transistors constructing a current mirror circuit in which an input side and an output side are connected to the first pair of transistors via first and second resistors, respectively; and an output transistor to which potential at the output side of the current mirror circuit is applied as an input.

Description:
FIELD OF THE INVENTION 
     This invention relates to a comparing detector circuit and, more particularly, to a comparing and amplifying detector circuit for performing voltage comparison and amplification and detection of temperature. The invention further relates to a comparing and amplifying detector circuit ideal for use in a power MOSFET having an internal protection function. 
     BACKGROUND OF THE INVENTION 
     A comparator of the kind disclosed in, e.g., the specification of Japanese Patent Kokai (Laid-Open) Publication JP-A-5-14073 has been proposed as a comparing and amplifying detector circuit in the prior art. The comparator, which uses a differential amplifier, employs depletion-type MOS transistors as amplifying elements and is adapted in such a manner that a digital signal is obtained even for an input voltage in the low-level range. FIG. 10 is a diagram showing a circuitry of the comparator disclosed in this publication. A constant current, which is obtained by a depression-type transistor  201  whose drain is connected to a power supply and whose gate and source are tied together, is input as a reference current to the input side of enhancement-type transistors  202 ,  207  that construct a current mirror circuit. An output current of the current mirror circuit is supplied as a driving current to transistors  204 ,  206  forming a differential pair and having sources that are tied together, gates to which input terminals  10 ,  11  are respectively connected and drains that are respectively connected to load elements (depletion-type transistors whose drains are connected to the power supply and each of whose gate and source are tied together)  203 ,  205 . A drain of the transistor  206  is connected to the input of an inverter comprising a depletion-type transistor  208  and an enhancement-type transistor  209 , namely to a gate of the transistor  209 . A signal applied to this inverter is inverted and amplified thereby and output at an output terminal  12 . 
     A circuit of the kind shown in FIG. 12 is known as a comparator used in electrical equipment in automobiles. The comparator has a power supply  1 , a control IC  13  arranged on control ground  16 ; a battery  222 , a low-side PID (intelligent power device)  220  and a load  221  arranged on power ground  18 : interface resistors  211 ,  212 ,  214 ,  215 ,  217  and  218 ; transistors  213 ,  216 ; and a voltage regulator diode  219 . 
     In the operation of the circuit shown in FIG. 12, the output voltage of the control IC  13  is potentially divided by the resistors  211 ,  212  and the resulting voltage is applied to the base of the NPN transistor  213 . By turning the transistor  213  on and off, the PNP transistor  216  is turned on and off, the voltage of the battery  222  is clamped by the voltage regulator diode  219  and a signal is applied to an input of the low-side IPD  220 . 
     The specification of Japanese Patent Kokai (Laid-Open) Publication JP-A-6-244414 discloses an arrangement serving as a temperature detector circuit in which, as shown in FIG.  13 (A), a constant current obtained by a depletion-type transistor  223  flows into a diode group of serially connected diodes  224 , and a potential at a connection node between the depletion-type transistor  223  and the diode group  224  is input to a gate of an enhancement-type transistor  226  and is compared with a threshold voltage VT of the transistor  226 , whereby temperature is detected utilizing the temperature dependence illustrated in FIG.  13 B. 
     SUMMARY OF THE DISCLOSURE 
     In the course of eager investigations toward the present invention, the following problems have been encountered. 
     The circuits according to the prior art set forth above have certain problems, described below. 
     The comparator depicted in FIG. 10 requires that threshold voltage VT of the transistor  209  be changed in conformity with the input voltages used. In the case of a semiconductor integrated circuit, therefore, an additional process for changing the threshold voltage VT of transistor  209  is necessary and the device has very little versatility. 
     The reason for this is as follows: 
     Since the depletion-type transistors  203 ,  205  are both constant-current sources, the following inequality: 
     
       
         (current of transistors  203 ,  205 )&lt;(current of transistor  207 )&lt;(sum of currents of transistors  203  and  205 ) 
       
     
     is a condition for allowing a gate voltage of the transistor  209  to be changed with respect to inputs  10 ,  11 . Consequently, as shown in FIG. 11, the depletion-type transistor  206  limits the current of the transistor  205  within the range: 
     (voltage of input  10 )≦(voltage of input  11 ), and therefore the drain voltage of the transistor  207  becomes: 
     (voltage of input  10 )−(threshold voltage VT of transistor  206 ), and the gate voltage of the transistor  209  becomes approximately the voltage of power supply  1 . 
     Further, the depletion-type transistor  204  limits the current of the transistor  203  within the range: 
     (voltage of input  10 )≧(voltage of input  11 ), and therefore the drain voltage of the transistor  204  becomes: 
     (voltage of input  11 )−(threshold voltage VT of transistor  204 ), and the gate voltage of the transistor  209  becomes a voltage that is approximately the drain voltage of transistor  207 . 
     Thus, the gate voltage of the transistor  209  ranges from the voltage of the power supply  1  to [(voltage of input  11 )−(threshold voltage VT of transistor  204 )]. 
     In the circuit shown in FIG. 12, a resistance-containing transistor constituted by the resistors  211 ,  212  and transistor  213  and a resistance-containing transistor constituted by the resistors  214 ,  215  and transistor  216  are required between the control IC  13  and low-side IPD  220 . This makes it difficult to miniaturize the device. 
     The reason for this is as follows: 
     The output voltage of the ordinary control IC  13  is 
     
       
           VOH≧VDD× 0.7 
       
     
     
       
           VOL≦ 0.3× VDD   
       
     
     where VOH represents the high level of the output voltage and VOL the low level of the output voltage. Further, VDD is the voltage of the power supply  1 , e.g., 5±0.5 V. When a fluctuating voltage  17  (e.g., ±1.5 V) between grounds is taken into account, the high and low levels of the control IC  13  cannot be discriminated from the low-side IPD  220 . 
     A problem which arises with the circuit shown in FIG.  13 (A) is a wide range of variation in detected temperature. The reason for this is as follows: 
     Let the temperature dependence of the forward voltage drop (VF) of diode group  224  be, e.g., 2 mV/° C.×5 stages=10 mV/° C., and let variation of the threshold voltage VT of transistor  226  be ±300 mV. Under these conditions, the range of variation in detected temperature will be ±300 mV÷10 mV/° C.=±30° C. 
     The present invention has been devised in view of the foregoing problems, and an object is to provide a comparator circuit that is capable of operating irrespective of the input voltages. 
     Another object of the present invention is to provide a comparing detector circuit that does not require resistor-containing transistors, thus making it possible to miniature devices having the circuit. 
     A further object of the present invention is to provide a detector circuit in which detection variance is reduced and precision improved. 
     According to a first aspect of the present invention, the foregoing objects are attained by providing a voltage comparator circuit comprising: a first pair of transistors to which first and second input signal voltages are input for functioning as a buffer; a second pair of transistors constructing a current mirror circuit in which an input node and an output node are connected to the first pair of transistors via first and second resistors, respectively; and an output transistor to which potential at the output node of the current mirror circuit is applied as an input. 
     According to a first variant to the first aspect, there is provided a voltage comparator circuit comprising: first and second current paths between a power supply and ground, the first current path including a first transistor, to which a first input signal is applied, and a first resistor, and the second current path including a second transistor, to which a second input signal is applied, and a second resistor; a current mirror circuit having an input node connected to the first resistor and an output node connected to the second resistor; and an output transistor to which a potential at the output node of the current mirror circuit is applied as an input. 
     The output from the output transistor is connected to an output terminal and to a load element, thereby constructing an inverting amplifying-type output circuit. 
     According to a second variant to the first aspect, there is provided a voltage comparator circuit comprising: first and second transistors, which construct a source follower, having gates to which first and second input signal voltages are respectively applied, and drains connected to a power supply; first and second resistors having one end connected to sources of the first and second transistors, respectively; third and fourth transistors constructing a current mirror circuit, the third transistor having a source connected to ground and a drain and a gate connected together and connected to the other end of the first resistor, and the fourth transistor having a source connected to ground, a drain connected to the other end of the second resistor and a gate commonly connected to the gate of the third transistor; a fifth transistor having a source connected to ground, a gate whose input is a drain potential of the fourth transistor, and a drain connected to an output terminal; and a load element connected between the power supply and the drain of the fifth transistor. 
     According to a third variant to the first aspect, there is provided a voltage comparator circuit comprising: first and second transistors, which construct an emitter follower, having bases to which first and second input signal voltages are respectively applied, and collectors connected to a power supply; first and second resistors having one end connected to emitters of the first and second transistors, respectively; third and fourth transistors constructing a current mirror circuit, the third transistor having an emitter connected to ground and a collector and a base connected together and connected to the other end of the first resistor, and the fourth transistor having an emitter connected to ground, a collector connected to the other end of the second resistor and a base commonly connected to a base of the third transistor; a fifth transistor having an emitter connected to ground, a base whose input is a collector a potential of the fourth transistor, and a collector connected to an output terminal; and a load element connected between the power supply and the collector of the fifth transistor. 
     According to a second aspect of the present invention, a comparing and amplifying detector circuit has first and second grounds of different potentials, wherein a first power supply on the first ground and a second power supply of the second ground are connected, and a first potential obtained by potentially dividing, by resistances, a potential between potential of the first power supply and output potential of a first control circuit connected between the first ground and the first power supply, and a second potential obtained by dividing, by resistances, a potential between the potential of the first power supply and potential of the first ground, are input to a voltage comparator. 
     As this voltage comparator the voltage comparator circuit described in any one of aforementioned aspect or variants may be used. 
     According to a third aspect of the present invention, a temperature detector circuit comprises: a first diode group of serially connected diodes; a second diode group of serially connected diodes; first load element and second load element forming load of current that flows into the first diode group and second diode group, respectively; and a voltage comparator whose inputs are potential at a node between the first diode group and the first load element and potential at a node between the second diode group and the second load element; the number of diodes in the first diode group being different from the number of diodes in the second diode group. 
     According to a variant to the third aspect, there is provided a temperature detector circuit comprising: a first diode group of serially connected diodes; a second diode group of serially connected diodes; first and second current sources for supplying currents to the first and second diode groups, respectively; and a voltage comparator whose inputs are a first potential at a node between the first diode group and the first current source and a second potential at a node between the second diode group and the second current source; wherein the number of diodes in the first diode group is different from the number of diodes in the second diode group. 
     The diode groups may be replaced by transistors each having a first resistor connected between an emitter and base and a second resistor connected between a base and collector. 
     The first and second current sources both may be comprised of depletion-type transistors. 
     According to a fourth aspect of the present invention, a temperature detector circuit has a first transistor, which constructs an input side of a current mirror circuit, connected to ground via a diode and to a power supply via a third transistor, which serves as an active load, and a first resistor; a second transistor, which constructs an output side of the current mirror circuit, connected to the power supply via a second resistor; and a voltage comparator to which the terminal potentials of the first and second resistors are applied as inputs. 
     According to a variant to the fourth aspect, there is provided a temperature detector circuit comprising: a first transistor, which constructs an input side of a current mirror circuit, connected to ground via a diode; a second transistor constructing an output side of the current mirror circuit; a third transistor, which serves as a current source, connected between a power supply and a common node of first and second resistors; the first and second transistors being connected to the first and second resistors, respectively; and a voltage comparator whose inputs are a first potential at a node between the first transistor and the first resistor and a second potential at a node between the second transistor and the second current resistor. 
     In the circuits according to third and fourth a aspects, or variants thereof the voltage comparator may be the voltage comparator described in any one of the first aspect and its variants. 
     Other aspects, features and advantages of the present invention will be apparent from the entire disclosure including claims and the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
     Any features of the claims, which are not explicitly recited in the description are incorporated herein by reference to any of the claims, upon necessity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing the construction of a first embodiment of the present invention; 
     FIG. 2 is a circuit diagram showing the construction of a second embodiment of the present invention; 
     FIG. 3 is a circuit diagram showing the construction of a third embodiment of the present invention; 
     FIG. 4 is a circuit diagram showing another example of construction of the third embodiment of the present invention; 
     FIG. 5 is a characteristic diagram useful in describing the operation of the third embodiment; 
     FIG. 6 is a circuit diagram showing the construction of a fourth embodiment of the present invention; 
     FIG. 7 is a circuit diagram showing another example of construction of the fourth embodiment of the present invention; 
     FIG. 8 is a characteristic diagram useful in describing the operation of the fourth embodiment; 
     FIG. 9 is a sectional view showing an example of an arrangement in a case where the present invention is created in a semiconductor device; 
     FIG. 10 is a circuit diagram showing a comparing and amplifying detector circuit according to the prior art; 
     FIG. 11 is a characteristic diagram useful in describing the operation of the circuit shown in FIG. 10; 
     FIG. 12 is a circuit diagram showing the construction of another example of a comparing and amplifying detector circuit according to the prior art; 
     FIG.  13 (A) is a circuit diagram showing the construction of another example of a comparing and amplifying detector circuit according to the prior art; and 
     FIG.  13 (B) is a graph useful in describing the operation of the circuit of FIG.  13 (A). 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     Preferred modes of practicing the present invention will now be described. 
     According to one aspect of the present invention, as shown in FIG. 1, the sum of (a difference voltage between first and second input voltages) and (threshold voltage VT of a transistor  4 ) is applied to a gate of an output transistor  9  whose threshold voltage is VT, whereby the difference voltage between the input voltages is directly super imposed on the threshold voltage VT so that the output is turned on and off or the input voltage difference amplified irrespective of the absolute values of the input voltages. 
     This voltage comparator comprises transistors  2 ,  5  constructing a buffer circuit (a source follower) to which the input voltages are applied, transistors  4 ,  7  constructing a current mirror circuit, resistors  3 ,  6  connected between the outputs of the buffer circuit (the sources of the transistors) and the input and output sides of the current mirror circuit, and the transistor  9  for turning the output of the device on and off, or for amplifying the difference between the input voltages. 
     A current  10  flows into the transistor  4  on the input side of the current mirror circuit. The current  10  is equal to: 
     
       
         [(voltage at input  10 )−(threshold voltage VT of transistor  2 )−(threshold voltage VT of transistor  4 )]/(resistance value of resistor  3 ). 
       
     
     A current of the same current value flows into the transistor  7  on the output side of the current mirror circuit. 
     A voltage is applied to the transistor  9  as its gate voltage. This voltage is equal to [(voltage at input  11 )−(threshold voltage VT of transistor  5 )−(resistance value of resistor 6×10)]. By adopting identical characteristics for the transistors  2  and  5 , for the resistors  3  and  6  and for the transistors  4  and  7  (e.g., by matching the channel widths W, channel lengths L or W/L ratios of the transistors and by adopting identical sizes, or example, of the resistors), the gate voltage of the transistor  9  becomes equal to: 
     
       
         [(voltage at input  10 )−(voltage at input  11 )+(threshold voltage VT of transistor  4 ). 
       
     
     Thus the output of the device can be turned on and off, or the difference between the input voltages can be amplified, irrespective of the absolute values of the input voltages. 
     According to another aspect of the present invention, the output voltage of a control IC and the voltage at control ground are pulled up and the voltages are compared by a comparator. More specifically, as shown in FIG. 2, the device has a resistor or transistor  19  and a resistor  20  for pulling output voltage  15  of a control IC up toward the power supply voltage; a resistor or transistor  21  and a resistor  22  for pulling up the voltage of ground; and a comparator  24 . 
     The relationship between the voltage at the control output terminal  15  and control ground  16  is independent of a fluctuating voltage  17  between grounds. Accordingly, two voltages which are obtained by potentially dividing both voltages across these nodes  15 ,  16  and a power supply terminal  14  by the resistors  19 ,  20 ,  21 ,  22 , are compared by the comparator  24 . Alternatively, a constant-current source using depression-type transistors or the like is constructed in place of the resistors  19 ,  21 , the constant-current source is used to pull up both voltages by constant voltages and the resulting voltages are compared by the comparator  24 . 
     A circuit constructed in a semiconductor integrated circuit device exhibits little dependence upon the absolute value of the transistor threshold voltage VT because relative-value variation is much smaller than absolute-value variation and absolute-value variation of diodes is small. More specifically, as shown in FIG. 3, the circuit has transistors  101 ,  103  for supplying relative current values, i.e., a current ratio, diode groups  102 ,  104  for varying terminal voltage in response to temperature, and the comparator  24  for detecting a difference in voltage variation. 
     Alternatively according to a further aspect, as shown in FIGS. 6 and 7, the circuit has a diode  111  for varying terminal voltage in response to temperature, a current mirror circuit  110 ,  113  for applying current amplification to the variation in voltage, resistors  108 ,  112  (FIG. 6) and  115 ,  116  (FIG. 7) for changing the variation in current to voltage, and the comparator  24 . 
     A large constant current resulting from the depletion-type transistor  101  in FIG. 3 is applied to the diode group  102 , the number of diodes of which is small, and a small constant current resulting from the depletion-type transistor  103  is applied to the diode group  104 , the number of diodes of which is large. As a result, temperature is sensed utilizing a disparity in temperature dependence due to current, as illustrated in FIG.  5 . 
     Alternatively, identical constant currents are applied to the diode group  102  of the smaller number of diodes and to the diode group  104  of the larger number of diodes and large junction area, whereby temperature is sensed utilizing a disparity in temperature dependence due to current. 
     Alternatively, current amplification by the current mirror circuit  110 ,  113  in FIGS. 6 and 7 is varied by the diode  111 , whose terminal voltage varies in response to temperature, and changes in voltage across the resistors  108 ,  112  (FIG. 6) and  115 ,  116  (FIG.  7 ), which are for changing current variation to voltage, are detected by the comparator  24 . 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the drawings in order to explain further the modes of the invention set forth above. 
     FIG. 1 is a circuit diagram showing the construction of a voltage comparator embodying the present invention. As shown in FIG. 1, the voltage comparator according to this embodiment comprises transistors  2 ,  5  whose drains are connected to the power supply and whose gates are connected to input terminals  10 ,  11 , respectively; resistors  3 ,  6  having one end connected to transistors  2 ,  5 , respectively; transistor  4  whose drain and gate are connected to the other end of the resistor  3  and whose source is grounded; transistor  7  whose drain is connected to the other end of the resistor  6 , whose gate is connected to the gate of the transistor  4  and whose source is grounded; transistor  9  whose source is grounded and whose gate is connected to a node at which the drain of the transistor  7  and the resistor  6  are connected; and transistor  8  whose gate and source are tied together and connected to the drain of the transistor  9 , and whose drain is connected to the power supply. The drain of the transistor  9  is connected to output terminal  12 . The transistors  4  and  7  construct a current mirror circuit, and the transistor  8  constitutes the load of the transistor  9 . 
     Letting VIN 10  represent the input voltage at input terminal  10 , VT 2 , VT 4  the threshold voltages of the transistors  2 ,  4 , and R 3  the resistance value of the resistor  3 , we have 
     
       
           I   0 =( VIN   10 − VT   2 − VT   4 )/ R   3   (1) 
       
     
     which represents the current that flows into the transistor  4  on the input side of the current mirror circuit. Letting VIN 11  represent the input voltage at input terminal  11 , VT 5  the threshold voltage of the transistor  5 , and R 6  the resistance value of the resistor  6 , we have 
     
       
           VG   9 = VIN   11 − VT   5 −( R   6 ×10)  (2) 
       
     
     which represents the voltage applied as the gate voltage of the transistor  9 . 
     By adopting identical characteristics for the transistor  2  and  5 , for the resistors  3  and  6  and for the transistors  4  and  7  (as by matching width and length etc.), the threshold voltages of the transistors  2  and  5  become equal (VT 2 =VT 5 =VT), the resistance values of the resistors  3  and  6  become equal (R 3 =R 6 =R), and the gate voltage of transistor  9  becomes as follows:                          V                 G9     =       V                 I                 N11     -     V                 T     -       (   R   )     ×       {       V                 I                 N10     -     V                 T     -     V                 T4       )     /   R           }     )               =       V                 I                 N10     -     V                 I                 N11     +     V                 T4                     (   3   )                                
     Accordingly, by adopting identical characteristics (as by matching width and length etc.) for the transistors  4  and  7 , with the threshold voltage of transistor  9  being VT, the transistor  9  can turn the output  12  on and off or can amplify and output the input voltage difference (VIN 10 −VIN 11 ) regardless of the absolute values of the input voltages. 
     It should be noted that as for the resistors  3  and  6 , it is sufficient if the both would have identical characteristics. Thus there is no limitation upon resistance elements, and the transistors  2 ,  5  may be enhancement-type transistors or bipolar transistors. 
     Further, the transistors  4 ,  7 ,  9  may be MOSFETs or bipolar transistors, and the transistor  8  may be a depression-type resistor or may be replaced by a resistor as far as it functions as the same load. 
     Furthermore, if the voltage drops across the resistors  3  and  6  are identical, it will suffice if the resistance ratio between the resistors  3  and  6  is approximately the reciprocal of the mirror ratio of the current mirror circuit (the ratio of the current drive capability of the output transistor  7  to that of the input transistor  4 ; the emitter-area ratio in the case of bipolar transistors; the ratio between the W/L ratios in the case of MOS transistors). 
     For example, if the transconductance parameter of the transistor  7  is N times that of the transistor  4 , the resistance value R 6  of resistor  6  and the resistance value R 3  of resistor  3  will be related as follows: R 6 /R 3 =1/N. 
     FIG. 2 is a circuit diagram illustrating the construction of a second embodiment of the present invention. As shown in FIG. 2, this embodiment has power supply  1 , control IC  13  arranged on control ground  16 ; resistors  19 ,  20  connected between power supply terminal  14  and control output terminal  15  of control IC  13 ; resistors  21 ,  22  connected between power supply terminal  14  and control ground; and comparator  24 , whose power source is power ground  18  and power supply terminal  14  and whose inputs are the potential obtained by potential division using resistors  19 ,  20  (at a node between  19  and  20 ) and the potential obtained by potential division using resistors  21 ,  22  (at a node between  21  and  22 ). The comparator  24  is identical with that of the embodiment shown in FIG.  1 . 
     Letting VDD represent the voltage of power supply  1 , VO the voltage at control output terminal  15  and R 19 , R 20 , R 21  and R 22  the resistance values of the resistors  19 ,  20 ,  21  and  22 , respectively, the voltage obtained by potentially dividing the voltage across the power supply terminal  14  and control output terminal  15  by the resistors  19 ,  20  is given by the following, with control ground  16  serving as the reference: 
     
       
           VDD×R   20 /( R   19 + R   20 )+ V×R   19 /( R   19 + R   20 ) 
       
     
     and the voltage obtained by potentially dividing the voltage across the power supply terminal  14  and control ground  16  by the resistors  21 ,  22  is given by the following: 
       VDD×R   22 /( R   21 + R   22 ) 
     The difference between both voltages, therefore, which is unrelated to the fluctuating voltage  17  between grounds, is detected by the comparator  24 . 
     It should be noted that a constant-current source using depletion-type transistors or the like may be constructed in place of the resistors  19 ,  21 , the constant-current source may be used to pull up the voltages at the control output terminal  15  and control ground  16  by constant voltages based upon the product of the resistance of resistor  20  or  22  and each constant-current value, and the resulting voltages may be compared by the comparator  24 . 
     In case where the resistors are used, the difference between two inputs of the comparator becomes smaller than the voltage difference between the control output terminal  15  and the control ground  16 . However, if the constant current source is used, the input&#39;s difference is identical to the difference between the control output terminal  15  and the control ground  16 , thus, the comparator output is I little influenced by the performance of the comparator  24 . 
     In order to produce the depletion-type transistors however, additional manufacturing steps will be required. Accordingly, the selection can be made based upon the construction of the overall semiconductor IC device. 
     It should be noted that the comparator  24  is not limited to the construction shown above and that a voltage comparator having a different construction may be used. 
     FIG. 3 is a circuit diagram showing the construction of a temperature detector according to a third embodiment of the present invention. According to this embodiment, as shown in FIG. 3, the temperature detector has depletion-type transistors  101 ,  103  whose drains are connected to the power supply and whose gates are connected to their sources; diode groups  102 ,  104  connected to the sources of the depletion-type transistors  101 ,  103 , respectively; and comparator  24  for comparing the two inputs thereto, namely the potential at the node at which the depletion-type transistor  101  and diode group  102  are connected and the potential at the node at which the depletion-type transistor  103  and diode group  104  are connected. The number of diodes in the diode group  102  is smaller than the number of diodes in the diode group  104 . The comparator  24  has a construction identical with that of the embodiment shown in FIG.  1 . 
     A large constant current resulting from the depletion-type transistor  101  in FIG. 3 is applied to the diode group  102  of the smaller number of diodes, and a small constant current resulting from the depletion-type transistor  103  is applied to the diode group  104  of the larger number of diodes. As a result, temperature is sensed utilizing a disparity in temperature dependence due to current, as illustrated in FIG.  5 . 
     Alternatively, identical constant currents are applied to the diode group  102  of the smaller number of diodes and to the diode group  104  of the larger number of diodes and large junction area, whereby temperature is sensed utilizing a disparity in temperature dependence due to current. 
     In a modification of this embodiment, as shown in FIG. 4, the diode groups  102 ,  104  may be replaced by an arrangement in which resistors  105 ,  106  are connected between the emitter and base and between the base and collector of a transistor  107 . Let VBE represent the voltage across the emitter and base of the transistor  107 , R 105  and R 106  the resistance values of the resistors  105  and  106 , respectively, and VF the forward voltage drop across the diodes. By arranging it so that the following relation holds: 
     
       
           VBE=VF ×( R   105 + R   106 )/ R   105   
       
     
     it becomes possible to effect a setting to any value, whereas a setting only to a whole-number multiple of the forward voltage drop VF of the diodes can be achieved with the circuit of FIG.  3 . 
     Thus, taking into account the fact that relative-value variation is much smaller than absolute-value variation and absolute-value variation of diodes is small in a semiconductor integrated circuit device, a circuit exhibiting little dependence upon the absolute value of the transistor threshold voltage VT is constructed, thereby making it possible to achieve a range of detected-temperature variation on the order of, say, about ±9° C., whereas the range is about ±32° C. with the prior-art temperature detector circuit shown in FIG.  13 (A), inclusive of variation other than that of the absolute value of threshold voltage VT. 
     FIG. 6 is a circuit diagram showing the construction of a fourth embodiment of the present invention. This temperature detector according to the fourth embodiment comprises diode  111  whose cathode is grounded; enhancement-type transistor  110  whose source is connected to the anode of the diode  111  and whose drain and gate are connected; depletion-type transistor  109 , whose source and gate are connected to the drain of the transistor  110 ; resistor  108  connected between the drain of the transistor  109  and the power supply; enhancement-type transistor  113  whose source is grounded and whose gate is tied to the gate of the transistor  110 ; resistor  112  connected between the drain of the transistor  113  and the power supply; and comparator  24 , whose two inputs are the potential at a node at which the resistor  108  and transistor  109  are connected and the potential at a node at which the resistor  112  and transistor  113  are connected. 
     The constant current of the depletion-type transistor  109  is supplied to the resistor  108 , enhancement-type transistor  110  and diode  111 , the sum of the threshold voltage VT of transistor  110  and forward voltage drop VF of diode  111  is applied to the gate of the enhancement-type transistor  113 , the drain current of transistor  113 , which conforms to the gate voltage thereof, is applied to the resistor  112 , and the terminal voltages of the resistors  108 ,  112  are compared by the comparator  24 . 
     When temperature varies, the voltage impressed upon the gate of the transistor  113  changes mainly owing to the temperature-induced change in the forward voltage drop VF of the diode  111 , as illustrated in FIG. 8, and the ratio of the current of transistor  110  to the current of transistor  113  changes. By making the current ratio at which temperature is desired to be sensed the ratio of the resistance value of resistor  112  to the resistance value of resistor  108 , temperature can be sensed by the comparator  24 . 
     FIG. 7 is a circuit diagram showing a modification of the construction of the fourth embodiment. As shown in FIG. 7, a constant current resulting from the depletion-type transistor  114  is split between a path comprising resistor  115 , transistor  110  and diode  111  and a path comprising resistor  116  and transistor  113 . When temperature varies, the voltage impressed upon the gate of the transistor  113  changes mainly owing to the temperature-induced change in the forward voltage drop VF of the diode  111 , as illustrated in FIG. 8, and the ratio of the current of transistor  110  to the current of transistor  113  changes. This is similar to the arrangement shown in FIG.  6 . 
     By making the current ratio at which temperature is desired to be sensed the ratio of the resistance value of resistor  116  to the resistance value of resistor  115 , temperature can be sensed by the comparator  24 . 
     In accordance with this embodiment, it is possible to achieve a range of detected-temperature variation on the order of, say, ±24° C., whereas the range is ±32° C. with the prior-art temperature detector circuit shown in FIG.  13 (A), inclusive of variation other than that of the absolute value of threshold voltage VT. Though the range of detected-temperature variation is broader than in the case of FIG. 3, the number of diodes can be reduced, thus making it possible to further miniaturize the semiconductor IC device. 
     FIG. 9 is a diagram showing the construction of a fifth embodiment of the present invention. This illustrates an example of the cross section of a semiconductor substrate in a case where any of the circuits shown in FIGS. 1,  2 ,  3  and  6  are fabricated on a chip. As shown in FIG. 9, the device comprises an N− layer  152 , P wells  153 , an N well  154 , a P layer  155 , an N+ layer  157 , electrodes  158 , a polysilicon layer  159 , insulating layers  160 , a P+ layer  161 , a P-type polysilicon layer  162  and an N-type polysilicon layer  163 . As shown in FIG. 9, an N-channel MOSFET, a polysilicon resistor, a PNP transistor, a polysilicon diode and a power MOSFET are constructed. 
     In the arrangement of FIG. 9, the transistor is constituted by an N-channel MOSFET, the resistor by a polysilicon resistor and the diode by a polysilicon diode. This illustrates an example of a power MOSFET with an internal protection function. By changing the N type to P type and the P type to N type in FIG. 9, the device can be constructed by a P-channel MOSFET and NPN transistor used in the case of a P-channel power MOSFET. Further, the arrangement need not be one in which the power MOSFET is provided on the same substrate. Further, each device may be constructed on an insulating layer or in a single crystal underlying an insulating layer. 
     In accordance with the present invention, as described above, the following advantages are obtained: 
     The first advantage is that output can be turned on and off or a difference between input voltages amplified irrespective of the absolute values of input voltages. 
     The reason for this is that, according to the present invention, the sum of a difference voltage between two input voltages and threshold voltage VT of a transistor ( 4  in FIG. 1) is applied to the gate of an output transistor ( 9  in FIG. 1) whose threshold voltage is VT, whereby the difference voltage between the input voltages is directly superimposed on the threshold voltage VT so that the output is turned on and off or the input voltage difference amplified irrespective of the absolute values of the input voltages. 
     The second advantage of the present invention is that transistors with an internal resistance are no longer required, thus making it possible to miniaturize the device. 
     The reason for this is that, according to the present invention, the output voltage of a control IC and the voltage at control ground are pulled up and the voltages are compared by a comparator. As a result, high and low levels of the control IC can be discriminated from the side of power ground without using transistors having an internal resistance. 
     A third advantage of the present invention is that the range over which detected temperature exhibits variance can be reduced. 
     The reason for this is that relative-value variation is much smaller than absolute-value variation and absolute-value variation of diodes is small. In the present invention, it is possible to construct a circuit that is little affected by the absolute value of transistor threshold voltage. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 
     It should be noted that other aspects and objects of the present invention will become apparent in the entire disclosure and that modifications may be done without departing the gist and scope of the present invention as disclosed herein and appended herewith. 
     Also it should be noted that any combination of the disclosed and/or claimed elements, matters and/or items may fall under the modifications aforementioned.