Abstract:
A signal level conversion circuit  1  includes a first differential amplifier circuit  10  and a second differential amplifier circuit  20 . The first differential amplifier circuit  10  multiplies a potential difference between a first input signal and a second input signal by G 1  thereby providing an output signal. The second differential amplifier circuit  20  multiplies a potential difference between the output signal of the first differential amplifier circuit  10  and the second input signal by G 2  thereby providing an output, where the two gains satisfy the relation of G 1 ×G 2 &lt;0 and 0&lt;−(G 1 +1)×G 2 &lt;2.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to signal level conversion circuits, physical quantity detection devices, and electronic apparatuses. 
         [0003]    2. Related Art 
         [0004]    A variety of electronic apparatuses and systems that use various types of sensors such as gyro-sensors and acceleration sensors and perform predetermined control based on detected signals provided by the sensors, such as, car-navigation devices and personal navigation devices (PND) are widely used. 
         [0005]    Such electronic apparatuses and systems may be configured to amplify a sensor signal with a reference voltage signal in order to match the level of the sensor signal with a signal level required in a set of succeeding stages. For example, JP-A-07-046055 proposes a signal amplifier circuit having amplifiers connected in two stages and capable of independently performing an offset adjustment and a spun adjustment. Also, JP-A-07-038354 proposes a gain switching circuit having amplifiers connected in two stages and capable of amplifying an analog signal with high accuracy. 
         [0006]    However, when a sensor signal is amplified with a reference voltage signal, noise that the reference voltage itself has would be superposed on the sensor signal, which makes it difficult to achieve a low-noise implementation. 
       SUMMARY 
       [0007]    In accordance with an advantage of some aspects of the invention, it is possible to provide a signal level conversion circuit that is capable of converting the signal level of a first input signal without amplifying noise superposed on a second input signal, and a physical quantity detection device and an electronic apparatus that use the signal level conversion circuit. 
         [0008]    (1) In accordance with an embodiment of the invention, a signal level conversion circuit includes a first differential amplifier circuit that multiplies a potential difference between a first input signal and a second input signal by G 1  thereby providing an output signal, and a second differential amplifier circuit that multiplies a potential difference between the output signal of the first differential amplifier circuit and the second input signal by G 2  thereby providing an output signal, where G 1 ×G 2 &lt;0 and 0&lt;−(G 1 +1)×G 2 &lt;2. 
         [0009]    According to the embodiment described above, the first signal multiplied by G 1 ×G 2  and the second signal multiplied by {−(G 1 +1)×G 2 } are superposed on an output signal of the signal level conversion circuit. As 0&lt;−(G 1 +1)×G 2 &lt;2, when the circuit in the succeeding stage obtains a difference between the output of the signal level conversion circuit in accordance with the present embodiment and the second input signal, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level. 
         [0010]    (2) In the signal level conversion circuit, G 1  and G 2  may be G 1 &lt;0 and G 2 &gt;0, respectively. 
         [0011]    As G 1 &lt;0, the difference between the first signal and the second signal is inverted and amplified by the first differential amplifier circuit and, as G 2 &gt;0, the difference between the output signal of the first differential amplifier circuit and the second signal is non-inverted and amplified. With this configuration, G 1  and G 2  that satisfy 0&lt;−(G 1 +1)×G 2 &lt;2 can be selected. 
         [0012]    (3) In the signal level conversion circuit, G 1  and G 2  may be G 1 &gt;0 and G 2 &lt;0, respectively. 
         [0013]    As G 1 &gt;0, the difference between the first signal and the second signal is non-inverted and amplified by the first differential amplifier circuit and, as G 2 &lt;0, the difference between the output signal of the first differential amplifier circuit and the second signal is inverted and amplified. With this configuration, G 1  and G 2  that satisfy 0&lt;−(G 1 +1)×G 2 &lt;2 can be selected. 
         [0014]    (4) In the signal level conversion circuit, G 1  and G 2  may satisfy −(G 1 +1)×G 2 =1. 
         [0015]    With this configuration, the signal level of the first input signal can be converted without amplifying noise superposed on the second input signal. Accordingly, by obtaining a difference between the output signal of the signal level conversion circuit and the second input signal, noise components originated from noise superposed on the second input signal can be cancelled. 
         [0016]    (5) In the signal level conversion circuit, the second input signal may be a reference voltage signal corresponding to a reference voltage of the first input signal. 
         [0017]    (6) The signal level conversion circuit may further include a third differential amplifier circuit that amplifies or attenuates a potential difference between the output signal of the second differential amplifier circuit and the second input signal, and outputs the same. 
         [0018]    According to the signal level conversion circuit described above, the first signal multiplied by G 1 ×G 2  and the second signal multiplied by {− (G 1 +1)×G 2 } are superposed on an output signal of the second differential amplifier circuit. Accordingly, by obtaining a difference between the output signal of the second differential amplifier circuit and the second input signal by the third differential amplifier circuit, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level. In particular, by selecting G 1  and G 2  so as to satisfy −(G 1 +1)×G 2 =1, noise components originated from noise superposed on the second input signal can be cancelled. 
         [0019]    (7) In accordance with another embodiment of the invention, a physical quantity detection device includes any one of the signal level conversion circuits described above, a sensor element that detects a physical quantity, and a physical quantity signal generation section that generates a physical quantity signal having a signal level according to the physical quantity based on a signal generated by the sensor element. The physical quantity signal and a reference voltage signal are supplied to the signal level conversion circuit as the first input signal and the second input signal, respectively. 
         [0020]    (8) In accordance with still another embodiment, an electronic apparatus includes any one of the signal level conversion circuits described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a diagram showing a signal level conversion circuit in accordance with a first embodiment of the invention. 
           [0022]      FIG. 2  is a diagram showing a signal level conversion circuit in accordance with a second embodiment of the invention. 
           [0023]      FIG. 3  is a diagram showing a signal level conversion circuit in accordance with a third embodiment of the invention. 
           [0024]      FIG. 4  is a diagram showing a signal level conversion circuit in accordance with a fourth embodiment of the invention. 
           [0025]      FIG. 5  is a diagram showing an exemplary configuration of an angular velocity detection device that is an example of a physical quantity detection device. 
           [0026]      FIG. 6  is a plan view of an oscillator of a gyro-sensor element. 
           [0027]      FIG. 7  is a diagram for describing an operation of the gyro-sensor element. 
           [0028]      FIG. 8  is a diagram for describing an operation of the gyro-sensor element. 
           [0029]      FIG. 9  is a functional block diagram of an electronic apparatus. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0030]    Preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings. It is noted that the embodiments described below will not unduly limit the contents of the invention to be described in the scope of patent claims. Further, not all of the configurations described below would necessarily be essential for the invention. 
       1. Signal Level Conversion Circuit 
     1-1. First Embodiment 
       [0031]      FIG. 1  is a diagram showing a signal level conversion circuit in accordance with a first embodiment of the invention. As shown in  FIG. 1 , a signal level conversion circuit  1  in accordance with the first embodiment is configured with a first differential amplifier circuit  10  and a second differential amplifier circuit  20 . 
         [0032]    The first differential amplifier circuit  10  is configured with a resistance  11  having a resistance value R 1 , a resistance  12  having the resistance value R 1 , a resistance  13  having a resistance value R 2 , a resistance  14  having the resistance value R 2 , and a differential amplifier  15 . 
         [0033]    The resistance  11  has one end connected to an input terminal I 1  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  14  and an inverting input terminal (− input terminal) of the differential amplifier  15 . The other end of the resistance  14  is connected to an output terminal of the differential amplifier  15 . 
         [0034]    The resistance  12  has one end connected to an input terminal I 2  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  13  and a non-inverting input terminal (+ input terminal) of the differential amplifier  15 . The other end of the resistance  13  is grounded to a ground potential. 
         [0035]    When the voltage of a signal (first input signal) inputted in the input terminal I 1  is V 1 , and the voltage of a signal (second input signal) inputted in the input terminal I 2  is V 2 , the voltage of an output signal of the first differential amplifier circuit  10  (an output voltage of the differential amplifier  15 ) V 3  is given by the following formula (1). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   1 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     3 
                   
                   = 
                   
                     
                       
                         - 
                         
                           
                             R 
                             2 
                           
                           
                             R 
                             1 
                           
                         
                       
                        
                       
                         ( 
                         
                           
                             V 
                             1 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       G 
                        
                       
                           
                       
                        
                       1 
                       × 
                       
                         ( 
                         
                           
                             V 
                             1 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0036]    In the formula (1), G 1 =−R 2 /R 1  is a gain of the first differential amplifier circuit  10 , and G 1 &lt;0. In other words, the first differential amplifier circuit  10  is a differential amplifier circuit that inverts and amplifies a potential difference (V 1 −V 2 ) between the first input signal and the second input signal by G 1  (&lt;0) and outputs the same. 
         [0037]    The second differential amplifier circuit  20  is configured with a resistance  21  having a resistance value R 3 , a resistance  22  having the resistance value R 3 , a resistance  23  having a resistance value R 4 , a resistance  24  having the resistance value R 4 , and a differential amplifier  25 . 
         [0038]    The resistance  21  has one end connected to the input terminal I 2  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  24  and an inverting input terminal (− input terminal) of the differential amplifier  25 . The other end of the resistance  24  is connected to an output terminal of the differential amplifier  25 . 
         [0039]    The resistance  22  has one end connected to an output terminal of the differential amplifier  15 , and another end commonly connected to one end of the resistance  23  and a non-inverting input terminal (+ input terminal) of the differential amplifier  25 . The other end of the resistance  23  is grounded to a ground potential. 
         [0040]    The voltage of an output signal of the second differential amplifier circuit  20  (an output voltage of the differential amplifier  25 ) V 4  is given by the following formula (2). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   2 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     4 
                   
                   = 
                   
                     
                       
                         
                           R 
                           4 
                         
                         
                           R 
                           3 
                         
                       
                        
                       
                         ( 
                         
                           
                             V 
                             3 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         G 
                          
                         
                             
                         
                          
                         2 
                         × 
                         
                           ( 
                           
                             
                               V 
                               3 
                             
                             - 
                             
                               V 
                               2 
                             
                           
                           ) 
                         
                       
                       = 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0041]    Here, G 2 =R 4 /R 3  is a gain of the second differential amplifier circuit  20 , and G 2 &gt;0. In other words, the second differential amplifier circuit  20  is a differential amplifier circuit that non-inverts and amplifies a potential difference (V 3 −V 2 ) between the output signal of the first differential amplifier circuit  10  and the second input signal by G 2  (&gt;0) and outputs the same. 
         [0042]    An output terminal O of the signal level conversion circuit  1  is connected to the output terminal of the differential amplifier  25 , and an output signal of the second differential amplifier circuit  20  (an output signal of the differential amplifier  25 ) is an output signal of the signal level conversion circuit  1 . In other words, the voltage of the output signal of the signal level conversion circuit  1  is V 4 . 
         [0043]    The following formula (3) can be obtained by substituting Formula (2) for Formula (1). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   3 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           V 
                           4 
                         
                         = 
                         
                           G 
                            
                           
                               
                           
                            
                           2 
                           × 
                           
                             { 
                             
                               
                                 G 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                 × 
                                 
                                   ( 
                                   
                                     
                                       V 
                                       1 
                                     
                                     - 
                                     
                                       V 
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                               - 
                               
                                 V 
                                 2 
                               
                             
                             } 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             G 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               1 
                             
                           
                           - 
                           
                             
                               ( 
                               
                                 
                                   G 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0044]    When −(G 1 +1)×G 2 =1, Formula (3) can be modified to the following formula (4), 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   4 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           V 
                           4 
                         
                         = 
                         
                           
                             G 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               1 
                             
                           
                           + 
                           
                             V 
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               - 
                               
                                 ( 
                                 
                                   1 
                                   + 
                                   
                                     G 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 ) 
                               
                             
                             × 
                             
                               V 
                               1 
                             
                           
                           + 
                           
                             V 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0045]    Here, as G 2 &gt;0, |G 1 ×G 2 |=|1+G 2 |&gt;1, and therefore V 1  being amplified and the V 2  without being amplified (amplified by 1) are added together. As an example, if G 1 =−1.5 and G 2 =2, V 4 =3V 1 +V 2 . In other words, V 1  being amplified by −3 and V 2  without being amplified (or amplified by 1) are added together. As another example, if G 1 =−1.125 and G 2 =8, V 4 =−9V 1 +V 2 . In other words, V 1  being amplified by −9 and V 2  without being amplified (or amplified by 1) are added together. 
         [0046]    For example, when V 1  is set as an output voltage of a sensor that detects a given physical quantity (a voltage of a sensor signal (a physical quantity signal)) V 0 , and V 2  is set as a reference voltage V ref  for the sensor signal, when −(G 1 +1)×G 2 =1, V 4 =G 1 ×G 2 ×V 0 +V ref . Therefore, by performing a differential operation between V 4  and V ref , noise superposed on V ref  can be completely cancelled. 
         [0047]    In this manner, when −(G 1 +1)×G 2 =1, the signal level conversion circuit in accordance with the first embodiment generates an output signal in which a first signal being amplified and a second input signal without amplified (or amplified by 1) are added together. Further, by subtracting a voltage equivalent to the voltage of the second input signal from the voltage of the output signal of the signal level conversion circuit  1  in accordance with the first embodiment, noise components corresponding to noise superposed on the second input signal can be completely cancelled. However, when 0&lt;−(G 1 +1)×G 2 &lt;2, by subtracting a voltage equivalent to the voltage of the second input signal from the voltage of the output signal of the signal level conversion circuit  1  in accordance with the first embodiment, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level (∵−1&lt;−(G 1 +1)×G 2 −1&lt;1). 
       1-2. Second Embodiment 
       [0048]      FIG. 2  is a diagram showing a signal level conversion circuit in accordance with a second embodiment. As shown in  FIG. 2 , a signal level conversion circuit  1  in accordance with the second embodiment is configured with a first differential amplifier circuit  30  and a second differential amplifier circuit  40 . 
         [0049]    The first differential amplifier circuit  30  is configured with a resistance  31  having a resistance value R 1 , a resistance  32  having the resistance value R 1 , a resistance  33  having a resistance value R 2 , a resistance  34  having the resistance value R 2 , and a differential amplifier  35 . 
         [0050]    The resistance  31  has one end connected to an input terminal I 2  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  34  and an inverting input terminal (− input terminal) of the differential amplifier  35 . The other end of the resistance  34  is connected to an output terminal of the differential amplifier  35 . 
         [0051]    The resistance  32  has one end connected to an input terminal I 1  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  33  and a non-inverting input terminal (+ input terminal) of the differential amplifier  35 . Also, the other end of the resistance  33  is grounded to a ground potential. 
         [0052]    When the voltage of a signal (first input signal) inputted in the input terminal I 1  is V 1 , and the voltage of a signal (second input signal) inputted in the input terminal I 2  is V 2 , the voltage of an output signal of the first differential amplifier circuit  30  (an output voltage of the differential amplifier  35 ) V 3  is given by the following formula (5). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   5 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     3 
                   
                   = 
                   
                     
                       
                         
                           R 
                           2 
                         
                         
                           R 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             V 
                             1 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       G 
                        
                       
                           
                       
                        
                       1 
                       × 
                       
                         ( 
                         
                           
                             V 
                             1 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0053]    Here, G 1 =R 2 /R 1  is a gain of the first differential amplifier circuit  30 , and G 1 &gt;0. In other words, the first differential amplifier circuit  30  is a differential amplifier circuit that non-inverts and amplifies a potential difference (V 1 −V 2 ) between the first input signal and the second input signal by G 1  (&gt;0) and outputs the same. 
         [0054]    The second differential amplifier circuit  40  is configured with a resistance  41  having a resistance value R 3 , a resistance  42  having the resistance value R 3 , a resistance  43  having a resistance value R 4 , a resistance  44  having the resistance value R 4 , and a differential amplifier  45 . 
         [0055]    The resistance  41  has one end connected to an output terminal of the differential amplifier  35 , and another end commonly connected to one end of the resistance  44  and an inverting input terminal (− input terminal) of the differential amplifier  45 . The other end of the resistance  44  is connected to an output terminal of the differential amplifier  45 . 
         [0056]    The resistance  42  has one end connected to the input terminal I 2  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  43  and a non-inverting input terminal (+ input terminal) of the differential amplifier  45 . The other end of the resistance  43  is grounded to a ground potential. 
         [0057]    The voltage of an output signal of the second differential amplifier circuit  40  (an output voltage of the differential amplifier  45 ) V 4  is given by the following formula (6). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   6 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     4 
                   
                   = 
                   
                     
                       
                         - 
                         
                           
                             R 
                             4 
                           
                           
                             R 
                             3 
                           
                         
                       
                        
                       
                         ( 
                         
                           
                             V 
                             3 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         G 
                          
                         
                             
                         
                          
                         2 
                         × 
                         
                           ( 
                           
                             
                               V 
                               3 
                             
                             - 
                             
                               V 
                               2 
                             
                           
                           ) 
                         
                       
                       = 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0058]    Here, G 2 =−R 4 /R 3  is a gain of the second differential amplifier circuit  40 , and G 2 &gt;0. In other words, the second differential amplifier circuit  40  is a differential amplifier circuit that inverts and amplifies a potential difference (V 3 −V 2 ) between the output signal of the first differential amplifier circuit  30  and the second input signal by G 2  (&lt;0) and outputs the same. 
         [0059]    An output terminal O of the signal level conversion circuit  1  is connected to the output terminal of the differential amplifier  45 , and an output signal of the second differential amplifier circuit  40  (an output signal of the differential amplifier  45 ) is an output signal of the signal level conversion circuit  1 . In other words, the voltage of the output signal of the signal level conversion circuit  1  is V 4 . 
         [0060]    The following formula (7) can be obtained by substituting Formula (6) for Formula (5). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   7 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           V 
                           4 
                         
                         = 
                         
                           G 
                            
                           
                               
                           
                            
                           2 
                           × 
                           
                             { 
                             
                               
                                 G 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                 × 
                                 
                                   ( 
                                   
                                     
                                       V 
                                       1 
                                     
                                     - 
                                     
                                       V 
                                       2 
                                     
                                   
                                   ) 
                                 
                               
                               - 
                               
                                 V 
                                 2 
                               
                             
                             } 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             G 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               1 
                             
                           
                           - 
                           
                             
                               ( 
                               
                                 
                                   G 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0061]    When −(G 1 +1)×G 2 =1, Formula (7) can be modified into the following formula (8). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   8 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           V 
                           4 
                         
                         = 
                         
                           
                             G 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             
                               V 
                               1 
                             
                           
                           + 
                           
                             V 
                             2 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             
                               - 
                               
                                 ( 
                                 
                                   
                                     G 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                   
                                     
                                       G 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                     + 
                                     1 
                                   
                                 
                                 ) 
                               
                             
                             × 
                             
                               V 
                               1 
                             
                           
                           + 
                           
                             V 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
         [0062]    Here, as G 1 &gt;0, |G 1 ×G 2 |=|G 1 /(G 1 +1)|&lt;1, and therefore V 1  being attenuated and the V 2  without being amplified (amplified by 1) are added together. As an example, if G 1 =3 and G 2 =−0.25, V 4 =0.75V 1 +V 2 . In other words, V 1  being attenuated to −0.75 times its original level and V 2  without being amplified (or amplified by 1) are added together. As another example, if G 1 =1.5 and G 2 =−0.4, V 4 =0.6V 1 +V 2 . In other words, V 1  being attenuated to −0.6 times its original level and V 2  without being amplified (or amplified by 1) are added together. 
         [0063]    For example, when V 1  is set as an output voltage of a sensor that detects a given physical quantity (a voltage of a sensor signal (a physical quantity signal)) V 0 , and V 2  is set as a reference voltage V ref  for the sensor signal, when −(G 1 +1)×G 2 =1, V 4 =G 1 ×G 2 ×V 0 +V ref . Therefore, by performing a differential operation between V 4  and V ref , noise superposed on V ref  can be completely cancelled. 
         [0064]    In this manner, when −(G 1 +1)×G 2 =1, the signal level conversion circuit in accordance with the second embodiment generates an output signal in which a first signal being attenuated and a second input signal without amplified (or amplified by 1) are added together. Further, by subtracting a voltage equivalent to the voltage of the second input signal from the voltage of the output signal of the signal level conversion circuit  1  in accordance with the second embodiment, noise components corresponding to noise superposed on the second input signal can be completely cancelled. However, when 0&lt;−(G 1 +1)×G 2 &lt;2, by subtracting a voltage equivalent to the voltage of the second input signal from the voltage of the output signal of the signal level conversion circuit  1  in accordance with the second embodiment, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level (∵−1&lt;−(G 1 +1)×G 2 −1&lt;1). 
       1-3. Third Embodiment 
       [0065]      FIG. 3  is a diagram showing a signal level conversion circuit in accordance with a third embodiment of the invention. As shown in  FIG. 3 , a signal level conversion circuit  1  in accordance with the third embodiment is configured with a first differential amplifier circuit  10 , a second differential amplifier circuit  20 , and a third differential amplifier circuit  50 . 
         [0066]    As the first differential amplifier circuit  10  and the second differential amplifier circuit  20  have the same configuration as those of the first embodiment, their components are appended with the same reference numbers, and their description will be omitted. 
         [0067]    The third differential amplifier circuit  50  is configured with a resistance  51  having a resistance value R 5 , a resistance  52  having the resistance value R 5 , a resistance  53  having a resistance value R 6 , a resistance  54  having the resistance value R 6 , and a differential amplifier  55 . 
         [0068]    The resistance  51  has one end connected to an input terminal I 2  of the signal level conversion circuit  1 , and another end commonly connected to one end of the resistance  54  and an inverting input terminal (− input terminal) of the differential amplifier  55 . The other end of the resistance  54  is connected to an output terminal of the differential amplifier  55 . 
         [0069]    The resistance  52  has one end connected to an output terminal of the differential amplifier  25 , and another end commonly connected to one end of the resistance  53  and a non-inverting input terminal (+ input terminal) of the differential amplifier  55 . The other end of the resistance  53  is grounded to a ground potential. 
         [0070]    The voltage of an output signal of the third differential amplifier circuit  50  (an output voltage of the differential amplifier  55 ) V 5  is given by the following formula (9). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   9 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     5 
                   
                   = 
                   
                     
                       
                         
                           R 
                           6 
                         
                         
                           R 
                           5 
                         
                       
                        
                       
                         ( 
                         
                           
                             V 
                             4 
                           
                           - 
                           
                             V 
                             2 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         G 
                          
                         
                             
                         
                          
                         3 
                         × 
                         
                           ( 
                           
                             
                               V 
                               4 
                             
                             - 
                             
                               V 
                               2 
                             
                           
                           ) 
                         
                       
                       = 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
         [0071]    Here, G 3 =R 6 /R 5  is a gain of the third differential amplifier circuit  50 , and G 3 &gt;0. In other words, the third differential amplifier circuit  50  is a differential amplifier circuit that non-inverts and amplifies a potential difference (V 4 −V 2 ) between the output signal of the second differential amplifier circuit  20  and the second input signal by G 3  (&gt;0) and outputs the same. 
         [0072]    An output terminal O of the signal level conversion circuit  1  is connected to the output terminal of the differential amplifier  55 , and an output signal of the third differential amplifier circuit  50  (an output signal of the differential amplifier  55 ) is an output signal of the signal level conversion circuit  1 . In other words, the voltage of the output signal of the signal level conversion circuit  1  is V 5 . 
         [0073]    The following formula (10) can be obtained by substituting Formula (3) for Formula (9). 
         [0000]    
       
         
           
             
               
                 
                   Formula 
                    
                   
                       
                   
                    
                   10 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           V 
                           5 
                         
                         = 
                         
                           G 
                            
                           
                               
                           
                            
                           3 
                           × 
                           
                             ( 
                             
                               
                                 G 
                                  
                                 
                                     
                                 
                                  
                                 1 
                                 × 
                                 G 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                 × 
                                 
                                   V 
                                   1 
                                 
                               
                               - 
                               
                                 
                                   ( 
                                   
                                     
                                       G 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                     + 
                                     1 
                                   
                                   ) 
                                 
                                 × 
                                 G 
                                  
                                 
                                     
                                 
                                  
                                 2 
                                 × 
                                 
                                   V 
                                   2 
                                 
                               
                               - 
                               
                                 V 
                                 2 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                         
                           
                             G 
                              
                             
                                 
                             
                              
                             1 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             2 
                             × 
                             G 
                              
                             
                                 
                             
                              
                             3 
                             × 
                             
                               V 
                               1 
                             
                           
                           - 
                           
                             
                               { 
                               
                                 
                                   
                                     ( 
                                     
                                       
                                         G 
                                          
                                         
                                             
                                         
                                          
                                         1 
                                       
                                       + 
                                       1 
                                     
                                     ) 
                                   
                                   × 
                                   G 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 + 
                                 1 
                               
                               } 
                             
                             × 
                             G 
                              
                             
                                 
                             
                              
                             3 
                             × 
                             
                               V 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
         [0074]    When −(G 1 +1)×G 2 =1, Formula (10) can be modified into the following formula (11). 
         [0000]      Formula 11 
         [0000]        V   5   =G 1 ·G 2 ·G 3 ·V   1   (11)
 
         [0075]    In other words, in the output signal of the signal level conversion circuit  1 , noise components corresponding to noise superposed on the second input signal can be completely cancelled. Further, by adjusting the gain G 3  of the third differential amplifier circuit  50 , the total gain G 1 ×G 2 ×G 3  can be set to a desired value. 
         [0076]    For example, when V 1  is an output voltage of a sensor that detects a given physical quantity (a voltage of a sensor signal (a physical quantity signal)) V 0 , and V 2  is a reference voltage V ref  for the sensor signal, when −(G 1 +1)×G 2 =1, V 5 =G 1 ×G 2 ×G 3 ×V 0 . Therefore, noise superposed on V ref  can be completely cancelled. 
         [0077]    In this manner, when −(G 1 +1)×G 2 =1, the signal level conversion circuit in accordance with the third embodiment amplifies or attenuates the first signal G 1 ×G 2 ×G 3  times, and noise components corresponding to noise superposed on the second input signal can be completely cancelled. However, when 0&lt;−(G 1 +1)×G 2 &lt;2, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level (∵−1&lt;−(G 1 +1)×G 2 −1&lt;1). 
       1-4. Fourth Embodiment 
       [0078]      FIG. 4  is a diagram showing a signal level conversion circuit in accordance with a fourth embodiment of the invention. As shown in  FIG. 4 , a signal level conversion circuit  1  in accordance with the fourth embodiment is configured with a first differential amplifier circuit  30 , a second differential amplifier circuit  40 , and a third differential amplifier circuit  50 . 
         [0079]    As the first differential amplifier circuit  30  and the second differential amplifier circuit  40  have the same configuration as those shown in  FIG. 2 , their components are appended with the same reference numbers, and their description will be omitted. Also, as the third differential amplifier circuit  50  has the same configuration as that shown in  FIG. 3 , its components are appended with the same reference numbers, and their description will be omitted. 
         [0080]    The voltage V 5  of the output signal of the signal level conversion circuit  1  is given by the formula (10), and can be modified into the formula (11) when −(G 1 +1)×G 2 =1. 
         [0081]    Therefore, like the third embodiment, when −(G 1 +1)×G 2 =1, the signal level conversion circuit in accordance with the fourth embodiment amplifies or attenuates the first signal G 1 ×G 2 ×G 3  times, and noise components corresponding to noise superposed on the second input signal can be completely cancelled. However, when 0&lt;−(G 1 +1)×G 2 &lt;2, a noise component originated from noise superposed on the second input signal can be attenuated to {−(G 1 +1)×G 2 −1} times its original level (∵−1&lt;−(G 1 +1)×G 2 −1&lt;1). 
       2. Physical Quantity Detection Device 
       [0082]    A physical quantity detection device in accordance with an embodiment of the invention includes a sensor element that detects a given physical quantity, and generates a physical quantity signal with a signal level according to the physical quantity based on a signal generated by the sensor element. The physical quantity detection device in accordance with the present embodiment is applicable for detection of any one of various physical quantities, such as, for example, angular velocity, angular acceleration, acceleration, force, temperature, magnetic, and the like. 
         [0083]      FIG. 5  is a diagram showing an exemplary configuration of an angular velocity detection device, which is an example of the physical quantity detection device in accordance with the present embodiment. 
         [0084]    An angular velocity detection device  2  in accordance with the present embodiment is configured with a gyro-sensor element  100  and an angular velocity detector IC  60 . 
         [0085]    The gyro-sensor element  100  (an example of the sensor element) is configured with a vibrator having driver electrodes and detection electrodes disposed thereon and sealed in an unshown package. Generally, the air-tightness within the package is maintained in order to reduce the impedance of the vibrator to increase the oscillation efficiency as much as possible. 
         [0086]    The vibrator of the gyro-sensor element  100  may be made of piezoelectric single crystal, such as, for example, crystal quartz (SiO 2 ), lithium tantalate (LiTaO 3 ), lithium niobate (LiNbO 3 ) and the like, or piezoelectric material such as piezoelectric ceramics such as lead zirconate titanate (PZT) and the like, or may have a structure in which a piezoelectric thin film of zinc oxide (ZnO), aluminum nitride (AIN) or the like sandwiched between driving electrodes is arranged on a portion of a silicon semiconductor surface. The excitation device for driving vibration and the detection device for detection vibration of the gyro sensor element may be of the type using piezoelectric effect but also of the electrostatic type using Coulomb force. 
         [0087]    In accordance with the present embodiment, the gyro-sensor element  100  may be configured with a so-called double T-shaped vibrator having two T-shaped driving vibration arms. The vibrator of the gyro-sensor element  100  may be of a tuning fork type or a tuning bar type in a triangular prism shape, a quadrangular prism shape, a columnar pillar shape or the like. The vibrator may be of a type having a silicon semiconductor substrate processed into a comb-teeth shape. 
         [0088]      FIG. 6  is a plan view of the vibrator of the gyro-sensor element  100  in accordance with the present embodiment. 
         [0089]    The gyro-sensor element  100  of the present embodiment has a double T-shaped vibrator formed from a Z-cut crystal quartz substrate. The vibrator made of crystal quartz has extremely small variations in its oscillation frequency against temperature changes, and thus has an advantage in that the angular velocity detection accuracy can be made higher. It is noted that an X-axis, a Y-axis and a Z-axis shown in  FIG. 6  are the axes of quartz crystal. 
         [0090]    As shown in  FIG. 6 , the vibrator of the gyro-sensor element  100  includes two driving base portions  104   a  and  104   b  having driving vibration arms  101   a  and  101   b  extending respectively from the driving base portions  104   a  and  104   b  in the +Y axis direction and the −Y axis direction. Driving electrodes  112  and  113  are formed respectively on the side surface and the upper surface of the driving vibration arms  101   a , and driving electrodes  113  and  112  are formed respectively on the side surface and the upper surface of the driving vibration arms  101   b . The driving electrodes  112  and  113  are connected respectively to a driving circuit  200  through an external output terminal  61  and an external input terminal  62  of the angular velocity detection IC  60  shown in  FIG. 5 . 
         [0091]    The driving base portions  104   a  and  104   b  are connected respectively to a rectangular detection base portion  107  through coupling arms  105   a  and  105   b  extending in the −X axis direction and the +X axis direction, respectively. 
         [0092]    Detection vibration arms  102  extend from the detection base portion  107  in the +Y axis direction and the −Y axis direction, respectively. Detection electrodes  114  and  115  are formed on the upper surface of the detection vibration arms  102 , respectively, and common electrodes  116  are formed on the side surface of the detection vibration arms  102 , respectively. The detection electrodes  114  and  115  are connected respectively to a detection circuit  300  through external input terminals  63  and  64  of the angular velocity detection IC  60  shown in  FIG. 5 . Also, the common electrodes  116  are grounded. 
         [0093]    When an AC voltage is applied as a driving signal between the driving electrodes  112  and the driving electrodes  113  of the driving vibration arms  101   a  and  101   b , the driving vibration arms  101   a  and  101   b  have flexural vibration (excitation vibration) in a manner that mutual approach and separation of the tips of the two driving vibration arms  101   a  and  101   b  are repeated as indicated by arrows B due to inverse-piezoelectric effect. 
         [0094]    If an angular velocity is applied about the Z-axis as a rotation axis to the vibrator of the gyro-sensor element  100  in this state, the driving vibration arms  101   a  and  101   b  are subjected to a Coliolis force in a direction perpendicular to both of the direction of flexural vibration indicated by the arrows B and the Z-axis. As a result, as shown in  FIG. 8 , the coupling arms  105   a  and  105   b  vibrate as indicated by arrows C. Then, the detection vibration arms  102  have flexural vibration as indicated by arrows D, linked with the vibration of the coupling arms  105   a  and  105   b  (as indicated by arrows C). The flexural vibration of the detection vibration arms  102  and the flexural vibration (excitation vibration) of the driving vibration arms  101   a  and  101   b  associated with the Coliolis force are shifted in phase by 90 degrees. 
         [0095]    When the two driving vibration arms  101   a  and  101   b  are mutually equal in the magnitude of vibration energy or the magnitude of amplitude of vibration generated when the driving vibration arms  101   a  and  101   b  have flexural vibration (excitation vibration), the vibration energy is balanced between the driving vibration arms  101   a  and  101   b , such that the detection vibration arms  102  do not flexurally vibrate in a state in which no angular velocity is applied to the gyro-sensor element  100 . However, when the vibration energy becomes imbalance between the driving vibration arms  101   a  and  101   b , flexural vibration is generated in the detection vibration arms  102  even in a state in which no angular velocity is applied to the gyro-sensor element  100 . Such flexural vibration is called leakage vibration, which is flexural vibration indicated by arrows D, like the vibration based on the Coliolis force, but in the same phase as that of the driving signal. 
         [0096]    Then, AC charges based on these flexural vibrations are generated by the piezoelectric effect in the detection electrodes  114  and  115  on the detection vibration arms  102 . Here, the AC charges generated based on a Coliolis force change according to the magnitude of the Coliolis force (in other words, the magnitude of the angular velocity applied to the gyro-sensor element  100 ). On the other hand, AC charge generated based on leakage vibration is constant irrespective of the magnitude of angular velocity applied to the gyro-sensor element  100 . 
         [0097]    It is noted that a rectangular weight portion  103  wider than each of the driving vibration arms  101   a  and  101   b  is formed at the tip of each of the driving vibration arms  101   a  and  101   b . By forming the weight portion  103  at the tip of each of the driving vibration arms  101   a  and  101   b , a greater Coliolis force can be generated, and a desired resonance frequency can be obtained with relatively short vibration arms. Similarly, a weight portion  106  wider than each of the detection vibration arms  102  is formed at the tip of each of the detection vibration arms  102 . By forming the weight portion  106  at the tip of each of the detection vibration arms  102 , greater AC charges can be induced at the detection electrodes  114  and  115 . 
         [0098]    In this manner, the gyro-sensor element  100  outputs AC charges based on the Coliolis force (angular velocity components) about the Z-axis as a detection axis, and AC charges based on leakage vibration (vibration leakage components) in the excitation vibration through the detection electrodes  114  and  115 . 
         [0099]    Referring back to  FIG. 5 , the angular velocity detection IC  60  is configured with a driving circuit  200 , a detection circuit  300 , a reference power supply circuit  400  and a memory  410 . 
         [0100]    The reference power supply circuit  400  generates a reference voltage V ref  from a power supply voltage supplied through a power supply input terminal  65 . 
         [0101]    The driving circuit  200  is configured with a I/V conversion circuit (a current-voltage conversion circuit)  210 , a comparator  220 , AGC (Automatic Gain Control) circuit  230  and a start-up circuit  240 . 
         [0102]    A drive current that flows to the vibrator of the gyro-sensor element  100  is converted to an AC voltage signal by the I/V conversion circuit  210  with the reference voltage V ref  as the reference. 
         [0103]    The AC voltage signal outputted from the I/V conversion circuit  210  is inputted in the comparator  220  and the AGC circuit  230 . The comparator  220  compares the voltage of the inputted AC voltage signal with the reference voltage V ref , and outputs a binary signal (a rectangular wave voltage signal). 
         [0104]    The AGC circuit  230  changes the amplitude of the binary signal outputted from the comparator  220  according to the amplitude of the AC voltage signal outputted from the I/V conversion circuit  210 , and controls so as to keep the drive current constant. 
         [0105]    The binary signal outputted from the comparator  220  is supplied to the driving electrodes  112  of the vibrator of the gyro-sensor element  100  through the external output terminal  61 . 
         [0106]    In this manner, the gyro-sensor element  100  continuously excites a predetermined driving vibration shown in  FIG. 7  by an oscillation loop circulating through the driving circuit  200 . Also, by maintaining the driving current at constant, the driving vibration arms  101   a  and  101   b  of the gyro-sensor element  100  can obtain a constant vibration velocity. Therefore, the vibration velocity that is a source of generation of a Coliolis force becomes constant, whereby the sensitivity can be stabilized better. 
         [0107]    The start-up circuit  240  includes an oscillation source for causing the gyro-sensor element  100  to have flexural vibration at the time of power-on, and is separated from the oscillation loop when the amplitude of the AC voltage signal outputted from the I/V conversion circuit  210  exceeds a predetermined threshold value. 
         [0108]    The detection circuit  300  is configured with charge amplifiers  310  and  312 , a differential amplifier  314 , a high-pass filter  316 , an amplifier  318 , a synchronous detector  320 , an amplifier  322 , a low-pass filter  324 , an amplifier  326 , a signal level conversion circuit  328 , and amplifier  330 . 
         [0109]    AC charge containing an angular velocity component and a vibration leakage component is inputted in the charge amplifier  310  from the detection electrode  114  on the vibrator of the gyro-sensor element  100  through the external input terminal  63 . Similarly, AC charge containing an angular velocity component and a vibration leakage component is inputted in the charge amplifier  312  from the detection electrode  115  on the vibrator of the gyro-sensor element  100  through the external input terminal  64 . The charge amplifiers  310  and  312  convert the respectively inputted AC charges into AC voltage signals. The output signal of the charge amplifier  310  and the output signal of the charge amplifier  312  are mutually in inverse phase (shifted in phase by 180 degrees). 
         [0110]    The differential amplifier  314  differentially amplifies the output signal of the charge amplifier  310  and the output signal of the charge amplifier  312 . Components in same phase are cancelled, and components in inverse phase are amplified by addition. 
         [0111]    The high-pass filter  316  cancels DC components contained in the output signal of the differential amplifier  314 . 
         [0112]    The amplifier  318  amplifies the output signal of the high-pass filter  316 , and outputs an AC voltage signal with the reference voltage V ref  as the reference. 
         [0113]    The synchronous detector  320  performs synchronous detection of the output signal of the amplifier  318  with the binary signal outputted from the comparator  220 . The synchronous detector  320  can be configured as a switching circuit that selects the output signal of the amplifier  318  as is when the voltage level of the binary signal is higher than the reference voltage V ref , and selects an inverted signal of the output signal of the amplifier  318  inverted with respect to the reference voltage V ref  when the voltage level of the binary signal is lower than the reference voltage V ref . 
         [0114]    The output signal of the amplifier  318  contains an angular velocity component and a vibration leakage component. The angular velocity component is in the same phase with the binary signal outputted from the comparator  220 , but the vibration leakage component is in inverse phase with the binary signal. Therefore, the angular velocity component is coherently detected by the synchronous detector  320 , but the vibration leakage component is not detected. 
         [0115]    The amplifier  322  amplifies or attenuates the output signal of the synchronous detector  320  to output a signal with a desired voltage level. The low-pass filter  324  removes high frequency components contained in the output signal of the amplifier  322 , and extracts signals in a frequency range decided by the specification. 
         [0116]    The output signal of the low-pass filter  324  is amplified or attenuated to a signal with a desired voltage level by the amplifier  326 . The output signal of the amplifier  326  is a signal with a voltage level according to the angular velocity with the reference voltage V ref  as the reference, in other words, an angular velocity signal (an example of a physical quantity signal). 
         [0117]    The signal level conversion circuit  328  is any one of the signal level conversion circuits in accordance with the embodiments described in conjunction with  FIGS. 1 through 4 , receives the output signal (the angular velocity signal) of the amplifier  326  at the input terminal I 1  and the reference voltage V ref  at the input terminal I 2 , and outputs a signal that is differentially amplified through the output terminal O. The gain of the signal level conversion circuit  328  is decided according to gain adjustment data set in advance in the memory  410 . The output signal of the signal level conversion circuit  328  is outputted externally through the external output terminal  66 . 
         [0118]    The reference voltage V ref  is inputted in the amplifier  330  (a voltage follower), and outputted to the outside through the external output terminal  67 . 
         [0119]    In this manner, by incorporating the signal level conversion circuit in accordance with any one of the embodiments, a physical quantity detection device that outputs a physical quantity signal with low noise can be realized. 
       3. Electronic Apparatus 
       [0120]      FIG. 9  is a functional block diagram showing an exemplary configuration of an electronic apparatus in accordance with an embodiment of the invention. An electronic apparatus  500  in accordance with the present embodiment is configured with a signal generation section  600 , a CPU  700 , an operation section  710 , a display section  720 , a ROM (Read Only Memory)  730 , a RAM (Random Access Memory)  740 , and a communication section  750 . It is noted that the electronic apparatus in accordance with the present embodiment may be configured with a portion of the constituting elements (the sections) shown in  FIG. 9  omitted, or with other constituting elements added. 
         [0121]    The signal generation section  600  includes a signal level conversion circuit  610 , generates a given signal in response to the control of the CPU  700  and outputs the signal to the CPU  700 . 
         [0122]    The CPU  700  performs various kinds of calculation processing and control processing according to programs stored in the ROM  730 . More specifically, the CPU  700  controls the signal generation section  600 , and executes various kinds of calculation processing with signals generated by and received from the signal generation section  600 . Also, the CPU  700  performs various kinds of processing according to operation signals from the operation section  710 , processing to transmit display signals for displaying various kinds of information on the display section  720 , processing to control the communication section  750  for performing data communications with the outside, and the like. 
         [0123]    The operation section  710  may be formed from with an input device configured with operation keys, button switches and the like, and outputs operation signals in response to operation by the user to the CPU  700 . 
         [0124]    The display section  720  is a display device configured with an LCD (Liquid Crystal Display) and the like, and displays various kinds of information based on display signals received from the CPU  700 . 
         [0125]    The ROM  730  stores programs for the CPU  700  to execute various kinds of operation processing and control processing, and various kinds of programs and data for realizing predetermined functions. 
         [0126]    The RAM  740  is used as a work area for the CPU  700 , and temporarily stores programs and data readout from the ROM  730 , data inputted from the operation section  710 , operation results executed by the CPU  700  according to various kinds of programs, and the like. 
         [0127]    The communication section  750  performs various kinds of controls for establishing data communications between the CPU  700  and external devices. 
         [0128]    By incorporating the signal level conversion circuit in accordance with any one of the embodiments described above as the signal level conversion circuit  610  in the electronic apparatus  500 , processing with higher accuracy can be realized. In particular, by incorporating the signal level conversion circuit in accordance with the third embodiment or the fourth embodiment, the differential operation in a succeeding stage of the physical quantity detection device may be made unnecessary to be executed, and therefore the cost of the entire system may be reduced. 
         [0129]    It is noted that the electronic apparatus  500  can be realized as any one of various kinds of electronic apparatuses, such as, for example, a skidding prevention device for vehicles, a rollover detection device for vehicles, a cellular phone, a navigation device, a pointing device such as a mouse or the like, a digital camera, a game controller and the like. 
         [0130]    It is noted that the invention is not limited to the embodiments described above, and many changes can be made and implemented within the range of the subject matter of the invention. 
         [0131]    The invention may include compositions that are substantially the same as the compositions described in the embodiments (for example, a composition with the same function, method and result, or a composition with the same objects and result). Also, the invention includes compositions in which portions not essential in the compositions described in the embodiments are replaced with others. Also, the invention includes compositions that achieve the same functions and effects or achieve the same objects of those of the compositions described in the embodiments. Furthermore, the invention includes compositions that include publicly known technology added to the compositions described in the embodiments. 
         [0132]    The entire disclosure of Japanese Patent Application No. 2010-240736, filed Oct. 27, 2010 is expressly incorporated by reference herein.