Abstract:
A temperature characteristic correction method enabling easy setting of correction points, while reducing deviations of an output signal from a target value and preventing power supply noise and power consumption from increasing. The method includes storing correction patterns, each of which includes correction points set at a temperature interval that differs between the correction patterns. The method further includes storing correction data for each correction point in each correction pattern, selecting a correction pattern corresponding to the temperature dependent characteristic of the input signal from the correction patterns, and correcting the temperature dependent characteristic of the input signal with the selected correction pattern and the correction data corresponding to the selected correction pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-088449, filed on Mar. 28, 2006, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an amplification circuit for detecting and amplifying an output signal of a sensor, such as an angular velocity sensor or an acceleration sensor. 
         [0003]    Sensors have been miniaturized over recent years and have finer output signals. Such a sensor requires an amplification circuit for detecting and amplifying sensor output. Output signals from the sensor and the amplification circuit are dependent on temperature. Thus, the amplification circuit is required to correct such temperature dependent characteristics. Accordingly, there is a need for performing such a correction process accurately and easily. 
         [0004]    In the prior art, a digital correction process and an analog correction process have been put into practice as a process performed by the sensor amplification circuit to correct the temperature dependent characteristic of a sensor output. The digital correction process uses correction data prestored for every predetermined temperature step in a storage means. Correction data corresponding to an ambient temperature is read from the memory device when the ambient temperature changes. Then, the read correction data is used to correct an output signal of the sensor amplification circuit. 
         [0005]    In the analog correction process, when the temperature dependent characteristic of the sensor output has a predetermined gradient, a gradient is set for the temperature characteristic of the amplification circuit to offset the predetermined gradient of the temperature characteristic of the sensor output. When the sensor output changes along a curve with respect to temperature changes, the gradient of the temperature dependent characteristic of the amplification circuit is switched in accordance with the temperature. In this way, the curve is approximated using a plurality of straight lines to correct the output signal of the sensor amplification circuit. 
         [0006]      FIG. 1  shows a sensor amplification circuit  100  including a digital correction circuit for digitally correcting the temperature dependent characteristic of a sensor output. A bridge type sensor  1  is supplied with constant current from a current source  3  included in an IC chip  2 . Output voltages Vs 1  and Vs 2  of the sensor  1  are applied to an amplification circuit unit  4  included in the IC chip  2 . 
         [0007]    The amplification circuit unit  4  includes input-stage amplifiers  5   a  and  5   b  for receiving the output voltages Vs 1  and Vs 2  of the sensor  1 , an amplifier  6  for amplifying the difference between output voltages of the input-stage amplifiers  5   a  and  5   b , an amplifier  7  for amplifying an output signal of the amplifier  6 , and an output-stage amplifier  8  for amplifying an output voltage of the amplifier  7  and generating an output signal Vout. 
         [0008]    The input-stage amplifiers  5   a  and  5   b  include feedback resistors R 1   a  and R 1   b , which are variable resistors. The resistances of the feedback resistors R 1   a  and R 1   b  are adjusted to adjust the gain of the amplification circuit unit  4 . The amplifier  6  includes an input terminal connected to ground GND via a voltage adjustment circuit  9 . The voltage adjustment circuit  9  is adjusted to adjust the offset voltage of the amplification circuit unit  4 . 
         [0009]    The amplifier  7  includes a feedback resistor R 2 , which is a variable resistor. The resistance of the feedback resistor R 2  is adjusted to adjust the gain of the amplification circuit unit  4 . The output-stage amplifier  8  includes an input terminal connected to a ground GND via a voltage adjustment circuit  10 . The voltage adjustment circuit  10  is adjusted to adjust the offset voltage of the amplification circuit unit  4 . 
         [0010]    Although not shown in  FIG. 1 , each of the resistors R 1   a , R 1   b , and R 2  includes a plurality of resistors connected in series and a plurality of switches respectively connected in parallel to the resistors. Each of the switches is switched to adjust the resistance of each of the resistors R 1   a , R 1   b , and R 2  in steps. In the same manner, each of the voltage adjustment circuits  9  and  10  includes a plurality of resistors connected in series and a plurality of switches respectively connected in parallel to the resistors. Each of the switches is switched to adjust in steps the voltage value of each of the voltage adjustment circuits  9  and  10 . 
         [0011]    The amplification circuit unit  4  digitally corrects the temperature characteristic of the sensor  1  in accordance with the operation of a control circuit  11  to generate a corrected output signal Vout. The control circuit  11  is connected to a temperature sensor  12  and a memory device  13   a . The temperature sensor  12  detects the ambient temperature. The memory device  13   a  prestores correction data corresponding to each temperature for adjusting the resistances of the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuits  9  and  10 . The control circuit  11  reads correction data corresponding to the ambient temperature from the memory device  13   a  based on a detection signal of the temperature sensor  12 , converts the read correction data into control data for adjusting the resistances, and stores the control data into a data latch unit  13   b . The resistances of the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuits  9  and  10  are adjusted based on the control data stored in the data latch unit  13   b.    
         [0012]      FIG. 2  is a graph showing the correction operation for the temperature dependent characteristic performed by the sensor amplification circuit  100 . Characteristic curve X 1  shown in  FIG. 2  indicates the level of an output signal of the amplification circuit unit  4  when the correction operation is not performed. As shown in  FIG. 2 , the characteristic curve X 1  indicates a higher output level for a higher temperature. It is preferable that the characteristic curve X 1  be corrected in a manner that the temperature characteristic be flat at a predetermined target value (zero level in  FIG. 2 ) with no temperature dependency. That is, it is preferable that the temperature characteristic be expressed by a straight line having a zero-gradient and intersecting with the vertical axis at the predetermined target value. 
         [0013]    In  FIG. 2 , characteristic curve X 2  indicates the level of an output signal of the amplification circuit unit  4  obtained through the temperature dependent characteristic correction performed by the amplification circuit unit  4  based on the operation of the control circuit  11 . The characteristic curve X 2  indicates the level of an output signal obtained by adjusting the resistances of the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuits  9  and  10  in the amplification circuit unit  4  at intervals of 10° C. 
         [0014]    As shown in  FIG. 2 , the characteristic curve X 2  indicates that the level of the output signal converges on its target value at each of correction points P 1  to P 10 , which are set at intervals of 10° C. However, the characteristic curve X 2  deviates from the target value between the correction points. The deviations occur along the temperature dependent characteristic expressed using the characteristic curve X 1 . Thus, the characteristic curve X 2  is not a straight line having a zero-gradient but is a curve indicating that the level of the output signal changes in a sawtooth-like manner depending on the temperature. 
         [0015]      FIG. 3  shows a sensor amplification circuit  200  including an analog correction circuit for performing analog correction of a temperature dependent characteristic of a sensor output. An output-stage amplifier  14  has a first input terminal for receiving a sensor output Vs, which is similar to the output voltage of the sensor  1  shown in  FIG. 1 , and a second input terminal for receiving output voltage Va of an analog correction amplifier  15 . 
         [0016]    Voltage Vt having a temperature dependent characteristic as shown in  FIG. 4(   a ) and reference voltage Vref that is not temperature-dependent and is constant as shown in  FIG. 4(   b ) are respectively applied to the two input terminals of the analog correction amplifier  15  via a switch circuit  16 . The voltage Vt is generated by a forward voltage at a PN junction of a transistor or a diode, and has a temperature dependent characteristic. Further, the voltage Vt changes linearly with respect to temperature changes at a gradient of, for example, −2 mV/° C. The reference voltage Vref is generated using a bandgap reference voltage. 
         [0017]    The switch circuit  16  switches the voltage Vt and the reference voltage Vref respectively applied to the two input terminals of the analog correction amplifier  15 . The switch circuit  16  either applies the voltage Vt to the first input terminal and the reference voltage Vref to the second input terminal or the reference voltage Vref to the first input terminal and the voltage Vt to the second input terminal. 
         [0018]    A feedback resistor R 3 , which is a variable resistor, is connected between the first input terminal and output terminal of the analog correction amplifier  15 . A variable resistor R 4  and a voltage adjustment circuit  17  are connected between the second input terminal of the analog correction amplifier  15  and ground GND. 
         [0019]    In the same manner as the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuits  9  and  10  shown in  FIG. 1 , each of the resistors R 3  and R 4  and the voltage adjustment circuit  17  includes a plurality of resistors connected in series and a plurality of switches respectively connected in parallel to the resistors. Each of the switches is switched to adjust the resistances of the resistors R 3  and R 4  or the voltage value of the voltage adjustment circuit  17  in steps. 
         [0020]    The analog correction amplifier  15  outputs the output voltage Va that changes linearly based on changes in the ambient temperature shown in  FIG. 4(   c ). The switch circuit  16  selects whether the output voltage Va is to increase or decrease when the ambient temperature increases. The gradient of the output voltage Va is adjusted by adjusting the resistances of the resistors R 3  and R 4 . Further, the offset voltage of the output signal Vout of the output-stage amplifier  14  is adjusted by adjusting the voltage value of the voltage adjustment circuit  17 . 
         [0021]    As shown in  FIG. 4(   d ), when the sensor output Vs changes linearly with respect to the ambient temperature, the gradient of the output voltage Va of the analog correction amplifier  15  is set to offset the gradient of the sensor output Vs. As a result, the output signal Vout that is not temperature-dependent as shown in  FIG. 4(   e ) is output from the output-stage amplifier  14 . 
         [0022]      FIG. 5  is a graph showing the correction operation of the temperature dependent characteristic actually performed by the sensor amplification circuit  200  including the analog correction amplifier  15 . The characteristic curve X 1  shown in  FIG. 5  indicates the level of an output signal of the output-stage amplifier  14  when the correction operation is not performed. As shown in  FIG. 5 , the characteristic curve X 1  is corrected so as to obtain a temperature characteristic expressed by a characteristic curve, which is flat at a predetermined target value with no temperature dependency. To enable such correction, the characteristic curve X 1  is first approximated using two straight lines L 1  and L 2 . The resistances of the resistors R 3  and R 4  and the voltage adjustment circuit  17  are selected in a manner to offset the gradients and the offset values of the straight lines L 1  and L 2 . For example, the resistances of the resistors R 3  and R 4  are selected in a manner to cause switching between the straight lines L 1  and L 2  at 10° C. 
         [0023]    In  FIG. 5 , the characteristic curve X 3  indicates the temperature dependent characteristic that has been corrected via the analog correction process. As shown in  FIG. 5 , the characteristic curve X 3  is substantially flat near the target output value. However, the characteristic curve X 3  deviates from the target output value in the vicinity of 10° C. at which the switching between the approximate straight lines L 1  and L 2  occurs. Accordingly, an accurately flat temperature characteristic cannot be obtained. 
         [0024]    Japanese Laid-Open Patent Publication No. 2003-84728 describes a voltage generation circuit that includes a circuit for performing temperature compensation through analog control and a circuit for performing temperature compensation through digital control. The voltage generation circuit switches between analog control and digital control in accordance with the temperature region. 
         [0025]    Japanese Laid-Open Patent Publication No. 11-64123 describes a bridge circuit that includes a compensation resistor for performing rough compensation and a compensation unit for generating a finely compensated digital overvoltage. 
         [0026]    Japanese Laid-Open Patent Publication No. 11-194061 describes a structure for performing temperature compensation in a sensor drive circuit with a digital compensation means. 
         [0027]    Japanese Laid-Open Patent Publication No. 2001-143183 describes a structure similar to the analog correction amplifier shown in  FIG. 3 . 
       SUMMARY OF THE INVENTION 
       [0028]    The characteristic curve X 2  digitally corrected by the sensor amplification circuit  100  shown in  FIGS. 1 and 2  converges on the target output value at the correction points P 1  to P 10  that are set at intervals of 10° C. but deviates from the target output value between the correction points. The deviations occur along the temperature dependent characteristic expressed by the characteristic curve X 1  of the sensor  1 . Thus, the characteristic curve X 2  is not a straight line having a zero-gradient but is a curve that changes in a sawtooth-like manner depending on temperatures. 
         [0029]    The sawtooth deviations from the target output value may be reduced by increasing the correction points. However, an increase in the number of correction points increases the amount of data to be stored in the memory device  13   a . As a result, the number of times correction data corresponding to each temperature region is read from the memory device  13   a  increases, and the number of times the resistances are changed in the sensor amplification circuit  100  increases. This increases power supply noise and power consumption of the sensor amplification circuit  100 . 
         [0030]    The characteristic curve X 3  obtained through analog correction by the sensor amplification circuit  200  shown in  FIGS. 3 and 5  deviates from the target output value at temperatures at which the characteristic curve X 1  deviates from the approximate straight lines L 1  and L 2 . The deviations from the target output value may be reduced by increasing approximate lines. However, an increase in the number of approximate straight lines increases the number of times the resistances of the resistors R 3  and R 4  are changed to switch the approximate straight line gradient. This increases power supply noise and power consumption of the sensor amplification circuit  200 . 
         [0031]    The above publications all fail to describe a structure that performs both digital correction and analog correction to reduce deviations of an output signal from a target output value while preventing power supply noise and power consumption from increasing. 
         [0032]    The present invention provides a sensor amplification circuit enabling easy setting of correction points while reducing deviations of an output signal from a target output value and preventing power supply noise and power consumption from increasing. 
         [0033]    One aspect of the present invention is a method for correcting a temperature dependent characteristic of an input signal. The method includes storing a plurality of correction patterns, each including a plurality of correction points set at a temperature interval that differs between the correction patterns. Further, the method includes storing correction data for each of the correction points in each of the correction patterns, selecting a correction pattern corresponding to the temperature dependent characteristic of the input signal from the plurality of correction patterns, and correcting the temperature dependent characteristic of the input signal with the selected correction pattern and the correction data corresponding to the selected correction pattern. 
         [0034]    A further aspect of the present invention is an amplification circuit for a sensor. The amplification circuit includes a memory device for storing a plurality of correction patterns set in accordance with various temperature dependent characteristics of an input signal. Each of the correction patterns includes a plurality of correction points set at a temperature interval that differs between the correction patterns. The memory device further stores correction data for each of the correction points. A correction circuit corrects the temperature dependent characteristic of the input signal with the correction data for each of the correction points in the correction patterns. A temperature sensor detects ambient temperature. A control circuit for operating the correction circuit based on the correction pattern and correction data corresponding to the ambient temperature detected by the temperature sensor. 
         [0035]    Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
           [0037]      FIG. 1  is a schematic circuit diagram showing a sensor amplification circuit in the prior art; 
           [0038]      FIG. 2  is a graph showing a correction operation for correcting a temperature dependent characteristic performed by the prior art sensor amplification circuit; 
           [0039]      FIG. 3  is a schematic circuit diagram showing a sensor amplification circuit in the prior art; 
           [0040]      FIGS. 4(   a ) to  4 ( e ) are graphs showing various temperature dependent characteristics; 
           [0041]      FIG. 5  is a graph showing a correction operation for correcting a temperature dependent characteristic performed by a sensor amplification circuit in the prior art; 
           [0042]      FIG. 6  is a schematic circuit diagram showing a sensor amplification circuit according to a first embodiment of the present invention; 
           [0043]      FIG. 7  is a schematic block diagram showing a control unit of the sensor amplification circuit in the first embodiment; 
           [0044]      FIG. 8  is a table showing a correction pattern map; 
           [0045]      FIG. 9  is a table showing a correction pattern map; 
           [0046]      FIG. 10  is a graph showing a correction pattern in the first embodiment; 
           [0047]      FIG. 11  is a graph showing another correction pattern in the first embodiment; 
           [0048]      FIG. 12  is a graph showing a further correction pattern in the first embodiment; 
           [0049]      FIG. 13  is a graph showing a correction operation of the sensor amplification circuit in the first embodiment; 
           [0050]      FIG. 14  is a graph showing a correction pattern according to a second embodiment of the present invention; and 
           [0051]      FIG. 15  is a graph showing a correction pattern according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0052]    In the drawings, like numerals are used for like elements throughout. 
         [0053]      FIG. 6  shows a sensor amplification circuit  300  including a digital correction circuit  18  for performing digital correction on a temperature dependent characteristic of a sensor output and an analog correction circuit  19  for performing analog correction on a temperature dependent characteristic of a sensor output. 
         [0054]    A bridge type sensor  1  is supplied with a constant current from a current source  3  included in an IC chip  21 . Output voltages Vs 1  and Vs 2  of the sensor  1  are applied to an amplification circuit unit  22  in the IC chip  21 . 
         [0055]    The amplification circuit unit  22  includes input-stage amplifiers  5   a  and  5   b  for receiving the output voltages Vs 1  and Vs 2  of the sensor  1 , an amplifier  6  for amplifying the difference between output voltages of the input-stage amplifiers  5   a  and  5   b , an amplifier  7  for amplifying an output signal of the amplifier  6 , and an output-stage amplifier  8  for amplifying an output voltage of the amplifier  7  to generate an output signal Vout. 
         [0056]    The input-stage amplifiers  5   a  and  5   b  include feedback resistors R 1   a  and R 1   b , which are variable resistors. The resistances of the feedback resistors R 1   a  and R 1   b  are adjusted to adjust the gain of the amplification circuit unit  22 . The amplifier  6  includes an input terminal connected to ground GND via a voltage adjustment circuit  9 . The voltage adjustment circuit  9  is adjusted to adjust the offset voltage of the amplification circuit unit  22 . 
         [0057]    The amplifier  7  includes a feedback resistor R 2 , which is a variable resistor. The resistance of the feedback resistor R 2  is adjusted to adjust the gain of the amplification circuit unit  22 . 
         [0058]    The output-stage amplifier  8  receives an output signal of the amplifier  7  and an output voltage Va of an analog correction amplifier  15  to generate an output signal Vout based on the input signals. 
         [0059]    As shown in  FIG. 7 , each of the feedback resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuit  9  includes a plurality of resistors r connected in series and a plurality of switches sw respectively connected in parallel to the resistors. Each of the switches sw is switched to adjust in steps the resistance of each of the resistors R 1   a  and R 1   b  or the voltage value of the voltage adjustment circuit  9 . 
         [0060]    Voltage Vt, which has a temperature dependent characteristic, and a reference voltage Vref, which is not temperature-dependent and is constant, are respectively applied to the two input terminals of the analog correction amplifier  15  via a switch circuit  16 . The voltage Vt is generated from a forward voltage at a PN junction of a transistor or a diode and has a temperature dependent characteristic that linearly changes the voltage with respect to temperature changes at a gradient of, for example, −2 mV/° C. The reference voltage Vref is generated by a reference voltage generation circuit  23  using, for example, a bandgap reference voltage. 
         [0061]    The switch circuit  16  switches the voltage Vt and the reference voltage Vref applied to the two input terminals of the analog correction amplifier  15 . More specifically, the switch circuit  16  either applies the voltage Vt to the first input terminal and the reference voltage Vref to the second input terminal or the reference voltage Vref to the first input terminal and the voltage Vt to the second input terminal. 
         [0062]    A feedback resistor R 3 , which is a variable resistor, is connected between an output terminal and the first input terminal of the analog correction amplifier  15 . A variable resistor R 4  and a voltage adjustment circuit  17  are connected between the second input terminal of the analog correction amplifier  15  and ground GND. 
         [0063]    As shown in  FIG. 7 , each of the resistors R 3  and R 4  and the voltage adjustment circuit  17  includes a plurality of resistors r connected in series and a plurality of switches sw respectively connected in parallel to the resistors. Each of the switches sw is switched to adjust in steps the resistance of each of the resistors R 3  and R 4  or the voltage value of the voltage adjustment circuit  17 . 
         [0064]    The amplification circuit unit  22  generates the output signal Vout obtained through digital correction and analog correction of the temperature characteristic of the sensor  1  in accordance with the operation of a control circuit  24 . The control circuit  24  is connected to a temperature sensor  12  and a memory device  25 . The temperature sensor  12  detects the ambient temperature. As shown in  FIG. 7 , the memory device  25  prestores a large number of correction patterns  0  to n, which are used to correct the resistances of the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuit  9 . 
         [0065]    The control circuit  24  stores control data for adjusting the resistances in the amplification circuit unit  22  in a data latch unit  26  based on a pre-selected one of the correction patterns  0  to n and a detection signal of the temperature sensor  12 . The control data stored in the data latch unit  26  is then used to adjust the resistances of the resistors R 1   a , R 1   b , R 2 , R 3 , and R 4  and the voltage adjustment circuits  9  and  17 . 
         [0066]      FIG. 8  shows an example of a correction pattern map (first correction pattern map) M 1  stored in the memory device  25 . The correction pattern  0  corresponds to the characteristic curve X 1  shown in  FIG. 10 . The characteristic curve X 1  has a gradient that becomes steeper at higher temperatures. In the pattern  0 , the temperature interval between the correction points P 1  to P 10  is narrowed as the temperature becomes higher. In  FIG. 10 , the temperature range of −30 to 60° C. is divided into temperature regions  1  to  9 , and correction points P 1  to P 10  are set at the boundaries of these regions. 
         [0067]    Further, the memory device  25  prestores correction data for correcting the output signal Vout to its target value at each of the correction points P 1  to P 10 . The memory device  25  also stores gradient data that is set to offset the gradient of the characteristic curve X 1  in each of the temperature regions. 
         [0068]      FIG. 9  shows a gradient data selection map (second correction pattern map) M 2  that is stored in the memory device  25 . The gradient data selection map M 2  sets gradient data A, B, C, etc. for the temperature regions  1  to  9  of the correction pattern  0 . The gradient data associates a greater gradient with a temperature region having a narrower temperature interval. 
         [0069]    In  FIG. 8 , the correction pattern  1  corresponds to the characteristic curve X 12  shown in  FIG. 11 . The characteristic curve X 12  has a gradient that becomes steeper at low and high temperatures in the temperature range of −30 to 60° C. The characteristic curve X 12  has a negative gradient in the low-temperature portion of the temperature range. The characteristic curve X 12  has a positive gradient in the high-temperature portion of the temperature range. In  FIG. 11 , the temperature range of −30 to 60° C. is divided into temperature regions  1  to  13 , and correction points P 1  to P 14  are set at the boundaries of these regions. 
         [0070]    In the pattern  1 , the temperature interval between the correction points P 1  to P 14  narrows in the low-temperature portion and the high-temperature portion. The correction pattern map M 2  sets gradient data C, B, etc. for the temperature regions  1  to  13  of the correction pattern  1 . 
         [0071]    In  FIG. 8 , the pattern  2  corresponds to the characteristic curve X 13  shown in  FIG. 12 . The characteristic curve X 13  has a constant gradient in the temperature range of −30 to 60° C. More specifically, the characteristic curve X 13  is a straight line in this temperature range. The pattern  2  has correction points P 1  and P 2  that are respectively set at the two ends of this temperature range. The correction pattern map M 2  sets the same gradient data for the entire temperature region of the correction pattern  2 . 
         [0072]    The operation of the sensor amplification circuit  300  having the correction pattern maps M 1  and M 2  will now be described. 
         [0073]      FIG. 13  is a graph showing the correction operation performed when the output voltages Vs 1  and Vs 2  of the sensor  1  have the characteristics shown by the characteristic curve X 1 . In this case, the control circuit  24  first performs setting to select the correction pattern  0 . The control circuit  24  then reads the temperature regions  1  to  9  of the pattern  0  from the correction pattern map M 1  stored in the memory device  25 , and sets the read temperature regions. The control circuit  24  also reads correction data associated with each of the correction points P 1  to P 10 , calculates control data for adjusting the resistances of the resistors R 1   a , R 1   b , and R 2  and the voltage adjustment circuit  9  of the digital correction circuit  18 , and stores the control data in the data latch unit  26 . 
         [0074]    The control circuit  24  also reads gradient data associated with each of the temperature regions from the correction pattern map M 2 , calculates control data for adjusting the resistances of the resistors R 3  and R 4  and the voltage adjustment circuit  17  of the analog correction circuit  19 , and stores the control data into the data latch unit  26 . 
         [0075]    In this state, when the output voltages Vs 1  and Vs 2  expressed by the characteristic curve X 1  are applied by the sensor  1 , the digital correction circuit  18  operates to correct the characteristic curve X 1  to a predetermined target output value (zero level in  FIG. 13 ) at each of the correction points P 1  to P 10 . 
         [0076]    The analog correction circuit  19  operates based on the gradient data to correct the characteristic curve X 1  in each of the temperature regions between the correction points P 1  to P 10 . In  FIG. 13 , the gradient of the output voltage Va of the analog correction amplifier  15  adjusted based on the gradient data is indicated by dotted lines. This operation eliminates the temperature dependent characteristic from the characteristic curve X 1 . In this manner, the characteristic curve X 1  is corrected to a characteristic curve X 14 , which is flat approximately at a predetermined target value with no temperature dependency. The corrected characteristic curve X 14  is then output as the output signal Vout. 
         [0077]    When the output voltages Vs 1  and Vs 2  of the sensor  1  have the characteristics shown by the characteristic curve X 12  of  FIG. 11 , the control circuit  24  performs setting to select the correction pattern  1 . The control circuit  24  then reads the temperature regions  1  to  13  of the pattern  1  from the correction pattern map M 1  stored in the memory device  25  and sets the read temperature regions. The control circuit  24  also reads correction data associated with each of the correction points P 1  to P 14 , calculates control data, and stores the control data into the data latch unit  26 . 
         [0078]    Further, the control circuit  24  reads the gradient data associated with each of the temperature regions of the pattern  1  from the correction pattern map M 2 , calculates control data, and stores the control data in the data latch unit  26 . 
         [0079]    In this state, when the output voltages Vs 1  and Vs 2  expressed by the characteristic curve X 12  are applied by the sensor  1 , the digital correction circuit  18  operates to correct the characteristic curve X 12  to a predetermined target value at each of the correction points P 1  to P 13 . Further, the analog correction circuit  19  operates based on the gradient data to correct the characteristic curve X 12  in each of the temperature regions between the correction points P 1  to P 14 . 
         [0080]    This operation eliminates the temperature dependent characteristic from the characteristic curve X 12 . As a result, the characteristic curve X 12  is corrected to a characteristic curve, which is flat approximately at a predetermined target value with no temperature dependency. The corrected characteristic curve is then output as the output signal Vout. 
         [0081]    When the output voltages Vs 1  and Vs 2  of the sensor  1  have the characteristics shown by the characteristic curve X 13  of  FIG. 12 , the control circuit  24  performs setting to select the correction pattern  2 . The control circuit  24  then reads the temperature regions of the pattern  2  from the correction pattern map M 1  stored in the memory device  25  and sets the read temperature regions. The control circuit  24  also reads correction data associated with each of the correction points P 1  and P 2 , calculates control data, and stores the control data into the data latch unit  26 . 
         [0082]    The control circuit  24  also reads gradient data of the pattern  2  from the correction pattern map M 2 , calculates control data, and stores the control data into the data latch unit  26 . 
         [0083]    In this state, when the output voltages Vs 1  and Vs 2  expressed by the characteristic curve X 13  are applied by the sensor  1 , the digital correction circuit  18  and the analog correction circuit  19  operate to correct the characteristic curve X 13 . The corrected characteristic curve is then output as the output signal Vout. 
         [0084]    The sensor amplification circuit  300  of the first embodiment has the advantages described below. 
         [0085]    (1) The temperature characteristic curve of the sensor output is corrected at the correction points that are set at temperature intervals that narrow as the gradient of the temperature characteristic curve becomes steeper. This improves the correction accuracy for the temperature dependent characteristic of the sensor output. 
         [0086]    (2) The memory device  25  prestores correction patterns for different temperature dependent characteristics of sensor outputs and performs the correction process by reading the correction pattern corresponding to the characteristic that is to be corrected. Thus, different temperature dependent characteristics of the sensor are easily corrected. The characteristic curve of the sensor  1  is corrected using one of the preset correction patterns selected in accordance with the temperature dependent characteristic of the sensor  1  without having to detect the temperature dependent characteristics of the sensor  1  individually. 
         [0087]    (3) In the temperature regions set for each correction pattern, analog correction is performed using gradient data that is preset for the correction pattern. The gradient data is obtained easily. This improves the correction accuracy of the correction performed in each of the temperature regions. 
         [0088]    (4) The gradient data of the temperature regions associates a steeper gradient for a temperature region defined by a narrower temperature interval. This improves the correction accuracy of the correction performed in each of the temperature regions. 
         [0089]    (5) The temperature interval of correction points widens in temperature regions at which the gradient of the sensor output temperature characteristic is small. This reduces the number of times the correction data or the gradient data is read from the memory device  25  and the number of times the digital correction circuit  18  and the analog correction circuit  19  adjust the resistances. This prevents power supply noise of the sensor amplification circuit  300  from being generated and reduces the power consumption of the sensor amplification circuit  300 . 
         [0090]    (6) The temperature interval of correction points widens in temperature regions at which the gradient of the temperature characteristic curve is small. Further, the temperature interval of correction points narrows in temperature regions at which the gradient of the temperature characteristic curve is large. This improves the correction accuracy without increasing the total number of the correction points. 
       Second Embodiment 
       [0091]      FIG. 14  is a graph showing a correction operation performed by a sensor amplification circuit  300  according to a second embodiment of the present invention. In the second embodiment, the temperature regions of the preset correction patterns are finely adjusted to further improve correction accuracy. 
         [0092]    More specifically, temperature regions of a correction pattern corresponding to the characteristic curve X 15  are finely adjusted in a manner that correction points P 4  to P 10  are moved to correction points P 4   a  to P 10   a . This generates a correction pattern corresponding to characteristic curve X 16 . 
         [0093]    As a result, the correction accuracy of a sensor output having a temperature dependent characteristic differing from the temperature dependent characteristics of the preset correction patterns is improved. 
       Third Embodiment 
       [0094]      FIG. 15  is a graph showing a correction operation performed by a sensor amplification circuit  300  according to a third embodiment of the present invention. In the third embodiment, correction points P 1  to P 10  of preset correction patterns are shifted, for example, to a low-temperature side within the same temperature range to further improve correction accuracy. 
         [0095]    More specifically, the correction points P 1  to P 10  of a correction pattern corresponding to the characteristic curve X 17  are shifted to the low-temperature side by 10° C., that is, the correction points P 1  to p 10  are shifted to correction points P 2   b  to P 10   b . This generates a correction pattern corresponding to characteristic curve X 18 . 
         [0096]    As a result, the correction accuracy of a sensor output having a temperature dependent characteristic differing from the temperature dependent characteristics of the preset correction patterns is improved. 
         [0097]    It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
         [0098]    The temperature dependent characteristic may be corrected by only the digital correction performed by the digital correction circuit  18  at the correction points of the selected correction pattern. In this case, the analog correction is not performed in the regions between the correction points. Because the correction points at set at narrower temperature intervals for temperature regions in which the gradient of the temperature dependent characteristic is large, the digital correction improves correction accuracy as compared with the digital correction of the prior art. 
         [0099]    The temperature dependent characteristic may be corrected only by the analog correction using the gradient data in the temperature regions of the selected correction pattern. 
         [0100]    The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.