Patent Document

CROSS REFERENCES TO RELATED APPLICATION  
       [0001]     The present application relates to and incorporates by reference Japanese Patent application No. 2004-86820 filed on Mar. 24, 2004.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a power supply circuit which supplies driving power to a signal processing circuit in a physical quantity sensor.  
         [0004]     2. Description of the Related Art  
         [0005]     Physical quantity sensors have now been used in a variety of applications in the industry. One type of physical quantity sensors is, for example, an “infrared sensor,” which is disclosed in Japanese Patent Application Laid-open Publication No. 2003-270047. The “infrared sensor” disclosed in the publication No. 2003-270047 incorporates a sensor element for detecting infrared which is adhered via an adhesive on one surface of the circuit substrate to make possible a smaller sensor and lower cost. A gap portion is configured by not coating the adhesive on the entire circumference of the recessed portion formed in the sensor element and by providing a region in a portion of the circumference in which no adhesive is coated. The gap portion can thus communicate the space in the recessed portion and the outside to prevent the sealed space formed in the recessed portion. Even if, therefore, any heat is applied to the sensor element, the volumetric gas expansion in the relevant recessed portion can be prevented to avoid the damage of the sensor element due to the damage of the thin-walled portion (membrane portion) of the relevant recessed portion.  
         [0006]     An output (hereinafter referred to as a “sensor output”) of the physical quantity sensor such as the “infrared sensor” disclosed in the publication No. 2003-270047 is usually subject to predetermined signal processing performed by a signal processing circuit. The relevant signal processing circuit may be formed on the same semiconductor substrate that has the physical quantity sensor thereon. Most of the physical quantity sensors are formed on a semiconductor substrate such as silicon, so that their sensor outputs may have temperature characteristics or have different characteristics for different production lots. To absorb such a variation in the characteristics of the sensor output, the relevant signal processing circuit includes, for example, an adjustment circuit such as the “trimming circuit in the physical quantity sensor,” which is disclosed in another Japanese Patent Application Laid-open Publication No. 2002-350256.  
         [0007]     In an adjusting circuit such as the “trimming circuit in the physical quantity sensor” disclosed in the publication No. 2002-350256, however, the relevant signal processing circuit itself and its environment may have different temperatures between in trimming adjustment before shipping products and in sensor usage after shipping products. The temperature environment of the physical quantity sensor may also be different, particularly, as in the “infrared sensor” disclosed in the publication No. 2003-270047, in the case of the relevant physical quantity sensor (sensor element) being mounted on the substrate (circuit substrate) in which the signal processing circuit is formed. In this case, there is thus a technological problem in which the trimming adjustment before shipping products may not work effectively.  
         [0008]     Specifically, with reference to the “trimming circuit in the physical quantity sensor” disclosed in the publication No. 2002-350256, the circuit includes, as a signal processing circuit, a logic circuit part, a trimming voltage control circuit part, and an analog circuit part. Each of the circuit parts to has different operating conditions, such as the operating positions, operating speeds, and operating times, between in trimming adjustment and in sensor usage. Between the two conditions, therefore, each of the circuit parts consumes different amounts of current, and each of the relevant circuit parts to generates different amounts of heat, so that the relevant signal processing circuit itself and its environment have different temperatures. Such a temperature difference may have an impact on the temperature characteristics of the relevant signal processing circuit as well as the physical quantity sensor. This may raise, therefore, the problem of so-called adjustment-deviation in that even if the characteristics-adjustment data is accurately measured for the trimming adjustment in the trimming adjustment before shipping products, the targeted characteristics may be difficult to obtain in the sensor usage after shipping products. Such a problem is hereinafter simply referred to as “adjustment deviation.” 
       SUMMARY OF THE INVENTION  
       [0009]     The present invention was made to solve the above-mentioned problems and aims to provide a power supply circuit which is able to prevent the adjustment deviation due to the different operating conditions of the signal processing circuit.  
         [0010]     To achieve the above-described object, as one aspect of the present invention, there is provided a power supply circuit supplying voltage to a signal processing circuit processing a signal from a sensor element, both of the senor element and the signal processing circuit being incorporated in a physical quantity sensor and the voltage being provided from outside the sensor, comprising: a control device controlling the voltage so that a total amount of both power consumed by the power supply circuit and power consumed by the signal processing circuit is constant; and an output line outputting power-supply voltage subjected to the control of the control device to the signal processing circuit.  
         [0011]     It is preferred that all of the sensor element, the signal processing circuit, and the power supply circuit are incorporated in the physical quantity sensor. In this configuration, for example, the control device is configured to control the total amount of consumed power to be constant by supplying to the signal processing circuit a portion of power provided by the voltage provided from outside the sensor and absorbing a variation in the power consumed by the signal processing circuit by a remaining portion of the power provided by the voltage provided from outside the sensor ((the constant power consumption).  
         [0012]     It is also preferred that the power supply circuit further comprises a thermal-connection device connecting the power supply circuit to the signal processing circuit in a heat-transferable manner.  
         [0013]     Therefore, even if the signal processing circuit has varied power consumption and increases or decreases its amount of heat generated, such constant power consumption can maintain a constant total amount of the heat generated by the relevant power supply circuit and signal processing circuit. On the other hand, the relevant power supply circuit and signal processing circuit are connected in a heat-transferable manner, so that even if the signal processing circuit generates a varied amount of heat, the relevant power supply circuit increases or decreases its amount of generated heat accordingly, thereby maintaining a constant temperature of the combination of the circuits (the maintenance of the constant temperature of the power supply circuit and signal processing circuit).  
         [0014]     It is preferred that the thermal-connection device also connects with the physical quantity sensor in a heat-transferable manner, so that the three components of the relevant power supply circuit, signal processing circuit, and physical quantity sensor are mutually connected in a heat-transferable manner. Thus a constant temperature at the combination of the power supply circuit and signal processing circuit, as well as the relevant physical quantity sensor, can be maintained as described above.  
         [0015]     It is also preferred that the thermal-connection device is a semiconductor substrate on which the power supply circuit is configured. For example, either the relevant power supply circuit and signal processing circuit, or, the relevant power supply circuit, signal processing circuit, and physical quantity sensor can be configured on the same semiconductor substrate to easily establish electrical connections thereamong in a heat-transferable manner.  
         [0016]     By way of example, the physical quantity sensor is an infrared sensor. This prevents the adjustment deviation due to the different operating conditions of the signal processing circuit which signal-processes the sensor output of the relevant infrared sensor, and the adjustment deviation due to the different operating conditions of the signal processing circuit including the relevant infrared sensor. In addition, for example, the relevant infrared sensor and relevant power supply circuit can be configured on the same semiconductor substrate to relatively easily prevent the adjustment deviation due to the different operating conditions of the signal processing circuit. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     In the accompanying drawings:  
         [0018]      FIG. 1A  schematically shows an example of a mechanical configuration of an infrared sensor according to an embodiment of the present invention and schematically shows a plan view of the infrared sensor with a cap removed;  
         [0019]      FIG. 1B  schematically shows another example of a mechanical configuration of the infrared sensor according to an embodiment of the present invention and shows a cross sectional view taken along line  1 B- 1 B in  FIG. 1A ;  
         [0020]      FIG. 2  shows a circuit diagram of an example of an electrical configuration of the infrared sensor according to the present embodiment; and  
         [0021]      FIG. 3  shows a block diagram of a configuration example of the signal processing circuit shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     With reference to  FIGS. 1A and 1B  to  3 , an embodiment of the power supply circuit according to the present invention will now be described.  
         [0023]     In this embodiment, referring to  FIGS. 1A and 1B  to  3 , a description is given to an example of an infrared sensor  20 , in which the power supply circuit according to the present invention is applied to a power supply circuit  55  which supplies drive power to a signal processing circuit  51  of a sensor element  40 . Referring to  FIGS. 1A and 1B , the mechanical configuration of the infrared sensor  20  is first described.  
         [0024]     As shown in  FIGS. 1A and 1B , the infrared sensor  20  mainly includes a stem  21 , cap  22 , filter  23 , lead pin  25 , semiconductor substrate  30 , and sensor element  40 , The stem  21  is a disk-shaped member formed by cutting or press working or the like of a metal plate. The stem  21  has one side on which is secured via adhesive or the like the semiconductor substrate  30  which is mounted with a sensor element  40 . The stem  21  also has thereon three lead holes  21   a , each of which lead pin  25  can pass through.  
         [0025]     The cap  22  is a metal plate pressed into a cylindrical shape having a bottom, which shape can cover one side of the stem  21 . An opening  22   a  is provided at almost the center of the bottom, which can act as a receiving window for infrared which is to be detected by the sensor element  40 . The opening  22   a  is closed by the filter  23  made of ceramics or single crystal such as silicon or germanium which is transparent to infrared.  
         [0026]     The lead pin  25  is an electric wire rod including copper wire plated by gold or tin. The lead pin  25  is provided passing through the lead hole  21   a  of the stem  21 . A hermetic glass  26  is air-tightly filled and seals between the external wall of the lead pin  25  passing through the lead hole  21   a  and the internal wall of the lead hole  21   a . This allows the interior space of the infrared sensor  20  defined by the stem  21 , cap  22 , filter  23 , lead pin  25 , and hermetic glass  26  to contain the semiconductor substrate  30  or sensor element  40  and to fill with nitrogen or inactive gas which absorbs no infrared.  
         [0027]     The semiconductor substrate  30  is made of silicon, for example, The semiconductor substrate  30  is sized so that the below-discussed signal processing circuit  51  or power supply circuit  55  or the like can be formed thereon and the sensor element  40  can be mounted thereon, Specifically, the semiconductor-manufacturing process can form on the semiconductor substrate  30  the signal processing circuit  51  which performs a predetermined signal processing for the sensor output from the sensor element  40  mounted on the semiconductor substrate  30 , and the power supply circuit  55  which supplies drive power to the signal processing circuit  51 , or the like.  
         [0028]     The sensor element  40  is provided with a semiconductor substrate such as silicon, on one side of which a recessed portion  40   a  is formed to form a membrane portion as a thin-walled portion. The sensor element  40  is, for example, a thermopile-type infrared detection element which sets the thick-walled portion around the membrane portion as the reference point and generates a voltage signal according to the temperature difference between the reference-point temperature and the membrane-portion temperature. The electrical equivalent circuit of the sensor element  40  can thus be expressed as a series circuit including a direct-current voltage source “e” and a resistor “r,” as shown in  FIG. 2 . Adhesive  35  adhesively secures the sensor element  40  to the semiconductor substrate  30 . A wire  45  such as a gold wire electrically connects an electrode  41  of the sensor element  40  with an electrode  31  of the semiconductor substrate  30  or with the lead pin  25 . This allows the sensor output from the sensor element  40  to be input via the relevant wire  45  to the signal processing circuit  51  on the semiconductor substrate  30  or to the lead pin  25 .  
         [0029]     The infrared sensor  20  configured as described above allows the sensor element  40  to receive infrared which enters the cap  22  through the filter  23 . The sensor element  40  converts the energy carried by the received infrared into an electrical signal (voltage). The electrical signal is then input as a sensor output into the signal processing circuit  51  or the like of the semiconductor substrate  30  and is output from the lead pin  25  to the outside after receiving a predetermined signal processing.  
         [0030]     Referring now to  FIGS. 2 and 3 , the electrical configuration of the infrared sensor  20  will be described.  FIG. 2  shows a circuit diagram of an example of the electrical configuration of the infrared sensor  20 .  FIG. 3  shows a block diagram of the configuration example of the signal processing circuit  51  shown in  FIG. 2 .  
         [0031]     As shown in  FIG. 2 , the infrared sensor  20  mainly includes, in electrical point of view, a sensor element  40  electrically connected to the semiconductor substrate  30  and both of a signal processing circuit  51  and a power supply circuit  55 . In the present embodiment, by way of example, both the circuits  51  and  55  are formed on the semiconductor substrate  30 . The power supply circuit  55  and the signal processing circuit  51  are mutually connected by a line LN, so that power-supply voltage (Vcc 1  in  FIG. 2 ), which is subjected to control carried out in the circuit  55 , is outputted from the power supply circuit  55  to the signal processing circuit  51  via the line LN. The power supply circuit  55  is also connected to a terminal TM receiving predetermined voltage to be inputted from outside the sensor.  
         [0032]     The sensor element  40  equals a series circuit including the direct-current voltage source “e” and resistor “r,” as described above. The signal processing circuit  51  is now described below with reference to  FIG. 3 , which shows its details.  
         [0033]     As shown in  FIG. 3 , the signal processing circuit  51  mainly includes an amplification circuit (AMP)  51   a , a multiplexer circuit (MUX)  51   b , a temperature-dependent voltage source (Temp)  51   c , an A/D converter (A/D)  51   d , a digital signal processor (DSP)  51   e , a read-only semiconductor memory device (ROM)  51   f , a D/A converter (D/A)  51   g , an operational amplifier (OP)  51   h , a control circuit (CTRL)  51   i , an oscillation circuit (0SC)  51   j , and an input/output interface circuit (I/O)  51   k.    
         [0034]     The sensor output is an input from the sensor element  40  as a voltage between the input terminals. The amplification circuit  51   a  first amplifies the sensor output by a predetermined gain and then inputs it via the multiplexer circuit  51   b  to the A/D converter  51   d . In addition to the amplified sensor output, A/D converter  51   d  also receives from the multiplexer circuit  51   b  a temperature-dependent voltage signal input from the temperature-dependent voltage source  51   c  as a signal to be AD-converted. The A/D converter  51   d  converts the sensor signal from the analog value into the digital value, and outputs the signal to the digital signal processor  51   e . The signal digital processor  51   e  then reads from ROM  51   f  a correction data necessary for the relevant sensor signal and performs four operations (predetermined signal processing) of the digital value based on the relevant sensor signal and correction data. Note that the correction data is previously stored in ROM  51   f  as a correction digital data for the different characteristics of each sensor element  40 . This is able to correct the offset, sensitivity, nonlinearity, and the temperature dependency thereof which reside in the sensor element  40  or signal processing circuit  51 , thereby providing the highly accurate infrared sensor  20 .  
         [0035]     Such a type of the signal processing circuit  51  can perform a plurality of samplings for the same sensor signal to provide an averaging process or a digital filter. In this circuit example using the signal processing circuit  51 , its output data is an analog voltage value, so that the D/A converter  51   g  converts the signal to the analog signal, which is then outputted via the voltage follower configured in the operational amplifier  51   h . The voltage follower usually serves to compensate the poor current-driving ability of D/A converter  51   g  itself.  
         [0036]     The input/output interface circuit  51   k  mainly transfers the writing data of ROM  51   f . The input/output interface circuit  51   k  is also used to input commands for the control of operations such as reading the sensor data before adjustment and reading the writing data, or the like. The oscillation circuit  51   j  generates a clock signal for the digital circuit or the original signal for the clock signal. The control circuit  51   i  controls the amplification circuit  51   a , multiplexer circuit  51   b , A/D converter  51   d , digital signal processor  51   e , ROM  51   f , D/A converter  51   g , or the like and adjusts their operation timings or the like.  
         [0037]     The signal processing circuit  51  as configured above has, in this embodiment, two operation modes: an operation mode “in trimming adjustment before shipping products” (hereinafter referred to as “in-adjustment mode”), and an operation mode “in sensor usage after shipping products” (hereinafter referred to as “in-use mode”). Specifically, in trimming adjustment before shipping products, the signal processing circuit  51  performs a characteristics-measuring process for obtaining sensor outputs under various conditions to obtain the different characteristics data for each sensor element  40 . Not-shown another computer or the like analyzes the characteristics data thus obtained to calculate the data which is to be written in ROM  51   f  as the correction data. The correction data thus calculated is written into ROM  51   f  via the input/output interface circuit  51   k  from the outside (for example, not-shown another computer). The in-adjustment mode mainly performs such a characteristics-measuring process and ROM-writing process.  
         [0038]     The in-use mode, on the other hand, performs processes such as selecting a plurality of ROMs  51   f  according to the sensor output from the sensor element  40 , then performing a predetermined signal processing by the digital signal processor  51   e , and additionally, outputting an analog signal via the voltage follower by the D/A converter  51   g  and operational amplifier  51   h . These two operation modes thus have different positions, different operation speeds, and different operation times at which the circuits operate in the signal processing circuit  51 . The signal processing circuit  51  therefore consumes different amount of current and generates different amount of heat accordingly in those two operation modes. Particularly, if the sensor element  40  is mounted on the semiconductor substrate  30  included in the signal processing circuit  51  as in this embodiment, the difference in the amount of heat generated between the two operation modes leads to the difference in the ambient temperature of the sensor element  40  and contributes the “adjustment deviation” as described before. The infrared sensor  20  according to the present embodiment thus has the power supply circuit  55  configured as shown in  FIG. 2  which supplies the drive power to the signal processing circuit  51 , thereby resolving the above-described “adjustment deviation.” It is noted that the power supply circuit  55  is formed on the semiconductor substrate  30  on which the signal processing circuit  51  is also formed.  
         [0039]     Specifically, as shown in  FIG. 2 , the operational amplifier OP and the resistors Ra and Rb make up a circuit in the power supply circuit  55 . This circuit is able to supply a portion of the power input provided as the input voltage Vcc 0  at the terminal TM to the signal processing circuit  51  as the power-supply voltage Vcc 1  via the resistor Rmon, and is able to control the current I through the resistor Rmon to always be constant regardless of the amount of the current consumption I′ in the signal processing circuit  51 . The resistors Ra and Rb thus divide the input voltage Vcc 0  to generate the reference voltage Vref which is received by the voltage follower by the operational amplifier OP. The output of the operational amplifier OP connects to the resistor Rmon and the power-supply voltage Vcc 1  of the signal processing circuit  51 .  
         [0040]     The operational amplifier OP thus controls its output to always be the reference voltage Vref using a voltage follower circuit, thereby always providing a constant voltage across the resistor Rmon, thereby providing constant current through the relevant resistor Rmon. The current “I” through the resistor Rmon is, on the other hand, I=(Vcc 0 −Vref)/Rmon, which divides into current “I′” through the signal processing circuit  51  and current “I” through the operational amplifier OP. Even if, therefore, the current I′ through the signal processing circuit  51  varies, the current i through the operational amplifier OP changes to compensate for the variation of the current I′, so that the amount of current I, the total of the currents (I′+i), remains unchanged.  
         [0041]     In this way, the power supply circuit  55 , which includes the voltage follower circuit by the operational amplifier OP, and the divider resistors Ra and Rb for generating reference voltage Vref, controls the total of the power consumption of the relevant power supply circuit  55  and the power consumption of the signal processing circuit  51  to be constant by supplying, through the line LN, to the signal processing circuit  51  a portion of the power input as the input voltage Vcc 0 , and absorbing the variation of the power consumption of the signal processing circuit  51  by the remaining portion of the power input as the input voltage Vcc 0 .  
         [0042]     It is noted that although there are additional currents such as the current through divider resistors Ra and Rb, and the current through the non-inverting input of the operational amplifier OP, these remain constant as long as the input voltage Vcc 0  is constant, thereby generating a constant amount of heat. No additional circuits for stabilizing the relevant current are thus necessary. In addition, because the divider resistors Ra and Rb are provided primarily for the reference voltage Vref, they generally have resistor values of dozens of kΩ or more. The input impedance of the operational amplifier OP generally has a very high value of 1 MΩ or more. These components thus generally consume currents of the order of less than a milliampere, and, on the other hand, the signal processing circuit  51  generally draws the current I of the order of a milliampere or more. The divider resistors Ra and Rb or the like may thus generate a negligible amount of heat compared to the amount of heat generated by the signal processing circuit  51 . This embodiment thus does not take into account of the current through the divider resistors Ra and Rb or the like.  
         [0043]     A description is given here below of the operation of the power supply circuit  55  with reference to specific examples. Assuming, for example, that the input voltage Vcc 0  to the power supply circuit  55  is 5.0 V, and the current I′ through the signal processing circuit  51  (hereinafter referred to as the “current consumption I′ of the signal processing circuit  51 ′”) has 10 mA in the above-described in-adjustment mode and 8 mA in the above-described in-use mode. In addition, the reference voltage Vref is set at 4.7 V, and the relevant resistor Rmon value is set at 25 Ω to have the current I through the resistor Rmon at 12 mA.  
         [0044]     If, therefore, the signal processing circuit  51  is in the in-adjustment mode, for example, the signal processing circuit  51  has the current consumption I′ of 10 mA and then the power consumption of 47 mW (=4.7 V×10 mA). The current i through the operational amplifier OP is then the current I through the resistor Rmon (12 mA) minus the current consumption I′ of the signal processing circuit  51  (10 mA), thereby providing the current i=2 mA (−12 mA−10 mA) and the power consumption of 9.4 mW=4.7 V×2 mA. The resistor Rmon has a potential difference of 0.3 V (=5.0V−4.7 V) across it and always carries a current of 12 mA, so that Rmon consumes power of 3.6 mW (=0.3 V×12 mA). If, therefore, the signal processing circuit  51  is in the in-adjustment mode, the signal processing circuit  51  consumes power of 47 mW and the power supply circuit  55  consumes power of 13 mW (=9.4 mW+3.6 mW), so that the whole of the semiconductor substrate  30  consumes power of 60 mW (=47 mW+13 mW).  
         [0045]     If, on the other hand, the signal processing circuit  51  is in the in-use mode, for example, the signal processing circuit  51  has the current consumption I′ of 8 mA and then the power consumption of 37.6 mW (=4.7 V×8 mA). The current i through the operational amplifier OP is then the current I through the resistor Rmon (12 mA) minus the current consumption I′ of the signal processing circuit  51  (8 mA), thereby providing the current i=4 mA (=12 mA−8 mA) and the power consumption of 18.8 mW (˜4.7 V×4 mA). The resistor Rmon always carries a current of 12 mA and consumes power of 3.6 mW as described above. If, therefore, the signal processing circuit  51  is in the in-use mode, the signal processing circuit  51  consumes power of 37.6 mW and the power supply circuit  55  consumes power of 22.4 mW (−18.8 mW+3.6 mW), so that the whole of the semiconductor substrate  30  consumes power of 60 mW (=37.6 mW+22.4 mW).  
         [0046]     In the specific examples as described above, it is thus understood that regardless of whether the operation mode of the signal processing circuit  51  is the in-adjustment mode or the in-use mode, the whole of the semiconductor substrate  30  consumes power of 60 mW (the constant power consumption). Because of the signal processing circuit  51  and power supply circuit  55  formed on the same semiconductor substrate  30  as described above, the constant power consumption by the whole of the semiconductor substrate  30  regardless of the operation mode of the signal processing circuit  51  can provide a constant amount of heat generated by the semiconductor substrate  30  (the maintenance of the constant temperature of the signal processing circuit  51  and power supply circuit  55 ). Even if, thus, the signal processing circuit  51  generates a varied amount of heat in the different operation modes, the whole of the semiconductor substrate  30  can generate a constant amount of heat. Even if, therefore, the sensor element  40  is mounted on the semiconductor substrate  30  as in this embodiment, it is possible to maintain a constant ambient temperature of the relevant sensor element  40  to prevent the impact on the temperature characteristics or the like of the sensor element  40 . Thus this can prevent the cause of the “adjustment deviation” as described before.  
         [0047]     As described above, the power supply circuit  55  for supplying the drive power to the signal processing circuit  51  of the sensor element  40  included in the infrared sensor  20  according to this embodiment is configured so that the resistors Ra and Rb divide the input voltage Vcc 0  to generate the reference voltage Vref, which is received by the voltage follower by the operational amplifier OP, and the output of the operational amplifier OP connects to the resistor Rmon and the power-supply voltage Vcc 1  of the signal processing circuit  51 . The power supply circuit  55  can thus control the total of the power consumption of the relevant power supply circuit  55  and the power consumption of the signal processing circuit  51  to be constant by supplying to the signal processing circuit  51  a portion of the power input as the input voltage Vcc 0  and absorbing the variation of the power consumption of the signal processing circuit  51  by the remaining portion of the power input as the input voltage Vcc 0 . In addition, the signal processing circuit  51  and the power supply circuit  55  are formed on the same semiconductor substrate  30  to make possible the heat transfer with the signal processing circuit  51 .  
         [0048]     The variation of the power consumption of the signal processing circuit  51  is thus absorbed to control the total of the power consumption of the relevant power supply circuit  55  and the power consumption of the signal processing circuit  51  to be constant (the constant power consumption). Even if, therefore, the signal processing circuit  51  has varied power consumption and increases or decreases its amount of heat generated, such constant power consumption can maintain a constant total amount of heat generated by the relevant power supply circuit  55  and signal processing circuit  51 . The relevant power supply circuit  55  and signal processing circuit  51  are, on the other hand, connected in a heat-transferable manner, so that even if the signal processing circuit  51  generates a varied amount of heat, the relevant power supply circuit  55  increases or decreases the amount of generated heat accordingly, thereby maintaining a constant temperature of the combination of the circuits (the maintenance of the constant temperature of the power supply circuit  55  and signal processing circuit  51 ). This can thus prevent the adjustment deviation due to the different operating conditions of the signal processing circuit  51 . It is noted that Rmon may depend on temperature for the purpose of preventing the adjustment deviation. This is because the current I with the temperature dependence can still provide the same amount of heat generated in trimming adjustment and in sensor usage, Accordingly, the foregoing embodiment enables the present invention to have the various advantages which can be summarized as follows.  
         [0049]     At first, even if the signal processing circuit has varied power consumption, the variation is absorbed to control the total of the power consumption of the relevant power supply circuit and the power consumption of the signal processing circuit to be constant (the constant power consumption). Even if, therefore, the signal processing circuit has varied power consumption and increases or decreases its amount of heat generated, such constant power consumption can maintain a constant total amount of the heat generated by the relevant power supply circuit and signal processing circuit. The relevant power supply circuit and signal processing circuit are, on the other hand, connected in a heat-transferable manner, so that even if the signal processing circuit generates a varied amount of heat, the relevant power supply circuit increases or decreases the amount of generated heat accordingly, thereby maintaining a constant temperature of the combination of the circuits (the maintenance of the constant temperature of the power supply circuit and signal processing circuit). This can thus prevent the adjustment deviation due to the different operating conditions of the signal processing circuit.  
         [0050]     Secondary, a constant temperature at the combination of the power supply circuit and signal processing circuit is maintained as described above, as well as the relevant physical quantity sensor. Hence this is able to prevent the adjustment deviation due to the different operating conditions of the signal processing circuit including the physical quantity sensor.  
         [0051]     Third, for example, the relevant power supply circuit and signal processing circuit, or the relevant power supply circuit, signal processing circuit, and physical quantity sensor are configured on the same semiconductor substrate to easily connect them in a heat-transferable manner. Such a configuration thus makes it possible to relatively easily prevent the adjustment deviation due to the different operating conditions of the signal processing circuit.  
         [0052]     Fourth, the adjustment deviation is prevented, which is due to the different operating conditions of the signal processing circuit which signal-processes the sensor output of the relevant infrared sensor. Moreover, the adjustment deviation is also prevented, which is due to the different operating conditions of the signal processing circuit including the relevant infrared sensor. In addition, for example, the relevant infrared sensor and relevant power supply circuit can be configured on the same semiconductor substrate to relatively easily prevent the adjustment deviation due to the different operating conditions of the signal processing circuit.  
         [0053]     By the way, in  FIG. 2  exemplifying the foregoing embodiment, the sensor element  40  has been described such that the sensor element  40  physically separated from the signal processing circuit  51 , through being electrically connected to the circuit  51 . However this is not a decisive form of the sensor element  40 . Some physical quantity sensors include an integrated type of sensor, in which a sensor element is integrated (incorporated) in a signal processing circuit to form a single device, unit, or circuit. Accordingly, the signal processing circuit according to the present invention should be construed to include, in terms of its physical configuration, the sensor element.  
         [0054]     The present invention may be embodied in several other forms without departing from the spirit thereof. The present embodiments and modifications as described is therefore intended to be only illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the claims.

Technology Category: 5