JP2012093244A - Physical amount detection circuit and physical amount detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical amount detection circuit and a physical amount detection method capable of improving detection sensitivities of a physical amount within the entire physical amount detection range while maintaining linearity of a voltage change in relation to a physical amount change.SOLUTION: A physical amount detection circuit 1 includes: a humidity sensor (physical amount sensor) in which a resistance value is exponentially changed in relation to a humidity (physical amount) change; a plurality of resistors each of which is serially connected to the humidity sensor; and an arithmetic processing unit 4 for weighting and totaling voltage values that are resistance-voltage-divided by the humidity sensor and any of the plurality of resistors to convert the values so as to change linearly to the humidity change. The plurality of resistors include a first resistor 31 exhibiting a resistance value equal to that of the humidity sensor 21 at a lower limit value within the humidity detection range, and a second resistor 32 exhibiting a resistance value equal to that of the humidity sensor 22 at an upper limit value within the humidity detection range.

Description

  The present invention relates to a physical quantity detection circuit and a physical quantity detection method.

  There is a physical quantity sensor that converts a change in physical quantity into a change in resistance value. A physical quantity detection circuit in which a resistance voltage divider that detects a physical quantity (humidity) using such a physical quantity sensor (for example, a resistance change type humidity sensor) is formed is known (see, for example, Patent Document 1 and Patent Document 2). ). Such a physical quantity detection circuit detects a physical quantity by converting a change in resistance in the physical quantity sensor into a change in voltage using a resistance voltage divider.

JP-A-6-34586 JP 2001-208709 A

By the way, some physical quantity sensors, such as a resistance change type humidity sensor, change in resistance (element value change) with respect to a change in physical quantity exponentially. When such a physical quantity sensor is used for a resistance voltage divider (element voltage divider), the voltage converted by the resistance voltage divider may exhibit a large non-linearity as a whole with respect to a change in physical quantity. In this case, the detection sensitivity (resolution) is reduced if the detection sensitivity is outside the high detection sensitivity centered on the fixed resistance value (fixed element value) of the resistance voltage divider.
In order to improve this non-linearity, the conventional physical quantity detection circuit uses a negative feedback approximation type that approximates by applying negative feedback as described in Patent Document 1 and Patent Document 2, or a microcomputer, for example. There is known a polynomial approximation type that approximates by a third-order or higher order polynomial.

However, in the above-described negative feedback approximation type or polynomial approximation type physical quantity detection circuit, the above-described non-linearity is improved. However, if the detection sensitivity centering on the fixed resistance value of the resistance voltage divider is outside the high detection range, the detection is performed. The problem of reduced sensitivity (resolution) is not improved.
In other words, the conventional physical quantity detection circuit has a problem that the detection sensitivity of the physical quantity cannot be improved in the entire physical quantity detection range while maintaining the linearity of the voltage change with respect to the change of the physical quantity.

  The present invention has been made to solve the above problem, and its purpose is to improve the physical quantity detection sensitivity in the entire physical quantity detection range while maintaining the linearity of the voltage change with respect to the physical quantity change. A detection circuit and a physical quantity detection method are provided.

  In order to solve the above problems, the present invention provides a physical quantity sensor whose element value changes exponentially with respect to a change in physical quantity, and a plurality of elements connected in series with each other and having different element values. An arithmetic processing unit that performs weighted summation of the voltage values respectively divided by the physical quantity sensor and any of the plurality of elements, and converts the voltage value to change linearly with respect to the change in the physical quantity, The plurality of elements include a first element having an element value equal to an element value of the physical quantity sensor at a lower limit value in the physical quantity detection range, and an element of the physical quantity sensor at an upper limit value in the physical quantity detection range. A physical quantity detection circuit including a second element having an element value equal to the value.

  Further, the present invention is characterized in that, in the above invention, the number of the plurality of elements is an odd number.

  According to the present invention, in the above invention, the plurality of elements include a third element having an element value larger than the element value of the first element and smaller than the element value of the second element. It is characterized by.

  Further, the present invention is characterized in that, in the above invention, the element value of the third element is equal to the element value of the physical quantity sensor in the median value in the physical quantity detection range.

  Moreover, the present invention is characterized in that, in the above invention, the physical quantity sensor provided in the physical quantity detection circuit is plural, and is connected in series to the plural elements.

  Further, according to the present invention, in the above invention, the physical quantity detection circuit sequentially switches any one of the plurality of elements, and sequentially outputs a voltage value divided by the physical quantity sensor and the switched element. It is characterized by including a switch unit for outputting.

  Further, according to the present invention, in the above invention, the arithmetic processing unit multiplies the voltage value divided by the physical quantity sensor and any of the plurality of elements by a weighting coefficient, and outputs a multiplication result. And a second operational amplifier circuit unit that calculates a sum of outputs corresponding to the plurality of elements in the first operational amplifier circuit unit.

  In the invention described above, the arithmetic processing unit may detect the voltage value and convert the digital value into digital information, and digital information converted by the A / D conversion unit. And a digital operation unit that performs a digital operation for multiplying and summing the weighting coefficients.

  Further, the present invention is characterized in that in the above invention, the plurality of elements are three elements.

  In the present invention, the element is a resistor, and the physical quantity sensor is a resistance change type humidity sensor.

  Further, the present invention is a physical quantity detection method using a physical quantity sensor whose element value changes exponentially with respect to a change in physical quantity, and a plurality of elements each connected in series with the physical quantity sensor and having different element values. The plurality of elements include a first element having an element value equal to an element value of the physical quantity sensor at a lower limit value in the physical quantity detection range, and an upper limit value in the physical quantity detection range. A second element having an element value equal to the element value of the sensor is included, and the voltage value divided by each of the physical quantity sensor and any of the plurality of elements is weighted and summed to change the physical quantity. On the other hand, the physical quantity detection method includes an arithmetic processing procedure for converting the linearity to change linearly.

  ADVANTAGE OF THE INVENTION According to this invention, the detection sensitivity of a physical quantity can be improved in the whole physical quantity detection range, maintaining the linearity of the voltage change with respect to the change of a physical quantity.

It is a schematic block diagram which shows the physical quantity detection circuit by 1st Embodiment. It is a graph which shows the voltage change with respect to the change of the humidity in this embodiment. Is a graph showing an example of an inflection point in the curve of the resistance-divided voltage value V _O in the present embodiment. It is a schematic block diagram which shows the physical quantity detection circuit by 2nd Embodiment. It is a schematic block diagram which shows the physical quantity detection circuit by 3rd Embodiment.

Hereinafter, a physical quantity detection circuit according to an embodiment of the present invention will be described with reference to the drawings.
In the present embodiment, an example in which the physical quantity is humidity will be described. Therefore, here, the physical quantity sensor is described as a humidity sensor. Humidity indicates relative humidity RH (Relative Humidity).

<First Embodiment>
First, a first embodiment of the present invention will be described.
FIG. 1 is a schematic block diagram showing a physical quantity detection circuit 1 according to the present embodiment.
In the present embodiment, the physical quantity detection circuit 1 has three humidity sensors 21 to 23 and three (multiple and odd number) voltage dividing resistors (first resistor 31 and second resistor) having different resistance values. A mode including the resistor 32 and the third resistor 33) will be described.
In this figure, the physical quantity detection circuit 1 includes humidity sensors 21 to 23, a first resistor 31, a second resistor 32, a third resistor 33, an arithmetic processing unit 4, a capacitor 5, a resistor 6, and an AC power source 7. I have. As described above, the physical quantity detection circuit 1 includes a plurality of humidity sensors 21 to 23 each of which is divided by a plurality of resistors (first resistor 31, second resistor 32, and third resistor 33). .

The humidity sensors 21 to 23 are, for example, resistance change type humidity sensors, and their resistance values change exponentially with respect to changes in physical quantity (humidity). The humidity sensor 21 has one end connected to one end of the capacitor 5 and the other end connected to the node N1. The humidity sensor 22 has one end connected to one end of the capacitor 5 and the other end connected to the node N2. The humidity sensor 23 has one end connected to one end of the capacitor 5 and the other end connected to the node N3.
Here, for example, when the humidity sensors 21 to 23 change from a humidity of 20% to a humidity of 80%, an example in which the resistance value changes from about 4800 kΩ (kilohm) to 6 kΩ will be described.

  The first resistor 31 has one end connected to the node N1 and the other end connected to the ground line. That is, the first resistor 31 is connected in series with the humidity sensor 21 to form a resistance voltage divider. That is, the first resistor 31 functions as a voltage dividing resistor. The resistance value of the first resistor 31 is, for example, 4800 kΩ. Moreover, although mentioned later for details, the 1st resistance 31 shows the resistance value equal to the resistance value of the humidity sensor 21 in the lower limit in the detection range of humidity (physical quantity). Here, the resistance value equal to the resistance value of the humidity sensor 21 may include a substantially equal resistance value. The humidity detection range is, for example, a range from 20% humidity to 80% humidity. That is, the first resistor 31 has a resistance value substantially equal to the resistance value of the humidity sensor 21 when the humidity is 20%.

  The second resistor 32 has one end connected to the node N2 and the other end connected to the ground line. That is, the second resistor 32 is connected in series with the humidity sensor 22 and forms a resistance voltage divider. That is, the second resistor 32 functions as a voltage dividing resistor. The resistance value of the second resistor 32 is, for example, 6 kΩ. Although the details will be described later, the second resistor 32 exhibits a resistance value equal to the resistance value of the humidity sensor 22 in the upper limit value in the humidity (physical quantity) detection range. Here, the resistance value equal to the resistance value of the humidity sensor 22 may include an approximately equal resistance value. That is, the second resistor 32 has a resistance value substantially equal to the resistance value of the humidity sensor 32 when the humidity is 80%.

  The third resistor 33 has one end connected to the node N3 and the other end connected to the ground line. That is, the third resistor 33 is connected in series with the humidity sensor 23 to form a resistance voltage divider. That is, the third resistor 33 functions as a voltage dividing resistor. The resistance value of the third resistor 33 is, for example, 150 kΩ. The third resistor 33 has a resistance value larger than the resistance value of the first resistor 31 and smaller than the resistance value of the second resistor 32. Although the details will be described later, the third resistor 33 has a resistance value equal to the resistance value of the humidity sensor 23 in the median value in the humidity (physical quantity) detection range. Here, the resistance value equal to the resistance value of the humidity sensor 23 may include an approximately equal resistance value. That is, the third resistor 33 has a resistance value substantially equal to the resistance value of the humidity sensor 32 when the humidity is 50%.

  The AC power supply 7 has a cathode terminal connected to the ground line and an anode terminal connected to one end of the capacitor 5. The AC power supply 7 generates an AC pulse signal of 1 kHz (kilohertz), for example, and supplies a voltage to the humidity sensors 21 to 23 via the capacitor 5. The humidity sensors 21 to 23 are polarized when a DC voltage is applied for a long time, and the resistance value fluctuates. Therefore, the AC power supply 7 generates an AC voltage and supplies it to the humidity sensors 21 to 23.

The capacitor 5 has one end connected to one end of the humidity sensors 21 to 23 and the other end connected to the anode terminal of the AC power source 7. The capacitor 5 transmits the AC pulse signal supplied from the AC power source 7 to the humidity sensors 21 to 23.
The resistor 6 has one end connected to one end of the capacitor 5 and the other end connected to the ground line. The resistor 6 causes the voltage supplied from the AC power supply 7 to flow through the ground line and discharge it within a predetermined time. Thereby, the response speed of the three resistance voltage dividers can be improved. The capacitor 5 and the resistor 6 also function as a high-pass filter that cuts a low-frequency signal.
The DC power supply 8 has an anode terminal connected to the power supply line VDD and a cathode terminal connected to the ground line. The DC power supply 8 supplies a power supply voltage to each part of the physical quantity detection circuit 1.

  Based on the voltage values output from the three resistance voltage dividers, the arithmetic processing unit 4 converts the voltage into a voltage (change amount) that changes linearly with respect to a change in humidity. Here, the three resistance voltage dividers are the above-described resistance voltage divider of the humidity sensor 21 and the first resistor 31, the resistance voltage divider of the humidity sensor 22 and the second resistor 32, and the humidity sensor 23 and the third resistor. It is a resistance voltage divider with the resistor 33. The arithmetic processing unit 4 performs weighted summation on the respective voltage values output from the three resistance voltage dividers, and converts the voltage values into a voltage that changes linearly with respect to a change in humidity. That is, the arithmetic processing unit 4 is divided by the humidity sensors 21 to 23 and any of the three (plural) resistors (the first resistor 31, the second resistor 32, and the third resistor 33). The voltage values are weighted and summed and converted so as to change linearly with respect to changes in physical quantities.

The arithmetic processing unit 4 includes an amplification rectification unit 41 and an addition circuit unit 42.
The amplification rectification unit 41 (first operational amplification circuit unit) includes the humidity sensors 21 to 23 and any of three (plural) resistors (first resistor 31, second resistor 32, and third resistor 33). Each voltage value divided by the resistance is multiplied by a weighting coefficient, and the multiplication result is output to the adding circuit unit 42. The weighting coefficient here is the first weighting coefficient. The amplification rectification unit 41 causes the capacitors 56, 66, and 76 to hold as large a voltage as possible by multiplying the first weighting coefficient.
Specifically, the amplification rectification unit 41 multiplies the voltage divided by the first resistor 31 based on the AC voltage supplied from the AC power supply 7 by a weighting coefficient, rectifies the voltage into a DC voltage, and It functions as an operational amplifier circuit that outputs to N5. In addition, the amplification rectification unit 41 multiplies the voltage divided by the second resistor 32 based on the AC voltage supplied from the AC power supply 7 by a weighting coefficient, rectifies the voltage to a DC voltage, and outputs it to the node N7. Functions as an operational amplifier circuit. Further, the amplification rectification unit 41 multiplies the voltage divided by the third resistor 33 based on the AC voltage supplied from the AC power supply 7 by a weighting coefficient, rectifies the voltage to a DC voltage, and outputs it to the node N9. Functions as an operational amplifier circuit.

  The amplification rectifier 41 includes resistors (43-45, 52-54, 62-64, 72-74), operational amplifiers (51, 61, 71), diodes (55, 65, 75), and capacitors (56, 66, 76).

The resistor 43 has one end connected to the node N1 and the other end connected to the non-inverting input terminal of the operational amplifier 51. The resistor 52 and the resistor 53 are connected in series between the node N5 and the ground line via the node N4.
In the operational amplifier 51 (operational amplifier circuit), a non-inverting input terminal is connected to the node N1 via the resistor 43, an inverting input terminal is connected to the node N4, and an output terminal is connected to one end of the resistor 54. The operational amplifier 51 amplifies the voltage value divided by the humidity sensor 21 and the first resistor 31 by the resistance ratio of the resistor 52 and the resistor 53. That is, the operational amplifier 51 multiplies the voltage value divided by the humidity sensor 21 and the first resistor 31 by the weighting coefficient. Here, the weighting coefficient is set by the resistance ratio between the resistor 52 and the resistor 53.

The resistor 54 has one end connected to the output terminal of the operational amplifier 51 and the other end connected to the anode terminal of the diode 55. The diode 55 has an anode terminal connected to the other end of the resistor 54 and a cathode terminal connected to the node N5. The diode 55 rectifies the output signal of the operational amplifier 51 that is output via the resistor 54, thereby preventing a reverse current flow. The capacitor 56 is connected between the node N5 and the ground line, and holds the output voltage of the operational amplifier 51.
The resistor 54 functions to loosen the rise of the voltage at the node N5, and charges the capacitor 56 over time. Thereby, the resistor 54 suppresses current and suppresses electromagnetic noise.

The resistor 44 has one end connected to the node N2 and the other end connected to the non-inverting input terminal of the operational amplifier 61. The resistor 62 and the resistor 63 are connected in series between the node N7 and the ground line via the node N6.
In the operational amplifier 61 (operational amplifier circuit), a non-inverting input terminal is connected to the node N2 via the resistor 44, an inverting input terminal is connected to the node N6, and an output terminal is connected to one end of the resistor 64. The operational amplifier 61 amplifies the voltage value divided by the humidity sensor 22 and the second resistor 32 by the resistance ratio of the resistor 62 and the resistor 63. That is, the operational amplifier 61 multiplies the voltage value divided by the humidity sensor 23 and the second resistor 32 by the weighting coefficient. Here, the weighting coefficient is set by the resistance ratio between the resistor 62 and the resistor 63.

The resistor 64 has one end connected to the output terminal of the operational amplifier 61 and the other end connected to the anode terminal of the diode 65. The diode 65 has an anode terminal connected to the other end of the resistor 64 and a cathode terminal connected to the node N7. The diode 65 rectifies the output signal of the operational amplifier 61 that is output via the resistor 64, and prevents a reverse current flow. The capacitor 66 is connected between the node N7 and the ground line, and holds the output voltage of the operational amplifier 61.
Note that the resistor 64 functions to loosen the rise of the voltage at the node N7 and charges the capacitor 66 over time. Thereby, the resistor 64 suppresses current and suppresses electromagnetic noise.

The resistor 45 has one end connected to the node N3 and the other end connected to the non-inverting input terminal of the operational amplifier 71. The resistor 72 and the resistor 73 are connected in series between the node N9 and the ground line via the node N8.
In the operational amplifier 71 (operational amplifier circuit), the non-inverting input terminal is connected to the node N2 via the resistor 45, the inverting input terminal is connected to the node N8, and the output terminal is connected to one end of the resistor 74. The operational amplifier 71 amplifies the voltage value divided by the humidity sensor 23 and the third resistor 33 by the resistance ratio of the resistor 72 and the resistor 73. That is, the operational amplifier 71 multiplies the voltage value divided by the humidity sensor 22 and the third resistor 33 by the weighting coefficient. Here, the weighting coefficient is set by the resistance ratio between the resistor 72 and the resistor 73.

The resistor 74 has one end connected to the output terminal of the operational amplifier 71 and the other end connected to the anode terminal of the diode 75. The diode 75 has an anode terminal connected to the other end of the resistor 74 and a cathode terminal connected to the node N9. The diode 75 rectifies the output signal of the operational amplifier 71 output through the resistor 74, and prevents a current from flowing backward. The capacitor 76 is connected between the node N9 and the ground line, and holds the output voltage of the operational amplifier 71.
Resistor 74 functions to loosen the rise of the voltage at node N9 and charges capacitor 76 over time. Accordingly, the resistor 74 suppresses current and suppresses electromagnetic noise.

  The adder circuit unit 42 (second operational amplifier circuit unit) adds the three output voltages (voltages at the node N5, the node N7, and the node N9) output from the amplification rectifier unit 41, and outputs the amplified voltage to the signal line. Output to VSUM. That is, the adder circuit unit 42 calculates the sum of outputs corresponding to the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) in the amplification rectifier 41. Note that the adding circuit unit 42 is a voltage dividing / simple adder composed of resistors 81 to 83 and a resistor 422 in order to maintain the positive polarity of the humidity signal with the entire circuit with a single power source.

The adding circuit unit 42 includes resistors (81 to 83, 422 to 424) and an operational amplifier 421.
The resistor 81 has one end connected to the node N5 and the other end connected to the node N10. The resistor 82 has one end connected to the node N7 and the other end connected to the node N10. The resistor 83 has one end connected to the node N9 and the other end connected to the node N10. The resistor 422 has one end connected to the node N10 and the other end connected to the ground line. The resistors 81 to 83 have different resistance values, and function as weighting coefficients (second weighting coefficients) when adding the three output voltages supplied from the amplification rectification unit 41. The weighting coefficient here is set by the mutual relationship between the resistance values of the resistors 81 to 83 and the resistance value of the resistor 422.
The resistors 423 and 424 are connected in series between the signal line VSUM and the ground line via the node N11.

  The operational amplifier 421 has a non-inverting input terminal connected to the node N10, an inverting input terminal connected to the node N11, and an output terminal connected to the signal line VSUM. The operational amplifier 421 weights each of the three output voltages output from the amplifying / rectifying unit 41 and adds them. The operational amplifier 421 functions as a non-inverting amplifier circuit. Note that the addition result is amplified by a coefficient set by the resistance ratio between the resistor 423 and the resistor 424.

Next, the operation of the physical quantity detection circuit 1 according to the present embodiment will be described taking the case of detecting humidity as an example.
In the physical quantity detection circuit 1, first, the AC power supply 7 generates an AC pulse signal, and supplies a voltage to the humidity sensors 21 to 23 via the capacitor 5. The AC voltage supplied from the AC power supply 7 is resistance-divided by the humidity sensors 21 to 23 and each of the three resistors (first resistor 31, second resistor 32, and third resistor 33). It is output to the processing unit 4.

  Next, the amplification rectification unit 41 of the arithmetic processing unit 4 is divided into resistance components by the humidity sensors 21 to 23 and any of the three resistors (first resistor 31, second resistor 32, and third resistor 33). The pressed voltage value is multiplied by a weighting coefficient (first weighting coefficient), and the multiplication result is output to the adding circuit unit 42.

At this time, the operational amplifier 51 multiplies the voltage divided by the first resistor 31 by a weighting coefficient. The diode 55 rectifies the output voltage of the operational amplifier 51 into a DC voltage and outputs it to the node N5. Capacitor 56 holds the voltage output to node N5.
The operational amplifier 61 multiplies the voltage divided by the second resistor 32 by a weighting coefficient. The diode 65 rectifies the output voltage of the operational amplifier 61 to a direct current voltage and outputs it to the node N7. Capacitor 66 holds the voltage output to node N7.
The operational amplifier 71 multiplies the voltage divided by the third resistor 33 by a weighting coefficient. The diode 75 rectifies the output voltage of the operational amplifier 71 to a DC voltage and outputs it to the node N9. Capacitor 76 holds the voltage output to node N9.

Next, the addition circuit unit 42 adds the three output voltages (voltages at the node N5, the node N7, and the node N9) output from the amplification rectification unit 41, and outputs the amplified voltage to the signal line VSUM. At this time, the operational amplifier 421 weights each of the three output voltages output from the amplification rectification unit 41 (by the second weighting coefficient) and adds the weights. Further, the operational amplifier 421 amplifies the addition result by the resistance ratio between the resistor 423 and the resistor 424 and outputs the result to the signal line VSUM. That is, the operational amplifier 421 amplifies to 0 to 1 V (0 to 100% RH) that is easy to handle because the output of the voltage dividing / simple adder composed of the resistors 81 to 83 and the resistor 422 is small.
As described above, the physical quantity detection circuit 1 has a voltage value (node N1, node N2, and node) divided by the three resistors (first resistor 31, second resistor 32, and third resistor 33). The voltage at N3) is multiplied by the first and second weighting factors and summed. Further, the physical quantity detection circuit 1 outputs a voltage indicating the summed calculation result to the signal line VSUM. The voltage output to the signal line VSUM is converted by the arithmetic processing unit 4 into a voltage that changes linearly with respect to a change in humidity.

Next, the weighted sum processing executed by the arithmetic processing unit 4 will be described in detail. Here, the voltage at the signal line VSUM is V _SUM , the voltage at the node N1 is V _{O — 4800k} , the voltage at the node N2 is V _{o — 6k} , and the voltage at the node N3 is V _{o — 150k} .
In the physical quantity detection circuit 1, _VSUM is expressed by the relational expression (1).

In Expression (1), a, b, and c are weighting coefficients. D is a coefficient for correcting the voltage value of V _SUM to a predetermined voltage range.
Also, equation (1) can be replaced as equation (2).

In Equation (2), R _4800k is the resistance value of the first resistor 31, R _6k is the resistance value of the second resistor 32, and R _150k is the resistance value of the third resistor 33. . Moreover, _RS is the resistance value of the humidity sensors 21-23. V _i is an input voltage supplied to the humidity sensors 21 to 23. Note that the input voltage V _i is included in V _{O — 4800k} , V _{o — 6k} , and V _{o — 150k} , respectively, in Equation (1).
The arithmetic processing unit 4 performs a process equivalent to the process shown in Expression (1) or Expression (2).

Next, the above-described expression (1) and the detection result of the physical quantity detection circuit 1 will be described.
In the example described here, the coefficient is set to “0.6”, b is set to “0.86”, c is set to “1.90”, and d is set to “0.33”. Yes.
FIG. 2 is a graph showing voltage changes with respect to changes in humidity in the present embodiment.
In this figure, the graph shows the relationship between humidity and output voltage. In this graph, the horizontal axis represents humidity (%), and the vertical axis represents output voltage (V (volt)).

Waveform L1 shows a change in voltage V _{O — 4800k at} node N1 with respect to a change in humidity. In the waveform L1, the detection sensitivity (resolution) near 20% humidity is high, and the detection sensitivity (resolution) near 80% humidity is low. Here, high detection sensitivity (resolution) means that the resistance change is large with respect to the humidity change, and the resistance-divided voltage change is large. A low detection sensitivity (resolution) indicates that a change in resistance is small with respect to a change in humidity and that a change in resistance-divided voltage is small.
Waveform L2 shows the change in voltage V _{O — 150k at} node N3 with respect to the change in humidity. In the waveform L2, the detection sensitivity (resolution) near 50% humidity is high, and the detection sensitivity (resolution) near 20% humidity and 80% humidity is low.
A waveform L3 indicates a change in the voltage V _{O — 6k at} the node N2 with respect to a change in humidity. In the waveform L3, the detection sensitivity (resolution) near 80% humidity is high, and the detection sensitivity (resolution) near 20% humidity is low.

The waveform L4 is a waveform obtained by calculating the voltage _VSUM indicating the humidity detection result from the voltages in the waveform L1, the waveform L2, and the waveform L3, using the above-described coefficient and Equation (1). In the waveform L4, the voltage _VSUM indicating the humidity detection result changes linearly in the humidity detection range (range from 20% humidity to 80% humidity).

  A waveform L5 is a signal line when the resistance values of the resistors (52, 53, 62, 63, 72, 3, 81 to 83, 422 to 424) of the physical quantity detection circuit 1 are set to the above-described coefficients. It is a simulation waveform of the voltage output to VSUM. As shown by the waveform L5, the physical quantity detection circuit 1 changes linearly in the same manner as the waveform L4. That is, the physical quantity detection circuit 1 linearly changes the voltage value obtained by resistance-dividing the humidity sensors 21 to 23 in the humidity detection range (a range from humidity 20% to humidity 80%) with respect to the humidity change. Convert to voltage.

  The resistance values of the first resistor 31, the second resistor 32, and the third resistor 33 are set as follows.

The resistance value of the first resistor 31 is set to be approximately equal to the resistance value (4800 kΩ) of the humidity sensor 21 at the lower limit value in the humidity detection range. That is, as indicated by the waveform L1, the resistance value of the first resistor 31 is set such that the detection sensitivity of the humidity sensor 21 is maximized at the lower limit value in the humidity detection range.
In the waveform L1, a point P1 is an inflection point of a curve indicating a change in the voltage value V _{O — 4800k} that is resistance- _divided with respect to a change in humidity. The resistance value of the first resistor 31 is set so that the humidity value corresponding to the inflection point is the lower limit (RH1) in the humidity detection range. Here, the inflection point is a point that becomes “0” when the second-order differentiation described later is performed.

The resistance value of the second resistor 32 is set to be approximately equal to the resistance value (6 kΩ) of the humidity sensor 22 at the upper limit value in the humidity detection range. That is, as indicated by the waveform L3, the resistance value of the second resistor 32 is set such that the detection sensitivity of the humidity sensor 22 is maximized at the upper limit value in the humidity detection range.
In the waveform L3, a point P3 is an inflection point of a curve indicating a change in the voltage value V _{O — 6k} that is resistance- _divided with respect to a change in humidity. The resistance value of the second resistor 32 is set so that the humidity value corresponding to this inflection point is the upper limit value (RH3) in the humidity detection range.

The resistance value of the third resistor 33 is set substantially equal to the resistance value (150 kΩ) of the humidity sensor 23 at the median value in the humidity detection range. That is, as indicated by the waveform L2, the resistance value of the third resistor 33 is set so that the detection sensitivity of the humidity sensor 23 is maximized at the median value in the humidity detection range.
In the waveform L2, a point P2 is an inflection point of a curve indicating a change in the voltage value V _{O — 150k} that is resistance- _divided with respect to a change in humidity. The resistance value of the third resistor 33 is set such that the humidity value corresponding to this inflection point is approximately the median value (RH2) in the humidity detection range.

The voltage value V _O divided by the resistance value R is expressed by the relational expression (3).

In the formula (3), RH is relative humidity. RA is a change base value with respect to the relative humidity RH, and RB is a residual resistance value. V _i is an input voltage value.

FIG. 3 is a graph showing an example of an inflection point in the curve of the voltage value V _O divided by resistance in the present embodiment.
In this graph, the vertical axis represents the voltage value V _O divided by resistance, and the horizontal axis represents the relative humidity RH. Note that the input voltage V _i in Expression (3) is omitted as “1”.
In this figure, the waveform L7 is an example of a curve represented by Expression (3). The waveform L8 is a curve obtained by differentiating the curve of the waveform L7 once. The waveform L9 is a curve obtained by differentiating the curve of the waveform L7 twice. In this figure, the inflection point P4 is a point of the waveform L7 corresponding to the point where the waveform L9 becomes “0”. That is, the inflection point P4 is a point where the detection sensitivity of the humidity sensor 21 is maximized.

  As described above, the physical quantity detection circuit 1 includes the humidity sensors 21 to 23 (physical quantity sensor) whose resistance values change exponentially with respect to changes in humidity (physical quantity), and three resistors (first resistance 31). , A second resistor 32, a third resistor 33), and an arithmetic processing unit 4. The three resistors 31 to 33 are connected in series with the humidity sensors 21 to 23, respectively. Further, the arithmetic processing unit 4 weights and sums the voltage values divided by the humidity sensors 21 to 23 and any of the three resistors 31 to 33, and changes linearly with changes in humidity. Convert as follows. Further, the three resistors 31 to 33 have a first resistor 31 that exhibits a resistance value substantially equal to the resistance value of the humidity sensor 21 at the lower limit value in the humidity detection range, and an upper limit value in the humidity detection range. A second resistor 32 having a resistance value substantially equal to the resistance value of the humidity sensor 22 is included.

  Thereby, the physical quantity detection circuit 1 can improve the detection sensitivity near the lower limit value and the detection sensitivity near the lower limit value in the humidity detection range. Further, the physical quantity detection circuit 1 converts the voltage value obtained by resistance-dividing the humidity sensors 21 to 23 into a voltage that linearly changes with respect to a change in humidity by weighting and summing the voltage values obtained by the resistance division. be able to. Therefore, the physical quantity detection circuit 1 can improve humidity (physical quantity) detection sensitivity in the entire humidity (physical quantity) detection range while maintaining linearity of voltage change with respect to humidity (physical quantity) change.

  Further, the three resistors include a third resistor 33 having a resistance value larger than the resistance value of the first resistor 31 and smaller than the resistance value of the second resistor 32. The resistance value of the third resistor is substantially equal to the resistance value of the humidity sensors 21 to 23 at the median value in the humidity (physical quantity) detection range. Thereby, the physical quantity detection circuit 1 can improve the detection sensitivity of the central region in the humidity detection range. Therefore, the physical quantity detection circuit 1 can further improve the humidity (physical quantity) detection sensitivity in the entire humidity (physical quantity) detection range while maintaining the linearity of the voltage change with respect to the humidity (physical quantity) change.

The arithmetic processing unit 4 includes an amplification rectification unit 41 (first operational amplification circuit unit) and an addition circuit unit 42 (first operational amplification circuit unit). The amplification rectification unit 41 weights each voltage value divided by the humidity sensors 21 to 23 and the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33). And the multiplication result is output. The adder circuit unit 42 calculates the sum of the outputs corresponding to the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) in the amplification rectifier 41.
As a result, the physical quantity detection circuit 1 applies the voltage value obtained by resistance-dividing the humidity sensors 21 to 23 to the change in humidity without performing approximation by a negative feedback approximation type or a polynomial approximation type using a microcomputer. It can be easily converted into a linearly changing voltage. Therefore, the physical quantity detection circuit 1 improves the detection sensitivity of the humidity (physical quantity) in the entire humidity (physical quantity) detection range while maintaining the linearity of the voltage change with respect to the change of the humidity (physical quantity) by a circuit having a simple configuration. can do.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.
FIG. 4 is a schematic block diagram showing the physical quantity detection circuit 1a according to the present embodiment.
In the present embodiment, the physical quantity detection circuit 1a includes one humidity sensor 20 and three (a plurality and an odd number) voltage dividing resistors (first resistor 31, second resistor 32, and third resistor 33). ) Will be described.
In this figure, the physical quantity detection circuit 1a includes a humidity sensor 20, a first resistor 31, a second resistor 32, a third resistor 33, an arithmetic processing unit 4a, a capacitor 5, a resistor 6, an AC power source 7, and a switch unit 91. -93. In this figure, the same components as those in FIG. The physical quantity detection circuit 1a according to the present embodiment includes switch units 91 to 93, and switches between the first resistor 31, the second resistor 32, and the third resistor 33 to perform voltage division with one humidity sensor 20. Is different from the physical quantity detection circuit 1 in the first embodiment.

The humidity sensor 20 is, for example, a resistance change type humidity sensor, and the resistance value changes exponentially with respect to a change in physical quantity (humidity). The humidity sensor 20 has one end connected to one end of the capacitor 5 and the other end connected to the node N1a.
Here, for example, when the humidity sensor 20 changes from a humidity of 20% to a humidity of 80%, an example in which the resistance value changes from about 4800 kΩ to 6 kΩ will be described.

The first resistor 31 has one end connected to the node N1a and the other end connected to the drain terminal of the MOS switch 912. That is, the first resistor 31 is connected in series with the humidity sensor 20 to form a resistance voltage divider. The resistance value of the first resistor 31 is the same as that of the first embodiment.
The second resistor 32 has one end connected to the node N1a and the other end connected to the drain terminal of the MOS switch 922. In other words, the second resistor 32 is connected in series with the humidity sensor 20 to form a resistance voltage divider. The resistance value of the second resistor 32 is the same as that of the first embodiment.
The third resistor 33 has one end connected to the node N 1 a and the other end connected to the drain terminal of the MOS switch 932. That is, the third resistor 33 is connected in series with the humidity sensor 20 to form a resistance voltage divider. The resistance value of the third resistor 33 is the same as that of the first embodiment.

  The switch units 91 to 93 sequentially switch any one of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33), depending on the humidity sensor 20 and the switched resistor. The voltage values divided by the resistors are output in order.

The switch unit 91 switches to a state in which resistance division by the first resistor 31 is performed based on a signal supplied via the signal line VSW1. The switch unit 91 includes resistors (911, 913), MOS switches (912, 914), and a capacitor 915.
The resistor 911 has one end connected to the signal line VSW1 and the other end connected to the gate terminal of the MOS switch 912. The resistor 913 has one end connected to the signal line VSW1 and the other end connected to the gate terminal of the MOS switch 914.

The MOS switch 912 is a switch formed by, for example, an NMOS transistor (N channel type metal oxide semiconductor field effect transistor). The MOS switch 912 has a source terminal connected to the ground line, a gate terminal connected to the signal line VSW1 via the resistor 911, and a drain terminal connected to the other end of the first resistor 31. The MOS switch 912 switches between the other end of the first resistor 31 and the ground line between a conductive state and a non-conductive state based on a signal supplied via the signal line VSW1.
The MOS switch 914 is a switch formed by, for example, an NMOS transistor. The MOS switch 914 has a source terminal connected to the node N5, a gate terminal connected to the signal line VSW1 via a resistor 913, and a drain terminal connected to the cathode terminal of the diode 55. The MOS switch 914 switches between the diode 55 and the node N5 between the conductive state and the non-conductive state based on a signal supplied via the signal line VSW1.

  The capacitor 915 has one end connected to the gate terminal of the MOS switch 914 and the other end connected to the ground line. Capacitor 915 forms a low-pass filter with resistor 913 to mitigate feedthrough that occurs when MOS switch 914 operates. Here, the feedthrough is a phenomenon in which a displacement current flows through the capacitance between the gate terminal and the source terminal of the MOS switch and between the gate terminal and the drain terminal.

The switch unit 92 switches to a state in which resistance division by the second resistor 32 is performed based on a signal supplied via the signal line VSW2. The switch unit 92 includes resistors (921, 923), MOS switches (922, 924), and a capacitor 925.
The resistor 921 has one end connected to the signal line VSW2 and the other end connected to the gate terminal of the MOS switch 922. The resistor 923 has one end connected to the signal line VSW 2 and the other end connected to the gate terminal of the MOS switch 924.

The MOS switch 922 is a switch formed by, for example, an NMOS transistor. The MOS switch 922 has a source terminal connected to the ground line, a gate terminal connected to the signal line VSW2 via the resistor 921, and a drain terminal connected to the other end of the second resistor 32. The MOS switch 922 switches between the other end of the second resistor 32 and the ground line between a conductive state and a non-conductive state based on a signal supplied via the signal line VSW2.
The MOS switch 924 is a switch formed by, for example, an NMOS transistor. The MOS switch 924 has a source terminal connected to the node N7, a gate terminal connected to the signal line VSW2 via the resistor 923, and a drain terminal connected to the cathode terminal of the diode 65. The MOS switch 924 switches between the diode 65 and the node N7 between a conductive state and a non-conductive state based on a signal supplied via the signal line VSW2.

  The capacitor 925 has one end connected to the gate terminal of the MOS switch 924 and the other end connected to the ground line. Capacitor 925 forms a low-pass filter with resistor 923 to mitigate feedthrough that occurs when MOS switch 924 operates.

The switch unit 93 switches to a state in which resistance division by the third resistor 33 is performed based on a signal supplied via the signal line VSW3. The switch unit 93 includes resistors (931, 933), MOS switches (932, 934), and a capacitor 935.
The resistor 931 has one end connected to the signal line VSW3 and the other end connected to the gate terminal of the MOS switch 932. The resistor 933 has one end connected to the signal line VSW 3 and the other end connected to the gate terminal of the MOS switch 934.

The MOS switch 932 is a switch formed by, for example, an NMOS transistor. The MOS switch 932 has a source terminal connected to the ground line, a gate terminal connected to the signal line VSW3 via the resistor 931, and a drain terminal connected to the other end of the third resistor 33. The MOS switch 932 switches between making the other end of the third resistor 33 and the ground line conductive or non-conductive based on a signal supplied via the signal line VSW2.
The MOS switch 934 is a switch formed by, for example, an NMOS transistor. The MOS switch 934 has a source terminal connected to the node N9, a gate terminal connected to the signal line VSW3 via the resistor 933, and a drain terminal connected to the cathode terminal of the diode 75. The MOS switch 934 switches whether the diode 75 and the node N9 are turned on or off based on a signal supplied via the signal line VSW3.

  The capacitor 935 has one end connected to the gate terminal of the MOS switch 934 and the other end connected to the ground line. Capacitor 935 forms a low-pass filter with resistor 933 to mitigate feedthrough that occurs when MOS switch 934 operates.

The arithmetic processing unit 4a includes an amplification rectification unit 41a and an addition circuit unit 42a.
The amplification rectification unit 41a (first operational amplification circuit unit) is resistance by the humidity sensor 20 and any of the three (plural) resistors (first resistor 31, second resistor 32, third resistor 33). The divided voltage value is multiplied by a weighting coefficient, and the multiplication result is output to the adding circuit unit 42a. The weighting coefficient here is the first weighting coefficient.
The amplification rectification unit 41a is the same as the amplification rectification unit 41 in the first embodiment, except that the output timing to the node N5, the node N7, and the node N9 is switched by the switch units 91 to 93 described above. Note that the input of the amplification rectifier 41a is the voltage of the node N1. In the amplification rectification unit 41a, the resistors 43 to 45 are respectively connected to the node N1a.

  The adder circuit unit 42a (second operational amplifier circuit unit) adds the three output voltages (voltages at the node N5, the node N7, and the node N9) output from the amplification rectifier unit 41a, and adds the amplified voltage to the signal line. Output to VSUM. That is, the adder circuit unit 42a calculates the sum of the outputs corresponding to the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) in the amplification rectifier unit 41a.

The adder circuit unit 42 a includes resistors (81 to 83 and 422 to 424), an operational amplifier 421, and a capacitor 425. The adder circuit unit 42a is the same as the adder circuit unit 42 in the first embodiment except that a capacitor 425 is provided.
The capacitor 425 has one end connected to the signal line VSUM and the other end connected to the node N11. Here, the operational amplifier 421 also functions as a low-pass filter that cuts a high frequency component with respect to the signal at the node N10 by inserting the capacitor 425 in the negative feedback.

Next, the operation of the physical quantity detection circuit 1a according to the present embodiment will be described taking the case of detecting humidity as an example.
The operation of the physical quantity detection circuit 1a is the first except that the switching operation of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) by the switch units 91 to 93 is added. This is the same as the operation of the physical quantity detection circuit 1 in the embodiment. Therefore, in this embodiment, the switching operation of the three resistors (first resistor 31, second resistor 32, and third resistor 33) by the switch units 91 to 93 will be described.

  A pulse signal that periodically enters an H (high) state is supplied to the signal lines VSW1 to VSW3. Note that the periods in which the signals in the signal lines VSW1 to VSW3 are in the H state are supplied with the time shifted in the order of the signal lines VSW1 to VSW3, and the periods in which the signals are in the H state do not overlap.

  When the signal on the signal line VSW1 is in the H state, the MOS switch 912 and the MOS switch 914 are turned on. Thereby, resistance voltage division is performed by the humidity sensor 20 and the first resistor 31, and the voltage divided by the first resistor 31 is output to the node N1a. The amplification rectifier 41a multiplies the voltage value supplied from the node N1a by a weighting coefficient, and outputs the multiplication result to the node N5 via the MOS switch 914.

  When the signal on the signal line VSW2 is in the H state, the MOS switch 922 and the MOS switch 924 are turned on. As a result, the resistance voltage is divided by the humidity sensor 20 and the second resistor 32, and the voltage divided by the second resistor 32 is output to the node N1a. The amplification rectification unit 41a multiplies the voltage value supplied from the node N1a by a weighting coefficient, and outputs the multiplication result to the node N7 via the MOS switch 924.

  When the signal on the signal line VSW3 is in the H state, the MOS switch 932 and the MOS switch 934 are turned on. Thereby, resistance voltage division is performed by the humidity sensor 20 and the third resistor 33, and the voltage divided by the third resistor 33 is output to the node N1a. The amplification rectification unit 41a multiplies the voltage value supplied from the node N1a by a weighting coefficient, and outputs the multiplication result to the node N7 via the MOS switch 934.

  The adder circuit unit 42a adds the three output voltages (voltages at the node N5, the node N7, and the node N9) output from the amplification rectifier unit 41a, and outputs the amplified voltage to the signal line VSUM.

  As described above, the physical quantity detection circuit 1a uses the first and second weighting coefficients by dividing the voltage value divided by the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33). Multiply by to sum. Further, the physical quantity detection circuit 1a outputs a voltage indicating the summed calculation result to the signal line VSUM. The voltage output to the signal line VSUM is converted into a voltage that changes linearly with respect to a change in humidity by the arithmetic processing unit 4a.

  Here, in the present embodiment, as in the first embodiment, the coefficients in Expression (1) are, for example, a is “0.6”, b is “0.86”, and c is “1. 90 "and d are set to" 0.33 ", respectively. A waveform L6 in FIG. 2 is obtained when the resistance values of the resistors (52, 53, 62, 63, 72, 3, 81 to 83, 422 to 424) of the physical quantity detection circuit 1a are set to be the above-described coefficients. FIG. 6 is a simulation waveform of a voltage output to the signal line VSUM. As shown in the waveform L5, in the physical quantity detection circuit 1a, the voltage output to the signal line VSUM changes linearly like the waveforms L4 and L5.

  As described above, the physical quantity detection circuit 1a includes the humidity sensor 20 (physical quantity sensor) whose resistance value changes exponentially with respect to changes in humidity (physical quantity), and the three resistors (first resistor 31, first resistor 31). 2 resistors 32, a third resistor 33), an arithmetic processing unit 4a, and switch units 91-93. Three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) are connected in series with the humidity sensor 20, respectively. In addition, the switch units 91 to 93 sequentially switch any one of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33), and the resistors switched to the humidity sensor 20. The voltage values divided by the resistance are sequentially output. Further, the arithmetic processing unit 4a weights and sums the voltage values divided by the humidity sensor 20 and any of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33). Thus, conversion is performed so as to change linearly with changes in humidity. The three resistors include a first resistor 31 that exhibits a resistance value substantially equal to the resistance value of the humidity sensor 20 at the lower limit value in the humidity detection range, and the humidity sensor 20 at the upper limit value in the humidity detection range. And a second resistor 32 having a resistance value substantially equal to the resistance value. The three resistors include a third resistor 33 that exhibits a resistance value substantially equal to the resistance value of the humidity sensor 20 at the median value in the humidity detection range.

  Thereby, the physical quantity detection circuit 1a can improve the detection sensitivity near the lower limit value and the detection sensitivity near the lower limit value in the humidity detection range. In addition, the physical quantity detection circuit 1a can convert the voltage value obtained by resistance-division of the humidity sensor 20 into a voltage that linearly changes with respect to the change of humidity by weighting and summing the voltage values obtained by resistance division. it can. Therefore, as in the first embodiment, the physical quantity detection circuit 1a maintains the linearity of the voltage change with respect to the change in the humidity (physical quantity), and the detection sensitivity of the humidity (physical quantity) in the entire humidity (physical quantity) detection range. Can be improved.

  Furthermore, the physical quantity detection circuit 1a switches and uses any one of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) by the switch units 91 to 93. Thereby, a humidity sensor can be reduced to one. Moreover, since the physical quantity detection circuit 1a uses one humidity sensor, it is possible to eliminate variations in resistance values among a plurality of humidity sensors. Therefore, the physical quantity detection circuit 1a can improve the detection accuracy as compared with the first embodiment.

<Third Embodiment>
Next, a third embodiment of the present invention will be described.
FIG. 5 is a schematic block diagram showing the physical quantity detection circuit 1b according to the present embodiment.
In the present embodiment, the physical quantity detection circuit 1b includes one humidity sensor 20 and three (multiple and odd number) voltage dividing resistors (first resistor 31, second resistor 32, and third resistor 33). ) And performing weighted summation by digital arithmetic processing will be described.

In this figure, the physical quantity detection circuit 1b includes a humidity sensor 20, a first resistor 31, a second resistor 32, a third resistor 33, an arithmetic processing unit 4b, a capacitor 5, and a switch unit 90. In this figure, the same components as those in FIG.
The arithmetic processing unit 4 b includes an A / D (analog / digital) converter 43 (A / D conversion unit) and a microcomputer 44.
The A / D converter 43 converts the voltage value divided by the humidity sensor 20 and any one of the three (plural) resistors (the first resistor 31, the second resistor 32, and the third resistor 33). Detect and convert to digital information. The A / D converter 43 outputs digital information of the converted voltage value to the microcomputer 44.

  The microcomputer 44 is formed including, for example, a CPU (Central processing unit) and a memory, and realizes processing for detecting humidity, which will be described later, by a program. The microcomputer 44 performs digital arithmetic processing for multiplying each of the digital information converted by the A / D converter 43 by a weighting coefficient and summing them up. The microcomputer 44 supplies an AC pulse signal to the capacitor 5 and supplies a voltage to the humidity sensor 20 via the capacitor 5. Further, the microcomputer 44 supplies a control signal for switching three resistors (first resistor 31, second resistor 32, and third resistor 33) to the switch unit 90.

  The switch unit 90 sequentially switches any one of three resistors (first resistor 31, second resistor 32, and third resistor 33), and the resistance is divided by the humidity sensor 20 and the switched resistor. The pressed voltage value is output in order. The switch unit 90 includes analog switches 901 to 903.

  The analog switch 901 is connected between the first resistor 31 and the ground line. The analog switch 901 has a control terminal connected to one of the output ports of the microcomputer 44. The analog switch 901 switches between the first resistor 31 and the ground line between a conductive state and a non-conductive state based on a control signal supplied from the microcomputer 44.

  The analog switch 902 is connected between the second resistor 32 and the ground line. The analog switch 902 has a control terminal connected to one of the output ports of the microcomputer 44. The analog switch 902 switches between the second resistor 32 and the ground line between a conductive state and a non-conductive state based on a control signal supplied from the microcomputer 44.

  The analog switch 903 is connected between the third resistor 33 and the ground line. The analog switch 903 has a control terminal connected to one of the output ports of the microcomputer 44. The analog switch 903 switches between the third resistor 33 and the ground line between a conductive state and a non-conductive state based on a control signal supplied from the microcomputer 44.

  In the present embodiment, the change in the resistance value with respect to the humidity of the humidity sensor 20 will be described here by way of an example in which the change is the same as in the first and second embodiments. The resistance values of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) are the same as those in the first and second embodiments.

Next, the operation of the physical quantity detection circuit 1b according to the present embodiment will be described taking the case of detecting humidity as an example.
In the physical quantity detection circuit 1b, first, the microcomputer 44 makes any one of the analog switches 901 to 903 conductive. Next, the microcomputer 44 generates an AC pulse signal and supplies a voltage to the humidity sensor 20 via the capacitor 5. For example, when the microcomputer 44 makes the analog switch 901 conductive, the AC voltage supplied to the humidity sensor 20 via the capacitor 5 is resistance-divided by the humidity sensor 20 and the first resistor 31, and A / It is output to the D converter 43.
The A / D converter 43 detects the voltage divided by the humidity sensor 20 and the first resistor 31 and converts it into digital information. Then, the A / D converter 43 outputs the converted digital information to the microcomputer 44.

  The microcomputer 44 acquires digital information of the voltage value output from the A / D converter 43. The microcomputer 44 switches the analog switches 901 to 903 to acquire the digital information of the voltage values in the same manner for the second resistor 32 and the third resistor 33.

Next, the microcomputer 44 weights each digital information of the voltage divided by the humidity sensor 20 and the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33). Multiply the coefficients and perform a digital operation to sum. In this digital arithmetic processing, the arithmetic processing shown as the equation (1) is performed according to the equation.
As described above, the physical quantity detection circuit 1b converts the voltage value divided by the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) into digital information and performs weighting. The summing process is executed by digital arithmetic processing. The voltage obtained by this digital arithmetic processing is converted into a voltage that changes linearly with respect to a change in humidity by the arithmetic processing unit 4b.

  As described above, the physical quantity detection circuit 1b includes the humidity sensor 20 (physical quantity sensor) whose resistance value changes exponentially with respect to changes in humidity (physical quantity), and the three resistors (first resistor 31, first resistor 31). 2 resistor 32, third resistor 33), an arithmetic processing unit 4b, and a switch unit 90. The three resistors 31 to 33 are connected to the humidity sensor 20 in series. In addition, the switch unit 90 sequentially switches any one of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) according to the humidity sensor 20 and the switched resistor. The voltage values divided by the resistors are output in order. Further, the arithmetic processing unit 4 b converts the voltage value divided by the humidity sensor 20 and any of the three resistors 31 to 33 into digital information by the A / D converter 43. The arithmetic processing unit 4b performs weighted summation of the voltage value converted into digital information, and converts the voltage value into a voltage that changes linearly with respect to a change in humidity.

  In addition, the above three resistors include a first resistor 31 that exhibits a resistance value substantially equal to the resistance value of the humidity sensor 20 at the lower limit value in the humidity detection range, and a humidity at the upper limit value in the humidity detection range. A second resistor 32 having a resistance value substantially equal to the resistance value of the sensor 20 is included. The three resistors described above include a third resistor 33 that exhibits a resistance value substantially equal to the resistance value of the humidity sensor 20 at the median value in the humidity detection range.

  Thereby, the physical quantity detection circuit 1b can improve the detection sensitivity near the lower limit value and the detection sensitivity near the lower limit value in the humidity detection range. Further, the physical quantity detection circuit 1b can convert the voltage value obtained by resistance-dividing the humidity sensor 20 into a voltage that linearly changes with respect to the change in humidity by weighting and summing the voltage values obtained by the resistance-divided voltage. it can. Therefore, as in the first and second embodiments, the physical quantity detection circuit 1b maintains humidity (physical quantity) in the entire detection range of humidity (physical quantity) while maintaining linearity of voltage change with respect to change in humidity (physical quantity). The detection sensitivity can be improved.

  Furthermore, the physical quantity detection circuit 1b switches and uses one of the three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) by the switch unit 90. Thereby, a humidity sensor can be reduced to one. Further, since the physical quantity detection circuit 1b uses one humidity sensor, it is possible to eliminate variations in resistance values among a plurality of humidity sensors. Therefore, the physical quantity detection circuit 1b can improve the detection accuracy as in the second embodiment, compared to the first embodiment.

  Further, in the physical quantity detection circuit 1b, the microcomputer 44 executes the arithmetic processing shown in the equation (1) by digital arithmetic processing. Therefore, the result of weighted summation can be obtained with higher accuracy than analog calculation processing using an operational amplifier. Therefore, the physical quantity detection circuit 1b can detect the humidity more accurately than in the first and second embodiments.

According to the embodiment of the present invention, the physical quantity detection circuit 1 (or 1a) is a humidity sensor (physical quantity sensor) 21 whose resistance value (element value) changes exponentially with respect to a change in humidity (physical quantity). To 23 (or 20) and a plurality of resistors (elements) connected in series with the humidity sensors 21 to 23 (or 20) (first resistor 31, second resistor 32, third resistor 33), The voltage values obtained by resistance voltage division (element voltage division) by each of the humidity sensors 21 to 23 (or 20) and any of a plurality of resistors (first resistor 31, second resistor 32, and third resistor 33). An arithmetic processing unit 4 (or 4a) that converts the weighted sum to change linearly with respect to a change in humidity is provided. The plurality of resistors include a first resistor 31 (first element) that exhibits a resistance value equal to the resistance value of the humidity sensor 21 (or 20) at the lower limit value in the humidity detection range, and a humidity detection range. The second resistor 32 (second element) showing a resistance value equal to the resistance value of the humidity sensor 22 (or 20) is included.
Thereby, the physical quantity detection circuit 1 (or 1a) improves the detection sensitivity of the humidity (physical quantity) in the entire detection range of the humidity (physical quantity) while maintaining the linearity of the voltage change with respect to the change of the humidity (physical quantity). Can do.

Further, the number of the plurality of resistors (elements) (the first resistor 31, the second resistor 32, and the third resistor 33) is an odd number. Further, the plurality of resistors (first resistor 31, second resistor 32, and third resistor 33) are larger than the resistance value (element value) of the first resistor 31 (first element), A third resistor 33 having a resistance value smaller than that of the first resistor 32 (second element) is included. The resistance value of the third resistor 33 (third element) is equal to the resistance value of the humidity sensors 21 to 23 (physical quantity sensor) at the median value in the humidity (physical quantity) detection range.
Thereby, the physical quantity detection circuit 1 can improve the detection sensitivity of the central region in the humidity detection range. Therefore, the physical quantity detection circuit 1 can further improve the humidity (physical quantity) detection sensitivity in the entire humidity (physical quantity) detection range while maintaining the linearity of the voltage change with respect to the humidity (physical quantity) change.

Further, the physical quantity detection circuit 1 includes a plurality of humidity sensors 21 to 23 (physical quantity sensors), and a plurality of resistors (elements) (first resistor 31, second resistor 32, third resistor 33). Are connected in series.
Thus, the voltage values divided by the plurality of resistors (the first resistor 31, the second resistor 32, and the third resistor 33) can be detected at a time in synchronization with each other. it can.

Further, the physical quantity detection circuit 1a (or 1b) sequentially switches any one of a plurality of resistors (elements) (the first resistor 31, the second resistor 32, and the third resistor 33), and the humidity sensor 20 And switch units 91 to 93 (or) 90 that sequentially output voltage values obtained by resistance voltage division (element voltage division) by the switched resistors.
Thereby, a humidity sensor can be reduced to one. Moreover, since the physical quantity detection circuit 1a uses one humidity sensor, it is possible to eliminate variations in resistance values (element values) among a plurality of humidity sensors. Therefore, the physical quantity detection circuit 1a can improve detection accuracy.

In addition, the arithmetic processing unit 4 (or 4a) includes either one of the humidity sensors 21 to 23 (or 20) and a plurality of resistors (elements) (the first resistor 31, the second resistor 32, and the third resistor 33). An amplification rectification unit 41 (or 41a) (first operational amplification circuit unit) that multiplies each of the voltage values obtained by resistance division (element voltage division) by a weighting coefficient and outputs the multiplication result, and amplification rectification unit 41 (Or 41a) an adder circuit unit 42 (or 42a) (second circuit) for calculating the sum of outputs corresponding to a plurality of resistors (first resistor 31, second resistor 32, third resistor 33) Operational amplifier circuit portion).
As a result, the voltage value obtained by dividing the humidity sensors 21 to 23 by resistance without changing the physical quantity detection circuit 1 (or by approximation using a negative feedback approximation type or a polynomial approximation type using a microcomputer) can be used as a change in humidity. Therefore, the physical quantity detection circuit 1 can maintain the linearity of the voltage change with respect to the change of the humidity (physical quantity) and maintain the humidity with a simple configuration circuit. The detection sensitivity of humidity (physical quantity) can be improved in the entire detection range of (physical quantity).

Further, the arithmetic processing unit 4b detects a voltage value divided by a plurality of resistors (elements) (first resistor 31, second resistor 32, and third resistor 33). The A / D converter 43 (A / D converter) that converts to digital information and the digital information converted by the A / D converter 43 are multiplied by a weighting coefficient, and the digital operation is performed to sum them up. And a computer 44 (digital operation unit).
As a result, the physical quantity detection circuit 1b can obtain a weighted sum total with higher accuracy than analog calculation processing using an operational amplifier. Therefore, the physical quantity detection circuit 1b can detect the humidity more accurately than in the first and second embodiments.

The plurality of resistors described above are three resistors.
Thereby, in the humidity (physical quantity) detection range, the detection sensitivity in the vicinity of the lower limit value, the upper limit value, and the vicinity of the center can be improved while suppressing an increase in circuit scale.

Also, humidity sensors (physical quantity sensors) 21 to 23 (or 20) and humidity sensors 21 to 23 (or 20) whose resistance values (element values) change exponentially with respect to changes in humidity (physical quantities) and humidity sensors 21 to 23 (or 20), respectively. A physical quantity detection method using a plurality of resistors (elements) (first resistor 31, second resistor 32, and third resistor 33) connected in series includes humidity sensors 21 to 23 (or 20) and a plurality of resistors. Each of the resistors (first resistor 31, second resistor 32, third resistor 33) is weighted and summed up by the voltage divided by each of the resistors (element voltage division), so that the humidity (physical quantity) changes. And a calculation processing procedure for conversion so as to change linearly. The plurality of resistors include a first resistor 31 (first element) that exhibits a resistance value equal to the resistance value of the humidity sensor 21 (or 20) at the lower limit value in the humidity (physical quantity) detection range, and humidity. The upper limit value in the (physical quantity) detection range includes a second resistor 32 (second element) that exhibits a resistance value equal to the resistance value of the humidity sensor 22 (or 20).
Thereby, the detection sensitivity of humidity (physical quantity) can be improved in the entire humidity (physical quantity) detection range while maintaining the linearity of the voltage change with respect to the change of humidity (physical quantity).

  The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention. In each of the embodiments described above, the configuration in which three resistors (the first resistor 31, the second resistor 32, and the third resistor 33) used for voltage division have been described. . In this case, equation (1) can be expanded to n terms as shown in equation (4).

In the formula (4), _{a n} of the formula (1) and in (2) (a × d) , (b × d), and (c × d), respectively _a 1, _{a 2,} and _{a 3} Corresponding to In addition, when the resistance used for voltage division is two or more n, the resistance value may be set so that the detection sensitivity is uniform within the humidity detection range, or in a specific humidity range. It may be set non-uniformly so as to improve the detection sensitivity.

  Further, in each of the above embodiments, the form in which the physical quantity is humidity has been described. However, any physical quantity sensor whose resistance value changes exponentially with respect to a change in the physical quantity may be applied to other physical quantities. . In the case of a humidity sensor, it is necessary to apply an AC voltage, but in the case of a physical sensor that can apply a DC voltage, the AC power supply 7 may be replaced with a DC power supply. In this case, the capacitor 5 and the resistor 6 are not necessary.

  In each of the above-described embodiments, the form using the resistance change type humidity sensor has been described. However, another form using a circuit element value conversion type physical quantity sensor may be used. For example, a capacitance or inductance may be used for the circuit element value (element value). For example, when a capacitance conversion type humidity sensor is used, a capacity partial pressure (element partial pressure) using a capacitor as an element is used.

Further, in each of the embodiments described above, the first resistor 31 may be set to a resistance value that is close to the lower limit value in the humidity detection range and has the maximum detection sensitivity in the value within the humidity detection range. This is because when the first resistor 31 is set in accordance with the lower limit value in the humidity detection range, the resistance value is too large compared to a feasible value, which may not be realized. Therefore, in consideration of the feasible resistance value, the resistance value of the first resistor 31 may be set so that the detection sensitivity is maximized at a value close to the lower limit value in the humidity detection range.
In addition, the second resistor 32 may be set to a resistance value that is close to the upper limit value in the humidity detection range and at which the detection sensitivity becomes maximum at a value within the humidity detection range. This is because when the second resistor 32 is set in accordance with the upper limit value in the humidity detection range, the resistance value is too small compared to a feasible value and may not be realized. Also, the smaller the resistance value, the greater the power consumption. Therefore, in consideration of the feasible resistance value, the resistance value of the second resistor 32 may be set so that the detection sensitivity is maximized at a value close to the upper limit value in the humidity detection range.

In the second embodiment, the amplification rectification unit 41a has been described as having three operational amplifiers and diodes. However, the amplifier rectification unit 41a may be configured such that one operational amplifier and one diode are used and switched by a switch. _However, since the voltage drops in the order of _{V O_4800k> V o_6k> V o_150k} , if the operational amplifier and the diode was Tsunishi 1, sometimes the detection accuracy decreases. In the embodiment with three operational amplifiers and diodes, it is possible to change the amplification factor of the operational _amplifier, it can be increased in the order of _{V O_4800k <V o_6k <V o_150k} . Therefore, in the form provided with three operational amplifiers and diodes, it is possible to prevent a decrease in detection accuracy.

In the second and third embodiments, the switch units 90 to 93 have been described using MOS switches or analog switches. However, a photocoupler may be used.
In the third embodiment, the plurality of resistors (the first resistor 31, the second resistor 32, the third resistor 33) and the switch unit 90 are provided with a multiplying D / A (digital / analog) conversion. It may be replaced with a vessel. Moreover, although the form which uses the microcomputer 44 for weighted addition processing was demonstrated, the form implement | achieved by the hardware for exclusive use which is not equipped with CPU is sufficient. For example, an FPGA (Field-Programmable Gate Array) or CPLD (Complex Programmable Logic Device) may be used. The arithmetic processing unit 4b may be applied to a form including a plurality of humidity sensors as in the first embodiment.

1, 1a, 1b Physical quantity detection circuit 4, 4a, 4b Arithmetic processing unit 5, 56, 66, 76, 425 Capacitor 6, 43, 44, 45, 52, 53, 54, 62, 63, 64, 72, 73, 74, 81, 82, 83, 422, 423, 424 Resistance 7 AC power supply 8 DC power supply 20, 21, 22, 23 Humidity sensor 31 1st resistance 32 2nd resistance 33 3rd resistance 41, 41a Amplification rectification part 42, 42a Adder circuit part 43 A / D converter 44 Microcomputer 51, 61, 71, 421 Operational amplifier 55, 65, 75 Diode 90, 91, 92, 93 Switch part 901, 902, 903 Analog switch 911, 913, 921 , 923, 931, 933 Resistors 912, 914, 922, 924, 932, 934 MOS switches 915, 92 5,935 capacitor

Claims (11)

A physical quantity sensor whose element value changes exponentially with respect to a change in physical quantity, and
A plurality of elements each connected in series with the physical quantity sensor and exhibiting different element values;
An arithmetic processing unit that performs weighted summation of voltage values respectively divided by the physical quantity sensor and any of the plurality of elements, and converts the voltage values to change linearly with respect to changes in the physical quantity; and
The plurality of elements include
A first element showing an element value equal to an element value of the physical quantity sensor at a lower limit value in the physical quantity detection range;
A physical quantity detection circuit comprising: a second element having an element value equal to an element value of the physical quantity sensor in an upper limit value in the physical quantity detection range. The physical quantity detection circuit according to claim 1, wherein the number of the plurality of elements is an odd number. The plurality of elements include
3. The physical quantity detection circuit according to claim 1, further comprising a third element having an element value larger than an element value of the first element and smaller than an element value of the second element. . The element value of the third element is
The physical quantity detection circuit according to claim 3, wherein a median value in the physical quantity detection range is equal to an element value of the physical quantity sensor. 5. The physical quantity detection according to claim 1, wherein the physical quantity sensor provided in the physical quantity detection circuit includes a plurality of physical quantity sensors and is connected in series to the plurality of elements. circuit. The physical quantity detection circuit includes:
2. The switch unit according to claim 1, further comprising: a switch unit configured to sequentially switch any one of the plurality of elements and sequentially output a voltage value divided by the physical quantity sensor and the switched element. Item 5. The physical quantity detection circuit according to any one of Item 4. The arithmetic processing unit includes:
A first operational amplifier circuit unit that multiplies a voltage value divided by each of the physical quantity sensor and any of the plurality of elements by a weighting coefficient and outputs a multiplication result;
7. A second operational amplifier circuit unit that calculates a sum of outputs corresponding to the plurality of elements in the first operational amplifier circuit unit. 8. The physical quantity detection circuit according to item. The arithmetic processing unit includes:
An A / D converter that detects the voltage value and converts it into digital information;
7. A digital arithmetic unit that performs digital arithmetic processing that multiplies each digital information converted by the A / D conversion unit by a weighting coefficient and sums the digital information. 7. 2. A physical quantity detection circuit according to item 1. The physical quantity detection circuit according to claim 1, wherein the plurality of elements are three elements. The element is a resistor;
The physical quantity detection circuit according to claim 1, wherein the physical quantity sensor is a resistance change type humidity sensor. A physical quantity detection method using a physical quantity sensor whose element value changes exponentially with respect to a change in physical quantity, and a plurality of elements connected in series with each other and showing different element values,
The plurality of elements include
A first element showing an element value equal to an element value of the physical quantity sensor at a lower limit value in the physical quantity detection range;
A second element indicating an element value equal to an element value of the physical quantity sensor in an upper limit value in the detection range of the physical quantity, and
And a calculation processing procedure that includes weighting and summing voltage values respectively divided by the physical quantity sensor and any of the plurality of elements, and converting the voltage values to change linearly with respect to the change in the physical quantity. A physical quantity detection method.

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