JP3200641B2 - Temperature sensor system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor system, and more particularly, to a small and lightweight temperature sensor system for accurately measuring temperature by using a thin film transistor as a temperature sensor.

[0002]

2. Description of the Related Art Conventionally, a temperature sensor system using a thermocouple or a resistor has been used as a temperature sensor.

For example, a temperature sensor using a thermocouple is:
The heat current generated by the temperature difference between the connection points of the two types of metal wires is taken out by cutting out the middle of one of the metal wires, and the heat current is amplified by an amplifier and measured as a temperature by a voltmeter or the like.

A temperature sensor using a resistor measures a temperature by utilizing a temperature change of a resistance value of a pure metal such as a high-purity platinum wire, and usually, a metal wire used as a sensor is used. Are assembled in a three-wire bridge, and a voltage change due to a change in the resistance value is amplified by an amplifier or the like, and the temperature is measured.

[0005]

However, in such conventional temperature sensor systems, since the output of each temperature sensor is small, it is necessary to connect a high-performance amplifier to amplify the output. In addition, there is a problem that not only the price is expensive but also the temperature sensor system becomes large as a whole because a complicated electronic circuit is required.

Accordingly, an object of the present invention is to provide a small and inexpensive temperature sensor system that can accurately measure temperature with a simple electronic circuit.

[0007]

According to the temperature sensor system of the present invention, a source electrode and a drain electrode are arranged opposite to each other with a semiconductor layer interposed therebetween, and both sides of the semiconductor layer, the source electrode and the drain electrode are interposed therebetween. A temperature sensor system provided with a first gate electrode and a second gate electrode opposed to the semiconductor layer via an insulating film, respectively, wherein the first gate electrode or the second A sense state control means for controlling a voltage applied to one of the two gate electrodes to control a sense state and a reset state of the temperature sensor; and Measuring means for measuring a time required until the output current rises to a predetermined current value or until the output change of the temperature sensor reaches a predetermined value. , By providing a temperature calculating means for calculating the temperature from the measurement results of the measuring means, it has achieved the above objects.

Further, a source electrode and a drain electrode are disposed opposite to each other with the semiconductor layer interposed therebetween, and both sides of the semiconductor layer, the source electrode and the drain electrode are respectively opposed to the semiconductor layer with an insulating film interposed therebetween. A temperature sensor system comprising a temperature sensor provided with opposed first and second gate electrodes, wherein a voltage applied to one of the first gate electrode and the second gate electrode of the temperature sensor is provided. Control means for controlling a sense state and a reset state of the temperature sensor, an output current value of the temperature sensor at a predetermined timing in a sense state by the sense state control means, and a predetermined time elapses from the predetermined timing. Measuring means for measuring an output current value of the temperature sensor when the temperature is measured, and calculating a temperature from a measurement result of the measuring means. And temperature calculation means for, by providing, have achieved the above objects.

[0009]

According to the temperature sensor system of the present invention, the temperature sensor has a source electrode and a drain electrode opposed to each other with a semiconductor layer interposed therebetween. A first gate electrode opposed to the semiconductor layer via an insulating film on each side and a second
A gate electrode is provided, and a voltage applied to one of the first gate electrode and the second gate electrode of the temperature sensor is controlled by sense state control means to set the temperature sensor to a sense state. The time required until the output current of the temperature sensor rises to the predetermined current value from the time of the state or until the output change of the temperature sensor reaches the predetermined value is measured by the measuring means, and the temperature is calculated from the measurement result of the measuring means. The temperature is calculated by the means.

Therefore, the temperature sensor can take out the thermal excitation carrier generated corresponding to the measured temperature as an output current and measure the time when the current value changes, thereby calculating the temperature and amplifying the output. Therefore, a high-precision electronic circuit is not required, the temperature sensor system can be made small and inexpensive, and the temperature can be measured accurately. In addition, the output current value of the temperature sensor at a predetermined timing in the sensing state and the output current value of the temperature sensor when a predetermined time has elapsed from the predetermined timing are measured, and the temperature is calculated from the measurement result. By extracting the thermal excitation carriers generated corresponding to the temperature as output current and measuring the amount of change in the current value for a predetermined time, the temperature can be calculated, and a high-precision electronic circuit for amplifying the output is provided. It is not necessary, and the temperature sensor system can be made small and inexpensive, and the temperature can be measured accurately.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIGS. 1 to 5 show an embodiment of a temperature sensor system. FIG. 1 is a side sectional view of a temperature sensor used in the temperature sensor system, and FIG. FIG. 3 is an explanatory diagram of a voltage applied to each electrode of the temperature sensor of FIG. 1 and its state change, FIG. 4 is a characteristic curve diagram showing a top gate voltage-drain current characteristic at room temperature, and FIG. FIG. 6 is a circuit diagram showing a temperature sensor system.

In FIG. 1, the temperature sensor 1 basically has a configuration in which an inverted staggered thin film transistor and a coplanar thin film transistor are combined into a single semiconductor layer.

That is, in the temperature sensor 1, a bottom gate electrode 3 made of chromium (Cr) or the like is formed on an insulating substrate 2 made of glass or the like, and the bottom gate electrode (BG) 3 and the insulating substrate 2 are formed. 2, a bottom gate insulating film 4 made of silicon nitride (SiN) is formed.

A semiconductor layer 5 is formed on the bottom gate insulating film 4 at a position facing the bottom gate electrode (BG) 3, and the semiconductor layer 5 is made of i-type amorphous silicon (ia- Si). A source electrode (S) 6 and a drain electrode (D) 7 made of chromium (Cr) or the like are formed on the semiconductor layer 5 at positions facing each other at a predetermined interval with the semiconductor layer 5 interposed therebetween. Yes,
These source electrode (S) 6 and drain electrode (D) 7
Are connected to the semiconductor layer 5 via n @ + silicon layers 8 and 9 made of amorphous silicon in which a dopant such as phosphorus is diffused. These bottom gate electrode (BG) 3, bottom gate insulating film 4, semiconductor layer 5, source electrode (S) 6, and drain electrode (D) 7 constitute a bottom transistor (inverted staggered thin film transistor).

The portion between the source electrode (S) 6 and the drain electrode (D) 7 and the semiconductor layer 5 between the source electrode (S) 6 and the drain electrode (D) 7 is a top gate insulating film 10 made of silicon nitride. And on the top gate insulating film 10, the bottom gate electrode (BG) 3
And a top gate electrode (TG) 11 made of a conductive material. The top gate electrode (TG) 11 is described later electronic - not only the channel region of the semiconductor layer 5 in order to generate a hole pairs (carriers), as shown in FIG. 1, n ⁺ silicon layer 8, 9 the upper surface Is desirably formed to have a size that also covers. Although not shown, an overcoat film made of silicon nitride is formed so as to cover the top gate electrode (TG) 11 and the top gate insulating film 10 to protect the overcoat film.
A top transistor (coplanar thin film transistor) is formed by the top gate electrode (TG) 11, the top gate insulating film 10, the semiconductor layer 5, the source electrode (S) 6, and the drain electrode (D) 7.

The temperature sensor 1 is entirely covered with a film having a good light-shielding property in order to prevent the influence of light at the time of temperature measurement. As will be described later, hole-electrons excited by heat are used. The temperature is measured using the pair.

In this temperature sensor 1, for example, the bottom gate electrode (BG) is 1000 ° (angstrom), the bottom gate insulating film 4 is 2000 ° , and the semiconductor layer 5 is 150 °.
0Å , the source electrode (S) and the drain electrode (D) are 50
0 ° , the ohmic contact layers 8 and 9 are 250 ° , the top gate insulating film 10 is 2000 ° , the top gate electrode (T
G) is formed at 500 ° and the overcoat film is formed at 4000 ° , and the distance between the source electrode (S) and the drain electrode (D) on the semiconductor layer 5 is formed at 7 μm.

As described above, the temperature sensor 1 has a configuration in which an inverted staggered thin film transistor and a coplanar thin film transistor are combined, and an equivalent circuit thereof can be shown in FIG.

Next, the operation of the temperature sensor 1 will be described.

As shown in FIG. 3, the temperature sensor 1 controls the voltage applied to the bottom gate electrode (BG) and the voltage applied to the top gate electrode (TG), thereby selecting the selected state, the non-selected state, and the sense state. The state and the reset state can be controlled.

That is, as shown in FIGS. 3C and 3D, when a positive voltage, for example, +10 [V] is applied to the bottom gate electrode (BG) of the temperature sensor 1, the semiconductor layer 5
An n-channel is formed. Here, a positive voltage, for example, +5, is applied between the source electrode (S) and the drain electrode (D).
When [V] is applied, electrons are supplied from the source electrode (S) side, and a current flows. In this state, as shown in FIG. 3D, when a negative voltage, for example, −20 [V] at a level that eliminates the n-channel due to the electric field of the bottom gate electrode (BG) is applied to the top gate electrode (TG). , The electric field from the top gate electrode (TG) is applied to the bottom gate electrode (B
G) works in a direction to reduce the influence of the electric field on the channel layer. As a result, the depletion layer extends in the thickness direction of the semiconductor layer 5, and pinches off the n-channel. At this time, the temperature sensor 1 causes the top gate electrode (T
An electron-hole pair is induced on the G) side. However, since -20 [V] is applied to the top gate electrode (TG), the induced holes are accumulated in the channel region, and the top gate electrode (TG) is accumulated. The electric field of the electrode (TG) is canceled. Therefore, an n-channel is formed in the channel region of the semiconductor layer 5, and a current flows. The current (hereinafter, drain current) I _DS flowing between the source electrode (S) and the drain electrode (D) is
It changes according to the number of holes induced by heat, that is, according to temperature.

As shown in FIG. 3C, the temperature sensor 1 applies a positive voltage (+10) to the bottom gate electrode (BG).
[V]), the top gate electrode (TG)
Is set to, for example, 0 [V], holes can be discharged from trap levels between the semiconductor layer 5 and the top gate insulating film 10 to refresh, that is, reset. That is, when the temperature sensor 1 is used continuously,
The trap level between the top gate insulating film 10 and the semiconductor layer 5 is filled with holes generated by thermal excitation and holes injected from the drain electrode (D), and the channel resistance also decreases. The drain current I _DS increases. Therefore, 0 [V] is applied to the top gate electrode (TG) to discharge the holes and reset.

Further, as shown in FIGS. 3A and 3B, the temperature sensor 1 has a bottom gate electrode (BG).
When no positive voltage is applied, no channel is formed in the semiconductor layer 5 and the drain current I _DS does not flow.
It can be in a non-selected state. That is, the temperature sensor 1 can control the selected state and the non-selected state by controlling the voltage (hereinafter, bottom gate voltage) V _BG applied to the bottom gate electrode (BG). In this unselected state, as shown in FIG. 3A, when 0 V is applied to the top gate electrode (TG), the semiconductor layer 5 and the top gate insulating film 10
The holes can be ejected from the trap level between and reset.

The temperature sensor 1 performing such an operation is:
In the above operation, as shown in FIG. 3C and FIG. 3D, in the selected state where +10 [V] is applied as the bottom gate voltage V _BG , the voltage applied to the top gate electrode (TG) (hereinafter referred to as “TG”) By switching the top gate voltage) V _TG between 0 [V] and -20 [V], it can be used as a temperature sensor.

[0026] That is, in the selection state, when the room temperature, the drain current characteristic curve of the temperature sensor 1 when changing the top gate voltage VTG, shown as in FIG. 4, the top gate voltage V _TG 0 At the time of [V], the drain current IDS flows at 1 [A] or more, but when the top gate voltage V _TG becomes -12 [V] or less, the drain current I _DS decreases sharply and the top gate voltage V _TG becomes -15 [V]. V] or less, it decreases to 1p [A] or less. Therefore, a difference of 10 ⁶ times the drain current I _DS can be obtained at the time of reset and at the time of sensing, and the amplification factor of the bottom transistor at this time changes depending on the temperature at the time of measurement, and the S / N ratio Can be increased.

When the top gate voltage V _TG is switched from 0 [V] to −20 [V] using the temperature as a parameter, that is, the elapsed time [sec] from when the reset state is switched to the sense state. The relationship with the drain current I _DS is shown in FIG.

That is, when switching from the reset state of FIG. 3C to the sensing state of FIG.
At ° C, the drain current I _DS changes over time, as shown by the drain current characteristic curve T1 in FIG. That is, in this case, when the state is switched to the sense state, the drain current I _DS rapidly increases from about 1 pA (pico amps) after about 5 seconds, and
At about 0 seconds, it increases to 0.01 μA (microampere), and at about 30 seconds, 1 μA
Increase to a degree and saturate. When the temperature is 30 ° C., the drain current I _DS changes with time, as shown by the drain characteristic curve T2 in FIG. That is, in this case, when the state is switched to the sense state, the drain current I _DS rapidly increases from about 1 pA after about 8 seconds have elapsed, and reaches 0.
01 μA, and after about 40 seconds, 1 μA
Increase to a degree and saturate. Further, when the temperature is 25 ° C., the drain current I _DS changes as shown by the drain characteristic curve T3 in FIG. That is, in this case,
When switched to the sense state, the drain current I _DS
It gradually increases from about 1 pA after about 22 seconds, increases to 0.001 μA after about 35 seconds, and then gradually saturates. When the temperature is 20 ° C., the drain current I _DS changes as shown by the drain characteristic curve T4 in FIG. That is, in this case,
When switched to the sense state, the drain current I _DS
When about 28 seconds have passed, it rapidly increased from about 1 pA, and when about 30 seconds passed, it increased to 10 pA. Thereafter, it gradually increased, and when about 45 seconds passed, 0.001.
It becomes about μA, and then gradually saturates.

Therefore, the temperature sensor 1 is shown in FIG.
In the selected state shown in FIG. 3D, the output of the temperature sensor 1, that is, the drain current _IDS is changed to a predetermined current from the point in time when the reset state shown in FIG. 3C is switched to the sense state shown in FIG. By measuring the time until the temperature rises to the value, the temperature at that time can be calculated from the elapsed time. At this time, the higher the temperature, the shorter the time it takes to rise to the predetermined current value. For example, the drain current I _DS becomes 0.
Looking at the time required to reach 001 μA in FIG. 5, there is a difference of about 10 seconds between 35 ° C. and 30 ° C., and a difference of about 8 seconds between 25 ° C. and 20 ° C. Similarly, looking at the time until the drain current I _DS becomes 10 pA, it takes about 5 seconds at 35 ° C. and 30 ° C.
There is a difference of about 7 seconds between 5 ° C and 20 ° C. Therefore, the temperature at that time can be accurately calculated by measuring the time required until the drain current _IDS rises to a predetermined current value from the time when the sensing state is set.

The temperature sensor 1 can determine the temperature at that time by measuring the time until the output change of the temperature sensor 1 reaches a predetermined value. For example, in FIG. 5, the drain current I _DS is 1 pA to 0.001.
Comparing the time required to reach μA, it is about 11 seconds at 35 ° C., about 23 seconds at 25 ° C., and about 30 seconds at 20 ° C., showing a correlation.

After switching from the reset state to the sense state, the drain current I _{DS at} a predetermined timing is set.
By measuring the current value of the drain current I _{DS and} the current value of the drain current I _DS when a predetermined time has elapsed from the predetermined timing,
The temperature at that time can be calculated from the difference between the current values. For example, as can be seen from FIG.
Although the drain current I _DS after a predetermined time increases, for example, when 5 seconds elapse after the switching of the sense state, the drain current I _DS becomes 35 °
C is about 10 μA, about 30 μC about 1 μA, about 25 μC about 0.1 μA, and about 20 μC about 0.05 μA.
Accordingly, in the sense state, (in the above sense state switching time point from the reset state) predetermined timing by measuring a current value of the drain current I _DS when the predetermined time elapses, it is possible to calculate the temperature at that time .

As described above, the drain current I _DS is such that the temperature sensor 1 has a configuration in which an inverted staggered thin film transistor and a coplanar thin film transistor are combined, and the temperature sensor 1 itself has an amplifying action. In addition, since the S / N ratio is large, a high-precision amplifier for amplifying the output is not required unlike the related art, and the drain current _IDS can be accurately detected by a simple electronic circuit. As a result, the temperature can be accurately detected by the small temperature sensor 1 with a simple circuit configuration.

FIG. 5 is a diagram showing an example of a temperature sensor system 20 for measuring a temperature using the characteristics of the temperature sensor 1.
1, a temperature sensor 1, a clock generation unit 22, a counter circuit 23, a data processing unit 24, and the like.

The clock generator 22 includes a transmission circuit, a frequency divider, and the like, and outputs a clock signal of a predetermined frequency and a reset signal to the drive circuit 21 and the counter circuit 23.

The drive circuit 21 receives a clock signal and a reset signal input from the clock generator 22 and
A top gate voltage _VTG is output to the temperature sensor 1 as a sense signal and a reset signal, and the driving of the temperature sensor 1, particularly, the sense / reset state of the temperature sensor 1 is controlled.

The temperature sensor 1 outputs an output signal V _OUT , that is, a drain current I _DS to the counter circuit 23, and its source electrode (S) is grounded.

The counter circuit 23 includes a clock generator 22.
A reset signal input from, to determine the sense state of the temperature sensor 1, the clock generator until the output signal V _OUT of the temperature sensor 1 from the time of the temperature sensor 1 becomes sense state reaches a predetermined value The number of clock signals input from the counter 22 is counted, and the counted number is output to the data processing unit 24.

The data processing section 24 has a CPU (Central Pr
ocessing Unit), RAM (RandomAccess Memory ) and ROM (includes a Read Only Memory) or the like, in its RAM or the ROM, the drain current I _DS (output signal V _{OU T)} and the elapsed time at each temperature shown in FIG. 5 And a program as the temperature sensor system 20 are stored in advance. The data processing unit 24 controls the above-described selection / non-selection state of the temperature sensor 1 and searches the ROM based on the count number input from the counter circuit 23 to convert the temperature into a temperature.

In such a circuit configuration, the temperature sensor system 20 includes the bottom gate voltage V _BG of the temperature sensor 1.
And a top gate voltage V _TG, FIG. 3 (C) and FIG. 3
As shown in (D), by controlling, the sense / reset control in the selected state is performed, and the time required for the output signal V _OUT of the temperature sensor 1 to reach a predetermined value from the start of the sense state is counted. The measurement is performed by the circuit 23, and the count is converted into temperature data.

That is, +10 [V] is applied to the bottom gate voltage V _BG of the temperature sensor 1, and the drive circuit 21 sends a sense signal and a reset signal to the temperature sensor 1 by the reset signal and the clock signal output from the clock generator 22. A signal is output, and as shown in FIG.
After resetting the top gate voltage V _TG to 0 [V] and resetting the top gate voltage V _TG to −20 [V],
Temperature sensor 1 is in the sensing state. As described above, the temperature sensor 1 is set in the sense state, and the drain voltage is increased by +10.
[V], the temperature sensor 1 according to the temperature at that time
Output signal V _OUT changes.

That is, an electron-hole pair is induced in the semiconductor layer 5 of the temperature sensor 1 according to the temperature at that time, and the output signal V _OUT rises with time as shown in FIG. .

Therefore, the counter circuit 23 counts the time required from when the reset state is switched to the sense state to when the output signal V _OUT reaches a predetermined value, and outputs the count to the data processing unit 24. The data processing unit 24 converts the count number input from the counter circuit 23 into a temperature corresponding to the count number and outputs the converted temperature.

As described above, the output signal V of the temperature sensor 1
Utilizing the characteristic that _OUT changes according to temperature, the output signal V
_The time required for _OUT to reach a predetermined value is counted, and the temperature is determined based on this count.Therefore, unlike conventional products, the peripheral circuits are not affected by noise, and the peripheral circuits are simplified and miniaturized. And the temperature at that time can be accurately obtained.

In FIG. 6, the time required from when the temperature sensor 1 switches from the reset state to the sense state until the output signal V _OUT of the temperature sensor 1, that is, the drain current I _DS reaches a predetermined value is shown. By measuring,
The temperature is required, but is not limited to this. For example, in FIG. 6, the output signal V _OUT of the temperature sensor 1 is input to the data processing unit 24, and the counter circuit 23 measures the time from a predetermined timing in the sensing state of the temperature sensor 1 until a predetermined time elapses. , Data processing unit 2
4 is output. Then, based on the measurement time of the counter circuit 23, the data processing unit 24 determines the value of the output signal V _OUT of the temperature sensor 1 at the predetermined timing and the output signal of the temperature sensor 1 when a predetermined time has elapsed from the predetermined timing. captures the value of V _{OU T} from the temperature sensor 1 may be obtained the temperature from the difference between the output signal V _OUT.

[0045]

According to the temperature sensor system of the present invention,
In the temperature sensor, a source electrode and a drain electrode are disposed opposite to each other with a semiconductor layer interposed therebetween, and the temperature sensor is opposed to the semiconductor layer with an insulating film on both sides of the semiconductor layer, the source electrode and the drain electrode, respectively. A first gate electrode and a second gate electrode facing each other, and a voltage applied to one of the first gate electrode and the second gate electrode of the temperature sensor is controlled by a sense state control means. The temperature sensor is set to the sensing state, and the time required from the time when the temperature sensor is set to the sensing state to when the output current of the temperature sensor rises to a predetermined current value or until the change in the output current of the temperature sensor reaches the predetermined value is measured by the measuring means. Measure,
Since the temperature is calculated by the temperature calculating means from the measurement result of the measuring means, the temperature sensor takes out the thermal excitation carrier generated corresponding to the measured temperature as an output current and measures the time required for the current value to change. As a result, the temperature can be calculated, a high-precision electronic circuit for amplifying the output is not required, the temperature sensor system can be made small and inexpensive, and the temperature can be accurately measured. Can be.

Further, the output current value of the temperature sensor at a predetermined timing in the sensing state and the output current value of the temperature sensor when a predetermined time has elapsed from the predetermined timing are measured, and the temperature is calculated from the measurement result. The temperature sensor can take out the thermal excitation carriers generated corresponding to the measured temperature as an output current and measure the amount of change in the current value in a predetermined time, thereby calculating the temperature, and amplifying the output. A high-precision electronic circuit is not required, the temperature sensor system can be made small and inexpensive, and the temperature can be measured accurately.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a temperature sensor applied to an embodiment of a temperature sensor system according to the present invention.

FIG. 2 is an equivalent circuit of the temperature sensor of FIG.

FIG. 3 is an explanatory diagram of voltages applied to respective electrodes of the temperature sensor of FIG. 1 and changes in the state thereof.

FIG. 4 is a characteristic curve diagram showing a relationship between a top gate voltage and a drain current at room temperature.

FIG. 5 is a characteristic curve diagram showing a relationship between a drain current and time in a sense state using temperature as a parameter.

FIG. 6 is a circuit block diagram of a temperature sensor system using the temperature sensor of FIG. 1;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Temperature sensor 2 Insulating substrate 3 Bottom gate electrode (BG) 4 Bottom gate insulating film 5 Semiconductor layer 6 Source electrode (S) 7 Drain electrode (D) 8, 9n ⁺ silicon layer 10 Top gate insulating film 11 Top gate electrode (TG) 20 Temperature sensor system 21 Drive circuit 22 Clock generation unit 23 Counter circuit 24 Data processing unit

Claims (2)

(57) [Claims] 1. A semiconductor device comprising a source electrode and a drain electrode opposed to each other with a semiconductor layer interposed therebetween. The source electrode and the drain electrode are disposed on both sides of the semiconductor layer, the source electrode and the drain electrode with an insulating film interposed therebetween. A temperature sensor system comprising a temperature sensor provided with opposed first and second gate electrodes, wherein a voltage applied to one of the first gate electrode and the second gate electrode of the temperature sensor is provided. A sense state control means for controlling a sense state and a reset state of the temperature sensor, and from the time when the sense state is set to the sense state by the sense state control means until the output current of the temperature sensor rises to a predetermined current value, or Measuring means for measuring a time required until a change in the output current of the temperature sensor reaches a predetermined value; and calculating a temperature from a measurement result of the measuring means. And a temperature calculating means for outputting the temperature. 2. A source electrode and a drain electrode are disposed opposite to each other with a semiconductor layer interposed therebetween, and the semiconductor layer, the source electrode and the drain electrode are disposed on both sides of the semiconductor layer with an insulating film interposed therebetween. A temperature sensor system comprising a temperature sensor provided with opposed first and second gate electrodes, wherein a voltage applied to one of the first gate electrode and the second gate electrode of the temperature sensor is provided. Control means for controlling a sense state and a reset state of the temperature sensor by controlling the temperature sensor output current value at a predetermined timing in the sense state by the sense state control means and a predetermined time from the predetermined timing Measuring means for measuring an output current value of the temperature sensor when the temperature is measured; and calculating a temperature from a measurement result of the measuring means. And a temperature calculating means.