JPS6038628A - Temperature sensor - Google Patents

Abstract

PURPOSE:To achieve a higher speed and a higher accuracy of the temperature measurement with the lowering of voltage by performing preheating while emplying non-linear characteristic with a P-N junction. CONSTITUTION:A sensor tip 11 directly contacting body heat comprises a circuit made up of transistors Tr1-Tr3 and resistances R1-R3 to obtain a reference voltage Vret stably and a diode D1 as non-linear preheating element. An A/D converting section 16 applies the output of an operational amplifier 14 to an arithmetic processing section 17 and based on the results of the processing, a display section 18 indicates the temperature of body heat. In this case, the preheating is done utilizing non-linear current voltage characteristic based on the P-N reverse characteristic of the D1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature sensor used in an electronic thermometer or the like.

[Technical background of the invention and its problems]

Generally, devices that measure body temperature electronically utilize the fact that a bias current is passed through the sensor and the resulting voltage changes with temperature. By the way, as a countermeasure when shortening the side heating time is required, the sensor can be rapidly heated to near body temperature by passing a large current through the sensor itself, and the sensor's self-heating effect can be used to rapidly heat the sensor to near body temperature (hereinafter, this method will be used). There is a method called the Breheat method that shortens the temperature measurement time (for example, Japanese Patent Laid-Open No. 54-25882).

Japanese Patent Publication No. 54-87281. Publication No.). In this type of PC, the sensor bias current during temperature measurement is generally extremely small to avoid self-heating, and therefore the voltage drop ratio in the sensor during preheating and temperature measurement is It becomes extremely thick (approximately 1000 times), making it difficult to realize one circuit.For example, if the bias current during temperature measurement is 100 ttk and the generated voltage is 0.5V.

The resistance is 5Ω, and the bias current during preheating is 10Ω.
For 0+nA, the IL pressure becomes 5Ω×100mA-500V, which is completely impractical.

In general, the terminal voltage of a sensor is expressed by a temperature-sensitive component and a non-temperature-sensitive component. El(Jf
) must be subtracted by In order to obtain the final temperature-sensitive voltage, it is necessary to amplify the temperature-sensitive component with an amplifier. In this case, drifts (changes due to ambient temperature) of the reference voltage and the offset voltage of the amplifier become factors that reduce the accuracy of the temperature-sensitive voltage.

[Purpose of the invention]

The present invention was made in view of the above-mentioned circumstances.
The present invention aims to provide a temperature sensor that can be increased in speed and accuracy, and can be reduced in cost without using expensive parts.

[Summary of the invention]

In the present invention, in order to make the above preheating method possible, a sufficient voltage is generated for the bias current during temperature measurement, and the current voltage is This gives nonlinearity to the characteristics. An example of this nonlinearity is
The change in the total voltage of the circuit may be 20 times or less for a 100 times change in the total current flowing into the circuit, but it is better if this value is as small as possible. Fig. 1 shows an example of the current-voltage characteristics during preheating, and the characteristic line when t is an excessive voltage with respect to the large current during preheating (in the case of linear flow pressure characteristics), m indicates the desired nonlinear current 1E voltage characteristic line.

In addition, in the present invention, as a method of obtaining a highly accurate temperature-sensing voltage by removing the factors that reduce the accuracy of the temperature-sensing voltage due to the above-mentioned drift, the voltage at the two terminals of the SenzaTeg can be converted into a voltage in a very short time using the same amplifier. The output is amplified and outputted in a divided manner, each output value is, for example, digitally converted and held as digital data, and the differential voltage is taken and used as temperature information. That is, the reference voltage, offset voltage, etc. become zero in the differential output, and temperature information can be obtained only from the voltage between two terminals of the sensor. In order to implement this method, the senna only needs to output two voltages, and the voltage difference between the two voltages changes (preferably linearly) with temperature changes.

[Embodiments of the invention]

The present invention will be described in detail below with reference to the drawings. In Fig. 2, 11 is a seven-chip chip 7' (integrated circuit) that is directly exposed to body temperature, and this circuit has transistors Tr, ~Tr,
, a circuit that stably obtains the reference voltage Vref, which is composed of resistors RI-Rs, and a diode D1 as a nonlinear predetermined element. 121 to 124 are external lead-out terminals. The amplifying section 13 has a fourth angle 14 and an electric current 15! ~153
, switch S1 and resistors R4 to R7. The A/D (analog/digital) converter 16 receives the output V of the operational amplifier 14. ut is A/D converted and arithmetic processing unit (microcomputer) 17
performs calculations, data storage, etc., which will be described later, and the display section 18 displays temperatures such as body temperature.

In the circuit shown in FIG. 2, if the 1E voltage and current of each part are determined as shown, the following equation holds true.

Here, q is the electronic charge, k is Boltzmann's constant, and Tt2, so 3 R3I2=-ΔvBE11. (3) 2, and 3 vref ”” ”nr:5 + 甫ΔvEl ”'(4
). As is well known, the first term on the right-hand side of equation (4) has a negative temperature coefficient of -2.2 mV/℃, but the second term on the right-hand side of equation (4) has a stop temperature coefficient (as seen from equation 12). It has a temperature coefficient of It is known that the value becomes approximately zero due to the positive and negative cancellation effects of the first and second terms on the right side of equation (4).

That is, from equation (4), a reference voltage ref without temperature dependence can be obtained from the circuit of the sensor chip f1 in FIG.

On the other hand, from the input terminal conditions of the amplifier 14 in FIG. Therefore, Vs (temperature-sensitive component + non-temperature-sensitive component), R, I
, output V. The relationship between ut is == GV8-rt, t, ``'α0 where 7 G-10-...(1]) 6.For voltage VB, switch S is set to the fixed contact A side. When it is turned down, vs. ``”vIIE5''・0-2 When the switch S is turned to the fixed contact B side.

Next, in equation 01, input offset voltage V of operational amplifier 14
. , f is introduced, VOu, = G (V8
+Vof, )-R,I, ・Q4. As shown in the αυ equation, the gain G of the operational amplifier 14 is stable because it is determined by the resistance ratio, but the drift of vOff and R7I causes the output V. This is considered to be a cause of error in ut.

The procedure for obtaining the temperature voltage in FIG. 2 is as follows. At the current temperature, switch S'! ! i: Output voltage V when turned to the A side. u t (A) is the following formula % formula % 3 Next, the output vout (B
Therefore, vout(^" vout(B) is converted by A/Ill conversion It, +!HH16 respectively and held in the arithmetic processing unit 12, and the difference ΔVout by ゛tun1" is calculated, Δvout "" out(A) -vout(B), and the effects of R, I and V.ff can be removed, and the non-temperature-sensitive component of vBI13 (approximately 0.6V ) by the second term in the parentheses of the αη equation, the temperature-sensitive component (-2.2mV/C) can be efficiently detected.In other words, temperature information that is highly sensitive and stable with respect to temperature can be obtained. can be obtained in the form of digital information Δvout.

Furthermore, in equation (1), ■□ changes linearly with temperature, and ref can be made almost constant with temperature, so Δvout can be regarded as a linear function of temperature, and its The gradient and constant terms can be arbitrarily adjusted by c, lt, , R, etc. Here, the arithmetic processing unit 17 obtains the temperature that can be claimed from the linear 1)'A number of Δvout vs. is displayed on the display section 18.

On the other hand, in order to achieve higher speeds due to breathing, it is necessary to provide nonlinearity to the current-voltage characteristics as described above, and the diode D1 provides nonlinear characteristics. In other words, the preheating current IP is lower than the bias current IB during temperature measurement.
is 100 to 1000 times the value, and if there is no diode D1, vref will rise significantly, far exceeding the practical voltage value, but with the presence of DX, vref will rise above the reverse breakdown voltage of Dl. do not. This Daimate DX
As for p pJ JP for isolation,
Alternatively, a PN junction with low reverse breakdown voltage, such as an emitter paste junction, is used. As a result, ref rises due to the inflow of preheating current IP, and when it reaches the reverse withstand voltage of D, most of the current IP rises due to the breakdown phenomenon, flows through the part, and heats the entire sensor Tezzo.In order to make this heating effect efficient, , diodes D, are desirably constructed in a 41 structure so as to be widely distributed over the entire chip.

The current-voltage characteristics and temperature-differential voltage characteristics of the sensor section were measured using the circuit shown in FIG. 3 corresponding to FIG. 2, and the results are shown in FIGS. 4 and 5, respectively. It can be seen from FIG. 4 that the nonlinearity of the bleed heat reservoir has been obtained, and from FIG. 5 it can be seen that the temperature sensing characteristic with good linearity of the temperature measurement reservoir has been obtained. The voltage on the vertical axis of this Figure 5 is 0n)
It corresponds to the temperature-sensitive component in the parentheses of the equation, that is, V□3.

1 Vref of the characteristic line in Figure 5 / 21d, R4 =
R,=33 was obtained from Ω.

FIG. 6 shows an embodiment of the present invention. In other words, in order to obtain the voltage V having a relatively large temperature coefficient, it is obtained from the base-emitter voltage of the transistor Tr5ty in FIG.
In FIG. 6, a method is adopted in which a voltage vtem corresponding to the voltage v1 is obtained from the temperature detection voltage circuit section (2) of the temperature sensor circuit.

This circuit makes it possible to obtain a voltage having twice the temperature coefficient as compared to the method shown in FIG. 2 by utilizing the base-to-emitter voltage of two transistors, transistors Trjz and Tr13. Further, as shown in FIG. 7, the bias current t is generated by the transistor Tri4 and the resistor R15. The voltage Vtem is made to become stable VC when the Item of and reaches a certain value (approximately 200μ8 or more in this case) with respect to m. That is, the bias current Item
When Vtem increases, the voltage across the resistor R15 rises, increasing the emitter current of the transistor Tr14, and the transistor Q7 absorbs the increase in Item, suppressing the increase in the voltage Vtem. .

In addition, in order to obtain the output voltage ref with a relatively small temperature coefficient, the resistor R11 is
and transistor TrH are added.

The effect is similar to that described above regarding vtem, and is to suppress the dependence of the bias curve (2) on ref for obtaining the voltage Vref. When this Iref increases, the voltage across the resistor R11 increases and the transistor Tr1
This increases the emitter current of Iref, and the transistor Tr11 absorbs the increase in Iref.

Note that the present invention is not limited to the above-mentioned embodiments, and can be applied in various ways without departing from the gist of the present invention.

For example, the diode I) may be connected in parallel to the resistors R, , R3, etc. Further, in the embodiment, the temperature coefficient of vref is selected to be very small, but vc may be selected so that the temperature coefficient of vB or vBm has the opposite sign of 5. In addition, in the embodiment, die 4
--An unconventional "Il," based on the PN reverse characteristic of the DI
I used the current characteristics to heat up, but lit ---
i or multiple (e.g., in series) PN junctions in the forward direction i, i1
．． Ijtf, military pressure characteristics”? It is also possible to simulate the effect of rotation (, ・k) using the non-pressure characteristics of

〔Effect of the invention〕

As explained above, according to the present invention, the non-linear characteristics of the PN junction are used to prevent V from being heated, so the voltage can be lowered, sufficient practicality can be obtained, and temperature measurement can be made faster. Become. In addition, since it is possible to eliminate drift in the reference voltage and amplifier offset L% pressure, it is possible to improve the accuracy of temperature measurement, and there is no need to use expensive parts.
The jc temperature sensor has advantages such as cost reduction and bias dependence suppressing effect.

[Brief explanation of the drawing]

Figure 1 is the sensor current 1-piece pressure characteristic diagram, Figure 2 is the temperature sensor circuit diagram, Figure 3 is the experimental circuit diagram used to obtain the characteristic diagram of the same circuit, and Figure 4 is the diagram obtained with the same circuit. Voltage 'rM, current characteristic diagram, Figure 5 is a temperature characteristic diagram obtained with the same circuit, Figure 6 is a circuit diagram of 11 examples of the present invention, Figure 7 is ■1of, ■ by the same circuit. This is a characteristic diagram showing the bias current dependence of te□1. 11...Sensor chip, 121-124 ・Terminal, 1
3... Amplification section, 14... Operational amplifier, 151-15
3... Current source, 16... A/D converter, 17...1
``Pj'!A-processing section, 18...display section, D, .
, diode, S... switch, TrN + 'rr
j4・、、Transistor, RN, R15"'Resistance. Applicant's agent Patent attorney Takehiko Suzue Director-General of the Agency 1 Mr. Kazuo Wakasugi 111 indications Patent Application No. 146091/1983 2 Name of the invention/Temperature sensor 3, 1 Relationship with the old incident Patent applicant Tohaku Grodacts Co., Ltd./ 1 agent (i, sleeve if-) Specification (1) Page 12, line 7 of the specification 1 Transistor Q7
Correct the word "J" by saying "transistor"'r14J. (Delete the statement ``Also, in the embodiments...'' from line 6 to line 1111 of page 13 of 21.

Claims (1)

[Claims] a first means for preheating the sensor chip by the heating effect of the current using the current-voltage characteristics of a PN junction provided in the circuit of the temperature sensor chip; and a voltage from the sensor chip with a relatively large temperature coefficient; Two voltages, the output voltage and the output voltage having a relatively small temperature coefficient or a temperature coefficient of opposite sign, are input from the same input terminal of the same amplifier in a very short time compared to the ambient temperature time constant and are amplified and held. a second means for obtaining temperature information by calculating the difference between the two voltages; a third means for obtaining a voltage having a relatively large temperature coefficient; and a third means for obtaining a voltage having a relatively large temperature coefficient; A temperature sensor characterized in that the fourth means for obtaining an output voltage having a temperature coefficient of has the effect of suppressing the dependence of the bias current on the third and fourth means.