JPH0518677Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Application of the Invention) The present invention relates to an improvement of a temperature sensor circuit using a temperature sensor whose resistance value changes according to temperature changes.

(Background of the idea) An example of a conventional temperature sensor circuit is shown in FIG.

Temperature sensor whose resistance value changes according to temperature changes
R _s and resistors R ₁ , R ₂ , R ₃ , and R ₄ form a bridge circuit. +V is a power supply, and t ₁ and t ₂ are output terminals of the temperature sensor circuit.

For example, assume that the temperature sensor R _s is 100Ω at 0°C, and the resistance value changes by 0.4Ω with a temperature change of 1°C, and R ₁
= R ₂ = R ₄ = 400 Ω, R ₃ = 300 Ω, and the sensor current I _{s flowing through the temperature sensor R s =} 1 mA, the change in output voltage △E due to a 1°C temperature change is 0.4 mV/°C
becomes. Also, if the sensor current I _s =0.1mA,
The change in output voltage △E due to a temperature change of 1℃ is
It becomes 40μV/℃. In this way, in the conventional temperature sensor circuit, when the sensor current I _s is small, 1
It was not possible to increase the amount of change ΔE in the output voltage due to the temperature change in degrees Celsius.

Therefore, if the output voltage is amplified by a differential width amplifier, the differential width amplifier requires two or more highly accurate operational amplifiers, resulting in an increase in cost.

(Purpose of the invention) The purpose of the invention is to solve the above-mentioned problems and to use a single-ended type that can increase the change in output voltage due to a temperature change of 1°C even when the sensor current is small. An object of the present invention is to provide a temperature sensor circuit.

(Characteristics of the invention) In order to achieve the above object, the present invention connects a temperature sensor and a second resistor in series, and connects the temperature sensor to one end of the power supply and the second resistor to the other end of the power supply. the first resistor and the third resistor are connected in series so that the difference between the power supply voltage and the output voltage between the output terminals is applied to the series circuit. is connected to one end of the power supply, the third resistor is connected to one end of the output terminal, a connection point between the temperature sensor and the second resistor is connected to a non-inverting input terminal of an operational amplifier, and the third resistor is connected to one end of the output terminal. A connection point between the first resistor and the third resistor is connected to an inverting input terminal of the operational amplifier, and one end of the output terminal connected to the third resistor is connected to an output terminal of the operational amplifier,
The present invention is characterized in that the ratio of the third resistor to the first resistor is set to a large value, so that the change in voltage drop at the temperature sensor is non-invertingly amplified by an operational amplifier.

(Example of idea) FIG. 1 shows an embodiment of the present invention.

The temperature sensor R _s and the second resistor R ₁₂ are connected in series, and this series circuit is connected between the power supply +V and ground. The first resistor R ₁₁ and the third resistor R ₁₃ are connected in series between the output terminals t ₁ and t ₂ of the temperature sensor circuit, and this series circuit is also connected between the power supply +V and the ground. Output terminals t ₁ and t ₂ are output terminals t ₁
It is a single-ended type with ground potential being . The connection point X between the temperature sensor R _s and the second resistor R ₁₂ is connected to the non-inverting input terminal of the operational amplifier A, and the first resistor
The connection point Y between R ₁₁ and the third resistor R ₁₃ is the operational amplifier A.
connected to the inverting input terminal of The output terminal t ₂ connected to the third resistor R ₁₃ is connected to the output terminal of the operational amplifier A. The third resistance to the first resistance R ₁₁
The ratio of R ₁₃ and the second resistor to the temperature sensor R _s
The ratio of _R12 is set to a large value, for example, several tens to several hundreds.

Assuming that R ₁₂ =R ₁₃ , when R _s =R ₁₁ , operational amplifier A operates to maintain the output voltage at the same potential as ground in order to maintain the connection point X and the connection point Y at the same potential. At this time, the voltage drop across the resistor R ₁₁ and the resistor R ₁₃ becomes as shown by L ₁ in FIG. 2.

When a change △e occurs in the voltage drop of the temperature sensor R _s due to a temperature change, the voltage drop change △e is non-invertingly amplified by (R ₁₁ +R ₁₃ )/R ₁₁ times by the operational amplifier A, and is output to the output terminal t. ₁ , output voltage change from t ₂ △
Output as E. Resistance R ₁₁ and resistance at this time
The voltage drop across R ₁₃ will be shown as L ₂ in FIG.

Note that the voltage drop change △e is (R ₁₁ + R ₁₃ )/
The reason why R increases by ₁₁ times is as follows.

Since the operational amplifier A is considered as an ideal operational amplifier, the input current Ii is set to 0. The power supply +V shall maintain a constant voltage value.

ey=V+If×R ₁₁ ...If=(E-V)/(R ₁₁ +R ₁₃ )...Substitute the formula into the equation and get ey=V+R ₁₁ (E-V)/(R ₁₁ +R ₁₃ ) = (E・R ₁₁ +V・R ₁₃ )/(R ₁₁ +R ₁₃ )
... From the formula E = ey (R ₁₁ + R ₁₃ ) / R ₁₁ −V・R ₁₃ /R ₁₁ ... To find the change in E with respect to the change in ey,
Differentiating the equation with respect to ey and finding dE/dey yields the following linear equation: dE/dey=(R ₁₁ +R ₁₃ )/R ₁₁ .

Since A is an ideal operational amplifier, ex=ey always
The feedback current If is increased or decreased until ex = ey is always maintained. (Commonly known as imaginary shot) Therefore, replace ey in the formula with ex, and consider the change in E (amplification degree) with respect to the change in ex as △E/△ex=(R ₁₁ + R ₁₃ )/R ₁₁ ... be able to. (△ex in the formula means △e.) For example, the temperature sensor R _s is 100Ω at 0°C, and the resistance value changes with a temperature change of 1°C, as in the one in Figure 3.
Assume that the resistance changes by 0.4Ω, R ₁₁ = 100Ω, R ₁₂ = R ₁₃ =
Assuming 10KΩ, +V = +2V, sensor current I _s flowing through temperature sensor R _s = 0.2 mA, voltage drop change △e
is 0.08mV/℃, and the change in output voltage △E is
It becomes 8mV/℃ which is 100 times higher. Therefore, a large output voltage can be obtained even with a current much smaller than the sensor current flowing through the temperature sensor R _s shown in FIG.

Note that since the output terminal _t1 is a single-ended type that is grounded, processing in the next stage, such as A/
D conversion or amplification can be easily performed.

(Effect of the invention) As explained above, according to the invention, a temperature sensor and a second resistor are connected in series, the temperature sensor is connected to one end of the power supply, and the second resistor is connected to the other end of the power supply. the first resistor and the third resistor are connected in series so that the difference between the power supply voltage and the output voltage between the output terminals is applied to the series circuit. is connected to one end of the power supply, the third resistor is connected to one end of the output terminal, a connection point between the temperature sensor and the second resistor is connected to a non-inverting input terminal of an operational amplifier, and the third resistor is connected to one end of the output terminal. A connection point between the first resistor and the third resistor is connected to an inverting input terminal of the operational amplifier, and one end of the output terminal connected to the third resistor is connected to an output terminal of the operational amplifier,
Since the ratio of the third resistor to the first resistor is set large and the change in voltage drop at the temperature sensor is non-invertingly amplified by the operational amplifier, even when the sensor current is small, The amount of change in output voltage due to a temperature change of 1° C. can be increased. Furthermore, since the output is of a single-ended type, subsequent processing can be facilitated.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
This figure is also a characteristic diagram, and FIG. 3 is a circuit diagram showing a conventional temperature sensor circuit. R _s ... Temperature sensor, R ₁₁ ... First resistor, R ₁₂
... Second resistor, R ₁₃ ... Third resistor, A ... Operational amplifier, +V ... Power supply, t ₁ , t ₂ ... Output terminal,
X, Y...Connection point.

Claims (1)

[Claims for Utility Model Registration] A temperature sensor and a second resistor are connected in series, the temperature sensor is connected to one end of the power supply, and the second resistor is connected to the other end of the power supply, A resistor and a third resistor are connected in series, and the first resistor is connected to one end of the power supply, and the third resistor is connected to one end of the power supply so that the difference between the power supply voltage and the output voltage between the output terminals is applied to the series circuit. 3 resistors are each connected to one end of the output terminal, a connection point between the temperature sensor and the second resistor is connected to a non-inverting input terminal of an operational amplifier, and the first resistor and the third resistor are connected to one end of the output terminal. is connected to the inverting input terminal of the operational amplifier; one end of the output terminal connected to the third resistor is connected to the output terminal of the operational amplifier; A temperature sensor circuit with a large resistance ratio.