JPH02269922A - Temperature sensor circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for an A/D converter and to reduce the cost by outputting temperature which is measured by a sensor directly as a frequency signal. CONSTITUTION:The sensor circuit is provided with an astable multivibrator MV1 which has a constant current source as a load and charges and discharges a capacitor to determine its oscillation frequency, a bias circuit BAS1 which determines the level of a charging signal for charging the capacitor through the constant current source, and a temperature element which is provided as a circuit element of the bias circuit BAS1 and generates the charging signal corresponding to measured temperature. Then the temperature element of the bias circuit BAS1 varies the charging signal applied to the capacitor of the astable multivibrator MV1 to output an oscillation frequency corresponding to the measured temperature. Consequently, the need for an A/D converter in the circuit is eliminated and the cost is reducible.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a temperature sensor circuit that outputs a signal corresponding to a measured temperature, and particularly to a temperature sensor circuit that can output a frequency signal corresponding to a measured temperature. Regarding.

<Prior art> Conventional temperature sensors include those using transistors and IC temperature sensors. Focusing on this point, we can insert this transistor into the feedback circuit of an amplifier and output an analog signal corresponding to this base-emitter voltage at its output terminal, or we can use IC technology to integrate the temperature sensor and the subsequent amplifier circuit. One known device is one that is integrated into one chip and outputs an analog temperature signal to its output terminal.

Problems to be Solved by the Present Invention> However, in a circuit using such a conventional temperature sensor, the signal obtained at the output terminal is an analog signal, so when performing digital processing, this analog signal is It must be converted to a digital signal and requires an analog/digital converter. For this reason, there is a problem in that it becomes an obstacle to space saving when downsizing or cost reduction by reducing the number of parts.

Means for Solving the Problems> In order to solve the above problems, the present invention provides an astable multivibrator which has a constant current source as a load and whose oscillation frequency is determined by charging and discharging a capacitor; The device includes a bias circuit that determines the magnitude of a charging signal that charges the capacitor via this constant current source, and a temperature element that is provided as a circuit element of this bias circuit and generates a charging signal that corresponds to the measured temperature. It is designed to output an oscillation frequency corresponding to the signal.

Function: The oscillation frequency of the astable multivibrator is changed by changing the charging signal applied to the capacitor by the temperature element of the bias circuit, and the oscillation frequency is changed in accordance with the measured temperature.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of one embodiment of the present invention.

(h, Q2 is a 1H transistor, the emitters of these are mutually connected to a common potential point COM, the base of transistor Q1 is connected to the collector of transistor Q2 via capacitor C2, and the base of transistor Q2 is connected to capacitor C1. are connected to the collector of the j-transistor Q1 through the J-transistor Q1.

A power supply voltage Vcc is applied to the collector of the transistor Q1 via the transistor Q3, and to the base of the transistor Q2 via the transistor Q4. Further, the power supply voltage Vcc is applied to the collector of the transistor Q2 through the transistor Q5, and the power supply voltage Vcc is applied to the base of the transistor Q through the transistor Q6.

Transistors Q3 and Q5 are transistor Q4.
．． It is formed to have a base area twice that of the QB. Therefore, collector current 11 flowing through transistors Q4 and Q6 for the same base voltage
2. I22 is twice the collector current r++, I21, flowing through transistors Q3 and Q5.

These transistors Q+, ~Q5, capacitors C, .
C2 and the like constitute a multivibrator MV, and its oscillation output is taken out from the output terminal T.

BASI is a bias circuit, and this bias circuit BA
S is 1-rungis 2 where the base and collector are connected
0 day, and a resistor R1 having a predetermined temperature coefficient that functions as a temperature sensor T E + . This series circuit of the transistor Qa+ and the resistor R1 is connected to the power supply terminal T2 and the power supply terminal 'r3. The power supply voltage VCC is applied to the power supply terminals T2 and T3. Note that the power supply terminals 1 and 3 are connected to a common potential point COM.

The base of transistor Qe+ is connected to the bases of transistors Q3 to Q5 that function as constant current sources,
These are configured as mirror circuits.

Next, the operation of the temperature sensor circuit configured as described above will be explained with reference to FIG. 2.

FIG. 2(A) shows the oscillation waveform of the transistor Q1, and FIG. 2(B) shows the oscillation waveform of the transistor Q2.

First, when transistor Q is off and Q2 is on, the base voltage Vb2 of transistor Q2 is held at a voltage of about 0.5V (Figure 2 (b)), so its collector voltage VC2 is almost zero. Hold at potential (Figure 2 (b)
) has been done.

Therefore, since the capacitor C2 is charged by the collector current I22 of the transistor Q6 and increases linearly toward a positive potential, the base voltage Vb+ of the transistor Q1 also increases accordingly (FIG. 2(A)). At this time, the collector voltage VCI of transistor Q1 is
Since it is charged to a positive value by the collector current II+ of 3, it increases linearly toward a positive value (Figure 2 (a))
.

When the base voltage Vb+ of the transistor Q exceeds approximately 0.5V, it is clamped to this value, the transistor Q1 is turned on, and its collector voltage VCI becomes approximately zero potential. Therefore, the base voltage Vb2 of the transistor Q2 suddenly becomes a negative potential due to the negative charge held in the capacitor C1. However, since transistors 1 to Q are in the on state, the negative charge of capacitor C is charged in the positive direction by the collector current 112 of transistor Q4 and is neutralized, and as a result, the base voltage of transistor Q2 is Vb2 increases linearly (Fig. 2 (
B)). Therefore, the collector voltage vc of transistor Q2
1 also increases linearly (Figure 2 (b)).

Then, when the base voltage Vb+ of transistor Q2 increases and turns on, transistor Q1 turns on,
Return to initial state. Thereafter, these states are repeated to continue oscillation.

The on/off period t of each of the above transistors Ql and Q2
The sum of 4 and t2 corresponds to the oscillation period, which is the period for charging the capacitors C1 and 02.

Therefore, in a simple way, let C, = C2 = C, and VT is the voltage across capacitor Cv, and Is2 = 122 = I
A, Is + −I2 + =IB (=2 I
A), the oscillation period is given by the following equation.

'r' = t + + t 2 = CT V
T/la... (1) On the other hand, the current IA
is a copy of the bias current IBI flowing through the transistor Qa+ of the bias circuit B A S +, so it is IA-I8 + VCC/R+, and applying this relationship to equation (1), the deviation is T = C7VT R+ /
Vcc cv R1 (2).

Therefore, if the resistor R1 of this bias circuit BAS is made to have a temperature coefficient, a frequency output fT corresponding to the temperature can be extracted.

Here, the calculation is made as I B , :VcC/R1, but in reality, it is calculated from the power supply voltage VCC to 1-transistor Qs+
It is necessary to subtract the base/emitter voltage Vaε0 of .

Here, for example, CT = 50 pF, R+
= I MΩ, the frequency output fT is 5 KHz, and if the temperature coefficient of the resistor R1 is 2000 ppm/'C, the temperature dependence is lOH2/'C.

Next, a second embodiment of the present invention shown in FIG. 3 will be described. In the following description, parts having the same functions as those of the embodiment shown in FIG. 1 are given the same reference numerals, and the description thereof will be omitted as appropriate.

This embodiment is similar to the embodiment shown in FIG.
This is an improvement that eliminates the influence of CC fluctuations.

Temperature sensor' instead of temperature sensor TE in FIG.
A bias circuit BAS2 is configured using rE2. The bases of the transistors Q7 and Q8, whose collectors and bases are connected, are respectively power supply terminals'■゛2
It is connected to the. Further, the collector of the transistor Q9, whose collector and base are connected, is connected to the collector of the transistor Qe, and the collector of the h-transistor Q7 is connected to the transistor Q.

. are connected to their respective collectors. Furthermore, the bases of transistors Q9 and Q+o are connected to each other,
1 to the emitter of transistor Qs is connected to the emitter of transistor Q+o via resistor R2. The collector of transistor Q++, which has a diode D connected between its base and emitter, is connected to the collector of transistor Qa+, and the base of transistor Q++ is connected to transistor Q.

0 and the emitters are respectively connected to the power supply terminal T3. Note that the emitter areas of transistors 1 to Q9 are selected to be twice as large as the emitter area of transistors 1 to 9.

In the above configuration, transistors Q7 and QB constitute a mirror circuit, and the same collector currents I7 and I8 flow through their collectors, respectively. These collector currents I7.1 flow into transistors Q+o and Q9 as the same current, but their emitter areas differ by a factor of two, so there is a difference in the base-emitter voltage of these transistors. occurs and the following (3
) A differential voltage Δ■ is generated.

ΔV=JT-1n2/q-(3) where A is Boltzmann's constant, T is absolute temperature, and q is unit charge.

Therefore, the current flowing through resistor R2 is Δv/R2, and twice this current flows to the collector of transistor Q++ for the next (
4) flows as a collector current 182 shown in equation 4).

l82=2ΔV/R2=2#T-in2/qR2・= (4) This equation (4) does not include the term of the power supply voltage Vcc, and the collector current IB2 is not affected by this. Therefore, the multivibrator MV to which a current that is a copy of this collector current IB2 is supplied is not affected by the power supply voltage.

For example, the temperature coefficient of ΔV is +3000PI) m/°C1
If the temperature coefficient of the resistor R2 is +3000 PIm/°C, the collector current IB2 has a temperature coefficient of 111000 pp/''C.

Therefore, a frequency output corresponding to this is obtained at the output terminal T.

Next, a third embodiment of the present invention shown in FIG. 4 will be described. In this embodiment, the load of the multivibrator in the embodiment shown in FIG. 1 is configured as a constant current source having no temperature dependence.

BAS3 is a bias circuit corresponding to the bias circuit BAS in FIG. 1, and TE3 is a temperature sensor TE.
This is a temperature sensor corresponding to . This temperature sensor TE,
For example, it is constructed by connecting a large number of diodes in series in the forward direction.

The collector of the transistor QB2 whose base/collector is connected is connected in series with a constant current source CC and is connected to a power supply terminal T.
2, connected to T3. Its base is connected to the base of transistor Qa+, which transistor Q
a+ and temperature sensor TE3 are connected in series to power supply terminals T2 and T3.

In addition, the npn type transistors Q3- to Q6-, which are the loads of the multivibrator Mv2, are connected in series with the collectors of these transistors Q1 to Qco+, Q4+, and Q5.
++ and Qe+ are connected, and power supply voltage VCC is applied to their emitters. The bases of these transistors Q3+ to Q6 are connected to the base of transistor Qa+.

Therefore, transistor QB2 and Qa + , Q3 + ~
Qs+ constitutes a mirror circuit, and a current that is a copy of the constant current 10 of the constant current source cc is passed through the temperature sensor 'rE3 and each transistor Q3- to Q6-. By the way, the constant current source CC has a positive temperature coefficient, while the base/emitter voltage of the i transistor Q's 2 has a negative temperature coefficient, so these temperature coefficients are set to be equal. Constant current ■. is a constant current that is independent of temperature. Therefore, the currents 11, -1■, and 2-1I22-2I2+- flowing through each of the 1-transistors Q3- to Q6- are constant currents that are independent of temperature.

Here, temperature sensor 1゛E3 to which a constant current is flowing
Since the voltage V8 across it changes depending on the measurement temperature,
The voltage charged to the capacitors C1 and C2 also corresponds to the measured temperature. As a result, Multivibrator M■2
The oscillation frequency changes in accordance with the measured temperature measured by the temperature sensor TE3.

<Effects of the Invention> As specifically explained above with the examples, the present invention has the following effects:
The temperature measured by the temperature sensor can be directly output as a frequency signal, eliminating the need for a conventional analog/digital converter, contributing to cost reductions, such as reducing the number of parts and saving space. do.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention, Fig. 2 is a waveform diagram explaining the operation of the embodiment shown in Fig. 1, and Fig. 3 is a circuit diagram showing the configuration of the first embodiment of the present invention. Main part circuit diagram showing the configuration of
FIG. 4 is a circuit diagram showing the configuration of a third embodiment of the present invention. MV, , MV2...Multi-vibrator, BAS1
~BAS3...bias circuit, TE, ~TE3・
...Temperature sensor, CC...constant current source, Vcc...power supply voltage. -Toshi O○ 'T'

Claims (1)

[Claims] An astable multivibrator that has a constant current source as a load and whose oscillation frequency is determined by charging and discharging a capacitor, and a bias circuit that determines the magnitude of a charging signal that charges the capacitor via this constant current source. and a temperature element that is provided as a circuit element of the bias circuit and generates the charging signal corresponding to the measured temperature, and outputs the oscillation frequency corresponding to the temperature signal.