JPS5856818B2 - density and kay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic thermometer using a field effect transistor as a temperature sensing element.

Conventionally, the common method for temperature measurement is to detect and amplify the unbalanced voltage of a bridge circuit that has a thermistor, which is a temperature-sensitive resistance element, on one side, and then perform digital measurement using an A-D converter. Amplifier circuit, high precision A-
A D conversion circuit is required.

In addition, thermistors, which are temperature-sensitive resistance elements, have the advantage of being able to measure the temperature of small places and have very good temperature sensitivity, but they have strong non-linearity between resistance and temperature and must be careful of self-heating. However, it is suitable for measuring minute temperatures and temperature differences.

However, when the measurement temperature range is wide, the nonlinearity between resistance and temperature is large, so if the resistance value change is used directly, only a nonlinear output can be obtained, which does not meet the requirements for direct control. .

For this reason, pure resistors were inserted in series and parallel to approximate the change in resistance value using a linear approximation, but the accuracy was poor.

The present invention uses a field-effect transistor as a temperature-sensitive element to detect temperature by utilizing the temperature characteristics of the field-effect transistor.The present invention has a simple circuit configuration, has few sources of error, and is small and highly accurate. The aim is to obtain an electronic thermometer.

Generally, the temperature characteristics of the drain current ID and threshold voltage VTH of a MOS transistor are expressed by the following equation.

Vo......Gate-source voltage (hereinafter abbreviated as gate voltage) μ0......Mobility of electrons in the inversion layer, MO8
The dVTH temperature dependence of the drain current ID of the T-transistor can have positive, zero, or negative values by appropriately selecting (■G-■TH) and □.

dVTH □ and (VG-VTR) and ID temperature coefficient relationship T dVTH The relationship is shown in Figure 1.

This figure is a diagram showing the change in the ID temperature coefficient due to (Vo-VTR) when T is the parameter.

FIG. 2 shows the characteristics of the P-channel MO8I-transistor between ID and temperature T.

The present invention detects temperature by utilizing the temperature dependence of the drain current ID described above.

FIG. 3 shows an embodiment of a thermometer using the present invention.

FIG. 4 is a diagram showing operating waveforms of each part in FIG. 3.

A clock signal is generated in a standard signal generator and sent to a frequency divider circuit I via wiring F.

Q2, Q3, Q4, which are the outputs of the frequency divider circuit ■,
Q, enters the NAND gate 2, and the output signal of the NAND gate 2 enters the Q1 signal of the frequency divider circuit (■) and the NOR gate 3, and a low-period intermittent pulse signal is obtained on the wiring A, which is then applied to the switch 5.
A signal is supplied to the control terminal of the switch 6 through the control terminal of the switch 6, the NAND gate 1-12°, and the impark 4.

When the bypass signal is supplied to the switch 5 from the wiring A, the switch 5 is turned on and the switch 6 is turned off.

When the switch 5 is turned on, the capacitor 7 supplies a charging voltage to the wiring C of the voltage comparator 11 in accordance with the charging time constant formed by the P-MOS transistor 7 and the capacitor 8.

When this supply voltage reaches the comparison voltage of the voltage comparator 11 (threshold voltage of the inverter 11), the voltage comparator 11
The output wiring becomes bi-level and the NAND gate 12
is supplied to

The clock signal of the wiring F is measured by the measuring section 13 and the temperature is displayed on the display section 14 during the time period when the wiring person and the wiring operator are at bi-level.

When the signal on the wiring A changes from a by signal to a low signal, switch 5 is turned off and switch 6 is turned on.

When the switch 6 is turned on, the charging voltage charged in the capacitor 8 is discharged, and when the voltage becomes lower than the comparison voltage of the voltage comparison section 11, the output of the voltage comparison section 11 becomes a low level signal.

By varying either resistor 9 or 10, P-
Since the temperature coefficient of the MOS transistor can be varied, it is desirable to vary the temperature coefficient in accordance with the capacitor 8.

Note that it is important to vary the temperature coefficient so that it does not become zero.

As described above, in the embodiment shown in FIG. 3, the charging and discharging of the time constant circuit including the MOS transistor is intermittently controlled by the gate time of a fixed pulse width, and the pulse width corresponding to the measured temperature is determined by the voltage comparator. The gate time is detected and the detected gate time is measured and displayed.

In the embodiment shown in FIG. 3, a P0MOS transistor is used as the temperature sensing element, but the temperature can also be detected using a similar method using an NMOS transistor.

As described above, according to the present invention, highly accurate measurements can be easily carried out with a smaller and simpler configuration than in the past, and an electronic thermometer suitable for the circuit integration ratio can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the ID temperature coefficient of a MOS transistor. FIG. 2 is a diagram showing the temperature characteristics of Ip of a P-channel MOS transistor. FIG. 3 is a circuit diagram showing one embodiment of the present invention. FIG. 4 is a diagram showing operating waveforms of each part in FIG. 3. 1.21... Frequency divider circuit, 2,12...
NAND gate, 3, 26...NOR gate
G, 4... Inverter, 5, 6... Switch, 7, 24... P. MOS transistor, 8... Capacitor, 9,
10...Resistor, 11...Voltage comparator,
13...Measurement section, 14...Display section.

Claims (1)

[Claims] 1. A standard signal generating section, a frequency dividing circuit for forming an intermittent pulse signal from the standard signal of the standard signal generating section, a field effect transistor as a temperature sensing element, a capacitor connected in series with the field effect transistor, and the field effect transistor. and a power supply connected to both ends of the series circuit of the capacitor, a voltage comparator circuit that detects the voltage of the capacitor, and a voltage comparator circuit that detects the number of signals derived from the standard signal generator while the output pulse of the voltage comparator circuit is at a predetermined level. The field effect transistor has a threshold voltage that changes depending on the temperature, a first switch element is connected between the field effect transistor and the power supply, and a second switch element is connected in parallel to the capacitor. , said first
and a second switch element are opened and closed in a complementary manner by the intermittent pulse signal.