Temperature sensor device

Provided is a temperature sensor device operable at a lower voltage. The temperature sensor device detects temperature based on an output voltage of a forward voltage generator for generating a forward voltage of a PN junction. The forward voltage generator includes a level shift voltage generation circuit, and an output voltage of the temperature sensor device is given based on the forward voltage of the PN junction and a voltage of the level shift voltage generation circuit.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2011-006101 filed on Jan. 14, 2011, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a temperature sensor device for detecting temperature.

2. Description of the Related Art

Conventionally, a temperature sensor device for detecting temperature, which utilizes a forward voltage of the PN junction, is well known (see, for example, Japanese Patent Application Laid-open No. Hei 5-248962).

FIG. 7is a circuit diagram illustrating a conventional temperature sensor device. The conventional temperature sensor device includes a constant current source circuit701and Darlington-connected bipolar transistors702,703, and704supplied with a constant current from the constant current source circuit701.

An emitter of the bipolar transistor704is connected to an output terminal. An output voltage of the temperature sensor device is the sum of forward voltages of the PN junctions of the bipolar transistors. The forward voltage of the PN junction changes in accordance with temperature, and hence the output voltage is a voltage that changes in accordance with temperature.

In the temperature sensor device configured as described above, temperature detection accuracy of the temperature sensor device is enhanced as the sensitivity with which the output voltage changes in accordance with temperature becomes higher. Therefore, the temperature detection accuracy of the temperature sensor device can be enhanced by increasing the sum of the forward voltages of the PN junctions. In general, it is known that the temperature sensitivity of the forward voltage of the PN junction is approximately 2.5 mV/° C.

In the case of the temperature sensor device ofFIG. 7, the number of effective stages of PN junctions is three, and hence the sum of the forward voltages is three times the forward voltage of one PN junction. Therefore, the sensitivity with which the output voltage changes in accordance with temperature is approximately 7.5 mV/° C., which is three times the temperature sensitivity of the forward voltage of one PN junction.

In the conventional temperature sensor device, however, if the number of effective stages of PN junctions is increased for enhancing the sensitivity with which the output voltage changes in accordance with temperature, the sum of the forward voltages of the PN junctions becomes larger. Therefore, the conventional temperature sensor device has a problem that an operating voltage cannot be suppressed to be lower. This problem results in inefficiency in the sense that a low voltage range of a power supply voltage supplied from a battery or the like cannot be used.

SUMMARY OF THE INVENTION

The present invention has been devised in order to solve the above-mentioned problem, and realizes a temperature sensor device operable at a lower voltage.

The present invention provides a temperature sensor device including a forward voltage generator for generating a forward voltage of a PN junction, for detecting temperature based on an output voltage of the forward voltage generator, in which the forward voltage generator includes a level shift voltage generation circuit, and an output voltage of the temperature sensor device is given based on the forward voltage of the PN junction and a voltage of the level shift voltage generation circuit.

According to the present invention, the temperature sensor device operable at a lower voltage can be provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a circuit diagram illustrating a temperature sensor device according to an embodiment of the present invention. The temperature sensor device of this embodiment includes a constant current source circuit701, Darlington-connected bipolar transistors702,703, and704supplied with a constant current from the constant current source circuit701, and voltage sources101,102, and103.

The voltage source101is connected between an emitter of the bipolar transistor702and a base of the bipolar transistor703. The voltage source102is connected between an emitter of the bipolar transistor703and a base of the bipolar transistor704. The voltage source103is connected between an emitter of the bipolar transistor704and an output terminal. Here, voltages V1, V2, and V3of the voltage sources101,102, and103do not have temperature characteristics.

Next, an operation of the temperature sensor device of this embodiment is described.

A forward voltage of the PN junction is represented by Vpn. In this case, a voltage V(A) at the point A, a voltage V(B) at the point B, and a voltage V(C) at the point C are calculated as follows, respectively.
V(A)=1×Vpn−V1  (1)
V(B)=2×Vpn−(V1+V2)  (2)
V(C)=3×Vpn−(V1+V2+V3)  (3)

The voltage V(C) is a voltage at the output terminal, and accordingly an output voltage of the temperature sensor device is given as 3×Vpn−(V1+V2+V3). That is, the output voltage of the temperature sensor device of this embodiment is lower than the output voltage of the conventional temperature sensor device by the voltage (V1+V2+V3). It follows that the temperature sensor device of this embodiment is capable of suppressing an operating voltage to be low even when the number of effective stages of PN junctions is increased. The voltages V1, V2, and V3do not have temperature characteristics, and hence the sensitivity with which the output voltage changes in accordance with temperature is comparable to that in the conventional temperature sensor device.

In other words, it can be said that the operating voltage can be suppressed to be lower, though the sensitivity with which the output voltage changes in accordance with temperature is comparable to that in the conventional temperature sensor device.

According to the temperature sensor device of this embodiment, by employing the configuration described above, it is possible to provide a temperature sensor device operable at a lower voltage.

Note that, in the temperature sensor device of this embodiment, the voltage source is provided to the emitter of each bipolar transistor, but not all the voltage sources need to be provided. For example, even with only the voltage source101, the effect to achieve low voltage operation of the temperature sensor device can be expected.

Further, in the temperature sensor device of this embodiment described above, the number of effective stages of PN junctions is three. However, it is apparent that the same effect can be obtained irrespective of the number of effective stages of PN junctions.

FIG. 2is a circuit diagram illustrating a specific example of the voltage source included in the temperature sensor device of this embodiment. For simplification, a specific example of only the voltage source101is illustrated.

The voltage source101includes a current source201and a MOS transistor202.

The voltage V1of the voltage source101is applied based on a gate-source voltage of the MOS transistor202biased by the current source201.

As another example, the voltage source may be a circuit as illustrated inFIG. 3. The voltage source101includes current sources201and301and MOS transistors202and302. That is, the voltage source may be realized by Darlington-connected MOS transistors.

As still another example, the voltage source may be a circuit as illustrated inFIG. 4. The voltage source101includes a current source401and a resistor402. The voltage V1of the voltage source101is applied based on a resistance of the resistor402biased by the current source401.

In this case, if there are fluctuations in resistance of the resistor402, the influence of the fluctuations in resistance can be reduced by configuring the current source401by a circuit as illustrated inFIG. 5, for example. The current source401performs impedance conversion on a voltage supplied by a voltage source501, and generates a current obtained through division by a resistance of a resistor502. That is, the current source401uses the resistor502of the same type as the resistor402to output a current I for canceling the fluctuations in resistance of the resistor402. Note that, the circuit of the current source401illustrated inFIG. 5is an example, and the current source401is not limited to this circuit.

Note that, in the temperature sensor device of this embodiment described above, the voltage of the voltage source does not have temperature characteristics, but may have temperature characteristics. Particularly when the voltage source has controlled positive temperature characteristics, a higher-sensitive temperature sensor device can be provided.

For example, such a temperature sensor device may be configured by using, as the current source401ofFIG. 4, the current source ofFIG. 5in which a resistor having negative temperature characteristics is used as the resistor502, and using the resistor402having positive temperature characteristics.

Further, the temperature sensor device of this embodiment described above is a temperature sensor using a forward voltage of the PN junction of a bipolar transistor, but a diode element may be used instead. As an example, a temperature sensor device includes a constant current source601, three-stage diodes, and a voltage source602as illustrated inFIG. 6. An output voltage is determined by subtracting a voltage of the voltage source602from a voltage generated in the three-stage diodes. The operating voltage can be suppressed to be lower, though the sensitivity is substantially comparable to that in the case where no voltage source602is provided.