Sensing device

Abstract

To provide a technique for improving sensor detection accuracy of a sensing device.SOLUTION: The sensing device includes a sensor that outputs an analog signal according to an index to be measured, an AD converter that receives the analog signal output from the sensor and outputs a digital signal that is a pulse train having a duty ratio according to the magnitude of the analog signal, and a microcomputer that receives the digital signal output from the AD converter and converts the digital signal into the index to be measured or an index corresponding thereto. The AD converter and the microcomputer store a plurality of conversion maps describing the relationship between the magnitude of the analog signal and the duty ratio.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a sensing device. [Background technology]

[0002] Patent Document 1 discloses a sensing device. This sensing device includes a sensor that outputs an analog signal corresponding to temperature, and an AD (Analog-to-Digital) converter that receives the analog signal output from the sensor and outputs a digital signal indicating the temperature of the sensor. The AD converter is configured to set a correction value for the analog signal output by the sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-249374 Summary of the Invention [Problem to be solved by the invention]

[0004] In sensing devices like those described above, the measurement resolution is determined by the AD converter. That is, the conversion of an analog signal, which can represent an infinite number of values, into a digital signal, which can only represent a finite number of values, places a limit on the precision of the measurement. Therefore, widening the measurement range of the target index results in a decrease in resolution, and increasing the resolution results in a narrower measurement range.

[0005] In view of the above, the present specification provides a technique that can achieve the required resolution while ensuring a measurement range in a sensing device. [Means for solving the problem]

[0006] The technology disclosed in this specification is embodied in a sensing device that includes a sensor that outputs an analog signal in response to a measurement target index, an AD converter that receives the analog signal output from the sensor and outputs a digital signal that is a pulse train with a duty ratio that corresponds to the magnitude of the analog signal, and a microcomputer that receives the digital signal output from the AD converter and converts the digital signal into the measurement target index or a corresponding index.

[0007] The AD converter and the microcomputer store multiple conversion maps that describe the relationship between the magnitude of the analog signal and the duty ratio. The AD converter selects a conversion map to use from the multiple conversion maps depending on the magnitude of the analog signal received from the sensor, and outputs a predetermined switching command signal when the conversion map to use is changed. The microcomputer switches the conversion map to use from the multiple conversion maps when it receives the switching command signal from the AD converter.

[0008] In the above-described configuration, when converting an analog signal to a digital signal, the conversion map to be used can be switched depending on the magnitude of the analog signal. With this configuration, a conversion map with a relatively low resolution can be used for the entire measurement range, while a conversion map with a relatively high resolution can be used for a portion of the measurement range. This makes it possible to ensure a sufficiently wide measurement range while achieving the required resolution in a specific range. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram showing the configuration of a sensing device 4 according to the embodiment. [Figure 2]In the embodiment, Fig. 2(A) shows a first conversion map 23a, and Fig. 2(B) shows a second conversion map 23b. In each of the conversion maps 23a and 23b, the horizontal axis indicates the magnitude of the analog signal, and the vertical axis indicates the duty ratio of the digital signal. Fig. 2(C) is a time chart showing both the analog signal input to the AD converter 20 and the digital signal output from the AD converter 20. [Figure 3] Regarding the modified example, Fig. 3(A) shows a first conversion map 23a, Fig. 3(B) shows a second conversion map 23b, and Fig. 3(C) shows a third conversion map 23c. In the third conversion map 23c, the horizontal axis also represents the magnitude of the analog signal, and the vertical axis represents the duty ratio of the digital signal. Fig. 3(D) is a time chart showing both the analog signal input to the AD converter 20 of the modified example and the digital signal output by the AD converter 20. DETAILED DESCRIPTION OF THE INVENTION

[0010] The sensing device 4 of this embodiment will be described with reference to the drawings. As an example, the sensing device 4 of this embodiment measures the temperature of a semiconductor element 10 in a power control device 2 mounted on an electric vehicle. The semiconductor element 10 is a switching element, and may be, for example, an IGBT (Insulated Gate Bipolar Transistor). Note that the sensing device 4 of this embodiment is not limited to being used in the power control device 2, and can be similarly employed in other types of devices and equipment.

[0011] As shown in FIG. 1, the sensing device 4 of this embodiment includes a temperature-sensitive diode 12, an AD converter 20, a photocoupler 30, and a microcomputer 40. The temperature-sensitive diode 12 is built into the semiconductor element 10. The temperature-sensitive diode 12 is a sensor for measuring the temperature of the semiconductor element 10, and its resistance value changes depending on the temperature of the semiconductor element 10. One terminal of the temperature-sensitive diode 12 is connected to a constant current source 26 of the AD converter 20, and the other terminal is connected to ground. As a result, the voltage value of the temperature-sensitive diode 12 changes depending on the temperature of the semiconductor element 10. The voltage value of the temperature-sensitive diode 12 is input to the AD converter 20 as an analog signal indicating the temperature of the semiconductor element 10.

[0012] The AD converter 20 converts the analog signal received from the temperature sensing diode 12 into a digital signal and outputs it. The digital signal output by the AD converter 20 is a pulse train with a duty ratio corresponding to the magnitude of the analog signal. The AD converter 20 includes a map switching unit 22 and a digital signal output unit 24. The map switching unit 22 stores multiple conversion maps 23a, 23b. The multiple conversion maps 23a, 23b include a first conversion map 23a and a second conversion map 23b. As shown in FIG. 2, each of the conversion maps 23a, 23b describes the relationship between the magnitude of the analog signal output by the temperature sensing diode 12 and the duty ratio of the digital signal output by the digital signal output unit 24. As will be described in detail later, the two conversion maps 23a, 23b have different relationships between the magnitude of the analog signal and the duty ratio of the digital signal. The map switching unit 22 selects a conversion map to be used by the digital signal output unit 24 from among a plurality of conversion maps 23a and 23b according to the magnitude (voltage value) of the analog signal received from the temperature sensing diode 12.

[0013] The digital signal output unit 24 converts the analog signal (voltage value) output by the temperature sensing diode 12 into a digital signal using the conversion maps 23a, 23b selected by the map switching unit 22. When the conversion map to be used is changed, the map switching unit 22 outputs a map switching pulse as a switching command signal. There are no particular limitations on the type of map switching pulse, but the map switching pulse in this embodiment has a pulse width greater than one period of the pulse train of the digital signal.

[0014] The photocoupler 30 is interposed between the AD converter 20 and the microcomputer 40. As a result, the circuit including the semiconductor element 10 and the AD converter 20 is electrically insulated from the circuit including the microcomputer 40 by the photocoupler 30. The digital signal output from the AD converter 20 is transmitted to the microcomputer 40 via the photocoupler 30. Note that the photocoupler 30 is not necessarily required.

[0015] The microcomputer 40 receives the digital signal output from the AD converter 20 and converts the digital signal into voltage value information (i.e., temperature information). The microcomputer 40 has a memory 42. The memory 42 stores a first conversion map 23a and a second conversion map 23b. The microcomputer 40 converts the signal from the AD converter 20 into voltage value information using the first conversion map 23a or the second conversion map 23b. Switching between the conversion maps 23a and 23b to be used is performed in response to the map switching pulse described above. That is, when the microcomputer 40 receives a map switching pulse from the AD converter 20, it switches the conversion map to be used from the multiple conversion maps 23a and 23b stored in the memory 42. In this embodiment, the converted voltage value is used for various processes as information indicating the temperature of the semiconductor device 10 (or information corresponding thereto).

[0016] The operation of the sensing device 4 of this embodiment will be described with reference to Fig. 2. As shown in Fig. 2(A) and (B), the relationship between the magnitude of the voltage value output by the temperature sensitive diode 12 and the duty ratio of the digital signal output by the digital signal output unit 24 differs between the two conversion maps 23a and 23b. Specifically, in the first conversion map 23a shown in Fig. 2(A), a duty ratio of 0 to 100% is set for a voltage range of 0 to 5V, whereas in the second conversion map 23b shown in Fig. 2(B), a duty ratio of 0 to 100% is set for a voltage range of 1 to 2V.

[0017] As shown in FIG. 2C, while the voltage value output by the temperature-sensitive diode 12 is equal to or greater than 2 V, the AD converter 20 performs AD conversion using the first conversion map 23a. When the voltage value output by the temperature-sensitive diode 12 falls below 2 V, the AD converter 20 switches the conversion map used from the first conversion map 23a to the second conversion map 23b and performs AD conversion using the second conversion map 23b. At this time, the AD converter 20 also outputs a map switching pulse. Thereafter, when the voltage value output by the temperature-sensitive diode 12 falls below 1 V, the AD converter 20 switches the conversion map used from the second conversion map 23b to the first conversion map 23a and performs AD conversion using the first conversion map 23a. At this time, the AD converter 20 also outputs a map switching pulse. Thereafter, the AD converter 20 similarly selects a conversion map to use from the multiple conversion maps 23a and 23b depending on the magnitude (voltage value) of the analog signal received from the temperature-sensitive diode 12. In the microcomputer 40 as well, the conversion map to be used is switched in response to the map switching pulse output by the AD converter 20.

[0018] As described above, in the sensing device 4 of this embodiment, when converting an analog signal to a digital signal, the conversion maps 23a and 23b to be used can be switched depending on the magnitude of the analog signal. With this configuration, the first conversion map 23a, which has a relatively low resolution, can be used for the entire measurement range (0 to 5 V), while the second conversion map 23b, which has a relatively high resolution, can be used for a portion of the measurement range (1 to 2 V). This makes it possible to achieve the required resolution in a specific range while ensuring a sufficiently wide measurement range.

[0019] A modified example of the sensing device 4 will be described with reference to FIG. 3. As shown in FIGS. 3A, 3B, and 3C, the sensing device 4 of this modified example includes a third conversion map 23c in addition to a first conversion map 23a and a second conversion map 23b. These three conversion maps 23a, 23b, and 23c have different conversion relationships between the voltage value output from the temperature sensing diode 12 and the duty ratio of the digital signal. Specifically, the first conversion map 23a of FIG. 3A sets a duty ratio of 0 to 100% for a voltage range of 0 to 5V. The second conversion map 23b of FIG. 3B sets a duty ratio of 0 to 100% for a voltage range of 1 to 2V. The third conversion map 23c of FIG. 3C sets a duty ratio of 0 to 100% for a voltage range of 3 to 4V.

[0020] In this modification, as shown in FIG. 3D, while the voltage value output by the temperature-sensitive diode 12 is equal to or greater than 4 V, the AD converter 20 performs AD conversion using the first conversion map 23a. When the voltage value output by the temperature-sensitive diode 12 falls below 4 V, the AD converter 20 switches the conversion map used from the first conversion map 23a to the third conversion map 23c and performs AD conversion using the third conversion map 23c. At this time, the AD converter 20 also outputs a map switching pulse. In this modification, when the conversion map used is switched from the first conversion map 23a to the third conversion map 23c, the AD converter 20 outputs the map switching pulse twice in succession. With this configuration, the AD converter 20 can reliably notify the microcomputer 40 of the switch from the first conversion map 23a to the third conversion map 23c. Thereafter, when the voltage value output by the temperature sensitive diode 12 falls below 3 V, the AD converter 20 switches the conversion map to be used from the third conversion map 23 c to the first conversion map 23 a, and performs AD conversion using the first conversion map 23 a. At this time, the AD converter 20 also outputs a map switching pulse.

[0021] When the voltage value output by the temperature-sensitive diode 12 falls below 2 V, the AD converter 20 switches the conversion map used from the first conversion map 23 a to the second conversion map 23 b, performs AD conversion using the second conversion map 23 b, and also outputs a map switching pulse. Thereafter, when the voltage value output by the temperature-sensitive diode 12 falls below 1 V, the AD converter 20 switches the conversion map used from the second conversion map 23 b to the first conversion map 23 a, performs AD conversion using the first conversion map 23 a, and also outputs a map switching pulse. Thereafter, in a similar manner, the AD converter 20 selects a conversion map to use from the multiple conversion maps 23 a, 23 b, and 23 c depending on the magnitude (voltage value) of the analog signal received from the temperature-sensitive diode 12. The microcomputer 40 also switches the conversion map to use depending on the map switching pulse output by the AD converter 20.

[0022] As described above, in the sensing device 4 of this modified example, when converting an analog signal to a digital signal, the conversion maps 23a, 23b, and 23c to be used can be switched depending on the magnitude of the analog signal. With this configuration, the first conversion map 23a, which has a relatively low resolution, can be used for the entire measurement range (0 to 5 V), while the second conversion map 23b and the third conversion map 23c, which have a relatively high resolution, can be used for several ranges within the measurement range (1 to 2 V, 3 to 4 V). This makes it possible to achieve the required resolution in several specific ranges while ensuring a sufficiently wide measurement range. [Explanation of symbols]

[0023] 2: Power control device, 4: Sensing device, 10: Semiconductor element, 12: Temperature sensitive diode, 20: AD converter, 22: Map switching unit, 23a: First conversion map, 23b: Second conversion map, 23c: Third conversion map, 24: Digital signal output unit, 26: Constant current source, 30: Photocoupler, 40: Microcomputer, 42: Memory

Claims

[Claim 1] a sensor that outputs an analog signal in response to a measurement target index; an AD converter that receives the analog signal output from the sensor and outputs a digital signal that is a pulse train having a duty ratio corresponding to the magnitude of the analog signal; a microcomputer that receives the digital signal output from the AD converter and converts the digital signal into the measurement target index or an index corresponding thereto; Equipped with the AD converter and the microcomputer store a plurality of conversion maps that describe the relationship between the magnitude and the duty ratio of the analog signal; the AD converter selects a conversion map to be used from the plurality of conversion maps in accordance with the magnitude of the analog signal received from the sensor, and outputs a predetermined switching command signal when the conversion map to be used is changed; the microcomputer switches the conversion map to be used from among the plurality of conversion maps when receiving the switching command signal from the AD converter; Sensing device.

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