Amplifiers and equipment

Abstract

To provide an amplification device which can reduce noise while increasing the resistance to radiation.SOLUTION: A plurality of MOS transistors receive an input of input signals included in differential signals in a differential amplification unit 200 of an amplification device 100 and are formed of SiC-nMOS 1 and 2 as n-type MOS transistors in which the channel is made of a wide-band semiconductor material with a larger band gap than the band gap of Si. Also, the drain currents of the SiC-nMOS 1 and 2 are lower than the reference value of a drain current at the intersection of the function showing the relation between the noise density and the drain current of the SiC-nMOS 1 and 2 and the function showing the relation between the noise density and the drain current of the SiC-pMOS 1 as a p-type MOS transistor having a channel made of the same wide-band semiconductor material.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to an amplification device and equipment.

Background Art

[0002] In a nuclear power plant or the like, it is required to measure various physical quantities such as temperature, water level, and radiation dose in a radiation environment where it is exposed to radiation. However, since semiconductor elements included in the electronic circuit of a measuring instrument for measuring physical quantities deteriorate due to the ionization action of radiation when irradiated with radiation, it is particularly difficult to operate the measuring instrument stably in a high-radiation environment. In particular, a failure of a measuring instrument due to radiation degradation of an operational amplifier, which is an amplification device generally used in a power supply circuit, becomes a problem.

[0003] To address the above problem, it is effective to change the material of the semiconductor element used in the operational amplifier from conventional Si (silicon) to SiC (silicon carbide) with excellent radiation resistance. For example, Patent Document 1 discloses an operational amplifier using an n-type MOS transistor (Metal-Oxide-Semiconductor Field-Effect Transistor: MOSFET) using SiC in a differential amplification section.

[0004] However, a SiC element, which is a semiconductor element using SiC, has a problem that it is more susceptible to the influence of noise than a Si element, which is a semiconductor element using Si.

[0005] In contrast, Patent Document 2 discloses a technique for reducing the influence of external noise, which is external noise, on an amplification device by providing a pseudo-capacitance in a printed circuit board under a SiC element.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, the inventors of this application have discovered through experiments that, as described in Reference Document 2, the reduction of external noise is insufficient for certain applications of SiC-based amplification devices. Specifically, flicker noise generated by the SiC element itself may prevent sufficient noise reduction.

[0008] Furthermore, the inventors of this invention have discovered that MOS transistors using SiC have different noise characteristics than conventional MOS transistors using Si. Specifically, the inventors have discovered that in MOS transistors using Si, the noise is always lower in p-type MOS transistors than in n-type MOS transistors, but in MOS transistors using SiC, the noise magnitude reverses between n-type and p-type MOS transistors depending on the drain current. For this reason, when an n-type MOS transistor using SiC is used in a differential amplifier section, as in the technology described in Patent Document 1, the noise may increase depending on the drain current, and a sufficient noise reduction effect may not be obtained.

[0009] The objective of the present invention is to provide an amplification device that can reduce noise while improving radiation resistance. [Means for solving the problem]

[0010] An amplifier according to one aspect of the present disclosure is an amplifier having a differential amplifier section that amplifies the voltage difference between each input signal included in a differential signal, wherein the differential amplifier section has a plurality of MOS transistors to which each input signal included in the differential signal is input, and the MOS transistors are n-type MOS transistors in which the channels are formed of a wideband semiconductor material with a band gap larger than silicon, and the drain current of the n-type MOS transistor is lower than a reference value which is the value of the drain current at the intersection of a function representing the relationship between the noise density and drain current of the n-type MOS transistor and a function representing the relationship between the noise density and drain current of a p-type MOS transistor with a channel formed of the wideband semiconductor material. [Effects of the Invention]

[0011] According to the present invention, it becomes possible to reduce noise while improving radiation resistance. [Brief explanation of the drawing]

[0012] [Figure 1] This is a configuration diagram showing an amplification device according to the first embodiment of this disclosure. [Figure 2] This diagram shows the configuration of a conventional amplification device. [Figure 3] This figure shows the noise characteristics of a SiC-MOS transistor. [Figure 4] This is a configuration diagram showing a more detailed configuration of the amplification device according to the first embodiment of this disclosure. [Figure 5] This is a configuration diagram showing an application device according to the second embodiment of this disclosure. [Figure 6] This is a configuration diagram showing an application device according to the third embodiment of this disclosure. [Figure 7] This figure illustrates the relationship between voltage noise density and frequency in a conventional configuration. [Figure 8] This diagram illustrates the relationship between voltage noise density and frequency in the configuration of this disclosure. [Modes for carrying out the invention]

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments and can be arbitrarily modified without departing from the technical idea of the present disclosure. In addition, in this specification, the same members may be denoted by the same reference numerals, and duplicate descriptions may be omitted. Also, the content shown in the drawings may be changed from the actual configuration within a range that does not impair the gist of the present disclosure for the convenience of illustration.

[0014] FIG. 1 is a configuration diagram showing an amplification device according to a first embodiment of the present disclosure.

[0015] The amplification device 100 shown in FIG. 1 is an operational amplifier that amplifies the voltage difference between a pair of input signals included in a differential signal and outputs it as an output signal. The amplification device 100 has a non-inverting input terminal IN+ and an inverting input terminal IN−, which are two input terminals to which the differential signal is input, and an output terminal Vout that outputs the output signal. In addition, the amplification device 100 has power input terminals Vss and Vdd to which a power supply voltage for driving each circuit of the amplification device 100 is input.

[0016] In addition, the amplification device 100 includes a differential amplification unit 200 that amplifies the voltage difference between a pair of input signals included in the differential signal. The differential amplification unit 200 is composed of a pair of SiC-nMOS 1 and 2, which are n-type MOS transistors formed with SiC for the channel

[0017] Note that conventionally, in an amplification device such as an operational amplifier, semiconductor elements such as MOS transistors have been used. When radiation irradiates the insulating layer of this semiconductor element, electron-hole pairs are generated by the Compton effect, and thereby, fixed charges and interface levels are formed at the interface between the insulating layer and the semiconductor. In this case, fluctuations in the threshold voltage of the semiconductor element occur, and the characteristics of the semiconductor element deteriorate.

[0018] In contrast, in the amplifier device 100 of the present embodiment, by using SiC, which has excellent radiation resistance performance, as the semiconductor material for forming the channel, the radiation resistance performance of the amplifier device 100 is significantly improved. In this regard, the inventors of the present application have confirmed through experiments that while a conventional amplifier device using Si as the semiconductor material fails in a radiation environment of several kGy, the amplifier device 100 of the present embodiment using SiC as the semiconductor material operates normally even in a radiation environment on the order of MGy.

[0019] In all MOS transistors in the amplifier device 100, it is preferable to use SiC-MOS transistors in which the channel is formed of SiC. However, at least in the MOS transistors of the differential amplifier section 200 that have a large impact on the characteristics of the amplifier device 100, SiC-MOS transistors may be used. Further, the semiconductor material for forming the channel is not limited to SiC as long as it is a wide-bandgap semiconductor material having a larger bandgap than conventional Si.

[0020] FIG. 2 is a diagram showing the configuration of a conventional amplifier device using Si as the semiconductor material.

[0021] In a conventional MOS transistor in which the channel is formed of Si, flicker noise is always lower in a p-type MOS transistor than in an n-type MOS transistor. For this reason, in the conventional amplifier device 100a shown in FIG. 2, in order to obtain a stable output with less noise, the differential amplifier section 200a is composed of a pair of conventional p-type MOS transistors 1a and 2a in which the channel is formed of Si.

[0022] In contrast, in the amplifier device 100 of the present embodiment, as described above, SiC-MOS transistors in which the channel is formed of SiC are used as the MOS transistors. Since the noise characteristics of SiC-MOS transistors are different from those of conventional MOS transistors, considering the noise characteristics, the differential amplifier section 200 of the amplifier device 100 is composed of SiC-nMOS1 and 2, which are n-type MOS transistors in which the channel is formed of SiC, as shown in FIG. 1.

[0023] Figure 3 shows the noise characteristics of SiC-MOS transistors, and more specifically, the current noise density of a SiC-nMOS, a wideband n-type MOS transistor with a SiC channel, and a SiC-pMOS, a wideband p-type MOS transistor with a SiC channel. The noise characteristics shown in Figure 3 are newly obtained results from experiments conducted by the inventors of this application.

[0024] In Figure 3, the vertical axis represents current noise density, and the horizontal axis represents drain current. Also shown are linear function 301, which represents the change in current noise density with respect to drain current in SiC-nMOS, and linear function 302, which represents the change in current noise density with respect to drain current in SiC-pMOS. Note that the SiC-nMOS and SiC-pMOS compared are equivalent in aspects other than channel structure (e.g., area).

[0025] As shown by linear functions 301 and 302, the slope of the current noise density with respect to the drain current differs between SiC-nMOS and SiC-pMOS, with the slope being steeper for SiC-nMOS than for SiC-pMOS. Therefore, there is an intersection point 303 between linear functions 301 and 302. The magnitude of the current noise density is lower for SiC-nMOS than for SiC-pMOS when the drain current is lower than the reference value, which is the drain current value at intersection point 303, and conversely, when the drain current is higher than the reference value, the magnitude of the current noise density is lower for SiC-pMOS than for SiC-nMOS.

[0026] Therefore, from the viewpoint of noise reduction, it is preferable that the differential amplifier section 200 of the amplifier 100 be composed of a pair of SiC-nMOS (SiC-nMOS 1 and 2) and that the drain current of the SiC-nMOS be driven at or below a reference value. In Figure 3, the operating region, which is the range of drain current used in the differential amplifier section 200 of the amplifier 100, is set to or below a reference value.

[0027] The reference value varies depending on design conditions such as the size of the MOS transistor and the defect density of the SiC semiconductor substrate of the MOS transistor, but it is typically within the range of 50 μA to 200 μA. In the example in Figure 3, the reference value is 100 μA.

[0028] Figure 4 is a circuit diagram showing a more detailed configuration of the amplifier 100 of this embodiment.

[0029] As shown in Figure 4, in addition to the terminals shown in Figure 1, the amplifier 100 further has a control terminal Iset for inputting an idling current to be supplied to the amplifier 100 when there is no signal.

[0030] Furthermore, the amplifier 100 includes SiC-nMOS 1 to 5, SiC-pMOS 6 to 8, and a capacitor 9.

[0031] As shown in Figure 1, SiC-nMOS 1 and 2 constitute the differential amplifier section 200. The gate terminal of SiC-nMOS 1 is connected to the inverting input terminal IN-, and the gate terminal of SiC-nMOS 2 is connected to the non-inverting input terminal IN+.

[0032] Furthermore, SiC-pMOS 6 and 7 constitute a current mirror circuit. The source terminals of SiC-pMOS 6 and 7 are connected to the power input terminal Vdd, and the gate terminals of SiC-pMOS 6 and 7 are connected to each other and to the drain of SiC-nMOS 1. In addition, the drain of SiC-pMOS 6 is connected to the drain of SiC-nMOS 1, and the drain of SiC-pMOS 7 is connected to the drain of SiC-nMOS 2.

[0033] Furthermore, the gate of SiC-pMOS8 is connected to the drain of SiC-nMOS2, the drain of SiC-pMOS7, and capacitor 9, the source of SiC-pMOS8 is connected to the power input terminal Vdd, and the drain of SiC-pMOS8 is connected to capacitor 9 and the output terminal Vout.

[0034] Furthermore, the gates of SiC-nMOS3~5 are connected to the control terminal Iset, the drain of SiC-nMOS3 is connected to the control terminal Iset, the drain of SiC-nMOS4 is connected to the sources of SiC-nMOS1 and 2, and the drain of SiC-nMOS5 is connected to the drain of SiC-pMOS8. The sources of SiC-nMOS3~5 are connected to the power input terminal Vss.

[0035] As described above, the differential amplifier section 200 is composed of SiC-nMOS 1 and 2, and an amplifier 100 can be configured in which the number of SiC-nMOS (1 to 5) is greater than the number of SiC-pMOS (6 to 8).

[0036] As described above, according to this embodiment, the multiple MOS transistors to which each input signal included in the differential signal in the differential amplifier section 200 of the amplifier 100 is input are composed of SiC-nMOS1 and 2, which are n-type MOS transistors whose channels are formed from a wideband semiconductor material with a larger band gap than Si. Furthermore, the drain current of SiC-nMOS1 and 2 is lower than the reference value, which is the value of the drain current at the intersection of the function representing the relationship between the noise density and drain current of SiC-nMOS1 and 2 and the function representing the relationship between the noise density and drain current of SiC-pMOS1, a p-type MOS transistor whose channel is formed from the same wideband semiconductor material.

[0037] Therefore, the differential amplifier section 200, which is most affected by flicker noise, can be constructed using SiC-nMOS 1 and 2 with channels formed from a wideband semiconductor material that has higher radiation resistance than conventional Si, and can be driven with a drain current that produces low flicker noise. This makes it possible to reduce noise while improving radiation resistance.

[0038] Furthermore, in this embodiment, the number of SiC-nMOS transistors included in the amplifier 100 is greater than the number of SiC-pMOS transistors included in the amplifier 100. Therefore, it is possible to further reduce flicker noise.

[0039] Figure 5 is a configuration diagram showing an application device according to the second embodiment of this disclosure.

[0040] The application device 500 shown in Figure 5 is an example of a device equipped with the amplifier 100 of the first embodiment shown in Figures 1 and 4, and is a pressure measuring device that measures pressure and outputs a measurement signal indicating that pressure.

[0041] The application device 500 includes a measurement unit 501 and a control unit 502.

[0042] In this embodiment, the measurement unit 501 is a pressure sensor that measures pressure and outputs an analog signal corresponding to that pressure. However, the measurement unit 501 is not limited to a pressure sensor; it can be any sensor that measures a predetermined physical quantity such as temperature, flow rate, water level, or ultrasound. Furthermore, in this embodiment, the measurement unit 501 supports a sensing method that requires a power supply circuit.

[0043] The control unit 502 performs predetermined processing on the analog signal from the measurement unit 501. More specifically, the control unit 502 includes the amplification device 100 shown in Figure 1, and the predetermined processing includes at least amplification processing in which the amplification device 100 amplifies an operating signal corresponding to the analog signal from the measurement unit 501. Furthermore, the predetermined processing is not particularly limited as long as it includes amplification processing, but for example, it is a process that converts the analog signal into a digital measurement signal.

[0044] According to this embodiment, the application device 500 is equipped with the amplifier 100 shown in Figure 1 as an amplification device, making it possible to reduce noise while improving the radiation resistance of the application device 500. As a result, the output fluctuation of the measuring device is reduced, and accurate measurement values ​​can be obtained stably even in a radiation environment.

[0045] Figure 6 is a configuration diagram showing an application device according to the third embodiment of this disclosure.

[0046] The application device 600 shown in Figure 6 differs from the application device 500 shown in Figure 5 in that it further includes a high-pass filter 503 between the measurement unit 501 and the control unit 502.

[0047] The high-pass filter 503 is a filter that attenuates signals in the low-frequency band lower than the set frequency in the analog signal output from the measurement unit 501, and outputs signals in the frequency band higher than the set frequency. In this embodiment, the high-pass filter 503 attenuates signals in the low-frequency band lower than the operating frequency band of the analog signal used in the application device 500.

[0048] With the above configuration, flicker noise, which increases in the low-frequency range, can be efficiently reduced, allowing for more stable and accurate measurements even in radiation environments.

[0049] Figure 7 is a diagram illustrating the relationship between voltage noise density and frequency in a conventional configuration.

[0050] Noise generated in electrical circuits can be broadly classified into flicker noise and broadband noise, as shown in Figure 7. Flicker noise, also known as 1 / f noise, is noise that originates from the circuit itself and is a low-frequency noise in which the power is inversely proportional to the frequency. Broadband noise is a wideband noise that occurs over a wide range of frequencies.

[0051] In devices that measure physical quantities with relatively little fluctuation, such as the pressure measuring device 600 of this embodiment, the device is particularly susceptible to the effects of low-frequency noise, specifically flicker noise. Therefore, reducing flicker noise is necessary to obtain accurate and stable measurement values.

[0052] Figure 8 is an explanatory diagram showing the relationship between voltage noise density and frequency in the configuration of this embodiment.

[0053] In this embodiment, SiC-nMOS 1 and 2 are used in the differential amplifier section 200 of the amplifier 100 included in the control unit 502 of the application device 600, and the overall flicker noise is reduced by driving the drain current of the SiC-nMOS 1 and 2 at or below a reference value. Furthermore, by attenuating signals in the low-frequency band lower than the operating frequency band of the application device 600 using the high-pass filter 503, a more stable output with less noise is achieved.

[0054] As explained above, in this embodiment, a high-pass filter 503 is provided that attenuates the low-frequency band of the analog signal, making it possible to further reduce noise.

[0055] The embodiments of the Disclosure described above are illustrative for illustrative purposes and are not intended to limit the scope of the Disclosure to those embodiments only. Those skilled in the art can implement the Disclosure in various other forms without departing from the scope of the Disclosure. [Explanation of symbols]

[0056] 1-5: SiC-nMOS 6-8: SiC-pMOS 9: Capacitor 100: Amplifier 200: Differential amplifier 500, 600: Application equipment 501: Measurement unit 502: Control unit 503: High-pass filter

Claims

1. An amplifier having a differential amplifier section that amplifies the voltage difference between each input signal included in a differential signal, The differential amplifier section is It has multiple MOS transistors to which each input signal included in the differential signal is input, The aforementioned MOS transistor is an n-type MOS transistor in which the channel is formed of a wide-band semiconductor material with a band gap larger than that of silicon. The drain current of the n-type MOS transistor is lower than a reference value, which is the value of the drain current at the intersection of a function representing the relationship between the noise density and drain current of the n-type MOS transistor and a function representing the relationship between the noise density and drain current of a p-type MOS transistor whose channel is formed from the wideband semiconductor material. The aforementioned wideband semiconductor material is silicon carbide, in the amplification device.

2. The amplification device according to claim 1, wherein the reference value is within the range of 50 μA to 200 μA.

3. The amplification device according to claim 1, wherein the amplification device includes an n-type MOS transistor in the differential amplification section, and comprises a wideband n-type MOS transistor and a wideband p-type MOS transistor whose channels are formed of the wideband semiconductor material, and the number of the wideband n-type MOS transistors is greater than the number of the wideband p-type MOS transistors.

4. A measurement unit that outputs an analog signal of a predetermined physical quantity, The system includes a control unit that performs predetermined processing on the analog signal, The control unit comprises the amplification device described in claim 1 as an amplification device for amplifying the voltage difference of the differential signal corresponding to the analog signal.

5. The apparatus according to claim 4, wherein the physical quantity is pressure, temperature, flow rate, water level, or ultrasound.

6. The apparatus according to claim 5, further comprising a high-pass filter that attenuates a low-frequency band lower than the set frequency of the analog signal and inputs it to the control unit.

7. The apparatus according to claim 6, wherein the low-frequency band is lower than the operating frequency band of the analog signal used in the control unit.

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