AMPLIFICATION DEVICE AND MEASURING INSTRUMENT

Abstract

An amplification device includes: an amplification circuit in which a differential amplification unit, to which a pair of input signals is supplied as input, consists of a pair of SiC transistors as a channel and which amplifies and provides as output a voltage difference between the pair of input signals; and a voltage control unit which controls the respective input signal terminal voltages to which the pair of input signals is supplied as input so that they are equal to or less than the voltages of a positive supply and a negative supply provided to the amplification circuit.

Description

Title of the invention: AMPLIFICATION DEVICE AND MEASURING INSTRUMENT CONTEXT OF THE INVENTION

[0001] 1. Field of the invention

[0002]

[0003] The present invention relates to an amplification device and a measuring instrument which are used in a radiation environment.

[0004] 2. Description of the state of the art

[0005]

[0006] Various measurements of temperature, water level, radiation, etc. are required in environments such as nuclear power plants, which are exposed to radiation. Furthermore, since a semiconductor element contained in an electronic circuit of a measuring instrument deteriorates due to the ionization effect of radiation, it is difficult to use the electronic circuit, especially in an environment with a high level of radiation.

[0007]

[0008] One of the factors of failure of the measuring instrument due to radiation is the failure of an amplification device comprising the semiconductor element. The deterioration of an op amp (short for operational amplifier) ​​generally used in the amplification device due to radiation causes a decrease in the output level, resulting in poor performance of the measuring instrument. Since the op amp performs an amplification operation based on a potential difference between the input terminals by means of the differential amplification circuit, which is constituted of at least two transistors, when each transistor deteriorates, the performance of the op amp is likely to deteriorate (failure).

[0009]

[0010] As a method of normal operation of the electronic circuit having the semiconductor element in a radiation environment, it is effective to use a method of changing the semiconductor material of the op amp by replacing the conventional silicon (Si) element with an element made of silicon carbide (SiC) which has excellent radiation resistance.

[0011]

[0012] The experiments carried out by the inventors have shown that, in an op amp using SiC (hereinafter referred to as "SiC op amp"), a drift of a output value occurred due to the influence of external noise or radiation. JP 2020-043187 A discloses a method for reducing output value drift during use by exposing a semiconductor element using SiC to radiation in advance and incorporating the semiconductor element into an actual machine when the deterioration converges. Summary of the invention

[0013]

[0014] Although it is effective to reduce the drift of the output value of the SiC op amp by the method described above, since this method uses the source that produces the radiation, management becomes complicated and costs increase. Furthermore, it has recently been found that it is necessary to take into account drift due to electrical stress. Specifically, it has been experimentally found that in the case where the input voltage of the SiC op amp exceeds 80% of a supply voltage Vdd or a supply voltage Vss of the SiC op amp, positive charges are trapped in defects present at an interface between an oxide film (insulation layer) and a semiconductor layer, and the offset voltage drifts. Electron-hole pairs are generated at the interface due to the radiation, but the electrons move at high speed and are likely to pass through the interface.Furthermore, the holes move at low speed and are therefore likely to remain at the interface.

[0015]

[0016] Unlike a conventional op amp using Si (hereinafter referred to as "Si op amp"), the SiC op amp has many defects at the interface. Therefore, it has recently been found that it is necessary to sufficiently take into account the drift of an output value (offset voltage) due to electrical stress, i.e., a high input voltage, in order to stabilize the output of the SiC op amp.

[0017]

[0018] The present invention has been made in view of the above-mentioned circumstances, and one of the objects of the present invention is to provide an amplification device and a measuring instrument which have excellent radiation resistance and can reduce the drift of an output value without requiring complicated management.

[0019]

[0020] In order to solve the above-mentioned problem, an amplification device according to one aspect of the present invention comprises: an amplification circuit in which a differential amplification unit to which a pair of input signals is input consists of a pair of transistors using SiC as a channel and which amplifies and outputs a voltage difference between the pair of input signals; and a voltage control unit which controls the voltages of respective signal input terminals to which the pair of input signals are input so that they are equal to or lower than voltages of a positive supply and a negative supply supplied to the amplification circuit.

[0021] Furthermore, a measuring device according to one aspect of the present invention comprises a measuring unit which outputs a signal according to a measurement result for a target, and an amplifying device which amplifies the signal output by the measuring unit and has the above configuration.

[0022]

[0023] According to the amplification device and the measuring instrument of at least one aspect of the present invention, the radiation resistance is excellent and the drift of the output value can be reduced without requiring complicated management. Therefore, the amplification device and the measuring instrument according to one aspect of the present invention can achieve an accurate and stable output in a radiation environment.

[0024] Problems, configurations and effects other than those described above will be explained by the following description of embodiments. Brief description of the drawings

[0025]

[0026] [Fig.l] [Fig.l] is a diagram illustrating a basic configuration of an amplification device according to one embodiment of the present invention;

[0027] [Fig.2] [Fig.2] is a graph illustrating an example of a drift level of an offset voltage after applying an overvoltage in an op amp using SiC;

[0028] [Fig.3] [Fig.3] is a diagram illustrating an example circuit configuration in a case where the amplification device is constituted by the op amp using SiC according to an embodiment of the present invention;

[0029] [Fig.4] [Fig.4] is a diagram explaining a drift threshold value versus an input voltage for each type of op amp; and

[0030] [Fig.5] [Fig.5] is a diagram illustrating an example of a schematic configuration of a measuring instrument using the amplification device according to an embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0031]

[0032] Exemplary embodiments of the present invention (hereinafter referred to as "embodiments") will be described below with reference to the accompanying drawings. In this specification and the accompanying drawings, identical or similar components are designated by the same reference numerals, and redundant descriptions may be omitted or only descriptions emphasizing a difference may be provided. The number of components may be one or more, unless otherwise indicated.

[0033]

[0034] [Basic configuration of the amplification device]

[0035] [Fig. 1] is a diagram illustrating a basic configuration of an amplification device according to one embodiment of the present invention.

[0036] The amplification device 1 illustrated in [Fig.l] comprises an op amp 10 and a voltage control unit 20. Vin- and Vin+ are input signals of the amplification device 1 (voltage control unit 20), and Vout is an output signal of the op amp 10.

[0037]

[0038] Op amp 10 is an example of an amplification circuit using a semiconductor element. Op amp 10 is powered by a positive supply voltage Vdd and a negative supply voltage Vss. Op amp 10 delivers an output signal Vout to the input signal of the differential pair.

[0039]

[0040] The voltage control unit 20 is powered by an input signal Vin- and an input signal Vin+. According to the voltages of the input signal Vin- and the input signal Vin+, the voltage control unit 20 controls the voltages (inverted phase positive phase "+") of the input signal with respect to a differential amplification unit 19 of the op amp 10.

[0041]

[0042] In a semiconductor element for use in an electronic circuit such as an op amp, when an insulating layer is exposed to radiation, electron-hole pairs are generated by the Compton effect, and fixed charges and interface states are formed at an interface between the insulating layer and the semiconductor layer. Due to this influence, the operating threshold voltage fluctuates and the characteristics of the semiconductor element deteriorate.

[0043]

[0044] Furthermore, the inventors solved the above-mentioned problem by modifying the material of the semiconductor element used for the op amp, by replacing the conventional Si (silicon) with SiC (silicon carbide), which is a semiconductor broadband op amp with excellent radiation resistance performance. In other words, the use of SiC can limit the generation of an interface state due to radiation and significantly improve the radiation resistance of the semiconductor element. Specifically, it has been confirmed that the conventional Si op amp fails at several kGy, while the op amp using SiC normally performs its amplification function, even at levels in the order of MGy.

[0045]

[0046] As described above, the op amp using SiC can significantly reduce the influence of radiation. However, the op amp using SiC is characterized by the presence of many lattice defects at the interface between the semiconductor layer and the oxide layer, compared with the conventional op amp using Si.

[0047]

[0048] The experiments conducted by the inventors allowed them to observe that when the op amp using SiC was subjected to a strong electrical stress on the input voltage, positive charges were trapped in network faults, and that the offset voltage drifted. More precisely, when a voltage equal to or greater than 90% of the absolute value of the supply voltage Vdd (positive supply) or the supply voltage Vss (negative supply) intended to drive the op amp is applied to the input terminal, the drift becomes pronounced. In the following description, the expression "% of the supply voltage" denotes a percentage relative to the absolute value of the supply voltage.

[0049]

[0050] [Offset voltage drift level after applying an overvoltage]

[0051] [Fig. 2] is a graph illustrating an example of drift of an offset voltage after applying an overvoltage in an op amp using SiC. In [Fig. 2], the vertical axis represents the drift level [mV] of the offset voltage, and the horizontal axis represents the elapsed time [h] after the overvoltage was applied.

[0052]

[0053] [Fig.2] illustrates the transition of the op amp offset voltage after voltages of 80%, 90% and 100% relative to the magnitudes of the supply voltage Vdd and the supply voltage Vss have been applied to the reverse phase and positive phase input terminals of the SiC op amp.

[0054]

[0055] It is noted that in the case where the reversed phase and positive phase input voltages are at 80% of the supply voltage Vdd and the supply voltage Vss, the offset voltage drift level is small, and the drift converges within 1 minute.

[0056] When the reverse phase and positive phase input voltages exceed 80% of the supply voltage Vdd and the supply voltage Vss, a drift of the offset voltage is observed.

[0057]

[0058] Furthermore, in the case where the reversed phase and positive phase input voltages are 90% or more of the supply voltage Vdd and the supply voltage Vss, the drift level of the offset voltage becomes very high. In the experiment, the drift level further increased when the input voltage exceeded 3.5 V (87.5%) with respect to the supply voltage of ±4 V, this increase becoming even more pronounced when the input voltage exceeded 90%. As described above, it is observed that the drift level tends to gradually increase when the input voltage becomes greater than 80% of the supply voltage.

[0059]

[0060] It is noted that the drift level shows almost no difference between the 90% and 100% cases one minute after the application of the overvoltage, but when one hour or more elapses, the magnitude of the increase in the drift level in the 90% case is smaller than in the 100% case. It can be seen that in the 90% case, the convergence tends to be faster than in the 100% case.

[0061]

[0062] Based on the above results, it is preferable that the input voltages of the SiC op amp are equal to or lower than the values ​​of the supply voltage Vdd and the supply voltage Vss, or preferably equal to or lower than 90% thereof. Strictly speaking, it is preferable that the input voltage is equal to or lower than 87.5%.

[0063] More preferably, it is preferable that the input voltages of the SiC op amp are equal to or less than 80% of the voltages of the supply voltage Vdd and the supply voltage Vss in order to ensure more stable operation of the amplification device (measuring instrument). However, it goes without saying that the input voltage is equal to or greater than the operating threshold voltage of the transistor constituting the SiC op amp.

[0064]

[0065] In order to realize the SiC op amp in which the drift level of the offset voltage is small, in the amplification device 1 according to the present embodiment, the differential amplification unit of the amplification circuit (SiC op amp) is constituted by a pair of SiC transistors as a channel (path current). The amplification device 1 is further configured to include a voltage control unit that controls the voltages of respective signal input terminals (inverted input, non-inverted input) to which a pair of input signals are input so that they are equal to or lower than the values ​​of the supply voltage Vdd and the supply voltage Vss.

[0066]

[0067] The above configuration can reduce the drift level of the offset voltage due to the electrical stress of the SiC op amp without requiring complicated conventional management. Therefore, in the radiation environment, the amplification device 1 can establish a stable output for a long period of time.

[0068]

[0069] [Circuit configuration in the case where the amplification device consists of an op amp using SiC]

[0070] [Fig.3] is a diagram illustrating an example of circuit configuration in a case where the amplification device 1 consists of the op amp 10 using SiC.

[0071]

[0072] In the op amp 10, a pair consisting of an n-type MOS field effect transistor 11 and an n-type MOS field effect transistor 12 using SiC as a channel constitutes the differential amplification unit 19 in an initial stage of a differential pair circuit unit. The field effect transistor is hereinafter referred to as "FET". A gate of the n-type MOSFET 11 is connected to a signal input terminal 31 to which the input signal Vin- (inverted input) is input. Furthermore, the gate of the n-type MOSFET 12 is connected to a signal input terminal 32 to which the input signal Vin+ (non-inverted input) is input.

[0073]

[0074] The drain of the n-type MOSFET 11 is connected to the drain of a p-type MOSFET 13 on an upper stage. The source of the p-type MOSFET 13 is connected to an input terminal 34 to which the positive supply voltage Vdd is supplied.

[0075]

[0076] Similarly, the drain of the n-type MOSFET 12 is connected to the drain of a p-type MOSFET 14 on an upper stage. The source of the p-type MOSFET 14 is connected to the power input terminal 34 to which the positive supply voltage Vdd is supplied.

[0077]

[0078] A midpoint between the drain of the n-type MOSFET 11 and the drain of the p-type MOSFET 13 is connected to a midpoint between the gate of the p-type MOSFET 13 and the gate of the p-type MOSFET 14. In other words, the p-type MOSFET 13 and the p-type MOSFET 14 constitute a current mirror circuit.

[0079]

[0080] The source of the n-type MOSFET 11 is connected to the drain of the n-type MOSFET 15, and the source of the n-type MOSFET 12 is connected to the drain of the n-type MOSFET 15. The source of the n-type MOSFET 15 is further connected to a power input terminal 35 to which the negative supply voltage Vss is supplied.

[0081]

[0082] A midpoint between the n-type MOSFET 12 and the p-type MOSFET 14 is connected to the gate of the p-type MOSFET 16 and to one end of a capacitor CL. The source of the p-type MOSFET 16 is connected to the power input terminal 34, and its drain is connected to a signal output terminal 33 which outputs the output signal Vout. Furthermore, the other end of the capacitor Cl is also connected to the signal output terminal 33. The capacitor Cl is a phase compensation capacitor.

[0083]

[0084] The anode of a Zener diode DI is connected to the signal input terminal 31, and the cathode of the Zener diode DI is connected to the power input terminal 34. Furthermore, the anode of a Zener diode D2 is connected to the signal input terminal 32, and the cathode of the Zener diode D2 is connected to the power input terminal 34.

[0085]

[0086] In addition, the cathode of a Zener diode D3 is connected to the signal input terminal 31, and the anode of the Zener diode D3 is connected to the power input terminal 35. Furthermore, the cathode of a Zener diode D4 is connected to the signal input terminal 32, and the anode of the Zener diode D4 is connected to the power input terminal 35. The Zener diodes D1 to D4 constitute a voltage control unit 20.

[0087]

[0088] Zener diodes DI and D3 serve as overvoltage protection elements between signal input terminal 31 and power input terminal 34 and between signal input terminal 31 and power input terminal 35. Accordingly, the voltage applied to n-type MOSFET 11 of op amp 10 via signal input terminal 31 can be controlled to protect op amp 10.

[0089]

[0090] Similarly, Zener diodes D2 and D4 are provided as overvoltage protection elements between signal input terminal 32 and power input terminal 34 and between signal input terminal 32 and power input terminal 35. Accordingly, the voltage applied to n-type MOSFET 12 of op amp 10 via signal input terminal 32 can be controlled to protect op amp 10.

[0091]

[0092] In addition, the amplification device 1 comprises a control terminal 36 for a quiescent current Iset. The control terminal 36 is connected to the drain and the gate of the n-type MOSFET 18. The source of the n-type MOSFET 18 is connected to the power input terminal 35.

[0093] Further, control terminal 36 is connected to the gate of n-type MOSFET 15.

[0094] In addition, the control terminal 36 is connected to the gate of the n-type MOSFET 17. The drain of the n-type MOSFET 17 is connected to the drain of the p-type MOSFET 16, and its source is connected to the power input terminal 35.

[0095]

[0096] The control terminal 36 for the quiescent current Iset is a circuit for adjusting the drive current of the op amp 10, but is not essential. The consumption current of the op amp 10 can be adjusted by means of the quiescent current Iset. When the drive current of the op amp 10 is higher, the op amp 10 is more stable, but the consumption current increases. In this regard, the drive current is adjusted by adjusting the quiescent current by means of a resistor (not shown) connected to the control terminal 36.

[0097]

[0098] In the present embodiment, two transistors (differential amplification unit 19) that form at least one differential pair in the op amp 10 are considered to be similar to the n-type MOSFETs 11 and 12. It is noted that the differential amplification unit 19 may be constituted by a pair of p-type MOSFETs instead of a pair of n-type MOSFETs. In this case, a p-type and an n-type are modified as appropriate for other MOSFETs. SiC is used as a semiconductor material for two MOSFETs constituting the differential amplification unit. However, the MOSFET is an example of a transistor, and another field effect transistor may be used.

[0099]

[0100] In addition, SiC can be used as the semiconductor material of two transistors (p-type MOSFETs 13 and 14) constituting the current mirror circuit on the upper stage side of the differential amplifier unit 19. It is noted that the function of the current mirror circuit can be replaced by a resistor, although the amplification factor decreases.

[0102] Of course, SiC can be used for other transistors constituting the op amp 10. From the point of view of radiation resistance performance, the other transistors are preferably made of SiC elements, but can be made of Si elements provided that the radiation dose is relatively low.

[0103]

[0104] Zener diodes D1 to D4 are set so that the voltages applied to signal input terminals 31 and 32 do not exceed the range of supply voltage Vdd and supply voltage Vss. More specifically, in the case of a supply voltage of Vdd = 4 V and Vss = -4 V, Zener diodes D1 to D4 are set so that the voltages of signal input terminals 31 and 32 are not greater than or equal to 4 V and less than or equal to -4 V. For example, in a case where input signal Vin+ of 5 V is input to amplification device 1, the voltage of signal input terminal 32 is clamped (limited) to 4 V by Zener diodes D2 and D4. Therefore, the non-inverting input of op amp 10 is limited to 4 V, which is the same as the supply voltage Vdd.

[0105]

[0106] The amplification device 1 according to the present embodiment described above is characterized in that an overvoltage protection element (voltage control unit 20) is provided in the input portion of the op amp 10 using SiC as a channel. According to the present embodiment, without requiring complicated conventional management, the drift of the offset voltage can be reduced by means of a simple configuration even in the radiation environment. Therefore, in the amplification device 1 including the op amp 10, a stable output can be obtained over a long period of time.

[0107]

[0108] In the above configuration, the circuit elements constituting the voltage control unit 20, i.e., the overvoltage protection elements (e.g., the Zener diodes D1 to D4) can be configured so that they are integrated into the chip of the op amp 10. Such a configuration can reduce the drift of the offset voltage at low cost without changing the size of the conventional op amp. In other words, the op amp 10 and the voltage control unit 20 are integrated into a single chip in the form of a SiC integrated circuit (IC). The single-chip case has a cost advantage because the circuit area can be reduced.

[0109]

[0110] Conversely, the overvoltage protection element (voltage control unit 20) can be externally attached as a peripheral circuit of the op amp 10. In this case, the circuit scale of the op amp 10 added to the voltage control unit 20 is larger than that of the conventional op amp, but this provides the advantage that the value of the protection voltage can be changed flexibly. When the voltage control unit 20 is provided as a peripheral circuit, it is easy to change the protection voltage (circuit constant) according to the power supply voltage to drive the op amp 10. [YES]

[0112] In the present embodiment, the Zener diode is used as an overvoltage protection element, but the overvoltage protection circuit (voltage control unit 20) may be implemented using an element other than the Zener diode. For example, in addition to a level clamp circuit ([Fig. 3]) using a Zener diode, a level clamp circuit using a diode, a level clamp circuit using a varistor, a protection circuit using a protection capacitor, or the like may be considered as an overvoltage protection circuit. In a case where the protection capacitor is used as an overvoltage protection element, capacitors are connected between the signal input terminal 31 and ground and between the signal input terminal 32 and ground.

[0113]

[0114] Furthermore, in the above configuration, from the viewpoint of radiation resistance performance, it is desirable that the surge protection element is made of a SiC element. However, the surge protection element may be made of a Si element provided that the radiation dose is relatively low.

[0115]

[0116] In the above description, the setting value (setting voltage) of the voltage to be protected by the overvoltage protection element (voltage control unit 20) is set within the range of the positive supply voltage Vdd and the negative supply voltage Vss, but the present invention is not limited to this example. As described above, in order to further reduce the drift of the offset voltage, the setting value of the overvoltage protection element is preferably set to 90% or less (e.g., 87.5%) of the supply voltage Vdd and the supply voltage Vss. More preferably, it is preferable that the setting value is 80% or less.

[0117]

[0118] [Op amp type and drift occurrence threshold value for input voltage]

[0119] [Fig.4] is a diagram explaining the threshold value of drift occurrence versus input voltage for each type of op amp. In [Fig.4], the vertical axis represents the voltage [V] of the input signal and the horizontal axis represents the time [h].

[0120]

[0121] In a conventional Si op amp, the voltage value of the input signal at which the drift of the offset voltage occurs with respect to the supply voltage Vdd and the supply voltage Vss (hereinafter referred to as "drift occurrence threshold value") is high. The drift occurrence threshold value is a value of the input voltage at which the offset voltage of the op amp drifts unacceptable in terms of quality or set in advance. For example, in the case of a supply voltage of 4 V, the drift occurrence threshold value Thsi of the Si op amp is a value well exceeding 4 V. Therefore, in a normal application, the drift caused by the input voltage is less likely to be a problem in the Si op amp. In [Fig.4], ARSi indicates an allowable input range of the Si op amp.

[0122]

[0123] Furthermore, it has been experimentally found that in the SiC op amp, drift occurs when the input signal exceeds the supply voltage. This phenomenon is considered to be due to the trapping of positive charges at the interface of the semiconductor layer of the MOSFET constituting the SiC op amp. SiC has more defects at the interface of the semiconductor layer near the oxide film than Si, so that a greater number of positive charges are trapped in the defects.

[0124]

[0125] In this regard, in the SiC op amp, the drift occurrence threshold value ThsiC is set to be equal to or lower than the supply voltage (e.g., 4 V), and the input voltage is controlled to be equal to or lower than the supply voltage. As a result, it is possible to reduce the trapping of positive charges in the interface defects of the SiC op amp and establish a stable output with less drift of the offset voltage over a long period of time even in the radiation environment. The setting value of the overvoltage protection element can be determined based on the drift occurrence threshold value ThsiC. In [Fig.4], ARS;c indicates an allowable input range of the SiC op amp.The ARSiC permissible input range is narrower than the Si op amp's ARSi permissible input range, and has an upper limit value lower than the supply voltage.

[0127] It should be noted that in a semiconductor element such as op amp 10, SiC is used as a semiconductor having a band gap greater than that of Si, but it is possible to use gallium nitride (GaN), a diamond semiconductor, or the like.

[0128]

[0129] [Measuring instrument using the amplification device of the present invention]

[0130] A measuring instrument using an amplification device according to a mode of embodiment of the present invention will then be described with reference to [Fig.5].

[0131]

[0132] [Fig.5] is a diagram illustrating an example of a schematic configuration of a measuring instrument 40 using the amplification device 1 according to an embodiment of the present invention.

[0133] The illustrated measuring instrument 40 comprises a measuring unit 41 and the amplification device 1.

[0134]

[0135] The measuring unit 41 is a circuit which provides an output signal as a function of the measurement result of a physical quantity, a characteristic, or other of a target.

[0136] The amplification device 1 receives a pair of input signals Vin- and Vin+ output by the measurement unit 4L. After that, the amplification device 1 amplifies the difference between the voltages of the input signals Vin- and Vin+ and outputs the output signal Vout. As illustrated in FIGS. 1 and 3, the positive supply voltage Vdd and the negative supply voltage Vss are supplied to the amplification device 1. When the voltage of the pair of input signals exceeds the supply voltage Vdd or the supply voltage Vss, the voltage control unit 20 ([Fig. 3]) controls the input voltage to be a setting voltage equal to or lower than the supply voltage. The op amp 10 performs an amplification operation based on the pair of input signals, the voltage values ​​of which have been adjusted by the voltage control unit 20.

[0137]

[0138] A pressure transmitter will be described herein as an example of the measuring instrument. In pressure transmitters operating in a high radiation environment, it is necessary to reduce an initial drift. More specifically, the time required for the output level to stabilize from the moment the SiC op amp power supply is turned on can be as long as 60 to 200 minutes in the SiC op amp, while this time is about 10 minutes in the conventional Si op amp. The drift of the offset voltage is about 1 mV to several mV and is therefore small enough to be undetectable in some applications. However, For a pressure transmitter that measures a tiny differential pressure, the drift results in a measurement error of about 0.1 to 0.3%.

[0139]

[0140] Experiments conducted by the present inventors have found that the rise characteristics of the power supply voltage and the input voltage of the op amp when the power supply is turned on are factors having influence on the drift of the offset voltage. Specifically, it has been experimentally found that the drift occurs when the power supply voltage or the input voltage deviates from the permissible input range of the SiC op amp for several 1s to several ms until the power supply voltage or the input voltage stabilizes. In the case of an example in which the input voltage deviates from the permissible input range, there may be mentioned a clicking sound (waveform fluctuation), noise, or the like.

[0141]

[0142] Furthermore, according to the amplification device 1 having the configuration described above, it is possible to reduce the drift of the offset voltage of the SiC op amp without requiring complicated conventional management, and to achieve high radiation resistance and operating stability. It is therefore possible to establish an accurate and stable output in a radiation environment. The amplification device 1 according to the present embodiment is then applied to the measuring instrument 40, thereby contributing to improving the reliability of the operation of a facility.

[0143]

[0144] The amplification device according to the present embodiment can be applied to a measuring instrument that measures a state (physical quantity or characteristic) of an object supposed to be used in the radiation environment. The measuring unit 41 can be any sensor, provided that the measuring unit uses a detection method for measuring pressure, temperature, flow rate, water level, radiation, ultrasonic waves or the like. Furthermore, the measuring unit 41 can be an image sensor. In addition, the measuring instrument of the present embodiment can also be applied to systems and fields such as equipment exploiting radiation in a nuclear power plant or the like, medical care and space measurements.

[0145]

[0146] It should be noted that it is desirable that the measuring unit 41 does not include an electronic circuit, or that it is made of an analog circuit that is relatively more resistant to radiation than a digital circuit, or of a wide bandgap semiconductor, such as SiC, which has excellent resistance to radiation.

[0147]

[0148] The present invention is not limited to the embodiments described above, and it goes without saying that various other application examples and various other modifications may be used without departing from the spirit of the present invention described. For example, in the embodiment described above, the configurations have been presented in detail and specifically in order to describe the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to those which include all the components described. Furthermore, it is possible to add, replace or delete other components for a part of the configuration of the embodiment.

Claims

Claims

1. An amplification device comprising: an amplification circuit in which a differential amplification unit to which a pair of input signals is input is constituted of a pair of transistors using SiC as a channel and which amplifies and outputs a voltage difference between the pair of input signals; and a voltage control unit which controls the voltages of respective signal input terminals to which the pair of input signals is input so as to be equal to or lower than voltages of a positive power supply and a negative power supply supplied to the amplification circuit.

2. The amplification device according to claim 1, wherein the voltage control unit limits each of the pair of input signals inputted to the differential amplification unit of the amplification circuit to be equal to or less than 90% of an absolute value of each voltage of the positive power supply and the negative power supply.

3. The amplification device according to claim 2, wherein the voltage control unit limits each of the pair of input signals inputted to the differential amplification unit of the amplification circuit to be equal to or less than 80% of an absolute value of each voltage of the positive power supply and the negative power supply.

4. The amplification device according to claim 1, wherein the voltage control unit comprises an overvoltage protection element which is provided between a signal input terminal to which one input signal of the pair of input signals is input and each of a power input terminal to which a voltage of the positive power supply is input and a power input terminal to which a voltage of the negative power supply is input, and an overvoltage protection element which is provided between a signal input terminal to which another input signal of the pair of input signals is input and each of a power input terminal to which a voltage of the positive power supply is provided and a power input terminal to which a voltage of the negative power supply is supplied, and in a case where an input signal having a voltage exceeding a setting voltage is input to each signal input terminal, causes each overvoltage protection element to limit a voltage of each signal input terminal to be equal to or lower than voltages of the positive power supply and the negative power supply supplied to the amplification circuit.

5. An amplification device according to claim 4, wherein in a case where an input signal having a voltage exceeding a setting voltage is input to each signal input terminal, the voltage control unit causes each overvoltage protection element to limit the voltage of each signal input terminal to be equal to or less than 90% of an absolute value of each voltage of the positive power supply and the negative power supply.

6. An amplification device according to claim 4, wherein in a case where an input signal having a voltage exceeding a setting voltage is input to each signal input terminal, the voltage control unit causes each overvoltage protection element to limit the voltage of each signal input terminal to be equal to or less than 80% of an absolute value of each voltage of the positive power supply and the negative power supply.

7. The amplification device according to claim 1, wherein the voltage control unit comprises a capacitor which is provided between a signal input terminal to which one input signal of the pair of input signals is input and ground, and a capacitor which is provided between a signal input terminal to which another input signal of the pair of input signals is input and ground, and in a case where an input signal having a voltage exceeding a setting voltage is input to each signal input terminal, causes each capacitor to limit the voltage of each signal input terminal to be equal to or less than

8.

9.

10. to the positive supply and negative supply voltages supplied to the amplifier circuit. An amplification device according to claim 1, wherein the amplification circuit is an operational amplifier. An amplification device according to claim 1, wherein a circuit element constituting the voltage control unit is integrated in the same chip as that of the amplification circuit.A measuring instrument comprising a measuring unit which outputs a signal according to a measurement result for a target, and an amplification device which amplifies the signal outputted by the measuring unit, wherein the amplification device comprises an amplification circuit in which a differential amplification unit to which a pair of input signals is input is constituted of a pair of transistors using SiC as a channel and which amplifies and outputs a voltage difference between the pair of input signals; and a voltage control unit which controls the voltages of respective signal input terminals to which the pair of input signals is input to be equal to or lower than the voltages of a positive power supply and a negative power supply supplied to the amplification circuit.

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