Radiation-hardened multiplexer

Abstract

To provide a radiation-resistant multiplexer superior radiation resistance with a simple configuration.SOLUTION: A radiation-resistant multiplexer 100 includes: an analog switch circuit 101 composed of SiC-MOSFETs that have a wider band gap than that of silicon; a multiplexer circuit 110 that has analog switch circuit 101 in the output stage; and a gate signal control unit 120 that has an operation mode that applies a gate signal that turns off all channels of the multiplexer circuit 110.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a radiation-resistant multiplexer.

Background Art

[0002] For example, there is a nuclear power plant which requires the preservation of circuit devices in a radiation environment. In an environment exposed to radiation such as a nuclear power plant, semiconductor elements included in the electronic circuits of measuring instruments deteriorate due to the ionization effect of radiation. Therefore, it is particularly difficult to use electronic circuits in a high-radiation environment.

[0003] For example, for the aggregation of a large number of cables in a plant, it is effective to use a multiplexer, which is an electronic circuit using semiconductors, to reduce the wiring. However, due to the above reasons, it is difficult to apply it in a nuclear power plant.

[0004] As one of the factors causing failures of these electronic circuits due to radiation, there is characteristic degradation of MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). Due to the accumulation of charges by radiation irradiation, the characteristics of MOSFET deteriorate due to an increase in leakage current, etc., which becomes a major cause of failures of electronic circuits.

[0005] As a method for operating an electronic circuit normally in a radiation environment, a technique of changing MOSFET from a conventional Si (silicon) semiconductor using Si to a SiC (silicon carbide) element with excellent radiation resistance is effective.

[0006] A multiplexer composed of a plurality of MOSFETs can also improve the radiation resistance performance as described in Patent Document 1 by being composed of SiC as described above.

[0007] Claim 3 of Patent Document 1 states, "A radiation-resistant circuit characterized in that the pMOS and nMOS of the analog switch circuit are made of semiconductors made of silicon carbide." [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-32396 [Overview of the project] [Problems that the invention aims to solve]

[0009] By using the SiC MOSFETs mentioned above, radiation resistance can be significantly improved compared to conventional Si elements. However, even SiC elements can degrade in performance if exposed to radiation for extended periods. In particular, in environments where radiation levels increase rapidly and significantly, such as in severe accidents at nuclear power plants, the degradation of the elements may prevent them from providing stable operation.

[0010] This invention has been made in view of these circumstances, and aims to provide a radiation-resistant multiplexer with excellent radiation resistance and a simple configuration. [Means for solving the problem]

[0011] To solve the above problems, the radiation-hardened multiplexer of the present invention comprises: an analog switch circuit composed of MOSFETs having a bandgap wider than that of silicon; a multiplexer circuit having the analog switch circuit as an output stage; and a gate signal control unit having an operating mode that applies a gate signal to turn off all channels of the multiplexer circuit. The multiplexer circuit sets one or more of the multiple input channels as dummy channels that do not use an input signal, and the gate signal control unit sets a predetermined ON time for the dummy channels. It is characterized by the following: Other aspects of the present invention will be described in the embodiments described below. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a radiation-resistant multiplexer with excellent radiation resistance and a simple configuration. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows the configuration of a radiation-hardened multiplexer according to the first embodiment of the present invention. [Figure 2] This figure shows an example of the configuration of an analog switch circuit for a radiation-hardened multiplexer according to the first embodiment of the present invention. [Figure 3] This figure shows an example of the switching sequence of input signals in the multiplexer circuit of a radiation-hardened multiplexer according to the first embodiment of the present invention. [Figure 4] This figure shows an example of a control signal for the multiplexer circuit of a radiation-hardened multiplexer according to the first embodiment of the present invention. [Figure 5] This diagram shows, in table form, the operation of the radiation-hardened multiplexer's all-channel OFF function according to the dose rate in a radiation-hardened multiplexer according to the first embodiment of the present invention. [Figure 6] This diagram shows the configuration of a 4-input, 1-output multiplexer as an example. [Figure 7] Figure 6 shows the radiation exposure effect of a comparative example 4-input 1-output multiplexer. [Figure 8] This figure shows the configuration of a radiation-hardened multiplexer according to a second embodiment of the present invention. [Figure 9] This figure shows an example of the switching sequence of input signals in the multiplexer circuit of a radiation-hardened multiplexer according to a second embodiment of the present invention. [Figure 10] This figure shows an example of a control signal for a multiplexer circuit of a radiation-hardened multiplexer according to a second embodiment of the present invention. [Figure 11] This figure shows the configuration of a radiation-hardened multiplexer according to a third embodiment of the present invention. [Figure 12] This figure shows an example of a control signal for the multiplexer circuit of a radiation-hardened multiplexer according to a third embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and for example, a combination of a plurality of embodiments can be made, or it can be arbitrarily modified without departing from the technical idea of the present invention. Also, in this specification, the same members are denoted by the same reference numerals, and duplicate explanations are omitted. The illustrated content may be changed from the actual configuration within a range that does not impair the gist of the present invention for convenience of illustration.

[0015] (Principle Explanation) As described above, if radiation is continuously irradiated, the characteristics of SiC devices may deteriorate. The inventors experimentally confirmed the radiation degradation characteristics in the energized state using γ-rays for a multiplexer using the developed SiC-MOSFET in the output stage.

[0016] FIG. 6 is a diagram showing the configuration of a 4-input 1-output multiplexer (MUX) 1 of a comparative example. As shown in FIG. 6, the 4-input 1-output multiplexer 1 of the comparative example includes a multiplexer circuit 10 using SiC-MOSFETs. The multiplexer circuit 10 includes four analog switch circuits 11 to 14, and channel signals CH1, CH2, CH3, and CH4 are input to the respective first terminals. The channel signals CH1, CH2, CH3, and CH4 are output signals of each multiplexer circuit in the previous stage not shown, or output signals of measuring instruments installed inside the primary containment vessel (PCV: containment vessel of a nuclear power plant). Also, the respective second terminals of the analog switch circuits 11 to 14 are connected to each other and serve as the output terminal of the multiplexer circuit 10. An output signal OUT is output from this output terminal. Also, control signals A1, A2, and G of a decoder circuit not shown are input to the multiplexer circuit 10. A positive power supply VDD (not shown) and a negative power supply VSS (not shown) are supplied to the multiplexer 10.

[0017] FIG. 7 is a diagram showing the influence of radiation irradiation on the 4-input 1-output multiplexer 1 of the comparative example in FIG. 6. The horizontal axis in FIG. 7 indicates the integrated dose [kGy], and the vertical axis in FIG. 7 indicates the leakage current. FIG. 7 is an example in the case where the channel signal CH1 of the 4-input 1-output multiplexer 1 is turned ON (the analog switch circuit 11 is turned ON), and the channel signals CH2, 3, and 4 are turned OFF (the analog switch circuits 12, 13, and 14 are turned OFF).

[0018] In the test results, it was newly discovered that the multiplexer circuit 10 made of SiC has the characteristic that only the leakage current of the turned-ON channel CH1 increases, and the leakage currents of the turned-OFF channels CH2, 3, and 4 hardly increase. The present invention utilizes this new finding and improves the radiation resistance by providing an OFF time for all channels in the SiC-made multiplexer circuit.

[0019] Supplementary explanations will be given about SiC and the multiplexer (MUX). <Differences between Si and SiC> Since the oxide film near the interface of Si is clean, there are few defects. In SiC, defects exist in the oxide film near the interface. Although SiC reduces defects with nitrogen termination etc., it has more defects than Si.

[0020] <Radiation influence on the multiplexer (MUX)> Since the multiplexer is a digital device, its integration degree is about one digit higher than that of analog devices, and since a plurality of MOSFETs are mounted, it is vulnerable to radiation. By changing the analog switch circuit constituting the multiplexer from Si to wide-bandgap SiC, the influence of charge accumulation by radiation can be reduced. It has been experimentally confirmed that this can significantly reduce the degradation due to radiation. By using SiC for the analog switch circuit constituting the multiplexer, it was confirmed that it could operate up to an integrated dose of 500 [kGy]. However, an increase in leakage current was observed in the ON channel, as shown in Figure 7. Depending on the measurement target and cable length, an error of several percent may occur with thermocouples laid over long distances within the PCV.

[0021] (First embodiment) Figure 1 shows the configuration of a radiation-hardened multiplexer (MUX) according to the first embodiment of the present invention, based on the basic principles described above. A 4-input, 1-output multiplexer will be explained as an example. Furthermore, gamma rays will be used as an example of radiation. [Radiation-resistant multiplexer 100] As shown in Figure 1, the radiation-hardened multiplexer (MUX) 100 comprises a multiplexer circuit 110 composed of SiC-MOSFETs (MOSFETs having a bandgap wider than that of silicon) and a gate signal control unit 120 having an operating mode that turns off the gate voltage of all channels of the multiplexer circuit 110.

[0022] <Multiplexer circuit 110> The multiplexer circuit 110 is equipped with four analog switch circuits 101 (SW1 to SW4), each receiving input signals S1, S2, S3, and S4 at its first terminal (SW1 to SW4 are collectively referred to as SW). Input signals S1, S2, S3, and S4 are output signals from measuring instruments installed inside the PCV. Furthermore, if the radiation-hardened multiplexer 100 consists of a combination of multiple stages of multiplexer circuits, input signals S1, S2, S3, and S4 are output signals from each preceding multiplexer circuit.

[0023] Furthermore, the analog switch circuits 101 (SW1~SW4) output output signals X1, X2, X3, and X4 to their second terminals. The second terminals of each of the analog switch circuits 101 (SW1~SW4) are connected to each other and serve as the output terminals of the multiplexer circuit 110. The output signal OUT is output from these output terminals. Furthermore, the multiplexer circuit 110 receives control signals A1, A2, and 7G for switching the analog switch circuits 101 (SW1 to SW4). The analog switch circuits 110 are supplied with a positive power supply VDD and a negative power supply VSS.

[0024] In Figure 1, the 4-input, 1-output multiplexer circuit 110 is provided with analog switch circuits 101 for output signals X1 to X4, corresponding to input signals S1 to S4. Control signals for switching these switches are input from three locations: A1, A2, and G. The output signal is output from OUT.

[0025] The radiation resistance of the multiplexer circuit 110 can be significantly improved by using SiC MOSFETs instead of conventional Si. However, experimental studies have shown that even with a SiC multiplexer, exposure to radiation on the order of MGy or higher increases the leakage current, which can affect the measurement error of the input signal (see Figure 7 in the comparative example below).

[0026] <Configuration of analog switch circuit 101> Figure 2 shows an example of the configuration of the analog switch circuit 101. The analog switch circuit 101 is constructed by connecting a p-type MOSFET, pMOS111, and an n-type MOSFET, nMOS112, in parallel. The pMOS111 and nMOS112 are made using semiconductors with a wider (higher) bandgap than Si, such as SiC (silicon carbide).

[0027] The gate electrode 1001 of the pMOS111 receives switching signal A. The gate electrode 1002 of the nMOS112 is input to a switching signal A￣ (where "￣" represents an inverting signal). The analog switch circuit 101 is switched on or off by switching signals A and A-. When the analog switch circuit 101 is switched on, switching signal A is set to a low potential (negative potential, L) and switching signal A- is set to a high potential (positive potential, H), causing both pMOS 111 and nMOS 112 to conduct (ON). When the analog switch circuit 101 is turned off, switching signal A is set to a high potential (positive potential, H) and switching signal A- is set to a low potential (negative potential, L), causing both pMOS 111 and nMOS 112 to turn off.

[0028] The analog switch circuit 101 is installed in a radiation area with high radiation doses, for example, inside the containment vessel (PCV) of a nuclear power plant.

[0029] <Effects of radiation on analog switch circuit 101> Next, we will explain the effects of radiation on the analog switch circuit 101. Since the analog switch circuit 101 is in an environment exposed to radiation, the pMOS 111 and nMOS 112 semiconductor elements that make up the analog switch circuit 101 may degrade due to radiation. This radiation-induced degradation is more pronounced the lower the band gap of the semiconductor. Therefore, pMOS and nMOS semiconductor elements using Si (silicon), which has a relatively low band gap, are susceptible to radiation-induced degradation. To reduce this radiation-induced degradation, SiC, which has a higher band gap than Si, is used in the pMOS111 and nMOS112 shown in Figure 2. However, even with pMOS111 and nMOS112 using SiC, which has a relatively high band gap, the leakage current increases only in the ON channel CH, and radiation-induced degradation may occur.

[0030] In pMOS111 and nMOS112 using SiC, continuous exposure to radiation causes degradation of pMOS(111) before that of nMOS(112). Specifically, the ionization effect of radiation increases the leakage current.

[0031] <Gate signal control unit 120> The gate signal control unit 120 performs gate signal control on the multiplexer circuit 110, which is composed of SiC-MOSFETs, to turn off all channels.

[0032] Figure 3 shows an example of the switching sequence of input signals in the multiplexer circuit 110. In Figure 3, the horizontal axis represents time, and the vertically aligned S1 to S4 represent the input signals of the 4-input 1-output multiplexer circuit 110. OFF in Figure 3 indicates that all channels are turned OFF. The bidirectional arrows a to e in Figure 3 represent the operating time for each mode.

[0033] The multiplexer circuit 110 designates one or more of its multiple input channels as an active channel that uses the input signal, and the gate signal control unit 120 makes the OFF time for all channels of the multiplexer circuit 110 longer than the ON time for the active channel.

[0034] In Figure 3, by providing an ON time for each channel (active channel) (two-way arrows a-d in Figure 3) as well as a time when all channels are OFF (two-way arrow e in Figure 3), the rate of degradation can be reduced even in a radiation environment, enabling stable use for extended periods.

[0035] In the operating mode where the all-channel OFF function is activated, observing the input signal is difficult. Therefore, if there is a sharp change in the input signal while the "operating mode" is running with the all-channel OFF function, it may not be possible to observe it. For this reason, it is more suitable for measuring instruments where sharp changes in measured values ​​do not occur and measurement intervals on the order of milliseconds or seconds are acceptable, such as pressure gauges and thermometers, as the impact of the OFF function is less. However, by controlling the above "operating mode," it is also possible to apply it to safety systems that require constant monitoring and to measuring instruments with sharp changes.

[0036] In Figure 3, the multiplexer circuit 110 is switched in the order of S1, S2, S3, S4, and all channels OFF, but this order can be changed arbitrarily depending on the application.

[0037] Here, increasing the time all channels are OFF (double-headed arrow e in Figure 3) improves radiation tolerance. On the other hand, in low-radiation environments, the measurement accuracy of each channel can be improved by setting the time all channels are OFF (double-headed arrow e in Figure 3) to 0 or as short as possible. It is desirable to arbitrarily change the time all channels are OFF based on the radiation dose around the multiplexer (see Normal Operation, DBA, LOCA, SA in Figure 5).

[0038] Figure 4 shows an example of a control signal for the multiplexer circuit 110. Multiplexers are generally controlled by digital signals of 1 and 0. Therefore, in this embodiment, the switching operation will be explained using control signals of 1 and 0. A1 and A2 in Figure 4 are control signals for switching the switches of the multiplexer circuit 110. G in Figure 4 is a control signal for activating the all-channel OFF function.

[0039] The leftmost column in Figure 4 shows which switches are ON, while OFF indicates that all channels are OFF. For example, when (A1, A2, G) = (0, 0, 0), it means that X1 is ON and X2, X3, and X4 are OFF. When G = 1, all channels are OFF regardless of the signals of A1 and A2.

[0040] The gate signal control unit 120 (Figure 1) has an operating mode in which it applies a gate signal that turns off all channels of the multiplexer circuit 110, as shown in G=1 in Figure 4.

[0041] The control method described above is just one example of the operation of the all-channel OFF function; the control signal levels, switching order, and the correspondence between control signals and switching operations can be freely selected.

[0042] Figure 5 is a table showing the operation of the radiation-hardened multiplexer 100's all-channel OFF function according to the dose rate. As shown in Figure 5, the "All Channels OFF function" is turned OFF or ON in each of the following scenarios: normal operation, DBA (Design Basis Accident), LOCA (Loss of Coolant Accident), and SA (Severe Accident). A DBA is a hypothetical accident that represents the characteristics of a power reactor facility and is considered sufficiently typical in terms of the radiation impact on employees and the nearby public. LOCA is an accident in which piping or other components connected to the reactor are damaged, causing the reactor coolant to leak out. SA is an event that significantly exceeds the design baseline event and can result in serious damage to the reactor core. Note that the asterisk (*) in Figure 5 for DBA indicates that the default setting is OFF for the "All Channels OFF function," but it is desirable to turn ON the "All Channels OFF function" if the dose rate increases above normal operating levels.

[0043] Thus, the gate signal control unit 120 (Figure 1) turns the "all-channel OFF function" operating mode OFF or ON in normal operation, DBA, LOCA, and SA, respectively.

[0044] The operation of the radiation-hardened multiplexer 100, configured as described above, will be explained below. The radiation-hardened multiplexer (MUX) 100 comprises a multiplexer circuit 110 composed of SiC-MOSFETs and a gate signal control unit 120 having an operating mode that turns off the gate voltage of all channels of the input signal input to the multiplexer circuit 110.

[0045] The gate signal control unit 120 performs gate signal control on the multiplexer circuit 110, which is composed of SiC-MOSFETs, to turn off all channels. For example, as shown in Figure 3, the gate signal control unit 120 provides a time for all channels to be OFF in addition to the ON time for each channel.

[0046] [Effects of the first embodiment] As described above, the radiation-hardened multiplexer 100 (Figure 1) according to this embodiment comprises an analog switch circuit 101 composed of MOSFETs (in this embodiment, SiC-MOSFETs) having a bandgap wider than that of silicon, a multiplexer circuit 110 having the analog switch circuit 101 as an output stage, and a gate signal control unit 120 having an operating mode that applies a gate signal to turn off all channels of the multiplexer circuit 110.

[0047] This configuration allows for an OFF time for all channels in the SiC multiplexer circuit 110. By turning off all channels, the increase in leakage current in the analog switch circuit 101 is suppressed, thereby delaying the progression of radiation degradation. This reduces the rate of degradation even in radiation environments, enabling stable use over long periods. As a result, it offers excellent radiation resistance and enables normal multiplexer switching operation even in harsh radiation environments with a simple configuration.

[0048] In high-radiation environments such as nuclear power plants, the radiation-resistant multiplexer 100 (Figure 1) according to this embodiment can achieve both high radiation resistance and operational stability. This can contribute to improving the reliability of plant operation.

[0049] In the radiation-hardened multiplexer 100A (Figure 1), the multiplexer circuit 110 sets one or more of its multiple input channels as an active channel that uses the input signal, and the gate signal control unit 120 makes the OFF time for all channels of the multiplexer circuit 110 (bidirectional arrow e in Figure 3) longer than the ON time for the active channel (bidirectional arrows a to d in Figure 3).

[0050] By doing so, the effect of slowing down the progression of radiation degradation by turning off all channels can be effectively achieved, further improving radiation resistance. Furthermore, by shortening the time that the all-channel-off function is activated, it can also be applied to safety systems that require constant monitoring and to measuring instruments with rapid changes.

[0051] Furthermore, while SiC-MOSFETs are preferable for MOSFETs with a bandgap wider than that of silicon, any semiconductor can be used as long as it can produce n-type and p-type MOSFETs and has a wider bandgap than Si.

[0052] Furthermore, although this embodiment uses a 4-input, 1-output multiplexer (MUX) as an example, the same applies when the number of inputs increases, such as to 16-input, 1-output or 32-input, 1-output.

[0053] (Second embodiment) Figure 8 shows the configuration of a radiation-hardened multiplexer according to a second embodiment of the present invention. The same reference numerals are used for components identical to those in Figure 1, and the explanation of the redundant parts is omitted.

[0054] As shown in Figure 8, the radiation-hardened multiplexer (MUX) 100A is composed of SiC-MOSFETs and includes a multiplexer circuit 110 that makes one or more of the multiple input channels dummy channels that do not use an input signal, and a gate signal control unit 120A that has an operating mode that sets a predetermined ON time for the dummy channels of the multiplexer circuit 110. The radiation-hardened multiplexer 100A shown in Figure 8 differs from the radiation-hardened multiplexer 100 shown in Figure 1 in two ways: it has only two control signals, A1 and A2, and one of the input signals is a dummy channel (GND).

[0055] The radiation-hardened multiplexer (MUX) 100A has an operating mode in which the multiplexer circuit 110 sets one or more of the multiple input channels as a dummy channel (GND) that does not use an input signal, and the gate signal control unit 120A sets a predetermined ON time for the dummy channel (GND).

[0056] The gate signal control unit 120A has an operating mode in which the ON time of the dummy channel (GND) is made longer than the ON time of the active channel.

[0057] <Purpose of the dummy channel (GND)> (1) The GND input signal of the multiplexer circuit 110 is an unused channel and will not be affected by degradation. Therefore, by using a dummy channel (GND) for GND, the effects of degradation are borne by the dummy channel (GND), thereby delaying the progression of radiation degradation in the active channels (active channels) to which input signals S1 to S3 are input. By increasing the ON time of the dummy channel (GND), it is possible to improve radiation tolerance. However, increasing the ON time of the dummy channel (GND) reduces the ON time of the active channels, which affects the measurement accuracy of the channels.

[0058] (2) The 100A radiation-hardened multiplexer uses a dummy channel (GND) as a pilot signal to measure changes in leakage current due to radiation. The pilot signal is a known signal (e.g., a fixed DC voltage). A pilot signal is input to the dummy channel (GND), and the analog switch circuit 101 transmits this pilot signal. In SiC, pMOS transistors degrade faster than nMOS transistors due to radiation. This radiation degradation affects the current flowing through pMOS 111 and nMOS 112 differently. By inputting a pilot signal and detecting the signal distortion caused by the difference in degradation between pMOS 111 and nMOS 112 ("degradation monitoring"), the radiation-induced degradation state of the analog switch circuit 101 can be diagnosed.

[0059] Figure 9 shows an example of the switching sequence of input signals in the multiplexer circuit 110. Components identical to those in Figure 3 are denoted by the same reference numerals, and explanations of the overlapping parts are omitted. As shown in Figure 9, the radiation-hardened multiplexer 100A reduces radiation degradation of the active channels (S1, S2, S3) (bidirectional arrows a-c in Figure 9) by having the multiplexer circuit 110 designate one or more of the multiple input channels as dummy channels (GND) that do not use input signals, and by having the gate signal control unit 120 provide an ON time (bidirectional arrow f in Figure 9) for the dummy channels (GND).

[0060] Furthermore, the radiation-hardened multiplexer 100A uses a dummy channel (GND) in addition to the active channels (S1, S2, S3) by switching them sequentially. This order can be changed as needed depending on the application.

[0061] Here, increasing the ON time of the dummy channel (double-headed arrow d in Figure 5) improves radiation resistance. On the other hand, in low-radiation environments, setting the ON time of the dummy channel (double-headed arrow d in Figure 9) to 0 or as short as possible improves the measurement accuracy of each channel. It is desirable to arbitrarily change the ON time of this dummy channel based on the radiation dose around the multiplexer.

[0062] Figure 10 shows an example of a control signal for the multiplexer circuit 110. Components identical to those in Figure 4 are denoted by the same reference numerals, and explanations of the overlapping parts are omitted. Similar to Figure 4, the switching operation will be explained using control signals of 1 and 0. A1 and A2 are control signals for switching the multiplexer switches. The leftmost column in Figure 10 shows which switches are ON. For example, when (A1, A2) = (0, 0), it indicates that X1 is ON and X2, X3, and X4 are OFF.

[0063] The control method described above is just one example of the operation of the all-channel OFF function; the control signal levels, switching order, and the correspondence between control signals and switching operations can be freely selected.

[0064] In the above configuration, the radiation-hardened multiplexer 100A has a gate signal control unit 120A that sets the ON time for the dummy channel (GND). This makes it possible to reduce the degradation of the active channels (S1, S2, S3). By making the ON time of the dummy channel (GND) longer than the ON time of the active channels, further improvement in radiation hardening performance is possible.

[0065] [Effects of the second embodiment] In the radiation-hardened multiplexer 100A (Figure 8) according to the second embodiment of the present invention, the multiplexer circuit 110 sets one or more of the multiple input channels as a dummy channel (GND) that does not use an input signal, and the gate signal control unit 120A sets an ON time for the dummy channel (GND).

[0066] The GND input signal of the multiplexer circuit 110 is an unused channel and will not be affected by degradation. By having the dummy channel (GND) bear the burden of degradation, radiation degradation of the active channels (S1, S2, S3) can be reduced. Furthermore, the radiation resistance of the multiplexer can be improved with a simpler configuration than the radiation-resistant multiplexer 100 (Figure 1) according to the first embodiment.

[0067] In the radiation-hardened multiplexer 100A (Figure 8), the multiplexer circuit 110 uses one or more of the multiple input channels as active channels that use the input signal, and switches between the active channels and the dummy channel (GND) in sequence.

[0068] In this way, by sequentially switching between the active channel and the dummy channel (GND), the cumulative radiation degradation can be distributed across each channel. As a result, the progression of radiation degradation can be delayed for the entire device, enabling stable operation over long periods.

[0069] In the radiation-hardened multiplexer 100A (Figure 8), the gate signal control unit 120A makes the ON time of the dummy channel (GND) (bidirectional arrow d in Figure 5) longer than the ON time of the active channels (bidirectional arrows a-c in Figure 5).

[0070] By doing so, the ON time of GND can be made longer than the ON time of the active channels, further improvement in radiation tolerance is possible. The longer the ON time of the dummy channel (GND), the better the radiation tolerance can be. In low-radiation environments, the measurement accuracy of each channel can be improved by making the ON time of the dummy channel (GND) zero or as short as possible.

[0071] In the radiation-hardened multiplexer 100A (Figure 8), a pilot signal (for example, a known signal such as a fixed DC voltage) is input to the dummy channel (GND), and the change in the leakage current of the analog switch circuit 101 due to radiation is measured.

[0072] By doing so, the radiation resistance of the multiplexer can be improved with a simple configuration, and degradation due to radiation exposure can be diagnosed (the degree of degradation of the multiplexer can be diagnosed).

[0073] (Third embodiment) Figure 11 shows the configuration of a radiation-hardened multiplexer according to a third embodiment of the present invention. The same reference numerals are used for components identical to those in Figure 1, and the explanation of the redundant parts is omitted.

[0074] As shown in Figure 11, the radiation-hardened multiplexer (MUX) 100B comprises a multiplexer circuit 110B composed of SiC-MOSFETs and a gate signal control unit 120B having an operating mode that turns off the gate voltage of all channels of the input signal input to the multiplexer circuit 110B. The radiation-hardened multiplexer 100B shown in Figure 11 differs from the radiation-hardened multiplexer 100 shown in Figure 1 in that the analog switch circuits corresponding to each signal line are doubled in parallel. The radiation-hardened multiplexer 100B features a multiplexer circuit 110B that includes two or more analog switch circuits SW in parallel, corresponding to each channel.

[0075] The multiplexer circuit 110B is equipped with eight analog switch circuits (SW11 and SW21, SW12 and SW22, SW13 and SW23, SW14 and SW24), and input signals S1, S2, S3, and S4 are input to the first terminal of each. The circuit configuration of the analog switch circuits (SW11 and SW21, SW12 and SW22, SW13 and SW23, SW14 and SW24) is similar to, for example, the analog switch circuit 101 shown in Figure 2.

[0076] Furthermore, the analog switch circuits (SW11 and SW21, SW12 and SW22, SW13 and SW23, SW14 and SW24) output output signals X1 and Y1, X2 and Y2, X3 and Y3, and X4 and Y4 to their second terminals. The second terminals of each of the analog switch circuits (SW11 and SW21, SW12 and SW22, SW13 and SW23, SW14 and SW24) are connected to each other and form the output terminals of the multiplexer circuit 110B. The output signal OUT is output from these output terminals. Furthermore, the multiplexer circuit 110 receives control signals A1, A2, and A3 for switching between analog switch circuits (SW11 and SW21, SW12 and SW22, SW13 and SW23, and SW14 and SW24).

[0077] In Figure 11, the 4-input, 1-output multiplexer circuit 110B is provided with analog switch circuits for output signals X1-X4 and Y1-Y4, corresponding to input signals S1-S4. Control signals for switching these analog switch circuits 101 are input from three locations: A1, A2, and A3. The output signal is output from OUT.

[0078] In the above configuration, the radiation-hardened multiplexer (MUX) 100B, in environments with low radiation dose rates, switches the gate signal control unit 120B to switch X (analog switch circuits SW11, SW12, SW13, SW14) to use switch X (analog switch circuits SW11, SW12, SW13, SW14). Furthermore, if switch X (analog switch circuits SW11, SW12, SW13, SW14) is degraded by radiation, the gate signal control unit 120B switches to switch Y (analog switch circuits SW11, SW12, SW13, SW14). By providing redundancy to the analog switch circuit 110B in this way, it is possible to improve radiation hardiness.

[0079] The switch from switch X (analog switch circuits SW11, SW12, SW13, SW14) to switch Y (analog switch circuits SW11, SW12, SW13, SW14) may be switched automatically when a certain cumulative dose is exceeded, or it may be switched manually at any time.

[0080] Alternatively, as in the radiation-hardened multiplexer 100B of the second embodiment, one of the input signals may be set to GND or a pilot signal (see Figures 8 and 9) to monitor the degree of degradation, and a mechanism may be used to switch to switch Y when a certain degree of degradation is exceeded.

[0081] Figure 12 shows an example of the control signal for the multiplexer circuit 110B. Components identical to those in Figure 4 are denoted by the same reference numerals, and explanations of the overlapping parts are omitted.

[0082] Similar to Figure 4, the switching operation will be explained using control signals of 1 and 0. A1, A2, and A3 are control signals for switching the multiplexer switches.

[0083] The leftmost column in Figure 12 shows which switches are ON. For example, when (A1, A2, A3) = (0, 0, 0), it indicates that X1 is ON and X2, X3, X4, Y1, Y2, Y3, and Y4 are OFF.

[0084] The control method described above is just one example of the operation of the all-channel OFF function; the control signal level, switching order, and the correspondence between the control signal and the switching operation can be selected.

[0085] [Effects of the third embodiment] A radiation-hardened multiplexer 100B (Figure 11) according to a third embodiment of the present invention comprises a multiplexer circuit 110B that includes two or more analog switch circuits SW corresponding to each channel, connected in parallel.

[0086] By doing so, the analog switch circuit 110B can be made redundant, thereby improving its radiation resistance. Specifically, (1) if one switch group deteriorates due to radiation, it can be switched to the other switch group. Alternatively, (2) by sequentially switching between one switch group and the other switch group, the cumulative radiation degradation can be distributed within the analog switch circuit. In either case (1) or (2) above, the progression of radiation degradation can be delayed for the entire device, enabling stable use over a long period of time.

[0087] It should be noted that the present invention is not limited to the configurations described in the embodiments above, and its configuration can be modified as appropriate without departing from the gist of the invention as described in the claims. There are various types of SiC, and any type is applicable.

[0088] The above-described embodiments are explained in detail for the purpose of clearly illustrating the present invention, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0089] 100, 100A, 100B Radiation-Resistant Multiplexer (MUX) 110, 110A, 110B Multiplexer Circuit 101 Analog Switch Circuit 111 pMOS (MOSFETs with a bandgap wider than that of silicon) 112 nMOS (MOSFETs with a bandgap wider than that of silicon) 120 Gate signal control unit SiC-MOSFET: A MOSFET with a bandgap wider than that of silicon. SW1~SW4 Analog Switch Circuit S1, S2, S3, S4 Input Signals GND dummy channel

Claims

1. An analog switch circuit composed of MOSFETs (metal-oxide-semiconductor field-effect transistors) having a bandgap wider than that of silicon, A multiplexer circuit having the aforementioned analog switch circuit as its output stage, The system includes a gate signal control unit having an operating mode that applies a gate signal to turn off all channels of the multiplexer circuit, The multiplexer circuit sets one or more of the multiple input channels as dummy channels that do not use an input signal. The gate signal control unit provides a predetermined ON time for the dummy channel. A radiation-resistant multiplexer characterized by the following features.

2. The MOSFET in the analog switch circuit is configured to have a semiconductor made of silicon carbide. The radiation-resistant multiplexer according to feature 1.

3. The multiplexer circuit sets one or more of the multiple input channels as active channels that use the input signal. The gate signal control unit sets the OFF time for all channels of the multiplexer circuit to be longer than the ON time for the active channel. The radiation-resistant multiplexer according to feature 1.

4. The multiplexer circuit sets one or more of the multiple input channels as active channels that use the input signal. The active channel and the dummy channel are used by switching between them in sequence. The radiation-resistant multiplexer according to feature 1.

5. The gate signal control unit sets the ON time of the dummy channel to be longer than the ON time of the active channel. The radiation-resistant multiplexer according to feature 4.

6. A pilot signal is input to the dummy channel, and the change in the leakage current of the analog switch circuit due to radiation is measured. The radiation-resistant multiplexer according to feature 1.

7. The multiplexer circuit comprises two or more of the analog switch circuits corresponding to each channel, arranged in parallel. The radiation-resistant multiplexer according to feature 1.

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