Output circuit, electronic device, and signal transmission system

Abstract

The present invention provides an output circuit capable of lowering output impedance while using a diamond semiconductor, and an electronic device and a signal transmission system that include said output circuit. To that end, an output circuit (10) includes a field-effect transistor configured to be of the p-channel type and formed on a diamond substrate. The field-effect transistor comprises: a diamond transistor (Q5) that constitutes a drain ground circuit and outputs an output voltage (Vo2) from the source in accordance with an input voltage (Vi2) inputted to the gate; and a diamond transistor (Q6) that supplies a bias current to the diamond transistor (Q5). The diamond transistor (Q6) has normally-on characteristics and constitutes a current source due to the gate and the source being connected to each other.

Description

Output circuit, electronic device and signal transmission system

[0001] The present invention relates to an output circuit, an electronic device, and a signal transmission system, and more particularly to an output circuit having a diamond FET (Field Effect Transistor), and an electronic device and a signal transmission system having the output circuit.

[0002] Patent Document 1 discloses a field-effect transistor that has high radiation resistance while maintaining circuit characteristics. The field-effect transistor includes a non-doped diamond layer whose surface is hydrogen-terminated, a gate electrode formed on the hydrogen-terminated region via an insulating layer, and source and drain electrodes formed on both sides of the insulating layer via p+ diamond layers. The field-effect transistor maintains a transconductance of 0.5 mS / mm or more at room temperature, even after being irradiated with 5 MGy of X-rays.

[0003] Japanese Patent Application Laid-Open No. 2022-104826

[0004] In recent years, there has been an increasing demand for semiconductor devices that can operate stably in harsh environments, such as high-radiation environments such as those found in nuclear reactors and aerospace, and high-temperature environments such as those found in industrial machinery and automotive applications. Conventional silicon-based semiconductor elements have difficulty functioning properly in these harsh environments. For this reason, the use of wide-bandgap semiconductors has been widely considered. Diamond semiconductors, in particular, are expected to be suitable for harsh environments due to their strong bonding, large bandgap, and high thermal conductivity.

[0005] On the other hand, low output impedance is generally required for the output circuit. For example, using a push-pull circuit or the like configured with complementary transistors can easily meet this requirement. In diamond semiconductors, p-channel transistors with practical level performance can be realized, for example, by a configuration such as that shown in Patent Document 1. However, it is difficult to realize n-channel transistors with practical level performance. Therefore, a mechanism for lowering output impedance under such constraints is required.

[0006] One possible mechanism for lowering the output impedance is to use a source follower circuit, for example. A source follower circuit generally consists of a drain-grounded transistor and a current source that supplies a bias current to the transistor. The current source can be realized, for example, by a transistor to which a fixed voltage is applied to the gate. However, with diamond semiconductors, it is difficult to obtain semiconductors such as bandgap reference circuits and Zener diodes, and it is not easy to obtain a desired fixed voltage corresponding to the required bias current value. For this reason, it has not been easy to use a source follower circuit with diamond semiconductors.

[0007] Therefore, one object of the present invention is to provide an output circuit that uses a diamond semiconductor and is capable of lowering the output impedance, and an electronic device and a signal transmission system that include such an output circuit.

[0008] The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0009] Among the inventions disclosed in this application, a brief outline of a representative embodiment will be described as follows.

[0010] An output circuit according to one embodiment includes a p-channel field-effect transistor formed on a diamond substrate. The field-effect transistor forms a common-drain circuit and includes an output transistor that outputs an output voltage from its source in response to an input voltage input to its gate, and a bias transistor that supplies a bias current to the output transistor. The bias transistor has normally-on characteristics, and forms a current source by connecting its gate and source.

[0011] To briefly explain the effect obtained by a representative embodiment of the invention disclosed in this application, it becomes possible to reduce output impedance while using a diamond semiconductor.

[0012] 1A is a cross-sectional view showing an example of a device configuration of a diamond FET used in an output circuit according to one embodiment. FIG. 1B is a diagram showing an example of the electrical characteristics of the diamond FET shown in FIG. 1A. FIG. 1C is a circuit diagram showing an example of a configuration of a main part of an electronic device according to a first embodiment. FIG. 1D is a schematic diagram showing an example of a configuration of a main part of a signal transmission system according to a second embodiment. FIG. 1E is a circuit diagram showing a detailed configuration example and an operation example of the electronic device in FIG. 3. FIG. 1F is a circuit diagram showing an example of an equivalent circuit of the signal transmission system shown in FIG. 3. FIG. 1G is a waveform diagram showing an example of an input voltage and an output voltage when a compensation circuit is not provided in FIG. 5. FIG. 6A is a Bode plot showing an example of frequency characteristics in FIG. 6A. FIG. 6G is a waveform diagram showing an example of an input voltage and an output voltage when a compensation circuit is provided in FIG. 5. FIG. 7A is a Bode plot showing an example of frequency characteristics when the output resistance of the output stage is reduced compared to FIG. 6B. FIG. 7B is a Bode plot showing an example of frequency characteristics when the output resistance of the output stage is reduced compared to FIG. 7B. FIG. 1G is a diagram showing guideline parameter values ​​of the compensation circuit according to the scale of the system in the signal transmission systems shown in FIGS. 3 and 5. FIG. 1H is a graph showing an example of the relationship between the transmission line length and the time constant of the load in FIG. 11 is a graph showing an example of the relationship between the transmission line length and the capacitance value of the compensation capacitor in FIG. 10 .

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, the same components are generally designated by the same reference numerals, and repeated description thereof will be omitted.

[0014] <About the Diamond FET> Figure 1A is a cross-sectional view showing an example of the device configuration of a diamond FET used in an output circuit according to one embodiment. Figure 1A shows a p-channel field effect transistor (FET) formed on a diamond substrate. In the specification, such a p-channel field effect transistor will be simply referred to as a diamond transistor Q. The diamond transistor Q shown in Figure 1A comprises a diamond substrate 15, p+ contact layers 16a, 16b, an insulating film 17, a source (S) electrode 18, a drain (D) electrode 19, and a gate (G) electrode 20.

[0015] The insulating film 17 is disposed on the diamond substrate 15 and has a thickness of, for example, about 5 nm to 100 nm. ２ O ３ , SiO ２ , CaF ２ , HfO ２ , AlN, BN, Si ３ N ４ , SiON, Ta ２ O ５ , TiO ２ , W.O. ３ , LaF ３ , MgF ２ , Y.F. ３ , LiF, LiF ３ The insulating film 17 is composed of any one of the above or any combination thereof. Spaces such as an air layer, a vacuum layer, and an air gap are also considered to be a type of insulating film 17. The gate (G) electrode 20 is disposed on the diamond substrate 15 via the insulating film 17.

[0016] The p+ contact layers 16a and 16b are disposed on both sides of the insulating film 17 on the diamond substrate 15, and have a thickness of, for example, approximately 20 nm to 300 nm. The p+ contact layers 16a and 16b are formed by implanting a predetermined concentration of boron (B) into the diamond material. A source (S) electrode 18 is disposed on the diamond substrate 15 via one of the p+ contact layers 16a. A drain (D) electrode 19 is disposed on the diamond substrate 15 via the other p+ contact layer 16b.

[0017] The source (S) electrode 18, the drain (D) electrode 19, and the gate (G) electrode 20 are made of, for example, gold (Au), ruthenium (Ru), aluminum (Al), titanium (Ti), molybdenum (Mo), copper (Cu), chromium (Cr), lead (Pb), zinc (Zn), or platinum (Pt), or a combination thereof. The film thickness of each electrode is, for example, about 10 nm to 100 nm.

[0018] In this configuration, hole carriers are accumulated on the surface of the diamond substrate 15, for example, by hydrogen termination, i.e., by forming C—H bonds. Such a diamond FET is also called a hydrogen-terminated diamond FET. The accumulation of hole carriers forms a two-dimensional hole gas layer (2DHG), in other words, a channel 21, on the surface of the diamond substrate 15. Furthermore, a depletion layer is formed in the channel 21, and the thickness of this depletion layer changes depending on the gate-source voltage Vgs. As a result, the concentration of the two-dimensional electron gas, and therefore the magnitude of the drain-source current Ids, can be controlled by the gate-source voltage Vgs.

[0019] In some cases, the p+ contact layers 16a and 16b are not necessary. For example, when a hydrogen-terminated diamond FET is used, an electrode made of gold (Au) is in ohmic contact with the diamond substrate 15. In this case, the source (S) electrode 18 and the drain (D) electrode 19 can be formed without the p+ contact layers 16a and 16b.

[0020] Figure 1B is a diagram showing an example of the electrical characteristics of the diamond FET shown in Figure 1A. Figure 1B shows how the characteristics of the drain-source current Ids with respect to the drain-source voltage Vds change depending on the gate-source voltage Vgs. Details will be described later, but in the embodiment, a plurality of diamond transistors Q as shown in Figure 1A are used. At least a portion of the plurality of diamond transistors Q has normally-on characteristics, in other words, depletion-type characteristics, as shown in Figure 1B.

[0021] When having normally-on characteristics, even when the gate-source voltage Vgs is 0V, by applying a negative drain-source voltage Vds, a negative drain-source current Ids flows. That is, by applying a negative voltage to the drain with respect to the source, a current flows from the source to the drain. Note that other parts of the multiple diamond transistors Q may have either normally-on or normally-off characteristics. When having normally-off characteristics, the drain-source current Ids does not flow when the gate-source voltage Vgs is 0V, but flows when a negative gate-source voltage Vgs is applied.

[0022] In addition, the diamond transistor Q shown in Figure 1A is a p-channel type. Therefore, as shown in Figure 1B, the more the positive gate-source voltage Vgs increases, the more the drain-source current Ids approaches zero, and the more the negative gate-source voltage Vgs increases, the more the negative drain-source current Ids increases. That is, the more a positive voltage is applied to the gate relative to the source, the more the drain-source current Ids approaches zero, and the more a negative voltage is applied to the gate relative to the source, the more a large current flows from the source to the drain. In the example of Figure 1B, when the gate-source voltage Vgs exceeds about 4V, the drain-source current Ids becomes zero.

[0023] Here, compared to silicon materials, diamond materials can operate at temperatures about 5 times higher, voltages about 30 times higher, and have thermal conductivity about 20 times higher. Therefore, it is expected that a circuit including a diamond transistor Q as shown in Figure 1A will be used in harsh environments where silicon materials cannot withstand sufficiently.

[0024] However, when a circuit is constructed using the diamond transistor Q, there are specific constraints that differ from those when a circuit is constructed using, for example, a MOSFET (Metal Oxide Semiconductor FET) on a silicon substrate, etc. One of these constraints is that it is difficult to realize an n-channel diamond transistor at a practical level, as opposed to the p-channel diamond transistor Q shown in Figure 1A.

[0025] For this reason, when configuring a circuit using the diamond transistor Q, it is not possible to apply a push-pull circuit that combines p-channel and n-channel types, which is common in MOSFETs, etc., and various ingenuity is required. As one of them, a mechanism is required to reduce the output impedance using only p-channel types. Therefore, it is beneficial to use the output circuit shown in each embodiment described below, and the electronic device and signal transmission system having the output circuit. Note that the configuration of the diamond transistor Q is not limited to the configuration example shown in Figure 1A, and it is sufficient that it is at least a p-channel field effect transistor formed on a diamond substrate.

[0026] (First embodiment) <Configuration and operation of electronic device> Figure 2 is a circuit diagram showing an example configuration of the main parts of an electronic device according to a first embodiment. The electronic device 10 shown in Figure 2 includes an amplifier stage (amplifier circuit) 11 and an output stage (output circuit) 12 provided subsequent to the amplifier stage 11, in other words, as the final stage. The amplifier stage 11 includes diamond transistors Q1-Q4, resistor elements R1, R3, and R4, and a coupling capacitor Cc2.

[0027] The diamond transistor Q4 is a bias transistor and supplies a bias current to the diamond transistors Q1 and Q2 in parallel. The source of the diamond transistor Q4 is supplied with a high-potential power supply voltage, here the positive power supply voltage VDp. The diamond transistor Q4 is connected between the gate and source, specifically, via a resistor element R4 connected to the source, thereby forming a current source. The current value of the current source is set based on the resistance value of the resistor element R4.

[0028] The drain of the diamond transistor Q1 is supplied with a low-potential power supply voltage, here a negative power supply voltage VDn. The source of the diamond transistor Q1 is connected to the drain of the diamond transistor Q4 and the source of the diamond transistor Q2 via a common node Nc. In addition, the bias current from the diamond transistor Q4 is shunted and supplied to the sources of the diamond transistors Q1 and Q2.

[0029] Diamond transistors Q1 and Q2 are amplifying transistors that form a differential pair in a differential amplifier circuit. In this case, diamond transistor Q4 forms a tail current source for the differential amplifier circuit and serves as a tail transistor that supplies tail current to diamond transistors Q1 and Q2. Diamond transistors Q1 and Q2 also form a common-source circuit in the differential amplifier circuit.

[0030] The amplifier stage 11 receives the input voltage V ＩＮ is input as an input voltage Vi1 via a coupling capacitor Cc1. The diamond transistor Q1 inputs the input voltage Vi1 to its gate. The drain current of the diamond transistor Q1 changes according to changes in the input voltage Vi1. In this example, since there is no need to convert the drain current into a voltage and output it, the drain of the diamond transistor Q1 is fixed to the negative power supply voltage VDn.

[0031] On the other hand, the change in the drain current of diamond transistor Q1 is transmitted as a change in the drain current of diamond transistor Q2 through the source of diamond transistor Q2, while balancing with the amount of constant current absorbed from diamond transistor Q4.At this time, due to the action of the constant current source constituted by diamond transistor Q4, a current is input to the source of diamond transistor Q2, which is the same amount as the change in the drain (source) current generated by diamond transistor Q1, but the increase / decrease direction is opposite.In addition, the sum of the drain (source) current values ​​of diamond transistors Q1 and Q2 is always equal to the current value of the constant current source by diamond transistor Q4.

[0032] In this case, the diamond transistor Q2 has a reference power supply voltage VS, here the ground power supply voltage (0V), supplied to its gate. Therefore, no voltage is input to the gate of the diamond transistor Q2, and a current equivalent to the inverse of the increase or decrease in the current change that occurred in the diamond transistor Q1 is input to its source. As a result, a drain current equivalent to the reverse direction of the change in drain current in the diamond transistor Q1 flows through the diamond transistor Q2. This drain current forms an output current Io1 between the source and drain of the diamond transistor Q2.

[0033] A negative power supply voltage VDn is supplied to the drain of the diamond transistor Q3. As in the case of the diamond transistor Q4, the gate and source of the diamond transistor Q3 are connected, specifically, via a resistor element R3 connected to the source, thereby forming a current source. The current value of the current source is set based on the resistance value of the resistor element R3.

[0034] Furthermore, the current source configured by the diamond transistor Q3 is connected to the drain of the diamond transistor Q2, and functions as a current source load that converts the output current Io1 to an output voltage Vo1. Therefore, the diamond transistor Q3 is a load transistor that converts the output current Io1 of the amplifying transistors (Q1, Q2) to an output voltage Vo1. The output current Io1 is converted to an output voltage Vo1 by the equivalent resistance value of the current source load.

[0035] The coupling capacitor Cc2 blocks the DC component of the output voltage Vo1 of the diamond transistor Q3 and passes the AC component. As a result, the output stage 12 inputs the input voltage Vi2, which is the AC component, via the coupling capacitor Cc2. The resistor R1 is connected between the gate of the diamond transistor Q1 and the reference power supply voltage VS. The resistor R1 is, for example, a high-resistance element having a resistance value of the M ohm level, and determines the bias point of the gate voltage of the diamond transistor Q1 to the reference power supply voltage VS.

[0036] The output stage (output circuit) 12 includes diamond transistors Q5 and Q6 and resistor elements R5-R7, and outputs the output voltage V ＯＵＴ The diamond transistor Q6 is a bias transistor and supplies a bias current to the diamond transistor Q5. The source of the diamond transistor Q6 is supplied with a positive power supply voltage VDp. The diamond transistor Q6 is connected between the gate and source, specifically, via a resistor element (first resistor element) R6 connected to the source, thereby forming a current source. The current value of the current source is set based on the resistance value of the resistor element R6.

[0037] A negative power supply voltage VDn is supplied to the drain of the diamond transistor Q5. The source of the diamond transistor Q5 is connected to the drain of the diamond transistor Q6 via a resistor element (second resistor element) R7. As a result, a bias current from the diamond transistor Q6 is supplied to the source of the diamond transistor Q5.

[0038] The diamond transistor Q5 is an output transistor that constitutes a common-drain circuit. The diamond transistor Q5 inputs the input voltage Vi2 from the coupling capacitor Cc2 of the amplifier stage 11 to its gate. The diamond transistor Q5 then outputs an output voltage Vo2 from its source in response to the input voltage Vi2 input to its gate. Specifically, the diamond transistor Q5 outputs the output voltage Vo2 so as to follow the input voltage Vi2, i.e., so as to maintain a gate-source voltage corresponding to the bias current relative to the input voltage Vi2.

[0039] A resistor element (second resistor element) R7 is connected between the source of the diamond transistor Q5 and the drain of the diamond transistor Q6. The output voltage Vo2 from the diamond transistor Q5 is connected to the output voltage V ＯＵＴ The resistor element R7 outputs the output voltage V ＯＵＴ The resistor R5 is a high-resistance element connected between the gate of the diamond transistor Q5 and the reference power supply voltage VS. The resistor R5 determines the bias point of the gate voltage of the diamond transistor Q5 to the reference power supply voltage VS. However, the resistors R5 and R7 may be omitted as appropriate, depending on the specifications of the electronic device 10, for example.

[0040] In this way, the diamond transistor (output transistor) Q5, together with the diamond transistor (bias transistor) Q6 that constitutes the current source, constitutes a drain-grounded circuit, in other words, a source follower circuit. Note that here, an electronic device 10 having an amplifier stage (amplifier circuit) 11 is used as an example. The amplifier stage 11 is an example of a front-stage circuit that outputs an input voltage Vi2 to the diamond transistor Q5. However, the front-stage circuit is not limited to the amplifier stage 11, and may be any circuit that outputs the input voltage Vi2 with a relatively high output impedance.

[0041] Furthermore, the electronic device 10 does not necessarily have to have a front-stage circuit, in this example, the amplifier stage 11, but only needs to have at least an output stage (output circuit) 12, i.e., a source follower circuit. Furthermore, if the electronic device 10 has the amplifier stage 11, the amplifier stage 11 only needs to be composed of at least a diamond transistor Q, and is not limited to the circuit shown in FIG.

[0042] Here, in the output stage 12, in order to make the diamond transistor Q6 function as a current source, it is necessary to apply a fixed voltage to the gate of the diamond transistor Q6. If the diamond transistor Q6 has normally-off characteristics, a voltage generation circuit may be required to generate this fixed voltage, i.e., a gate voltage lower than the source voltage. However, it is usually not easy to realize a voltage generation circuit without using a push-pull circuit or the like. On the other hand, for example, a method of generating a fixed voltage by resistively dividing the positive power supply voltage VDp and the reference power supply voltage VS using a high-resistance element can also be considered. However, using a large number of high-resistance elements may be undesirable from the standpoint of noise.

[0043] Therefore, the diamond transistor Q6 has a normally-on characteristic as shown in FIG. 1B. This makes it possible to use the positive power supply voltage VDp as a fixed voltage to the gate. However, if left as is, it becomes difficult to adjust the current value of the current source to an arbitrary value. Therefore, the resistor element R6 is provided. The larger the resistance value of the resistor element R6, the lower the source voltage and the smaller the current value. It should be noted that the diamond transistor Q5 does not particularly need to have a normally-on characteristic.

[0044] 2, i.e., transistors, resistors, and capacitors, are formed as integrated circuits on a common diamond substrate, or are mounted as discrete components on a wiring board and connected on the wiring board. Alternatively, some of the elements shown in FIG. 2 are formed as integrated circuits on a common diamond substrate, and other elements are composed of discrete components. In this case, the integrated circuits and discrete components are mounted on a wiring board and connected on the wiring board.

[0045] <Regarding Output Impedance> For example, the output impedance of the amplifier stage 11 shown in Figure 2 is mainly determined by the equivalent resistance value of the current source load configured using the diamond transistor Q3. In order to increase the gain, the output impedance can be, for example, several tens of kΩ or more. For this reason, for example, when the output voltage Vo1 of the amplifier stage 11 is input to an input circuit with a relatively small input impedance, in other words, a load, the magnitude of the output voltage Vo1 can be significantly reduced.

[0046] On the other hand, the output impedance of the output stage 12 is determined by approximately "1 / gm" using the mutual conductance gm of the diamond transistor Q5. For example, if the mutual conductance gm is 1m-4m [S], the output impedance is 1k-250 [Ω]. Therefore, by using a source follower circuit as shown in FIG. 2 as the output stage 12, the output impedance of the electronic device 10 can be lowered. As a result, even if the input impedance of the load is not so large, the output voltage V ＯＵＴ The size of the

[0047] The electronic device 10 shown in FIG. 2 can be installed in harsh environments, such as high-radiation environments such as nuclear reactors and aerospace, or high-temperature environments such as industrial machinery and automotive applications. Furthermore, the use of diamond semiconductors can achieve high Baliga and Johnson figures of merit. Therefore, the electronic device 10 is beneficial not only in harsh environments, but also in fields requiring high-power and high-frequency operation. Specific examples include the power industry, communications such as 6G (6th Generation), and quantum computing. Even in these fields, achieving low output impedance makes it easier to achieve desired output performance, frequency performance, and the like.

[0048] <Major Effects of the First Embodiment> As described above, the output circuit according to the first embodiment has a source follower circuit configured using a p-channel diamond transistor Q. Furthermore, the current source in the source follower circuit is configured using a diamond transistor Q having normally-on characteristics. This makes it possible to reduce the output impedance of an electronic device while using a diamond semiconductor, under the constraints that a push-pull circuit or the like cannot be used and that it is difficult to generate an arbitrary fixed voltage. And, since the output impedance can be reduced while using a diamond semiconductor, it is possible to realize a practical electronic device that can operate, for example, even in harsh environments.

[0049] Second Embodiment <Outline of Signal Transmission System> Fig. 3 is a schematic diagram showing an example of the configuration of the main parts of a signal transmission system according to a second embodiment. The signal transmission system shown in Fig. 3 includes a detector 30, an electronic device 10a, a transmission line 32, and an input circuit 33. Of these, the detector 30 and the electronic device 10a are installed in a harsh environment 25, such as a high temperature and high radiation environment. As a specific example, the harsh environment 25 is an environment with a temperature of 150°C or higher and / or an absorbed dose of 20 μGy / h or higher. On the other hand, the input circuit 33 is installed in a normal environment 26.

[0050] The detector 30 detects a target parameter such as an environmental parameter. The electronic device 10a includes an amplifier stage 11a and an output circuit 14 provided at the subsequent stage, i.e., the final stage. The output circuit 14 includes an output stage 12a and a compensation circuit 13. The amplifier stage 11a and the output stage 12a have, for example, the configuration shown in FIG. 2 and are configured using diamond transistors Q. The amplifier stage 11a amplifies the detection signal from the detector 30. The output stage 12a outputs the signal amplified by the amplifier stage 11a, in this case, an output voltage V ＯＵＴ is outputted to the input circuit 33 via the compensation circuit 13.

[0051] For example, the heat resistance and radiation resistance of silicon material are said to be about 150-200°C and about 1kGy, respectively. In contrast, the heat resistance and radiation resistance of diamond material are said to be 500°C or higher and 10MGy or higher. Therefore, the amplifier stage 11a and output stage 12a, which are composed of diamond transistors Q, can operate normally even in the harsh environment 25 described above.

[0052] The compensation circuit 13 is inserted into the output wiring 34 of the output stage 12a, which is directed toward the load that is the output destination of the electronic device 10a, in this case, the input circuit 33. In detail, the compensation circuit 13 is inserted into the output wiring 34 between the source of the diamond transistor (output transistor) Q5 shown in Figure 2 and the input end of the transmission line 32. The compensation circuit 13, which will be described in detail later, is provided to expand the bandwidth of the transmission signal.

[0053] The transmission line 32 receives the output voltage V ＯＵＴ is input through the compensation circuit 13, and the input output voltage V ＯＵＴ to the input circuit 33. The transmission line 32 is, for example, a coaxial cable having a transmission line length L. The transmission line length L is a length necessary to separate the harsh environment 25 from the normal environment 26. The transmission line length L is, for example, 0.1 m or more, and in reality, can be 1 m or more.

[0054] The input circuit 33 constitutes, for example, a signal processing device, and outputs the output voltage V ＯＵＴand performs predetermined signal processing. The input circuit 33 is configured using general elements formed on a substrate other than a diamond substrate, and whose operation is guaranteed only in the normal environment 26. Specifically, the input circuit 33 is configured, for example, by MOSFETs, bipolar transistors, etc. formed on a silicon substrate or SiC substrate.

[0055] As a specific example, let us assume that the signal transmission system shown in Fig. 3 is a radiation detection system. Fig. 4 is a circuit diagram showing a detailed configuration example and an operation example of the electronic device 10a in Fig. 3. In a radiation detection system, a charge-sensitive preamplifier (CSA) such as that shown in Fig. 4 is typically used as the amplification stage 11a and the output stage 12a.

[0056] 3 detects radiation and generates a charge pulse Qpls corresponding to the radiation dose. The detector 30 is, for example, a semiconductor detector such as an avalanche photodiode (APD), or a scintillator. A charge-sensitive preamplifier (CSA) converts the charge pulse Qpls from the detector 30 into a voltage pulse Vpls, thereby generating an output voltage V ＯＵＴ The charge-sensitive preamplifier (CSA) generates the output voltage V ＯＵＴ , that is, the voltage pulse Vpls is output to the input circuit 33 via the compensation circuit 13 .

[0057] Specifically, the charge-sensitive preamplifier (CSA) is configured with an integrating circuit having a negative feedback configuration, as shown in FIG. 4. That is, the charge-sensitive preamplifier (CSA) includes an amplifier circuit 35 such as an operational amplifier, and a feedback circuit 36 ​​that negatively feeds back the output of the amplifier circuit 35 to the input. The feedback circuit 36 ​​includes a feedback capacitor Cf and a feedback resistor Rf connected in parallel. More specifically, the amplifier circuit 35 includes a plurality of amplifier stages 11 cascaded together, as shown in FIG. 2, and an output stage 12 provided after the amplifier stages 11, i.e., at the final stage.

[0058] The charge-sensitive preamplifier (CSA) performs an integration operation by charging a feedback capacitor Cf with the charge (Qin) accompanying the charge pulse Qpls from the detector 30, and outputs the integrated value as a voltage pulse Vpls. The amplitude of the voltage pulse Vpls is determined approximately by "-Qin / Cf". The feedback resistor Rf is ＯＵＴ In order to prevent saturation, the charge (Qin) stored in the feedback capacitor Cf is discharged with a time constant of, for example, 50 μsec.

[0059] This generates a voltage pulse Vpls, i.e., an output voltage V ＯＵＴ has a waveform that rises in response to the charge pulse Qpls and then gradually falls over a period of time such as 50 μsec. The input circuit 33 shown in FIG. 3 , i.e., the signal processing device, includes, for example, an amplifier and a waveform shaping circuit. The signal processing device processes the voltage pulse Vpls transmitted via the transmission line 32 to calculate the radiation dose.

[0060] <Example of required specifications> In such a radiation detection system, the rise time Tr of the voltage pulse Vpls is required to be sufficiently shorter than the discharge time constant of the feedback circuit 36, such as 50 μsec, and to have a length that corresponds to the pulse width of the charge pulse Qpls, etc. As an example, the rise time Tr of the voltage pulse Vpls is required to be 1 / 100 or less of the discharge time constant, that is, at least 0.5 μsec or less.

[0061] The radiation detection system needs to transmit the voltage pulse Vpls having a rise time Tr of 0.5 μsec or less to the input circuit 33 without causing distortion in the waveform. In other words, if distortion occurs in the waveform, the accuracy of calculating the radiation dose in signal processing in the input circuit 33 may decrease.

[0062] 3, a first-order lag low-pass filter is formed mainly due to the output impedance, i.e., output resistance, of the output stage 12a and the parasitic capacitance, in other words, the load capacitance, of the transmission line 32. For example, in order to transmit the voltage pulse Vpls having the rise time Tr of 0.5 μsec or less to the input circuit 33 without causing waveform distortion, the low-pass filter needs to have a pass band, in other words, a cutoff frequency, of 0.7 MHz or more, as described below.

[0063] That is, the output voltage Vout of a first-order lag low-pass filter is generally given by equation (1) using the time constant τ of the low-pass filter and time t. The time constant τ is the time required for the output voltage Vout to change from 0% to approximately 63%. Vout={1-exp(-t / τ)} (1)

[0064] On the other hand, the rise time Tr is the time required for the output voltage Vout to change from 10% to 90%. Based on equation (1), the time ta required for the output voltage Vout to change from 0% to 10% is ta = 0.105τ. The time tb required for the output voltage Vout to change from 0% to 90% is tb = 2.303τ. As a result, the rise time Tr is Tr = 2.198 (= 2.303 - 0.105)τ. Thus, the relationship between the time constant τ and the rise time Tr is given by equation (2): τ = Tr / 2.198 ... (2)

[0065] Here, the cutoff frequency fc of the first-order lag low-pass filter is given by equation (3) using the time constant τ. Substituting equation (2) into equation (3), the cutoff frequency fc is fc = 0.35 / Tr. As a result, the cutoff frequency fc required to transmit a voltage pulse Vpls having a rise time Tr of 0.5 μsec without distortion is fc = 0.7 MHz. In other words, the first-order lag low-pass filter must have a cutoff frequency fc of 0.7 MHz or higher, in other words, a passband. fc = 1 / (2πτ) (3)

[0066] <Issues in Signal Transmission Systems> Here, the transmission line 32 shown in Fig. 3, for example, a coaxial cable, can have a parasitic capacitance of 100 pF / m. In a signal transmission system used in a harsh environment 25, such as a radiation detection system, the transmission line length L can reach 50 m in some cases. In this case, the parasitic capacitance, in other words, the load capacitance, is 5000 pF.

[0067] On the other hand, by applying the source follower circuit described in the first embodiment, the output resistance of the output stage 12a can be reduced to, for example, several hundred to 1 kΩ. If the output resistance is set to 1 kΩ, the cutoff frequency fc of the low-pass filter described above is 31.8 kΩ (= 1 / (2πCR) = 1 / (2π * 5000p * 1 kΩ)) [Hz], which is significantly different from 0.7 MHz [Hz]. Furthermore, even if the output impedance is reduced by using the negative feedback configuration shown in FIG. 4, a sufficient passband may not be obtained. Therefore, the compensation circuit 13 shown in FIG. 3 is provided.

[0068] <Details of the Compensation Circuit> Fig. 5 is a circuit diagram showing an example of an equivalent circuit of the signal transmission system shown in Fig. 3. In Fig. 5, the output circuit 14 includes an output stage 12a and a compensation circuit 13. The output stage 12a includes a voltage source that generates an input voltage Vin and an output resistor R ＯＵＴ The compensation circuit 13 is a compensating resistor element R inserted in series with the output wiring 34 of the output stage 12a. Ｓ and the compensating resistor R Ｓ A compensation capacitor C is connected in parallel to Ｓ Z1 is the impedance of the compensation circuit 13.

[0069] A compensating resistor R constituting the compensation circuit 13 Ｓ and a compensation capacitor C ＳFor example, the compensation circuit 13 is formed as an integrated circuit on a diamond substrate on which the output stage 12a and the like are formed. That is, the entire electronic device 10a is formed as an integrated circuit on the same diamond substrate. Alternatively, the compensation circuit 13 is mounted as a discrete component on a wiring substrate on which the output stage 12a and the like are mounted, and is connected to the output stage 12a on the wiring substrate. Alternatively, a portion of the compensation circuit 13 is formed as an integrated circuit on the diamond substrate, and another portion is composed of discrete components. In this case, the integrated circuit and the discrete components are mounted on a wiring substrate and connected on the wiring substrate.

[0070] Here, in particular, by forming the entire electronic device 10a as an integrated circuit on the same diamond substrate, the following effects can be obtained: (a) high integration and miniaturization, (b) signal noise reduction, (c) improved reliability, and (d) reduced manufacturing costs. Regarding (a), this satisfies the demand for miniaturization in harsh environments 25 where such demands may be high. Regarding (b), since the diamond substrate allows for efficient heat dissipation, noise can be reduced, including in the input / output signals of the compensation circuit 13. Regarding (c), since the diamond substrate has high durability against high temperatures, radiation, etc., stable operation of the electronic device 10a can be guaranteed for a long period of time. Regarding (d), it is possible to reduce component costs and mounting costs that may arise from discrete components.

[0071] As shown in FIG. 5, the transmission line 32 has a parasitic resistance R Ｃ and parasitic capacitance, in other words, load capacitance C Ｌ The input circuit 33 is an input resistor, in other words, a load resistor R Ｌ It is expressed as the parasitic resistance R Ｃ , the output resistance R ＯＵＴ , the load 40 to which the output of the output circuit 14 is connected is a load resistance R Ｌ and load capacitance C Ｌ The output voltage Vout of the low-pass filter is input to the load 40. Z2 is the impedance of the load 40.

[0072] In this way, an impedance Z1 is formed at the input end of the transmission line 32 by the compensation circuit 13. On the other hand, an impedance Z2 is formed at the output end of the transmission line 32 by the load 40. The output voltage Vout of the low-pass filter is obtained by voltage division between the impedances Z1 and Z2. In other words, an attenuator is formed by the impedances Z1 and Z2. By using such a configuration, the gain of the output voltage Vout of the low-pass filter decreases, but the pass band can be expanded accordingly.

[0073] Next, a detailed explanation will be given of the operation principle of the compensation circuit 13. First, the impedance Z1 of the compensation circuit 13 is determined by the compensating resistor R Ｓ and the resistance value of the compensation capacitor C Ｓ The impedance Z2 of the load 40 is expressed by the equation (4) using the capacitance value of the load resistance R Ｌ Resistance value and load capacitance C Ｌ Using the capacitance value of

[0074]

[0075] The output voltage Vout of the low-pass filter is determined by the impedances Z1 and Z2 in equations (4) and (5) and the output resistance R of the output stage 12a. ＯＵＴ and the parasitic resistance R of the transmission line 32 Ｃ Furthermore, the time constant τ of the compensation circuit 13 is expressed by the following equation (6). Ｓ (=C Ｓ R Ｓ ) and the time constant τ of the load 40 Ｌ (=C Ｌ R Ｌ ) and transforming equation (6), the output voltage Vout is expressed by equation (7).

[0076]

[0077] Here, “τ Ｓ = τ Ｌ =τ”. That is, the compensating resistor R Ｓ and a compensation capacitor CＳ The time constant τ of the compensation circuit 13 Ｓ , the load resistance R Ｌ and load capacitance C Ｌ The time constant τ of the load 40 Ｌ In this case, the output voltage Vout shown in equation (7) is expressed by equation (8).

[0078] Also, "R ０ =R ＯＵＴ +R Ｃ " and "R Ｔ =R ＯＵＴ +R Ｃ +R Ｓ +R Ｌ ", and rearranging equation (8), the output voltage Vout is expressed by equation (9). As a result, the transfer function G(s) of the output voltage Vout with respect to the input voltage Vin is expressed by equation (10). As can be seen from equation (10), the transfer function G(s) is expressed by the gain "R Ｌ / R Ｔ " and the time constant "τ Ｎ = τ(R ０ / R Ｔ )" of the compensation circuit 13. Ｓ , the time constant τ of the load 40 Ｌ The transfer function G(s) of the first-order lag low-pass filter can be obtained by defining it to be equivalent to

[0079]

[0080] By providing the compensation circuit 13, the time constant τ of the first-order lag low-pass filter in equation (10) Ｎ can be made shorter than when the compensation circuit 13 is not provided. As a result, the pass band can be widened. Ｔ " to "R ＴＴ (=R ＯＵＴ +R Ｃ +R Ｌ )" to obtain the same transfer function G(s) as in the case of equation (10). ＴＴ <R Ｔ", the time constant "τ Ｎ = τ(R ０ / R ＴＴ )" is the time constant "τ Ｎ = τ(R ０ / R Ｔ )" will be longer.

[0081] <Verification Results> Fig. 6A is a waveform diagram showing an example of the input voltage Vin and the output voltage Vout when the compensation circuit 13 is not provided in Fig. 5. Fig. 6B is a Bode diagram showing an example of the frequency characteristics in Fig. 6A. In this example, the parasitic resistance R Ｃ and the load resistance R Ｌ The resistance values ​​of the load capacitances C Ｌ The capacitance value of is set to 5000 pF. These resistance and capacitance values ​​are also used in FIGS. 7A, 7B, 8, and 9, which will be described later.

[0082] In addition, in FIG. 6A, the output resistance R of the output stage 12a ＯＵＴ is set to 1 kΩ. In this case, for example, the mutual conductance gm of the diamond transistor Q5 in FIG. 2 is about 1 mS. Thus, the output resistance R ＯＵＴ When the impedance is 1 kΩ and the compensation circuit 13 is not provided, the input voltage Vin having a pulse width of 10 μsec is transmitted as the output voltage Vout with a large distortion of the waveform, as shown in Fig. 6A. The cutoff frequency fc of the low-pass filter is 32 kHz, as shown in Fig. 6B, which is significantly different from 0.7 MHz.

[0083] 7A is a waveform diagram showing an example of the input voltage Vin and the output voltage Vout when the compensation circuit 13 is provided in FIG. 5. FIG. 7B is a Bode diagram showing an example of the frequency characteristics in FIG. 7A. The only difference between FIG. 7A and FIG. 7B and FIG. 6A and FIG. 6B is the presence or absence of the compensation circuit 13. In this example, the compensation resistor R Ｓ is set to 500 kΩ. Ｓis set to 1000 pF. That is, the time constant (C Ｓ R Ｓ ) is the time constant (C Ｌ R Ｌ ) is the same as

[0084] In this way, the output resistance R ＯＵＴ When the impedance is 1 kΩ and the compensation circuit 13 is provided, as shown in Fig. 7A, an input voltage Vin having a pulse width of 10 μsec is transmitted as an output voltage Vout with waveform distortion improved to some extent compared to the case of Fig. 6A. As shown in Fig. 7B, the cutoff frequency fc of the low-pass filter is 186 kHz, which is higher than the case of Fig. 6B. However, the cutoff frequency fc still does not reach 0.7 MHz.

[0085] 8 shows the difference between the output resistance R of the output stage 12a and that of FIG. ＯＵＴ In this example, the output resistance R of the output stage 12a is lowered. ＯＵＴ is set to 250 [Ω]. In this case, for example, the mutual conductance gm of the diamond transistor Q5 in FIG. 2 is about 0.4 mS. In this way, the output resistance R ＯＵＴ When the impedance is 250 Ω and the compensation circuit 13 is not provided, the cutoff frequency fc of the low-pass filter is 122 kHz as shown in Fig. 8, which is higher than the case of Fig. 6B. However, the cutoff frequency fc still does not reach 0.7 MHz.

[0086] 9 shows the output resistance R of the output stage 12a in comparison with FIG. 7B. ＯＵＴ 8, the output resistance R of the output stage 12a is lowered. ＯＵＴ is set to 250 [Ω]. The parameter values ​​of the compensation circuit 13 are the same as those in FIG. 7B. ＯＵＴWhen the impedance is 250 [Ω] and the compensation circuit 13 is provided, the cutoff frequency fc of the low-pass filter is 730 kHz, as shown in Fig. 9. In other words, the cutoff frequency fc can be made higher than 0.7 MHz.

[0087] <Regarding the parameters of the compensation circuit> Fig. 10 is a diagram showing guideline parameter values ​​of the compensation circuit 13 according to the scale of the system in the signal transmission systems shown in Figs. 3 and 5. Fig. 10 shows small-scale systems, medium-scale systems, and large-scale systems as system applications. Examples of small-scale systems include in-vehicle equipment and aerospace equipment. Examples of medium-scale systems include railway systems and factory automation systems. Examples of large-scale systems include nuclear power plants and marine exploration systems.

[0088] The transmission line length L of the transmission line 32 is 0.1-1 m for a small-scale system, 1-10 m for a medium-scale system, and 10-100 m for a large-scale system. Ｌ is assumed to be 100 kΩ, and the parasitic capacitance of the transmission line 32, i.e., the load capacitance C Ｌ In this case, the time constant τ of the load 40 is Ｌ (=C Ｌ R Ｌ ) is 1 μm to 10 μm [sec] in a small-scale system, 10 μm to 100 μm [sec] in a medium-scale system, and 100 μm to 1000 μm [sec] in a large-scale system.

[0089] Compensating resistor R Ｓ In this example, the load resistance R Ｌ For example, the resistance value of the compensating resistor R Ｓ The resistance value of the load resistance R Ｌ In this case, the compensation capacitor C Ｓ The capacitance value is 2-20 pF in a small-scale system, 20 pF-200 pF in a medium-scale system, and 200 pF-2000 pF in a large-scale system.

[0090] 11A shows the relationship between the transmission line length L and the time constant τ of the load 40 in FIG. Ｌ 11A is a graph showing an example of the relationship between the time constant τ Ｌ is the transmission line length L, and therefore the load capacitance C Ｌ 11B shows the relationship between the transmission line length L and the compensation capacitor C Ｓ 11B is a graph showing an example of the relationship between the capacitance value of the compensating resistor R Ｓ After fixing the resistance value of the transmission line length L and the compensation capacitor C Ｓ The relationship between the capacitance value and the

[0091] In FIG. 11B, a compensating resistor R Ｓ As can be seen from the above-mentioned equation (10), the resistance value determines the balance between the gain in the pass band and the width of the pass band. Specifically, increasing the resistance value reduces the gain while widening the pass band. Conversely, decreasing the resistance value increases the gain while narrowing the pass band.

[0092] For this reason, the compensating resistor R Ｓ The resistance value of the resistor C should be fixed to a certain extent depending on the required specifications of the system, for example, the gain specifications. Ｓ 11B, it is preferable to set the capacitance value of the compensation capacitor C so that it increases as the transmission line length L increases, for example, so that it is proportional to the transmission line length L. In this case, in order to be able to generally cope with various transmission line lengths L, for example, Ｓ may be composed of a variable capacitor.

[0093] <Major Effects of the Second Embodiment> As described above, the signal transmission system according to the second embodiment can also achieve the same effects as those described in the first embodiment. Furthermore, by combining the output stage 12a of the source follower circuit, which has a low output impedance, with the compensation circuit 13, it is possible to expand the bandwidth of the transmission signal via the transmission line 32. As a result, it is possible to improve the waveform quality of the transmission signal while using a diamond semiconductor.

[0094] The invention made by the inventor has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0095] 10, 10a: electronic device, 11, 11a: amplifier stage, 12, 12a: output stage (output circuit), 13: compensation circuit, 14: output circuit, 30: detector, 32: transmission line, 33: input circuit, 34: output wiring, 40: load, C Ｌ :Load capacity, C Ｓ : Compensation capacitor, L: Transmission line length, Q: Diamond transistor, Qpls: Charge pulse, R6, R7: Resistive elements, R Ｌ :Load resistance, R Ｓ : Compensation resistor, V ＩＮ , Vin, Vi: input voltage, V ＯＵＴ , Vout, Vo: output voltage, Vpls: voltage pulse

Claims

1. An output circuit having a p-channel field effect transistor formed on a diamond substrate, wherein the field effect transistor comprises: an output transistor that forms a drain-grounded circuit and outputs an output voltage from its source in response to an input voltage input to its gate; and a bias transistor that supplies a bias current to the output transistor, wherein the bias transistor has normally-on characteristics and forms a current source by connecting its gate and source.

2. An output circuit according to claim 1, wherein the bias transistor has a gate-source connection via a first resistor element connected to the source.

3. An output circuit according to claim 1, further comprising a second resistance element connected between the source of said output transistor and the drain of said bias transistor.

4. An output circuit according to claim 1, further comprising a compensation circuit inserted in an output wiring extending from the source of the output transistor to a load that is the output destination of the output circuit, the compensation circuit comprising: a compensation resistor element inserted in series in the output wiring; and a compensation capacitor connected in parallel to the compensation resistor element.

5. An output circuit according to claim 4, wherein the load is represented by a load resistance and a load capacitance connected in parallel, and the time constant defined by the compensating resistance element and the compensating capacitor is determined to be equal to the time constant defined by the load resistance and the load capacitance.

6. An output circuit according to claim 4, wherein the output circuit is formed as an integrated circuit on the same diamond substrate.

7. An electronic device comprising: the output circuit according to claim 1; and a pre-stage circuit that outputs the input voltage to the output transistor.

8. A signal transmission system having an output circuit that outputs an output voltage, a transmission line that transmits the output voltage from the output circuit, and an input circuit that inputs the output voltage transmitted via the transmission line, wherein the output circuit is configured as a p-channel type and has a field effect transistor formed on a diamond substrate, and the field effect transistor forms a drain-grounded circuit and includes an output transistor that outputs the output voltage from its source in accordance with an input voltage input to its gate, and a bias transistor that supplies a bias current to the output transistor, and the bias transistor has normally-on characteristics and forms a current source by connecting its gate and source.

9. A signal transmission system according to claim 8, wherein the bias transistor has a gate and a source connected via a first resistance element connected to the source.

10. A signal transmission system according to claim 8, wherein the output circuit further comprises a compensation circuit inserted in the output wiring between the source of the output transistor and the input end of the transmission line, the compensation circuit comprising: a compensation resistor element inserted in series in the output wiring; and a compensation capacitor connected in parallel to the compensation resistor element.

11. A signal transmission system according to claim 10, wherein the transmission line and the input circuit are represented by a load resistance and a load capacitance connected in parallel, and the time constant of the compensating resistive element and the compensating capacitor is determined to be equivalent to the time constant of the load resistance and the load capacitance.

12. A signal transmission system according to claim 11, wherein the capacitance of the compensation capacitor is set to increase as the length of the transmission line increases.

13. A signal transmission system according to claim 11, wherein the transmission line has a length of 0.1 m or more, and the input circuit is constructed using elements formed on a substrate different from the diamond substrate.

14. A signal transmission system according to claim 11, wherein the output circuit is installed in an environment where the temperature is 150°C or higher, or where the absorbed dose is 20 μGy / h or higher.

15. A signal transmission system according to claim 11, wherein the signal transmission system is a radiation detection system having a detector that detects radiation and generates charge pulses according to the radiation dose, the output circuit is provided with a charge-sensitive preamplifier that generates the output voltage by converting the charge pulses from the detector into voltage pulses and outputs the output voltage to the input circuit, the charge-sensitive preamplifier having an amplification stage and an output stage provided subsequent to the amplification stage, and the output stage having the output transistor and the bias transistor.

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