Drive circuit, array circuit, and neuromorphic device

Abstract

This drive circuit comprises: a load resistor; a resistance changing element having at least a first terminal and a second terminal, and capable of changing a resistance value; and a constant current source that decides the magnitude of current flowing through the load resistor on the basis of an input voltage and the resistance value of the resistance changing element, wherein the voltage between both ends of the load resistor is output as an output voltage.

Description

[Technical field]

[0001] The present invention relates to a drive circuit, an array circuit, and a neuromorphic device. [Background technology]

[0002] Research and development is currently underway into neuromorphic devices that perform calculations using neural networks.

[0003] In relation to this, a method is known in which a resistance change element whose resistance value changes due to a magnetoresistance effect such as a giant magnetoresistance effect or a tunnel magnetoresistance effect is used to perform calculations by a neural network (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 183573 Summary of the Invention [Problem to be solved by the invention]

[0005] In the calculation by the neural network, the resistance value of the variable resistance element is used as a weight, and the current generated by the input pulse signal passing through the variable resistance element is output as the result of the multiplication calculation. That is, in such a multiplication calculation, the magnitude of the current changes according to the change in the resistance value of the variable resistance element. However, since it is difficult to widen the range in which the resistance value of the variable resistance element can be changed, the change in the magnitude of the current according to the change in the resistance value of the variable resistance element may be indistinguishable from the change due to noise. [Means for solving the problem]

[0006] One aspect of the present invention is a drive circuit comprising a load resistor, a variable resistance element having at least a first terminal and a second terminal and capable of changing the resistance value, and a constant current source that determines the magnitude of a current flowing through the load resistor based on an input voltage and the resistance value of the variable resistance element, and outputs the voltage across the load resistor as an output voltage. Effect of the Invention

[0007] According to the present invention, it is possible to provide a drive circuit, an array circuit, and a neuromorphic device that can improve the resolution of the change in resistance value of a resistance change element. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing an example of the configuration of a drive circuit 1 according to an embodiment. [Diagram 2] 1 is a diagram showing an example of the configuration of a drive circuit 1 when a bipolar transistor is used as a constant current source CP. [Diagram 3] 3 is an equivalent circuit showing the drive circuit 1 shown in FIG. 2. [Figure 4] 1 is a diagram showing an example of the configuration of a drive circuit 1 including a three-terminal variable resistance element MS. [Diagram 5] 2 is a diagram showing an example of a configuration of an array circuit 2. FIG. [Figure 6] FIG. 13 is a diagram showing another example of the configuration of the array circuit 2. [Figure 7] FIG. 13 is a diagram showing yet another example of the configuration of the array circuit 2. [Figure 8] FIG. 2 is a diagram showing an example of the configuration of a drive circuit 1B. [Figure 9] 1 is a conceptual diagram showing an example of how a constant current source CP of a drive circuit 1A and a three-terminal variable resistance element MSA are stacked on a substrate as an integrated circuit using a top-pin structure. FIG. [Figure 10] 1 is a conceptual diagram showing an example of how a constant current source CP of a drive circuit 1A and a three-terminal variable resistance element MSA are stacked on a substrate as an integrated circuit in a bottom-top-pin structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Embodiment> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a conductor that transmits an electric signal will be described as a transmission line. The transmission line may be, for example, a conductor printed on a substrate, or a conductor such as a linear conductor. In this embodiment, when a voltage is referred to, it means a potential difference from a predetermined reference potential, and illustration and description of the reference potential are omitted. Here, the reference potential may be any potential. In the following, as an example, a case where the reference potential is the ground potential will be described. In this embodiment, when a voltage across a member having a certain resistance value is referred to, it means a potential difference occurring across the member, and does not necessarily mean a potential difference from the ground potential.

[0010] <Drive circuit configuration> FIG. 1 is a diagram showing an example of the configuration of a drive circuit 1 according to the embodiment.

[0011] The driving circuit 1 is a circuit that is driven by an input voltage Vin input to an input terminal, and outputs an output voltage Vout. The driving circuit 1 is used, for example, as an analog circuit that performs multiplication in a neural network. The driving circuit 1 may also be used as a circuit that achieves other purposes.

[0012] The drive circuit 1 includes a load resistor RL, a resistance change element MS, and a constant current source CP. The drive circuit 1 outputs the voltage across the load resistor RL as an output voltage Vout.

[0013] First, the connection state of the load resistor RL, the resistance change element MS, and the constant current source CP in the drive circuit 1 will be described.

[0014] The load resistor RL has two terminals, a terminal E11 and a terminal E12. Resistance change element MS has two terminals, a terminal E21 and a terminal E22. The constant current source CP has three terminals: a terminal E31, a terminal E32, and a terminal E33.

[0015] The terminal E11 of the load resistor RL is connected to a constant voltage source Vdd. The constant voltage source Vdd is a voltage source that supplies a voltage Vc of a predetermined magnitude. That is, the voltage Vc is applied to the terminal E11 of the load resistor RL. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E11 and the constant voltage source Vdd as long as the function of the drive circuit 1 is not impaired.

[0016] A terminal E12 of the load resistor RL is connected to a terminal E31 of the constant current source CP. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E12 and the constant current source CP as long as the function of the drive circuit 1 is not impaired.

[0017] The terminal E32 of the constant current source CP is a terminal to which the input voltage Vin is input. Therefore, an external circuit, an external device, etc. capable of supplying the input voltage Vin to the terminal E32 is connected to the terminal E32. In FIG. 1, such external circuits, external devices, etc. are omitted for the sake of simplicity. Note that, other elements, other members, other circuits, other devices, etc. may be connected between the terminal E32 and these external circuits, external devices, etc., as long as the function of the drive circuit 1 is not impaired.

[0018] The terminal E33 of the constant current source CP is connected to the terminal E21 of the resistance change element MS. Note that, other elements, other members, other circuits, other devices, etc. may be connected between the terminal E33 and the resistance change element MS as long as the function of the drive circuit 1 is not impaired.

[0019] The terminal E22 of the resistance change element MS is connected to the ground. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E22 and the ground as long as the function of the drive circuit 1 is not impaired.

[0020] Next, the configurations of the load resistor RL, the resistance change element MS, and the constant current source CP will be described.

[0021] The load resistor RL is, for example, composed of one or more resistive elements, but may be another member having a resistance value capable of functioning as a load resistor.

[0022] A transmission line for detecting the output voltage Vout is connected to both ends of the load resistor RL. In order to simplify the drawing, an external device for detecting the output voltage Vout is omitted in FIG.

[0023] The resistance change element MS is a magnetoresistance effect element whose resistance value changes due to a magnetoresistance effect such as a giant magnetoresistance effect or a tunnel magnetoresistance effect. In other words, the resistance change element MS is an element capable of changing its resistance value based on the magnetoresistance effect. Specifically, the resistance change element MS is, for example, a spin transfer torque (STT; Spin Transfer Torque) type magnetoresistance effect element using spin transfer torque, a spin orbital torque type magnetoresistance effect element using spin orbital torque (SOT; Spin Orbital Torque), a domain wall motion type magnetoresistance effect element using the motion of a domain wall in a ferromagnetic layer, or the like.

[0024] 1, the resistance change element MS is a two-terminal magnetoresistance effect element. In this case, the resistance change element MS is, for example, an STT type magnetoresistance effect element, and the resistance value changes when a spin-polarized current is passed through it. Note that the two-terminal resistance change element MS may be another magnetoresistance effect element, such as a magnetoresistance effect element whose resistance value changes when a magnetic field is applied.

[0025] The constant current source CP determines the magnitude of the current flowing through the load resistance RL based on the input voltage Vin and the resistance value of the resistance change element MS. More specifically, when the input voltage Vin is applied to the terminal E32, the constant current source CP passes a current whose magnitude is determined based on the input voltage Vin applied to the terminal E32 and the resistance value of the resistance change element MS through the load resistance RL. As a result, in the drive circuit 1, a voltage whose magnitude is determined according to the magnitude of the input voltage Vin and the resistance value of the resistance change element MS is generated as a voltage across the load resistance RL. The drive circuit 1 outputs the voltage across the load resistance RL thus generated as an output voltage Vout. Note that when the input voltage Vin is applied to the terminal E32, the constant current source CP passes a current that is a combination of the current flowing through the terminal E32 and the current flowing through the load resistance RL through the resistance change element MS.

[0026] The driving circuit 1 having such a configuration can detect the change in the resistance value of the resistance change element MS as a change in the output voltage Vout. Here, the range in which the resistance value of the resistance change element MS, which is a magnetoresistance effect element, changes cannot be arbitrarily expanded, at least by currently known methods. For this reason, when the resistance value of the resistance change element MS is changed in multiple steps, the change in the resistance value of the resistance change element MS per step becomes small. However, in the driving circuit 1, the change in the output voltage Vout corresponding to the change in the resistance value of the resistance change element MS per step can be increased by adjusting the resistance value of the load resistor RL. For this reason, it is desirable that the resistance value of the load resistor RL in the driving circuit 1 is selectable. The fact that the resistance value of the load resistor RL is selectable means, for example, that the load resistor RL is a variable resistor, that each of a plurality of resistor elements having different resistance values ​​can be attached to the driving circuit 1 as the load resistor RL, and the like. The larger the resistance value of the load resistor RL, the larger the change in the output voltage Vout corresponding to the change in the resistance value of the resistance change element MS per step is made by the driving circuit 1. This allows the user of the driving circuit 1 to easily amplify the change in the output voltage Vout corresponding to the change per step in the resistance value of the resistance change element MS to a desired level. In other words, the driving circuit 1 can improve the resolution of the change in the resistance value of the resistance change element MS.

[0027] Here, the constant current source CP may have any configuration as long as it is capable of determining the magnitude of the current flowing through the load resistance RL based on the input voltage Vin and the resistance value of the resistance change element MS.

[0028] FIG. 2 is a diagram showing an example of the configuration of the drive circuit 1 when a bipolar transistor is used as the constant current source CP.

[0029] In the example shown in Fig. 2, the terminal E31 of the constant current source CP is the collector terminal of a bipolar transistor. Also, in this example, the terminal E32 of the constant current source CP is the base terminal of the bipolar transistor. Also, in this example, the terminal E33 of the constant current source CP is the emitter terminal of the bipolar transistor. That is, in this example, the constant current source CP is a common-emitter bipolar transistor.

[0030] 2, when an input voltage Vin is applied to terminal E32 of constant current source CP, a base current flows to terminal E32. As a result, a collector current flows through load resistor RL, and an emitter current, which is a sum of the base current and collector current, flows through resistance change element MS.

[0031] Here, the magnitude of the collector current flowing through the load resistance RL is the magnitude of the base current flowing through terminal E32 of the constant current source CP amplified by hfe. hfe is the current amplification factor. Therefore, the magnitude of the collector current does not depend on the magnitude of the voltage Vc supplied by the constant voltage source Vdd or the resistance value of the load resistance RL. This means that the magnitude of the current flowing through the load resistance RL is determined by the input voltage Vin and the resistance value of the resistance change element MS. For these reasons, the constant current source CP shown in Figure 1 can be realized using a bipolar transistor.

[0032] The reason why a constant current source CP can be realized using a bipolar transistor will be explained using the equivalent circuit shown in Figure 3. Figure 3 is an equivalent circuit showing the drive circuit 1 shown in Figure 2. Resistor rb shown in Figure 3 indicates the resistance between the base and emitter of the bipolar transistor. Resistor re shown in Figure 3 indicates a resistor connected between the emitter terminal and ground, that is, a resistance change element MS. The constant current source shown in Figure 3 is a current source that flows a collector current ic that is hfe times the base current ib when an input voltage Vin is applied between the base and emitter shown in Figure 3 and a base current ib flows through resistor rb.

[0033] In the equivalent circuit shown in FIG. 3, the emitter current ie is expressed as the sum of the base current ib and the collector current ic, as shown in the following equation (1).

[0034] i=i+i (1)

[0035] In addition, the collector current ic is expressed by the current amplification factor hfe and the base current ib as shown in the following equation (2).

[0036] ic = hfe × ib (2)

[0037] From the above equations (1) and (2), the following equation (3) is obtained.

[0038] ie=ib+hfe×ib=ib(1+hfe) ···(3)

[0039] On the other hand, the input voltage Vin is expressed by the following equation (4) using Ohm's law.

[0040] Vin=rb×ib+re×ie =rb×ib+re×ib(1+hfe) =ib(rb+re(1+hfe)) (4)

[0041] Therefore, the collector current ic is expressed as follows:

[0042] ic=hfe×ib =hfe×(Vin / (rb+re×(1+hfe))) ···(5)

[0043] Here, when a bipolar transistor with hfe=150 is used as the constant current source CP, (1+hfe)~hfe. It is also known that the resistance rb between the base and emitter rapidly decreases when the base-emitter voltage is set to 0.75V or more. Therefore, rb can be ignored in the above equation (5). From the above, the above equation (5) can be approximated as the following equation (6).

[0044] ic ≒ hfe × (Vin / (re × hfe)) = Vin / re (6)

[0045] Therefore, the bipolar transistor can determine the magnitude of the current flowing through the load resistor RL by the input voltage Vin and the resistance value of the resistance change element MS. That is, the bipolar transistor is an example of an element that can be used as a constant current source CP.

[0046] Here, when the magnitude of the current flowing through the load resistor RL is determined by the input voltage Vin and the resistance value of the variable resistance element MS, the resistance value of the variable resistance element MS can be used as a weight for the multiplication operation by the neural network. In this case, as described above, the driving circuit 1 is used as an analog circuit that performs the multiplication operation in the neural network. When the driving circuit 1 is used as an analog circuit that performs the multiplication operation in the neural network, the user can amplify the resistance value of the variable resistance element MS, i.e., the change in the weight, to a desired magnitude and detect it. In other words, this improves the detection resolution of the change in the resistance value of the variable resistance element MS. Therefore, in this case, the result of the multiplication operation by the neural network is less likely to be disturbed by noise. In other words, the driving circuit 1 can suppress the calculation result of the neural network from being disturbed by noise in this case.

[0047] The driving circuit 1 described above uses a two-terminal magnetoresistance effect element as the resistance change element MS. However, the two-terminal magnetoresistance effect element often requires a complex circuit design to change the resistance value. Therefore, it is preferable that the driving circuit 1 includes a three-terminal magnetoresistance effect element as the resistance change element MS.

[0048] Fig. 4 is a diagram showing an example of the configuration of a drive circuit 1 including a three-terminal variable resistance element MS. For ease of explanation, the drive circuit 1 shown in Fig. 4 will be referred to as drive circuit 1A in the following description in order to distinguish it from the drive circuits 1 shown in Figs. 1 and 2.

[0049] The drive circuit 1A includes a load resistor RL, a resistance change element MSA, a constant current source CP, a switch element SH, and a resistance control circuit WC. The drive circuit 1A may be configured without either or both of the switch element SH and the resistance control circuit WC. In the drive circuit 1A, the configuration of the load resistor RL and the configuration of the constant current source CP are the same as those described in FIG. 1. Therefore, in FIG. 4, the description of the configuration of the load resistor RL and the configuration of the constant current source CP will be omitted.

[0050] The resistance change element MSA is a three-terminal type magnetoresistance effect element. Therefore, in this example, the resistance change element MSA is an SOT type magnetoresistance effect element, a domain wall motion type magnetoresistance effect element, etc. In the following, as an example, a case where the resistance change element MSA is a domain wall motion type magnetoresistance effect element will be described.

[0051] The resistance change element MSA has three terminals, terminal E21, terminal E22, and terminal E23. When a voltage is applied between terminals E22 and E23, a domain wall in the resistance change element MSA moves, changing the resistance value of the resistance change element MSA. That is, terminals E22 and E23 are terminals used in writing a resistance value to the resistance change element MSA. On the other hand, when a voltage is applied between terminals E21 and E23, the driving circuit 1A outputs an output voltage Vout. That is, terminals E21 and E23 are terminals used in reading the resistance value of the resistance change element MSA (for example, reading the result of a multiplication operation when the driving circuit 1A is used as an analog circuit that performs a multiplication operation in a neural network).

[0052] The terminal E21 is connected to a terminal E33 of the constant current source CP via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminals E21 and E33 as long as the functions of the drive circuit 1 are not impaired.

[0053] The terminal E22 is connected to one of the two terminals of the switch element SH via a transmission line. The other of the two terminals of the switch element SH is connected to an output terminal of the resistance control circuit WC via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E22 and the switch element SH as long as the function of the drive circuit 1 is not impaired. Note that other elements, other members, other circuits, other devices, etc. may be connected between the switch element SH and the resistance control circuit WC as long as the function of the drive circuit 1 is not impaired.

[0054] The terminal E23 is connected to the ground via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E23 and the ground as long as the functions of the drive circuit 1 are not impaired.

[0055] The switch element SH may be any element that can switch the state between the resistance change element MS and the resistance control circuit WC between a conducting state and an insulating state in response to a received operation or an input signal. Although the switch element SH is depicted as a two-terminal element in FIG. 4, it may be a three-terminal element or an element having four or more terminals.

[0056] The resistance control circuit WC is a circuit that applies a voltage between the terminals E22 and E23 of the resistance change element MSA by outputting a pulse signal from the output terminal, thereby changing the resistance value of the resistance change element MSA. The resistance control circuit WC may be any circuit as long as it is a circuit that can change the resistance value of the resistance change element MSA by such a method.

[0057] As described above, even in the configuration including a three-terminal magnetoresistance effect element, the drive circuit 1A determines the magnitude of the current flowing through the load resistance RL based on the input voltage Vin and the resistance value of the resistance change element MSA. Even in this case, the drive circuit 1A outputs the voltage across the load resistance RL as the output voltage Vout. This allows the drive circuit 1A to improve the detection resolution of the change in resistance value of the resistance change element MSA by the output voltage Vout based on the resistance value of the load resistance RL. As a result, even in this case, when the drive circuit 1A is used as an analog circuit that performs a multiplication operation in a neural network, it is possible to suppress the operation result of the neural network from being disturbed by noise. And, by including the three-terminal resistance change element MSA, the drive circuit 1A can easily change the resistance value of the resistance change element MSA while suppressing the operation result of the neural network from being disturbed by noise. This is extremely desirable because it makes it easier to design a circuit that performs the operation of the neural network and leads to suppressing an increase in the manufacturing cost of the circuit.

[0058] The switch element SH is used, for example, to cut off current from flowing through the resistance control circuit WC when a collector current is passed through the load resistance RL. Therefore, when the resistance control circuit WC does not change the resistance value of the resistance change element MSA, the switch element SH electrically insulates between the resistance change element MSA and the resistance control circuit WC, and when the resistance value is changed, the switch element SH electrically connects between the resistance change element MSA and the resistance control circuit WC. This allows the drive circuit 1A to prevent the resistance control circuit WC from being broken and to stabilize the output voltage Vout with respect to the input of the input voltage Vin.

[0059] <First Modification of the Embodiment> The following describes Modification 1 of the embodiment. In Modification 1 of the embodiment, a plurality of drive circuits 1 constitute an array circuit 2. In the following, as an example, a case where each of the drive circuits 1 among the plurality of drive circuits 1 constituting the array circuit 2 is the drive circuit 1A shown in FIG. 4 will be described.

[0060] Fig. 5 is a diagram showing an example of the configuration of the array circuit 2. In the example shown in Fig. 5, the array circuit 2 includes N driving circuits 1A. N may be any integer equal to or greater than 2. In Fig. 5, these N driving circuits 1A are each shown distinguishably as driving circuit 1A-1, driving circuit 1A-2, ..., driving circuit 1A-N.

[0061] In the array circuit 2, as shown in FIG. 5, the N driving circuits 1A are connected in parallel with a shared load resistance RL. In addition, in the array circuit 2, the N driving circuits 1A are connected in parallel with a shared resistance control circuit WC. That is, the array circuit 2 includes one load resistance RL, N constant current sources CP, N resistance change elements MSA, N switch elements SH, and one resistance control circuit WC. Note that other elements, other members, other circuits, other devices, etc. may be connected between each of the N driving circuits 1A and the load resistance RL as long as the function of the array circuit 2 is not impaired. Also, other elements, other members, other circuits, other devices, etc. may be connected between each of the N driving circuits 1A and the resistance control circuit WC as long as the function of the array circuit 2 is not impaired.

[0062] Here, in this specification, when the array circuit 2 has one load resistance RL, it does not mean that the load resistance RL is composed of one resistance element. In this specification, when the array circuit 2 has one load resistance RL, it means that the array circuit 2 has, as one load resistance RL, a collection of one or more resistance elements that function as the load resistance RL across which the output voltage Vout is generated. In other words, in the array circuit 2, the load resistance RL is composed of one or more resistance elements.

[0063] In the example shown in FIG. 5, the collector terminal of the constant current source CP included in each of the N driving circuits 1A is connected to the terminal E12 of the load resistor RL via a transmission line. In this example, an input voltage Vin is applied independently to the base terminal of the constant current source CP included in each of the N driving circuits 1A. Here, in FIG. 5, the input voltage Vin applied to the base terminal of the constant current source CP of the i-th driving circuit 1A-i is represented by an input voltage Vin-i. Here, i represents any integer from 1 to N. Note that the input voltages Vin applied to the base terminals of the constant current sources CP of some or all of the N driving circuits 1A may be different from each other or may be the same. That is, for example, the input voltages Vin-1 and Vin-2 may be voltages of different magnitudes from each other or may be voltages of the same magnitude.

[0064] In addition, in the array circuit 2, the load resistance RL of each of the N driving circuits 1A is shared, so that a current consisting of the collector currents from the constant current sources CP of each of the N driving circuits 1A flows through the load resistance RL. For example, when only the two driving circuits 1A, driving circuit 1A-1 and driving circuit 1A-2, pass a collector current, a current consisting of the collector current from driving circuit 1A-1 and the collector current from driving circuit 1A-2 flows through the load resistance RL. This allows the array circuit 2 to function as a product-sum calculation circuit that calculates the sum of the results of product calculations performed by each of the N driving circuits 1A when the driving circuits 1A are used as analog circuits that perform product calculations in a neural network.

[0065] Furthermore, in the array circuit 2, the resistance control circuit WC has N output terminals. Each of these N output terminals is connected so as not to overlap with any of the terminals E22 of the N resistance change elements MSA. This allows the resistance control circuit WC to independently change the resistance value of each of the N resistance change elements MSA in the array circuit 2.

[0066] <Modification 2 of the embodiment> The second modification of the embodiment will be described below. The second modification of the embodiment is a modification of the first modification of the embodiment. In the first modification of the embodiment, the load resistance RL is connected between the constant voltage source Vdd and the collector terminal of the constant current source CP, so the voltage across the load resistance RL is not a potential difference from the ground potential. In the second modification of the embodiment, the load resistance RL is connected between the constant voltage source Vdd and the ground, so that the input voltage Vin and the output voltage Vout to each of the N driving circuits 1A are positive potentials with the ground potential as a reference potential.

[0067] Fig. 6 is a diagram showing another example of the configuration of the array circuit 2. In the following, for convenience of explanation, the array circuit 2 shown in Fig. 6 will be referred to as an array circuit 2A in order to distinguish it from the array circuit 2 shown in Fig. 5.

[0068] In the array circuit 2A, as shown in Fig. 6, the N driving circuits 1A are connected in parallel with a shared load resistance RL. However, in the array circuit 2A, the N driving circuits 1A are connected to the load resistance RL via a current mirror CM. Also, in the array circuit 2, the N driving circuits 1A are connected in parallel with a shared resistance control circuit WC. That is, the array circuit 2 includes one load resistance RL, a current mirror CM, N constant current sources CP, N resistance change elements MSA, N switch elements SH, and one resistance control circuit WC.

[0069] The current mirror CM includes two field effect transistors, a field effect transistor F1 and a field effect transistor F2. The drain terminals of the field effect transistor F1 and the field effect transistor F2 are connected to a constant voltage source Vdd via a transmission line. The source terminal of the field effect transistor F1 is connected to the collector terminals of the N constant current sources CP via a transmission line. The source terminal of the field effect transistor F2 is connected to a terminal E11 of the load resistor RL via a transmission line. The terminal E22 of the load resistor RL is grounded to the ground via a transmission line. The gate terminal of the field effect transistor F1 is connected to the gate terminal of the field effect transistor F2 and the source terminal of the field effect transistor F1 via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the current mirror CM and each of the N constant current sources CP as long as they do not impair the function of the array circuit 2A. Furthermore, other elements, other members, other circuits, other devices, etc. may be connected between each of the N driving circuits 1A and the resistance control circuit WC as long as they do not impair the function of the array circuit 2. Furthermore, in the array circuit 2A, the connection modes other than the connection mode related to the current mirror CM are the same as the connection mode of the array circuit 2, so descriptions thereof will be omitted.

[0070] As a result, the current mirror CM passes a current to the load resistance RL that is equal to the total collector currents flowing through the collector terminals of the N constant current sources CP. When the current flows through the load resistance RL, the voltage across the load resistance RL is a positive potential with the ground potential as the reference potential. On the other hand, in the array circuit 2A, the input voltage Vin applied to the base terminals of the N constant current sources CP is also a positive potential with the ground potential as the reference potential. This is because the ground potential of the input voltage Vin and the ground potential of the output voltage Vout are common in the array circuit 2A. This makes it easier for circuit designers to design a circuit including the array circuit 2A. That is, the array circuit 2A can easily design a circuit including the array circuit 2A while suppressing the result of the product-sum operation of the neural network from being disturbed by noise.

[0071] <Modification 3 of the embodiment> The third modification of the embodiment will be described below. The third modification of the embodiment is a modification of the first modification of the embodiment. In the third modification of the embodiment, the array circuit 2 can increase or decrease the magnitude of the current flowing through the load resistor RL without changing the magnitude of the input voltage Vin applied to the base terminal of each of the N constant current sources CP. For example, when the array circuit 2 is used as a circuit that performs a product-sum operation in a neural network, this corresponds to adding or subtracting a bias constant term to or from the result of the product-sum operation in the neural network.

[0072] FIG. 7 is a diagram showing yet another example of the configuration of the array circuit 2. In the following, for convenience of explanation, the array circuit 2 shown in FIG. 7 will be referred to as an array circuit 2B in order to distinguish it from the array circuit 2 shown in FIG. 5. In the example shown in FIG. 7, the array circuit 2B includes four drive circuits 1 including two-terminal type resistance change elements MS. In FIG. 7, these four drive circuits 1 are shown as drive circuit 1-1, drive circuit 1-2, ..., drive circuit 1-N so that they can be distinguished from one another. Note that the array circuit 2B may be configured to include a three-terminal type drive circuit 1A instead of the two-terminal type drive circuit 1.

[0073] In the array circuit 2B, as shown in FIG. 7, the four driving circuits 1 are connected in parallel with a shared load resistance RL via a transmission line. For this reason, the terminal E12 of the load resistance RL is connected to the terminal E21 of each of the four driving circuits 1 via a transmission line. In addition, in the array circuit 2, the terminal E22 of each of the four resistance change elements MS is grounded to the ground via a transmission line. The terminal E12 of the load resistance RL is connected to the output terminal of the current flow-in / out circuit IO via a transmission line. That is, the array circuit 2B includes one load resistance RL, four constant current sources CP, four resistance change elements MS, and a current flow-in / out circuit IO. Note that other elements, other members, other circuits, other devices, etc. may be connected between the load resistance RL and each of the four constant current sources CP as long as the function of the array circuit 2B is not impaired. Also, other elements, other members, other circuits, other devices, etc. may be connected between the load resistance RL and the current flow-in / out circuit IO as long as the function of the array circuit 2B is not impaired. In addition, other elements, other members, other circuits, other devices, etc. may be connected between the current input / output circuit IO and each of the four constant current sources CP, as long as the function of the array circuit 2B is not impaired. In addition, other elements, other members, other circuits, other devices, etc. may be connected between the terminals E21 of each of the four constant current sources CP and the resistance change element MS, as long as the function of the array circuit 2B is not impaired. In addition, other elements, other members, other circuits, other devices, etc. may be connected between each of the four resistance change elements MS and the ground, as long as the function of the array circuit 2B is not impaired.

[0074] The current input / output circuit IO may be any circuit that can at least one of inputting a current to the load resistor RL and outputting a current from the load resistor RL. In the example shown in Fig. 7, the current input / output circuit IO includes a constant current source CP, a constant current source CP2, a DC voltage source DP, and a resistance change element MS.

[0075] The constant current source CP2 is a constant current source having two terminals, and supplies a current of a predetermined magnitude to the constant current source CP3 in response to the voltage Vc supplied from the constant voltage source Vdd.

[0076] One of the two terminals of the constant current source CP2 is connected to the constant voltage source Vdd through a transmission line. The other of the two terminals of the constant current source CP2 is connected to the terminal E31 of the constant current source CP3 through a transmission line. The terminal E32 of the constant current source CP3 is connected to the high potential terminal of the DC voltage source DP through a transmission line. The terminal E33 of the constant current source CP3 is connected to the terminal E21 of the resistance change element MS through a transmission line. The terminal E22 of the resistance change element MS is grounded to the ground through a transmission line. The low potential terminal of the DC voltage source DP is grounded to the ground through a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the constant current source CP2 and the constant voltage source Vdd as long as the function of the current inflow / outflow circuit IO is not impaired. In addition, other elements, other members, other circuits, other devices, etc. may be connected between the constant current source CP2 and the constant current source CP as long as the function of the current input / output circuit IO is not impaired. In addition, other elements, other members, other circuits, other devices, etc. may be connected between the constant current source CP and the DC voltage source DP as long as the function of the current input / output circuit IO is not impaired. In addition, in the current input / output circuit IO, other elements, other members, other circuits, other devices, etc. may be connected between the constant current source CP and the resistance change element MS as long as the function of the current input / output circuit IO is not impaired. In addition, in the current input / output circuit IO, other elements, other members, other circuits, other devices, etc. may be connected between the resistance change element MS and the ground as long as the function of the current input / output circuit IO is not impaired.

[0077] The current input / output circuit IO configured as above flows the difference between the currents flowed by the constant current source CP2 and the constant current source CP3 toward the constant current source CP of each of the four driving circuits 1. This allows the current input / output circuit IO to reduce the current flowing through the load resistance RL. The magnitude of this difference changes according to the change in the resistance value of the resistance change element MS included in the current input / output circuit IO. In other words, the user can adjust the extent to which the magnitude of the current flowing through the load resistance RL of the array circuit 2B is reduced by changing the resistance value.

[0078] In addition, when the current input / output circuit IO does not include the constant current source CP3 and the DC voltage source DP, that is, when the constant current source CP2 is connected between the constant voltage source Vdd and the resistance change element MS, the current input / output circuit IO increases the magnitude of the current flowing through the load resistance RL according to the resistance value of the resistance change element MS included in the current input / output circuit IO. In other words, in this case, the user can adjust the range by which the magnitude of the current flowing through the load resistance RL of the array circuit 2B is increased by changing the resistance value.

[0079] In this way, in the array circuit 2B, the current input / output circuit IO can adjust the magnitude of the current flowing through the load resistor RL. As described above, this corresponds to adding / subtracting a bias constant term to / from the result of the product-sum operation in the neural network when the array circuit 2B is used as a circuit that performs product-sum operation in the neural network. In other words, in this case, the array circuit 2B can add / subtract a bias constant term to / from the result of the product-sum operation in the neural network.

[0080] The array circuit 2 shown in the first to third modified examples of the embodiment described above can be used as a circuit that performs a product-sum operation using a neural network. That is, a neuromorphic device can be configured by using the array circuit 2. In other words, a neuromorphic device including the array circuit 2 can perform a product-sum operation using a neural network while suppressing the disturbance of the operation result due to noise. Note that the array circuit 2 may be configured to be provided in any type of circuit, electronic device, device, member, etc., instead of a neuromorphic device.

[0081] <Fourth Modification of the Embodiment> The following describes the fourth modification of the embodiment. In the fourth modification of the embodiment, the drive circuit 1 is realized by a current mirror instead of a bipolar transistor. For convenience of explanation, the drive circuit 1 according to the fourth modification of the embodiment will be referred to as a drive circuit 1B below.

[0082] FIG. 8 is a diagram showing an example of the configuration of the drive circuit 1B.

[0083] The drive circuit 1B includes a load resistor RL, a resistance change element MS, a constant current source CP3, and a field effect transistor F3. The drive circuit 1B outputs the voltage across the load resistor RL as an output voltage Vout. The drive circuit 1B may not include the field effect transistor F3. The load resistor RL and the resistance change element MS are configured similarly to those described in FIG. 1, and therefore will not be described.

[0084] First, the connection state of the load resistor RL, the resistance change element MS, the constant current source CP3, and the field effect transistor F3 in the drive circuit 1B will be described.

[0085] The constant current source CP3 has three terminals: a terminal E41, a terminal E42, and a terminal E43.

[0086] The terminal E11 of the load resistor RL is connected to a constant voltage source Vdd. That is, a voltage Vc is applied to the terminal E11 of the load resistor RL. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E11 and the constant voltage source Vdd as long as the function of the drive circuit 1B is not impaired.

[0087] A terminal E12 of the load resistor RL is connected to a terminal E41 of the constant current source CP3. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E12 and the constant current source CP3 as long as they do not impair the function of the drive circuit 1B.

[0088] A transmission line for detecting the output voltage Vout is connected to both ends of the load resistor RL. In order to simplify the drawing, an external device for detecting the output voltage Vout is omitted in FIG.

[0089] A terminal E42 of the constant current source CP3 is connected to a terminal E21 of the resistance change element MS via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E42 and the resistance change element MS as long as the function of the drive circuit 1B is not impaired.

[0090] The terminal E43 of the constant current source CP3 is grounded via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E43 and the ground as long as they do not impair the function of the drive circuit 1B.

[0091] The terminal E22 of the resistance change element MS is a terminal to which the input voltage Vin is input. Therefore, an external circuit, an external device, etc. capable of supplying the input voltage Vin to the terminal E22 is connected to the terminal E22. In FIG. 8, in order to simplify the drawing, such external circuits, external devices, etc. are omitted. Note that other elements, other members, other circuits, other devices, etc. may be connected between the terminal E22 and these external circuits, external devices, etc., as long as the function of the drive circuit 1B is not impaired.

[0092] The drain terminal of the field effect transistor F3 is connected to an external circuit, an external device, etc. via a transmission line. These external circuits, external devices, etc. are external circuits, external devices, etc. connected to the terminal E22 of the resistance change element MS. This drain terminal is a terminal that provides a reference potential of the input voltage Vin. That is, in the fourth modification of the embodiment, the input voltage Vin is a potential difference from the potential of this drain terminal. Note that other elements, other members, other circuits, other devices, etc. may be connected between this drain terminal and these external circuits, external devices, etc., as long as the function of the drive circuit 1B is not impaired.

[0093] The gate terminal of the field effect transistor F3 is connected to the drain terminal of the field effect transistor F3 via a transmission line. That is, the field effect transistor F3 is a bias circuit. Note that other elements, other members, other circuits, other devices, etc. may be connected between the gate terminal and the drain terminal as long as the function of the drive circuit 1B is not impaired.

[0094] The source terminal of the field effect transistor F3 is grounded via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the source terminal and the ground as long as they do not impair the function of the drive circuit 1B.

[0095] Here, the constant current source CP3 is a current mirror including two field effect transistors, a field effect transistor F4 and a field effect transistor F5.

[0096] The drain terminal of the field effect transistor F4 is connected to the terminal E42 of the constant current source CP3, the gate terminal of the field effect transistor F4, and the gate terminal of the field effect transistor F5 via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between this drain terminal and the terminal E42 as long as the function of the drive circuit 1B is not impaired. Also, other elements, other members, other circuits, other devices, etc. may be connected between this drain terminal and each of these two gate terminals as long as the function of the drive circuit 1B is not impaired.

[0097] The source terminal of the field effect transistor F4 is connected to the terminal E43 of the constant current source CP3 and the source terminal of the field effect transistor F5 via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between each of these two source terminals and the terminal E42, as long as the function of the drive circuit 1B is not impaired. Also, other elements, other members, other circuits, other devices, etc. may be connected between these two source terminals, as long as the function of the drive circuit 1B is not impaired.

[0098] The drain terminal of the field effect transistor F5 is connected to the terminal E41 of the constant current source CP3 via a transmission line. Note that other elements, other members, other circuits, other devices, etc. may be connected between the drain terminal and the terminal E41 as long as they do not impair the function of the drive circuit 1B.

[0099] The driving circuit 1B configured as above also determines the magnitude of the current flowing through the load resistor RL based on the input voltage Vin and the resistance value of the variable resistance element MS, similarly to each of the driving circuits 1 and 1A. This allows the driving circuit 1B to improve the resolution of the change in the resistance value of the variable resistance element MS. As a result, for example, when the driving circuit 1B is used as an analog circuit that performs a multiplication operation in a neural network, the user can amplify and detect the resistance value of the variable resistance element MS, that is, the change in the weight, to a desired magnitude. This can also be said to improve the detection resolution of the change in the resistance value of the variable resistance element MS. Therefore, in this case, the result of the multiplication operation by the neural network is less likely to be disturbed by noise. In other words, in this case, the driving circuit 1B can suppress the calculation result of the neural network from being disturbed by noise.

[0100] In the driving circuit 1B as well, the resistance change element MS may be replaced with a three-terminal magnetoresistance effect element.

[0101] <Drive circuit configuration> A method for configuring the drive circuit 1 described above will be described below. The constant current source CP and the resistance change element MS of the drive circuit 1 may be stacked on a substrate as an integrated circuit. In the following, as an example, a case where the constant current source CP of the drive circuit 1A and the three-terminal resistance change element MSA are stacked on a substrate as an integrated circuit will be described. FIG. 9 is an image diagram showing an example of how the constant current source CP of the drive circuit 1A and the three-terminal resistance change element MSA are stacked on a substrate as an integrated circuit by a top pin structure. In FIG. 9, the substrate is omitted to simplify the drawing.

[0102] In the example shown in FIG. 9, when the constant current source CP and the resistance change element MSA are viewed toward the stacking direction in which the constant current source CP and the resistance change element MSA are stacked, the constant current source CP and the resistance change element MSA are almost overlapped in a top pin structure. In other words, in this example, the constant current source CP, which is a bipolar transistor, is arranged on the bottom surface of the resistance change element MSA arranged in a top pin structure so that the constant current source CP and the resistance change element MSA overlap in this case. This makes it possible to prevent the integrated circuit of the drive circuit 1 from becoming large. In addition, in FIG. 9, in order to simplify the figure, transmission lines and the like connected to the terminals E21, E22, and E23 of the resistance change element MSA and the terminals E31, E32, and E33 of the constant current source CP are omitted. Also, the domain wall DW shown in FIG. 9 shows an example of a domain wall of the resistance change element MSA, which is a domain wall motion type magnetoresistance effect element.

[0103] Here, the layer L1 of the resistance change element MS is an example of a domain wall displacement layer in a domain wall displacement type magnetoresistance effect element. The layer L2 of the resistance change element MS is an example of a non-magnetic layer in the magnetoresistance effect element. The layer L3 of the resistance change element MS is an example of a magnetization fixed layer in which the magnetization direction is fixed among the layers in the magnetoresistance effect element.

[0104] The constant current source CP and the resistance change element MS may be stacked on the substrate in a bottom-top-pin structure. In this case, the constant current source CP and the resistance change element MSA of the drive circuit 1 are stacked on the substrate as shown in Fig. 10. Fig. 10 is an image diagram showing an example of a state in which the constant current source CP of the drive circuit 1A and the three-terminal resistance change element MSA are stacked on the substrate as an integrated circuit in a bottom-top-pin structure.

[0105] In the example shown in FIG. 10, when the constant current source CP and the resistance change element MSA are viewed toward the stacking direction in which the constant current source CP and the resistance change element MSA are stacked, the constant current source CP and the resistance change element MSA are almost overlapped in a bottom-top pin structure. In other words, in this example, the constant current source CP, which is a bipolar transistor, is arranged on the bottom surface of the resistance change element MSA arranged in a bottom-top pin structure so that the constant current source CP and the resistance change element MSA overlap in this case. Even in this case, the integrated circuit of the drive circuit 1 can be prevented from becoming large. The transmission line LL1 shown in FIG. 10 is an example of a transmission line that connects the terminal E33 of the constant current source CP and the terminal E21 of the resistance change element MS. The transmission line LL2 shown in FIG. 10 is an example of a transmission line that is connected to an external device that inputs the input voltage Vin to the constant current source CP. The transmission line LL3 shown in FIG. 10 is an example of a transmission line that connects the terminal E31 of the constant current source CP and the load resistor RL. 10 is an example of a transmission line that connects the terminal E23 of the resistance change element MS to the ground. Also, the transmission line LL5 shown in Fig. 10 is an example of a transmission line that connects the constant current source CP to the resistance control circuit WC.

[0106] As described above, the driving circuit according to the embodiment (in the above-described examples, the driving circuit 1, the driving circuit 1A, and the driving circuit 1B) includes a load resistance (in the above-described examples, the load resistance RL), a variable resistance element (in the above-described examples, the variable resistance element MS) having at least a first terminal (in the above-described examples, the terminal E21 of the variable resistance element MS) and a second terminal (in the above-described examples, the terminal E22 of the variable resistance element MS), capable of changing the resistance value based on the magnetoresistance effect, and a constant current source (in the above-described examples, the constant current source CP) that determines the magnitude of the current flowing through the load resistance based on the input voltage (in the above-described examples, the input voltage Vin) and the resistance value of the variable resistance element, and outputs the voltage across the load resistance (in the above-described examples, the voltage between the terminal E11 of the load resistance RL and the terminal E12 of the load resistance RL) as an output voltage (in the above-described examples, the output voltage Vout). This allows the driving circuit to improve the resolution of the change in the resistance value of the variable resistance element.

[0107] Furthermore, the drive circuit may be configured such that the load resistor has a selectable resistance value.

[0108] Furthermore, in the drive circuit, a configuration may be used in which the resistance change element has a third terminal (terminal E23 of the resistance change element MS in the example described above) in addition to the first terminal and the second terminal.

[0109] In addition, in the drive circuit, a configuration may be used in which the resistance change element is a domain wall motion type.

[0110] In addition, in the drive circuit, a configuration may be used in which the resistance value of the resistance change element changes when a voltage is applied between the second terminal and the third terminal, and the drive circuit further includes a resistance control circuit (in the example described above, the resistance control circuit WC) that applies a voltage between the second terminal and the third terminal.

[0111] Furthermore, the drive circuit may have a configuration in which a switch element (switch element SH in the example described above) is connected between at least one of the second terminal and the third terminal and the resistance control circuit.

[0112] In addition, in the drive circuit, a configuration may be used in which one of the two terminals of the load resistor is connected to a constant voltage source (in the example described above, the constant voltage source Vdd), and the constant current source is a bipolar transistor having a base terminal to which an input voltage is applied, a collector terminal connected to the other of the two terminals of the load resistor, and an emitter terminal connected to a first terminal of the resistance change element.

[0113] The drive circuit may have a configuration in which a variable resistance element and a bipolar transistor are stacked as an integrated circuit.

[0114] Furthermore, the array circuits according to the embodiments (in the examples described above, the array circuit 2, the array circuit 2A, and the array circuit 2B) may have a configuration in which resistance change elements and bipolar transistors are stacked as an integrated circuit.

[0115] In addition, in the array circuit, a load resistor shared by multiple driving circuits and a constant current source in each of the multiple driving circuits are connected via a current mirror (current mirror CM in the example described above), and a configuration in which the ground potential of the input voltage and the ground potential of the output voltage are shared may be used.

[0116] In addition, the array circuit may be configured to connect a current input / output circuit (in the example described above, the current input / output circuit IO) that is capable of at least one of flowing current into the load resistance and flowing current out of the load resistance.

[0117] In addition, the array circuit may be configured to connect a current input / output circuit (in the example described above, the current input / output circuit IO) that is capable of at least one of flowing current into the load resistance and flowing current out of the load resistance. [Explanation of symbols]

[0118] 1, 1-1, 1-2, 1A, 1A-1, 1A-2, 1A-i, 1A-N, 1B, 1-N...drive circuit, 2, 2A, 2B...array circuit, CM...current mirror, CP, CP2, CP3...constant current source, DP...DC voltage source, F1, F2, F3, F4, F5...field effect transistor, IO...current inflow / outflow circuit, MS, MSA...resistance change element, RL...load resistor, SH...switch element, Vdd...constant voltage source, WC...resistance control circuit

Claims

1. The load resistance, a resistance change element having at least a first terminal and a second terminal and capable of changing a resistance value based on a magnetoresistance effect; a constant current source that determines the magnitude of a current flowing through the load resistor based on an input voltage and a resistance value of the variable resistance element; Equipped with The voltage across the load resistor is output as an output voltage. Drive circuit.

2. The load resistor has a selectable resistance value.

2. The drive circuit according to claim 1.

3. The resistance change element has a third terminal in addition to the first terminal and the second terminal.

3. A drive circuit according to claim 1 or 2.

4. The resistance change element is a domain wall motion type.

4. The drive circuit according to claim 3.

5. When a voltage is applied between the second terminal and the third terminal, the resistance change element changes a resistance value, the drive circuit further includes a resistance control circuit that applies a voltage between the second terminal and the third terminal; 5. The drive circuit according to claim 4.

6. a switch element is connected between at least one of the second terminal and the third terminal and the resistance control circuit; 6. The drive circuit according to claim 5.

7. One of the two terminals of the load resistor is connected to a constant voltage source, the constant current source is a bipolar transistor including a base terminal to which the input voltage is applied, a collector terminal connected to the other of the two terminals of the load resistor, and an emitter terminal connected to a first terminal of the resistance change element; A driving circuit according to any one of claims 1 to 6.

8. The resistance change element and the bipolar transistor are stacked as an integrated circuit.

8. The drive circuit according to claim 7.

9. A plurality of drive circuits according to any one of claims 1 to 8 are provided, The plurality of driving circuits are connected in parallel with each other, with the load resistance being shared. Array circuit.

10. the load resistor shared by the plurality of drive circuits and the constant current source in each of the plurality of drive circuits are connected via a current mirror; The ground potential of the input voltage and the ground potential of the output voltage are common.

10. The array circuit of claim 9.

11. A current input / output circuit capable of at least one of inputting a current to the load resistor and outputting a current from the load resistor is connected.

11. An array circuit according to claim 9 or 10.

12. 12. An array circuit comprising: an array circuit according to claim 9, Neuromorphic devices.

Images