JP2009182745A - Signal amplifying circuit and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a weak signal amplifying circuit for achieving low noise and a high power gain by amplifying output power of a superconducting quantum interference device in a region including a microwave region in particular. <P>SOLUTION: One or a plurality of pulse amplifying circuits are provided in a serial configuration by utilizing the matter that a superconducting circuit can amplify and reproduce an output pulse string of the superconducting quantum interference device, and otherwise, in a parallel configuration in which a plurality of pulse strings generated through a branching circuit is amplified, and a synthesizing circuit subsequently synthesizes and outputs the plurality of pulse strings, an output of the superconducting quantum interference device is amplified. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric signal amplification technique, and more particularly to a minute signal amplification circuit using a superconducting element.

  As described in Non-Patent Document 1, a superconducting quantum interference device is a device using a superconducting Josephson junction, and is used as an amplifying device having a low noise in a wide frequency range from a direct current to a microwave band. Yes. Basically, a superconducting quantum interference device is a device that converts a magnetic field into a voltage, but by forming a coil that creates a magnetic field in the device, it can be used as an amplifier that converts a current into a voltage.

  When used as an amplifier, a superconducting quantum interference device is normally used as an analog device that amplifies a voltage proportional to an input current. However, when observed on a very short time scale, the superconducting quantum interference device outputs a number of voltage pulse trains proportional to the input magnetic field. In the conventional readout method, the integrated voltage is read out without taking out the pulse train as it is.

  Non-patent document 2 is cited as a document describing a technique related to the present invention. Non-Patent Document 2 refers to a circuit that performs operations such as replication of an output voltage pulse train of a superconducting quantum interference device and power amplification of individual pulses using a superconducting Josephson junction.

J. et al. Clarke and A.C. “The SQUID Handbook” by Braginski, Wiley-Vch, 2004 RSFQ Logic / Memory Family, K.M. K. Likharev and V.M. K. Semenov (IEEE Trans. On Appl. Supercond. Vol1. Pp. 3-28, 1991)

  Although the superconducting quantum interference device is very low noise and suitable for amplifying a minute electric signal, the output power that can be taken out is as small as 1 μW or less (Non-patent Document 1). This is because the output voltage is limited to about 2 mV and the current that can be practically applied is up to about 100 μA. This problem is particularly serious in the microwave region where it is difficult to take a technique such as arraying superconducting quantum interference elements (Non-patent Document 1).

  The present invention has been made in view of such a situation, and the problem to be solved by the present invention is to reduce the noise by amplifying the output power of the superconducting quantum interference device particularly in a region including a microwave region. It is another object of the present invention to provide a minute signal amplifier circuit that realizes a high power gain.

  In order to solve the above-described problems, the present invention amplifies the output of the superconducting quantum interference device by utilizing the fact that the output pulse train of the superconducting magnetic flux quantum device can be amplified and duplicated by a superconducting circuit.

  That is, the present invention has, as one aspect thereof, in a signal amplification circuit, a superconducting quantum interference device to which a signal to be amplified is input, and an amplification that amplifies and outputs the power of a pulse output from the superconducting quantum interference device. And a signal amplifying circuit including the circuit.

  It is conceivable that at least a part of the amplifier circuit includes one or a plurality of pulse amplifier circuits which are circuits for amplifying the magnitude of the input pulse train. For example, a signal amplifier circuit composed of a superconducting quantum interference device and a single pulse amplifier circuit may be used. When the amplifier circuit includes a plurality of pulse amplifier circuits, at least a part of the plurality of pulse amplifier circuits may be connected in series with each other. By connecting a plurality of pulse amplification circuits in series, a larger amplification factor can be obtained as compared with the case of using them alone.

  When the plurality of pulse amplifier circuits connected in series each have a Josephson junction, the critical current of the Josephson junction of one pulse amplifier circuit of the plurality of pulse amplifier circuits connected in series is the current of the pulse amplifier circuit. If it is larger than the critical current of the Josephson junction of another pulse amplification circuit connected in series with the previous stage, the pulse train enlarged by the previous stage pulse amplification circuit can be further enlarged by the subsequent stage pulse amplification circuit. .

  As at least a part of the amplifier circuit, a branch circuit that outputs a plurality of pulse trains that are the same as the input pulse train, and a synthesis circuit that synthesizes and outputs a plurality of pulse trains output by the branch circuit may be provided. That is, as the amplifier circuit, a branch circuit and a synthesis circuit may be provided instead of the pulse amplifier circuit or together with the pulse amplifier circuit. In this case, if a switch for turning on / off the connection between at least one of the outputs of the branch circuit and the synthesis circuit is further provided, the number of pulse trains synthesized by the synthesis circuit can be reduced by controlling on / off of the switch. It becomes possible to control the power amplification factor of the signal amplifier circuit.

  The branch circuit can be composed of, for example, one pulse amplification circuit and a plurality of pulse amplification circuits connected in parallel to the output of the one pulse amplification circuit.

  A configuration example of the pulse amplifier circuit includes first, second, third, and fourth inductors connected in series in the same order, and a node between the first and second inductors is a first Josephson junction. It is conceivable that the node between the third and fourth inductors is connected to the second Josephson coupling, and the node between the second and third inductors is connected to the current source.

  According to another aspect of the present invention, there is provided a method for amplifying a signal, the step of inputting a signal to be amplified to a superconducting quantum interference device, and the output of the superconducting quantum interference device to an amplifying circuit. And a signal amplification method including an amplification step of amplifying power.

  In this signal amplification method, it is conceivable that at least part of the amplification step includes a step of amplifying the size of the input pulse train by a pulse amplification circuit. In that case, the magnitude of the pulse train may be gradually amplified by a plurality of pulse amplifier circuits connected in series with each other. In this way, by connecting a plurality of pulse amplification circuits in series, a larger amplification factor can be obtained as compared with the case where they are used alone. The plurality of pulse amplifier circuits connected in series each have a Josephson junction, and the critical current of the Josephson junction of one pulse amplifier circuit of the plurality of pulse amplifier circuits connected in series is the pulse amplifier circuit If the pulse current is larger than the critical current of the Josephson junction of the other pulse amplifier circuit connected in series with the previous stage, the pulse train enlarged by the previous stage pulse amplifier circuit may be further enlarged by the subsequent stage pulse amplifier circuit. I can do it.

  In the signal amplification method described above, as at least a part of the amplification stage, a branch stage that generates a plurality of pulse trains that are the same as the input pulse train in a branch circuit, and a plurality of pulse trains that are generated in the branch stage are combined in a synthesis circuit It is good also as including the synthetic | combination stage output in this way. In this case, if a switch provided between at least one of the outputs of the branch circuit and the synthesis circuit includes a step of controlling connection of at least a part of the input from the branch circuit to the synthesis circuit, the switch is turned on / off. By controlling, it becomes possible to control the number of pulse trains synthesized by the synthesis circuit, and the power amplification factor of the signal amplification circuit can be made variable.

  The branch circuit can be composed of one pulse amplification circuit and a plurality of pulse amplification circuits connected in parallel to the output of the one pulse amplification circuit.

  The pulse amplification circuit includes, for example, first, second, third, and fourth inductors connected in series in the same order, and a node between the first and second inductors is connected to the first Josephson junction, It is conceivable that the node between the third and fourth inductors is connected to the second Josephson coupling, and the node between the second and third inductors is connected to the current source.

  As a first effect of the present invention, the output power of the superconducting quantum interference device can be increased. As a result, the power gain of the signal amplification circuit using the superconducting quantum interference device can be improved.

  A minute signal amplifier circuit 1 according to an embodiment of the present invention will be described. Referring to FIG. 1, the minute signal amplification circuit 1 includes a superconducting quantum interference device 2, a current source 3, and an amplification circuit 4.

  The superconducting quantum interference device 2 is a circuit as shown in FIG. The two Josephson junctions 21 and 22 are short-circuited by a superconducting loop having an inductance L (hereinafter simply referred to as a loop). A tap is provided at the midpoint of the loop, and the loop is biased with a bias current Ibias close to the critical current Ic therefrom. In this state, the number of pulse trains depending on the magnetic flux Φ penetrating the loop is output. When the coil 23 is provided close to the loop and the current Iin flowing therethrough is changed, the magnetic flux passing through the loop changes according to Iin, and the number of pulse trains to be output changes accordingly. When the pulse train is integrated and taken out over time, the output voltage V appears to change in an analog manner according to the input current Iin. This is the amplification principle of the superconducting quantum interference device.

  The amplifying circuit 4 does not integrate the output pulse of the superconducting quantum interference device with time, and amplifies the output of the superconducting quantum interference device 2 in the form of a pulse with a digital amplifying circuit. In comparison, the circuit has a large amplification effect. The configuration of the amplifier circuit 4 can be broadly divided into (1) a circuit that amplifies only the magnitude of each pulse without changing the number and interval of pulses of the pulse train output from the superconducting quantum interference device 2, and (2) A circuit that obtains an amplification effect as a whole by synthesizing these replicas after generating a plurality of replicas of the pulse train output from the conduction quantum interference device 2, and (3) a circuit that combines (1) and (2) There are three.

(1) Amplifying the magnitude of a pulse This type of minute signal amplifier circuit 11 will be described with reference to FIG. The output pulse of the superconducting quantum interference device (SQUID) 2 is amplified by an amplifier circuit 41 corresponding to the amplifier circuit 4. The amplifier circuit 41 includes pulse amplifier circuits 40a and 40b. Although the pulse amplification circuits 40a and 40b are basically circuits having the same structure, the magnitudes of the critical currents Ic of the Josephson coupling in the circuits are different, and the critical currents of the Josephson coupling of the pulse amplification circuit 40b in the subsequent stage are: It is larger than that of the previous stage pulse amplification circuit 40a.

  Except for the magnitude of the critical current, the pulse amplifier circuits 40a and 40b are the same circuit. Both circuits will be described as a pulse amplifier circuit 40 with reference to FIG. The pulse amplification circuit 40 connects the coils 401, 402, 403, and 404 connected in series, the Josephson junction 405 that connects the coil 401 and the coil 402 to the ground, and the ground between the coil 403 and the coil 404. It consists of a Josephson junction 406. The critical currents of Josephson junctions 405 and 406 are both Ic. The pulse amplification circuit 40 performs an operation of outputting the pulse train input from the left end input terminal of the coil 401 as it is from the right end output terminal of the coil 404. Since the magnitude of the pulse train to be output depends on the critical current Ic of the Josephson junction, the pulse amplification circuit 40 has an effect of amplifying the input pulse train by increasing Ic.

  Even if only one stage of the pulse amplification circuit 40 is used as the amplification circuit 4 of the minute signal amplification circuit 1, the amplification action can be obtained, but the critical current Ic of the pulse amplification circuit 40 is the Josephson of the superconducting quantum interference device 2 in the previous stage. The critical current of the Son junctions 21 and 22 and the critical current Ic of the Josephson junction of other pulse amplification circuits cannot be made extremely large. In view of this point, the amplification circuit 41 of the minute signal amplification circuit 11 has two pulse amplification circuits 40 connected in series. In FIG. 3, the cases of Ic, 1.4Ic, and 2Ic are shown as examples of the critical currents of the superconducting quantum interference device 2 and the pulse amplification circuits 40a and 40b, respectively, but FIG. Then, the number of stages of the pulse amplifier circuit 40 is not limited to two, but may be three or more, and the critical current ratio is not limited to this.

(2) What generates a plurality of replicas of a pulse train and synthesizes them to amplify them A plurality of replicas of a pulse train are generated, and these are combined to amplify power as a whole. See FIG. To explain. In the minute signal amplification circuit 12, a branching synthesis circuit 42 is used as the amplification circuit 12. The branch synthesis circuit 42 includes branch circuits 421, 422, and 423 that output the same pulse train as the input pulse train from two systems, and a synthesis circuit 424 that synthesizes a plurality of input pulse trains.

  The pulse train inputted from the left end of the branch circuit 421 is duplicated by the branch circuit 421 and outputted as two pulse trains, and each pulse train is further duplicated by the branch circuits 422 and 423 and outputted as two pulse trains. Thus, the pulse train input to the branch circuit 421 is duplicated into the same four pulse trains. The synthesis circuit 424 synthesizes these four pulse trains. In this way, the branching and synthesizing circuit 42 can obtain an amplification effect as a whole.

  The same circuit can be used for the branch circuits 421, 422, and 423. Taking the branch circuit 421 as an example, these branch circuits will be further described with reference to FIG. The branch circuit 421 includes three pulse amplification circuits 40c, 40d, and 40e having the same structure as the pulse amplification circuit 40 illustrated in FIG. The output of the pulse amplifier circuit 40c is divided into two, and each is input to the pulse amplifier circuits 40d and 40e, and the respective outputs become the outputs out1 and out2 of the branch circuit 421. The pulse trains output from the two output terminals are exactly the same, and the same result as that obtained by copying the input pulse train is obtained.

  In the example of FIG. 5, four copies of the pulse train are generated using three branch circuits, but the configuration of the branch circuit is not limited to this. For example, each of the four pulse trains output from the branch circuits 422 and 423 is provided. May be further input to the branch circuit to generate eight pulse trains. Thus, by passing several stages through the branch circuit, the number of replicas of the output pulse train of the superconducting quantum interference device 2 can be increased. By synthesizing all the finally obtained copies by the synthesis circuit 424, it is possible to give an amplification effect as a whole.

(3) Combination of (1) and (2) Amplification of the size of the pulse train and amplification by branch synthesis of the pulse train may be combined. For example, if the output of the amplifier circuit 41 is input to the branching and synthesizing circuit 42, the branching and synthesizing circuit 42 can perform amplification by generating and synthesizing a plurality of copies with respect to the pulse train that has become large in the amplifier circuit 41.

  In the following Examples 1 and 2, a simulation of an amplification effect at a specific circuit constant will be described.

  The superconducting quantum interference device shown in FIG. 7 is used. In the superconducting quantum interference device 7, the current Iin from the signal source 9 is input to the input coil Lin. Lin is coupled to the inductance L1 of the superconducting quantum interference device 7 itself by a coupling constant k. These coils form a loop with two Josephson junctions. Both of the critical currents of the Josephson coupling are Ic1. A bias current I1 is supplied to this loop. The bias current I1 is about twice as large as the critical current Ic1, and generates a voltage according to the current input to Lin. Power amplification is performed by taking out the current generated by this voltage as power with the load resistor Rd.

  When the superconducting quantum interference device 7 was configured with circuit constants as shown in Table 1 and a simulation was performed in which a 1 GHz, 2 μApp sine wave was input, the current component of 1 GHz flowing through the output resistor was 845 nApp. This corresponds to a power of 0.89 pW. However, the output resistance 10Ω in this case is optimized to the circuit configuration of FIG.

  FIG. 8 shows a minute signal amplifier circuit 13 in which two stages of pulse amplifier circuits 40 of FIG. 4 are added to the superconducting quantum interference device 7. In the minute signal amplification circuit 13, the Josephson coupling critical current value Ic2 of the first-stage pulse amplification circuit 40f is made larger than the critical current value Ic1 of the superconducting quantum interference device 7, thereby amplifying the power of each pulse. To do. Furthermore, power amplification is performed by setting the critical current value Ic3 of the Josephson junction of the second stage pulse train amplifier circuit 40g to be larger than Ic2.

  The small signal amplification circuit 13 is configured with circuit constants as shown in Table 2, and a simulation is performed in which a sine wave of 1 GHz and 2 μApp is input. However, the output resistance Rd is an optimum value of 5Ω in this case. The 1 GHz component of the current flowing through the output resistor was 2.06 μApp. This corresponds to a power of 2.65 pW. Compared with the output of the superconducting quantum interference device 7 alone, nearly four times as much power can be taken out.

  FIG. 9 shows a minute signal amplifier circuit 14 in which a branching and synthesizing circuit is added to the superconducting quantum interference device 7. The minute signal amplification circuit 14 branches the output of the superconducting quantum interference device 7 into two systems. When the small signal amplifier circuit 14 is configured with circuit constants as shown in Table 3 and a simulation is performed in which a sine wave of 1 GHz and 2 μApp is input, a current component of 1 GHz flowing through a 5Ω output resistor is 1 per piece. It was 89μApp. This corresponds to a power of 2.23 pW. When the outputs branched into two systems are combined, the power becomes 4 pW or more, and a power amplification factor of 4 times or more is obtained as compared with the output 0.89 pW of the superconducting quantum interference device 7 alone.

  As mentioned above, although this invention was demonstrated according to embodiment and an Example, this invention is not limited to this, It cannot be overemphasized that it can change on the technical idea of this invention. Absent.

  For example, as described above, the pulse amplifier circuit 40 is connected in series to greatly amplify the pulse train, but the number of stages of the pulse amplifier circuit 40 may be arbitrarily determined.

  The branch circuit 421 is a circuit that performs two outputs for one input and can be said to be a branch circuit having two branches. However, the number of branches is not limited to two, and may be three or more.

  Furthermore, a configuration in which the pulse amplification circuit 40 and the branch circuit 421 are arbitrarily mixed may be employed, or a configuration including a circuit other than a circuit that amplifies the pulse magnitude, a branch circuit, and a synthesis circuit may be employed. For example, the amplifier circuit 4 may be a circuit in which the pulse amplifier circuit 40 and the branch synthesis circuit 42 are connected in series as described above, or a pulse amplification circuit may be provided for each of the outputs of the branch circuits 422 and 423 of the branch synthesis circuit 42. 40 may be provided to amplify the magnitude of the pulse, and then synthesized by the synthesis circuit 424.

  In addition, when the output of the superconducting quantum interference device is branched by a branch circuit, a minute signal amplifier circuit is provided in which the power gain is variable in multiple stages by providing a switch in part or all of the branched output. It is good. For example, in the minute signal amplifier circuit 12 of FIG. 5, a case is considered in which a switch is provided between each of the total four outputs of the two outputs of the branch circuit 422 and the two outputs of the branch circuit 423 and the synthesis circuit 424. In this case, four switches are provided between the branch circuits 422 and 423 and the synthesis circuit 424. Depending on the on / off state of these switches, the number of inputs to the synthesis circuit 424 is 0, 1, 2, 3, Therefore, the output of the synthesis circuit 424 is also variable in five stages.

  Since the superconducting circuit according to the present invention is easily manufactured by a normal superconducting circuit manufacturing process, it can be industrially mass-produced and has industrial applicability. Examples of main applications include amplification of micro microwave signals in quantum computation and signal amplification in the field of micro measurement.

1 is a circuit diagram of a minute signal amplifier circuit 1 according to an embodiment of the present invention. 2 is a circuit diagram of a superconducting quantum interference device 2. FIG. 2 is a functional block diagram of a minute signal amplifier circuit 11 which is an example of a minute signal amplifier circuit 1; FIG. FIG. 3 is a circuit diagram of a pulse amplifier circuit 40 as an example of the amplifier circuit 4 or a component thereof. 2 is a functional block diagram of a minute signal amplifier circuit 12 which is an example of the minute signal amplifier circuit 1. FIG. 4 is a circuit diagram of a branch circuit 421. FIG. 3 is a circuit diagram of a superconducting quantum interference device 7. FIG. 1 is a circuit diagram of a minute signal amplifier circuit 13 that is Embodiment 1 of the present invention. FIG. It is a circuit diagram of the minute signal amplifier circuit 14 which is Embodiment 2 of the present invention.

Explanation of symbols

1, 11, 12, 13, 14 Minute signal amplification circuit 2, 7 Superconducting quantum interference device (SQUID)
3, 407, 40c7, 40d7, 40e7, 8 Current source 4, 41, 42 Amplifier circuit 21, 22, 405, 406, 40c5, 40c6, 40d5, 40d6, 40e5, 40e6 Josephson junction 23 Coil 40, 40a, 40b, 40c, 40d, 40e, 40f, 40g, 40h, 40i Pulse amplification circuit 401, 402, 403, 404 Coil 421, 422, 423 Branch circuit 424 Synthesis circuit

Claims (16)

In the signal amplification circuit,
A superconducting quantum interference device to which a signal to be amplified is input;
A signal amplifier circuit comprising: an amplifier circuit that amplifies and outputs the power of a pulse output from the superconducting quantum interference device.   2. The signal amplification circuit according to claim 1, comprising at least one pulse amplification circuit as a circuit for amplifying the magnitude of an inputted pulse train as at least a part of the amplification circuit. The signal amplifier circuit according to claim 2,
The amplifier circuit includes a plurality of the pulse amplifier circuits,
A signal amplification circuit, wherein at least some of the plurality of pulse amplification circuits are connected in series with each other. The signal amplifier circuit according to claim 3.
Each of the plurality of pulse amplification circuits connected in series has a Josephson junction,
The critical current of the Josephson junction of one pulse amplification circuit of the plurality of pulse amplification circuits connected in series is the critical current of the Josephson junction of another pulse amplification circuit connected in series to the previous stage of the pulse amplification circuit. A signal amplifier circuit characterized by being larger than the above.   5. The signal amplifier circuit according to claim 1, wherein at least part of the amplifier circuit includes a branch circuit that outputs a plurality of pulse trains that are the same as the input pulse train, and a plurality of pulse trains that are output by the branch circuit. A signal amplifying circuit comprising a combining circuit for combining and outputting.   6. The signal amplifying circuit according to claim 5, further comprising a switch for turning on / off a connection between at least one of the outputs of the branch circuit and the synthesis circuit.   7. The signal amplifier circuit according to claim 5, wherein the branch circuit includes one pulse amplifier circuit and a plurality of the pulse amplifier circuits connected in parallel to an output of the one pulse amplifier circuit. A signal amplifying circuit comprising: The signal amplifier circuit according to any one of claims 1 to 7,
The pulse amplification circuit includes first, second, third and fourth inductors connected in series in the same order.
A node between the first and second inductors is connected to a first Josephson junction;
A node between the third and fourth inductors is connected to a second Josephson coupling;
A signal amplifier circuit, wherein a node between the second and third inductors is connected to a current source. In a method for amplifying a signal,
Inputting a signal to be amplified into a superconducting quantum interference device;
An amplification step of amplifying the power of the pulse by inputting the output of the superconducting quantum interference device to an amplifier circuit.   10. The signal amplification method according to claim 9, further comprising a step of amplifying the magnitude of the inputted pulse train by a pulse amplification circuit as at least a part of the amplification step.   11. The signal amplification method according to claim 10, wherein the size of the pulse train is gradually amplified by the plurality of pulse amplification circuits connected in series with each other. The signal amplification method according to claim 11, wherein
Each of the plurality of pulse amplification circuits connected in series has a Josephson junction,
The critical current of the Josephson junction of one pulse amplification circuit of the plurality of pulse amplification circuits connected in series is the critical current of the Josephson junction of another pulse amplification circuit connected in series to the previous stage of the pulse amplification circuit. A signal amplification method characterized by being larger than the above.   13. The signal amplification method according to claim 9, wherein, as at least a part of the amplification stage, a branch stage for generating a plurality of pulse trains that are the same as the input pulse train by a branch circuit and the branch stage are generated. And a synthesis step of synthesizing and outputting the plurality of pulse trains by a synthesis circuit.   14. The signal amplification method according to claim 13, wherein connection of at least a part of an input from the branch circuit to the synthesis circuit is controlled by a switch provided between at least one of the outputs of the branch circuit and the synthesis circuit. A signal amplification method comprising the steps of:   15. The signal amplification method according to claim 13, wherein the branch circuit includes one pulse amplification circuit and a plurality of the pulse amplification circuits connected in parallel to the output of the one pulse amplification circuit. A signal amplification method comprising: The signal amplification method according to any one of claims 9 to 15,
The pulse amplification circuit includes first, second, third and fourth inductors connected in series in the same order.
A node between the first and second inductors is connected to a first Josephson junction;
A node between the third and fourth inductors is connected to a second Josephson coupling;
A signal amplification method, wherein a node between the second and third inductors is connected to a current source.

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