JP5414031B2 - AC voltage generating circuit using Josephson element and AC voltage standard circuit - Google Patents

Description

  The present invention relates to an AC voltage generation circuit, an AC voltage standard circuit, and an AC voltage standard device using a Josephson element capable of generating an ideal smooth AC waveform having a high amplitude.

  Currently, the AC voltage standard is used as a reference for calibration of measuring instruments such as AC voltage. In recent years, with the improvement of measurement accuracy of measuring instruments used in industries such as manufacture of electronic equipment and communication measurement, a high-performance AC voltage standard is desired. The AC voltage standard is an apparatus that generates an ideal sine wave voltage, and it is desired to output a voltage having a higher amplitude and frequency with higher accuracy.

  In the superconducting technology field, high-performance circuits using Josephson elements have been developed. FIG. 4 is a schematic diagram of a Josephson element. The Josephson element is an element utilizing a tunnel effect having a sandwich structure in which a thin barrier layer 2 (insulator insulator or normal conductor normal conductor) is sandwiched between two superconductors (superconductors) 1. The Josephson element has a Josephson junction (SIS or SNS junction). When a Josephson element is irradiated with a microwave of a certain frequency f and a current is further passed, a constant voltage (V = hf / 2e) determined only by the microwave frequency f is generated at both ends of the element. . Here, e is the elementary electric charge, and h is the Planck constant. If no current is passed, the generated voltage is completely zero. The current flowing here is called a bias current. FIG. 5 is a diagram showing the relationship between the bias current I and the voltage V in the Josephson element. As shown in FIG. 5, by controlling the value of the bias current, a highly accurate constant voltage step (hf / 2e) determined only by the microwave frequency f is generated at both ends of the element. Further, since the frequency of the microwave can be controlled with very high accuracy, the voltage value obtained at both ends of the Josephson element can also be controlled with very high accuracy. However, in general, the voltage per Josephson element is as small as several tens of μV. Therefore, in order to obtain a necessary voltage (1 V or more), an array in which several tens of thousands of Josephson elements are connected in series is configured so that 1 V can be obtained as a whole.

  Currently, a programmable Josephson voltage standard (PJVS) system using an array in which Josephson elements are connected in series is known (see Patent Documents 1 to 3). In the programmable Josephson voltage standard (PJVS) system, an arbitrary DC voltage can be generated, which is put into practical use as a DC voltage standard (DC PJVS). In order to obtain an arbitrary voltage from a programmable Josephson voltage standard (PJVS) array, a device for operating as a digital-to-analog converter has been devised.

  The Programmable Josephson Voltage Standard (PJVS), which has been put to practical use as a DC voltage standard, has been developed, and research on the AC Programmable Josephson Voltage Standard (AC PJVS) for synthesizing AC voltage has been promoted as an AC voltage standard. (See Non-Patent Document 1).

  The programmable Josephson voltage standard (PJVS) is configured as a digital-to-analog converter to generate a voltage of arbitrary amplitude. An array in which a large number of Josephson elements are connected in series is divided into segments having the number of elements proportional to a power of 2, for example, and a bias current source is connected to each segment. A constant high-accuracy voltage is output from the segment supplied with the bias current. Conversely, when the bias current is set to zero, the voltage of the segment becomes completely zero. By controlling ON / OFF of the bias current of each segment in this manner, a voltage having an arbitrary value can be generated from the array in a programmable manner.

The principle of the AC programmable Josephson voltage standard (AC PJVS) will be described below. AC PJVS has basically the same circuit configuration as DC PJVS. The DC PJVS supplies a DC bias current and outputs a DC high-accuracy voltage, whereas the AC PJVS does not turn on / off the bias current (I0, I1, I2,..., In) supplied to each segment. The high-accuracy voltage value V _PJVS from the array is changed momentarily to synthesize a sine wave voltage by controlling OFF in time.

  FIG. 6 is a circuit diagram of a programmable Josephson voltage standard (PJVS) for generating a sinusoidal voltage waveform as an example of an alternating voltage waveform. The circuit diagram of FIG. 6 shows a programmable Josephson voltage standard (PJVS) element unit 61 and a sine wave voltage waveform input device 64, a pulse pattern conversion device 65, and a pulse pattern generation device, which are means for controlling a bias current source. 66.

The programmable Josephson voltage standard (PJVS) element 61 includes sections (S0, S1, S2,..., Sn) in which a predetermined number (for example, powers of 2) of Josephson elements (x) are connected in series. Is connected to a bias current source (I0, I1, I2,..., In), and a predetermined number of these sections (segments S0, S1, S2,..., Sn) are connected in series. It has a structure to do. For example, segment S0 is the number of one element that is 2 to the power of 0, segment S1 is the number of 2 elements that is the power of 2, segment S2 is the number of 4 elements that is the square of 2, segment S3 Is the number of 8 elements, which is the cube of 2, and the segment Sn is composed of 2 ⁿ elements, which is the power of 2 ⁿ .

FIG. 7 is a diagram showing current-voltage characteristics of the bias current I _i and the generated voltage V _i in the segment Si in which Josephson elements having the number of powers of 2 (2 ⁱ ) are connected in series. As shown in FIG. 7, by controlling the bias current, high-precision constant voltage step V _i occurs which is determined only by the frequency f of the number of elements at both ends and a microwave of each segment Si. When each bias current source is switched and controlled, a ternary voltage value V _i can be obtained from the corresponding segment. Each bias current source may be controlled by, for example, three values of zero / plus / minus.
V _i = (hf / 2e) × a _i × 2 ⁱ
However, a _i = 0, +1, −1

Then, as shown in FIG. 6, by controlling these bias current sources by a signal from the pulse pattern generation device 66, an arbitrary expression represented by the following equation can be obtained from an array of programmable Josephson voltage standard (PJVS) elements. The voltage Vout having high accuracy and high amplitude can be obtained. The voltage output of the programmable Josephson voltage standard (PJVS) element is denoted as _VPJVS .
Vout = (hf / 2e) (a ₀ × 2 ⁰ + a ₁ × 2 ¹ +... A _n × 2 ⁿ )
However, a _i = 0, +1, −1

  Next, an example in which a sine wave voltage having a desired AC frequency, which is the purpose of the AC voltage standard, is synthesized will be described. FIG. 8 is a diagram of a composite sine wave voltage waveform generated by the programmable Josephson voltage standard method. When an arbitrary desired AC frequency is set to f, a sine wave 1 period T = 1 / f is sampled by N division, and a bias current is switched every sampling period Ts = 1 / Nf, during which a programmable Josephson voltage standard (PJVS) The device is operated so that the voltage from the array of elements is constant. The AC PJVS has an advantage that it is easy to obtain a voltage value as high as 1 V or more by connecting Josephson elements in multiple stages. Since each sampling time needs to hold the voltage at a constant value, the synthesized voltage waveform is not a true sine waveform but a pseudo sine waveform approximated by a stepped waveform.

  As an AC voltage standard method other than the programmable Josephson voltage standard (PJVS) method, a method based on a high-speed single flux quantum (RSFQ) circuit (hereinafter referred to as “high-speed single flux quantum method AC voltage standard” or “ RSFQ system ”). (See Non-Patent Document 2). The RSFQ method uses a Josephson element as in the PJVS method, but generates a high-accuracy voltage based on a principle different from that of the PJVS method.

The principle of the high-speed single flux quantum (RSFQ) AC voltage standard will be described. One of the basic properties related to the superconducting phenomenon is the quantization of magnetic flux. Flux in the ring constituted by superconductor is quantized, it can take on only integer multiple of the [Phi _0. Φ ₀ is a minimum unit of quantized magnetic flux, and is called a single flux quantum (hereinafter referred to as “SFQ”). The high-speed single flux quantum circuit (Rapid SFQ: RSFQ circuit) using SFQ as an information carrier is a superconducting circuit characterized by ultra-high-speed operation of several tens of gigahertz and low power consumption characteristics. Research has been conducted on performance integrated circuits. The high-speed single flux quantum circuit AC voltage standard is an application of this high-speed single flux quantum circuit to AC voltage waveform generation. FIG. 9 is a circuit diagram of a high-speed single flux quantum AC voltage standard. The high-speed single-flux-quantum AC voltage standard is mainly composed of a superconducting quantum interference device (SQUID) array 92 for outputting a high-precision voltage and a high-speed single unit for driving it at an ultra-high speed. A magnetic flux quantum circuit (hereinafter referred to as a SQUID array driving circuit) 93 is formed. As shown in FIG. 9, the superconducting quantum interference element (SQUID) array 92 includes N SQUID cells (SCi) each composed of two Josephson elements and two inductances (SC1, SC2,. ... SCN) are connected. Similarly, the SQUID array driving circuit is divided into N cells (C1, C2,... CN: called driving cells) and coupled to each SQUID cell (SC1, SC2,... SCN) by mutual inductance. doing. When a desired voltage waveform is input to the voltage waveform input device 94, the voltage waveform is subjected to pulse density modulation and converted into a 0/1 bit sequence via a pulse pattern conversion device 95 and a pulse pattern generation device 96. The pulse generator 97 outputs the pulse series Vin at high speed (i). The SQUID array driving circuit 93 and the SQUID array 92 in the subsequent stage are circuits for performing pulse density demodulation after the pulse sequence Vin is converted into a high-precision quantized voltage pulse sequence. The operation will be described below. When the generated high-speed pulse series Vin is input to the SQUID array driving circuit 93, it is converted into a series of voltage pulses (SFQ pulses) quantized in the same circuit (ii). The converted SFQ pulse propagates from the top to the bottom from the drive cell C1 to the drive cell CN. On the other hand, each driving cell is coupled to each corresponding SQUID cell by mutual inductance, and the SFQ pulse that has passed through the driving cell propagates to the SQUID cell through this coupling. When the SFQ pulse is input to the SQUID cell, the SFQ pulse is immediately output from the SQUID cell, and is amplified to a high-precision quantized pulse having N times the amplitude by the N-stage SQUID cell (iii). A cable or the like is actually connected after the SQUID array to extract the output voltage. Since the cable bandwidth is actually finite, it is equivalent to a low-pass filter or integrating circuit connected, so that the sequence of high-precision quantized voltage pulses is subjected to pulse density demodulation and finally _Specifically , it can be taken out as a highly accurate voltage waveform output V _RSFQ (iv).

  In this RSFQ system AC voltage standard, a desired voltage waveform is synthesized by using this SFQ pulse as a carrier. Since the SFQ pulse is a quantized voltage pulse having a picosecond time width, there is an advantage that a highly accurate arbitrary voltage can be obtained by generating and controlling a necessary number of pulses. In addition, there is an advantage that an arbitrary high-precision and wide-band voltage waveform can be generated by the high-speed pulse density modulation / demodulation function of the RSFQ circuit.

Further, as an AC voltage standard system other than the programmable Josephson voltage standard (PJVS) system, there is a pulse drive (PD) type AC voltage standard system (see Patent Document 4). FIG. 10 is a circuit diagram of a pulse drive AC voltage standard. The pulse drive type AC voltage standard element 101 is composed of a circuit of a Josephson element array in which about 10,000 Josephson elements are connected in series, and outputs a voltage V _PD from both ends. Desired voltage waveform information is input to the voltage waveform input device 134. The voltage waveform information output from the voltage waveform input device 134 is subjected to pulse density modulation by the pulse pattern conversion device 138 to convert predetermined voltage amplitude information into pulse density information. This density information is converted into a 0/1 bit sequence by the pulse pattern generation device 139 and output as a high-speed pulse sequence Vin from the pulse generation device 140 (i). When the high-speed pulse series Vin is input to the pulse drive system voltage standard element 101, it is converted into a series of high-accuracy voltage pulses quantized by the Josephson elements in the array, and as a pulse series having an amplitude proportional to the number of elements. Is output (ii). The Josephson element array is actually connected to a cable or the like to extract the output voltage. Since the cable bandwidth is actually finite, it is equivalent to a low-pass filter or integrating circuit connected, so that the sequence of high-precision quantized voltage pulses is subjected to pulse density demodulation and finally Specifically, it can be taken out as a highly accurate voltage waveform output _VPD (iii).

JP 2004-172692 A JP 2005-300317 A JP 2000-514957 A JP 2006-148271 A

C. A. Hamilton, C.I. J. et al. Burroughs, and R.A. L. Kautz, “Josephson D / A Converter with Fundamental Accuracy”, IEEE Transactions on instrumentation and measurement, vol. 44, no. 2, pp. 223-225, April 1995. C. A. Hamilton, “Josephson Voltage Standard on Single-Flux-Quantum Voltage Multipliers” IEEE Transactions on applied superconductivity, vol. 2, no. 3, pp. 139-142, Sep. 1992.

  The AC PJVS based on the programmable Josephson voltage standard (PJVS) has the advantage that it is easy to earn a voltage value as high as 1 V or more by connecting Josephson elements in multiple stages, but in principle it is synthesized. The voltage waveform thus made does not become a true sine waveform, but becomes a pseudo sine shape approximated by a stepped waveform. In addition, since the voltage waveform rises sharply (or falls) at the switching time of the bias current, there is a drawback that harmonic components resulting from this are included. The harmonic components tend to attenuate when transmitted through the output cable, causing a voltage error.

  On the other hand, the high-speed single flux quantum AC voltage standard has the advantage that any high-precision and wide-band voltage waveform can be synthesized at high speed due to the voltage pulse quantum nature and high-speed pulse density modulation / demodulation function of the RSFQ circuit. For example, it is difficult to increase the number of elements and increase the voltage because the circuit configuration is complicated and susceptible to variations in circuit parameters, and only a low voltage of about 10 mV or less can be obtained. Therefore, the high-speed single magnetic flux quantum AC voltage standard has a problem that a desired voltage amplitude exceeding 10 mV cannot be obtained.

  The pulse-driven AC voltage standard has the advantage of being able to synthesize any high-accuracy and wide-band voltage waveform at high speed due to the quantum nature of the voltage pulse and the high-speed pulse density modulation / demodulation function. Due to instability due to mode noise, it is difficult to increase the number of element stages, and there is a disadvantage that only a low voltage amplitude of about 100 mV or less can be obtained.

  The present invention is intended to solve these problems, and an object thereof is to realize an AC voltage generation circuit, an AC voltage standard circuit, and an AC voltage standard device that output a voltage waveform having a high amplitude with high accuracy. Is. Furthermore, the present invention aims to output a sine waveform closer to a true sine waveform, not a stepped pseudo waveform generated by AC PJVS, in a circuit using a Josephson element, and has a high amplitude of 1 V or more. It is intended to output a sine wave voltage having

  And this invention has the following characteristics, in order to achieve the said objective.

  The AC voltage generation circuit using the Josephson element according to the present invention includes a plurality of segments each including a predetermined number of Josephson elements connected in series, and controls the bias current applied to each segment, thereby controlling a stepped AC current. It is characterized by comprising a first circuit for generating a voltage and a second circuit made of a Josephson element for generating a quantized voltage pulse. Further, a programmable Josephson voltage standard is used as the first circuit.

  The second circuit of the present invention is characterized by outputting a differential waveform between a desired AC voltage waveform and a stepped AC voltage waveform. The AC voltage generation circuit of the present invention is characterized in that a first circuit and a second circuit are connected in series and the sum of the output voltages is used as the output voltage. In the AC voltage generation circuit of the present invention, the desired AC voltage waveform is typically a sine wave waveform, and the second circuit is the difference between the sine AC voltage waveform and the stepped pseudo sine waveform. A waveform is output.

  The second circuit of the present invention is characterized in that a differential waveform is synthesized and output by performing pulse density modulation / demodulation using a quantized voltage pulse. The AC voltage generation circuit of the present invention is characterized in that a high-speed single magnetic flux quantum circuit or a pulse drive circuit is used as the second circuit. The AC voltage generation circuit of the present invention can synthesize an ideal smooth sine wave having a high amplitude of 1 V or more.

  The AC voltage generation circuit of the present invention is a circuit used for an AC voltage standard.

  An AC voltage standard apparatus according to the present invention includes the AC voltage generation circuit according to the present invention, and includes means for calculating a differential waveform between a sine wave waveform and a pseudo sine wave waveform. In the AC voltage standard apparatus, at least a circuit portion including the Josephson element is placed in a low temperature state for superconductivity.

  According to the present invention, it is possible to generate an alternating voltage that outputs a voltage waveform having a high amplitude with high accuracy in a circuit using a Josephson element. In addition, according to the AC voltage standard circuit and AC voltage standard device of the present invention, it is approximated to a more true sine waveform rather than a staircase-like pseudo waveform generated by AC PJVS, and thus has a high amplitude of 1 V or more. The voltage waveform can be output with high accuracy, and a smooth and completely accurate sine wave voltage can be synthesized. Further, in the AC voltage generation circuit, the harmonic component due to the voltage waveform is substantially eliminated at the switching time of the bias current, so that a voltage error can be eliminated. In addition, as a mode of combining the first circuit (for example, PJVS system) and the second circuit (for example, a high-speed single magnetic flux quantum circuit or a pulse drive circuit), each circuit using a multichip mounting technique is used. Can be created easily and at low cost. Further, if these chips are integrated in one chip, further cost reduction can be achieved.

The circuit diagram of 1st Embodiment of the alternating voltage generation circuit using the Josephson element of this invention. The figure which shows the alternating voltage waveform for demonstrating this invention. The circuit diagram of 2nd Embodiment of the alternating voltage generation circuit using the Josephson element of this invention. The schematic diagram of a Josephson element. The figure which shows the relationship between the bias current I and the voltage V in a Josephson element. FIG. 2 is a circuit diagram of a programmable Josephson voltage standard (PJVS) for generating a sinusoidal voltage waveform. The figure which shows the current-voltage characteristic of the bias current and generated voltage in a segment. The figure of the synthetic | combination sine wave voltage waveform produced | generated by the programmable Josephson voltage standard system. The circuit diagram of a high-speed single flux quantum system AC voltage standard. The circuit diagram of a pulse drive system alternating voltage standard.

  The present invention is a hybrid AC waveform output circuit obtained by fusing a programmable Josephson voltage standard system (PJVS system) and other systems.

(First embodiment)
A first embodiment of an AC voltage waveform output circuit using the Josephson element of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram in which a programmable Josephson voltage standard (PJVS) system and an RSFQ system AC voltage standard are connected in series to realize a hybrid system of both. FIG. 2 is a diagram showing an AC voltage waveform for explaining the present invention.

  The PJVS system and the RSFQ system are connected in series, and an ideal sine wave voltage waveform output is obtained as the sum voltage of both. The PJVS method generates a step-like pseudo sine waveform having a high amplitude of 1 V or more. Therefore, the difference voltage between the true sine waveform and the pseudo sine waveform is generated by the RSFQ method capable of generating a continuous / broadband arbitrary voltage waveform. As a result, an ideal smooth sine wave having an amplitude of 1 V or more can be synthesized as the sum voltage of the PJVS method and the RSFQ method.

  The circuit of FIG. 1 is configured by connecting a programmable Josephson voltage standard element 11 and a SQUID array 12 of a high-speed single magnetic flux quantum system AC voltage standard in series. Further, the circuit of FIG. 1 includes a sine wave-pseudo sine wave difference waveform calculation device 17.

The programmable Josephson voltage standard element 11 is a segment (S 0, S 1, S 2,...) Of an array in which a large number of Josephson elements (×) are connected in series and having an element number proportional to a power of 2. Sn) and a bias current source (I0, I1, I2... In) is connected to each of these segments. Furthermore, in order to control the bias current source, a sine wave voltage waveform input device 14, a pseudo sine wave waveform pulse pattern conversion device 15 and a pulse pattern generation device 16 are provided. The sine wave voltage waveform input device 14 is a device for inputting voltage amplitude / frequency information of a desired ideal sine wave. The pseudo sine wave waveform pulse pattern conversion device 15 is the same as the conventional pulse pattern conversion device 65 (FIG. 6) for outputting the conventional sine wave waveform shown in FIG. Good. This is a device that approximates and converts this into a step-like pseudo sine waveform based on the ideal sine wave information obtained from the sine wave voltage waveform input device 14. The pulse pattern generation device 16 is a device for determining a bias current supply pattern (zero / minus / plus) for obtaining a pseudo sine waveform and transmitting a control signal to a subsequent bias current source. This configuration is the same as the conventional programmable Josephson voltage standard element circuit. The programmable Josephson voltage standard element 11 outputs a step-like pseudo sine waveform V _PJVS (see FIG. 2A) having a high amplitude.

  The sine wave-pseudo sine wave differential waveform calculation device 17 of the present invention is programmable based on an ideal sine wave waveform based on the output signal of the sine wave voltage waveform input device 14 and an output signal from the sine wave voltage waveform input device 14. The difference waveform from the pseudo sine wave waveform output from the Josephson voltage standard element 11 is calculated. Specifically, based on the ideal sine wave information obtained from the sine wave voltage waveform input device 14 and the pseudo sine wave information obtained from the pseudo sine waveform pulse pattern conversion device 15, the difference waveform between them is calculated. . Based on the differential voltage waveform information from the sine wave-pseudo sine wave differential waveform calculation device 17, the pulse pattern conversion device 18 performs pulse density modulation on the differential waveform, and converts the waveform amplitude information into pulse train density information. . The pulse pattern generation device 19 converts and generates pulse density information into a 0/1 bit sequence and outputs it. The pulse generator 20 converts the 0/1 bit sequence into a pulse signal sequence and outputs it as Vin.

The SQUID array driving circuit 13 includes N driving cells (C1, C2,... CN). When the pulse signal series Vin from the pulse generator 20 is input into the circuit, it is converted into a quantized high-accuracy voltage pulse (SFQ pulse) series, and from the top to the bottom from the driving cell C1 to the driving cell CN. Propagate to. On the other hand, each driving cell (C1, C2,... CN) is coupled to each corresponding SQUID cell (SC1, SC2,... SCN) by mutual inductance, and the SFQ pulse passing through the driving cell is this Propagates to the SQUID cell through the combination. When an SFQ pulse is input to the SQUID cell, the SFQ pulse is immediately output from the SQUID cell. The SFQ pulse series is finally amplified to a series of high-precision quantized voltage pulses having an N-fold amplitude and output from the SQUID array 12. Actually, a cable for taking out the voltage is connected to the subsequent stage, but the frequency band is limited, so the band is limited, and the pulse density demodulation is performed by the integral action to return to the amplitude information. Finally, it is output as a highly accurate arbitrary voltage waveform V _RSFQ .

In this way, a step-like pseudo sine waveform V _PJVS having a high amplitude is generated by _PJVS . On the other hand, the difference obtained by the difference waveform calculation device is generated by an RSFQ voltage standard that can generate a wideband arbitrary waveform (V _RSFQ ). Then, as the output _{V PJVS} and RSFQ system voltage output _{V RSFQ} the total voltage of the standard elements of PJVS element _(V PJVS ₊ V _RSFQ), can be synthesized accurate true sine wave.

  Here, FIG. 2 is a diagram for explaining the principle of the present invention. FIG. 2A shows a voltage waveform from the programmable Josephson voltage standard circuit. As shown in FIG. 8 in the description of the background art, a step-like pseudo sine wave waveform is generated. For example, a large amplitude waveform of 1 V or more is generated. FIG. 2B shows a voltage waveform from the RSFQ method. The difference voltage between the true sine wave waveform and the pseudo sine waveform generated by the PJVS method is generated by the RSFQ method. According to the RSFQ method, an arbitrary waveform can be synthesized at a high speed although the amplitude is not high. FIG. 2C is a diagram showing that a true sine waveform is synthesized as the sum of the voltage waveforms of both by connecting PJVS and RSFQ circuits in series. By combining the PJVS method and the RSFQ method, a smooth and ideal sine waveform can be synthesized.

  The operation of the RSFQ method in FIG. 1 for generating the waveform in FIG. 2B will be described in detail below. In FIG. 1, a sine wave-pseudo sine wave difference waveform calculation device 17, a pulse pattern conversion device 18, a pulse pattern generation device 19, a pulse generation device 20, a SQUID array drive circuit 13 and a SQUID array 12 mainly perform the operation. . The pulse pattern conversion device 18 performs pulse density modulation on the difference waveform based on the difference voltage waveform information obtained from the sine wave-pseudo sine wave difference waveform calculation device 17, and converts the amplitude information of the difference waveform into the pulse train density. It is a device that converts information. The pulse pattern generation device 19 is a device that converts, generates, and outputs pulse density information into a 0/1 bit sequence. The pulse generator 20 is a device that converts a 0/1 bit sequence into a pulse signal and outputs the pulse signal. The pulse series Vin input to the SQUID array driving circuit 13 is immediately converted into a highly accurate voltage pulse (SFQ pulse) series quantized in the circuit. Since the amplitude of the SFQ pulse is very small, it is necessary to amplify it in order to obtain a sufficient amplitude. The SQUID array 12 and the SQUID array driving circuit 13 for driving the SFQ pulse are amplified while maintaining the quantum property. The input signal Vin converted into the SFQ pulse is then propagated sequentially from the drive cell C1 in the SQUID array drive circuit 13 to the drive cell CN. Each drive cell is coupled to the SQUID cell by mutual inductance, and the SFQ pulse propagates to the SQUID cell corresponding to the moment when it passes through the drive cell, and is immediately output as an SFQ pulse from the SQUID cell. At this time, the SQUID array 12, which is a serial connection of N stages of SQUID cells, outputs a high-precision quantized voltage pulse obtained by amplifying the amplitude of the SFQ pulse N times. As described above, the pulse density modulated pulse signal sequence (i) is input as Vin to the SQUID array driving circuit 13 and then converted to the SFQ pulse sequence (ii), and then amplified N times from the output immediately after the SQUID array 12. Are output as a series of high-precision quantized voltage pulses (iii). A pulse density demodulation is performed by a low-pass filter connected to the subsequent stage, and the amplitude information is returned to be output as a highly accurate arbitrary voltage waveform to generate the waveform of FIG. 2B (iv).

(Second Embodiment)
A second embodiment of an AC voltage waveform output circuit using the Josephson element of the present invention will be described below with reference to FIGS. FIG. 3 is a circuit diagram in which a programmable Josephson voltage standard (PJVS system) element and a pulse drive system AC voltage standard element are connected in series to realize a hybrid system of both.

A programmable Josephson voltage standard element (PJVS system) and a pulse drive system AC voltage standard are connected in series, and an ideal sine wave voltage waveform output is obtained as the sum voltage of both. The PJVS method generates a step-like pseudo sine waveform V _PJVS having a high amplitude of 1 V or more. Therefore, the differential voltage between the true sine waveform and the pseudo sine waveform _VPJVS is generated by a pulse drive system voltage standard that can generate an arbitrary voltage waveform having a continuous and wide band. As a result, an ideal smooth sine wave having an amplitude of 1 V or more can be synthesized as the sum voltage of the PJVS method and the pulse drive method voltage standard.

  The circuit of FIG. 3 is configured by connecting a programmable Josephson voltage standard element 31 and a pulse drive AC voltage standard element 32 in series. Further, the circuit of FIG. 3 includes a sine wave-pseudo sine wave differential waveform calculation device 37.

The programmable Josephson voltage standard element 31 divides an array in which a large number of Josephson elements (×) are connected in series into segments having the number of elements proportional to the power of 2, and for each of these segments The bias current source is connected. Further, in order to control the bias current source, a sine wave voltage waveform input device 34, a pseudo sine wave waveform pulse pattern conversion device 35, and a pulse pattern generation device 36 are provided. The sine wave voltage waveform input device 34 is a device for inputting voltage amplitude / frequency information of a desired ideal sine wave. The pseudo sine wave waveform pulse pattern conversion device 35 is the same as the pulse pattern conversion device 65 (FIG. 6) for outputting a conventional sine wave waveform that is stepped as shown in FIG. Good. This is a device that approximates and converts this into a step-like pseudo sine waveform based on the ideal sine wave information obtained from the sine wave voltage waveform input device 34. The pulse pattern generation device 36 is a device for determining a bias current supply pattern (zero / minus / plus) for obtaining a pseudo sine waveform and transmitting a control signal to a subsequent bias current source. This configuration is the same as the conventional programmable Josephson voltage standard element circuit. The programmable Josephson voltage standard element 31 outputs a step-like pseudo sine waveform V _PJVS (see FIG. 2A) having a high amplitude.

  The sine wave-pseudo sine wave difference waveform calculation device 37 of the present invention is programmable based on an ideal sine wave waveform based on the output signal of the sine wave voltage waveform input device 34 and an output signal from the sine wave voltage waveform input device 34. The waveform of the difference from the pseudo sine wave waveform output from the Josephson voltage standard element 31 is calculated. Specifically, based on the ideal sine wave information obtained from the sine wave voltage waveform input device 34 and the pseudo sine wave information obtained from the pulse pattern conversion device 35 for pseudo sine waveform, the difference waveform between them is calculated. To do. Based on the difference voltage waveform information from the sine wave-pseudo sine wave difference waveform calculation device 37, the pulse pattern conversion device 38 performs pulse density modulation on the difference waveform, and converts the waveform amplitude information into pulse train density information. . The pulse pattern generation device 39 converts and generates pulse density information into a 0/1 bit sequence and outputs it. The pulse generator 40 converts the 0/1 bit sequence into a pulse signal and outputs it as Vin.

The high-speed pulse signal sequence generated by the pulse generator 40 is input to the pulse drive system voltage standard element 32. This is composed of a circuit of a Josephson element array in which a large number (about 10,000) of Josephson elements (x) are connected in series. When high-speed pulse signal sequences Vin is input, precision voltage waveform is output from both ends V _PD Josephson element array. Details of the operation will be described below. In FIG. 3, when a pulse signal sequence (i) is input as Vin to the Josephson array 32, it is converted into a high-accuracy voltage pulse (SFQ pulse) sequence quantized in each Josephson element in the array (ii). ). Since the elements are connected in series, the array is output from both ends of the element as a series of high-precision quantized voltage pulses amplified by the number of elements. Actually, a cable for taking out the voltage is connected to the subsequent stage, but the frequency band is limited, so the band is limited, and the pulse density demodulation is performed by the integral action to return to the amplitude information. Then, it is output as a highly accurate arbitrary voltage waveform _VPD , and the waveform of FIG. 2B is generated (iii).

As the sum of the voltage waveform output _{V PD} of the programmable Josephson voltage voltage waveform output _{V PJVS} and pulse-voltage standard element 32 of the standard elements 31, by outputting to give a total voltage _(V PJVS ₊ V _PD), exact Synthesize a true sine waveform. An ideal smooth sine wave having an amplitude of 1 V or more can be synthesized.

  In implementing the present invention, in the case of the example of the first embodiment, as a form of combining the PJVS system and the RSFQ system, the PJVS chip and the RSFQ chip are connected in series using a multichip mounting technique. Create it. In the example of the second embodiment, the PJVS chip and the pulse drive voltage standard chip are connected in series using a multichip mounting technique as a combination of the PJVS system and the pulse drive system voltage standard. To create. In addition, it is conceivable to integrate these chips in one chip, and further cost reduction can be achieved.

  Although an example in which an ideal sine wave voltage waveform is synthesized by connecting a PJVS system and a pulse driving system (or RSFQ system) in series has been described, Josephson, which is a similar system instead of the pulse driving system, is used. An ideal alternating current sine wave waveform can also be synthesized by generating a differential waveform using an arbitrary voltage waveform synthesis method and connecting it in series with the PJVS method.

  Further, the AC voltage standard apparatus of the present invention, as described in the first and second embodiments, has a sine wave waveform and a pseudo sine wave, such as the sine wave-pseudo sine wave difference waveform calculation devices 17 and 37. Means are provided for calculating a differential waveform. Here, the AC voltage standard apparatus of the present invention is placed in a low temperature state because at least the circuit portion including the Josephson element is a superconducting circuit.

  The AC voltage generation circuit of the present invention can obtain an ideal smooth sine wave waveform with high amplitude, and is therefore highly accurate as an AC voltage standard. It is useful not only for primary standards and secondary standards, but also for quality control departments in the workplace.

1, superconductor 2, thin barrier layer 11, 31, programmable Josephson voltage standard element 12, high-speed single-flux-quantum AC voltage standard SQUID array 13, SQUID array drive circuit 14, 34, sinusoidal voltage waveform input device 15, 35, Pulse pattern conversion device for pseudo sine wave waveform 16, 36, Pulse pattern generation device 17, 37, Sine wave-pseudo sine wave differential waveform calculation device 18, 38, Pulse pattern conversion device 19, 39, Pulse pattern generation Device 20, 40, Pulse generator 32, Pulse drive system voltage standard 61, Programmable Josephson voltage standard (PJVS) element 64, Sine wave voltage waveform input device 65, Pulse pattern converter 66, Pulse pattern generator 94, Voltage waveform Input device 95, Pulse pattern conversion device 9 The pulse pattern generator 97, a pulse generator 134, a voltage waveform input device 138, a pulse pattern converter 139, a pulse pattern generator 140, a pulse generator

Claims (6)

An AC voltage generation circuit using a Josephson element,
A first circuit that includes a plurality of segments each having a predetermined number of Josephson elements connected in series, and that generates a stepped AC voltage by controlling a bias current applied to each segment;
A second circuit comprising a Josephson element that generates a quantized voltage pulse,
The second circuit is a circuit that outputs a differential waveform between a desired AC voltage waveform and the stepped AC voltage waveform,
An AC voltage generating circuit, wherein the first circuit and the second circuit are connected in series and a sum of output voltages of the respective circuits is used as an output voltage. The desired AC voltage waveform is sinusoidal waveform, said stepped AC voltage waveform is a stepped pseudo sine waveform, the second circuit, the sine wave teeth shaped and the step-like pseudo 2. The AC voltage generation circuit according to claim 1, wherein a differential waveform from the sine wave waveform is output.   3. The AC voltage generation circuit according to claim 1, wherein the second circuit synthesizes and outputs the differential waveform by performing pulse density modulation / demodulation using a quantized voltage pulse.   3. The AC voltage generation circuit according to claim 1, wherein the second circuit includes a high-speed single flux quantum circuit.   The AC voltage generation circuit according to claim 1, wherein the second circuit includes a pulse driving circuit.   An AC voltage standard circuit using the AC voltage generation circuit according to claim 1.

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