JPH0624259B2 - Analog / digital converter - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to an analog / digital converter. More specifically, the present invention relates to the construction of a novel analog / digital converter utilizing superconductors.

Conventional technology Under the superconducting phenomenon, a substance shows complete diamagnetism, and no potential difference appears even though a finite steady current flows inside.

The application fields of this superconductivity phenomenon are MHD power generation, power transmission,
In the field of electric power such as power storage, in the field of power such as magnetic levitation trains, electromagnetic propulsion vessels, etc., as well as in ultra-sensitive sensors for magnetic fields, high frequencies, radiation, etc. It is expected to be a technology that can realize not only reduction of power consumption but also extremely high-speed operation in the field of electronics represented by Josephson devices. There is.

By the way, superconductivity was a phenomenon observed only at extremely low temperatures. That is, even in Nb ₃ Ge, which was said to have the highest superconducting critical temperature Tc as a conventional superconducting substance, the extremely low temperature of 23.2 K was considered as the limit of the superconducting critical temperature for a long time.

Therefore, conventionally, in order to realize the superconducting phenomenon, the boiling point is
The superconducting material was cooled to below Tc using 4.2K liquid helium. However, the use of liquid helium imposes an extremely large technical burden and cost burden on the cooling equipment including the liquefaction equipment, and has hindered the practical application of the superconducting technology.

However, in recent years, it has been reported that the complex oxide sintered body can become a superconductor at a high critical temperature, and the practical application of the superconducting technology by the non-low temperature superconductor is being promoted. In the previously reported examples, Y-Ba-Cu system, La
-Ba-Cu-based or La-Sr-Cu-based composite oxides having a crystal structure similar to the perovskite type are particularly mentioned as those exhibiting a superconducting phenomenon at liquid nitrogen temperature or higher.

Problems to be Solved by the Invention As described above, the development of a novel superconducting material has made it possible to use the superconducting phenomenon in a more general environment. Therefore, its application is being promoted in many fields,
It is even said that superconducting technology will transform the modern industrial structure.

The present invention provides a completely novel analog-to-digital converter that was created and developed as a result of studying the effective use of the novel superconducting material as described above.

Means for Solving the Problems That is, according to the present invention, for a predetermined critical condition, a conversion unit formed by coupling in series a plurality of superconducting flow paths in which critical conditions different from each other with a certain difference are set, And a detection unit having means for detecting interruption of the superconducting flow in each of the superconducting flow paths, wherein a change in current superposed with an analog signal applied to the conversion unit is converted into a digital signal corresponding to the applied current. Analogue featuring output /
A digital converter is provided.

Further, in the analog / digital converter according to the present invention, the superconducting flow path is formed by the following general formula: (α _1-x β _x ) γ _y δ _z [where element α is an element included in Group IIa of the periodic table] And the element β is an element included in Group IIIa of the periodic table,
The element γ is the periodic table Ib, IIb, IIIb, IVa or VIII.
It is an element contained in group a, δ is O, and x, y, z
Are numerical values satisfying x = 0.1 to 0.9, y = 1.0 to 4.0, and 1 ≦ z ≦ 5, respectively]. Here, as a particularly advantageous combination of elements, Ba
A combination of —Y—Cu, Ba—La—Cu, Sr—La—Cu and the like can be mentioned. Since a composite oxide in which these elements are combined or a composite oxide based on this shows a superconducting phenomenon at a temperature higher than the temperature of liquid nitrogen, the practicality of a superconducting circuit formed using this is extremely high.

The main feature of the analog / digital converter according to the present invention is that the analog / digital converter is provided with a conversion unit formed by connecting a plurality of superconducting flow paths having different critical currents in series.

That is, the superconducting flow path generally has a predetermined critical current density, critical magnetic field, critical temperature, and the like. The superconducting flow path has no electrical resistance in environments below these critical conditions, and thus no voltage develops in this current path. On the other hand, when the environment deviates from these critical conditions, the superconducting phenomenon is broken and the material forming the superconducting flow path becomes a normal conductor or an insulator governed by Ohm's law. It goes without saying that in this state, a voltage corresponding to the applied current or applied voltage is generated at both ends of the superconducting flow path.

The converter of the analog / digital converter according to the present invention comprises:
A plurality of superconducting flow paths having different critical currents are connected in series. Therefore, when a current superposed with an analog signal is applied to this detection unit in the state where a predetermined current equal to or less than the minimum critical current is flowing, according to the change of this current, the superconducting flow path From the lower critical condition, some corresponding to changes in the condition exceed the critical condition and become normal conductors. Therefore, a predetermined voltage is generated across the superconducting flow path. That is, the analog / digital converter signal input to the analog / digital converter according to the present invention is for converting a change in current on which an analog signal is superimposed into a digital signal.

The detection part of the analog / digital converter according to the present invention comprises:
For example, a circuit that detects the voltage generated as described above can be used. Therefore, for example, by setting the critical conditions of a plurality of superconducting flow paths so as to be different stepwise with a certain difference, and further by inputting the detected voltage to a predetermined encoder, for example, as a binary signal as a digital signal. Can be output.

In addition, the superconducting flow path can be formed as a Josephson junction, and in this case, extremely high speed operation can be realized. With this structure, the superconducting flow paths having different critical conditions forming the conversion unit can be physically controlled by the junction area of the Josephson junction or the like.

In consideration of practicality, the analog / digital converter according to the present invention can be advantageously constituted by a thin film formed by physical vapor deposition on a predetermined substrate. Here, the physical vapor deposition may include a sputtering method and an ion plating method as advantageous methods.
In this case, it is advantageous to use a substrate having a surface texture having a perovskite structure or a structure similar thereto so that a thin film to be formed can easily adopt a perovskite structure exhibiting high superconducting properties. Specifically, it is advantageous to use SrTiO ₃ single crystal, MgO single crystal, sapphire, or the like as the substrate.

Hereinafter, the present invention will be described in more detail with reference to the drawings. However, what is disclosed below is only one embodiment of the present invention,
It does not limit the technical scope of the present invention.

First Embodiment FIG. 1 is a diagram schematically showing the structure of an analog / digital converter, in particular a converter, constructed according to the present invention.

As shown in FIG. 1, this conversion portion is formed by stacking superconducting members S ₁ , S ₂ ... S _i ... S _{n + 1} whose cross-sectional areas change stepwise. . At the joint between the superconducting members S ₁ , S ₂ ... S _i ... S _{n + 1} , a thin insulating layer is interposed between the superconducting members, and at this portion, there is mutual insulation. Josephson junctions J ₁ , J ₂ ... J _n having different critical currents are formed. Also,
A pair of terminals P _{1 and} P ₀ for applying a current to the assembly are engaged with both ends of the assembly of these superconducting members, and each superconducting member S ₁ , S _2, ... For S _i ... S _{n + 1} ,
Terminals P ₂ for voltage detection, which will be described later, P _3, ... P _n are coupled.

Here, FIG. 2 is a graph showing the relationship between the current input by superimposing an analog signal and the critical current density in each Josephson junction.

That is, a predetermined current I _0, which is smaller than the critical current of the junction S ₁ which is the Josephson junction having the minimum critical current condition, is made to flow to the above-mentioned assembly by the terminals P _{1 and} P ₀ . For the assembly in this state, when the input current increases due to the applied analog signal, as can be seen from FIG. 2, there is a junction J _i and a junction J _{1 having} a lower critical condition than that.
Superconductivity is broken in the junction from J _i to J _i-1 and electrical resistance is generated. Therefore, a DC voltage is generated at the terminals from the detection terminals P ₂ to P _i .

In this way, by inputting the voltage corresponding to the change of the environmental magnetic field output from each of the detection terminals P ₂ , P _3, ... P _n to the encoder coupled as shown in FIG. 3, For example, a digital binary signal can be obtained.

In addition, in the embodiment, the assembly of the superconducting flow paths is formed by a plurality of Josephson junctions having different bonding areas connected in series, but it is also possible to form the assembly by superconducting materials having different cross-sectional areas. It goes without saying that it is within the scope of the present invention to stack and form superconducting materials having different critical conditions, and to mix these setting methods.

EFFECTS OF THE INVENTION As described in detail above, the analog / digital converter according to the present invention outputs a digital signal corresponding to an analog signal by inputting the superimposed current of the analog signal. This operation is straightforward and is achieved by a very simple structure as an analog / digital converter.

Further, in the mode in which the conversion unit forming the analog / digital converter is formed as an assembly of Josephson junctions, extremely high speed operation can be realized.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the structure of an analog / digital converter, in particular a converter, constructed according to the present invention, and FIG. 2 explains the operation of the converter shown in FIG. FIG. 3 is a graph, and FIG. 3 is a diagram schematically showing a configuration when an encoder is connected to the conversion unit shown in FIG. [Main reference numbers] S ₁ , S ₂ …… S _n …… Superconducting member, J ₁ , J ₂ …… J _n …… Josephson junction, P ₀ , P ₁ …… Current application terminal, P ₂ , P ₃ ...... P _n ...... Voltage detection terminal

Claims (16)

[Claims] 1. A conversion part formed by connecting in series a plurality of superconducting flow paths in which different critical conditions are set with a certain difference from a predetermined critical condition, and a superconducting flow in each of the superconducting flow paths. And a detection unit having means for detecting the interruption of the analog signal, and outputs a change in current superposed with the analog signal applied to the conversion unit as a digital signal corresponding to the applied current. Digital converter. 2. The analog / digital converter according to claim 1, wherein the critical condition set in each of the superconducting flow paths is a critical current in each of the superconducting flow paths. 3. The analog / digital converter according to claim 1, wherein the critical condition set for each of the superconducting flow paths is a critical magnetic field of each superconducting flow path. 4. The analog / digital converter according to claim 1, wherein the superconducting flow path includes a Josephson junction. 5. A means for detecting the interruption of the superconducting current,
5. A set of circuits for respectively detecting a voltage generated in a current path in a predetermined section including each of the superconducting flow paths, according to any one of claims 1 to 4. Analog / digital converter. 6. The method of claim 1 wherein the output of the means for detecting interruption of the superconducting current is coupled to a circuit which produces a binary signal in response to the operation of the superconducting flow path. The analog / digital converter according to any one of items 1 to 5. 7. The analog / signal according to any one of claims 1 to 6, wherein the superconducting conductive channel is a superconducting material thin film formed on a substrate. Digital converter. 8. The analog / digital converter according to claim 7, wherein the thin film of superconducting material is a thin film formed on the substrate by a physical vapor deposition method. 9. The analog according to claim 8, wherein the thin film is a complex oxide thin film formed by sintering a deposited layer formed by wet coating on the substrate. / Digital converter. 10. The analog according to any one of claims 7 to 9, wherein the substrate is formed on a SrTiO ₃ single crystal, MgO or sapphire substrate. / Digital converter. 11. The superconducting flow path is formed of a material that is a conductor in a non-superconducting state, according to any one of claims 1 to 10. Analog / digital converter. 12. The superconducting flow path and / or Josephson junction has the following general formula: (α _1-x β _x ) γ _y δ _z [where element α is an element included in Group IIa of the periodic table]. And the element β is an element included in Group IIIa of the periodic table,
The element γ is the periodic table Ib, IIb, IIIb, IVa or VIII.
It is an element contained in group a, δ is O, and x, y, z
Are numerical values that satisfy x = 0.1 to 0.9, y = 1.0 to 4.0, and 1 ≦ z ≦ 5, respectively.]. 11. The analog / digital converter according to any one of items 1 to 11. 13. The analog / digital converter according to claim 12, wherein the complex oxide has a perovskite type crystal structure. 14. The element α is Ba and the element β is Y.
14. The analog / digital converter according to claim 12 or 13, wherein the element γ is Cu. 15. The element α is Ba and the element β is La
14. The analog / digital converter according to claim 12 or 13, wherein the element γ is Cu. 16. The element α is Sr and the element β is La
14. The analog / digital converter according to claim 12 or 13, wherein the element γ is Cu.