JPS60254908A - Josephson filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a Josephson filter, and particularly to a Josephson filter using equivalent inductance of a Josephson junction.

(2) Background of the technology A Josephson junction is two superconductors separated by a discontinuum. Methods for forming the separation include forming a weak bond, forming a nine-point connection, and forming a tunnel barrier. are known, and the Josephson tunnel junction is the most commonly used.

(3) Problems with conventional technology As shown in Figure 1, conventional Josephson junctions do not include inductance as a circuit parameter, so when configuring an LR filter using Josephson junctions, built-in inductance or resistance is required. Because of this, the characteristics of the inductance and resistance R cannot be changed after pattern formation, and the parameters thereof are fixed.

(4) Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks, and aims to obtain an LR filter whose cut-off frequency is electrically set by changing the equivalent inductance of a Josephson junction using a bias current and a control current. This is the purpose.

(5) Structure of the Invention According to the present invention, the above object is achieved by providing a Josephson filter characterized in that the filter is constructed using the equivalent inductance of a Josephson junction.

(6) Examples of the invention One embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a circuit in which the Josephson filter of the present invention is used as a bypass filter, and 1 is an input terminal to which an analog signal 3 having a predetermined frequency component is applied. Error signal 3 is applied through resistor R to Josephson junction element J1.

R3 is a load resistor connected in parallel to the Josephson junction element J1, and one end of the Josephson junction element J1 and the load resistor R3 are grounded. 3 is a bias input terminal.

When the differential inductance of the Josephson junction with the above configuration is taken into account, the basic equation of the Josephson junction element is generally expressed by the following equation.

I g = I c sinΦ ・・・・・・・・・(
1) Differentiating the above (11) with respect to t, dt dt Subtracting □ from dφ, dt Substituting the above equation (3) into equation (2), cosΦ in equation (4) becomes cos 'Φ ten s-t rr-
”-Φ=1, cos 2Φ=1-sin'Φ (
From equation 11, sinΦ is 1g. Since V=L□ in general, the differential inductance corresponding to Lt in equation (5) can be expressed as follows. This result was also confirmed from the simulation results.

From the above formula, when 0≦Ig, L is Φo / 2πIc≦L
Remove the range.

That is, by changing the bias current 1g, the value of the differential inductance L can be set to any value.

That is, in FIG. 1, if a signal 3 having an arbitrary frequency component is applied to the input terminal 1 and an appropriate DC current is applied to the bias input terminal 2 as the bias current Ig to the Josephson junction element J1, the load resistance R3 In this case, an output signal 4 having a frequency component higher than a predetermined cutoff frequency fc can be extracted. In this case, the cutoff frequency fC is determined by the time constant of the differential inductance L of the Josephson junction element J1 and the load resistance R3, and since the differential inductance can be changed appropriately by the bias current, the cutoff frequency can also be selected to an appropriate value. become.

What is shown in FIG. 3 is a circuit diagram when it is used as a low-pass filter, and the same parts as in FIG. 2 are given the same reference numerals and redundant explanation will be omitted. josephson junction element jl
A load resistor R3 is provided in front of the input terminal 1, that is, on the input terminal 1 side, and when the bias current 1g is changed as shown in Fig. 2, the Josephson junction element J1 becomes Φo / 2π Ic≦ It becomes the differential inductance of L.

Signal 3 with a predetermined frequency component applied to input terminal 1
The output signal 4 having lower frequency components passes through the Josephson junction element J1 and functions as a low-pass filter.

In the above embodiment, the case was explained in which the bias current 1g was changed, but as is clear from the fourth equation, even if the critical current 1c is changed, the bypass filter and low-pass filter as shown in FIGS. Since the equivalent inductance can be varied, the cutoff frequency can be appropriately selected. 4 and 5 show still another embodiment of the present invention.

As shown in Figure 6, the Josephson junction element is 5QUID.
The 5QUID is composed of multiple Josephson junction elements J0 and 2JO connected in parallel with a superconducting inductance LO.

The inductance LO is magnetically coupled to the control line 5, and the inductance RO is for damping the resonant circuit formed by the inductance 0 and the junction capacitance. Such a 5QUID is indicated by the symbol J1 shown in FIGS. 4 and 5. In the present invention, a bypass filter (Fig. 4) and a low-pass filter (Fig. 5) are constructed using the 5QUID, and by passing a control current IH through the control line 5, the inductance LO and magnetic field shown in Fig. 6 are Since the critical current 1c changes due to the gaseous coupling, the differential inductance changes.

At this time, since the bias current Ig is given to the inductance LO, even if the bias current rg is changed, the differential inductance changes in the same way, and the control current IH and the bias current Ig flowing through the control line 5 are changed simultaneously. By doing so, it becomes possible to obtain a wider dynamic range of the differential inductance L.

(7) Effects of the Invention Since the present invention is constructed and operated as described above, it is possible to construct an LR filter in which the cutoff frequency can be appropriately selected using the equivalent differential inductance of the Josephson junction element.
Furthermore, in order to vary the inductance, it is only necessary to change the bias current or critical current, so it has the feature that filters with various characteristics can be easily constructed.

[Brief explanation of the drawing]

Figure 1 shows the equivalent circuit of a conventional Josephson junction element;
The figure is a circuit diagram of a bypass filter using the Josephson junction element of the present invention, Figure 3 is a circuit diagram of a low-pass filter using the Josephson junction element of the present invention, and Figure 4 is a 5QUID configuration of the Josephson junction element of the present invention. FIG. 5 is a circuit diagram of a low-pass filter having a 5QUID configuration of Josephson junction elements according to the present invention. FIG. 6 is a circuit diagram of a 5QUID configuration of Josephson junction elements. 1...Input terminal, 2...Bias input terminal, 3
...Input signal, 4...Output signal, 5...Control line, JIJo, 2JO...Josephson junction element. R3...Load resistance Figure 1 Figure 4 Figure 5 Figure 6

Claims (5)

[Claims] (1) A Josephson filter characterized in that the filter is constructed using the equivalent inductance of a Josephson junction. (2) The Josephson non-filter according to claim 1, wherein the equivalent inductance of the Josephson junction is a differential inductance. (3) The Josephson filter according to claim 1, characterized in that the equivalent inductance is changed by changing the Iasumi flow. (4) The Josephson filter according to claim 1, wherein the equivalent inductance is changed by changing a control current. (5) The Josephson filter according to claim 1, characterized in that the equivalent inductance is changed by changing the control current to a uniform value.