JPH0256844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Josephson current amplifier suitable for use in Josephson digital circuits.

Josephson digital circuits using Josephson effect elements or Josephson junctions are expected to be extremely high-speed, consume less power, and have higher density than digital circuits using conventional semiconductor circuit elements. For these reasons, it is viewed as extremely promising for the future. When building switching gates and other logic circuit elements using Josephson junctions, two types of operating principles can be followed. There are two types: magnetic field induction type and current column type. At present, these two methods coexist, and it is a matter of choosing which method to use depending on the required design specifications, etc., but regardless of which method is used, these logic circuits are It can be constructed not only from circuit elements related to logic functions such as switching gates, logical sums, AND gates, shift registers, multivibrators, etc., but also Josephson current amplifiers that amplify the output current of each circuit element as an important component. It is a request.

In particular, the Josephson logic circuit elements currently being developed, which are based on either of the above methods, are difficult to achieve sufficient fan-out by themselves, and a large operating margin must be ensured for stable operation. Considering this, the amplification function of the circuit output current is almost indispensably required.

In order to consider the circuit element output current amplification in more detail, let us refer to FIG.

There is a certain circuit element G, a digital signal Ii in the current dimension is input to its input terminal Ti, and is output to the output of this circuit element G by the processing function of the characteristics uniquely given to this circuit element. Assume that a current signal Im is obtained. And this circuit element output current
It is assumed that Im is input as an input current Is to the input terminal Ts of a current amplifier A, is amplified by a gain times that of the current amplifier in the current amplifier, and then flows out from the amplifier output terminal To as an output current Io. Naturally, amplifier A requires energy to be supplied from the outside, and the external energy supply terminal or circuit current terminal is set to Tg, and the supplied energy or circuit current is set to Ig.

Incidentally, in circuit elements such as various gates, input and output generally need to be separated.
Otherwise, the output current Im will be fed back to the input side, causing other circuit elements in the previous stage to malfunction, and the output current will decrease accordingly, reducing the effective fanout and causing the circuit elements in the next stage to malfunction. This is because problems such as not being able to drive the motor may occur.

However, as shown in FIG. 1, a certain circuit element G and an amplifier A that amplifies its output current Im and outputs an output voltage Io having logically the same information.
In substantially one logic circuit stage consisting of The input current of amplifier A should be
There is no particular need for separation between Is to Im and the output current Io.

Rather, from the point of view of reducing power consumption, it is preferable in terms of energy utilization efficiency to add input current Is in a superimposed manner to externally supplied energy or circuit current Ig given to the amplifier and extract it as output current Io.

On the other hand, as a current amplifier, it is naturally desirable to have a large gain, and good design is also required. Another necessary condition is that the operating margin of the circuit element G that generates the output current to be amplified is not limited.

After briefly summarizing the requirements for this type of Josephson current amplifier, the general configuration of a conventional Josephson current amplifier will be described with reference to FIG. 2.

A typical Josephson current amplifier in the past is of the Josephson single junction type, using only one Josephson junction J, as shown in FIG. The input terminal Ts into which the input current Is as an output current from the previous stage circuit element flows, and the circuit current terminal or gate terminal Tg into which the rotational current Ig flows, respectively, after passing through current adding resistors R1 and R2. It is connected to one end of Josephson junction J, and an output terminal To for output current Io is similarly drawn out from this connection point. The other end of Josephson junction J is generally dropped to ground, and the output current Io is connected to the output terminal To
selectively obtained during the output load resistor RL connected between and ground.

To briefly explain the operation, the gate current Ig is selected to a magnitude that does not, by itself, cause the Josephson junction J to switch into a voltage state.
Therefore, when there is no input current Is, the value of the output current is naturally zero. When an input current Is is applied, the input current Is and the gate current Ig are summed through the summing resistor and flow into the Josephson junction J, exceeding the critical current value of the junction, so that the Josephson junction J changes from voltage state to Switch to high impedance state.

In this case, the added currents flow toward the output load resistor RL, which has a relatively low resistance at this point, as if to bypass the Josephson junction J, which has become a high impedance state. The output current Io passes through the output terminal To.

If we consider this conventional Josephson current amplifier in accordance with the desirable elements of a Josephson current amplifier mentioned above, we can see that the input current Is is superimposedly added to the circuit current or gate current Ig, and the output current Io is In this respect, this conventional single-junction Josephson current amplifier is also worth evaluating.

However, as is well known, in such single-junction devices, the operating margin is uniformly determined to be about 33% by simple plotting on the threshold other value curve. Therefore, if the operating margin of the circuit element in the previous stage to be amplified is smaller than this value, there is no problem, but if it is larger, the circuit element G
The overall operating margin of one logic circuit stage consisting of and amplifier A is that of this amplifier, that is,
This will limit it to approximately 33%. and,
In reality, this fear is stronger.

For example, in the current injection type logic circuit element mentioned above, the basic switching gate is a four-junction current injection type closed loop switching gate (Japanese Patent Application Laid-Open No. 56-32830,
57-99034), and there are various circuit elements that utilize this, but this type of circuit element can easily have an operating margin of 60% or more, and therefore, such circuit elements If the conventional Josephson current amplifier A shown in FIG. 2 is used to amplify the output current of , the inherent wide operating margin will be sacrificed. The above-mentioned four-junction current-injection closed-loop switching gate has become well known to those skilled in the art through subsequent research and publications triggered by the above-mentioned application, and is abbreviated as 4JL gate, and this term is also used as this term. It is treated as a quasi-academic term in the industry.

The present invention has been accomplished primarily to provide a Josephson current amplifier that can eliminate the drawbacks of the conventional examples as described above. That is, the present invention aims to provide a Josephson current amplifier that has good power utilization efficiency, obtains a large amplification degree, and has good designability without impairing the operating margin of the logic circuit element that amplifies the output current.

FIG. 3 shows a Josephson current amplifier 1 as a preferred embodiment of the present invention. The Josephson current amplifier 1 of the present invention employs the above-mentioned 4JL gate configuration as one of its main components. That is, four Josephson junctions J1, J2, J3, and J4 constitute one closed loop, and two opposing points of this closed loop are provided with a circuit current terminal or gate terminal g and a ground terminal e, respectively. The closed loop is divided into left and right branch circuits or branches using the field , and two Josephson junctions are included in each branch circuit.

In the branch circuit in which Josephson junctions J1 and J2 are provided, a control current terminal c is provided between these two Josephson junctions.

As can be seen in the above-mentioned publication, in general, in this basic gate configuration, Josephson junctions J1 and J2 in the branch circuit with the control terminal are
The critical currents Io1 and Io2 are selected to be approximately 1/2 to 1/3 of the critical currents Io3 and Io4 of Josephson junctions J3 and J4 in the other branch circuit. The details of the reason are already known to those skilled in the art and will therefore be omitted, but this is to ensure a predetermined sequence-dependent operation and obtain a current gain.

Furthermore, Josephson current amplifier 1 of the present invention
Now, the circuit current terminal or gate terminal g of the basic gate is used as it is as the circuit current terminal or gate terminal Tg of the present Josephson current amplifier 1, and the control terminal c of the basic gate is also used as the signal input terminal Ts of the present amplifier 1. I am using it.

The output terminal To is also similarly led out from the gate terminal as in a normal basic gate and connected to one end of a load resistor RL which is equivalently in parallel with the closed loop. Closed loop ground terminal e is connected to the reference potential of this circuit system, typically ground.

A characteristic feature of the Josephson current amplifier 1 is that a bypass resistor Rb is provided in parallel to the first junction J1 between the signal input terminal Ts and the gate terminal Tg so as to bypass the first junction J1. This is what is happening. Conversely, this Josephson current amplifier 1 is based on the above-mentioned Japanese Patent Application Laid-Open No. 56-328360.
This patent has succeeded in providing an effective Josephson current amplifier as described below with minimal modification to the basic gate configuration disclosed in the publication.
The operation of the Josephson current amplifier 1 will be explained as follows.

Under conditions where only the gate current Ig is applied, this gate current is divided in the left and right branch circuits in the closed loop according to the impedance ratio of the branch circuits, and flows out to ground. In this case, as mentioned earlier, assuming that Io1=Io2=Io...(1) Io3=Io4=NIo N=2~3...(2), the value of gate current Ig is , the shunt into the left branch circuit is chosen to have a size that will not cause Josephson junctions J1 and J2 in this left branch circuit to switch into a voltage state.

In this state, the signal current is applied to the signal input terminal Ts as the output current from the appropriate circuit element in the previous stage.
When Is flows in, most of this signal current initially flows through Josephson junction J2, which is the current path with the lowest impedance.

The surplus between most of this signal current and the branch circuit branch of the circuit current or gate current Ig described above is such that the gate current value is large enough to switch Josephson junction J2 into a voltage state. , this Josephson junction J2 is in a voltage state or a high impedance state.

Then, the input signal current flows into the right branch circuit via the Josephson junction J1 remaining in the left branch circuit, but this Josephson junction J
Regarding 1, since the signal current Is and the divided portion of the gate current Ig have opposite phases, this junction J1 does not switch to a voltage state, even though the threshold current value of the single element is small. Both currents begin to flow in a superimposed manner toward the series Josephson junctions J3 and J4 in the right branch circuit.

Although the critical current values of both junctions J3 and J4 in the right branch circuit are somewhat large as mentioned above,
It is relatively easy to set the current values of both the signal current and the gate current to exceed this value, and since they are set in this way, the inflow of both currents Ig and Is causes the current in this right branch circuit to Both junctions J3, J4 are switched to a voltage state.

In this case, if the load resistance RL has an appropriate value, most of the circuit current or gate current Ig will flow to the load resistance through the output terminal Ts. On the other hand, the signal current Is is
This is attempted to be superimposed on the circuit current Ig flowing out from the output terminal Ts through the Josephson junction J1, which remains in a zero voltage state, but when this amplifier is applied for the purpose described in this book, In the first place, the value of the input signal current Is as the output current of the appropriate circuit element in the previous stage is expected to be larger than a certain degree, so normally the Josephson junction J1 remaining until the end also has a function of passing this signal current. Switch to voltage state by Then, this time, Josephson junction J which was last switched to voltage state
This signal current Is comes to be superimposed on the circuit current Ig via the bypass resistor Rb, which is provided in parallel with the Josephson current amplifier 1, resulting in an output that can be specified at the output terminal To of the Josephson current amplifier 1. The current Io is the mutual surplus of these two currents. In other words, one of the desirable requirements mentioned above, that is, the use of the input signal current as the output current, is satisfied.

However, since this Josephson current amplifier 1 utilizes the basic gate configuration described above for the actual switching section, it can similarly obtain a large current gain and has the same operating margin as this type of basic gate. can be taken significantly.

For example, as shown in FIG.
When using the switching gate G disclosed in No. 99034 to amplify the output current, if this gate G and Josephson current amplifier 1 are considered as one stage circuit,
The addition of the current amplification function does not impair the inherently large operating margin of the gate section G, and the operating margin of this stage can be defined only by the operating margin of the gate section G. can. As mentioned earlier, if the operating margin of this gate section G is, for example, 60%, then the Josephson current amplifier 1, which has a similar configuration in the amplification function section or switching section, will also have the same 60%.
A certain operating margin can be easily secured.

The details of the gate section G with the input resistor Ri shown in FIG. When inputting to terminal Ti, first, the lower Josephson junction Jb in the left branch circuit changes the circuit current.
The voltage state is switched by the superposition of the shunt of Ig ₁ and this input current Ii, and then both Josephson junctions Jc and Jd in series in the right branch circuit are switched clockwise via the circuit current Ig ₁ and Josephson junction Ja. It switches to a voltage state by superimposing it with the input signal current Ii. Finally, during the transition period when the circuit current Ig ₁ flows into the input resistor Ri via the Josephson junction Ja, which remains in the zero voltage state, the Josephson junction Ja also switches to the voltage state and holds hand,
The circuit current _Ig1 flows out to the load resistance Rm as an output current Im. In this state, the circuit current Ig ₁ flowing into the circuit current terminal Tg ₁ or the output current Im is reliably separated from the input signal current Ii.
This is because all Josephson junctions of the closed loop switch to a voltage state and no circuit current flows into this loop, and the input signal current Ii likewise flows through the input resistor Ri without flowing into the closed loop.

The relative relationship between the critical current value of each Josephson junction of the present Josephson current amplifier 1 and the critical current value of each Josephson junction of the gate part G is expressed by the equations (1) and (2) described above. Choosing an appropriate value that satisfies both is a common design matter. For example, in both the gate section G and the present Josefson current amplifier 1, the critical current value relationship between the Josephson junctions in the left and right branch circuits is selected to be the same as 1:3, but the above-mentioned critical currents of the Josephson junctions J1 and J2 are The value Io may be selected to be approximately twice that of Josephson junctions Ja and Jb in the gate portion G.

The basic gate G shown in Figure 4 was originally developed for the purpose of obtaining the same logic value or positive logic as the input signal in the form of current amplification. The circuit system can be thought of as a two-stage cascade amplifier. However, it is of course not limited to this, and the gate section G may be of any type as long as it has a current output.
The current amplification effect of the Josephson current amplifier 1 can be obtained. As mentioned at the beginning, the present Josephson current amplifier 1 does not act exclusively on current injection type logic circuit elements G, but can also be effectively used for magnetic field coupling type ones.

In any case, as detailed above, according to the present invention, a Josephson current amplifier, which is required as an important component for realizing a Josephson computer, can be realized without the drawbacks of the conventional ones. By superimposing the input signal current on the output current, it is possible to obtain extremely large effects such as improving energy utilization efficiency, securing gain, preventing reduction in operating margin, and simplifying the configuration.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram when connecting a Josephson current amplifier to a Josephson logic circuit element;
The figure is a schematic diagram of a typical example of a conventional Josephson current amplifier, FIG. 3 is a schematic diagram of an embodiment of a Josephson current amplifier of the present invention, and FIG. 4 is an application of the third illustrated embodiment. FIG. 2 is an example circuit configuration diagram. In the figure, 1 is the Josephson current amplifier of the present invention as a whole, J1 to J4 are Josephson junctions, RL is a load resistance, and Rb is a bypass resistance.

Claims (1)

[Claims] 1. A closed loop is constructed using four Josephson junctions, a circuit current terminal and a ground terminal are provided at two opposing points in the closed loop, and an output terminal is drawn out from the circuit current terminal. On the other hand, the closed loop is divided into left and right branch circuits using the circuit current terminal and ground terminal, and two of the four Josephson junctions are inserted in each branch circuit. A Josephson current amplifier characterized in that a signal input terminal is formed between the Josephson junctions, and a bypass resistor is provided in parallel to the Josephson junction located between the signal input terminal and the circuit current terminal. .