JPH0425729B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a pulse edge detection circuit suitable for detecting signals in Josephson integrated circuits.

Prior Art and Problems In general, as shown in FIG. 1, a pulse edge detection circuit detects when a signal pulse Pin that rises at time t1 and falls at time t2 is input to the pulse edge detection circuit D. It operates to detect, for example, the falling edge (or rising edge) of the signal pulse Pin, output the signal Pout at time t2 (or t1), and transmit the detection of an edge in the signal pulse Pin to the subsequent circuit.

A concrete representation of the pulse edge detection circuit D is as shown in FIG.

In the figure, Sin is the input signal line, Sout is the output signal line, Sb is the bias current supply line, _L0 is the primary inductor, _L1 is the secondary inductor, L is the inductor, Rp and Rf are the resistances, A, B, and C represent Josephson junctions, and I _S , _IL , I _O , I _P , I _B , and φ _S represent currents, respectively.

Figure 3 is a timing chart for the main signals in the circuit shown in Figure 2;
The operation will be explained with reference to this timing chart.

First, at time t0, which is the initial state, the current I _P flows through the Josephson junction A, so almost no bias current I _B flows. This is because the inductance of the bias current supply line Sb is larger than that of the output signal line Sout.

Next, at time t1, when the control current φ _S flows, the Josephson junction A switches and the current is transferred to the bias current supply line Sb, and the Josephson junction C
Bias current I _B flows through (2 pieces).

In the above state, the input signal line Sin at time t2
When the signal pulse current I _S propagates to the input signal line Sin, a negative differential current I _L flows through the inductance loop including the junctions B and C magnetically coupled to the input signal line Sin and the resistor Rf.

The Josephson junction C, in which this differential current I _L acts in a direction to cancel the bias current I _B , does not switch.

However, at time t3, the signal pulse current I _S
When falls, a positive differential current I _L flows. In this case, since the currents I _L and I _B are added, Josephson junction C switches and the current flows to the output signal line Sout.
Head to. At this point, the output signal current I _O flows, and the signal is transmitted to the subsequent stage.

Junction B, resistors Rf and Rb in this circuit each play the following roles.

That is, the junction B limits the differential current I _L by the critical current value of the junction current B. Resistor Rf adjusts differential current I _L. The resistor Rp provides a damping effect on the current transferred to the output signal line Sout when the Josephson junction C switches.

Now, in the conventional circuit shown in Fig. 2, the bias current I _B is caused to flow through the inductance loop including Josephson junctions CB and C on the secondary side, which are magnetically coupled to the input signal line Sin, and the Josephson junction C. The problem is that the bias current supply line Sb is not isolated from the bias current supply line Sb. That is, in the configuration of the conventional example, Josephson junction C
The transfer current to the output signal line Sout that occurs when the output signal line Sb switches flows into the inductance loop on the secondary side including Josephson junction B, and the output signal current I _O transferred to the subsequent stage of the output signal line Sb decreases. As a result, the operation of the subsequent circuit becomes unstable.

Purpose of the Invention The present invention is to completely separate the input signal line and the output signal line in a pulse edge detection circuit configured using Josephson elements, and to send a sufficient output signal current to the subsequent circuit. This is intended to contribute to the stable operation of the subsequent circuit.

Embodiment of the invention FIG. 4 is a circuit diagram of a main part of an embodiment of the invention,
The same parts as those described in connection with FIG. 2 are indicated by the same symbols.

In the figure, J1 and J2 are asymmetrical (J1≠J
2) SQUID (Superconducting Quantum)
In the two-junction Josephson device constituting a quantum interference device (interference device), L ₂ and L ₃ are inductors, R ₁ and R _L are resistances, I _R is load current, and M is mutual inductance.

FIG. 5 is a timing chart regarding the main signals in one embodiment of the present invention shown in FIG.
The figure is a diagram showing the threshold characteristics of an asymmetric SQUID, and the operation will be explained next with reference to these figures.

In this embodiment, it is assumed that a bias current I _B synchronized with the clock pulse is flowing.

When the input signal pulse current I _S flows while the bias current I _B flows, the inductors L ₁ , L ₂ and the resistor
A differential current I _L of the input signal pulse current I _S flows through a differential current generation loop consisting of R ₁ . Since the differential current generation loop is magnetically coupled to the SQUID, the differential current I _L becomes a control current for the SQUID, and the operating point shown in FIG. 6 moves from point P1 to point P2. At this time, since the differential current I _L is negative, the SQUID is not switched.

Next, if the input signal pulse current I _S falls and transitions to a zero current state, a positive differential current I _L flows through the differential current generation loop, contrary to the above,
The operating point moves to point P3. At this time, since the threshold curve is crossed, the SQUID switches, and the current is transferred to the load resistor R _L and flows as the load current I _L.

In this way, the falling edge of the input signal pulse current _IS can be detected. Incidentally, if the coupling polarity of the inductors L ₀ and L ₁ is reversed from the illustrated example, it is also possible to detect a rising edge.

Since the SQUID in this embodiment and the differential current generation loop that controls it are magnetically coupled, it can be understood that input and output are completely separated.

Effects of the Invention According to the present invention, the present invention includes a differential current generation loop having an inductor and a resistor that are magnetically coupled to an input signal line, and an asymmetric SQUID that is magnetically coupled to the differential current generation and controlled by the differential current. A pulse edge detection circuit is provided, in which the input signal line and differential current generation loop on the input side are completely separated from the asymmetric SQUID on the output side, so that the current on the input side The load current on the output side, that is, the output signal current, does not decrease at all due to the influence of this, and since sufficient current is supplied to the subsequent circuit, the operation of the circuit will not become unstable.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram explaining the operation of a pulse edge detection circuit, Fig. 2 is a main part circuit diagram specifically showing a conventional pulse edge detection circuit, and Fig. 3 is a diagram illustrating the operation of a pulse edge detection circuit.
A timing chart regarding main signals for explaining the operation of the pulse edge detection circuit shown in the figure.
The figure is a timing chart regarding main signals to explain the operation of the embodiment shown in Fig. 4, and Fig. 6 is a diagram showing threshold characteristics to explain the operation of the embodiment also shown in Fig. 4. It is. In the figure, J1 and J2 are Josephson elements that constitute an asymmetric SQUID, L ₀ , L ₁ , L ₂ , and L ₃ are inductors, R ₁ and R _L are resistors, Sin is an input signal line, and Sout is an output signal line. , Sb is the bias current source, M is the mutual inductance, I _S is the signal pulse current, I _L is the differential current, I _R is the load current, I _B
is the bias current.

Claims (1)

[Claims] 1. Pulse edge detection characterized by comprising a differential current generating loop having an inductor and a resistor magnetically coupled to an input signal line, and an asymmetric SQUID magnetically coupled to the differential current generating loop and controlled by the differential current. circuit.