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IEEE Transactions on Applied Superconductivity

Operation of a 1-bit quantum flux parametron shift register (latch) by 4-phase 36-GHz clock

M. Hosoya, W. Hioe, Kazumasa Takagi, Eiichi Goto

Published Jun 1, 1995• 16 citations
Publisher

Abstract

The Quantum Flux Parametron (QFP) is a SFQ-type logic device which uses a single flux quantum (SFQ) to represent 1-bit of information. QFP circuits use a multi-phase external ac power which also acts as the clock for synchronization, hence QFP circuits are highly pipelined. The clock frequency must be increased to improve the throughputs of the circuits, so the control of a high frequency clock is a key technology for the QFP. This paper describes a clock distribution technique which utilizes the characteristics of a standing wave. Using this technique, the operation of a 1-bit QFP shift register by a 4-phase clock up to 36 GHz is shown. In the 4-phase clock operation of QFPs, the input is given in phase 1, the QFP switches in phase 2, the output is held during phase 3, and the QFP resets in phase 4. Therefore, the 4-phase 36-GHz operation means that each QFP switches or resets in less than 7 ps.>

DOI
10.1109/77.403181

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International Journal of High Speed Computing•Jun 1, 1991•0 citations
The Quantum Flux Parametron (QFP) is a SFQ-type logic device which uses a single flux quantum (SFQ) to represent 1-bit of information. QFP circuits use a multi-phase external ac power which also acts as the clock for synchronization, hence QFP circuits are highly pipelined. The clock frequency must be increased to improve the throughputs of the circuits, so the control of a high frequency clock is a key technology for the QFP. This paper describes a clock distribution technique which utilizes the characteristics of a standing wave. Using this technique, the operation of a 1-bit QFP shift register by a 4-phase clock up to 36 GHz is shown. In the 4-phase clock operation of QFPs, the input is given in phase 1, the QFP switches in phase 2, the output is held during phase 3, and the QFP resets in phase 4. Therefore, the 4-phase 36-GHz operation means that each QFP switches or resets in less than 7 ps.>
The authors present 4- and 12-b shift registers capable of operating from DC up to 8.56 and 4.24 GHz, respectively. These circuits' total on-chip power dissipation is estimated to be roughly 10 nW. A novel clock current distribution network permits such high clock frequency and such low on-chip power dissipation. The clock is applied as a standing wave and is distributed by inductive division. With this clock current distribution scheme, no power is dissipated along the clock lines. In spite of the circuits' low output amplitude (tens of microvolts) and of the large crosstalk with the clock frequency, the output waveforms are captured in time domain at microwave frequencies. Also, for the 12-b device, 10/sup 15/ error free operations per quantum flux parametron (QFP) are demonstrated. Finally, the 12-b shift register is the largest QFP circuit reported to date; it is composed of 48 QFPs and one DC SQUID.>
A quantum flux parametron (QFP), a single quantum flux superconductive device that has a potential of up to 100-GHz switching with nW-order power dissipation, is considered. The potential of the QFP and key technologies when QFPs are applied to a Josephson supercomputer are described. Switching speed, stability, and power dissipation of a QFP are discussed. QFP gates, circuits, and systems are next described. Then, ultra-fast clock distribution using a standing wave is explained. High-speed operation at more than 10 GHz and 10/sup 14/ error-free operations per QFP have been demonstrated. Finally described is a high-density packaging scheme by three-dimensional integration, which is very important for ultra-high speed circuits because the propagation delay becomes dominant in such circuits.>
The quantum flux parametron QFP is a very fast superconducting logic device. Previously, the high frequency operation of the QFP was assessed by analysing the output of the device in the frequency domain. This paper shows for the first time that time domain measurements are possible in spite of the low voltage amplitude of the output signal and relatively large crosstalk with the clock frequency. The time-domain waveform of a single-bit shift register with logic inversion working at a clock frequency of 5 GHz is recorded.
The D-gate is a quantum flux parametron (QFP) logic gate which was proposed to reduce input interaction and improve input margin. It is basically a 2-input multiplexer with two select signals. By giving appropriate inputs, a single gate can also perform 2-input AND, 2-input OR, 2-input XOR, 3-input majority, 3-input parity or 1-bit equality. Since it is a QFP device, it has a self-latching effect which can be exploited for pipelined designs of many combinational logic functions. However, because QFP logic is a clocked logic expected to operate at 10 GHz or more, propagation delay becomes an important issue in circuit design.
The quantum flux parametron (QFP) is a flux-transfer, flux-activated Josephson logic device which realizes much lower power dissipation than other Josephson logic devices. Being a two-terminal device, its correct operation may be affected by coupling to other QFPs. The problems include backcoupling form active QFPs through inactive QFPs (relay noise), coupling between QFPs activated at different times because of clock skew (homophase noise), and interaction between active QFPs (reaction hazard). Previous QFP circuits worked by wired-majority, which is a linear input logic and has low input margin. A logic gate (D-gate) using a QFP to perform logic operations has been analyzed and tested by computer simulation. Relay noise, homophase noise, and reaction hazard are substantially reduced. Moreover, the inputs have little interaction, and hence input margin is greatly improved. Using only D-gates it is possible to realize any combinational logic function. Important logic functions can be realized using one gate, such as a two-input multiplexer, majority, and parity. Since the QFP has a latching effect, D-gates can realize fully pipelined circuits without additional registers.
The Quantum Flux Parametron (QFP) is a Josephson Junction device using the polarity of a quantum magnetic flux to represent a binary information. A quantum unit of magnetic flux in a QFP can be controlled to realize majority logic operation, consequently AND and OR logics can be realized. Together with negation, which can be realized by a flux-inverting transformer, various computing logic devices can be constructed. In addition, the QFP is also a latching device so that a flux can be confined in the device to realize memory function. Due to the homogenous nature of memory and logic circuits as well as the flux nature of the signal which can be transmitted inductively, an entirely new Josephson supercomputer with memory and CPU pipelining arranged in a 3D setting was conceived. The computer with 40 processors is expected to run at a maximum speed of 20 GFLOPS of scalar processing.