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Superconductor Science and Technology

Design and demonstration of an on-chip AC power source for adiabatic quantum-flux-parametron logic

Takashi Mukaiyama, Naoki Takeuchi, Yuki Yamanashi, Nobuyuki Yoshikawa

Published Feb 6, 2013• 8 citations
Publisher

Abstract

Adiabatic quantum-flux-parametron (AQFP) logic is a promising technology for use in future high-end computers because its bit energy can be potentially reduced to the order of thermal energy. AQFP gates are driven by an AC bias current, which changes their potential energy adiabatically. In the present paper, we propose an on-chip AC power source, which is composed of a Josephson relaxation oscillator and a superconducting resonator, to drive the AQFP gates. We designed and implemented the AC power source using a Nb Josephson integrated circuit process. We confirmed that the AC power source can generate a 4.4 GHz sinusoidal current from a DC bias current and that the output amplitude of the AC power source can be controlled by varying the DC bias current.

DOI
10.1088/0953-2048/26/3/035018

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Adiabatic quantum-flux-parametron (AQFP) logic is a promising technology for use in future high-end computers because its bit energy can be potentially reduced to the order of thermal energy. AQFP gates are driven by an AC bias current, which changes their potential energy adiabatically. In the present paper, we propose an on-chip AC power source, which is composed of a Josephson relaxation oscillator and a superconducting resonator, to drive the AQFP gates. We designed and implemented the AC power source using a Nb Josephson integrated circuit process. We confirmed that the AC power source can generate a 4.4 GHz sinusoidal current from a DC bias current and that the output amplitude of the AC power source can be controlled by varying the DC bias current.
Adiabatic quantum-flux-parametron (AQFP) logic devices can operate under extremely low bit energy approaching the thermal limit by varying their potential energy adiabatically using ac bias currents. We have proposed an on-chip ac power source, which is composed of a Josephson relaxation oscillator and a superconductingLCresonator in order to drive AQFP circuits at 5 GHz or higher frequencies. We herein experimentally confirmed the correct switching operation of an AQFP gate at 4.94 GHz using the proposed on-chip ac power source. Furthermore, we confirmed that the ac power source can drive approximately 800 AQFP gates.
Adiabatic quantum flux parametron (AQFP) is a very energy-efficient superconductor logic. In AQFP logic, dynamic energy dissipation can be drastically reduced due to adiabatic switching operations using ac excitation currents. In the present study, we evaluated circuit yields using a large-scale AQFP circuit composed of as many as 10,000 AQFP gates with approximately 20,000 Josephson junctions. We measured eleven chips from four wafers and obtained circuit yields of 48% for 1,000-gate circuits and 22% for 10,000-gate circuits, respectively. In all the circuits, which worked correctly, the margins of excitation currents were as wide as approximately ±20%.
Ultra-low-power adiabatic quantum flux parametron (QFP) logic is investigated since it has the potential to reduce the bit energy per operation to the order of the thermal energy. In this approach, nonhysteretic QFPs are operated slowly to prevent nonadiabatic energy dissipation occurring during switching events. The designed adiabatic QFP gate is estimated to have a dynamic energy dissipation of 12% of I c Φ 0 for a rise/fall time of 1000 ps. It can be further reduced by reducing circuit inductances. Three stages of adiabatic QFP NOT gates were fabricated using a Nb Josephson integrated circuit process and their correct operation was confirmed.
We report recent progress on adiabatic quantum-flux-parametron (AQFP) logic, which is an energy-efficient superconductor logic based on quantum flux parametron (QFP). The switching energy of an AQFP gate can be arbitrarily reduced via adiabatic switching, in which the shape of the potential energy gradually varies between single-well and double-well shapes as the result of using ac excitation magnetic fluxes. First, we show the operation principle of AQFP and explain adiabatic switching in light of potential energy shapes. We also show calculated switching energy and bit error rates to demonstrate that the switching energy of AQFP can be significantly reduced while keeping a low error rate. Then, we report recently developed AQFP subsystems, which include an 8-bit carry look-ahead adder, a register file, and a long-interconnect driver. Our demonstration reveals that AQFP technology is ready to be applied in microprocessor design.
We have been investigating an ultra-low-power adiabatic quantum-flux-parametron (AQFP) logic, the energy dissipation of which can be decreased by changing its potential energy slowly or adiabatically. In the present study, we designed basic AQFP logic gates and an AQFP 1-bit full adder, and examined their operations through simulations and experiments. The AQFP 1-bit full adder is composed of 46 Josephson junctions, which is approximately one-quarter the number of junctions of a full adder using conventional rapid single-flux-quantum logic. The measurement results indicated that the AQFP 1-bit full adder has a wide current bias margin of as large as ±27.8%.
Adiabatic quantum-flux-parametron (AQFP) logic is a promising technology for future energy-efficient, high- performance information processing systems because it has significantly low power consumption due to the adiabatic switching of Josephson junctions. We are developing a high-performance field-programmable gate array (FPGA) using superconducting AQFP circuits to reduce its energy consumption. The all-AQFP FPGA consists of logic blocks, switch blocks, connection blocks, and memory using AQFP circuits. In particular, the memory is composed of AQFP buffer chains, enabling high-density and low-power memory. The switch blocks can perform data routing as well as several logic functions, including majority,and, andorfunctions, which increases the design flexibility of the all-AQFP FPGA. We fabricated a one-unit all-AQFP FPGA and demonstrated its reconfigurable operation at low speed. It was found that much lower power consumption can be achieved in the new FPGA than in the other superconducting FPGAs.