ED3-7

Investigation of transmission line effects in gate-to-gate wiring of adiabatic quantum-flux-parametron circuits

Dec.2 10:40-10:55 (Tokyo Time)

*Kazuhito Asai1, Naoki Takeuchi2, Yuki Yamanashi1,2, Nobuyuki Yoshikawa1,2

Department of Electrical and Computer Engineering, Yokohama National University, Japan1

Institute of Advanced Sciences, Yokohama National University, Japan2

Adiabatic quantum-flux-parametron (AQFP) circuits are known as extremely energy efficient circuits due to adiabatic change of the energy potential during the switching process. They can operate at high clock frequencies of 5-10 GHz with power consumption about 5 orders of magnitude lower compared to CMOS circuits [1].
The gate-to-gate interconnections for AQFP logic circuits is formed by superconducting wires and regarded as ideal inductance at present. In the long interconnection wires, however, the effect of the parasitic capacitance is not negligible, and the transmission line effect has to be considered. In this study, we investigated the transmission effects of the gate-to-gate-wires in the AQFP circuits by circuit simulations.

The circuit diagram used in the simulations is shown in Fig. 1. The values of the device parameters of transmission line per 1 μm, as well as the characteristic impedance Z0 and the propagation delay time τp are set to Ln = 0.065 pH, Cn = 0.0005036 pF, Z0 = 8.03 Ω, and τp = 0.0081 ps, respectively. When the array of the AQFP buffers with the long interconnection wire in between are operated by the excitation current at the frequency f = 5 GHz, it was found that reflections with the substantial amplitude are observed between the buffers. They reduce the bias current margins and induce malfunction when the wire length exceeds about 745 mm. We investigated the amplitude of the reflections in the interconnection wires by using FFT for the AQFP buffers with the different values of McCumber parameters and with the different damping in the transmission lines. The signal-to-noise ratio in the interconnect wires was calculated and the criteria to ensure the correct operation was obtained. Based on these investigations, we will show the ways to reduce the reflections in the long interconnection wires in the AQFP circuits.

Reference
[1] N. Takeuchi, et al., Supercond. Sci. Technol. 28, 015003, 2015.

Keywords: Adiabatic quantum-flux-parametron, superconducting wires, transmission line effect, FFT
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