High speed power system for josephson logic

Abstract

The design of an ac power distribution system suitable for 16 chips with 1k Josephson logic circuits each was tested for power signal amplitude variations and phase skews over the frequency range 0–500 MHz. The lowest resonant frequency resulting from transformer inductance and power line capacitance to ground occurs at 450 MHz — somewhat higher, and therefore better, than that predicted by simulations. The frequency response of ac currents delivered to the chips is nearly flat from 50 MHz to 250 MHz. Below 50 MHz, currents decrease because the resistive load becomes comparable to the inductive; and above 250 MHz, currents increase as the frequency approaches the resonance. Amplitude and phase variations are independently measured by a novel technique using Josephson devices on chip. Phase skews in the system are quite small, for example, at 200 MHz the maximum phase difference in the system is less than 2 degrees. Amplitude variations are more significant — about 16% at 200 MHz which while acceptable, are larger than anticipated below the lowest resonant frequency and may be due to test limitations arising from placing the entire system on a single chip. © 1980 IEEE