Power Design for Gigabit Josephson Logic Systems

An ac power system design in described for powering, at near gigahertz frequencies, 16K Josephson latching logic circuits distributed uniformly over 16 chips. The power system distributes a sinusoidal current waveform from a single source to the many chip quadrants through a tree system of thin-film transformers that have branching secondaries and multiple turn primaries to maintain nearly constant current amplitudes throughout the system and small phase skews at the logic-circuit level. The sinusoidal waveform is clipped on-chip to provide the trapezoidal waveform required by the logic circuits. The ratio of the duration of the up-portion of the trapezoidal half-cycle to the half-cycle period (the logic cycle) is defined as the active duty cycle for the logic. The 16K circuit-power design is capable of providing an 80-percent duty cycle at a 1.7-ns logic cycle while keeping current levels in the system below 300 mA. An approximate expression is derived that predicts that for any power-system design of this type the product of the system size, the highest frequency of operation, and the chip-quadrant current level is a constant.