Jan. 30, 2002 NIST researchers recently demonstrated sine-wave synthesis on three superconducting integrated circuit chips using palladium-gold barrier junctions. The demonstration chips were used to make comparisons with conventional alternating current (AC) voltage standards at the part-per-million level, and provided 0.1 volt and 5 megahertz sine-wave outputs.
This is a major step toward the goal of developing a waveform synthesizer—using Josephson junctions—which would provide precisely defined output voltages (up to one volt), frequencies (up to one gigahertz) and waveforms of any arbitrary shape. Such a system would have practical application as an AC voltage standard source and for calibrating high-performance test and measurement instruments.
The research so far has led to a circuit with the largest direct current (DC) output voltage per junction to date using two series-coupled 3,750-junction arrays (for a total of 7,500 junctions). Constant voltage steps were measured on this circuit across a broad range of frequencies from 3 to 18 gigahertz. Also, due to the improved microwave filters incorporated in the circuits, a different circuit with 1,000 junctions was driven at bit stream drive frequencies more than a factor of two higher than any previous Josephson array circuit. This is significant because higher drive frequency directly corresponds to higher output voltage.
This progress has provided confidence that circuits can be fabricated for use with a fixed-speed, 10 gigabits-per-second, low-cost bit stream generator that is under construction.
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