Tuning of the RSFQ gate speed by different Stewart-McCumber parameters of the Josephson junctions

At the typical operating temperature of 4.2 K, the theoretical upper limit of the clock frequency of the Low-Temperature Superconductive (LTS) Nb based Rapid Single Flux Quantum (RSFQ) digital circuits is several hundred GHz. Nevertheless, the few middle-scale RSFQ circuits reported on up to now ope...

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Bibliographic Details
Published in:IEEE transactions on applied superconductivity 2005-06, Vol.15 (2), p.284-287
Main Authors: Dimov, B., Khabipov, M., Balashov, D., Brandt, C.M., Buchholz, F.-Im, Niemeyer, J., Uhlmann, F.H.
Format: Article
Language:English
Subjects:
Applied sciences
Asynchronous RSFQ electronic
Circuit optimization
Circuit properties
Clocks
Delay
delay tuning
Design. Technologies. Operation analysis. Testing
Digital circuits
Electric, optical and optoelectronic circuits
Electronic circuits
Electronics
Exact sciences and technology
Frequency
Gates
Integrated circuits
Josephson junctions
Niobium
Operating temperature
Oscillators, resonators, synthetizers
Quantum mechanics
ring-shaped RSFQ oscillators
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Superconductivity
Superconductors
Temperature
Tuning
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Summary:At the typical operating temperature of 4.2 K, the theoretical upper limit of the clock frequency of the Low-Temperature Superconductive (LTS) Nb based Rapid Single Flux Quantum (RSFQ) digital circuits is several hundred GHz. Nevertheless, the few middle-scale RSFQ circuits reported on up to now operate at only some tens of GHz. An important performance-limiting factor is in this case the clock signal distribution, so nowadays asynchronous RSFQ designs are often considered. Our previous studies have shown that it is an important advantage of a given asynchronous RSFQ cell library to contain gates with tunable delays. We have already shown by simulations that the RSFQ gate delays are best adjusted by changing the Stewart-McCumber parameter /spl beta//sub c/ of the Josephson junctions-this method tunes the delay within a large interval of values while scarcely affecting the margins and the fabrication yield of the RSFQ gates. In order to prove this statement experimentally, we have designed, fabricated, and tested several ring-shaped oscillators with identical topologies but different Stewart-McCumber parameters of the Josephson junctions. Their operating speeds and margins are measured and compared.
ISSN:1051-8223
1558-2515
DOI:10.1109/TASC.2005.849791