Investigation of basic properties of an HTS sigma–delta modulator

Abstract We fabricated and tested a high-temperature superconducting sigma–delta modulator using interface-engineered Josephson junctions. Proper dc-characteristics were obtained with a sampling frequency of 100 GHz at 20 K. To achieve high-speed sampling, Josephson junctions with a higher critical-current normal-resistance product were used. Circuit simulations with thermal noise were performed for the analysis of switching characteristics and SFQ dynamics. Further numerical analysis was made for the estimation of signal to noise ratio. Resultant bit accuracy was found to be 10.4 for 122 MHz input signal band.

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