Analog signal correlator using superconductive integrated components

Analog superconductive components have been integrated to form a device capable of cross-correlation between wideband analog input signals. The device contains a tapped niobium delay line, tunnel-junction mixers, a lumped-element L-C resonator, and a tunnel-junction comparator. The tapped delay line is realized by a niobium stripline folded in a meander pattern on a rectangular silicon substrate. An array of Nb/Nb
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O
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/Pb tunnel junctions acts as a mixer to form the product of delayed samples of two carrier-offset analog signals counterpropagating along the transmission line. The resultant mixer products from the junction arrays are integrated and stored in a high-Q (≈ 600) resonator consisting of a lumped-element L-C network, tuned to the offset frequency. The low-leakage capacitor dielectric is formed from electrolytically anodized niobium. A superconductive tunnel junction imbedded in the resonator circuit is operated as a variable-threshold comparator to detect the time-integrated current stored in the resonator. Performance results from such a time-integrating correlator are presented, along with a discussion of the important design issues as they relate to analog signal processing.