Analog-to-digital conversion with superconductors

Shön Sloat, H.J. Whitehouse

Oleg A. Mukhanov, Deepnarayan Gupta, Alan M. Kadin +1 more

Ultrafast switching speed, low power, natural quantization of magnetic flux, quantum accuracy, and low noise of cryogenic superconductor circuits enable fast and accurate data conversion between the analog and digital domains. Based on rapid single-flux quantum (RSFQ) logic, these integrated circuits are capable of achieving performance levels unattainable by any other technology. Two major classes of superconductor analog-to-digital converters (ADCs) are being developed - Nyquist sampling and oversampling converters. Complete systems with digital sampling at rates of /spl sim/20 GHz and above have been demonstrated using low-temperature superconductor device technology. Some ADC components have also been implemented using high-temperature superconductors. Superconductor ADCs have unique applications in true digital-RF communications, broadband instrumentation, and digital sensor readout. Their designs, test results, and future development trends are reviewed.

Donald L. Miller, John X. Przybysz, A. Hodge Worsham +1 more

Anna De Escobar, Richard Hitt, Oleg A. Mukhanov +1 more

Wireless applications would be less expensive, more flexible, and more robust if they had more digital and less analog circuitry. The problem is implementing digital signal processing at radio frequencies. Conventional data converters (ADCs and DACs) and digital circuits are simply not fast enough. However, superconductors can provide ultra fast mixed signal and digital circuits with the linearity and dynamic range required for true direct, digital-RF processing. These superconducting circuits are digital ICs based on Josephson junctions and "rapid-single-flux-quantum" logic (RSFQ), where switching speeds up to 750 GHz have been demonstrated enabling true digital-RF architecture at clock speeds eventually up to 160 GHz. This permits direct conversion between analog RF and digital baseband signals, replacing frequency and protocol-specific analog hardware with flexible digital processors. Data conversion in high frequency wireless applications at frequencies up to 50 GHz will soon become practical. Hypres recently delivered a HF-VHF all digital RF receiver (ADR) prototype to ONR. Testing of this ADR has demonstrated the superior performance of superconducting ICs in cryocooled systems. A US Navy laboratory is now evaluating the world's first complete prototype digital RF receiver capable of direct digitization from DC to 2 GHz

Sebastian Kempf

Deepnarayan Gupta, Amol Inamdar, Dmitri E. Kirichenko +2 more

A wide variety of applications, ranging from radio-frequency (RF) receivers for broadband communications and signal detection, on earth and in space, would benefit from high-performance superconductor analog-to-digital converters (ADCs), based on magnetic flux quantization and fast switching Josephson junctions. Superconductor ADCs are capable of very high sample rates (100 GHz or more), very high linearity, and high sensitivity. Nyquist-rate ADCs use the high sample rate to digitize a wide instantaneous bandwidth (tens of GHz) and are useful for wideband spectrum monitoring as well as high-end scientific instrumentation. Delta and delta-sigma oversampling ADCs use the high linearity to achieve programmable trade-off between dynamic range and instantaneous bandwidth. These lowpass and bandpass ADCs have been used for direct digitization of narrower (tens to hundreds of MHz) RF bands in the 1-20 GHz range for a variety of communications, intelligence, electronic warfare, and radar applications. Another application area of these cryogenic ADCs is for outputs of cryogenic sensor arrays and terahertz mixers. Recent advances in various classes of ADCs for different applications are described.