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
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
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, especially at SATCOM frequencies. 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 simple circuit switching speeds up to 750 GHz have been demonstrated. This permits direct conversion between analog RF and digital baseband signals, replacing frequency and protocol-specific analog hardware with flexible digital processors. HYPRES recently developed and delivered an X-band All Digital RF Receiver (XADR) prototype system for the US Army CERDEC and PM DCATS. The concept of this ADR is to replace the entire analog RF receive chain between the antenna and the baseband demodulator with a high performance digital RF equivalent. The first XADR prototype system has been successfully demonstrated at the Joint SATCOM engineering Center (JSEC). End to end link testing, over the satellite has been successfully completed using an existing AN/GSC-39 X-band earth terminal, an XTAR satellite, the X-band ADR and a SATCOM modem.
Digital superconductor electronics has been experiencing rapid maturation with the emergence of smaller-scale, lower-cost communications applications which became the major technology drivers. These applications are primarily in the area of wireless communications, radar, and surveillance as well as in imaging and sensor systems. In these areas, the fundamental advantages of superconductivity translate into system benefits through novel Digital-RF architectures with direct digitization of wide band, high frequency radio frequency (RF) signals. At the same time the availability of relatively small 4K cryocoolers has lowered the foremost market barrier for cryogenically-cooled digital electronic systems. Recently, we have achieved a major breakthrough in the development, demonstration, and successful delivery of the cryocooled superconductor digital-RF receivers directly digitizing signals in a broad range from kilohertz to gigahertz. These essentially hybrid-technology systems combine a variety of superconductor and semiconductor technologies packaged with two-stage commercial cryocoolers: cryogenic Nb mixed-signal and digital circuits based on Rapid Single Flux Quantum (RSFQ) technology, room-temperature amplifiers, FPGA processing and control circuitry. The demonstrated cryocooled digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals in X-band and performing signal acquisition in HF to L-band at ∼30GHz clock frequencies.
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.
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.
Superconductive technology offers unparalleled digital and mixed-signal circuit performance, advancing digital processing from baseband to RF stages. This allows elimination of analog filters and mixers with generally poorly controlled phase performance, causing intersymbol interference limiting an overall communication system performance. HYPRES has been developing superconducting circuit components for application to digital RF communication transceivers. The components include low-pass and band-pass analog-to-digital converters, digital decimation and correlation-based filters, digital up/down-converters, and low-time-jitter clock sources. All of these are based on ultra-fast Rapid Single Flux Quantum (RSFQ) digital circuits, with clock rates up to 20 GHz demonstrated with 3-micron technology, and being scaled to 40 GHz and above. In this paper, we will discuss design and performance of some of these components. 1.
Ultra fast switching speed of superconducting digital circuits enable realization of Digital Signal Processors with performance unattainable by any other technology. Based on rapid-single-flux technology (RSFQ) logic, these integrated circuits are capable of delivering high computation capacity up to 30 GOPS on a single processor and very short latency of 0.1ns. There are two main applications of such hardware for practical telecommunication systems: filters for superconducting ADCs operating with digital RF data and recursive filters at baseband. The later of these allows functions such as multiuser detection for 3G WCDMA, equalization and channel precoding for 4G OFDM MIMO, and general blind detection. The performance gain is an increase in the cell capacity, quality of service, and transmitted data rate. The current status of the development of the RSFQ baseband DSP is discussed. Major components with operating speed of 30GHz have been developed. Designs, test results, and future development of the complete systems including cryopackaging and CMOS interface are reviewed.