Superconducting micro-electronics (SME) technology is capable of realizing extremely high speed digital receivers performing direct digitization of microwave signals with very low power consumption. SME technology uses integrated circuits based on Josephson junctions and rapid single-flux quantum (RSFQ) logic operating at 4°K. The analogue-to-digital converter (ADC) is a basic building block of such receivers. Quantization and sampling are two fundamental parts of ADCs. Flash ADCs are the fastest converters and consist of comparators and a resistor network. \nThis thesis investigates the use of a multi-layer niobium-based low-temperature superconducting process to implement a resistor network. Several configurations for resistors are investigated both electrically and thermally. The resistors are designed to maintain their values from DC to 50GHz. Floating metal structures are added and optimized to minimize the inductance of the structure in order to obtain frequency-independent resistors over a frequency range of 50GHz. Several resistors and R-2R ladder networks are fabricated in the same process and measured in an RF cryogenic probe station at the Centre for Integrated RF Engineering (CIRFE) Lab at the University of Waterloo. Theoretical thermal analysis, is also carried out for these resistors to investigate temperature variations through the structures when operating at different power levels. The investigation is important for making sure that the resistors’ dissipated heat does not raise the local temperature above the transition temperature of niobium.
Superconducting micro-electronics (SME) technology is capable of realizing extremely high speed digital receivers performing direct digitization of microwave signals with very low power consumption. SME technology uses integrated circuits based on Josephson junctions and rapid single-flux quantum (RSFQ) logic operating at 4°K. The analogue-to-digital converter (ADC) is a basic building block of such receivers. Quantization and sampling are two fundamental parts of ADCs. Flash ADCs are the fastest converters and consist of comparators and a resistor network. \nThis thesis investigates the use of a multi-layer niobium-based low-temperature superconducting process to implement a resistor network. Several configurations for resistors are investigated both electrically and thermally. The resistors are designed to maintain their values from DC to 50GHz. Floating metal structures are added and optimized to minimize the inductance of the structure in order to obtain frequency-independent resistors over a frequency range of 50GHz. Several resistors and R-2R ladder networks are fabricated in the same process and measured in an RF cryogenic probe station at the Centre for Integrated RF Engineering (CIRFE) Lab at the University of Waterloo. Theoretical thermal analysis, is also carried out for these resistors to investigate temperature variations through the structures when operating at different power levels. The investigation is important for making sure that the resistors’ dissipated heat does not raise the local temperature above the transition temperature of niobium.
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.
Superconducting digital technology based on Rapid Single Flux Quantum logic (RSFQ) is a digital technology characterized by high speed, low power consumption and low operational temperatures. RSFQ is attractive for many applications and in particular for high frequency Digital Signal Processing (DSP) and for digital control of mK devices like superconducting qubits. Due to the 30 GHz clock speed, RSFQ DSP could be used to implement a Successive Interference Canceller for multi-user detection in a 3G wireless systems. The being developed DSP consists of a digital core, an RSFQ Multiply Accumulate unit (MAC), RSFQ fast cache memory and external semiconductor memory.The first part of this thesis is focusing on architecture and implementation of the hierarchical CMOS-RSFQ hybrid memory for the RSFQ DSP. The architecture ofthe RSFQ cache is optimized in order to reach the highest speed and reliable data communication with CMOS memory. Aspects of block synchronization betweenthe RSFQ cache and the RSFQ digital core are discussed and solved using a new developed RSFQ gate, C3. For design of different components of the DSP, a designapproach based on validated VHDL models is proposed and experimentally verified.The second part of this thesis is focusing on the design oflow-dissipative RSFQ circuits for interface to the superconducting qubits. Power dissipation ofRSFQ circuits is minimized. A low-temperature thermal model of resistively shunted Josephsonjunctions is developed and applied to optimize the shape of the shunt resistors in order to reduce their electron temperature. Depending on the available fabricationprocess the lowest noise temperature of RSFQ circuit can be in the range from 90 mK to 180 mK.
Superconducting microelectronics (SME) technology has the potential of realizing very high speed digital receivers capable of performing direct digitization of radio frequency signals with very low power consumption. The SME receiver is implemented on a single chip using Niobium based low temperature superconductive (LTS) Josephson Junction (JJ) technology by HYPRES. Analogue RF filters are still required at the receiver front end and are key components of the overall superconductor digital receiver. SME receivers usually require two types of RF filters; a wideband bandpass filter and a bandstop filter (a notch filter). The notch filter is required to eliminate interference and unwanted signals in the passband. In this thesis, design of highly miniaturized lumped element wideband and bandstop filters is investigated and some challenges are addressed. The filters are fabricated by the HYPRES process and therefore can be integrated with the SME receiver on the same chip. \nIn a wideband filter, the coupling between the adjacent resonators is high. Achieving such a strong coupling is one of the challenges of designing wideband filters. The wideband filters realized with distributed elements usually suffer from very low spurious frequency. As the bandwidth of the filter becomes wider, the spurious peak of the second harmonic gets closer to the passband of the filter. In the first part of this work, the possibility of realizing lumped element superconducting bandpass filters (BPF) with a relative bandwidth of 80% is investigated. \nIn the second part of the thesis, design and realization of lumped element superconducting bandstop filters (BSF) is discussed. The challenge for designing a bandstop filter is providing a good match over a wide frequency range. So narrowband inverters cannot be used. Instead, usually λ/4 matched transmission lines provide 90° phase shift between the resonators of a notch filter. The possibility of replacing the long transmission line with other means or eliminating the inverters and using both shunt and series resonators are investigated. Having both series and shunt resonators introduces some new challenges that are addressed in the thesis and discussed thoroughly. \nA tunable notch resonator is presented. The tunability is provided by a superconducting MEMS varactor that is realized in our group by doing some post processing on the device fabricated by HYPRES. The tunability range of the device at cryogenic temperatures is investigated. A 3-pole tunable BSF is also designed that uses the same tunable resonators. The tunability of the filter is investigated through simulation.
Software-Defined Radio (SDR), as explained in [1], is a promising concept for the wireless communication industry since the entire transceiver function can be implemented in software, avoiding the replacement of hardware each time the system has to be upgraded. However, the practical implementation of such a system is depended on the hardware, which consists of precise, ultra highspeed electronic devices such as Analog-to-Digital Converters (ADCs). The present state-of-the-art semiconductor ADCs cannot be used for the implementation of SDR in the near future [2]. Some of the factors that hamper the implementation are the requirements of very high speed of a few tens of GHz and the high resolution (e.g. 16 bits) at these speeds. On the other hand, using the Low-Temperature Superconducting (LTS) technology [3], which relays on the quantum mechanical property of superconductors, very high-speed electronic devices with the accuracy of a flux quantum, can be constructed. In a closed superconducting loop, the magnetic flux can exist only in discrete quantized amounts equal to the multiples of the magnetic flux quantum, φ0 = h/2e ~ 2.07x10 Wb. The theoretical speed limit of such a Rapid Single Flux Quantum (RSFQ) device is close to 1 THz [4]. These RSFQ circuits are the fastest of all devices built in any known technology. The basic building block of an RSFQ circuit is the Josephson Junction (JJ), which is formed when two superconductors are separated by an interface. Since RSFQ circuits work at extremely high speeds, testing and verification of such a device is a difficult and challenging task. Direct testing at these speeds is not possible at this moment. Furthermore, the costs of the equipment required for such tests would be extremely high. Hence methods have to be developed to reduce the requirements of external
Arrays of cryogenic microbolometers and other cryogenic detectors are being developed for infrared imaging. If the signal from each sensor is amplified, multiplexed, and digitized using superconducting electronics, then this data can be efficiently read out to ambient temperature with a minimum of noise and thermal load. HYPRES is developing an integrated system based on SQUID amplifiers, a high-resolution analog-to-digital converter (ADC) based on RSFQ (rapid single flux quantum) logic, and a clocked RSFQ multiplexer. The ADC and SQUIDs have already been demonstrated for other projects, so this paper will focus on new results of a digital multiplexer. Several test circuits have been fabricated using Nb Josephson technology and are about to be tested at T = 4.2 K, with a more complete prototype in preparation.
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.