The current state of development of electronic technology and the rapid development of wireless information transmission systems requires the search for new technologies that would meet the requirements of increasing the frequency of signal transmission. The idea of the idea of generators operation of clock pulse generators as devices of digital information processing is revealed in the work, in particular the physical model of the clock pulse generator on the basis of Josephson transitions is constructed. The scheme of the clock generator is given and its description is made. The linearization of the two-contact superconducting quantum interference sensors (SQIS) voltage response function is described with the representation of the solution of the differential equation as a function of the voltage response versus time. Based on the proposed solution of the differential equation, the dependence of the change in the phase difference of the wave functions on the parameters of the equivalent PD scheme is investigated, the research results are presented in the form of graphs.
The current state of development of electronic technology and the rapid development of wireless information transmission systems requires the search for new technologies that would meet the requirements of increasing the frequency of signal transmission. The idea of the idea of generators operation of clock pulse generators as devices of digital information processing is revealed in the work, in particular the physical model of the clock pulse generator on the basis of Josephson transitions is constructed. The scheme of the clock generator is given and its description is made. The linearization of the two-contact superconducting quantum interference sensors (SQIS) voltage response function is described with the representation of the solution of the differential equation as a function of the voltage response versus time. Based on the proposed solution of the differential equation, the dependence of the change in the phase difference of the wave functions on the parameters of the equivalent PD scheme is investigated, the research results are presented in the form of graphs.
Digital superconducting systems based on Josephson junctions make generally use of the synchronous timing strategy. Today, one of its most promising applications is the high speed and high dynamic range signal sensing. A digital signal acquisition system should have a high resolution as well as a short sampling interval with a well known and constant time period. Short term clock fluctuations (clock jitter) induced by thermal noise can significantly disturb the system operation due to hazards of timing constraint violations. This uncertainty in the time period is currently a strong limitation for further improvements of fast signal sensing systems based on superconductive electronics. Recently, several theoretical and experimental studies describe the timing jitter in simple circuits, like Josephson transmission lines. In the presented work, we analyse different fabrication technologies for rapid single flux quantum (RSFQ) electronics and predict their timing jitter by the numerical solution of stochastic differential equations. We obtained a very good agreement between our simulation data and recent experimental results.
Using of traditional logic elements in digital electronics has ensured the development of a wide range of electronic devices for many years. In parallel, research and development of logical elements are carried out on the basis of other non-traditional physical phenomena or effects, in particular logic elements based on the phenomenon of superconductivity, the prospect of which is the use of very small energy consumption and ultrahigh performance. For superconducting logic elements, using various Josephson cryoelectronic structures, known as Josephson cryotrons, based on the stationary and non-stationary effects of Josephson. On the basis of the Josephson cryotrons, one can create Josephson elements of computer memory, and Josephson elements of digital logic. The main requirements for the Josephson cryotrons are a stable operating mode and high speed or short switching time. Information about the mode of operation and the speed give us the transition characteristics of the cryotrons - the time dependence of the voltage on the cryotron while changing its logical state, which can be obtained either experimentally, or theoretically. This work aims at a search for new ways of increasing the switching rate of digital logical operators by employing physical structures other than the traditional semiconductor-based schemes. We propose the principles of designing digital logical operators based on Josephson cryotrons, whose operation utilizes the stationary and dynamical Josephson effects, and describe the operational principles of the logical elements “AND” and “OR” bases on tunneling Josephson junctions “superconductor-insulator-superconductor”. Our proposed mathematical models for the commutation processes in such logical elements allowed us to calculate their transition characteristics during the switching and to determine the main parameters in such models. It was shown that the logical elements “AND” and “OR” can be implemented on individual cryotrons and that their logical state can be controlled by input signals in a form of current pulses. Such logical elements meet all the requirements for digital logical elements and have switching time of about 2-3 ps, which indicates their significantly increased switching rate.
Superconducting Josephson devices have been developed for various electronics fields such as highly sensitive magnetometers, voltage standards, and high-speed digital signal processing. In this paper, the author describes two kinds of superconducting digital-to-analog （D/A） converters that generate quantum voltages. One is a balanced-ternary D/A converter comprising asymmetric superconducting quantum interference devices, in which the generation of either a positive or a negative zero-crossing Shapiro step is controlled by an external magnetic flux. The other is a single-flux-quantum （SFQ） D/A converter, in which SFQ pulse-frequency modulation is employed. They generate quantum voltage defined by the reference microwave frequency and the AC Josephson effect.
Possible approaches to the creation of Josephson superconducting circuits with a high linearity of transformation of a magnetic signal into voltage and a wide dynamic range have been described. Realization of such circuit by the creation of a special spatial inhomogeneity in chains of Josephson junctions and connection of these chains into a differential circuit has been considered. A new method for linearizing the transfer function of a single two-junction superconducting quantum interference device, which is an elementary cell of the chain, by connecting to it an additional loop playing the role of a nonlinear transformer of the magnetic flux has been described. For both approaches, the basic analytical expressions describing the synthesized circuits are presented. The data on numerical calculation and experimental measurements of samples produced on the basis of niobium technology with the critical current density of Josephson junctions of 4.5 kA/cm 2 are reported. The approaches developed in the work can serve as a basis for the creation of highly efficient gigahertz superconducting amplifiers for cellular and satellite communications and can be applied for improving the characteristics of SQUID-based devices.
Analog-to-digital converters of radio signals, which are based on the phenomenon of superconductivity and the Josephson effect, are proposed to use in order to increase the efficiency of digital antenna arrays. Digital beamforming systems were analysed. Application of the proposed approach was shown to promote processing signals directly at carrier frequencies in the SHF and EHF bands. This approach allows to exclude frequency mixers, local oscillators and intermediate frequency filters from a receiving module. A parallel scheme with comparators on superconducting quantum interferometers is proposed for constructing a superconducting ADC. A digital Gray code is formed at the output of the ADC. The proposed scheme being utilizing, when the input signal increases, each comparator passes through several thresholds, and if Gray codes are applied, only one of the output bits changes between consecutive numbers. Therefore, Gray codes are less sensitive to errors that arise due to small differences in comparator’s thresholds. This promotes reduction of the bit error probability. As an outcome the performed analysis, it was shown that generators of single-quantum pulses on single Josephson junction with a hysteresis-free current-voltage characteristic can be used for constructing comparators, that provides obtaining a high time resolution. The dependence of time resolution on Josephson junction parameters, namely dielectric thickness, relative dielectric permeability and critical current density, was investigated. The resolution was shown to be equal units — tenths of a ns, and this allows using such devices for signal processing at frequencies of several hundred GHz. The time resolution changes with changes in the critical current density of a Josephson junction and in the dielectric thickness and it is almost independent on the relative dielectric permittivity. The sensitivity of the comparator on a single Josephson junction was evaluated. An analytical expression was obtained, it can be applied to estimate how parameters of the Josephson junction equivalent circuit, namely, electrostatic capacity, nonlinear conductivity, and critical current impact on the sensitivity of the comparator. The conducted studies showed that the sensitivity can be units of nA, which exceeds significantly the sensitivity of similar circuits based on semiconductors.
The recent developments in quantum technologies, as well as advanced detection experiments, have raised the need to detect extremely weak signals in the microwave frequency spectrum. To this aim, the Josephson travelling wave parametric amplifier, a device capable of reaching the quantum noise limit while providing a wide bandwidth, has been proposed as a suitable cryogenic front-end amplifier. This work deals with the numerical study of a Josephson travelling wave parametric amplifier, without approximations regarding the nonlinearity of the key elements. In particular, we focus on the investigation of the system of coupled nonlinear differential equations representing all the cells of the Josephson travelling wave parametric amplifier, with proper input and output signals at the boundaries. The investigation of the output signals generated by the parametric amplification process explores the phase-space and the Fourier spectral analysis of the output voltage, as a function of the parameters describing the pump and signal tones that excite the device. Beside the expected behavior, i.e., the signal amplification, we show that, depending on the system operation, unwanted effects (such as pump tone harmonics, incommensurate frequency generation, and noise rise), which are not accounted for in simple linearized approaches, can be generated in the whole nonlinear system.