Reconfigurable Logic Devices Research Articles

Design methodology of single-flux-quantum flip-flops composed of both 0- and π-shifted Josephson junctions

A methodology for designing single-flux-quantum (SFQ) flip-flops composed of both conventional (0-) and π-shifted Josephson junctions is investigated. We investigated the implementation of a storage loop, which can store flux quantum and is indispensable to express binary logic states in superconductor logic circuits. As all SFQ flip-flops have storage loops, the investigated design methodology can be applied to their design. We designed several SFQ flip-flops composed of 0- and π-shifted Josephson junctions using the investigated design methodology. The performances of the designed SFQ flip-flops were quantitatively evaluated by using an analog circuit simulator which we developed. We confirmed the correct operation of various SFQ flip-flops composed of 0- and π-shifted Josephson junctions with wide operating margins. Moreover, we observed that the investigated design methodology is suitable for SFQ flip-flops with complementary outputs because a storage loop composed of both 0- and π-shifted Josephson junctions has a symmetric structure and the complementary output function can be realized by using the storage loop. Our investigation indicates that the number of Josephson junctions and static power consumption of a non-destructive read-out flip-flop with complementary outputs (NDROC) can be reduced to less than half of those of the conventional NDROC, which has two storage loops composed of 0-Josephson junctions, to realize the complementary output function. The investigated design methodology is expected to be applied to not only SFQ circuits but also other superconducting logic circuits and novel reconfigurable logic devices using programmable 0-π Josephson junctions.

Multistates and Polyamorphism in Phase-Change K2Sb8Se13.

The phase-change (PC) materials in the majority of optical data storage media in use today exhibit a fast, reversible crystal → amorphous phase transition that allows them to be switched between on (1) and off (0) binary states. Solid-state inorganic materials with this property are relatively common, but those exhibiting an amorphous → amorphous transition called polyamorphism are exceptionally rare. K2Sb8Se13 (KSS) reported here is the first example of a material that has both amorphous → amorphous polyamorphic transition and amorphous → crystal transition at easily accessible temperatures (227 and 263 °C, respectively). The transitions are associated with the atomic coordinative preferences of the atoms, and all three states of K2Sb8Se13 are stable in air at 25 °C and 1 atm. All three states of K2Sb8Se13 exhibit distinct optical bandgaps, Eg = 1.25, 1.0, and 0.74 eV, for the amorphous-II, amorphous-I, and crystalline versions, respectively. The room-temperature electrical conductivity increases by more than 2 orders of magnitude from amorphous-I to -II and by another 2 orders of magnitude from amorphous-II to the crystalline state. This extraordinary behavior suggests that a new class of materials exist which could provide multistate level systems to enable higher-order computing logic circuits, reconfigurable logic devices, and optical switches.

Multifunctional Logic Applications of a Single Molecule: A Molecular Photo‐Switch Performing as Simple and Complex Gates, Memory Element, and a Molecular Keypad Lock

AbstractCarbazole (CZ) can act as a photo‐switch leading to a multifunctional logic system when triggered by fluoride (F–) ions, H2O and light, through efficient interaction of the pyrrole unit with the anions. Here we are reporting a unimolecular platform of CZ (and case specific CZ‐F–) that can be configured as NOT, YES, complimentary IMPLICATION and INHIBIT, a new complex logic gate performing IF‐THEN and NOT operations and a memory element with cyclic “Erase‐Read‐Write‐Read” ability with feedback loop mechanism. The fluorescence responses of the CZ system also have been exploited to design a potential highly secured molecular keypad lock operating with a purely opto‐chemical password composed with optical and chemical input keys. The system displays the applications of light responsive molecules as multifunctional, reconfigurable molecular logic devices that may lead towards true molecular information processing units.

Voltage-Controlled Reconfigurable Spin-Wave Nanochannels and Logic Devices

Though confinement of spin waves (SWs) through nanochannels (NCs) is essential for the development of magnonic logic hardware, voltage-controlled reconfigurable SW nanochannels and logic devices have remained elusive. Here numerical micromagnetic simulations show that NCs of arbitrary shape and size, down to a few tens of nanometers, can be easily configured to transmit SWs with variable wave vectors as needed, even in the absence of a magnetic field. Operation of reconfigurable logic devices using the NCs is also demonstrated. This study is expected to have a large impact on the development of all-voltage-controlled low-power nanoscale magnonic devices.

Axially modulated arch resonator for logic and memory applications

We demonstrate reconfigurable logic and random access memory devices based on an axially modulated clamped-guided arch resonator. The device is electrostatically actuated and the motional signal is capacitively sensed, while the resonance frequency is modulated through an axial electrostatic force from the guided side of the microbeam. A multi-physics finite element model is used to verify the effectiveness of the axial modulation. We present two case studies: first, a reconfigurable two-input logic gate based on the linear resonance frequency modulation, and second, a memory element based on the hysteretic frequency response of the resonator working in the nonlinear regime. The energy consumptions of the device for both logic and memory operations are in the range of picojoules, promising for energy efficient alternative computing paradigm.

Cuts Guided Deterministic Buckling in Arrays of Soft Parallel Plates for Multifunctionality.

Harnessing buckling instability in soft materials offers an effective strategy to achieve multifunctionality. Despite great efforts in controlling the wrinkling behaviors of film-based systems and buckling of periodic structures, the benefits of classical plate buckling in soft materials remain largely unexplored. The challenge lies in the intrinsic indeterminate characteristics of buckling, leading to geometric frustration and random orientations. Here, we report the controllable global order in constrained buckling of arrays of parallel plates made of hydrogels and elastomers on rigid substrates. By introducing patterned cuts on the plates, the randomly phase-shifted buckling in the array of parallel plates transits to a prescribed and ordered buckling with controllable phases. The design principle for cut-directed deterministic buckling in plates is validated by both mechanics model and finite element simulation. By controlling the contacts and interactions between the buckled parallel plates, we demonstrate on-demand reconfigurable electrical and optical pathways, and the potential application in design of mechanical logic gates. By varying the local stimulus within the plates, we demonstrate that microscopic pathways can be written, visualized, erased, and rewritten macroscopically into a completely new one for potential applications such as soft reconfigurable circuits and logic devices.

A single nano cantilever as a reprogrammable universal logic gate

The current transistor-based computing circuits use multiple interconnected transistors to realize a single Boolean logic gate. This leads to higher power requirements and delayed computing. Transistors are not suitable for applications in harsh environments and require complicated thermal management systems due to excessive heat dissipation. Also, transistor circuits lack the ability to dynamically reconfigure their functionality in real time, which is desirable for enhanced computing capability. Further, the miniaturization of transistors to improve computational power is reaching its ultimate physical limits. As a step towards overcoming the limitations of transistor-based computing, here we demonstrate a reprogrammable universal Boolean logic gate based on a nanoelectromechanical cantilever (NC) oscillator. The fundamental XOR, AND, NOR, OR and NOT logic gates are condensed in a single NC, thereby reducing electrical interconnects between devices. The device is dynamically switchable between any logic gates at the same drive frequency without the need for any change in the circuit. It is demonstrated to operate at elevated temperatures minimizing the need for thermal management systems. It has a tunable bandwidth of 5 MHz enabling parallel and dynamically reconfigurable logic device for enhanced computing.

The structure, logic of operation and distinctive features of the system of triggers and counting signals formation for gamma-telescope GAMMA-400

Scientific project GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) relates to the new generation of space observatories intended to perform an indirect search for signatures of dark matter in the cosmic-ray fluxes, measurements of characteristics of diffuse gamma-ray emission and gamma-rays from the Sun during periods of solar activity, gamma-ray bursts, extended and point gamma-ray sources, electron/positron and cosmic-ray nuclei fluxes up to TeV energy region by means of the GAMMA-400 gamma-ray telescope represents the core of the scientific complex. The system of triggers and counting signals formation of the GAMMA-400 gamma-ray telescope constitutes the pipelined processor structure which collects data from the gamma-ray telescope subsystems and produces summary information used in forming the trigger decision for each event. The system design is based on the use of state-of-the-art reconfigurable logic devices and fast data links. The basic structure, logic of operation and distinctive features of the system are presented.

Tunable nanoelectromechanical resonator for logic computations.

There has been remarkable interest in nanomechanical computing elements that can potentially lead to a new era in computation due to their re-configurability, high integration density, and high switching speed. Here we present a nanomechanical device capable of dynamically performing logic operations (NOR, NOT, XNOR, XOR, and AND). The concept is based on the active tuning of the resonance frequency of a doubly-clamped nanoelectromechanical beam resonator through electro-thermal actuation. The performance of this re-configurable logic device is examined at elevated temperatures, ranging from 25 °C to 85 °C, demonstrating its resilience for most of the logic operations. The proposed device can potentially achieve switching rate in μs, switching energy in nJ, and an integration density up to 106 per cm2. The practical realization of this re-configurable device paves the way for nano-element-based mechanical computing.

Reconfigurable logic via gate controlled domain wall trajectory in magnetic network structure.

An all-magnetic logic scheme has the advantages of being non-volatile and energy efficient over the conventional transistor based logic devices. In this work, we present a reconfigurable magnetic logic device which is capable of performing all basic logic operations in a single device. The device exploits the deterministic trajectory of domain wall (DW) in ferromagnetic asymmetric branch structure for obtaining different output combinations. The programmability of the device is achieved by using a current-controlled magnetic gate, which generates a local Oersted field. The field generated at the magnetic gate influences the trajectory of the DW within the structure by exploiting its inherent transverse charge distribution. DW transformation from vortex to transverse configuration close to the output branch plays a pivotal role in governing the DW chirality and hence the output. By simply switching the current direction through the magnetic gate, two universal logic gate functionalities can be obtained in this device. Using magnetic force microscopy imaging and magnetoresistance measurements, all basic logic functionalities are demonstrated.

Suitability Analysis of FPGAs for Heterogeneous Platforms in HPC

High performance computing (HPC) systems currently integrate several resources such as multi-cores (CPUs), graphic processing units (GPUs) and reconfigurable logic devices, like field programmable gate arrays (FPGAs). The role of the latter two has traditionally being confined to act as secondary accelerators rather than as main execution units. We perform a deep survey around state of the art research and implementation of HPC algorithms; we extract features relevant to each family and list them as key factors to obtain higher performance. Due to the broad spectra of the survey we only include the most complete references found. We provide a general classification of the 13 HPC families with respect to their needs and suitability for hardware implementation. In addition, we present an analysis based on current and future technology availability as well as in particular aspects identified in the survey. Finally we list general guidelines and opportunities to be accounted for in future heterogeneous designs that employ FPGAs for HPC.

Tuning of interlayer exchange coupling in Ni80Fe20/Ru/Ni80Fe20 nanowires

In this work, we demonstrate how the static and dynamic properties of Ni80Fe20/Ru/Ni80Fe20 nanowires can be tuned by varying the Ru spacer layer thickness. Specifically, changing the Ru thickness we have tuned the Ruderman-Kittel-Kasuya-Yosida exchange interaction, and thus the antiferromagnetic (AFM) strength between the Ni80Fe20 layers. We show that there is a strong correlation between the interlayer coupling and features in ferromagnetic resonance (FMR) modes. We found different mode-softening degree of the FMR curves as function of the strength of AFM coupling, together with a clear frequency gap at around zero field. These experimental results are in qualitative agreement with presented micromagnetic simulations that also include biquadratic interface exchange. Understanding these characteristics may offer insights for reconfigurable vertical magnetic logic devices and microwave filters.

Spin-orbit-torque engineering via oxygen manipulation.

Spin transfer torques allow the electrical manipulation of magnetization at room temperature, which is desirable in spintronic devices such as spin transfer torque memories. When combined with spin-orbit coupling, they give rise to spin-orbit torques, which are a more powerful tool for controlling magnetization and can enrich device functionalities. The engineering of spin-orbit torques, based mostly on the spin Hall effect, is being intensely pursued. Here, we report that the oxidation of spin-orbit-torque devices triggers a new mechanism of spin-orbit torque, which is about two times stronger than that based on the spin Hall effect. We thus introduce a way to engineer spin-orbit torques via oxygen manipulation. Combined with electrical gating of the oxygen level, our findings may also pave the way towards reconfigurable logic devices.

A CMOS IC-based multisite measuring system for stimulation and recording in neural preparations in vitro.

In this report, we describe the system integration of a complementary metal oxide semiconductor (CMOS) integrated circuit (IC) chip, capable of both stimulation and recording of neurons or neural tissues, to investigate electrical signal propagation within cellular networks in vitro. The overall system consisted of three major subunits: a 5.0 × 5.0 mm CMOS IC chip, a reconfigurable logic device (field-programmable gate array, FPGA), and a PC. To test the system, microelectrode arrays (MEAs) were used to extracellularly measure the activity of cultured rat cortical neurons and mouse cortical slices. The MEA had 64 bidirectional (stimulation and recording) electrodes. In addition, the CMOS IC chip was equipped with dedicated analog filters, amplification stages, and a stimulation buffer. Signals from the electrodes were sampled at 15.6 kHz with 16-bit resolution. The measured input-referred circuitry noise was 10.1 μ V root mean square (10 Hz to 100 kHz), which allowed reliable detection of neural signals ranging from several millivolts down to approximately 33 μ Vpp. Experiments were performed involving the stimulation of neurons with several spatiotemporal patterns and the recording of the triggered activity. An advantage over current MEAs, as demonstrated by our experiments, includes the ability to stimulate (voltage stimulation, 5-bit resolution) spatiotemporal patterns in arbitrary subsets of electrodes. Furthermore, the fast stimulation reset mechanism allowed us to record neuronal signals from a stimulating electrode around 3 ms after stimulation. We demonstrate that the system can be directly applied to, for example, auditory neural prostheses in conjunction with an acoustic sensor and a sound processing system.

Novel Application of Crystalline Indium-Gallium-Zinc-Oxide Technology to LSI: Dynamically Reconfigurable Programmable Logic Device Based on Multi-Context Architecture

A pass gate (PG) configured with a configuration memory (CM) composed of a c-axis aligned crystalline In-Ga-Zn-O (CAAC-IGZO) FET and a pass transistor composed of an NMOS FET is applied to a multi-context routing switch (MC-RS) of a dynamically reconfigurable programmable logic device (DRPLD) based on multi-context architecture (MC-DRPLD). The proposed PG (OS PG) requires fewer transistors than a conventional PG configured with an SRAM cell served as a CM (SRAM PG). A MC-RS configured with the OS PG (OS MC-RS) has enabled its layout area to be 40% less than that of a MC-RS configured with the SRAM PG (SRAM MC-RS). Further, the delays of the MC-RSs with 2 to 16 contexts have been reduced by 24% to 37%. The MC-DRPLD including the OS MC-RS can switch contexts in one clock (50 nsec) at a clock frequency of 20 MHz, which enables dynamic reconfiguration at high speed.

Magnetic-field-controlled reconfigurable semiconductor logic

Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices.

Multiplier-free DCT approximations for RF multi-beam digital aperture-array space imaging and directional sensing

Multi-beamforming is an important requirement for broadband space imaging applications based on dense aperture arrays (AAs). Usually, the discrete Fourier transform is the transform of choice for AA electromagnetic imaging. Here, the discrete cosine transform (DCT) is proposed as an alternative, enabling the use of emerging fast algorithms that offer greatly reduced complexity in digital arithmetic circuits. We propose two novel high-speed digital architectures for recently proposed fast algorithms (Bouguezel, Ahmad and Swamy 2008 Electron. Lett. 44 1249–50) (BAS-2008) and (Cintra and Bayer 2011 IEEE Signal Process. Lett. 18 579–82) (CB-2011) that provide good approximations to the DCT at zero multiplicative complexity. Further, we propose a novel DCT approximation having zero multiplicative complexity that is shown to be better for multi-beamforming AAs when compared to BAS-2008 and CB-2011. The far-field array pattern of ideal DCT, BAS-2008, CB-2011 and proposed approximation are investigated with error analysis. Extensive hardware realizations, implementation details and performance metrics are provided for synchronous field programmable gate array (FPGA) technology from Xilinx. The resource consumption and speed metrics of BAS-2008, CB-2011 and the proposed approximation are investigated as functions of system word size. The 8-bit versions are mapped to emerging asynchronous FPGAs leading to significantly increased real-time throughput with clock rates at up to 925.6 MHz implying the fastest DCT approximations using reconfigurable logic devices in the literature.

Detection and Diagnosis of Faults in the Routing Resources of a SRAM based FPGAs

Field programmable gate arrays (FPGAs) are the reconfigurable logic devices which are widely used in many applications like system prototyping, complex computing systems, automotive electronics and mobile devices. FPGAs have become very popular at present because of their features like high logic capacity, reconfigurability and regular structure with less area cost. However, increase in density and complexity also has resulted in more probability of defects. FPGAs are prone to different types of faults similar to other complicated integrated circuit chips. Faults may occur due to many reasons like environmental conditions or aging of the device. The rate of occurrence of permanent faults can be quite high in emerging technologies, and hence there is a need for periodic testing of such FPGAs. To effectively deal with the increased defect density, we need efficient methods for fault detection and correction. Here, we present an approach for testing FPGA interconnect that exploits the reprogramability of an FPGA to create builtin self test (BIST) logic by configuring it only during off-line testing. In this way, testability is achieved without any area overhead, since the BIST logic “disappears” when the circuit is reconfigured for its normal system operation. We have used XILINX ISE12.1 for simulation and synthesis.

High resolution Time of Flight determination based on reconfigurable logic devices for future PET/MR systems

This contribution shows how to perform Time of Flight (TOF) measurements in PET systems using low-cost Field Programmable Gate Array (FPGA) devices with a resolution better of 100ps. This is achieved with a proper management of the FPGA internal resources and with an extremely careful device calibration process including both temperature and voltage compensation. Preliminary results are reported.

Characterization of InMnSb epitaxial films for spintronics

Dilute (III, Mn)V ferromagnetic magnetic semiconductors have potential applications in spintronic devices as magnetic field sensors, spin transistors and reconfigurable logic devices. For such applications ferromagnetism at room temperature is a practical requirement. Previous work has shown that In1−xMnxSb films grown on GaAs (100) substrates by atmospheric pressure metalorganic vapour phase epitaxy were single phase and had high temperature ferromagnetism for Mn concentrations up to 2%. Here we present a study of InMnSb thin films at higher Mn concentration (10 at%) showing ferromagnetic properties at room temperature. Aberration corrected and analytical (scanning) transmission electron microscopy techniques were used to study the structure and elemental distribution of the In1−xMnxSb/GaAs system. The crystalline quality of the film and the presence of phase separation is evaluated in the context of a cluster-mediated ferromagnetism model.