Switch Cycle Research Articles

A modeling method for the TL buck DC-DC converter with input and output sharing the ground

For the improved three-level (TL) buck direct current-direct current (DC-DC) switching converter which is a high-order, discrete, non-linear, and time-variant dynamic system, the work multi-modalities and principle are analyzed, and the state space equation model is established by introducing the switch cycle averaging operator under low-frequency, small ripple, and small-signal assumption. The transfer function from control to output that is needed by closed-loop feedback system is deduced by introducing small-signal perturbation. The closed-loop control system is designed based on the transfer function model by applying feedback control theory. The experiment results show that closed-loop system has good dynamic and static performance, and further indicates that the mathematic models are reasonable.

IR-wavelength optical shutter based on ITO/VO2/ITO thin film stack

Two thin film IR-shutter structures based on ITO-VO2-ITO and ITO-VO2 thin film stacks were designed. Thin film structures of the shutters were optimized at the wavelength of 1550 nm. The switch operation of the components was based on the metal-insulator transition phenomenon of VO2. Shutter components were current controlled and the metal-insulator transition was induced by Joule heating effect. All the thin films were deposited by using pulsed laser deposition. Crystal structure, morphology, and optical characteristics of the produced components were studied. Components with three-layer structure were found to suffer from significant internal strain, which was relaxed by post-annealing the components in the furnace. The maximum change of the optical transmittance measured at the wavelength of 1550 nm from the three-layer components during the switch cycle was 26.5%. The corresponding value measured from two-layer component’s structure was 34.2%. The maximum modulation of the transmittance of the three-layer component was reached at the wavelength of 1250 nm, which was 34%.

Comparison of Memory Assignment Schemes for Switch Architectures with Shareable Parallel Memory Modules

Switching Architectures deploying shareable parallel memory modules are quite versatile in their ability to scale to higher capacity while retaining the advantage of sharing its entire memory resource among all input and output ports. The two main classes of such architectures, namely, the Shared Multibuffer‐(SMB‐) based switch and the Sliding‐Window‐(SW‐) based packet switch, both deploy parallel memory modules that are physically separate but logically connected. Inspite of their similarity in regards to using shareable parallel memory modules, they differ in switching control and scheduling of packets to parallel memory modules. SMB switch uses centralized control whereas the SW switch uses a decentralized control for switching operations. In this paper, we present a new memory assignment scheme for the Sliding‐Window (SW) switch for assigning packets to parallel memory modules that maximizes the parallel storage of packets to multiple memory modules. We compare the performance of a sliding‐window switch deploying this new memory assignment scheme with that of an SMB switch architecture under conditions of identical traffic type and memory resources deployed. The simulation results show that the new memory assignment scheme for the sliding window switch maximizes parallel storage of packets input in a given switch cycle, and it does not require speed‐up of memory modules. Furthermore, it provides a superior performance compared to that of the SMB switch under the constraints of fixed memory‐bandwidth and memory resources.

An artificial molecular switch that mimics the visual pigment and completes its photocycle in picoseconds.

Single molecules that act as light-energy transducers (e.g., converting the energy of a photon into atomic-level mechanical motion) are examples of minimal molecular devices. Here, we focus on a molecular switch designed by merging a conformationally locked diarylidene skeleton with a retinal-like Schiff base and capable of mimicking, in solution, different aspects of the transduction of the visual pigment Rhodopsin. Complementary ab initio multiconfigurational quantum chemistry-based computations and time-resolved spectroscopy are used to follow the light-induced isomerization of the switch in methanol. The results show that, similar to rhodopsin, the isomerization occurs on a 0.3-ps time scale and is followed by <10-ps cooling and solvation. The entire (2-photon-powered) switch cycle was traced by following the evolution of its infrared spectrum. These measurements indicate that a full cycle can be completed within 20 ps.

Enhanced hyaluronic acid production of Streptococcus zooepidemicus by an intermittent alkaline-stress strategy

Enhanced hyaluronic acid (HA) production of Streptococcus zooepidemicus by redirecting carbon flux through an intermittent alkaline-stress strategy. pH value was kept at 7.0 for the first 6 h, and then intermittently switched to 8.5 for 1 h and back to 7.0 for 1 h until the end of fermentation at 16 h (one pH switch cycle every 2 h). With this intermittent alkaline-stress strategy, HA production was increased to 6.5 +/- 0.2 g l(-1) from 5.0 +/- 0.1 g l(-1) of the control, in which pH was always kept at 7.0. In addition, biomass and lactic acid concentration decreased by 24% and 14%, respectively, while acetic acid concentration increased by 10% under intermittent alkaline stress. The redirection of carbon flux from lactic acid to acetic acid was further supported by the decreased lactate dehydrogenase activity and the increased acetate kinase activity. As indicated by the increased NADH oxidase (NOX) activity, intermittent alkaline-stress induced a more oxidative intracellular environment which would facilitate HA synthesis. Overproduction of HA was realized by redirecting carbon flux through the proposed intermittent alkaline-stress strategy. This study clearly demonstrated the importance of metabolic-pathway-analysis based fermentation strategy in industrial processes and provided an alternative optimization approach for high viscosity fermentation.

A new test facility for efficient evaluation of MEMS contact materials

A novel test facility for the efficient evaluation of microelectromechanical system (MEMS) switches and the development of alternative contact materials is described. The facility utilizes the upper cantilever from commercial MEMS contact switches, and tests these against alternative bottom contact materials within a modified atomic force microscope (AFM). The test closely approximates the real switch, but can accommodate a wider range of test conditions and contact materials. The facility allows alternative contact materials to be easily and quickly incorporated, and therefore evaluated by measuring the number of cycles to failure. The evolution of the wear surfaces of the switch contact materials under test can also be easily examined. In order to demonstrate the facility, the evolution of the contact resistance and wear of a commercial RF MEMS cantilever with Au contacts was monitored under accelerated test conditions, comparing the behavior of Au bottom contacts to an alternative Au–Ni alloy contact material. The Au–Ni (20 at.%) alloy displayed reduced wear rates and improved switch cycle lifetimes compared to pure Au, while retaining acceptable values of contact resistance.

A Quantitative Model of the Switch Cycle of an Archaeal Flagellar Motor and its Sensory Control

By reverse-engineering we have detected eight kinetic phases of the symmetric switch cycle of the Halobacterium salinarum flagellar motor assembly and identified those steps in the switch cycle that are controlled by sensory rhodopsins during phototaxis. Upon switching the rotational sense, the flagellar motor assembly passes through a stop state from which all subunits synchronously resume rotation in the reverse direction. The assembly then synchronously proceeds through three subsequent functional states of the switch: Refractory, Competent, and Active, from which the rotational sense is switched again. Sensory control of the symmetric switch cycle occurs at two steps in each rotational sense by inversely regulating the probabilities for a change from the Refractory to the Competent and from Competent to the Active rotational mode. We provide a mathematical model for flagellar motor switching and its sensory control, which is able to explain all tested experimental results on spontaneous and light-controlled motor switching, and give a mechanistic explanation based on synchronous conformational transitions of the subunits of the switch complex after reversible dissociation and binding of a response regulator (CheYP). We conclude that the kinetic mechanism of flagellar motor switching and its sensory control is fundamentally different in the archaeon H. salinarum and the bacterium Escherichia coli.

Structural Basis for the Function of the β Subunit of the Eukaryotic Signal Recognition Particle Receptor

Protein translocation across and insertion into membranes is a process essential to all life forms. In higher eukaryotes, this process is initiated by targeting the translating ribosome to the endoplasmic reticulum via the signal recognition particle (SRP) and its membrane-associated heterodimeric receptor (SR). This targeting step is regulated by three G proteins, SRP54, SRα, and SRβ, which act in concert. Little is known about the regulatory role of SRβ. Here, we present the 1.7 Å crystal structure of the SRβ-GTP subunit in complex with the interaction domain of SRα. Strikingly, the binding interface overlaps largely with the switch 1 region of SRβ. This finding, together with additional biochemical data, shows that the eukaryotic SR is a conditional and not an obligate heterodimer. The results suggest that the GTP/GDP switch cycle of SRβ functions as a regulatory switch for the receptor dimerization. We discuss the implications for the translocation pathway.

Sputtered Tantalum as a Structural Material for Surface Micromachined RF Switches

Micro-electro-mechanical systems (MEMS) are batch fabricated miniature systems with both electrical and non-electrical (e.g. mechanical) functionalities. Examples of such MEMS are miniature mechanical switches, acceleration sensors, gyroscopes etc… RF-MEMS devices are an emerging class of MEMS devices used for RF signal processing in telecommunication applications. For example, metal surface micro-machined switches are a promising alternative for current solid state switches or mechanical reed relays due to their potential for miniaturization, integration and improved performance. RF-MEMS switches normally consist of a metal bridge or cantilever electrode, which can be pulled in towards a bottom electrode by electrostatic forces [1]. The bridge material is often chosen to be Al or an Al-alloy because of its low resistivity [2]. During each switch cycle the metal top electrode goes through a mechanical stress cycle. These successive stress cycles might lead to reliability problems such as fatigue and/or creep. This is certainly the case for Al, which is known to have a low creep resistance [3]. Several alternatives have been investigated as alloying Al with other materials [4], or replacing Al with metals having better mechanical properties, specifically low creep, such as Tungsten (W) or Tantalum (Ta). Especially high melting point materials are interesting alternatives as the creep resistance is expected to increase with the melting point [5]. If we consider surface micromachined RF switches, the pull in voltage and sheet resistance are two important parameters that should be taken into consideration while selecting the switch material. In general, the pull in voltage depends on mean stress, lateral dimensions, layer thickness and Young's modulus. In case of stress free films, a material having a low Young's modulus is preferred for low pull-in voltage. As W is known to have high intrinsic stress [6], and a higher Young's modulus compared to Ta [7], it is instructive to consider Ta as a structural material for surface micromachining applications.

Motor pattern switching in the heartbeat pattern generator of the medicinal leech: membrane properties and lack of synaptic interaction in switch interneurons.

The motor program for heartbeat in the medicinal leech is produced by a central pattern generator that regularly switches between two alternative coordination states. A pair of switch heart interneurons reciprocally alternate between rhythmically active and inactive states to effect these switches. During spontaneous switches in the activity state of switch interneurons, there was no correlation between the duration of a particular activity state and beat period, indicating that the timing networks for the switch cycle and the beat cycle are relatively independent. Simultaneous recordings from two switch heart interneurons showed that a perturbation in the electrical activity of one does not influence switching of the other and that there is no synaptic interaction between them. Using voltage clamp, we characterized an L-like Ca2+ current (measured as Ba2+ currents), inactivating and non-inactivating K+ currents, a persistent Na+ current, and a hyperpolarization-activated inward current in switch interneurons. Dynamic clamp experiments show that "subtraction" of an artificial switch leak conductance (described previously by Gramoll et al. 1994) from a switch interneuron when it is in the inactive state causes it to display activity associated with the active state. We discuss how the switch leak conductance may interact with the intrinsic currents of switch interneurons to control their activity state.

Bandwidth considerations for multilevel converters

Multilevel converters can achieve an overall effective switch frequency multiplication and consequent ripple reduction through the cancellation of the lowest order switch frequency terms. This paper investigates the harmonic content and the frequency response of these multimodulator converters. It is shown that the transfer function of uniformly sampled modulators is a bessel function associated with the inherent sampling process. Naturally sampled modulators have a flat transfer function, but multiple switchings per switch cycle will occur unless the input is slew-rate limited. Lower sideband harmonics of the effective carrier frequency and, in uniform converters, harmonics of the input signal also limit the useful bandwidth. Observations about the effect of the number of converters, their type (naturally or uniformly sampled), and the ratio of modulating frequency and switch frequency are made.

Drift in switched-capacitor integrators

Imperfections in MOS devices which cause drift over time in the output voltage of a switched-capacitor integrator include junction leakage, offset voltages, charge pumping, and charge-injection (clock feedthrough) from the switches. The origins of these imperfections and techniques to minimise their effect are discussed. With careful processing and design, total drift in a typical CMOS integrator can be reduced to less than one femtoampere and one femtocoulomb per switch cycle. Such high precision integrators may be used as ‘storage registers’ in many systems requiring accurate retention of an analog value.