Discrete Switching Events Research Articles

Frequency-Domain Simulation of Electromagnetic Transients Using Variable Sampling Time-Step

This letter presents the extension of a previously proposed frequency-domain (FD) approach for the analysis of electromagnetic transients (EMTs), primarily due to a set of discrete switching events, in an electric power network. The method is based on dividing the analysis time window into a set of subwindows with equal or unequal time lengths and solving each in the FD. The sampling time step is also independently selected for each subwindow. The extended method, formerly proposed for a single transmission line, can readily use the concept of network equivalents, achieving efficient EMT solutions of large systems, and can simultaneously accommodate slow and fast dynamics.

Single Event Effects in Carbon Nanotube-Based Field Effect Transistors Under Energetic Particle Radiation

We present results from proton radiation experiments with carbon nanotube field effect transistors. Single event effects were observed consisting of drops in current, with very long durations (100 s of ms), and sudden, discrete switching events between quantized current levels. These studies are important for the development and understanding of advanced nano-electronic devices operating in the space radiation environment.

Robust Trajectory Tracking for a Class of Hybrid Systems: An Internal Model Principle Approach

This paper deals with the asymptotic tracking of periodic trajectories for hybrid systems having linear dynamics in each operating mode and isolated discrete switching events (switching systems). Parametric uncertainties are considered and the dimension of the state vector is allowed to vary among modes. To deal with the hybrid nature of the system, and the possible discontinuities of its solutions at switching times, a properly amended tracking control problem is defined and a feedback control law based on a discontinuous version of the classical internal model principle is proposed. The innovative design of the discrete-time dynamics of the compensator guarantees the robust existence of a steady-state response giving zero tracking error in the controlled output, and local convergence to it.

A hybrid systems model for power control in multicell wireless data networks

We present a power control scheme based on noncooperative game theory, using a fairly broad class of convex cost functions. The multicell CDMA wireless data network is modeled as a switched hybrid system where handoffs of mobiles between different cells correspond to discrete switching events between different subsystems. Under a set of sufficient conditions, we prove the existence of a unique Nash equilibrium for each subsystem, and prove global exponential stability of an update algorithm. We also establish the global convergence of the dynamics of the multicell power control game to a convex superset of Nash equilibria for any switching (handoff) scheme satisfying a mild condition on average dwell-time. Robustness of these results to feedback delays as well as to quantization is investigated. In addition, we consider a quantization scheme to reduce the communication overhead between mobiles and the base stations. Finally, we illustrate the power control scheme developed through simulations.

Unique characteristics of cold cathode carbon-nanotube-matrix field emitters

The attributes of electron field emission from disordered matrix arrays of carbon nanotubes are studied and found to be quite reproducible in spite of the disorder, density, and quality variations from sample to sample. At low applied electric fields, the electron field emission current-voltage characteristics qualitatively follow conventional Fowler-Nordheim behavior up to a critical current density. However, the current rise at low applied fields is anomalously steep, suggesting that the Fowler-Nordheim model is not sufficient to quantitatively characterize the emission. In the high-field region, the emission characteristics have a more complex behavior. In that regime, the instantaneous field emission is reminiscent of the low-field behavior, but discrete switching events lead to an overall current suppression. We attribute the sudden and well-defined onset of the switching events to interactions between neighboring nanotube tips. By correlating the switching behavior to the current-voltage characteristics, we rule out other physical processes that cause similar effects.

Correlation between broad-band noise and frequency fluctuations of narrow-band noise in the charge-density wave in NbSe3.

The broad-band noise (BBN) and the frequency fluctuations of the narrow-band noise (NBN) were simultaneously measured in small ${\mathrm{NbSe}}_{3}$ samples. The two variables were highly correlated. Some discrete switching events show up in both noises. When multiple NBN peaks were present, some large fluctuations appearing in the BBN did not appear in the frequency of the biggest NBN peak, indicating that parallel uncorrelated charge-density-wave conduction paths were present.

Size and self-field effects in giant magnetoresistive thin-film devices

Giant magnetoresistance (GMR) was measured as a function of device size for patterned NiCoFe/Cu and NiFe/Ag films. For the quasi-granular NiCoFe/Cu films, the normalized maximum change in resistivity /spl Delta//spl rho///spl rho/ was 8% for most of the samples. For the NiFe/Ag films, antiparallel alignment was achieved through magnetostatic coupling, not exchange fields, with a /spl Delta//spl rho///spl rho/ of 4.5%. The films were patterned into stripes with Au current leads for size-effect measurements. The height of the stripes varied from 0.5 to 16 /spl mu/m and the track width varied from 1 to 16 /spl mu/m. Discrete switching events and anomalous low-field dips in the response were observed for both materials for small device sizes. Self-field and heating effects due to the applied current were investigated for the NiFeCo/Cu films. The effect of the self-field produced by the applied current was separated from the thermal contribution and was found to reduce the response by over 32% for a current density of 10/sup 7/ A/cm/sup 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Observation of random-telegraph noise in resonant-tunneling diodes

We report the observation of random-telegraph noise in GaAs/Al0.4Ga0.6As resonant tunneling diodes. Measurements made on our devices from 57 to 70 K revealed discrete switching events with step heights ranging from 6 to 20 μV. Our studies indicated that the 20-μV switching sequences correspond to two-state thermally activated processes involving a single trap. At a bias of −0.4 V, the capture and emission activation energies of this trap are 81 and 51 meV, respectively, implying that the trap is located in the barrier. Our results suggest that the noise arises from transmission coefficient fluctuations due to hopping conduction of carriers through the barrier.

Single electron switching events in nanometer-scale Si MOSFET's

High-resolution ac measurements of drain conductance at low temperatures have been made on silicon MOSFET's with channels as narrow as 0.1 µm. These devices show discrete switching events in the channel resistance associated with individual electrons being captured and emitted from single interface traps. The voltage and temperature dependence of this switching gives detailed information on the characteristics of the trap and its distance from the interface. This switching is a component of low-frequency noise in MOSFET's and may be an important limit to the performance of small transistors.