Time-domain Device Research Articles

Autocorrelation Analysis and Near-Field Localization of the Radiating Sources With Cyclostationary Properties

Stochastic electromagnetic fields caused by the data transferring signals along the printed circuit boards are potentially harmful interference sources for modern digital electronic devices. The characterization of the near-field electromagnetic emissions from the electronic device in time domain was implemented by real-time digital oscilloscope in conjunction with the sequential scanning system of the near-field probes. Excluding of the periodic sample mean function reveals the hidden cyclostationarity of the data transferring process measured by the near-field scanning system. In this article, the quantitative autocorrelation analysis of the hidden cyclostationary properties of the random nonperiodic data sequences is presented. The time-domain evolution of the autocovariance cross sections estimated at each scanning point were exploited for spatial-time localization of the transmission line.

A power cycling degradation inspector of power semiconductor devices

We have proposed a failure analysis based on a real-time monitoring of power devices under acceleration test. The real-time monitoring enables to visualize the mechanism that leads to a failure by obtaining the change of structure inside the device in time domain with high spatial resolution. In this paper, we presented a new analytical instrument based on the proposed failure analysis concept. The essential functions of this instrument are (1) power stress control, (2) non-destructive inspection and (3) water circulation. An original design power-stress control system and a customized scanning acoustic microscopy system enable us a non-destructive inspection inside the device under power cycling test. This instrument exhibits a great advantage especially to monitor failure mechanisms without having to open the module.

New frontiers in time-domain diffuse optics, a review.

The recent developments in time-domain diffuse optics that rely on physical concepts (e.g., time-gating and null distance) and advanced photonic components (e.g., vertical cavity source-emitting laser as light sources, single photon avalanche diode, and silicon photomultipliers as detectors, fast-gating circuits, and time-to-digital converters for acquisition) are focused. This study shows how these tools could lead on one hand to compact and wearable time-domain devices for point-of-care diagnostics down to the consumer level and on the other hand to powerful systems with exceptional depth penetration and sensitivity.

Soil texture and salinity effects on calibration of TDR300 dielectric moisture sensor

Newly developed sensors have simplified real-time determination of soil water content (θm). Although the TDR300 is one of the most recent dielectric sensors, little is known with regard to the accuracy and dependency of its measurements of soil type and other environmental factors. In this study, the performance of TDR300 was investigated using liquids of known dielectric properties and a set of porous media with textures ranging from sandy to clayey. The experiments were conducted in the laboratory by mixing different amounts of water with each soil to obtain a sufficient range of soil water contents. For sand, the calculated permittivity values (εr) correlated adequately with Topp’s equation derived for time domain reflectometry. However, for the remaining inorganic porous media, εr values were overestimated compared with those resulting from Topp’s equation, especially for water contents exceeding 0.2 cm3/cm3. The results suggested that the relationship between θm and √εr was strongly linear (0.953< r2 <0.998). The most accurate results were provided by soil-specific calibration equations, which were obtained by the multi-point calibration equation. However, two-point calibration equations determined water content in all tested soils reasonably well, except for clay soil. A linear regression equation was developed that correlated the slope of the relationship θm–√εr with bulk soil electrical conductivity (EC). The regression slope was influenced more by soil EC than by soil texture. Also, TDR300 response was investigated in bi-layered systems (liquid–air and saturated porous media–air). In a bi-layered sensing volume characterised by strongly contrasting dielectric values, the appropriate bulk permittivity values for water and loam soil were determined by arithmetic rather than refractive index averaging, while for butanol and sand these values remained somewhere between the two averaging schemes, indicating that the upward infiltration calibration technique is inappropriate for the TDR300 sensor. Soil solute EC, as determined by measurements conducted in liquids and sand, significantly affected permittivity values at much lower levels than the limit of EC <2 dS/m, as suggested by the manufacturer. However, the relationship θm–√εr remained linear up to EC 2 dS/m, which corresponded to a bulk soil EC value of 0.6 dS/m. By contrast, for EC values >2 dS/m, the relationship θm–√εr was not linear, and, thus the TDR300 device calibration became increasingly difficult. Therefore, rather than operating as a time domain device, TDR300 operates as a water content reflectometer type device.

Comparison of StratusOCT and Cirrus HD-OCT Imaging in Macular Diseases

The Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA) device is a spectral-domain optical coherence tomography system that allows faster data acquisition than the previous generation StratusOCT (Carl Zeiss Meditec, Dublin, CA), which is a time-domain device. The authors compared images from both units to determine the clinical usefulness of spectral-domain optical coherence tomography technology in patients with macular diseases. Six consecutive patients were imaged with both the Cirrus HD-OCT and the StratusOCT devices and the images were compared. Cirrus HD-OCT images were typically more useful than StratusOCT images for assessing fine architectural details in macular pathology. The Cirrus HD-OCT software also facilitated a better understanding of three-dimensional data volumes. Commercially available spectral-domain optical coherence tomography is a clinically useful tool for visualizing and understanding macular diseases and offers benefits not inherent in previous generation machines.

Electron wave-packet transport through nanoscale semiconductor device in time domain

Future low-power downscaled metal-oxide-semiconductor (MOS) devices are in a size regime that requires a quantum-mechanical approach. Two theoretical approaches, the steady-state single plane-wave transport model and the time-dependent wave-packet transport model, have been discussed to study the electron transport through model nanoscale potential profiles. It has been shown that the single plane-wave transport model at steady state neglects the coupling among different plane waves induced by the potential profile variation induced by the external bias. Thus, the model is only valid when the external bias is rather small. The electron wave-packet transport theory models the electrons by wave packets consisting of all available plane waves in the contact from where the electrons originate. The couplings among different plane waves are included in the temporal evolution of the time-dependent Schrödinger equation. This model is thus more proper when studying nanoscale devices at normal device working configurations. The effects of gate bias and the device geometry on the wave-packet transport are then studied by model potentials of future downscaled devices, which explains the experimentally reported conventional I−V characteristics of nanoscale MOS field-effect transistors (MOSFETs) at room temperature, while the normal MOSFET functioning is expected to be impossible by the single plane-wave transport model due to the independent tunneling effects of individual plane waves.

High Speed Heterostructure Metal-Semiconductor-Metal Photodetectors

A. Colaa,∗, B. Nabet, Xiying Chen and F. Quaranta CNR-IMM sez. di Lecce, via Arnesano 73100 Lecce, Italy Electrical and Computer Engineering Dept., Drexel University 318 Commonwealth, Philadelphia, PA, 19104, USA In this work we review the properties of a class of metal−semiconductor– metal photodetectors based on heterojunction structures. Particularly, an AlGaAs/GaAs device is detailed in which the absorption region is in the GaAs layer, and a two-dimensional electron gas is formed at the heterointerface due to δ-doping of the widegap material. This heterostructure metal– semiconductor–metal photodetector also contains an AlGaAs distributed Bragg reflector that forms a resonant cavity for detection at 850 nm. The beneficial effect of the two-dimensional electron gas in the GaAs absorption layer in terms of speed and sensitivity is demonstrated by comparing samples with and without doping in the AlGaAs layer. The design and the physical properties of the grown epitaxial structure are presented, together with the static and dynamic characteristics of the device in time domain. In particular, photocurrent spectra exhibit a 30 nm wide peak at 850 nm, and time response measurements give a bandwidth over 30 GHz. A combination of very low dark current and capacitance, fast response, wavelength selectivity, and compatibility with high electron mobility transistors makes this device suitable for a number of application areas, such as Gigabit and 10 Gigabit Ethernet, wavelength division multiplexing, remote sensing, and medical applications.

Numerical device simulation of the composite triple-beat distortion of a cable television amplifier

The composite triple-beat (CTB) distortion of a cable television amplifier was simulated using numerical device simulation. The structures for the underlying bipolar transistors were created using numerical process simulation. Subsequent time-domain device simulation was performed in a mixed device-circuit mode for a 77-carrier input signal with a random phase relationship between carriers. Using a novel mathematical technique, the turn-on transient of the amplifier was subtracted from the periodic part of the output signal in order to reduce the simulation time required to resolve the CTB distortion. A Fourier transform mapped the resulting signal into the frequency domain, where the CTB distortion could be determined directly. This simulation methodology demonstrates the capability of correlating circuit level radio frequency figures of merit with the process conditions in a technology.

MESFET simulation oriented toward computer-aided microwave circuit design

A MESFET simulator designed to link physically based transistor simulation to microwave circuit simulation within an integrated CAD environment is described. The key features of the simulator are efficient implementation of a large-signal time-domain device simulation kernel; incorporation of extensive postprocessing of raw time-domain data; and an interactive, graphics-oriented user interface. An example that demonstrates the utility of the approach for assessing circuit models is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Computer-aided design of MMICs based on physical device models

A computer-aided design and characterisation technique is presented which uses comprehensive physical device models to represent the active devices in monolithic microwave integrated circuits (MMICs). Time-domain device and circuit models are used to analyse and design monolithic circuit elements and circuits. This approach is particularly useful for the investigation of large-signal (nonlinear) circuits, and allows the optimal design of microwave oscillators, large-signal amplifiers and other monolithic devices. In particular this technique has been used to predict successfully the frequency, power, stability and noise properties of MMIC oscillators. This method also allows the optimum geometry of the active devices to be obtained for specific applications.

High-frequency time-domain dielectric spectrometer for the determination of water in polymer coatings on metal substrates

High-frequency dielectric measurements on coatings for corrosion control are accomplished using a capacitor sample cell in conjunction with a dielectric spectrometer. Dielectric measurements at high frequencies provide information about water in coatings. The spectrometer is a time-domain device whereby the capacitor cell is pulsed and the response noted. Frequency data from 107 to 109 Hz are obtained from the time data using the Fourier transform. A new lumped capacitor sample cell designed for organic coatings is presented. High speed pulse generation, transmission, and capture are accomplished with a sampling oscilloscope system. A circuit is provided that interfaces the sampling oscilloscope to a small data-acquisition computer. The time data recorded with the data collection computer are sent to a large mainframe computer for mathematical processing. The function of the complete spectrometer system is described with attention given to the time referencing step and the Fourier transform technique. The spectrometer is tested using both a Teflon and a polyvinyl acetate–water system. Data for both systems are provided. An enhancement of the polyvinyl acetate β mechanism with addition of water, previously measured at lower frequencies and temperatures, is now observed at room temperature.

Gate-width dependence of GaAs FET transient response

An analysis of the transient response of the GaAs FET by means of a distributed model is presented. Using a numerical-technique based on the direct evaluation of the Bromwich integral for inverse-Laplace transform, the propagation delay and rise time of devices with different gate widths are obtained. Results indicate that propagation effect is significant when the gate width exceeds 150 µm for a typical MESFET. The presented method can serve as the basis of time-domain device parameter optimization in CAD routines.