A new criterion for linear 2-port stability using a singlegeometrically derived parameter

A stability parameter, μ(S), is defined for linear two-port circuits using a geometrical approach. It is shown that μ>1 alone is necessary and sufficient for a circuit to be unconditionally stable. This single parameter can replace the dual Rollet (K>1) and auxiliary conditions for determining unconditional stability. The parameters K and μ are compared by discussing their implications in terms of mapping circles     

Robust uncertainty principles: exact signal reconstruction from highly incomplete frequency information

This paper considers the model problem of reconstructing an object from incomplete frequency samples. Consider a discrete-time signal f/spl isin/C/sup N/ and a randomly chosen set of frequencies /spl Omega/. Is it possible to reconstruct f from the partial knowledge of its Fourier coefficients on the set /spl Omega/? A typical result of this paper is as follows. Suppose that f is a superposition of |T| spikes f(t)=/spl sigma//sub /spl tau//spl isin/T/f(/spl tau/)/spl delta/(t-/spl tau/) obeying |T|/spl les/C/sub M//spl middot/(log N)/sup -1/ /spl middot/ |/spl Omega/| for some constant C/sub M/>0. We do not know the locations of the spikes nor their amplitudes. Then with probability at least 1-O(N/sup -M/), f can be reconstructed exactly as the solution to the /spl lscr//sub 1/ minimization problem. In short, exact recovery may be obtained by solving a convex optimization problem. We give numerical values for C/sub M/ which depend on the desired probability of success. Our result may be interpreted as a novel kind of nonlinear sampling theorem. In effect, it says that any signal made out of |T| spikes may be recovered by convex programming from almost every set of frequencies of size O(|T|/spl middot/logN). Moreover, this is nearly optimal in the sense that any method succeeding with probability 1-O(N/sup -M/) would in general require a number of frequency samples at least proportional to |T|/spl middot/logN. The methodology extends to a variety of other situations and higher dimensions. For example, we show how one can reconstruct a piecewise constant (one- or two-dimensional) object from incomplete frequency samples - provided that the number of jumps (discontinuities) obeys the condition above - by minimizing other convex functionals such as the total variation of f.     

High-speed (/spl ges/1 GHz) electrical and optical adding, mixing, and processing of square-wave signals with a transistor laser

This letter reports the common-emitter operation (gain /spl beta/=/spl Delta/I/sub C///spl Delta/I/sub B/>1, 20/spl deg/C, I/sub B/=36 mA, /spl lambda/=970 nm) of a dual-input transistor laser, arranged with a separate base contact on either side of a single emitter, that adds, mixes, and processes high-speed square-wave electrical inputs and delivers separate electrical and optical outputs. Applying a square-wave electrical input X/sub 1/(t) to one base contact and X/sub 2/(t) at a second base input, we obtain, with the pulsewidth modulated because of mixing, an electrical output proportional to /spl beta//spl times/[X/sub 1/(t)+X/sub 2/(t)] and a laser output tracking the electrical output (h/spl nu//spl times/f[X/sub 1/(t)+X/sub 2/(t)]) and exceeding it in bandwidth (pulse sharpness).     

Alternating-direction implicit (ADI) formulation of the finite-difference time-domain (FDTD) method: algorithm and material dispersion implementation

The alternating-direction implicit finite-difference time-domain (ADI-FDTD) technique is an unconditionally stable time-domain numerical scheme, allowing the /spl Delta/t time step to be increased beyond the Courant-Friedrichs-Lewy limit. Execution time of a simulation is inversely proportional to /spl Delta/t, and as such, increasing /spl Delta/t results in a decrease of execution time. The ADI-FDTD technique greatly increases the utility of the FDTD technique for electromagnetic compatibility problems. Once the basics of the ADI-FDTD technique are presented and the differences of the relative accuracy of ADI-FDTD and standard FDTD are discussed, the problems that benefit greatly from ADI-FDTD are described. A discussion is given on the true time savings of applying the ADI-FDTD technique. The feasibility of using higher order spatial and temporal techniques with ADI-FDTD is presented. The incorporation of frequency dependent material properties (material dispersion) into ADI-FDTD is also presented. The material dispersion scheme is implemented into a one-dimensional and three-dimensional problem space. The scheme is shown to be both accurate and unconditionally stable.     

Optimal linear identifying codes

Identifying codes can be used to locate malfunctioning processors. We say that a code C of length n is a linear (1,/spl les/l)-identifying code if it is a subspace of F/sub 2//sup n/ and for all X,Y/spl sube/F/sub 2//sup n/ such that |X|, |Y|/spl les/l and X/spl ne/Y, we have /spl cup//sub x/spl isin/X/(B(x)/spl cap/C)/spl ne//spl cup/y/spl isin/Y(B(y)/spl cap/C). Strongly (1,/spl les/l)-identifying codes are a variant of identifying codes. We determine the cardinalities of optimal linear (1,/spl les/l)-identifying and strongly (1,/spl les/l)-identifying codes in Hamming spaces of any dimension for locating any at most l malfunctioning processors.     

Characterization of accumulation layer capacitance for extracting data on high-/spl kappa/ gate dielectrics

A new parameter extraction technique has been outlined for high-/spl kappa/ gate dielectrics that directly yields values of the dielectric capacitance C/sub di/, the accumulation layer surface potential quotient, /spl beta//sub acc/, the flat-band voltage, the surface potential /spl phi//sub s/, the dielectric voltage, the channel doping density and the interface charge density at flat-band. The parallel capacitance, C/sub p/(=C/sub sc/+C/sub it/), was found to be an exponential function of /spl phi//sub s/ in the strong accumulation regime, for seven different high-/spl kappa/ gate dielectrics. The slope of the experimental lnC/sub p/(/spl phi//sub s/) plot, i.e., |/spl beta//sub acc/|, was found to depend strongly on the physical properties of the high-/spl kappa/ dielectric, i.e., was inversely proportional to [(/spl phi//sub b/m/sup *//m)/sup 1/2/K/C/sub di/], where /spl phi//sub b/ is the band offset, and m/sup */ is the effective tunneling mass. Extraction of /spl beta//sub acc/ represented an experimental carrier confinement index for the accumulation layer and an experimental gate-dielectric direct-tunneling current index. /spl beta//sub acc/ may also be an effective tool for monitoring the effects of post-deposition annealing/processing.     

Asymptotic capacity of two-dimensional channels with checkerboard constraints

A checkerboard constraint is a bounded measurable set S/spl sub/R/sup 2/, containing the origin. A binary labeling of the Z/sup 2/ lattice satisfies the checkerboard constraint S if whenever t/spl isin/Z/sup 2/ is labeled 1, all of the other Z/sup 2/-lattice points in the translate t+S are labeled 0. Two-dimensional channels that only allow labelings of Z/sup 2/ satisfying checkerboard constraints are studied. Let A(S) be the area of S, and let A(S)/spl rarr//spl infin/ mean that S retains its shape but is inflated in size in the form /spl alpha/S, as /spl alpha//spl rarr//spl infin/. It is shown that for any open checkerboard constraint S, there exist positive reals K/sub 1/ and K/sub 2/ such that as A(S)/spl rarr//spl infin/, the channel capacity C/sub S/ decays to zero at least as fast as (K/sub 1/log/sub 2/A(S))/A(S) and at most as fast as (K/sub 2/log/sub 2/A(S))/A(S). It is also shown that if S is an open convex and symmetric checkerboard constraint, then as A(S)/spl rarr//spl infin/, the capacity decays exactly at the rate 4/spl delta/(S)(log/sub 2/A(S))/A(S), where /spl delta/(S) is the packing density of the set S. An implication is that the capacity of such checkerboard constrained channels is asymptotically determined only by the areas of the constraint and the smallest (possibly degenerate) hexagon that can be circumscribed about the constraint. In particular, this establishes that channels with square, diamond, or hexagonal checkerboard constraints all asymptotically have the same capacity, since /spl delta/(S)=1 for such constraints.     

On the threshold Voltage of strained-Si-Si/sub 1-x/Ge/sub x/ MOSFETs

The threshold voltage shifts (/spl Delta/V/sub t(SS)/ relative to V/sub t/ of Si-control devices) in strained-Si-Si/sub 1-x/Ge/sub x/ (SS) CMOS devices are carefully examined in terms of the shifted two-dimensional energy subbands and the modified effective conduction- and valance-band densities of states. Increased electron affinity as well as bandgap narrowing in the SS layer are shown to be the predominant components of /spl Delta/V/sub t(SS)/, whereas the density-of-state terms tend to be relatively small but not insignificant. The study reveals, for both n-channel and p-channel SS MOSFETs, important physical insights on the varied surface potential at threshold, defined by energy quantization as well as the strain, and on the shifted flat-band voltage that is also part of /spl Delta/V/sub t(SS)/. Models for /spl Delta/V/sub t(SS)/ dependent on the Ge content (x), with comparisons to published data, are presented and used to show that redesign of channel doping in the SS nMOSFET to increase the significantly reduced V/sub tn(SS)/ for off-state current control tends to substantively diminish the inherent SS CMOS relative speed enhancement, e.g., by more than 40% for x=0.20. Interestingly, the SS pMOSFET model predicts small increases in the magnitude of V/sub tp(SS)/.     

Validity of the Kirchhoff approximation for electromagnetic wave scattering from fractal surfaces

Valid application of the Kirchhoff approximation (KA) for scattering from rough surfaces requires that the surface radius of curvature exceed approximately the electromagnetic wavelength /spl lambda/. Fractal surface models have characteristic features on arbitrarily small scales, thereby posing problems in application of the electromagnetic boundary conditions in general as well as in the evaluation of surface radius of curvature pertinent to KA. Experiments and numerical simulations show variations in scattering behavior that are consistent with scattering from progressively smoother surfaces with increasing wavelength, demonstrating surface smoothing effects in the wave-surface interaction. We hypothesize control of KA scattering from fractal surfaces by an effective average radius of curvature as a function of the smallest lateral scale /spl Delta/x contributing to scattering at /spl lambda/. Solution of =/spl lambda/ for /spl lambda/ is one possible method for approximating the limit of KA validity, assuming that /spl Delta/x[/spl lambda/] is known. Investigation of the validity of KA for the calculation of scattering from perfectly conducting Weierstrass-Mandelbrot and fractional Brownian process fractal surface models shows that for both models the region of applicability of KA grows with increases in /spl lambda/ and the Hurst exponent H controlling large-scale roughness. Numerical simulations using the method of moments demonstrate the dependence of /spl Delta/x on /spl lambda/ and the surface parameters.     

Convergence and loss bounds for Bayesian sequence prediction

The probability of observing x/sub t/ at time t, given past observations x/sub 1/...x/sub t-1/ can be computed if the true generating distribution /spl mu/ of the sequences x/sub 1/x/sub 2/x/sub 3/... is known. If /spl mu/ is unknown, but known to belong to a class /spl Mscr/ one can base one's prediction on the Bayes mix /spl xi/ defined as a weighted sum of distributions /spl nu/ /spl isin/ /spl Mscr/. Various convergence results of the mixture posterior /spl xi//sub t/ to the true posterior /spl mu//sub t/ are presented. In particular, a new (elementary) derivation of the convergence /spl xi//sub t///spl mu//sub t/ /spl rarr/ 1 is provided, which additionally gives the rate of convergence. A general sequence predictor is allowed to choose an action y/sub t/ based on x/sub 1/...x/sub t-1/ and receives loss /spl lscr//sub x(t)y(t)/ if x/sub t/ is the next symbol of the sequence. No assumptions are made on the structure of /spl lscr/ (apart from being bounded) and /spl Mscr/. The Bayes-optimal prediction scheme /spl Lambda//sub /spl xi// based on mixture /spl xi/ and the Bayes-optimal informed prediction scheme /spl Lambda//sub /spl mu// are defined and the total loss L/sub /spl xi// of /spl Lambda//sub /spl xi// is bounded in terms of the total loss L/sub /spl mu// of /spl Lambda//sub /spl mu//. It is shown that L/sub /spl xi// is bounded for bounded L/sub /spl mu// and L/sub /spl xi///L/sub /spl mu// /spl rarr/ 1 for L/sub /spl mu// /spl rarr/ /spl infin/. Convergence of the instantaneous losses is also proven.     

Drain-bias dependence of threshold voltage stability of amorphous silicon TFTs

Amorphous silicon (a-Si:H) thin-film transistors (TFTs) used in emerging, nonswitch applications such as analog amplifiers or active loads, often have a bias at the drain terminal in addition to the gate that can alter their threshold voltage (V/sub T/) stability performance. At small gate stress voltages (0/spl les/V/sub ST//spl les/15 V) where the defect state creation instability mechanism is dominant, the presence of a bias at the TFT drain decreases the overall shift in V/sub T/(/spl Delta/V/sub T/) compared to the /spl Delta/V/sub T/ in the absence of a drain bias. The measured shift in V/sub T/ appears to agree with the defect pool model that the /spl Delta/V/sub T/ is proportional to the number of induced carriers in the a-Si:H channel.     

Wideband simple cylindrical dielectric resonator antennas

Bandwidths of the coaxial fed and aperture coupled cylindrical dielectric resonator antennas (DRAs) with broadside radiation patterns are enhanced by exciting the HEM/sub 11/spl Delta// (1相似文献   

Reliability of 50 nm low-noise metamorphic HEMTs and LNAs

The long-term stability of a 50 nm low-noise metamorphic HEMT technology has been investigated by biased accelerated lifetime tests on both MHEMT devices and two-stage LNAs for W-band applications. The lifetime tests were performed at three channel temperatures, a drain voltage of 1 V and a power density of 0.3 W/mm in air. Based on a -10% degradation of g/sub m max/ failure criterion an activation energy of 1.6 eV and a projected median lifetime of 2.7/spl times/10/sup 6/ h at T/sub ch/=125/spl deg/C were determined. The two-stage LNAs were stressed at a channel temperature of 185/spl deg/C for 4000 h. The S-parameters did not show any significant degradation after 4000 h of stress time if the positive threshold voltage shift was compensated for by a corresponding increase of the gate voltage. The reliability results demonstrate the stable operation of 50 nm MHEMTs and LNAs for W-band applications and beyond.     

Modeling and evaluation criterion for thermocompression flip-chip bonding

A single joint finite element model (FEM) using a newly developed configuration independent evaluation criterion has been created, and experimentally verified, to provide more accurate predictions of bond formation based on the joint design and assembly process parameters. This model is based on the joint interface mechanics resulting from joint bump compression. Previous studies used a deformation criterion that depended on a specific joint configuration to evaluate the effectiveness of the expected bond. This limited the applicability of the model results to the joint design for which the deformation criterion had been experimentally determined. The technique reported in this research, uses finite element models to compute detailed distributions of stresses/strains at the interface of a joint when it is plastically deformed under compression. The evaluation criterion is defined to be the change in the differential area at the bonding interface, and is shown mathematically as follows: /spl Delta/A=/spl epsi//sub xx/+/spl epsi//sub yy//spl ges/(/spl epsi//sub xx/+/spl epsi//sub yy/)/sub crit/. Models using this criterion allow for the comparison of the effects of various joint design and manufacturing process parameters on the bond joint mechanics, and the resulting probable bond joint quality. A determination of the minimum deformation required for joint formation can be obtained for any design within specified limits.     

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.     

Correlating drain-current with strain-induced mobility in nanoscale strained CMOSFETs

The correlation between channel mobility gain (/spl Delta//spl mu/), linear drain-current gain (/spl Delta/I/sub dlin/), and saturation drain-current gain (/spl Delta/Idsat) of nanoscale strained CMOSFETs are reported. From the plots of /spl Delta/I/sub dlin/ versus /spl Delta/I/sub dsat/ and ballistic efficiency (Bsat,PSS), the ratio of source/drain parasitic resistance (R/sub SD,PSS/) to channel resistance (R/sub CH,PSS/) of strained CMOSFETs can be extracted. By plotting /spl Delta//spl mu/ versus /spl Delta/I/sub dlin/, the efficiency of /spl Delta//spl mu/ translated to /spl Delta/I/sub dlin/ is higher for strained pMOSFETs than strained nMOSFETs due to smaller RSD,PSS-to-RCH,PSS ratio of strained pMOSFETs. It suggests that to exploit strain benefits fully, the RSD,PSS reduction for strained nMOSFETs is vital, while for strained pMOSFETs the /spl Delta/I/sub dlin/-to-/spl Delta//spl mu/ sensitivity is maintained until R/sub SD,PSS/ becomes comparable to/or higher than R/sub CH,PSS/.     

On the /spl theta/-coverage and connectivity of large random networks

Wireless planar networks have been used to model wireless networks in a tradition that dates back to 1961 to the work of E. N. Gilbert. Indeed, the study of connected components in wireless networks was the motivation for his pioneering work that spawned the modern field of continuum percolation theory. Given that node locations in wireless networks are not known, random planar modeling can be used to provide preliminary assessments of important quantities such as range, number of neighbors, power consumption, and connectivity, and issues such as spatial reuse and capacity. In this paper, the problem of connectivity based on nearest neighbors is addressed. The exact threshold function for /spl theta/-coverage is found for wireless networks modeled as n points uniformly distributed in a unit square, with every node connecting to its /spl phi//sub n/ nearest neighbors. A network is called /spl theta/-covered if every node, except those near the boundary, can find one of its /spl phi//sub n/ nearest neighbors in any sector of angle /spl theta/. For all /spl theta//spl isin/(0,2/spl pi/), if /spl phi//sub n/=(1+/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, it is shown that the probability of /spl theta/-coverage goes to one as n goes to infinity, for any /spl delta/>0; on the other hand, if /spl phi//sub n/=(1-/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, the probability of /spl theta/-coverage goes to zero. This sharp characterization of /spl theta/-coverage is used to show, via further geometric arguments, that the network will be connected with probability approaching one if /spl phi//sub n/=(1+/spl delta/)log/sub 2/n. Connections between these results and the performance analysis of wireless networks, especially for routing and topology control algorithms, are discussed.     

IF-sampling fourth-order bandpass /spl Delta//spl Sigma/ modulator for digital receiver applications

Bandpass modulators sampling at high IFs (/spl sim/200 MHz) allow direct sampling of an IF signal, reducing analog hardware, and make it easier to realize completely software-programmable receivers. This paper presents the circuit design of and test results from a continuous-time tunable IF-sampling fourth-order bandpass /spl Delta//spl Sigma/ modulator implemented in InP HBT IC technology for use in a multimode digital receiver application. The bandpass /spl Delta//spl Sigma/ modulator is fabricated in AlInAs-GaInAs heterojunction bipolar technology with a peak unity current gain cutoff frequency (f/sub T/) of 130 GHz and a maximum frequency of oscillation (f/sub MAX/) of 130 GHz. The fourth-order bandpass /spl Delta//spl Sigma/ modulator consists of two bandpass resonators that can be tuned to optimize both wide-band and narrow-band operation. The IF is tunable from 140 to 210 MHz in this /spl Delta//spl Sigma/ modulator for use in multiple platform applications. Operating from /spl plusmn/5-V power supplies, the fabricated fourth-order /spl Delta//spl Sigma/ modulator sampling at 4 GSPS demonstrates stable behavior and achieves a signal-to-(noise + distortion) ratio (SNDR) of 78 dB at 1 MHz BW and 50 dB at 60 MHz BW. The average SNDR performance measured on over 250 parts is 72.5 dB at 1 MHz BW and 47.7 dB at 60 MHz BW.     

Modeling study of the impact of surface roughness on silicon and Germanium UTB MOSFETs

We outlined a simple model to account for the surface roughness (SR)-induced enhanced threshold voltage (V/sub TH/) shifts that were recently observed in ultrathin-body MOSFETs fabricated on <100> Si surface. The phenomena of enhanced V/sub TH/ shifts can be modeled by accounting for the fluctuation of quantization energy in the ultrathin body (UTB) MOSFETs due to SR up to a second-order approximation. Our model is then used to examine the enhanced V/sub TH/ shift phenomena in other novel surface orientations for Si and Ge and its impact on gate workfunction design. We also performed a calculation of the SR-limited hole mobility (/spl mu//sub H,SR/) of p-MOSFETs with an ultrathin Si and Ge active layer thickness, T/sub Body/<10 nm. Calculation of the electronic band structures is done within the effective mass framework via the Luttinger Kohn Hamiltonian, and the mobility is calculated using an isotropic approximation for the relaxation time calculation, while retaining the full anisotropy of the valence subband structure. For both Si and Ge, the dependence of /spl mu//sub H,SR/ on the surface orientation, channel orientation, and T/sub Body/ are explored. It was found that a <110> surface yields the highest /spl mu//sub H,SR/. The increasing quantization mass m/sub z/ for <110> surface renders its /spl mu//sub H,SR/ less susceptible with the decrease of T/sub Body/. In contrast, <100> surface exhibits smallest /spl mu//sub H,SR/ due to its smallest m/sub z/. The SR parameters, i.e. autocorrelation length (L) and root-mean-square (/spl Delta//sub rms/) used in this paper is obtained from the available experimental result of Si<100> UTB MOSFETs, by adjusting these SR parameters to obtain a theoretical fit with experimental data on SR-limited mobility and V/sub TH/ shifts. This set of SR parameters is then employed for all orientations of both Si and Ge devices.     

Low-power low-voltage CMOS A/D sigma-delta modulator for bio-potential signals driven by a single-phase scheme

Since the 1970's, the analog switches in switched-capacitor (SC) circuits are operated by nonoverlapping bi-phase control signals (/spl phi//sub 1/, /spl phi//sub 2/). The nonoverlapping of these two phases is essential for successful SC operation since, a capacitor inside an SC circuit can discharge if two switches, driven by /spl phi//sub 1/ and /spl phi//sub 2/, are turned on simultaneously. Moreover, since 1983, two additional phases are generally used in many SC circuits, which consist of advanced versions of /spl phi//sub 1/ and /spl phi//sub 2/. These two additional phases overcome the problem of signal-dependent charge injection. This paper presents a low-power and low-voltage analog-to-digital (A/D) interface module for biomedical applications. This module provides an A/D conversion based on a mixed clock-boosting/switched-opamp (CB/SO) second-order sigma-delta (/spl Sigma//spl Delta/) modulator, capable of interfacing with several different types electrical signals existing in the human body, only by re-programming the output digital filter. The proposed /spl Sigma//spl Delta/ architecture employs a novel single-phase scheme technique, which improves the dynamic performance and highly reduces the clocking circuitry complexity, substrate noise and area. Simulated results demonstrate that the signal integrity can be preserved by exploring the gap between the high conductance region of pMOS and nMOS switches at low power-supply voltages and the fast clock transitions that exist in advanced CMOS technologies. The mixed CB/SO architecture together with the overall distortion reduction resulting from using the proposed single-phase scheme, result that the dynamic range of the modulator is pushed closer to the theoretical limit of an ideal second-order /spl Sigma//spl Delta/ modulator.