Root Cause of Charge Loss in a Nitride-Based Localized Trapping Memory Cell

Data retention loss mechanisms in nitride-based localized trapping memory devices are investigated with various electrical measurements and Medici simulations. First, the effect of program and erase cycles on device behavior is determined in terms of bottom oxide degradation and nitride charge profile evolution. Even if a strong degradation of the interface is observed, there is no important impact of this degradation on the cell behavior. However, the nitride charge profile evolves with cycling and leads to a three-pole electron-hole-electron profile over the channel region. Second, the interface trap annealing, the tunneling through the bottom oxide, and the lateral redistribution are studied in order to determine which mechanism plays the main role in the threshold voltage shift after cycling. The retention performance is dominated by a lateral redistribution of charges in the nitride layer.     

Monolithic AGC loop for a 160 Mb/s transimpedance amplifier

A new BiCMOS monolithic automatic gain control (AGC) amplifier with wide dynamic range is described. The forward gain path has 120 kΩ transimpedance, 140 MHz bandwidth, input noise current spectral density of 1.17 pA/√Hz and input signal current handling capability of 4 mA. An on-chip peak detector incorporating a 25 pA current source yields AGC hold times in the millisecond range     

Design and evaluation of optimal cepstral lifters for accessingarticulatory codebooks

It is noted that of great importance to the success of the articulatory approach to speech coding is the use of a good distortion measure between a given speech signal and the entries in a stored codebook of impulse responses and corresponding vocal-track shapes (articulatory codebook). One promising distortion measure is the weighted cepstral distortion. Since the impulse responses in the articulatory codebook do not include glottal characteristics, the authors derive optimal weighting functions (cepstral lifters) to reduce the influence of a varying glottal source on the cepstral distortion measure. This is done by examining the ensemble of cepstral coefficients of speech produced by an articulatory speech synthesizer that also includes a vocal-cord model. The obtained cepstral lifters are optimal for the given ensemble of cepstral coefficients and for given constraints on the weighting function. They are different for cepstral coefficients derived from the power spectrum (FFT cepstra) and for those derived from LPC (linear predictive coding) coefficients (LPC cepstra). The performances of the obtained cepstral lifters are compared in an articulatory codebook search     

High-power/low-threshold type-II interband cascade mid-IR laser-design and modeling

We present an optimized design and detailed numerical simulations for a mid-IR type-II interband InGaSb QW cascade laser (T2ICL) with InAs-In/sub 0.3/Ga/sub 0.7/Sb active quantum wells. It is shown that a 15-period T2ICL operating at 300 K and emitting at 3.15 /spl mu/m should achieve a much higher differential quantum efficiency (maximum of 0.9 W/A per facet at 300 K) than conventional mid-IR bipolar injection lasers, and a threshold current density much lower than for the intersubband quantum cascade laser.     

Ultra-low temperature sensitive deep-well quantum cascade lasers (λ - 4.8 μm) via uptapering conduction band edge of injector region

A new design feature for deep-well quantum cascade (QC) lasers, in which the conduction band edge of the injector region is uptapered, results in virtual suppression of carrier leakage out of the active regions of 4.8 mm emitting devices. For heatsink temperatures in the 20?90°C range the characteristic temperature coefficients for threshold, T₀, and slope efficiency, T₁, reach values as high as 278 and 285 K, respectively, which are nearly twice the values for conventional QC lasers. At 20°C, the threshold current density for uncoated, 30 period, 3 mm-long devices is only ~1.8 kA/cm².     

Implementation of an Aerostat Positioning System With Cable Control

The capabilities of a multi-tethered aerostat positioning system are investigated using experimental and simulation results. The system consists of a platform supported by a helium-filled aerostat and attached to three anchored ground tethers actuated using computer-controlled winches. The experimental system was designed to perform a proof-of-concept study of a novel large-scale radio telescope requiring a receiver to be positioned accurately at an altitude of up to 500 m. Results from a series of flight tests are presented with a comparison between the passive response of the system and the response using proportional, integral, and derivative (PID) controllers with a position feedback. The motion of the platform is smaller for all cases using the feedback control. To improve on the PID results, a dynamics model of the system is used to develop and simulate optimal and feedforward (FF) control strategies. The optimal linear quadratic Gaussian (LQG) controller offers a 50% improvement over the PID controller, and both the LQG and the PID feedback controllers were shown to benefit considerably from the addition of a FF control term that exploits the measurements of the system's main disturbance force     

Dynamic resource allocation in OFDM systems: an overview of cross-layer optimization principles and techniques

Recently, a lot of research effort has been spent on cross-layer system design. It has been shown that cross-layer mechanisms (i.e., policies) potentially provide significant performance gains for various systems. In this article we review several aspects of cross-layer system optimization regarding wireless OFDM systems. We discuss basic optimization models and present selected heuristic approaches realizing cross-layer policies by means of dynamic resource allocation. Two specific areas are treated separately: models and dynamic approaches for single transmitter/receiver pairs (i.e., a point-to-point communication scenario) as well as models and approaches for point-to-multipoint communication scenarios (e.g., the downlink of a wireless cell). This article provides basic knowledge in order to investigate future OFDM cross-layer-optimization issues     

Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.     

Influence of device engineering on the analog and RF performances of SOI MOSFETs

This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS).     

A Si bipolar monolithic RF bandpass amplifier

The application of monolithic inductors to the realization of Si bipolar monolithic RF amplifiers is investigated. As a test vehicle, a bipolar monolithic bandpass amplifier was fabricated and characterized. A 4-nH silicon integrated inductor was used to achieve a peak S ₂₁ gain of 8 dB, a simulated noise figure of 6.4 dB, and a matched input impedance of 50 Ω in the frequency range of 1-2 GHz