Power-up calibration techniques for double-sampling ΔΣ modulators

Two new start-up DAC calibration techniques are proposed for double-sampling DeltaSigma modulators. The first one is a modification of the existing calibration technique, while the second technique is proposed specifically for double-sampling DeltaSigma modulators. Dynamic element matching is used to eliminate "intra-DAC" mismatches, and digital correction for the remaining "inter-DAC" mismatches.     

Excess loop delay compensation for continuous-time ΔΣ modulators using interpolation

A new excess loop delay compensation technique for continuous-time DeltaSigma-modulators by using signal interpolation is presented. This technique uses an auxiliary differentiator in the feedforward path to construct a signal interpolation at the input of the quantiser to enable an early decision that compensates for excess loop delay. A simple tuning for the interpolation coefficient makes this technique suitable for lowpass, as well as bandpass, modulators. The proposed technique enables the compensation of any amount of delay and does not impose modification on loop filter transfer function or circuitry.     

Single-loop ΔΣ modulator with extended dynamic range

A single-loop delta?sigma modulator with extended dynamic range is proposed. It employs an auxiliary quantiser to process the quantisation error of the main quantiser. This simple addition guarantees improved stability over a wider signal input range and also reduces the sensitivity to the front-end DAC nonlinearity. Simulation results are provided to verify the effectiveness of this structure.     

Double-sampled ΔΣ modulator with relaxed feedback timing

A double-sampled delta-sigma (ΔΣ) modulator topology is proposed that can relax the critical timing constraints in the modulator feedback path. The speed requirements of the quantiser and dynamic element matching logic are thus greatly reduced. To verify the effectiveness of the proposed topology, a second-order double-sampled DS modulator is designed and simulated.     

Comparator-less digital implementation of AC-coupled ΣΔ A/D converters

A simple and successful design for a sigma-delta (ΣΔ) modulator with only digital active components is presented. Low frequency compensation of the input threshold variations of the digital gate used as a comparator achieves good spurious-free dynamic range. The only drawback is the addition of a low cutoff frequency, which results in an AC-coupled analogue-to-digital converter.     

Resonation-based cascade ΣΔ modulator for broadband low-voltage A/D conversion

A novel cascade SigmaDelta modulator architecture is presented that employs inter-stage resonation to increase its effective resolution compared to traditional cascades while presenting very relaxed output swing requirements and, subsequently, high robustness to nonlinearities of the amplifiers. In addition, the use of loop filters based on forward-Euler integrators, instead of backward-Euler integrators as proposed in earlier approaches, simplifies the switched-capacitor implementation and makes the proposed architecture very suited to wideband A/D conversion.     

Fast and accurate jitter simulation technique for continuous-time Σ/ spl Delta/ modulators

A fast and accurate technique for modelling and simulation of clock jitter in continuous-time Σ/ spl Delta/ (SD) modulators is introduced. In addition to its high speed compared to the traditional jitter simulation method, the proposed technique is still continuous-time based, which is more convenient than discrete-time based jitter modelling suggested in other publications. The mathematical principle of the proposed technique, as well as simulations results, are presented and compared to other simulation techniques.     

Improved architecture for low-distortion δσ ADC's

The low-distortion modulator is an effective ΔΣ ADC architecture for high-linearity and low-dissipation applications. However, it has several practical drawbacks. An improved low-distortion modulator topology that avoids these disadvantages is suggested.     

The κ-μ distribution and the η-μ distribution

This paper presents two general fading distributions, the κ-μ and the η-μ distribution, for which fading models are proposed. These distributions are fully characterized in terms of measurable physical parameters. The κ-μ distribution includes the Rice (Nakagami-n), the Nakagami-m, the Rayleigh, and the one-sided Gaussian distributions as special cases. The eta-mu distribution includes the Hoyt (Nakagami-q), the Nakagami-m, the Rayleigh, and the one-sided Gaussian distributions as special cases. Field measurement campaigns were used to validate these distributions. It was observed that their fit to experimental data outperformed that provided by the widely known fading distributions, such as the Rayleigh, Rice, and Nakagami-m. In particular, the κ-μ distribution is better suited for line-of-sight applications, whereas the η-μ distribution gives better results for non-line-of-sight applications     

Hybrid continuous-time/discrete-time cascade σδ modulator with adaptive inter-stage resonation

A novel architecture of a hybrid continuous-time/discrete-time cascade ΣΔ modulator that takes advantage of both circuit techniques, by including implicit anti-aliasing filtering and reduced sampling requirements, while presenting high robustness to circuit non-idealities, is presented. These circuital features are combined with programmable resonation to optimally distribute the zeros of the noise transfer function. In addition, the unity signal transfer function is implemented in all the modulator stages in order to reduce the integrator?s output swing. All these characteristics make the proposed architecture well suited to the implementation of reconfigurable A/D conversion in future generations of wireless telecom systems.     

The multivariate α-μ distribution

An infinite series formulation for the multivariate α-μ joint probability density function with arbitrary correlation matrix and non-identically distributed variates is derived. The expression is exact and general and includes all of the results previously published in the literature concerning the distributions comprised by the α-μ distribution. The general expression is then particularized to an indeed very simple, approximate closed-form solution. In addition, a multivariate joint cumulative distribution function is obtained, again in simple, closed-form manner. As an application example, the exact and approximate performances of the selection combining scheme given in terms of the outage probability is shown. Approximate and exact results are very close to each other for small as well as medium values of correlation.     

β-SiC-on insulator waveguide structures for modulators and sensor systems

In this work waveguide structures using the cubic polytype of SiC are analyzed. The β-SiC-on-insulator wageguides were fabricated by two different methods. In the first case, a technological process similar to that used for SIMOX material was used, a buried SiO₂ layer being formed by high-energy (2 MeV) ion implantation of oxygen in SiC/Si wafers. For the second case, the heteroepitaxy of SiC on SOI (SIMOX) wafers was used. The losses of the waveguides have been measured at 0.633, 1.3 and 1.55 μm in both TE and TM polarization and a detailed analysis and interpretation of the different loss mechanisms is presented. Using these two types of waveguides we have designed waveguide modulators using the Pockels effect. A 2D semiconductor device simulator was used to determine the electric field configuration in a double-Schottky diode structure and the local modulation of the refractive index was used to determine the effective index modulation of the guided mode. Optical simulations were performed using the spectral index and the effective index methods. Different 2D geometries are analyzed and the material parameters needed for fabricating such a device are determined. Such devices have potential for high-speed Si-based photonic devices compatible with silicon technology.     

3σ-rule-based early termination algorithm for mode decision in H.264

A low-complexity early termination algorithm for mode decision in H.264 is presented. The proposed algorithm is based on the statistical distribution of per-pixel motion cost, and it can skip the mode decision of the candidate macroblock modes with low probability. Simulation results reveal that the proposed algorithm can reduce the encoding time by 16.25% on average with the limited performance loss of about 0.023% dB.     

The β‐to‐γ Transition in BiFeO3: A Powder Neutron Diffraction Study

High‐temperature powder neutron diffraction experiments are conducted around the reported β–γ phase transition (～930 °C) in BiFeO₃. The results demonstrate that while a small volume contraction is observed at the transition temperature, consistent with an insulator–metal transition, both the β‐ and γ‐phase of BiFeO₃ exhibit orthorhombic symmetry; i.e., no further increase of symmetry occurs during this transition. The γ‐orthorhombic phase is observed to persist up to a temperature of approximately 950 °C before complete decomposition into Bi₂Fe₄O₉ (and liquid Bi₂O₃), which subsequently begins to decompose at approximately 960 °C.     

Relative intensity noise measurements of 5 μm quantum cascade laser and 1.55 μm semiconductor laser

The magnitude of the relative intensity noise (RIN) of a 5 mum distributed-feedback quantum cascade laser (DFB-QCL) was compared with a conventional 1.55 mum DFB laser diode (LD). The RIN for the DFB-QCL at a frequency of 1 MHz was 157 dBm at 10 mW light output, about 5 dB higher than that of the DFB-LD, which could almost be fully explained by the semi-classical noise model. The resonant tunnelling induced noise, which might be a cause of the RIN degradation, was not observed.     

Diode lasers emitting at 3 μm with 300 mW of continuous-wave output power

Type-I double-quantum-well GaSb-based diode lasers operating at 3 mum with room-temperature continuous-wave output power above 300 mW and peak power-conversion efficiency near 8 were designed and fabricated. Laser heterostructure comprised quinary AlGaInAsSb alloy as barrier and waveguide material. Use of quinary alloy resulted in adequate hole confinement. The waveguide thickness was chosen to maximise modal differential gain. Continuous-wave threshold current density about 100 A/cm² per quantum-well and slope efficiency of 100 mW/A were demonstrated at 17degC.     

Highly Accurate Closed-Form Approximations to the Sum of α-μVariates and Applications

Sums of fading envelopes occur in several wireless communications applications, such as equal-gain combining, signal detection, outage probability, intersymbol interference, etc. The exact evaluation of the sum statistics is known to be very intricate. One of the purposes of this Letter is to provide highly accurate closed-form approximations to the probability density function and cumulative distribution function of the sum of independent identically distributed (i.i.d.)α-μ(generalized gamma) variates. Based on and as an extension of such an approach, simple precise approximations for the performance metrics of equal-gain combining and maximal-ratio combining receivers operating on i.i.d. /spl alpah/-μ fading channels are proposed. Samples examples are given to illustrate that, for practical purposes, exact and approximate solutions are indistinguishable from each other.     

Nanoscale Ferroelectricity in Crystalline γ‐Glycine

Ferroelectrics are multifunctional materials that reversibly change their polarization under an electric field. Recently, the search for new ferroelectrics has focused on organic and bio‐organic materials, where polarization switching is used to record/retrieve information in the form of ferroelectric domains. This progress has opened a new avenue for data storage, molecular recognition, and new self‐assembly routes. Crystalline glycine is the simplest amino acid and is widely used by living organisms to build proteins. Here, it is reported for the first time that γ‐glycine, which has been known to be piezoelectric since 1954, is also a ferroelectric, as evidenced by local electromechanical measurements and by the existence of as‐grown and switchable ferroelectric domains in microcrystals grown from the solution. The experimental results are rationalized by molecular simulations that establish that the polarization vector in γ‐glycine can be switched on the nanoscale level, opening a pathway to novel classes of bioelectronic logic and memory devices.     

Mid-infrared GaSb-based EP-VCSELl emitting at 2.63 μm

Electrically-pumped GaSb-based vertical-cavity surface-emitting lasers emitting up to 2.63 μm at room temperature are reported. The whole structure was grown monolithically in one run by solid-source molecular beam epitaxy. This heterostructure is composed of two n-doped AlAsSb/GaSb DBRs, a type-I GaInAsSb/AlGaAsSb multiquantum- well active region and an InAsSb/GaSb tunnel junction. A quasi-CW (1 μs, 5 %) operation was obtained at room temperature for 35 μm-diameter devices with threshold current of 85 mA.