Double-sampling single-loop /spl Sigma//spl Delta/ modulator topologies for broad-band applications

This paper presents novel double sampling high-order single loop sigma-delta modulator structures for wide-band applications. To alleviate the quantization noise folding into the inband frequency region, two previously reported techniques are used. The digital-to-analog converter's sampling paths are implemented with the single-capacitor approach and an additional zero is placed at the half of the sampling frequency of the modulator's noise transfer function (NTF). The detrimental effect of this additional zero on both the NTF and signal transfer function is also resolved through the proposed modulator architectures with a low additional circuit requirement.     

Digital Background Calibration of Residue Amplifier Non-idealities in Pipelined ADCs

In this paper, a digital background calibration technique for pipelined analog-to-digital converters (ADCs) is presented to continuously mitigate the conversion errors arising from the residue amplifier imperfections. The introduced method indirectly measures the digitized residue errors based on a novel principle. In the proposed method, the digitized residue errors are measured through the probability distribution of the digitized residue and a two-level pseudorandom noise sequence. Behavioral simulations are provided for a 12-bit pipelined ADC architecture to show the effectiveness of the proposed technique. The simulation results show that the signal-to-noise and distortion ratio is improved from 42.94 to 72.85 dB using the presented calibration technique. The required number of samples for convergence is approximately 5 \(\times \) \(10^{6}\) clock cycles.     

Microcrystalline structure and quasi-crystal formation in rapidly quenched (Al-Ti)-(Fe,Mn) alloys

We have performed an X-ray diffraction study of several microcrystalline binary and ternary alloys of the (Al-Ti)-(Mn-Fe-Ni) system prepared by melt-spinning. The results indicate that while Ti₂Ni is fully amorphous, Ti₂Fe forms metastable crystalline phase(s) with little or no i-phase fractions. The spectra of microcrystalline binary Ti-Mn alloys present similarities to that of the i-phase. Ternary (AlTi)_1–x Fe _x (AlTi)_1–x Mn _x are found to be isostructural near x=30 at% but seem not to contain significant i-phase while the ternary Al-rich Al₇₂Ti₁₀Mn₁₈ seems to be partially quasi-crystalline (QC). Electron diffraction patterns obtained for binary Ti₅₆Mn₄₄ whose X-ray spectrum resembles that of the i-phase show spots with five-fold symmetry together with a periodic lattice and a lot of streaking.     

Direct observation of local atomic order in a metallic glass

The determination of the atomic configuration of metallic glasses is a long-standing problem in materials science and solid-state physics. So far, only average structural information derived from diffraction and spectroscopic methods has been obtained. Although various atomic models have been proposed in the past fifty years, a direct observation of the local atomic structure in disordered materials has not been achieved. Here we report local atomic configurations of a metallic glass investigated by nanobeam electron diffraction combined with ab initio molecular dynamics simulation. Distinct diffraction patterns from individual atomic clusters and their assemblies, which have been theoretically predicted as short- and medium-range order, can be experimentally observed. This study provides compelling evidence of the local atomic order in the disordered material and has important implications in understanding the atomic mechanisms of metallic-glass formation and properties.     

Enhanced electrical conductivity in polystyrene nanocomposites at ultra-low graphene content

We compared the electrical conductivity of multiwalled-carbon-nanotube/polystyrene and graphene/polystyrene composites. The conductivity of polystyrene increases from ～6.7 × 10(-14) to ～3.49 S/m, with an increase in graphene content from ～0.11 to ～1.1 vol %. This is ～2-4 orders of magnitude higher than for multiwalled-carbon-nanotube/polystyrene composites. Furthermore, we show that the conductivity of the graphene/polystyrene system can be significantly enhanced by incorporation of polylactic acid. The volume-exclusion principle forces graphene into the polystyrene-rich regions (selective localization) and generates ～4.5-fold decrease in its percolation threshold from ～0.33 to ～0.075 vol %.