L. Quintanilla

A 32-mW 320-MHz continuous-time complex delta-sigma ADC for multi-mode wireless-LAN receivers

We present an experimental continuous-time complex delta-sigma multi-bit modulator, implemented in standard 0.25-/spl mu/m CMOS technology and meeting all major requirements for application in IEEE 802.11a/b/g wireless LAN receivers. The clock frequency is 320 MHz, producing an oversampling ratio of 16 for 20 MHz channel bandwidths. The modulator supports two operation modes for zero-IF and low-IF receiver architectures respectively, requires a single 2.5-V power supply, and dissipates only 32 mW of power. The measured peak signal-to-noise ratio is 55 dB. Further experimental results using sine-wave and OFDM test signals are also presented.

Low-power pipeline ADC for wireless LANs

In this paper, a 10-bit 40-MS/s analog-to-digital converter (ADC) is presented. A power consumption of 12 mW was achieved by using a time-interleaved and pipelined architecture with shared operational amplifiers. This circuit was fabricated in a 2.5-V 0.25-/spl mu/m technology with metal-oxide-metal capacitors. Experimental results are within design ranges and are in good agreement with simulation data. It turns out that the proposed Nyquist-rate ADC provides a potential solution for low-power high-speed applications, e.g., wireless LANs.

Structural analysis of injection-moulded semicrystalline polymers by Fourier transform infra-red spectroscopy with photoacoustic detection and differential scanning calorimetry: 1. Poly(ethylene terephthalate)

Abstract Fourier transform infra-red spectroscopy coupled with photoacoustic detection (PA FT i.r.) has proved to be a useful tool for finding out about quantitative structural changes in solid materials. Poly(ethylene terephthalate) (PET) is a well known semicrystalline polymer that shows important changes on annealing. In order to obtain a complete picture of isomer distributions in industrial PET samples, spectroscopic measurements were correlated with differential scanning calorimetry (d.s.c.). The results obtained indicate that the structural characteristics of the thermally treated samples are related to the fabrication process. Two different strata in the plates can be distinguished: a skin layer and the core. The correlation between the apparent degree of crystallinity of the surface obtained by d.s.c. and the percentage of trans isomer obtained by PA FT i.r. allows the latter parameter to be separated into crystalline and amorphous trans isomer and to follow its evolution with the annealing process. Amorphous trans isomer vanishes at the primary isomerization (∼ 100°C) while crystalline trans and gauche conformations show sigmoidal evolution. At higher annealing temperatures (> 140°C) the ordered trans conformation shows an approximately linear increase at the expense of the gauche conformation. Finally, a direct correlation between the ordered trans isomer and the apparent degree of surface crystallinity can be made.

Structural analysis of injection-moulded semicrystalline polymers by Fourier-transform infra-red spectroscopy with photoacoustic detection and differential scanning calorimetry: 2. Polyamide-6,6

Abstract In this paper, a study of the structural changes due to annealing of injection-moulded polyamide-6,6 has been carried out. The spectroscopic behaviour of polyamide-6,6 is quite similar to that of poly(ethylene terephthalate) (PET). Using the band at 1650 cm −1 as an internal reference band, the intensity changes of the bands situated at 1146 and 936 cm −1 were followed. The former decreases when the annealing temperature exceeds 180°C whereas the latter increases. Furthermore, the bandwidth of the band at 936 cm −1 decreases from 23 to 20 cm −1 for annealing above 180°C. These spectroscopic changes were related to gauche/trans isomerism induced by the thermal treatment. Moreover, polyamide-6,6 verifies a two-phase conformational model, similarly to PET. As far as the thermal behaviour is concerned, two endothermic peaks at low (LM peak) and high (HM peak) temperature were found in thermograms of samples annealed above 150°C, and these displayed similar behaviour to those found in PET. The LM peak can be attributed to melting of crystals with increasing perfection and fold-surface smoothing of the crystalline layers due to the annealing treatment, and the HM peak to melting of the recrystallized crystalline structure during heating in differential scanning calorimetry (d.s.c.). On the other hand, the influence of the fabrication process in polyamide-6,6 seems not to be as important as in PET. The correlation between Fourier-transform infra-red spectroscopy with photoacoustic detection (p.a.- FT i.r.) and d.s.c. measurements show that the amide group works as an important constraint that limits the mobility of the crystalline molecules, and most of the conformational changes occur in the amorphous phase for annealing temperatures above 180°C. In the ordered phase, a slight crystallinity increase beyond this temperature can be related to crystalline perfection and fold-surface smoothing.

Elastin-like recombinamer catalyst-free click gels: characterization of poroelastic and intrinsic viscoelastic properties.

Elastin-like recombinamer catalyst-free click gels (ELR-CFCGs) have been prepared and characterized by modifying both a structural ELR (VKVx24) and a biofunctionalized ELR-bearing RGD cell-adhesion sequence (HRGD6) to bear the reactive groups needed to form hydrogels via a click reaction. Prior to formation of the ELR-CFCGs, azide-bearing and cyclooctyne-modified ELRs were also synthesized. Subsequent covalent crosslinking was based on the reaction between these azide and cyclooctyne groups, which takes place under physiological conditions and without the need for a catalyst. The correlation among SEM micrographs, porosity, swelling ratio, and rheological measurements have been carried out. The storage and loss moduli at 1Hz are in the range 1-10kPa and 100-1000Pa, respectively. The linear dependence of |G∗| on f(½) and the peak value of tan δ were considered to be consistent with a poroelastic mechanism dominating the frequency range 0.3-70Hz. The discrete relaxation spectrum was obtained from stress relaxation measurements (t>5s). The good fit of the relaxation modulus to decrease exponential functions suggests that an intrinsic viscoelastic mechanism dominates the transients. Several recombinamer concentrations and temperatures were tested to obtain gels with fully tuneable properties that could find applications in the biomedical field.

Deformation‐induced conformational changes in stretched samples of amorphous poly(ethylene terephthalate)

The combination of Fourier transform Raman spectroscopy and thermal analysis has been proved to be adequate for the study of the quantitative structural changes which take place in amorphous poly(ethylene terephthalate) on stretching. The two-phase conformational model previously proposed for annealed samples was applied to uniaxially stretched samples. The samples were deformed at different temperatures and speeds. Different conformer contents were found in the stretched sample depending on the stretching conditions. In general, deformation induces a conformational transition of gauche to trans. This behavior was lost at a narrow range of temperatures above the glass transition and at the lowest speeds, where the stretching seemed not to induce conformational changes. This different behavior has been associated to the high mobility of the polymer chains under these conditions, which imposes a different process of deformation marked by a high degree of chain slipping. This kind of deformation is present all along the sample and with the absence of necking in the uniaxial drawing process.

Structural analysis of poly(ethylene terephthalate) reinforced with glass fibre: 1. A photoacoustic Fourier transform infra-red study

Abstract Fourier transform infra-red spectroscopy coupled with photoacoustic detection (PA-FTi.r.) has proved to be a useful tool for finding out about quantitative structural changes in glass-fibre-reinforced poly(ethylene terephthalate) (PET) obtained by compression moulding and subsequently annealed. Analysis of the photoacoustic parameters indicates that the photoacoustic characteristics of the composite are very similar to those of the isolated matrix. It was demonstrated that glass-fibre-reinforced PET satisfies the same two-phase conformational model as the matrix. In contrast to the annealed matrix, the primary and secondary isomerizations cannot be detected in the composite. Therefore, the thermal treatment on the composite samples does not show further conformational changes. As a result, the manufacturing process seems to determine the composite microstructure, and its effect is quite similar to that observed in annealed matrix at the highest temperatures. Consequently, it can be considered that the trans isomer content in the amorphous phase is negligible in the composite.

Structural analysis of polyamide-6,6 reinforced with glass fibre by the use of Fourier transform infra-red spectroscopy with photoacoustic detection and differential scanning calorimetry

Abstract The effect of fibre reinforcement, industrial processing and subsequent annealing on the structure of polyamide-6,6 was analysed in this paper from the correlation between photoacoustic Fourier transform infra-red (PA FT i.r.) spectroscopic and differential scanning calorimetry (d.s.c.) thermal measurements. Using the band situated at 1650 cm −1 as an internal reference band, no spectral change was detected in the bands at 936 and 1146 cm −1 . Furthermore, the bands centred at 1335 and 1224 cm −1 , which are related to chain-folding, appear in the unannealed composite, whereas in the matrix these were only detected at the highest annealing temperatures. It seems that the manufacturing process used for the composite determines its microstructure and the subsequent annealing does not produce further conformational changes. On the other hand, the composite satisfies a two-phase conformational model, different from that of the matrix, which can be related to the strong interactions between the polymer and the glass fibres with surface treatment. In the thermal analysis, in contrast to the spectroscopic results, substantial changes in the endothermic melting peaks and in the degree of crystallinity can be noted. Up to an annealing temperature of ∼ 120–150°C, the composite crystallinity is constant and lower than the matrix crystallinity, but above this temperature the value rises and tends towards the values of the matrix. Furthermore, there was a more homogeneous crystalline distribution detected in the unannealed matrix, along with a greater size and perfection of the crystals than that seen in those of the unannealed composite. We suggest that the d.s.c. variation in the crystallinity can be attributed to an improvement in the fibre-matrix interface, in which the crystals of the interfacial phase change to more perfect ones as a result of the annealing treatment.

Parallel Continuous-Time

A parallel multibit continuous-time (CT) DeltaSigma analog-to-digital converter for an orthogonal-frequency-division-multiplexing (OFDM) ultrawideband receiver intended to operate according to the IEEE 802.15.3a or the ECMA 368 (ISO/IEC 26907) standards has been designed. The overall CT DeltaSigma converter consists of two modulators covering two unequal subbands (low-pass (LP) and bandpass (BP) subbands) that are arranged to operate in parallel and whose respective noise transfer functions (NTFs) are designed to match its corresponding frequency band. The composite NTF for the overall converter is defined as the minimum gain value out of these two individual NTFs. The LP and BP subbands were designed by using third- and fourth-order modulators, respectively, based on a 3-bit quantizer and operating at a clock frequency of 1056 MHz. NTF zero locations were optimized according to the criterion that all the in-band composite NTF gain maxima have approximately the same value. Combining OFDM signal characteristics and converter parameters, the effect of the quantization noise on the overall converter performance has been analytically derived. A simulation program has been realized to verify the performance of the converter.

\Delta\Sigma

This paper presents a digital correction technique for wide-band multibit error-feedback (EF) digital-to-analog converters (DACs). The integral nonlinearity (INL) error of the multibit DAC is estimated (on line or off line) by a calibration analog-to-digital converter (CADC) and stored in a random-access memory table. The INL values are then used to compensate for the multibit DACs distortion by a simple digital addition. The accuracy requirements for the error estimates are derived. These requirements can be significantly relaxed when the correction is combined with data-weighted averaging (DWA). Simulation and discrete-component measurement results are presented for a fourth-order 5-bit EF DAC. The results show a 14-bit DAC operating at an oversampling ratio of 8, which is suitable for digital subscriber line applications. The correction uses simple digital circuitry and a 3-bit CADC enhanced by DWA.