Quadrature Mismatch Shaping for Digital-to-Analog Converters

Quadrature sigma-delta analog-to-digital converters require a feedback path for both the I and the Q parts of the complex feedback signal. If two separate multibit feedback digital-to-analog converters (DACs) are used, mismatch among the unit DAC elements leads to additional mismatch noise in the output spectrum as well as an I/Q imbalance. This paper proposes new quadrature bandpass (QBP) mismatch shaping techniques. In our approach, the I and Q DACs are merged into one complex DAC, which leads to near-perfect I/Q balance. To select the unit DAC elements of the complex multibit DAC, the well-known butterfly shuffler and tree structure are generalized towards a complex structure, and necessary constraints for their correct functioning are derived. Next, a very efficient first-order QBP shaper implementation is proposed. Finally, the newly presented complex structures are simulated to prove their effectiveness and are compared with each other with respect to performance     

Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching

The branching stemming from midchain radical formation in n‐butyl acrylate polymerization is investigated via melt‐state ¹³C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated poly­merizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.

     

Increasing the stability of DNA-functionalized gold nanoparticles using mercaptoalkanes

In this work, the stability of DNA functionalized gold nanoparticles was examined in relation to their size, temperature, as well as the presence of mono- and bivalent ions. Furthermore, we report on the stabilizing effect of an additional post-functionalization with mercaptoalkanes, optionally bearing triethylene glycol (TEG) units. Although such so-called backfilling molecules are commonly used for planar gold surfaces, they have rarely been reported in combination with DNA-functionalized nanoparticles. Our results show that, conform the DLVO theory, smaller citrate-capped gold nanoparticles were more stable towards higher concentrations of salt. Citrate nanoparticles of 30 nm in size were only stable in sodium chloride concentrations up to ~0.05 M and up to 45 °C. The stability of these uncoated nanoparticles was even lower when bivalent salts were used (i.e. <2 × 10⁻⁴ M). Immobilization of DNA on these nanoparticles, on the other hand, improved the stability in salt solutions with at least one order of magnitude. The additional use of backfilling molecules stabilized the gold nanoparticles even further, without negatively affecting the DNA hybridization efficiency. DNA functionalization also had a positive impact on the thermal stability of the nanoparticles. Unfortunately, this beneficial effect was not observed after a subsequent backfilling step.

     

Improved design method for continuous-time quadrature bandpass /spl Sigma//spl Delta/ ADCs

In continuous-time quadrature bandpass /spl Sigma//spl Delta/ ADCs it is desirable to limit the number of cross-couplings. This can be achieved by implementing the loop as a cascade of complex integrators with only real coefficients. It is shown that this may result in a very poor approximation of the desired noise transfer function, because the effect of the DAC pulse is not taken into account correctly. A simple implementation that solves this problem is proposed.     

Stability of mixed PEO-thiol SAMs for biosensing applications

The secret of a successful affinity biosensor partially hides in the chemical interface layer between the transducer system and the biological receptor molecules. Over the past decade, several methodologies for the construction of such interface layers have been developed on the basis of the deposition of self-assembled monolayers (SAMs) of alkanethiols on gold. Moreover, mixed SAMs of polyethylene oxide (PEO) containing thiols have been applied for the immobilization of biological receptors. Despite the intense research in the field of thiol SAMs, relatively little is known about their biosensing properties in correlation with their long-term stability. Especially the impact of the storage conditions on their biosensing characteristics has not been reported before to our knowledge. To address these issues, we prepared mixed PEO SAMs and tested their stability and biosensing performance in several storage conditions, i.e., air, N2, ethanol, phosphate buffer, and H2O. The quality of the SAMs was monitored as a function of time using various characterization techniques such as cyclic voltammetry, contact angle, grazing angle Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the impact of the different storage conditions on the biosensor properties was investigated using surface plasmon resonance. Via the latter technique, the receptor immobilization, the analyte recognition, and the nonspecific binding were extensively studied using the prostate specific antigen as a model system. Our experiments showed that very small structural differences in the SAM can have a great impact in their final biosensing properties. In addition it was shown that the mixed SAMs stored in air or N2 are very stable and retain their biosensor properties for at least 30 days, while ethanol appeared to be the worst storage medium due to partial oxidation of the thiol headgroup. In conclusion, care must be taken to avoid SAM degradation during storage to retain typical SAM characteristics, which is very important for their general use in many proposed applications.     

A one-path subsampling quadrature receiver based on a ΣΔ modulator with distributed resonators

This article presents experimental results of a quadrature bandpass sigma–delta (ΣΔ) modulator based on distributed resonators. The modulator employs transmission lines and transconductors as main components and does not require switches in the loop filter as in the case of switched-capacitor (discrete-time) filters. In addition, the proposed complex modulator does not require a quadrature mixer in the receiver. As main feature, the modulator architecture introduces an innovative way to produce the I and Q outputs that is immune to path mismatch due to the sharing of all the analog circuitry for both paths. The one-bit second-order modulator ADC is able to convert IF signals at fs/2 and 3fs/2 (fs = 50 MHz), achieving an ENOB = 10 bits within a 1 MHz signal bandwidth. Therefore the modulator may be feasible for the typical IF frequencies used in cellular base stations. Furthermore, it provides an image rejection grater than 70 dB. The 0.35 μm BiCMOS chip consumes 28 mW at 3.3 V supply voltage.     

Metabolic phenotyping of human plasma by 1H‐NMR at high and medium magnetic field strengths: a case study for lung cancer

Accurate identification and quantification of human plasma metabolites can be challenging in crowded regions of the NMR spectrum with severe signal overlap. Therefore, this study describes metabolite spiking experiments on the basis of which the NMR spectrum can be rationally segmented into well‐defined integration regions, and this for spectrometers having magnetic field strengths corresponding to ¹H resonance frequencies of 400 MHz and 900 MHz. Subsequently, the integration data of a case–control dataset of 69 lung cancer patients and 74 controls were used to train a multivariate statistical classification model for both field strengths. In this way, the advantages/disadvantages of high versus medium magnetic field strength were evaluated. The discriminative power obtained from the data collected at the two magnetic field strengths is rather similar, i.e. a sensitivity and specificity of respectively 90 and 97% for the 400 MHz data versus 88 and 96% for the 900 MHz data. This shows that a medium‐field NMR spectrometer (400–600 MHz) is already sufficient to perform clinical metabolomics. However, the improved spectral resolution (reduced signal overlap) and signal‐to‐noise ratio of 900 MHz spectra yield more integration regions that represent a single metabolite. This will simplify the unraveling and understanding of the related, disease disturbed, biochemical pathways. Copyright © 2017 John Wiley & Sons, Ltd.     

A Subsampling Quadrature Σ∆ Modulator Based on Distributed Resonators for Use in Radio Receiver

The receiver architecture proposed in this brief seizes the subsampling properties of continuous-time sigma-delta (SigmaDelta) modulators based on distributed resonators to construct a quadrature receiver. The proposed architecture is based on a low-pass SigmaDelta modulator that subsamples an intermediate frequency signal around the sampling frequency and does not require quadrature mixers. Instead, the quadrature mixing is replaced by suitably choosing the sampling instants inside the loop. Two practical circuit implementations are proposed. The first one uses separate circuitry for the I and Q paths. The second architecture introduces an innovative way to produce the I and Q outputs that is immune to path mismatch due to the sharing of all the analog circuitry for both paths. The proposed modulator may be feasible for the typical IF frequencies used in cellular base stations.     

Design and implementation of a band-pass sigma delta modulator with distributed resonators

Continuous time band-pass sigma delta converters require the realization of high frequency resonators, which have been usually implemented with g _m-C or LC circuits. However, transmission lines have been for a long time a standard way to implement high Q resonators in RF circuits. Recently, some continuous-time sigma–delta (SD) modulator architectures using transmission lines have been proposed. Theoretical analyses have shown that this kind of architectures share some of the properties of both continuous-time (CT) and discrete-time (DT) modulators. On the other hand they have specific implementation problems which are not present in other modulator architectures. This paper makes a brief review of the particularities of these modulators and shows the experimental results of a band-pass modulator implemented in BiCMOS technology. As an advantage compared to standard continuous time designs, this modulator can be operated as a subsampling ADC, displays a better immunity to clock jitter and is tolerant to loop delay.     

Mismatch Insensitive Double-Sampling Quadrature Bandpass Σ∆ Modulation

In a double-sampling quadrature bandpass sigma-delta modulator, path mismatch between the double-sampling branches and between the I/Q paths occurs. In this paper, an analytical study is presented which shows that this causes quantization noise and input signals to fold from the image band into the signal band and that this also results in a self-image component. To reduce the folding from the image band, a novel resonator is presented. This resonator has a bilinear input circuit so that noise and signals exhibits first-order shaping before folding in the band of interest. Next, three different modulator architectures based on the novel resonator are introduced. Finally, the remaining problem of self-image is tackled with a simple, yet efficient offline calibration strategy. Various design examples are shown and simulated to illustrate and prove the effectiveness of the proposed architectures and methods.