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This study focuses on the design of high-loop-delay modulators for parallel sigma-delta conversion. Parallel converters, allowing a global low oversampling ratio, consist of several bandpass modulators with adjacent central frequencies. To ensure the global performance, the noise transfer function (NTF) of each modulator must be adjusted regarding its central frequency. In this thematic, a new topology of sixth-order modulators based on weighted-feedforward techniques is developed. This topology offers an adequate control of the NTF at each central frequency by simple means. Additive signal paths are moreover proposed to obtain an auto-filtering signal transfer function. An optimisation method is also developed to calculate the optimised coefficients of the modulators at different central frequencies. The main concerns are improving the stability and reducing the sensitivity of the continuous-time circuit to analogue imperfections. This is essential for parallel conversion since, in each channel, the modulator works at a central frequency which differs from the fourth of the sampling frequency. The performance of the optimised modulator is compared with its discrete-time counterpart with good argument.

This article proposes a dual-band bandpass filter (BPF) based on stub-loaded resonator (SLR) with the second passband independently tunable. Varactors loaded on the end of the central stub are employed to independently tune the second passband. Two shunt quarter-wavelength open stubs and source-load (S-L) coupling are applied to generate transmission zeros (TZs) to enhance the selectivity and improve the out-band rejection. For verification, a tunable dual-band BPF is designed, fabricated and tested, which realizes frequency tuning range (FTR) of the second passband from 2.24 to 2.71 GHz with constant fractional bandwidth (CFBW) of 1.5±0.4%. The simulated and measured results are in good accordance.

Recent resting-state functional connectivity fMRI (RS-fcMRI) research has demonstrated that head motion during fMRI acquisition systematically influences connectivity estimates despite bandpass filtering and nuisance regression, which are intended to reduce such nuisance variability. We provide evidence that the effects of head motion and other nuisance signals are poorly controlled when the fMRI time series are bandpass-filtered but the regressors are unfiltered, resulting in the inadvertent reintroduction of nuisance-related variation into frequencies previously suppressed by the bandpass filter, as well as suboptimal correction for noise signals in the frequencies of interest. This is important because many RS-fcMRI studies, including some focusing on motion-related artifacts, have applied this approach. In two cohorts of individuals (n=117 and 22) who completed resting-state fMRI scans, we found that the bandpass–regress approach consistently overestimated functional connectivity across the brain, typically on the order of r=.10–.35, relative to a simultaneous bandpass filtering and nuisance regression approach. Inflated correlations under the bandpass–regress approach were associated with head motion and cardiac artifacts. Furthermore, distance-related differences in the association of head motion and connectivity estimates were much weaker for the simultaneous filtering approach. We recommend that future RS-fcMRI studies ensure that the frequencies of nuisance regressors and fMRI data match prior to nuisance regression, and we advocate a simultaneous bandpass filtering and nuisance regression strategy that better controls nuisance-related variability. •Bandpass filtering and nuisance regression are intended to reduce noise in RS-fMRI.•When RS-fMRI data are filtered, but regressors are not, noise is poorly controlled.•In addition, this approach reintroduces synchronous noise into RS-fMRI data.•Such noise leads to systematically inflated estimates of functional connectivity.•Simultaneous bandpass filtering and regression eliminates this source of bias.

Direct coupled filters have narrow stopband due to higher order modes passband. A compact dual layer band pass filter is proposed with wide stop band. The proposed filter provides the return loss of 16.87db and insertion loss of 2.5dB at the passband frequency 20.9 GHz. The filter size is half of the conventional direct coupled filters. The stop band covers up to 40 GHz with insertion loss below 35dB. The filter has no slot which makes it immune to the EMI/EMC problems.

HighlightsMXene/TiO2 hybrids are prepared by a simple calcination treatment, and their electromagnetic response is customized by in situ atomic reconstruction engineering.Based on the excellent electromagnetic response of MXene/TiO2 hybrids, a series of electromagnetic devices are constructed.Multi-spectrum stealth is realized covering visible-light, infrared radiation and GHz.With the diversified development of big data, detection and precision guidance technologies, electromagnetic (EM) functional materials and devices serving multiple spectrums have become a hot topic. Exploring the multispectral response of materials is a challenging and meaningful scientific question. In this study, MXene/TiO2 hybrids with tunable conduction loss and polarization relaxation are fabricated by in situ atomic reconstruction engineering. More importantly, MXene/TiO2 hybrids exhibit adjustable spectral responses in the GHz, infrared and visible spectrums, and several EM devices are constructed based on this. An antenna array provides excellent EM energy harvesting in multiple microwave bands, with |S11| up to − 63.2 dB, and can be tuned by the degree of bending. An ultra-wideband bandpass filter realizes a passband of about 5.4 GHz and effectively suppresses the transmission of EM signals in the stopband. An infrared stealth device has an emissivity of less than 0.2 in the infrared spectrum at wavelengths of 6–14 µm. This work can provide new inspiration for the design and development of multifunctional, multi-spectrum EM devices.

A compact ultra-wideband bandpass filter based on a multilayer printed circuit board (MPCB) structure is proposed in this paper. RO4450F prepreg is used to bond three RO4350B dielectric substrates with different thicknesses in the MPCB structure. The upper surfaces of the three dielectric substrates are respectively provided with copper-coated structures with different patterns. The blind holes and the defected ground structure (DGS) are added to the MPCB of an ultra-wideband bandpass filter. Two groups of loaded quarter-wavelength terminal-open stubs introduce two transmission zeros, which improves the roll-off rates and stopband characteristics, while simple DGS composed of rectangular slots introduces two resonance points in the passband to improve the return loss. Simulation and measurement are consistent. The insertion loss at the center frequency of 12.795 GHz is 0.58 dB and the fractional bandwidth of 3 dB is 40.33% from 10.215 GHz to 15.375 GHz. This bandpass filter can be widely used in wireless and satellite communication.

To address the growing demand for compact and high-performance microwave filters in modern communication systems, a mixed-mode bandpass filter is proposed in the article. A dual-layer substrate integrated waveguide resonator loaded with a capacitive patch (CP-DSIWR) is proposed and theoretically analyzed, with both patch modes and cavity modes existing. To construct the bandpass filter, two rows of metallic vias are designed in the CP-SIWR to enable coupling between the two types of the modes, with the structure being fed by microstrip line. A slot is embedded in the center of the capacitive patch to tune the resonant frequencies. The simulated results of the filter show that TM 01 , TM 10 and TE 101 modes are excited, achieving a dual-band filtering response with tunable frequency characteristics. The filter is centered at 6.2 GHz and 12.9 GHz with a compact size of 0.57 λ g ×0.57 λ g . A prototype is fabricated and measured for validation, showing good agreement between the simulation and measured results.