Differential Filter Research Articles

Dim and Small Targets Detection in Sequence Images Based on Spatiotemporal Motion Characteristics

In order to effectively enhance the low detection rates of dim and small targets caused by dynamic backgrounds, this paper proposes a detection algorithm for dim and small targets in sequence images based on spatiotemporal motion characteristics. With regard to the spatial domain, this paper proposes an improved anisotropic background filtering algorithm that makes full use of the gradient differences between the target and the background pixels in the eight directions of the spatial domain and selects the mean value of the three directions with the lowest diffusion function in the eight directions as the differential filter to obtain a differential image. Then, the paper proposes a directional energy correlation enhancement algorithm in the time domain. Finally, based on the above preprocessing operations, we construct a dim and small targets detection algorithm in sequence images with local motion characteristics, which achieves target detection by determining the number of occurrences of the target, the number of displacements, and the total cumulative area in these sequential images. Experiments show that the proposed detection algorithm in this paper can effectively improve the detection of dim and small targets in dynamic scenes.

Synthesis of Wideband High-Quality Factor Delay- Tunable Fully Differential All-Pass Filters

In this article, all possible wideband fully differential second-order voltage-mode active all-pass filters (APFs) based on a common-source differential amplifier are systematically derived using two-port network modeling techniques and symbolic math CAD tools. The proposed APF structure is based on the generic two-transistor differential-pair and all possible combinations of the surrounding impedances. In particular, 26 transfer functions and a total of 180 APF circuits, all of which can have a pole quality factor ( $Q$ ) value greater than unity, are found to be possible. Hence, the proposed topology can be used to produce APFs with dispersive delay as well as flat delay for true time delay elements. The operation of some APFs is verified with simulations and a selected circuit with tunable peak delay is designed and fabricated in a 65-nm CMOS process. The implemented filter achieved a maximum peak delay of 88.4 ps at 31 GHz, a constant delay of 11.5 ps over the frequency band 5–20 GHz, and a delay $Q$ -factor ( $Q_{D}$ ) value of 3.74, while consuming 1.74 mW from a 1-V supply voltage. The fabricated circuit occupies an area of $0.11\times 0.348$ mm2 and experimentally demonstrates an APF with the highest $Q$ value of any published second-order APF known to the authors.

A Voltage-Controlled Tunable Differential Dual-Band Bandpass Filter With Compact Size and Wide Tuning Range

A compact differential tunable dual-band bandpass filter is achieved by using cascaded capacitor-loaded coupled microstrip lines and voltage-controlled varactors. Six differential-mode (DM) transmission zeros (TZs), four DM transmission poles (TPs), and four common-mode (CM) TZs can be obtained by controlling values and positions of capacitors and the even-odd mode impedances of coupled microstrip lines. What's more, the first three DM TZs, two TPs and three CM TZs will change with the capacitance of varactors. Thus, the proposed filter possesses a tunable lower passband and a fixed upper passband. Compared with the state-of-the-art differential tunable DBBFs, the proposed design has the advantages of wide tuning range, compact size, low number of control voltages, and simple structure. Theoretic analysis, parametric study and design procedure are carried out completely. A prototype with the size of 58.2 × 10.1 mm (1.13 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> × 0.20 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> is the microstrip guided wavelength at the center frequency of the upper passband) is designed for demonstration, which exhibits the center frequency of the lower passband can be tuned from 1.55 to 2.42 GHz. Meanwhile, the center frequency and 3-dB bandwidth of the upper passband keep constant at 3.79 GHz and 8.5%, respectively.

Comparison of methods of derivation of the yank-time signal from the vertical ground reaction force–time signal for identification of movement-related events

Temporal changes in ground reaction force magnitudes reflect movement strategy, and thus underlying muscle activation patterns, during movement tasks. Speculatively, these changes may be observed more readily when the force–time signal is differentiated, yielding the yank-time signal. However, the differentiation process, including the signal filtering used before or after differentiation, can significantly affect the signal-to-noise ratio (SNR) and likelihood of meaningful inference. The aim of the present study was to compare three methods of deriving the yank-time signal: Method 1 derived the yank-time signal using 2nd-order central differentiation subsequent to application of a 4th-order Butterworth filter; Method 2 included the same process as Method 1 but additionally filtered the yank-time data with a Savitzky-Golay smoothing filter; and Method 3 directly and simultaneously derived and smoothed the yank-time signal using a Savitzky-Golay digital differentiation filter. The current analyses revealed Method 2 had the best SNR, followed by Methods 3 and 1, but caused a small loss of signal amplitude. With regards to timing of inflection points in the yank-time data, no significant difference was observed. Therefore, Method 3 led to the best derivation of the yank-time signal due to its efficiency and preservation of signal characteristics and good SNR. Also, a strong association between the first maximum point of the yank-time signal and the start of the downward movement of the body’s centre of mass during a countermovement jump, as identified by 3-D motion analysis, was observed. Thus, subtle events (e.g. start of downward movement) can be easily observed in the yank-time signal.

Research and Analysis of Tunable Differential N-Path Band-Pass Filter

Traditional filters usually have low Q and gain values and it is difficult to adjust their center frequencies. Moreover, it is very complicated to analyze their transmission charateristics through conventional methods. Therefore, in this paper, a tunable differential N-path bandpass filter that uses a new adjoint network method to analyze the transmission characteristics of the differential N-path structure is proposed. The filter circuit adopts a novel circuit structure consisting of two differential N-path structures, two transconductance amplifiers and an off-chip transformer. The differential structure eliminates even harmonics, the transconductance amplifier increases the circuit gain and the off-chip transformer acts as a balun, improving the filter’s Q value and achieving impedance matching. Unlike the traditional switching capacitance method used for analyzing the differential circuit structure, the method proposed in this paper does not involve complicated calculus operations. In fact, the method greatly simplifies these complex operations, and the transmission function of the circuit can be obtained through simple algebraic operations. The proposed filter was designed using TSMC 180[Formula: see text]nm CMOS process. Simulation results for a differential four-path bandpass filter formed under 1.2[Formula: see text]V supply voltage show that the gain of the filter is greater than 8.5 dB, the center frequency can be adjusted from 0.1[Formula: see text]GHz to 1[Formula: see text]GHz, the in-band insertion loss S11 is greater than 10 dB, the out-of-band IIP3 is greater than 10 dBm, the out-of-band rejection is 28 dB and the noise figure is less than 2.2 dB at [Formula: see text][Formula: see text]MHz.

Dual‐wideband differential bandpass filter with intrinsic common‐mode suppression based on hybrid transmission structure

Based on the microstrip-line/slot-line hybrid transmission structure, a novel method of realizing dual-wideband differential bandpass filter (DDBPF) is proposed and demonstrated in this paper. By virtue of hybrid transmission structure, the proposed DDBPF has intrinsic common mode (CM) rejection. Moreover, the dual-wideband transmission performance of differential mode (DM) signal can be approached by using two dual-mode stub-loaded stepped-impedance resonators. The two passbands of the proposed DDBPF are respectively centered at 2.76 GHz and 4.12 GHz which fractional bandwidths are 20.7% and 11.4%. The DM harmonic suppression can extend to 43.5 GHz with rejection level of 13 dB. The CM attenuation of DDBPF can reach 60 dB within DM passband. Furthermore, the CM suppression with attenuation level of 20 dB is ranging from 0.5 GHz to 43.5 GHz. The measurement results are in good agreement with the simulation results, which validates the effectiveness of proposed design methodology.

A standard and harmonic blocker tolerant receiver front-end using a harmonic rejection differential N-path notch filter and blocks withstand to possible variations

Harmonic rejection differential N-path notch filter has been used as a miller passive filter along with low noise amplifier in this paper. By using it, both the standard and harmonic blockers are rejected at the RF input node and after the antenna. The noise figure of the front-end at the presence of standard and harmonic blockers (0 dBm) is less than 10 dB inside the whole RF bandwidth of front-end. The total power consumption, conversion gain and harmonic rejection are less than 33.15 (mW), and more than 66.5 and 80 (dB) over the RF bandwidth, respectively. Moreover, the proposed architecture is robust to the temperature and power supply variations such that the NF is less than 4.3 and 3.97 (dB) over the temperature and power supply changes, respectively. The proposed structure has been analyzed and simulated at the schematic level using CMOS 90 nm technology with a 1.5 V voltage supply.

Modeling and Analysis of a Differential Mode Active EMI Filter With an Analog Twin Circuit

Conventional passive EMI filters are bulky and occupy up to 30% of converter volume and weight. Active EMI filters are a key technology that enables the volume reduction of passive components in the EMI filter. The effectiveness of traditional active EMI filter for volume reduction is limited by the additional overhead from the passive components for noise sensing and compensation to ensure stability. In this article, a novel active EMI filter is proposed and demonstrated for differential mode noise attenuation. The filter consists of a twin circuit made up of low voltage/current components that mimic the high-power passive filter components in the main circuit. Unlike the conventional active EMI filter, the proposed filter uses compensation networks which consists of low-voltage surface-mount components only. The modeling of the entire circuit is carried out, and verified with small-signal measurements. The filter is then tested in a converter and the experimental results are shown to be consistent with the model and the small-signal measurements.

Ground Moving Vehicle Detection and Movement Tracking Based on the Neuromorphic Vision Sensor

Moving-objects detection is a critical ability for an autonomous vehicle. Facing the high detection requirements and the slow target-extraction problem of a common camera, this article proposes to utilize neuromorphic vision sensor (DVS) for detecting the moving objects and estimating their movement states. For a better detection work, the DVS image’s noise points are filtered and the CTRV kinematics model is built in advance. In order to distinguish the overlapped or nearby bodies and get the accurate clustering number, this article proposes a 3-D improved $K$ -means method. As the clustering centers can be influenced by the movement easily, the moving objects’ clustering centers appear unstable, so the movement estimation also fluctuates. In order to obtain stable movement estimation, this article proposes a strong tracking center differential external Kalman filter (SCDEKF) to track the moving objects, and the method has higher accuracy and less computational load. In order to verify the advantages of proposed methods, a simulation environment was established in the Gazebo, and the common cameras were also added in simulation for comparison with the DVS sensor. The simulation results show that the 3-D improved $K$ -means method with DVS can cluster the moving objects accurately, and the SCDEKF can provide more accurate movement estimation than the traditional EKF method. Finally, two experiments were conducted to prove the methods’ superiority. The main contribution is to solve the exploitation problems faced by the short-term borne sensor and promote its application in transportation.

Compact closed‐loop resonator filters with wide spurious free band and extended common‐mode noise suppression

A theoretical analysis is presented for miniaturised filters with an extended stopband and extended common-mode (CM) rejection, using loaded closed-loop resonators. A numerical method is presented to solve the equations extracted from the ideal transmission line model. Selection of critical resonator parameters to minimise filter area while simultaneously maximising the differential-mode (DM) stopband or the CM noise suppression is explored. The trade-off between size, stopband and CM rejection is presented and used to design three filters at 1 GHz, which are designed to verify the proposed concept. First, a differential second-order filter with an extended DM stopband ( dB) up to and extended CM noise suppression ( dB) up to 6.42 is realised to show the parameter trade-offs. Then optimal resonators are used to develop a compact singled-ended filter () with an extended stopband ( dB) up to and the smallest size. Lastly, a second order filter with an optimal extended CM rejection ( dB) up to is presented. Measured results are presented. All three filters stand out compared to other works by exhibiting the smallest footprint relative to the operating frequency.

Topology optimization for designing periodic microstructures based on finite strain viscoplasticity

This paper presents a topology optimization framework for designing periodic viscoplastic microstructures under finite deformation. To demonstrate the framework, microstructures with tailored macroscopic mechanical properties, e.g., maximum viscoplastic energy absorption and prescribed zero contraction, are designed. The simulated macroscopic properties are obtained via homogenization wherein the unit cell constitutive model is based on finite strain isotropic hardening viscoplasticity. To solve the coupled equilibrium and constitutive equations, a nested Newton method is used together with an adaptive time-stepping scheme. A well-posed topology optimization problem is formulated by restriction using filtration which is implemented via a periodic version of the Helmholtz partial differential equation filter. The optimization problem is iteratively solved with the method of moving asymptotes, where the path-dependent sensitivities are derived using the adjoint method. The applicability of the framework is demonstrated by optimizing several two-dimensional continuum composites exposed to a wide range of macroscopic strains.

A cross-coupled symmetric floating impedance scaler with enhanced bandwidth and accuracy

Capacitors realized using symmetric floating impedance scaling (SFIS) are area efficient. They are preferred for the implementation of fully differential filters for biomedical applications. The SFIS reported in the literature has poor accuracy and lower effective bandwidth. In this paper, a cross coupled symmetric floating impedance scaling (CC-SFIS) with enhanced bandwidth and accuracy is proposed. To evaluate its performance, a 500 pF capacitor is implemented in UMC 180 nm CMOS technology with a base capacitor (Cb) of 10 pF using both CC-SFIS and source follower based SFIS (SF-SFIS). The magnitude and phase of the impedance of the capacitor realized using CC-SFIS and SF-SFIS are obtained through post-layout simulations. CC-SFIS requires 53.68% lower area, 62.39% lower power consumption, and 88% higher accuracy than SF-SFIS. Fully differential 2nd order Butterworth low pass filters with cutoff frequency of 100Hz are implemented in UMC 180 nm technology using both CC-SFIS and SF-SFIS capacitors. Their performances are evaluated through simulation. From this, it is found that the deviation in the cut off frequency of the filter using CC-SFIS is smaller (2%) compared to that using SF-SFIS (40%) circuit.

Feature Extraction for Transient Chemical Sensor Signals in Response to Turbulent Plumes: Application to Chemical Source Distance Prediction

This paper describes the design of a low-pass differentiator filter with linear phase and finite impulse response (FIR) for extracting transient features of gas sensor signals (the so-called “bouts”) which are relevant for accurately estimating the source-receptor distance in a turbulent plume. Our current proposal addresses the shortcomings of previous ‘bout’ estimation methods, namely: (i) they were based in non-causal digital filters precluding real time operation, (ii) they used non-linear phase filters leading to waveform distortions and (iii) the smoothing action was achieved by two filters in cascade, precluding an easy tuning of filter performance. The presented filter preserves the signal waveform in the bandpass region for maximum reliability concerning both bout detection and amplitude estimation. Thanks to its FIR design, the filter can be implemented with nonrecursive structures, thus being inherently stable and allowing an easy algorithmic implementation and optimization. As a case study, we apply the proposed filter to predict the source-receptor distance from recordings obtained with a metal oxide (MOX) gas sensor in a wind tunnel. We demonstrate that proper tuning of the proposed filter can reduce the prediction error to 8 cm (in a distance range of 1.45 m) improving previously reported performances in the same dataset by a factor of 2.5. The performance of bout-based features are also benchmarked against traditional source-receptor distance estimators such as the mean, variance and maximum of the response. We also study how the length of the measurement window affects the performance of different signal features and how to tune the filter parameters to make the predictive models insensitive to wind speed. A MATLAB implementation of the proposed filter and all analysis code used in this study is provided.

Fiber bundle topology optimization of hierarchical microtextures for wetting behavior in Cassie-Baxter mode

This paper presents the topology optimization of hierarchical microtextures for wetting behavior in the Cassie-Baxter mode, considering a structural unit of the hierarchical microtexture composed of base and secondary structures. The geometrical configuration of the considered structural unit can be described as a fiber bundle composed of an external surface of the base structure and the pattern of the secondary structures. Thus, two design variables are defined, one for the external surface of the base structure, and the other for the pattern of the secondary structures. The Young-Laplace equation, including a term depending on the mean curvature of the external surface, is used to describe the liquid/vapor interface imposed with a surface tension in the Cassie-Baxter mode. To overcome the difficulty of numerically computing the second-order derivative of the external surface, two partial differential equation filters are sequentially applied to the design variable of the base structure to ensure the numerical accuracy and feasibility of using an efficient linear-element-based finite element method to solve the Young-Laplace equation. To improve the performance of the hierarchical microtextures, the volume of the liquid bulges suspended at the liquid/vapor interface in the Cassie-Baxter mode, before the transition into the Wenzel mode, is minimized to optimize the match between the external surface of the base structure and the pattern of the secondary structures. In the topology optimization process, penalization of the material density of the surface tension is achieved by an artificial Marangoni phenomenon. In numerical examples, solid surfaces are tiled into textures with axial symmetry, radial symmetry, chirality, and quasiperiodicity; and structural units are derived consisting of base structures with peak shapes and dense secondary structures surrounding the crests of the peaks. The optimized performance of the derived structural units has been confirmed by comparisons.

Multilayered Balanced Dual-Band Bandpass Filter Based on Magnetically Coupled Open-Loop Resonators with Intrinsic Common-Mode Rejection

A new dual-band balanced bandpass filter based on magnetically coupled open-loop resonators in multilayer technology is proposed in this paper. The lower differential passband, centered at the Global Positioning System (GPS) L1 frequency, 1.575 GHz, was created by means of two coupled resonators etched in the middle layer of the structure, while the upper differential passband, centered at a Wi-Fi frequency of 2.4 GHz, was generated by coupling two resonators on the top layer. Magnetic coupling was used to design both passbands, leading to an intrinsic common-mode rejection of 39 dB within the lower passband and 33 dB within the upper passband. Simulation and measurement results are provided to verify the usefulness of the proposed dual-band differential bandpass filter.

Novel Differential Bandpass Filter Using Spoof Surface Plasmon Polaritons

In this article, a novel differential bandpass filter based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. It consists of a pair of double-layer SSPPs using double-sided parallel-strip line (DSPSL), a pair of single-layer SSPPs, and a 180° phase inverter. The transmission characteristics of the proposed SSPPs’ structure are analyzed by the differential-mode and common-mode method, and also applied to design the differential filter. To validate the design concept, a differential filter sample has been designed, fabricated, and measured. The simulated and measured results indicate a 3-dB fractional bandwidth of 25.5% (frequency 5.5 GHz), and a wide 20-dB common-mode suppression from 2.9 to 8 GHz can be achieved for the differential filter.

A wide linear range CMOS OTA and its application in continuous-time filters

In this paper, we have proposed a highly linear Operational Transconductance Amplifier (OTA) with wide linear input range. The proposed OTA utilizes conventional source degeneration with an auxiliary differential pair which increases the linear range significantly by reducing the distortion components. The proposed OTA is targeted for current mode circuit applications including low-frequency continuous time filters. A second-order fully differential filter architecture is also implemented by using this proposed OTA. The linear OTA and the filter are implemented in SCL 180 nm CMOS process technology with 1.8 V supply voltage. The proposed OTA achieves third order harmonic distortion ($${\textit{HD}}_3$$) of $$-\,74.3$$ dB, inter modulation distortion ($${\textit{IM}}_3$$) of $$-\,75.5$$ dB for $$600\,\hbox{mV}_{p-p}$$ differential input with 1 MHz signal frequency and a linear range of 0.9 V for 1% transconductance variation. The filter is designed for 100 kHz cutoff frequency and achieves $${\textit{HD}}_3$$ of $$-\,68.75$$ dB and $${\textit{IM}}_3$$ of $$-\,64.3$$ dB for $$300\,\hbox{mV}_{p-p}$$, 10 kHz input signal.

Daily GRACE satellite data evaluate short-term hydro-meteorological fluxes from global atmospheric reanalyses

Changes in terrestrial water storage as observed by the satellite gravity mission GRACE (Gravity Recovery and Climate Experiment) represent a new and completely independent way to constrain the net flux imbalance in atmospheric reanalyses. In this study daily GRACE gravity field changes are used for the first time to investigate high-frequency hydro-meteorological fluxes over the continents. Band-pass filtered water fluxes are derived from GRACE water storage time series by first applying a numerical differentiation filter and subsequent high-pass filtering to isolate fluxes at periods between 5 and 30 days corresponding to typical time-scales of weather system persistence at moderate latitudes. By comparison with the latest atmospheric reanalysis ERA5 of the European Centre for Medium-Range Weather Forecasts (ECWMF) we show that daily GRACE gravity field models contain realistic high-frequency water flux information. Furthermore, GRACE-derived water fluxes can clearly identify improvements realized within ERA5 over its direct predecessor ERA-Interim particularly in equatorial and temperate climate zones. The documented improvements are in good agreement with rain gauge validation, but GRACE also identifies three distinct regions (Sahel Zone, Okavango Catchment, Kimberley Plateau) with a slight degradation of net-fluxes in ERA5 with respect to ERA-Interim, thereby highlighting the potentially added value of non-standard daily GRACE gravity series for hydro-meteorological monitoring purposes.

Differential Kalman Filter Design for GNSS Open Loop Tracking

Global navigation satellite system (GNSS) positioning in an urban environment is in need for accurate, reliable and robust positioning. Unfortunately, conventional closed-loop tracking fails to meet the demand. The open loop tracking shows improved robustness, however, the precision is unsatisfactory. We propose a differential Kalman filter for open loop, of which the measurement vector contains the differential values of open loop navigation results between adjacent epochs. The differential Kalman filter makes use of the satellite geometry (i.e., spatial domain) and motion relationship (i.e., temporal domain) to filter frequency and code phase estimations of conventional open loop tracking. The improved performances of this architecture have been analyzed theoretically and demonstrated by road tests in an urban environment. The proposed architecture shows more than 50% accuracy improvement than the conventional open-loop tracking architecture.

Analysis of nonidealities of N‐path circuits using impulse response

SummaryThis paper presents a new method to analyze nonidealities of N‐path circuits. This method utilizes Fourier transform of the impulse response of an N‐path circuit in the time domain to calculate the transfer functions. The time domain analysis makes the method simple and intuitive. Instead of conventional sophisticated calculations, this method limits the analysis to some integral calculations. This analysis can take into account two common nonidealities: parallel capacitance and overlapping clocks. The accuracy of the analysis is verified by simulations for both cases. Further, the analysis has been expanded to differential filters.