Proposed Filter Structure Research Articles

A simple and modular quasi stepped impedance resonator based reconfigurable bandpass filter for 5G applications

A small-sized quasi-stepped impedance resonator (SIR) based single-band to dual-band reconfigurable bandpass filter is presented in this work. The proposed quasi-SIR filter is modular in nature and can be easily scaled to higher- or lower-frequency bands. To this end, a single- to dual-band reconfigurable modified SIR is designed. The designed reconfigurable resonator was then used to develop a single-band to dual-band reconfigurable filter. The proposed filter structure comprises two resonators loaded with PIN diodes to provide the switching. The filter allows switching between single and dual-band frequencies. In the OFF state, PIN diodes provide single-band resonance with a resonant frequency of 3.8 GHz. While the ON state of PIN diodes provides dual-band resonance of 3.35 GHz and 4.3 GHz. The structure of the filter is modular and is designed, analysed, and fabricated on a low-cost FR4 dielectric substrate with a 4.3 dielectric constant and 0.78 mm thickness. The measured results are in good agreement with the simulation results. The filter is designed to operate in the sub-6 GHz band, a designated band for 5G communication, and is thus suitable for incorporation in 5G devices with reconfigurability applications.

A Low-Power 30MHz ,6th Order Band-pass Differential Gm-C Filter on Chip Using Floating Current Source

A 30MHz center frequency, 6th order Butterworth and elliptic band-pass filter using a leap-frog Gm-C structure in this work. A continuous time differential voltage mode Gm-C biquad and its adjoin voltage - mode version are described, employing FCS (Floating Current Source) circuits as building blocks. The improved current source structure is simple and includes fewer transistors. This provides an effective use of the chip area and brings simplicity to the design of circuits. The proposed filter structure does not contain the resistor which is very important for integration. All capacitors in proposed filter are grounded which reduces the parasitic effects. The proposed filter has been successfully implemented by TSMC 0.18μm CMOS process. Simulation results are given to confirm the theoretical analysis.

First-Order Universal Active Filter Configuration Using Single VCII+

A new universal active filter configuration is presented in this paper which is capable of realizing all three first-order filter responses namely all pass (AP), low pass (LP) and high pass (HP) using a single second generation voltage conveyor (VCII+), a virtually grounded capacitor and two resistors. The proposed circuit offers tunability of the cut-off frequency, gain (for HP filter) and simultaneous availability of two filter outputs, one at a low impedance node (HP/AP), the other output, namely the LPF will require a voltage buffer to avoid loading. The nonideal analysis of filter responses based on the nonideal model of VCII+ is carried out by considering all the parasitic immittances and nonideal gains and found that they have no significant effect on the performance of the proposed filter structure. Sensitivity analysis with respect to active and passive components has also been carried out. The functionality of the presented circuit has been validated through simulations and experimental results, where the VCII+ was implemented using the macro model of the commercially available CFOA IC AD844. Additionally, the proposed circuit has been tested using a CMOS VCII+ implemented with 0.18[Formula: see text][Formula: see text]m TSMC technology parameters. The tests include advanced evaluations based on Monte Carlo simulations.

Design of a Three-Phase Three-Level Back-to-Back Bridge Interconnection-Based Filter Scheme

This article proposes a systematic design methodology for a back-to-back bridge structure to be used with three-phase bidirectional AC-AC converters (also called an active front end) feeding a motor with long unshielded cables. The bridge provides a path for circulating common-mode (CM) harmonics, resulting in low motor-bearing voltage, suppression of motor winding over-voltage, superior low-frequency conducted emissions attenuation, and wide band performance. The proposed filter structure is designed using simplified sets of derived analytical attenuation pertaining to different groups of harmonics. Consequently, each filter component is optimized for low weight using specific core materials depending on current-ripple content. Following the physical design, parasitic models for the converter, filter, motor, and long cables are developed in the time domain to allow prediction of CM and differential-mode (DM) voltages as well as reducing the filter’s impact on high-frequency emissions. The overall design methodology is validated through emissions characterization using a 12-kW rated three-level neutral point clamped (NPC) converter in a back-to-back configuration.

A robust sliding window adaptive filtering technique for phonocardiogram signal denoising

AbstractObjectiveThe digital sound recording of several heart sounds (HSs) is named phonocardiogram (PCG) signal. Analysing these PCG signals is essential for diagnosing diverse sorts of heart disorders. Nevertheless, owing to troubling surrounding noise signals, PCG signal recording is challenging. So, before utilising PCG for advanced processing, de‐noising the PCG signal is executed. A new sliding window adaptive noise cancellers (SWANC)‐centred filter technique is proposed in this paper for de‐noising along with recovering the PCG signal effectively.MethodUtilising the least mean square (LMS), an SW optimum adaptive filter (AF) structure is introduced in this work for estimating a De‐noised signal (DS) with better accuracy. Here, via the SWAF stage, a noisy signal is processed. An SW of fixed duration slides over the signal; also, the signal is filtered utilising the AF in each window. Utilising this SWAF architecture, this method approximates the PCG signal's clean version with better accuracy.ResultsThe proposed robust SWAF is analogized to experimental PCG signals that were corrupted by Gaussian noise (GN) together with pink noise (PN) with distinct noise levels (NLs). From the physionet database, the experiential data are acquired. The outcomes exhibited that a remarkable performance was attained by the robust SWAF model.DiscussionA 2–10 times decrease in MSE values was attained by the proposed filter structure when analogized with conventional LMS filter configuration. Further, the SNR is improved by 3 times and comparatively, the PSNR enhancement was 4%–25%. The association betwixt the clean signal along with its estimate is greater than 0.92.ConclusionA cost‐efficient hardware installation of ANC with higher accuracy was offered by the SW LMS AF model. For obtaining desired convergence speed and accuracy, such models are tested for real‐time performances in the future.

Linear assistance filter design for electric power steering systems with improved delay margin

This paper studies the achievable delay margin using lead-lag filter structures for Electric Power Steering systems. We propose an approximation of the delay margin as an explicit function of filter parameters. Our results provide useful guidelines for adjusting the different filter parameters to ensure system stability in the presence of a time delay. Simulation results show that the proposed filter structures can attenuate vibrations and improve steering feel and road feel. As a consequence, the influence of the delay on the system can be minimised with little performance degradation.

Resonator Reuse Approach for Implementing Narrowband Bandpass–Bandstop Cascade Based on Mode Orthogonality

This brief is to present a resonator reuse approach in implementing a high-attenuation notch next to a passband. Each resonator is utilized twice in producing bandpass and bandstop responses at the same time, which leads to size reduction. The filter structure employs cylindrical cavity resonators and utilizes the two orthogonal TM110 modes in each cavity resonator. The proposed filter has an excellent insertion loss since the TM110 mode has a high unloaded Q-factor. For verifying the proposed filter structure, we have designed and fabricated a second-order waveguide filter having a second-order bandpass-bandstop filter cascade response.

Resistorless First-Order Universal Filter Structures Employing OTAs with Independent Controllability of Gain and Pole Frequency

This communication presents two new first order universal active filter configurations employing operational transconductance amplifiers (OTA) and use grounded capacitor which is prominently suitable for integrated chip (IC) fabrication. One of the proposed topologies provides voltage mode (VM) and transconductance mode (TCM) of operations while the other circuit provides current mode (CM) in addition with transresistance mode (TRM) filter functions. All three first order filter functions namely low pass filter (LPF), high pass filter (HPF) and all pass filter (APF) are configurable with appropriate choice(s) of input voltage/current signals. An equal transconductor condition (which can be easily achieved) is required for the realization of APF functions. The proposed filter configurations possess high input impedance and high output impedance and also offer independent electronic tunability of pole frequency/cut-off frequency. The gain of filters realized in VM, TCM and TRM has independent electronic tunability feature and can be adjusted through transconductor. For the usability of proposed filters, multi-phase sinusoidal oscillator has also been demonstrated. To assure the workability of the proposed filter structures, PSPICE simulations with CMOS OTA implemented in 0.18 µm TSMC technology parameters has been used. Various simulation results including Monte-Carlo simulations, process corner analysis, total harmonic distortions (%THD) and temperature analysis have also been appended. Experimental results employing off-the-shelf IC LM13700 type OTAs have also been included to verify the theoretical propositions of first order universal filters and multiphase sinusoidal oscillators.

Broadband dual‐band bandstop filters based on step‐impedance stubs and transmission‐line networks

In this paper, a novel basic structure of a dual-band bandstop filter (DBSF) without coupled lines is proposed. In order to improve the performance, some optimizations are made to the basic structure, and two DBSF structures with multi-transmission zeros and multi-transmission poles are obtained. These filters have the advantages of simple structure, high selectivity, and high stopband rejection, among which the deepest stopband can be better than 45 dB. In addition, an extraction method of transmission zeros and transmission poles based on the S-parameter theory is proposed. The ideal 3-dB fractional bandwidths of the basic structure are 37.8% and 18.7%, respectively, 54.1% and 25.9% for the first improved structure, respectively, and 75.1% and 34.2% for the second improved structure, respectively. EM simulation results and measured results are highly unified to verify the proposed filter structure.

A robust low-cost adaptive filtering technique for phonocardiogram signal denoising

ObjectivePhonocardiogram (PCG) represents the recordings of various heart sounds. To diagnose the different ailments of the heart, it is required to analyze these PCG signals. However, recording PCG signals is challenging since it is prone to surrounding noise signals. Therefore, there is a need to denoise the PCG signal before being used for advanced processing. This paper proposes an Adaptive Noise Cancellers-based filter model for effectively denoising and recovering the PCG signal. MethodThis work introduces an optimum adaptive filter structure for estimating a noise-free signal with high accuracy using Least Mean Square (LMS) algorithm. A noisy signal is processed through multiple adaptive filter stages connected in series in the proposed work. Multiple stages are automatically added, and each stage filter’s step size process is dynamically changed. The estimate of clean PCG signal approximated using this multistage cascaded adaptive filter architecture is subsequently used in the next module to recover the clean PCG signal with high accuracy. ResultsThe proposed robust multistage adaptive filter is evaluated for denoising synthetic and experimental PCG signals corrupted by Gaussian and pink noise of various input Signal to noise (SNR) levels. The experimental data are taken from the physionet database (Classification of Heart Sound Recordings: The PhysioNet/Computing in Cardiology Challenge 2016). The results demonstrate that the robust multistage filter model performs remarkably well. DiscussionCompared with various filter configurations, the proposed filter structure achieves an 8-50% reduction in MAE values and the 45–87% reduction in MSE values. Further, there is an improved SNR of 15–60%, ANR of 15–65%, and PSNR improvement by 7–25% comparatively. The correlation between the clean signal and its estimate obtained using the proposed filter model is more than 0.99. ConclusionUsing an LMS adaptive filter in the proposed filter model offers a cost-effective hardware implementation of Adaptive Noise Canceller with high accuracy. In the future, the suggested robust multistage adaptive filter model can be tested for real-time performance when improved convergence speed and accuracy are desired.

CMOS Compatible First-Order Current Mode Universal Filter Structure and its Possible Tunable Variant

A novel first-order universal filter structure supporting current mode operation is proposed in this paper. The filter has a single active building block based realization and utilizes an extra-X second-generation current conveyor as an active building block. Additionally, the proposed circuit employs a grounded resistor and a grounded capacitor as passive components. The circuit has the ability to deliver the all-pass, high-pass, and low-pass functionalities simultaneously without meeting any passive components matching constraint. High output impedance and load insensitive outputs are other remarkable signal processing features offered by the proposed filter structure. Theoretical behavior of the proposed filter is described by presenting ideal, non-ideal, parasitic, and stability analyses. Additionally, the resistorless variant of the proposed filter is also shown to impart the tunability feature. Personal simulation program with integrated circuit emphasis (PSPICE) simulation results are presented to verify the theoretically described performance of the proposed universal filter. Complementary metal oxide semiconductor (CMOS) realization of extra-X second-generation current conveyor is utilized for the purpose of simulations, therefore, the filter is CMOS compatible.

Mixed-Mode Electronically-Tunable First-Order Universal Filter Structure Employing Operational Transconductance Amplifiers

In this paper, a new mixed-mode first-order universal filter configuration is presented that employs three operational transconductance amplifiers (OTAs) and one grounded capacitor (eminently suitable for IC chip fabrication). All three first-order generic filter functions, namely low pass filter (LPF), high pass filter (HPF) and all pass filter (APF) in all the four possible modes, namely voltage mode (VM), current mode (CM), transresistance mode (TRM) and transconductance mode (TCM) can be realized. The proposed configuration offers high input impedance and high output impedance. The pole frequency of the filter can be controlled electronically by varying a single transconductance. Nonideal analysis of the proposed filter structure has also been carried out and the results have been compared with those obtained from ideal analysis. The performance of the presented filter configuration has been corroborated through PSPICE simulations as well as experimental results. The various simulation and experimental results validate the practical viability of the proposed configurations.

A Low-Cost Multistage Cascaded Adaptive Filter Configuration for Noise Reduction in Phonocardiogram Signal.

Phonocardiogram (PCG), the graphic recording of heart signals, is analyzed to determine the cardiac mechanical function. In the recording of PCG signals, the major problem encountered is the corruption by surrounding noise signals. The noise-corrupted signal cannot be analyzed and used for advanced processing. Therefore, there is a need to denoise these signals before being employed for further processing. Adaptive Noise Cancellers are best suited for signal denoising applications and can efficiently recover the corrupted PCG signal. This paper introduces an optimal adaptive filter structure using a Sign Error LMS algorithm to estimate a noise-free signal with high accuracy. In the proposed filter structure, a noisy signal is passed through a multistage cascaded adaptive filter structure. The number of stages to be cascaded and the step size for each stage are adjusted automatically. The proposed Variable Stage Cascaded Sign Error LMS (SELMS) adaptive filter model is tested for denoising the fetal PCG signal taken from the SUFHS database and corrupted by Gaussian and colored pink noise signals of different input SNR levels. The proposed filter model is also tested for pathological PCG signals in the presence of Gaussian noise. The simulation results prove that the proposed filter model performs remarkably well and provides 8–10 dB higher SNR values in a Gaussian noise environment and 2-3 dB higher SNR values in the presence of colored noise than the existing cascaded LMS filter models. The MSE values are improved by 75–80% in the case of Gaussian noise. Further, the correlation between the clean signal and its estimate after denoising is more than 0.99. The PSNR values are improved by 7 dB in a Gaussian noise environment and 1-2 dB in the presence of pink noise. The advantage of using the SELMS adaptive filter in the proposed filter model is that it offers a cost-effective hardware implementation of Adaptive Noise Canceller with high accuracy.

Design of narrow bandwidth Si[formula omitted]N[formula omitted] stressor cladded cascaded IBG filter

In this paper design and performance estimation of a narrow-band optical filter operating at 1550 nm is presented. The narrowband filter consists of cascaded integrated Bragg grating (IBG) filters each having periodic Si3N4 cladding on silicon strip waveguide based on SOI platform. The filter design also includes the effect of stress, which is generated at the Si-Si3N4 interface on their optical performance. The design of the proposed filter for a set of target specifications such as centre wavelength, bandwidth (BW), extinction ratio (ER), insertion loss (IL), and side-lobe suppression ratio (SLSR) has been done using the conventional transfer matrix method (TMM) in absence of stress and also using a modified TMM (MTMM), which is suitable for filter designs in presence of stress. It has been demonstrated in this work that using cascaded IBG filters narrowband operation can be achieved along with wideband operation. The efficacy of the proposed filter structure has been demonstrated for two different 3-dB bandwidths of 15 nm and 1.6 nm. The study reveals that the filter, which is designed using conventional TMM for a set of target specifications, shows similar optical performance when estimated using finite-element method (FEM) in absence of stress. In presence of stress, conventional TMM method fails to design the cascaded IBG filter that shows dissimilar performance when analysed using FEM. Under stressed condition, the proposed MTMM is found to design the cascaded IBG filter effectively exhibiting similar performance when tested using FEM. The study reveals that in presence of stress the MTMM can design filter, which offers deviation of <5.8%, <4.97%, <0.01% and <6.3% for ER, BW, resonance wavelength and side-lobe suppression ratio, respectively; from the FEM estimated filter performance, for a given set of targeted specifications.

Compact dual-mode microstrip bandpass filter based on slotted square patch resonator

PurposeThe purpose of this paper is to present the design of a compact microstrip bandpass filter (BPF) in dual-mode configuration loaded with cross-loop and square ring slots on a square patch resonator for C-band applications.Design/methodology/approachIn the proposed design, the dual-mode response for the filter is realized with two transmission zeros (TZs) by the insertion of a perturbation element at the diagonal corner of the square patch resonator with orthogonal feed lines. Such TZs at the edges of the passband result in better selectivity for the proposed BPF. Moreover, the cross-loop and square ring slots are etched on a square patch resonator to obtain a miniaturized BPF.FindingsThe proposed dual-mode microstrip filter fabricated in RT/duroid 6010 substrate using PCB technology has a measured minimum insertion loss of 1.8 dB and return loss better than 24.5 dB with a fractional bandwidth (FBW) of 6.9%. A compact size of 7.35 × 7.35 mm2 is achieved for the slotted patch resonator-based dual-mode BPF at the center frequency of 4.76 GHz. As compared with the conventional square patch resonator, a size reduction of 61% is achieved with the proposed slotted design. The feasibility of the filter design is confirmed by the good agreement between the measured and simulated responses. The performance of the proposed filter structure is compared with other dual-mode filter works.Originality/valueIn the proposed work, a compact dual-mode BPF is reported with slotted structures. The conventional square patch resonator is deployed with cross-loop and square ring slots to design a dual-mode filter with a square perturbation element at its diagonal corner. The proposed filter exhibits compact size and favorable performance compared to other dual-mode filter works reported in literature. The aforementioned design of the dual-mode BPF at 4.76 GHz is suitable for applications in the lower part of the C-band.

SVM-Based Switching Filter Hardware Design for Mixed Noise Reduction in Digital Images Using High-Level Synthesis Tools

Impulse and Gaussian are the two most common types of noise that affect digital images due to imperfections in the imaging process, compression, storage and communication. The conventional filtering approaches, however, reduce the image quality in terms of sharpness and resolution while suppressing the effects of noise. In this work, a machine learning-based filtering structure has been proposed preserves the image quality while effectively removing the noise. Specifically, a support vector machine classifier is employed to detect the type of noise affecting each pixel to select an appropriate filter. The choice of filters includes Median and Bilateral filters of different kernel sizes. The classifier is trained using example images with known noise parameters. The proposed filtering structure has been shown to perform better than the conventional approaches in terms of image quality metrics. Moreover, the design has been implemented as a hardware accelerator on an FPGA device using high-level synthesis tools.

High throughput and energy efficient linear phase FIR filter architectures

High throughput, low complex and energy efficient linear phase FIR filter structures with low latency are highly desirable for most of the portable signal processing applications. Improving the throughput and energy efficiency while ensuring low latency and complexity is a difficult problem due to the trade-off between performance metrics. To this end, the design of linear phase filter based on the application of retiming and pipelining is proposed. The CPD, PDP, ADP and ELT of the proposed 16-tap linear phase FIR filter is reduced by 64.83%, 80.1%, 61.58%, and 62.49% respectively in comparison with FIR filter using flexible retiming and by 18.29%, 30.99%, 16.56%, and 12.82% respectively in comparison with the recent retiming based high throughput FIR filter. The 16-tap ECG denoising filter developed from the proposed filter structure provides excellent performances in terms of CPD, PDP, ADP and ELT as the algorithmic transformations are applied to an exact multiplier-less linear phase filter structure. It filters out PLI of 50 Hz, its harmonics and high frequency noises while providing improved denoising performances. The CPD, PDP, ADP and ELT of the proposed multiplier-less ECG denoising filter is reduced by 82.44%, 97.55%, 93.51%, and 81.27% respectively in comparison with a typical 17-tap FIR notch filter and by 70.06%, 99.82%, 99.68%, and 98.12% respectively in comparison with a typical Bartlett window based 256-tap FIR notch filter. Structural model VHDL coding is used for developing filters. For synthesis, Cadence software with gpdk 45 nm standard cell library is used and for simulation modelsim is used.

Combination of HP and LP filters for narrow band antialiasing filter

Abstract The discrete time signal processing requires an anti-aliasing filter at the input and a reconstruction filter at output. Some filters of biquads structure are characterized by a decreasing of the attenuation at high frequencies, caused by the final value of the output resistance of the operational amplifier. In this paper we discuss a design of combined BP filter without mentioned decrease. The proposed filter structure was verified by SPICE simulation.

A microstrip quasi-elliptic bandpass filter implemented using stub loaded resonators

A highly selective microstrip bandpass filter consists of electromagnetically coupled U-shaped open ring resonators is presented in this paper. The resonators are directly loaded with open-circuited inductive stubs and the feed-lines are interdigital coupled to the resonators. The proposed filter structure provides sufficient degree of freedom to control the centre frequency, fractional bandwidth and transmission zeros. It is shown that the fractional bandwidth of this filter can be adjusted from 15.3 to 9.8% and center frequency from 3.3-3.8 GHz with negligible effect on the stopband characteristics. In addition, the transmission zero f tz2 can be relocated from 3.8 to 4.4 GHz and f tz1 from 3.1 to 2.7 GHz independently. Filter structure is simple, easy and economical to manufacture as fabricated on a conventional dielectric substrate using standard PCB technology. It is found that the simulation and measured results are in good correlation. The sharp selectivity, low losses and wide stop band characteristics make the proposed filter applicable in cognitive radio systems and in high interference environments.

Miniaturized quad‐band filter with improved selectivity using split ring resonators and metallic strips

A miniaturized bandpass filter of quad-band response with high selectivity is reported in this paper. The developed filter utilizes two sets of symmetric open-ended split-ring resonators (SRR), L-shaped and C-shaped strips along with rectangular stubs. Initially, open-ended SRR is connected with a C-shaped metallic strip to serves as a dual passband filter. Then by adding another SRR along with L-shape metallic strip and rectangular stub, it was converted into triple band and quad-band respectively. The operating frequency of the proposed filter structure can be controlled with the variation in the length ratio of resonators. In addition, transmission zero can be increased because of coupling between source/load and resonators which improves selectivity. The quad-band bandpass filter operates at 0.6/1.1/2.25/3.1 GHz, along with 3-dB fractional bandwidths of 17.9% (0.56-0.67 GHz), 17.7% (1.03-1.23 GHz), 5.8% (2.20-2.33 GHz), and 13.3% (2.88-3.29 GHz). It offers compactness with an electrical footprint area of 0.11λg × 0.10λg (23.5 mm × 21.0 mm) without feedline, where λg denotes the guided wavelength at 0.6 GHz. The measured and simulated outcomes were in virtuous correlation.