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Distortions of electrocardiograms (ECGs) caused by mandatory high-pass and low-pass analog RC filters in ECG devices are always present. The fidelity of the ECG waveform requires limiting the RC cutoff frequencies of the diagnostic (0.05–150 Hz) and monitoring systems (0.5–40 Hz). However, the use of fixed frequency bands is a compromise between enhanced noise immunity and ECG distortions. This study aims to propose active inverse high-pass and low-pass filters which are able to compensate for distortions in digital recordings of RC-filtered ECGs, thereby overcoming the limitations imposed by analog filtering. A new straightforward design of an inverse high-pass filter (IHPF) uses an integrator as the forward-path gain block, with a feedback loop containing an active digital filter equivalent to the analog RC high-pass filter. In contrast, the inverse low-pass filter (ILPF) employs a constant-gain block in the forward path to ensure stability and prevent phase delay, while its feedback path features an active digital counterpart of the RC low-pass filter. Second-order inverse filters are created by cascading two first-order stages. The proposed filters were validated according to essential performance requirements for electrocardiographs. The low-frequency (impulse) responses of IHPFs with cutoff frequencies of 0.05–5 Hz exhibit no overshoot and undershoot by magnitudes of 0.1–25 µV, well within the ±100 µV compliance limit defined for a test rectangular pulse (3 mV, 100 ms). The high-frequency responses of ILPFs with cutoff frequencies of 10–150 Hz present a relative amplitude drop of only 0.2–2.5%, far below the 10% limit for peak amplitude reduction of a triangular pulse (1.5 mV) with 20 ms vs. 200 ms widths. For any of the eight ECG leads (I, II, and V1–V6) available in the standard signal (ANE20000), the IHPF (0.05–5 Hz) presents ST-segment deviations <5 μV (within the ±25 μV limit) and R- and S-peak deviations <±3.5% (within the ±5% limit). The ILPF (10–150 Hz) preserves R- and S-peak amplitudes with deviations less than −1%. Diagnostic-level recovery of ECG waveforms distorted by first- and second-order analog RC filters in ECG devices is possible with the innovative and comprehensive inverse filter design presented in this study. This approach offers a significant advancement in ECG signal processing, effectively restoring essential waveform components even after aggressive, noise-robust analog filtering in ECG acquisition circuits. Although validated for ECG signals, the proposed inverse filters are also applicable to other biosignal front-end circuits employing RC coupling.

In the last decade, the proactive diagnosis of diseases with artificial intelligence and its aligned technologies has been an exciting and fruitful area. One of the areas in medical care where constant monitoring is required is cardiovascular diseases. Arrhythmia, one of the cardiovascular diseases, is generally diagnosed by doctors using Electrocardiography (ECG), which records the heart’s rhythm and electrical activity. The use of neural networks has been extensively adopted to identify abnormalities in the last few years. It is found that the probability of detecting arrhythmia increases if the denoised signal is used rather than the raw input signal. This paper compares six filters implemented on ECG signals to improve classification accuracy. Custom convolutional neural networks (CCNNs) are designed to filter ECG data. Extensive experiments are drawn by considering the six ECG filters and the proposed custom CCNN models. Comparative analysis reveals that the proposed models outperform the competitive models in various performance metrics.

The use of a filter bank of IIR filters for the spectral decomposition and analysis of signals has been popular for many years. As such, a new filter-bank resonator-based structure, representing an extremely hardware-efficient structure, has received a good deal of attention. Recently, multiple-resonator (MR)-based and general cascaded-resonator (CR)-based filters have been proposed. In comparison to single-resonator-based analyzers, analyzers with a higher multiplicity of resonators in the cascade provide lower side lobes and a higher attenuation in stopbands. In previous works, it was shown that the CR-based filter bank with infinite impulse response (IIR) filters, which is numerically more efficient than one with finite impulse response (FIR) filters, is suitable for dynamic harmonic analysis. This paper uses the same approach to design complex digital filter banks. In the previous case, the optimization task referred to the frequency responses of harmonic filters. In this work, the harmonic filters of the mother filter bank are reshaped so that the frequency response of the sum (or difference, depending on the parity of the number of resonators in the cascade) of two adjacent harmonic filters is optimized. This way, an online adaptive filter base can be obtained. The bandwidth of the filters in the designed filter bank can be simply changed online by adding or omitting the output signals of the corresponding harmonics of the mother filter.

Many signal processing applications require digital filters with variable frequency characteristics, especially the filters with variable bandwidth and center frequency. Due to their linear phase and inherent stability, finite impulse response (FIR) filters are the popular choice in the majority of the applications. Once a variable cutoff frequency (VCF) FIR lowpass filter is designed, variable bandwidth and center frequency filters with bandpass/highpass/bandstop response and reconfigurable filter banks can be realized from the same. In this paper, we present a comprehensive review of the existing variable cutoff frequency FIR filter design techniques, including the developments in the recent two decades. We provide the basic concepts, design, and architectural details for each of these techniques and the significant developments/incremental works thereof. Qualitative, as well as quantitative comparisons, are provided to assist the reader in choosing the most suitable VCF filter design technique for a particular application.

It is known that the class of hoops is ideally determined, in the sense that every filter of any hoop is a 1‐class of a unique congruence relation on . This confirms that every filter in a hoop determines one and only one quotient structure. So, given a hoop and a filter π of , it is natural to question ourselves what should be the defining properties of π so that the quotient is a join hoop (respectively, a Wajsberg hoop, cancellative hoop, and an MV‐algebra) and what should be the property of π such that is a subdirectly irreducible. In this paper, we answer these questions by introducing some new types of filters in hoops called J ‐filters, w ‐filters, MV‐filters, c ‐filters, and completely prime filters, respectively.

The demand for filters is increasing as the frequency bands for 5G expand. RF filters become the segment with the largest market share of RF front-end chips. More crowded frequency bands, as well as thinner and lighter communication equipment, necessitate higher filter performance. In this paper, several technologies for the implementation of Radio Frequency filter are presented. Essentially three types are considered: (i) Lumped Element (LC) Filter and Integrated Passive Devices (IPD) technology; (ii) Acoustic Wave Filter; and (iii) a composite filter design that combines acoustic and IPD technologies. Benefits and drawbacks of these diverse configurations in terms of their technical performance and current applications are examined, and several models are presented and simulated using ADS software.

This paper considers the filtering problem for a class of multi-input multi-output systems with nonlinear time-varying uncertain dynamics, random process and measurement noise. An extended state based Kalman filter, with the idea of timely estimating the unknown dynamics, is proposed for better robustness and higher estimation precision. The stability of the proposed filter is rigorously proved for nonlinear timevarying uncertain system with weaker stability condition than the extended Kalman filter, i.e., the initial estimation error, the uncertain dynamics and the noises are only required to be bounded rather than small enough. Moreover, quantitative precision of the proposed filter is theoretically evaluated. The proposed algorithm is proved to be the asymptotic unbiased minimum variance filter for constant uncertainty. The simulation results of some benchmark examples demonstrate the feasibility and effectiveness of the method.

A class of balanced dual-band bandpass filters (BPFs) with planar transversal-signal-interference coupled-line sections is reported. In their building balanced dual-band BPF stage under differential-mode excitation, a second-order quasi-elliptic-type dual-band bandpass filtering transfer function is obtained. Specifically, from the transversal interaction among their two open-ended and virtually-short-ended half-wavelength coupled-line paths, sharp-rejection differential-mode dual passbands with several out-of-band transmission zeros at both sides are realized. To attain high common-mode suppression levels within the differential-mode passbands, two open-ended line segments are connected at the symmetry plane of the devised balanced dual-band BPF stage. Moreover, higher-order schemes based on in-series-cascaded multi-stage designs to further increase differential-mode selectivity and in-band common-mode rejection are illustrated. The operational principles and parametric-analysis design rules of the engineered transversal-coupled-line-based balanced dual-band BPF approach are detailed. Additionally, for a rigorous interpretation of their zero/pole characteristics, a digital-modeling framework is applied to them to connect RF balanced filters with their discrete-time versions. For practical-validation purposes, a microstrip prototype of two-stage/fourth-order balanced dual-band BPF is built and tested. It exhibits measured differential-mode dual passbands with center frequencies of 1.464 GHz and 2.294 GHz, 3-dB fractional bandwidths of 8.74% and 9.68%, and in-band common-mode rejection levels above 23.16 dB and 31.36 dB, respectively.

With the rapid development of electronic technology, the filter circuit has been widely used in various occasions. Therefore, based on the study of various analog filter circuit principles, this paper users the Multisim simulation platform to design the corresponding low-pass and band-pass filters. In order to verify the performance of the filter circuit, the normal signal, noise signal and filter output signal are respectively observed by oscilloscope after noise is introduced, and then the performance is analyzed according to the waveform and parameters. The experimental results show that all the designed filters can achieve good filtering effect.

A novel efficient and enhanced combinational window family is proposed for developing the prototype filter for a two-channel quadrature mirror filter bank, where the gradient-based optimization technique is employed to minimize the distortions in amplitude. The filter bank design issue is formulated to build a low pass prototype filter with optimum responses in passband and stopband region, with filter coefficient at quadrature frequency ( π /2) being ( 1 / 2 ) . The prototype filter is designed with the proposed combinational window function, whose frequency at cut-off is altered iteratively by a gradient-based optimization algorithm. Upon realization of convergence, the reconstruction error in the analysis filter bank is minimized. The proposed design significantly reduces peak reconstruction error with better tail-end attenuation when compared with other existing combinational windows along with reduction in computational time. The results of several design examples have been simulated, and they validate the improved and efficient design of the proposed window design over other combinational windows optimized with the computationally efficient proposed algorithm.