Showing papers on "Low-pass filter published in 2018"
TL;DR: A single-channel single lead ECG based MI diagnostic system validated using noisy and clean datasets and yields an accuracy of 99.74% using 10-fold cross validation (CV) technique, which can be installed in clinics for detecting MI.
87 citations
TL;DR: Improvement in ramp-rate based algorithms, application of dual energy storage for large solar photovoltaic plant, and regulation in control of solar photvoltaic ramp-rates is suggested in this paper, which will contribute to decrease in energy storage’s capacity and degradation, and increase in its operation life.
Abstract: Solar photovoltaic generator is an intermittent source and mitigating its output power ramp-rate is crucial as they threaten the stability of the utility grid. This paper is aimed at bringing out the latest comprehensive review on different ramp-rate control smoothing methods under three broad classifications: (i) moving average and exponential smoothing based methods, (ii) filter based methods, and (iii) ramp-rate based algorithms. Application of moving average and low pass filter from filter based methods is widely chosen by the researchers for solar photovoltaic ramp-rate control. Therefore, a detailed analysis on these methods supported by simulation results is carried out to analyze the capability of these methods to control the solar photovoltaic ramp-rate. On application of these methods, it was found that there will be an increase in the energy storage’s degradation and size. In addition, reduction in energy storage’s operating life can also be found. Later, a detailed comparison on different techniques are summarized in the discussion section, from which it was found that the ramp-rate based algorithms are advantageous than moving average and filter based method. The advantages of the ramp-rate based algorithms are discussed as well. In addition, the disadvantages of the existing ramp-rate based algorithms are also highlighted. Finally, the necessitate for, (i) improvement in ramp-rate based algorithms, (ii) application of dual energy storage for large solar photovoltaic plant, and (iii) regulation in control of solar photovoltaic ramp-rates is suggested in this paper. These suggestions will contribute to decrease in energy storage’s capacity and degradation, and increase in its operation life.
67 citations
TL;DR: The proposed GSA based FOLBFs consistently achieve the best solution quality with the fastest convergence rate as compared with the designs based on Real coded Genetic Algorithm (RGA) and Particle Swarm Optimization (PSO).
57 citations
TL;DR: In this article, a low pass filter is used for interconnection of inverter to the grid which is mainly LCL filter and depending on control way, there are four control strategies.
Abstract: This paper deals with the modeling and control of the grid-connected photovoltaic (PV) inverters. In this way, the paper reviews different possible control structures that can be used for grid-connected inverters and then examines their capabilities. The controllers that are used are classic PI controllers and inverter is working in current control mode. A low pass filter is used for interconnection of inverter to the grid which is mainly LCL filter and depending on control way, there are four control strategies. In this paper, at first, control design methodology for each strategy is proposed and then performance comparison between these strategies is carried out. The performance analysis is carried out from different point of view such as grid voltage disturbance rejection and stability under different grid short circuit levels. The inverter output impedance is used as a criterion for inverter performance evaluation which has an important role in grid voltage disturbance rejection and system stability in different grid short circuit levels. Finally the best strategy will be introduced by using the simulation results in Matlab/Simulink software.
53 citations
50 citations
TL;DR: The equivalence between secondary control and wash out filter-based power sharing strategy for islanded MG is demonstrated, and the generalized washout filter control scheme has been obtained.
Abstract: As a supplement of the droop control, the concept of secondary controlled microgrid (MG) has been extensively studied for voltage and frequency restoration. However, the low band-width communication (LBC) channels are needed to exchange information between the primary and secondary controllers, and the performance of the secondary controller degrades due to the uncertain communication delay and data drop-out in the LBC lines. Recently, a washout filter-based power sharing method was presented without communication lines and additional control loops. In this paper, the equivalence between secondary control and washout filter-based power sharing strategy for islanded MG is demonstrated, and the generalized washout filter control scheme has been obtained. Additionally, the physical meaning of control parameters of secondary controllers is also presented. Besides, a complete small-signal model of the generalized washout filter-based control method for islanded MG system is built, which can be utilized to design the control parameters and analyze the stability of MG system. Finally, extensive simulation and experimental results are provided to confirm the validity and effectiveness of the derived equivalent control scheme for islanded MG.
48 citations
TL;DR: A new method is proposed for arc detection in the pantograph–catenary system based signal processing and S-transform and the real-time processing of the proposed method is examined by applying to the current signal received from a locomotive.
Abstract: pantograph–catenary system is one of the critical components used in electrical trains. It ensures the transmission of the electrical energy to the train taken from the substation that is required for electrical trains. The condition monitoring and early diagnosis for pantograph–catenary systems are very important in terms of rail transport disruption. In this study, a new method is proposed for arc detection in the pantograph–catenary system based signal processing and S-transform. Arc detection and condition monitoring were achieved by using current signals received from a real pantograph–catenary system. Firstly, model based current data for pantograph–catenary system is obtained from Mayr arc model. The method with S-transform is developed by using this current data. Noises on the current signal are eliminated by applying a low pass filter to the current signal. The peak values of the noiseless signals are determined by taking absolute values of these signals in a certain frequency range. After the data of the peak points has been normalized, a new signal will be obtained by combining these points via a linear interpolation method. The frequency-time analysis was realized by applying S-transform on the signal obtained from peak values. Feature extraction that obtained by S-matrix was used in the fuzzy system. The current signal is detected the contdition as healthy or faulty by using the outputs of the fuzzy system. Furthermore the real-time processing of the proposed method is examined by applying to the current signal received from a locomotive.
46 citations
TL;DR: In this article, the authors proposed a method to compute the optimum capacitance requirement of the LCL -filter based on reactive power compensation of the filter rather than calculating it as a percentage of base capacitance.
Abstract: LCL -filter is among the best performing filters for grid-connected voltage source inverters Designing of the filter parameters (grid-side and inverter-side inductors and capacitor), takes an iterative approach due to the coherence between the parameters and design requirements such as IEEE-519 Std for harmonic current limitations, reactive power compensation limit, and maximum allowable voltage drop across the filter to limit the switching losses Most of the proposed LCL -filter optimization strategies emphasize on reducing the total inductance and losses of the filter while meeting the design requirements There is less emphasis given on the capacitor selection and optimizing its value Therefore, this paper proposes a method to compute the optimum capacitance requirement of the LCL -filter based on reactive power compensation of the filter rather than calculating it as a percentage of base capacitance of the filter as found in the literature The proposed design methodology compared to the previously proposed designs is capable of reducing filter capacitance by 50% while meeting the harmonic limitation demanded by IEEE-519 Std and also considers the impact of the total inductance on reactive power compensation Based on the proposed methodology an LCL -filter with minimum total inductance and capacitance is realized Functionality of the proposed LCL -filter is verified and validated through simulations and experimental results
44 citations
TL;DR: In this paper, a package integration of 5G filters with ultrashort 3D interconnects allows for low interconnect losses that are similar to that of on-chip filters, but low component insertion loss of off-chip discrete filters.
Abstract: Package-integrated and ultra-thin low-pass filter (LPF) and bandpass filter (BPF) with footprint smaller than $0.5\lambda _{0}\times 0.5\lambda _{0}\times 0.025\lambda _{0}$ at the operating frequencies of 28- and 39-GHz bands are presented for 5G and mm-wave small-cell application. Such package integration of 5G filters with ultrashort 3-D interconnects allows for low interconnect losses that are similar to that of on-chip filters, but low component insertion loss of off-chip discrete filters. These thin-film filters exhibit a cross-sectional height of $188.5~\mu \text{m}$ and can be utilized either as embedded components or integrated passive devices in module packages. Three topologies of LPF and BPF in total are modeled, designed, and fabricated on precision thin-film buildup layers on glass substrate as a core. Large-area panel-compatible semiadditive patterning (SAP) process is utilized to form high-precision topologies to aid the low-cost fabrication of ultraminiaturized filters. SAP also enables the realization of ultra-thin traces to precisely model high-impedance inductive lines compared to conventional subtractive etching and printing techniques. This results in filters with low insertion loss, low VSWR, and high selectivity. The simulated and measured results of filters show an excellent correlation.
43 citations
TL;DR: This paper presents a differential fourth-order low-pass filter suitable for electrocardiography (ECG) acquisition formed by cascading two compact and power-efficient biquads operating in the subthreshold region that performs comparably to the recent state-of-the-art nanowatt-class low- pass filter.
Abstract: This paper presents a differential fourth-order low-pass filter suitable for electrocardiography (ECG) acquisition. It is formed by cascading two compact and power-efficient biquads operating in the subthreshold region. Each biquad combines two capacitors and a flipped voltage follower circuit. The filter attains a cutoff frequency adjustable to cover the entire range of ECG (150–250 Hz). The filter prototype has been fabricated in a 0.35- $\mu \text{m}$ CMOS technology. It occupies an area of $362\,\,\mu \text {m} \times 466 \,\,\mu \text{m}$ and operates from a 0.6-V supply. Measurements confirm that the filter consumes 0.9-nW static power for a 101-Hz cutoff frequency and contributes the input-referred noise of 46.27 $\mu \text{V}_{\mathbf {rms}}$ . For a 60-Hz input frequency, the filter achieves a dynamic range of 47 dB where the third-harmonic distortion of −60 dB is produced. This leads to the figure of merit of $46.5 \times 10^{-18}$ J. When the chip area is also concerned, the proposed filter performs comparably to the recent state-of-the-art nanowatt-class low-pass filter.
42 citations
TL;DR: A model enabling a thorough analysis of the multisine-based WPT system focusing on the bandwidth of the signal and the rectifier is established, providing insight into the output voltage and power, as a function of the input waveform for different circuit models.
Abstract: The use of multisine signals to improve the efficiency of wireless power transfer (WPT) for low average received power was proposed recently. Several measurement-based studies illustrated the gain that can be achieved for different circuit or waveform instances, focusing on the impact of a time-varying amplitude on the rectifying efficiency. This paper first establishes a model enabling a thorough analysis of the multisine-based WPT system focusing on the bandwidth of the signal and the rectifier. This model enables a codesign of signal and rectifier for optimal WPT. The proposed model provides insight into the output voltage and power, as a function of the input waveform for different circuit models. By including the input matching and the clamper, our model is generic and can include a wide range of rectifiers with different voltage multiplication approaches. The key insight gained from our analysis is that there is a tradeoff between the frequency spacing of the tones of the multisine signal and the cut-off frequency of the low-pass RC filter, as a main property of the rectifier circuit. Our model predicts the measured power conversion efficiency and voltage with an error below 0.1 and 0.2 V, respectively.
TL;DR: A compact power-efficient CMOS buffer to operate as a nanopower lowpass biquadratic cell that attains a near 0-dB passband gain without gain compensation and consumes the least power from the lowest supply voltage is developed.
Abstract: This paper develops a compact power-efficient CMOS buffer to operate as a nanopower lowpass biquadratic cell. Unlike other recently reported CMOS biquads with passband gains that are attenuated by the bulk effect, this biquad attains a near 0-dB passband gain without gain compensation. It acquires the same levels of input and output common-mode voltages making it useful for cascade realization of a higher order lowpass filter. To demonstrate the potential application of the proposed biquad, a fourth-order lowpass filter was designed based on the proposed biquad circuit and fabricated in the 0.35- ${\mu }\text{m}$ CMOS process to serve electrocardiography readout systems. Measurement results show that the filter consumes 4.26-nW static power from a 0.9-V supply providing a 100-Hz cutoff frequency. The prototype chip occupies a silicon area of 0.11 mm2 and contributes an input-referred noise of $80.5~{\mu }\text{V}_{\mathrm {rms}}$ . For a 60-Hz input frequency associated with −50-dB third-order harmonic distortion, a dynamic range of 48.2 dB is achieved. The lowest power supply rejection ratio of 40 dB was obtained at 100 Hz. Compared with the previous state-of-the-art designs in the category of nanopower filters, the proposed filter consumes the least power from the lowest supply voltage.
TL;DR: In this article, the coefficients of three fractional-order low-pass transfer functions are presented to aid in the design of these filters based on their arbitrary quality factors, and the results are verified by PSpice simulation of a conveyor-based lowpass filter with fractional order of 1.5 and quality factor Q ǫ = 5.
Abstract: The coefficients of three fractional-order low-pass transfer functions are presented to aid in the design of these filters based on their arbitrary quality factors. These coefficients are found by minimizing the error between these fractional-order transfer functions and the second-order transfer function using numerical least squares optimization. Coefficients and design equations are presented for fractional-orders between one and two. Stability of the transfer functions with the presented coefficients is examined and possibilities of characteristic frequency shifting are shown. The results are verified by PSpice simulation of a conveyor-based low-pass filter with fractional order of 1.5 and quality factor Q = 5.
TL;DR: In this article, the authors proposed a two-stage digital finite impulse response (FIR) filter solution to compensate solar power intermittency and improve distribution grid power quality by optimizing the size of battery capacity for the desired level of solar power smoothing.
Abstract: A new method for the control of a battery energy storage system and its implementation on a 25 kW solar system to compensate solar power intermittency and improve distribution grid power quality is presented in this paper The novelty of the proposed method is to provide a systematic way to optimize the size of the battery capacity for the desired level of solar power smoothing This goal is achieved by designing a two-stage filter solution The first stage is a fast response digital finite impulse response (FIR) filter that makes a trade-off between smoothing of the solar output and battery capacity This paper proposes an optimal design of a minimum-length, low-group-delay FIR filter by employing convex optimization, discrete signal processing, and polynomial stabilization techniques The new strategy proposed in this paper formulates the design of a length- $N$ low-group-delay FIR filter as a convex second-order cone programming, which guarantees that all the filter zeros are inside the unit circle (minimum-phase) A quasi-convex optimization problem is formulated to minimize the length of the low-group-delay FIR filter The second-stage filter is designed to level the battery charging load The effectiveness and performance of the proposed approach is demonstrated by simulation results and also over a real-case implementation
TL;DR: In this article, a fractional order element (FOE) was realized by varying different fabrication parameters such as the percentage of carbon black, the curing temperature, and the solvent type.
Abstract: In this paper, Fractional Order Elements (FOEs), fabricated by using a carbon black nano structured dielectrics, are presented. FOEs have been realized by varying different fabrication parameters such as the percentage of carbon black, the curing temperature, and the solvent type. Results on the experimental frequency characterization of one FOE device are given. The FOE has been, then, used for demonstrating the possibility of realizing a fractional order RC filter. The frequency analysis of the RC filter shows the coherence of the fractional order between the FOE and corresponding RC circuit.
TL;DR: This study proposes an accurate and fast decouplings of fundamental frequency oscillations using a mathematic-cancellation decoupling cell that provides accurate synchronisation under any abnormal grid condition at the lowest computational complexity when compared with the existing state-of-the-art PLLs.
Abstract: The presence of direct current (DC) offset and harmonics–interharmonics (HIHs) in grid voltage input signal of phase-locked loop (PLL) results in inaccurate controller response. The inaccuracies are due to the low- and high-frequency oscillations that appear in the PLL estimated phase, amplitude and frequency. The suppression of fundamental frequency oscillations caused by DC offset (DO) in the input voltage signal must be carried out without compromising the dynamic response of the system. The use of low-pass filters, for example, results in undesirable, slow response. This study proposes an accurate and fast decoupling of fundamental frequency oscillations using a mathematic-cancellation decoupling cell. Higher-frequency oscillations generated by HIHs are eliminated by a different harmonic compensation network (HCN) that is also proposed in this study. The performance of conventional techniques is limited because they eliminate only specifically selected harmonics. The proposed PLL, however, eliminates any number of HIHs present in the grid with the least computational complexity and without any prior knowledge. Furthermore, its advanced features provide accurate synchronisation under any abnormal grid condition at the lowest computational complexity when compared with the existing state-of-the-art PLLs. The advanced performance of the proposed HIHDO-PLL is verified through simulation and experimental results.
TL;DR: A power-efficient operational-transconductance-amplifier-capacitor (OTA-C) filter for biomedical applications is presented with detailed noise analysis and reconfigurability and performance of the proposed filter is presented.
Abstract: A power-efficient operational-transconductance-amplifier-capacitor (OTA-C) filter for biomedical applications is presented with detailed noise analysis. This filter consists of a cascade of biquadratic sections, each of which is configured via a serial-peripheral-interface circuit embedded with non-volatile memories to provide low pass or bandpass response. All filter parameters, including the gains, natural frequency, and quality factor, are orthogonally adjustable by programming charges on floating-gate bias transistors. The reconfigurable biquadratic section is composed of four power-efficient linearized OTAs. Each OTA consists of complementary hextuple-diffusor-quadruple-differential-pairs (HDQDPs) and a floating-gate common-mode feedback scheme. A developed computer algorithm for transistor dimension optimization is adopted to extend the input linear range of the HDQDP based on nonlinearity cancellation. A prototype chip is designed and fabricated in a $0.35~ \mu {\mathrm{ m}}$ CMOS process to demonstrate reconfigurability and performance of the proposed filter. Each biquadratic section occupies $0.12{\mathrm{ mm}}^{2}$ with a frequency tuning range more than five decades. Measured spurious-free dynamic ranges (SFDR) at the low pass and bandpass outputs from one of the biquadratic sections are 52.6 and 54.55 dB, respectively, when the natural frequency is programmed at 2 kHz with power consumption of 107.2 nW. A fourth-order Chebyshev low pass and an eighth-order Butterworth bandpass responses are implemented with characterized SFDRs of 50.43 and 48.3 dB, respectively.
23 Oct 2018
TL;DR: A filter prototype comprised of parallel resonators and admittance inverters has been developed and has been applied to the design of a third-order absorptive filter with distributed-type of filter centered at 3 GHz with the fractional bandwidth of 0.1.
Abstract: In this paper, we present a design methodology for absorptive bandpass filters. A filter prototype comprised of parallel resonators and admittance inverters has been developed. All design parameters in the filter prototype are given in terms of the center frequency, the bandwidth, the port impedance, and the normalized lumped-element lowpass filter prototype values. The presented filter prototype has been applied to the design of a third-order absorptive filter with distributed-type of filter centered at 3 GHz with the fractional bandwidth of 0.1. It is shown that the theory, the circuit simulation, the full-wave simulation, and the measurement are in a good agreement.
26 Oct 2018
TL;DR: The hybrid control design provides more design freedom compared to the equivalent linear control design, which leads to a factor two improvement in low-frequency disturbance suppression of a state-of-the-art scanning stage of an industrial wafer scanner.
Abstract: In this paper a hybrid low-pass filter is developed and subsequently embedded in a PID-based control design. The hybrid element switches between gain and integrator mode, depending on the evaluation of specifically designed switching conditions. Given the properties of the hybrid low-pass filter, which are mainly expressed by reduced phase lag as compared to a linear-equivalent low-pass filter, the bandwidth of the PID-based control design can potentially be increased. Based on describing function analysis, this bandwidth increase is obtained while identical robustness properties of the closed-loop system in terms of bounds imposed on the closed-loop sensitivity function are guaranteed. In this sense, the hybrid control design provides more design freedom compared to the equivalent linear control design, which leads to a factor two improvement in low-frequency disturbance suppression of a state-of-the-art scanning stage of an industrial wafer scanner.
TL;DR: Simulations and experimental results of the electronical control of the order and pole frequency of the proposed fractional (1+α)-order low-pass filter are compared.
Abstract: A proposal of a fractional (1+α)-order low-pass filter is presented in this paper. The proposed filter operates in the current-mode and it is designed using Multi-Output Current Followers (MO-CFs), Dual-Output Current Follower (DO-CF), Dual-Output Adjustable Current Amplifier (DO-ACA) and Adjustable Current Amplifiers (ACAs) as active elements within the presented topology of the filter. The filter possesses ability to electronically control its order and also the pole frequency by changing the current gain of current amplifiers (ACAs) already present in the structure. Three different values of the order and pole frequency of the proposed low-pass filter were tested as an example. Design of the proposed filter is supported by simulation and experimental results. Simulations of the circuit are carried out in PSPICE simulator with behavioral models of used active elements. The experimental laboratory measurements are performed with the help of available devices forming equivalent circuits. Simulations and experimental results of the electronical control of the order and pole frequency are compared in this contribution.
TL;DR: In this article, a new OTRA-based multifunction Inverse filter configuration is presented which is capable of realizing low pass, high pass and band pass filters using only two OTRAs and five to six passive elements.
Abstract: A new OTRA-based multifunction Inverse filter configuration is presented which is capable of realizing low pass, high pass and band pass filters using only two OTRAs and five to six passive elements. To the best knowledge of the authors, any inverse filter configuration using OTRAs has not been reported in the literature earlier. The effect of the major parasitics of the OTRAs and their effect on the performance filter have been investigated and measured through simulation results and Monte-Carlo analysis. The workability of the proposed circuits has been confirmed by SPICE simulations using CMOS-based-OTRA realizable in 0.18 µm CMOS technology. The proposed circuits are the only ones which provide simultaneously the following features: use of reasonable number of active elements (only 2), realizability of all the three basic filter functions, employment of all virtually grounded resistors and capacitors and tunability of all filter parameters (except gain factor, H_0 for inverse high pass).
The centre/cut-off frequency of the various filter circuits lying in the vicinity of 1 MHz have been found to be realizable, which has been verified through SPICE simulation results and have been found to be in good agreement with the theoretical results.
TL;DR: A new compact microstrip tunable bandpass filter with continuous control of center frequency and bandwidth is proposed in the paper and a prototype is fabricated and measured.
Abstract: A new compact microstrip tunable bandpass filter with continuous control of center frequency and bandwidth is proposed in the paper. The proposed design is based on short parallel-coupled lines, which are tuned by properly loading varactors. The structure exhibits a pair of transmission poles and one-side passband edge transmission zero that can be flexibly adjusted for required positions. A thorough theoretical analysis is derived to estimate the performance of the proposed filter and verify the initial values of design parameters. To verify the design concept, a prototype is fabricated and measured. The fabricated circuit has an extreme compact size (smaller than $0.03\lambda _{g}\times 0.1\lambda _{g}$ ). The simulated and measured results agree well with the derived theory, and indicate wide tunable center frequencies (0.56–1.15 GHz) and 1-dB bandwidth (65–180 MHz).
TL;DR: In this article, a microstrip low-pass filter using triangle-shaped resonators is presented, which has a very flat group delay in the passband, which is the minimum value in comparison with the published works.
Abstract: In this paper, a compact microstrip lowpass filter (LPF) using triangle-shaped resonators is presented. The designed LPF includes three symmetric triangle-shaped resonators to provide a suitable passband and sharp response. A suppressing unit composed of several suppressing cells is designed to obtain a wide rejection band and low insertion loss in the passband. The fabricated LPF has been measured and indicts that it has −3 dB cut off frequency at 5.15 GHz. The rejection band has been expended from 5.51 GHz to 43.2 GHz with maximally flat return loss in this region nearby to 0 dB. Also, simulation and experimental results show that the proposed filter has a very flat group delay in the passband, which is the minimum value in comparison with the published works since 2017.
TL;DR: In this article, the authors proposed a variable filter inductor with three-time higher inductance at low currents compared to its inductance value at rated current, which not only reduces current harmonics under all operating conditions but also helps to stabilize the microgrid by inducing less LCL resonant propagation.
Abstract: Three-phase LCL filters, compared to L or LC filters, are preferred in high-power converters in microgrid applications because of their better capability of harmonic attenuation. Fixed value inductors are mostly adopted in traditional designs to achieve low current harmonics at rated power. However, due to the intermittent nature of renewable energies, microgrid converters have to operate under light-load conditions, which sometimes result in worse harmonics performance. This paper proposes a variable filter inductor, which has three-time higher inductance at low currents compared to its inductance value at rated current. It not only reduces current harmonics under all operating conditions but also helps to stabilize the microgrid by inducing less LCL resonant propagation. The inductor's magnetic design is illustrated and verified by finite-element simulation. MATLAB/PLECS circuit simulation shows a reduction of current harmonics when using the variable inductor under light-load conditions. Experimental results from a 1-MVA prototype confirm the theoretical expectations.
TL;DR: A new method for designing multiband bandpass filters (BPFs) with multiple transmission zeros are presented, and for the first time, different numbers of open stubs are used to realize multiband BPFs with two to seven passbands.
Abstract: This paper presents a new method for designing multiband bandpass filters (BPFs). The filter consists of low-pass filter and two open stub-loaded shorted stubs. Multiple transmission zeros (TZs) are produced by the open stub-loaded shorted stub, and multiple passbands can be realized. For the first time, different numbers of open stubs are used to realize multiband BPFs with two to seven passbands. The center frequencies and the last passband bandwidth can be tuned in a certain range by adjusting the TZs and transmission poles. First, a wideband BPF is presented to introduce the design concept. Theoretical analysis is done to illustrate the design principle. Then, a wide single-band BPF and a dual-band BPF are designed to demonstrate the design method. The design procedure is summarized to guide the design process. Finally, tri-/quad-/quint-/sext-/sept-band BPFs are designed according to the design principle. All the BPFs are manufactured. Measured results show good agreement with simulated ones.
TL;DR: As further modification to the proposed approach, the possibility of realising pole–zero symmetry is presented, which makes the new proposed tuning method useful for both existing and future designs.
Abstract: An approach of tuning first-order filters is proposed in this study. The proposed approach is based on employing feedback in first-order filter circuits, wherein a scaled output is combined with the input signal, so as to facilitate easy tuning of filter parameters. Various options of tuning the filter parameters are explored by employing feedback from low-pass, high-pass or all-pass outputs. The approach enables easy tuning of filter parameters by varying the gain of an external amplifier, without adjusting the passive elements comprising the filter core. A new current-mode filter circuit is further proposed, which employs a recently introduced active element, namely an extra-X current conveyor. The new approach is used in the designed first-order filter circuit. The new proposed circuit benefits by employing only a grounded capacitor, exhibits low-input and high-output impedances. The approach of tuning filter parameters through external means, without disturbing filter core, and the new proposed circuit are verified through simulations with promising results. As further modification to the proposed approach, the possibility of realising pole–zero symmetry is presented, which makes the new proposed tuning method useful for both existing and future designs.
TL;DR: In this paper, the spectral evolution properties in single-frequency Raman fiber amplifier (RFA) based on different pump schemes are analyzed theoretically for the first time based on the gain dynamics.
Abstract: In this paper, the spectral evolution properties in single-frequency Raman fiber amplifier (RFA) based on different pump schemes are analyzed theoretically for the first time based on the gain dynamics. It reveals that the walk-off effect in counter-pumped scheme acts as a natural low-pass filter for single-frequency RFA. When multilongitudinal mode rare-earth-doped fiber laser is used as the pump source for RFA, strong temporal fluctuations of the pump source would lead to spectral broadening in copumped scheme, while single-frequency operation could be maintained in the countered-pumped case because of the natural low-pass filter.
TL;DR: A simple yet effective dc offset removal technique based on adaptive low-pass filters is introduced in this letter and can be applied as an add-on to any PLL structures without altering their design.
Abstract: The presence of dc offset in the inputs of a phase-locked loop (PLL) introduces fundamental frequency oscillations in the estimated quantities. Due to their low frequency in a synchronous reference frame, removal of these oscillations is a challenging task. Recent design studies of pre/in-loop filtering based advanced PLLs show that incorporation of dc offset removal in a filtering stage reduces the bandwidth of the PLL. This degrades the dynamic performance of the PLL and results in slower response time. To tackle this issue, a simple yet effective dc offset removal technique based on adaptive low-pass filters is introduced in this letter. The proposed technique can be applied as an add-on to any PLL structures without altering their design. Therefore, its application has a minimal effect on the dynamic performance of the PLL under study. The effectiveness of the proposed technique is evaluated experimentally by applying it to different PLL structures.
TL;DR: A novel switched-capacitor low-pass filter architecture is presented, in which a feedback path is added to a charge-rotating real-pole filter to implement complex poles and the selectivity is enhanced, and the in-band loss is reduced compared with the real- pole filter.
Abstract: A novel switched-capacitor low-pass filter architecture is presented. In the proposed scheme, a feedback path is added to a charge-rotating real-pole filter to implement complex poles. The selectivity is enhanced, and the in-band loss is reduced compared with the real-pole filter. The output thermal noise level and the tuning range are both close to those of the real-pole filter. These features make the filter suitable for high speed, low noise, and low power applications. A fourth-order filter prototype was implemented in a 180-nm CMOS technology. The measured in-band loss is reduced by 3.3 dB compared with that of a real-pole filter. The sampling rate of the filter is programmable from 65 to 300 MS/s with a constant dc gain. The 3-dB cut-off frequency of the filter can be tuned from 490 to 13.3 MHz with over 100-dB maximum stop-band rejection. The measured in-band third-order output intercept point is 28.7 dBm, and the averaged spot noise is 6.54 nV/ $\surd $ Hz. The filter consumes 4.3 mW from a 1.8 V supply.