Low-pass Filter Structure Research Articles

Single-Layer Mode Composite Coplanar Waveguide Dual-Band Filter With Large Frequency Ratio

A dual-band filter of a large frequency ratio is proposed, studied, and developed in this article, which is based on mode composite coplanar waveguide (MCCPW). Both low and high bands of the dual-band filter can be designed independently with a high degree of design freedom. The filter can achieve more than ten times the frequency difference between the two bands, which is usually hard to accomplish by conventional dual-band filter design techniques. All harmonics between the two bands can be suppressed by a cascaded low-pass filter and impedance matching structure to form a qualified dual-band frequency response. The characteristic of the proposed MCCPW dual-band filter makes it a promising candidate for multiband systems, especially in 5G communication systems. The demonstrated MCCPW dual-band filter is fabricated with a single-layer substrate. Measured results are in good agreement with simulated results, which validate the feasibility and superiority of the proposed filtering technique.

Design of Computationally Efficient Sharp FIR Filter Utilizing Modified Multistage FRM Technique for Wireless Communications Systems

Modern wireless communications gadgets demand multi-standard communications facilities with least overlap between different input radio channels. A sharp digital filter of extremely narrow transition-width with lower stop band ripples offers alias-free switching among the preferred frequency bands. A computationally competent low pass filter (LPF) structure based on the multistage frequency response masking (FRM) approach is proposed for the design of sharp finite impulse response (FIR) filters which are suitable for wireless communications applications. In comparison of basic FRM with other existing multistage FRM structures, the proposed structure has a narrow transition bandwidth and higher stop band attenuation with significant reduction in terms of the number of computational steps. A design example is incorporated to demonstrate the efficiency of the proposed approach. Simulation results establish the improvement of the proposed scheme over other recently published design strategies.

Knowledge-based single-tone digital filter implementation for DSP systems

The requirement for efficient digital signal processing (DSP) systems and its solutions increases highly over the last few years. DSP techniques as well as its algorithms are necessary for day to day life tool namely smartphone, set-top unit (STU), video and acoustic players, digital cameras, digital television, etc. This paper describes a comparative study on knowledge-based digital filter structure namely transposed form, direct form, and systolic array. To implement the parallel processing the systolic array structure is often used. A Goertzel algorithm is implemented in the field-programmable gate array (FPGA) Altera EP4CE115F29C7 device which is used to determine the discrete Fourier transform (DFT). Finally, filtering technique is implemented efficiently by dividing filter coefficients and data into odd and even which increases the computational speed. The computational speed and functional verification results are achieved by using MATLAB. The Altera DSP builder and Simulink are used for the implementation of Goertzel algorithm. The 64-tap systolic low-pass filter structures offer 213.97-μs-less delay than the transposed form, 1700 μs, and direct form, 3900 μs, structures. Similarly for 2048-tap low-pass filter using sub-filter offers 49.397-ms computational speed and direct filtering offers 53.257 ms.

Design of an Oscillation-Based BIST System for Active Analog Integrated Filters in 0.18 µm CMOS

In this paper, an oscillation-based built-in self-test system for active an analog integrated circuit is presented. This built-in self-test system was used to detect catastrophic and parametric faults, introduced during chip manufacturing. As circuits under test (CUT), second-order Sallen-Key, Akerberg-Mossberg and Tow-Thomas biquad filters were designed. The proposed test hardware detects parametric and catastrophic faults on changeable limits. The influence of both oscillation and test hardware on fault detection limits were investigated and analyzed. The proposed oscillation based self-test system was designed and simulated in 0.18 µm complementary metal-oxide semiconductor (CMOS) technology. Due to the easiness of implementation and configuration for testing of different active analog filters, such self-test systems can be effectively used in modern integrated circuits, made of a large number of devices and circuits, such as the multi-standard transceivers used in the core hardware of software-defined radios. Using the proposed test strategy, the fault tolerance limits for catastrophic faults varied from 96% to 100% for all injected faults in different structures of low pass filters (LPF). The detection range of parametric faults of passive components’ nominal value, depending on the used structure of the filter, did not exceed –0.74% – 0.72% in case of Sallen-Key, –3.31% – 1.00% in case of Akerberg-Mossberg and –2.39% – 1.44% in case of Tow-Thomas LPF.

Higher order lumped element absorptive low‐pass and bandpass filter structures

Here, the authors present a class of lumped-element low-pass and bandpass absorptive filter circuits. To begin with, the authors discuss a new type of absorptive low-pass filter (LPF) structure that has an excellent impedance matching performance in both passband and stopband. This work provides low-pass prototype values for the proposed absorptive LPFs in terms of those for the conventional reflective filters, namely g -parameters, so that the new type of absorptive LPF can be designed in a straightforward manner. In addition, it is shown that traditional low-pass-to-bandpass frequency transformations can be applied to the absorptive low-pass prototype cases in the design of absorptive bandpass filters (BPFs). Second- and third-order LPF and BPFs are designed and measured to verify the new type of absorptive filter and its design method.

A Low-Cost Compact Low-Pass Filtering Power Divider Based on Elliptic Function with Wide Attenuation Band

A filtering power divider (FPD) with low-pass property and wideband harmonic suppression is presented in this paper. The microstrip structure of the FPD is designed based on elliptic function. The open stubs are embedded in the transmission line to obtain low-pass effect. An isolation resistor of 100Ω is connected between the two output ports to achieve good isolation. The operating frequency of the power divider is 2.9 GHz and the low-pass filter (LPF) has the cut-off frequency of 3 GHz with a sharpness factor of 55 dB/GHz. The attenuation band is extended up to 20 GHz (simulated) with a suppression of −19 dB. The maximum insertion loss in the passband for the FPD is −3.6 dB and the structure occupy an area of 0.7 × 0.21 . A lumped equivalent circuit of the LPF structure is also proposed. The LPF and the FPD both are fabricated using low-cost substrate FR4 of height (h) of 0.8 mm, a dielectric constant (εr ) of 4.4, conductor thickness (t) of 0.04 mm and loss tangent (δ) of 0.02. For experimental verification, the measured data are compared with the simulated ones.

Modelling and validation of microwave LPF using modified rectangular split ring resonators (SRR) and defected structures

We propose a design of lowpass filter (LPF) using modified rectangular split ring resonator (SRR) that acts as a unit cell of metamaterials. Initially, a conventional LPF of 4.5 GHz is designed and the low impedance line is replaced to produce a sharp cut-off with a modified SRR structure. A brief parametric study is done to establish a relationship between the inner perimeter of the SRR to the cut-off frequency of the proposed LPF. Same study is also done for the outer perimeter. Using this relationship, another LPF of 2.4-GHz cut-off frequency is obtained. Defected ground structures (DGS) and microstrip structures (DMS) are incorporated with the 2.4-GHz LPF structure for the removal of harmonics and better pass-band characteristics. The IE3D simulation results and the circuit simulation results are in good agreement with the measured results. The obtained structure can thus be used for several useful applications such as in Bluetooth, Wi-Fi, cordless phones, computers, and other wireless communication devices.

Super-compact ultra-wideband microstrip band-pass filter with improved performance using defected ground structure-based low-pass filter

A super-compact ultra-wideband (UWB) microstrip band-pass filter (BPF) with good selectivity and wide stopband is proposed in this paper. The super-compactness along with wide stopband of the proposed filter is achieved by integrating modified multimode resonator-based UWB BPF and defected ground structure (DGS)-based compact low-pass filter (LPF). The LPF structure is designed using four non-uniform configurations of DGS units along with a 50 Ω microstrip line. Each DGS unit is formed by cascading three isosceles U-shaped DGSs. Further, an equivalent RLC circuit model of the LPF is proposed to validate the numerical simulation and experimental results of LPF. The proposed filter has simulated passband frequency range 3–11 GHz with wide stopband: attenuation better than 40 dB and 25 dB over the frequency ranges 11.7–20.5 GHz and 11.2–30 GHz respectively. The experimental results for the proposed filter are nearly in agreement with corresponding numerical simulation results.

Multi Mode Resonators Based Triple Band Notch UWB Filter

A compact and highly selective triple band notch UWB (3.3 GHz -10.7 GHz) filter is presented. Low insertion loss UWB pass band characteristics is achieved by two coupled multi mode resonators (MMR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and MMR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). Desired triple band notch characteristics and sharp UWB filter characteristics are achieved by introducing transmission zeroes (TZs). Three band notches are implemented to mitigate the potential interferer signals at 4.42 GHz (Radio altimeter ITU band), 5.54 GHz (WLAN) and 7.64 GHz (Satellite communications). Wide upper stop band is realized by incorporating a stepped impedance low pass filter structure. The filter is realized on a RT/Duroid 5880 substrate (ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 2.2 and thickness = 0.8 mm) and measured to validate the predicted results. The group delay of the filter is relatively constant and less than 0.45 ns over the desired pass band.

Electrical impedance matching networks based on filter structures for high frequency ultrasound transducers

An electrical impedance matching (EIM) network is proposed to achieve the broad bandwidth of a high frequency ultrasound transducer and to improve the signal-to-noise ratio (SNR) of an ultrasound image. The proposed EIM network is based on a general filter structure, i.e., either low-pass filter (LPF) or high-pass filter (HPF) structure composing a capacitor and an inductor. Either filter type can be selected depending on the spectral characteristics of a transducer. The prominent advantage of the proposed method is the capability to broaden the spectrum of a transducer by means of modifying its original spectrum. The values of the electronic components are computed with the measured electrical impedances of a transducer and an imaging system. In this paper, the EIM between a custom-made 50MHz ultrasound needle transducer and a commercial pulser/receiver system was conducted to verify the characteristics and performance of the proposed method. The experimental results demonstrated that the proposed EIM network is capable of achieving the best performance of the transducer, i.e., broad bandwidth and high SNR that are desirable for the high quality of high frequency ultrasound images.

A Novel Type-1 Frequency-Locked Loop for Fast Detection of Frequency and Phase With Improved Stability Margins

The synchronous reference frame phase-locked loop (SRF-PLL) is a widely used synchronization technique in power electronics and power systems applications due to its ease of implementation and robust performance. The conventional SRF-PLL is a type-2 control system due to the use of proportional-integral controller as loop filter. With higher bandwidth design, it can achieve fast detection of frequency and phase under ideal grid conditions. However, its bandwidth should be sufficiently lowered to obtain proper disturbance rejection under unbalanced and distorted grid conditions. This results in a slower detection speed. Recently, several advanced PLLs with pre/in-loop filtering stage have been proposed to improve the detection speed. A major challenge with the PLLs is how to further improve their dynamic performance without compromising the disturbance rejection capability and stability. To resolve this issue, in this paper, a novel type-1 frequency-locked loop (FLL) is proposed. The disturbance rejection capability of the proposed FLL is improved using a modified structure low-pass filter with selective harmonics filtering ability. As the proposed FLL is type-1 control system, it achieves better dynamic performance with higher stability margins. The effectiveness of the proposed FLL is confirmed through experimental results and comparison with advanced type-2 PLLs.

Design of the adaptive log-domain low-pass filter

This paper presents the structure and realization method of the current-controlled adaptive low-pass filter which based on the design of LC ladder network. After amplifying, amplitude limiting and shaping, the input voltage signal was converted into frequency signal. Then by the broadband frequency-current conversion circuit it was converted into current signal which has a linear relationship with input frequency. The current signal was as the bias current to adjust the cut-off frequency of the log-domain low-pass filter. So that frequency of the filter can automatically track the input signal frequency. In this paper, the design principle was introduced in detail, the design formulas were derived and the circuit of adaptive second order log-domain low-pass filter was given. The filter can realize the scope of the cut-off frequency up to 30MHz. The tracking range for the input frequency is from 1MHz to 30MHz. The simulation results show the effectiveness of design method.

A Novel Design of a Ring Resonator Low Pass Filter

This paper presents a novel structure of low pass filter designed by using microstrip technology. The proposed filter consists of a modified ring resonator with open stubs and two input/output feed lines. Based on series of optimization and a specific design method, a compact low pass filter with good electrical performances is obtained. In order to characterize the frequency response of the proposed filter, the simulations are carried out using two different solvers (ADS Agilent and CST-MWS). Furthermore, to validate the conception approach the circuit is manufactured and measured. The experimental results shows a wide attenuation band with a good rejection level up to 6 GHz, a cutoff frequency of 2.66 GHz and a reduced insertion loss level. In addition, a good agreement between the simulation and the measured results is achieved.

High performance LPF Structure with sharp roll‐off and low VSWR

A symmetrical compact microstrip lowpass filter (LPF) with ultra-wide rejection band and low voltage standing wave ratio (VSWR) using a novel structure of stepped impedance and butterfly-shaped resonators is presented and fabricated. The LPF has a 3 dB cut-off frequency at 1.513 GHz. The series structure of the butterfly-shaped resonators result in a high roll-off rate of 187.8 dB/GHz. By generating multiple transmission zeros, a wide stopband (with 35 dB rejection degree) is achieved. To reach a small circuit, the bended transmission line is properly utilised. Moreover, 171% relative stopband bandwidth and dimensions of 0.087λ g × 0.157λ g (λ g is the guided wavelength at 1.513 GHz) are other specifications of this LPF. In addition, an acceptable match is obtained between the simulated and measured responses. In the end, the LPF achieves a high figure-of-merit of 82288.

An ultrawideband SPST switch using defected ground structure low pass filter in 65-nmCMOS technology

In this article, we propose a novel concept of applying a defected ground structure low pass filter (DGS LPF) to the design of switches. We highlight that the DGS structure has such advantages as consuming less silicon area and providing another degree of design freedom to optimize the switch performances. To prove the concept, we analyze, design, and characterize a single-pole single-throw (SPST) switch using a DGS LPF in 65-nm CMOS technology. We show that the DGS LPF SPST switch with active size of 125 × 88 µm2 can cover an ultrawideband from DC to 77 GHz. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:758–768, 2015.

Fast adaptive pose tracking control for satellites via dual quaternion upon non-certainty equivalence principle

This paper presents the implementation of the high performance adaptive control algorithm for 6-DOF systems described by dual quaternions. The fast adaptation is achieved from the introduced stable adaptation dynamics in the closed-loop system which cannot be expected in the conventional adaptive controller designed upon the certainty equivalence framework. The development of the proposed adaptive control algorithm relies on the two newly introduced algebraic operations. The one is a dual filter for a dual relative error signal. The dual filter essentially has a linear low-pass filter structure and enables us to recast the system dynamics into a linear parameter-affine system dynamics in dual quaternions combined with dual control inputs. The other is an isomorphism between a dual quaternion and a vector for the error measurement. Using this isomorphism, the stability proof of the closed-loop dual quaternion system based on the proposed Lyapunov-like function is rewritten in the form of familiar matrix/vector algebra. In order to demonstrate the performance improvement, numerical simulation results are given, which compare the proposed adaptive control method with the conventional one from the certainty-equivalence principle.

Single‐pole multiple‐throw switches with defected ground structure low‐pass filter

In this study, the authors present a novel concept for the design of single-pole multiple-throw (SPMT) switches using defected ground structure low-pass filter (DGS LPF). The DGS LPF produces enhanced inductance to compensate the parasitic capacitance of the control transistors. As a result, the SPMT switch will consume much less silicon area. The concept is experimentally validated with a single-pole double-throw (SPDT) switch and a single-pole four-throw (SP4T) switch in 65-nm CMOS. The active area of the SPDT and SP4T switches are less than 130 × 150 μm2 and 180 × 165 μm2, respectively.

Significant Reduction of Electromagnetic Interference for Fine-Motion Control Rod Drive in a Nuclear Reactor

A significant reduction of electromagnetic interference (EMI) for a fine-motion control rod drive (FMCRD) in a nuclear reactor is presented in this paper. A reactor design with the FMCRD can achieve high performance. However, the FMCRD produces electromagnetic noise, which affects the startup-range neutron monitoring (SRNM) system. Moreover, because the FMCRD and the SRNM system are arranged near each other under a reactor vessel, the SRNM unit is influenced by the FMCRD electromagnetic noise, leading to uncertain monitoring results and system alarms. Strong EMI could even result in a system trip. To alleviate the EMI, a grounded metal sheet is wrapped around the FMCRD cable, partially shielding it from radiation. To further overcome the EMI, a proposed three-dimensional (3-D) low-pass filter (LPF) structure is combined with the SRNM wire for noise reduction. To implement the 3-D LPF structure, an industrial passive electronic device (zippered cable shielding) is adopted in this paper. This approach not only achieves a remarkable noise amplitude reduction but also minimizes the radiated emissions from the FMCRD cables, yielding an improved and stabilized nuclear reactor. In addition, a real-time analytical method is utilized to capture events while the FMCRDs are active, and the captured waveforms are transferred to the frequency domain by using a fast Fourier transform to analyze the experiment data, lending more insight into the actual situation.

Design of Miniaturized Microstrip LPF and Wideband BPF With Ultra-Wide Stopband

This letter presents a novel lowpass filter (LPF) structure which consists of a section of high-impedance microstrip line (HIML) with a pair of radial stubs (RSs) loaded at its center and a pair of stepped-impedance open stubs (SIOSs) loaded on both ends of HIML. The RSs loaded HIML exhibits a lowpass property and has a wide stopband. The loaded SIOSs not only can improve the roll-off rate of LPF significantly but also is able to extend the stopband. Based on such a LPF structure, a pair of highpass shorted HIMLs are paralleled on both sides of LPF to construct a wideband bandpass filter (BPF) with wide stopband. To validate the proposed method, two filters, i.e., a LPF with cutoff frequency fc at 1.07 GHz and a BPF centered at f0 = 0.89 GHz with -3 dB fractional bandwidth of 87%, are designed and fabricated. The measured results show the fabricated LPF has a -20 dB isolation bandwidth from 1.27 fc to 13.7fc while the fabricated BPF has a -20 dB isolation bandwidth from 1.56 f0 to 15 f0. Moreover, the fabricated LPF and BPF also have the compact size of 0.107 λgc ×0.083 λgc and 0.123 λg0 ×0.073 λg0, respectively. Good agreement can be observed between the simulation and measurement.

An improvement of defected ground structure lowpass/bandpass filters using H-slot resonators and coupling matrix method

A novel compact wideband high-rejection lowpass filter (LPF) using H-DGS is presented. The proposed filter has neither open stub nor cascaded high-low impedance elements. It consists of two coupled H-slots in the ground plane along with a compensated line. The effect of the new slot on the filter performance is examined. The comparison with the conventional filters shows that the proposed one guarantees a large rejected-band of 20dB from 2.5 to 16 GHz. Experimental measurements by means of HP8719D network analyzer agree well with simulated results which are carried out by Microwave Office. Based on H-DGS LPF Structure, a novel bandpass filter (BPF) will be is designed and tested verified by using both J-inverter and coupling matrix methods.