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This work demonstrates a Continuous-Time (CT) Ladder filter using transconductance amplifiers as an approximate delay stage implemented on a large-scale Field Programmable Analog Array (FPAA) and characterized on an SoC FPAA. We experimentally demonstrate a reprogrammable CT Analog linear-phase filter by utilizing the ladder filter delay element and Vector-Matrix Multiplication (VMM) both compiled on the SoC FPAA. Using the Ladder Filter as a programmable CT delay operation enables a traditionally difficult analog signal operation. This effort extensively models and characterizes the ladder filter delay stage in terms of its transfer function, delay tunability, power requirements, distortion, and SNR. The theoretical development is compared to experimental measurements on an SoC FPAA with programmable ladder filter delay of $2.9\mu \text{s}$ and $4.2\mu \text{s}$ for multiple input frequencies (e.g. 5kHz, 20kHz). In addition, we show that VMMs can compensate the non-idealities found in the ladder filter delay-line operation.

In this paper, a class-J power amplifier for operation in the X-band realized in SiGe bipolar technology is presented. The proposed design combines the high efficiency of class-J operation with solutions to mitigate AM-PM distortion down to a level compatible with high spectral efficiency modulation schemes like 64-QAM. The design of a transformer-based output matching network and the trade-off between efficiency and pure class-J operation related to a non-ideal second harmonic termination are discussed. The main sources of AM-PM distortion are identified in the base-emitter and collector-based bipolar junction transistor capacitance variation with power level and solutions that make the design less sensitive to these impairments are proposed. Linear MIM capacitors are used at the power amplifier (PA) core output to realize the proper class-J second harmonic termination, while an input matching network based on a Bessel ladder filter is adopted to make the signal phase at the PA core input less sensitive to base-emitter capacitance variation. A class-J PA previously designed for maximum power-added efficiency (PAE) is used as a reference throughout the paper to highlight the trade-off’s entailed by AM-PM distortion reduction. The designed PA features a peak gain of 15 dB at 10 GHz and 8-to-12 GHz −3 dB bandwidth. The saturated power is 22 dBm with a 33% PAE, while the output $p_{1\,\text {dB}}$ is 19 dBm. The AM-PM distortion at $p_{1\,\text {dB}}$ is 5 degrees.

This paper proposes an analytical design procedure for the LLCL and the LCCL filters for grid integration of high-power voltage-source converters. The low switching frequency and stringent limits on grid-injected harmonics in high-power applications lead to large smoothing filters. In order to reduce the size and weight, high-order filters are already proposed and wise design procedures with the main goal of minimizing the overall filter size are being suggested. In this paper, the parameters of the LLCL and the LCCL filters are designed in the per-unit system to satisfy the requirements on the injected grid current and at the same time minimize the overall filter size through minimizing the total energy stored in the filter components. The experimental results of a downscaled laboratory prototype with a low switching frequency prove the effectiveness of the proposed design procedure.

We present a new design method for bandpass filters capable of adjusting center frequencies, bandwidths, and notches. For designing such filters, filter topologies employing frequency-tunable resonators in cul-de-sacs are developed. The cul-de-sac resonators are mainly responsible for constructing notches, while the resonators in main paths form passbands. For verifying the presented design method, we have designed two bandpass filters. Each filter consists of two different resonator types: microstrip-line resonators for forming passbands and substrate-integrated waveguide resonators for producing notches. The measured results of the two designed filters show that frequency-tunable notches can be placed next to the passbands without producing unwanted resonant peaks that are usually observed in bandpass-bandstop filter cascades. This indicates that the filters designed using the presented topologies can replace bandpass-bandstop filter cascades.

This brief presents a filter-integrated high-efficiency class-F power amplifier (PA). The hybrid cavity–microstrip filtering circuit is employed not only to realize output impedance matching and the third-harmonic manipulation but also to provide high-selectivity bandpass responses. To fulfill the requirements of high-efficiency class-F PAs, cavity resonators and microstrip feeding structures are involved, and their benefits are fully exploited. The metal cavity resonator features a high $Q$ value and, thus, low loss in the passband, resulting in high efficiency. Moreover, metal walls of cavities act as heat sink for the transistor. The microstrip feeding structures are used to improve the skirt selectivity and manipulate the third harmonic. Moreover, it features easy integration with the transistor, and thus, the transition between cavity and microstrip lines is eliminated. The hybrid filter is characterized based on filter synthesis theory. Complex impedance conversion analysis is carried out to guide the impedance transformation from 50 $\Omega$ to a complex one desired by the transistor. For demonstration, a filtering PA operating at 2.4 GHz is designed and measured. It exhibits both high-selectivity bandpass responses and good PA performance with maximum power-added efficiency of 70.9% at 40.8-dBm output power.

Use of parallel resonance to notch filter the fundamental ripple frequency on a switching regulator output offers advantages in the combined metric of size and power compared to traditional low-pass solutions. Availability of barium strontium titanate varactors with capacitance of several nanofarads now makes automatic tuning of parallel resonance alignment with the ripple fundamental a feasible alternative. A phase-lock automatic-tuning circuit is demonstrated. The effective use of this technique as the power-supply filter used to power a 16 bit ADC is shown. The suitability of the resulting filter and regulator to full surface mount encapsulation is demonstrated.

In this paper, a variation-aware and reliable design of a fully integrated radio frequency (RF) bandpass filter realized using a voltage differencing transconductance amplifier is presented. The filter is characterized by its high frequency operation, low power consumption, high quality factor, and it is insensitive to process, voltage, and temperature variations. Sensitivity analysis has been performed to analyze the circuit performance in the presence of parasitics. The inductor-less approach finds its application in integrated building blocks of RF front ends, thus eliminating the requirement of off-chip filters in transceivers. Centered at 2.511 GHz and operating within the 36.21 MHz 3-dB bandwidth, the filter draws 0.168 mA from a ±1 V power supply, attains a voltage gain of 72.6 dB, a quality factor of 69.34 and noise figure of ~29.6 dB. In addition, it has a dynamic range of 125.84 dB-Hz and a 1-dB compression of −1.5 dBm which translates into a figure of merit as high as 94 dB.

High-order passive filters, such as the well-known LCL filters, are normally employed in the grid-connected power conversion systems to effectively attenuate the switching frequency harmonic introduced by the modulation of power converters. Although much more compact than the conventional single-inductor L filters, such passive filters are still bulky and expensive when compared with their active counterparts, e.g., the semiconductor switches. In order to improve the system power density and reduce its cost, the magnetic integration technique has been widely adopted so that the discrete inductors of passive filters are replaced by the integrated inductor, resulting in smaller magnetic cores and, therefore, the decreased volumes of passive filters. For conventional magnetic integrated LCL filters, the converter-side inductor and the grid-side inductor are integrated together and their coupling coefficient is intentionally minimized. In this letter, this coupling coefficient is fully utilized and properly designed, and the resulting coupling effect is equivalent to inserting an additional inductor into the filter capacitor branch loop. The integrated inductor and the filter capacitor can form an integrated LLCL filter, which exhibits the advantages of both the LLCL filter and magnetic integration, e.g., enhanced harmonic attenuation, reduced filter inductances, and system volume without adding the extra trap inductor. Finally, experimental results obtained from a single-phase grid-connected voltage-source converter interfaced by the proposed integrated filter are presented to validate its effectiveness.

Common-mode (CM) noise on differential signals can be suppressed by planar electromagnetic bandgap (EBG) technologies. In this study, two new CM filter structures were designed, fabricated, and measured. The filters are based on a previously proposed geometry, a “sandwich-type” EBG structure that resonates at the desired filter frequency; however, the new filters are placed on the top of the PCB as a surface-mount component, instead of being implemented within the PCB stackup. Stripline and microstrip versions of the surface-mount filter are considered. The filters can be easily removed and substituted with another one that is designed to filter a different frequency but maintains the same footprint and external dimensions. In addition, the surface-mount filter allows us to incorporate dc blocking capacitors into the microstrip version of the filter, thus providing two functions in one package. The total radiated power (TRP) of the implemented filter is investigated and discussed. RF absorbing material and traditional shielding are considered to reduce the TRP.

N-path switched- RC circuits are a promising solution for realizing tunable high- Q filters on chip. Here, a novel method of embedding phase-shifting functionality into the two-port N- path filter response by shifting the phase of the input and output clock sets relative to each other is introduced. Furthermore, a two-port design allows us to embed variable attenuation that can be useful in applications such as wideband self-interference cancellers and phased-array front ends, where filtering, phase shifting, and variable gain are functionally required. The effect of the embedded phase shift is analyzed with linear periodically time-variant theory and has been verified through simulations and measurement. Measurement results are presented for a two-port N- path filter implemented in a 65-nm CMOS 0.8-1.4-GHz highly reconfigurable self-interference canceling receiver. The two-port filter achieves 13-dB gain control and full 360° phase-shift range for the in-band transfer function.

This brief presents a novel wide-bandwidth second-order voltage-mode all-pass filter derived from a canonical single transistor bandpass filter. The core of the circuit consists of only one transistor, two resistors, and two energy storage elements. The operation of the proposed filter is validated experimentally. A filter implemented in an IBM 0.13- $\mu\mbox{m}$ CMOS was measured to have a 55-ps group delay across a 6-GHz bandwidth while consuming 18.5 mW from a 1.5-V supply. This work experimentally demonstrates a CMOS all-pass filter that operates at multigigahertz frequencies and achieves the highest delay-bandwidth product compared to previously published CMOS all-pass filters known to the authors.

A general cascaded filter design technique is implemented to get a tunable narrow-band filter response based on the general Chebyshev bandpass filter. A cavity combline microwave filter is fabricated by cascading two asymmetrical filters without using an isolator between them. Tuning is provided by means of the screws on top of each resonator of the cavity combline filter. An optimization is applied to get the desired response. The designed example is presented together with the simulation and measurement results. The measured data are in good agreement with the simulation results.

In this letter, we propose a new coupling matrix synthesis method for dual-band filter. Different from traditional frequency transformation method, which transforms a low-pass prototype into a dual-band filter, we transform two low-pass prototypes into a dual-band filter. The dual-band filter synthesized by this method can have different orders, bandwidths, or return losses in different passbands. And the filter-prescribed transmission zeros can also be realized. To verify this method, asymmetric and symmetric dual-band filters are synthesized.

This letter demonstrates the dual transmission zeros (TZs) of bandpass elliptic prototype filters that can be directly implemented with two resonators in microstrip. An experimental filter based on the proposed alternate circuits is designed and fabricated. In order to improve the rejection of stopband, two additional TZs are introduced to the proposed filter. By means of directly implementing an elliptic bandpass filter in microstrip, the insertion loss of the presented filter can be less than 0.8 dB, and the $\Delta {f}_{3~\mathrm {dB}}/\Delta {f}_{20~\mathrm {dB}}$ result is better than 0.583, which means the proposed filter has a good selectivity.

In this letter, we present a third-order frequency-agile substrate-integrated waveguide (SIW) filter with a pair of transmission zeros. In addition, a relationship between the symmetric and asymmetric topologies for having same frequency responses is derived in this letter so that the coupling values of the asymmetric filter topology can be directly obtained from those of the symmetric one. For practical implementation, we also present a new methodology for physical implementation of a source-to-multiresonator coupling for frequency-tunable SIW resonator structure. The filter has been fabricated and measured for verifying the presented filter topology.

The development of 3-D reconfigurable microwave multiband bandpass filters in substrate-integrated evanescent-mode-cavity-resonator technology is presented. The proposed filter approach exploits multiband quasi-bandpass sections whose tunable resonators do not directly interact with one another. In this manner, a multiband filtering transfer function with independently frequency-controllable passbands and interband transmission zeros is realized. Moreover, the number of active passbands can be dynamically selected in this filter architecture through their spectral merging as well as their intrinsic switching-OFF through resonators’ detuning. These operational capabilities are theoretically demonstrated by means of several coupling-matrix-level synthesis examples. Furthermore, for experimental-validation purposes, a triple-band second-order prototype with three electronically tunable transmission bands in the range 2.2–2.8 GHz is designed, manufactured, and tested.

A synthetic transmission-line N-path bandpass filter technique that lowers the in-band insertion loss and increases the out-of-band rejection of the traditional N-path filter is analyzed. The performance limitations of the traditional N-path filter in terms of in-band insertion loss and limited rejection are reviewed. Measurement results from 0.1 to 1.6 GHz of a single-ended, four-stage synthetic transmission-line N-path filter fabricated in a 65-nm CMOS technology that achieves less than 5-dB insertion loss across the tuning range, 30–50-dB out-of-band rejection, in-band third-order distortion input-referred intercept point (IIP3) of $+$ 29 dBm, and a $+$ 11-dBm input-referred 1-dB compression point $({\rm P}1{\rm dB}_{\rm Jam})$ out-of-band jammer tolerance are presented.

This paper presents a complete 50–64 Gb/s serializing transmitter including a 4-tap equalizer. An LC-based FFE structure is proposed. The FFE improves the bandwidth of the delay line and the output combiner by applying the design methodology of LC-ladder filters. Proper arrangement of the output combiner reduces the required number of inductors and hence reduces the area. In addition, a novel 4:1 multiplexer (MUX) is used as the final stage of the serializer to reduce power. Designed and fabricated in 65 nm CMOS technology, the transmitter achieves a maximum data rate of 64.5 Gb/s with an energy efficiency of 3.1 pJ/bit.

A cognitive radio terminal using vacant frequency bands of digital TV (DTV) channels, i.e., TV white space, strongly requires a compact tunable filter covering a wide frequency range of the DTV band (470 to 710 MHz in Japan). In this study, a T-type ladder filter using ultra-wideband shear horizontal mode plate wave resonators was fabricated, and a low peak insertion loss of 0.8 dB and an ultra-large 6 dB bandwidth of 240 MHz (41%) were measured in the DTV band. In addition, bandpass filters with different center frequencies of 502 and 653 MHz at 6 dB attenuation were numerically synthesized based on the same T-type ladder filter in conjunction with band rejection filters with different frequencies. The results suggest that the combination of the wideband T-type ladder filter and the band rejection filters connected with variable capacitors enables a tunable filter with large tunability of frequency and bandwidth as well as large rejection at the adjacent channels of an available TV white space.

This brief presents a compact switchable dual-band filter with four operating states. The filter is established by adding switching circuits to a concurrent dual-band filter. The original concurrent dual-band filter has hybrid coupling paths and uses two stepped-impedance quarter-wavelength resonators that are shared by the two passbands, so fewer resonators are required. In addition, the central frequencies and bandwidths of the two desired passbands can be separately designed without time-consuming trial and error. Two types of switching circuit are added to the original concurrent dual-band filter to obtain a switchable dual-band filter. The switching mechanisms are analyzed and discussed. The proposed switchable dual-band filter has four possible operating states, so the two passbands can be activated or deactivated independently. The simulated and measured results verify the performance of the proposed structure.

This brief presents a flexible gm-C complex filter for Bluetooth-low-energy receivers. Each complex pole is realized sharing a bias current among transconductors, leading to an ultralow-power solution. The filter, which is designed in the 130-nm complimentary metal–oxide–semiconductor technology, has a power dissipation of only 42 μW from a 0.8-V supply voltage. With a center frequency and a passband of 2 and 1 MHz, respectively, the simulated filter provides a rejection of the adjacent channel of 34 dB and a spurious-free dynamic range of 52.7 dB.

The prediction of peak voltages in high-power bandpass filters is presented using a new method in order to overcome the limitations of previously reported techniques. The concepts of coupling matrix, frequency transformation, and resonator stored energy are used to arrive at a compact formulation, which accounts for both circuital and electromagnetic (EM) filter characteristics. The resulting expression is independent of the detailed filter design. An analytical method is therefore obtained, enabling RF power-handling studies of bandpass filters without restrictions on filter bandwidth or resonator geometry. Explicit formulas are derived and applied to examples representative of a variety of applications, i.e., rectangular-waveguide ${\rm TE}_{101}$ —mode Chebyshev and coaxial TEM-mode Bessel filters. EM simulations and experimental results verify the validity of the presented method.

In this paper, a novel bidirectional control principle of active tuned hybrid power filter (ATHPF) based on the active reactor using active techniques is proposed. The proposed control principle, in essence, is to continuously adjust the filter inductance of the active reactor by regulating active power filter (APF) output current in terms of its magnitude and direction. Therefore, the ATHPF using the bidirectional control principle can simultaneously supply different impedances at different selective suppressed harmonic frequencies. The bidirectional control principle can perform both the normal active tuning function and the abnormal active detuning function. To be specific, the normal active tuning function refers to the harmonic elimination with filtering performance independent of the deviation of passive filter parameters, while the latter, the abnormal active detuning function, refers to the flexible protection against harmonic over-current without losing two harmonic elimination and reactive power compensation at the occurrence of harmonic over-current. Experimental results verify the effectiveness of the ATHPF with the bidirectional control principle in selective harmonic elimination and flexible protection against harmonic over-current.

In this paper, we provide a new third-order bandstop filter (BSF) topology with attenuation control capability. The proposed BSF topology contains inter-resonator coupling structures and it can duplicate the frequency responses of the conventional BSF topology, which does not have inter-resonator couplings. In addition, the proposed topology can control the attenuation level by adjusting the resonant frequency of each resonator, and this characteristic cannot be obtained from the conventional one. Two BSFs utilizing the conventional and proposed topologies are designed, fabricated, and measured to support the presented theory. Two filters have been designed and fabricated employing frequency tunable substrate integrated cavity resonators. The measurement verifies that the BSF utilizing the presented topology is capable of adjusting the attenuation level as well as reproducing the conventional bandstop responses.

A novel coaxial stepped-impedance resonator (SIR) filter is proposed based on conventional multi-layer printed-circuit board (PCB) technology. The resonator results in a measured unloaded quality factor (Qu) of 185 at 3.7 GHz, has compact size, is self-shielded and has very low electromagnetic (EM) coupling to nearby RF circuits. The 3-D filter topology easily lends to advanced filter design with multiple transmission zeroes using cross coupling and source-to-load coupling on the top printed-circuit board layer. Two third-order fixed-band bandpass filters, and two fourth-order tunable bandpass filters are demonstrated in this technology. The fixed-band filters have an insertion loss of 1.6 dB with a fractional bandwidth of 6.5% at 3.6 GHz and occupy a size of 9 × 12 mm 2 . The tunable filter covers 2.1-2.9 GHz with a fractional bandwidth of 3.5%, and an insertion loss of 4.2-9.2 dB, limited by the silicon varactors. Multiple transmission zeroes are used in these designs to significantly improve the filter selectivity. Application areas are in fixed and tunable filters with very compact size and high shielding from nearby circuits for advanced communication systems.

One of the most critical aspects of virtual analog simulation of circuits for music production consists in accurate reproduction of their nonlinear behavior, yet this goal is in many cases difficult to achieve due to the presence of implicit differential equations in circuit models, since they naturally map to delay-free loops in the digital domain. This paper presents a novel and general method for non-iteratively implementing these loops in such a way that the linear response around a chosen operating point is preserved, the topology is minimally affected, and transformation of nonlinearities is not required. This technique is then applied to a generalized model of the Moog ladder filter, resulting in an implementation that outperforms its predecessors with only a modest computational load penalty. This digital version of the filter is shown to offer strong stability guarantees w.r.t. parameter variation, allows the extraction of different frequency response modes by simple mixing of individual ladder stage outputs, and is suitable for real-time sound synthesis and audio effects processing.

Microstrip/coplanar waveguide (CPW) hybrid bandpass filter with electromagnetic (EM) coupling has been developed, and a hybrid tri-band bandpass filter has been proposed. For each passband, the filter center frequency can be easily controlled, and the bandwidth can be adjusted. The hybrid bandpass filters have simple topologies, high frequency selectivity, and multiple passbands. The tri-band filter has been fabricated and measured, and the design has been demonstrated.

In this letter, we present a new absorptive bandstop filter topology that is capable of operating in the microwave regime (C-Band) and is capable of creating large attenuation using resonators which are comprised of printed circuit elements and surface mount elements. This particular topology allows for a high level of miniaturization when compared to transmission line realizations. Simulated and measured results are presented and show good correlation. We demonstrate a prototype absorptive bandstop filter that operates within the C-band, achieves $>$ 50 dB of rejection, and has a total size of 7 mm $\times$ 8.2 mm.

This letter presents a novel reconfigurable dual- band bandpass filter (DBBPF) with independently controlled passbands and constant absolute bandwidths (ABW). The design procedures follow the traditional synthesis approach of filters. Moreover, in order to meet the requirement of constant ABW, theoretical analysis and calculation are carried out to determine proper parameters of coupling regions. Finally, the proposed DBBPF exhibits 21.8% fractional tuning range of the first passband from 0.98 to 1.22 GHz and 17.9% of the second passband from 1.63 to 1.95 GHz, and 3-dB ABWs are 76 $\pm$ 4 MHz and 100 $\pm$ 4 MHz, respectively.

The demand of highly-integrated multi-band transceivers has driven the development of blocker-tolerant software-defined radios that can avoid the cost (and loss) of the baluns and SAW filters [1, 2, 3].

This paper systematically investigates the design of single transistor second-order active filters out-lining all possible architectures and possible impedance settings using an exhaustive MAPLE search code for all stable cases with the minimum number of passive elements (two resistors and two energy storage elements). The search is performed on six general voltage-input voltage-output transfer functions, derived using a small-signal two-port network transistor model. Selected LC and RC filter designs are verified experimentally. The results presented here fill both a circuit-theoretic gap and an application-oriented gap related to single transistor filter design which, apart from a few examples in the literature, has not been rigorously addressed.

We introduce a ladder filter-based programmable time-delay element for beamforming in ultra-wideband (UWB) systems. Such a lumped-element realization becomes possible by approximating e -std as a ratio of polynomials (based on Taylor and Pade expansions). When compared with conventional methods based on the tapped delay-line architecture, the proposed technique achieves lower power dissipation, higher delay range and resolution, and better area efficiency. A prototype delay line designed for the 3.1-10.6 GHz UWB range achieves a delay range of 140 ps and a gain range of -30 dB to +10 dB. Fabricated in a 0.25 μm SiGe BiCMOS process, the delay element occupies an active area of 1 mm 2 and consumes 53 mW from a 2.5 V supply. A four-antenna beamforming system using the delay element can achieve a scanning range of ±61 ° with 0.86 ° resolution for an antenna spacing of 15 mm.

Compared with the L filter, the LCL filter is more suitable for high-power low-switching-frequency applications due to its better attenuation characteristics on high frequencies. However, the parameter design for the LCL filter is more complex since both the inhibiting effect of the high-frequency harmonic current and the influence to the controller response performance of the converter should be considered. In this paper, the model of the LCL filter and the design criteria of the LCL filter for a shunt active power filter (SAPF) are analyzed in the beginning. Then, the impacts of all parameters of the LCL filter on SAPF are intuitively drawn on a graph by theoretical derivation. Finally, a novel parameter design and optimization method for the LCL filter is proposed. The validity and effectiveness of the proposed method are proved by simulated and experimental results of a single-phase SAPF prototype at the end of this paper.

The harmonic problem in electric power systems, far from improving, has been increasing in recent years. To mitigate this problem, active filters have been proposed; however, they do not present a complete solution for any type of load and system. This paper develops a control strategy for a compensator based on a hybrid filter topology. This topology is formed by an active power filter of series connection and a passive filter of parallel connection. The proposed strategy is based on minimizing the root-mean-square value of the voltage at the point of common coupling so that the source transfers the power demanded by the load. Thus, the determination of the reference signal is posed as a constrained optimization problem. The strategy was proposed for four- and three-wire systems, and it allowed the compensation of current harmonics and reactive power of harmonic current source and harmonic voltage source loads. An experimental prototype was developed, which has allowed verification of their performance.

A novel balanced filter realized in the form of substrate integrated waveguide (SIW) is proposed and studied in this paper. Based on the inherently horizontal and vertical symmetry of the SIW, this filter presents inherently high-performance balanced property with advantages of no identical pair requirement, being free from the limitation of symmetrical topology, easy and flexible design, high common-mode (CM) suppression, and robust CM suppression when comparing with conventional counterparts. Several prototypes are designed, fabricated, and measured to verify the expected properties.

This paper describes a novel design for a direct-coupled cavity filter realization using a ridge gap waveguide technology. A ridge gap waveguide transmission line with two coaxial feed connectors is designed and operated within the frequency band of 10-13 GHz. A cavity is coupled to the transmission line to achieve bandstop filter characteristic. Then, the structure of the filter is modified in a way to generate a bandpass feature. The final manufactured prototype is a fourth-order bandpass filter, operating at the center frequency of 11.59 GHz with a bandwidth of 72 MHz. The proposed design has potential applications in channeling filters for telecommunication satellites.

This paper presents a design methodology for developing a Butterworth type 100Hz low-pass second order Sallen-and-Key active filter. The proposed design method is intended to design filtering systems based on commercial components. Since these components have tolerances, a relative sensitivity analysis is included in order to satisfy design specifications. Experimental results show a maximum relative error, er=2.0%, at the cut-off frequency; the Op-Amp UA741 is used.

This paper proposes a method for designing high-order linear-phase finite-length impulse response (FIR) filters which are required as, e.g., the prototype filters in filter banks (FBs) and transmultiplexers (TMUXs) with a large number of channels. The proposed method uses the Farrow structure to express the polyphase components of the desired filter. Thereby, the only unknown parameters, in the filter design, are the coefficients of the Farrow subfilters. The number of these unknown parameters is considerably smaller than that of the direct filter design methods. Besides these unknown parameters, the proposed method needs some predefined multipliers. Although the number of these multipliers is larger than the number of unknown parameters, they are known a priori. The proposed method is generally applicable to any linear-phase FIR filter irrespective of its order being high, low, even, or odd as well as the impulse response being symmetric or antisymmetric. However, it is more efficient for filters with high orders as the conventional design of such filters is more challenging. For example, to design a linear-phase FIR lowpass filter of order 131071 with a stopband attenuation of about 55 dB, which is used as the prototype filter of a cosine modulated filter bank (CMFB) with 8192 channels, our proposed method requires only 16 unknown parameters. The paper gives design examples for individual lowpass filters as well as the prototype filters for fixed and flexible modulated FBs.

This paper presents a tunable bandpass filter with a reconfigurable-pole response. 2-, 3-, and 4-pole states can be obtained based on employing series resonators with RF switches. The synthesis for the proposed filter is established, and the bandwidth for each pole state can be selected based on theory. The filter is built on a Duroid substrate with er=10.2 and h=25 mil. The tuning for the center frequency is done using Schottky diodes, and the selection of the filter poles is achieved using RF microelectromechanical systems switches. A tuning of 0.73-1.03 GHz is achieved with a 1-dB fractional bandwidth of 3.9%-5.2%. The rejection levels at 200-MHz offset frequency of 2-, 3-, and 4-pole states are 28, 36, and 45 dB, respectively. This filter topology can find applications in reconfigurable radios with dynamic rejection levels.

In this paper, a vector fitting (VF) based analytical extraction method, which is capable of accurately extracting the coupling matrix and the uneven unloaded Qs of each electric resonators of a filter, is presented. Having had the complex poles and residues determined using VF, the coupling matrix can be obtained by a sequence of complex orthogonal transformations. As a side product, the unloaded Qs for each resonator will be directly obtained from the complex diagonal elements of the coupling matrix. To demonstrate the effectiveness of the proposed method, an ideal demonstrative example along with two practical challenging filter tuning examples, namely, an eight-pole dual-mode dielectric filter and an eight-pole dual-mode predistortion filter, are demonstrated. An excellent match between the responses of the measured data and those from the extracted coupling matrix with actual unloaded Q factors can be seen.

Multidimensional linear phase perfect reconstruction filter bank (MDLPPRFB) can be designed and implemented via lattice structure. The lattice structure for the MDLPPRFB with filter support N(MΞ) has been published by Muramatsu , where M is the decimation matrix, Ξ is a positive integer diagonal matrix, and N(N) denotes the set of integer vectors in the fundamental parallelepiped of the matrix N. Obviously, if Ξ is chosen to be other positive diagonal matrices instead of only positive integer ones, the corresponding lattice structure would provide more choices of filter banks, offering better trade-off between filter support and filter performance. We call such resulted filter bank as generalized-support MDLPPRFB (GSMDLPPRFB). The lattice structure for GSMDLPPRFB, however, cannot be designed by simply generalizing the process that Muramatsu employed. Furthermore, the related theories to assist the design also become different from those used by Muramatsu . Such issues will be addressed in this paper. To guide the design of GSMDLPPRFB, the necessary and sufficient conditions are established for a generalized-support multidimensional filter bank to be linear-phase. To determine the cases we can find a GSMDLPPRFB, the necessary conditions about the existence of it are proposed to be related with filter support and symmetry polarity (i.e., the number of symmetric filters ns and antisymmetric filters na). Based on a process (different from the one Muramatsu used) that combines several polyphase matrices to construct the starting block, one of the core building blocks of lattice structure, the lattice structure for GSMDLPPRFB is developed and shown to be minimal. Additionally, the result in this paper includes Muramatsu's as a special case.

This letter presents a new filter, based on substrate integrated folded waveguide (SIFW) technology, which exhibits compact size and good out-of-band rejection. The filter is based on a SIFW cavity, which guarantees size reduction, and the out-of-band rejection is controlled by the suppression and tuning of the high-order cavity modes. A detailed investigation of the cavity mode spectrum is presented, to illustrate the operation principle and the design of the filter. The interesting feature of this filter is the possibility to design the pass band and the return band by simply tuning the mode spectrum of the cavity, which is practically unaffected by the connection to the excitation ports. The fabrication and testing of a prototype operating at 4.5 GHz validate the proposed filter topology.

This letter proposes a new design method for a bandstop filter with two stopbands. Contrary to a conventional method, the presented method allows for achieving two stopbands without increasing the number of the couplings between resonators and the transmission line connecting the input and output ports. In addition, a filter designed using the presented method can not only have different center frequencies but also have different bandwidths by adjusting the resonant frequencies of the resonators. For verification of the proposed approach a dual-stopband filter using four tunable substrate-integrated waveguide resonators has been designed and measured.

This paper reports the first co-design configuration of a power amplifier (PA) in cascade with a high- Q bandpass filter. By matching the filter's input port directly to the transistor's drain node, the conventional output matching network (OMN) of a PA is entirely eliminated. This leads to smaller size/volume, minimized loss, and enhanced overall performance. To enable this co-design method, the matching-filter synthesis theory is proposed and investigated in detail in this paper. Based on this theory, a 3% bandwidth (centered at 3.03 GHz) two-pole filter, implemented using high- Q evanescent-mode cavity resonators, is designed as the PA OMN to provide optimized fundamental and harmonic impedances for a commercial 10-W GaN transistor. Simulation and measured results show that the co-designed PA-filter module yields a desired Chybeshev filter behavior while maintaining excellent PA performance in the passband with 72% efficiency, 10-W output power, >10-dB gain, and 60-dBm output third-order intercept point. This co-designed module experimentally presents a 8% higher overall efficiency compared to a control group developed using a conventional independent PA and filter, which further validates the effectiveness of this method.

A common-mode (CM) filter based on the LCL filter topology is proposed in this paper, which provides a parallel path for ground currents and which also restricts the magnitude of the EMI noise injected into the grid. The CM filter makes use of the components of a line to line LCL filter, which is modified to address the CM voltage with minimal additional components. This leads to a compact filtering solution. The CM voltage of an adjustable speed drive using a PWM rectifier is analyzed for this purpose. The filter design is based on the CM equivalent circuit of the drive system. The filter addresses the adverse effects of the PWM rectifier in an adjustable speed drive. Guidelines are provided on the selection of the filter components. Different variants of the filter topology are evaluated to establish the effectiveness of the proposed circuit. Experimental results based on EMI measurement on the grid side and the CM current measurement on the motor side are presented. These results validate the effectiveness of the filter.

Powerline interference is one of the most dominant problems in detection and processing of biopotential signals. This work presents a new fully integrated notch filter exhibiting high linearity and low power consumption. High filter linearity is preserved utilizing active-RC approach while IC implementation is achieved through replacing passive resistors by R-2R ladders achieving area saving of approximately 120 times. The filter design is optimized for low power operation using an efficient circuit topology and an ultra-low power operational amplifier. Fully differential implementation of the proposed filter shows notch depth of 43 dB (78 dB for 4th-order) with THD of better than -70 dB while consuming about 150 nW from 1.5 V supply.

This paper presents a general procedure to obtain Butterworth filter specifications in the fractional-order domain where an infinite number of relationships could be obtained due to the extra independent fractional-order parameters which increase the filter degrees-of-freedom. The necessary and sufficient condition for achieving fractional-order Butterworth filter with a specific cutoff frequency is derived as a function of the orders in addition to the transfer function parameters. The effect of equal-orders on the filter bandwidth is discussed showing how the integer-order case is considered as a special case from the proposed procedure. Several passive and active filters are studied to validate the concept such as Kerwin-Huelsman-Newcomb and Sallen-Key filters through numerical and Advanced Design System (ADS) simulations. Moreover, these circuits are tested experimentally using discrete components to model the fractional order capacitor showing great matching with the numerical and circuit simulations.

In this brief, an efficient implementation of reconfigurable warped digital filter with variable low-pass, high-pass, bandpass, and bandstop responses is presented. The warped filters, obtained by replacing each unit delay of a digital filter with an all-pass filter, are widely used for various audio processing applications. However, warped filters require first-order all-pass transformation to obtain variable low-pass or high-pass responses, and second-order all-pass transformation to obtain variable bandpass or bandstop responses. To overcome this drawback, the proposed method combines the warped filters with the coefficient decimation technique. The proposed architecture provides variable low-pass or high-pass responses with fine control over cut-off frequency and variable bandwidth bandpass or bandstop responses at an arbitrary center frequency without updating the filter coefficients or filter structure. The design example shows that the proposed variable digital filter is simple to design and offers substantial savings in gate counts and power consumption over other approaches.

In this paper, we show a new bandstop filter circuit topology. Unlike conventional bandstop filter circuit topologies, the new circuit topology has inter-resonator coupling structures. The presence of these inter-resonator coupling structures enables convenient switching from a bandstop to a bandpass filter. Using the new bandstop filter topology, this paper demonstrates a design of a frequency-agile bandstop-to-bandpass switchable filter. The filter is composed of tunable substrate-integrated cavity resonators and can be switched to have either a bandstop or bandpass response. Switching is achieved by turning on and off switches placed within the filter structure. A prototype of the proposed design is fabricated and the concept is verified experimentally.

This paper shows an approach for the broad-band modeling of passive power-supply filter structures, which may be applied to the virtual filter design. The most important advantage of this technique is the possibility of considering the parasitic and functional behavior of a power-supply filter in the same simulation. The approach provides a 3-D model of the filter structure based on a differential field solver. Moreover, the passive components are approximated by combined behavioral-physical 3-D models, which allow the simulation of this structure and the physical volumetric modeling of the current distribution in the components. Thus, the functional behavior of the filter is modeled taking into account all the high-frequency effects (equivalent serial inductance, equivalent serial resistance, parasitic capacitances, punch-grid issues, couplings between components, couplings between interconnections, losses in the plastic environment, etc.). This paper provides a validation of the approach by measurements of a simplified hardware sample and of an industrial filter sample as well.