Tunable Active Filter Research Articles

A compact and tunable active inductor-based bandpass filter with high quality factor for Wireless LAN applications

A fully-differential compact and tunable second-order bandpass filter (BPF) with high quality factor using a novel active inductor (AI) has been proposed for 3.6 GHz WLAN applications. The proposed AI employs a differential amplifier as a feedforward transconductor and a common-source (CS) transistor as a feedback transconductor in a symmetrical configuration. The combination of a cascode scheme and a resistor in the feedback path enhances the quality factor of the AI, thereby increasing the mid-band gain of the BPF. In order to achieve independent tuning of both the center frequency and mid-band gain of the BPF, a varactor capacitor is utilized. The proposed second-order BPF is designed with a center frequency and a bandwidth of 3.675 GHz and 10 MHz, respectively. Post-layout simulation, process corner, and temperature sweep analysis results are conducted with 65 nm CMOS technology at 1.2 V supply voltage. The proposed filter has a tuning range of 3.655–3.695 GHz and attains a mid-band gain of 67.5 dB, a noise figure of 14.5 dB, and a 1-db compression point of −12.39 dBm. Additionally, the BPF consumes a DC power of 1.22 mW and occupies an active area of only 8.85 μm × 10.3 μm.

The Dynamic Tunability of Memristor-Based Active Filters.

When the memristor was fabricated for the first time, it launched an entirely new field of research. Many of the published papers regarding memristors are primarily theoretical and are based on computer simulations. Some recent papers analyze the memristor's programming circuits, but to the best of the authors' knowledge, no memristor has been embedded into a commercial analog circuit. This paper is practically oriented and it is based on the experimental results obtained by measurements on the circuit prototype. We present a solution for automated programming of a commercially available memristor and its implementation in tunable active bandpass filter design. The novelty of this paper is that the active bandpass filter's central frequency could be programmed during the filter operation, so a pause for memristor state-switching is not required. The experimental results are promising, and open up possibilities for the memristor's application in analog systems.

Nonlinearity-Compensated Short-Range FMCW Radar for Weak Target Imaging

An easily implementable, low-cost, and portable broadband frequency-modulated continuous wave (FMCW) synthetic aperture radar (SAR) system is presented for short-range imaging applications. Design considerations and radar performance metrics are discussed in detail while investigating systematic and nonsystematic performance-limiting factors. This article introduces a signal processing procedure based on a closed-form comprehensive mathematical model to characterize the impact of the nonlinear frequency sweep on radar performance. Based on the proposed model, the nonlinearity is compensated using the time-resampling technique and without needing a reference response. A single-zone calibration does not provide enough accuracy when multiple targets are widely distributed in the cross-range direction. A range-and angle-dependent calibration scheme is proposed to mitigate the second-order effects more precisely, which are otherwise difficult to model mathematically. Detecting less reflective targets in the presence of a strong scatterer is challenging. A range-gating method based on a tunable active bandpass filter (BPF) is proposed to improve the radar system’s sensitivity by suppressing the dominant reflection and enhancing the weaker scatterer. The results are verified by developing SAR images of targets in free space and through a residential wall.

A Second Order 1.8–1.9 GHz Tunable Active Band-Pass Filter with Improved Noise Performances

In this paper, a novel active tunable band-pass filter with improved noise performances is presented. This filter is based on a negative resistance circuit (or active capacitance), where the gain obtained with a transistor is used to compensate for inductor losses. Moreover, the capacitance of the resonator is obtained through a voltage-controlled reverse-biased varactor, which allows for frequency tuning. Despite the active component, the proposed filter also has good noise performance. Measurements show a tunability range from 1.816 GHz to 1.886 GHz, with a bandwidth of 38 MHz. The insertion loss maximum value is 0.4 dB, while the noise figure value has a minimum value of 2.5 dB at the center frequency within the tunability range.

75–86-GHz Signal Generation Using a Phase-Controlled Quadrature-Push Quadrupler Driven by a QVCO or a Tunable Polyphase Filter

This article demonstrates a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band local-oscillator generation technique in 120-nm SiGe BiCMOS technology with high output power and high efficiency. The circuit employs a frequency quadrupler that is driven with differential quadrature inputs that are provided by either a quadrature voltage-controlled oscillator (QVCO) or a tunable active polyphase filter (PPF) circuit. The quadrupler employs a phase-controlled quadrature-push (PCQP) topology using stacked devices with a lower class-C common-emitter (CE) amplifier generating a current that is then modulated by an upper common-base (CB) amplifier driven out-of-phase with the lower devices. Such a structure generates a strong fourth-order harmonic. Four such stacks driven at their input using accurate differential quadrature signals increase the fourth-harmonic output power while suppressing other harmonics. The differential quadrature signals for the quadrupler are provided using either a PPF circuit or a capacitive injection-locking QVCO, which achieves wide tuning range and low phase noise. Both approaches are evaluated through the measurement of separate test circuits. The LO circuit using the QVCO provides 8–11.5-dBm output power over 75.2–83 GHz, power efficiency of 2.2–4.1%, including QVCO and buffer power, >20-dB harmonic rejection in the lower frequency range, and >14.4-dB harmonic rejection in the upper frequency range. The LO circuit using the active PPF provides 8.4–11.2-dBm output power over 75.6–82.8 GHz, power efficiency of 2.4–4.8%, including PPF and buffer power, and >23-dB harmonic rejection.

Resonant and Sensing Performance of Volume Waveguide Structures Based on Polymer Nanomaterials.

Organic–inorganic photocurable nanocomposite materials are a topic of intensive research nowadays. The wide variety of materials and flexibility of their characteristics provide more freedom to design optical elements for light and neutron optics and holographic sensors. We propose a new strategy of nanocomposite application for fabricating resonant waveguide structures (RWS), whose working principle is based on optical waveguide resonance. Due to their resonant properties, RWS can be used as active tunable filters, refractive index (RI) sensors, near-field enhancers for spectroscopy, non-linear optics, etc. Our original photocurable organic–inorganic nanocomposite was used as a material for RWS. Unlike known waveguide structures with corrugated surfaces, we investigated the waveguide gratings with the volume modulation of the RI fabricated by a holographic method that enables large-size structures with high homogeneity. In order to produce thin photosensitive waveguide layers for their subsequent holographic structuring, a special compression method was developed. The resonant and sensing properties of new resonant structures were experimentally examined. The volume waveguide gratings demonstrate narrow resonant peaks with a bandwidth less than 0.012 nm. The Q-factor exceeds 50,000. The sensor based on waveguide volume grating provides detection of a minimal RI change of 1 × 10−4 RIU. Here we also present the new theoretical model that is used for analysis and design of developed RWS. Based on the proposed model, fairly simple analytical relationships between the parameters characterizing the sensor were obtained.

Tunable Active Inductor-Based Second-Order All-Pass Filter as a Time Delay Cell for Multi-GHz Operation

In this paper, a CMOS wideband second-order voltage-mode all-pass filter as a time delay cell is proposed. The proposed all-pass filter is made up of solely two transistors as active elements and four passive components. This filter demonstrates a group delay of approximately 60 ps within a bandwidth of 5 GHz, achieving maximum delay–bandwidth product. The proposed circuit is highly linear and has an input-referred 1-dB compression point $$P_{1\mathrm{{dB}}}$$ of 2 dBm. The power consumption of the proposed circuit is only 10.3 mW. On the other hand, an active inductor is employed in the all-pass filter instead of a passive RLC tank; therefore, the three passive components are eliminated, in order to tune the time delay and improve the size. In this case, even though the power consumption increases, the time delay can be controlled across an improved bandwidth of approximately 10 GHz. Moreover, the circuit demonstrates a 1-dB compression point $$P_{1\mathrm{{dB}}}$$ of 18 dBm. The proposed all-pass filter is simulated in TSMC 180-nm CMOS process parameters.

Automated Calibration System for RF Configurable Voltage-Controlled Filters

This brief presents a complete hardware–software system for automated calibration and test of RF, configurable voltage-controlled devices, such as active filters. The proposed system consists of a programmable interface, based on a microcontroller and high-resolution digital-to-analog converters, and a dedicated front-end with an optimization software, hosted on a computer. The designed software is able to communicate with the instrumentation (signal or vector analyzer) to which the tunable circuit is connected, and analyzing the run-time measured data the algorithm generates suitable tuning signals through the hardware interface connected to the device under test, therefore allowing to obtain the desired behavior and to calibrate the circuit. The proposed system has been tested on RF tunable active filters with good performances in terms of both convergence speed and accuracy.

Recent Advances in Resonant Waveguide Gratings

AbstractResonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide‐mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto‐optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

A Tunable Low Noise Active Bandpass Filter Using a Noise Canceling Technique

A monolithic tunable low noise active bandpass filter is presented in this study. Biasing voltages can control the center frequency and quality factor. By keeping the gain constant, the center frequency shift is 300 MHz. The quality factor can range from 90 to 290 at the center frequency. By using a noise cancelling circuit, noise is kept lower than 2.8 dB. The proposed filter is designed using MMIC technology with a center frequency of 2.4 GHz and a power consumption of 180 mW. ED02AH technology is used to simulate the circuit elements.

Tunable Blocker-Tolerant On-Chip Radio-Frequency Front-End Filter With Dual Adaptive Transmission Zeros for Software-Defined Radio Applications

This paper presents a tunable active bandpass filter (BPF) with adjustable transmission zeros (TZs) close to the passband for software-defined radio (SDR) applications. The RF front-end frequency selectivity is enhanced by the creation of TZs that also improve the out-of-band (OOB) input-referred third-order intercept point (IIP3). The filter is based on two-path signal cancellation and consists of a tunable BPF in parallel with two tunable bandstop filters. This combination ensures the correct amplitude and phase relationships across a wide tuning range to create adjustable TZs without sacrificing the gain of the passband. This paper presents in detail the design considerations and guidelines, as well as analysis of the filter performance in the presence of nonidealities such as parasitics and imperfect clock signal shape. The proposed filter is implemented with high- $Q~N$ -path filter blocks in a 65-nm CMOS process. The passband of the filter is tunable from 0.1 to 1.4 GHz with a 3-dB bandwidth of 9.8–10.2 MHz, a gain of 21.5–24 dB, a noise figure of 3–4.2 dB, and a total power consumption of 50–73 mW. TZs are created on both sides of the passband with a minimal offset of 25 MHz and are tunable across a 20-MHz range with up to a 60-dB rejection. The measured blocker 1-dB compression point is 8 dBm and the OOB IIP3 is 23 dBm. The reported filter provides a promising on-chip filtering solution for multistandard multifrequency SDR applications with improved interference mitigation capabilities.

5/60 GHz $0.18~\mu m$ CMOS Dual-Mode Dual- Conversion Receiver Using a Tunable Active Filter for 5-GHz Channel Selection

A dual-mode dual-conversion receiver with two far-apart carrier frequencies, 5 and 60 GHz, and two very different channel bandwidths, tens-MHz and GHz, is demonstrated in a standard $0.18~\mu \text {m}$ CMOS technology. The dual conversion architecture receives 60-GHz mode using Schottky diodes at the first conversion stage and merges 5-GHz mode at the second conversion stage. The 5-GHz RF channel selection is achieved by inserting a 20-MHz bandwidth tunable active filter after a 5-GHz low-noise amplifier for the noise concern and before the second down-conversion mixer to relax the linearity requirement of subsequent stages. A tunable active filter with improved linearity using a transformer-coupled scheme is employed. As a result, the narrow 20 MHz channel bandwidth selection at 5-GHz mode shows a 500 MHz tuning range with noise figure of 9 dB and conversion gain of 28 dB. For 60-GHz operation, the 3-dB IF bandwidth is 1 GHz with noise figure of about 20 dB and conversion gain of −3 dB.

A Wide Tuning Range Active Filter for the 5G in CMOS Technology

Recently, tunable active filters, highly solicited in mobile radio network and wireless systems, have known great improvements in terms of bandwidth selectivity and frequency tuning. Active inductor based filters known by their ease of integration and frequency tuning possibilities have been widely studied in the literature, however, stated works never exceeded 10 GHz. This paper proposes a topology of an active filter operating in the millimetre band around 30 GHz using a CMOS 0.35 µm from Austria Micro Systems foundry with a tuning range up to 16 GHz and a centre frequency of 34.3 GHz and 38 GHz. A very high quality factor is obtained with this topology with input and output reflections of respectively -18 dB and -16 dB and very low noise figure around 1. This filter will be used in the implementation of 5G transceivers in the millimetre band.

Current-programmable Universal Biquad Filter Based on Modified Current Differencing Transconductance Amplifier

This paper presents a new current programmable active element called Modified Current Differencing Transconductance Amplifier (MCDTA). The parameters of the circuit - input resistance and transconductance - can be tuned by control currents. The circuit with several external components - diodes and grounded capacitors - makes it possible to build basic analog circuits: first order and second order tunable active filters, rectifiers, peak detectors and others. This paper discusses a universal biquad filter based on the MCDTA with different tuning capabilities. The simulation results show that it can be used as a part of a programmable analog signal processing system.

Electronically tunable inverse active filters employing OTAs and grounded capacitors

This paper introduces inverse active filters employing operational transconductance amplifiers (OTAs) and grounded capacitors. The filter circuits can realise inverse low-pass, inverse band-pass and inverse high-pass transfer functions by addition of the circuit currents. Additionally, the circuit parameters ω0, Q and H can be set orthogonally or independently by adjusting the bias currents of the OTAs. The inverse filter circuits enjoy very low sensitivities to active and passive components. The achievement examples are given together with simulation results by PSPICE.

TUNABLE ACTIVE FILTERS FOR RF AND MICROWAVE APPLICATIONS

In this paper, we present a low-voltage tunable active filter for microwave applications. The proposed filter is based on a single-transistor active inductor (AI), that allows the reduction of circuit area and power consumption. The three active-cell bandpass filter has a 1950 MHz center frequency with a -1 dB flat bandwidth of 10 MHz (Q ≈ 200), a shape factor (30–3 dB) of 2.5, and can be tuned in the range 1800–2050 MHz, with constant insertion loss. A dynamic range of about 75 dB is obtained, with a P1dB compression point of -5 dBm. The prototype board, fabricated on a TLX-8 substrate, has a 4 mW power consumption with a 1.2 V power supply voltage.

A tunable and reconfigurable MMIC active filter in GaAs technology

The filter presented in this article is an active band-pass filter whose center frequency and bandwidth can be tuned. It is composed of channels inserted into a distributed structure, and the frequency agility is obtained by activating one or more of them. The concept is validated with measurements realized on a 3-channel prototype structure implemented in the United Monolithic Semiconductors (UMS) PPH25 GaAs technology from UMS. This filter is tunable throughout the X and Ku bands. This first prototype yields encouraging results: the center frequency can be tuned between 9.7 and 14 GHz, with an average gain of 10 dB throughout this range and a noise figure between 7 and 11 dB. The filter occupies 13.5 mm2 of area and consumes 10.5 mA per active stage from a 4 V supplying voltage. It is designed for wideband and agile receivers.

Highly compact tunable stop-band active filter for advanced communication systems

In this paper a novel electronically tunable active stop-band filter design is reported. This filter is designed in the UHF band to avoid the degradation of the receiver sensitivity when interfering signals at fixed or changing frequency are coupled to the antenna of the receiver front-end. The presented solution shows low insertion loss far from the notch frequency while rejecting the interfering signals by more than 40 dB regardless of their frequencies. The filter architecture is simple; it is based on a main transmission line segment to which a quarter-wavelength line segment is coupled. The fact of loading the end of the coupled line by a novel tunable active capacitor circuit introduced in this paper allows tuning simultaneously the filter frequency and the band-stop depth while reducing the power consumption and maintaining the device electrically stable. Moreover, by using the semi-lumped approach, the filter is compacted of more than 70 % in comparison to the conventional quarter-wavelength coupled line. The concept is demonstrated using low cost FR4 substrate and surface mount technology. The complete design has been fully simulated and experimental prototypes realized. Measurements are demonstrating the benefits of the proposed design.

Tunable active bandpass filter design

A tunable active bandpass filter that uses control voltage to select passband frequency response is presented. The proposed topology basically consists of a cascoded current-injection active inductor so as to tune passband frequency response from 2.35 to 3.66 GHz and extend the available bandwidth.

A Low-Noise Amplifier With Tunable Interference Rejection for 3.1- to 10.6-GHz UWB Systems

An ultrawideband common-gate low noise amplifier with tunable interference rejection is presented. The proposed LNA embeds a tunable active notch filter to eliminate interferer at 5-GHz WLAN and employs a common-gate input stage and dual-resonant loads for wideband implementation. This LNA has been fabricated in a 0.18-?m CMOS process. The measured maximum power gain is 13.2 dB and noise figure is 4.5-6.2 dB with bandwidth of 3.1-10.6 GHz. The interferer rejection is 8.2 dB compared to the maximum gain and 7.6 dB noise figure at 5.2 GHz , respectively. The measured input P1dB is -11 dBm at 10.3 GHz. It consumes 12.8 mA from 1.8-V supply voltage.