Tuning Circuit Research Articles

A power-efficient and re-configurable analog artificial neural network classifier

This paper presents a power-efficient and re-configurable radial basis function-artificial neural network (RBF-ANN) for real-time pattern classification tasks. We have developed a MATLAB-based behavioral model, which can be employed to facilitate the off-chip learning of the proposed network with a hybrid learning algorithm. Besides, a generic design methodology is presented to ease implementing different scales of neural networks. For the RBF-ANN, an analog tunable Gaussian kernel circuit is used as an activation neuron while a current-mode computation is employed to improve the power efficiency. The proposed network is designed and simulated in 0.18 μm X-FAB CMOS process for a non-linear XOR-pattern classification and voice activity detector (VAD), respectively. It is found that the network's weights obtained using the developed model in MATLAB are well-matched with the Spectre simulation (Virtuoso) results with a maximum relative error of 7.1%. Consequently, the proposed model can be effectively employed for the off-chip training of RBF-ANN. Besides, the preliminary simulation results of the VAD depict that the classification accuracy reaches as large as 95% in a noisy environment of babble with an acoustic signal to noise ratio (SNR) of 10 dB. Meanwhile, the power efficiency of the proposed network gets significantly improved compared to the recent prior arts.

Calculation of the efficiency of electrically small MF antenna for mine communications

Today, the developers of electrically small antenna equipment are faced with the problem of reliable modeling of electrically small antennas. The existing methods of computer modeling of electrically small antennas, as experience has shown, are resource-intensive. One of the ways to solve this problem is to use the method of replacing the antenna with an equivalent electrical circuit. This method is based on the assumption that any part of the antenna can be replaced by equivalent values of inductance, capacitance or active resistance, which can be investigated together with the elements of the tuning and matching circuit. The resulting equivalent electrical circuit can be analyzed by the methods of the theory of electrical circuits, and most of the antenna characteristics of interest to the developer can be determined. These include efficiency, quality factor, frequency dependences of impedance and voltage standing wave ratio (VSWR). In this work, a sample of an electrically small resonant medium frequency (MF) antenna and its equivalent circuit are presented, and its characteristics are analyzed using the theory of electrical circuits. The graphs of the dependence of the efficiency on the frequency at the resonant tuning of the antenna are plotted.

Ferrite-Less Frequency-Tuned Printed-Coil Resonator With Rear Metallic Plate for RFID Applications

The communication distance of Radio Frequency Identification (RFID) system is affected by the environment. This study presents a compact ferrite-less frequency-tuned printed-coil (PC) resonator, which introduces the additional PC resonators as well as the tunable matching circuits to the coil-based antennas, to address the rear metallic effect and the impedance mismatch effect caused by the environment variation for RFID system. The tunable matching circuit using the proposed negative voltage generator achieves low power consumption of only 0.5 mW. The usefulness of the proposed technique is experimentally validated with the rear metallic plate and the interference of water. Measurements show that compared with the commercial PC resonator, the proposed technique reduces the gaps between the coil and the rear metallic plate from 2.9 mm to 1.1 mm when the detected distance is 4.1 mm and, furthermore, improves the detected distance of the system from 3 mm to 17 mm with the interference of water.

Sensitive Near-Field Slit Probe with High Spatial Resolution for Passive Millimeter-Wave Microscopy

A novel type of near-field slit probe with high sensitivity and high spatial resolution is proposed. We tested the implementation of this in passive millimeter-wave microscopy at frequencies around 50 GHz. The slit probe comprises a standard rectangular waveguide incorporating a triple-screw tuner penetrating into the waveguide, followed by a four-section quarter-wave transformer, and a metal-coated silicon chip with a micro-slit aperture fabricated at the probe tip using a bulk micromachining technique. The probe allows the transmission of the thermal radiation collected at the probe aperture to the radiometric receiver used in passive millimeter-wave microscopy to be maximized, resulting in highly sensitive measurements. The system noise temperature of the radiometric receiver including the slit probe used in the passive measurements was found to be 1800 K, meaning that a temperature resolution of 0.18 K with the integration time set to 1 s was achieved. This system noise temperature is four times better than that when a tapered slit probe with no tuning circuit was used. Image acquisition with a spatial resolution of better than 100 μm was demonstrated over the temperature range from 210 to 310 K.

2.4 GHz GaN HEMT Class-F Synchronous Rectifier Using an Independent Second Harmonic Tuning Circuit.

This paper proposes a class-F synchronous rectifier using an independent second harmonic tuning circuit for the power receiver of 2.4 GHz wireless power transmission systems. The synchronous rectifier can be designed by inverting the RF output port to the RF input port of the pre-designed class-F power amplifier based on time reversal duality. The design of the class-F power amplifier deploys an independent second harmonic tuning circuit in the matching networks to individually optimize the impedances of the fundamental and the second harmonic. The synchronous rectifier at the 2.4 GHz frequency is designed and implemented using a 6 W gallium nitride high electron mobility transistor (GaN HEMT). Peak RF-dc conversion efficiency of the rectifier of 69.6% is achieved with a dc output power of about 7.8 W, while the peak drain efficiency of the class-F power amplifier is 72.8%.

LiNbO3 waveguide with embedded Ag nanowire and 3L MoS2 for strong light confinement and ultra-long propagation length in the visible spectral range.

A vertical slot LiNbO3 waveguide with an Ag nanowire and 3L MoS2 embedded in the low-refractive index slot region is proposed for the purpose of improving light confinement. We find that the proposed waveguide has a novel dielectric based plasmonic mode, where local light field is enhanced by the Ag nanowire. The mode exhibits an extremely large figure of merit (FoM) of 6.5×106, one order of magnitude larger than that the largest FoM of any plasmonic waveguide reported in the literature to date. The waveguide also has an extremely long propagation length of 84 cm in the visible wavelength at 680 nm. Furthermore, the waveguide has a low sub-micro bending loss and can be directly connected to all-dielectric waveguides with an extremely low coupling loss. The proposed vertical slot LiNbO3 waveguide is a promising candidate for the realization of ultrahigh integration density tunable circuits in the visible spectral range.

Alternating Current Sensing Slot Antenna

Dual operations of AC current sensing and Bluetooth transmission using a reconfigurable slot antenna are described here. The novel current sensing setup comprises of a tunable antenna connected to a current transformer and AC/DC converter to create a smart AC current sensing mechanism. The tunable antenna consists of a double-layer slot antenna on a thin, flexible substrate with a tuning circuit consisting of capacitive-coupled biasing tracks on the backside. Capacitive coupling isolates circuits at DC while providing connectivity at radio frequency (RF). Tracks act as the capacitors for the tuning biasing circuit. A double-sided copper clad Mylar substrate is etched to produce the slot antenna on one side and the biasing circuit using inexpensive Varactor diodes on the other side. The antenna tunes over a wide frequency range of approximately 2:1. The antenna is able to sense currents by providing a frequency response when connected to the sensing system. The current sensing antenna can also detect the operational or non-operational states of the appliances and devices. This low-cost setup of antenna on a flexible substrate can assist in detecting the power and current monitoring in household electrical devices providing an energy-efficient solution while also operating as a transmitter via Bluetooth. The measured reflection coefficients and radiation patterns are in a good agreement with the simulated results and noticeably clear sensing of current is achieved.

Memristors as Candidates for Replacing Digital Potentiometers in Electric Circuits

Digital potentiometers are substantial components for the design of many mixed-signal electronic circuits and systems. Their capability to program resistance value almost instantly provides hardware designers an additional level of freedom. Unfortunately, this feature is limited to DC and lower frequencies, due to parasitic effects. Nowadays, memristors as continuously tunable resistors are becoming candidates for potentiometer successors. Memristors are two-terminal non-volatile devices which have less significant parasitic effects and a wide resistance range. The memristance value can be changed on the fly. Using nanotechnology, memristor implementation has a nanoscale footprint with nanosecond transition between resistive states. In this paper, we present a comparison between the frequency characteristics of digital potentiometers and the only commercially available memristors. Memristor parasitic effects dominate at higher frequencies which extends the bandwidth. In order to present the advantages of memristive circuits, we have analyzed and implemented tunable circuits such as a voltage divider, an inverting amplifier, a high-pass filter, and a phase shifter. A commercially available memristor by KnowM Inc. is used for this purpose. Experimental results obtained by the measurements verify that a memristor has equal or better characteristics than a digital potentiometer. Memristive realizations of voltage dividers and inverting amplifiers have a wider bandwidth, while filters and phase shifters with a memristor have almost identical frequency characteristics as the corresponding realizations with a digital potentiometer.

Modeling and Analysis of the Piezoelectric Vibration Energy Harvester with Externally Connected Inductor

Piezoelectric energy harvesters are promising in the powering of wireless sensor networks with their ability to utilize ambiently available energy. A notable feature to be noted is the electromechanical coupling in the system. To explore the influence of tuning circuit, we develop here in this contribution a fully nonlinear model of a piezoelectric vibration energy harvester with a tuning circuit consisting of a resistor in parallel connection with an inductor. A linearized electromechanical model is obtained with small-amplitude base excitation. A series of numerical simulations are done to showcase the influence of the tuning circuit and uncover the parametric dependence of system output performances. It is concluded that the addition of connected inductor help improve the level of output voltage and power, while the working bandwidth of the system is widened to some degree. Advice is then provided upon the theoretical design and practical application of piezoelectric energy harvesters.

Low-power CMOS circuit design of audio frequency shift keying for emergency alert system

Emergency alert systems are highly essential during natural disasters like earthquake, flooding, volcanic eruption, landslides and hurricanes to make the public alert. Existing emergency alert systems use siren, text alert and broadcasting, but they are slow and may not alert at the right time in crucial situations. An Audio Frequency Shift Keying (AFSK) is designed to alert the public in emergency without hearing the text of the alert. It is designed with low power relaxation oscillator and voltage-controlled oscillator using CMOS technology. In this work, a relaxation oscillator is designed with inductor-less circuit for wideband tuning and provides huge area saving in the design. The control unit is designed to select the audio signal with two different oscillation frequencies based on input data. The public would be able to get awareness about the condition of natural disaster based on frequency of audio signal. An AFSK is designed with an operating voltage of 400 mV that consumes only 6.18 µW of power while implementing using 180 nm CMOS technology.

A 8800 μm² CCO-Based Voltage-Droop and Temperature Detector in 65 nm

The Vcc level and temperature of IC’s are important parameters which determine the power/performance. Resonances in the package and platform can cause significant AC voltage droops which can degrade functionality, requiring additional guard-band. Prior-art droop detectors utilize digital delay circuits, such as tunable replica circuits to measure these droops. However, the delay is a strong function of temperature as well as the DC Vcc level, making it difficult to differentiate the AC droop across different voltage and temperature levels. It is proposed to utilize a current controlled oscillator (CCO) with an analog bias to mitigate the voltage and temperature dependencies, such that only the AC droop is measured. The CCO frequency is independent of the DC Vcc level, while the temperature is also characterized along with the AC droop, such that both temperature and droop levels can be extracted. The sensor can measure droops and temperature to an accuracy of 10mV and ± 3 °C respectively. The circuit occupies $8800~\mu \text{m}^{2}$ in 65nm with a power consumption of $297~\mu \text{W}$ . This circuit is very useful to characterize the power grid in design for test (DFT) applications as well as on-the-fly real time chip operation.

Liquid–metal-bridge∼island design: seamless integration of intrinsically stretchable liquid metal circuits and mechanically deformable structures for ultra-stretchable all-solid-state rechargeable Zn–air battery arrays

The demonstrated “liquid-metal-bridge∼island” architecture enables the fabrication of ultra-stretchable solid-state micro-Zn–air battery arrays with tunable open circuit voltage/peak power (1.35–5.24 V/38–145 mW), large elongation (400%), and excellent integration capability.

Engineering tunability through electro-optic effects to manifest a multifunctional metadevice.

Ultrafast modulation of the refractive index exhibits either linear or nonlinear electro-optic (EO) effect, which is extensively utilized in tunable photonic circuits. Silicon, a mature material for on-chip devices, lacks a strong electro-optic (EO) Pockels effect. Utilization of the Pockels effect alters the intrinsic property (refractive index) of the material that manifests tunability and offers expanded functionalities. Driven by the limited space constraints in data storage, sensing, and imaging applications, we propose an electrically tunable meta-device whose resonance wavelength and focal length can be tuned by varying applied electric fields in the visible range. The fundamental unit of a metalens is the barium titanate (BTO) diffractive optical element placed on indium titanium oxide (which serves as an electrode) with SiO2 as the substrate. The metalens' tunability is characterized by point spread function (PSF), full-width half-maximum (FWHM), and imaging bandwidth that demonstrates the tuning of resonance wavelength and focal length. Moreover, polarization-insensitive meta-holograms are realized at a wavelength of 633 nm without utilizing propagation and Pancharatnam–Berry (PB) phase. The proposed study can find exciting applications in machine vision, broadband microscopy, and spectroscopy.

Mid-Range Wireless Power Transfer System for Various Types of Multiple Receivers Using Power Customized Resonator

This paper presents a high-efficiency wireless power transfer (WPT) system that can charge multiple receivers (Rx's) of various types. For system analysis, the transmitted power and received power levels are derived using the parameters of the resonators based on electro-magnetic (EM) resonance. Using the analysis results, the power customized resonator (PCR) not only for deriving sufficient output power from the transmitter (Tx) but also for appropriately distributing the received power to the various and multiple Rx's is proposed. In addition to the PCR, the Tx unit is designed to work as a load-dependent voltage source using a differential Class-E power amplifier (PA) through a wide range of load impedances. Therefore, the Tx can naturally adapt to the required Tx power levels with a high efficiency corresponding to various Rx configurations without additional tunable circuits or adaptive control schemes. The WPT system, including the load-dependent voltage source for the Tx, full-bridge rectifiers for the Rx's, and the proposed PCR, was designed for the 6.78 MHz frequency band. The proposed system is validated for use with multiple mobile devices by conducting experiments with nine charging cases using three types of Rx's. For all cases, high system efficiencies of 70.7-85.5% were maintained over received power levels of 8.6-45.7 W at a charging distance of 30 mm, and each of the three types of Rx's were experimentally verified to receive sufficient power.

Effect ofLeft and Right Coronary Flow Waveforms on Aortic Sinus Hemodynamics and Leaflet Shear Stress: Correlation with Calcification Locations.

Coronary flow induces hemodynamic alterations in the aortic sinus region. The objectives of this study are to: (1) investigate the differences among sinus hemodynamics and leaflet wall shear stresses engendered by the left versus right versus non-coronary flow and (2) correlate respective wall shear stresses with leaflet calcification in patients. A left heart simulator flow loop with a tunable coronary circuit provided physiological coronary flow waveforms corresponding to the left coronary cusp case (LCC), right coronary cusp case (RCC), and non-coronary cusp case (NCC). High spatio-temporal resolution particle image velocimetry was conducted to quantify leaflet wall shear stress and sinus vorticity fields and to measure aortic leaflet tip kinematics. Thirty-one patients with severe calcific aortic valve disease were segmented from CT data for the calcific volumes in their respective left, right, and non-coronary cusps. Leaflet tip position during systole shows the RCC has a wider leaflet opening compared to LCC and NCC. Velocity and vorticity fields combined with leaflet position data show that sinus vorticity is diminished (peak ~ 43 s-1) in the LCC while RCC and NCC maintain high vorticity (~ 1200 and ~ 950 s-1 respectively). WSS magnitudes greater than 0.3 Pa show 20 and 81% greater occurrences in the LCC and RCC respectively compared to NCC. Significant differences [X2(2,n = 31) = 7.31,p=0.0258] between the calcification levels in each cusp of the patient population. Coronary flow differences between LCC, RCC, and NCC show significant impact on leaflet kinematics and sinus flow hemodynamics. Clinical data correlations of the coronary flow cases indicate the left coronary cusp has a higher likelihood of calcification compared to the right.

A 1.5–5-GHz Integrated RF Transmitter Front End for Active Matching of an Antenna Cluster

A recently proposed method for realizing frequency-reconfigurable antennas across a wideband is based on adjusting the feed amplitudes and phases of a multiport antenna. In this article, we demonstrate the feasibility of the method, for the first time, with a conjunction of an integrated RF transmitter and a four-element antenna cluster. The implementation performs on-chip amplitude and phase tuning with supply scaling and delay tuning circuits to tune the antenna cluster without requirement of matching network. The antenna cluster is built with four closely spaced antenna elements implemented on a printed circuit board. The transmitter integrated circuit (IC) is implemented in a 28-nm CMOS process with the chip size of 0.85 mm $\times0.95$ mm, including pads. The proof-of-concept implementation demonstrates tunability across a wideband from 1.5 to 5 GHz.

Adaptive damping tuning and circuit implementation for broad bandwidth energy harvesting

This paper presents a circuit to tune the electrical damping for optimal power harvesting at time varying excitation frequencies. Optimization of parameters, such as electrical damping to match the mechanical damping and the resonant frequency to match the excitation frequency have long been known. However, the electrical damping optimized at the resonant frequency is not necessarily the optimum point when the excitation frequency changes. This result is especially important in vibration energy harvesting systems since the vibration source is generally not at a single fixed frequency. The proposed circuit detects the excitation frequency and tunes the electrical damping based on a function, obtained from mechanical system modeling and simulation. A frequency detection circuit and a boost converter operating in critical conduction mode are used. Both modeling and experiment results show that the impedance tuning circuit provides the required optimal damping at different excitation frequencies and achieves a much broader bandwidth compared with the conventional system. When the excitation frequency increases to 1.1–1.4 times the natural frequency, the proposed adaptive damping tuning increases the power output by 30%–100% compared to the traditional one.

Design and Analysis of 2.4 GHz Low-Noise, High-Gain 0.18 μm CMOS Cascode Low-Noise Amplifier for IRNSS Applications

Low-Noise Amplifier (LNA) plays a crucial part in Radio Frequency (RF) front-end architecture. This paper mainly focuses on designing LNA for Indian Regional Navigation Satellite System (IRNSS) receiver. IRNSS operates on two frequency bands (L5 and S band) and this design is proposed for S band with the center frequency of 2492.028 MHz. Cascode topologies are considered to be conventional ones and they provide higher gain and better reverse isolation. Four different approaches of single-stage cascode topology, such as Common Source (CS) cascode, Common Gate (CG) cascode, shunt-resistive feedback cascode and current reuse cascode, were designed and their performance metrics, based on gain, Noise Figure (NF), return losses and stability, are presented. Focused on the gain and noise figure improvements, Common Source (CS) cascode with interstage series LC circuit LNA was designed and optimized with input and output matching circuitries. The proposed optimized circuit uses current reuse technique along with CS stage to improve the power gain and to achieve low-noise figure. The interstage LC circuit is mainly implemented to act as a tuning circuit to achieve a narrow range of frequency. The proposed work is simulated using 180 nm CMOS technology Generic Process Design Kit (GPDK) and achieve a power gain (S21) of 24.89, 0.994 dB NF, −16.2 dB input return loss (S11) and −11.06 dB output return loss (S22), with higher reverse isolation around −30.47 dB at 1.8 V power supply.

ADMX SLIC: Results from a Superconducting LC Circuit Investigating Cold Axions.

Axions are a promising cold dark matter candidate. Haloscopes, which use the conversion of axions to photons in the presence of a magnetic field to detect axions, are the basis of microwave cavity searches such as the Axion Dark Matter eXperiment (ADMX). To search for lighter, low frequency axions in the sub- 2×10^{-7} eV (50MHz) range, a tunable lumped-element LC circuit has been proposed. For the first time, through ADMX SLIC (Superconducting LC Circuit Investigating Cold Axions), a resonant LC circuit was used to probe this region of axion mass-coupling space. The detector used a superconducting LC circuit with piezoelectric driven capacitive tuning. The axion mass and corresponding frequency ranges 1.7498-1.7519×10^{-7} eV (42.31-42.36MHz), 1.7734-1.7738×10^{-7} eV (42.88-42.89MHz), and 1.8007-1.8015×10^{-7} eV (43.54-43.56MHz) were covered at magnetic fields of 4.5T, 5.0T, and 7.0T, respectively. Exclusion results from the search data, for coupling below 10^{-12} GeV^{-1}, are presented.

Broadband RF Characterization and Extraction of Material Properties in 3-D Printed Composite Substrates for Magnetically Tuned Circuits

3-D additive printing technology has been employed recently for the manufacturing of a wide variety of tunable radio frequency (RF) components. In particular, this article is focused on the extraction of magnetically tuned 3-D printed materials suitable for RF circuits. The design and modeling of tunable RF circuits require an accurate electromagnetic (EM) characterization of the 3-D printed dielectric [polylactide (PLA)] as a primary substrate, magnetic particles (CoFeO) as the tunable component in the composite substrate, and copper traces at RF frequencies. The extraction of complex permittivity, permeability, and conductivity parameters is reported over broadband (50–7000 MHz) and narrowband Wi-Fi bands (2.4 and 5.4 GHz) using the best fitting of EM simulated to measured scattering ( $S$ ) parameters. Broadband characterization is performed using best-fit modeling of three different physical lengths of microstrip transmission lines that are fabricated on unknown 3-D printed PLA substrates. Error analysis of this approach was evaluated on commercially available RT/Duroid substrate as a baseline. An accurate narrowband extraction procedure around the resonance frequency of 3-D printed annular ring resonators (ARRs) at 2.4 and 5.4 GHz is performed by the best fitting of simulated material RF properties to measured results. Further modeling improvements are presented through completely 3-D printed circuits that include the bottom and top copper traces with extracted conductivity of one tenth of bulk copper. Moreover, a 50-MHz tuning of ARR operating at Wi-Fi bands is observed and complex permeabilities are extracted at zero and 2-kG external magnetic field for the 3-D printed composite substrate.