Maximum Stable Gain Research Articles

Ultra-Wideband Dielectric Resonator Antenna Design Based on Multilayer Form

In this paper, an ultra-wideband dielectric resonator antenna (DRA) is investigated. It basically covers the bandwidth from 6 GHz to 16 GHz and achieves a relative bandwidth of 90.9%. It is found that a wide bandwidth can be reached with a small DRA by adopting multilayer form. Thus, the dimension of the designed DRA element which is composed of nine-element phased-scanning linear array is as small as 6.9mm x 8.2mm x 11 mm. While the maximum stable zenith gain is 6.2dB, the lobe width is 3 dB. The operating frequency range of the antenna array is from 5.42GHz to 16.5GHz, achieving a 101.1% relative bandwidth. A large scanning angle of ±60° is realized within the operating frequency band, with good scanning pattern and cross polarization. To verify the design and simulation, a 1 × 9 DRA array is fabricated, and measurements are carried out.

Sound Quality Improvement for Hearing Aids in Presence of Multiple Inputs

Modern-day hearing aids are capable of receiving acoustic signals over a wireless link and also from the surroundings through the microphone. If the hearing aid receives input only from the acoustic environment, feedback cancellation proceeds according to the existing methodologies for bias reduction. However, the wirelessly received signal and the acoustic environment input, when emitted from the same source, can be very similar to each other or with a time-delayed version of each other, thereby having a high correlation between them. Both inputs can also be emitted from different sources and, thus, be less correlated with each other. In the aforementioned scenarios, acoustic confusion can occur for the user as the hearing aid receives both signals simultaneously. To improve the output signal quality and to reduce bias in an adaptive feedback cancellation system with a wirelessly received signal as well as an acoustic environment input, we propose a cost function, and the optimization of the feed-forward path and of the shaping filter for the wireless signal. The feed-forward path is designed to be a cascade of the required acoustic enhancement along with an FIR filter. We derive expressions for an optimum shaping filter and for an optimized feed-forward path. Improvement in loudspeaker output signal quality, normalized misalignment and maximum stable gain for each of the above-mentioned scenarios is assessed through numerical simulations.

Null-Steering Beamformer-Based Feedback Cancellation for Multi-Microphone Hearing Aids With Incoming Signal Preservation

In hearing aids, acoustic feedback occurs due to the coupling between the hearing aid loudspeaker and microphone(s). In order to reduce the acoustic feedback, adaptive filters are commonly used to estimate the feedback contribution in the microphone(s). While theoretically allowing for perfect feedback cancellation, in practice the adaptive filter converges to an optimal solution that is typically biased due to the closed-loop acoustical system of the hearing aid. In order to avoid the adaptation to a biased optimal solution, in this paper we propose to use a fixed beamformer to cancel the acoustic feedback contribution for an earpiece with multiple integrated microphones and loudspeakers. By steering a spatial null in the direction of the hearing aid loudspeaker, we show that theoretically perfect feedback cancellation can be achieved. While previous null-steering beamforming approaches did not control for distortions of the incoming signal, in this paper we propose to incorporate a constraint based on the relative transfer function (RTF) of the incoming signal, aiming to perfectly preserve this signal. We formulate the computation of the beamformer coefficients both as a least-squares optimization procedure, aiming to minimize the residual feedback power, and as a min–max optimization procedure, aiming to directly maximize the maximum stable gain of the hearing aid. Experimental results using measured acoustic feedback paths from a custom earpiece with two microphones in the vent and a third microphone in the concha show that the proposed fixed null-steering beamformer using the RTF-based constraint provides a reduction of the acoustic feedback and substantially increases the added stable gain while preserving the incoming signal. This can even be achieved for unknown acoustic feedback paths and incoming signal directions.

Zero attracting proportionate normalized subband adaptive filtering technique for feedback cancellation in hearing aids

Acoustic feedback cancelers (AFC) employing normalized subband adaptive filtering (NSAF) in conjunction with proportionate gain allocation strategy (PNSAF) have been utilized to mitigate the effect of acoustic feedback in hearing aids. However, it was found to exhibit fast convergence at the initial stage whereas slowing down the convergence at later phase of the adaptation process. In an endeavor to overcome this, l1 norm-based penalty element is incorporated with the PNSAF algorithm proposing a new zero attracting PNSAF (ZA-PNSAF) based AFC system. Further, re-weighted ZA-PNSAF (RZA-PNSAF) algorithm is newly introduced to address the varying sparsity conditions. The efficacy of the proposed method is demonstrated by higher maximum stable gain (MSG) (3–5 dB) and PESQ (perceptual evaluation of speech quality) values obtained over existing algorithms. In addition, the convergence and mean square deviation (MSD) analysis of the proposed algorithm are also carried out. Analysis of the ZA-PNSAF algorithm is validated through comparison of the simulated and analytical MSD values.

Feedback reduction system influence on additional gain before feedback and maximum stable gain in open-fitted hearing aids

Objective: The primary purpose of this study was to update existing data on additional gain before feedback and maximum stable gain in commercially available, open-fit hearing instruments. A secondary purpose was to evaluate ratings of sound quality with feedback reduction systems active.Design: Additional gain before feedback, maximum stable gain and subjective sound quality ratings were obtained for six commercially available hearing instruments utilising modern feedback reduction systems.Study sample: Twenty adults (22–46 years) with normal hearing participated in gain measurement testing. Thirty adults (22–39 years) with normal hearing provided ratings of sound quality.Results: Mean additional gain before feedback for 2000–4000 Hz ranged from 5 to 16 dB across manufacturers. Mean maximum stable gain in the same frequency region ranged from 25 to 35 dB across manufacturers. However, meaningful performance differences between participants within each given manufacturer were also identified. Sound quality ratings were not related to the type of feedback reduction algorithm.Conclusions: AGBF and MSG continue to vary significantly both across manufacturers as well as individual ears within a given manufacturer. User satisfaction and performance with hearing aids might be improved by identifying the feedback reduction system optimal for the individual patient.

Impact of high k spacer on RF stability performance of double gate junctionless transistor

AbstractIn this paper, radio frequency (RF) stability performance of double gate junctionless transistor for different spacer material, the width of spacer, and bias conditions is reported. The impact of gate oxide thickness and gate work function on RF performance of double gate junctionless transistor is also presented. The analog and RF figure of merit, namely, intrinsic gain, unity gain cut‐off frequency, stern's stability factor, critical frequency, maximum attainable gain, and maximum stable gain, are investigated with the help of numerical simulation. The result shows that the fringing fields of high k spacers have a major impact on the gate to source and gate to drain capacitance. The device design guideline along with bias and geometrical parameters are reported for the optimized structure. The optimized device structure exhibits better RF stability.

Flexible InGaZnO TFTs With ${f}$ $_{\textsf{max}}$ Above 300 MHz

In this letter, the AC performance and influence of bending on flexible IGZO thin-film transistors, exhibiting a maximum oscillation frequency (maximum power gain frequency) ${f}_{\textsf {max}}$ beyond 300 MHz, are presented. Self-alignment was used to realize TFTs with channel length down to 0.5 $\mu \text{m}$ . The layout of these TFTs was optimized for good AC performance. Besides the channel dimensions, this includes ground-signal-ground contact pads. The AC performance of these short channel devices was evaluated by measuring their two port scattering parameters. These measurements were used to extract the unity gain power frequency from the maximum stable gain and the unilateral gain. The two complimentary definitions result in ${f}_{\textsf {max}}$ values of (304 ± 12) and (398 ± 53) MHz, respectively. Furthermore, the transistor performance is not significantly altered by mechanical strain. Here, ${f}_{\textsf {max}}$ reduces by 3.6% when a TFT is bent to a tensile radius of 3.5 mm.

High breakdown voltage and high driving current in a novel silicon-on-insulator MESFET with high- and low-resistance boxes in the drift region

In this paper a novel silicon-on-insulator metal oxide field effect transistor (SOI-MESFET) with high- and low-resistance boxes (HLRB) is proposed. This structure increases the current and breakdown voltage, simultaneously. The semiconductor at the source side of the channel is doped with higher impurity than the other parts to reduce its resistance and increase the driving current as low-resistance box. An oxide box is implemented at the upper part of the channel from the drain region toward the middle of the channel as the high-resistance box. Inserting a high-resistance box increases the breakdown voltage and improves the RF performance of the device because of its higher tolerable electric field and modification in gate-drain capacitance, respectively. The high-resistance region reduces the current density of the device which is completely compensated by low-resistance box. A 92% increase in breakdown voltage and an 11% improvement in the device current have been obtained. Also, maximum oscillation frequency, unilateral power gain, maximum available gain, maximum stable gain, and maximum output power density are improved by 7%, 35%, 23%, 26%, and 150%, respectively. These results show that the HLRB-SOI-MESFET can be considered as a candidate to replace Conventional SOI-MESFET (C-SOI-MESFET) for high-voltage and high-frequency applications.

Small-signal parameter extraction of asymmetric DCDMG AlGaN/GaN HEMT

PurposeThis paper aims to report small-signal parameter extraction and simulation of enhanced dual-channel dual-material gate AlGaN/GaN high electron mobility transistor (HEMT) for the first time for the characterization of a device in microwave range of frequency.Design/methodology/approachFor parameter extraction, a standard and well-known direct parameter extraction methodology is applied. Extrinsic elements of small-signal circuit model are extracted from measured S-parameters obtained using pinch-off cold field effect transistor (FET) biasing in the first step at a low frequency range and at a higher frequency range in the second step to ensure higher extraction accuracy. Intrinsic elements are extracted from intrinsic Y-parameters that are obtained after de-embedding all the extrinsic parasitic elements of the device. Figure of merits of radio frequency are also derived from the measured results and S-parameters of the proposed device.FindingsSmall signal parameters of the proposed device circuit model are extracted using the standard direct parameter extraction technique. Analysis of microwave figure of merits for device include maximum oscillation frequency, cut-off frequency, current gain, transducer power gain, available power gain, maximum stable gain, transconductance, drain conductance, stern stability factor and time delay.Practical implicationsThe paper bridges the gaps between theory and experimental practices by validating extracted results with reported results of structurally matching devices.Originality/valueAn enhanced device structure investigated for small signal parameters incorporates field plate over dual metal engineered gate to provide better electric field uniformity, effective suppression of short channel effect, reduction in current collapse, improvement in carrier transport efficiency and enhancement in drain current capabilities.

Digitally grown AlInAsSb for high gain separate absorption, grading, charge, and multiplication avalanche photodiodes

We report on the growth of high quality GaSb-based AlInAsSb quaternary alloy by molecular beam epitaxy (MBE) to fabricate avalanche photodiodes (APDs). By means of high resolution X-ray diffraction (HRXRD) and scanning transmission electron microscope (STEM), phase separation phenomenon of AlInAsSb random alloy with naturally occurring vertical superlattice configuration was demonstrated. To overcome the tendency for phase segregation while maintaining a highly crystalline film, a digital alloy technique with migration-enhanced epitaxy growth method was employed, using a shutter sequence of AlSb, AlAs, AlSb, Sb, In, InAs, In, Sb. AlInAsSb digital alloy has proved to be reproducible and consistent with single phase, showing sharp satellite peaks on HRXRD rocking curve and smooth surface morphology under atomic force microscopy (AFM). Using optimized digital alloy, AlInAsSb separate absorption, grading, charge, and multiplication (SAGCM) APD was grown and fabricated. At room temperature, the device showed high performance with low dark current density of ∼14.1 mA/cm2 at 95% breakdown and maximum stable gain before breakdown as high as ∼200, showing the potential for further applications in optoelectronic devices.

Theoretical transient analysis of a hearing aid feedback canceller with a saturation type nonlinearity in the direct path

Feedback cancellation in a hearing aid is essential for achieving high maximum stable gain to compensate for the losses in severe to profound hearing impaired people. The performance of adaptive feedback cancellers has been studied by assuming that the feedback path can be modeled as a linear system. However, limited dynamic range, low-cost loudspeakers, and nonlinear power amplifiers may distort the hearing aid output signal. In this way, linear-based predictions of the canceller performance may lead to significant deviations from its actual behavior. This work presents a theoretical performance analysis of a Least Mean Square based shadow filter that is applied to set up the coefficients of a feedback canceller, which is subject to a static saturation type nonlinearity at the output of the direct path. Deterministic recursive equations are derived to predict the mean square feedback error and the mean coefficient vector evolution between updates of the feedback canceller. These models are defined as functions of the canceller parameters and input signal statistics. Comparisons with Monte Carlo simulations show the provided models are highly accurate under the considered assumptions. The developed models allow inferences about the potential impact of an overdriven loudspeaker over the transient performance of the direct method feedback canceller, serving as insightful tools for understanding the involved mechanisms.

Analysis of a prediction error method employing orthonormal basis functions in adaptive feedback cancellation for hearing aids

Hearing aids often suffer from acoustic feedback, which limits the achievable amplification and may severely degrade sound quality by creating howling artifacts. A potential method of feedback cancellation comprises predicting the feedback path (FP) using an adaptive filter. However, a large model error, or bias, is introduced due to signal correlations. To reduce the bias in the FP estimate, a prediction-error-method (PEM) has been used, which is based on a closed-loop identification of the FP and the auto-regressive modeling of the desired signal. This approach, which represents the FP using an FIR filter, requires a large number of parameters. Furthermore, in a reverberant environment, even a high order of the FIR filter may be insufficient to fully represent the FP, which reduces the convergence rate and limits the maximum stable gain of the system. In this contribution, we introduce a PEM-based method that utilizes orthonormal basis functions to precisely predict the acoustic FP in hearing aids. Simulation results with measured data show that the proposed method outperforms the standard PEM adaptation algorithm in terms of convergence rate and maximum stable gain.

TCAD Simulations and Small Signal Modeling of DMG AlGaN/GaN HFET

This article presents extraction of small signal model parameters and TCAD simulation of novel asymmetric field plated dual material gate AlGaN/GaN HFET first time. Small signal model is essential for design of LNA and microwave electronic circuit by using the proposed superior performance HFET structure. Superior performances of device are due to its dual material gate structure and field plate that can provide better electric field uniformity, suppression of short channel effects and improvement in carrier transport efficiency. In this article we used direct parameter extraction methodology in which S-parameters of device were measured using pinchoff cold FET biasing. The measured S-parameters are then transformed into Y-parameters to extract capacitive elements and then in to Z-parameters to extract series parasitic elements. Intrinsic parameters are extracted from Y-parameters after de-embedding all parasitic elements of devce. Microwave figure of merits and dc performance are also studied for proposed HFET. The important figure of merits of device reported in the paper include transconductance, drain conductance, current gain, transducer power gain, available power gain, maximum stable gain, maximum frequency of oscillation, cut-off frequency, stability factor and time delay. Reported results are validated with experimental and simulation results for consistency and accuracy.

Robust stability analysis and improved design of phase‐locked loops with non‐monotonic nonlinearities: LMI‐based approach

SummaryDue to nonlinear nature of several phase detectors, linear approximation method often leads to performance degradation in many phase‐locked loops (PLLs), particularly when the phase errors are sufficiently large. A third or higher order PLL, in spite of the ability to track a wider variety of inputs and having higher operating‐frequency range, requires more design attention in order to ensure stable tracking. In this work, with the nonlinearities inserted into the system's model, suitable criteria that take into account the nonlinearities' non‐monotonicity, sector and slope bounds are employed to establish robust stability conditions. The result is applicable to any PLLs without order and type restrictions. For Type‐1 PLLs, the resulting condition can be used to search for the maximum stable loop gain, which is also linked to the lock‐in range of the system. In the later part of this work, the focus is devoted towards designing PLLs with high lock‐in range, which is performed via mixing the proposed method with H∞ synthesis. The searches for the parameters in both PLL analysis and design are expressed in terms of convex linear matrix inequalities, which are computationally tractable. To illustrate the improvement introduced via this approach, several numerical examples and simulations are included with comparisons over conventional methods. Copyright © 2017John Wiley & Sons, Ltd.

Повышение быстродействия прибора PHEMT на основе GaAs с помощью профилированного дельта-легирования оловом

The PHEMT epitaxial structures with a doping profile in the form of tin nanowires were fabricated using vicinal GaAs substrate disoriented by 0.3° in relation to accurate orientation (100). Investigation of electron transport properties of the structures with nanowires of tin atoms on vicinal GaAs substrates have been presented. It was determined that non-optimal growth temperature of cap layers leads to degradation of electrophysical parameters of the samples and prevent forming of tin one-dimensional channels. Anisotropy of the saturation current on current-voltage characteristics was obtained when current flow along and across nanowires. Field effect transistors with special topology for orthogonal current flow were fabricated and frequency characteristics were measured. The evident anisotropy of the frequency characteristics for PHEMT was shown. Gain coefficient MSG (Maximum Stable Gain) of the fabricated PHEMT for current flow along nanowires correlates to best-achieved values of MSG for GaAs PHEMT.

Attenuating the ear canal feedback pressure of a laser-driven hearing aid

Microphone placement behind the pinna, which minimizes feedback but also reduces perception of the high-frequency pinna cues needed for sound localization, is one reason why hearing-aid users often complain of poor sound quality and difficulty understanding speech in noisy situations. In this paper, two strategies are investigated for minimizing the feedback pressure (thereby increasing the maximum stable gain, MSG) of a wide-bandwidth light-activated contact hearing aid (CHA) to facilitate microphone placement in the ear canal (EC): (1) changing the location of the drive force and its direction at the umbo, and (2) placing an acoustic damper within the EC to reduce the feedback pressure at the microphone location. The MSG and equivalent pressure output (EPO) are calculated in a 3D finite element model of a human middle ear based on micro computed tomography (micro-CT) images. The model calculations indicate that changing the umbo-force direction can decrease feedback pressure, but at the expense of decreased EPO. However the model shows improvements in MSG without sacrificing EPO when an acoustic damper is placed in the EC. This was verified through benchtop experimentation and in human cadaver temporal bones. The results pave the path towards a wide-bandwidth hearing aid that incorporates an EC-microphone design.

Wideband millimetre‐wave CMOS power amplifier using transistor‐based inductive source degeneration and specially shielded transformer

This study presents integration of transistor based inductive source degeneration and specially shielded transformer into a millimetre-wave power amplifier (mm-wave PA) operating at wideband. A new configuration of high Q distributed inductor is devised and embedded in CMOS transistor source to enhance stability, maximum stable gain and bandwidth of mm-wave CMOS PAs. The source inductance selection is conveniently investigated by the proposed admittance matrix condensation. In power splitting and combining part, a novel X-shape pattern-ground shielding is inserted in high turn ratio transformer to ameliorate wideband matching. Based on these techniques, a fully differential mm-wave PA was implemented in 65 nm low-power CMOS with 0.25 mm2 core area. The measurement results show that its differential drive gain and common mode rejection ratio are above 10 and 26 dB, respectively, in a wide frequency range of 41 to 61 GHz, while the power added efficiency (PAE) is still above 10.8% at 46–62 GHz. This CMOS PA also achieves 11.9 dBm output referred 1-dB compression point (P 1 dB) and 15.2 dBm saturated power (P sat) with 12.4% peak PAE.

Compact low noise amplifier with high stable gain using distributed CRLH metamaterial

In this letter, a compact low noise amplifier (LNA) with high stable gain using distributed elements with composite right/left-handed (CRLH) metamaterial is presented. In the proposed LNA, the CRLH is composed of distributed elements with a compact meander-line structure. The transistor (TR) in the proposed LNA is selected as a HEMT device due to its low noise and high stable gain performances. In this structure, the CRLH is adopted as the input and output matching networks in the LNA. The operating frequency of the proposed LNA is 2.0 GHz, the minimum noise figure is 0.71 dB, and the maximum stable gain is 10.4 dB. Also, the total size of the proposed LNA is 10.8 × 13.6 mm2. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1715–1720, 2016

Temporal-Bone Measurements of the Maximum Equivalent Pressure Output and Maximum Stable Gain of a Light-Driven Hearing System That Mechanically Stimulates the Umbo.

That maximum equivalent pressure output (MEPO) and maximum stable gain (MSG) measurements demonstrate high output and high gain margins in a light-driven hearing system (Earlens). The nonsurgical Earlens consists of a light-activated balanced-armature transducer placed on the tympanic membrane (Lens) to drive the middle ear through direct umbo contact. The Lens is driven and powered by encoded pulses of light. In comparison to conventional hearing aids, the Earlens is designed to provide higher levels of output over a broader frequency range, with a significantly higher MSG. MEPO provides an important fitting guideline. Four fresh human cadaveric temporal bones were used to measure MEPO directly. To calculate MEPO and MSG, we measured the pressure close to the eardrum and the stapes velocity, for sound drive and light drive using the Earlens. The baseline sound-driven measurements are consistent with previous reports. The average MEPO (n = 4) varies from 116 to 128 dB SPL in the 0.7 to 10 kHz range, with the peak occurring at 7.6 kHz. From 0.1 to 0.7 kHz, it varies from 83 to 121 dB SPL. For the average MSG, a broad minimum of about 10 dB occurs in the 1 to 4 kHz range, above which it rises as high as 42 dB at 7.6 kHz. From 0.2 to 1 kHz, the MSG decreases linearly from approximately 40 dB to 10 dB. With high output and high gain margins, the Earlens may offer broader-spectrum amplification for treatment of mild-to-severe hearing impairment.

A Semidefinite Programming Approach to Min-max Estimation of the Common Part of Acoustic Feedback Paths in Hearing Aids

The convergence speed and the computational complexity of adaptive feedback cancellation algorithms both depend on the number of adaptive parameters used to model the acoustic feedback paths. To reduce the number of adaptive parameters it has been proposed to decompose the acoustic feedback paths as the convolution of a time-invariant common part and time-varying variable parts. Instead of estimating all parameters of the common and variable parts by minimizing the misalignment using a least-squares cost function, in this paper we propose to formulate the parameter estimation problem as a min-max optimization problem aiming to maximize the maximum stable gain (MSG). We formulate the min-max optimization problem as a semidefinite program and use a constraint based on Lyapunov theory to guarantee stability of the estimated common pole-zero filter. Experimental results using measured acoustic feedback paths show that the proposed min-max optimization outperforms least-squares optimization in terms of the MSG. Furthermore, the results indicate that the proposed common part decomposition is able to increase the MSG and reduce the number of variable part parameters even for unknown feedback paths that were not included in the optimization. Simulation results using an adaptive feedback cancellation algorithm based on the prediction-error-method show that the convergence speed can be increased by using the proposed feedback path decomposition.