Maximum Stable Gain Research Articles

Millimeter-Wave GaN High-Power Amplifier MMIC Design Guideline Considering a Source via Effect

A millimeter-wave (mmWave) gallium nitride (GaN) high-power amplifier (HPA) monolithic microwave-integrated circuit (MMIC) was implemented, considering a source via effect. In this paper, we introduce guidelines for designing GaN HPA MMICs, from device sizing to meeting high-power specifications, power matching considering source via effects, schematic design of three-stage amplifier structures, and electromagnetic (EM) simulation. Based on the results of load pull simulation and small-signal maximum stable gain (MSG) simulation, the GaN high-electron-mobility transistor (HEMT) size was selected to be 8 × 70 μm. However, since the source via model provided by the foundry was significantly different from the EM results, it was necessary to readjust the power matching considering this. Additionally, when selecting the source via size, the larger the size, the easier the matching, but since the layout of the peripheral bias circuit is not possible, a compromise was required considering the actual layout. To prevent in-band oscillation, an RC parallel circuit was added to the input matching circuit, and low-frequency oscillation was solved by adding a gate resistor on the PCB module. The proposed PA was fabricated with a commercial 0.1 μm GaN HEMT MMIC process. It exhibited 38.56 to 39.71 dBm output power (Pout), 14.2 to 16.7 dB linear gain, and 14.1% to 18.2% power-added efficiency (PAE) in the upper Ka band. The fabricated GaN power amplifier MMIC shows competitive Pout in the upper Ka band above 33 GHz.

Gas gains over 104 and optimisation using 55Fe X-rays in low pressure SF6 with a novel Multi-Mesh ThGEM for directional dark matter searches

The Negative Ion Drift (NID) gas SF6 has favourable properties for track reconstruction in directional Dark Matter (DM) searches utilising low pressure gaseous Time Projection Chambers (TPCs). However, the electronegative nature of the gas means that it is more difficult to achieve significant gas gains with regular Thick Gaseous Electron Multipliers (ThGEMs). Typically, the maximum attainable gas gain in SF6 and other Negative Ion (NI) gas mixtures, previously achieved with an 55Fe X-ray source or electron beam, is on the order of 103 [1,2,3,4]; whereas electron drift gases like CF4 and similar mixtures are readily capable of reaching gas gains on the order of 104 or greater [5,9,7,8,6]. In this paper, a novel two stage Multi-Mesh ThGEM (MMThGEM) structure is presented. The MMThGEM was used to amplify charge liberated by an 55Fe X-ray source in 40 Torr of SF6. By expanding on previously demonstrated results [10], the device was pushed to its sparking limit and stable gas gains up to ˜50000 were observed. The device was further optimised by varying the field strengths of both the collection and transfer regions in isolation. Following this optimisation procedure, the device was able to produce a maximum stable gas gain of ˜90000. These results demonstrate an order of magnitude improvement in gain with the NID gas over previously reported values and ultimately benefits the sensitivity of a NITPC to low energy recoils in the context of a directional DM search.

Cryogenic RPWELL: a novel charge-readout element for dual-phase argon TPCs

The first operation of a cryogenic Resistive Plate WELL (RPWELL) detector in the saturated vapor of liquid argon is reported. The RPWELL detector was composed of a Thick Gas Electron Multiplier (THGEM) electrode coupled to a metallic anode via Fe2O3/YSZ ceramics (Fe2O3 in weight equal to 75%), with tunable bulk resistivity in the range 109–1012 Ω·cm. The detector was operated at liquid argon temperature in saturated argon vapor (90 K, 1.2 bar) and characterized in terms of its effective charge gain and stability against discharges. Maximum stable gain of G≈17 was obtained, without discharges. In addition, preliminary results from novel 3D-printed thermoplastic plates doped with carbon nanotubes are presented.

Switched Combination of Simplified Kalman Filter and Affine Projection Algorithm for Acoustic Feedback Cancellation

Acoustic coupling between the microphone and the loudspeaker is a major issue in open-fit digital hearing aids. When compared to a close-fit hearing aid, an open-fit dramatically reduces signal quality and limits the potential maximum stable gain. Adaptive feedback cancellation (AFC) is a practical method for reducing the influence of acoustic coupling. However, because to the high correlation between the loudspeaker signal and the incoming signal, it might induce bias in calculating the feedback path if not carefully considered, especially when the incoming signal is spectrally coloured, as in speech and music. For decreasing this bias, the prediction error method (PEM) is well recognised. In this paper we proposed a switched PEM based hybrid combination of simpliedkalman filter and affine projection algorithms (H-SKF-APA), with soft-clipping that allows for further increase in convergence/tracking rates, resulting in a better ability to recover from an unstable or howling state. Simulation results showed that the proposed algorithm performed better.

Electrothermal Performance of AlGaN/GaN Lateral Transistors with >10 μm Thick GaN Buffer on 200 mm Diameter‐Engineered Substrates

Herein, the electrical and thermal performance of lateral AlGaN/GaN high electron mobility transistors (HEMTs) and metal‐insulator‐semiconductor field effect transistors (MISFETs) fabricated with 11 μm thick GaN buffer layers on 200 mm diameter Qromis Substrate Technology (QST) substrates are investigated. The QST substrate has a polycrystalline core engineered to be coefficient of thermal expansion (CTE)‐matched to GaN to minimize wafer bow and residual stress in the GaN film as a result of epitaxial growth. Raman spectroscopy is used to determine the biaxial residual stress in the GaN buffer of the as‐fabricated devices. Electrical characterization is demonstrated on the HEMTs including DC and pulsed output characteristics, DC transfer characteristics, Hall mobility, carrier concentration, sheet resistance, median transition frequency, and maximum stable gain. Finally, the thermal performance of the AlGaN/GaN MISFET is assessed via thermoreflectance thermal imaging at DC power densities up to 19 W mm−1. The thermal resistance of the MISFET, calculated using the peak temperature rises on the gate electrode for DC power densities <10 W mm−1, is measured to be 15.4 mm K W−1, which is comparable with state‐of‐the‐art GaN‐on‐Si lateral transistors.

Surface-oxide-controlled InGaAs/InAlAs inverted-type metal-oxide-semiconductor high electron mobility transistors for sub-THz high-power amplifiers

Herein, we successfully improved the maximum oscillation frequency and maximum stable gain (MSG) across a wide bias range of surface-oxide-controlled (SOC) InGaAs/InAlAs inverted-type metal-oxide-semiconductor high-electron-mobility transistors (inverted MOS-HEMTs) by reducing the gate leakage current and drain conductance (g d). H2O vapor treatment selectively decreased the narrow band gap indium oxide at the surface of the In-based epitaxial layer via the SOC process before the gate oxide deposition. Furthermore, the calculation of band profiles indicated that the gd reduction was possibly attributed to the suppression of impact ionization in the InGaAs channel by inverted MOS-HEMTs. Consequently, SOC-inverted MOS-HEMTs demonstrated a high MSG of >12 dB at 100 GHz across a wide bias range.

Evaluation of deep marginal feedback cancellation for hearing aids using speech and music.

Speech and music both play fundamental roles in daily life. Speech is important for communication while music is important for relaxation and social interaction. Both speech and music have a large dynamic range. This does not pose problems for listeners with normal hearing. However, for hearing-impaired listeners, elevated hearing thresholds may result in low-level portions of sound being inaudible. Hearing aids with frequency-dependent amplification and amplitude compression can partly compensate for this problem. However, the gain required for low-level portions of sound to compensate for the hearing loss can be larger than the maximum stable gain of a hearing aid, leading to acoustic feedback. Feedback control is used to avoid such instability, but this can lead to artifacts, especially when the gain is only just below the maximum stable gain. We previously proposed a deep-learning method called DeepMFC for controlling feedback and reducing artifacts and showed that when the sound source was speech DeepMFC performed much better than traditional approaches. However, its performance using music as the sound source was not assessed and the way in which it led to improved performance for speech was not determined. The present paper reveals how DeepMFC addresses feedback problems and evaluates DeepMFC using speech and music as sound sources with both objective and subjective measures. DeepMFC achieved good performance for both speech and music when it was trained with matched training materials. When combined with an adaptive feedback canceller it provided over 13 dB of additional stable gain for hearing-impaired listeners.

A deep learning solution to the marginal stability problems of acoustic feedback systems for hearing aids

For hearing aids, it is critical to reduce the acoustic coupling between the receiver and microphone to ensure that prescribed gains are below the maximum stable gain, thus preventing acoustic feedback. Methods for doing this include fixed and adaptive feedback cancellation, phase modulation, and gain reduction. However, the behavior of hearing aids in situations where the prescribed gain is only just below the maximum stable gain, called here "marginally stable gain," is not well understood. This paper analyzed marginally stable systems and identified three problems, including increased gain at frequencies with the smallest gain margin, short whistles caused by the limited rate of decay of the output when the input drops, and coloration effects. A deep learning framework, called deep marginal feedback cancellation (DeepMFC), was developed to suppress short whistles, and reduce coloration effects, as well as to limit excess amplification at certain frequencies. To implement DeepMFC, many receiver signals in closed-loop systems and corresponding open-loop systems were simulated, and the receiver signals of the closed-loop and open-loop systems were paired together to obtain parallel signals for training. DeepMFC achieved much better performance than existing feedback control methods using objective and subjective measures.

Asymmetric‐fed triband antenna for military radars and 5G applications using microstrip technology

Achieving antenna size reduction while maintaining high efficiency and multiband characteristics with wide bandwidths across all the operating frequency bands is highly demanded and challenging in microstrip antennas. A novel compact triband quasi-rho-shaped and cost-effective antenna is designed on a 7 × 7 × 1 mm3 FR4 substrate having a permittivity of 4.4 and a loss tangent of 0.02. With an electrical size of 0.39λ0 × 0.39λ0 × 0.056λ0, where λ0 is the free space wavelength at 16.84 GHz, a circular slot and asymmetric microstrip feed are used to achieve the desires performance. The proposed antenna is designed, simulated, and optimized using high-frequency structure simulator (HFSS) software, and its prototype is fabricated to validate its electromagnetic performance. Furthermore, an equivalent circuit is proposed using the Foster canonical model. The proposed antenna exhibits a maximum stable gain of 5.32 dB and an average radiation efficiency of 77.87% in all the operating frequency bands. The measurement results show that the antenna covers (16.84–18.15 GHz), (24.78–27.40 GHz), and (34.47–37.22 GHz) bands centred at 17.39 GHz, 25.98 GHz, and 35.83 GHz, respectively, with a minimum wide bandwidth (S11 ≤ −10 dB) of 1.31 GHz. The acquired results illustrate that the quasi-rho-shaped antenna is suitable for military radars and 5G applications.

In-vivo characterisation of an implanted microphone and totally implantable active middle ear implant

Objective To objectively evaluate acoustic sensitivity of the implanted microphone, and maximum stable gain of a totally implantable active middle ear implant. Design Prospective, single centre evaluation. Study sample Fourteen adult patients. Results Microphone sensitivity is approx. 10 dB lower than an externally worn conventional hearing aid, at frequencies up to 4000 Hz, and substantially lower at higher frequencies. The masking level due to microphone noise, which determines the softest test tones that can be detected, is estimated at <20 to <30 dB HL up to 1000 Hz, and <40 dB HL at higher frequencies. Maximum stable effective gain is the maximum amplification achievable without causing feedback whistling. In sensorineural hearing loss (SNHL) cases, it is 30–40 dB at frequencies up to 2000 Hz, allowing to compensate for even the maximum recommended hearing loss (60–70 dB HL). In both SNHL and mixed hearing loss (MHL) cases, maximum stable effective gain is lower (+20 to −30 dB) around 3000–6000 Hz. Conclusions Microphone sensitivity is high enough to achieve aided thresholds of 20–40 dB HL. A strong correlation between actuator coupling efficiency and maximum stable effective gain implies that any effort to improve actuator efficiency should also increase the available gain.

A Switched Algorithm for Adaptive Feedback Cancellation Using Pre-Filters in Hearing Aids.

Acoustic coupling between microphone and loudspeaker is a significant problem in open-fit digital hearing aids. An open-fit compared to a close-fit hearing aid significantly lowers the signal quality and limits the achievable maximum stable gain. Adaptive feedback cancellation (AFC) enables an efficient approach to reduce the impact of acoustic coupling. However, without careful consideration, it can also introduce bias in estimating the feedback path due to the high correlation between the loudspeaker signal and the incoming signal, especially when the incoming signal is spectrally coloured, e.g., speech and music. The prediction error method (PEM) is well known for reducing this bias. The presented study aims to propose a switched PEM with soft-clipping (swPEMSC) that allows for further improvement in convergence/tracking rates, resulting in a better ability to recover from unstable/howling status. This swPEMSC employs a new update rule inspired by a soft-clipping based stability detector (SCSD). It allows to pick up either the PEMSC-NLMS or PEMSC-APA depending on the magnitude of the effective feedback signal; howling corresponds to a large feedback signal. The PEMSC-NLMS with a small step-size ensures a low steady-state error, but slow convergence/tracking rates, while PEMSC-APA with a large step-size allows for fast convergence/tracking rates, but a high steady-state error. By combining those approaches, the proposed approach can take advantage of good characteristics from both. Experimental results using different types of incoming signals and an abrupt change of feedback paths show that the swPEMSC can shorten unstable periods (howling) by improving the convergence and tracking rates while retaining a low steady-state error and good signal quality.

Полевой транзистор миллиметрового диапазона длин волн на основе псевдоморфной гетероструктуры с дополнительными потенциальными барьерами

The results of millimeter – wave field – effect transistors with a 0.14 µm T – gate on pseudomorphic heterostructures Al0.3Ga0.7As – In0.22Ga0.78As – Al0.3Ga0.7As with additional potential barriers based on two-way donor-acceptor channel doping study are presented. At a frequency of 40 GHz in a wide range of gate voltages, a maximum stable gain of more than 15 dB is achieved. The maximum frequency of the device generation is about 250 GHz, the specific current density at the open channel is about 0.7 A / mm, the breakdown voltage of the gate-drain, depending on the version, is 22 -31 V.

A 120–150 GHz Power Amplifier in 28-nm CMOS Achieving 21.9-dB Gain and 11.8-dBm Psat for Sub-THz Imaging System

This paper presents a high-gain D-band power amplifier (PA) fabricated with 28-nm CMOS technology for a sub-terahertz frequency modulated continuous wave imaging system. It adopts two-channel power combining using artificial transmission lines to absorb the parasitic capacitance of the ground-signal-ground pad. The layout of the transistors and neutralization capacitors are optimized to improve the maximum stable gain, stability, and robustness. Asymmetrically magnetically coupled resonators are used in inter-stage and input matching networks to extend the operating bandwidth. The PA achieves a peak power gain of 21.9 dB and maximum output power of 11.8 dBm with 10.7% of power-added efficiency. Also, this PA can achieve higher than 10 dBm output power over the frequency range of 120–150 GHz.

Extremely-Low Threshold Voltage FinFET for 5G mmWave Applications

An optimized doping process is used to achieve extremely-low threshold voltage (ELVT) FinFETs for low-power mmWave applications based on 12nm node technology platform. With the VTH ≈ 100mV ELVT FinFET shows 15% IEFF improvement at the same VDD compared to its super-low threshold voltage (SLVT) counterpart, while mismatch and reliability performances are comparable. FT/FMAX of 305GHz/ 315GHz and comparable Maximum Stable Gain (MSG) to SLVT FinFET gives ELVT FinFET an advantage for mmWave 5G low-power applications. Local oscillator (LO) chain blocks are investigated as a circuit level example to confirm the benefits of ELVT FinFET. An optimized LO transmission Line (TL) driver using ELVT FinFETs results in 9% and 8% reduction in VDD and power consumption respectively at the same phase-noise (PN) level as the SLVT based design. If operated at the same V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> of 0.525V ELVT FinFET can improve the VCO Figure of Merit (FOMVCO) by 2.8dB.

Millimeter-Wave Donor–Acceptor-Doped DpHEMT

In this article, we present GaAs millimeter-wave pseudomorphic high-electron-mobility transistor (pHEMT) using sophisticated AlGaAs-InGaAs–GaAs heterostructure with an In0.22Ga0.78As quantum well located inside an external quantum well formed by space charge regions in AlGaAs layers. In a heterostructure with this design, high mobility [5800 cm2/( $\text {V}\cdot \text {s}$ )] and high density ( ${4.7}\times {10}^{{12}}$ cm $^{-{2}}$ ) of two-dimensional electron gas at 300 K were obtained. The localization of hot electrons in an external quantum well leads to an increase in their drift velocity and to enhance the dc and RF performances of the device. A field-effect transistor based on such a heterostructure with a T-gate of $0.14~\mu \text{m}$ in length shows a specific current density of about 0.7 A/mm, transconductance of about 250 mS/mm, gate–drain breakdown voltage in the range 23–31 V, which corresponds to more than 2 W/mm specific output RF power according to a simple estimate. The transistor demonstrates impressive RF characteristics, the maximum stable gain (MSG) of more than 15 dB at 40 GHz and more than 10 dB at 67 GHz, ${f}_{t} = {45}$ GHz and ${f} _{\text {max}} = {250}$ GHz. The MSG at 40 GHz increases with increasing distance between the gates in the drain and is almost constant in the range 25–55 GHz.

Vertical nanowire III–V MOSFETs with improved high‐frequency gain

High-frequency performance of vertical InAs/InGaAs heterostructure nanowire MOSFETs on Si is demonstrated for the first time for a gate-last configuration. The device architecture allows highly asymmetric capacitances, which increases the power gain. A device with L g = 120 nm demonstrates f T = 120 GHz, f max = 130 GHz and maximum stable gain (MSG) = 14.4 dB at 20 GHz. These metrics demonstrate the state-of-the-art performance of vertical nanowire MOSFETs.

Effects of traps in the gate stack on the small-signal RF response of III-V nanowire MOSFETs

We present a detailed study of the effect of gate-oxide-related defects (traps) on the small-signal radio frequency (RF) response of III-V nanowire MOSFETs and find that the effects are clearly identifiable in the measured admittance parameters and in important design parameters such as h21 (forward current gain) and MSG (maximum stable gain). We include the identified effects in a small-signal model alongside results from previous investigations of III-V RF MOSFETs and thus provide a comprehensive physical small-signal RF model for this type of transistor, which accurately describes the measured admittance parameters and gains. We verify the physical basis of the model assumptions by calculating the oxide defect density from the measured admittances.

A Prospective, Single-centre Evaluation of Carina Microphone Sensitivity and Maximum Stable Gain in Adult Recipients

A Prospective, Single-centre Evaluation of Carina Microphone Sensitivity and Maximum Stable Gain in Adult Recipients

Acoustic Feedback Suppression for Multi-Microphone Hearing Devices Using a Soft-Constrained Null-Steering Beamformer

Acoustic feedback occurs in hearing aids 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 typically converges to a biased optimal solution due to the closed-loop acoustical system of the hearing aid. Previously it has therefore been proposed to suppress the acoustic feedback contribution for an earpiece with multiple integrated microphones and loudspeakers using a fixed null-steering beamformer and hence avoiding a biased adaption. While previous null-steering beamforming approaches aimed at perfect preservation of the incoming signal using its relative transfer function (RTF), in this article we propose to use a soft constraint that allows to trade off between incoming signal preservation and feedback suppression. 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 evaluations were performed using measured acoustic feedback paths from a custom earpiece with two microphones in the vent and a third microphone in the concha. Results show that the proposed fixed null-steering beamformer using the RTF-based soft constraint provides a reduction of the acoustic feedback by 7–8 dB compared to the previously proposed RTF-based hard constraint while limiting the distortions of the incoming signal in the beamformer output.

Analysis of the back-barrier effect in AlGaN/GaN high electron mobility transistor on free-standing GaN substrates

The effect of AlGaN back-barrier on AlGaN/GaN high electron mobility transistors (HEMTs) using free-standing GaN wafer has been investigated in this work. With the introducing back-barrier structure, the leakage path underneath the buffer (native nitrogen-vacancies and GaOx compounds of the HVPE-grown free-standing GaN surface) layer can be suppressed by lift-up the conduction band. As compared with AlGaN/GaN HEMTs on SiC wafer, AlGaN/GaN HEMTs on free-standing GaN wafer show enhanced drain current (700 mA/mm), improved transconductance (143 mS/mm), less current collapse (12%), higher current gain cut-off frequency (13 GHz), and maximum stable gain cut-off frequency (24 GHz), which is attributed to the higher epi quality layer on free-standing GaN wafer.