Search Results (167)

With their superior switching speed, GaN high-electron-mobility transistors (HEMTs) enable high power density, reduce energy losses, and increase power efficiency in a wide range of applications, such as power electronics, due to their high breakdown voltage. GaN-HEMT devices are subject to long-term reliability due to the self-heating effect and lattice mismatch between the SiC substrate and the GaN. Depletion-mode GaN HEMTs are utilized for radio frequency applications, and this work investigates three wide-bandgap (WBG) GaN HEMT fixed-frequency oscillators with output buffers. The first GaN-on-SiC HEMT oscillator consists of an HEMT amplifier with an LC feedback network. With the supply voltage of 0.8 V, the single-ended GaN oscillator can generate a signal at 8.85 GHz, and it also supplies output power of 2.4 dBm with a buffer supply of 3.0 V. At 1 MHz frequency offset from the carrier, the phase noise is −124.8 dBc/Hz, and the figure of merit (FOM) of the oscillator is −199.8 dBc/Hz. After the previous study, the hot-carrier stressed RF performance of the GaN oscillator is studied, and the oscillator was subject to a drain supply of 8 V for a stressing step time equal to 30 min and measured at the supply voltage of 0.8 V after the step operation for performance benchmark. Stress study indicates the power oscillator with buffer is a good structure for a reliable structure by operating the oscillator core at low supply and the buffer at high supply. The second balanced oscillator can generate a differential signal. The feedback filter consists of a left-handed transmission-line LC network by cascading three unit cells. At a 1 MHz frequency offset from the carrier of 3.818 GHz, the phase noise is −131.73 dBc/Hz, and the FOM of the 2nd oscillator is −188.4 dBc/Hz. High supply voltage operation shows phase noise degradation. The third GaN cross-coupled VCO uses 8-shaped inductors. The VCO uses a pair of drain inductors to improve the Q-factor of the LC tank, and it uses 8-shaped inductors for magnetic coupling noise suppression. At the VCO-core supply of 1.3 V and high buffer supply, the FOM at 6.397 GHz is −190.09 dBc/Hz. This work enhances the design techniques for reliable GaN HEMT oscillators and knowledge to design high-performance circuits. Full article

Near-field acoustic holography (NAH) provides an effective way to achieve wide-band, high-resolution visualization measurement of the sound insulation performance of building components. However, based on Green’s function, the microphone array’s inherent amplitude and phase mismatch errors will exponentially amplify the sound field inversion process, significantly reducing the measurement accuracy. To systematically evaluate this problem, this study combines numerical simulation with actual measurements in a soundproof room that complies with the ISO 10140 standard, quantitatively analyzes the influence of array system errors on NAH reconstructed sound insulation and acoustic images, and proposes an error correction strategy based on channel transfer function normalization. The research results show that when the array amplitude and phase mismatch mean values are controlled within 5% and 5°, respectively, the deviation of the weighted sound insulation measured by NAH can be controlled within 1 dB, and the error in the key frequency band of building sound insulation (200–1.6k Hz) does not exceed 1.5 dB; when the mismatch mean value increases to 10% and 10°, the deviation of the weighted sound insulation can reach 2 dB, and the error in the high-frequency band (≥1.6k Hz) significantly increases to more than 2.0 dB. The sound image shows noticeable spatial distortion in the frequency band above 250 Hz. After applying the proposed correction method, the NAH measurement results of the domestic microphone array are highly consistent with the weighted sound insulation measured by the standard method, and the measurement difference in the key frequency band is less than 1.0 dB, which significantly improves the reliability and applicability of low-cost equipment in engineering applications. In addition, the study reveals the inherent mechanism of differential amplification of system errors in the propagating wave and evanescent wave channels. It provides quantitative thresholds and operational guidance for instrument selection, array calibration, and error compensation of NAH technology in building sound insulation detection. Full article

Fine-grained recognition tasks face significant challenges in differentiating subtle, class-specific details against cluttered backgrounds. This paper presents an efficient architecture built upon the Res2Net backbone, significantly enhanced by a dynamic Sparse Attention mechanism. The core approach leverages the inherent multi-scale representation power of Res2Net to capture discriminative patterns across different granularities. Crucially, the integrated Sparse Attention module operates dynamically, selectively amplifying the most informative features while attenuating irrelevant background noise and redundant details. This combined strategy substantially improves the model’s ability to focus on pivotal regions critical for accurate classification. Furthermore, strategic architectural optimizations are applied throughout to minimize computational complexity, resulting in a model that demands significantly fewer parameters and exhibits faster inference times. Extensive evaluations on benchmark datasets demonstrate the effectiveness of the proposed method. It achieves a modest but consistent accuracy gain over strong baselines (approximately 2%) while simultaneously reducing model size by around 30% and inference latency by about 20%, proving highly effective for practical fine-grained recognition applications requiring both high accuracy and operational efficiency. Full article

Facial authentication has gained widespread adoption as a biometric authentication method, offering a convenient alternative to traditional password-based systems, particularly on mobile devices equipped with front-facing cameras. While this technology enhances usability and security by eliminating password management, it remains highly susceptible to spoofing attacks. Adversaries can exploit facial recognition systems using pre-recorded photos, videos, or even sophisticated 3D models of victims’ faces to bypass authentication mechanisms. The increasing availability of personal images on social media further amplifies this risk, making robust anti-spoofing mechanisms essential for secure facial authentication. To address these challenges, we introduce FaceCloseup, a novel liveness detection technique that strengthens facial authentication by leveraging perspective distortion inherent in close-up shots of real, 3D faces. Instead of relying on additional sensors or user-interactive gestures, FaceCloseup passively analyzes facial distortions in video frames captured by a mobile device’s camera, improving security without compromising user experience. FaceCloseup effectively distinguishes live faces from spoofed attacks by identifying perspective-based distortions across different facial regions. The system achieves a 99.48% accuracy in detecting common spoofing methods—including photo, video, and 3D model-based attacks—and demonstrates 98.44% accuracy in differentiating between individual users. By operating entirely on-device, FaceCloseup eliminates the need for cloud-based processing, reducing privacy concerns and potential latency in authentication. Its reliance on natural device movement ensures a seamless authentication experience while maintaining robust security. Full article

Based on the GSMC 180 nm SiGe BiCMOS process, a parallel-summation logarithmic amplifier is presented in this paper. The logarithmic amplifier adopts a cascaded structure of nine-stage fully-differential limiting amplifiers (LA) to achieve high dynamic range. The ten-stage rectifier completes the conversion of amplified voltage to a logarithmic current signal. A log slope adjuster is proposed. It can provide slopes of 17–30 mV/dB by configuring an off-chip resistor to meet the detection requirements of different input power. Meanwhile, a power-down control unit is designed to reduce the power consumption to only 162 μW in standby mode. The post-simulation results show that under 5 V power supply voltage, the dynamic range exceeds 80 dB and the 3 dB bandwidth is 20 MHz–4 GHz. It also has a fast response time of 42 ns with a power consumption of 109 mW in normal operation mode. Full article

This paper presents a broadband near-field probe designed for measuring the normal magnetic field ($H_z$) in radio frequency (RF) circuits operating within a frequency range of 2–8 GHz. The proposed probe uses a cost-effective 4-layer printed circuit board (PCB) structure made with an FR-4 substrate. The probe primarily consists of an $H_z$ detection unit, a broadband microstrip balun, and a coaxial-like output. The broadband balun facilitates the conversion from differential to single-ended signals, thereby enhancing the probe’s common-mode rejection capability. This design ensures that the probe achieves both cost efficiency and high broadband measurement performance. Additionally, this work investigates the feasibility of employing microstrip lines as calibration standards for the $H_z$ probe. The probe’s structural parameters and magnetic field response were initially determined through simulations, and the calibration factor was subsequently verified by calibration experiments. In practical measurements, the field distributions above a microstrip line and a low-noise amplifier (LNA) were captured. The measured field distribution of the microstrip line was compared with simulation results to verify the probe’s performance. Meanwhile, the measured field distribution of the LNA was utilized to identify the radiating components within the amplifier. Full article

Against global carbon neutrality goals and China’s “dual carbon” strategy, this study examines how green technology innovation shapes corporate carbon performance through a dual-path mechanism—improving enterprises’ resource utilization efficiency and environmental governance capabilities. Leveraging data from Chinese A-share listed firms (2007–2022) and methods including fixed effects, instrumental variables, and Heckman two-stage models, key findings include: (1) Green technology innovation significantly improves carbon performance. (2) This effect operates through two pathways: enhancing total factor productivity (TFP) and strengthening environmental governance. (3) Green media and investor attention amplify the positive impact of green innovation on carbon performance. (4) The effect remains significant but shows diminishing marginal returns over 1–4 future periods. (5) Non-state-owned enterprises and non-high-carbon industries exhibit more pronounced improvements. This research provides micro-level evidence for “technology-driven low-carbon transformation”, offering theoretical support for policy differentiation and corporate green technology strategies, with practical implications for achieving China’s “dual carbon” objectives. Full article

Bio-inspired joints play a pivotal role in legged robots, directly determining their motion capabilities and overall system performance. While shape memory alloy (SMA) actuators present superior power density and silent operation compared to conventional electromechanical drives, their inherent nonlinear hysteresis and restricted strain capacity (typically less than 5%) limit actuation range and control precision. This study proposes a bio-inspired joint integrating an antagonistic actuator configuration and differential dual-diameter pulley collaboration, achieving amplified joint stroke (±60°) and bidirectional active controllability. Leveraging a comprehensive experimental platform, precise reference input tracking is realized through adaptive fuzzy control. Furthermore, an SMA-driven bio-inspired leg is developed based on this joint, along with a motion retargeting framework to map human motions onto the robotic leg. Human gait tracking experiments conducted on the leg platform validate its motion performance and explore practical applications of SMA in robotics. Full article

Fully differential amplifier circuits are well suited for instrumentation front ends and signal-conditioning applications. They offer high common-mode rejection ratios (CMRRs) regardless of the passive component tolerances but remain sensitive to imbalances in active devices. By using power supply bootstrapping (PSB), the CMRRs of these circuits can be improved, where they become independent of mismatches in both passive and active components. This technique works by forcing the power supply nodes to follow the common-mode input voltage, which significantly enhances the CMRR. However, this approach introduces stability issues that must be addressed through dedicated compensation strategies without degrading the overall performance. In this work, the theoretical background, a design methodology, and experimental validation are presented. The proposed technique was applied to a fully differential amplifier built with general purpose operational amplifiers. Prior to the PSB, the amplifier exhibited a CMRR of 90 dB at 1 kHz. A straightforward application of PSB led to instability in the common-mode behavior; however, with the proposed compensation method, the amplifier achieved stable operation and an improved CMRR of 130 dB. Full article

Energy-efficient integrated circuits require scaled-down supply voltages, posing challenges for analog design, particularly for operational transconductance amplifiers (OTAs) essential in high-accuracy CMOS feedback systems. Below 1 V, gate-driven OTAs are limited in common-mode input range and minimum supply voltage. This work investigates CMOS Bulk-Driven (BD) sub-threshold techniques as an efficient alternative for ultra-low voltage (ULV) and ultra-low power (ULP) designs. Although BD overcomes MOS threshold voltage limitations, historical challenges like lower transconductance, latch-up, and layout complexity hindered its use. Recent advancements in CMOS processes and the need for ULP solutions have revived industrial interest in BD. Through theoretical analysis and computer simulations, we explore BD topologies for ULP OTA input stages, classifying them as tailed/tail-less and class A/AB, evaluating their effectiveness for robust analog design, while offering valuable insights for circuit designers. Full article

This paper presents a fully integrated bandpass filter (BPF) with high tunability based on a novel differential active inductor (DAI), designed for sensor interface circuits operating in the ultra-high frequency (UHF) band. The design of the proposed DAI is based on a symmetrical configuration, utilizing a differential amplifier for the feedforward transconductance and a common-source (CS) transistor for the feedback transconductance. By integrating a cascode scheme with a feedback resistor, the quality factor of the active inductor is significantly improved, leading to enhanced mid-band gain for the bandpass filter. To facilitate independent tuning of the BPF‘s center frequency and mid-band gain, an active resistor adjustment and bias voltage control are employed, providing precise control over the filter’s operational parameters. Post-layout simulations and process corner results are conducted with 0.13 µm CMOS technology at 1.2 V supply voltage. The proposed second order BPF achieves a broad tuning range of 280 MHz to 2.426 GHz, with a passband gain between 8.9 dB and 16.54 dB. The design demonstrates a maximum noise figure of 16.54 dB at 280 MHz, an input-referred 1 dB compression point of −3.78 dBm, and a third-order input intercept point (IIP3) of −0.897 dBm. Additionally, the BPF occupies an active area of only 68.2×30 µm², including impedance-matching part, and consumes a DC power of 14–20 mW. The compact size and low power consumption of the design make it highly suitable for integration into modern wireless sensor interfaces where performance and area efficiency are critical. Full article

The dynamic response of pump valve motion directly influences the volumetric efficiency of drilling pumps and serves as a critical factor in performance enhancement. This study presents a coupled fluid–structure interaction (FSI) analysis of a novel secondary cushioned pump valve for drilling systems. A validated 3D transient numerical model, integrating piston–valve kinematic coupling and clearance threshold modeling, was developed to resolve the dynamic interactions between reciprocating mechanisms and turbulent flow fields. The methodology addresses critical limitations in conventional valve closure simulations by incorporating a geometrically adaptive mesh refinement strategy while maintaining computational stability. Transient velocity profiles confirm complete sealing integrity with near-zero leakage (<0.01 m/s), while a 39.3 MPa inter-pipeline pressure differential induces 16% higher jet velocities in suction valves compared to discharge counterparts. The secondary cushioned valve design reduces closure hysteresis by 22%, enhancing volumetric efficiency under rated conditions. Parametric studies reveal structural dominance, with increases in cylindrical spring stiffness lowering discharge valve lift by 7.2% and velocity amplitude by 2.74%, while wave spring optimization (24% stiffness enhancement) eliminates pressure decay and reduces perturbations by 90%. Operational sensitivity analysis demonstrates stroke frequency as a critical failure determinant: elevating speed from 90 to 120 rpm amplifies suction valve peak velocity by 59.87% and initial closing shock by 129.07%. Transient flow simulations validate configuration-dependent performance, showing 6.3 ± 0.1% flow rate deviations from theoretical predictions (Q_{t_max} = 40.0316 kg/s) due to kinematic hysteresis. This study establishes spring parameter modulation as a key strategy for balancing flow stability and mitigating cushioning-induced oscillations. These findings provide actionable insights for optimizing high-pressure pump systems through hysteresis control and parametric adaptation. Full article

In order to meet the application requirements for high-precision and low-noise accelerometers in micro-vibration measurement and navigation fields, this paper presents the design and testing of an ultra-high-capacitance resolution capacitive readout circuit with attofarad-level precision. First, a differential charge amplifier circuit is employed for the first stage of capacitance detection. To suppress noise interference in the circuit, a frequency-domain modulation technique is utilized to mitigate low-frequency noise. Subsequently, a differential subtraction circuit is implemented to reduce common-mode noise. Additionally, an improved filtering circuit is designed to suppress noise interference in the final stage. The test results indicate that the designed circuit operates at a carrier frequency of 1 MHz, achieving a capacitance resolution of up to 0.103 aF/H${\mathrm{z}}^{1/2}$ and a noise floor of 25.6 $\mathsf{\mu }$g/H${\mathrm{z}}^{1/2}$, thereby meeting the requirements for high-precision and low-noise capacitance detection in MEMS accelerometers. Full article

Continuous-time Sigma-Delta (CTSD) Analog-to-Digital Converter (ADC) is widely used in wireless receivers due to its built-in anti-aliasing and resistive input. In order to achieve a wide bandwidth while ensuring low power consumption, this paper proposes a CT 2-2 Multi-stAge Noise-sHaping (MASH) ADC for wireless communication. In order to reduce power consumption, the loop filter adopts a feedforward structure, and the operational amplifier uses complementary differential input pairs and feedforward compensation. The pseudo-random sequence injection and Least Mean Squares (LMS) algorithm are adopted to calibrate the digital noise cancelation filter to match the analog transfer function. The simulation results obtained in 40 nm CMOS show that the presented 2-2 CT MASH ADC achieves a 76.8 dB signal-to-noise-and-distortion ratio (SNDR) at a 50MHz bandwidth (BW) with a 1.6 GHz sampling rate and consumes 29.7 mW power under 1.2/0.9 V supply, corresponding to an excellent figure of merit (FoM) of 169.1 dB. Full article

Conventional operational amplifier designs often experience parameter performance issues during the transition between complementary input differential stages, which restricts the full rail-to-rail common mode voltage swing. This paper presents an innovative charge pump architecture featuring a feedback supply selector that optimizes the transition performance. The proposed approach employs a switched-capacitor technique to boost the supply voltage by 1.5 V relative to the input voltage, thereby enabling the use of a single pMOS differential input stage. The novel supply selector dynamically chooses the maximum available voltage between the external supply and the boosted output, ensuring efficient transistor switching and improved biasing. Schematic-level and post-layout simulations in a 250 nm CMOS process validate the design under varied load currents, supply voltages, temperatures, and process corners. Results show a significant reduction in output voltage ripple, with a maximum value of 48 mV achieved post-layout, and enhanced overall efficiency, even under higher load currents. This architecture provides a robust and scalable solution for advanced operational amplifiers, particularly in fields where high performance and stability are critical. Full article