Amplifier Technique Research Articles

Design of Interface ASIC with Power-Saving Switches for Capacitive Accelerometers

High-precision, low-power MEMS accelerometers are extensively utilized across civilian applications. Closed-loop accelerometers employing switched-capacitor (SC) circuit topologies offer notable advantages, including low power consumption, high signal-to-noise ratio (SNR), and excellent linearity. Addressing the critical demand for high-precision, low-power MEMS accelerometers in modern geophones, this work focuses on the design and implementation of closed-loop interface ASICs (Application-Specific Integrated Circuits). The proposed interface circuit, based on switched-capacitor modulation technology, incorporates a low-noise charge amplifier, sample-and-hold circuit, integrator, and clock divider circuit. To minimize average power consumption, a switched operational amplifier (op-amp) technique is adopted, which temporarily disconnects idle op-amps from the power supply. Additionally, a class-AB output stage is employed to enhance the dynamic range of the circuit. The design was realized using a standard 0.35 μm CMOS process, culminating in the completion of layout design and small-scale engineering fabrication. The performance of the MEMS accelerometers was evaluated under a 3.3 V power supply, achieving a power consumption of 3.3 mW, an accelerometer noise density below 1 μg/√Hz, a sensitivity of 1.65 V/g, a measurement range of ±1 g, a nonlinearity of 0.15%, a bandwidth of 300 Hz, and a bias stability of approximately 36 μg. These results demonstrate the efficacy of the proposed design in meeting the stringent requirements of high-precision MEMS accelerometer applications.

A mixed-mode on-chip automatic frequency tuning technique for biopotential amplifiers

A mixed-mode on-chip automatic frequency tuning technique for biopotential amplifiers

(Invited) Group IV Mid-Infrared Optoelectronics Leveraging Nanoscale Growth Substrates

Mid-infrared (MIR) optoelectronic devices are of utmost importance to a plethora of applications such as night vision, thermal sensing, autonomous vehicles, free-space communication, and spectroscopy. To this end, leveraging the ubiquitous silicon-based processing has emerged as a powerful strategy that can be accomplished through the use of group IV germanium-tin (GeSn) alloys. Indeed, due to their compatibility with silicon and their tunable bandgap energy covering the entire MWIR range, GeSn semiconductors are frontrunner platforms for compact and scalable MIR technologies. However, the GeSn large lattice parameter has been a major hurdle limiting the quality of GeSn epitaxy on silicon wafers. These limitations are further exacerbated as Ge1−xSnx layers and heterostructures with Sn contents at least one order of magnitude higher than the solubility are needed for device structures relevant to MWIR applications. In this regime, the as-grown layers are typically under a significant compressive strain, which impacts the bandgap directness and increases its energy at the Γ point, thus hindering the device performance and limiting the covered range of the MIR spectrum. This compressive strain build-up not only affects the band structure but also limits the incorporation of Sn atoms in the growing layer, making the control of Sn content a daunting task.In this presentation, we will show and discuss how sub-20 nm Ge nanowires provide effective compliant substrates to grow Ge1−xSnx alloys with a composition uniformity over several micrometers with a very limited build-up of the compressive strain. Ge/Ge1−xSnx structures with Sn content spanning the 6 to 18 at.% range are achieved. We will also demonstrate the integration of the obtained materials in optoelectronic device processing leading to tunable detectors and emitters [1,2]. For instance, photodetectors based on these materials were found to exhibit a high signal-to-noise ratio at room temperature and provide a tunable cutoff wavelength covering the 2.0 µm to 3.9 µm range. Additionally, the processed detectors were also integrated in uncooled imagers enabling the acquisition of high-quality images under both broadband and laser illuminations without the use of the lock-in amplifier technique. Finally, progress towards achieving nanoscale GeSn lasers will also be discussed [2].

Fully dynamic zoom ADC with energy-efficient residue feedforward and two-step summation

This paper proposes a fully dynamic zoom ADC based on residue feedforward and correlated level shifting (CLS)-assisted floating inverter amplifier (FIA) technique with 200 × bandwidth/power scalability, by only changing the clock frequency. A CLS-assisted FIA which achieves 65 dB DC gain is employed to reduce errors from finite FIA gain. An energy-efficient residue feedforward path extracted from the input of the SAR ADC's comparator minimizes the leakage of the SAR ADC's quantization noise into the band. A novel two-step summation approach is proposed to minimize capacitor areas compared to a traditional passive switched-capacitor adder. The post-simulated results show the prototype ADC with near-constant energy efficiency, which scales power from 5 μW to 822 μW, achieves high resolution (>100 dB) during the scalable bandwidth. At 20 kHz BW, it achieves 106.2 dB DR, 102.0 dB SNDR, leading to FoMDR of 180.0 dB and FoMSNDR of 175.8 dB.

DC-Coupled Biasing Technique for Quantized-Analog Amplifiers

DC-Coupled Biasing Technique for Quantized-Analog Amplifiers

All-fiber, high-speed, and high-resolution dispersion measurements of chirped fiber Bragg gratings.

In this work, an all-fiber high-speed and high-resolution dispersion measurement approach for chirped fiber Bragg gratings (CFBGs) is proposed and demonstrated. Dispersion information (1-4 order) of CFBGs that with different dispersion are determined experimentally, which agree well with the theoretical results. The measurement speed, accuracy, and repeatability are also studied and discussed. Compared with the well-developed techniques, the proposed new method is not only time-saving but with higher accuracy and repeatability. The method and results of high-order dispersion information of CFBGs are reported for the first time to our best knowledge, which will greatly benefit the fiber chirped pulse amplifier (CPA) and ultrafast laser techniques.

Application of Lock-in Amplifier Technique in Signal Blind Source Separation

Abstract In the realm of signal processing, frequency error stands as a critical challenge that cannot be overlooked, particularly in scenarios characterized by noise disturbances and constantly changing environmental variables, as it significantly undermines the precision of waveform separation. Faced with a spectrum of frequency error phenomena stemming from hardware instability, such as clock drift, transmission distortion, and environmental changes, this paper proposes a waveform separation scheme centered around a core closed-loop control architecture aimed at addressing such challenges. Leveraging the high-performance STM32F407 microcontroller platform, the system harnesses the powerful algorithmic advantages of Fast Fourier Transform (FFT) to precisely locate and delineate the spectral characteristics of signals. Furthermore, we creatively integrate lock-in amplifier technology into the meticulously designed closed-loop control system, coupled with state-of-the-art zero-crossing detection algorithms for in-depth optimization. The research findings demonstrate outstanding signal-to-noise ratio performance within predefined target frequency bands for the separation device based on lock-in amplifier technology, showcasing not only remarkable resilience against interference but also the ability to accurately separate and reconstruct target signal components with high fidelity from complex and dynamic signal environments. This significantly enhances the robustness and accuracy of the entire system.

Dynamics of potential‐induced structural changes at the Ag(111)/alkaline interface

AbstractThe dynamics of the structural changes in the electrochemical double layer at the interface between a Ag(111) electrode and 0.1 M KOH electrolyte have been probed using surface X‐ray diffraction measurements. The X‐ray measurements utilised a lock‐in amplifier technique to obtain a time resolution down to the millisecond scale. Two potential step regions were explored in an attempt to separate the dynamics of the reversible adsorption/desorption of hydroxide species (OHad) and the subsequent cation (K+) ordering in the double layer. By probing different positions in reciprocal space, sensitive to different structural changes, the time‐dependent response of the electrode surface was probed and time constants for the different associated processes were obtained.

Mid-infrared Imaging Using Strain-Relaxed Ge1-xSnx Alloys Grown on 20 nm Ge Nanowires.

Germanium-tin (Ge1-xSnx) semiconductors are a front-runner platform for compact mid-infrared devices due to their tunable narrow bandgap and compatibility with silicon processing. However, their large lattice parameter has been a major hurdle, limiting the quality of epitaxial layers grown on silicon or germanium substrates. Herein, we demonstrate that 20 nm Ge nanowires (NWs) act as effective compliant substrates to grow extended defect-free Ge1-xSnx alloys with a composition uniformity over several micrometers along the NW growth axis without significant buildup of the compressive strain. Ge/Ge1-xSnx core/shell NWs with Sn content spanning the 6-18 at. % range are achieved and processed into photoconductors exhibiting a high signal-to-noise ratio at room temperature with a cutoff wavelength in the 2.0-3.9 μm range. The processed NW devices are integrated in an uncooled imaging setup enabling the acquisition of high-quality images under both broadband and laser illuminations at 1550 and 2330 nm without the lock-in amplifier technique.

The Design of Low Power Op-amp for Biomedical Application

This work presents a low-power operational amplifier (op-amp) circuit design which optimized and tailored specifically for biomedical circuit application in low power environment. The proposed op-amp design incorporates the folded cascode differential amplifier technique with a low voltage supply 1.2 V, utilizing current biasing, current mirrors, and adopted low-power circuit topologies. AC and DC analysis are carried out to analyse the performance of the proposed design. Extensive simulations executed using industrial standard EDA tool have validated the circuit design, and demonstrated a gain of 70.94 dB, UGBW of 4.90 MHz, GM of 52.70 dB, PM of 82.02 degrees, PSRR of 82.77 dB, CMRR of 100.78 dB, and total power dissipation of only 28.07 mW. Low power consumption is essential for biomedical circuit applications, and the result shows a significant power reduction without compromising other performance parameters. The proposed op-amp circuit design is suitable to be implemented in low-power and high-performance biomedical devices.

A high current efficiency multipath nested feedforward compensation technique for two-stage amplifier

In this paper, a high current efficiency two-stage amplifier using multipath nested feedforward compensation (MNFC) method is proposed. For the purpose of achieving the high current efficiency, the first stage of the amplifier uses a recycling folded cascode amplifier (RFC) and a nested small-gain stage is added between the two stages of the amplifier so that there are two paths in the feedforward path. This two-stage amplifier improves the phase margin (PM) and extends the gain bandwidth (GBW) by using the MNFC technique which can eliminate the non-dominant pole. The chip area of this two-stage MNFC amplifier which using 0.18μm CMOS process is 0.01272 mm2. The simulated and measured results shows that the phase margin(PM), DC gain, gain-bandwidth(GBW), average 1% settling time, slew rate- (SR-) and slew rate+ (SR+) is 72.7°, 104.4 dB, 4.29 MHz, 246.2 ns, 16 V/μs, and 6.15 V/μs, respectively, when the load capacitance is 120 pF. The supply voltage of this circuit is 1.8 V and the power consumption is 0.13 mW.

Meta Analytic Review on Recent Advancements of Class AB Power Amplifiers

The ever-increasing complexity and prohibitive fabrication costs associated with VLSI circuits necessitate the development of techniques that prioritize low power consumption and high-speed analog blocks. In today’s era of smart IoT devices, which are pervasive and heavily reliant on efficient battery backups, the demand for low power architectures is paramount to preserve battery life and reduce weight. Simultaneously, maintaining high-speed performance and incorporating additional features is crucial in the wireless industry. Amplifiers, being fundamental front-ends in transceiver design, significantly impact the overall performance of transceivers. Consequently, this study aims to provide a comprehensive and systematic review of amplifier techniques, with a specific focus on low-power and high-speed approaches, following the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) methodology. The findings presented herein identify the current state of research in the defined area and highlight potential avenues for future exploration.

Spectral power profile optimization of a field-deployed wavelength-division multiplexing network enabled by remote EDFA modeling

We propose a technique for modeling erbium-doped fiber amplifiers (EDFAs) in optical fiber networks, where the amplifier unit is located at a distant node outside the laboratory. We collect data on an optical point-to-point link with the amplifier as the only amplification stage. Different amplifier operating points are modeled using probe signals and by adjusting the settings of the amplifier through a control network. The data are used to train a machine learning algorithm integrated within a physical EDFA model. The obtained mathematical model for the amplifier is used to model all amplifiers of a network and links with multiple amplification stages. To confirm the modeling accuracy, we thereafter predict and optimize launch power profiles of two selected links in the network of 439.4 km and 592.4 km lengths. Maximum/average channel optical signal-to-noise ratio prediction errors of 1.41/0.68 dB and 1.62/0.83 dB are achieved for the two multi-span systems, respectively, using the EDFA model trained on the single span system with margin-optimized launch power profiles. Up to 2.2 dB of margin improvements are obtained with respect to unoptimized transmission.

Concurrent recordings of slow DC-potentials and epileptiform discharges: Novel EEG amplifier and signal processing techniques

Ionic currents within the brain generate voltage oscillations. These bioelectrical activities include ultra-low frequency electroencephalograms (DC-EEG, frequency less than 0.1 Hz) and conventional clinical electroencephalograms (AC-EEG, 0.5–70 Hz). Although AC-EEG is commonly used for diagnosing epilepsy, recent studies indicate that DC-EEG is an essential frequency component of EEG and can provide valuable information for analyzing epileptiform discharges. During conventional EEG recordings, DC-EEG is censored by applying high-pass filtering to i) obliterate slow-wave artifacts, ii) eliminate the bioelectrodes' half-cell potential asymmetrical changes in ultralow-low frequency, and iii) prevent instrument saturation. Spreading depression (SD), which is the most prolonged fluctuation in DC-EEG, may be associated with epileptiform discharges. However, recording of SD signals from the scalp's surface can be challenging due to the filtering effect and non-neuronal slow shift potentials. In this study, we describe a novel technique to extend the frequency bandwidth of surface EEG to record SD signals. The method includes novel instrumentation, appropriate bioelectrodes, and efficient signal-processing techniques. To evaluate the accuracy of our approach, we performed a simultaneous surface recording of DC- and AC-EEG from epileptic patients during long-term video EEG monitoring, which provide a promising tool for diagnosis of epilepsy. Data Availability StatementThe data presented in this study are available on request.

Gain enhancement technique for S-band polymer-based waveguide amplifiers.

The S-band polymer-based waveguide amplifier has been fabricated, but how to improve the gain performance remains a big challenge. Here, using the technique of establishing the energy transfer between different ions, we successfully improved the efficiency of Tm3+:3F3→3H4 and 3H5→3F4 transitions, resulting in the emission enhancement at 1480 nm and gain improvement in S-band. By doping the NaYF4:Tm,Yb,Ce@NaYF4 nanoparticles into the core layer, the polymer-based waveguide amplifier provided a maximum gain of 12.7 dB at 1480 nm, which was 6 dB higher than previous work. Our results indicated that the gain enhancement technique significantly improved the S-band gain performance and provided guidance for even other communication bands.

A Low-Power Common-Mode Detector with PVT-Compensation Technique for Dynamic Amplifier in Delta-Sigma Modulator

A Low-Power Common-Mode Detector with PVT-Compensation Technique for Dynamic Amplifier in Delta-Sigma Modulator

Efficiency Enhancing Technique for Rod Fiber Picosecond Amplifiers with Optimal Mode Field Matching

A high power and high quality picosecond laser is crucial in MEMS fabrication regarding micromachines. Optimal seed beam coupling is an important precondition to enhance laser efficiency. However, empirical coupling limits its development. In this paper, the physical parameters related to coupling are determined. The relationships among them are established under optical mode matching constraints to satisfy optimal seed beam coupling. According to a theoretical analysis, the focal length cut-off and the optimal coupling position of the coupling lens are acquired. A maximum transmittance of 87.2% is acquired with a 6 W input seed power in the validation experiment. In further power amplification experiments, a diffraction-limited beam quality is achieved, with M2X = 1.111, M2Y = 1.017, an optical efficiency of 60.5% and a slope efficiency of 66%, benefiting from the previous theoretical guidance.

An octave bandwidth Class-J power amplifier with second harmonic termination control

A purely passive design technique for a class-J power amplifier (PA) is proposed, based on complex terminations at the fundamental frequency and the second harmonic, which increases the bandwidth while maintaining high efficiency. Using combined analytical derivation and numerical simulations, the drain impedance termination locus curve is obtained in the drain efficiency and DC voltage spaces. Successive application of the newly proposed de-normalization technique avoids the drain DC voltage manipulation used elsewhere. This is due to the resulting variable reactance of the output drain-source capacitor, optimal over a wide frequency range. Following the proposed procedure and the obtained optimal parametric space, a GaN HEMT-based PA is designed, fabricated, and tested displaying a very good agreement of the predicted and measured results.

A linearity enhancement technique for low-noise transconductance amplifiers in SAW-less receivers

A new linearization technique for the transconductance of MOS transistors has been proposed. In the presented method a new composite transistor has been proposed. Moreover, composite transistors with different operating points are connected in parallel to boost the transconductance and cancel the distortion of the overall structure. The superiority of the proposed technique over the previously reported methods is that it also improves the linearity for high-power input signals. A detailed analysis has been given to prove the effectiveness of the newly proposed technique. In order to verify the analysis, a Low-Noise Transconductance Amplifier has been designed exploiting the presented approach and the extensive post-layout simulation results demonstrate at least 26 dB and 7 dB improvements in IIP3 and 1-dB compression point, respectively.

A Manifold Regularization Approach for Low Sampling Rate Digital Predistortion With Band-Limited Feedback

Digital predistortion (DPD) is an effective linearization technique for RF power amplifiers (PAs), but conventional full sampling (FS) DPD systems use ADCs with three to five times signal bandwidth, and high-speed ADCs are expensive and power-hungry. In this article, we develop a novel band-limited DPD for reducing feedback sampling rate and acquisition bandwidth based on a general framework for semisupervised learning called manifold regularization (MR), which utilizes the geometry of unlabeled data to construct regularization terms for mitigating the overfitting problem. Considering the properties of DPD, we design a basis MR term and introduce it into the classical MR to obtain the extended MR (ExMR) method. To validate the proposed ExMR DPD method, experiments were conducted on two different RF PAs operating at 2.4 and 39 GHz, respectively. The test results demonstrate that the proposed ExMR DPD can linearize the RF PA with a 40-MHz acquisition bandwidth at 100-MHz input. The proposed method significantly reduces the cost and power consumption of the DPD system in comparison with the conventional FS DPD method, which provides a promising solution for broadband communication systems.