Large-signal Response Research Articles

Self-adhesive and conductive hydrogels and their applications in bioelectronics

At present, the market pressure strain sensors mainly include intrinsic conductivity, composite conductivity, and flexible metal conductivity. Most of the strain sensors can met various basic requirements such as strain sensitivity and mechanical properties. However, biocompatibility and the ease of use are still areas to be explored and improved. This paper proposes a novel strategy to fabricate a kind of self-adhesive and conductive hydrogel using natural biomacromolecule gelatin, tannic acid (TA) and conductive polymer PEDOT: PSS. The sensor is biocompatible, nontoxic, and can be directly attached to the skin without the use of adhesive tape, and sufficiently large electrical signal response can be collected under stress. The presence of tannic acid forms a cross-linking network with the gelatin in the organic hydrogel, which can effectively increase the toughness (which can reach 203.62 kPa/m3). PEDOT: PSS provides the conductivity for the hydrogel, and hydrogel with 0.3wt% PEDOT: PSS content have a conductivity of about 2.1ms/cm. Therefore, this study found the possibility of making a flexible electronic element by using a composite of PEDOT: PSS, gelatin, and TA.

A center-of-gravity-based framework for small- and large-signal frequency analysis of interconnected power systems

In this paper, a unified framework to study small- and large-signal frequency response based on the notion of center-of-gravity (COG)-based dynamic equivalents is presented. The method combines the ability of COG equivalents to capture short-term system response with that of unsupervised probabilistic learning techniques to extract the (slow) dominant oscillation patterns associated with observational data. First, a reduced-order representation is obtained in which the overall system dynamics is represented by the interaction of geographical or coherent areas with a virtual COG at which the total system power equations are at balance. Then, a small-signal representation is derived from which key linear relationships between the frequency of the local centers of inertia (COIs) and the COG are determined. Next, the physical properties of the model are studied, and alternative procedures to compute COG equivalents are explored. Finally, the effectiveness of the developed models is demonstrated through applications to two sample systems, thereby verifying their accuracy.

Generalized framework for the step response of semiconducting materials to optically switched electrical bias input in terahertz emission spectroscopy

In this paper, a generalized framework for the step response of semiconducting materials to optically switched electrical bias input in terahertz emission spectroscopy was developed, introducing a complex response function into the frequency domain. A comprehensive formula was obtained for calculating the transient current from the poles of the response function under bias field. This formula was found to give transient currents of an exponentially saturated, overshooting, or oscillating nature for three different regimes of charge transport in an isolated energy band. Furthermore, it was clarified how the transient terahertz emission is linked to the response function and its retarded contribution. When either true current or polarization current is linear with respect to bias field and dominates the transient current, the retarded contribution is identified as the small-signal ac complex conductivity. Two different spectral examples of the retarded contribution were given for actual terahertz Bloch oscillations in biased semiconductor superlattices, describing the small-signal response of polarization current under the Wannier–Stark localization and the large-signal response of true current under interminiband mixing.

Impact of Carrier Transport and Capture on VCSEL Dynamics

Using a vertical-cavity surface-emitting laser (VCSEL) equivalent circuit model based on two carrier rate equations to include effects of carrier dynamics, we study the impact of carrier transport and capture on the small- and large-signal modulation response of high-speed VCSELs. The model also accounts for parasitics, current-induced self-heating, and gain compression. A variation of the effective capture time from 1 to 15 ps is found to have a large impact on the small-signal modulation response, with the 3 dB bandwidth decreasing from 40 to 15 GHz and the response transitioning from under-damped to over-damped. This is primarily due to the increasing low frequency parasitic-like roll-off with increasing effective capture time. A significant effect on the optical waveforms produced by the VCSEL under 56 Gbit/s on-off keying (OOK) non-return-to-zero (NRZ) and pulse-amplitude modulation 4 (PAM4) modulation is observed, with a short effective capture time leading to horizontal eye closure caused by timing jitter (TJ) and intersymbol interference (ISI) and a long effective capture time leading to vertical eye closure caused by long rise- and fall-times. However, for high modulation speed, a short effective capture time is needed and the photon lifetime should be set for clear eye opening. We also show the impact of the effective capture time on the output power vs current characteristics and map the dependence of internal temperature, carrier densities, carrier escape and leakage rates, and spontaneous recombination rates on current for different effective capture times.

A transient-enhanced low-dropout regulator with dynamic current boost technique voltage buffer

In this paper, a dynamic current boost technique voltage buffer is presented to enhance the large signal response of low dropout regulators (LDOs). The proposed buffer consists of AC coupling networks and active RC network. Without consuming excess power, this LDO achieves substantial improvement in load transient response. Meanwhile, an enhanced recycling-folded-cascode (RFC) amplifier is employed due to its higher gain, bandwidth and slew rate. In order to ensure the stability of full load, this design adopts simple Miller compensation with a nulling resistor without external equivalent series resistance. Moreover, this paper makes a detailed analysis of LDO in theory and the extensive experimental data verified it. The proposed LDO is successfully fabricated in SMIC 0.18μm CMOS process. The input voltage is 1.8–2.2V and the maximum load current is 200 mA. The experiment results indicate that the undershoot is 84 mV and there is no overshoot when the load current is varied from 0 to 200 mA within 100 ns under the load of 1μF load capacitor.

Embedded Inductors Using Composite Magnetic Materials for 12–1-V Integrated Voltage Regulators

Substrate-embedded inductors enable the miniaturization of power modules and integrated voltage regulators (IVRs) with higher power efficiencies and performance. However, embedded inductors for single-stage 12- or 48–1-V high-conversion-ratio IVRs present new performance challenges due to limitations in magnetic materials, limited space, high frequency, and low duty cycle. In this work, we analyze seven embedded inductor designs fabricated with four metal-polymer composites magnetic materials. These inductors have inductances ranging from 20 to 500 nH, dc resistances between 14 and 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega $ </tex-math></inline-formula> , and saturation currents from 100 mA to over 5 A. Each inductor is characterized for its small-signal spectra with and without dc bias current and for its large-signal response. With all these measurements, a relation between the small- and large-signal losses is made, showing that using the new <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathrm{ acx}}$ </tex-math></inline-formula> metric, they are related by a factor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa $ </tex-math></inline-formula> . The measurements show that, in the megahertz range, the large-signal losses can be over four times larger than the small-signal ones. These analyses allow us to understand the material properties and modeling new magnetic materials targeted for high-conversion-ratio IVRs with input voltages greater than 5 V.

Proposed Inductor Power Loss Metric and Novel Embedded Toroidal Inductor for Integrated Voltage Regulators

High-density package embedded inductors enable the miniaturization of high conversion ratio integrated voltage regulators (IVRs). In this work we present a new embedded inductor structure along with a new performance metric called Effective AC Resistance per unit Inductance, and how the inductor sets constraints to the power stage topology. The proposed performance metric depends on the converter duty cycle and frequency and uses the inductor current harmonics, its inductance and resistance spectra, and the large-signal response to compute the inductor losses. No information of the inductor volume or its magnetic field distribution is used. The proposed embedded inductor structure shows a toroidal field distribution using a combination of slots through a magnetic sheet and vias through these slots. The new structure enables the fabrication of several inductors in the same magnetic substrate for multi-phase IVR. The proposed inductors are fabricated and the metric is demonstrated with measurements using a high saturation magnetic material, where an interesting relation between the small and large signal losses was observed.

Improved reversed nested miller frequency compensation techniques using flipped and folded flipped voltage follower with resistor for three stage amplifier

This paper presents three circuits to improve frequency compensation in three stage amplifier for large capacitive load of 100 pF. The first proposed circuit introduces Flipped Voltage Follower (FVF) in inner loop of Reversed Nested Miller Compensation (RNMC) to combat RHP zero whereas both second and third proposed circuits employ A Folded Flipped Voltage Follower (FFVF). The third proposed circuit uses an additional resistor in the outer compensation loop for double pole-zero cancellation. Further feed forward path has been used in all proposed circuits to improve the large signal response. The functionality is verified using TSMC 0.18 µm CMOS technology parameters in Tanner tool. The simulation results show maximum gain-bandwidth product (GBW) of 30 MHz, minimum phase margin (PM) of 60° and slew rate (SR) of 10 V/µS, and minimum common mode rejection ratio (CMRR) of 37.2 dB at unity gain frequency. The input-referred noise of the proposed circuits varies from 16.6 nV/Hz to 18.2 nV/Hzat unity gain frequency. Corner analysis is also included to show the robustness of the circuits.

Large-Signal Equivalent Circuit for Datacom VCSELs

Increasing the baud rate in optical interconnects (OIs) will require the use of more sophisticated driver and receiver electronics. This will help overcome the stagnated bandwidth of the Vertical-Cavity Surface-Emitting Laser (VCSEL) and the pin-photodetector. Next generation OIs operating at single lane rates of 50+ Gbaud will therefore require careful co-optimization of the electronics and the optoelectronics. To facilitate this work there is a need of an accurate equivalent circuit for the optoelectronic components, functioning over a broad drive current and ambient temperature range. The VCSEL is the most important and complex to model due to its non-linear behavior and strongly varying characteristics with drive current and ambient temperature. For this purpose, a large-signal equivalent circuit dedicated for high-speed datacom VCSELs has been developed and is presented here. The distributed electrical parasitics in the device layout are carefully considered, the intrinsic speed limitation from carrier transport effects in the Separate-Confinement-Heterostructure (SCH) and the carrier-photon interaction in the Quantum Wells (QWs) are included, and self-heating effects in the device are monitored. The circuit is purposely based on physical instead of empirical models so that it can provide usable feedback to VCSEL designers. For circuit demonstration, it is implemented in Keysight's Advanced Design System (ADS) software and thereafter applied to replicate the performance of a state-of-the-art 28-GHz-bandwidth VCSEL at different temperatures and drive currents. Comparison is made between simulated and measured steady-state characteristics, small-signal behavior, and large-signal response under 28 Gbaud On-Off-Keying (OOK) and Pulse-Amplitude-Modulation 4 (PAM4) modulation, showing good agreement.

Coupled-Cavity VCSEL with an Integrated Electro-Absorption Modulator: Small- and Large-Signal Modulation Analysis

We consider an integrated electro-absorption modulator within a coupled-cavity VCSEL structure (EAM-VCSEL). We derive expressions for the modulation transfer function (MTF) of the EAM-VCSEL for small-signal modulation of either VCSEL injection current or EAM losses. For current modulation, the cut-off frequency remains limited by relaxation oscillation frequency. For EAM loss modulation, the MTF curve is much flatter and its shape around the relaxation oscillation frequency displays either a well-pronounced maximum, both a maximum and a minimum or a sharp minimum only depending on the bias point of the EAM losses. Such features have been found experimentally in Marigo-Lombart et al., J. Physiscs: Photonics, 1, 2019, but remained unexplained hitherto. Furthermore, the cut-off frequency remains beyond 100 GHz for moderate and week coupling between the VCSEL and EAM cavities. Such ultrahigh bandwidth modulation is due to the fact that the changes of EAM impact much less the optical power distribution along the EAM-VCSEL and, consequently, the confinement factor and photon density in the VCSEL cavity. The three cases of strong, intermediate and weak coupling are also considered when carrying out the large-signal modulation response of the EAM-VCSEL and a clear open-eye diagram is demonstrated at 100 Gbs for an optimal EAM cavity length.

Detection of nanotesla AC magnetic fields using steady-state SIRS and ultra-low field MRI

Objective. Functional magnetic resonance imaging (fMRI) is commonly used to measure brain activity through the blood oxygen level dependent (BOLD) signal mechanism, but this only provides an indirect proxy signal to neuronal activity. Magnetoencephalography (MEG) provides a more direct measurement of the magnetic fields created by neuronal currents in the brain, but requires very specialized hardware and only measures these fields at the scalp. Recently, progress has been made to directly detect neuronal fields with MRI using the stimulus-induced rotary saturation (SIRS) effect, but interference from the BOLD response complicates such measurements. Here, we describe an approach to detect nanotesla-level, low-frequency alternating magnetic fields with an ultra-low field (ULF) MRI scanner, unaffected by the BOLD signal. Approach. A steady-state implementation of the stimulus-induced rotary saturation (SIRS) method is developed. The method is designed to generate a strong signal at ultra-low magnetic field as well as allowing for efficient signal averaging, giving a high contrast-to-noise ratio (CNR). The method is tested in computer simulations and in phantom scans. Main results. The simulations and phantom scans demonstrated the ability of the method to measure magnetic fields at different frequencies at ULF with a stronger contrast than non-steady-state approaches. Furthermore, the rapid imaging functionality of the method reduced noise efficiently. The results demonstrated sufficient CNR down to 7 nT, but the sensitivity will depend on the imaging parameters. Significance. A steady-state SIRS method is able to detect low-frequency alternating magnetic fields at ultra-low main magnetic field strengths with a large signal response and contrast-to-noise, presenting an important step in sensing biological fields with ULF MRI.

Large signal analysis of multiple quantum well transistor laser: Investigation of imbalanced carrier and photon density distribution

In this paper, we present a large-signal and switching analysis for the Heterojunction Bipolar Transistor Laser (HBTL) to reveal its optical and electrical behavior under high current injection conditions. Utilizing appropriate models for carrier transport, nonlinear optical gain, and optical confinement factor, we have simulated the large-signal response of the HBTL in relatively low and high modulation frequencies. Our results predict that for multiple quantum well (MQW) structures at low frequencies, there should not be a difference in either the carrier density or the photon density. However, the carrier concentration can be differently distributed between subsequent wells in the case of a high speed yet large-signal input. This leads to increased linewidth instead as it depends on ΔNqw. We show the effect of different structural parameters on the switching behavior by performing a switching analysis of the single quantum well and MQW structures using computationally efficient numerical methods. A set of coupled rate equations are solved to investigate the large-signal and switching behavior of MQW-HBTL. Finally, to have a comprehensive judgment about this optoelectronic device, we introduce a relative performance factor taking into account all the optoelectronic characteristics such as the output power, ac current gain, modulation bandwidth, and base threshold current, as well as turn-on time in order to design a suitable TL for optoelectronic integrated circuits.

A Large-Signal Model for a Peak Current Mode Controlled Boost Converter With Constant Power Loads

A large-signal averaged model is obtained to analyze the startup response of a boost converter loaded with a constant power load (CPL) and a peak current mode control (CMC). An analytical methodology is developed for the stability analysis during both startup and steady state. The proposed model corresponds to two operating modes: 1) a reduced-order saturated model during startup mode and 2) an unsaturated full-order model taking place when the system reaches the vicinity of the steady state. The duration of the startup period is also determined using the same model. To verify the validity of the derived large-signal model and the theoretical results derived from it, numerical simulation results from this model are compared with those obtained from a detailed switched model and experimental measurements demonstrating that the model can faithfully predict both the large-signal dynamic response during startup as well as the steady-state regime of the system.

Dynamic Phasor-Based Reduced-Order Models of Wireless Power Transfer Systems

Wireless power transfer (WPT) systems in dynamical applications, such as roadway-powered electrical vehicles, require dynamical models for the analysis and control. Conventional modeling methods for WPT systems lead to high-order models as each resonant voltage or current is described by two slowly varying real-valued variables. Other modeling methods may reduce the order but suffer from disadvantages, such as the lack of analytical expressions, loss of generality, and incomplete modeling. This paper develops a systematic and intuitive modeling approach using time-domain dynamic phasors and proposes reduced-order models by applying appropriate s -domain approximations to the linear parts of the system. A dual-side pulse-density-modulation WPT system is completely modeled as an example. Both the equivalent circuits and the mathematical descriptions are presented. The derived models are verified by large-signal step responses and small-signal frequency responses measured during experiments. As compared with the full-order models, the proposed reduced-order models have much more concise formulae while retaining high accuracy.

23 × 12 μm three‐stage amplifier using sub‐threshold active cascode compensation capable of driving very‐large‐load with no‐upper‐limit

An ultra-area-efficient three-stage amplifier is proposed by using sub-threshold active cascade compensation, which is able to drive very-large or ultra-large capacitive loads without sacrificing stability and power. Besides, external feed-forward path and slew-rate enhancer can significantly improve the large-signal transient response of the circuit. Designed and verified in 28 nm CMOS technology, the proposed amplifier occupies die area of 0.00028 mm 2 and consumes a power of 16.5 μW from 1.05 V supply. In addition, it can provide over 85 dB DC gain and is stable for any load larger than 4 nF, while the size of the entailed compensation capacitance is only 40 fF.

Current Mode Control of a Series LC Converter Supporting Constant Current, Constant Voltage (CCCV)

This paper introduces a control algorithm for soft-switching series LC converters. The conventional voltage-to-voltage controller is split into a master and a slave controller. The master controller implements constant current, constant voltage (CCCV) control, required for demanding applications, for example, lithium battery charging or laboratory power supplies. It defines the set-current for the open-loop current slave controller, which generates the pulse width modulation (PWM) parameters. The power supply achieves fast large-signal responses, e.g., from 5 V to 24 V , where 95% of the target value is reached in less than 400 s . The design is evaluated extensively in simulation and on a prototype. A match between simulation and measurement is achieved.

A Robust on-Wafer Large Signal Transistor Characterization Method at mm-Wave Frequency

Accurate on-wafer large signal characterization of RF transistor is crucial for the optimum design of wireless communication circuits. We report a novel and systematic measurement method for the accurate acquisition of input and output power of on-wafer transistors up to 40GHz. This method employs external couplers to extract the travelling waves, combined with a novel large signal calibration algorithm to calculate the power at on-wafer probe tip. The accuracy of this method was bench marked versus conventional approaches in a real measurement bench, and further been verified by characterizing the large signal response of a 0.25μm GaN HEMT device. It is concluded that the measurement uncertainty has been greatly decreased with this new method, especially at mm-wave frequencies.

Application-Oriented Investigation of Parasitic Limitation on Multilevel Modulation of High-Speed VCSELs

In this paper, we present an application-oriented investigation of parasitic limitation on the large signal performance of VCSELs when multilevel modulation is applied. VCSELs with different damping are taken into consideration. The parasitic parameters are extracted by fitting the measured $S_{11}$ data toward a frequency of 40 GHz. In the large signal analysis, four-level pulse amplitude modulation (PAM-4) signaling is embedded into the tool of VCSEL integrated spatio-temporal advanced simulator (VISTAS) and analyzed with extracted parameters. The transmitter and dispersion eye closure quaternary (TDECQ) of the 50-Gb/s PAM-4 signals from VCSEL model is evaluated to understand the relationship between parasitic parameters and signal quality. It is found that the over-damped VCSEL would benefit from larger parasitic bandwidth for PAM-4 modulation while the under-damped VCSEL with moderate parasitic bandwidth would present the best large signal response for PAM-4 modulation. The results indicate that for multilevel modulation, the parasitic parameters need to be carefully designed according to the VCSEL intrinsic parameters to achieve better large signal performance. By co-optimizing the key parasitic parameters, the parasitic circuit design criteria for each type of VCSEL are provided to obtain the best large signal performance under multilevel modulation. The results could provide a designing guidance for VCSELs aiming at multilevel modulation applications.

A 1.2-V 2.41-GHz Three-Stage CMOS OTA With Efficient Frequency Compensation Technique

A performance-boosting frequency-compensation technique, called feed-forward Gm-stage and regular Miller plus indirect compensation (FGRMIC), is presented in this paper. The proposed structure consists of three parts that ensure the stability and significantly improve the performance, such as gain–bandwidth product (GBW), slew rate, and sensitivity. The first part is a feed-forward transconductance stage, and the second part is a Miller capacitor in series with one resistor. The third part is an indirect compensation capacitor combined with a resistor. Detailed theoretical analysis and design considerations are provided to demonstrate the stability of the compensation scheme. Measurement results show that the implemented amplifier, driving a 2-pF load capacitance, achieves a GBW of 2.41 GHz with a phase margin of 82.6° while consuming 12.6 mW with a 1.2-V supply voltage in a TSMC 65-nm CMOS technology. Large-signal step response indicates that the implemented three-stage FGRMIC amplifier settles with 1% settling error within 1.41 ns.

High-Performance Three-Stage Single-Miller CMOS OTA With No Upper Limit of &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${C}_{L}$ &lt;/tex-math&gt; &lt;/inline-formula&gt;

This brief presents a low-power, area-efficient three-stage CMOS operational transconductance amplifier (OTA) suitable for very large capacitive loads, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . A single Miller capacitor and an inverting current buffer embedded in the input stage are exploited to implement the frequency compensation network. An additional feed-forward path and a slew rate enhancer are also utilized to improve the large-signal transient response. Detailed small-signal analysis reveals that the proposed OTA does not exhibit an upper limit of drivable C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> . The OTA is fabricated in a standard 0.35-μm technology and occupies 0.0027 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of die area. Under 1.4-V supply and 6.36-μA quiescent current consumption, it provides a dc gain greater than 110 dB and is stable for any C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> larger than 5 nF. Comparison with the state of the art shows remarkable improvement of both small- and large-signal performance.