Bias Current Level Research Articles

Thermal sensing capability and current–voltage–temperature characteristics in Pt/n-GaP/Al/Ti Schottky diodes

We have discussed the thermal sensing capability under a constant current level and current versus voltage (I–V) traces by measuring the temperature of high series resistance Pt/n-GaP/Al/Ti Schottky structures in the 100−320 K range. The Rs values of 35 Ω and 4.50 × 103 kΩ for the device have been determined from I–V traces at 320 and 100 K, respectively. The thermal sensing (V–T) curves are expected to give a straight line at each current level. However, the V–T curves have deviated upward from linearity due to the high Rs value of the device after a certain temperature. The deviation point from linearity in V–T traces shifts to higher temperatures with an increase in bias voltage and current level. Thereby, the straight-line interval portion of the V–T curve has become too small with an increase in the current value. The thermal sensing coefficient α changed from 2.49 mV/K at 10 μA to 3.21 mV/K at 0.50 nA. Therefore, it has been concluded that the Pt/n-GaP/Al/Ti Schottky barrier (SB) is preferable for thermal sensor applications at the small current levels of 0.50, 1.0, 2.0, and 10.0 nA with high sensitivity up to a minimum temperature of 100 K. From I–V curves, qΦb0 and ideality factor values have ranged from 1.200 eV and 1.066 at 320 K to 0.854 eV and 1.705 at 100 K. It has been reported in the literature that the large SB height leads to a better temperature response.

Active Modelocking Improvement of MIR-QCL by Integrating Graphene as a Saturable Absorber

The active mode-locking technique of quantum cascade lasers is highly affected by the bias current level and the magnitude of the modulated signal because of the spatial hole burning effect. The laser generates a stable pulse train near the threshold current and for a high modulation magnitude. We show in this paper an improvement of these conditions with an integration of a single-layer graphene which works as a saturable absorber. The light-matter interaction in the laser active region is described by the two-level Maxwell-Bloch equations and in graphene layer by the Maxwell-Ampere equation and Maxwell-Bloch equations. These system equations are solved using the Finite-Difference Time-Domain (FDTD) method which has the main advantage of not involving any approximation. The weakly coupled splitting scheme is adopted for the time discretization of Maxwell and Bloch equations. The graphene saturable absorption is modelled by a saturable conductivity in Maxwell-Ampere equation and with the dipole moment and carrier density in Maxwell-Bloch equations. For a QCL structure with a gain recovery time of 50 ps, simulation results show better stability of the mode-locking over a broad range of injection current and for smaller magnitude of the modulated signal. QCL structure with gain recovery time close to 1 ps reveals the generation of two pulses per roundtrip linked to spatial hole burning. The carrier grating strength can be reduced by changing the boundary conditions of the cavity such as with a high reflectivity mirror in front of graphene layer.

High-Frequency Characterization and Parametrized Modeling of DC-Biased Surface-Mount Ferrite Beads for EMI Suppression Applications

Circuit models of ferrite beads used for electromagnetic (EM) noise filtering are important for prediction and effective reduction of EM noise on power or signal lines. A methodology for impedance characterization and modeling of surface-mount ferrite beads is proposed in this article. The presented methodology combines series and shunt characterization methods to extract the equivalent circuit model of ferrite beads. The extracted models consist of frequency-independent elements and they are valid up to 1 GHz, to cover the bandwidth required by the EM compatibility standards for measurements of EM emissions. The values of the lumped elements of the extracted model are optimized to fit the measured impedance characteristics for each ferrite bead at bias current levels up to 5 A. Finally, the values of the lumped elements are parametrized with respect to the bias current from 0 to 5 A and the normalized error of the model compared to the measurements is calculated and found to be less than 10 $\boldsymbol{^{\mathrm{-3}}}$ .

A 75-Mb/s RGB PAM-4 Visible Light Communication Transceiver System With Pre- and Post-Equalization

Visible light communication (VLC) technology employing light-emitting diodes (LEDs) as light sources has the advantages of using the license-free spectrum, being power and cost-efficient and having high security. However, common LED devices have the limitations of narrow bandwidths, nonlinear optical and frequency responses over different bias current levels, which cause inter-symbol interference and signal distortion, especially under high order modulation schemes with large current swings. In view of this, a compact PAM-4 VLC transceiver system employing a white LED as the light source with pre- and post-equalization is proposed. The white LED consists of a red, a green and a blue LED unit (RGB LED). Controlled by 3-bit thermometer codes, three separate drivers with feed-forward equalizers (FFEs) drive the RGB LED units to produce the PAM-4 optical signal. The driving currents from the three drivers with FFEs can be calibrated using digital and analog tunings to eliminate the differences in optical and frequency responses of the RGB LED units. A cascaded continuous-time linear equalizer (CTLE) is used at the receiver side as post-equalization to compensate for the narrow bandwidth of LED units. Based on experimental results, the proposed RGB PAM-4 VLC system can improve the highest achievable data rate by 1.67 times from 28 to 75 Mb/s using the pre- and post-equalization scheme.

Research on Influence of Converter Transformer Grouping and Receiving End Power Grid Structure on Converter Transformer DC bias

When ±800kV UHVDC project was put into operation, DC bias problem can not be ignored. In this paper, a calculation model for DC bias current is established based on Xiluodu-Zhexi UHVDC project data. Converter transformer grouping and receiving end power grid structure are considered. The converter transformer DC bias current is calculated by node voltage method. The influence of different converter transformer grouping modes, distance between grounding electrode and substation, and the feeder length and the number of feeder loop are analysed. The results show that, single-phase converter transformer bias current is maximum with full load and 6 converter transformers under 1/2 monopole earth mode. And bias current level of converter can be reduced in planning and designing.

Picosecond and femtosecond asymmetric switching using a semiconductor optical amplifier-based Mach-Zehnder interferometer.

In this paper, we numerically analyze nonlinear asymmetric switching using a semiconductor optical amplifier (SOA) phase-shifter-based Mach-Zehnder interferometer (MZI), for the first time, to the best of our knowledge. The self-phase modulation (SPM) effect and nonlinear phase shift in each MZI arm are investigated for different input pulse intensities and linear gains in both picosecond and femtosecond regimes. The input light signal is split unequally over the two arms, where SOAs are placed and act as nonlinear phase shifters in each arm. The finite difference beam propagation method is used to solve the modified nonlinear Schrodinger equation to analyze the wave propagation. In this work, the main nonlinear effects in SOA, such as group velocity dispersion, Kerr effect, two-photon absorption, carrier heating, and spectral hole burning, are considered. Furthermore, the effect of SPM on distortion of the pulse shape and its spectrum, which can be used for pulse shaping in a picosecond-switching scheme, is studied. We depicted red and blue shifts that each pulse experiences in the process of switching in picosecond and femtosecond regimes, respectively. Based on the results for sub-picosecond input pulses, by controlling the bias current level in the MZI arms, the pulse distortion due to nonlinear effects of SOAs can be decreased at the switch output port, and symmetric pulse can be obtained. Switching with higher speed is possible in bulk SOAs in the femtosecond regime using asymmetric MZI-switching structure.

Reverse recovery transient characteristic of PEDOT:PSS/n-Si hybrid organic-inorganic heterojunction

We study the junction behavior of poly (3,4-ethylenedioxythiophene):polystyrenesulphonate/n-Si hybrid organic/inorganic heterojunction by reverse recovery transient (RRT) characterization. RRT response for PEDOT:PSS/n-Si hybrid junction is reported for various n-Si doping concentration and forward bias current injection level. The presence of settling time of 8.3–23.5 μs in the RRT response in contradiction to Schottky junction model commonly assumed for PEDOT:PSS/n-Si hybrid structure. The decrease in the minority carrier lifetime from 126.8 μs to 39.5 μs with increased n-Si doping concentration, suggests that minority carriers are stored at n-Si side of the junction, which is consistent with a p+-n junction model for the hybrid structure. The minority carrier lifetime is found to depend on forward bias current injection level, attributed to trap-saturation effect of the recombination-centers at the PEDOT:PSS/n-Si junction. The DC-IV characteristics of the PEDOT:PSS/n-Si hybrid junction are also consistent with the notion of diffusion and trap assisted recombination dominated dark current. The diffusion dominated transport of PEDOT:PSS/n-Si leads to an ideal p+-n junction behavior that leverages on the good transport properties of Si. Our findings are important in the modeling and optimization of the characteristics of electronic devices based on the organic/Si hybrid junction.

Comprehensive vertical-cavity surface-emitting laser model for optical interconnect transceiver circuit design

Directly modulated vertical-cavity surface-emitting lasers (VCSELs) are commonly used in short-reach optical interconnect applications. To enable efficient optical interconnect transceiver systems operating at data rates up to 25 Gb/s and beyond, cosimulation environments, which allow for the optimization of driver circuitry with accurate compact VCSEL models, are necessary. A comprehensive VCSEL model, which captures thermally dependent electrical and optical dynamics and provides direct current, small-, and large-signal simulation capabilities with self-consistency, is presented. The device’s electrical behavior is described with an equivalent circuit, which captures both large-signal operation and electrical parasitics, while the optical response is captured with a rate-equation-based model. Bias and temperature dependencies are incorporated into both key electrical and optical model parameters. Experimental verification of the model is performed at 25 Gb/s with a 990-nm VCSEL to study the impact of bias current level and substrate temperature.

Radiation Hardness Test of BJTs under Designated Application

Performance and properties of bipolar junction transistor (BJT) devices are affected due to the harsh radiation environment. This report reviews the typical effects occurring in BJT devices due to irradiation with x-rays. The defect parameters on the device tested is obtained by in situ experimental technique. In order to study the self-annealing behaviour in BJTS due to ionizing and displacement modifications, damage efficiencies at different bias current levels are compared. The study reveals that higher gain degradation dispersion occurs at lower bias current level. Damage creation in the BJTs is dominated by the excitation mechanism of valence electron to the conduction band. This leads to the production of a large number of excited atoms and increases the holes in the valence band. The increase of holes in the base region due to trapping will increase the probability of recombination and reducing the number of electrons that reaches the collector region.

Theory and Analysis for Optimization of On-Chip Thermoelectric Cooling Systems

We established a novel theoretical analysis framework for optimizing the cooling system configuration of chips employing thermoelectric cooling (TEC) elements by extending the theory of inverse-positive matrices and the eigenvalue/eigenvector theory in linear algebra. In this brief, we present a new theorem and its formal proof, which is the key enabler to achieving a provably optimal solution for configuring bias current levels of TEC devices.

1.2 V Sinh‐Domain allpass filter

AbstractA first‐order Sinh‐Domain allpass filter topology is introduced in this paper. It is constructed from a class‐AB current mirror and appropriately configured non‐linear transconductor cells. Due to the inherent class‐AB nature of Sinh‐Domain filters, the proposed topology offers the capability for handling currents at levels greater than that of the dc bias current level. Also, it offers the well‐known features of companding filters such as electronic adjustment of its frequency characteristics and the capability for operation in a low‐voltage environment. In addition, a four‐phase sinusoidal oscillator design example has been provided. The behaviour of the proposed topology has been evaluated and compared with other already known configurations, where the most important performance factors have been considered. Copyright © 2013 John Wiley & Sons, Ltd.

Offset Compensation Based on Distributed Hall Cell Architecture

A new offset reduction strategy for CMOS Hall devices is proposed. The novelty is to fragment the Hall device into multiple Hall blocks, distributed over the silicon area and easy to interconnect. The suitable number of Hall blocks and the bias current level in each block can be adjusted according to the requirements in terms of offset, offset drift and signal to noise ratio. A chip was fabricated in 0.35 μm CMOS standard technology to demonstrate the potential of this architecture. The chip shows promising results, and in particular, a very low offset drift was observed at the front-end output stage (of the order of 10 nT/°C).

Bidirectional chaos synchronization and communication based on mutually coupled semiconductor lasers with asymmetrical bias currents

In this paper, a bidirectional chaos secret communication system, based on mutually coupled semiconductor lasers (MCSLs) with asymmetrical bias currents, is proposed, and the synchronization characteristics and the communication performances of such a system are numerically investigated. The results show that the stable leader-laggard chaos synchronization can be achieved under relatively large asymmetrical bias current levels. Meantime, the influence of the intrinsic parameter variations of the laser on the synchronization quality is also considered, and the simulation reveals that this system still possesses good robustness to the parameter variations. Moreover, the influences of delay time and mutually coupling strength between the two lasers on chaos communication performance have also been discussed. Finally, unidirectional and bidirectional secret communication performances of such a system are examined under the chaos masking (CMS) encryption scheme, and the security of this system is also discussed.

A Subhertz Nanopower Low-Pass Filter

This brief presents a first-order low-pass filter topology capable of providing cutoff frequencies down to 2 mHz with power consumption of 5 nW. The circuit is intended for signal conditioning applications, particularly for use with very low frequency physiological signals in low-power portable medical equipment. To achieve a low-frequency cutoff, the filter is based around the use of a clocked transconductor, which provides low transconductance while using a relatively high bias current level. The circuit is implemented in a 0.35-μm technology with a 1-V supply and has 32- μVRMS measured noise and a 64-dB dynamic range. In terms of power consumption and cutoff frequency the reported filter outperforms previous filters from the literature.

Chaos synchronization in mutually coupled semiconductor lasers with asymmetrical bias currents

We experimentally and numerically investigated the chaos synchronization characteristics of mutually coupled semiconductor lasers (MCSLs) with asymmetrical bias currents. Experimental results show that, asymmetrical bias current level of two MCSLs has obvious influence on chaos synchronization between them, and stable leader-laggard chaos synchronization can be realized under relatively large asymmetrical bias current levels. Moreover, the influences of frequency detuning and mutually coupling strength between the two lasers on chaos synchronization performance have also been discussed. Theoretical simulations basically conform to our experimental observations.

Conversion between anticipating and lag chaos synchronization induced by different bias current levels in mutually delay-coupled semiconductor lasers

Based on a mutually delay-coupled semiconductor lasers (SLs) system, through adjusting the bias current of a SL and fixing that of the other one, the conversion between anticipating and lag chaos synchronization of this system has been experimentally observed for the first time. Experimental results show that for two SLs with the similar operation parameters, the SL biased at a relatively higher current level plays a leader role due to its relatively higher output power. Considering that the SL with a higher bias current level will oscillate at a longer wavelength, the SL with a longer wavelength becomes the leader, which provides a synchronization conversion scheme via by purely electronic current drive. Furthermore, the corresponding theoretical analyses have been given, and show that whether the SL with a longer or shorter wavelength becomes the leader mainly depends on the approach of the driving of frequency detuning between the two SLs.

EAM-SOA millimeter-wave frequency up-converter for radio-over-fiber applications

We present an optical scheme for photonic frequency up-conversion at the millimeter-wave bands based on Semiconductor Optical Amplifier. The proposed scheme modulates the bias current with the Intermediate Frequency in order to achieve frequency mixing of an incoming optical signal modulated with the Local Oscillator. Theory indicates that the proposed scheme supports data bandwidths in the tens of GHz for LO values above 10 GHz. This scheme allows for photonic integration of the considered optical devices. A laboratory demonstration of the scheme for up-conversion to the 40 GHz band, using narrow-band IF signals, showed relatively low thresholds for the optical input power and bias current level to achieve error free operation: − 14.5 dBm 100 mA for a 64-QAM signal. Spurious-Free Dynamic Range showed an acceptable performance, with a linearity about 52.5 dB·Hz 2/3 for an optical input power of − 6 dBm.

Simultaneous all-optical individual channel clock extraction and wavelength conversion using an optically injected Fabry-Perot laser diode

We propose and demonstrate a novel technique that uses a FabryPerot laser diode （FPLD） to perform simultaneous alloptical individual channel clock extraction and wavelength conversion. The nonlinear dynamical period1 oscillation can occur when a semiconductor laser is optically injected. By utilizing the crossgain modulation effect and the period1 oscillation harmonic frequencylocked in an optically injected semiconductor laser, we can extract the wavelength conversional individual channel optical clock from the opticaltimedivisionmultiplexing （OTDM） signal. In a FPLD, we numerically simulate the extraction of 20 GHz optical clock at 1550 nm from the 2×20 Gb/s OTDM signal at 1555 nm, and experimentally obtain the -105 dBc/Hz phase noise frequency division clock of 1236 GHz to 618 GHz with simultaneous wavelength conversion from 155024 nm to 154591 nm. Moreover, we investigate the influence of the injection optical power level, wavelength detuning, the FPLD's bias current level and the longitudinal mode selection on the optical clock extraction. This method is potential to technologically apply in the alloptical demultiplexing and wavelength routing in the OTDM mixed wavelengthdivisionmultiplexing （WDM） communication system.

Limits on the performance of RF-over-fiber links and their impact on device design

This paper is divided into two major parts. Following a brief introduction that establishes some definitions and assumptions, Section II updates our earlier study on the limits of the RF performance of optical links. Section III reviews progress since our 1997 review paper in the development of devices enabling link performance closer to these limits, including (but not limited to): 1) cascade lasers that permit broad-band direct modulation links with gain >0 dB; 2) injection-locked edge- and surface-emitting lasers at 1300 and 1550 nm with modulation frequency responses as great as 40 GHz; 3) modulators with improved performance, especially electroabsorption modulators that now have switching voltages as low as 0.36 V, or handle optical powers as great as 60 mW, or have bandwidths as great as 50 GHz (but not all three of these in one device yet); and 4) high-speed photodetectors with high saturation currents, e.g., a 20-GHz device with a saturation current of 90 mA and a 55-GHz device with saturation at 50 mA. We conclude in Section IV by summarizing the component developments necessary for higher performance RF-over-fiber links, i.e.: 1) semiconductor lasers (for direct modulation) that have higher slope efficiency and bandwidth and lower relative intensity noise (RIN) at reasonable bias current levels; 2) continuous wave (CW) lasers (for external modulation) with higher fiber-coupled power and lower RIN; 3) higher frequency lower loss external modulators with more linear transfer functions and lower V/sub /spl pi// that can withstand larger CW optical powers; and 4) photodetectors with higher responsivity and bandwidth that respond linearly even when illuminated by greater average optical powers.

Fiske steps studied by flux-flow resistance oscillation in a narrow stack ofBi2Sr2CaCu2O8+δjunctions

We have experimentally investigated the fluxon dynamics in a narrow ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ stack with junction length $L\ensuremath{\sim}1.8\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. As an evidence of high-frequency excitation by a collective cavity mode, under an (in-plane) external magnetic field, the current-voltage characteristics show prominent Fiske steps with the corresponding resonance frequencies of $75--305\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}$. Further study of flux-flow resistance oscillation with various $c$-axis currents clarifies the correlation with Fiske steps by distinguishing two different regions, i.e., the static flux-flow region at low bias current level and dynamic Fiske step region at high bias current level.