Considerations and simulations of subfrequency excitation of seriesintegrated resonant tunneling diodes oscillator

A subfrequency pulse initiation of an oscillator of two series-integrated RTD's is considered and simulated. A voltage-dependent current source is adopted to separate the input and output power to represent a circulator in simulations. Simulations show, for example, a 100 GHz integrated RTD oscillator can be excited by a 50 GHz pulse with about 1 ns decay time (a characteristic decay time of 0.2 ns) without the DC instability problem, while a voltage ramp of 1 ns rise or fall time is far too slow to initiate such an oscillator. The mechanism that RTD's are driven by subfrequency into the negative differential resistance (NDR) from the positive differential resistance (PDR) is analyzed in detail. A preliminary analysis of the transition from 50-100 GHz oscillation is also presented     

DC instability of the series connection of tunneling diodes

An oscillator with a series connection of tunneling diodes produces significantly higher power than a single diode oscillator. However, a circuit with series-connected tunneling diodes biased simultaneously in the negative differential resistance (NDR) region of the I-V curve is dc unstable. This dc instability makes the series connection oscillator fundamentally different from a single diode oscillator. Associated with the dc instability are the phenomena of minimum oscillation amplitude and frequency. Due to the minimum oscillation amplitude, it is critical to provide the impedance match between the oscillator circuit and the series connection at the desired oscillation amplitude level. An in depth, comprehensive analysis of the dc instability is given here. Based on this analysis, a numerical procedure is developed to accurately predict the minimum oscillation amplitude and frequency. Time domain simulations which give further insight into series-connection oscillator behavior are discussed. The effect of increasing the number of diodes on the oscillator performance is explored as well. Based on numerical and simulation results, oscillators with several tunnel diodes connected in series were designed and tested. Experimental results that confirm the existence of the minimum oscillation amplitude are presented for oscillators with two, three, and four tunnel diodes     

A model for flicker frequency noise of oscillators

A stationary statistical model is proposed for oscillator frequency fluctuations, leading to a flicker power spectral density for frequency fluctuations and to the corresponding time domain frequency instability (logarithmic behavior).     

Bifurcations in electrooptic bistable devices with short delay times in the feedback

We have investigated experimentally the behavior of a hybrid bistable electrooptic device with a delayed feedback when the delay time is comparable to the time constant of the device. The behavior is governed by a nonlinear difference-differential equation. The threshold of instability and the period of the oscillations observed close to threshold agree relatively well with the predictions obtained from a linear stability analysis of this equation. For larger input signals or feedback, bifurcations take place. We then observe period-2, period-4, and chaotic behavior following the period-doubling scheme of Feigenbaum. For delay times shorter than the time constant this bifurcation behavior can still be observed for large input signals. Furthermore, for such short delay times the threshold for onset of instabilities was observed to exhibit hysteresis, so different thresholds were observed when the input signal was increasing and decreasing.     

Hierarchical Pattern Formation in Thin Polymer Films Using an Electric Field and Vapor Sorption

The experimental observation of electric‐field‐induced instabilities of polymer films exposed to toluene vapors is reported. When using a laterally structured electrode, the pattern that forms in the polymer film is governed by the interplay of the intrinsic film instability and the periodicity of the electrode structure. By adjusting the applied voltage, it is possible to switch between two different pattern‐replication modes. A further important parameter is the aspect ratio of the structured electrode. For high ratios of polymer film thickness to capacitor‐plate spacing, structures with hierarchical length scales have been observed.     

On the design of CCII+ based relaxation oscillator employing single grounded passive element for linear period control

There have been an increasing number of publications on current conveyor oscillator structures in recent years. For most topologies presented, independent frequency and oscillation condition control by a single element is possible, they use minimum number of components employing grounded passive elements, but none of them allow linear period control which is essential for numerous applications. The oscillator presented here based on the nonlinear behavior of the CCII+ allows single element linear period control over three decades of the period, is suitable for integration, and is free from high frequency limitations of operational amplifier counterparts.     

Characteristics and kinetics of laser-pumped Ti:sapphireoscillators

The experimental performance of a gain-switched Ti:sapphire laser oscillator pumped by a frequency-doubled Q-switched Nd:YAG laser system is presented for a variety of operating conditions. A theoretical model developed for this oscillator predicts well its performance. The observed curved input-output energy plots for the oscillator result from the kinetics of gain switching and fluorescence decay during the gain buildup period. Fluorescence decay also produces observed oscillator thresholds higher than those normally predicted by the standard gain-equals-loss condition. Gain-switched parasitic modes, with a higher threshold but shorter round-trip time than the resonator mode, cause the resonator mode to oscillate only over a finite range of pump energies. Spectroscopic investigations show that the Ti:sapphire cross-section spectrum is well fit by a Poisson distribution, giving a peak cross section of 3×10^-19 cm² for the π polarization     

Polymer‐Modified Mesoporous Silica Thin Films for Redox‐Mediated Selective Membrane Gating

Controlling structure and function to switch ionic transport through synthetic membranes is a major challenge in the fabrication of functional nanodevices. Here we describe the combination of mesoporous silica thin films as structural unit, functionalized with two different redox‐responsive ferrocene‐containing polymers, polyvinylferrocene (PVFc) and poly(2‐(methacryloyloxy)ethyl ferrocenecarboxylate) (PFcMA), by using either a grafting to, or a grafting from approach. Both mesoporous film functionalization strategies are investigated in terms of polymer effect on ionic permselectivity. A significantly different ionic permselective behavior can be observed. This is attributed to different polymer location within the mesoporous film, depending on the functionalization strategies used. Additionally, the influence of chemical oxidation on the ionic permselective behavior is studied by cyclic voltammetry showing a redox‐controlled membrane gating as function of polymer location and the pH value. This study is a first step of combining redox‐responsive ferrocene‐containing polymers and mesoporous membranes, and thus towards redox‐controlled ionic transport through nanopores.     

AM mode-locking of a free-electron laser oscillator

The authors present experimental and theoretical studies of a mode-locked free-electron laser (FEL) oscillator. In the experiment the FEL uses a continuous electron beam and operates in the microwave regime. AM mode-locking is performed by modulating the attenuation of the FEL ring cavity by a PIN diode modulator. The modulation period is tuned to match the RF roundtrip time in the ring cavity. The experimental results show the evolution of a single radiation macropulse, consisting of narrow micropulses in synchrony with the sinusoidal locking signal. The micropulse period (~37 ns) equals the roundtrip time and the modulation period. The micropulse width (~5 ns) is limited by the FEL slippage time and by the dispersion in the waveguide ring cavity. The effect of the mode locking consisting in suppressing asynchronous oscillations is clearly observed in the experiment. A theoretical model of the AM mode-locked FEL oscillator operating in the small signal regime is presented. This model includes the slow time variation of the e-beam energy and waveguide dispersion. The theoretical analysis agrees well with the experimental results     

Large signal instability in active-R and a class of compensated active-RC filters

Analysis of the large signal instability in compensated active-RC and active-R filters with high pole-Q and pole-frequency is presented. The instability is produced by an oscillator loop formed by two operational amplifiers (OA's). The condition for and the frequency of oscillations are derived.     

Frequency equation for the submicron CMOS ring oscillator using the first order characterization

By utilizing the first order behavior of the device,an equation for the frequency of operation of the submicron CMOS ring oscillator is presented.A 5-stage ring oscillator is utilized as the initial design,with different Beta ratios,for the computation of the operating frequency.Later on,the circuit simulation is performed from 5-stage till 23-stage,with the range of oscillating frequency being 3.0817 and 0.6705 GHz respectively.It is noted that the output frequency is inversely proportional to the square of the device length,and when the value of Beta ratio is used as 2.3,a difference of 3.64％ is observed on an average,in between the computed and the simulated values of frequency.As an outcome,the derived equation can be utilized,with the inclusion of an empirical constant in general,for arriving at the ring oscillator circuit's output frequency.     

Flexible Breathable Nanomesh Electronic Devices for On‐Demand Therapy

Flexible electronics are drawing tremendous interest for various applications in wearable healthcare biomonitoring, on‐demand therapy, and human–machine interactions. However, conventional plastic substrates with uncomfortableness, mechanical mismatches, and impermeability have limited the application of flexible on‐skin electronic devices for healthcare biomonitoring and on‐demand therapy. Herein, flexible breathable electronic devices with the capabilities of real‐time temperature sensing and timely on‐demand anti‐infection therapy at wound sites are presented. These devices are assembled from a crosslinked electrospun moxifloxacin hydrochloride (MOX)‐loaded thermoresponsive polymer nanomesh film with a conductive pattern. The conductive polymer nanomesh film demonstrates excellent flexibility, reliable breathability, and robust environmental stability. Furthermore, the assembled temperature sensor displays a linear relationship between the electrical resistance and temperature, potentially enabling real‐time biomonitoring of tissue temperature at the wound site. Smart artificial electronic skins (E‐skins) are assembled from the thermoresponsive polymer nanomesh film for spatial touching sensing mapping of temperature changes. Furthermore, the flexible temperature sensor is coupled with a wireless transmitter for real‐time wireless temperature monitoring. Notably, the thermoresponsive polymer nanomesh film can also be assembled as a highly efficient flexible heater to trigger the on‐demand release of antibiotics loaded in the fibers to eliminate bacterial colonization in the wound site once infection has occurred.     

Colpitts混沌电路的研究

对典型Colpitts振荡电路进行分析,并进行了Pspice仿真,观察状态变量随参数变化的动力学行为及频谱分布情况.对改进型Colpitts电路进行仿真,对比仿真结果可知正是寄生电容CCB影响了典型Colpitts电路产生高频混沌信号.     

Comparative study of NBTI as a function of Si film orientation and thickness in SOI pMOSFETs

Negative bias temperature instability of SOI pMOSFET is investigated as a function of Si film orientation and film thickness. It is observed that NBTI induced threshold voltage shift is bigger for (1 1 0) MOSFETs in comparison to (1 0 0) MOSFETs and it decreases with the decrease of Si film thickness. The possible reason for less degradation of thinner Si film devices is explained by the small gate current due to low oxide field. The activation energy is independent on Si film orientation. The dependence of recovery behavior on the Si film orientation is studied by comparing of a conventional stress-measurement-stress technique with un-interrupted stress technique. It is also observed that the NBTI effect is underestimated and the recovery phenomenon is more profound in (1 1 0) MOSFETs.     

39-GHz optoelectronic oscillator using broad-band polymerelectrooptic modulator

An optoelectronic oscillator (OEO) producing a 39-GHz microwave signal has been demonstrated using a novel electrode-poled push-pull polymer modulator. This is the highest reported OEO operating frequency to date. Preliminary measurement of the phase noise shows performance in the range of commercial synthesizers and behavior with respect to cavity length in accordance with theory. It is also observed that dispersion penalty is a significant factor at this high frequency     

Phase noise in self-injection-locked oscillators - theory and experiment

Phase-noise analysis of the self-injection-locked oscillator is presented in this paper. The analysis is developed for different oscillator models and arbitrary self-injection feedback loops. The results are illustrated with specific cases of simple time-delay cable and a high-Q factor resonator. It is shown that the behavior of the phase noise is similar to an oscillator locked to an external low phase-noise source. The output phase noise can be reduced at the noise offset frequency near the carrier frequency, and returning to the free-running oscillator noise far from the carrier frequency for certain stable feedback delay ranges. The phase-noise reduction is affected by the self-injection signal strength and feedback transfer function for different oscillator equivalent-circuit models. The theory is verified by using a self-injection-locked GaAs MESFET oscillator operating at the X-band with delay cable loops. The self-injection-locked technique may be used to improve the phase noise of the existing oscillators.     

Use of a surface-acoustic-wave (SAW) device to monitor etching of thin films

The use of a surface-acoustic-wave (SAW) device to monitor etching of thin films is described. The device is a delay-line-stabilized SAW oscillator in which the propagation path is coated with a thin film of the material to be etched. Removal of material decreases the mass loading on the delay line and this increases the frequency of the oscillator. The frequency of a 75-MHz oscillator is found to increase by more than 690 KHz for 1-µm decrease in film thickness. Using dual-oscillator arrangement, one can simultaneously monitor substrate temperature as well as thickness of material removed.     

基于高超声速平台前斜视多通道SAR-GMTI杂波抑制方法

针对高超声速(HSV)平台雷达系统,该文提出一种基于高超声速平台前斜视多通道合成孔径雷达地面动目标检测(SAR-GMTI)杂波抑制方法。该方法先进行时域距离走动校正和距离压缩,并补偿距离向通道相位误差实现距离向包络对齐;然后再对方位多普勒扩展的信号进行3阶线调频傅里叶变换(CFT)压缩,并补偿方位向通道相位误差实现方位向包络对齐;接着在距离时域-方位CFT域利用数字波束形成(DBF)技术对杂波及其模糊分量置零进行空时自适应处理(STAP),从而可以有效抑制静止杂波及其模糊分量并提取出无模糊的运动目标回波信号。     

Sideband suppression in free electron lasers using a grating rhomb

The phase shift produced by a grating rhomb is included in free-electron laser (FEL) pulse calculations to investigate whether or not grating rhombs can be used to suppress the sideband instability. The idea is that because the group travel time through a rhomb is an increasing function of the laser wavelength, an FEL oscillator can be designed such that the optical pulse at a chosen central wavelength and the pulse of electrons overlap spatially when they enter the wiggler. Over many passes, light in a small bandwidth about the chosen wavelength receives the greatest amplification because it overlaps the electrons, and light at sideband instability wavelengths that does not overlap the electrons is suppressed by losses in the oscillator cavity. For a 5-m tapered wiggler, the range in rhomb dispersion and cavity loss that yields acceptable FEL performance is defined. At low values of cavity loss, for example 15%, a wide range of rhomb dispersion exists for which both the sideband instability is largely suppressed and the energy extracted from the electrons is high. At larger values of cavity loss, for example 30%, a critical value for rhomb dispersion exists below which the laser pulse is compressed by the rhomb, leading to reduced energy extraction