Increased linear dynamic range by low biasing the Mach-Zehndermodulator

Operating a Mach-Zehnder modulator at an optical bias below the conventional 50% (quadrature) bias is investigated. Theoretical distortion curves as a function of bias have been calculated and experimentally verified. These curves show that (single octave) linear dynamic range increases as the bias is lowered, so long as optical power at the detector can be maintained just below the saturation level or laser noise limit. This method thus provides a way for very large optical power to be used to benefit linear dynamic range. Theoretically, 20 dB of excess optical power, attenuated through low biasing, can result in an increase in linear dynamic range of 15 dB     

基于灰色模型和混沌时间序列的卫星钟差预测算法

为了提高非线性卫星钟差预测的精度,降低单一钟差预测模型对钟差预测的风险,提出了一种组合模型的卫星钟差预测算法.该算法首先采用db1小波对卫星钟差序列进行3层多分辨率分解和单支重构,得到一个趋势分量和三个细节分量,然后运用灰色预测模型对重构后的趋势分量和混沌一阶加权局域预测法对重构后的细节分量分别进行预测,最后将各分量预测结果相加后得到总的钟差预测值.以GPS卫星钟差数据做算例分析,在6小时的钟差预测中,算法绝对误差最大值比单一的灰色预测模型误差小1.3ns以上.将该组合预测模型用于非线性卫星钟差预测中,可以提高钟差预测的精度和可靠性.     

An Analysis of the Equivalent Resistance of PIN Diodes at Microwave Frequencies

The PIN diode is an especial charge controldevice. The middle zone of a PIN diode between theheavily doped P-type semiconductor ( P ) and N-typesemiconductor ( N ) is so called region I with highresistivity, as shown in Fig.1. The region I of apractical PIN diode consists of the high resistivity Pmaterial called I(π)-type or high resistivity N materialcalled I(υ)-type. The density of carriers in the region Iis controlled mainly by the applied bias voltage.Therefore, the resistance o…     

Theory and Measurement of Back Bias Voltage in IMPATT Diodes

The derivation of the back bias voltage is shown to require carrying the derivation of the Read equation to one order of approximation higher than that which is necessary to obtain the quasi-static result. A new term is shown to be needed in the expression for the back bias voltage which changes its sign to positive under conditions in which the older analyses indicate a negative back bias. Experimental measurements of V/sub bb/ as a function of V/sub RF/ were made using a network analyzer and are in agreement with the new analysis. At frequencies considerably below the range at which our measurements were made, a strong negative back bias voltage is caused by the saturation current.     

Au/(Si/SiO2)/p-Si结构中电流输运机制的研究

用射频磁控溅射法制备了Si/SiO2薄膜,利用Au/(Si/SiO2)/p-Si结构的I-V特性曲线对其输运机制进行了分析。结果表明,在较高的正向电场下,载流子主要是以电场协助隧穿(Fowler-Nordheim隧穿)方式通过氧化层,而在低场范围内和反向电场下,电流的产生则以热电子发射的方式为主。     

Calibration Enabled Scalable Current Sensor Module for Quiescent Current Testing

Semiconductor testing is aimed at screening fabrication defects that impact expected functionality. While catastrophic defects result in non working devices, parametric faults result in marginalities and are of increasing concern with deep sub-micron process technologies. This work presents a scheme to monitor Circuit-Under-Test (CUT) static bias current to identify catastrophic as well as parametric faults. All circuits require a deterministic amount of DC bias current which may vary outside the specifications when faults exist within the circuit. We propose a compensated current measurement Built-in-Current-Sensor (BICS) scheme, which can be used for sub-system level/circuit-level bias current measurements. The BICS provides accessibility to internal blocks and enables isolated parametric testing. Calibration routine enables process independence and provides robustness. The BICS is compatible with Very-Low-Cost Automatic Test Equipment (VLC-ATE), and can be used for detailed parametric testing in the production environment.     

基于ADS平台不对称Doherty功率放大器的仿真设计

为在高线性的前提下提高WCDMA基站系统中功率放大器的效率,仿真设计了一款工作于2.14 GHz频段不对称功率驱动的Doherty功率放大器。基于ADS平台,采用MRF6S21140H LDMOS晶体管,通过优化载波放大器和峰值放大器的栅极偏置电压改善三阶互调失真(IMD3),同时通过调节输入功率分配比例改善由于峰值放大器对载波放大器牵引不足导致的失配问题,从而改善不对称Doherty功率放大器的输出性能。仿真结果表明,当载波放大器的栅极偏置电压为2.84 V,峰值放大器的栅极偏置电压为0.85 V并且输入功率比例为1:2.3,输出功率为44 dBm时其功率附加效率(PAE)为24.21%,IMD3为-44.46 dBc,和传统AB类平衡功率放大器相比PAE提高了8.58%,IMD3改善了6.98 dBc。     

1.5-W CW S-band GaInP/GaAs/GaInP double heterojunction bipolartransistor

We report the first large-signal power result from a double heterojunction bipolar transistor (DHBT) based on the GaInP/GaAs/GaInP material system. A CW output power of 1.51 W and a power added efficiency of 52% were achieved at 3 GHz. Because the GaInP collector has a relatively high bandgap of 1.89 eV, high DC bias voltage operation with collector bias extending to 20 V (for a 40-V swing) is possible in this GaInP/GaAs/GaInP DHBT. This high DC bias voltage operation represents a unique advantage over the more conventional AlGaAs/GaAs HBT     

Terahertz detector utilizing two-dimensional electronic fluid

We report on the first implementation of a terahertz detector utilizing two-dimensional (2-D) electronic fluid in a high electron mobility transistor (HEMT) operating at 2.5 THz. The terahertz radiation induced a dc drain-to-source voltage proportional to the radiation intensity. The measured dependencies of the detector responsivity on the gate bias are in good agreement with the gate bias dependence of the normalized responsivity predicted by the detector theory. This result shows the potential for developing a new family of electronics devices-plasma wave electronics devices-operating at terahertz frequencies     

Electric-field controlled light-emissive characteristics in nanoscale for polymer/fullerene organic solar cells

Bulk-hetero-junction (BHJ) organic photovoltaic cells (OPVCs) consisting of a poly(3-hexylthiophene) (P3HT) as a donor and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) as an acceptor were fabricated and their light-emissive characteristics as a function of applied bias were investigated. The nanoscale luminescence spectra at different positions on the P3HT/PCBM based photovoltaic cells were measured using a laser confocal microscope (LCM) with a high spatial resolution. For the P3HT/PCBM OPVCs with a relatively thin active layer, the light-emissive characteristics were changed considerably with varying applied bias. We observed that the luminescence intensity increased with increasing reverse bias under light illumination, this result was confirmed by the LCM photoluminescence mapping images. This result originates from the increase of free charges due to the de-trapping effect of trapped charge transfer excitons near the interface, through the external electric-field and incident light.     

Bias dependence of GaAs and InP MESFET parameters

A comparative analysis of the bias dependence of critical RF parameters in GaAs and InP metal-semiconductor field-effect transistors (MESFET's) led to the following conclusions. 1) The drain-gate feedback capacitance in GaAs MESFET's is lower than in InP MESFET's, because of a stronger tendency in GaAs to form stationary Gunn domains at the typical drain bias levels employed. 2) The drain-source output resistance in InP MESFET's is lower than in GaAs MESFET's mainly for high drain current units, a fact which is linked to a substrate related softer pinch-off behavior in InP. 3) The current-gain cutoff frequency fT, in the current saturation range of the GaAs MESFET decreases strongly with drain bias as a result of the formation of the stationary Gunn domain. In the InP MESFET, this effect is weaker. At the optimum bias, fT is only 10-20 percent higher in InP MESFET's than in GaAs ones.     

The relationship between gate bias and hot-carrier-inducedinstabilities in buried- and surface-channel PMOSFETs

For accurate predictions of device reliability with respect to hot-carrier effects, it is necessary to establish worst-case stress bias conditions. Detailed measurements of hot-carrier-induced instabilities in short-channel PMOSFETs have revealed that stress gate bias conditions corresponding to peak gate currents result in maximum shifts in device parameters. However, for some parameters, notably those measured at low drain bias, comparable shifts are observed for stress gate bias conditions that correspond to peak substrate currents. These observations are valid for both buried-channel (n-type polysilicon gate) and surface-channel (p-type polysilicon gate) PMOSFETs. An interpretation of these results based on the generation of tapped oxide charge and interface traps is proposed     

Back-gate bias effect on the subthreshold behavior and theswitching performance in an ultrathin SOI CMOS inverter operating at 77and 300 K

The effect of back-gate bias on the subthreshold behavior and the switching performance in an ultrathin SOI CMOS inverter operating at 300 and 77 K is investigated using a low-temperature device simulator. The simulation results show that the nonzero back-gate bias induces hole pile-up at the back interface, which causes opposite effects on the NMOS and PMOS subthreshold characteristics at 300 and 77 K. Throughout the transient process, at 300 K, for V_B=-5 V operation, hole pile-up at the back interface always exists in the NMOS device. Compared to the zero back-gate bias case, at V_B=-5 V, the risetime of the SOI CMOS inverter is over 5% shorter at 77 and 300 K and the falltime is 5% longer. Prepinch-off velocity saturation in the NMOS device dominates the pull-down transient as a result of the smaller electron critical electric field     

InGaAs PIN光电探测器的暗电流特性研究

从理论上分析了In0.53Ga0.47As PIN光电探测器在不同掺杂浓度及反向偏压下的暗电流特性,并与研制的器件的实测结果进行了比较和讨论.模拟结果表明:在低偏压下,器件中的产生复合电流起主要作用,偏压增大时,隧道电流起主要作用,且In0.53Ga0.47As光吸收层的载流子浓度对器件的暗电流有很大的影响,实测器件特性与模拟结果完全符合.文中还对器件结面积和电极尺寸等对暗电流的影响进行了比较和分析.     

An improved Early voltage model for advanced bipolar transistors

An improved Early voltage model reflecting the effect of bias variation is developed. The bias dependencies of the Early voltage are more prominent as the base width of the bipolar transistor decreases. Thus, using the conventional constant Early voltage model can result in considerable errors in modeling the advanced bipolar transistors which possess very thin base region. Comparisons between the present model and the conventional model at different bias conditions support this assertion. SPICE simulations are performed to demonstrate the impact of this study on the small-signal performance of bipolar-transistor integrated circuits     

Examination of CCDs using voltage contrast with a scanning electron microscope

The voltage contrast mode of a scanning electron microscope (SEM) is utilized to observe charge-coupled devices (CCDs) which have been cross sectioned. A new cross sectioning technique which uses anisotropic etching to accurately define the axis along which fracture occurs is presented. Lapping is not required in this technique, as smooth surfaces result from the controlled fracturing. SEM imaging of the region just beneath a CCD double-level, polycrystalline silicon electrode structure revealed a region of contrast which appeared and disappeared under the presence and absence of an applied pulsed bias. Application of a pulsed bias to the CCD output gate is seen to result in the transient charging of the output floating diffusion, while application of a dc bias is seen to not result is such charging.     

Monte Carlo modeling of electron transport in repeated overshootstructures

Repeated velocity overshoot has been proposed as a way of obtaining high average velocities over significant distances in semiconductor devices. The potential of this concept is examined using a fully-self-consistent particle-field Monte Carlo simulation. Numerical results are presented for realistic periodic overshoot structures for a range of bias conditions and operating temperatures of 77 and 300 K. Local velocity overshoot peaks are observed in the simulated structures, but the average carrier velocity and current at each bias point are in all cases less than those associated with transport in bulk material at the same bias point. The physical mechanisms underlying this result are analyzed. It is found that ensemble (diffusion) effects, which were neglected in the original proposal of the repeated overshoot concept, strongly influence the results that are achievable in practice     

AWGN信道下PSK信号幅度与信噪比的估计

研究了AWGN信道下PSK信号幅度和信噪比的估计问题，提出了一种基于迭代的直接判决反馈估计算法，并对其性能进行了分析和仿真。仿真结果表明：低信噪比下经过多次迭代后，由于误码导致的估计偏差可得到较大程度的补偿，估计器的性能接近有数据辅助时的性能，明显优于直接判决反馈时的性能。     

一种新型宽带微波有源网络偏置电路的优化设计

利用径向传输线理论对微波有源网络的扇形偏置电路进行了分析。导出了扇形阵偏置电路的目标函数。此目标函数用于计算机辅助设计宽带微带偏置电路，取得了很好的效果。     

High-power microwave 0.25-μm gate doped-channel GaN/AlGaNheterostructure field effect transistor

We report on the high-power performance of the 0.25-μm gate Doped-Channel GaN/AlGaN Heterostructure Field Effect Transistors (DC-HFETs). At a drain bias voltage of 18 V and drain bias current of 46 mA, these 100-μm wide devices exhibit high gain at 8.4 GHz with a power density reaching 1.73 W/mm. The devices also display high gain at moderate power over a wide range of frequencies. This high gain at high frequency is a result of an optimal doping level in the AlGaN layer that gives rise to a high sheet charge density while maintaining a high-channel electron mobility. These results demonstrate the excellent microwave power capability of the GaN/AlGaN based heterostructure field effect transistors