Monte Carlo approach to transient analysis of HBTs with differentcollector designs

The transient analysis of heterojunction bipolar transistors (HBTs) using the Monte Carlo technique is presented. Three HBT structures with conventional (A), inverted field (B), and undoped (C) collectors were simulated. The transient behavior of the collector currents show that the time constants are 1.466, 0.722, and 0.863 ps at a collector current of 3.5×10⁴ A/cm² for devices A, B and C, respectively. This suggests that the inverted field structure may be the best choice for high-speed applications     

Modeling and analysis of ZnSe-Ge HBTs

A Gummel-Poon model is developed for ZnSe-Ge-GaAs heterojunction bipolar transistors (HBTs). In this structure, undoped Ge spacers are placed at the emitter-base and collector-base junctions. Injected current components as well as bulk, spacer, and space charge recombination current components are modeled. Early voltage and bandgap narrowing effects are included in the model. The device performance was simulated and compared with the experimental results. The paper shows a good agreement between our model and the experimental results. The paper shows also that using spacers would improve the device performance. The advantages of this model is that it is analytical, compact, and can be easily implemented in CAD tool programs to simulate single or double HBTs with similar or dissimilar materials structure for the emitter and collector.     

Structure optimization of multi-finger power SiGe HBTs for thermal stability improvement

The two-dimensional temperature profile of a power SiGe HBT with traditional uniform emitter finger spacing is calculated, which shows that there is a higher temperature in the central region of the device. With the aid of the theoretical analysis, an optimized structure of the HBT with non-uniform emitter finger spacing is presented. The peak temperature is lowered by 23.82 K, and the thermal resistance is also improved by 15.09% compared with that of the uniform one. The improvements above are ascribed to the increasing the spacing between fingers, and hence suppressing the heat flow from adjacent fingers to the center finger. Based on the analytical results, two types of HBTs with uniform emitter finger spacing and non-uniform emitter finger spacing are fabricated and their temperature profiles and thermal resistance are measured. The measured results agree well with the calculated results, verifying the accuracy of the calculations. For the HBT with non-uniform emitter finger spacing, the peak temperature and the thermal resistance are improved markedly over a wide biasing range compared with that of the uniform one. Therefore, both the calculated results and the experimental results verify that the optimized structure of power HBT with non-uniform emitter finger spacing is superior to the uniform emitter spacing structure for enhancing the thermal stability of power devices over a wide biasing range.     

改善SiGe HBTs热稳定性的Ge组分分布优化与设计

The impact of the three state-of-the-art germanium(Ge) profiles(box,trapezoid and triangular) across the base of SiGe heterojunction bipolar transistors(HBTs) under the condition of the same total amount of Ge on the temperature dependence of current gainβand cut-off frequency f_T,as well as the temperature profile,are investigated.It can be found that although theβof HBT with a box Ge profile is larger than that of the others,it decreases the fastest as the temperature increases,while theβof HBT with a triangular Ge profile is smaller than that of the others,but decreases the slowest as the temperature increases.On the other hand,the f_T of HBT with a trapezoid Ge profile is larger than that of the others,but decreases the fastest as the temperature increases,and the f_T of HBT with a box Ge profile is smaller than that of the others,but decreases the slowest as temperature increases.Furthermore,the peak and surface temperature difference between the emitter fingers of the HBT with a triangular Ge profile is higher than that of the others.Based on these results,a novel segmented step box Ge profile is proposed,which has modestβand f_T,and trades off the temperature sensitivity of current gain and cut-off frequency,and the temperature profile of the device.     

光纤孤子的“双陷”型非线性管理

为了研究光纤系统中由色散参量和 “双陷”型非线性参量可能导致的孤子现象,通过分步傅里叶数值算法求解了变系数（1+1）维非线性薛定谔方程。结果发现,光纤孤子在两种“双陷”型非线性光学系统中具有一系列有趣的性质,如单孤子脉冲在可变参量背景下由“双陷”型非线性结构诱发的周期性振荡;双孤子脉冲在常参量背景下由“双陷”型非线性结构诱导的走离效应;三个孤子脉冲在两种“双陷”型非线性光学系统中体现的特殊相互作用、融合效应等。     

Design of wide-band optical heterodyne balanced mixer receivers

The optical heterodyne balanced mixer, or dual-detector receiver, offers significant advantages over a single detector receiver. Balanced mixer receivers are particularly attractive for use in optical heterodyne communication systems because they conserve local oscillator power and cancel excess intensity noise present in the local oscillator. Simple circuit models that illustrate the noise performance, small signal gain, and bandwidth of a balanced mixer receiver are developed. A figure-of-merit for receiver noise performance is also derived. An example design of a gigahertz bandwidth optical heterodyne balanced mixer receiver and the techniques used to characterize near-quantum-limited receiver performance are discussed.     

Design considerations for millimeter-wave power HBTs based on gainperformance analysis

Critical design issues involved in optimizing millimeter-wave power HBTs are described. Gain analysis of common-emitter (CE) and common-base (CB) HBTs is performed using analytical formulas derived based on a practical HBT model. While CB HBT's have superior maximum-gain at very high frequencies, their frequency limit is found to be determined by the carrier transit time delay. Thus, to fully exploit the potential gain in a CB HBT, it is essential to maintain a high f_T even at high collector voltages. The advantage of using CB HBT's in a multifingered device geometry is also discussed. Unlike CE HBTs, CB HBTs are capable of maintaining a high gain even if the device size is scaled up by increasing the number of emitter-fingers. Moreover, it is found that reducing the wire parasitic capacitance allows emitter ballasting resistance to be used without affecting the gain. Fabrication of HBTs based on these design considerations led to excellent power performance in a CB unit-cell HBT at 25-26 GHz, featuring output power of 740 mW and power-added efficiency of 42%     

高功率光隔离器的热效应分析与优化

为提高光隔离器在高功率激光条件下的工作性能,基于琼斯理论研究了隔离器的热致退偏效应,设计了一种外置补偿晶体的隔离器,着重分析了隔离器隔离度及热透镜效应随入射光功率的变化规律。结果表明:通过调整氟化钙晶体的晶轴方向和长度,隔离器的热致退偏和热透镜效应可以得到有效抑制。在100 W激光条件下,外置补偿晶体后隔离度提高了16.3 dB,功率损耗降低8%。研究结果可优化设计隔离器结构,有效提升高功率隔离器的隔离度并减小功率损耗。     

卡式红外光学系统光机分析及结构优化

光学仪器通常都工作在一定的温度环境中,温度变化将造成光机系统的结构尺寸以及光学介质的特性等参数发生变化。针对卡式红外光学系统工作环境温度变化范围大的特点,进行了热补偿结构设计。并利用有限元方法,对主镜及其支撑结构进行了分析,明确了导致镜面变形和结构参数变化的主要因素为大范围的温度变化。在此基础上,对支撑结构进行了改进和参数的优化设计。研究结果表明:改进后的结构是合理可行的。     

Time-multiplexed signals and parallel signal analysis/switch optimization for MEMS-based optical cross-connect

The calibration of the numerous mirror pairs, or switches, in MEMS-mirror optical cross-connect systems is a critical process in their manufacture. Because the number of switch connections for these systems scales quadratically to the number of inputs/outputs, this places great demands on the equipment used to perform testing. We propose and demonstrate a calibration technique for generic optical subsystems based on optical time-division multiplexing (OTDM).     

Intermodulation analysis of crystal mixer

An expression for the amplitude of the intermodulation products and harmonics produced in a crystal mixer is derived using the coefficients of the power series expansion of the device. Using this expression and an exponential approximation of the current through a diode [i = i0(ε^αv- 1)], the amplitude of intermodulation produced in a crystal mixer is found to be 2i0ε^αV0R0Is(αV1)Ib(αV2). In(x) is an nth order modified Bessel function of the first kind. The quantities s and b are the signal harmonic and the oscillator harmonic, R0is the output resistance, and V0, V1, and V2are the bias, signal, and oscillator voltages, respectively. The quantities i0, α, R0, and V2are found from the dc E-I diode characteristics, the mixer bias current, and the loss in the desired signal. Experimental tests on a mixer operating from 450 Mc to 850 Mc show that the signal input power necessary to produce a given intermodulation output power can be predicted within 6 db.     

Self-heating effect compensation in HBTs and its analysis andsimulation

A simple technique, inserting a specified resistance in the bias circuit, to compensate self-heating effect in DC and pulse characteristics of HBTs is proposed and demonstrated. Utilizing the bias scheme dependence of HBT behaviors, the compensation is achieved due to the cancellation of the positive and negative thermal-electric feedback inside HBTs. An analytical expression relating the specified resistance with the physical parameters of HBT is presented. The accurate simulation of both the self-heating effect and its compensation is, for the first time, demonstrated with a modified Gummel-Poon model     

System- and circuit-level optimization of PLL designs for DVB-T/H receivers

This article proposes a framework for the optimization of voltage-controlled oscillator (VCO) designs in frequency synthesizers for digital video broadcasting ?C terrestrial/handheld (DVB-T/H) receivers. Linear time-invariant phase-domain model of a charge-pump phase-locked loop (PLL) is devised and includes both flicker (1/f) and thermal noise contributions from the loop oscillators. By modeling the entire receiver, it is shown that there are combinations of flicker and thermal noise contributions that result in a constant sum of inter-carrier interference (ICI) and adjacent channel interference, and constant symbol error rate as well. Consequently, optimization of the VCO phase noise spectrum is defined while maintaining the standard-specified symbol-error rate. Link-level performance evaluation is carried out to validate the stipulated trade-off. The effect of ICI mitigation schemes is discussed. Circuit-level VCO design approaches utilizing the derived trade-off are finally presented. The proposed optimization procedure is generic and is also applicable to other systems based on Orthogonal Frequency-Division Multiplexing.     

基于蒙特卡洛分析的InP-HBT微波特性精度估计

为了验证电路的可靠性,对InP异质结双极晶体管的微波特性进行了基于蒙特卡洛方法的波动分析。器件微波特性的波动程度不同,波动范围越大说明对本征参数的提取精度要求越高,可以通过输出特性推断测量可允许的精度范围。微波特性由模型S参数、电流增益截止频率和最大振荡频率组成,根据π型拓扑结构小信号模型本征参数的不确定度曲线,可以导出蒙特卡洛数值分析所需的标准差。蒙特卡洛分析结果表明,在不同的频率不同的偏置条件下,对测量参数准确性的要求差异较大,验证了电路在不同情况下的可靠性。     

多模光纤带宽的计算与优化

文章对多模光纤的带宽进行了理论分析,并进行仿真计算和优化,找出了不同工作波长下多模光纤最优折射率指数(gopt),同时对50/125μm新一代多模光纤的带宽进行了分析.     

XGM全光波长变换性能分析与优化设计

对基于半导体光放大器（ＳＯＡ）交叉增益调制（ＸＧＭ）的全光波长变换（ＡＯＷＣ）进行了性能分析,并提出了ＡＯＷＣ的简化系统模型,利用此模型详细分析了码速为２．５,５和１０Ｇｂｉｔ／ｓ归雾码的变换光消光比（ＥＲ）和信噪比（ＳＮＲ）与探测光功率（Ｐｃｗ）、信号光功率（Ｐｓ）和泵浦电流的关系,分析了优化设计ＡＯＷＣ的途径。     

Electron optical synthesis and optimization

A novel approach to electron/ion optical synthesis and optimization is presented. Low-aberration field distributions are sought by dynamic programming or optimal control procedures in the form of continuous curves constructed of cubic splines. A very simple algorithm is proposed for the reconstruction of the electrodes or pole-pieces. High-quality electrostatic lens designs are shown as practical examples.     

一种光环行器优化设计方法

针对光纤通信系统中最常用的晶体型三端口光环形器,详细论述了器件的工作原理,分析了现有方案中存在的光路不对称问题,提出了一种优化设计方法,通过引入位移型的Wollaston棱镜和改进型的位移晶体,设计出一种光路完全对称的器件结构,提高了光路调试和器件封装的效率.