Influence of circuit parameters on Gunn-oscillator performance

Output power and tuning range of Gunn oscillators are determined as functions of the resonant-load resistance. Differing n0L products (1.2 and 4.8 ×1012cm-2) lead to strikingly different results which are related to the delayed-and quenched-domain resonant modes, respectively.     

Influence of self-induced thermal effects on second-harmonic generation

In optical nonlinear crystals used for second-harmonic generation the presence of absorption at the fundamental wavelength can lead to index of refraction inhomogeneities that reduce the conversion efficiency.     

Effect of carrier frequency offset on performance of MC-CDMAsystems

The bit error probability of the downlink of an MC-CDMA system is analysed taking into account the effect of a carrier frequency offset for Rayleigh and Rician fading channels. Derived results show that the performance of an MC-CDMA system is very sensitive even to a relatively small frequency offset     

石英晶片外观缺陷对频率的影响

研究了石英晶片外观缺陷对频率的影响。石英晶片其自身存在的外观缺陷包括:崩边、玷污、缺角等,这些缺陷可能会影响到成品石英晶体电参数的性能,例如影响石英晶体的频率特性、电阻特性、DLD特性等。目前石英晶片在镀电极前均需要进行外观缺陷检测,国内大多采用人工目测检测的方式,光学方法的石英晶片的缺陷自动检测技术还不成熟。无论哪种检测方法,都具有比较大的主观性,目前还没有建立有关石英晶片对石英晶体电参数的影响关系的研究报道。因此需要研究石英晶片外观缺陷对石英晶体电参数的影响的对应关系,以便能更准确地分选出对石英晶片电参数有影响的存在外观缺陷的石英晶片。     

4H-SiC MESFET频率特性研究

研究了4H-SiCMESFET的频率特性与器件几何及物理参数的关系。发现常温300K时,4H-SiCMESFET的截止频率随沟道掺杂浓度增加而上升;随沟道厚度的增加而降低;随栅长的增加而下降;随工作温度的增加变化很小,500K以上时略有降低。300K下,在沟道掺杂为4×1017cm-3、沟道厚度为0.25mm、栅长0.30mm、栅压偏置为-5V时,模拟得到的截止频率fT达到18.62GHz,显示该器件在高频、高温、大功率领域的极大优越性和应用前景。     

Influence of the trench corner design on edge termination of UMOS power devices

In this article, the voltage blocking capability of UMOS power devices is experimentally demonstrated to be limited by the onset of a premature breakdown at the corners of the trench located at the device periphery. With the aid of numerical simulations performed in cylindrical co-ordinates, it is shown for the first time that a race-track shape of the trench gate fingers alleviates the electric fields at the trench corners and maximizes the UMOS voltage blocking capability. In addition, it is also shown that the breakdown voltage at the trench corners can be made to exceed the UMOS unit cell breakdown voltage by using a deep p diffusion around the trenches located at the device periphery.     

On the theory and performance of trellis termination methods forturbo codes

The performance of a turbo code can be severely degraded if no trellis termination is employed. This paper investigates the implications of the choice of trellis termination method for turbo codes, and explains the origin of the performance degradation often experienced without trellis termination. An efficient method to derive the distance spectrum of turbo codes for different trellis termination methods is presented. Further, we present interleaver design rules that are tailored to each termination method. Using interleavers designed with these restrictions, we demonstrate that the performance difference between various termination methods is very small, including no trellis termination at all. For example, we demonstrate a turbo code with a 500-bit interleaver that exhibits no sign of an error floor for frame error rates as low as 10^-8, even though no trellis termination is employed     

Effects of frequency offset on MC/CDMA system performance

The effects of frequency offset on a multicarrier code-division multiple-access system are theoretically analyzed and verified by computer simulations for the downlink channel. Both equal gain combining and maximal ratio combining are considered in combining subcarrier signals in the analysis     

High frequency performance of SiC heterojunction bipolartransistors

A compact heterojunction bipolar transistor (HBT) model was employed to simulate the high frequency and high power performances of SiC-based bipolar transistors. Potential 6H-SiC/3C-SiC heterojunction bipolar transistors (6H/3C-HBT's) at case temperatures of 27°C (300 K) through 600°C (873 K) were investigated. The high frequency and high power performance was compared to AlGaAs/GaAs HBT's. As expected, the ohmic contact resistance limits the high frequency performance of the SiC HBT. At the present time, it is only possible to reliably produce 1×10^-4 Ω-cm² contact resistances on SiC, so an f_T of 4.4 GHz and an f_max of 3.2 GHz are the highest realistic values. However, assuming an incredibly low 1×10^-6 Ω-cm² contact resistance for the emitter, base, and collector terminals, an f_T of 31.1 GHz and an f_max of 12.7 GHz can be obtained for a 6H/3C-SiC HBT     

Influence of eccentricity on the frequency limitations of circular-pad via-holes

We study the influence of the technologically caused eccentricity of a circular-pad via-hole. We derive an eigenvalue equation using a rigorous method based on a linear transformation of the via-hole polar coordinates. The eigenvalue equation is used to compute the modal resonant frequencies and the modal fields of the eccentric via. It is shown that the via-hole misalignment shifts the modal frequencies and influences its frequency band. The proposed model is verified with published experimental data, and is also compared with results generated with the full-wave simulator Agilent Momentum-2002.     

场频率变化对辐射场与原子间耦合系数的影响

对二能级原子与单模辐射场相互作用系统的哈密顿量进行分析,找出光场与原子之间耦合系数与光场频率及谐振腔体积之间的关系。通过利用谐振腔的腔镜振动机制,研究了腔镜振动对光场模式及对腔体积的影响,最终找出辐射场与原子之间耦合系数与场频变化之间的关系。     

冷积银膜的二次谐波研究

冷积金属膜在退火过程中对外场的二次谐波响应,理论预计可同时观察到局域的和非局域的表面等离子体激光(SPP)对二次谐波的增强.在超高真空环境下和120～400K退火范围内观察到了冷积银膜表面这两种SPP激发,讨论了它们与入射场的角度关联特性.     

基于自适应控制电路实现的宽带高性能频率源

基于自适应控制技术,在宽带捷变频频率合成器的设计方案中同时引入自动调节滤波电路和带温度预校准功能的自动电平控制电路,有效降低了输出信号杂散,提高了输出信号的功率平坦度, 相比传统的利用分段滤波方式实现的宽带频率源,减小了模块体积。文中不仅详细介绍了这2个电路的实现过程,还从易于工程实现的角度出发,着重介绍了一些能有效降低调试工作量的方法。设计所得的频率合成器输出频率1 000 MHz~1 900 MHz,步进2 MHz,在–45 ℃~ +85 ℃的温度范围内,实现了杂散抑制优于–70 dBc,输出功率10 dBm±0.3 dBm的技术指标。     

Theory on phase-matched second-harmonic generation in biaxialplanar waveguides

A theoretical study on the optimization of second harmonic generation (SHG) in a planar waveguide in a biaxial nonlinear material is presented. Numerically computed curves show the dependence of the SHG efficiency on the condition of lateral focusing in the planar waveguide, of double refraction and of phase matching. The calculations take full account of double refraction and diffraction in the paraxial approximation in the planar guide. It is shown that in the absence of double refraction and under optimum focusing conditions the generated second harmonic power increases in proportion to L^3/2, where L is the length of the planar waveguide     

Influence of sampling period on time and frequency stability measurements

Because of the introduction of SDH based networks, the exigence of performing stability measurements on timing signals is becoming more and more stringent. In this paper, the influence of the measurement sampling period on the behaviour of the stability quantities is analysed and useful information for specification design and assessment purposes are provided.     

Optical study of elastic second-harmonic generation

A detailed theoretical analysis of the problem of elastic second-harmonic generation (SHG) by longitudinal ultrasonic beams of finite dimension propagating in isotroplc media or along certain pure mode axes in crystals has been made. A formulation for optical SHG by Gaussian laser beams, adapted to the ultrasonic case, has allowed calculation of the intensity profile and angular intensity distribution of the second-harmonic beam as a function of distance from the generating fundamental frequency transducer. These calculations were confirmed experimentally, using the beam probing techniques of Bragg diffraction, for both focused and unfocused longitudinal beams, in the frequency range 200-500 MHz, propagating along the Z axis in crystal quartz. Ultrasonic diffraction of the fundamental beam is shown to result in reduction of second-harmonic intensity compared to the intensity normally calculated from plane-wave theory. Consideration of this reduction allowed an accurate value of the third-order elastic constant c333to be determined from the measured second-harmonic intensity. The effect of reflection at a crystal-air interface on SHG has also been investigated.     

高斯光束横向分布对激光器性能的影响

本文采用半经典激光理论,研究了稳定腔内高斯驻波场对激光器性能的影响,结果表明,高斯分布对激光器的阈值和频率牵引有明显的影响.     

Characteristics of all-optical ultrafast gate switches using cascade of second-harmonic generation and difference frequency mixing in quasi-phase-matched lithium niobate waveguides

In all-optical gate switches that employ the cascade of second-harmonic generation and difference frequency mixing in quasi-phase-matched (QPM) lithium niobate (LN) devices, walkoff between the fundamental and second-harmonic pulses causes crosstalk of the switch. We numerically calculate the switching performance of QPM-LN waveguide devices with consideration for the crosstalk effect, and discuss the favorable choice of the nonlinear optical tensor element for the LN crystal. In the analyses, the device length is maximized for a given bit rate under the condition that the crosstalk is maintained below a critical level that is determined by the allowable power penalty for the switched signal. It is shown that the time offset between the gate and signal pulses can compensate for the walkoff, and can significantly improve the switching efficiency. In ultrafast operation beyond 1 Tbps, the use of the nonlinear optical tensor element d/sub 31/ is found to be favorable when compared to the use of the commonly used maximum tensor element d/sub 33/.