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21.
It is shown that the overdamped response of single-quantum-well lasers due to a large gain compression can be countered by the destabilizing effect of an intracavity saturable absorber. Modulation bandwidths (3 dB) of up to 13 GHz for single-quantum well lasers were obtained using this technique 相似文献
22.
A novel linearised bipolar amplifier topology, integrating both reduction of baseband distortion and self-adaptive biasing techniques, is presented. The linearising circuit suppresses more than 25 dB of the spectral regrowth for the first-order sidelobes and reduces up to 36% DC bias power of the amplifying transistor 相似文献
23.
Lau J.H. Lee S.-W.R. Chang C. 《Components and Packaging Technologies, IEEE Transactions on》2000,23(2):323-333
Three different types of underfill imperfections were considered; i.e., (1) interfacial delamination between the underfill encapsulant and the solder mask on the PCB (crack initiated at the tip of underfill fillet), (2) interfacial delamination between the chip and the underfill encapsulant (crack initiated at the chip corner), and (3) the same as (2) but without the underfill fillet. Five different combinations of coefficient of thermal expansion (CTE) and Young's modulus with the aforementioned delaminations were investigated. A fracture mechanics approach was employed for computational analysis. The strain energy release rate at the crack tip and the maximum accumulated equivalent plastic strain in the solder bumps of all cases were evaluated as indices of reliability. Besides, mechanical shear tests were performed to characterize the shear strength at the underfill-solder mask interface and the underfill-chip passivation interface. The main objective of the present study is to achieve a better understanding in the thermo-mechanical behavior of flip chip on board (FCOB) assemblies with imperfect underfill encapsulants 相似文献
24.
Taguchi experiments are designed and carried out with five critical factors that influence the solder bumping of a 200 mm (8 in) wafer by the stencil printing method. These factors are: paste types, squeeze forces, snap-off heights, aperture shapes, and aspect ratios. They are varied to form a two-level L8 orthogonal array experiment. Analysis of mean (ANOM) and analysis of variance (ANOVA) are used to choose the most influential factors. After fixing the most influential factors, a two-level L4 orthogonal array experiment is followed to optimize the remaining material and process parameters. Important results are summarized in this paper which could be very useful for wafer bumping with the stencil printing method 相似文献
25.
The rapid development of computing software has facilitated multifarious research in integrated circuit (IC) packaging. Complicated and complex processes can be visualized via simulation modeling with this software. The applications of aided software enhance the fundamental physicochemical understanding and visualization of the IC encapsulation process. In this article, fluid–structure interaction (FSI) during IC encapsulation through computer-aided simulation is reviewed based on the amount of substantial work conducted from the past decades to the present. FSI phenomena in various IC encapsulations, such as wire sweep, paddle shift, lead frame deformation, IC chip, and through-silicon via (TSV) deformation, is considered in the review. The significance and challenges of FSI analysis are also highlighted in this article. 相似文献
26.
Bhoopendra Kumar Sanjay Kumar Dhurandher Isaac Woungang 《International Journal of Communication Systems》2018,31(2)
In the recent years, wireless applications and services have grown tremendously, resulting to a shortage of radio spectrum. On one hand, most of the available radio spectrum has already been allocated to different users and service providers. On another hand, research and statistics have revealed that the spectrum utilization usability is very limited. To address this dilemma, the concept of cognitive radio has emerged, which promotes the use of overlay and underlay transmission techniques to boost the utilization of radio spectrum resources. This paper provides a comprehensive survey of these 2 techniques and compares them qualitatively based on several network parameters. Next, this paper simulates overlay and underlay transmission techniques in OMNeT++ simulator on different network parameters, namely, Primary user arrival rate, throughput, sensing duration, and energy consumption. Our findings reveal that neither the overlay nor the underlay technique is sufficient itself to fulfill the demands for future wireless systems, and adopting a hybrid access technique consisting of a joint utilization of overlay and underlay approaches is desirable. Furthermore, the key challenges and open research issues in radio spectrum resources utilization are discussed. 相似文献
27.
Cooperative communication technology exploiting distributed spatial diversity is a promising solution for the future high data-rate cellular and ad-hoc wireless communications. To characterize the performance of a cooperative network, the cooperative diversity is commonly used. In this paper, we revisit the concept of diversity and look into the essence of cooperative diversity. We analyze the diversity performance of a general cooperative relaying system with multiple branches. Moreover, each branch consists of one or more hops. Unlike in other analyses, the assumptions that each node being only equipped with a single antenna and that all channel characteristics belonging to the same family are NOT required in our study. Using the decode-and-forward (DF) relaying protocol as an illustration, we provide analytical results on the diversity gain and the coding gain. The results also encompass most of the existing results as special cases. We further show the relationship between the diversity order of a branch and those of the constituent links; and the relationship between the diversity order of the network and those of the constituent branches. In particular, we show that for the uncoded DF protocol, the full diversity order can be achieved by using simple hard-decision detection at the destination. The requirement is to set appropriate signal-to-noise-ratio (SNR) thresholds for the multi-hop branches. To improve the bandwidth efficiency, we also randomly select one branch, among those branches satisfying the SNR-threshold requirement, for the transmission. We show that such a scheme accomplishes the full diversity order and produces a good error performance. 相似文献
28.
Wei Zhou Chak Wah Tang Jia Zhu Kei May Lau Zeng Y. Liu H.G. Tao N.G. Bolognesi C.R. 《Electron Device Letters, IEEE》2007,28(7):539-542
Good-quality metamorphic InP buffer layers have been successfully grown on GaAs substrates by metal-organic chemical vapor deposition. Characterization by atomic force microscope, transmission electron microscopy, high-resolution X-ray diffraction, and Hall measurements indicated that the layers are of high crystalline quality, good mobility, and excellent surface morphology. On this buffer, we demonstrated the first metamorphic InP/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) with good material quality and device performance. Metamorphic DHBTs showed direct-current and radio-frequency characteristics that are comparable to those grown on lattice-matched InP substrates. 相似文献
29.
Hwang‐Cheng Wang Isaac Woungang Kuo‐Chang Ting Chih‐Cheng Tseng Fang‐Chang Kuo Hung‐Te Huang 《International Journal of Communication Systems》2016,29(17):2534-2541
With the adoption of long‐term evolution standard for 4G mobile communications, the deployment of femtocell base stations (FBSs) to cope with the surging traffic in mobile wireless communication is becoming increasingly popular. However, with the random installation of FBSs, the problem of interference among FBSs is still a challenge. In this paper, assuming the presence of a femtocell management system that can control and coordinate the densely deployed FBSs, a novel power backoff scheme is proposed that determines the appropriate transmit power of each FBS so that the interference is reduced. Simulation results for randomly deployed FBSs in an environment with shadowing using MATLAB are provided, showing that our proposed methods can effectively mitigate the co‐tier downlink interference while improving the system capacity in a densely deployed femtocell network with shared spectrum use. Quantitatively, the average interference is reduced by roughly 90% to 100% of dBm, and the average capacity is increased by more than 80%. These results attest to the effectiveness of the proposed scheme. 相似文献
30.
Sudip Misra P. Venkata Krishna Kiran Isaac Abraham 《Wireless Personal Communications》2011,56(1):55-72
Providing effective medium access for wireless networks is a challenging task. Most of the existing protocols of IEEE 802.11
Medium Access Control (MAC) work towards the goal of achieving effective channel access by developing various backoff procedures.
In this paper, we make an attempt to develop a new medium access protocol named Learning Automata (LA) based Wireless Channel
Reservation (LAWCR). We use an LA approach to implement reservation for channel access for single hop wireless networks. Also,
sequence procedure is used to improve the reservation mechanism. The performance of the proposed LAWCR scheme show significant
improvements over the legacy DCF protocol with respect to important criteria such as the average time spent in the buffer
and the throughput. 相似文献