Advances in Digital Front-End and Software RF Processing:Part I

One of the biggest technology trends in wirelessbroadband, radar, sonar, and broadcasting systems issoftware radio frequency processing and digitalfront-end. This trend encompasses a broad range oftopics, from circuit design and signal processing to systemintegration. It includes digital up-conversion (DUC) and     

基于FPGA的可见光/红外双通道实时视频融合系统

在已有基于色彩传递的双通道自然感彩色视频图像融合算法及DSP实时处理平台的基础上,采用Xilinx公司的XC5VLX50T FPGA为核心处理器件,配以少量外围器件研制成基于FPGA的可见光/红外双路自然感彩色视频融合系统,可为观察者提供包含可见光/热红外信息的自然感彩色融合视频图像.系统输出图像色彩更接近自然,使得两个通道的原有信息同时得到了更好的表现.基于FPGA的双通道自然感彩色融合系统不仅可实现实时视频融合,而且相对原有DSP处理系统,处理延时明显缩小,可在1帧内完成相关的预处理和色彩传递处理,适合动态场景下的双通道(微光/微光、可见光/热红外、微光/热红外、中波/长波热红外等)视频自然感彩色融合系统应用.     

Effects of Ca and Mn Additions on the Microstructure and Dielectric Properties of (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> Ceramics

Dielectric ceramics based on the solid solution (1 − x)Bi_0.5Na_0.5TiO₃ (BNT)-xCaTiO₃ (CT) were synthesized by the conventional solid-state route. BNT with various contents of CT formed a complete solid solution and exhibited a rhombohedral structure. CT in this solid solution with BNT was observed to decrease the dielectric constant at higher temperatures and raise the dielectric constant at lower temperatures. On the other hand, decreased ferroelectricity was observed with increasing CT concentration, resulting in a downward shift of the depolarization temperature and a decrease of the dissipation factor. With the addition of Mn²⁺ to 0.86BNT-0.14CT, the temperature characteristics of capacitance were improved (−55°C to 250°C, ΔC/C _25°C ≤ ±15%). By doping with 1.5 wt.% Mn²⁺, the dielectric constant at room temperature reached over 900, with a dielectric loss of less than 1%.     

A Micromachined Reconfigurable Metamaterial via Reconfiguration of Asymmetric Split‐Ring Resonators

A micromachined reconfigurable metamaterial is presented, whose unit cell consists of a pair of asymmetric split‐ring resonators (ASRRs); one is fixed to the substrate while the other is patterned on a movable frame. The reconfigurable metamaterial and the supporting structures (e.g., microactuators, anchors, supporting frames, etc.) are fabricated on a silicon‐on‐insulator wafer using deep reactive‐ion etching (DRIE). By adjusting the distance between the two ASRRs, the strength of dipole–dipole coupling can be tuned continuously using the micromachined actuators and this enables tailoring of the electromagnetic response. The reconfiguration of unit cells endows the micromachined reconfigurable metamaterials with unique merits such as electromagnetic response under normal incidence and wide tuning of resonant frequency (measured as 31% and 22% for transverse electric polarization and transverse magnetic polarization, respectively). The reconfiguration could also allow switching between the polarization‐dependent and polarization‐independent states. With these features, the micromachined reconfigurable metamaterials may find potential applications in transformation optics devices, sensors, intelligent detectors, tunable frequency‐selective surfaces, and spectral filters.     

基于位置信息的无线小区自组织网络拓扑控制研究

针对无线小区自组织网络节点连接性不高的问题,在网络节点所处的平面上引入空间约束机制,通过加入位置信息和增大平面以降低网络节点间干扰的方法来减小网络总干扰。分析了网络源节点的广播成功率,计算了网络节点的空间位置下界,并分别就单数据流和多数据流的情况下网络的有效性加以讨论。实验仿真表明,这种新型的网络拓扑控制方法可以有效提高无线自组织网络的相关性能。     

A New Current-Mode Incremental Signaling Scheme With Applications to Gb/s Parallel Links

A new current-mode incremental signaling (CMIS) scheme and a new fully differential current-integrating receiver for high-speed parallel links are presented. The proposed signaling scheme requires only N+1 physical paths for N parallel bits. It possesses the intrinsic advantages of current-mode signaling including high data rates, large signal swing, low switching noise injection, and superior signal integrity. The current-integrating receiver consisting of a transimpedance front-end, an integrator, and a sense amplifier with active inductor shunt peaking offers the key advantages of a low and tunable input impedance for channel termination, large bandwidth, and effective suppression of transient noise coupled to the channels. To assess the effectiveness of the proposed signaling scheme and the current-integrating receiver, a 4-bit parallel link consisting of four bipolar current-mode drivers, five 10-cm microstrip lines with FR4 substrate, and four proposed current-integrating receivers is implemented in UMC 0.13-mum 1.2-V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3.3V device models. Simulation results demonstrate that the proposed CMIS scheme and the current-integrating receiver are capable of transmitting parallel data at 2.5GB/s     

An Investigation of Negative Differential Resistance and Novel Collector–Current Kink Effects in SiGe HBTs Operating at Cryogenic Temperatures

In this paper, a new negative-differential-resistance (NDR) effect and a novel collector-current kink effect are investigated in the cryogenically operated SiGe heterojunction bipolar transistors (HBTs). Theory based on an enhanced positive-feedback mechanism associated with heterojunction barrier effect at deep cryogenic temperatures is proposed to explain both the observed NDR and the collector-current kink. The accumulated charge induced by the barrier effect acts at low temperatures to enhance the total collector-current, indirectly producing both phenomena. This theory is confirmed using the calibrated 2-D DESSIS simulations over temperature. These unique cryogenic effects also have significant impact on the ac performance of SiGe HBTs operating at high injection. Technology evolution plays an important role in determining the magnitude of the observed phenomena, and the scaling implications are addressed. In addition, the present NDR effect is also compared with previously reported NDR and hysteresis effects observed in highly scaled SiGe HBTs operating under forced-I_B-base bias. The input drive condition of the transistor during its use in circuits, either under pure forced-current bias or under pure forced-voltage bias, or more practically, somewhere in between, determines the magnitude of the observed NDR and is of potential concern for circuit designers and must be carefully modeled     

Multirobot-Based Nanoassembly Planning with Automated Path Generation

In this paper, a novel approach of automated multirobot nanoassembly planning is presented. This approach uses an improved self-organizing map to coordinate assembly tasks of nanorobots while generating optimized motion paths at run time with a modified shunting neural network. It is capable of synchronizing multiple nanorobots working simultaneously and efficiently on the assembly of swarms of objects in the presence of obstacles and environmental uncertainty. Operation of the presented approach is demonstrated with experiments at the end of the paper.     

Deploying P2P networks for large-scale live video-streaming service [Peer-to-Peer Multimedia Streaming]

Peer-to-peer (P2P) networks have been adopted for Internet live video-streaming service, and several practical systems have been deployed in past years due to the inherent scalability and ease of deployment. However, most of these systems are commercial and proprietary, and hence little research was done in the area of characterizing practical system performance properties. In this article, we mainly present our experience on a practical P2P-based live video- streaming system called GridMedia, which was employed to broadcast live the Chinese Spring Festival Gala show over the Internet. Benefiting from two sets of flush-crowd traces with about 15,239 and 224,453 concurrent users in a 300 kb/s streaming session in 2005 and 2006, we perform a trace study to understand the service capacity, quality of streaming service, connection heterogeneity, user geographic distribution, and request and online duration characteristics. Our observations shed light on those systems and further improvements in the arena of large-scale live video-streaming service over the Internet.     

Observation of Threshold-Voltage Instability in Single-Crystal Silicon TFTs on Flexible Plastic Substrate

We report the first observation of threshold-voltage instability of single-crystal silicon (Si) thin-film transistors (TFTs) that are fabricated on low-temperature flexible plastic substrate. Single-crystal Si of 200-nm thickness is transferred from silicon-on-insulator (SOI) onto an indium-tin-oxide-coated polyethylene terephthalate host substrate after selectively removing the buried-oxide layer from the SOI. TFTs of n-type were then fabricated on the transferred single-crystal Si layer with 1.8-mum thick SU-8-2 epoxy as the gate dielectric layer. It is observed that the threshold voltage (V_th) of these TFTs shifts to higher and lower values under high positive and negative gate-voltage stress, respectively. A logarithmic time-dependence of the V_th shift at high bias stress was clearly indicated. These results suggest that the instability of the threshold voltage of the single-crystal Si TFTs is attributed to the charge trapping in the gate dielectric layer.