A Compact Direct Digital Frequency Synthesizer for System-on-chip

A compact direct digital frequency synthesizer (DDFS) for system-on-chip (SoC) is developed in this paper. For smaller chip size and lower power consumption, the phase to sine mapping data is compressed by using sine symmetry technique, sine-phase difference technique, quad line approximation (QLA) technique and quantization and error read only memory (QE-ROM) technique. The ROM size is reduced by 98 % using the techniques mentioned above. A compact DDFS chip with 32-bit phase storage depth and a 10-bit on-chip digital to analog converter(DAC) has been successfully implemented using standard 0.35um CMOS process. The core area of the DDFS is 1.6mm(2). It consumes 167 mW at 3.3V, and its spurious free dynamic range (SFDR) is 61dB.

农田防护林生态系统结构研究进展

农田防护林生态系统结构决定着生态功能 ,其时空结构是该领域研究的核心 ,旨在探讨形成结构的完整性、稳定性、持久性的组件间的相互关系 .将其分为树体结构、林带结构、林网结构、景观结构 4个层次 ,针对各层次中结构研究的原理、方法及成果进行了综述 .通过树木个体的形态、质态结构研究 ,应用分形图形学的手段可实现动态结构的可视化 ,以研究林带树体结构的生成机理 ;精确界定林带结构的分维疏透度 ,探讨农田防护林带最佳结构理论 ,以构建防护林带最佳结构计算机生成模型 ;确立多物种、多层次的窄林带小网格的林网优化模式 ;评价农田防护林景观的合理性、稳定性、持续性 ,是今后的重要研究方向 .

Tree-ringbased drought reconstruction (a.d. 1855-2001) for the Qilian mountains；northwestern China

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