利用精密单点定位技术评估晶振频率稳定度

在评估晶振频率稳定度时，目前常用一个频率稳定度比待测晶振高3倍以上的时钟作为参考，造成测试成本高昂。在分析精密单点定位（Precise Point Positioning,PPP）技术原理的基础上，提出了一种基于PPP技术的频率稳定度评估方法，并利用该方法对一款秒稳达到10-12的高稳定度恒温晶振（Oven Controlled Crystal Oscillator，OCXO）进行了评估，评估结果与利用氢原子钟为参考的传统频率稳定度评估方法基本吻合。最后给出了该方法对不同等级晶振的评估能力。该方法结构简单，测试方便且成本低廉，能满足常用时频设备（如通信设备、卫星导航接收机）的晶振评估需求。     

基于比时法的晶振频率测量建模与分析

受器件老化、随机噪声等因素影响,晶振频率变化较复杂。以GPS秒脉冲作为测量标准,构建了晶振频率随时间变化的测量系统,通过对测量数据进行一元回归统计处理,分离出了晶振实际频率与其标称频率的相对偏差及晶振的各种随机误差,并分析了这两种误差对晶振准确度及稳定度的影响。该方法可为频率源误差测量分析提供借鉴作用。     

电子元器件实用知识讲座(10)

<正> 第十讲 石英、陶瓷和保险元件 本讲介绍石英晶体元件、陶瓷谐振元件及保险元件的性能、种类、参数和外形识别等实用知识。 一、石英晶体元件 1.石英晶体元件的结构和特性 石英晶体元件通常简称为晶振元件、晶振子、晶体或晶振等。它是一种主要用以取代LC谐振回路的谐振元件,所以也常被称作石英谐振器或晶体诸振元件。晶振元件一般由石英晶片、晶片支架和封装外壳等构成。石英是一种结晶体,在结晶体上按一定方位切割成的薄片就是石英晶片。按切割晶片的方位不同,可将晶片分为AT、BT、CT、DT、X、Y等多种切型。不同切型的晶片其特性亦不尽相同,其中尤以频率温度特性相差较大,通常AT型晶片的频率温度特性较好,所以应用也广。 晶片支架的作用是固定晶片及引出电极。晶片支架一般可分为焊线式和夹紧式两种。通常低、中频率的晶振采用焊线式,高领晶振用夹紧式。晶振元件的外壳以金属壳的最为多见,其特点是体积小,密封性好,价格较低廉,彩电、录像机、游戏机及电子手表中大多采用这种晶振元件。还有一     

石英晶振真空传感器及真空计的研制

本文研究了音叉型石英晶体谐振器的谐振阻抗与周围气压的关系，设计了一种全新的自稳幅自跟踪晶体振荡电路和精密动态阻抗测试电路，以测量石英晶振的谐振阻抗。实验测得，当晶振周围气体压强从１０－２Ｐａ上升到大气压时其谐振阻抗相对变化也几乎以相同数量级单调增加，阻抗随气压变化关系与理论分析和国外文献报道一致。利用石英晶振的气压敏感性，本文研制了一种新型的石英晶体真空计，量程从０．１Ｐａ到２×１０５Ｐａ，全量程内无须进行量程切换，各点测量误差小于１２％。     

低噪声100MHz晶体振荡器的设计考虑

本文通过对晶体振荡器内部噪声及噪声与短期频率稳定度关系的分析,利用幂律频谱密度的阿仑方差估算晶振的毫秒级短稳。提出晶振电路低噪声设计的主要原则,给出100MH_z晶振短稳主要指标。     

高精度MEMS硅谐振压力传感器闭环控制系统

硅谐振压力传感器因其数字频率信号输出和高精度的特点,被广泛应用于航空航天、工业控制等领域。硅谐振压力传感器的闭环控制系统决定硅谐振压力传感器的性能指标,系统的稳定性分析和参数优化则是谐振传感器的研究难点。基于系统状态方程从理论上推导了控制策略,提出系统稳定性判定依据。利用Simulink仿真搭建系统模型,并通过电路测试验证。结果表明,在满足稳定性判据的条件下,研制的硅谐振压力传感器基频为42 kHz,品质因数为30 000。在量程范围为3～130 kPa、温度为-55～85℃时,该谐振压力传感器的精度高达0.01%F.S.,实现了恒幅控制与实时频率跟踪。     

倍频器在数字MMDS发射机中的应用

现代数字电视技术的发展对发射机本振信号源的相位噪声、频率稳定度等参数提出了越来越高的要求，针对数字MMDS发射机的技术要求，设计了一种由低相噪晶振和倍频电路组成的本振源，它具有相噪低、频率稳定度高、重复性好的特点，满足了数字信号传输的要求．     

基于GPS驯服技术的高稳频踪设计

针对高稳定度频标在国民经济发展中有着巨大需求,提出一种基于GPS驯服技术实现的高稳频踪设计方法。与传统的驯服技术相比较。该方法采用数字锁相环加Kalman滤波算法来实现恒温晶振跟踪GPS,综合了GPS秒脉冲的较高长期稳定度和恒温晶振较高短期稳定度的优点,既滤除GPS秒脉冲的随机误差,又解决GPS失锁时恒温晶振无法保持高频率准确度输出问题。结果表明,该方法能够实现了较高的频率准确度和稳定性,输出的频率准确度优于5×10^-11,能够用于时间频率的测量基准。     

关于接收机的相位噪声

接收机的相位噪声实际上专指频率合成器的相位噪声,而频率合成器的相位噪声是衡量其短期稳定度的一个技术指标,目前国内外的频率合成器基本采用锁相环(PLL)或多个锁相环的方式.频率合成器的频率稳定度包括长期稳定度和短期稳定度.长期稳定度一般由基准频率源(通常为恒温晶振或温度补偿晶振,或由外部基准频率源)决定,短期频率稳定度由锁相环决定(环路参数、部件如压控振荡器).相位噪声早期也称为相位抖动,在时域多用阿仑方差表示,在频域多用相位噪声(偏离载波某个频偏处的单位带宽内相位噪声功率相对主载波的功率低多少,通常用dBc/Hz表示,dBc中的c表示相对值)表示.     

优良短期稳定度10 MHz恒温晶振研制

分析了恒温晶振工作原理的基础上,提出了改善恒温晶振短期稳定度的方法。通过开展低噪声主振电路设计、高精度控温电路设计、精密双层恒温槽设计及合理选用关键元器件等具体措施,研制出具有优良短期稳定度的10 MHz恒温晶振,并对短期稳定度测试方法进行了研究。通过TSC5115短稳测试仪测试,该10 MHz恒温晶振短期稳定度达到了2×10-13/s,体积为65mm×65mm×35mm。     

Dielectric anisotropy of new liquid-crystal mixtures and its effect on dynamic scattering

New liquid crystalline compounds with a high negative dielectric anisotropy and wide temperature range have been prepared, and their dynamic-scattering properties compared with other materials. These compounds give a slightly lower threshold voltage, followed by a rapid increase of dynamic scattering above threshold, and should provide improved performance in low-voltage display devices.     

Fabrication and performance of selectively oxidized vertical-cavitylasers

We report the high yield fabrication and reproducible performance of selectively oxidized vertical-cavity surface emitting lasers. We show that linear oxidation rates of AlGaAs without an induction period allows reproducible fabrication of buried oxide current apertures within monolithic distributed Bragg reflectors. The oxide layers do not induce obvious crystalline defects, and continuous wave operation in excess of 650 h has been obtained. The high yield fabrication enables relatively high laser performance over a wide wavelength span. We observe submilliamp threshold currents over a wavelength range of up to 75 nm, and power conversion efficiencies at 1 mW output power of greater than 20% over a 50-nm wavelength range     

Switching and memory effects in amorphous chalcogenide thin films

The performance of threshold- and memory-switching devices is discussed. The threshold devices were prepared by vacuum deposition from the Ge-As-Te-Si system and exhibited threshold voltages over a wide range from less than 2.0 V to greater than 50 V. Lifetimes of the order of 10⁶-10⁸switching operations before failure were obtained and the operation of the threshold device with a capacitative load was demonstrated. Memory-switching devices were prepared from the Ge-As-Te system. The bistable operation is discussed and it is concluded that the bistable impedance states are due to the presence, or absence, of a crystalline filament between the electrodes. Typical pulse levels required to produce the transition between the impedance states were 2 × 10^-2A for 5 × 10^-3s and 5 × 10^-2A for 5 × 10^-6s. The devices possess fairly stable characteristics and currently have lifetimes of 10²- 10³operations before failure; this is expected to improve with device development.     

ZnO近紫外波长纳米激光器的研究

随着纳米科技的兴起,纳米激光的研究成为了又一个新的重要课题.ZnO纳米微晶有两种结构可以产生随机激光,一是六角柱形蜂窝状微晶结构,二是颗粒粉末状结构,产生的近紫外激光波长是387.5 nm,光泵浦阈值是50 kW/cm2.采用气相输运的催化外延晶体生长过程来制备ZnO纳米线阵列构成的光致纳米激光器,激光波长383 nm,线宽仅为0.3 nm,光泵浦阈值是40 kW/cm2.     

Laser-induced breakdown in crystalline and amorphous SiO2

The 1.06 μm breakdown thresholds of crystalline and amorphous SiO2were compared. These materials showed dependences of the breakdown threshold on the focal volume which are consistent with a multiphoton-assisted electron avalanche damage mechanism.     

p-type conduction in ion-implanted amorphized Ge

The electrical transport properties of n-type crystalline-Ge amorphized by ion implantation have been determined by resistivity and Hall effect measurements in the 64–255 K temperature range. Amorphous layer was realized by implanting Ge⁺ ions in Ge single crystal maintained at ∼77 K at fluences above the amorphization threshold. The samples exhibited a surprising lower sheet resistance with respect of un-implanted crystalline Ge, resulting from positive charge carriers and very high mobility. Experimental observations are consistent with a p-type conduction induced by surface states and a high mobility channel at the amorphous-crystal interface.     

用HREELS和UPS研究多孔硅的电子结构

使用高分辨电子能量损失谱(HREELS)和紫外光电子能谱(UPS)研究了新腐蚀的多孔硅(PS)样品的电子结构。实验结果表明,从HREELS谱中能量损失阚值测得的PS的能隙移到2．9eV,与文献报道的光激发谱(PLE)结果相近。UPS结果表明PS的费米能级到价带顶的距离不同于单晶Si。结合HREELS和UPS结果可以初步得出PS与Si界面的能带排列。     

Quantum Dot Lasers Fabricated by Self-organized Growth

Quantum dot lasers have excellent characteristics such as timperature stability of threshold current and ultra-high material gain.Quantum dot structures fabricated by self-organized growth have high crystalline perfection,high quantum yield of radiative recombination and high size homogeneity .Main advantages and operating properties of quantum dot alsers fabricated by self-organized growth are briefly introduced.     

Synthesis and characterization of p-type NiO films suitable for normally-off AlGaN/GaN HFETs application

p-type NiO films were prepared at different oxidizing temperatures in O₂ ambient for normally-off AlGaN/GaN HFETs application. The crystalline structure, electrical properties and band gap of NiO films are dependent upon temperatures. Compared with the conventional Ni-gated HFETs, NiO-gated HFETs present positively shifted threshold voltage and smaller gate leakage current, while the drain current density shows slightly degradation. Combining the recess structure and NiO gate, normally-off GaN HFETs was achieved with a threshold voltage of approximately 0.5 V. The band diagram of the NiO/AlGaN/GaN structure demonstrates that the p-type conductivity and large conduction band offset between NiO and GaN cause the lift-up potential, which result in 2DEG depletion and positive threshold voltage shift.     

Growth of rubrene crystalline thin films using thermal annealing on DPPC LB monolayer

High crystalline thin films of 5,6,11,12-tetraphenylnaphthacene (rubrene) can be obtained after in situ thermal post annealing using SiO₂ gate dielectric modified with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer obtained via Langmuir–Blodgett transfer. Such formed rubrene crystalline films are interconnected and highly ordered with defined molecular orientation. Organic thin film transistors (OTFTs) with high performance are reproducibly demonstrated with the mobility of 0.98 cm²/V s, the threshold voltage of −8 V and the on–off current ratio of higher than 10⁷. The results indicate that our approach is a promising one for preparing high quality rubrene crystalline films.