【作者】 秦鹏；

【导师】 周健军；

【作者基本信息】 上海交通大学 ， 软件工程， 2010， 硕士

【摘要】 近年来,多媒体广播系统在全世界许多国家发展迅速。作为多媒体广播的一种,固定和可移动的数字电视接收系统也在逐渐形成行业标准,比如说几年内已广泛应用于欧洲的数字地面/手持多媒体广播(DVB-T/H).中国移动多媒体广播(CMMB)类似于DVB标准,在地面信号传输中采用UHF频段(470～798兆赫兹)。为满足如此宽的信号频带要求,在下变频过程中需要频率合成器提供相应的本地振荡(LO)频率。宽带压控振荡器(VCO)是频率合成器中的核心元件。使用电容阵列以保持LC谐振回路中可变电容的小尺寸,是同时实现宽调谐范围和低频率敏感性的最有效方法之一。双核技术(实际上使用两个VCO)可以更进一步的增加调谐范围。本论文中实现了一种双核宽带低调谐敏感度(tuning sensitivity)的VCO。为满足接收机的高动态范围要求,VCO需要具有相应的不过分影响接收机灵敏度的频谱纯度。对于宽带VCO来说,在全频段达到像窄带VCO一样的优越相位噪声性能非常困难,因此这对设计者来说是一个挑战。本文通过引用经典的相位噪声模型来分析相位噪声的产生,并且讨论了几种减小相位噪声的方法。为了详细阐述VCO的工作原理,文中也包含了正反馈和负阻机制的分析。对于起振条件的研究,文中同时运用了大信号和小信号分析两种方法。因为VCO工作在四倍LO频率处,为了提供LO信号,在VCO之后有附加两个电流模逻辑(CML)二分频器。二分频器,包括用于二分频器之后,为下级电路提供大电压摆幅的缓冲器在文中也都有介绍。每个模块的工作电流都经过优化,以达到要求的功耗。为了克服VCO工作时非理想因素的干扰,还需要一些其他电路。在供电电压和VCO的电压输入端之间需要一个用于电压校准的放大器,以稳定VCO的输入电压,消除来自电源线上的干扰。版图设计也需要格外小心,尽量避免不必要的寄生效应,以减少性能的损耗。在论文的末尾会简要提及一些版图设计的注意事项。前仿真和后仿真的结果都表明,本文中设计的VCO能满足CMMB系统指标。更多还原

【Abstract】 Mobile broadcasting systems is being developed rapidly in many countries during recent years. The system for fixed and portable reception of digital television, known as digital video broadcasting -terrestrial/handheld (DVB-T/H), has been available in Europe for several years. China Mobile Multi-Media Broadcasting (CMMB) is a similar standard to DVB which also uses Ultra-High Frequency (UHF) band (470～798MHz) for territorial signal transmission.Because of such broad band requirement, a frequency synthesizer with wide tuning range is necessary to provide corresponding local oscillation (LO) frequency available for frequency down conversion. Wide band voltage controlled oscillator (VCO) is at the heart of frequency synthesizer. One of the most effective ways to achieve wide tuning range and low tuning sensitivity at the same time is to use a switched-capacitor bank while keeping the varactor size small in LC tank. Dual core (actually two VCO cores) application may extend the tuning range further. In this thesis, a dual core VCO with low tuning sensitivity is proposed.For receivers with high dynamic range requirements, the VCO must achieve a correspondingly high spectral purity so as not to degrade receiver’s sensitivity excessively. This is a big challenge since conventional wideband VCO can not achieve excellent phase noise over whole frequency range as the narrow band VCOs have done. Classical phase noise models are used in this thesis for analyzing the origin of phase noise, and several methods of reducing phase noise are discussed. To interpret the operation of VCO in detail, basic positive feedback and negative resistance mechanism is also involved. Large signal and small signal analysis is applied to explain start up condition for VCO.Proposed VCO operates at fourfold LO frequency so two current mode logic (CML) frequency dividers are used. Implementation of divide-by-2 circuits is introduced. There are also two buffers following dividers to provide large voltage swing for the next stage. Current consumption of all circuit blocks is optimized to achieve low power requirement.To overcome non-ideality in VCO, additional circuit is used. A regulation amplifier is added between power supply and supply voltage of VCO, which reduces the power supply sensitivity and its phase noise contribution. Carefully layout drawing is very important since parasitic effects should be decreased as much as possible in order not to degrade circuit performance. A brief discussion of VCO layout is in the end of this thesis.Both pre-simulation and post-simulation results are included to support the analysis of this thesis, and the proposed specifications are satisfied.更多还原