Lesson 8 Clock Sources.ppt

《电子信息工程专业英语教程》 Unit 3 Electronic System Components Lesson 8 Clock Sources 信息工程学院电子系 韩建峰 Lesson 8 Clock Sources Terminology Oscillator TCXO, PLL, VCO Detector Terminology Oscillator 振荡器 Resonant 谐振的 Series Resonant 串联谐振 Parallel Resonant 并联谐振 Resonating frequency 谐振频率 TCXO: Temperature Compensated Crystal Oscillator 温度补偿晶体振荡器 PLL: Phase Locked Loop 锁相环 VCO: Voltage Controlled Oscillator 压控振荡器 detector n.检测器，检波器，探测元件 phase detector n.鉴相器, 相位检测器 frequency detector n.鉴频器, 频率检测器 Outline Clock Devices Crystals, Crystal Oscillators, Compensated Oscillators, Voltage Controlled Oscillator, Frequency Synthesizers, Clock Buffers Clock Parameters Clock Jitter, Skew, Tolerance/Accuracy, Stability, Aging, Slew, Duty Cycle A basic piezoelectric quartz crystal Two kinds of crystals Series Resonant Parallel Resonant An oscillator with the crystal as the feedback element Provides the most accurate and stable output frequency. The preferred clock source in most high-speed digital systems requiring clocks. Try to adjust the variation in frequency due to temperature and voltage Temperature Compensating Oscillators (TCXO) The output of VCO is controlled by a voltage control input pin. Use one or more PLL to generate one to many different frequencies on their outputs, from one or more reference sources. A PLL has two inputs a reference input a feedback input. A PLL corrects frequency in two ways frequency correction Phase correction A device in which the output waveform directly follows the input waveform. Have a propagation delay Skew will exist on the outputs The deviations in a clock’s output transitions from their ideal positions. Cycle-cycle jitter Period jitter Long-term jitter Causes of jitter Power supply noise The internal PLL of the synthesizer Random mechanical noise from vibrations of the crystal Random thermal noise from crystal, or any other resonating device. The variation in arrival time of two signals