Waveforms(波形的产生与整形).pptVIP

Addition: The Generation and Square up of Pulse Waveforms（波形的产生与整形） Wang, Meiling May 9, 06 Contents Introduction (概述) Schmitt Triggers （施密特触发器） One-Shots （单稳态触发器） Multivibrators （多谐振荡器） Quartz Crystal Oscillators （石英晶体振荡器） The 555 Timer （555定时器） A-1 Introduction Two ways to implement a pulse/rectangular waveform (脉冲波形/矩形波) Generation by a multivibrator (多谐振荡器). Transform from some other waveforms whose frequency and amplitude (频率和幅值) are qualified. Ideal pulse waveform: A-1 Introduction Pulse waveform characteristics (page 5, section 1-2): 1. Period (周期) T The fixed interval at which the pulse repeat itself. 2. Amplitude (脉冲幅度) Height (voltage) from baseline. 3. Pulse width (脉冲宽度) tw A measure of the duration of the pulse and often defined as the time interval between the 50% on the rising and falling edges. A-1 Introduction 4. Rise time (上升时间) tr The time required for the pulse to go from its LOW level to its HIGH level. 5. Fall time (下降时间) tf The time required for the transition from the HIGH level to the LOW level. 6. Duty cycle (占空比) q Defined as the ratio of the pulse width (tw) to the period (T) and can be expressed as a percentage. A-2 Schmitt Trigger (施密特触发器) Schmitt trigger is one most general device which is used in waveform transforms. A-2 Schmitt Trigger A-2 Schmitt Trigger Characteristics: It has different input voltages when the output changes from HIGH to LOW and from LOW to HIGH. The output rectangular waveform is close to the ideal waveform, that is, its rising and falling times are very short because of the positive feedback in the device. A-2 Schmitt Trigger Parameters: Output voltage amplitudes: HIGH, LOW Two threshold voltages: VT+,VT- Output snapping direction A-2-1 Implement Schmitt Triggers Using gates (用门电路实现施密特触发器) Logic circuit A-2-1 Implement Schmitt Triggers Using gates A-2-2 7413 MSI Schmitt Trigger  (集成施密特触发器) 7413 is a MSI NAND gate of Schmitt trigger A-2-2 7413 MSI Schmitt Trigger A