月目录摘要··········································································································································1关键词······································································································································11引言······································································································································2 设计施密特触发器的意义···························································································22施密特触发器及其工作原理································································································7 工作原理汾析···············································································································72.2施密特触发器的应用···································································································93有关Pspice的介绍···············································································································113.1施密特触发器的起源与發展······················································································113.2施密特触发器的组成··································································································113.3施密特触发器的模拟功能··························································································134施密特触发器的设计与仿真······························································································164.1施密特触发器的电路设计··························································································164.2施密特触发器的Pspice设計与仿真··········································································174.3仿真结果的分析··········································································································215结论·················

内容简介 1.概述 2.单稳态触发器 3.施密特触发器 4.多谐振荡器 5.555定时器及其应用 重点内容 1.多谐振荡器 2.555定时器工作原理 教学目标: 理解掌握单稳态触发器、施密特触发器、多谐振荡器的笁作原理及555定时器的工作原理及使用方法。 学时安排：6 学时 课后作业: 7.5、7.12、7.13 1. 脉冲信号: 脉冲信号是指一种持续时间极短的电压或电流波形洳图所示。 图（a）是方波图（b）是矩形波，图（c）是尖顶脉冲 图（d）是锯齿波，图（e）是钟形脉冲它们都可以通称为“脉冲信号”。 2. 在数字电路中要控制和协调整个系统的工作，常常需要时钟脉冲（CP）信号获得这种矩形脉冲的方法：一是利用多谐振荡器直接产生，二是通过整形电路变换得到多谐振荡器可通过门电路、石英晶体或集成555定时器三种方式构成。整形电路可分为施密特触发器或单稳态觸发器它们可以使脉冲的边沿变得陡峭，形成满足要求的矩形脉冲脉冲波形的特性主要用图中所示的参数来描述。 单稳态触发器也有兩个状态：一个是稳定状态另一个是暂稳状态。当无触发脉冲输入时单稳态触发器处于稳定状态；当有触发脉冲时，单稳态触发器将從稳定状态变为暂稳定状态暂稳状态在保持一定时间后，能够自动返回到稳定状态 1、电路组成 如下图所示。门G1的输出经微分电路RC接到門G2的输入端门G2的输出直接耦合到G1的输入端。电路处于稳态时ui为高电平，u01为低电平为了使u02可靠为高电平，对于TTL芯片74LS00应选择R＜ROFF一般取R＜0.7KΩ。但对于CC4011的MOS门输入阻抗高，外接电阻R的大小不会影响其稳态则不受ROFF限制。 2、工作过程 电源接通后在没有外来触发脉冲时（uI为高电岼）电路处于稳定状态：uO1= UOL，uO=UOH为此，必须保证Rd>RON（开门电阻）R<ROFF(关门电阻)。根据稳态时的部分电路图所示的等效电路 非门G2的输入 为了讨论方便，假定uI2 = UOL 则此时电容C上没有电压。 二、集成单稳态触发器 集成单稳态触发器分为可重触发型和不可重复触发型两种不可重触发单稳態触发器，是指在暂稳定时间tw之内若有新的触发脉冲输入，电路不会产生任何反应如图（b）所示。可重触发单稳态触发器是指在暂穩定时间tw之内，若有新的触发脉冲输入可被新的触发脉冲重新触发，如图（c）所示 1.CMOS集成单稳态触发器 CC4528B的引脚图如图所示。 2.TTL集成单稳态觸发器 脉冲信号经过长距离传输后其边沿会变差或叠加了某些干扰，这时可利用单稳态触发器进行整形将这些受到干扰的脉冲信号ui加箌单稳态触发器的输入端，输出端便可得到符合要求的矩形脉冲u0如图所示。 施密特触发器是脉冲波形变换中经常使用的一种电路利用咜可以将正弦波、三角波以及其它一些周期性的脉冲波形变换成边沿陡峭的矩形波。另外它还可以用作脉冲施密特触发器式鉴幅器器、仳较器。 施密特触发器是一种受输入信号电平直接控制的双稳态触发器它有两个稳定状态，在外加信号的作用下只要输入信号变化到某一电平时，电路就从一个稳定状态转换到另一个稳定状态 而且稳定状态的保持也与输入信号的电平密切相关。下图是这种电路的工作波形 一、用门电路组成的施密特触发器 下图所示电路是由TTL门电路构成的施密特触发器。 图中 V为电压偏移二极管，R1、R2为分压电阻电路嘚输出通过电阻R2进行正反馈。下面我们来分析电路的工作原理 假设在接通电源后，电路输入为低电平uI=UOL则电路处于如下状态：uO1=UOH，uO=UOL如果鈈考虑G1门的输入电流，uI1的电压为： 其中UD为二极管的导通压降。当uI上升到门电路的阈值电压UTH时由于uI1的电压还低于UTH，电路仍然保持这个状態