Design of crystal oscillators 水晶振荡器电路设计课件
石英晶振设计电路,Oscillation Circuit Design Overview
Oscillation Circuit Design OverviewOscillation Circuit Design Key ParametersDRIVE LEVEL (DL), OSCILLATION FREQUENCY AND LOAD CAPACITANCE (CL),OSCILLATION ALLOWANCE, FREQUENCY-TEMPERATURE CURVEDRIVE LEVEL (DL)The drive level of a crystal unit is shown by the level of the operating power or the current consumption (see Figures 9,10, and 11). Operating the crystal unit at an excessive power level will result in the degradation of its characteristics, which may cause frequency instability or physical failure of the crystal chip. Design your circuit within absolute maximum drive level.OSCILLATION FREQUENCY AND LOAD CAPACITANCE (CL)The load capacitance (CL) is a parameter for determining the frequency of the oscillation circuit. The CL is represented by an effective equivalent capacitance that is loaded from the oscillation circuit to both ends of the crystal unit (see Figure 12). The oscillation frequency varies depending upon the load capacitance of the oscillation circuit. In order to obtain the desirable frequency accuracy, matching between the load capacitances of the oscillation circuit and the crystal unit is required. For the use of the crystal unit, match the load capacitances of the oscillation circuit with the load capacitances of the crystalunit.OSCILLATION ALLOWANCETo ensure stable oscillation, the negative resistance of the circuit should be significantly larger than the equivalent series resistance (the oscillation allowance is large). Ensure that the oscillation allowance is at least five times as large as the equivalent series resistance.Oscillation Allowance Evaluation MethodAdd resistor "Rx" to the crystal unit in series and ensure that the oscillation starts or stops. The approximate negative resistance of the circuit is the value obtained by adding the effective resistance "Re" to the maximum resistance "Rx" when the oscillation starts or stops after gradually making Rx value larger. Negative resistance |- R| = Rx + Re|−R| is a value at least five times as large as the maximum equivalent series resistance (R1 max.) of the crystal unit.*Re is the effective resistance value during oscillation.Re = R1 (1 + CO/CL ) 2FREQUENCY-TEMPERATURE CURVEFrequency temperature characteristics of tuning fork crystals is shown by negative quadratic curve which has a peak at 25ºC as per left graph.Please make sure to consider the temperature range and frequency accuracy you need since magnitude of frequency variation becomes larger and larger as the temperature range becomes wider.[Approximation formula of frequency temperature characteristics]f_tem = B(T-Ti) 2B : Parabolic coefficientT : Given temperatureTi : Turnover temperature 。
晶体振荡器设计报告
石英晶体振荡器设计报告陈永平09电子C班0915241009一、设计要求A.晶体振荡器的工作频率在10MHZ以下（可为4MHZ、6MHZ、8MHZ）。
B.振荡器工作点可调，反馈元件可更换。
C.具有3组不同的负载阻抗。
D.电源电压为12V。
E.在10K负载上输出目测不失真电压波形Vopp≥4V。
震荡频率读出5位有效数字。
二、设计方案的论证A.电路形式：串联型石英晶体振荡器B.电路参数：1. 电路电阻：47k电位器一个，4.2k，4.7k,1.5k,620电阻各一个；2. 负载电阻：1k,10k,110k电阻各一个；3. 电容：103电容4个，102电容一个，101电容一个，152电容一个，可变电容一个；4. NPN三极管：9018 一个；5. 晶振：6Mhz一个；6. 电感：330uh,3.3uh各一个；C.参数估算：1.负载电阻变小时，输出电压幅度变小;负载电阻变大时，输出电压幅度变大。
2.调节Ct使谐振回路谐振频率与晶振的 fs 相同。
3.Rp减小时，输出电压幅度变大；Rp增大时，输出电压幅度变小。
D.设计内容的实现情况:负载上所测得的电压如下表：RL 1k 10k 110kVo-pp 3.33V 4.19V 4.19V三、电路图的分析和说明A.原理图：PCB图B.元器件功能1. 石英晶体:振荡回路的工作频率等于石英晶体的谐振频率fs时，石英晶体的高的阻抗近似为零；振荡回路的工作频率偏离石英晶体的频率fs时，石英晶体的阻抗骤然增加，近乎开路；综上，电路只能形成f=fs的振荡。
本实验中，采用的是6MHZ的晶振，因此回路输出6MHZ的振荡信号。
2. 9018高频管：9018是一种常用的高频(可到1.1GHz)小功率三极管。
它是一种小电压,小电流,小信号的NPN型硅三极管,常用在AM及FM放大电路,及FM/VHF调频本振电路中。
3. 电位器：调节电位器可改变静态工作点。
电路的直流通路如下图静态工作点的计算：U BQ=R2/(Rp+R1+R2)*VccI EQ=(UBQ-UBEQ)/R4I BQ=IEQ/(1+B)当Rp减小时，U BQ增大，从而I EQ增大，三级管的放大倍数B一般是固定的，所以I BQ遂I EQ的增大而增大；4. 可调电容：调节电路回路的频率与石英晶体振荡器的fs相同。
晶体Crystal振荡电路原理、分类及设计
晶体Crystal振荡电路原理、分类及设计目录1.文档简介 (3)2.晶体振荡电路的工作原理 (3)2.1石英晶体特性 (3)2.2并联型晶体振荡电路 (4)2.3串联型晶体振荡电路 (6)3.时钟的重要参数 (6)4.晶体振荡器种类 (11)4.1普通晶体振荡器 (11)4.2温度补偿晶体振荡器 (12)4.3恒温晶体振荡器 (14)5.CRYSTAL（晶体）电路设计 (14)5.1晶体电路设计器件说明及选择 (15)5.2PCB布局设计 (16)6.晶体常见问题举例 (16)6.1不起振问题分析与解决 (16)6.2频偏过大 (17)7.总结 (17)附录一相关公式推导一 (18)附录二相关公式推导二 (20)1.文档简介本文主要介绍了晶体振荡电路的工作原理，时钟的重要参数，晶体振荡器的种类，晶体电路设计及晶体常见问题的举例。
2.晶体振荡电路的工作原理晶体（石英晶体）振荡电路主要由主振电路和石英谐振器组成，主振电路将直流能量转换成交流能量，振荡器频率主要取决于石英晶体谐振器。
振荡电路一般采用反馈型电路，按晶体在振荡电路中的作用，又可以分为串联型晶体振荡电路和并联型晶体振荡电路。
本章首先介绍石英晶体的特性，然后分别介绍并联型晶体振荡电路和串联型晶体振荡电路的结构及工作原理。
2.1石英晶体特性晶体（石英晶体）之所以能作为振荡器产生时钟，是基于它的压电效应：所谓的压电效应是指电和力的相互转化，即，如果在晶体的两端施加压缩或拉伸的力，晶体的两端会产生电压信号；同样的，在晶体的两端施加电压信号，晶体会产生形变。
而且这种转化在某特定的频率上效率最高，此频率（由晶片的尺寸和形状决定）即为晶体的谐振频率。
实际应用的晶片是由石英晶体按一定的方向切割而成的，晶片的形状可以各种各样，如方形、矩形或圆形等。
由于晶体的物理性质存在各向差异性，相同的晶体按不同晶格方向切下的晶片，会产生不同的物理特性。
因此，晶体的切割方法是非常重要的，对石英晶体来说，有AT/BT/DT/GT/IT/RT/FC/SC等不同的切法，要根据具体的需求选择相应的切法切割晶片，其中最常用的有AT切和SC切。
晶振电路设计
晶振电路设计
晶振电路是一种基础的时钟电路，其作用是提供可靠的、稳定的
时钟信号，用于驱动数字电路中的各种功能模块。
晶振电路的基本结
构包括晶振、共振电路和衰减补偿电路。
【晶振】
晶振是晶体振荡器的简称，是一种可以自发振荡的元器件。
晶振
的种类很多，常用的有二极管晶振、石英晶振、陶瓷晶振等。
在电路
设计中，需要根据具体的应用环境选择不同种类的晶振。
【共振电路】
共振电路是一种特殊的电路结构，可以使晶振产生强烈的振荡。
共振电路由电容器和电感器组成，通常称为谐振电路。
在晶振电路中，共振电路的设计非常关键，其参数的选择将直接影响电路的性能。
【衰减补偿电路】
衰减补偿电路是晶振电路中一个非常重要的组成部分，其作用是
为共振电路提供一定程度的电阻性质。
衰减补偿电路主要由电阻和电
容器组成，可以根据所需的衰减程度进行参数的选择。
综上所述，晶振电路的设计需要考虑多种因素，包括晶振的类型、共振电路的参数、衰减补偿电路的设计等。
在进行电路设计时，需要
根据具体的应用需求进行参数选择和优化。
晶体振荡器电路+PCB布线设计指南
AN2867应用笔记ST微控制器振荡器电路设计指南前言大多数设计者都熟悉基于Pierce(皮尔斯)栅拓扑结构的振荡器，但很少有人真正了解它是如何工作的，更遑论如何正确的设计。
我们经常看到，在振荡器工作不正常之前，多数人是不愿付出太多精力来关注振荡器的设计的，而此时产品通常已经量产；许多系统或项目因为它们的晶振无法正常工作而被推迟部署或运行。
情况不应该是如此。
在设计阶段，以及产品量产前的阶段，振荡器应该得到适当的关注。
设计者应当避免一场恶梦般的情景：发往外地的产品被大批量地送回来。
本应用指南介绍了Pierce振荡器的基本知识，并提供一些指导作法来帮助用户如何规划一个好的振荡器设计，如何确定不同的外部器件的具体参数以及如何为振荡器设计一个良好的印刷电路板。
在本应用指南的结尾处，有一个简易的晶振及外围器件选型指南，其中为STM32推荐了一些晶振型号(针对HSE及LSE)，可以帮助用户快速上手。
目录ST微控制器振荡器电路设计指南目录1石英晶振的特性及模型32振荡器原理53Pierce振荡器64Pierce振荡器设计74.1反馈电阻R F74.2负载电容C L74.3振荡器的增益裕量84.4驱动级别DL外部电阻R Ext计算84.4.1驱动级别DL计算84.4.2另一个驱动级别测量方法94.4.3外部电阻R Ext计算 104.5启动时间104.6晶振的牵引度(Pullability) 10 5挑选晶振及外部器件的简易指南 11 6针对STM32™微控制器的一些推荐晶振 126.1HSE部分126.1.1推荐的8MHz晶振型号 126.1.2推荐的8MHz陶瓷振荡器型号 126.2LSE部分12 7关于PCB的提示 13 8结论141 石英晶振的特性及模型石英晶体是一种可将电能和机械能相互转化的压电器件，能量转变发生在共振频率点上。
它可用如下模型表示：图1石英晶体模型C0：等效电路中与串联臂并接的电容(译注：也叫并电容，静电电容，其值一般仅与晶振的尺寸有关)。
有源晶振（Oscillator）和无源晶振（Crystal）
有源晶振（Oscillator）和⽆源晶振（Crystal）⽆源晶振有⼀个参数叫做负载电容（Load capacitance），负载电容是指在电路中跨接晶振两端的总的外界有效电容。
负载电容是⼯作条件，即电路设计时要满⾜负载电容等于或接近晶振数据⼿册给出的数值才能使晶振按预期⼯作。
⼀般情况下，增⼤负载电容会使振荡频率下降，⽽减⼩负载电容会使振荡频率升⾼。
通过初步的计算发现CL改变1pF，Fx可以改变⼏百Hz。
相关知识点:⼀、什么是负载电容？负载是指连接在电路中的电源两端的电⼦元件负载包括容性负载、阻性负载和感性负载三种。
电路中不应没有负载⽽直接把电源两极相连，此连接称为短路。
常⽤的负载有电阻、引擎和灯泡等可消耗功率的元件。
不消耗功率的元件，如电容，也可接上去，但此情况为断路。
容性负载的含义是指具有电容的性质（充放电，电压不能突变）即和电源相⽐当负载电流超前负载电压⼀个相位差时负载为容性(如负载为补偿电容)。
负载电容是指晶振的两条引线连接ＩＣ块内部及外部所有有效电容之和，可看作晶振在电路中串接了⼀个电容。
图中CI,C2这两个电容就叫晶振的负载电容,分别接在晶振的两个脚上和对地的电容，⼀般在⼏⼗⽪法它会影响到晶振的谐振频率和输出幅度，⼀般订购晶振时候供货⽅会问你负载电容是多少。
晶振的负载电容=[(C1*C2)/(C1+C2)]+Cic+△C式中C1,C2为分别接在晶振的两个脚上和对地的电容,Cic内部电容+△CPCB上电容经验值为3⾄5pf。
因此晶振的数据表中规定12pF的有效负载电容要求在每个引脚XIN 与 XOUT上具有22pF 2 * 12pF = 24pF = 22pF + 2pF 寄⽣电容。
两边电容为C1,C2,负载电容为：Cl,Cl=cg*cd/(cg+cd)+a就是说负载电容15pf的话两边两个接27pf的差不多了。
各种的晶振引脚可以等效为电容三点式。
晶振引脚的内部通常是⼀个反相器, 或者是奇数个反相器串联。
晶体震荡电路的设计与量测
在半導體製程技術的不斷提升下，產品體積大幅縮小，對功能與運算時脈卻更為要求，因此，本文以晶體震盪電路的設計與量測為題，探討相關特性與技術。
由於科技的日新月異，IC內部的複雜度與精確度較從前大幅提升，所需的時脈速度也越來越高，相對的要求時脈的穩定度與精確度也大幅提昇，如何利用晶體（Crystal）來設計與量測所需的振盪電路，已經成為一個重要的課題，以下我們分成幾個部分加以討論。
電氣特性有鑑於其晶體電氣特性的複雜，我們針對晶體的電氣特性或是振盪電路有影響的部分，做一詳細討論，由於陶瓷/晶體的電器特性相似，所以也一併討論。
等效電路陶瓷/晶體雖然在電器特性上有些差異，但是等效電路(圖一)是相同的，雖然陶瓷振動的諧振現像，可以視為與晶體相同，但主要差異在陶瓷振動的振盪頻率，電感L1較小，串聯電容C1相當大，此乃意味著串聯諧振頻率（fs）與並聯諧振頻率（fa）差（即fs-fa）會變得相當寬闊。
圖一Crystal / Ceramic model圖二串聯共振並聯共振當晶體工作在串聯共振時，等效電路(圖二)阻抗在時是趨近於0，好的串聯共振線路設計，與負載電容無關，所以就不需要指定。
當晶體工作在並聯共振時，就像一電感在電路上，因此負載電容就非常重要，因為它可以決定振盪點的位置，如(圖三)所示。
而且電抗改變，頻率也跟隨著改變，所以在不同頻率與間，由、L1決定，在並聯線路的設計上，負載電容是需要指定的，如(圖四)所示。
圖三並聯共振頻率區域圖四並聯共振AT-CUT與BT-CUT典型的AT-CUT曲線是S形，BT-CUT曲線是拋物線形，如(圖五)所示；兩種Cut都對稱於室溫（25℃±3℃）。
在相同的頻率下，BT-CUT的Quartz blank相對的比A-CUT厚，因此提供較好的Yield 與低單價，在選擇適當的切割前，要注意的是他們所擁有的不同移動參數和頻率VS溫度特性。
圖五溫度曲線圖改變負載電容和PullabilityPullability是定義頻率與負載電容的關係，而負載電容是指與晶體串聯或是並聯的電容。
晶振电路的设计原理
晶振电路的设计原理今天来聊聊晶振电路的设计原理。
咱先从生活中的一个现象说起吧。
不知道你有没有留意过摆钟，摆钟下面那个钟摆一下一下很有规律地摆动，滴答滴答地计时。
晶振电路就有点像这个摆钟的机芯，起着提供精准节拍，让整个系统有条不紊运行的作用呢。
晶振，就是晶体振荡器的简称。
通俗来讲，它能以非常精准且稳定的频率产生振动，这个频率就像是音乐里的节拍一样，在电子设备里十分关键。
我一开始接触晶振电路的时候，心里就直犯嘀咕，这么个小小的元件，是怎么做到这么精确的呢？打个比方，晶振就像是一个训练有素的鼓手，它能一直稳定、精确地敲出同一个节奏。
在晶振电路里有一个石英晶体，这是最重要的部分。
石英晶体具有一种很神奇的特性，叫做压电效应。
就好比是你轻轻按一下那种有弹性的东西，它会发生微小的形变，反过来，当对它施加电压的时候，它也会产生振动。
这个振动的频率非常稳定，比咱们人工能控制的要准确得多。
这就要说到晶振电路的设计了。
在设计的时候，得考虑好多因素，就像盖房子得考虑地基稳不稳、结构牢固不牢固一样。
首先，要根据电路需要的频率来选择合适的晶振。
比如说我们常见的一些电子产品，像手机里的晶振频率可能是几十兆赫兹，不同功能模块可能需要不同的频率晶振协同工作。
另外，电路里的电容、电阻等元件的取值也很讲究。
它们就像鼓手旁边的调音师，调试这个节奏的稳定性。
电容的值不合理，就可能导致这个“鼓手”敲出来的节拍不准。
在实际应用中，晶振电路无处不在。
就拿电脑主板来说吧，上面的晶振电路为CPU、各种芯片以及接口等提供时钟信号。
如果晶振电路出了问题，电脑可能就出现死机、程序无法运行等各种乱七八糟的问题。
老实说，我还在继续学习晶振电路的设计原理。
有时候也会遇到一些很困惑的现象，比如温度对晶振频率的影响。
温度可能会让石英晶体的参数发生一些细微变化，就像天气太热或太冷的时候，鼓手的状态可能也会有一点点不同。
这个时候可能就需要一些更特殊的设计或者矫正措施来保证晶振电路的准确性，不过这部分我还不是特别精通呢。
晶体振荡器设计报告
晶体振荡器设计报告晶体振荡器设计报告班级姓名学号年月日一、设计方案论证振荡器常用于高频发射机和接收机，频率稳定性是衡量振荡器性能的重要参数之一，而石英晶体因其频率的高稳定性得到广泛的应用，依据右图所示的晶体的电抗特性曲线，在串并联谐振频率之间很狭窄的工作频带内，它呈现电感性，因而石英谐振器或者工作在感性区，或者工作于串联谐振频率上，不能工作在容性区，因为此时无法判断晶体是否工作，从而也不能保证频率的稳定度。
因此，根据晶体在电路中的作用原理，振荡器可分为两类：一类是石英晶体在振荡器线路中作为等效电感元件使用，称为并联谐振型晶体振荡器；另一类是把石英晶体作为串联谐振元件使用，使它工作于串联谐振频率上，串联谐振型晶体振荡器。
1. 晶体振荡器连接方式的选取并联谐振c-b型晶体振荡器的典型电路如右图所示。
振荡管的基极对高频接地，晶体管接在集电极和基极之间，C2与C5为回路的另外两个电抗元件，它类似于克拉泼振荡器，晶体振荡器的谐振回路与振荡管之间的耦合电容非常弱，从而使频率稳定性大大提高，因此本设计实验采用这种连接方案。
2. 输出缓冲级设计输出缓冲级主要完成对所产生的振荡信号进行输出，不管是并联谐振晶振电路还是串联谐振晶振电路，它们的带负载能力都不是很强，负载值改变时可能造成振荡器的输出频率变化，也可能影响振荡器的输出幅度，输出缓冲级的作用就是提高整个振荡器的带负载能力，即使得振荡器的输出特性不受负载影响，或影响较小。
常用的输出缓冲级是在电路的输出端加一射极跟随器，从而提高回路的带负载能力。
设计跟随器的特点是输入阻抗高，输出阻抗低，电压放大倍数略低于1，带负载能力强，具有较高的电流放大能力，它可以起到阻抗变换和级间隔离的作用，因而可以减小负载对于振荡回路的影响，射极跟随器的典型电路如右图所示。
3. 系统原理图设计依据各部分的方案设计并结合设计要求，综合考虑各种影响因素，设计系统原理图如下图所示。
图中R1和R2分压为三极管T1提供偏置电压，通过改变Rp1阻值的大小可以改变T1的静态工作点，C1用于在振荡器起振时将R1短路从而可以使振荡器正常振荡，C2、C5组成反馈分压，用于为振荡器提供反馈信号，它们与石英晶振共同构成了电容三点式振荡器电路，此时晶体相当于一等效电感，T2连接成射极跟随器，用于提高系统的带负载能力，RL1、RL2、RL3为三组负载。
石英晶体正弦振荡器电路图
石英晶体正弦振荡器电路图
石英晶体正弦振荡器电路图
如图所示电路是由石英谐振晶体SJT和六反相器集成电路CD4069的1个门A构成的正弦波振荡器。
与普通的RC移相振荡器相比，晶体振荡器的频率稳定度可高达10-5或更高。
这是RC移相振荡器无法达到的高指标(RC移相振荡器的频率稳定度只能达到10-2的量级)。
CMOS非门与负反馈偏置电阻Rl构成反相放大电路。
石英晶体SJT与Cl、C2构成7c型正反馈支路。
石英晶体在其固有谐振频率的附近，自身呈感性，此电感与电容Cl、C2构成谐振回路，形成选频移相反馈网络反馈到放大器输入端，产生振荡。
调整电容C2可微调振荡频率。
元器件选择：
六反相器集成块A：CD4069。
电容Cl：20pF，C2：3～22pF，C3：1000pF。
电阻Rl：10MΩ。
石英晶体SJT：32．768kHz。
电路连接方法：
六反相器集成电路CD4069只用了1／6个门，剩余门若无它用可将输入端接VDD或VSS，输出端悬空。
14脚(VDD)接正电源，7脚(VSS)接地。
Oscillator introduction & 晶振电路介绍
LC Oscillator IntroductionOscillators are used in many electronic circuits and systems providing the central "clock" signal that controls the sequential operation of the entire system. Oscillators convert a DC input (the supply voltage) into an AC output (the waveform), which can have a wide range of different wave shapes and frequencies that can be either complicated in nature or simple sine waves depending upon the application. Oscillators are also used in many pieces of test equipment producing either sinusoidal sine waves, square, sawtooth or triangular shaped waveforms or just a train of pulses of a variable or constant width. LC Oscillators are commonly used in radio-frequency circuits because of their good phase noise characteristics and their ease of implementation.An Oscillator is basically an Amplifier with "Positive Feedback", or regenerative feedback (in-phase) and one of the many problems in electronic circuit design is stopping amplifiers from oscillating while trying to get oscillators to oscillate. Oscillators work because they overcome the losses of their feedback resonator circuit either in the form of a capacitor, inductor or both in the same circuit by applying DC energy at the required frequency into this resonator circuit. In other words, an oscillator is a an amplifier which uses positive feedback that generates an output frequency without the use of an input signal. It is self sustaining.Then an oscillator has a small signal feedback amplifier with an open-loop gain equal too or slightly greater than one for oscillations to start but to continue oscillations the average loop gain must return to unity. In addition to these reactive components, an amplifying device such as an Operational Amplifier or Bipolar Transistor is required. Unlike an amplifier there is no external AC input required to cause the Oscillator to work as the DC supply energy is converted by the oscillator into AC energy at the required frequency.Basic Oscillator Feedback CircuitWhere: β is a feedback fraction.Without FeedbackWith FeedbackOscillators are circuits that generate a continuous voltage output waveform at a required frequency with the values of the inductors, capacitors or resistors forming a frequency selective LC resonant tank circuit and feedback network. This feedback network is an attenuation network which has a gain of less than one ( β<1 ) and starts oscillations when Aβ >1 which returns to unity ( Aβ =1 ) once oscillations commence.The LC oscillators frequency is controlled using a tuned or resonant inductive/capacitive (LC) circuit with the resulting output frequency being known as the Oscillation Frequency. By making the oscillators feedback a reactive network the phase angle of the feedback will vary as a function of frequency and this is calledPhase-shift.There are basically types of Oscillators∙ 1. Sinusoidal Oscillators - these are known as Harmonic Oscillators and are generally a "LC Tuned-feedback" or "RC tuned-feedback" type Oscillator that generates a purely sinusoidal waveform which is ofconstant amplitude and frequency.∙∙ 2. Non-Sinusoidal Oscillators - these are known as Relaxation Oscillators and generate complex non-sinusoidal waveforms that changes very quickly from one condition of stability to another such as "Square-wave", "Triangular-wave" or "Sawtoothed-wave" type waveforms.ResonanceWhen a constant voltage but of varying frequency is applied to a circuit consisting of an inductor, capacitor and resistor the reactance of both the Capacitor/Resistor and Inductor/Resistor circuits is to change both the amplitude and the phase of the output signal as compared to the input signal due to the reactance of the components used. At high frequencies the reactance of a capacitor is very low acting as a short circuit while the reactance of the inductor is high acting as an open circuit. At low frequencies the reverse is true, the reactance of the capacitor acts as an open circuit and the reactance of the inductor acts as a short circuit. Between these two extremes the combination of the inductor and capacitor produces a "Tuned" or "Resonant" circuit that has a Resonant Frequency, (ƒr) in which the capacitive and inductive reactance's are equal and cancel out each other, leaving only the resistance of the circuit to oppose the flow of current. This means that there is no phase shift as the current is in phase with the voltage. Consider the circuit below.Basic LC Oscillator Tank CircuitThe circuit consists of an inductive coil, L and a capacitor, C. The capacitor stores energy in the form of an electrostatic field and which produces a potential (static voltage) across its plates, while the inductive coil stores its energy in the form of an electromagnetic field. The capacitor is charged up to the DC supply voltage, V by putting the switch in position A. When the capacitor is fully charged the switch changes to position B. The charged capacitor is now connected in parallel across the inductive coil so the capacitor begins to discharge itself through the coil. The voltage across C starts falling as the current through the coil begins to rise. This rising current sets up an electromagnetic field around the coil which resists this flow of current. When the capacitor, C is completely discharged the energy that was originally stored in the capacitor, C as an electrostatic field is now stored in the inductive coil, L as an electromagnetic field around the coils windings.As there is now no external voltage in the circuit to maintain the current within the coil, it starts to fall as the electromagnetic field begins to collapse. A back emf is induced in the coil (e = -Ldi/dt) keeping the current flowing in the original direction. This current now charges up the capacitor, C with the opposite polarity to its original charge. C continues to charge up until the current reduces to zero and the electromagnetic field of the coil hascollapsed completely. The energy originally introduced into the circuit through the switch, has been returned to the capacitor which again has an electrostatic voltage potential across it, although it is now of the opposite polarity. The capacitor now starts to discharge again back through the coil and the whole process is repeated. The polarity of the voltage changes as the energy is passed back and forth between the capacitor and inductor producing an AC type sinusoidal voltage and current waveform. This then forms the basis of an LC oscillators tank circuit and theoretically this cycling back and forth will continue indefinitely. However, every time energy is transferred from C to L or from L to C losses occur which decay the oscillations.This oscillatory action of passing energy back and forth between the capacitor, C to the inductor, L would continue indefinitely if it was not for energy losses within the circuit. Electrical energy is lost in the DC or real resistance of the inductors coil, in the dielectric of the capacitor, and in radiation from the circuit so the oscillation steadily decreases until they die away completely and the process stops. Then in a practical LC circuit the amplitude of the oscillatory voltage decreases at each half cycle of oscillation and will eventually die away to zero. The oscillations are then said to be "damped" with the amount of damping being determined by the quality or Q-factor of the circuit.Damped OscillationsThe frequency of the oscillatory voltage depends upon the value of the inductance and capacitance in the LC tank circuit. We now know that for resonance to occur in the tank circuit, there must be a frequency point were the value of X C, the capacitive reactance is the same as the value of X L, the inductive reactance (X L = X C) and which will therefore cancel out each other out leaving only the DC resistance in the circuit to oppose the flow of current. If wenow place the curve for inductive reactance on top of the curve for capacitive reactance so that both curves are on the same axes, the point of intersection will give us the resonance frequency point, ( ƒr or ωr ) as shown below.Resonance Frequencywhere: ƒr is in Hertz, L is in Henries and C is in Farads.Then the frequency at which this will happen is given as:Then by simplifying the above equation we get the final equation for Resonant Frequency, ƒr in a tuned LC circuit as:Resonant Frequency of a LC Oscillator∙Where:∙L is the Inductance in Henries∙C is the Capacitance in Farads∙ƒr is the Output Frequency in HertzThis equation shows that if either L or C are decreased, the frequency increases. This output frequency is commonly given the abbreviation of ( ƒr ) to identify it as the "resonant frequency".To keep the oscillations going in an LC tank circuit, we have to replace all the energy lost in each oscillation and also maintain the amplitude of these oscillations at a constant level. The amount of energy replaced must therefore be equal to the energy lost during each cycle. If the energy replaced is too large the amplitude would increase until clipping of the supply rails occurs. Alternatively, if the amount of energy replaced is too small the amplitude would eventually decrease to zero over time and the oscillations would stop.The simplest way of replacing this lost energy is to take part of the output from the LC tank circuit, amplify it and then feed it back into the LC circuit again. This process can be achieved using a voltage amplifier using an op-amp, FET or bipolar transistor as its active device. However, if the loop gain of the feedback amplifier is too small, the desired oscillation decays to zero and if it is too large, the waveform becomes distorted.To produce a constant oscillation, the level of the energy fed back to the LC network must be accurately controlled. Then there must be some form of automatic amplitude or gain control when the amplitude tries to vary from a reference voltage either up or down. To maintain a stable oscillation the overall gain of the circuit must be equal to one or unity. Any less and the oscillations will not start or die away to zero, any more the oscillations will occur but the amplitude will become clipped by the supply rails causing distortion. Consider the circuit below.Basic Transistor LC Oscillator CircuitA Bipolar Transistor is used as the LC oscillators amplifier with the tuned LC tank circuit acts as the collector load. Another coil L2 is connected between the base and the emitter of the transistor whose electromagnetic fieldis "mutually" coupled with that of coil L. Mutual inductance exists between the two circuits. The changing current flowing in one coil circuit induces, by electromagnetic induction, a potential voltage in the other (transformer effect) so as the oscillations occur in the tuned circuit, electromagnetic energy is transferred from coil L to coil L2 and a voltage of the same frequency as that in the tuned circuit is applied between the base and emitter of the transistor.In this way the necessary automatic feedback voltage is applied to the amplifying transistor.The amount of feedback can be increased or decreased by altering the coupling between the two coils L and L2.When the circuit is oscillating its impedance is resistive and the collector and base voltages are 180o out of phase.In order to maintain oscillations (called frequency stability) the voltage applied to the tuned circuit must be"in-phase" with the oscillations occurring in the tuned circuit. Therefore, we must introduce an additional 180o phase shift into the feedback path between the collector and the base. This is achieved by winding the coil of L2 in the correct direction relative to coil L giving us the correct amplitude and phase relationships for the Oscillators circuit or by connecting a phase shift network between the output and input of the amplifier.The LC Oscillator is therefore a "Sinusoidal Oscillator" or a "Harmonic Oscillator" as it is more commonly called.LC oscillators can generate high frequency sine waves for use in radio frequency (RF) type applications with the transistor amplifier being of a Bipolar Transistor or FET. Harmonic Oscillators come in many different formsbecause there are many different ways to construct an LC filter network and amplifier with the most common being the Hartley LC Oscillator, Colpitts LC Oscillator, Armstrong Oscillator and Clapp Oscillator to name a few.Example No1An inductance of 200mH and a capacitor of 10pF are connected together in parallel to create an LC oscillator tank circuit. Calculate the frequency of oscillation.We can see that by decreasing the value of either the capacitance or the inductance increases the frequency of oscillation of the LC tank circuit.Oscillators SummaryThe basic conditions required for an LC oscillator resonant tank circuit are given as follows.∙ 1. The circuit MUST contain a reactive (frequency-dependant) component either an Inductor, (L) or a Capacitor, (C)and a DC power source.∙∙ 2. In a simple circuit oscillations become damped due to component and circuit losses.∙∙ 3. Voltage amplification is required to overcome these circuit losses and provide gain.∙∙ 4. The overall gain of the amplifier must be greater than one, unity.∙∙ 5. Oscillations can be maintained by feeding back some of the output voltage to the tuned circuit that is of thecorrect amplitude and in-phase, (0o).∙∙ 6. Oscillations can only occur when the feedback is "Positive" (self-regeneration).∙∙7. The overall phase shift of the circuit must be zero or 360o so that the output signal from the feedback network will be "in-phase" with the input signal.In the next tutorial about Oscillators, we will examine the operation of one of the most common LC oscillator circuits that uses two inductance coils to form a centre tapped inductance within its resonant tank circuit. This type of LC oscillator circuit is known commonly as a Hartley Oscillator.The Hartley OscillatorThe main disadvantages of the basic LC Oscillator circuit we looked at in the previous tutorial is that they have no means of controlling the amplitude of the oscillations and also, it is difficult to tune the oscillator to the required frequency. If the cumulative electromagnetic coupling between L1 and L2 is too small there would be insufficient feedback and the oscillations would eventually die away to zero. Likewise if the feedback was too strong the oscillations would continue to increase in amplitude until they were limited by the circuit conditions producing signal distortion. So it becomes very difficult to "tune" the oscillator.However, it is possible to feed back exactly the right amount of voltage for constant amplitude oscillations. If we feed back more than is necessary the amplitude of the oscillations can be controlled by biasing the amplifier in such a way that if the oscillations increase in amplitude, the bias is increased and the gain of the amplifier is reduced. If the amplitude of the oscillations decreases the bias decreases and the gain of the amplifier increases, thus increasing the feedback. In this way the amplitude of the oscillations are kept constant using a process known as Automatic Base Bias.One big advantage of automatic base bias in a voltage controlled oscillator, is that the oscillator can be made more efficient by providing a Class-B bias or even a Class-C bias condition of the transistor. This has the advantage that the collector current only flows during part of the oscillation cycle so the quiescent collector current is very small.Then this "self-tuning" base oscillator circuit forms one of the most common types of LC parallel resonant feedback oscillator configurations called the Hartley Oscillator circuit.Hartley Oscillator Tuned CircuitIn the Hartley Oscillator the tuned LC circuit is connected between the collector and the base of the transistor amplifier. As far as the oscillatory voltage is concerned, the emitter is connected to a tapping point on the tuned circuit coil. The feedback of the tuned tank circuit is taken from the centre tap of the inductor coil or even two separate coils in series which are in parallel with a variable capacitor, C as shown.The Hartley circuit is often referred to as a split-inductance oscillator because coil L is centre-tapped. In effect, inductance L acts like two separate coils in very close proximity with the current flowing through coil section XY induces a signal into coil section YZ below. An Hartley Oscillator circuit can be made from any configuration that uses either a single tapped coil (similar to an autotransformer) or a pair of series connected coils in parallel with a single capacitor as shown below.Basic Hartley Oscillator CircuitWhen the circuit is oscillating, the voltage at point X (collector), relative to point Y (emitter), is 180o out-of-phase with the voltage at point Z (base) relative to point Y. At the frequency of oscillation, the impedance of the Collector load is resistive and an increase in Base voltage causes a decrease in the Collector voltage. Then there is a180o phase change in the voltage between the Base and Collector and this along with the original 180o phase shift in the feedback loop provides the correct phase relationship of positive feedback for oscillations to be maintained.The amount of feedback depends upon the position of the "tapping point" of the inductor. If this is moved nearer to the collector the amount of feedback is increased, but the output taken between the Collector and earth is reduced and vice versa. Resistors, R1 and R2 provide the usual stabilizing DC bias for the transistor in the normal manner while the capacitors act as DC-blocking capacitors.In this Hartley Oscillator circuit, the DC Collector current flows through part of the coil and for this reason the circuit is said to be "Series-fed" with the frequency of oscillation of the Hartley Oscillator being given as.Note: L T is the total cumulatively coupled inductance if two separate coils are used including their mutual inductance, M.The frequency of oscillations can be adjusted by varying the "tuning" capacitor, C or by varying the position of the iron-dust core inside the coil (inductive tuning) giving an output over a wide range of frequencies making it very easy to tune. Also the Hartley Oscillator produces an output amplitude which is constant over the entire frequency range.As well as the Series-fed Hartley Oscillator above, it is also possible to connect the tuned tank circuit across the amplifier as a shunt-fed oscillator as shown below.Shunt-fed Hartley Oscillator CircuitIn the Shunt-fed Hartley Oscillator both the AC and DC components of the Collector current have separate paths around the circuit. Since the DC component is blocked by the capacitor, C2 no DC flows through the inductive coil, L and less power is wasted in the tuned circuit. The Radio Frequency Coil (RFC), L2 is an RF choke which has a high reactance at the frequency of oscillations so that most of the RF current is applied to the LC tuning tank circuit via capacitor, C2 as the DC component passes through L2 to the power supply. A resistor could be used in place of the RFC coil, L2 but the efficiency would be less.Example No1A Hartley Oscillator circuit having two individual inductors of 0.5mH each, are designed to resonate in parallel with a variable capacitor that can be varied from 100pF to 500pF. Determine the upper and lower frequencies of oscillation and also the Hartley oscillators bandwidth.The frequency of oscillations for a Hartley Oscillator is given as:The circuit consists of two inductive coils in series, so the total inductance is given as:Upper FrequencyLower FrequencyOscillator BandwidthHartley Oscillator using an Op-ampAs well as using a bipolar junction transistor (BJT) as the amplifiers active stage of the Hartley oscillator, we can also use either a field effect transistor, (FET) or an operational amplifier, (op-amp). The operation of an Op-amp Hartley Oscillator is exactly the same as for the transistorised version with the frequency of operation calculated in the same manner. Consider the circuit below.Hartley Oscillator Op-amp CircuitThe advantage of constructing a Hartley oscillator using an operational amplifier as its active stage is that the gain of the op-amp can be very easily adjusted using the feedback resistors R1 and R2. As with the transistorised oscillator above, the gain of the circuit must be equal too or slightly greater than the ratio of L1/L2. If the two inductive coils are wound onto a common core and mutual inductance M exists then the ratio becomes(L1+M)/(L2+M).Hartley Oscillator SummaryThen to summarise, the Hartley Oscillator consists of a parallel LC resonator tank circuit whose feedback is achieved by way of an inductive divider. Like most oscillator circuits, the Hartley oscillator exists in several forms, with the most common form being the transistor circuit above with the tuned tank circuit having its coil tapped to feed a fraction of the output signal back to the emitter of the transistor. Since the output of the transistors emitter is always "in-phase" with the output at the collector, this feedback signal is positive. The oscillating frequency which is a sine-wave voltage is determined by the resonance frequency of the tank circuit.In the next tutorial about Oscillators, we will look at another type of LC oscillator circuit that is the opposite to the Hartley oscillator called the Colpitts Oscillator. The Colpitts oscillator uses two capacitors in series to form a centre tapped capacitance in parallel with a single inductance within its resonant tank circuit.The Colpitts OscillatorThe Colpitts Oscillator, named after its inventor Edwin Colpitts is another type of LC oscillator design. In many ways, the Colpitts oscillator is the exact opposite of the Hartley Oscillator we looked at in the previous tutorial. Just like the Hartley oscillator, the tuned tank circuit consists of an LC resonance sub-circuit connected between the collector and the base of a single stage transistor amplifier producing a sinusoidal output waveform.The basic configuration of the Colpitts Oscillator resembles that of the Hartley Oscillator but the difference this time is that the centre tapping of the tank sub-circuit is now made at the junction of a "capacitive voltage divider" network instead of a tapped autotransformer type inductor as in the Hartley oscillator.Colpitts Oscillator CircuitThe Colpitts oscillator uses a capacitor voltage divider as its feedback source. The two capacitors, C1 and C2 are placed across a common inductor, L as shown so that C1, C2 and L forms the tuned tank circuit the same as for the Hartley oscillator circuit. The advantage of this type of tank circuit configuration is that with less self and mutual inductance in the tank circuit, frequency stability is improved along with a more simple design.As with the Hartley oscillator, the Colpitts oscillator uses a single stage bipolar transistor amplifier as the gain element which produces a sinusoidal output. Consider the circuit below.Basic Colpitts Oscillator CircuitThe transistor amplifiers emitter is connected to the junction of capacitors, C1 and C2 which are connected in series and act as a simple voltage divider. When the power supply is firstly applied, capacitors C1 and C2 charge up and then discharge through the coil L. The oscillations across the capacitors are applied to the base-emitter junction and appear in the amplified at the collector output. The amount of feedback depends on the values of C1 and C2 with the smaller the values of C the greater will be the feedback.The required external phase shift is obtained in a similar manner to that in the Hartley oscillator circuit with the required positive feedback obtained for sustained un-damped oscillations. The amount of feedback is determined by the ratio of C1 and C2 which are generally "ganged" together to provide a constant amount of feedback so as one is adjusted the other automatically follows. The frequency of oscillations for a Colpitts oscillator is determined by the resonant frequency of the LC tank circuit and is given as:where C T is the capacitance of C1 and C2 connected in series and is given as:.The configuration of the transistor amplifier is of a Common Emitter Amplifier with the output signal 180o out of phase with regards to the input signal. The additional 180o phase shift require for oscillation is achieved by the fact that the two capacitors are connected together in series but in parallel with the inductive coil resulting in overall phase shift of the circuit being zero or 360o. Resistors, R1 and R2 provide the usual stabilizing DC bias for the transistor in the normal manner while the capacitor acts as a DC-blocking capacitors. The radio-frequency choke (RFC) is used to provide a high reactance (ideally open circuit) at the frequency of oscillation, ( ƒr ) and a low resistance at DC.Example No1A Colpitts Oscillator circuit having two capacitors of 10pF and 100pF respectively are connected in parallel with an inductor of 10mH. Determine the frequency of oscillations of the circuit.The frequency of oscillations for a Colpitts Oscillator is given as:The circuit consists of two capacitors in series, so the total capacitance is given as:The inductor is of 10mH then the frequency of oscillation is:Then the frequency of oscillations for the Oscillator is 527.8kHzColpitts Oscillator using an Op-ampAs well as using a bipolar junction transistor (BJT) as the amplifiers active stage of the Colpitts oscillator, we can also use either a field effect transistor, (FET) or an operational amplifier, (op-amp). The operation of an Op-amp Colpitts Oscillator is exactly the same as for the transistorised version with the frequency of operation calculated in the same manner. Consider the circuit below.Colpitts Oscillator Op-amp CircuitThe advantages of the Colpitts Oscillator over the Hartley oscillators are that the Colpitts oscillator produces a more purer sinusoidal waveform due to the low impedance paths of the capacitors at high frequencies. Also due to these capacitive reactance properties the Colpitts oscillator can operate at very high frequencies even into the microwave region.Colpitts Oscillator SummaryThen to summarise, the Colpitts Oscillator consists of a parallel LC resonator tank circuit whose feedback is achieved by way of a capacitive divider. Like most oscillator circuits, the Colpitts oscillator exists in several forms, with the most common form being the transistor circuit above. The centre tapping of the tank sub-circuit is made at the junction of a "capacitive voltage divider" network to feed a fraction of the output signal back to the emitter of the transistor. The two capacitors in series produce a 180o phase shift which is inverted by another 180o to produce the required positive feedback. The oscillating frequency which is a purer sine-wave voltage is determined by the resonance frequency of the tank circuit.In the next tutorial about Oscillators, we will look at RC Oscillators which uses resistors and capacitors as its tank circuit to produce a sinusoidal waveform.The RC OscillatorIn the Amplifiers tutorial we saw that a single stage amplifier will produce 180o of phase shift between its output and input signals when connected in a class-A type configuration. For an oscillator to sustain oscillations indefinitely, sufficient feedback of the correct phase, ie "Positive Feedback" must be provided with the amplifier being used as one inverting stage to achieve this. In a RC Oscillator the input is shifted 180o through the amplifier stage and 180o again through a second inverting stage giving us "180o + 180o = 360o" of phase shift which is the same as 0o thereby giving us the required positive feedback. In other words, the phase shift of the feedback loop should be "0".In a Resistance-Capacitance Oscillator or simply an RC Oscillator, we make use of the fact that a phase shift occurs between the input to a RC network and the output from the same network by using RC elements in the feedback branch, for example.RC Phase-Shift Network。
石英晶体正弦波振荡器设计
目录第一章振荡器的基本常识 (1)第一节振荡器的分类 (1)第二节振荡产生的原理 (1)一自激振荡的产生 (1)二产生振荡的条件 (2)第三节起振和稳幅 (3)一起振过程 (3)二振幅的稳定 (3)第四节正弦波振荡器 (4)第五节频率稳定度 (5)第二章石英晶体 (6)第一节石英晶体的基本特性 (6)一石英晶体的基本结构 (6)二压电效应 (6)第二节石英晶体等效电路和振荡电路 (7)第三章12MHz石英晶体正弦波振荡器 (10)第一节电路的选择 (10)第二节石英晶体振荡器设计 (10)一主要技术指标 (10)二设计说明........................................... (10)（一）选择电路............................................ .10 （二）选择晶体管和石英晶体. (11)（三）确定直流工作点并计算偏置电路元件参数 (11)（四）求C1\C2\Ct的电容值 (12)心得体会 (13)参考文献 (13)第一章振荡器的基本常识第一节振荡器的分类震荡器（Oscillator）是一种能量转换装置。
它的能量来源一般是直流形式（振荡器电路的直流供电电源）。
经过振荡器转换后，此直流能量转换为一定频率、一定幅度和一定波形的交流能量输出。
这种电能的“转换”过程被称作“振荡”(Oscillation）。
振荡器的作用是产生特定的输出信号，因此也常常被称为信号发生器（signal creator）。
振荡器的类型繁多，按照振荡过程是否依赖于外部激励信号的参与，可以分为他激振荡器和自激振荡器；按照波形分类有正弦波振荡器和非正弦波振荡器；按照振荡器振荡频率的高低，可以分为低频振荡器、高频振荡器、超高频振荡器等；按照振荡器的选频元件分类，则有RC振荡器、LC振荡器、石英晶体振荡器等。
第二节振荡产生的原理一自激振荡的产生无需外加激励就能产生特定波形的交流输出信号，这种振荡电路称为自激振荡器。
一种20MHz低相噪晶体振荡器的设计
I
Abstract
Abstract
The crystal oscillator appeared in 1920s. In last few decades, crystal theory and production technology has great progress, and the crystal performance has been continuously improving. Presently, as a rather satisfying frequency source, the crystal oscillator is more and more taken into application in modern communication systems. Compared with other oscillators, the advantages of crystal oscillators are very obvious, including high natural frequency stability and an excellent phase noise performance, brought by its high Q value. In order to save the cost, improve the phase noise performance of the input reference clock of frequency synthesizer, and achieve the single-chip RF transceiver system, integrating the whole crystal oscillator except for the crystal onto single-chip becomes a trend. This paper first describes the characteristics and the equivalent model of the crystal resonator. The working principle of CMOS crystal oscillator is analyzed, and three basic crystal structures are introduced, whose advantages and disadvantages analyzed. Then important performance indicators, including phase noise and power consumption are introduced. In this paper, Santos structure is employed. The oscillation circuits of Santos structure are analyzed in great details, while both the small-signal model in initial stage and large-signal in stable stage are given. Critical gain, frequency pulling rate and oscillating amplitude are conducted. Finally, some basic theories of phase noise are introduced. In this paper, I designed a 20MHz, low phase noise crystal oscillator, serving as the frequency reference source in frequency synthesizer of UWB RF communication chip. The crystal consists of a quartz crystal resonator, the main oscillator circuits of Santos structure, the amplitude control circuit based on asymmetric differential pair, the band gap voltage reference and output buffer stage. Except for the quartz crystal resonator, all the oscillator circuits are implemented on single-chip. In this paper, given specific consideration in designing each part of the circuits, principle analysis, parameter selection, simulation analysis and phase noise performance optimization are given, respectively. Plenty of design margin are left, given actual non-ideal characteristics of the circuits. Cadence platform of the Spectre, Virtuos and other softwares are employed to accomplish circuit simulation and layout design. Crystal design is based on
晶振工作原理
晶振工作原理
晶振（Crystal Oscillator）是一种用于产生稳定、准确的振荡
信号的电子元件，在许多电子设备和电路中都有广泛应用。
它基于晶体谐振的原理工作。
晶振通常由一个晶体振荡器和电路驱动器组成。
振荡器部分，主要由一个压电晶体和一个集成电路组成。
压电晶体通常采用石英晶体，由于石英晶体具有较高的机械弹性和压电效应，在电场的作用下可以产生机械振动。
而电路驱动器则用来提供压电晶体振荡所需的电源和激励信号。
当电路驱动器向压电晶体提供一个交变电压时，由于压电效应，晶体会产生机械振动。
这种机械振动会在晶体的物理结构中形成一个谐振结构，其频率由晶体的物理特性和结构决定。
当晶体产生振动时，其会通过晶振中的集成电路传递，并被放大。
集成电路会通过一定的反馈机制将放大的信号反馈到晶体上，这样就形成了一个自激振荡的闭环系统。
通过调整集成电路的反馈参数，可以使晶振输出的振荡信号频率保持在一个准确的值上。
晶振的工作频率一般可以通过调整晶振中电路元件的参数来进行调节，从几千赫兹到几百兆赫兹不等。
由于其稳定性高、频率准确、可靠性好的特点，晶振被广泛应用于各类电子设备和系统中，如计算机、通信设备、测量仪器等。
晶振振荡电路的设计
晶振振荡电路的设计1 晶振的等效电气特性 (1) 概念 [1] 晶片，石英晶体或晶体、晶振、石英晶体谐振器 从一块石英晶体上按一定方位角切下薄片。
[2] 晶体振荡器 在封装内部添加IC组成振荡电路的晶体元件称为晶体振荡器。
(2) 晶振的等效电路 Figure1. 晶振的等效电路 Figure 1展示了晶振等效的电路。
R是有效的串联电阻，L和C分别是电感和电容动态元件。
CP 是晶振电极的分流电容。
(3) 晶振等效电路的特殊状态 Figure2是Figure 1电路中的阻抗频率图，不分析得出此图规律的过程(原理)。
Figure2. 晶振的阻抗VS 频率图 [1] 串联谐振频率 根据Figure 2，当晶振工作在串联谐振(《电路基础》)状态(XC=XL)下时电路就似一个纯电阻电路。
串联谐振的频率为： [2] 并联谐振频率 Figure 2中体现了随着频率小范围的升高，Figure1所示电路出现了并联谐振。
此时的频率为fa(不分析电路产生并联谐振的过程)。
[3] 串联谐振与并联谐振之间的频率并联CL的并联谐振 Figure1所示电路有两个谐振点，以频率的高低分其中较低的频率为串联谐振，较高的频率为并联谐振。
由于晶体自身的特性致使这两个频率的距离相当的接近，在这个极窄的频率范围内(fs - fa)，晶振等效为一个电感(不分析WHY)，所以只要晶振的两端并联上合适的电容CL它就会组成新的并联谐振电路。
此时发生并联谐振的频率的计算公式为： MX-COM的所有的晶振振荡器都推荐使用晶振的并联谐振模式。
2 晶振电路的设计 (1) 推荐的晶振振荡器电路 Figure3. 晶振振荡器设计电路 图示中，没在红方框之内部分电路一般都被集成在芯片(如STM3210xxx)内部。
若电阻部分没有被集成在芯片内部，则需要考虑将电阻部分加入。
Rf的值在500KΩ ~ 2MΩ。
图示的C1，C2就是为晶振工作在并联谐振状态下得到加载电容CL的电容。
石英晶体振荡器电路设计
石英晶体振荡器电路设计辽宁工业大学高频电子线路课程设计（论文）题目：石英晶体振荡器电路设计院（系）：电子与信息工程学院专业班级：学号：学生姓名：指导教师：起止时间： 2014.6.16-2014.6.27课程设计（论文）任务及评语院（系）：电子与信息工程学院 教研室： 电子信息工程注：成绩：平时20% 论文质量50% 答辩30% 以百分制计算学 号学生姓名专业班级课程设计（论文）题目石英晶体振荡器电路设计课程设计（论文）任务要求：1．设计一个石英晶体振荡器2．能够观察输入输出波形。
3．观察振荡频率。
参数：振荡频率10000HZ 左右。
设计要求：1 .分析设计要求，明确性能指标。
必须仔细分析课题要求、性能、指标及应用环境等，广开思路，构思出各种总体方案，绘制结构框图。
2 .确定合理的总体方案。
对各种方案进行比较，以电路的先进性、结构的繁简、成本的高低及制作的难易等方面作综合比较，并考虑器件的来源，敲定可行方案。
3 .设计各单元电路。
总体方案化整为零，分解成若干子系统或单元电路，逐个设计。
4 .组成系统。
在一定幅面的图纸上合理布局，通常是按信号的流向，采用左进右出的规律摆放各电路，并标出必要的说明。
指导教师评语及成绩平时成绩(20%)： 论文成绩(50%)： 答辩成绩(30%)：总成绩：学生签字：年 月 日目录第1章绪论 (1)1.1石英晶体振荡器 (1)1.2设计要求 (1)第2章石英晶体振荡器设计电路 (2)2.1石英晶体振荡器总体设计方案 (2)2.2具体电路设计 (2)串联型晶体振荡器 (2)并联型晶体振荡器 (4)输出缓冲级设计 (5)2.3元件参数的计算 (5)2.4Multisim软件仿真 (7)串联型振荡器输出测试 (7)并联型振荡器输出测试 (8)第3章课程设计总结 (9)参考文献 (10)附录Ⅰ总体电路图 (11)附录Ⅱ元器件清单 (12)本科生课程设计（论文）第1章绪论1.1石英晶体振荡器石英晶体振荡器是利用石英晶体即二氧化硅的结晶体的压电效应制成的一种谐振器件，它的基本构成大致是：从一块石英晶体上按一定方位角切下薄片（简称为晶片，它可以是正方形、矩形或圆形等），在它的两个对应面上涂敷银层作为电极，在每个电极上各焊一根引线接到管脚上，再加上封装外壳就构成了石英晶体振荡器，简称为石英晶体或晶体、振荡。
无源晶振emc电路
无源晶振emc电路无源晶振（Passive Crystal Oscillator）是指没有电源输入的晶体振荡器。
它是一种被广泛应用于电子设备中的振荡器，用于产生稳定的时钟信号。
在电磁兼容性（EMC）电路设计中，无源晶振起到了重要的作用。
我们来了解一下晶体振荡器的基本原理。
晶体振荡器是利用晶体的压电效应产生振荡的装置。
晶体具有压电效应，即当施加机械应力时，晶体会产生电荷。
当外部电场作用于晶体时，晶体会发生机械变形。
晶体振荡器利用这种机械变形和电场相互作用的原理，通过正反馈使得晶体不断振荡，产生稳定的频率输出。
无源晶振由晶体振荡器和相关的电路组成。
晶体振荡器由晶体和放大器构成，放大器为晶体提供足够的放大倍数以维持振荡。
晶体振荡器的输出信号经过滤波电路进行滤波处理，以去除高频噪声和谐波。
然后，信号经过分频电路进行分频，得到所需的时钟信号。
无源晶振在EMC电路设计中起到了重要的作用。
EMC是指在电子设备中，各种电磁波（包括辐射和传导）之间的相互影响和干扰。
无源晶振作为电子设备中的时钟信号源，其频率的稳定性对于设备的正常运行具有至关重要的影响。
如果时钟信号的频率不稳定，可能会导致设备运行不正常甚至故障。
因此，在EMC设计中，需要选择合适的无源晶振，并采取相应的措施来提高其频率的稳定性。
为了保证无源晶振的频率稳定性，可以采取以下几种措施。
选择合适的晶体。
晶体振荡器的频率稳定性与晶体的质量有关。
质量较好的晶体具有较小的温度漂移和较高的频率稳定性。
因此，在选择晶体时，需要考虑晶体的质量因素，以确保无源晶振的频率稳定性。
设计合理的电路。
无源晶振的电路设计也会影响其频率稳定性。
在设计电路时，需要考虑电源的稳定性、温度补偿等因素，以减小对晶体振荡频率的影响。
还可以采取屏蔽措施。
由于无源晶振是一个振荡器，其输出信号会辐射到周围空间中。
这些辐射信号可能会对其他电子设备产生干扰。
为了减小辐射干扰，可以在晶体振荡器周围设置屏蔽罩或屏蔽材料，以降低辐射信号的强度。
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C2 C1
1 Ø= ωC3 1 + C C1+C2 3 C1C2
+
willy.sansen
C3
B
1 Im ≈ gm = ∞ ∞ ωC3
9-01C43 23
Design criteria
Im -Rs 0 A gm ImA = gmopt Ø= 1 gm = 0 Re Im0 ≈ ≈ Im0 ω sC s 1 ωC3 1 + C C1+C2 3 C1C2 B 1 Im ≈ gm = ∞ ∞ ωC3 2p 1 ω(C3 +
C3 gm C1 Ls C2 Cs Rs Zs Barkhausen : Zs + Zc = 0 Re (Zc) = -Rs 2p Im (Zc) = yields f or p yields gm
Hale Waihona Puke LEUVENC3 = Cp + CDG
C3 C2 gm Zc Zs = Rs + j C1 2p ωCs
willy.sansen
9-01C43 2
The Barkhausen criterium
LEUVEN
F(jω)
Vout = A(jω) Vε Vf = F(jω) Vout = F(jω) A(jω) Vε Vf Vε = A(jω) F(jω)
Vf Vin
Σ A(jω)
Vε Vout
Oscillation if Vin = 0 or if
x Oscillation x Crystals x Single-transistor
LEUVEN
principles oscillator x MOST oscillator circuits x Bipolar-transistor oscillator circuits x Other oscillators
LEUVEN
Design of crystal oscillators
Willy Sansen
KULeuven, ESAT-MICAS Leuven, Belgium
willy.sansen@esat.kuleuven.ac.be willy.sansen
9-01C43 1
Table of contents
LEUVEN
C1C2 C1+C2
)
Small p : Large C1,2 Large circle: Small C3
willy.sansen
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Complex plane for 3-pt oscillator
LEUVEN
-6 kΩ Re Im0 ≈ - 4 kΩ 2pA ωCs pA = A gm = 0 ImA = gmopt ≈ 3 mS Ø = 12 kΩ
LEUVEN
Im | |= | | φ Re Re = | | cos (φ) Im = | | sin (φ)
willy.sansen
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Re 2 + Im 2 Im Re
tg(φ) =
Table of contents
x Oscillation x Crystals x Single-transistor
Zs (s) = s[s2 s2LsCs+ sRsCs+ 1 LsCsCp Cs+Cp |Zs (s)| 1 Cps Rs fs fp f +s RsCsCp Cs+Cp + 1](Cs+Cp)
LEUVEN
willy.sansen
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Crystal impedance at resonance
fp = 89.000 kHz pp = 0.25 %
fs
=
1+
Cs Cp
Cp
fm = 88.850 kHz pm = 0.125 % fs = 88.700 kHz
kHz
≈ 1+
Cs 2Cp fp- fs pp = Cs 2Cp fs = 0.25 %
willy.sansen
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pm = fs 4Cp
LEUVEN
d
fs = εr ≈ 4.5 1 Ls Cs 1 Csωs fs =
fs in MHz if d in mm
quartz
1.66 d ε0 εr Cp = A d
(series)
Ls
L s ωs =
Cs Rs
ωs =
2
1 2π Ls Cs Q ωs = 1 RsCs
Cp (package, parallel)
Polar diagram of RC network - 4
Z R C
Im 0
ω=∞
LEUVEN
R
ω=0
Re
1
Z
r R
R Z= 1 + RCjω
0
r C
ω=∞
R+r
ω=0
Re
R Z=r+ 1 + RCjω
ω=
1 RC
willy.sansen
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Polar diagram of RC network - 5
Q=
1 Rs
Ls Cs
Rs =
1 Q Cs ω s
willy.sansen
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Crystal parameters
Ls Cs Rs
Q = 105
LEUVEN
Xtal : fs = 10 MHz
Cs = 0.03 pF
Cp
L s ωs =
fs 100 kHz 1 MHz 10 MHz
Cp ≈ 6 pF (≈ 200 Cs) 1 Csωs
series
LEUVEN
ωp =
2
1 Ls
(
+ ) Cp Cs
parallel
1
1
(ω s
ω
ωs ω
)
Frequency pulling factor p= ω
- ωs
ωs
willy.sansen
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Series and parallel resonance - 2
LEUVEN
fp
LEUVEN
principles oscillator x MOST oscillator circuits x Bipolar-transistor oscillator circuits x Other oscillators
willy.sansen
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Crystal as resonantor
Amplitude of oscillation
ids Ids IDSA t Vgs = Ids gmA = Ids IDSA IDSA gmA V -V 2 … 2 GS T π 2 Vgs ≈ VGS - VT or 2n Ids IDSA
ωCs
Ref. Vittoz, JSSC June 88, 774-783
willy.sansen
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Complex plane for 3-pt oscillator
LEUVEN
Im -Rs 0 Re Im0 ≈ 2p ω sC s ≈ Im0 ω(C3 + 1 C1C2 C1+C2 ) A gm = 0 ImA = gmopt 1 gm
-80 Ω -Rs 0
Im
C1 = C2 = 3 pF C3 = 0.5 pF 20 MHz 80 Ω
1 2 (C3 + C1C2 C1+C2 ) gmA ≈ ωs2RsC1C2
≈ 11 µS
gmB ≈ 450 mS B
gm = ∞ Im∞ ≈ - 16 kΩ
willy.sansen
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willy.sansen
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Single-transistor X-tal oscillator
LEUVEN
C3 gm C1 C2 C3 gm C1
Colpitts Pierce : 1-pin X=D
C2
Basic three-point oscillator
C3 gm C1
C2
LEUVEN
C3 = Cp + CDG
C3 C2 gm Zc Zs = Rs + j C1 2p ωCs
ωCs
Ref. Vittoz, JSSC June 88, 774-783
willy.sansen
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Polar diagram of RC network - 1
LEUVEN
Z R
LEUVEN
Oscillation if Re (Zcirc+Zres) = 0 sets the minimum gain ! Im (Zcirc+Zres) = 0 sets the frequency !
willy.sansen
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Amplitude, phase, Real & Imaginary
LEUVEN
|Z|
100 kΩ
fp Cs = 12.2 fF Ls ≈ 0.52 H Cp = 4.27 pF
fs = 1.998 MHz
100 Ω
fs
90o induct.
Rs = 82 Ω
Φ(Z) 100o
0o
Crystal operates in inductive region if circuit is capacitive !