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2025-11-09 19:33 本頁(yè)面
【正文】 如前所述，這意味著在振蕩器和外部件之間插入一根電纜。當(dāng)目標(biāo)微控制器不使用本身的振蕩器，而在輸入Xtal1獲得信號(hào)是通過另外的來源，當(dāng)具有TTL驅(qū)動(dòng)能力時(shí)，這個(gè)信號(hào)可用于仿真器。甚至在插入電纜后，會(huì)大大影響振蕩（特別是在高頻下），兩個(gè)低成本的仿真器用不同的方式處理這個(gè)問題。當(dāng)振蕩器不能工作時(shí)，那些晶體管通過Xtal1和Xtal2接地。然而有些微控制器有兩個(gè)板載振蕩器，一個(gè)直接是時(shí)鐘信號(hào)，一個(gè)是PLL時(shí)鐘。在這些情況下，微控制器2的輸入端總與微控制器1的輸出端相連而不是直接與Xtal相連。如圖9中展示了應(yīng)用標(biāo)準(zhǔn)的振蕩器電路應(yīng)用在上面的情況中。他也可用于幅度減少。由于水分的傳導(dǎo)，造成振蕩階段的非對(duì)稱偏差，恰恰這些偏差會(huì)影響振蕩，從而電路引進(jìn)了直流偏移。很顯然回路增益是通過交換兩個(gè)電容器改變的，并且通過分流對(duì)Xtal進(jìn)行補(bǔ)償。在圖5中的電路圖，引用“建議減小558振蕩器的干擾”（見參考），在此電路中，在管腳Xtal2上產(chǎn)生一個(gè)正弦波信號(hào)。 所有的5V的微控制器都由一個(gè)皮爾斯振蕩器（Xtal1,Xtal2)組成并且通過外部Xtal和兩個(gè)電容器實(shí)現(xiàn)振蕩。較小的電阻值允許一個(gè)較大的電容值，反之亦然。當(dāng)電容值和電容值在坐標(biāo)軸上或在下面的區(qū)域，則說明此時(shí)有合適的振蕩。對(duì)于晶體元件的參數(shù)要超過10個(gè)，首先是對(duì)于一個(gè)實(shí)際部件的評(píng)價(jià)不可能包括所有的參數(shù)。 振蕩器和外部元件都產(chǎn)生時(shí)鐘信號(hào)。但其影響的共振頻率非常小。 在外部器件中，頻率的決定性部件是石英晶體。在Xtal2輸出引腳上產(chǎn)生一個(gè)正弦波，跨電導(dǎo)是影響振蕩階段的相關(guān)參數(shù)。dVi/dIo（輸入電壓/輸出電流）定義為振蕩階段的跨電導(dǎo)，用符號(hào)購(gòu)gm表示跨電導(dǎo)，輸入電壓的變化造成輸出電流的變化，單位是A/V或是S（西門子）。它們的主要區(qū)別是在數(shù)字式逆變階段中連接輸入和輸出之間的是一個(gè)集成偏電阻（也稱為：反饋電阻）?！霸鯓哟_保振蕩？”從應(yīng)用的觀點(diǎn)看，這是一個(gè)非常有法律性的問題。本文章不再贅述。 在早期的電子業(yè)上，想要設(shè)計(jì)一個(gè)不震蕩的電路是非常困難的，因?yàn)闆]有可供參考的電路構(gòu)成特性的材料和非常有限的震蕩現(xiàn)象知識(shí)是造成這種結(jié)果的主要原因。APPLICATION NOTEXtal oscillators on 8bit microcontrollersAN96103 SummaryDesigningin 8bit microcontrollers occasionally raises questions regarding the crystal oscillator circuit. The support groups in Eindhoven and Zuerich have gained some experience in responding to these kind of customer questions. This report reflects some of this experience. For engineers in the field as well as development engineers involved in microcontroller based products that do not have specific oscillator knowledge, reading this report may result in some awareness of the oscillator issues making it easier to approach questions on this subject.1. What this note IS and what it is NOT.In the early days of electronics it was quite a challenge to design a circuit that did NOT oscillate. All kinds of unforseen ponent characteristics were the main reason for this, as well as limited knowledge of the oscillation phenomena. Electronics have e a long way since those days and today ponents characteristics are well defined. Oscillation has bee a science and integrating oscillators even more. On the subject of oscillation and of integration of crystal (Xtal)* oscillators there are many scientific publications and courses that provide high level knowledge on this subject. This report will NOT repeat that.In many digital circuits, oscillator circuits are also integrated on the same chip just to provide the clock signal for the digital electronics. Usually only the active parts of the oscillator part is embedded and not the passive frequency determining parts. These parts are usually traditional ponents supplied by other manufacturers. Thissituation is also valid for most currently supplied microcontrollers.“How to assure oscillation?” = a very legal question from the application point of view. This report IS based on application feedback from the field, providing some background and practical knowledge to e closer to the ultimate answer to this question.*(A crystal or quartz in a circuit diagram is very often indicated as Xtal.) oscillator stage.Most microcontroller devices have an oscillator circuit (Xtal1,Xtal2) that will oscillate with an external crystal and external capacitors. The oscillator stage is basically an inverter type gate consisting of a Nchannel and a P channel transistor. The main difference with a digital inverter stage is an integrated bias resistor (also called:feedback resistor) connected between output and input. This (semiconductor) resistor feeds back the output voltage to the input which will balan
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