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微型的HCMOS輸出溫補(bǔ)晶振很適合無線物聯(lián)網(wǎng)應(yīng)用ECS-TXO-2520-33-120-AN-TR，Startup time is the period when an oscillator is first turned on. During this period there will be instabilities until the oscillations stabilize. Start-up time is usually measured in microseconds (µS), but it is frequency dependent and controlled by the feedback loop. The magnitude of the closed loop gain has great influence on the startup time. Factors that negatively affect closed loop gain include the low drive level, higher values of crystal capacitive load (CL), and equivalent series resistance (ESR). Low gain can cause excessively long start-up time, and too high of gain can cause start-up to fail altogether or over drive the crystal structure. The ideal gain is dependent on the negative resistance of the oscillator circuit, where the drive must overcome the negative resistance to start-up and build the oscillator output.  Because of this the oscillator frequency directly influences the start-up time, so the time it takes to circulate the loop is considerably longer for a KHz oscillator than a MHz oscillator. Poor gain margin is a common problem in kHz oscillators, since drive levels are an order of magnitude lower and crystal ESR’s an order of magnitude higher. To overcome these issues careful design is required to match drive levels to suitable CL and ESR values.

The impedance of quartz crystal changes so dramatically with changes in the applied frequency, that all other circuit components can be considered as being of essentially continuous reactance. Consequently, when a crystal unit is used in the feedback loop of an oscillator, the frequency of the crystal unit will regulate itself so that it presents a reactance which satisfies the loop phase gain. A representation of the reactance vs. frequency of a quartz crystal unit is displayed in Figure 3.

啟動時(shí)間是石英晶體振蕩器第一次開啟的時(shí)間。在此期間，將出現(xiàn)不穩(wěn)定，直到振蕩穩(wěn)定。啟動時(shí)間通常以微秒 (µS) 為單位，但它取決于頻率并由反饋回路控制。閉環(huán)增益的大小對啟動時(shí)間影響很大。對閉環(huán)增益產(chǎn)生負(fù)面影響的因素包括低驅(qū)動電平、較高的晶體電容負(fù)載 (CL) 和等效串聯(lián)電阻 (ESR)。低增益會導(dǎo)致啟動時(shí)間過長，增益過高會導(dǎo)致啟動完全失敗或過度驅(qū)動晶體結(jié)構(gòu)。理想增益取決于振蕩器電路的負(fù)電阻，其中驅(qū)動器必須克服負(fù)電阻才能啟動并建立振蕩器輸出。因此，振蕩器頻率直接影響啟動時(shí)間，因此KHz振蕩器的循環(huán)循環(huán)時(shí)間比MHz振蕩器長得多。增益裕度差是kHz振蕩器的常見問題，因?yàn)轵?qū)動電平低一個(gè)數(shù)量級，而晶體ESR高一個(gè)數(shù)量級。為了克服這些問題，需要仔細(xì)設(shè)計(jì)以使驅(qū)動電平與合適的CL和 ESR值相匹配。