微型的HCMOS输出温补晶振很适合无线物联网应用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.

启动时间是石英晶体振荡器第一次开启的时间。在此期间，将出现不稳定，直到振荡稳定。启动时间通常以微秒 (µS) 为单位，但它取决于频率并由反馈回路控制。闭环增益的大小对启动时间影响很大。对闭环增益产生负面影响的因素包括低驱动电平、较高的晶体电容负载 (CL) 和等效串联电阻 (ESR)。低增益会导致启动时间过长，增益过高会导致启动完全失败或过度驱动晶体结构。理想增益取决于振荡器电路的负电阻，其中驱动器必须克服负电阻才能启动并建立振荡器输出。因此，振荡器频率直接影响启动时间，因此KHz振荡器的循环循环时间比MHz振荡器长得多。增益裕度差是kHz振荡器的常见问题，因为驱动电平低一个数量级，而晶体ESR高一个数量级。为了克服这些问题，需要仔细设计以使驱动电平与合适的CL和 ESR值相匹配。