Many engineers do not spend much thought on quartz crystals while designing their oscillator circuit. For them, it is a standard feature that will work anyway. In fact, it’s not that simple.
许多工程师在设计振荡器电路时，并没有花太多心思在石英晶体上。对他们来说，这是一个无论如何都会起作用的标准功能。事实上，事情并没有那么简单。
The oscillator circuit sets the heartbeat of the application and requires a careful matching between the quartz crystal and its other components. Otherwise the accuracy of the generated frequency suffers and the application may even fail in the field.
振荡器电路是设备应用的心跳，我们需要在石英晶体和其他组件之间进行仔细匹配。否则，所生成频率的精度会受到影响，应用设备甚至可能当场失效。
We at Genuway want to spare our customers such problems. Therefore, we do detailed analyses of our customers’ oscillator circuits, aiming at an optimal match between crystal and circuit. The following three parameters are examined in the course of these so called “OSF Tests”:
我们晶诺威科技技术团队真诚希望客户端尽可能避免遇到此类问题。因此，我们会对客户的振荡器电路进行详细分析，旨在实现晶体和电路之间的最佳匹配。在这些所谓的“OSF 测试”过程中，将检查以下三个参数：
1) Frequency Accuracy 频率精度
2) Oscillation Safety Factor (OSF) 振荡安全系数 （OSF）
3) Drive Level 驱动水平/激励功率
Frequency Accuracy 频率精度
The main task of an oscillator circuit is to produce a stable and accurate frequency over the entire application period and under all environmental conditions. For this to succeed the total load capacitance (CL) of the oscillator circuit must be as close as possible to the nominal load capacitance (nominal CL) of the crystal or ideally match it.
振荡器电路的主要任务是在整个应用期间和所有环境条件下产生稳定和准确的频率。为此，振荡器电路的总负载电容 （CL） 必须尽可能接近晶体的标称负载电容（标称 CL）或理想地匹配它。
Accordingly, the first step in the circuit analysis is to determine the total load capacitance (CL) that the quartz crystal “sees” at its two terminals. Since any direct contact with the circuit would falsify the measurement results, the measurement is carried out without contact using a near-field probe that is placed at a small distance above the circuit. The crystal is then soldered out of the circuit and measured with a Crystal Network Analyzer at nominal CL.
因此，电路分析的第一步是确定石英晶体在其两个端子上“看到”的总负载电容 （CL）。由于与电路的任何直接接触都会伪造测量结果，因此，如果可能的话，建议使用近场探头进行无接触测量。然后将晶体从电路中焊接出来，并使用晶体网络分析仪在标称 CL 下进行测量。
The greater the deviation of the total CL from the nominal CL of the crystal, the greater the frequency deviation. However, by examining the crystal in the analyzer, it is possible to determine what corrections are necessary to improve the frequency accuracy of the circuit.
总 CL 与晶体标称 CL 的偏差越大，频率偏差就越大。然而，通过检查分析仪中的晶体，可以确定需要进行哪些校正以提高电路的频率精度。
Oscillation Safety Factor (OSF) 振荡安全系数 （OSF）
In a second step, the oscillation safety of the oscillator circuit is checked. This term describes the circuit’s ability to start up quickly and reliably under all conceivable ambient conditions. The analysis therefore focuses on electronic resistance within the circuit.
在第二步中，检查振荡器电路的振荡安全性。该术语描述了电路在所有可以想象的环境条件下快速可靠地启动的能力。因此，分析的重点是电路内的电阻。
As you can see in Figure 1, a new additional resistor (R Pot) is built into the circuit in series with the quartz. The resistance of R Pot is then increased step by step until the oscillation stops. This method simulates a “worst-case ” and reveals the maximum permissible impedance for the quartz in the particular oscillator circuit.
如图1所示，电路中内置了一个附加电阻器（R），与石英晶体串联。然后逐步增加R电阻，直到振荡停止。该方法模拟“最坏情况”，并体现振荡器电路中石英晶体起振所需要的最大允许阻抗。
Fig. 1: Typical oscillation circuit (Pierce configuration) with an additional resistor to calculate the OSF
图 1：典型振荡电路（Pierce 配置），带有附加电阻器以计算 OSF
The ratio of the maximum impedance determined in this way and the ESR,max of the crystal ultimately results in the oscillation safety factor (OSF).
以这种方式确定的最大阻抗与晶体的 ESR，max 之比最终产生振荡安全系数 （OSF）。
For MHz crystals (AT-Cut), an OSF greater than 5 is considered sufficient for most standard applications. For safety-relevant applications, such as those found in the automotive sector or in medical technology, an OSF greater than 10 is usually required.
对于 MHz 晶体 （AT-Cut），对于大多数标准应用来说，大于5 倍的 OSF 被认为足够了。对于与安全相关的应用，例如汽车行业或医疗技术中的应用，通常需要大于10倍的 OSF。
For KHz crystals, OSF values between 3 and 5 must already be rated as good, and values greater than 5 as very good, due to the design these circuits for very low power consumption.
对于KHz晶体，3到5倍之间的OSF值为良好状态，大于5倍为最佳，因为这些电路的设计功耗非常低。
Drive Level 驱动水平/激励功率
In order to prevent an overload of the quartz, it is determined which power is acting on it. For this purpose, the first step is to measure the strength of the current flowing through the quartz using a HF current clamp (Fig. 2). The “Drive Level” of the quartz is calculated from this measurement result and the parameters of the circuit already determined. The Drive Level must not exceed the maximum value specified in the quartz data sheet.
为了防止石英晶体过驱，我们需要确定有多少功率作用在石英晶体上。为此，第一步是测量流过石英的电流强度（图 2）。石英的“驱动电平”是根据该测量结果和已经确定的电路参数计算得出的。驱动器电平不得超过石英晶体数据表中规定的最大值。
Fig. 2: In order to calculate the Drive Level, the current flowing through the quartz crystal is measured.
图 2：为了计算驱动电平，我们需要测量通过石英晶体的电流。
Exceeding the maximum Drive Level may lead to frequency deviations or, in the worst case, even to failure of the quartz.
超过最大驱动电平可能会导致频率偏差，在最坏的情况下，甚至会导致石英晶体失效。
Adapting the Oscillator Circuit 振荡器电路调整
An oscillator circuit that passes all three tests to satisfaction can be integrated into the intended application . However, if the tests reveal deficits, the circuit must be adapted. For example, if there are problems with frequency accuracy, a variation of the load capacitors in the circuit can reduce the difference between circuit CL and nominal CL of the quartz crystal and thus improve the frequency accuracy. Sometimes it is also necessary to replace the originally installed crystal with another type.
通过所有三项测试，振荡器电路可以集成到预期的应用中。但是，如果测试发现缺陷，则必须调整电路。例如，如果频率精度存在问题，需要对负载电容进行在此精准匹配，从而提高频率精度。有时还需要进行交换实验。
Any change to the circuit means that all the tests listed here must be carried out again. This makes the search for the perfect match between the quartz and the circuit a tinkering job that takes several hours.
对电路的任何更改都意味着在此进行所有上述测试。寻找石英晶体和电路之间的完美匹配，往往是一项需要连续数小时的辛苦且耐心的工作。
After completion of the OSF test, Genuway provides its customers with a detailed test report. This report contains all important measured values and, if required, also contains clear recommendations for adapting the circuit. In this way, any problems are often detected and avoided before series production starts.
完成 OSF 测试后，晶诺威科技为客户提供详细的测试报告。该报告包含所有重要的测量数据。如果需要，还包含调整电路的明确建议。这样，通常可以在批量生产开始之前发现并避免任何问题。
