IQD几皮法会破坏你的计时准确性LFXTAL052799CUTT
来源：http://www.jinluodz.com 作者：金洛鑫电子 2024年03月08
IQD几皮法会破坏你的计时准确性LFXTAL052799CUTT
石英晶体因其精确的频率而广泛用于电子应用中。对高精度时钟频率的需求正在增加，特别是由于物联网、5G和工业4.0。然而，在设计过程中的几个错误就可能破坏石英晶体的整体频率精度。
负载电容对石英晶振频率和我的应用有什么影响？
根据应用中所需的时序精度，这可能非常重要。电路的电容决定了晶体的谐振频率。这意味着如果电路中的电容发生变化，晶体的频率也会发生变化。在生产过程中，晶体被校准到其特定负载电容。由此可见，如果电路中的负载电容合适，晶体将在其容差范围内振荡。然而，负载电容的每次变化都会改变频率。这意味着在最坏的情况下，晶体将在其容差之外振荡。
确定晶体频率将偏移多少的参数是微调灵敏度。这表示如果负载电容变化1pF，频率将变化多少ppm。调整值可在1ppm/pF至100ppm/pF之间变化，石英水晶振子具体取决于各种因素，如空白的尺寸、电极的尺寸和形状、频率以及负载电容。一方面，根据经验法则，封装尺寸越大，调整灵敏度越高。因此，1.6x1.2mm晶体的切边将小于7.0x5.0mm贴片晶振晶体的切边。另一方面，你需要记住负载电容越低，调整就越高。因此，如果一个晶体的负载电容为10pF，另一个晶体的负载电容为20pF，则10pF晶体的调整会更高。在下图（图1）中，您可以看到调整是如何随负载电容变化的。
图1石英晶体的调整灵敏度取决于负载电容
因此，如果电路中的负载电容与石英晶振的额定负载不同，频率就会偏移。此外，根据额定负载电容以及电路中负载与额定负载之间的差异，频率变化可能会很大。在最坏的情况下，频率会超出规格，可能无法在您的应用中工作。这就是为什么在设计过程中更详细地观察负载电容如此重要的原因。
IQD几皮法会破坏你的计时准确性LFXTAL052799CUTT
How a few picoFarads can ruin your timing accuracy
Quartz crystals are widely used in electronic applications because of their accurate frequency. The demand for high precision clock frequencies is increasing, particularly owing to IoT, 5G and Industry 4.0. However, just a few mistakes during the design-in process can ruin the entire frequency accuracy of the quartz crystal.
What influence does load capacitance have on the frequency of the crystal and to my application?
Depending on the required timing accuracy in your application, this can be very important. The capacitance of the circuit defines the resonant frequency of the crystal. This means if the capacitance in the circuit changes, the frequency of the crystal changes as well. During the production process, the crystal is calibrated to its specific load capacitance. From this, it follows that with the right load capacitance in the circuit the crystal will oscillate within its tolerance. However, every change to the load capacitance will shift the frequency. This means that in the worst case scenario the crystal will oscillate outside its tolerance.
The parameter that identifies how much the frequency of the crystal will shift is the trim sensitivity. This shows by how many ppm the frequency will change, if the load capacitance is changed by 1 pF. The value of the trim can vary from 1 ppm/pF up to 100 ppm/pF and it depends on various factors, such as the size of the blank, the size and shape of the electrode, the frequency, as well as the load capacitance. On one hand, you can say as a rule of thumb, that the bigger the package size the bigger the trim sensitivity. Therefore, the trim of a 1.6 x 1.2 mm crystal will be smaller than the trim of a 7.0 x 5.0 mm crystal. On the other hand, you need to keep in mind that the lower the load capacitance, the higher the trim will be. Consequently, if you have a crystal with 10 pF load capacitance and a crystal with 20 pF load capacitance, the trim of the 10 pF crystal will be higher. In the picture below (Figure 1), you can see how the trim varies with the load capacitance.
Figure 1 Trim sensitivity of a quartz crystal depending on the load capacitance
Therefore, if the load capacitance in the circuit differs from the specified load of the crystal, the frequency will shift. In addition, depending on the specified load capacitance and the difference between the load in the circuit and the specified load, the frequency change can be dramatic. In the worst-case scenario, the frequency will be outside of the specification and it may not work in your application. This is why it is so important to look at the load capacitance in more detail during your design process.
| 进口贴片晶振 | 型号 | 频率 | 负载电容 | 频率公差 | 频率稳定性 |
| LFXTAL081314REEL | IQXC-240 | 37.4MHz | 5.00pF | ±7ppm | ±15ppm |
| LFXTAL081316REEL | IQXC-240 | 38.4MHz | 5.00pF | ±7ppm | ±15ppm |
| LFXTAL072539REEL | IQXC-26 | 24.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL078691CUTT | IQXC-26 | 24.0MHz | 20.00pF | ±10ppm | ±30ppm |
| LFXTAL081608CUTT | IQXC-26 | 24.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL081608REEL | IQXC-26 | 24.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL081609CUTT | IQXC-26 | 25.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL083890CUTT | IQXC-26 | 25.0MHz | 20.00pF | ±10ppm | ±20ppm |
| LFXTAL052799CUTT | IQXC-26 | 26.0MHz | 10.00pF | ±10ppm | ±30ppm |
| LFXTAL066742CUTT | IQXC-26 | 26.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL066742REEL | IQXC-26 | 26.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL069296CUTT | IQXC-26 | 26.0MHz | 8.00pF | ±15ppm | ±20ppm |
| LFXTAL070729CUTT | IQXC-26 | 26.0MHz | 12.00pF | ±10ppm | ±15ppm |
| LFXTAL081614CUTT | IQXC-26 | 26.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL081614REEL | IQXC-26 | 26.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL072541CUTT | IQXC-26 | 27.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL072541REEL | 进口晶振 | 27.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL081610CUTT | IQXC-26 | 27.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL072302CUTT | IQXC-26 | 30.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL081612CUTT | IQXC-26 | 30.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL056523CUTT | IQXC-26 | 32.0MHz | 8.00pF | ±20ppm | ±20ppm |
| LFXTAL056523REEL | IQXC-26 | 32.0MHz | 8.00pF | ±20ppm | ±20ppm |
| LFXTAL069526CUTT | IQXC-26 | 32.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL069526REEL | IQXC-26 | 32.0MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL079322CUTT | IQXC-26 | 32.0MHz | 12.00pF | ±10ppm | ±20ppm |
| LFXTAL079322REEL | IQXC-26 | 32.0MHz | 12.00pF | ±10ppm | ±20ppm |
| LFXTAL081613CUTT | IQXC-26 | 32.0MHz | 8.00pF | ±10ppm | ±20ppm |
| LFXTAL083149REEL | IQXC-26 | 32.0MHz | 6.00pF | ±10ppm | ±20ppm |
| LFXTAL072304CUTT | IQXC-26 | 37.4MHz | 8.00pF | ±15ppm | ±15ppm |
| LFXTAL081616CUTT | IQXC-26 | 37.4MHz | 8.00pF | ±10ppm | ±20ppm |
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