IQD幾皮法會破壞你的計時準確性LFXTAL052799CUTT
來源：http://www.ytxiaoping.cn 作者：金洛鑫電子 2024年03月08
IQD幾皮法會破壞你的計時準確性LFXTAL052799CUTT
石英晶體因其精確的頻率而廣泛用于電子應(yīng)用中。對高精度時鐘頻率的需求正在增加，特別是由于物聯(lián)網(wǎng)、5G和工業(yè)4.0。然而，在設(shè)計過程中的幾個錯誤就可能破壞石英晶體的整體頻率精度。
負載電容對石英晶振頻率和我的應(yīng)用有什么影響？
根據(jù)應(yīng)用中所需的時序精度，這可能非常重要。電路的電容決定了晶體的諧振頻率。這意味著如果電路中的電容發(fā)生變化，晶體的頻率也會發(fā)生變化。在生產(chǎn)過程中，晶體被校準到其特定負載電容。由此可見，如果電路中的負載電容合適，晶體將在其容差范圍內(nèi)振蕩。然而，負載電容的每次變化都會改變頻率。這意味著在最壞的情況下，晶體將在其容差之外振蕩。
確定晶體頻率將偏移多少的參數(shù)是微調(diào)靈敏度。這表示如果負載電容變化1pF，頻率將變化多少ppm。調(diào)整值可在1ppm/pF至100ppm/pF之間變化，石英水晶振子具體取決于各種因素，如空白的尺寸、電極的尺寸和形狀、頻率以及負載電容。一方面，根據(jù)經(jīng)驗法則，封裝尺寸越大，調(diào)整靈敏度越高。因此，1.6x1.2mm晶體的切邊將小于7.0x5.0mm貼片晶振晶體的切邊。另一方面，你需要記住負載電容越低，調(diào)整就越高。因此，如果一個晶體的負載電容為10pF，另一個晶體的負載電容為20pF，則10pF晶體的調(diào)整會更高。在下圖（圖1）中，您可以看到調(diào)整是如何隨負載電容變化的。
圖1石英晶體的調(diào)整靈敏度取決于負載電容
因此，如果電路中的負載電容與石英晶振的額定負載不同，頻率就會偏移。此外，根據(jù)額定負載電容以及電路中負載與額定負載之間的差異，頻率變化可能會很大。在最壞的情況下，頻率會超出規(guī)格，可能無法在您的應(yīng)用中工作。這就是為什么在設(shè)計過程中更詳細地觀察負載電容如此重要的原因。
IQD幾皮法會破壞你的計時準確性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.
| 進口貼片晶振 | 型號 | 頻率 | 負載電容 | 頻率公差 | 頻率穩(wěn)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 | 進口晶振 | 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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