Now the crystal oscillator is started and stays on 8.000 MHz. You know that this is a little false, don’t you? First, its actual frequency will drift with the ambient temperature. The shape of the temperature-to-frequency curve is not the same for different crystal cuts, but manufacturers ensure that the variation is minimized around the ambient temperature. In a nutshell, you can expect variations around 1 to 10 ppm (parts per million) when the ambient temperature changes by 10°C.

现在，晶体振荡器已启动并可保持在 8.000000MHz，即其内部的石英晶片每秒钟的振动8，000，000次。你知道这有点虚假，不是吗？首先，它的实际频率会随着环境温度而漂移。对于不同的晶体切割，温度-频率曲线的形状并不相同，但制造商确保在环境温度周围将变化降至。简而言之，当环境温度变化10°C时，您可以预期变化约为1到10 ppm（百万分之一）。

There are two solutions if you need a far more stable oscillator. The first one is to add a circuit that will measure the actual ambient temperature, and slightly tune the quartz oscillator with external components such as varicap diodes, based on some knowledge of the theoretical temperature-to-frequency error. Such oscillators, which are called temperature-compensated crystal oscillators (TCXOs), will provide stabilities of 0.1 to 0.5 ppm per 10°C.

如果您需要更稳定的晶体振荡器，有两种解决方案。种是添加一个测量实际环境温度的电路，并根据对理论温度-频率误差的一些了解，使用变分二极管等外部元件稍微调谐石英振荡器。这种振荡器称为温度补偿晶体振荡器（TCXO），可提供每10°C 0.1~0.5 ppm的稳定性。

If you need an even greater stability over temperature, you must pay more for oven-controlled crystal oscillators. The idea is simple. Heat the crystal to a fixed temperature so it will no longer drift if the ambient temperature changes. That is easy to say, but it is more difficult to do, especially for power- or cost-restricted applications.

如果您需要更高的温度稳定性，则需要为选择恒温晶体振荡器（OCXO）。恒温晶体振荡器的工作原理很简单：将晶体加热到固定温度，这样如果环境温度发生变化，晶体将不再漂移。这说起来容易，但做起来却面临难于取舍的问题，特别是对于功率或成本受限的应用。