The constant temperature crystal oscillator OCXO (Oven Controlled Crystal Oscillator) is the crystal oscillator with the highest frequency stability and accuracy. It has good performance in aging, temperature stability, long-term stability and short-term stability. As a precise time frequency signal source, it is widely used in electronic instruments such as global positioning system communication, measurement, spectrum and network analyzer. At present, most high stability crystal oscillators adopt the method of crystal constant temperature, and use the precise constant temperature control slot to adjust the temperature in the slot to the zero temperature coefficient point of the crystal resonator. In this way, the effect of temperature on the crystal oscillator frequency can be maximally overcome, and is widely used as a standard frequency source. The constant temperature crystal oscillator includes the following basic components.

恒温晶体振荡器OCXO( Oven Controlled Crystal Oscillator),是目前频率稳定度和精确度最高的晶体振荡器。它在老化率、温度稳定性、长期稳定度和短期稳定度等方面的性能都非常好,作为精密的时频信号源被广泛用于全球定位系统通信、计量、频谱及网络分析仪等电子仪器中。目前,绝大多数高稳定度晶体振荡器都采用了将晶体恒温的方法,使用精密的恒温控制槽,将槽内温度调节到晶体谐振器的零温度系数点上。这样,能最大限度地克服温度对晶体振荡器频率的影响,被广泛用作标准频率源。恒温晶体振荡器包括以下几个基本组成部分。

1.High precision quartz crystal resonator

1.高精度的石英晶体谐振器

Quartz crystal resonator is the core component of oscillator circuit. The correct choice of tangential angle is a necessary condition for making quartz resonators with good frequency and temperature coefficient, especially the quartz resonator used in a wide temperature range. At present, there are two kinds of quartz resonators used in constant temperature crystal oscillator, AT and SC. They have the characteristics of small frequency temperature coefficient, high Q value and low aging effect.

石英晶体谐振器是振荡电路的核心元件。正确选择切角是制作频率温度系数好的石英谐振器的必要条件,特别是在宽温度范围内使用的石英谐振器更是如此。目前恒温晶体振荡器中常用的石英谐振器有AT切和SC切两种。它们具有频率温度系数小,Q值高,老化效应小等特点。

2. stable oscillating circuit

2.稳定的振荡电路

As the constant temperature crystal oscillator requires high frequency stability, the stability of the oscillating circuit itself is also decisive in addition to a certain temperature control precision in the temperature control circuit. The basic function of the oscillating circuit in a thermostatic crystal oscillator is to convert the DC energy into an alternating current with a certain frequency, amplitude and high stability. This conversion is carried out with the participation of quartz resonators. The most prominent problem is the stability of frequency. Therefore, the analysis and design of oscillatory circuits take this as the premise.

由于恒温晶体振荡器要求频率稳定度高,除了在控温电路方面要达到一定的控温精度外,振荡电路本身稳定性也是起决定性作用的。恒温晶体振荡器中振荡电路的基本功能就是把直流电能转变成具有一定频率、幅度且频率高度稳定的交流电能,这种转换是在石英晶体谐振器的参与下进行的。其中最突出的问题就是频率的稳定性。所以分析、设计振荡电路都以此为前提。

3. precision thermostat box with perfect structure and good temperature control

3.结构完善、温控良好的精密恒温箱

The precision thermostat is a constant temperature system composed of thermostat, temperature control circuit and other auxiliary devices. In a crystal oscillator, the quartz resonator and the relevant circuit elements are kept at constant temperature. The function of the quartz resonator is to stabilize the temperature of the quartz resonator at the turning point temperature of the quartz resonator, so as to give full play to the small frequency temperature coefficient of the quartz resonator near the turning point temperature, so that it can be used reasonably. The design of a constant temperature slot which meets the requirements and the selection of a good temperature control circuit plays an important role in stabilizing the frequency. Therefore, a high stable crystal oscillator, not only should have stable oscillating circuit, but also must have a good performance thermostat to ensure the stability of the frequency, both are indispensable. With the gradual improvement of the stability requirements of the crystal oscillator, the demand for temperature control precision of the thermostat is getting higher and higher. At present, the temperature control accuracy of the constant temperature box should be within 0.001 centigrade at the frequency stability of the crystal oscillator at the order of 100~10.
With the continuous improvement of communication technology, the demand for constant temperature crystal vibration is becoming more and more high, making it constantly towards high precision and high stability, low noise and high frequency, low power, fast start, miniaturization.

精密恒温箱是由恒温槽,温度控制电路及其它辅助装置组成的恒温系统。在晶体振荡器中,用来使石英谐振器和有关电路元件保持恒温。其作用是把石英晶体谐振器的温度稳定在石英谐振器的拐点温度处,从而充分发挥拐点温度附近石英谐振器的频率温度系数小的特性,使其得到合理使用。设计一个符合要求的恒温槽和选择一个性能良好的温度控制电路对稳定频率起着举足轻重的作用。因此一个高稳定的晶体振荡器,不但应具有稳定的振荡电路,而且还必须有性能良好的恒温箱来保证其频率的稳定,两者缺一不可。随着对晶体振荡器稳定度要求的逐步提高,对恒温箱的控温精度要求也越来越高,目前,频率稳定度在100~10量级的晶体振荡器,其恒温箱的温度控制精度应在0.001℃以内。

随着通信技术的不断提高,对恒温晶振的要求越来越高,使其不断向着高精度与高稳定化,低噪声与高频化、低功耗、快启动、小型化方向发展。