Research On Temperature Compensated Crystal Oscillator Of Stress Compensation

The reference frequency sources are the important part of modern electronic Systems and military weapon equipment, whose performance influences the working performance of fighting platforms such as communication and navigation satellite, Doppler radar, precision guided munitions, and electronic countermeasure systems. Crystal oscillators are the widely-used frequency sources, when they are subject to crystal oscillators, temperature variations, frequency stability of the output signals degrade, and the phase noise in the spectrum is also dramatically changed. Traditional compensated crystal oscillators are used to achieve the purpose of frequency compensation by an external auxiliary line. Such compensation method will increase the oscillator power consumption, size and cost.This paper presents a compensation method based on stress, force also make crystal oscillator frequency offset occur, Traditional crystal oscillator should be designed to avoid adverse effects on the force. Stress compensated crystal oscillator takes advantage of the crystal oscillator stress-frequency characteristic to counteract offset generated due to temperature changes, this is the innovation of stress compensation. Since the temperature-frequency curves of AT-cut crystal is cubic curve, and stress-frequency curve is linear, stress compensation method can produce good results within a certain temperature range. Stress compensated crystal oscillator is produced by coating. Expansion coefficient of the metal thin film and crystal are not the same,with metal film plated crystal on a certain shape, the metal film will generate a force on the crystal when the temperature change, Modern coating technology has been very mature. Stress compensated crystal oscillator can be carried out in the crystal production process. By controlling the thickness of the coating can control the size of the compensation amount. In this paper, we are using overtone crystal instead of the traditional fundamental crystal. Overtone crystal has a better force frequency characteristic than the fundamental crystal. At the same time, it can reduce the effects of the crystal oscillator aging rate, noise and other unfavorable factors. This paper describes the theoretical basis and implementation of the method of the temperature compensation of stress compensation crystal oscillator, and a series of experiments associated were carried out. The new temperature compensated crystal oscillator can use AT-cut fundamental crystal, AT-cut overtone crystal and SC-cut overtone crystal. The crystal oscillator can be used not only to broaden the scope of the usable crystal, but also to reduce the frequency offset caused by temperature.Stress Compensation crystal oscillator selects the overtone crystal, the paper focuses on the design of the compensation process. With the use of successive coating, temperature-frequency characteristics will also change. We can get the optimum coating thickness. Bulky, expensive, high power consumption and other issues of traditional digital and microprocessor temperature compensated crystal oscillator are improved with new compensation method. The crystals of stress compensation have higher frequency stability. It will have a good market and bring more economic benefits for the Chinese electronics industry. Therefore, the stress compensated crystal oscillators have better research value and application prospects.