(TCXO), a voltage controlled crystal oscillator (VCXO), a thermostatically controlled crystal oscillator (OCXO), and a digitized / μp compensated crystal oscillator (TCXO), a temperature controlled crystal oscillator DCXO / MCXO) and several other types. Among them, the temperature-compensated crystal oscillator is the most simple one, in the Japanese industry standard (JIS), called the standard package crystal oscillator (SPXO). SPXO is now an example, a brief introduction to the structure and working principle of quartz crystal oscillator.

Quartz crystal, natural and man-made, is an important piezoelectric crystal material. Quartz crystal itself is not an oscillator, it only by means of active excitation and passive reactivity network can produce oscillation. SPXO is mainly composed of crystal resonators with high quality factor (Q) and crystal oscillator (ie, crystal oscillator) and feedback oscillator circuit. Quartz crystal oscillator is an important component of the oscillator, the crystal frequency (fundamental or nth harmonic frequency) and its temperature characteristics to a large extent depends on its cutting orientation. The basic structure of the quartz crystal resonator, (metal shell) package and its equivalent circuit shown in Figure 1.

As long as the crystal oscillator plate on the application of alternating voltage, it will make the mechanical deformation of the wafer vibration, this phenomenon is the so-called inverse piezoelectric effect. When the applied voltage frequency is equal to the natural frequency of the crystal resonator, piezoelectric resonance occurs, resulting in a sudden increase in the amplitude of the mechanical deformation. In the equivalent circuit of the crystal resonator shown in Fig. 1 (c), Co is a wafer

(A) the structure of the quartz crystal oscillator

(B) Metal shell package diagram (c) Equivalent circuit

And the metal plate between the electrostatic capacitance; L, C for the piezoelectric resonator equivalent parameter; R for the vibration friction loss of the equivalent resistance. The quartz crystal resonator has a series resonant frequency fos (1 / 2π), and there is also a parallel resonant frequency fop (1 / 2π). Since the difference between Co? C, fop and fos is small, and R? ΩOL, R? 1 /? OC, the quality factor Q of the resonant circuit is very high (up to several million), so that the quartz crystal resonator The composition of the oscillator frequency stability is very high, up to 10-12 / day. Quartz crystal oscillator oscillation frequency can be similar to the work in the fos, but also work in the vicinity of fop, so the quartz crystal oscillator can be divided into two types of parallel and parallel. It is easy to understand the working principle of the crystal oscillator by replacing the inductance (L) and capacitance (C) components of the LC oscillator with the quartz crystal resonator and its equivalent circuit.

The total accuracy of the SPXO (including the starting accuracy and the temperature, voltage and load changes) can reach ± 25ppm. SPXO has neither temperature nor temperature control measures, its frequency and temperature characteristics are almost entirely by the quartz crystal oscillator frequency and temperature characteristics of the decision. In the range of 0 ~ 70 ℃, SPXO frequency stability is usually 20 ~ 1000ppm, SPXO can be used as clock oscillator.