（晶振49SMD/49S产品图）

Crystal Oscillators have two leads, there is no polarity for crystals and hence can be connected in both directions.
两引线晶振属于晶体谐振器，即无源晶振系列，因此该两引脚没有极性，不具备方向性。

以晶诺威科技产晶振封装HC-49S为例，其主要电气参数如下：

• Load Capacitance负载电容：12 pF、15 pF、18pF、20 pF或定制

• Frequency Tolerance range调整频差范围：± 10ppm~± 30ppm

• Frequency Temperature Stability range频率温度稳定范围：±50ppm

• Resonance Resistance谐振电阻：40 ohms (max)

• Oscillation mode振荡模式：Fundamental mode基频

• Shunt Capacitance静电容：小于7pF

• Drive Level：小于100µW

• Operating Temperature Range工作温度：-20 to + 70°C；-40 to + 85°C

• Storage Temperature Range储藏温度范围: -55 to + 125°C

• Insulation Resistance绝缘阻抗: 500 M ohms

Popular Crystal Oscillators常用频率

8MHz, 11.0592MHz, 12MHz, 16MHz, 20MHz, 25MHz,32MHz等

关于晶体振荡器的简要说明

Crystal Oscillator is an Electronics Oscillator circuit which uses the mechanical resonance of a vibrating crystal of piezoelectric material to generate an electrical signal with an accurate frequency. It also has automatic amplitude control and frequency drift is also very low due to change in temperature. Crystal Oscillators are only suitable for high-frequency application.

晶体振荡器是一种电子振荡器电路，它利用具备压电特性的晶体来产生精确频率信号。它还具有自动幅度控制功能，并且在温度变化下，频率漂移也非常低。晶体振荡器仅适用于高频应用。

Electrical Equivalents等效电路

A crystal oscillator is a piezoelectric device used to convert electrical energy to mechanical energy. The conversion occurs at resonant frequency. The simplified electrical equivalent of crystal oscillator is given below:

晶体振荡器是一种用于将电能转化为机械能的压电器件。转换发生在谐振频率。晶体振荡器的简化等效电路如下所示:

Crystal oscillator works on the principle of the Inverse Piezoelectric Effect, the applied electrical field will generate a mechanical distortion across some material. Therefore, it utilizes the vibrating crystal’s mechanical resonance, which is made through a piezoelectric material for generating an electrical signal of a certain frequency.

晶体振荡器的工作原理是逆压电效应，施加的电场会在某些材料上产生机械变形。因此，它利用振动晶体的机械共振，这是通过压电材料产生一定频率的电信号。

The clock source used for microcontrollers are based on mechanical resonant devices such as crystal oscillator. All microcontrollers have particular pins for connecting crystal oscillator. The pins generally named as XTAL1 and XTAL2, here the connection of crystal oscillator with micro-controller is given below:

用于微控制器（MCU）的时钟源是基于机械谐振器件，如晶体振荡器。所有的微控制器都有用于连接晶体振荡器的特殊引脚。引脚一般命名为XTAL1和XTAL2，在这里晶体振荡器与微控制器的连接如下:

The reason for using two capacitors in series with crystal oscillator is to resonate with the crystal inductance which cause the crystal to oscillate on its fundamental parallel resonant mode.

使用两个电容器与晶体振荡器串联的原因是与晶体电感谐振，从而使晶体在其基频及并联谐振模式下振荡。

There are some factors which affect the frequency stability of an oscillator like variation in temperature, load and supply.
有一些因素会影响振荡器的频率稳定性，如温度、负载和电源的变化。