IQD低频振荡器设计的比较

IQD低频振荡器设计的比较：

Oscillator Types

Crystal-controlled oscillators can be divided into two basic groups: positive reactance or negative reactance. The positive reactance mode is commonly called a “parallel resonant” or “antiresonant” oscillator. A pierce oscillator is one commonly-known positive reactance oscillator. The negative reactance mode is usually referred to as a series oscillator. Statek crystals are designed and tuned for a specific mode of operation (Table 1). 

Pierce Oscillators

The pierce oscillator (Figure 1) utilizes a single inverter, with two phase-shift capacitors and the crystal providing 180ºC phase shift in the feedback loop. The crystal behaves electrically as though it were an inductor. The frequency of oscillation is 30ppm to 300ppm above the series resonant frequency of the crystal. If the crystal is removed from the circuit, the oscillator will usually stop oscillation. Compared to a series oscillator, the pierce oscillator generally starts slower and draws less current. Miniaturized portable equipment (battery powered), including hand held data entry terminals, utilizes the pierce oscillator. 

Series Oscillators

Generally a series oscillator (Figure 2) consists of two cascaded inverters with the crystal connected between the second inverter output and the first inverter input. The crystal behaves electrically as though it were a capacitor. The oscillator will usually free-run at a higher frequency if the crystal is removed. Compared to the pierce oscillator, it starts faster (typically 100 milliseconds) and draws higher current. 

Pierce or Series?

The choice of crystal or oscillator types depends primarily on performance requirements. Table 2 summarizes the performance characteristics of pierce and series oscillators. The CX-1V crystal has a higher Q than the CX-1H because it is sealed in an evacuated package. The CX-1H crystal has approximately 3 to 5 times higher motional resistance (lower Q) because it is hermetically sealed close to atmospheric pressure

IQD低频振荡器设计的比较

振荡器类型

晶体控制振荡器可分为两个基本组：正电抗和负电抗。正电抗模式通常被称为“平行共振”或“反共振”振荡器。穿透振荡器是一种常见的正电抗振荡器。负电抗模式通常被称为串联振荡器。Statek晶体为特定的操作模式设计和调整（表1）。

皮尔斯振荡器

穿透振荡器（图1）采用了一个单一的逆变器，带有两个相移电容和晶体，在反馈回路中提供180ºC的相移。晶体表现得像它是一个电感器。振荡的频率比晶体的串联谐振频率高出30ppm到300ppm石英晶振。如果将晶体从电路中移除，振荡器通常会停止振荡。与串联振荡器相比，穿孔振荡器通常启动速度较慢，吸引的电流更少。小型便携式设备（电池供电），包括手持数据输入终端，利用穿孔振荡器。

系列振荡器

一般是一个串联振荡器（图2）由两个级联逆变器组成，其晶体连接在第二逆变器输出和第一逆变器输入之间。这个晶体的电行为就像它是一个电容器一样。如果晶体被移除，振荡器通常会以更高的频率自由运行。与穿孔振荡器相比，它的启动速度更快（通常是100毫秒），并吸引更高的电流。

皮尔斯还是系列？

晶体或振荡器类型的选择主要取决于性能要求。表2总结了穿透器和串联振荡器的性能特性。CX-1V晶体比CX-1H具有更高的Q，因为它被密封在一个真空封装中。CX-1H晶体具有大约3-5倍的更高的运动阻力（较低的Q），因为它是在接近大气压力时被密封的。

表1基本振荡器电路推荐的州态晶体：