Statek低頻振蕩器設(shè)計的比較

Comparison of Low Frequency Oscillator Designs
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. 

Statek低頻振蕩器設(shè)計的比較

振蕩器類型

晶體控制振蕩器可以分為兩個基本組：正電抗或負電抗。正電抗模式通常稱為“并聯(lián)諧振”或“反諧振”振蕩器。皮爾斯振蕩器是一種通常已知的正電抗振蕩器。負電抗模式通常被稱為串聯(lián)振蕩器。Statek石英晶振是為特定的操作模式而設(shè)計和調(diào)諧的（表1）。

皮爾斯振蕩器

皮爾斯振蕩器（圖1）使用一個具有兩個相移的單個反相器電容器和晶體在反饋回路中提供180ºC相移。晶體的電學(xué)行為就像是一個電感器。振蕩頻率比晶體的串聯(lián)諧振頻率高30ppm至300ppm。如果晶體從電路中移除，石英晶體振蕩器通常會停止振蕩。與串聯(lián)振蕩器相比，皮爾斯振蕩器通常啟動較慢，消耗的電流較少。小型便攜式設(shè)備（電池供電），包括手持數(shù)據(jù)輸入終端，利用皮爾斯振蕩器，

串聯(lián)振蕩器

通常，串聯(lián)振蕩器（圖2）由兩個級聯(lián)反相器組成，貼片晶振晶體連接在第二反相器輸出和第一反相器輸入之間。這種晶體在電學(xué)上表現(xiàn)得就像一個電容器。如果晶體被移除，振蕩器通常將在更高的頻率下自由運行。與皮爾斯振蕩器相比，它的啟動速度更快（通常為100毫秒），并汲取更高的電流。

皮爾斯系列？

晶體或振蕩器類型的選擇主要取決于性能要求。表2總結(jié)了皮爾斯振蕩器和串聯(lián)振蕩器的性能特征。CX-1V晶體具有比CX-1H更高的Q，因為它被密封在抽空的封裝中。CX-1H晶體具有大約3到5倍高的運動電阻（較低的Q），因為它在接近大氣壓的情況下是密封的。

Statek低頻振蕩器設(shè)計的比較

表1。用于基本振蕩電路的推薦Statek晶體