Fox Quartz Crystal設(shè)計(jì)與制作，美國(guó)FOX公司是一家超級(jí)注重于品質(zhì)的元器件供應(yīng)商，為了好的品質(zhì)不惜一切代價(jià)在一個(gè)小細(xì)節(jié)上面死磕，只為了讓用戶好的體驗(yàn)，憑借著精湛的工藝，卓越的性能，過硬的品質(zhì)使得其在行業(yè)之中得到無數(shù)的稱贊，隨著不斷增長(zhǎng)的需求，福克斯公司意識(shí)到新的機(jī)會(huì)來臨，便利用長(zhǎng)期積累的經(jīng)驗(yàn)，針對(duì)新的需求開發(fā)高質(zhì)量低成本的石英晶振，產(chǎn)品具有輕薄小低功耗低損耗的特點(diǎn)，比較適合用于網(wǎng)絡(luò)設(shè)備，智能產(chǎn)品，電子數(shù)碼等領(lǐng)域.

晶體僅在最終應(yīng)用中提供頻率選擇元件。有外部并且需要增益級(jí)來實(shí)現(xiàn)最終所需的時(shí)鐘信號(hào)。這個(gè)晶體頻率范圍通常被認(rèn)為小于160MHz。這個(gè)頻率以上的晶體需要復(fù)雜的電路設(shè)計(jì)，調(diào)諧困難，需要專門的高頻晶體。

需要提供CMOS或BJT增益級(jí)，有許多可接受的配置。這個(gè)該級(jí)的輸入和輸出阻抗會(huì)影響電路Q。放大器噪聲水平會(huì)影響這兩者相位噪聲和抖動(dòng)。該級(jí)如何在有源增益區(qū)偏置對(duì)振蕩器至關(guān)重要啟動(dòng)。此外，該階段的帶寬會(huì)影響啟動(dòng)特性。如果振蕩器電路為了在泛音上操作晶體，放大器中需要一個(gè)頻率選擇裝置電路，以確保電路在所需的晶體泛音處僅具有所需的增益和相移。
振蕩器電路在晶體諧振時(shí)產(chǎn)生交流電流。此交流電流或驅(qū)動(dòng)器液位必須低于臨界值，否則晶體可能會(huì)損壞。過大的電流會(huì)導(dǎo)致晶體運(yùn)動(dòng)超過彈性極限而斷裂。XY切割（音叉）32.768KHz手表晶體必須限制在約5µA或更小，否則晶體的尖端將斷裂。
>1MHz的SMD無源晶體通常是AT切割晶體。這些設(shè)備可以容忍較寬的驅(qū)動(dòng)器級(jí)別范圍在達(dá)到毫瓦驅(qū)動(dòng)水平之前，不會(huì)發(fā)生斷裂。增加的老化可能發(fā)生在更高的µW驅(qū)動(dòng)范圍。過度驅(qū)動(dòng)晶體會(huì)激發(fā)不想要的振動(dòng)模式。這些可以導(dǎo)致在不同的狹窄溫度范圍內(nèi)出現(xiàn)嚴(yán)重的頻率跳躍。
在大多數(shù)情況下，晶體在無功負(fù)載下運(yùn)行。這樣可以調(diào)整最終最終應(yīng)用中的頻率。這通常需要校正頻率變化與水晶的時(shí)間。CLOAD值決定了頻率與負(fù)載電容的靈敏度。AT切割晶體對(duì)于低值可以具有30ppm/pF的靈敏度。使用更高的負(fù)載值電容降低了靈敏度，但增加了振蕩啟動(dòng)的難度。CLOAD溫度特性可以改變振蕩器的頻率對(duì)溫度的響應(yīng)。
晶體的頻率響應(yīng)由晶體穿過原子的切口決定石英晶體的平面。這導(dǎo)致了穩(wěn)定且可重復(fù)的溫度響應(yīng)。這個(gè)曲線圖顯示了AT切割晶體的不同切割的頻率-溫度響應(yīng)。每個(gè)曲線有2分鐘的弧度不同。

每條曲線是通過石英晶體的原子平面的切割的2分鐘弧的變化。

晶體有許多參數(shù)需要指定，以確保接收到符合最終應(yīng)用程序要求。
•頻率
•校準(zhǔn)，設(shè)定點(diǎn)為25°C

•CLOAD
•穩(wěn)定性，頻率與25°C溫度的關(guān)系
•工作溫度范圍
•Cl的最大ESR，晶體諧振電阻
•C0范圍，引腳間電容
•LMOTIONAL或CMOTIONAL，設(shè)置晶體的拉出能力
•驅(qū)動(dòng)級(jí)別
•頻率和電阻的驅(qū)動(dòng)電平依賴性（DLD）
•老化
•絕緣電阻
還有其他規(guī)范，如每°C允許的最大頻率變化，或平滑曲線允許的最大響應(yīng)（擾動(dòng)控制）。

進(jìn)貨檢驗(yàn)或測(cè)試需要專用設(shè)備：
•晶體阻抗計(jì)（CI計(jì)）
•具有特殊測(cè)試夾具和軟件的網(wǎng)絡(luò)分析儀
電路板布局對(duì)于實(shí)現(xiàn)最佳性能至關(guān)重要。以下是一些注意事項(xiàng)：
•導(dǎo)線長(zhǎng)度必須盡可能短。
•晶體引線阻抗高，對(duì)噪聲非常敏感。
•電容器和晶體封裝的接地節(jié)點(diǎn)不得涉及循環(huán)噪聲源的電流。
•如果引線上的泄漏路徑低于500K歐姆，這可能會(huì)影響振蕩器的啟動(dòng)并且還將使頻率偏移多達(dá)幾個(gè)ppm。

有關(guān)CLOAD的設(shè)計(jì)注意事項(xiàng)和選擇的更多信息，請(qǐng)參閱我們的應(yīng)用說明810。

振蕩器包括1-1.7中所述的使用晶體的所有考慮因素。幸運(yùn)的是當(dāng)使用振蕩器時(shí)，可以容易地解決使用晶體操作的復(fù)雜性。
•振蕩器安裝了一個(gè)未完成的晶體，在過程的最后部分，晶體的頻率在室溫下校準(zhǔn)。
•晶體與振蕩器電路的溫度系數(shù)相匹配。水晶改變角度或切口以偏移振蕩器電路的溫度系數(shù)。
•晶體引線通常密封在密封晶體封裝中最大限度地減少最終使用可能改變振蕩器性能的任何機(jī)會(huì)。
使用示波器、頻率可以很容易地測(cè)試或驗(yàn)證振蕩器的性能計(jì)數(shù)器和電源。Fox Quartz Crystal設(shè)計(jì)與制作.
The crystal only provides the frequency selective element in final application. There are external components required, and a gain stage is needed to achieve the final required clock signal. The crystal frequency range is normally considered to be less than 160MHz. Crystals above this frequency require complex circuit designs with difficult tuning and specialized high frequency crystals. 

A CMOS or a BJT gain stage needs to be provided, there are many accepted configurations. The input and output impedance of this stage affects the circuit Q. The amplifier noise level impacts both the phase noise and jitter. How this stage biases in the active gain region is critical for oscillator startup. Also, the bandwidth of this stage affects the startup characteristics. If the oscillator circuit is to operate the crystal on an overtone, then a frequency selective device is needed in the amplifier circuit to assure the circuit only has the needed gain and phase shift at the desired crystal overtone. 

The oscillator circuit results in AC current at the resonance of the crystal. This AC current or drive level has to be below a critical value or a crystal can be damaged. Excessive current can cause the crystal motion to exceed the elastic limit and fracture. The XY cut (tuning fork) 32.768KHz watch crystal has to be limited to about 5µA or less or the tines of the crystal will fracture.

The crystals >1MHz are typically AT cut crystals. These devices are tolerant of a wide drive level range. Fracture will not occur until milliwatt drive levels are reached. Added aging can occur in the higher µW drive ranges. Over driving the crystal can excite unwanted modes of vibration. These can result in severe frequency jumps over vary narrow temperature ranges.  

In most cases, crystals are operated with a reactive load. This permits adjustment of the final frequency in the final application. This is often needed to correct for the frequency change versus time of the crystal. The CLOAD value determines the frequency versus load capacitance sensitivity. AT cut crystals can have a sensitivity of 30ppm/pF for low values. Using higher values of load capacitance reduces sensitivity but increases the difficulty of startup of oscillation. The CLOAD’s temperature characteristics can change the frequency versus temperature response of the oscillator. 

The frequency response of the crystal is determined by the cut of the crystal through the atomic planes of the quartz crystal. This results in a stable and repeatable temperature response. The graph shows the frequency temperature response for different cuts of the AT cut crystal. Each curve is 2 minutes of arc different. 

The CLOAD temperature coefficient can alter this response by many minutes The CLOAD value and the capacitor is critical for the oscillator to meet the desired characteristics. The CSTRAY of the amplifier and the amplifier phase shift change vs. temperature both impact the frequency temperature characteristics.