低成本的SMD晶體ECS-160-18-5PXEN-TR是一款低損耗無(wú)鉛的環(huán)保晶振，負(fù)載電容是與晶體本身并聯(lián)的外部電路電容的數(shù)量。在這個(gè)例子中，我們看到石英晶振晶體并聯(lián)諧振模式總是高于串聯(lián)諧振頻率，并且以感抗為特征。在并聯(lián)諧振振蕩模式下，晶體的電感（動(dòng)感）與振蕩器的負(fù)載電容并聯(lián)，從而形成一個(gè) LC 諧振電路。該 LC 確定振蕩器頻率。

當(dāng)指定一個(gè)串聯(lián)諧振晶體時(shí)，負(fù)載電容可以忽略不計(jì)，因?yàn)榫w的運(yùn)動(dòng)電感和運(yùn)動(dòng)電容是唯一決定振蕩頻率的 LC 組件。

如果需要精確的頻率控制，則需要精確的負(fù)載電容規(guī)格。為了演示，假設(shè)一個(gè)晶體單元被指定以 20MHz 的頻率工作，容量為 20pF。假設(shè)隨后將晶振單元放置在評(píng)估為 30pF 的電路中。

然后晶體單元的頻率將低于指定值。相反，如果相關(guān)電路的評(píng)估值為 10pF，則頻率將高于指定值。頻率與負(fù)載電容之間的關(guān)系如圖 6 所示。

ECS晶振發(fā)布ECS-160-18-5PXEN-TR，CSM-7X是低成本SMD晶振的絕佳選擇。CSM-7X (5 px)最大外殼高度為4.3毫米。在電阻焊接金屬包裝中。較低的(5PLX)封裝的型材封裝高度為3.2 mm。
成本效益
低姿態(tài)
行業(yè)標(biāo)準(zhǔn)足跡
無(wú)鉛/符合RoHS標(biāo)準(zhǔn)
Load capacitance is the amount of external circuit capacitance in parallel with the crystal itself. In this example we see that the crystals parallel resonance mode is always above the series resonance frequency and is characterized by inductive reactance. In parallel resonance oscillation mode, the crystal's inductance (motional inductance) is in parallel with the oscillator's load capacitance, thereby forming an LC tank circuit. This LC determines the oscillator frequency.

When specifying a series resonant crystal, load capacitance can be ignored since the crystal's motional inductance and motional capacitance are the only LC components that determines oscillation frequency.

For example, where CL1 and CL2 are the load capacitors and CSis the circuit stray capacitance, usually3pF ~ 5pF. It must be noted that changes in the value of the load capacitance will result in changes in the output frequency of the oscillator.

If exact frequency control is needed, then a precise specification of load capacitance is required. To demonstrate, presume that a crystal unit is specified to operate at a frequency of 20MHz with a capacity of 20pF. Assume that the crystal unit is then placed in a circuit which presents an assessment of 30pF.

The frequency of the crystal unit will then be lower than the specified value. Contrarily, should the circuit in question present an assessment of 10pF, the frequency will be higher than the specified value. The association between frequency and load capacitance is shown in Figure 6.