[introduction] we know, follow the addition of frequency and the impedance of the capacitance below good position is reduced gradually. But in be applied actually, because capacitor is put in equivalent inductance (ESL) and it is on circuit board the installation inductance with constant presence, after frequency rises to a specific value the impedance of capacitance will be reduced no longer, the current that increases gradually however instead changes. This specific frequency is capacitance from syntonic frequency. Before syntonic frequency, capacitor presents the feature that allow a gender, after syntonic frequency, capacitor will present perceptual feature.
We know, follow the addition of frequency and the impedance of the capacitance below good position is reduced gradually. But in be applied actually, because capacitor is put in equivalent inductance (ESL) and it is on circuit board the installation inductance with constant presence, after frequency rises to a specific value the impedance of capacitance will be reduced no longer, the current that increases gradually however instead changes. This specific frequency is capacitance from syntonic frequency. Before syntonic frequency, capacitor presents the feature that allow a gender, after syntonic frequency, capacitor will present perceptual feature.
The characteristic impedance of practical electric capacity states formula is:
Parasitism inductance exists, affected capacitor to be in high frequency paragraph filter baud sex. And the influence that 3 terminal capacitance can carry its distinct structure advantage to improve parasitism inductance thereby, make thereby capacitor is in high frequency paragraph filter baud sex gets ameliorative.
3 terminal piece shape is multilayer following plan institute show the structure of capacitor of pottery and porcelain. Electrode of be well versed in is in the both ends of capacitor, both sides ground connection, every are dielectric among the layer, electrode of be well versed in and ground connection electrode are alternant cascade, form the structure that is similar to the capacitor that wear a heart thereby. A few remain inductance of electrode of be well versed in can rise to be similar to the inductance action of T filter, because this can reduce the effect of parasitism inductance. In addition, because ground connection carries join the distance is shorter, the inductance of this part is very accordingly tiny also. And, because ground connection carries join two end, because this assumes shunt-wound join position, inductance also will reduce an in part.
The principle graph that is 3 terminal capacitance below is enclosed and C0603 reach C0402 enclose. Among them 1, 3 bring a foot to be electrode of be well versed in, can regard power source as end, 2, 4 bring a foot to be GND electrode.
Next graphs are common of capacitance of two terminal pottery and porcelain and capacitance of 3 terminal pottery and porcelain insert loss performance to contrast. Sheet looks from the character of oneself of two kinds of capacitance, their capacitance is identical, because this is characteristic inside low frequency limits identical. But nadir of loss of two terminal capacitor nods accessory in 10MHz frequency, after frequency exceeds 10MHz function begins to drop. And 3 terminal capacitor just appears after exceeding 30MHz function drops. Reason the high frequency character of 3 terminal capacitor is better, the frequency band range of effective filter wave is wider extensive, apply to the Case that high frequency noise disturbs need purify.
Advantage of 3 terminal capacitance one: Low ESL. Because 3 terminal capacitance is put in electrode of two be well versed in and two terrestrial pole, the distance that electric current carries capacitance is shorter, and can have access of wave of filter of 4 electric current, this kind of structure makes the ESL of 3 terminal capacitance inferior, nod from syntonic frequency taller, and character of high frequency attenuation is better. Pass at the same time add thick, shorten method of high frequency circuit can realize lower ESL character.
Advantage 2: Reduce capacitance amount. Use low ESL capacitor, tenability and two terminal capacitor are identical function. Can get better high frequency character at the same time. Pursue as follows graph of impedance of character of a few kinds of capacitance, red is the impedance curve of individual 0.1uF common capacitance, cyan is the impedance curve of individual 1uF common capacitance, green is the impedance curve of the 3 terminal capacitance of individual 1uF, blue is the impedance curve of the common capacitance of 10 0.1uF, the 3 terminal capacitance that can see individual 1uF and 10 common capacitance of 0.1uF are in low frequency Duan Hegao frequency paragraph impedance character curve is same. The two terminal electric capacity that this specification uses 3 terminal capacitance to be able to replace more amount achieves same filter wave result.
Here also tells everybody a good news, village cropland already developed a car to use 1005M (C0402) the 4.3 μ F in dimension capacitor exceeds large electrostatic capacity 3 terminal are multilayer capacitor of pottery and porcelain ” NFM15HC435D0E3 ” , and had begun a quantity produce. Believe to be in before long can face the market to apply in the future.
(origin: High speed gentleman, author: Sun Xiaobing)
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