Illustrated filter capacitance of the use of experience, very detailed, do not believe you do not understand ~

Simple inductance circuit in the low impedance circuit in the use of good results, attenuation of more than 40dB, but in the high impedance circuit may not be a little effect.

The circuit of single capacitor has a good effect in high impedance circuit, but it is very poor in low impedance circuit.

The plurality of components of the filter will have a very good effect, but the premise is that the structure must be correct, the capacitor should be faced with high impedance, inductor face low impedance.

Because the capacitor leads have parasitic inductance, resistance, the actual capacitor model is capacitance, inductance (equivalent series inductance ESL), resistor (equivalent series resistance ESR) series of structure, with the resonant frequency, the capacitor should work under its resonant frequency to play a role.

Table I.: 1.6mm ceramic capacitor with lead length

This shows that the general capacitor resonant frequency is very low, can not be used in high-frequency, microwave band. In order to improve the resonant frequency, the surface mount capacitor, the three-port capacitor and the heart-piercing capacitor can be used.

Three-terminal capacitor:

Three-terminal capacitor installation:

The grounding end as short as possible, reduce the grounding end of the lead inductance.

Shortage of three-terminal capacitors:

Wear heart capacitance:

As the grounding end and the ground can be close contact, lead inductance is smaller, so the performance is more superior, to wear heart capacitance based on The feed filter is widely used in RF filtering.

Through the heart capacitance input and output terminal line through the upper and lower two grounding plates (so the name of the heart-piercing capacitor), the equivalent of up to two capacitors in parallel into a total capacitor. Because the grounding part is connected with the ground 360° in the circuit, the grounding inductance is very small.

In addition, the temperature and voltage have a great effect on the capacitance value.

This article is reproduced from: Gollum's Blog

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