Capacitance Calculation Formula

There are 33pf filtering capacitors in the audio line, mainly filtering out MHz RF interference. How can this problem be calculated,
Is the 217hz tdd_noise related to the filter capacitor? Or should I filter out series inductor or magnetic beads?

2 * pI * freq = SQRT (1/(L * C ))

That is to say, This capacitive resonance point has the smallest impedance.

You can check the encapsulation parameters of the resistance and capacitance of Murata.

Generally, about 0402 of the encapsulation is about 0.5nh inductance parasitic, and about 0603 is about 1nh. The larger the manufacturer is, the smaller the parasitic value is.


We assume that the 0603 capacitor is used, the parasitic inductance is 1nh, And the capacitance with the minimum frequency impedance at MHz is:

The calculation result is 31.272pf.

Q: Thank you for your answer. It is calculated based on the capacity resistance formula of Z (JW) = R + J [wL-1/(WC, find the minimum capacity for MHz signal (the theoretical value is 0 ?) For MHz signals, the capacitance of 33pf is equivalent to directly going to the ground.
In addition, when MHz is used, what is the impact on the circuit of this capacitor's ESR? Is it smaller?

Answer your second question.

1: capacitor model is l, C, r three series equivalent circuit. L c oscillates, so only R is left.
2: ESR is mainly about the DC near zero frequency. Below several hundred KH frequencies, R is about 2-10 ohm, generally 5ohm. The 1 GHz frequency is almost r less than 0.2 ohm.

Therefore, the capacitor ESR has no effect on the high frequency (> 1 MHz.

 

There is a calculation method in the project: (1/WC) ≤ system impedance/10 or wl) ≤ system impedance/10. If you want to filter out MHz RF interference, if the grounding capacitor is used, the minimum C value is 31.8pf.

 

Capacitance Calculation Formula