Self-Resonant Frequency

Self-Resonant Frequency (SRF)

Every real capacitor has parasitic inductance (ESL — Equivalent Series Inductance) from its leads and internal structure. This creates an LC circuit that resonates at the self-resonant frequency (SRF):

f_SRF = 1 / (2π × √(L × C))

Where:

• L = ESL in Henries
• C = capacitance in Farads

Below SRF: the component behaves as a capacitor (impedance decreases with frequency). Above SRF: the component behaves as an inductor (impedance increases with frequency).

This is critical for decoupling! A 100nF capacitor with 1nH ESL resonates at: f = 1 / (2π × √(1e-9 × 100e-9)) ≈ 15.9 MHz

Above 15.9 MHz, it stops decoupling! You need smaller capacitors (lower ESL) for higher frequencies.

Typical ESL values:

Your Task

Implement selfResonantFreq(C_nF, L_nH) returning SRF in MHz.