Capacitor Self-Resonant Frequency

A real capacitor is a series LC: its capacitance in series with the equivalent series inductance (ESL) of its body and leads. At the self-resonant frequency the two reactances cancel and the part looks purely resistive (the ESR); above it, the capacitor behaves as an inductor. Enter C and ESL to find the SRF, and add ESR and a frequency to get the Q and reactance there.

Equations & Parameters ▸

\(f_{SRF}=\dfrac{1}{2\pi\sqrt{L_{ESL}\,C}} \qquad X_C=\dfrac{1}{2\pi f C} \qquad Q=\dfrac{X_C}{\text{ESR}}\)

C	Capacitance (pF).
ESL	Equivalent series inductance (nH) — body + mounting. Sets the SRF.
ESR	Equivalent series resistance (Ω), optional — for the Q and the impedance minimum.
f	Frequency (MHz), optional — for the reactance and Q at that point.

Reference: Standard series-RLC model of a real capacitor; component-vendor SRF/ESR application notes.

Inputs

Capacitance, C

Nominal

ESL

Parasitic L

ESR (opt)

For Q

Frequency, f (opt)

MHz

Operating pt

Results

Resonance

Self-resonant frequency—

Impedance min (= ESR)—

At frequency

Reactance |X|—

Behaviour—

Q—

Diagram

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