# LC circuit resonance (basic novice question)

#### genekuli

Joined Oct 21, 2018
103
please tell me, do all (basic; cap. and coil) LC circuits resonate but at different frequencies OR, does one have to tune them (considering that the frequency is irrelevant to me)?
like if i use a capacitor and a wire coil, do i have to match them in order for it to resonate or will the LC circuit always innately resonate; but a different frequencies with different coils and capacitors?
thank you

#### Ylli

Joined Nov 13, 2015
1,053
Fr = 1/[2*pi*√(LC)]

Any combination of an L and a C will resonate at *some* frequency. That frequency is defined by the above equation.

#### crutschow

Joined Mar 14, 2008
28,170
This resonant oscillation occurs for any R and C in series or parallel (even if you don't want it) unless there is sufficient resistance in the circuit to critically damp the oscillation.
For example, high speed digital signals on a long PCB trace will exhibit overshoot and high-frequency ringing on the signal edges due to the stray trace series inductance and capacitance to ground.

Joined Mar 10, 2018
4,057
Typical LC circuit has a complex behaviour -

Series resonance impedance approaches 0, parallel infinity. But finite losses
cause resonance to be compromised, series not quite 0, parallel not quite
infinity. Further more it affects steepness of slope and delta freq width between
series and parallel resonance. The more loss the lower the slope, the wider
the freq between the two points. Crystals are very low loss so freq for both modes
very close, slope almost vertical.

Losses are from dielectric in capacitors and wire R in inductors, and core
material losses if used.

Regards, Dana.