LCSchwingkreis

The LCSchwingkreis, or LC-Schwingkreis, is a circuit consisting of an inductor (L) and a capacitor (C) connected in series or in parallel. It functions as a resonant circuit that can store and exchange energy between the magnetic field of the inductor and the electric field of the capacitor. At the resonant frequency, the circuit responds sharply to stimuli at that frequency, making it useful for tuning, filtering, and frequency selection in radio-frequency applications.

The resonant frequency is determined by f0 = 1/(2π√(LC) ), with the angular frequency ω0 = 1/√(LC). In a series configuration, the impedance is minimum at resonance (ideally zero aside from losses); in a parallel configuration, the impedance is maximum. Real circuits include losses, so the ideal sharpness of resonance is reduced.

The quality factor, Q, characterizes the sharpness of the resonance and depends on losses in the components. For a simple series-resonant circuit with a small series resistance R, Q ≈ ω0L/R. For a parallel-resonant circuit with a parallel loss resistance Rp, Q ≈ Rp/(ω0L). Parasitic elements such as stray capacitance, coil resistance, and core losses affect both the resonant frequency and Q, and temperature changes can shift L and C.

Common applications include tuning circuits in radios and receivers, selective filters, local oscillators, frequency synthesis, and impedance matching networks. A variable capacitor in an LCSchwingkreis enables receiver tuning over a range of frequencies.