Abstract: The quality factor is an important parameter for a resonant circuit.How to calculate the quality factor of a general RLC resonant circuit is discussed a lot in popular conferences and the quality factor is defined as the ration of voltages or currents.The RL and C parallel resonance circuit,which is the circuit model of practical resonant circuit,is discussed much fewer.The quality factor is calculated according to the definition,namely,the quality factor relates the maximum or peak energy stored to the energy dissipated in the circuit per cycle of oscillation.

Key words: quality factor, resonance, frequency