By hvhipot 
In a series resonant circuit, series resonance is observed (in which the voltage amplitudes on the capacitor and coil are equal to each other and Q times greater than the electromotive force of the generator), while in a parallel resonant circuit, current resonance exists (and the current amplitude in the parallel branch is Q times greater than the current amplitude in the straight chain part of the chain). Here, Q is the Q factor, which is a dimensionless coefficient that determines the ratio of the maximum energy of the reactive element to the energy consumed in the form of heat on the active resistor during that time period. The quality factor of a circuit is defined as:
Through series resonance, the total resistance of the circuit is minimized while the current in the circuit reaches its maximum value. At current resonance, the total conductivity of the circuit is minimized (maximum resistance), and the current in the circuit reaches its minimum value.
The relationship between current amplitude and frequency in a circuit (amplitude frequency characteristic of frequency response) is called the resonance curve. For serial and parallel circuits, this dependency is opposite.
The shape of the resonance curve indicates that the circuit has selectivity, that is, the ability to highlight specific frequency currents. The higher the quality factor of the circuit, the clearer the resonance curve.
An important parameter of a resonant circuit is the passband. Within this frequency range, the current (for parallel circuits) or voltage (for series circuits) decreases by three times (3 dB). In fact, to determine the bandwidth of any circuit, please use the frequency response shown in the figure, where the y-axis displays the ratio of the current to the maximum current of a series resonant circuit at resonance I/I 0, or the current ratio or coefficient ratio of I 0/I of a parallel resonant circuit at resonance when transmitting K/K 0; The horizontal axis represents frequency detuning.