Cutoff frequency of high-pass filter

Bandwidth is measured between the 0.707 current amplitude points. The 0.707 current points correspond to the half power points since P = I 2R , (0.707)2 = (0.5). Bandwidth, Δf is measured between the 70.7% amplitude points of series resonant circuit.

Rise time and 3 dB bandwidth are inversely proportional , with a proportionality constant of ~0.35 when the system’s response resembles that of an RC low-pass filter.

Bandwidth is given as the range between these frequencies. For a high pass filter, the cut off frequency will define the lower value of bandwidth . For a low pass filter, the cutoff frequency will define the higher value of bandwidth.