Electronic – Cutoff frequency of lowpass filter

filter

So as we know that the cutoff frequency of a filter can be determined from graph by dropping 3dB. But, how do we take the 3dB drop? From the highest point or from 0? In this case, this graph highest point is 1.2dB, so the 3dB drop should be -1.8dB or just -3dB?
Thanks.

graph

Best Answer

From the graph, first you have to find the DC gain. i.e, the gain at w = 0. It's approximately 0 here. Now drop 3 DBs from there. Find the meeting point of that 3-DB level with the graph. That is the cut-off frequency.