Hi, I want to find cutoff frequency of the two attached circuits. I just want to know is there any quicker way to find it. For the circuit2 I got it as 1/(2*pi*R*C) but I don't see the same in simulation, so I want to verify it with someone.
Simply calculate voltage transfer function.
Then evaluate cutoff frequency by symbolic math tool such as Mathematica, Maple, Maxima, Symbolic Math Toolbox in MATLAB, etc.
I don't think you can get a simple equation for finding the 3dB bandwidth for such multi element circuits.
But there are many freeware circuit simulators that can do this job:
circuit 2, because it has a resistor in series with the capacitor, does not have a traditional "cuttoff frequency". It has a frequency where insertion loss increases, but then quickly changes attenuation slope to only look like one series inductor.