.Measure magnitude

QSPICE
1

I have some trouble measuring the cutoff frequency, of a simple lowpass fitler with the .MEAS command.
the command that I’ve used - .MEAS fc FIND frequency WHEN mag(V(out))=-3, this just returns nan values.

Br.
Marc H. Munkstrup

2

mag(V(out))>=0 it is error.

3

I expect you want to find -3dB, and you are missing db() function. You was to find |V(out)|=-3, not in dB, but in linear magnitude, -3dB with linear magnitude is mag(V(out))=0.707

or use this instead :
.MEAS fc FIND frequency WHEN db(mag(V(out)))=-3

1 Like
4

Ahh of course, its not even possible for it to be -3 dB when it is the linear magnitude.
Thank you for clearifying :smile:
//Marc