How to calculate the 3rd harmonic distortion in Cadence?

[princerock]

Hi,

I'm designing an op amp and want to calculate the HD3. The input signal is 1KHz. I found that there's a "dft" function in the calculator. But how to set the variables in it? ("from", "to" means what?) And how to get the HD3 from the dft result?

btw: how long should I run the transient simulation to calculate the HD3?

Thank you for your help in advance!

 

[sunking]

you run .tr
from: start time
to: end time

you at least need 3*T, this is to say, for 1k Hz, you at least need 3ms.

run longer time such as 30ms

from 5ms to 35ms

 

[Vamsi Mocherla]

You can also run a fourier analysis. It uses the Fourier Integral to calculate the distortion products.