Stats

Locked Locked
Replies 7
Subscribers 126
Views 18888
Members are here 0

This discussion has been locked.

You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How to calculate THD using calculator?

I found the thd() in calculator only has 5 arguments (e.g. from, to, # samples, fundamental frequency).

For example, I'm doing a FFT with sample frequency of 8192KHz with from=1ms to=2ms and fundamental frequency is 5KHz.

I want to calculate the THD within 20 ~ 20KHz instead of 0 ~ 4096KHz which thd() does since it doesn't include Fmin/Fmax arguments.

Thanks,

greatqs over 14 years ago

Is there anyone can help? Thanks!
Cancel
Vote Up 0 Vote Down

Cancel
cad123 over 13 years ago

Is there somebody who can help me on how to plot THD in spectrw. I have a CMOS OTA design for which I have to evaluate HD3 and THD.
Thanks!
Cancel
Vote Up 0 Vote Down

Cancel
Andrew Beckett over 13 years ago

Did you actually try using the thd() function? If so, what did you try? Which version of the tools are you using?
Andrew.
Cancel
Vote Up 0 Vote Down

Cancel
foxbei1983 over 11 years ago

hi Andrew,
i've got the same question.
i'm using version 6.1.5 ISR17 calculator.
thanks!
Cancel
Vote Up 0 Vote Down

Cancel
foxbei1983 over 11 years ago

nobody answers this question? please help.
Cancel
Vote Up 0 Vote Down

Cancel
Andrew Beckett over 11 years ago

Your first post appeared at just before 6pm my time, and second after 10pm, having broken the forum guidelines and posted on an old thread. It wasn't clear which of the two questions in this thread you were asking, but given that this forum is covered by Cadence folks in their spare time (and I do have a life outside of work), being quite so pushy is a bit unreasonable.
If it is urgent, you should go to customer support at support.cadence.com
If not I will look into this once I'm back from being on vacation tomorrow.
Andrew ( just before 11pm UK time )
Cancel
Vote Up 0 Vote Down

Cancel
ShawnLogan over 11 years ago

The THD, as a parameter, is defined as the rms sum of all the fundamentally related harmonics in a signal. Hence, the function, I believe, computes the total harmonic distortion in a manner consistent with the definition (given the FFT length).

To compute the harmonic distortion for a lesser number of harmonics or over a particular frequency range, simply determine the power (or value of the dft function) for the relevat harmonics and perform the rms sum to compare it with the power in the fundamental.

An alternative might be to actually include a filter in your circuit analysis simulation that limits the bandwidth to the range of interest and then use the THD function on its output.

I hope this provides some help!

Shawn

http://www.aspowertechnologies.com/resources/pdf/Total%20Harmonic%20Distortion.pdf
Cancel
Vote Up 0 Vote Down

Cancel

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.