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How to calculate THD using calculator?

Last post Tue, Dec 3 2013 2:55 PM by smlogan. 7 replies.
 Started by greatqs 27 Apr 2011 04:42 AM. Topic has 7 replies and 2558 views
• Wed, Apr 27 2011 4:42 AM

• greatqs
• Joined on Tue, Feb 15 2011
• Posts 26
• Points 460
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,qs
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• Post Points: 20
• Mon, May 9 2011 1:28 AM

• greatqs
• Joined on Tue, Feb 15 2011
• Posts 26
• Points 460
Re: How to calculate THD using calculator?
 Is there anyone can help? Thanks!
• Post Points: 5
• Sun, Sep 2 2012 3:05 AM

• Joined on Sun, Sep 2 2012
• Guwahai, Assam
• Posts 2
• Points 40
How to calculate THD using calculator?
 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!
• Post Points: 20
• Mon, Sep 3 2012 9:29 AM

Re: How to calculate THD using calculator?
 Did you actually try using the thd() function? If so, what did you try? Which version of the tools are you using?Andrew.
• Post Points: 20
• Tue, Dec 3 2013 9:51 AM

• foxbei1983
• Joined on Tue, Dec 3 2013
• Posts 2
• Points 40
Re: How to calculate THD using calculator?
 hi Andrew, i've got the same question. i'm using version 6.1.5 ISR17 calculator.thanks!
• Post Points: 5
• Tue, Dec 3 2013 2:35 PM

• foxbei1983
• Joined on Tue, Dec 3 2013
• Posts 2
• Points 40
Re: How to calculate THD using calculator?
• Post Points: 35
• Tue, Dec 3 2013 2:44 PM

Re: How to calculate THD using calculator?
 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.comIf not I will look into this once I'm back from being on vacation tomorrow. Andrew ( just before 11pm UK time )
• Post Points: 5
• Tue, Dec 3 2013 2:55 PM

• smlogan
• Joined on Thu, Jul 17 2008
• Boston, MA
• Posts 41
• Points 700
Re: How to calculate THD using calculator?
 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!Shawnhttp://www.aspowertechnologies.com/resources/pdf/Total%20Harmonic%20Distortion.pdf
• Post Points: 5