how to calculate THD ??

For a single transient run, you can use the thd function in the calculator. Then you could do a two dimensional parametric sweep of Vx and Vy to get the curve you want.

Andrew.

 Thanks Andrew,

I am now able to calculate the THD for a single trans run for one input .

I think i am able to do the parametric sweep by using the Vx and Vy variables in the Parametric Analysis Rows at the same .I think that this called as two dimensional analysis if i am not wrong .(correct me if needed)

Can you please more elaborate on how to calculate the THD from this waveforms and plot the THD vs one of the inputs.Also i dont find the erplot button in my calculater to plot the buffer vale.?

You don't need the "erplot" button to do this. Just hit the evaluate button in the calculator (not sure what version you're using) after doing the parametric analysis. Alternative, having set up the single simulation, hit the Setup Outputs icon in ADE and set the expression for THD  as an output. If you run the single simulation, it will display the scalar result in the ADE output pane, but if you then do a parametric sweep, it will plot a waveform of the output versus the parameter being swept. If you then add a second variable to the sweep, it will plot a family of curves - just as you're after.

Regards,

Andrew.

How to measure THD and gain in cadence 5.10.41

This ought to work - I've no idea what you've done wrong. It should work - I did this:

 thd(VT("/out") 0 2.0/VAR("frq") 128 VAR("frq"))

Note that I had a design variable called frq, which is what I was sweeping. The transient was run for 2*frq (actually not that easy to do in IC5141, I think, but I was running from a netlist), and the fundamental was frq.

Maybe you should contact customer support?

Andrew

For calculating THD in ADE I found the equation as:

THD=sqrt(sum(f^(abs(Ai)^2),i=1:infty))/abs(Af)*100%

where `f' is the fundamental frequency and Ai are the complex coefficients.  I attached a picture below; I'm confused about the notation; typically I see THD calculated as:

THD=sqrt(sum((abs(Ai)^2),i=1:infty))/abs(Af)*100%

Dear Colub,

Cdub said:

I'm confused about the notation; typically I see THD calculated as:

THD=sqrt(sum((abs(Ai)^2),i=1:infty))/abs(Af)*100%

I believe the expression and your understanding are both the same. Reading the definition provided by Cadence f^Ao is indeed the amplitude of the fundamental (it calls it the DC component), and F^Ai are the amplitudes of the higher ith components. Hence the numerator represents the sum of the powers of the higher harmonics ( note f^Ao is specifically excluded from the summation). Do you agree Colub?

Shawn

Thank You for your reply, I am still a bit confused; if "F^Ai are the amplitudes of the higher ith components" then the denominator of the expression should be F^Af right? Have I misinterpreted your reply?

Cdub said:

I am still a bit confused; if "F^Ai are the amplitudes of the higher ith components" then the denominator of the expression should be F^Af right? Have I misinterpreted your reply?

Dear Cdub,

Referring to the text in the manual:

"The computation uses the dft function. Assume that the dft function returns complex coefficients A0, A1…, Af , ... .

Please note that fundamental frequency f is the frequency contributing to the largest power in the signal. A0 is the complex coefficient for the DC component and Ai is the complex coefficient for the ith harmonic where . Then, total harmonic distortion is computed as:"

 Hence the notation in the denominator, Af, is consistent with the frequency contributing to the largest power in the signal. Typically, this will be the amplitude of your fundamental.

Is this any more clear (sorry about my prior confusion!)?

Shawn

Hi Shawn! Thanks again for the reply. It seems like the notation of the numerator is not consistent with the notation of the denominator. Is there something I might be missing?

Thanks Again!