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Simulators >> Circuit Simulators >> who has used fourier2ch and fourier before?
https://designers-guide.org/forum/YaBB.pl?num=1178848636

Message started by driveforce on May 10^th, 2007, 6:57pm

Title: who has used fourier2ch and fourier before?
Post by driveforce on May 10^th, 2007, 6:57pm

Does anyone use fourier symbol in schematic? how to use it?

I usually run transient simulation and use DFT in the calculator to do spectrum analysis.
What is the difference between my appoach and using fourier symbol?

Thanks a lot.

Title: Re: who has used fourier2ch and fourier before?
Post by sheldon on May 11^th, 2007, 12:24am

Driveforce,

The fourier component implements the fourier analysis that is described in Ken's
book, DG to Spice and Spectre, and in published papers, please see

http://www.kenkundert.com/docs/cicc94.pdf

The differences are discussed in detail in the paper. You also might want to
see the e-mail thread mentioned in Yawei's thd discussion for some additional
discussion about using the DFT and Fourier Integral for data converters.

To use,
1) Add the component to your schematic
2) Connect the fourier component to the signal to be measured
For single-ended signals connect the signal to the component and ground the other pin
For differential signals connect the signals to the symbol
3) Fill in the values to be used for the analysis.

I have been using the fourier component for a while, but haven't had need to use the
two channel version.

Best Regards,

Sheldon

Title: Re: who has used fourier2ch and fourier before?
Post by driveforce on May 11^th, 2007, 12:51am

Hi, Sheldon,

Thanks for your reply.
Do you mean this thread?
http://www.designers-guide.org/Forum/YaBB.pl?num=1177831778

Thanks,
driveforce

Title: Re: who has used fourier2ch and fourier before?
Post by venki_vlsi on May 13^th, 2007, 8:08pm

hi..
i have used fourier component to findout THD in DAC design.There is no option to give sampling points in fourier component.

I also measured THD from DFT plot with 1024 points.Both the results r not same(THD is -36DB from fourier component and -21 dB from DFt plot)

Can u plz help me in this why they r not same and which is correct.

i got SFDR of more than 70db for 10 bit DAC but my THD is -36DB from fourier component and -21 dB from DFt plot.
Please give suggsetion how to improve THD.

Title: Re: who has used fourier2ch and fourier before?
Post by sheldon on May 13^th, 2007, 11:49pm

Venki,

Could you provide more information on your testbench
setup or a plot of the output spectrum?

Best Regards,

Sheldon

Title: Re: who has used fourier2ch and fourier before?
Post by venki_vlsi on May 14^th, 2007, 7:16pm

Hi sheldon Thnaks for reply.

My idea is to plot FFT analysis and calculate SFDR,THD,SNDR.
At the toplevel DAC schematic i kept fourier componet to one of the output of DAC and done transient analysis by applying sinusoidal signal to idela input of ADC .After the simulation got completed i got hormonic distortion in tabular format at the output logfile.In that distortion table he has metioned first 9 hormonics , fundemntal and THD=-36db.
From the FFT plot by using special functions THD i tried to findout THD for required time period and found to be -21dB.
Now problem is Which one is correct.
What i feel is that while calculationg THD from FFT its including hormonics at all frequencies(0 to FS/2). By then also 15db difference is too much.
What do u( friends) say?

Title: Re: who has used fourier2ch and fourier before?
Post by venki_vlsi on May 14^th, 2007, 7:27pm

hi this is setup which i used..i hope it will useful for other also..

This is for single ended output.If its for differnetial output, convert diff to single ended by using ideal diff component and attch fourier component to diff opamp output.

regards
venkats