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Design >> Analog Design >> Two tone TEST to check intermodulation
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Message started by yagi on Jan 26^th, 2007, 6:03am

Title: Two tone TEST to check intermodulation
Post by yagi on Jan 26^th, 2007, 6:03am

Hello everyone,
I am trying to do a intermodulation simulation for my system giving two sinusoidal frequencies at 20Mhz. But I dont know what two input frequencies to feed into my system to get the output spectrum using DFT function in spectre calculator. I tried feeding 20 and 19Mhz signals and did a DFT with hamming window but the two tones in spectrum are spread into bins on both sides.

Can anyone help me how to do this test and see the output spectrum with two singal tones and intermodulated tones.

Thanks,
Yagi

Title: Re: Two tone TEST to check intermodulation
Post by Ken Kundert on Jan 26^th, 2007, 7:18am

I believe the spreading is caused by the use of the Hamming window. With sinusoidal signals you should not need to use a windowing function.

-Ken

Title: Re: Two tone TEST to check intermodulation
Post by ACWWong on Jan 26^th, 2007, 7:55am

and you'll want to ensure the dft is over an interval that is a integer multiple of 1 us to get the right bin spacing for a 20MHz-19MHz = 1MHz....

Title: Re: Two tone TEST to check intermodulation
Post by Croaker on Jan 28^th, 2007, 12:37pm

Yup, if it helps, the points are spaced by fsampling/N where N is the number of points used in the FFT.