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Recommended Phase Noise Profile for EVM evaluation

Question asked by TNAKA on Nov 22, 2005
Latest reply on Nov 29, 2005 by TNAKA
Hi.

I'm trying to estimate EVM of pi/4-DQPSK transmitter using "QAM_ModExcOsc" and "N_Tones with Phase Noise".

I set phase noise profile as Lorentzian Spectrum,
e.g. PN1="100 -80 1e3 -80 10e3 -80 100e3 -80 -100 1e6 -120 10e6 -140 100e6 -140 1e9".

I have extraordinary large EVM for this phase noise profile.
But if I use a truncate phase noise profile,
PN2="100e3 -80 -100 1e6 -120 10e6 -140 100e6 -140 1e9", EVM value is fairly small.

And simulation time of PN1 is longer than PN2 although Tstep and Tstop are same.

Tstop value is fairly large since EVM evaluation needs many symbols. So a frequency resolution of simulation is small enough for capturing low frequency phase noise profile.
But EVM value using PN1 is extraordinary.

Here I have questions.

(1) What value should we set for lowest frequency of phase noise profile in evaluating EVM ?

(2) Why does it take longer simulation time if we use phase noise profile with lower frequency ?

?????????  

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