I have read many papers on ΔΣ modulator design & they depict phase noise plots for 2nd, 3rd & 4th order modulation.
   How do they obtain those phase noise plots for ΔΣ modulators ?
   Solely through MATLAB models or from SPICE simulation ??

Mayank wrote on Jun 14^th, 2010, 9:13pm:
If your main interest is a noise shaping characteristics of  ΔΣ modulator, use Signal Flow Model Simulator such as
   Mathworks Simulink
   Agilent Ptolemy
   Agilent SystemVue

Or use Event-Driven Simulators such as
   Cadence NCSim
   Synopsys VCS


If your interest is a characteristics of whole ΔΣ Fractional-N synthesizer including VCO,
use Berkeley Design Automation AFS Transient Noise Analysis.

See the followings.
http://www.designers-guide.org/Forum/YaBB.pl?num=1238242506
http://www.designers-guide.org/Forum/YaBB.pl?num=1259714206/2#2

Mayank,

   Does page 45 provide the measurement you are looking for?

http://www.designers-guide.org/Analysis/PLLnoise+jitter.pdf

                                                            Best Regards,

                                                              Sheldon

One should not simply apply an FFT to the output signal of the VCO/FDN
to determine L(Δf ) for the PLL. The result would be quite inaccurate
because the FFT samples the waveform at evenly spaced points, and so
misses the jitter of the transitions.

Quote:
This is no more than an advertisement of Fourier Integral Calculation in Cadence Spectre.
And it is not proper in general.

If sampling time step is enough small, we can never miss jitter.

sheldon wrote on Jun 16^th, 2010, 7:14am:
Very not correct.

sheldon wrote on Jun 16^th, 2010, 7:14am:
Again you are wrong. You are very missing point and don't understand point.

You refered L(Δf) in your append : http://www.designers-guide.org/Forum/YaBB.pl?num=1276575200/6#6
On the other hand, this is an evaluation of Sφ(Δf) based on well-known Spectrum Estimation Technique which is useful for getting small frequency resolution with small number of samples.
Here evenly spaced time step samples can be used.
http://www.designers-guide.org/Forum/YaBB.pl?num=1242749411

Statements which you refered regarding evaluation of L(Δf) are similar to old day's claim regarding advantage of Shooting Newton of Cadence Spectre compared to HB analysis.

Small frequency resolution requires very long capturing time.
On the other hand, we have to make time step very small so we can not miss jitter.

So if time steps are evenly spaced even for period where jitters are not included,
it is not efficient regarding total time points.
This is a claim of Fourier Integral Calculation in Cadence Spectre.

sheldon wrote on Jun 16^th, 2010, 7:14am:
But FFT of evenly spaced time step sampling data is used in actual instruments.
And it is very practical and useful level.

I can set RBW(Resolution Band Width) 1Hz in my Real Time Spectrum Analyzer based on FFT with practical sweep time.

Mayank wrote on Jun 16^th, 2010, 9:19pm:
No, you don't understand my append correctly.

This is no more than an advertisement of Fourier Integral Calculation in Cadence Spectre.
And it is not proper in general.
If sampling time step is enough small, we can never miss jitter.

Mayank wrote on Jun 16^th, 2010, 9:19pm:
I use Mathworks Simulink, although it is possible by using Mathworks MATLAB.

Mayank wrote on Jun 16^th, 2010, 9:19pm:
Yes.
See Figure-3 of http://www.designers-guide.org/Forum/YaBB.pl?num=1213204643/4#4
But DSM is modeled by MATLAB not Simulink here.

I recommd you use Simulink not MATLAB.

Mayank wrote on Jun 17^th, 2010, 3:03am:
In general, we know time resolution of generated jitters.
So if we use fixed time step solver in signal flow model simulator,
we have to set analysis time step lesser than time resolution of jitter.
In this case, FFT of many points are invoked.

Mathworks Simulink have both continuous and fixed time step solvers.
If you use continuous time solver in Mathworks Simulink,
you can use Mathworks MATLAB function to evaluate spectrum for data in "Workspace".

Mayank wrote on Jun 17^th, 2010, 3:03am:
This is not DSM for Fractional-N Synthesizer.

I can't find proper example of typical 3-cascaded-MASH-DSM for Fractional-N Synthesizer now.