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Simulators >> Circuit Simulators >> Spectral analysis for DAC in cadence spectre
https://designers-guide.org/forum/YaBB.pl?num=1336980521

Message started by user0088 on May 14^th, 2012, 12:28am

Title: Spectral analysis for DAC in cadence spectre
Post by user0088 on May 14^th, 2012, 12:28am

Hello all,

I am working on Sigma-Delta DAC, which last stage is SC Filter.
Modeling is performed in Cadence design environment.

Could you please advice how to put correct simulation settings for performing FFT and measuring SFDR.

Currently I am doing as the following:
1. Digitized sin signal is applied with Fin=125KHz frequency.
2. Transient analysis is done. Fclk=32MHz.
Run time is "8us+2048*31.25n"=72us
where 8us is a circuit stabilization time, 31.25n is a 1/32Mhz sampling period.

strobeperiod=Fclk/10 is used. !!!

3. Perform dft (with calculator)
From - 8us
To - 72us
Number of Samples - 2048
window type - Cosine2

Am I missing something????

The question arose....
The SFDR of of SC filter output shows about 80dB, whereas when I use IDEAL LP filter after SC filter the SFDR is significantly drops.

I looked at the specter of the SC filter out for [8u-x...72u-x] range also, where x=(0...9)*strobeperiod. There are some x values, for which SFDR is "not good".
So, therefore, the LP filter averages the values...... is it so????

Are my simulation settings correct?

Please help. Thanks in advance.