I have currently modelled a 3rd order Delta sigma Modulator (CTDSM). The specs are fs = 6MHz, OSR = 30, fB = 100kHz . For the current design I am getting the results for FFT before filtering as below.
Psignal = -1.2dBFS
PIBN = 70.7dBFS
PSNR = 69.5dBFS
Basically I have to downsample this to Nyquist rate (2fB)
For that, I have to design an FIR - LPFilter with minimum ripples, max attenuation and order less than OSR to get rid of the Out of Band noise which was Noise shaped to high frequency. For this
1) what kind of LPfilter should i choose in Matlab to model?
2) How to choose the specifiations (such as fPB, fSB, PBripple, SBripple etc.) of the filter such that I could preserve the previous SNR results before filtering (even if some dB less is also okay)