How to set the FIR filter specifications?

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)

Answer 1

[Kaashyap Pappu]

You can use the Filter Designer app to get started on the Filter design. You can select the FIR filter option, specify order or allow the App to determine the minimum order that would be necessary, define the passband and stopband frequencies and powers. Visualize the magnitude response and export the filter to your workspace.

Hope this helps!

[Jaikrishnan Mahalekshmi Sahasranamam]

Thanks Kaashyap. I will try that