Hi all,

Lst say a input signal IP with 0~200KHz bw is sampled at fs=16MHz (lets call it X), then pass through a 1st order CIC decimation filter (R=8, M=1) to get 2MHz output (lets call it Y).

Let define Δf as shifting the signal to center at f, so

X = IPΔ0 + IPΔ16M + IPΔ32M ...
and sinc is the sinc function without alias

1. What does the Y spectrum now look like ???

Should it be (X* sincΔ0)Δ0 + (X* sincΔ0)Δ2M +(X* sincΔ0)Δ4M ...
or X* sincΔ0 + X* sincΔ2M + X* sincΔ4M ...

2. How about the output spectrum if (R=4, M=2) ???

3. There is a function called mfilt.cicdecim in matlab. Does Y=mfilt.cicdecim*X ??? By multiplying IP with this transfer function, I am just not sure if the alias part would be taken into account.

4. How to calculate the SNR?

I am new to the signal processing world, and these kind of frequency conversion really confuse me...

Thanks for all your help,